Froth floatation is used to remove sulfide particles too small to be removed by means of centrifuging.

The process is based on the principle that sulfide particles tend to stick to water, while coal does not.

The first step in the process is to grind coal finely. Water and a floatation chemical are then added.

 

Beneficiation may be effective in removing up to half of all the pyritic sulfur found in coal.

None of the methods just described is effective, however, in removing organic sulfur intimately bound to coal particles.

One of the most popular methods of removing sulfur from coal during the combustion process is called fluidized bed combustion.

In this process, finely ground coal is mixed with limestone, suspended above a screen by jets of air blown upward through the screen, and then ignited. The abundance of air and very large surface area of coal result in highly efficient combustion.

At the same time, any sulfur dioxide formed during combustion is trapped by and reacts with the limestone: