Source: Dianlian Intelligent Manufacturing
Recommended unit: Huaneng Wuhan Power Generation Co., Ltd
Authors: Xiong Peng, Lu Lin, Luo Wei, Wang Feng, Zhou Zhen, Wan Hui, Tian Daoyuan, Zhou Jianliang, Liu Yansong, Yu Yajie
summary
EH oil system plays a vital role in the steam turbine speed control system, in which the oil quality of EH oil itself determines the reliability of EH oil system operation, there are many precision parts and throttle holes in EH oil system, unqualified EH oil is easy to cause the servo valve in the system to jam or throttle hole blockage, resulting in poor valve adjustment performance, and even affect the safe operation of the unit. In this paper, the influence of high-temperature thermal radiation of high-temperature oil motor on the oil quality of EH oil is analyzed, and the problems and potential dangers of EH oil system are analyzed, and after many on-site investigations, theoretical analysis and daily accumulated production experience, the transformation scheme of water cooling device of high-profile door oil motor is proposed, which can significantly reduce the temperature in the high-profile oil engine and ensure the stability and reliability of EH oil system.
1. Operation status and analysis
Shanghai Steam Turbine Factory introduced the 156 type unit produced by Westinghouse Company of the United States, and its supporting EH oil system is phosphate ester high-pressure anti-fuel, with a normal operating pressure of 14.5MPa and an operating oil temperature between 40~55°C. The high-profile valve oil motor is hung on the high-pressure main valve housing, and its installation position is shown in Figure 1.
Fig.1 Installation method of main valve joint control valve and high-profile valve oil motor
The oil motor is a single-side oil feed oil engine. The structure of the oil engine is shown in Figure 2 below
Fig.2. Structure of oil motor before transformation
Since it was put into production, the EH oil system has been in constant trouble, and the phenomenon of running and dripping is more common, especially the aging of the high-profile door sealing ring leads to frequent oil leakage, and the leakage occurs in less than 1 year after maintenance, and the adjustment door is often stuck and the adjustment performance is poor, which is highlighted by the high temperature of the high-profile door oil cylinder. During the operation of the unit, the temperature of the 6 high-level oil motors measured by the #2 unit of our factory before the transformation, the specific measurement data are shown in Table 1.
Table 1 Statistical table of cylinder block temperature of high-regulation oil motor during operation
It can be seen from the measured temperature of the cylinder block of the high-regulation oil motor that the EH oil in it has been in the cylinder body much higher than its normal working temperature range for a long time. When the load is stable, the valve is basically immobile, and the EH oil in the cylinder will be in this high temperature environment for a long time, especially #1 and #2高调一般处在全开不参与调节状态, which are closest to the main valve, and the relatively non-flowing EH oil in the cylinder is easy to crack and carbonize at high temperatures, resulting in EH oil oil particle size, acid value and other indicators exceeding the standard. It brings the jamming of precision adjustment instruments such as servo valves, so that the high-profile door often appears short-term high-frequency vibration or rejection, which poses a serious threat to the adjustment performance of the high-profile door and the stable operation of the unit. The life of the sealing ring at high temperature is greatly reduced, the maintenance cycle of the oil engine is greatly shortened, and the maintenance cost is increased, which seriously affects the safety and economy of the unit.
Second, improve ideas
According to the phenomenon investigation and the exchange of relevant information with the power plant of the same type of unit, it is found that the high temperature of the cylinder of the high-modulation oil motor is widespread, and the main reasons are as follows:
2.1 The installation position of the high-profile door is close to the housing of the high-profile door, the arrangement of the high-profile door body and the door rod and the actuator is relatively compact, and the auxiliary spring position can not be wrapped in the heat preservation, so the actual insulation temperature at the high-profile door body is higher or some parts are even not insulated, and the heat is transferred to the oil motor by heat conduction and heat radiation through the high-profile door frame and the bracket connected with the oil engine, resulting in the high temperature of the oil cylinder;
2.2 The oil engine is a one-sided oil inlet, in order to avoid overload of the oil return when the valve is closed, part of the pressure oil is returned to the upper chamber of the oil engine when the door is closed, so the oil flow of the upper chamber of the oil engine is slow, and it is easy to sinter and carbonize at high temperatures, forming a lot of particulate matter, blocking the servo valve and other precision instruments in the EH oil system;
2.3 The high and medium pressure cylinder is located in a relatively closed space surrounded by a makeup board, and the air convection heat dissipation at the valve part is slow, which is not conducive to the natural heat dissipation of the local temperature;
2.4 At present, EH oil pipes are made of stainless steel pipes, and there are basically no anti-radiation measures such as heat insulation outside the pipeline, and the high temperature also accelerates the deterioration of EH oil quality.
Therefore, in order to ensure the various indicators of EH oil quality during operation and effectively reduce the temperature of the oil engine cylinder block, we should try to reduce the heat conduction and heat radiation of the high-profile door housing, accelerate the flow of oil in the upper chamber of the oil engine, and strengthen the air flow in the area to enhance the natural heat dissipation.
3. Transformation plan
3.1 The high-profile oil motor mounting bracket is transformed, the original integral panel type is transformed into a reinforced rib type, the contact area between the mounting bracket and the valve housing is 0.08 square meters, the heat exchange area is reduced by half compared with the integral type, and the rib plate is not in contact with the valve housing in the middle, leaving a gap of 40m, which strengthens the natural ventilation and cooling, takes away a part of the heat, and effectively reduces the heat transfer.
