Limestone Injection is one of many technologies in the Clean Coal Technologies program, it is one of the environmental control techologies which would also include wet multicyclones, and electrostatic precipitators. The limestone injection process, is one of the combustion type processes, it uses a Limestone Injection Multistage Burner (LIMB) to remove sulfur from coal during the combustion cycle.

In the limestone injection process, the crushed coal and limestone are suspeneded in a boiler by an upward stream of hot air; the coal is burned in this bubbling fluidized mixture. The sulfur from combustion gases combine with the limestone to form a solid compound, rather than being released into the atmosphere. The sulfur reduction can be achined with either dry limestone or hydrated lime, however hydrated lime is much more expensive. Limestone injection techonology is currently being developed aimed at mercury control and capture, during the coal burning process; benefits will include low capital cost, low feed rates, and low operating cost.