h1. Medium-scale to large-scale combustion applications
Small particles combust relatively fast and can be combusted in entrained flow combustion applications for pulverized fuels. The particle size should be less than about 75µm [1|createpage.action?spaceKey=rebwp7&title=1&linkCreation=true&fromPageId=1740860]. It is quite energy intensive to crush biomass (e.g. wood) to such small particles. Therefore, entrained flow combustion is not usual for biomass combustion. The larger biomass particles are usually used in grate combustion applications or fluidized bed combustion (FBC) applications. In fluidized bed combustion applications there is an upper particle size resulting from the need for fluidization. In a so-called circulating fluidized bed (CFB), the discharged unburned particles are collected in a cyclone, and re-injected into the fluidizing bed. In a so-called bubbling fluidized bed (BFB) the air flow is kept low enough to allow for complete combustion without re-injection. In grate combustion applications the particle size can be rather large. The particle is kept on the grate within the combustion chamber for the length of time necessary to complete combustion. The particles are burned in a bed of particles; hence, the combustion process becomes more like the combustion of a large layer of particles.
[1|createpage.action?spaceKey=rebwp7&title=1&linkCreation=true&fromPageId=1740860] The Handbook of Biomass Combustion & Co-firing (2008) \\ \\