Monthly: June 2015

The article discusses the design and parameters of POWEN currently manufactured at ZFMG pumps, intended primarily for the domestic coal mining industry. Special attention was paid to multistage centrifugal pumps used in main mine drainage systems and centrifugal pumps for contaminated liquids. The more important needs of users and the manufacturer's activities to meet them are presented possible directions of further development of pump designs. The final part specifies the tasks to be carried out in terms of progress in this field.

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Pumps are the basic production of the Zabrzańska Fabryka Maszyn Górniczej POWEN and, for this reason alone, their development must be in the center of attention of the employees employed there. Until another way of moving fluids between two places is discovered, which is currently difficult to imagine, we will see constant improvement of these machines, which are used in many areas of life.

The development of pump production at ZFMG POWEN must keep up with the development of pumps on a global scale, and this article aims to outline the scale of needs and the scope of necessary actions in this direction. The article divides the pumps currently manufactured at ZFMG POWEN into 5 groups:

1. multistage centrifugal pumps - high pressure,

2. multistage centrifugal pumps - medium pressure,

3. centrifugal pumps for contaminated liquids

4. submersible pumps,

5. special pumps.

The rest of the article discusses pumps in accordance with the division made above, taking into account the fact that the production of pumps at ZFMG POWEN is primarily aimed at meeting the needs of coal mining.

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Multistage centrifugal pumps - high pressure.

The OW-AM and OWH multistage high-pressure centrifugal pumps currently manufactured at ZFMG POWEN are intended for main drainage of mines. The parameters of these pumps are related to the existing needs, in particular to the depth of the mining seams and the amount of water inflow per unit of time.

Figure 1 shows the collective operation chart of the OW-AM and OWH pumps, and Figure 2 shows the construction diagram of the OW-AM pump. OWH pumps have a structure similar to OW-AM pumps; however, they are characterized by a stronger construction of casings and stuffing boxes, which allows these pumps to operate in a series arrangement according to Fig. 3, in which the OWH pump takes over the pressure from the OW-AM pre-pump. Such a pumping unit currently enables single-level drainage of mines with a depth of up to 1400 m, which fully meets the needs in this area for the coming decades.

OW-AM and OWH pumps are centrifugal, multistage, horizontal pumps with closed rotors and vane guides. The pump casing has a modular structure. The rotating unit is mounted in plain bearings ring-lubricated with liquid grease. The axial thrust is balanced by the axial load relief system shown in Fig. 4. The shaft at the exit points from the hulls is sealed in stuffing boxes with a soft string sealant. The basic elements of the flow system of OW-AM pumps, such as: impellers, guide vanes, walls and protective rings, are made in 3 material versions:

• for clean and slightly polluted water – made of low-alloy cast iron,
• for highly mechanically polluted water - from bronze,
• for saline water – made of acid-resistant cast steel.

OWH pumps are manufactured in the last two material versions.

The development of the production of OW-AM and OWH pumps with flow systems made of bronze and acid-resistant cast steel has occurred at ZFMG POWEN over the last 3 years. This resulted in a significant improvement in the service life of these pumps. It should be stated, however, that the production volume of pumps in both these versions does not meet the current needs of users, and this is due to two main reasons:

• the condition of mine waters does not improve or even worsens. This is the result of, among others, lowering the extraction levels of mines, which is associated with higher water salinity. Users' care for settling tanks is also insufficient, which results in an increase in the share of mechanical impurities in the water, especially when hydraulic backfill is used,

• ZFMG POWEN's production capacity is insufficient given the current quantitative demand. This is due to, among others, hence, the labor consumption of making elements, e.g. from acid-resistant cast steel, is approximately 4 times higher than the labor consumption of making similar elements from cast iron.

Mining needs in the field of high-pressure centrifugal pumps.

The mining industry's needs in terms of high-pressure centrifugal pumps should be considered on many levels. First of all, these are quantitative needs, regarding both the supply of currently manufactured pumps, as well as spare parts for machines in operation, including many of those whose production has already been discontinued. Meeting these needs is the factory's first responsibility. The basic parameters of the OW-AM and OWH pumps, such as lifting height and efficiency, cover current needs 100%. Issues that remain to be solved include:

• improving the efficiency of manufactured pumps,
• reducing weight and dimensions,
• increasing durability by better adapting pumps to existing operating conditions.

Actions to improve the efficiency of high-pressure centrifugal pumps. 

In terms of improving the efficiency of currently manufactured OW-AM and OWH pumps, ZFMG POWEN cooperates with many scientific and research centers, including the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences in Gdańsk, the Institute of Power Machines and Devices of the Silesian University of Technology in Gliwice, the Institute of Fluid-Flow Machinery of the Lodz University of Technology in Łódź, Research and Development Center for Industrial Pumps in Warsaw and the KOMAG Mining Mechanization Center in Gliwice. Independently of this cooperation, own research is carried out based on model pumps with the structure shown in Fig. 5, which enable testing of many flow systems, comparison of test results and selection of the optimal system for a given size. This work will also be carried out in the coming years, and better-than-current flow systems will be implemented into production. Detailed tests of the flow systems of multistage pumps conducted by the Institute of Impulse of the Lodz University of Technology showed further reserves in the structure of the casings, embankments and guide vanes of the tested pumps. Through research, by determining the liquid velocity vectors in the flow channels and the pressure values ​​at individual points in the channel, the sources of energy losses in the tested pumps were determined. These are tedious but effective activities. ZFMG POWEN's cooperation with scientific and research centers in the field of research will result in an increase in pump efficiency in the near future, because the optimization of flow systems should be carried out primarily in this way.

Actions aimed at reducing the weight and dimensions of pumps.

There are many possibilities to reduce the weight and dimensions of pumps. However, a significant reduction in material consumption in pump production is only possible in special cases, which include:

• introduction of significant design changes resulting mainly from increased rotational speeds,
• the use of materials with greater strength or lower specific weight,
• reducing the thickness of particularly material-consuming elements.

In the current designs of OW-AM pumps, there are no greater reserves of strength that would allow the weight of the casings to be reduced by changing the wall thickness. Such reserves exist in OWH pumps, which were designed for use in series systems according to Fig. 3, assuming maximum pressures p_Max = 15,0 MPa. Due to the high demand of mines for these pumps in the lifting height range H = 700-1000 m, it is advisable to start the production of a second version of OWH pumps, adapted to work in a suction system. Such production will start in 1987. A significant reduction in the weight of the currently manufactured OW-AM and OWH pumps is possible by using centrifugal guide vanes with side discharge as shown in Fig. 7. Currently, only the OWH-250 pump has this design of guide vanes, and the remaining pumps of the OW- series AM and OWH have blades with a structure similar to that shown in Fig. 6. However, the greatest opportunities to reduce the consumption of materials in production, reduce the weight and dimensions of the pumps are provided by increasing the rotational speeds of these machines. This is, of course, also related to the issue of durability and increased requirements in terms of workmanship, but once these problems are solved, the benefits will be greatest.

Recently, ZFMG POWEN manufactured two prototype, 2-stage OW-6D pumps with the following parameters:

• Q = 500 m³/ h,
• H = 900 m,
• n = 2900 rpm.

Maximum number of pump stages i_Max = 8 allows the lifting height H to be obtained_Max = 1200 m. The implementation of these pumps into industrial production will enable the replacement of the currently produced OW-250AM + OWH-250 pump sets, driven by engines with a rotational speed of n=1450, with one OW-200D pump. In this system, it is possible to reduce the weight many times and significantly reduce the dimensions of the pump unit. This will have an impact on reducing the cost of building new pumping stations in the future. We plan to produce the next size of the OW-D series pump with a capacity of Q = 315 m³/h. However, implementing OW-D pumps for operation in existing pumping stations involves rebuilding foundations and pipelines, changing drive engines, and in many cases would also require rebuilding the electricity supply network. In many existing mines, such changes would be unprofitable. Therefore, OW-D pumps are intended primarily for new mines and new mining levels in existing mines.

The construction of vertical submersible pumps also offers significant opportunities to reduce the size of the main drainage pumping station. However, the use of these pumps in domestic mines requires a deeper analysis, the production of appropriate engines, and changes in some regulations regarding mine design.

Actions to increase the durability of pumps.

Of the several hundred main mine drainage pumps analyzed, most of them had a durability that was unsatisfactory to both the manufacturer and the user. Detailed data on the durability of these pumps are included in Table 1.

The low durability of pumps results from many reasons, including:

• inaccurate selection of pump parameters to characterize pipeline resistance,
• poor condition of mine water,
• insufficient attention of the staff to the pumps.

ZFMG POWEN, among others through the activities of service services and cooperation with mines and design offices, it has a certain impact on the elimination of this group of reasons for reducing the durability of pumps. However, this is a random activity, enabling the resolution of individual cases. The main efforts of designers are directed at adapting pumps to the existing, difficult working conditions in mines.

Mine water can be divided into three main groups:

• water slightly chemically and mechanically polluted,
• water with predominant mechanical pollution,
• highly saline waters.

In the first case, the durability of pumps made of typical materials is sufficient. In the case of heavily mechanically polluted waters, which occur in mines using hydraulic backfilling, making the flow system made of bronze extends the durability of the pump by 2-4 times compared to those made of low-alloy cast iron. However, the elements of the axial load relief system shown in Fig. 4 require frequent replacement. Eliminating this shortcoming is not easy; however, we have concepts of possible solutions. One of them is the installation of a dirt separator according to the ZFMG POWEN patent no. 135737 in accordance with Fig. 8. Model tests (10) conducted at the IMiUE of the Silesian University of Technology showed the effectiveness of such a separator, which eliminates 60-90% of mechanical impurities contained in the pumped water. The remaining part of the contamination consists of the least harmful grains with the smallest granulation. The implementation of this solution in the industrial production of OW-AM and OWH pumps will be possible after conducting operational tests in conditions of particular contamination of pumped water.

Another way to extend the durability of the unloading system is the solution shown in Fig. 9, used in the prototype OW-200D pump, in which there is partial unloading using an axial bearing built in the oil chamber. What is important in this case is that when starting and stopping the pump, the rings in the unloading system are separated from each other, and the entire load is carried by the axial bearing. The frequency of pump starts has a significant impact on the durability of the axial load relief system. The final solution is a main drainage pump without a relief disc. One possible solution is to build a pump with 2 rotor sections with opposite directions of flow of the pumped liquid. This design was used in the past in OWB pumps manufactured by ZF-MG POWEN. The production of these pumps was discontinued in the 3s, among others. due to the low durability of the internal stuffing box and complications related to its replacement. A return to this structure would be possible in one of three variants:

• with the possibility of using a dirt separator installed in front of the internal stuffing box in accordance with ZFMG POWEN patent no. 135737,
• with the pump shaft divided in the central part, which allows easy access to the stuffing box. This solution, shown in Fig. 10, was patented in the Polish Patent Office, patent number 129690,
• using an intermediate chamber between 2 rotor sections in accordance with ZFMG POWEN patent no. 134571.

However, these solutions require operational testing and can be implemented into industrial production after their completion.