3.2 The upper part of the high-profile oil cylinder is equipped with a cooling water jacket, as shown in Figure 3. The relatively clean condensate flowing in the cooling water jacket can directly take away the heat transmitted to the oil cylinder by heat conduction in the adjusting door housing in time, avoiding the increase of the cylinder temperature, and the water jacket directly acts on the upper end cover of the oil engine, which reduces the temperature of the copper sleeve and the piston rod sealing ring in the upper end cover, prevents the aging and failure of the sealing ring, and avoids anti-fuel leakage; The cooling water jacket is in direct contact with the oil engine mounting bracket, which reduces the temperature of the bracket and further reduces the heat transfer. The specific installation dimensions are shown in Figure 4 and Figure 5.
Fig.3. Structure diagram of the modified oil engine
Fig.4. Dimensions of the cooling device interface
Fig.5. Dimensions of cooling device valves and pipes
The relevant technical requirements for each high-profile door oil motor are as follows:
3.2.1 须加工冷却板一件（220X126X66）,材质：0Cr18Ni9；
3.2.2 须加工堵板一件（Φ110XΦ80X10），材质：0Cr18Ni9；
3.2.3 The high-profile piston rod needs to be reprocessed (about 55mm longer);
3.2.4 The extension rod connected to the displacement sensor needs to be reprocessed (lengthened by 56mm), and the quantity is 2 pieces;
3.2.5 2 stainless steel ball valves DN25 (low pressure);
3.2.6 4 pipe joints DN25 (stainless steel), 2 elbows DN25 each;
3.2.7 2 stainless steel metal hoses DN25 (low pressure), 2 meters long;
3.2.8 Replacement of original guide sleeves and seals.
3.2.9 Clean condensate is used for cooling water, the water temperature is not higher than 40°C, and the water pressure is not less than 0.4MPa.
3.3 In view of the slow oil flow in the upper chamber of the piston, which is not easy to take away the heat, and the heat transferred will deteriorate the oil in the upper chamber and deposition carbon deposits, a small hole channel can be processed at the lower part of the new piston rod. And install a 0.6mm throttle hole in the hole, so that the pressure oil at the lower part of the oil engine enters the upper part of the piston through the throttle hole, accelerates the oil volume of the upper chamber and the flow speed of the oil, and takes away the heat of the cylinder in time through the circulation flow of the oil itself, and prevents the oil from deposition to form particles to block the throttle hole or servo and other precision parts in the system. After accounting, the addition of six throttle holes on the piston rods of the six high-profile doors leads to an additional leakage of about 10L/min in the system, which is much smaller than the displacement of 90L/min of the oil pump, and will not cause a significant increase in the system flow and motor current, as shown in Figure 6.
Fig.6. Schematic diagram of the location of the throttle hole and the oil circuit flow
3.4 In view of the problem of increasing the temperature of the cylinder caused by the insulation of the valve housing at the rear of the cylinder, heat insulation and heat dissipation measures should be taken around the oil engine, and the insulation behind the high-profile valve cylinder should be replaced with a needle-punched blanket with good thermal insulation effect. At the same time, the cylinder block and the oil pipeline in this area can be coated with an anti-radiation coating to reduce heat transfer by thermal radiation.
3.5 If conditions permit, the vanity plate around the high and medium pressure can be canceled, so that the valve and cylinder block are directly exposed to the air, so as to increase the natural convection heat exchange, reduce the overall temperature of the outer layer of the cylinder, and reduce the ambient temperature of the EH oil system.
Fourth, the effect after transformation
After the above-mentioned transformation, after the EH oil system is thoroughly flushed, the equipment of the EH oil system is running well, and the temperature of the cylinder block of each oil engine is measured as shown in Table 2:
Table 2 Measured temperature of the oil engine block after the transformation
It can be seen from the measured data in the above table that the temperature of each high-profile valve cylinder has dropped significantly after the cooling water transformation of the oil engine, and the temperature of each measuring point is stable after long-term tracking and monitoring. The over-temperature and oil seepage of the oil motor have been significantly improved, and there is no obvious leakage of the oil engine during the overhaul cycle, resulting in load reduction treatment, and the adjustment performance of the high-profile door has also been significantly improved. This modification scheme in the original foundation changes relatively little, the effect is significant, relative to the frequent leakage and maintenance of manpower, financial consumption, there are considerable economic benefits, our plant #1, #3, #4机组也进行了同样的改造, have achieved considerable economic benefits, the same type of unit can be adopted.
5. Concluding remarks
The transformation of high-profile cooling water and other corresponding supporting transformations significantly reduce the temperature of high-profile door cylinders, improve the working environment of EH oil engine and EH oil, ensure the operation stability of EH oil quality and EH oil system equipment, avoid major safety accidents such as fire and accident shutdown caused by running and dripping, improve the safety, stability and economy of the unit, extend the equipment maintenance cycle, and save a lot of manpower and financial resources. At the same time, EH oil filtration and monitoring should be strengthened on a daily basis to ensure that the indicators of oil quality are within the qualified range, find out the factors affecting oil quality, eliminate potential safety hazards in a timely manner, and ensure the safe and reliable operation of EH oil system and related equipment.
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