Abstract: This paper introduces the improvement of economy of DG385-185 type water supply shaft seal system and the improvement of several schemes in Yibin Power Plant, and provides references for the improvement of similar equipment. Domestic 200MW unit 50% of the capacity of the water supply system, which is equipped with shaft seal water system has two kinds: with shaft seal pump and shaft seal pump. The main difference between the two is: seal collection backwater different. According to some power plants to improve the situation, the improvement of the system without shaft seal pump shaft seal water back into the front pump inlet, unsealed shaft seal pump, the economy, high safety. 1 transformation implementation 1.1 The first step transformation The original pressure back to the front pump inlet pressure to stop the shaft seal pump operation, the rest unchanged. The first step to improve the operation: the first run after the renovation found that the distance from the multi-stage water seal on the 1st pump leakage larger end of the pre-pump inlet pressure 0.6MPa near the operation, the return temperature of 70 ℃ And a large number of leakage, rejection of water; 0.7MPa (unit close to full load), the backwater thrown a great amount of water and backwater temperature of 85 ~ 95 ℃. Free end of the front pump inlet pressure 0.7MPa (unit close to full load) running a large number of rejection of water, return water temperature of 70 ℃. 1.2 The second step transformation According to the previous experience analysis of low pressure side backwater thrown large amount of water, high temperature, may be due to poor multi-stage water seal backwater, backwater can not be excreted in time; high pressure shaft seal water inlet is too large, while the low end Water is smaller, resulting in low-pressure side leakage, rejection of water, the temperature is too high; low-pressure rejection, leakage larger. 1.3 The third step transformation 1) According to the analysis of the above two transformations, the reasons for the failure of transformation are not in the pipeline itself, but the analysis of the system and equipment before reform is not enough to be re-analyzed. Analysis of the helical bushing, which has two: First, near the high-pressure end of the shaft seal before the transformation of water, after the transformation back to the front pump; Second, close to the end of the water before the transformation for the pressure back to water, after the transformation of the shaft seal Water. 2) for re-analysis. Screw bushing near the high-pressure port after the transformation back to the front of the pump: ①conducive to maintaining the screw bushing, screw bushing temperature stability; ② prevent cryogenic condensate into the pump (condensate water pressure in the operation and the front end of the sleeve pressure close to stop When the pressure is higher than the front bushing), to prevent uneven water heating and cooling caused by vibration and increased oxygen content in the feed water; ③ can make the spiral bushing and screw sleeve where the pressure from 1.2MPa reduced to 0.6 ~ 0 .7MPa (front pump inlet pressure). After the transformation of the shaft seal backwater, backwater temperature and pump load has nothing to do with is conducive to sealing. Screw bushing near the low-pressure port after the transformation of the shaft seal water inlet, the hub from the end face of about 60mm. After the transformation of the shaft seal backwater, backwater temperature and pump load. Through the above analysis, the screw bushing near the high-pressure port after the transformation for the pump solution back to the former; spiral bushing near the low-pressure port after the transformation of the shaft seal water inlet, the hub from the end face closer, when the need to improve the shaft seal water pressure Inevitably, there will be large water leakage and poor reliability. To this end, the following transformation. ①try to make two close to the screw bushing to increase the throttling length, as long as the shoulder between the two can be sealed into the sealant rope can be. ② As the direction of water changes, the sealed water tank body is modified as follows, and the shaft seal water inlet and outlet pipes are the same as the original inlet and outlet water. 3) after the transformation of the situation. After the above improvements, 1 to 3 pump is operating normally, no water, water leakage; backwater temperature 45 ~ 50 ℃, in any condition are normal, indicating that the transformation completely successful. 2 modified postscript Although the success of the transformation, but after the transformation due to the direction of water into and out of the original opposite, the pipeline crossing, the scene affected the aesthetic, and affect the thermal components overhaul. If you replace the sealed water tank body, the single price of 24,400 yuan, higher cost (two machines need 292800 yuan six pumps). To this end, to further make the following transformation. 1) Free-end sealed water tank and the drive side seal water tank exchange, shaft seal out of the water pipe to restore the original installation location. 2) Since the free end of the sealed water tank body and the drive side of the sealed water tank body is different, this will be the free end of the water tank body taper cut off part of the cut-off part welded to the drive side of the sealed water tank cone body, and on the lathe Processing, the two dimensions exactly match. Through the above transformation, with a total investment of not more than 15,000 yuan, No. 21 unit of Huangpizhuang Power Plant has been completely renovated and has achieved good results. 3 improved economy 3.1 The economy of operation According to Huangpi Pile Power Plant No. 21 machine in 1995 with the actual load hours 5363 calculation, shaft seal pump motor power of 30kW, the annual saving of 5363 × 30 = 160890kWh As the shaft seal pump running time is greater than the feed pump operation, more than the unit running time, which is not less than 180 × l03kWh. At the same time, the high temperature pressurized backwater (60t / h) no longer back into the condenser, and to the front pump inlet can reduce the loss of cold source, improve the thermal efficiency of the unit, its thermal economy can be calculated by the following formula. 1) When returning to the front pump, the parameter is Pl = 0.6MPa (front pump inlet pressure, the actual 0.6 ~ 0.7MPa); tl = 120 ℃ (Huangpi pile power plant 2l, 22 machine measured average); h1 = 504 kJ / kg. 2) When returning to the condenser, the parameter is P2 = -0.092MPa (run the actual parameters); t1 = 43.287 ℃ (P2 corresponding to the saturation temperature, the actual operating parameters below 39 ℃); h2 = 183.28 kJ / kg (actually lower). 3) Improved to reduce cold source loss Q = m × h = 60 × 103 × (504-183.28) / 360O = 5345.3 kJ / s Each year can save: 5363 × l2.5 = 67 × 103kWh Thus, each year can save 247 × 103kWh, 0 per kilowatt-hour. l8 yuan calculation, can produce 44,486 yuan economic value, and the required about l5m∮32 × 2 stainless steel tube ratio, without six months to recover all the investment. 3.2 Maintenance economy and safety After the improvement, pressure and back pressure can be maintained and the temperature is stable. The same temperature rise as that of the pump and deaerator can be maintained, so that the thermal deformation of the screw shaft sleeve and the shaft during operation is minimized, and the safety of the equipment is improved. At the same time, eliminating the shaft seal pump, you can no longer consume expensive mechanical seals and other spare parts, reducing maintenance. Second, you can also cancel the pressure back to water pressure monitoring system, electrical, thermal control system equipment and power consumption, pump attached valves, to further reduce maintenance costs. 3.3 The feasibility of operation Due to the abolition of the shaft sealing pump system, can reduce the operation, reduce labor intensity and the resulting misoperation, misoperation, improve unit safety. 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Key words: Feed pump; Seal system; Improvement