Condensation Section: The condensation section uses the latent heat of steam condensation to heat the feedwater. A set of baffles distributes the steam evenly along the length of the heater.
The steam entering this section flows to the tail of the heater under the guidance of the baffles. The vent pipes located at both ends of the shell remove non-condensable gases. Because the accumulation of non-condensable gases reduces the effective area, decreases heat transfer efficiency, and causes corrosion.
Drain Cooling Section: The drain cooling section transfers the heat from the drain leaving the condensation section to the condensate entering the heater, thereby reducing the drain temperature below the saturation temperature. The drain cooling section is a submerged structure, a sealed chamber made of welded steel plates. Inside the drain cooling section, spacer tubes position several intermediate baffle plates. The drain from the upstream low-pressure heater enters the drain cooling section of this stage through the drain port at the tail of this low-pressure heater, flows in a left-right serpentine pattern through the intermediate baffle plates, and exchanges heat with the main condensate before entering this stage. This increases the temperature of the main condensate entering the condensation section, and the cooled drain finally flows out of this low-pressure heater through the drain outlet at the lower front of the shell. By setting up the drain cooling section, the thermal efficiency of the unit is improved, and the heat rate is reduced.
Horizontal low-pressure heaters are generally equipped with a drain cooling section, while vertical low-pressure heaters are generally not equipped with a drain cooling section.
Each low-pressure heater is equipped with a continuous extraction pipeline to continuously extract non-condensable gases from the shell side of the low-pressure heater.
Water Chamber Assembly: The water chamber consists of a cylindrical shell, a body flange, and a tube sheet. The tube sheet is drilled with holes for inserting U-tubes. The water chamber assembly also includes feedwater inlet nozzle, outlet nozzle, vent nozzle, safety valve, chemical cleaning connection, and a partition plate to guide water flow as specified, as well as a manhole cover with sealing gasket, manhole seat or sealing cover.
Principles for Putting Low-Pressure Heaters into and out of Service
Start-up Principle: When putting a low-pressure heater into service, the water side should be put into operation first, then the steam side. The low-pressure heater can be started with the unit or started at constant pressure.
Shutdown Principle: When taking a low-pressure heater out of service, the steam side should be shut down first, then the water side. The low-pressure heater can be shut down with the unit or shut down at constant pressure.
High and low pressure heaters should normally be started and stopped with the unit. When putting a heater into service, the water side should be put into operation first, then the steam side; the reverse applies when taking it out of service. When starting or stopping a heater or when operating conditions change, the temperature change rate on the water side must not exceed the limit to prevent damage to the heater. During heater operation, the water level should be adjusted to normal. If abnormal water level changes are found, the cause should be investigated. After heater maintenance, when putting it into service, water should be filled to check for leaks. When checking for leaks, the inlet valve or water filling valve should be opened slightly, and the local water level gauge should be observed; the water level should not rise. If the water level rises, it indicates that the heater is leaking.
9. Precautions for Heater Operation
1) Under normal conditions, high and low pressure heaters should be started and stopped with the unit. If for some reason they cannot be started and stopped with the unit, they should be put into service in order from low to high pressure and taken out of service in order from high to low pressure.
2) Before putting a heater into service, check whether the automatic drain control, related alarm signals, and interlock protection are normal, and whether the water level gauge is intact.
3) When putting a heater into service, the water side should be put into operation first, then the steam side; when taking it out of service, the steam side should be shut down first, then the water side.
4) During normal unit operation, when putting a heater into service, pay attention to preheating the heater, and check whether the heater is leaking. Control the outlet water temperature change rate of the heater within the specified range.
5) During normal unit operation, when taking a heater out of service, check whether the emergency drain circuit of the upstream heater is normal. When stopping a high-pressure heater at high load, also pay attention to changes in condensate flow and deaerator water level. If the condensate flow is insufficient and the deaerator water level drops, start the standby condensate pump in time. When stopping a low-pressure heater, pay attention to changes in condensate outlet temperature and deaerator water level. If the temperature of the condensate entering the deaerator differs greatly from the deaerator operating water temperature, causing deaerator water level fluctuations and the make-up water cannot be put into automatic mode, switch to manual mode for make-up water. In addition, when stopping a leaking heater, only after confirming that the water side is completely isolated, allow isolating the steam side drain circuit. When isolating the water side via bypass, pay attention to changes in feedwater flow or condensate flow to prevent water interruption accidents.
6) During normal heater operation, check whether there is abnormal vibration or steam-water impact sound in the heater system. Check whether the automatic drain control, heater water level, inlet and outlet water temperatures, and terminal temperature difference are normal. Periodically test and check whether the heater-related interlock protection is normal..
