Technical Transformation of Working Liquid and Cooling Water of Power Plant Vacuum Pump

Technical transformation of power plant vacuum pump working fluid and cooling water Yang Shunfeng, Li Bin 2, Yang Yong 3 (1. Jiangsu Xu Mine Comprehensive Utilization Power Generation Co., Ltd., Xuzhou 221116, Jiangsu, China;. Jiangsu Xuzhou Datun Coal and Electricity Company, Xuzhou 221116, Jiangsu, China; 3. School of Power Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China The vacuum pump working fluid and cooling water were reformed and the effect was significant. The results showed that the vacuum pump output was improved, the unit's fuel consumption was reduced, and the vacuum pump's operating environment was improved. Security has been improved.

Solution one: Change the working fluid make-up water source, change from original condensate water to demineralized water.

1 Overview of power plant vacuum pumps The three main steam parameters that determine the thermal economy of the unit are the initial pressure, initial temperature, and exhaust pressure. From nt=1-g, it can be seen that the way to improve the cycle thermal efficiency is to increase the average endothermic temperature and lower the average exothermic temperature. In the case of certain initial steam parameters, lowering the final steam temperature parameter Pc will reduce the average temperature of the circulating heat release process and increase the steam turbine's internal power Wi. Therefore, it can be seen that the ideal cycle heat efficiency increases as the exhaust pressure Pc decreases.

Modern large-scale units are mostly condensing units. To increase the vacuum is to reduce the exhaust pressure Pc. The reason for the formation of vacuum in operation is that the low pressure cylinder exhausts the exhaust gas into the condenser and encounters the cooling water pipe with low temperature. Condensation into water, so a high vacuum is formed in the condenser; while the vacuum is maintained, the vacuum pump is required to extract the non-condensing gas in the condenser during normal operation, and large-scale units mostly use a water ring vacuum pump because of pumping. The unit's dry air consumption is lower.

The 2X300MW circulating fluidized bed unit of Jiangsu Xuyuan Comprehensive Utilization Power Generation Co., Ltd. was put into operation at the end of 2009. Among them, the 1st and 2nd units were extraction condensation units, and the design back pressure was 4.9kPa. Each unit was equipped with 2 vacuum pumps. The vacuum pump used by the company is TC11E type water ring vacuum pump produced by the company. The degree of design overcooling should not be less than 4.2C. If the degree of undercooling is too small, it will lead to local cavitation of the vacuum pump and seriously affect the suction capacity. The condensing design parameters are as follows: 165m2; cooling water volume 40356m3/h; cooling water circulation rate 63; condenser supercooling S0.54C; terminal difference S4C; condensate content S15pg/L. Vacuum pump working fluid replenishment taken from condensate, overflow To the trench; working fluid cooling water taken from the circulating water inlet pipe, back to the circulating water return pipe.

1.1 Water Ring Vacuum Pump Principle of Operation The impeller is installed in an eccentric position in the pump cylinder. The pump cylinder is filled with an appropriate amount of working fluid. Water is usually used as the working fluid. Therefore, it is called a water ring vacuum pump. When the impeller rotates, the working fluid is thrown around, a rotating liquid ring is formed between the inner wall of the pump cylinder and the impeller, and a crescent-shaped working chamber is formed between the impeller hub and the liquid ring, and the impeller blade will in turn form a cavity. Divided into a number of unconnected, unequal volume enclosed chambers, when the impeller is rotated to the right suction port, the volume of the right cavity will gradually increase in the direction of rotation, creating a vacuum, the pumped gas will be sucked into the air from the suction pipe In the chamber, at the same time, the volume of the left chamber gradually decreases in the direction of rotation, and the gas is compressed and discharged from the exhaust pipe.

1.2 The effect of the cooling system on the vacuum The principle of the water ring vacuum pump shows that when the vacuum pump is running, in order to maintain the suction capacity, the working water must maintain a certain degree of undercooling. If the water temperature increases, the working water of the vacuum pump will vaporize. The suction limit pressure depends on the temperature of the working fluid. It can be seen from the pressure saturation temperature comparison table that the saturation temperature corresponding to 4.9 kPa (the rated back pressure of the company's steam turbine) is about 32.5C, taking into account the 4.2C subcooling required for normal operation of the vacuum pump. In other words, at this time the vacuum pump seal water working fluid should be less than 28.3C to work properly.

