Fluid bed combustion

The method of combustion which comprises

• providing a layer of a first particulate material supported on a first distributor plate,
• said first particulate material being incombustible,
• fluidizing said first particulate material with a stream of air to provide a first fluidized bed,
• said first fluidized bed being contained in a first zone of height proper to prevent loss of said first particulate material,
• introducing into said first fluidized bed a minor proportion of a flowable combustible fuel,
• burning said flowable combustible fuel in said air to form combustion gas,
• providing downstream of said first fluidized bed a second layer of a second particulate material supported on a second distributor plate,
• said second particulate material containing a sorbent for a component of said combustion gas,
• fluidizing said second particulate material by passing said combustion gas through said second distributor plate to provide a second fluidized bed,
• said second fluidized bed being contained in a second zone of height proper to prevent loss of said second particulate material,
• transporting said combustion gas against discrete objects too heavy to be moved by said combustion gas flow to slow velocity into said second fluidized bed,
• providing a quantity of microchips by interparticle collision in said second fluidized bed at a rate to provide new reactive surface area as fast as reaction depletes formerly reactive surface area,
• introducing into said second fluidized bed a nonsorbent ballast, and
• controlling the depth of said second fluidized bed in order to control fluidization and elutriation.