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Cause Analysis and Treatment of Oil Fume Spraying in the Front Box and Middle Bearing Box of Steam Turbine

by:JNSN     2021-12-27
Overview of the oil system of No. 1.3 steam turbine unit No. 3 unit of Jiaozuo Power Plant is N200-130/535/535 type steam turbine produced by Dongfang Steam Turbine Factory. In 1999, the flow part reformation and the adjustment system DEH reformation were carried out. The oil system of the original design adopts the traditional main oil pump-injector system driven by the main shaft DC. The oil for the adjustment and security system is directly supplied by the main oil pump, the bearing oil is supplied by the injector, and the power oil for the injector is also directly from the main engine. Oil pump. The oil output of the main oil pump is divided into two ways, one leads to the regulation and security system, the other leads to the injector, two injectors are connected in parallel, one supplies oil to the lubrication system, and the other supplies oil to the main oil pump inlet. After the DEH transformation, the main oil pump leading to the regulation and security system is only used for the mechanical emergency interruption security part, and the control oil for the main steam valve and the governor steam valve is supplied by a separate high-pressure fire-resistant fuel system. A throttle orifice is provided at the oil inlet of each bearing to control the amount of lubricating oil of the bearing. The oil return of each bearing and the original adjusting part sleeve flows back to the main oil tank through the bearing box and the oil return header pipe. The oil return of the front middle tank shares an oil return header pipe, and the rest of the bearing oil returns share an oil return header pipe. The oil return pipeline has a gradually descending slope toward the fuel tank, so that the return oil in the pipe is half-full, so that the oil fume in each bearing box flows to the oil tank through the space on the oil surface, and then is exhausted by the exhaust fan. This oil system is equipped with two exhaust fans, and the exhaust system requires that the negative pressure of -10~-20mm water column in the bearing box is maintained. 2. Positive pressure oily fume in the front box and middle bearing box Jiaozuo Power Plant No. 3 unit front box and middle bearing box positive pressure oily fume is serious, because the front box and middle bearing box are located in the high temperature area of u200bu200bthe steam turbine, the oily smoke emitted is immersed in the cylinder If there is too much oil in the insulation close to the bearing box, it is very prone to fire when the operating conditions change. In actual production, both ends of the bearing housing have caught fire many times. In addition, during the normal operation of the unit, oil and gas are often spurted out of the automatic oil exhaust vent of the bearing box irregularly and intermittently. Sometimes due to high temperature and other reasons, the sprayed oil and gas burns and becomes a fire dragon, which is safe for the patrol personnel. And the safety of equipment operation poses a threat. According to investigations, from the second half of 2002 to May 2003, during a few months of minor repairs on the 3rd unit, there were dozens of fires. 3. Analysis of the reasons for the formation of high positive pressure in the front box and the middle bearing box. Poor smoke exhaust in the front box and the middle bearing box is the root cause of the positive pressure, and analysis of the main factors for the poor smoke exhaust of the No. 3 unit As follows:    (1) The oil level in the main oil tank is high, which causes air to accumulate in the square box of the lubricating oil return baffle, which results in poor oil return and smoke exhaust. We have investigated and compared with other units. In actual operation, the oil level of the main oil tank of this machine is controlled at 50-330mm, and the customary control is around 160mm, which is consistent with the design requirements of the operation guide. But when debugging the oil level of the main oil tank of the unit, it was found that lowering the oil level of the main oil tank can effectively reduce the higher positive pressure in the front tank. When the oil level of the main oil tank drops to the bottom edge of the front box and the oil return baffle box of the middle bearing box (except for the foam plate), the front box runs under negative pressure, but the oil level (40mm) of the main oil tank is already lower than The low alarm value of the oil level in the main oil tank. It can be concluded that in normal operation, the oil level of the main oil tank must be maintained so that the lubricating oil in the main oil tank floods the lower edge of the front box and the bottom of the oil return baffle box of the middle bearing box, plus the upper row of the oil return baffle box. If the steam hole is too small, it is easy to be blocked, so that the air accumulated in the square box of the oil return baffle cannot be discharged, and the oil return of the front box and the middle bearing box cannot be smoothly discharged to the oil tank.  (2) The oil level in the middle bearing box is too high, and the oil return pipe of the middle bearing box is submerged, resulting in poor oil return and smoke exhaust. The oil fume exhaust pipe port of the middle bearing box is designed to be placed on the back side of the No. 2 bearing and the middle pressure side of the middle bearing box. The inner space of the middle pressure side of the middle bearing box is smaller, and the inner space of the high pressure side is larger. The exhaust and suction spaces on both sides of the No. 2 bearing are connected by the oil return through holes on the underside of the bearing bush. Once the oil level in the middle bearing box rises and the oil return through holes are submerged, the exhaust on both sides of the No. 2 bearing will suck The spaces will not communicate with each other, and the oil fume on the high-pressure side of the middle bearing box will not be able to be discharged, resulting in positive pressure on the high-pressure side of the middle bearing box. When the pressure accumulates to a certain value, oil will inevitably be sprayed out. When the unit was running, the oil level in the middle bearing box was checked, and it was found that the running oil level had submerged the oil return through hole on the high and middle side under the No. 2 bearing and the oil return hole of the middle bearing box. Therefore, it can be considered that the high oil level in the middle bearing box is the direct cause of the positive pressure injection of the middle bearing box.  (3) With the changes in the operating conditions of the unit, the steam leakage at the shaft end of the steam turbine leaks into the bearing box, resulting in positive pressure in the bearing box, which has become the main cause of the intermittent fuel injection of the No. 3 unit. 4 Measures Taken In response to the main reasons for the serious positive pressure oily smoke in the front box and middle bearing box of the No. 3 engine analyzed above, the following measures have been taken:    (1) The oil return port of the front box and middle bearing box in the main oil tank A 100mm×300mm square hole is opened on the upper edge of the baffle box to solve the problem of poor oil return due to the presence of air in the baffle box at the oil return port of the front box and the middle bearing box. (2) Install a smoke exhaust pipe on the viewing window on the high pressure side of the middle bearing box on the left side of the middle bearing box and connect it to the exhaust fan system main pipe, which is controlled by a valve, and the middle bearing box is maintained by the adjustment of the smoke exhaust fan system. Slightly negative pressure.   After the transformation, there has been no oil injection incident in the middle bearing box since the operation. The front box and middle bearing box maintain a slight negative pressure according to the design requirements, eliminating the hidden dangers of major accidents that threaten the safety of life and the safety of unit equipment operation.
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