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 plant waste of electricity. 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 working principle
Circulating pumps in large power plants generally use 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
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 working in parallel
Figure 2 is the same performance when the pump running in 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 condition of equal head superimposed, you can get the 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, 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: parallel working flow when each pump is less than a separate pump work flow, while the separate pump work flow is less than double pump parallel work flow, that Qc
1.3, different performance pump working in parallel
Figure 3 shows 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 in parallel. 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 performances 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 smaller 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.
Figure 3 different performance pumps in parallel operation
Table 1 circulating pump performance test data and calculation results
2, circulating pump operation test research
Circulating water pump after two-speed transformation test performance with reference to "centrifugal pump, mixed flow pump, axial flow pump and the vortex pump test method (GB3216-89)" carried out.
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, export pressure gauge in place to replace the precision manometer. 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, circulating pump energy-saving operation analysis
The test and calculation results of the circulating pump after double-speed modification are shown in Table 1. The circulating water flow at single-pump low speed operation is 28500ma / h, the pump lift is 17.89m, the efficiency of the pump is 86.27% The water flow is 34200ma / h, the pump head is 20.12m, the efficiency of the pump is 82.29%; the circulating water flow of double pump at low speed parallel operation is 47500I, the pump lift is 22.77lrn, the efficiency of the pump is 85.62% Run-time circulating water flow of 53000m3 / h, pump head is 24.22m, the pump efficiency of 84.95%.
When the dual pumps run in low speed in parallel, the circulating water flow is much larger than the circulating water flow in single pump low speed operation. However, the circulating water flow rate in parallel is apportioned to the flow rate of each pump, but less than the flow rate in single pump low speed operation. The circulating pump head in parallel, compared with the single-pump low-speed operation of the head has been greatly improved. When the double pump is running in parallel with high and low speed, the circulating water flow is less than the sum of the flow when the two pumps are operated in parallel in parallel, but the pump head in the parallel connection is larger than the lift in the first two pumps in parallel. Test results and analysis of the same performance of the previous pump and pump performance in parallel with different theory is consistent with the theory.
From the test results, we can see that although the flow rate of single-pump low-speed operation is slightly smaller than the flow rate of single-pump high-speed operation, the pump efficiency is higher, and the power of single-pump low speed operation is much smaller than that of single pump high- Generator power. Therefore, in the winter choose a single pump operation should try to choose a single low-speed operation. Similarly, in the summer choose double pump parallel operation, but also should try to choose a higher pump efficiency, low power generator double pump low-speed parallel operation.
4 Conclusion
This paper first analyzes the working principle of the modified two-speed circulating pump running in parallel and analyzes the working principle of the circulating pump in the single-pump operation and double-pump operation in parallel. After the implementation of two-speed transformation of the circulating pump can have a single low-speed operation, single-pump high-speed operation, low-speed dual-pump parallel operation, high speed double pump parallel operation and double pump parallel operation of five kinds of high-speed operation, Unit load flexibility to choose.
Secondly, based on the pump performance test of single-parallel operation of two-speed circulating pump, the economical comparison of several operation modes is put forward. The measures to improve the operation efficiency of circulating pump are put forward to provide scientific and reasonable guidance for the energy-saving operation of circulating pump The basis.
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