Combustion air system for recovery boilers that burn waste liquors from processes for obtaining pulp.

Home for a recovery boiler with an arrangement for supplying secondary air in the form of air jets to said furnace, said hearth a front wall, a rear wall and side walls, spraying devices black liquor disposed on said walls a level and a plurality of air inlets located on several horizontal levels on said walls for introducing air into the furnace from an air supply, said arrangement comprising: - two horizontal air levels at different elevations are arranged above the level or levels lowest air and below the level or levels of black liquor spraying, - air is supplied from two opposite walls on said two levels and the air inlets are located so that the air jets are introduced into a pattern interlace It has an even number of jets on one opposite wall and an uneven number of jets on the other wall opuest to, and - the air jets of said two air levels are located substantially one above the other in substantially vertical rows, characterized in that each vertical row is formed by two air jets.