Suspension and Fuel-Bed Firing

There are three basic modes of burning solid fuels, each identified with a furnace design specific for that mode in suspension, in a bed at rest on a grate (fuel-bed firing), or in a fluidized bed. Although many variations of these generic modes and furnace designs have been devised, the fundamental characteristics of equipment and procedure remain intact. They will be described briefly. 

Conceptually speaking, the technology for combustors is similar to that used for coal combustion (see Chapter 9) if solid biomass fuels are used. Typically used configurations for biomass combustion include [41] (1) pile-burned, (2) stoker-fired, (3) suspension-fired, and (4) fluidized-bed combustors. 

Fluidized bed combustion of coal is used to reduce the emission of sulfur dioxide and NO into the enviromnent. In this technology the pulverized fuel is burnt in a fluidized bed combustor after being blended with limestone or dolomite, which act as soibents for SO2. The burning temperature is significantly lower than is common in the production of fly ashes in suspension-fired furnace chambers, at around 850°C. The process may take place at atmospheric pressure (atmospheric fluidized bed combustion, AFBC) or elevated pressure (pressurized fluidized bed combustion, PFBC). 

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