2 At the beginning of the transformation project, the working fluid of the vacuum pump was taken from the condensing water, and the cooling water of the working fluid was taken from the circulating water inlet pipe and backwater to the circulating water return pipe. In the summer, the temperature of the condensate water can reach 40C, and the circulating water inlet temperature can reach 30C. Therefore, it is difficult to ensure that the vacuum pump sealing water working fluid has an undercooling degree of 4.2C during actual operation. As the water temperature approaches saturation, its pumping capacity also decreases until it is saturated and vaporizes and it loses its ability to work. The vacuum level is as low as 88 kPa or less. In order to improve the output of the vacuum pump and ensure its normal operation, it is necessary to carry out technical transformation of its working fluid and cooling water. After the transformation, the vacuum pump working fluid and cooling water source diagrams are as shown in the figure. The specific reconstruction scheme is as follows: Yang Shunfeng (1981-), Male, Guizhou Songtao, assistant engineer, mainly related parameters before and after transformation from Table 1 Load Vacuum Exhaust Temperature Condensate A Circulation Water A Circulation Water B Circulation Water B Circulation Water Temperature (c) Water Temperature (C) Original Design Modification After the water, the backwater still returns to the circulating water return pipe.

Solution 3: Add another heat exchanger and take cooling water to the central air-conditioning cooling water. The company's central air-conditioning has one set of air-cooled units, two sets of water-cooled units, and two sets of compressors for each water-cooling unit. The summer set-up temperature is 8C. The cooling water of the vacuum pump can be ensured to be constant water and the required temperature of the working fluid of the vacuum pump can be reached. At the same time, in order to ensure the normal backup of the vacuum pump and prevent the vacuum pump from operating after the failure of the air-conditioning cooling water, the company decided to renovate only one vacuum pump. The other vacuum pump working fluid cooling water was supplied by industrial and circulating water, and the air-conditioning supply was operated in summer. Vacuum pump, the original regular switching to regular trial start.

After implementation of scheme 1 and scheme 2, due to the high ambient temperature in summer, the temperature of desalinated water and industrial water is also close to the working fluid saturation temperature of the vacuum pump. The working fluid of the vacuum pump is still in the vaporized state, so the effect is not obvious; scheme 3 ensures the cooling of the vacuum pump. The continuous water and the required temperature of the working fluid of the vacuum pump ensure the safety of the unit while improving the efficiency of the unit.

Finally determine the program for the transformation plan.

3 Transformation results and analysis 3.1 Economic performance According to Table 1, the vacuum is increased by 0.8 kPa before the reform, and the theoretical power coal consumption is reduced by 0.24 g/kWh; the average coal calorific value of the plant is 3,800 kcal/kg, which is converted into 0.912 kcal/kWh. The annual power generation capacity of the power plant is 3 billion megalitres. The vacuum pump can show the effect only when the circulating water temperature is higher than the working fluid vaporization temperature. In the calculation of six months, the preliminary calculation of the power generation amount of 1.5 billion kWh will reduce the annual calorific value of the furnace. : After the transformation of 1.5x109kW-hx, due to the large losses of the air-conditioning water to the bends of the 1st pipe, and the large number of users of 1 air-conditioning water, the effect of 1 machine is obviously inferior to that of 2 machines. Other power plants should pay attention to the future transformation work. this problem.

3.2 Safety In the process of vaporization of the working fluid in the pump, close to boiling of the working fluid will generate a large number of bubbles, and the bubble generation and rupture process will cause cavitation damage to the impeller. In the course of the first overhaul, the unit found that the cavitation erosion of the impeller was severe, which further proved the fact that the seal water vaporized. According to the pressure distribution formed by the water ring inside the impeller, the top of the blade and the root of the blade are the parts where cavitation is most likely to occur. The cavitation damages the dynamic balance of the impeller, causing strong vibration of the pump body and vibrating the auxiliary equipment of the vacuum pump (pressure vacuum gauge Pressure switch, inlet valve feedback device, etc., and it will issue a very large cavitation noise.Therefore, the vacuum pump working fluid not only improves the unit's economic efficiency, but also greatly enhances the unit's safety.

4 Conclusion Jiangsu Xu Mine Power Generation Co., Ltd. through the technical transformation of the condenser pump vacuum pump to improve the vacuum pump working fluid cooling water source, thereby reducing the vacuum pump seal water temperature, improve the vacuum pump output, so that the unit fuel consumption, efficiency gains, obtained Considerable economic benefits, while improving the vacuum pump operating environment to prevent vacuum pump cavitation, greatly improving the unit's safety.

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