Fluidized bed boiler use non combustible materials such as sand or ash as medium for taking heat transfer process with fluidize fuel hydro dynamically. A bed is required to burn fuel and combustion air is supplied in high pressure. Fluidized bed boiler can be classified as two types; circulating fluidized bed boiler and bubbling fluidized bed boiler.
1. Circulating fluidized bed boiler
This type supplies higher amount of combustion air than bubbling fluidized bed boiler type through the grid to the furnace. Therefore the combustion produces a bed with lower density and longer dimension up to the top furnace. Loop seal is used to catch solid non combustible particle and recycle it into furnace again. This condition increase boiler efficiency and low emission.
2. Bubbling fluidized bed boiler
This type requires less amount of combustion air than type circulating fluidized bed boiler. The combustion air is supplied through the grid or can be also called as distributor and maintain sand (non combustible particle) at the low level of furnace. This condition is different with the circulating type. Bubbling fluidized bed boiler is usually applied to burn fuel with high volatile matter and low quality such as sludge, waste and wood.