Abstract : This paper introduces the composition of steam turbine hydraulic pressure control (EH) system in Shenzhen Yueliangwan Gas Turbine Power Plant. The common faults of the system (EH system pressure is low, EH system oil temperature is high, steam inlet valve or regulating valve cannot be opened and the pipeline or The leakage of the valve was analyzed and the EH system maintenance and fault prevention measures were proposed.
As the actuator of the steam turbine digital electrohydraulic control (DEH) system, the basic function of the hydraulic control (EH) system is to accept the instructions of the DEH control system, control the opening of the steam inlet valves and the steam valve, and change the steam flow of the steam turbine. In order to meet the turbine speed and load adjustment requirements. Its other important function is to adjust the turbine speed in the event of a turbine overspeed and automatically close all steam inlet valves in an emergency. It can be seen that the EH system is related to the normal regulation and safe operation of the steam turbine, and its failure will directly threaten the normal operation of the turbine. This paper takes the steam turbine of Shenzhen Yueliangwan Gas Turbine Power Plant as an example to analyze and summarize the faults in its EH system, and put forward measures to prevent failures.
First, the system composition EH system consists of oil supply device, pipeline system, implementing agencies and overspeed protection and emergency interrupting device composed of four parts, its working media commonly used phosphate ester anti-combustion oil.
The oil supply device consists of a fuel tank, a pump unit, a pressure circuit, a filter cooling circuit, and the like. The pump group is generally selected constant pressure variable pump, can automatically adjust the flow, so that the pump outlet pressure remains constant, the common configuration is 2 units: one operation, one standby. The pressure circuit includes a flow meter, a filter, a check valve, a relief valve, and a storage bottle at the pump outlet. The filter cooling circuit includes an oil cooler and a bypass regeneration system (including a fine filter and a diatomaceous earth filter).
In addition to the connecting pipeline, the piping system generally includes two groups of high and low pressure accumulators, which are used to reduce the impact of large changes in the oil flow caused by the valve action on the system, and to regulate the voltage and store energy.
Actuators (commonly known as oil motives) are generally divided into two types: switch type and servo type. The orifice type is installed between the switch type oil drive and the main line. Servo type is not available.
When the steam turbine speed is up to 1.03 times the rated speed, it is necessary to quickly turn down the opening of all the regulating steam valves. This function is called over-speed protection (OPC); if the steam turbine does not operate normally, or the speed is soared by 1.15 times due to unexpected failures. At rated speed, if the OPC function alone is not sufficient to control the speed of the OPC to continue to rise, it is necessary to urgently block all inlet valves. This function is called emergency shutdown (AST).
Second, the EH system common failure analysis 2.lEH system pressure caused by low EH system pressure is mainly due to three aspects.
(1) Abnormal leakage in the system The most common abnormal leakage in the system is the failure of the fast unloading valve of the regulating valve, so that the drain port cannot be completely closed, the hydraulic pressure of the throttle regulating oil can not be maintained, and the servo valve is Uninterrupted replenishment. Because there is no orifice between the parent tube and the servo valve, the amount of oil leaked from this channel is large. This type of fault generally occurs only when the starter is unloaded, because the status of the quick unload valve at this time is changed. If the slide valve is stuck, it will cause the above fault. If the jamming is caused by impurities in the oil (most of the time), this failure is accidental, and the next time the oil pressure of the gate is normal, the valve can be cleaned and the oil can be improved. Solve; If the jam is caused by spring damage (this is less likely), the spring needs to be replaced. If it is due to oil degradation caused by the slide valve, the slider is corroded and worn, so that the gap between them increases, resulting in rapid unloading valve leakage, you can only replace the entire valve.
Inadequate shutoff of the backup pump's outlet check valve will also result in low pressure, which is usually found immediately after the pump is started.
In addition, the low setting of the overflow valve of the EH system will also result in low system pressure. In this case, the pressure is generally stable at a certain value and will not deteriorate.
(2) Blockage in the pipeline There is a maximum blockage in the pipeline. Plugging in the pump inlet and outlet strainers prevents the supply of oil to the system. As a result, the pressure in the manifold gradually decreases. If not treated, it will continue to deteriorate until the pressure is reached. It cannot be established at all. Pump outlet filter is generally equipped with pressure difference switch or pressure difference table, the plug is more easily found. It is difficult to find the plug of the pump inlet filter, except for the pressure drop or large fluctuation of the mother tube, and the abnormal sound of the pump. If this situation persists after replacing the inlet filter with normal maintenance frequency, it is necessary to check the quality of the anti-fuel oil and determine if the anti-fuel oleic acid value exceeds the limit, because the main feature of the oil deterioration is the sharp increase in the acid value. Most of the filter elements that were replaced by power plants after such failures were found not to contain particulate impurities but floc-like adherents, which were later confirmed by the manufacturer as degradation products after degradation of phosphate-based anti-fuel oils. Therefore, a thorough solution is to Improve anti-fuel oil products.
