1 Introduction
The second phase of Jigang Waste Heat Power Generation Project is a combined cycle generator set consisting of “2+2+2+1â€, that is, two coal presses per unit, two gas turbines, two boilers, and one steam turbine. .
The steam turbine is one of the main equipments for power generation of gas-steam combined cycle power generation project. The thermal energy of steam is converted into rotary mechanical energy. Because the turbine generator set is operated at high temperature and high pressure while rotating at high speed, the control system of the turbine control system is interlocked and protected. It is of great significance.
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The turbine system is controlled by dcs system, which mainly includes the detection of steam and steam system pressure, temperature, etc., bypass system, eh oil system, lubricating oil system, condensate system, vacuum system detection and related control. The bypass system of the turbine is a high and low voltage series system. During the startup process of the turbine, the circulation process of the working fluid can be accelerated, the heating and boosting speed of the unit can be improved, and the opening degree of the pressure reducing valve can be controlled according to the pressure setting value so that the system does not exceed the system. Pressure. The turbine can be effectively protected and the working fluid recovered when the unit is under load.
2 control system
2.1 System composition
The control system uses a dcs distributed control system with reliable redundancy. It consists of several parts: the upper monitoring station, the on-site control station, and the communication network ethernet. Including central i / o unit, extended i / o unit, cpu module, connection module, various i / o modules, to achieve data acquisition, loop control, sequence control and other functions. The dp network is connected to the remote station, and the communication network ethernet is used to connect to the monitoring station and transmit data.
Operating platform windows2000 professional+sp4, development software includes: control builder f professional software. For hardware configuration, process level and operator station configuration, establish a system-wide unified database.
Chinese version of digivis. Used for process display, alarm information management, trend archiving, various records, system diagnostics, operation control, etc.
Control it basic (xxx points). The limit of i/o points.
The trend server acts as a trend server and collects history.
In the implementation process of the lower programming software of the control system, the functions of the process flow and field equipment, signal processing, electric door control, GPS clock synchronization, system communication and other functions are developed by configuration software, and the configuration of the control loop is developed by function diagram. .
The monitoring interface completes the data acquisition, calculation, discrimination, alarm, protection, event sequence recording (soe), report statistics, curve analysis, and on-site of the system's analog quantity, switching quantity, pulse quantity, temperature quantity, protection information, etc. The protection and control unit layer issues commands to control and regulate electrical equipment. The interface is friendly, convenient, and the database is safe and reliable. In the centralized control room operation, the console is the center of the unit operation monitoring and control, and the crt operation station is arranged on the console. In addition to retaining several emergency buttons, all of them are operated by the upper computer, and the unit can also be monitored and operated with a large screen.
2.2 Main functions and control strategies
The turbine start is divided into three modes: automatic, manual, and semi-automatic. When the start is completed, the turbine speed is controlled at the minimum speed. In the idle/rated state, the minimum speed is the idle value, and in the sequential start state, the minimum speed is the low idle value. The automatic sequence start completes the automatic completion of the entire process from low idle hold to warm up to high idle speed to set ratio speed. The warm-up time and acceleration rate depend on whether the turbine is cold or hot.
In order to ensure the safe operation of the unit, various automatic protection devices are generally installed on the steam turbine. When the operating parameters exceed the allowable range of safe operation of the unit, it will act in time to automatically stop the turbine and avoid further expansion of the accident. The bypass system device is an important equipment of the generator set. The reliability of the bypass system equipment has a great impact on the safety and economic operation of the power plant. It ensures the safety and start-up of the thermal equipment; maximizes the service life of the unit; and improves the comprehensive economic benefits of the unit. .
