1 The thermal economic performance of thermal power plants depends on various losses and cycle efficiency during the working fluid cycle. It is known that the cold source loss during the ideal cycle is the largest loss in the energy conversion process of the power plant, and the condenser vacuum and condensation The exhaust steam temperature of the steamer directly affects this part of the loss, and the vacuum drop and the increase of the exhaust temperature of the low pressure cylinder also cause the expansion difference between the condenser and the low pressure cylinder to increase, causing the unit to vibrate and cause adverse effects.

Theoretically, the steam turbine exhaust temperature is the saturation temperature corresponding to the steam exhaust pressure at the last stage of the steam turbine, and the formula has a cycle efficiency of one to one Qtc/Qi (where Qtc is the loss of the cold source and Qi is the boiler heat intake). The vacuum of the unit directly affects the thermal cycle efficiency of the unit. The lower the exhaust gas temperature, the lower the Qtc cycle efficiency is. Therefore, it is important to ensure that the unit operates under designed vacuum and has an important effect on the thermal economy of the thermal power plant.

2 Example analysis Ezhou No. 1~2 steam turbine adopts the TCDF imported from Japan, but there are still many unqualified vacuum condensers. In July 2001, No. 1 steam turbine vacuum failed. For example, analyze the cause of the condenser's low vacuum.

2.1 Failure phenomenon Unit 1 vacuum is 89kPa under various loads and the vacuum condition of Unit 2 is good (92 2 units of circulating water system and vacuum system all adopt the same design (circulating water system design cooling water inlet temperature 30) Designed to meet the full load requirement of the unit at inlet water temperature of 36*C.

2.2 Cause Analysis There are many factors affecting the low condenser vacuum, which can be analyzed from three aspects: the efficiency of circulating water cooling, the degree of stringency of the condenser negative pressure system, and the ability of the vacuum system to maintain negative pressure. See the specific analysis.

The analysis chart of the reason for the low vacuum affecting the condenser firstly analyzes the cooling efficiency of the condenser circulating water. Checking the efficiency can be judged by two parameters: (1) the temperature rise of the inlet and outlet of the circulating cooling water, and (2) the condenser end difference.

There are two main factors affecting the cooling water cooling efficiency: (1) The cleanliness of the copper tubes of the condenser. If the condenser copper tube is clogged, the circulation cooling water flow will decrease, the cooling efficiency will decrease, and the vacuum will be affected. However, before the start-up of this unit, high-pressure water was flushed on the water side of the condenser, and the result of putting on the rubber ball cleaning device showed that the copper tube of the condenser was relatively clean, and the possibility of the copper tube being blocked was not high; (2) The electric butterfly valve in the middle of the water inlet and outlet of the condenser is not closed (Ezhou plant is designed for backwashing of the condenser conveniently). When the valve is not strict, the circulating cooling water will be short-circuited and cause cooling efficiency. Low, the reason for this can be judged by comparing the temperature rise of the inlet and outlet of the circulating water and the terminal difference of the condenser, and since the circulation pumps of the two units are constant speed pumps, there is no regulating valve on the circulating water system, and the circulation water flow is roughly Similarly, under the same load, the temperature rise of circulating water into and out of the water should also be approximately the same, when the temperature of the working conditions is compared with the temperature of the incoming and outgoing water of Unit 2 (vacuum pass 94kPa). This indicates that Unit 1 has a good cooling condition, thus eliminating the cause of circulating cooling water.

Second, analyze the tightness factor of the condenser negative pressure system. Condenser vacuum is established by the self-condensation of steam. In normal operation, the vacuum pump is used to maintain vacuum. Because there are many pipes and systems connected to the condenser, there are many parts that affect the vacuum tightness, but the vacuum system tightness test can be used to check the sealing performance of the vacuum system. The vacuum tightness test is under normal operation of the unit. , In the unit load more than 80%, in the circulating water conditions and the unit conditions unchanged, stop the two vacuum pumps to run, test the speed of condenser vacuum drop, the vacuum rate is to test the negative pressure system tightness The best sign is that if the vacuum tightness test result is not satisfactory (vacuum reduction rate >0.4 kPa/min), it indicates that the vacuum system has poor sealability, and a thorough inspection should be carried out, that is, all possible negative pressure components should be inspected and combined. The condenser is compared and judged by the condenser irrigating test done before or before the start-up, and the leak is found. For the leaks on the negative pressure system such as the valve leakage and the small trachoma, the impact on the vacuum is generally not more than 1 kPa. Through the vacuum tightness test, the test result of Unit 1 is qualified (vacuum reduction rate is 0.25 kPa/min), and the irrigation test result is good before the unit starts. Thereby eliminating the vacuum system may be imprecise.