In the case of highly saline waters, the selection of construction materials for individual elements of the flow system becomes particularly important. Under these conditions, the durability of rotors and vanes made of acid-resistant cast steel is several times higher than the durability of elements made of low-alloy cast iron. Making these elements from acid-resistant cast steel, despite the significantly increased labor consumption, is therefore completely justified.

The operation of the OW-250AM and OW-300AM pumps in the mines of Jaworznice-Mikołowski Gwarekt Węglowe shows that in conditions of highly saline water, other pump elements should also be made of materials resistant to their operation. Making pump casings from acid-resistant cast steel is technologically complex and results in a significant increase in labor intensity and production costs. Therefore, it is necessary to look for substitute solutions while maintaining both the manufacturer's production capabilities and the essential qualities of the product.

One possible solution is to use inserts made of salt-resistant materials in those parts of the hulls that are particularly vulnerable to damage and have a decisive impact on their durability. This applies primarily to fits and joints related to seals. This year documentation was developed for 2 pumps: OW-250 AMK and OWH-200K according to this concept, the main goal of which is to reduce the labor intensity and cost of pump construction while maintaining their operational advantages. The target solution will be to construct the pump from typical materials - cast iron and carbon cast steel protected in the boundary layers by metallic and non-metallic coatings applied to the base metal. Currently, ZFMG POWEN is not yet prepared to produce pumps using this technology. This note also applies to other pump manufacturers. Too wasteful use of expensive and rare materials is still a necessary evil for world technology.

Centrifugal pumps, multistage - medium pressure.

Currently, ZFMG POWEN produces centrifugal, multi-stage, medium-pressure pumps of the OS-AM series, used in mining primarily for auxiliary drainage of mines, with lifting heights up to approx. 250 m. The parameters of the OS-AM pumps are shown in Fig. 11, and in Fig. .12 shows the construction diagram of the pump.

OS-AM pumps were created by modernizing the OS-A series pumps produced until 1984. The modernization was based mainly on the wishes of users, including: bearing nodes were strengthened, legs and eyes for tie bolts were strengthened, adapting these nodes to specific mining conditions. Ease of disassembly and 2 new material versions have been introduced, similarly to the previously discussed OW-AM pumps, adapting OS-AM pumps to pumping saline and mechanically polluted water.

OS-AM pumps are - similarly to OW-AM and OWH - centrifugal, multi-stage centrifugal pumps, with a horizontal structure, with closed impellers and vane vanes, and with segmented casings. What distinguishes them from OW-AM and OWH pumps is the way in which the axial force is relieved. In the case of OS-AM pumps, the relief is provided by relief holes in the rear rotor discs, and the rest of the axial force is carried by the axial bearing. In the case of OS-AM pumps, all bearings - two radial and one thrust - are rolling bearings lubricated with liquid grease.

Mining needs in the field of medium-pressure centrifugal pumps and the activities of ZMFG in this area.

As in the case of high-pressure pumps, there is a significant quantitative demand for the supply of new OS-AM pumps and spare parts for machines used in mines. These needs are met first. The basic parameters of OS-AM pumps, such as lifting height and efficiency, basically cover the current needs of mines. The following issues remain to be solved, as in the case of OW-AM and OWH pumps:

• improving fitness,
• reducing weight and dimensions,
• increasing durability.

It can be added that the need to act in these directions will remain constant. The main directions of activities carried out are consistent with those given earlier when discussing the OW-AM and OWH pumps, so we will not repeat them. It is only necessary to take into account the differences in the design of medium- and high-pressure pumps. This comment applies in particular to the axial disc relief system, which is not present in OS-AM pumps.

In the coming years, instead of the OS-AM pumps, a new series of pumps marked with the OS-C symbol should be implemented into production, with slightly improved operating parameters and increased efficiencies. This year, a prototype of the first pump from the new series, marked OS-125C, will be manufactured, which will be subjected to laboratory and operational tests in 1987. The results of these tests, which will be conducted together with CMG KOMAG in Gliwice and OBR PP in Warsaw, will determine the pace of implementation of the entire OS-C series into production.

Centrifugal pumps for contaminated liquids.

Currently, ZFMG POWEN produces 4 types of single-stage pumps, used in many industries for pumping slightly and heavily mechanically polluted water. These pumps are marked with the symbols PH, PG, OŁ and PŁ. PH pumps according to Fig. 13 are single-stage pumps, with closed impellers mounted at the end of the drive shaft. They have a horizontal structure, with the inlet port along the shaft axis. They are intended for pumping water contaminated with coal, gravel, ore, sand, etc. with a granulation of up to 52 mm, depending on the size of the pump. Permissible density of the pumped mixture pmax = 1700 kg/m. The basic elements of the flow system are made of heat-treated alloy cast steel.

Figure 14 shows a fragment of the flow system of the PH pump, and Figure 15 shows a collective operation chart of the entire series. The design of PH pumps allows two pumps to be connected in series, which allows the lifting height of the pump unit to be doubled compared to the diagram in Fig. 2. One of the PH series pumps is also available in a version with a free-flow impeller. A fragment of the flow system of this pump, marked PH-15S, is shown in Fig. 100.

PG pumps according to Fig. 17 are single-stage pumps with open impellers, with a structure similar to PH pumps. The basic elements of the flow system shown in Fig. 18 are covered with rubber linings.

In recent years, we have been introducing more wear-resistant polyurethane floor coverings instead of rubber floor coverings. Currently, one size of pump with polyurethane linings is produced, marked PG-200P. This pump is built with a closed impeller as shown in Fig. 19.

PG-200P pumps in specific operating conditions, e.g. when pumping water with sand, have a durability much higher than that of the PH series pumps. Permissible density of the pumped mixture p_Max=1400 kg/m³.

Figure 20 shows a summary graph of the operation of PG pumps. It should be assumed that pumps with rubber linings constitute a declining production at ZFMG Powen.

OŁ pumps, the construction diagram of which is shown in Fig. 21, are single-stage pumps with closed impellers. These pumps have a horizontal structure with the inlet port located perpendicular to the shaft axis. The location of the impeller on the shaft of OŁ pumps is different than in PH pumps, so the shaft sealing gland is located on the inlet side - in front of the impeller, and is therefore exposed to much lower pressures than in PH pumps. OŁ pumps are used primarily in heavy liquid circulation in coal processing plants. Permissible density of the pumped mixture p_Max =2200 kg/m³. A summary graph of the operation of these pumps is shown in Fig. 22.

PŁ pumps, the construction diagram of which is shown in Fig. 23, are single-stage pumps, with closed, double-stream impellers, with casings divided in a horizontal plane passing through the shaft axis. They are used for slightly polluted water in water circuits of coal processing plants. Permissible density of the pumped mixture p_Max=1200 kg/m³, with dirt granulation up to 5 mm. A summary graph of the operation of PŁ pumps is shown in Fig. 24.

User needs for pumps for contaminated liquids.

Pumps for contaminated liquids currently manufactured at ZFMG POWEN enjoy a good reputation among most users. These are pumps with a simple design, similar to solutions used by leading foreign companies. However, users are interested in continuous improvement of these pumps, which should improve
mark, among others:

• high durability of the flow system elements,
• reliability and durability of stuffing boxes,
• certainty and reliability of the bearing system,
• the highest possible efficiency when pumping a specific mixture of water and solids,
• possibility of hydrotransport of solids of specific granulation over increasingly greater distances,
• easy disassembly and replacement of damaged elements.

Durability of flow system elements.

The durability of individual elements of the flow system is determined by the properties of the pumped medium and the construction materials used, as well as, to some extent, the geometric features of the element.

Among the construction materials, ZFMG POWEN's production most often uses alloyed, high-chrome, heat-treated cast steel and polyurethane linings. One of the directions of action for the coming years is to expand the use of polyurethane.

Currently, preparations are being made for the production of prototype pumps of the OŁ-AP series with polyurethane linings similar to those shown in Fig. 19.

For the PH series pumps, we are looking for a material with higher abrasion resistance than the currently used SP4 cast steel, while maintaining the best possible machinability. The results of operational tests of pumps also indicate the need to change the shape of some elements of the flow system to improve their durability. Based on these tests, for example, new molds for polyurethane impellers for PG-200P pumps were made. The implementation of 3 prototype pumps of the new OŁ-A series is underway. The design of these pumps includes the results of experience from many years of operation of OŁ pumps.

Reliability and durability of stuffing boxes.

In OŁ and PŁ series pumps, the stuffing boxes are located on the inlet side - in front of the impeller - and are therefore exposed to low pressures, assuming the operation of these pumps with the most common small inflow. The stuffing boxes in PH pumps operate at much higher pressures, as shown by their operating parameters in Fig. 15.

For obvious reasons, improving the stuffing boxes of pumps for contaminated liquids focuses the designers' attention on the PH series pumps. There are many possibilities in this regard, including:

• relieving the stuffing box using a pressure reducing device in the immediate vicinity of the stuffing box. Among many possible solutions, the system according to the ZFMG POWEN patent no. 25 is shown in Fig. 119111,
• using new solutions of stuffing boxes with soft packing or mechanical stuffing boxes with lubricants supplied to the stuffing boxes from the outside,
• use of new technologies for manufacturing stuffing box sleeves. In this field, ZFMG cooperates with, among others, with the Institute of Fluid-Flow Machinery and the Institute of Nuclear Technology in Warsaw. The target solution will contain the results of all three of the above. directions of action.

Safe and reliable operation of the bearing system.

The problem of durability of the bearing system occurs sporadically in the largest pumps of the PH series and only in particularly difficult operating conditions of these pumps. In this case, it is important that the user takes care of the pumps and follows the principle of immediate replacement of damaged components of the rotating system, especially the rotors, which are subject to natural wear when pumping media with highly abrasive properties. The user must remember that with increasing wear of the rotor, the magnitude of the forces loading the bearings changes, which is the result of an increase in the unbalance of the rotating masses. Savings understood incorrectly in this case may result in significant losses. The research conducted at ZFMG POWEN also shows an obvious conclusion: how important it is to use appropriate bearing lubricants. There cannot be any deviations from the manufacturer's recommendations in this respect.

Regardless of the above, actions are being taken to further improve the bearing systems in the pumps in question. A number of studies have been carried out in this area, and further research will be conducted in the near future.

Efficiency of pumps for contaminated liquids.

The specific nature of the use of pumps for contaminated liquids means that the problem that is so important for all machines - their energy consumption - is often in the background, giving way to primary issues such as:

• obtaining the ability to pump media containing solids of specific, often very large granulation,
• obtaining the highest possible durability of the flow system elements.

Understanding these issues, we must agree, for example, with the need to use, in specific cases, low-efficiency free-flow pumps according to Fig. 16, as well as 2- and 3-blade rotors with blade thicknesses significantly different from those optimal from the hydraulic point of view. Only after meeting the basic design assumptions can the pumps be optimized, e.g. in terms of improving energy efficiency.

In recent years, in particular thanks to research of the Central Mining Institute in Katowice, valuable data on possible directions for optimizing flow systems have been obtained. These studies show, among others, that flow systems designed for specific media achieve higher efficiencies in operational conditions than the efficiency of these systems when pumping clean water in laboratory conditions. New principles for designing impellers for these pumps were proposed. GIG's experience will be systematically used, and new flow systems will be implemented into production after laboratory and operational tests.

An issue independent of the above, and closely related to the energy consumption of pumps, is the selection of pump parameters for the system.

The methods of adjusting the parameters of the pump and the pumping system currently used in Poland and many other countries - with a medium or even high technical level - are becoming outdated and uneconomical. So far, the following are used for this purpose:

• throttling using orifices and valves,
• change in the geometric features of the rotor, in particular its outer diameter,
• changing the pump speed using a gear or torque converter.

However, the future belongs to variable frequency drives, which find practical application in only a few leading countries in the world. The first steps in this regard have also been made in Poland. Pump manufacturers can only wait for rapid progress in this field, and in particular for the implementation of production of converters enabling the regulation of the rotational speed of engines with a power of up to 250 and even 400 kW.

The benefits of using variable frequency drives include:

• stepless change of rotational speeds in the range of 0-1,15 values ​​of the rated motor speeds, which takes place practically without changing the motor efficiency,
• soft start eliminating high current surges occurring in typical induction motors,
• avoiding the need to produce and store impellers of different diameters, because the pump rotational speed can always be adjusted to the operating conditions by using an impeller with the optimal diameter,
• avoiding excessive headroom and pump capacity normally assumed to cover errors in the assessment of operating conditions.

Variable frequency drives provide particularly high savings in mixture hydrotransport systems in mines and power plants due to frequent changes in pump operating conditions in these installations.

Other issues related to hydrotransport.

Any design improvements that facilitate the assembly and disassembly of these machines are of great importance for pump users, and especially for renovation services. This is a field grateful to designers, and the possibilities in this area will never be exhausted. Continuous improvement of the design of pumps manufactured at ZFMG POWEN is, of course, also possible, assuming a reasonable balance between production costs and operating profits. The cooperation between the manufacturer and the users is very helpful in this respect. For ZF-MG POWEN, the current new needs regarding the parameters of pumps for contaminated liquids are of great importance. These needs concern in particular:

• possibility of pumping mixtures with grains of increasingly larger granulation,

• increasing the lifting height of pumps for hydrotransport over increasingly longer distances, without the need to build expensive pumping stations.

Work on the implementation of both of the above is in progress. tasks. In the near future, the PH-250 pump will undergo laboratory tests of the rotor enabling pumping mixtures with grains with a granulation of up to 90 mm.

Last year, based on the project of the Institute of Energy Machines and Devices of the Silesian University of Technology. in Gliwice, a prototype TM-125 pump with an interesting design was manufactured at ZFMG POWEN, intended for use in power plants and in hydrotransport installations over long distances. This pump achieved the assumed operating parameters:

Q = 200 m³/ h,

H = 250 m, n = 960 rpm, at p = 1000 kg/m³.

During operational tests at the power plant, in the slag and ash hydrotransport installation, the pump will pump a mixture with a density of up to 1700 kg/m³ and grain granulation up to 10 mm. Regardless of this, ZFMG POWEN is working on the production of a prototype unit for transporting sludge, marked ATS-150, with the following parameters:

Q=120 m³/ h,

H = 200 m, n = 1450 rpm,

permissible density pmax = 1700 kg/m³, permissible grain granulation up to 40 mm. The documentation for this unit was developed by ZFMG POWEN in cooperation with KWK Wieczorek, which will conduct operational tests of the prototype.

When discussing issues related to pumps for contaminated liquids, the focus was deliberately on stationary pumps, considering submersible pumps as a topic for separate considerations, with specific problems, although, of course, many comments apply equally to both groups of pumps.

Submersible pumps.

Currently, ZFMG POWEN produces submersible pumps marked with the symbols P-1B, P-2B, P-5A, PK-80 and PK-80S. Submersible pumps are portable centrifugal centrifugal pumps with an electric drive, used to operate with partial or total immersion in the pumped liquid. The elements of the flow system, made of abrasion-resistant materials, allow pumping mechanically contaminated liquids, and the flameproof motor casing enables the pumps to operate in areas at risk of methane explosion. Permissible density of the pumped medium p_Max=1200 kg/m³.

Working characteristics of the above-mentioned pumps are shown in Fig. 26, and the construction diagram of the P-1B pump is shown in Fig. 27. Other submersible pumps manufactured by ZFMG POWEN have a similar structure. The PK-80 and PK-80S pumps are distinguished by larger flow channels, which allows these pumps to be used for pumping urban and industrial sewage. P-1B and P-2B pumps are manufactured with open impellers, similarly to PG pumps according to Fig. 18.

The P-5A and PK-80 pumps are built with closed impellers with a structure similar to that shown in Fig. 14, while the PK-80S pumps have free-flow impellers as in Fig. 16. ZFMG POWEN is currently undergoing intensive work on the modernization of the pumps. submersibles, which we will briefly discuss below.

Mining needs for submersible pumps.

The development of mining entails an increase in requirements for the machines used in the mining process. Among the pumps manufactured by ZFMG POWEN, submersible pumps are most commonly used in mines. The requirements placed on the factory regarding these pumps are diverse - they concern both operating parameters, quality of workmanship, modern design, work automation, as well as meeting the basic quantitative demand.

Currently, ZFMG POWEN's production includes only submersible pumps with a capacity of up to 260 m³/h and lifting height up to 38 m according to Fig. 26. The production of these pumps in the amount of ten thousand pieces per year meets the most urgent needs of mines. Submersible pumps with higher operating parameters are currently imported from the so-called II payment zone, mainly from Flygt.

ZFMG's activities to meet the needs of the mining industry in the field of submersible pumps.

User needs and the analysis of the state of the art show us the directions of our activities, which include in particular:

• testing of flow systems of new generation submersible pumps in terms of their optimization, while ensuring non-overload power consumption characteristics. Work in this area is carried out in close cooperation with the Institute of Fluid-Flow Machinery of the Lodz University of Technology, and the results obtained so far in some cases exceed the achievements of leading foreign companies,

• implementing progress in the field of automation of submersible pump control. We carry out activities in this area in close cooperation with the Mining Automation Authority EMAG in Katowice, and detailed achievements in this field will be presented in a separate study,

• implementation of new sizes of submersible pumps in production in order to eliminate the import of pumps of this type. As a result of cooperation with IMP PŁ and GAG EMAG, a number of prototypes of new pumps were developed and manufactured, which undergo a series of laboratory and certification tests intended for machines intended for operation in mine undergrounds. Further sizes of new generation pumps will be manufactured in the coming months after the IMP of the Lodz University of Technology completes the work on the optimization of flow systems for these pumps,

• improving sealing nodes and adapting the selection of construction materials and manufacturing technologies to growing needs and changing working conditions. In this respect, we use extensive experience in the operation of submersible pumps in mines when pumping water with various characteristics.

New submersible pumps from ZFMG production.

In 1987, pumps marked P-1BA and P-2BA will be put into production, with parameters consistent with those shown in Fig. 26 for P-1B and P-2B pumps. A new feature in these pumps will be a temperature sensor that regulates the pump's operation, in particular its automatic switching on and off with a change in the degree of immersion of the pump in water. In the same year, new pumps will be introduced into production:

P-3C with power P = 22 kW and parameters corresponding to the P-5A pump according to the diagram in Fig. 26 and PK-80B and PK-80BS with power P = 5,5 kW and slightly higher parameters than those presented in Fig. 26 for pumps PK-80 and PK-80S.

Currently, preparations for the production of a new series of PC pumps, planned for implementation in 1988-1990, are also well underway. The new series of submersible pumps should include the following pump sizes:

• P-1C with a power of ... 1,1 kW for 220, 380 and 500 V
• P-2C” 4,5 kW, 380 and 500 V
• P-3C” 22 kW, 380 and 500 V
• P-4C” 45 kW, 500 V
• P-5C” 90 kW, 500 V

and the previously mentioned PK-80B and PK-80BS pumps with a power of 5,5 kW at 380 and 500 V. Pumps with a power of up to 5,5 kW will be built with connection and control equipment included in their design, which will simplify the connection of the pumps to networks. So far, in mining conditions, connection to the network was made through the KWSOI circuit breaker. Eliminating these switches from submersible pump installations is an undoubted achievement and a significant improvement in their operation. Implementation of the above production pumps will cover the basic needs of the mining industry in this area for the next few years.

Special pumps.

In addition to the pumps discussed earlier, ZFMG POWEN also produces the following pumps:
• piston type, marked with T and WT symbols
• vortex, marked with the symbols ZW, GS, S and PP.
For the purposes of this study, they are called special pumps. In this case, we will limit ourselves only to presenting their design and operating parameters, as well as a brief description of the purpose of these pumps. In the coming years, these pumps will continue to be produced, and progress in their design and manufacturing technology will include, among others: a derivative of the development of the production of pumps discussed earlier.

T-100/32 and T-140/32 piston pumps.

The T-100/32 pump according to Fig. 28 is part of the equipment of the AZ-2SM hydraulic power unit intended to power powered longwall supports, hydraulic shifters and other hydraulic devices adapted to the parameters of this unit. The pump unit can pump industrial water and oil-water emulsion. T-140/32 pumps have a similar application in AZE-4 units, with higher efficiency than AZ-2SM.

The operating parameters of both pumps are given in Table 2.

WT-30 piston pumps.

WT-30 pumps according to Fig. 29 are intended for pumping water containing small amounts of mechanical impurities. They are used primarily for pumping mud during large-diameter drilling. Flameproof electric motors and pneumatic motors are used to drive WT pumps. The operating parameters of these pumps are given in Table 3.

ZW-50 centrifugal pump.

The ZW-50 pump is part of the AQUA-1 sprinkler system. It is a multistage centrifugal pump with a structure similar to the OS-AM pumps according to Fig. 12. It is designed to operate with an inflow of up to 2 MPa. The operating characteristics of the ZW-50 pump are shown in Fig. 31.

GS-100K submersible pump.

GS-100K submersible pumps according to Fig. 30 are multi-stage centrifugal pumps with a vertical structure, intended for extracting water from wells and boreholes for utility purposes and for lowering the level of underground water. The use of these pumps is especially common in sulfur mines.

The elements of the flow system are made of plastic, which allows them to be easily replaced directly at the well without the need to transport the pump to a repair shop.

The operating characteristics of the GS-100K pumps are shown in Fig. 32.

Self-priming centrifugal pump S-12R.

The S-12R pump according to Fig. 33 is a self-priming centrifugal, circulation pump, two-stage, in a horizontal system. It is used to pump clean water in coal seam humidification devices. Moreover, it is used wherever a pump with low capacity and high lifting height should be used.

The operating characteristics of the S-12R pump are shown in Fig. 34.

Centrifugal pump with pneumatic drive PP-1T.

The PP-1T pump according to Fig. 35 is a light, portable centrifugal pump with a pneumatic drive. It is mainly used for drainage of faces, ditches, etc. It is adapted to pump mechanically polluted water with a permissible density pmax = 1200 kg/m³ and maximum grain granulation up to 5 mm.

The pump operating characteristics are shown in Fig. 36.

