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1 DCS failure reason of power failure Through the analysis of DCS power failure, it is found that the difference in infrastructure design and understanding of the original design is an important cause of the accident.
(1) The DCS of some units adopts a single UPS (shared with one export feeder) to provide power supply of two power sources. Some of the old units use DCSUPS of two units for alternate power supply. When the UPS of one unit of DCS is overhauled, Another unit control power supply is single-channel power supply.
(2) Some unit extraction check valves, fuel trip valves and other equipment use dual-coil control solenoid valves. When the control system loses power, the steam turbine is in danger of overspeed, and the boiler cannot completely remove the fuel; some newly-commissioned coal mills The oil pump and air preheater control adopts long signal control. Once the DCS loses power, it will cause the coal mill oil pump and air preheater to stop operation and cause equipment damage.
(3) Some of the old units do not have the function of digital electro-hydraulic control system (DEH). The turbine trip system adopts live action mode, and there is no reliable power supply (such as DC power supply) and power supply circuit structure. When the control system loses power, manual trip button Can not control the turbine, can only stop on-site stop steam turbine operation.
(4) Some units do not meet the operational requirements of the operator station and the configuration of a few important operation buttons under various working conditions of the unit, especially the emergency processing requirements. Some chiller control systems do not have a total fuel trip (MFT) relay set.
(5) The power monitoring and alarm system of some units DcS and main control and protection systems are not perfect.
2DCS power failure countermeasures (l) When designing the DCS power supply configuration, the power failure alarm function should be set for the UPS power supply, bypass power supply, and DC power supply, and each power supply voltage signal should enter the fault recorder and DCS, in order to monitor; DCS should be powered by 1 UPS, 1 road security power supply, or 2 independent UPS. The two-way power supply shall be taken from the machine and furnace work sections respectively; the systems such as the turbine emergency trip system (ETS), the turbine monitoring instrument (TSI), and the flame detection device shall adopt the same power supply structure as the DCS; and the UPS shall periodically perform switching tests. The switching time of the working power and standby power should be less than 5ms.
(2) When designing the DCS internal power supply configuration, two methods should be adopted: One is the 2N method, and each modular cabinet has 2 (or 4) power modules. Half of the power module is powered by the main power supply, and the other half of the power supply The module is powered by the secondary power supply, and the DC power output from the power module is connected in parallel to serve as the I/O module, the main controller and the working power of the field devices. The second is that the 2-way (A, B) AC incoming power supplies are mutually standby. , A (B) Road main power supply for the A (B) AC line power supply, when the A (B) line into the power loss, switch to B (A) Road into the line power supply, when A (B) When the line power is restored, switch back to the A(B) line power supply. After the switch, the A and B2 power supplies provide half of the power module of the control system, so that even if the power switch is unsuccessful, it will be at least half. The power module can work normally to maintain the normal operation of the DCS.
(3) The flame detection device, TSI, and thermal power meter power supply cabinets shall be powered by 2 AC power sources of different sources (the same power source as the DCS cabinet), or the switched power source may be used. Each operator station and engineering station shall use two-way switched power supply, or two-way power supply and switched power supply respectively to supply power to different operator stations so as to ensure that at least one operator station is available when one-way power is lost. Available. Dl module query voltage is recommended to use +48VDC power to increase signal anti-jamming capability. In addition, DCS and ETS, TSI, flame detection devices, etc., shall also be monitored for any 1-way power supply. If possible, alarms such as DCS power supply voltage overload, 2-way power supply deviation, fan failure, and isolation transformer over temperature alarms shall be designed. Discover DCS power system faults in a timely manner.
(4) When designing the console button configuration, two manual shutdown and shutdown buttons should be configured. Each button provides multiple pairs of normally open (closed) contacts. Only two shutdown (stop) buttons are pressed simultaneously. A manual stop or stop command was issued. Among them, some of the contacts are used as Dl signals to enter the furnace safety monitoring system (FSSS) and ETS constitute a software trip signal triggering shutdown, shutdown, some contacts in series access MFT trip relay, ETS trip solenoid valve (AST) control loop In the implementation of hardware tripping. The manual stop button of the feed water pump steam turbine and the start button of the AC and DC lube oil pumps must be designed as: Manual stop signal of the feed water pump steam turbine. One channel can be used to enter the DCS to participate in the logic operation, and one line can be connected in series to the control circuit of the tripping solenoid valve. , ensure the loss of power can be reliably shut down; AC and DC lubricating oil pump start button should be directly connected to the lubricating oil pump electrical starting circuit, while the low lubricating oil pressure signal should also be connected in series in the electrical start circuit, so that in the event of DCS loss of electricity When shutting down, the lubricant pump can start automatically without DCS control to ensure the safe operation of the turbine.
(5) In the configuration of the thermal protection system, an independent MFT trip relay group should be configured for the units that use DCS to implement MFT protection. The trip relay group can be designed with live action or loss of power. If it is designed as a live action, a parallel circuit consisting of two different power sources (one 220VAC, 110VDC) should be used. That is, any circuit action can stop the furnace. The 220VAC and DC 110VDC2 power supplies should all have a power failure alarm signal. If it is designed to be de-energized, you cannot use two AC power sources (short-term power loss may occur during AC power switching). You can use the DC power supplied by the FSSS's common cabinet. The output of the MFT trip relay group should not pass the DCS and should be directly connected to the trip circuit of the local equipment. ETS adopts the design of power-loss action. When the emergency shutdown system is integrated with the ETS or integrated with the DEH, the manual shutdown button output should be connected in parallel with the software trip signal from the control system in the critical shutdown circuit.
3 Conclusions Through the analysis of the relationship between tar catalytic cracking rate and catalytic pyrolysis temperature and gas phase residence time during the pyrolysis of tar pyrolysis, the least squares support vector machine was used to establish the catalyzed pyrolysis rate of rice stalk pyrolysis. Catalytic pyrolysis temperature, gas phase retention time change process model. Through the verification, the average relative error between the model value and the test value is 2.1727%, indicating that the model has good generalization ability and fitting effect, and can effectively simulate the characteristics of catalytic pyrolysis removal process of biomass pyrolysis gasification tar. On this basis, this paper optimizes the parameters of catalytic pyrolysis removal process for pyrolysis gasification of rice straw, and shows that when the catalytic pyrolysis temperature is 937.0101 °C and the gas phase residence time is 0.9041s, the rice straw pyrolysis gasification tar catalyst The lysis rate can reach a maximum of 95.4418%.
Abstract: While DCS effectively improves the production management level of power plants, it also has some negative effects on the safe operation of power plants. For example, DCS power failures can cause unplanned shutdown of thermal power units. The reasons for failure of DCS power failure were analyzed, and it was considered that the difference in infrastructure design and understanding was the main cause of power failure. In this regard, the DCS power distribution method and the uninterrupted power supply (U