What is "recovery boiler"

n. 1 A boiler for recover the sodium hydroxide and sodium sulfide used in a chemical wood pulp process. 2 Short for heat recovery boiler, a boiler used to recover heat from a hot process stream, such as flue gas from a gas turbine.

Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor, which contains lignin from previously processed wood. The black liquor is burned, generating heat, which is usually used in the process or in making electricity, much as in a conventional steam power plant. The invention of the recovery boiler by G.H. Tomlinson in the early 1930s was a milestone in the advancement of the kraft process.

Recovery boilers are also used in the (less common) sulfite process of wood pulping; this article deals only with recovery boiler use in the Kraft process.