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Boiler feed water is preheated in a heat exchanger called an economizer before entering the steam drum. The economizer uses hot combustion gases to preheat the boiler feed water in order to minimize the amount of heat lost to the stack.
Saturated steam is generated in the risers of the boiler. Before going to the steam header, the saturated steam leaves the steam drum and passes through the superheater where it reenters the firebox of the boiler and is superheated. Two other boilers of similar design and capacity as the main boiler provide superheated steam to the steam header. Steam users then draw the superheated steam from the steam header.
Fuel and air enter the firebox of the boiler where they are ignited and burned. The superheater, the downcomers, and risers are heated both by radiant and convective heat transfer. The hot combustion gases then preheat the boiler feed water in the economizer before passing out the stack.
A blowdown line is provided, where water is periodically drawn off to prevent a buildup of minerals and sediment in the boiler.
Boiler feed water to the steam drum is controlled by flow controller FIC-101. Boiler feed water temperature is indicated by TI-101. Boiler feed water temperature entering the steam drum is indicated by TI-102. Blowdown is controlled by flow controller FIC-103.
Steam drum pressure is indicated by PI-101 and superheated steam temperature is indicated by TI-103. Steam drum level is indicated by LIC-101. Steam rate is indicated by FI-102. The boiler may be isolated from the steam header by HIC-102.
Fuel rate to the boiler is indicated by FI-301 and air to the boiler is controlled by FIC-201. The burner switch acts as both an ignitor and a flame indicator. Fuel and air temperature are indicated by TI-301 and TI-201 respectively. Stack temperature is indicated by TI-202 and stack O2 is indicated by AIC-201.
Steam header pressure is controlled by PIC-501. The steam generated by the other 2 boilers is indicated by FI-401. The percentage of steam generated by the boilers is indicated by HIC-301 and HIC-401. Steam demand is controlled by FIC-601.