The difference between sand removal submersible pump and ordinary submersible pump
Conceptual differences - essential differences
Literally speaking, a sand removal submersible pump is a submersible pump used for draining water containing sediment and must be able to function normally for a certain period of time. A regular submersible pump is used for drainage of clean water or sewage. When draining water containing sediment, using a regular submersible pump can quickly damage the motor or impeller. However, some manufacturers have a vague concept and sell ordinary submersible pumps as sand removal submersible pumps, making it difficult for users to distinguish. Many manufacturers have launched various types of submersible pumps for sand removal. What are the effects of these products? It is also unknown. The fundamental basis for distinguishing between sand removal submersible pumps and ordinary submersible pumps should be product standards. The product standard specifies the type, variety, and structural form of the product, as well as the main technical performance indicators of the product. However, due to the lack of industry standards for sand discharge submersible pumps, there is no clear or unified definition of sand discharge submersible pumps (see "What is a sand discharge submersible pump and what is a mining vertical pump" for details). This has caused market chaos for submersible pumps for sand removal. In addition, the safety certification center issued nearly 2000 safety certification certificates for submersible sand pumps (most of which were clean water submersible pumps or submersible sewage pumps) without distinguishing them, leading to further confusion in the market for submersible sand pumps. The different components and concentrations of sediment in the slurry result in significant differences in the service life of submersible pumps for sand removal. A unified standard should be established to specify the composition, concentration, density, viscosity, and other parameters of the "standard" mortar. The water pump that can work normally in the standard mortar for XX hours should be called a "sand discharge submersible pump". A clean water pump that can only pump sand for one minute and then be scrapped cannot be called a submersible sand pump. This article only analyzes the differences between the "Wang Qingwu version" sand discharge submersible pump, the clean water submersible pump, and the submersible sewage pump as follows.
Different drainage conditions in product standards
According to the product standards, the drainage conditions specified for the sand removal submersible pump are different from those for ordinary submersible pumps: A clear water pump is designed for pumping clean water. The working condition requires that the water should be free of sediment. The submersible sewage pump is designed for pumping treated domestic wastewater (sewage). The working condition requires that water is allowed to contain 4% of non abrasive solids. The sand removal submersible pump (mining vertical pump) is designed for pumping conditions rich in sediment. Its standard stipulates that it is suitable for conveying liquids containing suspended solid particles (such as quartz sand, ore, rock, ash, coal, gravel, etc.). The maximum allowable density of the slurry for conveying media can be divided into three levels, which are: a. Low concentration working condition, density ≤ 1100kg/m3 Main usage: used in coal mining areas, conveying coal containing mud and crushed coal particles. Maximum allowable concentration (weight ratio): 29% clean coal slurry content, 20% tailings slurry content, 15% quartz sand content, and 13% tailings sand content. b. High concentration working condition, density ≤ 1300kg/m3 Main usage locations: slurry transportation in the process flow, or drainage in rock blasting construction without specific measures to control sediment content. Maximum allowable concentration (weight ratio): 40% of clean coal slurry and tailings slurry, 37% of quartz sand, and 33% of tailings sand. c. Ultra high concentration working condition, density ≤ 1500kg/m3 Main usage locations: professional sand mining, tailings sand transportation, or thick slurry transportation without specific measures to control sediment content. Maximum allowable concentration (weight ratio): 60% of clean coal slurry and tailings slurry, 40% of yellow clay, 54% of quartz sand, 48% of tailings sand, and 42% of iron concentrate. Note: a) Specific gravity values: Iron concentrate 4.9, tailings sand 3.3, quartz sand 2.65, yellow clay 2.6, tailings slurry 1.8, and clean coal slurry 1.45. b) Other media are selected according to the above parameters based on the slurry density and solid density.
The power of the matching motor is different
Pump output power P= ρ GQH ρ—— The density of the slurry transported by the pump; G - Gravitational acceleration; Q - Pump flow rate; H - pump head. The design of the water submersible pump is based on a water density of 1000kg/m3 and is equipped with a motor. When using it to pump sand slurry, the motor will definitely overload and it is easy to burn the motor. This is a very simple truth. In addition, the theoretical calculated output power of the water pump is much smaller than the actual output power. The matching motor power of the sand discharge submersible pump is not just a simple product of the motor power of the same specification clean water pump multiplied by the slurry density, but should be increased by an additional 1.3-2 times the surplus. This is because it is difficult to control the concentration of the slurry during the operation of the sand pump, and the density of the transported slurry fluctuates, resulting in corresponding changes in the output power of the sand pump. In addition, solid particles during the start-up and operation of the sand pump can cause certain obstacles to the rotation of the impeller (in severe cases, the impeller may get stuck), resulting in a further increase in the output power of the sand pump. The larger the solid particles in the slurry, the greater the uncertainty factor. Therefore, when selecting the motor power for sand pump design, not only should the rated output power of the water pump be considered, but also the maximum output power. The matching electric motor of the sand removal submersible pump (mining vertical pump) not only considers the slurry density, but also adds additional surplus. In addition, a forced water-cooled structure (double-layer motor casing or motor with a water guide sleeve) is also adopted. It is possible to significantly increase the motor power with minimal cost increase. The following are the test measurement results of the national testing center: When the Y series 4kW motor adopts a forced water cooling structure, it can pass the 5.5kW motor assessment, with a power output 1.38 times higher. When the Y series 55kW motor adopts a forced water cooling structure, it can pass the 82.5kW motor assessment, with a power output 1.5 times higher. When the Y series 1.1kW motor adopts a forced water-cooled structure, it can pass the assessment of the 2.2kW motor, with a power increase of 2 times. What is the limit to which this structure can increase motor power? We did not further verify, but conservatively estimate that the motor power can be increased by at least 1.3-1.5 times (the smaller the power, the greater the proportion of improvement). If this structure is not adopted, the motor power must be left with sufficient margin by other methods.
