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With the rapid development of electric power industry, more and more large-capacity and high-parameter units are put into construction. In order to ensure the safe operation of the unit, the control fluid of the regulating system adopts fire-resistant oil. Because the operation of fire-resistant oil is directly related to the safety of the unit, it is necessary to strengthen supervision and attention.

Units 1 2 of Songyu Power Plant are imported domestic units (N300 16.7/538/538) manufactured by Shanghai Steam Turbine Works with Westinghouse technology. The steam turbine speed control system adopts DEHⅱ Ⅱ digital electro-hydraulic regulator produced by Westinghouse, USA, and uses American AKZO EH oil. The normal control value of oil pressure in oil system is12.41MPa ~14.48 MPa. 1 unit connected to the grid in June1995+February, and put into commercial operation in September 1996; Unit 2 was connected to the grid in February 1996 and put into commercial operation in July 1997. After a period of operation, the deterioration of EH oil quality has endangered the safe and economic operation of the unit, especially the unit 2. Therefore, according to the characteristics of the unit, the reasons for the deterioration of EH oil are analyzed and studied.

1 Operation and maintenance of unit fire-resistant oil

1. 1 high pressure EH oil system

The high-pressure EH oil system consists of an oil supply device, an anti-fuel regeneration device and an oil pipe assembly. The oil supply device provides the oil and pressure required by the control part, while keeping the oil intact. Its main components are: oil tank, oil pump, oil pressure control block, accumulator, oil cooler and regeneration device.

1.2 problems in operation

Unit 2 1996 1997 is connected to the grid for power generation. 1February, 1997, it was found that the particle size of EH oil was unqualified, and it was qualified after filtration. In May, it was found that the water content exceeded the standard and the granularity increased, and then the control valve fluctuated several times. After that, due to the serious deterioration of EH oil, emulsion was formed, which often caused the high pressure difference of oil pump filter screen, resulting in the system oil pressure dropping from 14.2MPa to 13.2MPa, which endangered the safe operation of steam turbine. EH oil was shut down, but then the moisture content of EH oil in the oil system often exceeded the standard, and the acid value fluctuated with the operation of diatomite, reaching the highest of 0.532 mg/g,1February, 998. Due to the jamming of No.4 high-pressure regulating valve of Unit 2, it was applied to limit the unit load to 280MW, so as to avoid the peak as much as possible.

1.3 maintenance supervision

Before the unit is put into operation, the system can prepare for flushing according to the manufacturer's requirements. After adding EH oil to the system, you can flush the system and determine the cleanliness of the system until the system returns to normal operation. Test cycle of fire-resistant oil: once a week from startup to 1 month; Once a month in the first year. Important test items are: chlorine content (maximum

2 Causes and preventive measures of fuel deterioration resistance

There are many reasons for the deterioration of EH oil quality of Unit 2 in Songyu Power Plant, and it is considered that there are mainly the following aspects.

2. Design shortcomings of1eh oil system

(1) High temperature promotes the aging of EH oil. The oil motor is directly hung on the regulating valve of the main seat, and there is no cooling device. After testing the surface temperature of EH oil system components, many hot spots were found. The normal working temperature of EH oil should be lower than 65℃. Although the return oil temperature is 45℃ ~ 60℃, the actual contact temperature of fire-resistant oil is much higher than its anti-deterioration temperature.

(2) The O-type rubber sealing ring has poor high temperature resistance. Fluorinated rubber O-ring seals in oil engines become brittle due to long-term exposure to high temperature. The regulating valve is worn and broken during operation, such as small particles of "carbon black" blocking the oil motor, blocking the servo valve, the regulating valve shaking or unable to adjust, or leaking. The test of the replaced O-ring shows that when the temperature of the O-ring is lower than 250℃, its physical properties have little change. When the temperature rises to 260℃, the hardness of O-ring begins to change, and the sharp screwdriver can easily damage its surface. When the temperature reaches 290℃, the O-ring is easy to break. When the highest temperature is controlled at 3 10℃ during heating, fluorinated rubber slowly dissolves in EH oil, making EH oil turn dark brown, increasing viscosity and deteriorating oil quality. Therefore, it should be considered to choose a sealing ring with higher temperature resistance and suitable for EH oil system.

(3)EH oil tank is too small and the oil return speed is too fast. The fuel tank is only 725 liters, and the output of the pump is 38L/min. The circulation rate is obviously too high, which is easy to cause deterioration of EH oil. So you can consider changing the fuel tank a little bigger. On the other hand, the refueling speed is too fast and the impulse is large, which is easy to form bubbles, resulting in high gas content and accelerated aging. Therefore, it can be considered to increase the partition in the oil tank and increase the distance between the oil return port and the oil outlet, which is beneficial to defoaming and releasing air.

