Explanation of Fluidized Bed Coal Boiler Controls

Firing Configuration

• A fluidized bed provides constant streams of air that trap coal in a suspended state inside the furnace. The "fluidized" term refers to the constant air pressure against the coal fragments. The coal is ground into small particles and burned as a large, floating bed, constantly moved around buy the air currents beneath. The result is a suspended bed of intense heat used to power devices and bring water to boiling temperatures.

Temperature and Other Factors

• One of the primary controls in a fluidized bed coal boiler is the temperature of the bed itself. The fluidized bed produces sufficient heat but stays at a low enough temperature to avoid the production of more toxic substances that can occur when coal reaches high temperatures. As a result, these furnaces are suitable for heating the less-refined versions of coal with lower temperatures, which has less of an environmental impact.

Particulate Control

• Particulates are the leftover materials when the coal has been burned and exhaust is escaping the furnace, such as fly ash. The problem with a fluidized bed is that coal must already be ground into small particles. This creates a very fine layer of coal dust that is difficult to remove from the system using conventional methods. Controls for fluidized beds use electrostatic precipitators and other systems designed for filtering small particles.

Adding Particles

• Coal burners are infamous for producing a large amount of sulfur. To meet required standards, fluidized beds are mixed with limestone particles. The limestone and the coal are both suspended on the bed. Limestone acts as a counter or sponge for the sulfur, which is negated as the coal produces it inside the bed. The result is a layer of calcium sulfate that can then be collected and used as a byproduct.