Solid Fuel Firing Method in Steam Boiler

Solid fuel is one of type of fuel used in combustion process. The combustion process with solid fuel can be performed by mechanical spreader stoker or hand stoker firing. Solid fuel firing in steam boiler can be classified as underfeed stoker firing and overfeed stoker firing. The explanation about this firing method as follow:

1.      Underfeed stoker firing

Underfeed stoker firing is the process of combustion in which the new coal is heated by radiation in the presence of air and located under ignited fuel bed. The heating of coal is running less rapidly and release volatile matter combine with air, so generate low smoke. For illustration, please look figure 1.

Fig. 1 Underfeed Stoker Firing in Steam Boiler

2.      Overfeed stoker firing

Overfeed stoker firing is the process of combustion in which the unignited fuel or incoming coal is located above ignited fuel bed. The ignited fuel transfer heat to the incoming coal by radiation. Moreover coal is heated by convection from hot gases that has been through the combustion. Secondary air is added to perform complete combustion unless steam boiler will produce more smoke because the hot gases contain little oxygen. For illustration, please look figure 2.

Fig. 2: Overfeed Stoker Firing in Steam Boiler