3 bypass system (bpc)
The bypass system control strategy can meet the rapid start of each valve automatically or manually (remote control operation) under start-up, normal operation and load-shedding conditions. It can ensure that when the main steam and reheat steam operating pressure and temperature exceed the set range, the bypass device can be automatically turned on or off, and the pressure and temperature are automatically adjusted according to the operation of the unit until the normal value is restored. The bypass system ensures that the pressure or temperature of the new steam is higher than the set working pressure, and can be opened in time to release a part of the steam, thereby ensuring that the pressure entering the main valve is stabilized within a certain range. The steam entering the bypass eventually enters the condenser, and the secondary system is desuperheated in the bypass system due to the higher steam temperature. In addition, the bypass system is equipped with an interlock, when certain process parameters in the system are not met, a corresponding quick opening or fast closing action is generated. The bypass process is shown in Figure 1.
Figure 1 bypass flow chart
3.1 Function settings
The turbine bypass is a high- and low-pressure two-stage series bypass system. The high pressure bypass is controlled by a pressure reducing valve, a water spray isolation valve and a water spray regulating valve; the low pressure bypass is a pressure reducing valve, a first stage water regulating valve and a secondary water spraying valve. All valves are driven by a single speed electric actuator. The bypass control system has three main functions: start-up, overflow and safety (ie, three-way valve function), as well as functions such as recovery of working fluid, heating pipe, cleaning, reduction of steam valve and blade erosion.
(1) Start function: Its purpose is to improve the starting characteristics of the unit. It can improve the burning rate of the boiler during the starting process; the steam temperature can be optimally matched with the turbine cylinder temperature; thus shortening the startup time of the unit and reducing the life loss.
(2) Overflow function: The purpose is actually set for the unbalanced load between the absorption machine and the furnace. It can drain the remaining steam in the process of overloading the load; adjust the stable competing pressure; maintain the minimum steady-burning load of the boiler without oil.
(3) Safety function: replace the function of the boiler safety valve. After the unit bypass system is put into standby, when the difference between the actual pressure of the unit and the set value of the unit's high pressure bypass pressure is greater than the bypass overpressure offset setting value, the bypass system will automatically participate in the pressure regulation to maintain the main steam. The pressure is equal to the set value.
3.2 Regulation, control and protection of the bypass system
Before the boiler is ignited, the high and low pressure bypasses are closed. If the bypass system is put into operation automatically, the system opens the valve according to a certain curve. When the cranking parameters of the turbine are reached, deh sends a closing signal to the bpc, and the high and low voltage bypasses are closed according to a certain logic, and it is no longer turned on under normal operating conditions.
The bypass system can increase steam temperature and steam pressure during start-up conditions. Before the boiler is ignited until the turbine is rushed, the unit is put into the high and low pressure bypass system (also called high side and low side) to speed up the steam heating and boosting speed and shorten the unit startup time. It is also equipped with stable steam pressure and protection under accident conditions. It can adapt to the starting requirements under various conditions such as cold and hot state of the unit; pressure regulation during load change; protection against overheating, reduction of safety valve action, recovery of working fluid, etc. It also has an overflow function. It can also adapt to the steam turbine load rejection to maintain the empty load operation, and the turbine trips to achieve the shutdown without stopping the furnace.
(1) Pressure control: control main steam pressure, with fixed valve position control and constant pressure control. There is a low pressure limit on the low side and a high pressure limit to ensure that the low side valve position is fully closed after the unit is lifted. Temperature control: control the temperature of the high and low pressure bypass valves, maintain the cold section steam temperature and not make the condenser temperature too high; can realize the variable parameter adjustment under different steam flow conditions.
2) Protection function: bypass valve quick opening and fast closing function: For the safety of the unit and equipment, fast closing takes priority over quick opening; high side valve opening and low side valve opening; low side valve closing, high side valve closing; fast On: Under the accident condition of the unit, the bypass is opened quickly and the overpressure protection function is applied; the fast closing: the high bypass outlet temperature is too high or the low bypass is closed to make the high bypass fast; the condenser vacuum is low, the condenser temperature is low High, high water level of the condenser, low pressure of the lower side, and low water pressure make the low side fast.
