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Selection of Pump Combination Scheme and Its Optimization Procedure

20 Jan 2022Email

The pumping station is a structure that ensures the water pressure in the water supply system, and is used to raise the required water volume to the required height. From the overall perspective of the water supply system, the water transmission and distribution system composed of pump stations, water pipes, pipe networks and regulating structures is the subsystem with the largest investment. For the selection of pumps in pipe network design, technical and economic comparisons of the schemes are often carried out within the range of possible changes in flow and head. It should be based on the technical feasibility of using the scheme within the design life, that is, whether it can meet the requirements of various water use. The optimization of the pump combination and its characteristics is an important part of the design of the feed pump station (pump house), which is of great significance to the technical and economic benefits of the pump station after it is built. The operating energy consumption of water supply projects is mainly the energy consumption of various pump groups. Therefore, the optimal design of the pump combination scheme is essentially to minimize the energy consumption under the premise of satisfying the water supply flow and pressure.

The energy saving of the speed-regulated water pump is mainly reflected in two aspects: (1) After the speed of the water pump is adjusted, the working point of the water pump changes, and the efficiency of the water pump increases accordingly. (2) Under the premise of satisfying the service pressure, the water supply pressure of the water pump becomes lower due to the speed regulation of the water pump, which reduces the power consumption.

With the continuous expansion of the scale of water supply, speed control pumps have been widely used in water supply projects. In current designs, a combination of speed-regulated and constant-speed pumps is often used to reduce total energy consumption. What this article discusses is how to choose a pump set scheme for different flow rates and lifts, and how to change the working point of the pump device to improve the working efficiency of the pump when there is a speed-regulating pump in the selected scheme. The program in this paper is realized by high-level assembly language VC 6.0.

 

Calculation method and working principle

1. Curve fitting

Curve fitting is a very practical method, especially in the period of rapid development of modern computers, the fitting problem is even more important. Curve fitting is proposed in this way. Suppose we have obtained a set of experimental data (xi, yi), (i = 1, 2,..., m»n) that seem to be disorganized, and we hope to find out the law, that is, It is desirable to construct an approximate function s(x) to approximate the desired function y = f(x). The most commonly used method is the linear least squares method. The least squares solution is:

s*(X)=a0*φ0 a1*φ1 Λ ax*φx

The coefficients a0*, a1*, Λ, ax* of the least squares solution can be obtained by solving the normal equation.

As a common case of curve fitting, if the discussion is about algebraic polynomial fitting, that is, take

{φ0,φ1 , …,φn }={1, x, x2 , …, xn },

Then, the corresponding normal equation is

where ωi=ω(xi) represents the weight function, that is, the strength of the position of different points (xi, yi), for example, the weight ω(xi) at the point (xi, yi) can be used to represent the data (xi, yi) The number of repetitions in the experiment can also be used to indicate the accuracy of the number yi. The more accurate yi is, the more important its status is, and the greater the weight ω(xi) is.

Abbreviation "absMiddle>" as "∑".

 

2. Speed ​​control operation

Speed ​​control operation means that the pump runs under the drive of a speed-adjustable motor, and the operating point of the pump device is changed by changing the speed. If we talk about constant speed operating conditions, what is considered is how to make full use of the high-efficiency working "segment" on the Q-H curve of the centrifugal pump under the condition of a fixed single speed. Then, for the speed regulation operating condition, we will focus on how to make full use of the efficient working "zone" of the Q-H curve of the centrifugal pump formed by the speed change when the water consumption of the urban pipe network varies from hour to hour. Therefore, the speed regulation operation greatly expands the effective working range of the centrifugal pump, and is a very reasonable adjustment method in the operation of the pump station.

 

The realization of the program

The process of selecting the pump set scheme is as follows:

The program first uses the good interface function of VC 6.0 to draw the characteristic curve of the water pump. Next, determine the operation plan. If there are two pumps, then there are three operating schemes: ① 1# pump ② 2# pump ③ 1# pump, 2# pump in parallel. For the parallel connection of pumps, the author adopts the principle of flow superposition under equal lift. Curve fitting is performed on the obtained superposed flow and head values ​​to obtain the curve equation. This program can input the sampling point value through the dialog box for the number of curve fitting points.

You can use the interface dialog box to input data (flow rate, head), or directly click the left mouse button to input. If the suitable scheme is not adjustable in speed, the selected scheme number and its Q-H curve will be displayed on the interface. If the speed of the plan is adjustable, first adjust the speed of the speed-adjustable pump, and then superimpose the pumps included in the plan and fit the curve to obtain the characteristic curve of the pump after speed control. At the same time, the selected pump combination scheme and combination curve equation will be output on the interface.

3. Because in the water supply system, the energy consumption of the pumping station is relatively large. Therefore, achieving the goal of minimizing the cost of the pumping station will have obvious social and economic benefits. This program is implemented on the computer through VC 6.0, and it will have certain requirements for the selection of the pump set scheme.

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