Variable Frequency Speed Regulation Technology in Water Pump Control System
The power consumption of water pump accounts for 30% -50% of the cost of making water in the waterworks. How to reduce the power consumption and reduce the cost is the problem that every water plant devotes to study. This paper discusses how to choose the water pump reasonably, the goal of.
Pump is the city's water supply system, the most important energy-consuming equipment, according to a number of water pumps in the pump operation of the survey found that the actual operation of most of the pump head is less than the pump nameplate lift, and some even more than 30% difference. Resulting in the pump operating efficiency, energy waste is serious, often overload the motor running, the reasons for this phenomenon in addition to municipal infrastructure should be ahead of the water forecast is too large, the election method is not reasonable pump, pump is also important with improper one of the reasons.
At present, most of the water supply pipe network for the direct supply of water pipe network, the current specification provides the highest daily maximum flow to calculate the lift pump, and in most cases other than the maximum, the required lift below the maximum Calculate the lift. And when the highest working conditions of the pump operating point in the high-efficiency zone, the pump in most of the time the normal operating conditions will be moved to outside the high efficiency area, thus the pump operating efficiency is low, resulting in energy waste. Improve the method is to select the pump, the head should be based on the average water consumption to calculate the head, the number of pumps should not be too few and should be different types of pumps with each other.
In this paper, through examples to explore how to properly select the pump to reduce energy consumption to meet the needs of urban water changes.
A water plant original design water supply capacity of 100,000 M3 / day, water pump room selection of five single-stage double-suction centrifugal pump in the open, respectively 600S-75AT pump 3, pump head 58M, flow 3000M3 / h, with Motor power 630KW; 350S-75B pump 2, pump head 55M, flow 1080M3 / h, pump efficiency 78%, with motor power 220KW; current urban water demand in 2.6-3.6 thousand M3 / day, hours Flow in the 1600M3 / h - 3000M3 / h between the pump outlet pressure at about 0.4MPa, when the flow rate of about 2000M3 / h throughout the year for 8 months.
1, the problem: As the original design of water is too large, usually usually open a small pump that is 350S-75B can meet the demand, due to the original design of the pump head is high, the actual demand is low (factory pressure 0.40MPa) , When the pump outlet valve all open the pipe network pressure is low, the pump hour flow rate can reach 1600M3 / h, resulting in cavitation phenomenon, pump efficiency seriously deviated from the high efficiency zone, and the motor overload operation, motor heating, prone to burn motor . When the water demand to 1700 - 2000M3 / h, you must open two small 350S-75B pump, then all the two pumps to close the export of small ways to adjust the valve flow to meet the pipe network pressure requirements, which When two pumps very low efficiency, a lot of energy consumption in the valve, and valve damage serious. 2, the solution to the problem: First of all, we 350S-75B transformation, without replacing the original motor under the premise of re-use a KBS300-435AT pump head 43M, flow 1577M3 / h, pump efficiency 86.5%, so usually open 1 pump can meet the water demand, and the pump can run in the high efficiency area; again on the original large 600S-75AT pump transformation (this pump is not equipped with matching motor), replace a KBS400-500 pump head 42M, flow 2980M3 / H, the pump efficiency of 85%, with the motor 450KW, and in this unit installed on the frequency control device to meet the needs of a variety of water changes through the above transformation, can adapt to the next 3-5 years urban water changes Of the demand.
3, the energy consumption calculation:
According to the different water supply, under the condition of head 40M, according to the performance curve of the pump, the motor efficiency is calculated according to 92%, according to the formula W = QH / 102η (KWh), calculate the unit consumption before and after the transformation, From the table can be seen before and after the transformation effect. Η - pump overall efficiency, η = η1 • η2 η1 - pump operating efficiency; η2 - pump (M); - pump water efficiency (L / s) Motor efficiency; Fourth, the conclusions Based on the above calculation and analysis results, the following principles of a reasonable choice of pumps:
1, the vast majority of China's urban water supply network is not a water tower, the pump directly supply to meet user demand for water, in order to meet the needs of different water requirements, the number of pumps should not be too few, and the size of the pump with a reasonable, Ladder-type water supply to ensure that urban water demand.
2, the size of the pump with a small model, small pump flow should be 40% to 60% of large pump flow, too small or too large will make the pump between the different combinations of water ladder uneven, thereby reducing pump efficiency.
3, where possible, as far as possible on the motor speed control device, and the speed control device should be installed on a larger unit, the speed range should be controlled between 60% - 100%.