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

by:JNSN     2022-03-13
1. Overview of No. 3 Steam Turbine Unit Oil System Jiaozuo Power Plant No. 3 is a N200-130/535/535 steam turbine produced by Dongfang Steam Turbine Plant. The original design of the oil system adopts the traditional main oil pump-injector system driven by the main shaft DC. The oil used for the adjustment and security system is directly supplied by the main oil pump, the bearing oil is supplied by the oil injector, and the power oil of the oil injector also comes directly from the main oil. oil pump. The main oil pump is divided into two channels, one leads to the adjustment and security system, and the other leads to the oil injector. The 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 reconstruction, the main oil pump leading to the regulating security system is only used for the oil for the mechanical emergency shut-off security part. The control oil for the main steam valve and the speed regulating steam valve is supplied by a separate high-pressure fire-resistant oil system. An orifice plate is arranged at the oil inlet of each bearing to control the amount of lubricating oil of the bearing. The return oil of each bearing and the original adjusting part sleeve flows back to the main oil tank through the bearing housing and the return oil main pipe. The oil return of the front middle tank shares an oil return main pipe, and the other bearing oil returns share an oil return main pipe. The oil return pipe has a gradually descending slope towards the oil tank, so that the oil return in the pipe is half full, so that the oil fume in each bearing box can flow to the oil tank through the space on the oil surface, and then be discharged by the fume exhaust fan. The oil system is equipped with two smoke exhaust fans. The smoke exhaust system requires that the negative pressure of -10~-20mm water column be maintained in the bearing box. 2. Oil fumes from positive pressure in the front box and middle bearing box Jiaozuo Power Plant No. 3 unit has serious oil fumes from positive pressure in the front box and middle bearing box. Because the front box and middle bearing box are located in the high temperature area of u200bu200bthe steam turbine, the oil fumes immersed in the cylinder There is a lot of oil accumulated in the insulation near the bearing box, and fire is very likely to occur when the operating conditions change. In actual production, both ends of the bearing box have caught fire many times. In addition, during the normal operation of the unit, oil and gas are often sprayed out of the automatic oil exhaust hole in the middle bearing box irregularly and intermittently. and pose a threat to the safety of equipment operation. After investigation, from the second half of 2002 to May 2003, during the several months of minor repairs on the No. 3 unit, the number of fires was dozens of times. 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 formation of the positive pressure, and the main factors for the formation of the No. 3 machine are the main factors for the poor smoke exhaust As follows: (1) The high oil level of the main oil tank causes air to accumulate in the square box of the baffle plate of the lubricating oil return port, resulting in poor oil return and smoke exhaust. After investigation and comparison with other units, in actual operation, the oil level of the main fuel tank of this machine is controlled at 50-330mm, and the habit is controlled at about 160mm, which is in line with the design regulations of the operation instruction. However, when debugging the oil level of the main fuel tank of the unit, it was found that lowering the oil level of the main fuel tank can effectively reduce the high positive pressure in the front tank. When the oil level of the main oil tank drops to the lower edge of the square box (except the foam board) of the oil return port baffle of the front box and the middle bearing box, the front box is operated with negative pressure, but at this time the oil level of the main oil tank (40mm) is lower than Low alarm value for main tank oil level. It can be concluded that in normal operation, due to maintaining the oil level of the main oil tank, the lubricating oil in the main oil tank floods the lower edge of the square box of the oil return port baffle of the front box and the middle bearing box, and the upper row of the square box of the oil return port baffle. If the steam hole is too small, it is easy to be blocked, so that the air accumulated in the square box of the baffle of the oil return port cannot be discharged, so that the return oil 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 nozzle of the oil exhaust fume pipe of the middle bearing box is designed to be placed on the rear side of the No. 2 bearing and on the medium pressure side of the middle bearing box. The inner space of the medium pressure side of the middle bearing box is small, and the inner space of the high pressure side is large. The smoke exhaust and suction spaces on both sides of the No. 2 bearing are connected by the oil return through holes on the lower side of the bearing shell. Once the oil level in the middle bearing box rises and the oil return through holes are submerged, the smoke exhaust on both sides of the No. 2 bearing will be sucked. The space will not communicate with each other, and the oil fume on the high-pressure side of the middle bearing box will not 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 outward. When the unit was running, the oil level in the middle bearing box was checked, and it was found that the operating 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 in 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 oil injection in the middle bearing box. (3) With the change of the operating conditions of the unit, the steam leakage from the shaft end of the steam turbine leaked into the bearing box, resulting in positive pressure in the bearing box, which became the main reason for the intermittent fuel injection of the No. 3 engine. 4 Measures to be taken In view of the main reasons for the serious oil smoke from the positive pressure in the front box and middle bearing box of No. 3 engine analyzed above, the following measures were taken: (1) The oil return port of the front box and middle bearing box in the main oil tank On the upper edge of the baffle box, a 100mm×300mm square hole is opened to solve the problem of poor oil return due to the presence of air in the baffle box of the oil return port of the front box and the middle bearing box. (2) Install a smoke exhaust pipe on the peep 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 main pipe of the smoke exhaust fan system, control it with a valve, and adjust the middle bearing box by the smoke exhaust fan system. Micro negative pressure. After the renovation, so far, there has been no oil injection incident in the middle bearing box. The front box and the middle bearing box maintain a slight negative pressure according to the design requirements, eliminating the hidden danger of major accidents that threaten the safety of personal life and the operation of the unit equipment.
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