The detachment of the pipe fittings can also result in blockage of the pipe, the most common being the detachment of the flowmeter rotor at the outlet of the pump.
(3) The constant pressure variable pump failure The constant pressure variable pump has a low failure rate, so the probability of a low system pressure is low. The common case is that the internal components of the pump are stuck due to impurities in the oil and the pump is disassembled and cleaned. After cleaning, it can be reinstalled. Second, there is air in the pump body, which needs to be exhausted. Third, the motor or the coupling is faulty. It is necessary to check the cushion of the motor or the coupling. 2.2EH system oil temperature is high Although the fault will not trip, but can not be ignored, because the high oil temperature may lead to oxidation or cracking of the fuel resistance, resulting in a rapid increase in acid value or precipitate (such as floe), so that The oil quality deteriorated rapidly.
The cause of this failure is to start with the EH oil cooler and check whether the oil and water side piping is unblocked, whether there is blockage of the orifice plate, check whether the oil cooler switch valve is in place, and the cooling water flow rate and water temperature. . In addition, if the pump outlet valve setting value is higher than the parent tube relief valve setting, most of the oil flow directly from the overflow valve back to the tank, will also cause high oil temperature, this situation is generally It may appear after replacing the pump or relief valve.
2.3 Steam inlet valve or regulating valve can not open the throttle valve between the oil pump and the mother pipe. The servo valve of the regulating valve is equipped with a filter. If the orifice plate or oil filter is blocked, it will cause The corresponding valve cannot be opened. The failure of the quick unload valve of the steam inlet valve and the regulating valve can also cause the corresponding valve to open.
In actual operation, the power plant also experienced a fault in which one of the regulating gates was gradually turned off during normal operation. Because the oil returning oil pipe was in a high temperature zone and was locally overheated, the long-term operation caused the fuel-resistant oil to gradually block the return oil line. Reverse the oil motive.
2.4 pipeline or valve leakage EH system pressure is higher, generally above lOMPa, but also by the unit temperature and vibration, in the pipe material and welding process to ensure the quality of the case, sometimes there will be leakage phenomenon, mainly Pipe joints are more vibrated looser and the 0-ring seal is damaged. For the former, a hose can be used to release the stress and reduce the vibration, while the latter is guaranteed by reducing the working environment temperature and strengthening the inspection work.
Third, the EH system maintenance and fault prevention measures (1) regular oil testing, strengthen chemical supervision. When the anti-fuel oleic acid value in operation exceeds the standard, the diatomaceous earth filter element in the bypass regeneration system should be promptly replaced. According to the relevant guidelines, the new fuel-resistant acid value ω (KOH) ≤ 0.08 mg/g should be sampled before on-site replenishment. If the acidity value is significantly increased during the running test and the ω (KOH) reaches 0.20 mg/g, the diatomaceous earth filter element needs to be replaced. When the ω (KOH) exceeds 0.4 mg/g, the anti-fuel oil is difficult to be regenerated and must be replaced completely. .
(2) Periodically monitor the operating conditions of the diatomaceous earth and cellulose filter elements in the bypass regeneration system. When the oil temperature in the regeneration system is 43~54°C and the pressure reaches 0.21MPa, the filter element needs to be replaced.
(3) The anti-fuel oil operating temperature should be controlled below 55°C, and individual hot spots should not exceed 12O°C. For oil motives and tubing in high temperature areas, better insulation materials should be used for thermal insulation. The EH oil pipeline with unreasonable layout was modified to keep away from high temperature areas as far as possible.
(4) The EH pump current is regularly tracked. The pump current is an important indicator reflecting its flow. It can be used to detect in advance whether there is a risk of pressure drop in the system.
(5) Replace the filter element of the respirator at the top of the tank periodically. In the case where the diatomaceous earth in the regenerative device is near failure or at the end of the input, due to the high humidity of the air and the temperature difference between day and night, the moisture will invade the fuel tank through the respirator, and the filter element of the respirator becomes the first barrier to separate the moisture. The oxidation of water and oil is the main cause of the increase of oleic acid value, and an external circulation filter device can be added if conditions permit.