The development of pump construction and technology at ZFMG POWEN is possible and will be implemented. However, in order for technical progress to be implemented as quickly as possible, certain anticipatory actions must be taken to create conditions for proper development. These activities include:

• reorganization of the technical and research facilities at the factory using some of the experiences from the activities of ZDMP at ZFMG in the 1970s,
• modernization of the plant testing station to enable testing of new generation pumps,
• development of research methods in scientific centers in the country in the field of optimization of flow systems in order to accelerate design and research processes,
• ensuring the supply of domestic engines with power up to 0 MW and rotational speed n = 2 and n = 1450 rpm for driving OWH and OW-D pumps,
• ensuring the supply of domestic fittings with pressure up to 16 MPa for the installation of OWH and OW-D pumps in mines,
• ensuring the supply of engines for submersible pumps with a power of up to 90 kW in the quantity necessary for the production of PC pumps,
• ensuring the supply of domestic high-quality mechanical stuffing boxes for the production of PC pumps, and in the future also OS-C and equivalent PH pumps,
• increasing the supply of spare parts and castings from special alloys from the cooperation, in order to relieve ZFMG POWEN of a certain part of the production tasks.

The content of the article also indicates other tasks that determine the proper development of domestic pump production in the future: These tasks include:

• development of variable frequency drives,
• development of technology and covering metals with protective coatings,
• development of casting technology and implementation of new casting alloys in the production,
• development of automation and control in the dewatering process,
• verification of regulations regarding the design and model of mines,
• launching the production of submersible engines with a power of up to 2 MW in order to put into operation submersible pumps for the main drainage of mines.

engineer Wiesław Kańtoch

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Literature

1. Karassik. II:The centrifugal pumps out of the past -into the future. World Pumps – June 1984.
2. Zarzycki M.: The problem of pumps used in coal mining. Mechanization and Automation of Mining 1983, No. 4.
3. Kamiński Z.: Rudzki E.: Mining pumps for mechanically contaminated liquids. Mechanization and Automation of Mining 1983, No. 4.
4. Kańtoch W., Wilk St.: Mining, stationary drainage pumps. Mechanization and Automation of Mining 1983, No. 4.
5. Kania E., Zarzycki M.: Automation of mining drainage pumps. Mechanization and Automation of Mining 1983, No. 5.
6. Wilk St.: Directions of development of mining stationary drainage pumps. Mechanization and Automation of Mining 1983, No. 5.
7. Kania E., Pawlik R., Wróblewski A.: Assessment of a series of explosion-proof portable submersible pumps and proposed changes. Mechanization and Automation of Mining 1983, No. 5.
8. Rudzki E., Wróblewski A.: Pumps and fans produced by the Zabrzańska Fabryka Maszyn Górniczej POWEN. Mechanization and Automation of Mining 1983, No. 6.
9. Olejarczyk A., Miszko M., Marek J, Domagala W., Sikora Z., Nowak T., Kołodziej S.: Analysis of needs for main mine drainage and prospective determination of operating parameters. Prepared by the Main Office of Mining Studies and Projects BPG Katowice – 1984.10.05/XNUMX/XNUMX.
10. Korczak A., Trybus P., Jaszek Z., GerlichJ.: Model tests on the effectiveness of water purification in the relief disc system according to the ZFMG POWEN project. Prepared by the Institute of Machines and Energy Devices of the Silesian University of Technology.

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Author's comment after many years: 

“The article was written in the 80s. The economic realities of that period mentioned in it, such as difficulties in finding appropriate fittings on the market or problems with obtaining a sufficient amount of stainless steel, have fortunately changed. What is noteworthy is the accuracy of many technical forecasts. For example, at that time the use of frequency converters to regulate pump parameters was an issue bordering on science fiction, and yet it was indicated in the article as a direction in the development of pumping technology, which has been confirmed over the years. It is worth emphasizing that ZFMG POWEN, at a time when, as stated in the article, did not have sufficient production capacity to meet market demand, i.e. did not have to worry about the sale of its products, conducted research and development work on such a large scale. This action resulted mainly from the company's technical ambitions, as it was not forced by market competition. Many of the intentions discussed in the article have been realized. The company has since gone much further, for example by developing new ranges of high-pressure H and medium-pressure M pumps to replace previous designs. A less optimistic reflection is that due to the current economic problems of the mining industry, the possibilities of implementing modern technical solutions in this industry are decreasing, which is due to the policy of purchasing at the lowest price with no consideration of operating costs and lack of respect for copyrights to construction documentation. entitled to companies incurring expenditure on technological development. "

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summary

The article presents conclusions from 36 energy audits of pumping systems. The most important causes of energy losses and potential savings that can be achieved as a result of the proposed modernizations are presented. Examples of analyzed pump systems are presented.

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1.  Introduction – data source.

The article was written based on the results of 36 analyzes of pump systems carried out by the POWEN-WAFAPOMP SA Group and Energopomiar Gliwice sp. z o. o. in some cases jointly and in some cases independently. The analyzes included both formal energy audits conducted to obtain "white certificates" as well as assessment of the profitability of investments in the modernization of pumping systems. The audits covered pumping systems from various types of industry, but a significant part of them concerned pumping stations operating in water supply systems. The second significant group were water treatment and distribution systems in industrial plants, which were very similar to waterworks supplying water to the population. It should be emphasized that the vast majority of the analyzed pump systems operated in plants with a high technical level, among others, many of the analyzed pumps were already equipped with frequency converters.

A significant number of analyzed pump systems allow for drawing general statistical conclusions. However, it should be borne in mind that the analyzed pump systems were not representative of all pump systems, as they were selected by users for audit due to the alleged occurrence of excessive energy losses.

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2. Audit results.

The results of the pump audits conducted allow the following statements to be formulated.

There is a recurring group of causes of excessive energy losses:

a) Deteriorated technical condition of the pumps. The parameters of each pump gradually deteriorate during operation. This also applies to energy efficiency. If an appropriate renovation policy is not implemented, over time the resulting energy losses become significant. A common mistake is that renovation contractors are required to recreate the so-called "mobility efficiency" (low level of vibrations, low temperatures of individual structural nodes, etc.), however, no attention is paid to hydraulic parameters. The efficiency of the pump depends largely on the geometry and quality of the elements of the flow system (impellers, guide vanes). If the renovation is limited to replacing bearings and seals, and the elements of the flow system are not replaced or are replaced with non-original parts, the efficiency of the renovated pump may differ significantly from the efficiency of the new pump. Paradoxically, the use of frequency converters may often result in failure to detect deteriorated efficiency, because if the pump operates at a constant speed, as its technical condition deteriorates, it loses efficiency, which motivates the user to carry out repairs. However, if the pump operates with automatic speed control, as the technical condition deteriorates, the regulation system gradually increases the speed, thanks to which the pump maintains the required efficiency and pressure, but has increased power consumption, which is not always noticed. As an illustration on fig. 1. the results of efficiency measurements of five pumps of the same type operating in parallel on a common collector are shown.

As you can see, it was found that the maximum efficiency of individual pumps ranges from 62-80%, which proves that the technical condition varies greatly depending on the quality of the renovations. In the case of the pumping station concerned fig. 1. the pumps were correctly selected for the requirements and the maximum efficiency was close to the operating capacity. The fact that this maximum efficiency varied so significantly between pumps resulted in significant energy losses.

The source of losses in the form of pump efficiency reduced compared to the factory value, although seemingly obvious, is often not taken into account in practice. As a result, various types of modernization are considered, not taking into account that a similar effect can often be achieved at a lower cost by simply bringing the pump to the proper condition through properly performed renovation.

b) Pump parameters not adjusted to current requirements.

This reason is typical of many water supply pumping stations designed in the 80s or earlier, when the expected water demand was much higher. As a result, now, after a drop in demand, many pumps are operating at capacities much lower than optimal. It should be emphasized that the losses resulting from this cannot be completely eliminated by regulating the rotational speed, especially in water supply pumping stations, where the adopted method of operation is to maintain constant pressure in the collector regardless of the capacity. The use of speed control, of course, provides noticeable savings compared to throttling, but does not fully eliminate losses. This is due to the fact that the optimum efficiency of a centrifugal pump shifts along a parabola when reducing the rotational speed, and therefore the drop in efficiency is accompanied by a significant drop in pressure. Therefore, if the pressure is maintained constant while reducing the efficiency, the pump leaves the area of ​​the highest efficiency. This effect can be observed in the example characteristic showing the change in the efficiency of the centrifugal pump when the speed is changed, as in fig. 2.

Therefore, if there is too large a discrepancy between the nominal parameters of the pump and the current demand, it is not possible to achieve optimal efficiency by adjusting the rotational speed and it is advisable to replace the pump with a smaller one.

c) Suboptimal adjustment method.
Despite the increasingly common use of modern control methods, such as changing the rotational speed, less effective methods, such as throttling, are still used.

d) Suboptimal pumping system.
In addition to the above-mentioned causes of excessive losses related to pumps, there are cases where the concept of operation of the entire pump system is faulty. A typical example is the supply of several water collection points from a common collector, where different pressures are required. In such a situation, throttling loss occurs at the collection points where the required pressure is lower than that prevailing in the collector (forced by the required maximum reception pressure).

The individual above-mentioned causes of excessive energy losses most often occur together, although there have also been cases when one of the above reasons was clearly omitted. Out of 36 pumping systems audited, the following were found:

a) 26 cases of mismatch between parameters and requirements,
b) 19 cases of significantly deteriorated technical condition of pumps,
c) 7 cases of incorrect concept of the pump system,
d) 6 cases of non-optimal regulation method. The relatively rare occurrence of this reason, as stated above, resulted from the fact that the audits were carried out in plants of a high technical level, where modern regulation methods had already been implemented in many cases.

Energy savings opportunities can be found in almost 100% of pump systems. However, what is important is the scale of energy savings that can be achieved and the rate of return on investment in modernization projects. As part of the audits carried out, potential energy savings opportunities were assessed. If the pump system operates with variable parameters, the hourly distribution of parameters is important to estimate energy consumption. The calculation methodology used during the audits was to, whenever possible, try to obtain historical data covering a wide period, e.g. one year. Since many of the tested systems were equipped with parameter recording systems, it was possible to analyze hourly records of efficiency and lifting height (Q and H). If there were no user suggestions regarding expected changes in the system, it was assumed that the future distribution of parameters would coincide with the recorded historical distribution. Annual energy consumption was calculated by summing energy consumption in individual hours with the recorded parameters.

Out of 36 pumping systems audited, the following were found:
a) in 4 cases, it is possible to save up to 10% of energy,
b) in 15 cases, the possibility of saving 10-20% of energy,
c) in 8 cases, it is possible to save 20-30% of energy,
d) in 9 cases, it was possible to save more than 30% of energy.

As you can see, the scale of savings that can be achieved is high. Only in 4 cases out of 36 (i.e. in every 9th system) the potential savings did not exceed 10% of energy consumption, and in the remaining cases they were higher. It is worth emphasizing once again that this situation occurs in pump systems operating in plants with a good technical level, where in many cases modern methods of parameter regulation have already been implemented.

From an economic point of view, the amount of expenditure required to obtain the potential energy savings estimated above and the payback period are of fundamental importance. As part of the audit, economic indicators such as NPV (net present value) and internal rate of return (IRR) were calculated. This article will only present simple payback periods (SPBT) calculated based on the current electricity price. More complex economic indicators (NPV, IRR) involve the need to make certain assumptions arbitrarily, such as the amount of the discount rate or the forecast of changes in electricity prices in the following years, and are therefore not always fully comparable with each other.