Different structural features
When the water contains sediment, the main phenomena of damage to the submersible pump are "burning of the motor" and "impeller wear". The vast majority of them are caused by motor burning, which is due to motor overload and water ingress. Motor overload can be solved by increasing the power of the supporting motor or adopting a forced water-cooled structure (see above). The problem of motor water ingress, also known as "sand sealing", is a scientific research challenge. To extend the service life of the submersible pump for sand removal, it is necessary to solve the problems of "sand removal sealing" and "sand removal wear". The main challenge here is the problem of "sand sealing". There are many types of sand pumps used on land, such as slurry pumps, Mud Pumps, and underwater mud pumps. There are many manufacturers, but there are very few truly meaningful submersible sand pumps. Our solution to "sand sealing" is: a. Air sealed structure - the motor shaft extension end is separated from the mortar. b. Adopting a specially designed double end hard alloy mechanical seal to improve the reliability of the seal. The machine seal adopts oil lubrication, and there is a large amount of engine oil in the machine seal chamber, which can further prevent the entry of slurry. c. There is an independent "connecting chamber" between the machine seal chamber and the bearing chamber, which has a channel between the "connecting chamber" and the "water storage chamber". Even if the machine seal fails, a small amount of leaked slurry will flow into the "water storage chamber" and will not come into contact with the bearing, avoiding the loss of bearing grease and prolonging the bearing life. d. The motor is a closed chamber, and high temperature and high pressure will cause the slurry in the "water storage chamber" or "oil storage chamber" to leak out through the safety valve. e. The position of the winding inside the motor cavity is relatively high, so even if the motor cavity is filled with water, it will not directly contact the winding. This structure can extend the lifespan of the motor. The motor has a high insulation level and strong resistance to moisture and heat, which can further improve the lifespan of the motor. When conducting a moisture and heat resistance test on the motor of a sand removal submersible pump (mining vertical pump), all 0-rings of the motor were removed. Other submersible motor products were tested for sealing during certification and inspection. (When simulating the usage state, it is necessary to simulate the actual usage state of the submersible motor when the internal cavity has already been filled with water. Shanghai Electric Power Research Institute always insists on doing so. Otherwise, the humidity and heat resistance test of the submersible motor is meaningless.) Our solution to "sand erosion" is: a. Improving the material of the mouth ring can significantly increase the lifespan of the sand pump with minimal cost increase. b. The use of a spatial guide vane structure can avoid effective circumferential movement of sediment, which is more wear-resistant and has a longer lifespan than a volute structure. c. Low specific speed impeller, using herringbone blades to improve the narrow flow channel, increasing the distance between the impeller and the pump casing, reducing the length of the flow channel, improving the performance of sediment passage, controlling the flow rate, and reducing wear between sediment and the flow channel wall. d. The vulnerable parts of the impeller and pump body are made of thickened materials, wear-resistant materials, and alloy liners to enhance their wear resistance.
The design principles of water pumps are different
The clear water pump belongs to the product designed based on the principle of "one phase flow". The submersible pump for sand removal (mining vertical pump) needs to be designed according to the "two-phase flow" theory to improve the efficiency of the pump when pumping sand slurry.
Different safety performance
We believe that the submersible pump with a dry motor structure poses a risk of motor explosion when pumping sand slurry. Therefore, corresponding measures must be taken to solve safety issues for the sand removal submersible pump. Our solution is: a. The motor casing (including the motor upper cover, motor casing, and motor lower cover) of the sand removal submersible pump (mining vertical pump) adopts a welded structure to improve the strength of the casing. b. The minimum water pressure value for the strength inspection of the motor casing of the sand removal submersible pump (mining vertical pump) is 2.5 MPa (the admission certificate inspection requirement is 1 MPa), and the maximum pressure is up to 9 MPa. The strength of the motor housing and bolt specifications are designed according to this standard. c. The motor casing of the sand removal submersible pump (mining vertical pump) has a "water storage chamber" for collecting and storing condensate water, avoiding the generation of high-temperature steam inside the motor chamber. d. There are explosion-proof castings or explosion-proof fittings between the motor chamber of the sand removal submersible pump (mining vertical pump) and the "water storage chamber". e. The motor casing of the sand removal submersible pump (mining vertical pump) is equipped with a safety valve structure to prevent explosions. Based on the above analysis, we can conclude that the sand discharge submersible pump is completely different from the clean water submersible pump and the submersible sewage pump. Users must distinguish when selecting and purchasing, and not be deceived by counterfeit and inferior products.