Water jet cleaning.
Introduction.
In the sugar, energy, metallurgy, chemical, shipbuilding and other industries there is a need to use devices enabling the removal of contaminants arising in technological processes or during their operation.
Removal of impurities can be done mechanically or hydraulically. The effectiveness of cleaning depends on the amount of pressure generated in a given place to burst the contaminated sediment, regardless of the method used. In mechanical cleaning, burst pressure is caused by the sharp ends of the cleaning brush or knife blade. In hydraulic cleaning, it is caused by the water jet generated by the high-pressure pump. Using the hydraulic method of removing impurities gives:
- high cleaning efficiency,
- ability to remove dirt in hard-to-reach places,
- employing a small number of employees (practically two operators),
- using water as a cleaning agent, which is available in virtually all conditions.
These features result in the increasingly wider use of this method in industry.
The article describes the high-pressure cleaning device type WUC-1 manufactured by POWEN SA and presents the manufacturer's technology and experience in removing contaminants using this device.
Figure 1. WUC-1 High Pressure Cleaning Device. 1 – T-65/45 plunger pump, 2 – ZR-100/45 discharge valve, 3 – ZP-100/50 overflow valve, 4 – cleaning nozzle, 5 – lance, 6 – high-pressure lines, 7 – electrical equipment, 8 – manual ball valve or foot valve, 10 – water filter.
Construction, principle of operation, technical data and accessories of the WUC-1 device.
The WUC-1 device is shown in the photo and in Figure 1. The pump (item 1) sucks water from the hydrant or pipeline through the filter (item 10) and pumps it through the discharge valve to the supply main (item 6). This pipeline is made of sections of high-pressure hoses with a nominal diameter of dn = 12 mm and a working pressure of pr = 45 MPa. At the end of the power supply bus there is built-in cleaning equipment:
- manual shut-off ball valve (item 8), foot valve (item 8) or manual gun,
- fixed or flexible lance (item 5),
- fixed or rotating cleaning nozzle (item 4).
The water flow system (from the filter through the pump, discharge valve, hoses, lance and nozzle) is designed for the pressure generated by the pump, i.e. pr = 45 MPa. The discharge valve switches the pump to idle speed when the pump reaches a pressure of 45 MPa. During this time, the pump sucks water from the filter and pumps it back to the filter without pressure. If the discharge valve jams or hangs up, the pressure in the system increases to approximately 50 MPa and the overflow valve, located on the pump valve block, opens, through which the pump pumps water from the outside. In this way, the pump and the entire hydraulic system are protected against overload.
Technical data of the WUC-1 device
- Pump capacity – 65 dm3 / min
- Working pressure – 45 MPa
- Engine power – 55 kW
- Supply voltage – 380 or 500 V
- Engine shaft rotation speed – 1475 min-1
- Device weight -1225 kg
WUC-1 device accessories.
Depending on the application, the WUC-1 device can be equipped with various types of cleaning accessories. This equipment is always installed at the end of the bus. It includes: a hand or foot valve, a fixed or flexible lance, a fixed or rotating nozzle or a hand gun. The foot valve is opened and closed by the operator's foot. By pressing the pedal with your foot, it causes the liquid to flow through the valve, and when you remove it, it immediately closes the valve - cutting off the water flow from the valve to the lance. The foot valve is used when cleaning long pipes, e.g. in evaporators. Figures 2 and 3 show various versions of the lance. Figure 2 shows a fixed lance made of a pipe with an outer diameter of 20 mm (lances are also made from a 16 mm pipe), while Figure 3 shows a flexible lance that is used for cleaning bent pipes in heating devices.
Figure 2. Lance < p20.
Figure 3. Flexible lance.
Four types of fixed nozzles are provided for cleaning the pipes from sediments and scale, shown in Figure 4 (items 2, 4, 5 and 4). Fixed nozzles (items 5, 2 and 2) produce a stream in the direction of lance travel, while the nozzle (item 4) produces a stream of liquid in the opposite direction. In the case of a nozzle (item 3), the recoil force pulls the lance with the nozzle into the pipe. The nozzle (item XNUMX) allows you to clean pipes completely clogged with sediment or scale. The nozzle (item XNUMX) has a single hole and is designed to work with a hand gun.
Figure 5 shows the rotating nozzle. It is used to clean pipes or channels with a circular (cylindrical) cross-section.
Depending on the pipe diameter, a nozzle with the appropriate outer diameter and the required amount of water supplied, under appropriate pressure, is used. The WUC-1 device uses rotary nozzles with a maximum pressure. 45 MPa, with a water flow of 65 dm3/min.
Water cleaning efficiency.
Figure 4. Set of fixed nozzles.
Figure 5. Rotary nozzle. Figure 6. Nozzle characteristic data.
The effectiveness of water cleaning depends on the correct design of the cleaning system. The entire system - pump, water transport - pipes, conversion of water pressure into speed - nozzles, should be designed to create as little resistance as possible, as well as harmful turbulence and speed changes. Incorrect design, e.g. of the nozzle, or poor workmanship often leads to significant losses in water flow and loss of full effectiveness of the device.