In the 36 cases of audited pump systems discussed, the following were calculated:
a) in 2 cases, a simple payback period of over 10 years,
b) in 5 cases, a simple payback period of 5 – 10 years,
c) in 19 cases, a simple payback period of 2 – 5 years,
d) in 10 cases a simple payback period of less than 2 years.

It can therefore be concluded that the vast majority of the estimated payback periods for modernization were attractive or very attractive.

The results given above regarding possible energy savings and payback periods apply to modernization variants considered optimal. Various alternative variants were considered as part of the audits carried out. Since, as mentioned, different causes of energy losses often occurred together, various saving measures were possible. A typical situation was when by eliminating all causes of losses, it was possible to achieve maximum energy savings, which, however, involved significant expenditure, and at the same time it was possible to take partial action requiring less expenditure and giving a limited effect but with a more favorable rate of return on expenditure. As an example, we will discuss the pump system shown schematically in fig. 3.

The system consisted of a shore intake of raw water, which was pumped to a tower tank built on higher ground using a pump with a 1 MW engine. From this tank, water flowed by gravity onto the accelerators. The flows to individual devices were regulated with throttle valves. Based on the records from the recording system, a chart was prepared of the annual distribution of Q, H parameters for the pump at the intake (fig. 4.) and ordered chart (fig. 5.) showing how many hours per year the system worked with a specific efficiency.

Parameter distribution on fig.4. shows two operating modes of the system: with throttling (points arranged diagonally along the pump characteristic) and with rotational speed control (points arranged horizontally, i.e. with constant pressure in the collector maintained by changing the rotational speed). This illustrates the savings resulting from the use of rotational speed control, because during throttling, the excess pressure resulting from the pump characteristics at a given capacity over the pressure in the collector was lost on the throttling valves. Throttling work was not analyzed as part of the audit because it should not have occurred since the speed regulation was installed. However, as shown below, further energy savings were possible compared to operation with speed control. The measurements of the characteristics of the pump operating at the bank showed that it was in good technical condition because the measurement points were close to the factory characteristics. As seen from fig. 4. the speed-controlled pump operates at a lifting height of 70 m in the range of 1500 - 3500 m3/h. this operating range was plotted against the background of the pump characteristics at variable rotational speed (Fig. 6).

As you can see, the pump is operating below optimal efficiency. As a result, despite regulation by changing the rotational speed, the pump operates with an efficiency of 65-76%, while its maximum efficiency is close to 78%. The simplest modernization option was to use a pump with a lower nominal capacity. In order to reduce costs, it was proposed to rebuild the existing pump, including replacing the flow system (impeller, guide). This allowed us to avoid the costs of rebuilding the site. The characteristics of the modernized pump with the operating range marked are shown in fig. 7.

Calculations have shown that such modernization will save 15% of the energy consumed (compared to the operation of the current speed-controlled pump), i.e. 948 MWh per year, and the estimated outlays will pay off after six months.

Analysis of the system indicated the possibility of further savings. The lifting height of 70 m at which the pump operates at the intake is due to the fact that the height of the tower tank is approximately 20 m above ground level. The inflow height from this reservoir required for the operation of the accelerators is approximately 8 m, and the excess of 12 m results from the need for throttling to regulate flows. An alternative variant of the system operation was proposed, consisting in abandoning the tower tank and building a tank at ground level from which the accelerators would be powered by pumps with a lifting height of several meters operating with rotational speed regulation. This solution allows the pump lifting height at the intake to be reduced from 70 to approx. 58 m and a significant drop in power consumption. This is done at the expense of additional power consumption by new pumps feeding the accelerators, but calculations have shown that in this variant, 31% of energy can be saved compared to the current state, i.e. 2032 MWh per year. Due to the high expenditure (replacement of pumps at the intake, construction of a new tank and new pumping stations), the payback period in this case is longer and amounts to approximately 4.5 years.

It is worth emphasizing that conducting an energy audit in some cases allows you to avoid unnecessary expenditure on modernizations that will not bring the expected results. An example of this is a sewage pump currently operating in the capacity range of 500-800 m³/h with a lifting height of 10 m with adjustable rotational speed. The nominal parameters of the pump are Q = 1000 m³/hi H = 28 m. Due to such a difference between the current and nominal parameters, the user selected the pump for replacement, which seems to be a rational decision. Measurements made as part of the audit allowed us to estimate the system characteristics of the pump and determine that it is in good technical condition. The current operating parameters have been plotted against the pump characteristics (Fig. 8).

As you can see, in this case, despite the excess of nominal parameters, the pump operates in the area of ​​optimal efficiency at reduced rotational speed. The losses are only related to the underload of the engine, which, with significantly reduced power consumption, shows slightly worse efficiency. If a new pump was purchased with the currently required parameters, the purchase of a pump with such excess parameters as the existing pump would be unjustified, primarily due to the higher price. However, since the pump is already installed, replacing it with a smaller one is not justified because the existing one operates in a favorable efficiency range.

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   3.  Summary and Conclusions.

Data obtained from 36 audits of pumping systems in companies with good technical standards allow us to formulate the following conclusions:

• in the vast majority of the analyzed pump systems, significant savings potential was found,
• most of the proposed modernizations show attractive economic indicators,
• there is a recurring group of causes of energy loss,
• commonly used modernization projects involving only the installation of frequency converters do not exhaust the savings potential. Even in systems with modern speed control, there is room for further optimization. Other factors should be taken into account, such as mismatch of pump parameters to current needs, technical condition of the pumps, defects in the technology in the system,
• A common cause of excessive energy losses in pump systems, which is the deteriorated pump efficiency, is usually underestimated. One of the simplest ways to save energy for pumping is to pursue a renovation policy that ensures that the pumps maintain high energy efficiency throughout the entire period of operation,
• It is advisable to carry out professional audits of pumping systems because they enable the identification of sources of energy savings and, in some cases, avoid expenditure on unjustified modernization projects.

Dr. Eng. Grzegorz Pakula

MSc. Mateusz Kasprzyk

Introduction.

Correct design of a drainage pumping station requires a combination of knowledge from several fields. In addition to knowledge of drainage and hydrology, knowledge of hydrotechnical construction, power engineering, automation, and pumping technology is required. The intention of the author of this text is to provide designers of drainage pumping stations with basic information in this last field. This seems to be advisable, among other things, because the pumps used in this type of pumping stations have specific properties. The author is not a specialist in land improvement and hydrology, therefore the information contained in the text regarding these areas of knowledge is only general and limited to the scope necessary to understand pumping issues.

Drainage pumping stations.

Drainage pumping stations are used to pump water from areas from which natural, gravity drainage is not possible. This applies primarily to natural depressions or areas with no outflow, but also to areas from which the natural outflow of water has been prevented as a result of human activity, for example as a result of the construction of embankments of artificial reservoirs or flood embankments along rivers. An example diagram of a drainage pumping station is shown in fig. 1.

The pumping station usually has a tank (1) that collects incoming water and has a certain (usually small) retention, i.e. the ability to accumulate a certain volume. The purpose of the pumping station is to transfer water to the receiver (5), which is most often a river or other watercourse (canal, etc.). As a rule, the water level in the receiving reservoir is higher than in the inlet reservoir, otherwise the use of a pumping station would be unreasonable in terms of energy, as gravity drainage would be possible. In a typical case, the geometric difference in levels between the inlet tank and the receiving tank H g = H t – H s is small, i.e. of the order of a few meters. Both levels may change, e.g. due to the amount of rainfall, melting snow, etc. However, while the level in the inflow reservoir can be largely controlled by changing the efficiency of the pumping station, in practice it has no influence on the water level in the receiving river. The water level in the river is usually close to a certain average value most of the time Ht , and with this value, the pumping station should operate with maximum energy efficiency. However, it should be taken into account that in certain periods the level in the receiver may increase to Htmax and the pumping station must be able to operate at such an increased water level, although in such a case it may no longer be possible to operate at optimal efficiency.

Inflows to drainage pumping stations are usually significant compared to other types of pumping stations, i.e. at least in thousands of cubic meters per hour. These inflows show variability related to weather, season, etc., and periodically reach extremely high values. It should be realized that it is not possible to build pumping stations capable of receiving any, even catastrophic, flood inflows. Pumping stations should be designed to operate with maximum energy efficiency within a specific, typical range of inflows, as this determines operating costs through energy costs. They should also have the ability to pump the inflow increased to a certain extent. Since such increased flows only occur for short periods, pumping efficiency does not have to be the primary design criterion in such emergency cases, but there must be the ability to achieve the intended maximum efficiency. It must be accepted that the pumping station will not be able to protect the area from flooding in exceptional cases when inflows exceed this maximum value.

As it follows, the basis for designing a drainage pumping station operating with optimal efficiency is hydrological data regarding the water level in the receiver and the size of the inflow. The typical scope of work should be defined precisely. This should not be a problem in the case of modernization of a pumping station that has been operating for a long time, as data recorded during previous years of operation should then be available. However, the maximum parameters of the pumping station must be determined arbitrarily as a certain multiple of the normal parameters, taking into account the costs associated with increasing the parameters.

It should be added that if, as a result of a flood, the area where the pumping station operates is flooded (as in rys.1) then removing the effects by pumping water behind the embankment is a questionable solution. If the water level in the receiver is low again, it is more effective and less energetically expensive to break the embankment to allow gravity flow. A beneficial solution would be to prepare closed culverts in the embankments for such an occasion.

The method of discharging water to the receiver is important for the operation of the pumping station. In some cases this may be through an open channel. If pipelines are used (pos. 3, fig.1) the following rules should be followed, which have a significant impact on the energy consumption of pumping:

• The outlet of the pipeline should, as a rule, be located at the water level in the receiver. Locating the outlet above this level increases energy consumption by unnecessarily increasing the potential energy of the water, which is then lost in free fall as it exits the pipeline. Placing the outlet below the level in the receiver does not result in energy savings, because the geometric pumping height is then counted to this level.
• If there is a flood embankment to overcome (pos. 4, fig.1) the pipeline should, if possible, pass through it. Running the pipeline above the embankment does not have to result in a significant increase in energy consumption, because if the pipeline on the opposite side of the embankment goes down, the leverage effect occurs (although only when the flow is full cross-section). However, flow losses increase to some extent. Most importantly, however, running the pipeline above the shaft means that when the pump is started on an empty pipeline, it must cover a greater lifting height, which necessitates installing a higher-power engine. If the outlet from the pipeline is at the average water level in the receiver and the pipeline passes through the embankment (as in rys.1) then non-return flaps should be installed to prevent return flows in the event of an increase in the level in the receiver.
• Flow losses in pipelines should be minimized as they account for a significant part of energy consumption. If the total lifting height of the pumping station is of the order of several meters, several dozen centimeters of losses result in an increase in energy consumption of about ten percent. To avoid this, use diameters appropriate to the capacity, limit the number of fittings in the pipeline to the necessary minimum and use fittings with minimal resistance in the open state. This applies in particular to non-return flaps, which should be equipped with counterweights so that they open without the need to significantly increase the pressure upstream and, when opened, pose minimal resistance to flow.
• It is advisable to use diffusers that reduce the velocity at the pipeline outlet. The flow speed in pipelines recommended by standards is 2-3 m/s. This corresponds to kinetic energy v²/2g corresponding to a height of 20 – 46 cm. This energy constitutes the entire exit loss of this value. Therefore, it is advisable to slow down the velocity at the outlet (related to the conversion of kinetic energy into pressure) by increasing the cross-section of the pipeline at the outlet. This can result in permanent energy savings of several percent.

