This paper analyzes the working principle of the circulating water pump after the double-speed revamping from a theoretical point of view in parallel operation. Combining the performance test of the double-speed circulating water pump under the single and the parallel operation conditions, the economical comparison of various operating modes is made. The measures to improve the operating efficiency of circulating water pump are put forward, which provide the basis for scientific and reasonable guidance on energy saving operation of circulating water pump. Thermal power plants, circulating pumps is one of the auxiliary power larger. Unit of the power plant circulating water system, each unit is generally equipped with 2 circulating pumps, in operation is often a pump running alone or 2 pumps in parallel operation. As the unit is often in variable load operation, and affected by the season, when the circulating pump is only a single run, the circulating water flow may be insufficient, resulting in low condenser vacuum; when the circulating pump double pump parallel operation, and too much water too Large, resulting in power plant waste. Thus the implementation of two-speed circulating pump water pump and choose a reasonable mode of operation has great potential for energy saving. Hebei South a power plant 2 units for the subcritical, a reheat, single-shaft four-cylinder four-row steam 660MW pure condensing steam turbine. Each unit is equipped with three 1800HTCX-type oblique flow circulating pump, 2 runs, one spare. The plant was retrofitted to a circulating water pump at the end of 2008 to change the number of motor poles so that the motor could run at 2 speeds. In this paper, the working principle of the parallel operation of the modified two-speed circulating pump is analyzed first, and then the pump efficiency test of the two-speed circulating pump under the single and parallel operating conditions is carried out. And the economic comparison of various operating modes is made , Put forward measures to improve the operating efficiency of circulating pump, scientific and reasonable guidance for the circulating pump energy-saving operation provides the basis. 1, circulating pump works Large-scale power plant circulating pump generally uses two modes of operation: single pump operation or double pump operation in parallel. After two-speed transformation of the circulating pump parallel operation is generally double-pump low-speed parallel operation, dual-pump high-speed low-speed parallel operation and double-pump high-speed parallel operation. 1.1, a single pump working principle of the pipeline performance curve and the pump itself with the same performance curve drawn on the same chart, the intersection of the two curves is the pump operating conditions, also known as the working point. Shown in Figure 1, where I is the pump performance curve, â…¢ is the pipeline performance curve, M point is the pump operating conditions stable operation. Figure 1 Single pump operation Figure 2 The same performance pump in parallel operation 1.2, the same performance Pump parallel operation principle Figure 2 for the same performance when the pump running parallel performance curve. Figure I, II for the same performance pump performance curve, â…¢ for the pipeline characteristics of the curve, the performance of a single pump flow curve in the lift equal conditions can be superimposed, you can get parallel performance curve I + â…¡. Figure 2, the pipeline curve and pump parallel performance curve of the intersection M, that is, when working in parallel. Paralleled single pump condition, by the M point for the horizontal axis of the parallel with the single pump characteristic curve at point C, that is, each pump in parallel when the operating conditions point, at the same time we can see the parallel flow of each pump Q. Figure 2 shows the parallel work features: 2 pumps work in parallel when the lift and parallel work of a single pump head equal to the total flow of parallel delivery of each pump and flow. The parameters of each pump in parallel with the parameters of each pump in parallel after the comparison shows that: the parallel operation of each pump when the working flow is less than the individual pump working flow, while the separate pump working flow is less than double pump parallel working flow, Qc 1.3, different Performance of the pump working in parallel Figure 3 for the performance of different performance pump parallel operation. Figure I, â…¡ for the performance of two different pump performance curve, â…¢ for the pipeline characteristic curve, parallel work performance curve I + â…¡. As can be seen from Figure 3: Each pump before the parallel operating conditions were B, B two points, the flow of QB1, QB2. Compared with the working point of the pump in parallel, it can be seen that the flow QM of the two pumps in parallel is smaller than the sum of the flow QB1 and QB2 of each pump before the parallel connection. 2 pumps in parallel after the lift is greater than the head of each pump in parallel. The flow rate of two pumps with different performance in parallel is equal to the sum of the flow rates Qc1 and Qc2 of each pump in parallel. When the total flow rate in parallel is less than the sum of the flow rates when each pump operates in parallel before the parallel operation, the degree of decrease is proportional to the pump Increasing the number of parallel units, piping characteristics of the steep increase. Table 3 Performance Performance of Pumps in Parallel Table 1 circulating pump performance test data and calculation results 2, circulating pump operation test Two-speed modified circulating pump performance test reference to "centrifugal pump, mixed flow pump, axial flow pump and the vortex pump test method ( GB3216-89) ". Test conditions were selected as: single-pump high-speed operation, single-pump low-speed operation, double pump low speed parallel operation, a pump speed and a pump low speed parallel operation of four conditions. Circulation pump inlet and outlet water and condenser valves are fully open, change the connection method of two-speed motor to change the circulating pump speed. The test for each condition lasted 3min, and the circulating pump operated smoothly during the test. According to the test data, the design data and the related formula in the test standard, the performance of the circulating pump is calculated. The results of the experiment and the calculation are summarized in Table 1. Test pump outlet flow measured at the condenser population, the exit pressure gauge is replaced with a precision pressure gauge. For the parallel operation of two pumps, the calculation is based on the two pumps as a whole, the average outlet pressure, the motor power take the sum of the two pumps, the flow take the sum of the two pumps. 3, Analysis of energy saving operation of circulating pump Test and calculation results of circulating water pump after double-speed reformation are shown in Table 1: Circulating water flow of single pump at low speed is 28500ma / h, pump head is 17.89m, pump efficiency is 86.27 %; Single-pump high-speed operation of circulating water flow 34200ma / h, the pump head is 20.12m, the pump efficiency of 82.29%; double pump low speed parallel operation of the circulating water flow is 47500I chu pump head is 22.77lrn pump efficiency 85.62%; double pump level
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