Economic Operation Analysis of Circulating Water Pump in a Power Plant

. This paper calculates the main indexes of circulating water pump in a power plant, such as flow rate, head, shaft power and efficiency, and shows the test results. The results reach the guaranteed value of design technical specifications.


Introduction
The circulating water system in a power plant adopts the recirculating unit water supply system with natural ventilation cooling tower. Each unit is equipped with two double-speed motor circulating water pumps, one cooling tower with 100% capacity, one circulating water supply and return water pipe, one backwater ditch, four flat screen filters and connecting pipe valves. The system includes two connecting pipes and two electric valves between the two main pipes of circulating water supply, and several cast iron gates between the two backwater ditches.
The operation condition of circulating water pump is as follows, one unit operates with two pumps in summer; two units operate with three pumps in spring and autumn; one unit operates with one pump in winter or under low load. The circulating water system optimization is described in literature [1]- [4]. This paper calculates the flow rate, head, shaft power and efficiency of the two circulating pumps, and verifies whether they reach the guaranteed value given by the designed technical specifications, and draws the relating curves, and takes the results as an important reference for the formulation of overhaul plans.

Test Conditions
In order to adjust the flow rate of water supply, the outlet valves of circulating cooling water is respectively opened to 100%, 50% and 40%. Under each opening condition, the operation mode of circulating water system is switched to the isolated unit operation mode.

Test data and calculation results of circulating water pump
The original data and calculated result of A and B circulating pumps is respectively shown in Table 1 and  table 2. Based on the data, calculation results and the performance curve of the circulating water pump provided by the manufacturer, the head, shaft power and efficiency of the circulating water pump under different operating flow rates are shown in Table 3 to Table 6.
According to the calculation results, the curve is drawn. Flow-head curve and flow-efficiency curve of pump A and B are shown in figure 1 ~ figure 4 respectively.

Flow and Head Allowance of Circulating Water Pump
According to GB/T 3216-2005 Rotodynamic pumps Hydraulic performance acceptance tests Grade 2, the flow tolerance coefficient of pump is ±t Q ，t Q =0.08; the head tolerance coefficient is ±t H ， t H =0.05. Tolerance coefficients t Q ， t H guarantee points Q G and H G . By comparing the test results, guarantee value stipulated in the contract and relevant tolerance values specified in the standards, the guaranteed value of flow and head is evaluated.
As is seen from figure 5 and figure 6, the flow-head curves of pump A and pump B intersects with the tolerance cross. Therefore, the flow rate and head of pump A and pump B is guaranteed.

Circulating Water Pump efficiency
According to GB/T 3216-2005 Rotodynamic pumps Hydraulic performance acceptance tests Grade 2, the efficiency tolerance coefficient of the pump is ±t η ， t η =0.05. Tolerance coefficient η is applicable to guarantee points Q G and H G .。By comparing the test results, guarantee value stipulated in the contract and relevant tolerance values specified in the standards, the guaranteed value of flow and head is evaluated.. The calculation result is shown in table 7.

Conclusion
From the previous analysis of various indicators of circulating water pumps, the following conclusions can be drawn： 1 ) The flow rate, head and efficiency of the circulating pump A and B meet the guaranteed value of their design technical specifications.
2)When circulating water pump runs in parallel, it can meet the requirement of circulating cooling water quantity under design condition. For summer condition, further test certification is still needed.