Stoker firing has evolved for more than a century and a half. After serving as the backbones of the industry and small power for several decades, stokers have been sidelined for the past quarter century due to:

• Dwindling availability of good coals suitable for firing on stokers

• Tighter pollution requirements

• Increasing steam demands needing bigger unit sizes

• Emergence of fluidized bed combustion (FBC) boilers with superior features

Stokers would have become nearly obsolete if interest in biofuels, for which they are ideally suited, had not emerged. Several types of stokers have appeared and disap­peared over time, but four stokers continue in use for industrial and cogeneration (cogen) applications.