Abstract: This invention improves gas mixing and combustion, gaseous fluid flow and control of the char bed in recovery boilers burning black liquor or soda liquor, requires fewer primary air ports than conventional methods and can reduce capital and operating costs. Some primary air is introduced as powerful principal jets, from two opposing so-called active furnace walls. All or most of the remainder of the primary air is introduced as smaller jets, called scavenging jets, which prevent char from accumulating in the furnace corners and, in some cases, between the principal jets and are in the same plane as the principal jets. The momentum flux of each of the principal jets is approximately double or more than double that of each scavenging jet. Some of the primary air may be introduced as central jets, from the remaining two furnace walls and located in the same plane as the other ports, or on a second, somewhat higher plane. The momentum flux of the central jets is less than that of the principal jets.

Abstract: This invention improves fluid flow, gas mixing and combustion in the furnaces of recovery boilers which burn liquor from various pulping processes, namely, the kraft process, the soda process, the sodium-based sulphite process, the closed-cycle CTMP (chemical, thermal, mechanical pulp) process, the magnesium-based sulphite process and the ammonium-based sulphite process, which are employed in the manufacture of pulp and paper, and in the furnaces of boilers burning biomass, wood waste or other solid fuel. The invention improves the operation of new or retrofitted boilers in several ways and can reduce both the capital and operating costs. One embodiment comprises introducing a portion of the combustion air, and/or recycled flue gas, at any elevation in the furnace, from two opposing walls only, as jets arranged in a partially-interlaced manner, with the jets oriented in a more or less common plane which is inclined.