Specificity of pumps used in drainage pumping stations.

As can be seen from the above, in a typical case, drainage pumping stations use pumps with a capacity of several thousand cubic meters per hour and a lifting height of several meters. For such parameters, axial flow propeller pumps are used. They are included in the group of centrifugal pumps, but they are significantly different from other pumps in this category. The very principle of their operation is different. While in other centrifugal pumps the mechanism of transferring energy to the liquid through the impeller is based mainly on the use of centrifugal force, in the case of propeller pumps this mechanism is less important because the flow takes place in the axial direction. The pressure difference on both sides of the blade is important for accelerating the liquid (i.e. transferring its kinetic energy). For this reason, propeller pumps should use blades with special hydrodynamic profiles.

The characteristics of propeller pumps have a specific course. They are characterized by significant steepness, which means that the lifting height changes significantly as the capacity changes. To put it another way, it can be said that the propeller pump "tries" to maintain constant efficiency in the event of an increase in pressure on the discharge side that it must overcome. Propeller pumps therefore have a significant ability to adapt to operation with variable head.

Of course, the steepness of the characteristic should not be assessed optically, because the visible effect of steepness can be obtained by changing the scale of the graph. Steepness assessment involves calculating the gradient of the characteristic, i.e ΔH/ΔQ. To demonstrate the differences on Fig. 2 an example of the characteristics of a propeller pump is shown, and in Fig. 3 exemplary characteristics of a double-stream centrifugal pump.

Propeller pump with characteristics as per Fig. 2 has nominal parameters Q = 3900 m³/hi H = 8.8 m. With a decrease in efficiency by 20%, i.e. to 0.8 Q_n (3120 m³/h) the lifting height increases to 12.3 m, i.e. by 3.5 m or about 40% H_n.

For comparison, a centrifugal pump with characteristics as per Fig. 3 has nominal parameters Q = 1050 m³/h family = 44.5 m. With a decrease in efficiency by 20%, i.e. to 0.8 Q_n (840 m³/h) the lifting height increases to 48.5 m, i.e. by 4 m or about 9% H_n.

Propeller pumps also have a steeper efficiency curve, which is unfavorable because it means that they are highly efficient in a narrower performance range. For example, both pumps with Fig. 2 and 3 have a maximum efficiency close to 86%. Let's compare the operating ranges in which these pumps operate with an efficiency above 0.9 of the maximum efficiency, i.e. 0.9 x 86% = 77.4%. As can be seen from the above characteristics, the propeller pump maintains efficiency above 77.4% in the range of approximately 0.86 Q_n until about 1.13/XNUMX Q_n, and the centrifugal pump ranges from about 0.57 Q_n until about 1.43/XNUMX Q_n, i.e. almost three times wider.

The result of the fact that the characteristic curve of a propeller pump is steep (that is, the efficiency drops slowly with increasing lifting height) is that the power consumption increases with increasing lifting height (i.e. decreasing efficiency), reaching a maximum value at Q =0 i.e. with the bolt closed. Throttling of propeller pumps therefore increases power consumption. This is the opposite of other types of pumps, which usually have the lowest power consumption when the gate valve is closed. The propeller pump in the optimal operating range therefore has much lower power consumption than at low capacities. For economic reasons, drive motors are usually selected for the optimal operating range, which means that if the pump chokes strongly, the motor is overloaded. For example, a pump with characteristic z Fig. 2 in the optimal operating range (i.e. approx Q = 3900 m³/hi H = 8.8 m) has a power consumption of 110 kW. If common rules for selecting the engine power reserve were to be applied, an engine with a power of 132 kW would be sufficient. However, this would mean that due to overload, performance could not drop below 3500 m³/h, or in other words, the lifting height could not increase above 11 m. For this reason, a 160 kW motor would be recommended for this type of pump, which is sufficient to operate the pump within the section of the characteristic curve marked on Fig. 2 solid lines. Operating at even lower efficiency, in the section of the characteristic curve marked with dashed lines, would require even more engine power. In particular, to enable the pump to start when this gate valve is closed, an engine with a power of at least 250 kW would be necessary. However, such a solution is unfavorable due to the size, weight and price of the engine, due to the need to design the entire power supply system for higher power, and also due to the fact that an engine with such a high power in the optimal range of pump operation would be underloaded, and therefore showed lower efficiency. For the above reasons, propeller pumps are usually powered by engines with power selected for the expected optimal operating range, which do not enable the pump to operate at extremely low efficiencies. Pumping stations should therefore be designed so that the pump does not start when the gate valve is closed.

Propeller pumps most often operate in a vertical arrangement, although there are also solutions in a horizontal arrangement, where the pump shaft goes out through a bend outside the pipeline to the horizontal drive engine. The traditional solution was to use the so-called vertical shaft pumps, the hydraulic unit of which was immersed in water, the pumped liquid flowed through a pipe along the shaft and was discharged sideways through an elbow, and the stationary engine was placed above on a separate base. Recently, submersible propeller pumps have become widely used, in which the impeller is mounted directly on the end of the electric motor shaft, and the motor is sealed by mechanical seals operating in the oil chamber. The reason for using submersible pumps is to save costs when building pumping station infrastructure. Pumps are most often installed in the so-called tubular shafts. An example variant of this installation method is shown schematically in Fig. 4. The pump, which is a unit with the engine, is lowered into the shaft and seated under its own weight in a conical seat located at the bottom of the shaft. After the pump is installed, the shaft is closed from the top with a cover containing a sealed power cable outlet. The water is discharged through a horizontal pipeline extending perpendicularly from the shaft. In the sketch on Fig. 4 straight pipeline exit shown. Due to the above-mentioned need to minimize flow losses, it is advisable to use more complex design solutions for the pipeline exit from the shaft to minimize the resistance coefficient.

In order to avoid excessive power consumption when starting the pump while it is at a standstill, the discharge pipeline does not have to be flooded. The water may drop to the level in the inlet tank (dashed line on Fig. 4). After starting, the pump operates at a minimum lifting height, but due to its high efficiency it will fill the pipeline in a short time.

Regulation of pump parameters in drainage pumping stations .

The correct selection of pumps should enable them to operate with maximum energy efficiency. This issue would be simple if the pumping station operated at one fixed operating point determined by capacity Q and lifting height H. In practice, however, both of these parameters change. The required efficiency depends on the amount of water inflow, depending on weather conditions and the season. The geometric height changes similarly, resulting mainly from the water level in the receiver. If the increased inflow results from heavy rainfall, it is generally accompanied by an increase in the head as the water level in the receiving body increases. However, this does not have to be a rule, as an increase in the water level in the receiving river may result from rainfall that occurred in the upper part of its catchment area, while no increased inflows occurred in the vicinity of the pumping station. It follows that there is no strict relationship between the required capacity and the lifting height, and the pumping station should be able to operate with various combinations Q i H. It can only be said that it is unlikely that the increased inflow is accompanied by a decrease in the head, which would correspond to the characteristics of a pump operating without any regulation. Some method of regulating the pumping station parameters is therefore needed.

In the case of propeller pumps, throttling control is unfavorable, consisting in selecting pumps with excess capacity and throttling with a valve when reduced capacity is required. In the case of propeller pumps, the decrease in efficiency due to throttling is accompanied by an increase in power consumption, so throttling, which is never an energy-efficient control method, is extremely harmful in this case.

The steepness of the characteristic curve of propeller pumps is an advantageous feature in the sense that it allows them to maintain efficiency and remain in a favorable efficiency range with the head varying over a relatively wide range. For example, a propeller pump with the characteristics as below Fig. 2 with nominal parameters Q = 3900 m3/h H = 8.8 m and maximum efficiency of 85.8% operates with an efficiency above 0.9 ɳ Max with a lifting height of 5.5 to 11.5 m, then changing the capacity from 4400 to 3350 m3/h. Therefore, with very significant changes in lifting height (from 0.625 to 1.31 Hn), it is able to operate with an efficiency above 0.9 ɳ Max staying in the performance range of 0.86 to 1.13 Qn. This means that propeller pumps without an additional regulation method are able to adapt to significant changes in lifting height, e.g. caused by a change in the water level in the receiver, without a large change in performance.

At the same time, the steepness of the characteristics means that propeller pumps, working at a lifting height that varies only to a small extent, are unable to change the capacity on their own, and therefore adapting to the variable inflow volume requires a certain regulation method.

The design of centrifugal pumps allows for adjustment by changing the angle of the impeller blades. (Fig. 5) This is an advantageous control method in conditions where the capacity needs to be varied over a wide range at a constant lifting height. As can be seen from the characteristics shown in Fig. 5 the working field with the highest efficiency is arranged almost horizontally, along a line H = const. Unfortunately, the use of the blade angle change mechanism is only possible in larger stationary shaft pumps, while in smaller and medium-sized submersible propeller pumps, this adjustment method is usually not used.

The parameters of propeller pumps can also be adjusted by changing the rotational speed. (Fig. 6) When using this regulation method, the working area with optimal efficiency, as shown by the characteristics on Fig. 6, is located along a parabola, which means that when operating with a constant lifting height and variable efficiency, the pump leaves the optimal efficiency range quite quickly. Moreover, as the rotational speed increases, the power consumption increases rapidly, so a high-power drive (motor-inverter) should be used to regulate the efficiency in a wide range.

When operating with a constant (approximately) head, the pump capacity can be effectively regulated only within a certain range of the nominal capacity (in the order of nominal capacity +/- 25%). However, if the pumping station's efficiency is to vary over a wider range, regulating one pump becomes ineffective. In such a case, it is necessary to use several pumps operating in parallel and to activate the appropriate number of them. It may be advantageous to use not several pumps with the same capacity, but with different capacities. For example, if the capacity of the pumping station is to vary from 0.5 Q to 3 Q, instead of using three pumps with capacity Q it may be more advantageous to use two pumps with a capacity of 0.5 Q and two about efficiency Q, because then you can get a total efficiency of 0.5Q , Q , 1.5Q , 2Q , 2.5Q and 3Q, i.e. the required capacity range is covered with a smaller interval between the optimal pumping station capacities.

Intermediate capacities between capacities that are multiples of the nominal capacities of individual pumps can be obtained by adjusting one of two methods:

a) Application of regulation by changing the rotational speed on one or several pumps

b) Adjusting the pumping station's capacity to the inflow volume by changing the pump operating time. This solution allows the pump to operate at optimal efficiency, but requires an inlet tank with significant retention to collect excess incoming water during operation with a smaller number of pumps.

If the water level in the receiver remains approximately constant, the parameters of the drainage pumping station are adjusted by using one of the methods described above to regulate the capacity at a constant lifting height. The (approximate) constancy of the lifting height with variable capacity results from the fact that in a properly designed drainage pumping station, flow losses should be insignificant, and therefore the pipeline characteristics should be flat.