3.3 Bypass Control Strategy
(1) High-pressure bypass: In the high-side valve control mode, the target valve position and valve position change rate can be set through the bypass master control screen to adjust the main steam pressure. The high-pressure bypass pressure regulating valve opens the high-pressure bypass pressure regulating valve when the steam pressure in front of the electric isolation door is higher than the set value, and closes the regulating valve when the value is lower than the set value. The high side control principle is shown in Figure 2.
Figure 2 Principle of high voltage bypass control
y max -bp valve position maximum setting; bp-high side valve; p sactual - final main steam pressure setting value; dp-pressure deviation setting; ys - valve position command; bpe-high side water injection valve; Steam - main steam pressure; bd-high side isolation valve; pt-proportional integrator.
(2) Low-pressure bypass system: The function of the low-pressure bypass system is to bypass the reheat steam to the condenser during start-up or load rejection to achieve the purpose of protecting the preheater and the steam turbine.
The low pressure bypass system includes two systems of low side pressure control and low side temperature control.
Low-pressure bypass In the start-up phase of the unit, the operating personnel can set the minimum pressure pm in (external reference 1 × 105pa) to control the reheater outlet pressure to maintain a certain steam flow through the preheater. When the turbine is reversed, the pressure set value ps changes with the turbine speed regulation stage (representing the turbine load), and the low side slip pressure operates. The pressure setting ps = p rh + $p to ensure that the lbp valve is closed. In order to protect the condenser, the lbp valve is provided with a quick-closing device ssb. When any of the following conditions occurs, the quick-closing device will operate, and the lbp valve is closed within 2s: condenser pressure >-5.066×104pa; condenser Temperature > 80 ° C; water spray pressure < 5 × 105 pa; condenser water level is high.
For the low side temperature control system, the adjusted amount of the control system is not the low side temperature, but the opening of the low side temperature control valve, that is, the low side temperature control is a follow-up adjustment. The opening degree of the low side desuperheating regulating valve is determined by the reheating steam pressure, the opening degree of the low bypass pressure reducing valve and the reheating steam temperature, and the expression is as follows:
Let ta=max(t-250,0)
a=1+0.0043ta×0.14(0.5 p+1)
b=f(p)×20+0.2
c=1.18f(l)l
Then k=kp+a·b·c
Where t is the reheat steam temperature; p is the reheat steam pressure; l is the low bypass valve opening; kp is the minimum bypass of the low side desuperheating water regulating valve; k is the low bypass desuperheating water regulating valve opening.
3.4 Bypass safety control and protection
(1) When any of the following conditions is satisfied, the high side pressure reducing valve is strong:
Turbine overspeed 110% (bypass input);
The temperature after the high side is higher than 390 ° C (delay 10 s);
High side water spray pressure is low;
Deh requires a bypass.
(2) When there is no high side strong off signal, and the front pressure is greater than 6mpa, the high side pressure reducing valve is opened when any of the following conditions occurs:
Steam turbine trip;
Generator tripping;
The pressure in front of the machine is boosted too fast.
(3) Low side pressure protection. When any of the following conditions are met, the low side pressure reducing valve is closed:
Condenser vacuum is lower than (three take two) 85kpa;
Low side water spray pressure is low;
After the low side, the temperature is higher than 190 °C;
The condenser water level is high, deh requires the bypass to be bypassed (low side inlet pressure is less than 0.11mpa) when there is no low side strong closing signal, and the low side first stage water spray valve is greater than 10%, when any of the following conditions are met, low The side pressure reducing valve is opened: the high side is strong; the steam speed is 110%.
4 Conclusion
The operation results of the unit show that the bpc system plays a role in increasing the steam temperature and pressure during the process from the ignition of the boiler to the suspension of the turbine, which plays a role in improving the starting performance of the unit and shortening the starting time. The control system configuration software is transparent and the screen is rich. Compared with the hydraulic bypass system, the electric bypass system has the advantages of easy maintenance and easy operation. It ensures the reliable, safe and stable operation of the power plant and plays a major role in developing a circular economy, striving for the best benefits, and creating a clean factory.
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