2.2 Equipment installation, especially heat preservation, is problematic.

The pipeline of EH oil system is in the large cylinder of steam turbine, which has poor ventilation and is too close to the cylinder wall and steam pipeline. Compared with 1 and 2, 2 has poor thermal insulation, but this bag is not included. Comparing the component temperatures of No.2 and 1, it is found that the average surface temperature of the oil motor of No.2 high-pressure speed regulating valve is 19 1.4℃, which is 86.4℃ higher than that of 1. The average temperature of the high-pressure governor valve joint of Unit 2 is 229℃, which is 60.3℃ higher than 1+65438.7℃. The average tubing attached to the high-pressure governor valve of Unit 2 is 24 1℃, which is higher than that of Unit 1 21℃. Obviously, the thermal radiation of unit 2' s EH oil is much stronger than that of unit 1, so the deterioration of unit 2' s EH oil is very serious.

2.3 Insufficient operation and maintenance

2.3. 1 The bypass regeneration device was put into operation unreasonably.

There are two reasons why the oil inlet valve of EH oil regeneration device failed to fully open in operation:

First, after the two units are put into operation, the power plant considers that the full opening of the EH oil regeneration device may cause system pressure loss. Therefore, the regeneration device is not fully opened. In fact, this consideration is one-sided. The reason is that the inlet pipeline of the bypass regeneration system is connected to the pipeline throttled by the high pressure pipe, and this throttled pipeline makes about 3.8L/min oil flow through the filter assembly and return to the oil tank. Later, when trying to completely open the bypass regeneration inlet pressure valve, the system pressure did not decrease.

Secondly, the cylinder pressure of diatomite filter is often controlled by the pressure difference specified at the factory site, and the regeneration device is not allowed to be fully opened. The field supervisor once found that when the pressure difference was low (0. 1MPa), the temperature of diatomite filter barrel hardly increased. After the diatomite filter was disassembled, it was found that the second half was still dry, that is, the EH oil stopped flowing. Obviously, the EH oil regeneration device is missing.

From the above analysis, it can be seen that in the operation of the unit, the bypass device of EH oil regeneration should be put into operation synchronously, and the oil inlet valve should be fully opened as far as possible, so as to empty the filter in time. In addition, it should be noted that if the allowable pressure difference of regenerated adsorbent is 0.30MPa, the failure of filter element should be judged according to whether the acid value change exceeds the standard.

2.3.2 Electric heating of oil tank is out of control.

1March, 1998, EH oil needed heating and maintenance, but the heater was forgotten to turn off after it was put into operation, resulting in the EH oil temperature reaching 100℃. The heater should be equipped with a temperature control device to ensure that the temperature of the oil tank does not exceed 60℃.

2.3.3 The replacement process of diatomite is unreasonable. Before the new diatomite filter element is put into use, it should be dried first, then soaked in qualified oil, and then put into the filter cartridge after soaking for a short time. In this way, diatomite can fully absorb the moisture in the EH oil system, so that it can be put into normal operation with less exhaust during operation.

2.4 Environmental temperature affects the quality of oil.

In southern China, especially in rainy season, the air humidity is relatively high, often reaching above 85. The moisture and acid value of the EH oil of unit 2 were tracked and analyzed, and the results are shown in table 1.

When diatomite is close to failure or unadjusted, due to the high air humidity and the large temperature difference between day and night in the plant, water will invade the oil tank through the respirator, which will gradually increase the water volume. In addition, because the density of EH oil is higher than that of water 1. 13g/cm3(20℃), the water entering the oil tank is difficult to be discharged, which accelerates the deterioration of oil and gradually increases the acid value. Therefore, it is necessary to replace the desiccant silica gel (alumina) in the respiratory filter frequently or choose a more effective moisture-proof filler.

2.5 The oxidation resistance of imported fuel oil used is not ideal.

Songyu Power Plant found that the imported fire-resistant oil prepared by Shanghai Steam Turbine Factory can still be used under good working conditions, but when the working conditions are bad, its oxidation resistance decreases and the oil quality changes obviously. For example, after half a year's operation of 1 unit, the acid value of oil increased from 0.003mg/g to 0.026mg/g, and the change was not obvious. However, after half a year's operation of Unit 2, the acid value increased from 0.050mg/g to 0.45mg/g, and the acid value increased obviously.

Therefore, for units with poor operating environment, EH oil with good oxidation resistance should be considered if it cannot be replaced for a while. Domestic fire-resistant oil has good oxidation resistance and low price, so it can be considered as an alternative.

3 Conclusion

There are many reasons for anti-fuel deterioration, among which whether the regeneration device can be used well is an important aspect. In addition, high operating environment temperature, high water content and oxidation resistance of fire-resistant oil may all lead to deterioration of fire-resistant oil. As long as the preventive measures are actively sought for the existing problems, the fire-resistant oil can be used well in the operation of large units.

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