Design Specification for Analog Control System

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This post was last edited by cnooczhouyx on 2011-8-30 08:57. Design Specification for the Analog Control System of 2×135MW Cogeneration Units. Table of Contents: 1. Coordination Control System... 5 2. Fuel Flow Control... 7 4. Bed Temperature Control... 8 5. Primary Air Control... 8 6. Secondary Air Control... 8 7. Outlet Pressure Control of Secondary Air Fans (#1, #2 Secondary Air Fans)... 8 8. Furnace Pressure Control... 8 9. Bed Pressure Control... 9 10. Limestone Feeding Control... 9 11. Fuel Pressure Control... 9 12. Boiler Feedwater Control System... 9 13. First-stage Superheater Desuperheating Water Control System (Left and Right Sides)... 11 14. Main Steam Temperature Control System (Left and Right Sides)... 12 15. First-stage Reheater Desuperheating Water Control System (Left and Right Sides)... 12 16. Reheated Steam Temperature Control System (Left and Right Sides)... 12 17. Water Level Control of Boiler Drain Expansion Tank... 12 18. High-Pressure Bypass Pressure Control... 12 19. High-Pressure Bypass Temperature Control... 13 20. Low-Pressure Bypass Pressure Control... 13 21. Low-Pressure Bypass Temperature Control... 13 22. Deaerator Pressure Control... 13 23. Deaerator Water Level Control... 13 24. Condenser Water Level Control... 13 25. Water Level Control of #4 Low-Pressure Heater... 13 26. Water Level Control of #5 Low-Pressure Heater... 13 27. Water Level Control of #6 Low-Pressure Heater... 13 28. Steam Inlet Pressure Control for Steam Seals... 13 29. Pressure Control of High- and Medium-Pressure Steam Seal Header Tubes... 14 30. Temperature Control of High- and Medium-Pressure Steam Seal Header Tubes... 14 31. Pressure Control of Low-Pressure Steam Seal Header Tubes... 14 32. Temperature Control of Low-Pressure Steam Seal Header Tubes... 14 33. Temperature Control After the Condenser Desuperheating and Pressure Reducing Unit... 14 34. Steam Temperature Control After the Fuel Heating and Desuperheating Station... 14 35. Steam Temperature Control After the Heating Extraction Steam Desuperheater... 14 36. Desuperheating Control for Industrial Extraction Steam... 14 37. Desuperheating Control for Heating Steam... 14 38. Desuperheating Control for Purging Steam... 15 Note: All protection and interlock setpoints mentioned in this document are for reference only. On-site setting shall be based on the setting list prepared and approved by the production unit. The system can be put into use only after it has been tuned on-site and passed the tests. The analog control system for the Luoyang Yueneng Sunshine 2×135MW fluidized bed units: A brief description of the functions of each system is as follows: 1. Coordination control system – The coordination control system can receive remote load instructions from dispatchers or manual load instructions from operators. It coordinates the operation of the turbine and boiler so that the unit can meet the load requirements, maintain the main steam pressure at a set value, and ensure the safe and efficient operation of the entire unit. The system design includes a RUNBACK function; when there is an anomaly in the unit’s auxiliary equipment, the system automatically switches to a safe operation mode. The functions of various circuits in the system are as follows: 1.1 Generation of unit load commands: It can be manually set by operators at the operator station, or it can be set remotely by the AGC system. The set value undergoes upper and lower limit constraints as well as rate limiting, ultimately resulting in the unit load command. 1.2 Load RUNBACK function: A load RUNBACK request is generated when either of the following conditions is met. At this point, under coordinated control mode, the system automatically reduces the unit load to the output level of the auxiliary equipment. u Any exhaust fan stops; u Any secondary fan stops; u Any primary fan stops. 1.3 Frequency correction circuit: A frequency signal is introduced as a correction signal, enabling the unit to have primary frequency regulation capability. 1.4 Generation of the set value for the pressure before the machine: It can be manually set at the operator station, or it can be automatically generated by the functional block F(x) based on the machine’s variable-pressure operation curve; after applying upper and lower limits as well as speed restrictions, the set value for the pressure before the machine is determined. 1.5 Operation mode selection: The system has four operation modes (basic mode, turbine-following mode, boiler-following mode, and coordinated control mode). 1.5.1 Basic mode: that is, the manual mode, where both the turbine main controller and the boiler main controller are under manual control. 1.5.2 Turbine follow mode: Automatic main control of the turbine, with pressure control at the front of the controller ； The boiler is manually controlled to regulate the unit load. The turbine regulator accepts the pressure deviation before the turbine and maintains the pressure there at the set value. 