Third, analyze the effect of the condenser vacuum pumping system. Two vacuum pumps in Ezhou Power Plant are operated in parallel. In the normal operation of the unit, the vacuum pump only plays a role of maintaining vacuum. Because the condenser negative pressure system always has lax place, there is always a small amount of air entering the condenser, so even if After the vacuum tightness test passed, the vacuum will continue to drop after the vacuum pump is shut down. The operation personnel judged the vacuum pumping system's capacity to observe the current of the vacuum pump. After comparing the vacuum pump currents of No. 1 to No. 2, the current of the No.1 vacuum pump was found to be only 200A, and its historical record was 240A. No.1 vacuum pump current is 250A, and at the same time when the standby vacuum pump is started, the condenser vacuum has obviously recovered, which can be used to determine the reason why the condenser vacuum is low because the vacuum pump output is insufficient. To this end, the No. 1 unit vacuum pump was further inspected, and found that the cooler shell temperature was high during operation, and was measured with a thermometer as 60*C. It was considered that due to the low cooling efficiency of the vacuum pump cooler, the output of the vacuum pump was reduced. The air in the condenser can not be drawn out in time. Accumulation in the vicinity of the copper pipe of the condenser affects the heat transfer of the condenser and reduces the vacuum of the condenser. After further inspection of the two vacuum pumps, it was found that the scales of the coolers of the two vacuum pumps were serious. After cleaning them separately, the vacuum pump was restarted, the vacuum was returned to 94 kPa, and the operation of the condenser returned to normal.

3 Conclusions The low condenser vacuum in Unit 1 of the Ezhou Power Plant is due to the fouling of the vacuum pump cooler, which has a poor cooling effect, resulting in a reduction in the vacuum pump output.

For a power plant with multiple homogenous units, the comparative analysis method under the guidance of the basic thermodynamics principle can not only reasonably analyze the causes but also find out the differences quickly. It is a quick method for the analysis of problems that the power plant operators deserve.

(Continued from page 46) A foreign company has designed a new type of DRAG labyrinth disc-type minimum flow control valve, using a labyrinth disc as a decompression device, the actual operation is better.

2 Problems to be Solved in Selection of Feedwater Pump Unit Equipment 2.1 Performance Indicators In order to adapt to changes in the load of the unit during operation, the steam feed water pump and electric feed water pump require flexible adjustment performance in addition to the required flow, pressure and efficiency. The steam turbine feed water pump's small turbine speed range should generally be 2700~60001/min allowable load change rate is 10%/min; the electric feedwater pump group starts from the zero speed standby state to the feedwater pump outlet pressure and flow rate to reach the rated The time of the parameter is 12 2.2 The matching problem of the feed pump to the rotation speed of the small steam turbine The question of locking the feed pump core of the small steam turbine in the process of preheating and low speed start-up or pumping the hot pump in the hot state of the feed pump has once appeared in many power plants in China. After the jam occurs, the pump must be dismantled for inspection or returned to the factory for disposal. In particular, the performance of the new production unit is obvious and prominent at the initial stage, which has a serious impact on the normal operation of the unit.

The requirement for the spinning speed after the outage is a reflection of the quality of the feed pump rotor. If the spinning speed requirement is greater than 10i/min, it indicates that the pump's rotor hot state stiffness is not good, and jamming is likely to occur. At present, the general power plant adopts the practice of not throwing cars at the initial stage of production of new units (less than six months). It starts directly after warming the pump, and does not throw the car after the pump is stopped. After the system is cleaned, the pump unit operates reliably. Normal use of disc brakes. Hangzhou Steam Turbine Co., Ltd., in response to this problem, introduced Siemens technology to use a high-speed oil vortex disc drive device. The crankshaft rotation speed is greater than 1201/min. After the hot pump of the feed pump drops to a certain value, it can be input to the disc brake device. The problem that the worm gear of the electric disc brake device can only be input when the rotation speed drops to *0* solves the problem of sticking when the pump is put into the disc brake device after the hot pump of the water supply pump is turned on.

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