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1. Introduction *****The technical renovation project of Unit #1 in the power plant uses NG-220/9.8-Q type boilers manufactured by Hangzhou Boiler Factory, and the FSSS system is equipped with a MACS distributed control system produced by Beijing HollySys System Engineering Co., Ltd. As part of the DCS control system, the FSSS system has its control modules located at Station 12. The main equipment under consideration includes: the on-site ignition control cabinet, coke oven gas nozzles, ignition guns and high-energy igniters, blast furnace gas quick-shut valves and coke oven gas electric valves, as well as flame detection probes and flame signal conversion amplifiers, all of which are provided by Beijing Yuandong Control Co., Ltd. 2. Control Principle 2.1 Boiler furnace purging conditions: a. No boiler trip ； b. Close the electric valve of the coke oven gas main pipe ； c. Total air volume is greater than 30% ； d. Operation of the exhaust fan ； e. Blower in operation f. No flame in the entire furnace ； g. Operation of any cooling fan ； h. Secondary air damper opening ≥ 10% ； When the above purging conditions are met, pressing the purging button will initiate furnace purging; the timing can be manually set by the operator, after which the purging is completed. 2.2 Program control of coke oven gas 2.2.1 Ignition conditions for coke oven gas: a. Furnace purging completed ； b. Operation of any cooling fan ； c. Open the electric valve of the coke oven gas main pipe ； d. Coke oven gas main pressure > 1.8 Kp ； e. Activation of programmed ignition for cabinet A ； f.B cabinet programmable ignition activated ； 2.2.2 Program control mode for coke ovens: Steps to start the program: Press the start button → Insert the coke oven gas gun → Insert the ignition gun for coke oven gas; at the same time, open the electric valve for coke oven gas → The igniter starts firing (set time: 15 seconds); the electric valve for coke oven gas opens fully (a flame is detected after 2 seconds) → Retract the ignition gun (the electric valve for coke oven gas is open, the ignition gun is retracted, and a flame signal is present) → Ignition is successful. If a stable flame signal FSSS is not detected within 2 seconds after the quick-stop valve has been opened, the shutdown procedure will be automatically initiated. Program stop step: Press the stop button → Close the coke oven gas electric valve → Retract the coke oven gas gun → The program stops and ends. 2.3 Boiler Safety Protection Boiler safety protection items: a. High water level in the boiler drum. The protection signal for the water level in the boiler drum is generated by the water level electrical contact; the signal obtained through a three-out-of-two logic circuit is used as the protection signal. The high liquid level setpoint is +150mm, with a 2-second delay. b. The low water level signal in the boiler drum is also generated by the water level electric contact; the signal obtained through a three-to-two logic circuit is used as the protection signal. The low liquid level setpoint is –200 mm, with a 2-second delay. c. High boiler furnace pressure: The signals obtained from the three furnace pressure switches of the boiler, after being processed using a three-to-two logic scheme, are used as protection signals. The protection setting is +1500 Pa with a 2-second delay. d. Low boiler furnace pressure: The signals obtained from the three furnace pressure switches of the boiler, after being processed using a three-out-of-two logic, are used as protection signals. The protection setting value is -1500 Pa, with a delay of 2 seconds. e. Both supply fans have stopped. f. Both induced draft fans are stopped. g. Loss of all fuel. h. Loss of all flames 2.4 Protection system description: On the operation screen, set the protection enable/disable switch. In the event of special circumstances that require the removal of a certain protection, the operators shall carry out this action at the operator station. The boiler protection logic includes a first-memory function, which allows the stored information to be displayed on the operation screen, facilitating the identification of the cause of tripping. Result of protection action: Close all high gas speed cut-off valves ； Close the main electric valves for high-pressure and coke gas, as well as the angle valves ； Close the cooling water electric valve. 3 Debugging Process 3.1 Static Debugging First, check the wiring of the control circuit ； Then, an inspection of the control logic. Check the manual operation control logic, sequential control logic, and boiler protection control logic. Identify unreasonable protection and operation control logic, make modifications to them, and adjust certain parameters in the protection and control circuits ； Perform on-site inspection of the equipment ； Switch the transfer switch in the local control cabinet to the local control position, operate the buttons on the control panel of the control cabinet, check whether the actuators and igniters function properly, and observe whether the signal indicators on the control panel are correct ； Operation check for remote control: Switch the toggle switch in the local control cabinet to the remote control mode, then click on the controls on the operation screen to operate the device being controlled locally; the screen should show that the actions are performed correctly and that the feedback signals are accurate and reliable ； Check of the ignition program control: On the premise that remote single-operator control is functioning correctly, the program control is tested; the timing of each step as well as the relevant judgment conditions are adjusted. Faults are introduced artificially to conduct tests, and the control logic is modified so that the program control reaches an optimal state. 3.2 Dynamic Debugging 3.2.1 Start one supply fan and one exhaust fan at each test position, operate the cooling fans, and ensure that all other conditions for furnace purging are met. Initiate the purging procedure; during the purging timer, stop the supply fans on the operation screen, and the screen will indicate that purging has been interrupted and that MFT conditions apply. 3.2.2 Re-establish the conditions for purging and start the procedure again. Once purging is complete, the operation screen will show that purging is finished. Stop the supply fans once more on the screen, and the indication of completed purging will disappear; the boiler will trip, and it will be shown that all supply fans have stopped operating. 3.2.3 Re-establish the conditions for purging and start the procedure again. After purging is complete, the operation screen will show that purging is finished, and the conditions for boiler tripping will no longer apply. On the screen, open the electric valve for the coke oven gas main pipe; the screen will indicate that the pressure of the coke oven gas is sufficient. Under the ignition permission conditions, click the buttons “Allow programmed ignition for Cabinet A” and “Allow programmed ignition for Cabinet B”; the screen will then show that the ignition conditions are met. 3.2.4 Once the ignition conditions are satisfied, simulate a flame detection signal. On the screen, click the “Programmed ignition” button; the system will carry out the programmed ignition steps, and once the feedback status is confirmed as correct, the system will successfully ignite. 4 Problems Found During Debugging and Their Solutions During debugging, it was found that the control method for the fast-acting valve for incoming blast furnace gas required a normally closed contact from the DCS, meaning that the output relay had to remain powered continuously. However, the control system used by Helix could not guarantee the reliability of this control method. Therefore, an additional control circuit was added in front of the inlet control cabinet, allowing the DCS to reliably control the opening and closing of the fast-acting valve for blast furnace gas. Additionally, the FSSS logic provided by Helix had many issues, lacking proper logic conditions for startup as well as conditions for equipment protection. Under these circumstances, the FSSS programmed ignition program was redesigned. After numerous tests and runs, it has been proven that the protection logic and program control actions are correct and reliable. 5 Conclusion During all stages of the unit’s trial operation, the FSSS system protection was activated, and its operations were accurate and reliable. Programmable switching is seamless, flame detection is accurate, and the system operates stably. It meets the design requirements and ensures the safe and stable operation of the boiler.