|Fig.1: Simple Fowl Diagram of Steam Boiler|
The simple flow diagram of steam boiler in Figure 1 shows that steam boiler comprises various system, such us a feedwater system, a fuel system, a steam system, product of combustion system, a stack system, and a blowdown system. The inputs for the boiler are fuel and feedwater, whereas the output of steam boiler are combustion product and steam. Like the product of combustion, the blowdown of water from boiler is also waste.
Feedwater is water that is supplied to steam boiler. Water is supplied to the boiler either by gravity return (in small installation) or by a boiler feed pump. In steam boilers, the water absorbs heat until it reaches the boiling point. Converted into steam, it then collects in the highest part of the boiler because of the difference in density between steam and water.
Steam is generated within the boiler as a result of heat transfer from fuel to feedwater, and pressure in the steam boiler will force the steam to discharge through the main steam pipe. The gas at the burner is burned in the furnace within the boiler and becomes products of combustion, transfer heat to feedwater, moves out of the steam boiler under furnace pressure, and ultimately to atmosphere through a stack.
When feedwater is converted into steam, sediment is left behind ath the bottom of the biler, and this sediment is removed by blowdown either at scheduled intervals or continuously.
In terms of a real situation, the boiler flow diagram is complex. For example, the simple gas burner shown in the diagram is a complete combustion equipment system comprising many valve, controls, safety features, burning equipment, and piping. The combustion equipment system is designed to make the combustion efficiency as high as possible. The same principle is applicable to other system, such as steam systems, blowdown systems, and product of combustion system.