IV. Conclusion The failure of the power plant EH system is mostly caused by the deterioration of anti-fuel oil products. Anti-fuel oil products have become a weak point of the system and are the focus of maintenance work. Therefore, doing the above preventive measures is the most effective way to reduce the failure of the turbine EH system, and it is of great significance to ensure the safe and economical operation of the unit.
As the actuator of the steam turbine digital electrohydraulic control (DEH) system, the basic function of the hydraulic control (EH) system is to accept the instructions of the DEH control system, control the opening of the steam inlet valves and the steam valve, and change the steam flow of the steam turbine. In order to meet the turbine speed and load adjustment requirements. Its other important function is to adjust the turbine speed in the event of a turbine overspeed and automatically close all steam inlet valves in an emergency. It can be seen that the EH system is related to the normal regulation and safe operation of the steam turbine, and its failure will directly threaten the normal operation of the turbine. This paper takes the steam turbine of Shenzhen Yueliangwan Gas Turbine Power Plant as an example to analyze and summarize the faults in its EH system, and put forward measures to prevent failures.
First, the system composition EH system consists of oil supply device, pipeline system, implementing agencies and overspeed protection and emergency interrupting device composed of four parts, its working media commonly used phosphate ester anti-combustion oil.
The oil supply device consists of a fuel tank, a pump unit, a pressure circuit, a filter cooling circuit, and the like. The pump group is generally selected constant pressure variable pump, can automatically adjust the flow, so that the pump outlet pressure remains constant, the common configuration is 2 units: one operation, one standby. The pressure circuit includes a flow meter, a filter, a check valve, a relief valve, and a storage bottle at the pump outlet. The filter cooling circuit includes an oil cooler and a bypass regeneration system (including a fine filter and a diatomaceous earth filter).
In addition to the connecting pipeline, the piping system generally includes two groups of high and low pressure accumulators, which are used to reduce the impact of large changes in the oil flow caused by the valve action on the system, and to regulate the voltage and store energy.
Actuators (commonly known as oil motives) are generally divided into two types: switch type and servo type. The orifice type is installed between the switch type oil drive and the main line. Servo type is not available.
When the steam turbine speed is up to 1.03 times the rated speed, it is necessary to quickly turn down the opening of all the regulating steam valves. This function is called over-speed protection (OPC); if the steam turbine does not operate normally, or the speed is soared by 1.15 times due to unexpected failures. At rated speed, if the OPC function alone is not sufficient to control the speed of the OPC to continue to rise, it is necessary to urgently block all inlet valves. This function is called emergency shutdown (AST).
Second, the EH system common failure analysis 2.lEH system pressure caused by low EH system pressure is mainly due to three aspects.
(1) Abnormal leakage in the system The most common abnormal leakage in the system is the failure of the fast unloading valve of the regulating valve, so that the drain port cannot be completely closed, the hydraulic pressure of the throttle regulating oil can not be maintained, and the servo valve is Uninterrupted replenishment. Because there is no orifice between the parent tube and the servo valve, the amount of oil leaked from this channel is large. This type of fault generally occurs only when the starter is unloaded, because the status of the quick unload valve at this time is changed. If the slide valve is stuck, it will cause the above fault. If the jamming is caused by impurities in the oil (most of the time), this failure is accidental, and the next time the oil pressure of the gate is normal, the valve can be cleaned and the oil can be improved. Solve; If the jam is caused by spring damage (this is less likely), the spring needs to be replaced. If it is due to oil degradation caused by the slide valve, the slider is corroded and worn, so that the gap between them increases, resulting in rapid unloading valve leakage, you can only replace the entire valve.
Inadequate shutoff of the backup pump's outlet check valve will also result in low pressure, which is usually found immediately after the pump is started.
In addition, the low setting of the overflow valve of the EH system will also result in low system pressure. In this case, the pressure is generally stable at a certain value and will not deteriorate.
(2) Blockage in the pipeline There is a maximum blockage in the pipeline. Plugging in the pump inlet and outlet strainers prevents the supply of oil to the system. As a result, the pressure in the manifold gradually decreases. If not treated, it will continue to deteriorate until the pressure is reached. It cannot be established at all. Pump outlet filter is generally equipped with pressure difference switch or pressure difference table, the plug is more easily found. It is difficult to find the plug of the pump inlet filter, except for the pressure drop or large fluctuation of the mother tube, and the abnormal sound of the pump. If this situation persists after replacing the inlet filter with normal maintenance frequency, it is necessary to check the quality of the anti-fuel oil and determine if the anti-fuel oleic acid value exceeds the limit, because the main feature of the oil deterioration is the sharp increase in the acid value. Most of the filter elements that were replaced by power plants after such failures were found not to contain particulate impurities but floc-like adherents, which were later confirmed by the manufacturer as degradation products after degradation of phosphate-based anti-fuel oils. Therefore, a thorough solution is to Improve anti-fuel oil products.