Another type of issue arises when the pumping station must provide a certain capacity with significant changes in lifting height exceeding the range that the pump can cover due to the steepness of its characteristics. This situation occurs, for example, when the water level in the receiver increases rapidly. In such situations, regulation by changing the rotational speed can be used, however, as can be seen from the characteristics on Fig. 6 Increasing the lifting height at constant efficiency by increasing the rotational speed results in a quick exit from the optimal efficiency area, which is acceptable in emergency situations. However, increasing the rotational speed causes a sharp increase in power consumption, which requires the installation of drives (motor - inverter) with appropriate power. This not only increases the investment cost, but also causes the drive selected for the alarm condition to operate with significant underload in normal operation, and therefore with reduced efficiency.

An alternative may be to use pumps of different types, with similar performance but different lifting heights: pumps with increased lifting height operating sporadically in alarm conditions and pumps with lower lifting height operating in normal conditions.

An interesting solution may be to install pumps that allow them to operate in both parallel and series systems Fig. 7. This requires the use of a connection between two pipe shafts and shut-off valves. Under normal operating conditions (lower lifting heights), gate valve 2 is closed and gate valves 1 and 3 are open. Both pumps can then operate in parallel. However, in alarm states, when it is required to double the lifting height, after closing gate valves 1 and 3 and opening gate valve 2, the pumps operate in series, generating the required lifting height. In such a case, it is unnecessary to install a drive with increased power on any of the pumps.

Monitoring and control of pump operation in drainage pumping stations.

The current level of technological development allows the construction of pumping stations operating without service. Pumps can be equipped with sensors that record their operating parameters and allow for the assessment of technical condition, such as: temperature of bearings and motor windings, sensor for the presence of water in the oil chamber of seals, motor moisture sensor, rotation direction control, and the like, depending on the pump type. Data provided by sensors can be transmitted remotely to the central system, e.g. via the GSM network, and archived there. Data provided by the manufacturer on the warning and alarm levels of individual signals can be used for rational planning of inspections and renovations.

From the point of view of energy efficiency, the method of controlling pumps is important when a certain method of regulating the parameters of the pumping station is used. In the simplest case, adapting the pumping station's capacity to the inflow size consists only in turning on and off the appropriate number of pumps based on the water level sensor in the inlet tank. When a certain level is exceeded, additional pumps are turned on, and when the level falls below the lower threshold, they are turned off. In this case, the criterion for optimizing energy consumption is very simple - the level in the inlet tank should be kept as high as possible. The only limitation is the difference between the pumps' activation and deactivation levels. From the energy point of view, both levels should be as high as possible, but too small a difference between them would result in the pumps being turned on and off too frequently, which could adversely affect their durability.

In a situation where, in addition to turning the pumps on and off, it is possible to regulate the performance more precisely, e.g. by changing the rotational speed of one or several pumps, the choice of the optimal operating mode is no longer obvious. For each of the possible inflow combinations Q and lifting height H Various operating modes of the pumping station are possible, differing in the number of operating pumps, the length of the operating period between switching on and off, and the rotational speed of the regulated pumps. For example, for one speed-controlled pump, the same amount of water can be pumped by operating for a shorter period at a higher speed or for a longer period at a lower speed, and the energy consumption will differ in both cases. For a larger number of regulated pumps, the issue becomes even more complicated due to the increase in the number of possible combinations of the operating method. Staff with a typical level of knowledge of pumping technology are generally unable to independently select the optimal operating mode of the pumping station in terms of energy. To obtain optimal energy consumption indicators, it is therefore advisable to develop operating instructions for the pumping station depending on the current parameters Q i H. Such an instruction may take the form of an automatic pumping station control algorithm. Developing such an algorithm that ensures the operation of the pumping station with minimal energy consumption is not a trivial task and requires knowledge of pumping technology. Therefore, it should not be entrusted to companies specializing only in IT and industrial automation. Developing an optimal algorithm requires analyzing the characteristics of the pumps and their cooperation with a specific system. It is therefore advisable to involve the pump manufacturer or another company specializing in pump technology in its development. Optimal algorithms for controlling the operation of pumping stations may differ significantly for individual cases, so it is not advisable to use one general algorithm for all drainage pumping stations. It should be at least calibrated or modified for individual pumping stations depending on the specific nature of their operation. The optimal pumping station control algorithm should be considered already at the design stage, because without it it is not possible to choose a solution that ensures minimum energy consumption.

Summary.

The basis for the correct selection of pumps for a drainage pumping station must be the definition of the required parameters, and they should be divided into two ranges:

1. A range of primary work occurring at least 90% of the time. This range should be covered by pumps operating at an energy efficiency as close to maximum as possible. Covering the entire range of parameters required in basic operation requires the use of an effective control method, the selection of which should take into account the optimum between the investment cost and the cost of energy consumption. This optimal can be determined using the so-called LCC method, i.e. by searching for the minimum of the total pumping costs over the years, taking into account both investment costs and operating costs.
2. Range of alarm operation with increased parameters. The selection of pumps in this case should ensure that the pumping station achieves the required capacity at a specific lifting height. The selection criterion should mainly be the minimum investment cost, as energy efficiency is less important in case of sporadic operation in alarm conditions.
3. If more complex parameter control systems are used, full use of the energy saving opportunities they provide requires the use of a specific operating mode, the selection of which may exceed the competence of the operator. It is therefore advisable to develop an optimal control algorithm by specialists in the field of pump technology, which will be implemented by an automatic computer system based on the readings of measurement sensors.

The choice of the optimal solution for a specific pumping station largely depends on the range of variability of the required parameters in both normal and alarm modes. Duplicating one solution of a drainage pumping station does not always have to be optimal. Depending on the required parameters, you should analyze and choose one of the solutions discussed in the article.

Dr. Eng. Grzegorz Pakula

In the first part of the article it was stated that in many cases there is a need to correct pump parameters in order to better adapt them to the requirements of the pumping system.

In this respect, there are the following most commonly used options (let us emphasize once again that we are talking about a one-time correction of pump parameters, and not about their continuous regulation, which was mentioned in the first part).

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Reduction of rotor diameter.

This is a commonly used method of correcting (reducing) pump parameters, which can be used to a limited extent. The optimal operating point of the pump shifts in such a way that the efficiency decreases approximately in proportion to the impeller diameter and the lifting height with its square. The reduction of the rotor diameter is accompanied by a certain decrease in efficiency, the greater the reduction. It can be assumed that the efficiency drop is not significant if the diameter reduction does not exceed 10% for pumps with vane guides and 20% for pumps with a spiral. With this method, without significant damage to efficiency, it is possible to correct parameters in the range of 90-100% of efficiency and 81-100% of lifting height for pumps with guide vanes and 80-100% of efficiency and 64-100% of lifting height for pumps with a spiral. (These are approximate, average ranges for the entire pump population. Detailed data for individual pump types can be obtained from their manufacturers). Since the cost of reducing the diameter is not high, without complicated analyses, it can be assumed that this is the optimal method of correcting pump parameters in the limited range mentioned above.

Changing the outlet angle of the blades.

The pump lifting height can be increased by several percent by "undercutting" the blades on the passive side at the impeller outlet, which increases the outlet angle of the stream. This procedure does not have a significant impact on the pump's efficiency. The disadvantage of this method is that it must be performed using quite primitive ironwork methods, and in addition, the thinning of the blade at the outlet may shorten the life of the impeller in the long run when pumping media containing solids that "smooth" the outlet part of the blade.

Changing the number of steps.

In multistage pumps, the head varies in proportion to the number of stages while maintaining optimal efficiency. Therefore, if the correction of the parameters of a multistage pump is to involve a significant change in the lifting height at a fixed capacity, this is an appropriate method for this purpose. The pump can either be shortened completely by reducing the number of stages and using an appropriately shorter shaft and tie bolts, or its connection dimensions can be maintained by replacing the removed stages inside with sleeves guiding the liquid to the subsequent stages. If the pump did not have the maximum allowable number of stages, it can be expanded to a larger number of stages, which of course requires the use of a new shaft and tie bolts.

Changing the rotational speed.

Changing the rotational speed is commonly used as a control method, but it can also be considered as a way to make a one-time correction of parameters. The parameters of the optimal operating point change so that the efficiency is proportional to the rotational speed, and the lifting height varies with the square of the rotational speed. What is important is that in a very wide range, changing the speed does not result in deterioration of efficiency, and as a result, the scope of applicability of this method is wider than in the case of reducing the rotor diameter. Technically, changing the rotational speed is easiest to achieve in the case of gear-driven pumps by changing its gear ratio. However, also in the case of pumps driven directly by the engine, this can be achieved by using a frequency converter, which in this case is not used for smooth speed regulation, but for a one-time change. The disadvantage of this solution is the cost of the transducer, although with the current tendency to drop the prices of these devices, this solution may prove advisable even for a one-time correction, especially for lower supply voltages.

When analyzing such a solution, remember that additional energy losses occur in the inverter and in the motor operating at a lower frequency. The advantage is that further adjustments are possible if further changes to the required parameters are expected in the future.

Changing the rotational speed upwards is only possible to the extent that it does not exceed the strength capabilities of the pump components due to the increase in pressure and power consumption. In any case, when changing the rotational speed, the pump manufacturer should be consulted, as such a change may cause movement problems (e.g. resonance when operating at a critical speed, problems with the load capacity of plain bearings, seal operation, etc.).

Replacing the pump with another one.

Replacing the pump with a new one with different parameters that meet current requirements is an obvious, but usually expensive solution. For this reason, this solution is not usually used in cases that can be solved by other, cheaper methods. When making a decision, however, you should bear in mind the fact that purchasing a new pump is a long-term solution, as its operation with a properly conducted renovation policy will be possible for several dozen years. However, carrying out various types of treatments and modernizations on a pump that is largely worn out is a much shorter-term solution, as its technical condition (material fatigue, degeneration of fits after numerous regenerations, degree of corrosion and "washing out" of elements) may make it impossible to keep it in operation for a longer period of time. period. Therefore, due to, among others, on the operational reliability and costs of maintaining the pump in operation, purchasing a new pump should be considered as a real alternative, especially when the required change in parameters is significant.

Pump modernization - new flow system.