In practice, this means that much higher water pressures are needed to achieve better efficiency of the device when using a bad nozzle. Assuming the optimal selection of the nozzle for the pump capacity and its correct implementation, the water flow rate from the nozzle will depend solely on the pump's operating pressure. You should always remember that the water leaves the nozzle in the form of a concentrated beam - a stream that remains in this form at a distance equal to approximately 100 diameters of the nozzle holes.
This is where the distance of the water jet works most effectively. By moving the nozzle away from the cleaning surface, we move the water stream away, which becomes fragmented and weakened further away due to the strong inhibition of individual water droplets by the surrounding atmosphere. This creates fog further away from the nozzle, which has virtually no effectiveness - Fig. 6.
When water droplets come into contact with a contaminated surface, the water droplets suddenly slow down, which causes a local pressure on the cleaned surface similar to the pressure of the water in front of the nozzle. The high pressure of water droplets acting on hard deposits causes them to crack, then water penetrates into the resulting cracks - fissures and breaks up contaminants, and in the final phase removes them from the surface. This use of a high-pressure water stream is particularly useful where it is impossible to reach the surface being cleaned with a sharp tool. It is necessary to properly select the angle "a", the outer diameter of the nozzle "D" and the diameter of the outlet holes "d" - Fig. 6, for each pipe intended for cleaning with a water jet.
Water pressure selection.
Research carried out on the practical removal of contaminants with high-pressure water shows that the water pressure depends on the type of sediment, the level of content and the hardness of the contamination layer.
Water pressure in the range of 11-18 MPa is used to clean: pipes, channels, oil tanks, ship bunkers, construction equipment, filter beds, air heaters, cast iron castings. This pressure is also used in the food industry to remove soft malt and fruit deposits.
Water pressure in the range of 18-30 MPa is used to clean water structures, ship hulls from alkaline accretions, foundry molds, and brick surfaces of building facades.
In sugar factories, water pressure of 30-45 MPa is used to clean technological equipment. it is most difficult to remove scale in steel pipes with a nominal diameter of 0-33 mm installed in evaporators.
For cleaning pipes made of brass, the effective pressure is 30-35 MPa.
The WUC-1 device has the ability to regulate the pressure in the above range.
Selection of pump capacity.
Pump performance has a fundamental impact on cleaning efficiency. The greater the efficiency - the more water supplied at the required pressure, the more intensive the rinsing of contaminants. At the same time, as the efficiency and water pressure in the pump increase, the power of the engine driving the pump increases, and thus the weight and dimensions of the device. For specific operating conditions, it is possible to use a motor with a lower power.
Technology for cleaning evaporator pipes in sugar factories and pipes in energy equipment.
One of the most labor-intensive operations after a sugar campaign is cleaning evaporators. Each evaporator contains approximately 4000 pipes with a nominal diameter of 0-33 mm and a length of 3,2 m. The pipes are covered with limestone inside, which must be carefully removed to ensure their full patency and proper operation of the evaporator.
If there is a thick layer of stone and it is difficult to insert a 6-hole radial nozzle into the pipe to be cleaned, a 3-hole blade nozzle with a large angle of inclination of the holes through which water flows out is used. The sharp face of the nozzle allows it to enter the overgrown pipe, and the 3 oblique holes ensure initial bursting and removal of scale from the pipe. As practice shows, in order to thoroughly clean the pipe, it is necessary to clean it again with a 6-hole radial nozzle or a rotary nozzle. In the case of pipes with an internal diameter of less than 30 mm covered with stone, a 6-hole front nozzle or a rotary nozzle should be used.
Energy devices often have bent heating pipes. Cleaning such pipes is possible with a 6-hole suction nozzle, which has outlet holes directed in the opposite direction to the direction of pipe cleaning. It should then be attached to the flexible lance (Fig. 3). The flow of water through the nozzle holes creates a force that pulls the nozzle together with the lance into the pipe being cleaned. In this way, it is possible to clean pipes bent with gentle arcs, the bending radius of which is not smaller than the permissible bending radius of the flexible lance, which is R = 150 mm.
Figure 7. Cleaning the evaporator pipe dn = 33 overgrown with limestone.
Summary.
The WUC-1 device was subjected to operational tests during a renovation campaign at the Racibórz sugar factory. It was used to clean 7 evaporators with a total amount of approx. 28 thousand. pipes. The overall performance of the device was assessed positively. Further positive experiences with the WUC-1 device were obtained when cleaning tanks in sewage treatment plants.
Roman Pawlik.
The article was published in issue 2 of the "Pompy-Pompownie" magazine in 2000.
Author's comment after 15 years:
“In my opinion, the article has not lost its relevance after 15 years and its content is still valid. The WUC-1 device, after appropriate verification of the documentation in terms of compliance with current regulations, may be offered by GPW SA on the market.