1.5.3 Boiler following mode: Steam turbine main control in manual mode, for controlling the unit load ； The boiler is automatically controlled to regulate the pressure in front of the control unit. The boiler regulator accepts the pressure deviation before the machine and maintains the pressure there at the set value. A sensitivity coefficient is applied to the pressure deviation, allowing the strength of the regulator’s action to be adjusted accordingly under different loads. Additionally, [pre-pressure setting before the turbine] is introduced as a feedforward signal to enable the boiler to respond quickly to load requests and eliminate disturbances from the turbine side ； A drum pressure differential feedforward signal is introduced to eliminate internal disturbances from the fuel. 1.5.4 Coordination control mode: Both the turbine main controller and the boiler main controller are in automatic mode. For the turbine regulator, the pressure deviation ahead of the turbine and the load deviation are transmitted to the regulator through a nonlinear region; in other words, the turbine controls both the pressure and the load ； When the unit load command increases, the effect of the pressure deviation increases accordingly. Adding a nonlinear region to the load deviation allows for certain fluctuations in steam pressure ； A nonlinear region is added to the pressure deviation; when the pressure deviation exceeds the insensitive zone, the opening command for the control valve issued by the turbine regulator is restricted. 1.5.5 For boiler regulators, both pressure deviation and load deviation are fed into the regulator ； The proportional-integral constants of the regulator change with the load command, allowing the strength of the regulator’s action to be adjusted accordingly for different loads. Additionally, [pre-pressure setting before the turbine] is introduced as a feedforward signal to enable the boiler to respond quickly to load requests and eliminate disturbances from the turbine side ； A drum pressure differential feedforward signal is introduced to eliminate internal disturbances from the fuel. 2 Fuel quantity control: The speeds of the two weigh-fed coal feeders are adjusted in accordance with the main control commands of the boiler, thereby regulating the amount of fuel that enters the combustion chamber and changing the boiler’s load. 3 Oxygen level control: The diagram on the right shows the oxygen level control circuit of the control panel, which is used to maintain the oxygen content in the flue gas at the inlet of the air preheater. This helps to keep an appropriate excess air coefficient in the boiler, thereby ensuring a high combustion efficiency during its operation. The oxygen level correction signal is sent to both the upper and lower secondary air control circuits to adjust the distribution of secondary air. 4 Bed temperature control: Measurement of bed temperature: Given that (1) the elements used for measuring bed temperature are prone to damage, and (2) the temperature field in the combustion chamber is complex, multiple measurement points are employed to obtain a more accurate representation of the temperature inside the bed – 8 temperature measurement points in the lower part of the dense phase region of the combustion chamber, and 6 temperature measurement points in the middle part of that same region. 6 temperature measurement points at the upper part. 20 temperature measurement points are selected and averaged to form the controlled variable for the bed temperature regulator. The output of the bed temperature regulator passes through three function processors to generate airflow command signals, which are then sent to the upper secondary air, lower secondary air, and primary air systems; by adjusting the distribution of these air streams, the bed temperature is controlled. When the bed temperature changes, the changes in primary air and secondary air are always opposite to each other; that is, as the primary air increases (decreases), the secondary air decreases (increases) to maintain a constant total air volume. 5 Primary air control: The inlet guide vanes of the two primary air supplies are adjusted according to the boiler’s fuel volume, thereby regulating the total amount of primary air that enters beneath the circulating fluidized bed. In addition, it receives the primary air volume command signal from the bed temperature control circuit; as part of this command, the distribution of primary and secondary air is adjusted in order to regulate the bed temperature. 6 Secondary air control: The secondary air volume command consists of two components: one is the secondary air volume command generated based on the boiler’s instructions, and the other is the secondary air volume command derived from the bed temperature control circuit. The sum of these two values is then multiplied by the oxygen level correction factor determined by the oxygen level adjustment circuit to yield the final secondary air volume command. 7 Secondary fan outlet pressure control (#1, #2 secondary fans): The outlet pressure of the secondary fans is controlled by adjusting the opening degree of the hydraulic coupler of those fans. 8 Furnace pressure control: The furnace pressure is controlled using a three-select standard logic. The furnace pressure control system regulates the furnace pressure by controlling the hydraulic couplings of the two axial flow exhaust fans. The set value of the furnace pressure is determined by the operators on the operation screen, via the control panel of the hydraulic coupler of #1 exhaust fan. To balance the output of #1 and #2 exhaust fans, a hydraulic coupler command offset can be set at the ES/MA station of the #2 exhaust fan’s hydraulic coupler. The output of the furnace pressure regulator is sent to the ES/MA stations of the hydraulic couplings of the #1 and #2 exhaust fans via a bias balance weight (balance2). Lockout increase/decrease circuit: When the furnace pressure deviation is large in the positive direction (SP >> PV), the inlet damper of the induced draft fan is locked out and reduced. When the furnace pressure negative deviation is large (SP