6 Politekhnichna Street
Building 5, floor 8, room 801
The atmospheric deaerator type 25/8 preheats boiler feedwater and removes dissolved oxygen and free carbon dioxide, which can corrode equipment. In the 25/8 deaerator described here, water passes through jet and bubbling stages in the deaeration column and a further submerged-bubbling stage in the tank. Steam heats the water close to saturation; remaining gases are released and vented, while the treated water is held in the tank before use.
The automation system stabilises the steam pressure and water level in the tank. Steam flow is adjusted to regulate pressure, while the flow of chemically treated make-up water controls level. The system measures deaerator steam pressure, tank level, inlet-water temperature and tank-water temperature, and signals high or low process values and sensor faults.
A programmable controller receives the process measurements and operates the electrically actuated steam and water valves. Its keypad and graphic LCD display a process mimic, sensor values, actuator states, settings and an event log. Manual controls can bypass the controller for the actuators, allowing the process to continue if part of the controller-based system fails.
The water-level loop uses a three-position electric valve actuator. Tank level is calculated from a pair of pressure sensors, with the controller compensating for steam pressure above the water. Steam pressure is controlled by a single-loop PID algorithm: a 4–20 mA pressure signal is read by the controller, which sends a 0–10 V command to the steam-valve actuator. Pt1000 temperature sensors are rated for water temperatures up to 120 °C. The panel can operate independently or connect to a supervisory control system over Modbus RTU.
