1 Overview Yadian Xinbao #7 furnace model is HG220/100-HM11, rated steam flow 220T/H, rated steam pressure 9.81Mpa, rated steam temperature 540 °C. In order to improve the degree of automation of boiler control and reduce the workload of operators, Yadian Xinbao uses the Xinhua XDPS-400 distributed control system to transform DCS of #7 furnace, with functions covering DAS, MCS, SCS, and FSSS. DAS includes signal acquisition processing, flow chart display, trend display, alarm display, group display, list display, report record printing, historical data collection, SOE record reproduction, accident recall, etc.; MCS includes thermal load control, drum level control, Main steam temperature control and furnace negative pressure control; SCS includes the control and interlock of auxiliary fans such as induced draft fan, air blower, powder discharger, coal mill, and electric door; FSSS is responsible for furnace safety monitoring.
2 MCS input after transformation After the DCS transformation, compared with the traditional control instruments, the MCS investment has become much easier. The control strategy can be modified online and let you play. This is also the outstanding aspect of the XDPS-400 distributed control system.
2.1 Drum Water Level Control System The drum level control system still uses the traditional three-impulse control system. Since the control object is a rapid reaction link, the input of the automatic control system is much easier, so the main work is focused on the optimization of PID parameters. The current situation is that when the automatic control system is put into operation, the water level of the drum changes within 15mm, which can meet the boiler operation requirements.
2.2 main steam temperature control system As we all know, the main steam temperature as a control object is a large delay inertia link, simply relying on the traditional PID control water spray to keep the temperature within the required range is not easy. While the main steam temperature control of the Yadian Xinbao #7 furnace is designed to be a two-stage water spray desuperheating, the secondary water spray is not used, and only the primary spray water is used to control the main steam temperature. In this way, when the amount of water spray is changed, it takes longer time for the main steam temperature to change, so that the input of the main steam temperature automatic control system becomes more difficult.
In view of the current situation, the automatic adjustment of the main steam temperature also requires the use of PID function blocks. Obviously, PID control is only necessary. Regardless of how the P and I parameters match, it is difficult to keep the main steam temperature within the required range and adapt to the load change capability. Also weaker, automatic control systems are prone to shocks. The method to solve the problem first starts with additive feedforward. The traditional feedforward is usually based on the influence of the disturbance factor on the system plus an appropriate feedforward, but the main steam temperature has more disturbance factors and it has different disturbance effects. The dynamic response of the next system is also different.
From another point of view, when any disturbance occurs, although the main steam temperature has not changed significantly, it will inevitably show the trend of change. It is based on this that, when the main steam temperature of the Subsonic Xinbao #7 furnace was automatically adjusted, after a long period of observation and repeated experiments, the following feedforward effects were added.
The current value of the average of the main steam temperature is subtracted from the current value of 30 seconds, which reflects the change in the main steam temperature within 30 seconds. When the main steam temperature increases by more than 0.5°C for more than 2 seconds, the desuperheating water The valve is increased by 8% of the opening, and when the increase is less than 0°C and kept for more than 2 seconds, the previously increased 8% warm water valve opening is removed. Conversely, when the main steam temperature decreases by more than 0.5°C for more than 2 seconds, the desuperheating water valve reduces the opening by 8%. When the decreasing amplitude is less than 0°C and stays for more than 2 seconds, the previously reduced 8% warm water valve will be used. Opening degree plus. It should be particularly noted that the above feedforward is added to the PID output of the secondary tune and not to the FF input of the PID function block.
From the effect of actual investment, the above feedforward function plays a major role in the main steam temperature control system, and PID regulation only plays a role of auxiliary regulation, and the regulation effect can neither be too strong nor too weak. The PID control loop is still using cascade control, a main tone with two sub-adjustments, the main process variable is the average of the main steam temperature, and the secondary temperature is the temperature of the secondary desuperheater outlet. Due to the burning of the boiler, the left and right sides are not heated uniformly, and there is always a temperature deviation before the steam enters the final stage superheated steam mixing header. In order to make the right and left water jet valves act synchronously and the opening deviation is not too large, take the average of the outlet temperatures of the left and right secondary desuperheaters as the pilot temperature of the two secondary regulators. The main tuning parameters are: Kp=0.8, Ti=150, and the two subadjustments are: Kp=0.6 and Ti=200. This period of time since the start of the ignition of the boiler indicates that the regulation quality of the main steam temperature control system can meet the unit operation requirements, the temperature range of change is within 3°C, and its ability to adapt to load changes is extremely strong.
2.3 The furnace negative pressure control system The furnace negative pressure control system uses a single impulse control system. Because the control object is a rapid reaction link, the negative pressure of the furnace is very sensitive to the change of the opening of the wind deflector, so the adjustment effect of the PID should not be too large. In this way, the P and I parameters should not only be set properly, but also the rate limiting function block to limit the speed change of the wind deflector opening command. From the current situation, when the automatic control system is put into operation, the negative pressure change of the furnace is within 20Pa, which can meet the boiler operation requirements.
