Boiler Control:
I. Three-element control of boiler drum water level
The three-element control system for boiler drum water level refers to the system in which three signals—drum water level, steam flow, and feedwater flow—act on the controller, i.e., three controlled variables correspond to one controller.
Working principle:
In the three-element feedwater control system, the drum water level signal is the primary signal and also the feedback signal. When a disturbance causes the drum water level to change, the controller will act to change the opening of the feedwater valve so that the drum water level returns to the allowable fluctuation range. The steam flow signal is the main functional disturbance of the system; feedforward compensation for it can overcome controller misoperation caused by "false water level." The feedwater flow signal is the feedback signal of the inner loop, which can quickly eliminate internal disturbances of the system and stabilize the feedwater flow. The three-element control system can promptly overcome the disturbance effects of load (steam flow) and feedwater flow, and has high control accuracy. It is suitable for occasions where the drum volume is relatively small and load and feedwater disturbances are relatively large.
II. Boiler furnace FSSS system
The boiler furnace safety supervisory system, abbreviated as FSSS (Furnace Safeguard Supervisory System), is an important system for ensuring the safe operation of the boiler. During all stages of boiler startup, operation, and shutdown, it continuously monitors relevant boiler operating parameters, continuously performs logical judgments and calculations according to the safety conditions specified in the explosion-proof regulations, and through corresponding interlock devices enables combustion equipment to complete necessary operations according to established procedures. It prevents the accumulation of explosive air-fuel mixtures in the furnace passage and, when dangerous conditions or unsafe boiler operating conditions occur, rapidly cuts off all fuel entering the furnace. The FSSS system can not only automatically complete various operations and protective actions, but also avoid incorrect actions by operating personnel during manual operation, and can promptly execute quick actions that cannot be performed in time by manual operation, such as emergency cut-off and tripping, thereby preventing destructive accidents such as deflagration and explosion, and ensuring furnace safety as a protection and control system.