The detachment of the pipe fittings can also result in blockage of the pipe, the most common being the detachment of the flowmeter rotor at the outlet of the pump.
(3) The constant pressure variable pump failure The constant pressure variable pump has a low failure rate, so the probability of a low system pressure is low. The common case is that the internal components of the pump are stuck due to impurities in the oil and the pump is disassembled and cleaned. After cleaning, it can be reinstalled. Second, there is air in the pump body, which needs to be exhausted. Third, the motor or the coupling is faulty. It is necessary to check the cushion of the motor or the coupling. 2.2EH system oil temperature is high Although the fault will not trip, but can not be ignored, because the high oil temperature may lead to oxidation or cracking of the fuel resistance, resulting in a rapid increase in acid value or precipitate (such as floe), so that The oil quality deteriorated rapidly.
The cause of this failure is to start with the EH oil cooler and check whether the oil and water side piping is unblocked, whether there is blockage of the orifice plate, check whether the oil cooler switch valve is in place, and the cooling water flow rate and water temperature. . In addition, if the pump outlet valve setting value is higher than the parent tube relief valve setting, most of the oil flow directly from the overflow valve back to the tank, will also cause high oil temperature, this situation is generally It may appear after replacing the pump or relief valve.
2.3 Steam inlet valve or regulating valve can not open the throttle valve between the oil pump and the mother pipe. The servo valve of the regulating valve is equipped with a filter. If the orifice plate or oil filter is blocked, it will cause The corresponding valve cannot be opened. The failure of the quick unload valve of the steam inlet valve and the regulating valve can also cause the corresponding valve to open.
In actual operation, the power plant also experienced a fault in which one of the regulating gates was gradually turned off during normal operation. Because the oil returning oil pipe was in a high temperature zone and was locally overheated, the long-term operation caused the fuel-resistant oil to gradually block the return oil line. Reverse the oil motive.
2.4 pipeline or valve leakage EH system pressure is higher, generally above lOMPa, but also by the unit temperature and vibration, in the pipe material and welding process to ensure the quality of the case, sometimes there will be leakage phenomenon, mainly Pipe joints are more vibrated looser and the 0-ring seal is damaged. For the former, a hose can be used to release the stress and reduce the vibration, while the latter is guaranteed by reducing the working environment temperature and strengthening the inspection work.
Third, the EH system maintenance and fault prevention measures (1) regular oil testing, strengthen chemical supervision. When the anti-fuel oleic acid value in operation exceeds the standard, the diatomaceous earth filter element in the bypass regeneration system should be promptly replaced. According to the relevant guidelines, the new fuel-resistant acid value ω (KOH) ≤ 0.08 mg/g should be sampled before on-site replenishment. If the acidity value is significantly increased during the running test and the ω (KOH) reaches 0.20 mg/g, the diatomaceous earth filter element needs to be replaced. When the ω (KOH) exceeds 0.4 mg/g, the anti-fuel oil is difficult to be regenerated and must be replaced completely. .
(2) Periodically monitor the operating conditions of the diatomaceous earth and cellulose filter elements in the bypass regeneration system. When the oil temperature in the regeneration system is 43~54°C and the pressure reaches 0.21MPa, the filter element needs to be replaced.
(3) The anti-fuel oil operating temperature should be controlled below 55°C, and individual hot spots should not exceed 12O°C. For oil motives and tubing in high temperature areas, better insulation materials should be used for thermal insulation. The EH oil pipeline with unreasonable layout was modified to keep away from high temperature areas as far as possible.
(4) The EH pump current is regularly tracked. The pump current is an important indicator reflecting its flow. It can be used to detect in advance whether there is a risk of pressure drop in the system.
(5) Replace the filter element of the respirator at the top of the tank periodically. In the case where the diatomaceous earth in the regenerative device is near failure or at the end of the input, due to the high humidity of the air and the temperature difference between day and night, the moisture will invade the fuel tank through the respirator, and the filter element of the respirator becomes the first barrier to separate the moisture. The oxidation of water and oil is the main cause of the increase of oleic acid value, and an external circulation filter device can be added if conditions permit.
IV. Conclusion The failure of the power plant EH system is mostly caused by the deterioration of anti-fuel oil products. Anti-fuel oil products have become a weak point of the system and are the focus of maintenance work. Therefore, doing the above preventive measures is the most effective way to reduce the failure of the turbine EH system, and it is of great significance to ensure the safe and economical operation of the unit.
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