Pump modernization, consisting in maintaining the existing pump housing and designing a new flow system, seems to be an interesting alternative to purchasing a new pump, as it allows obtaining hydraulic parameters corresponding to the changed needs using the elements of the existing pump and without the need to make changes to the structure at the workplace. However, this method also has some weaknesses:

• If the pump bodies are to be retained, the scope of possible parameter corrections is limited. Flow rates (related to capacity) at ports, inlets and outlets are subject to certain design limitations and cannot be varied too widely without compromising pump efficiency;

• After a certain period of use, the body surfaces are corroded and washed out. This has little impact on the efficiency of a multi-stage pump with a high head, but has a significant negative impact on the efficiency of pumps with a high capacity in relation to the head, such as diagonal or double-jet pumps, since in this case flow losses (due to surface roughness) in the liquid discharge elements they constitute a significant percentage of the lifting height. Regeneration of these surfaces is difficult, and the use of coatings improving smoothness on highly degraded surfaces does not guarantee durability of their adhesion. As a result, the pump, even if it has a new, highly efficient flow system, loses its efficiency compared to the new pump;

• As mentioned when discussing point 5, the service life of such a modernized pump will be limited due to the wear of the elements;

• Unlike a new but well-known pump on the market, whose parameters are known, the parameters obtained from a flow system designed from scratch for a specific case are subject to uncertainty. The methods of designing pump hydraulics are not fully precise and depend to some extent on the experience and intuition of the designer. Even the best designers of flow systems do not always "hit" the expected parameters on the first try;

• Modernization, which involves designing a new flow system, is not a cheap procedure. Apart from the costs of the project itself (which depend on how much an experienced designer values ​​his knowledge), it should be remembered that this requires modeling of the rotor and a set of vanes. The market cost of such modeling is several dozen thousand zlotys, which excludes the profitability of individually designing a flow system for a moderately priced pump. Taking into account the fact that, as mentioned above, designing a high-efficiency flow system with given parameters usually requires making and testing several versions, the cost of modeling requires multiplying several times;

• Modeling a flow system takes up a significant volume, which means that the cost of its storage is significant. Therefore, there is a concern whether the modeling of a flow system designed for an individual case will be available years later when the need arises to replace the flow parts. This concern does not apply to mass-produced pumps;

• The formal and legal aspect should also be taken into account. Changing the flow system causes such significant changes in the pump parameters (pressure, axial forces, critical vibration speeds) that the pump cannot be operated after modernization on the basis of the documents on which it was put into operation. Modernization therefore requires the development of a new hazard analysis, declaration of compliance with standards, etc. in accordance with the requirements of the applicable machine safety assessment system. This increases the costs of modernization.

Make a choice.

Having at our disposal the six basic methods of correcting pump parameters (and in some cases other, non-standard methods suitable for special circumstances), we are faced with the need to make a choice. This choice should result from a technical and economic analysis, which is an obvious statement, but difficult to implement in practice. A reliable analysis of this type is difficult in practice for both technical and economic reasons.

From a technical point of view, it is impossible to fully predict the achieved effects, e.g. because it is not known in advance what efficiency the modernized pump will achieve (overly optimistic assumptions are often made in this respect), but also because the efficiency of individual pumps of the same type - in accordance with applicable standards - may differ from each other by several percent within the permissible tolerances. From the economic point of view, there is no generally applicable methodology for assessing such cases. Recently, the so-called LCC (Life Cycle Cost) method, which is based on finding a solution that gives the lowest sum of investment costs and operating costs. This method is correct in principle, but its use also allows for some freedom (e.g. it is not established in what period the operating costs should be taken into account - taking a shorter period prefers solutions with low investment outlays, but giving lower effects in operation, and assuming a longer period on the contrary; it is not clear what discount rate to use when taking into account costs in distant years, etc.). By properly manipulating the above-mentioned parameters, you can get different results. The author is aware of cases of extremely unreliable analyses, for example those in which the efficiency effects obtained as a result of modernization were related to the efficiency of an existing, worn-out pump reduced by several percent compared to a new pump, without taking into account that much better effects can be achieved could be obtained by replacing the worn-out pump with a new one, without any modernization. What's worse, verifying the obtained effects in practice is not easy, as it is common knowledge that measuring pump parameters in industrial conditions is often subject to serious errors (e.g. due to problems with precise performance measurement).

How to proceed?

In summary, in order to make progress in reducing the energy consumption of pumps, the following rules of conduct can be recommended:

• Start with a general audit of the pumping system to assess whether there is any potential for savings, and if so, what;

• Further attention should be focused on cases where the overall assessment shows that the pumps are not matched to the requirements, causing them to operate with reduced efficiency and where there is a prospect of savings by adjusting the parameters;

• All possibilities should be considered (e.g. the six mentioned above) and none of them should be rejected a priori, but all of them should be assessed, e.g. using the LCC method;

• Good practice is that in order for the assessment to be objective, the company that evaluates and selects possible methods should not be interested in their implementation. If a company proposing a certain solution itself makes a technical and economic comparison with other variants, there is a fear that such an analysis is more of a marketing nature than a substantive one. Due to the fact that the assumptions made at the beginning of this type of analysis are always simplifying and to some extent intuitive, it is advisable to seek the opinion of another, independent institution that will verify the adopted assumptions;

• When making a choice based on the results of the analysis, the investor should not use the conclusions uncritically, but should become familiar with the assumptions adopted and which constitute the basis for the analysis to make sure whether these assumptions are acceptable in a specific case. It is advisable to conduct a simulation calculation to check how changes in assumptions affect the results of the analysis;

• As a result of the analyses, clearly inappropriate solutions should be rejected. If there is a group of solutions to choose from that differ in effects to a small extent (within the accuracy limits of the method), additional factors not usually taken into account in a typical technical and economic analysis can be taken into account, such as the reputation of the contractor or the risk of obtaining effects different from those expected.

Dr. Eng. Grzegorz Pakula

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The article was published in "ECiZ" magazine no. 11/2010

It is a well-known fact that each pump operating at a constant rotational speed achieves parameters resulting from its characteristics, i.e. with a specific efficiency, it produces a specific lifting height and achieves a specific efficiency, from which parameters the power consumption results. Although the pump can operate with any combination of parameters resulting from the characteristic curve, it works properly only near the so-called nominal parameters, i.e. those for which it was designed. In this range, the pump achieves its highest efficiency. The more the actual operating point of the pump moves away from the nominal point, the more the efficiency differs unfavorably from the maximum, and other unfavorable phenomena appear in the form of increased vibration and noise levels. The point at which the pump operates in its characteristic curve depends on its cooperation with the system in which it is installed - the pump operating point is the efficiency at which the pump characteristics intersect with those of the pumping system. The correct selection of a pump therefore involves carefully calculating and drawing the characteristics of the pump system, and then finding a pump whose characteristics intersect with those of the system in terms of optimal efficiency.

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Proper selection is essential.

Although the above statements should be obvious to every mechanical engineer, in practice many pumps are incorrectly selected, as a result of which they operate with efficiency much lower than achievable. This fact results not only from the author's own observations, but is confirmed by research of such recognized institutions as the American Hydraulic Institute or the European association of pump manufacturers Europump. Their estimates show that as a result of improving the quality of pump selection for pumping systems, up to 40% energy savings can be achieved, which is much more than by increasing the efficiency of the pumps themselves. In the latter area, the possibilities of progress are limited, because currently pump designs are so refined that, as a result of further development of pump design methods and pump manufacturing technologies, an increase in efficiency greater than a few percent should not be expected. This statement applies to properly designed pumps produced by serious manufacturers, which does not exclude the existence of poor quality pumps on the market which, for energy reasons, should be replaced by products of an appropriate technical standard.

When selecting pumps for a system, two qualitatively different situations should be distinguished:

1. Fixed operating point, i.e. a situation in which the parameters required by the system do not change. In this case, there is no technical reason for the pump to operate outside its optimal range, and if so, it is an engineering error that requires correction by one of the methods discussed later in the text.

2. Parameters periodically change due to the changing demand of the system (during the daily period, depending on the seasons, etc.). If this situation occurs, it is not technically possible for the pump to operate optimally at constant speed in every situation. At most, you can minimize losses by selecting the pump for the most common combination of parameters. To improve the selection quality, some method of adjusting the pump parameters is needed. The data mentioned above, regarding the potential for energy savings of up to 40% in pump systems, primarily concern the use of better control methods, because the possibility of achieving savings of this order in the case of a fixed operating point occurs only in rare cases of grossly incorrect selection.

Parameter adjustment.

There are four most well-known methods of parameter regulation, each of which has strengths and weaknesses (only methods applicable to various types of pumps are listed here, methods applicable only to specific design solutions are omitted, such as regulation by changing the angle of blades in pumps propellers or by pre-rotation steering wheel):

a) Regulation by throttling with a valve on the discharge side - it does not require high investment outlays, but does not bring good energy effects. It is best suited for pumps and pumping systems with flat characteristics and for pumps with increasing power characteristics.

b) Regulation by bleed – suitable only for pumps with power consumption decreasing with efficiency (e.g. propeller pumps and some diagonal pumps).

c) Regulation by changing the rotational speed - requires significant investment outlays, but creates the potential for significant energy savings compared to, for example, throttling regulation. It gives the best results in pump systems where the amount of losses dominates over the static head (e.g. in circulation systems), but is less suitable for situations where the static head dominates (e.g. change in efficiency while maintaining a constant, high discharge pressure).

d) Regulation by changing the number of pumps operating in parallel (this is not a method of regulating a single pump, but the entire pumping station) - the advantage of this method is low cost, but the disadvantage is that pumps with lower capacities usually have lower efficiency than one larger pump replacing them. . This method is best suited to situations in which it is necessary to obtain pumping station capacity that varies significantly while maintaining approximately constant pressure in the discharge manifold.

Although, as mentioned, optimization of the control method has the greatest potential for energy savings, this issue will not be discussed here, as it requires much more space than the scope of this article allows. We will summarize the regulation issues by saying that this is a very important issue from the energy point of view and in each case it requires the selection of an individual, optimal solution (generally from among the above-mentioned four options).

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Selection for a permanent job.

In the following, we will focus on the simpler issue of selecting pumps for a fixed operating point. First of all, it is important to understand where the cases of incorrect selection come from in such a theoretically relatively simple and well-known situation. The following main reasons can be distinguished:

1. Simple selection error. In the case of large investments, pumps are often treated as secondary auxiliary machines and therefore their selection does not receive as much attention as the most important equipment. Designers of large installations are usually specialists in a given technological process, who do not always sufficiently understand pumping issues and do not always consult specialists in this field. If a large investment is implemented on a turnkey basis, the pump manufacturer is rarely the general contractor (tender participant) and therefore has limited opportunities to make arrangements with the user.

2. Excessive caution. Although the methods for calculating system characteristics are theoretically known, there is a range of uncertainty in estimating flow resistance. For this reason, in order to avoid a situation where the pump does not provide the expected performance, designers usually select it with a certain excess of lifting height. If this reserve is excessive, the pump "escapes" to higher capacities, leaving the optimal operating range.

3. Change in demand. Over the years, the required parameters may change in relation to the design assumptions. For example, such a situation is typical for water supply and heating networks, where, due to the development of cities and changes in technology, there are significant changes in the parameters required from pumps.

4. Layout optimization. It should be emphasized that one of the basic possibilities of saving energy for pumping is the optimization of pumping systems involving the reduction of losses. This may involve eliminating elements causing unnecessary choking (pipe sections with too small a diameter, incorrect fittings) or introducing new technologies (e.g. filters or heat exchangers with lower pressure losses). Paradoxically, introducing such changes leading to energy savings means that the pumps in the installation may find themselves outside the optimal operating range because they have excess lifting height. To take full advantage of the energy saving opportunities resulting from the reduction of resistance, the pump parameters must be modified.

Therefore, if, for any reason, the pump parameters do not meet the system requirements, their parameters should be adjusted to improve pumping efficiency.

The methods used for this purpose will be presented in the second part of the article.

Dr. Eng. Grzegorz Pakula

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The article was published in "ECiZ" magazine no. 11/2010