Combustion air system for recovery boilers, burning spent liquors from pulping processes

A furnace in a recovery boiler comprising:

• walls around a combustion area of the furnace, wherein said walls include a first and second wall opposite each other;
• at least one black liquor sprayer disposed on one or more of walls at a black liquor spray elevation level on said walls wherein said black liquor spray elevation level is devoid of air ports;
• and
• a plurality of secondary air ports arranged in two elevational rows on said first and second opposite walls, said secondary air ports provide jets of substantially all secondary air into the furnace, wherein
• said rows of secondary air ports are above on said walls a level or levels of primary air ports and below the black liquor spray elevation level,
• said secondary air ports in each row is vertically aligned with the secondary air ports in the other of said rows;
• in each row, an even number of jets of secondary air projects from the ports in the first wall and an odd number of jets project from the second wall to form an interlaced pattern of air jets, and
• the secondary air ports each have an area A and a width W, and a ratio of A to W2 is at least four.

An arrangement for supplying secondary air to a furnace for a recovery boiler furnace wherein:

• said furnace comprises a front wall, a rear wall and side walls, a black liquor spray device disposed on at least one of said walls at a black liquor injection horizontal level and a plurality of air ports located on a plurality of horizontal levels on at least one of said walls for introducing air into the furnace from an air supply, and
• said arrangement for supplying secondary air comprising first and second horizontal secondary air levels at different elevations arranged above a primary air level and below the black horizontal level, wherein substantially all secondary air flows through air ports at the first and second horizontal secondary air levels;
• secondary air jets are supplied from secondary air ports on two opposite walls on said two horizontal secondary air and the secondary air ports are located on said opposite walls such that the secondary air jets form an interlaced pattern in the furnace, and wherein there are an even number of secondary jets on one opposite wall and an uneven number of said jets on the other opposite wall at each of said first and second horizontal secondary air levels, and
• the air jets of said first and second horizontal secondary air levels are located substantially one above each other in substantially vertical columns, wherein each of said columns has a pair of secondary air ports.