2.4 Thermal load control system The thermal load control is the sub-adjustment of the main steam pressure control to control the steam flow. Since the #7 furnace in the parent control boiler only guarantees the load without adjusting the main steam pressure, the output of the main station can be used as an auxiliary. Adjusting the load (steam flow) set value, the sub-adjusted output finally controls the speed of the pulverizer, which changes the amount of pulverized coal entering the furnace, so that the boiler's heat absorption changes, the steam flow rate changes, and the load changes. From the perspective of current investment, when the thermal load automatic control system is put into operation, it can meet the boiler operation requirements.
3 After the transformation of the main logic of the SCS After the DCS transformation, many of the original can not be realized interlocking and sequence control logic, can be achieved through the configuration software. Not only is the equipment included in the SCS a very wide range, but also the reliability of the interlocking and protection system is greatly improved.
3.1 Boiler large interlock 3.1.1 When the total interlock is engaged and the two induced draft fans trip, the blower is jumped.
3.1.2 When the total interlock is engaged and the two blowers are tripped, the machine will be discharged.
MFT skips the powder machine.
3.1.3 The total interlock input and the A row powder stop light is on, then the jijia coal mill.
Coal mill low oil pressure linkage input and low oil pressure jump coal pulverizer signal is effective.
3.1.4 The total interlock input and the B row powder stop light is on, then jump B coal mill.
Coal mill low oil pressure linkage input and low oil pressure jump coal mill signal is effective, then jump B coal mill.
3.2 To powder power linkage 3.2.1 to powder linkage A B into the button press A to powder power input signal is 1 and B powder power input signal is 0, then give powder linkage A link.
3.2.2 To the powder linkage B-joint input button Press B to powder power input signal is 1 and A to powder power input signal is 0, then give powder linkage B joint armor input.
3.3 Milling system damper interlocking A milling powder #4 and A milling powder #7, A milling powder #6 and A milling powder #7 all have chains, the logic is as follows:
The "TOM" of the DEVICE corresponding to the door of the door of the door of a flour mill # 4 and the door of the door of the mill powder # 6 is 1. In other words, the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door of the door.
â— A 4 A 7 interlocking input and A 4 manual, A 7 cut automatically.
A 6 A 7 interlocking input and A 6 manual, A 7 cut automatically.
â— When A7 is automatic, when:
â–² A 6 A 7 interlocking input A discharge powder current is lower than the set lower limit, then A 7 open.
â–² A 4 A 7 interlocking input A discharge powder current is lower than the set lower limit, then A 7 open.
â–² A 6 A 7 interlocked input A discharge current is higher than the set upper limit, then A 7 off.
â–² A 4 A 7 interlocking input A discharge powder current is higher than the set upper limit, then A 7 off.
â–² A 6 A 7 interlocking input A current is located between the upper and lower limits, A 7 stop.
â–² A 4 A 7 interlocking input A current is located between the upper and lower limits, A 7 stop.
It should be noted that because A-powdered #4 and A-powdered #6 doors are always manual, as long as A4 A7 interlocking input or A6 A7 interlocking input, A7 will cut automatically. In addition, even in the case of chained investment, A7 can still be cut manually, this can be made manually. The buttons in the middle of the control screen milling door can only be cut manually, cutting automatically invalid!
The working logic of the flapper side B system is the same as that of the A side milling system.
3.4 Safety Door Interlock The overheater safety door and steam drum safety door OUTM are 3, that is, the output command is a long signal. When the reverse direction command is valid, the signal is reset; STP is 1, ie, the STOP command signal is valid.
3.4.1 Superheater safety door:
The main steam pressure 1 is greater than 10.8 MPa and the main steam pressure 2 is greater than 10.8 MPa, and the superheater safety door is opened when the main steam pressure is automatically input.
After it is turned on, it can be turned off manually and the signal is turned off for 15 seconds. If the open signal becomes active while the closed signal remains active, the close signal is reset and the overheater safety door opens.
3.4.2 Drum security door:
Drum pressure 1 is greater than 12.4 MPa and drum pressure 2 is greater than 12.4 MPa, and the drum opening is automatically activated.
After it is turned on, it can be turned off manually and the signal is turned off for 15 seconds. If the open signal becomes valid while the closed signal remains active, the close signal is reset and the drum safety door opens.
4 Conclusion # 7 furnace after DCS transformation, reducing the number of disk table, eliminating the need for a large number of monitoring instruments, so that the entire control room becomes simple and bright, convenient control of the operating personnel, reducing the intensity of the operator to monitor the disk. The entire boiler is also more stable and economical and safe. In short, the DCS reconstruction is successful in all aspects.
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