US 5,344,629 A · Reducing Z.sub.20 emissions

Abstract

The amount of N.sub.2 O in flue gases discharged from a fluidized bed combustion system is minimized by effecting vigorous and intimate mixing of the flue gases (with entrained particles) from a fluidized bed by increasing the velocity of the flue gases and then decreasing the velocity from the increased level, introducing a N.sub.2 O decomposing catalyst into the flue gases and particles immediately after increasing and decreasing of the velocity, and mixing the N.sub.2 O catalyst with the flue gases and particles, to effect decomposition of the N.sub.2 O. The catalyst is a calcium based sorbent, such as CaO or limestone, although and other catalysts also may be utilized. Normally the decomposition takes place without increasing the temperature of the flue gases. The increase in velocity is achieved by providing a constriction in the combustor vessel. The interior of the combustor vessel is lined with erosion resistant and thermal insulating material. Where the catalyst is calcium based sorbent, it is calcined, and the calcined particles are removed from the flue gases and recirculated to the fluidized bed, providing at least about 10 to 30% of the calcium based sulfur absorbing sorbent necessary to remove sulfur from the flue gases.

Claims21

Dependent claims

A method for reducing the emissions of N.sub.2 O in flue gases from the combustion of nitrogen containing fuel in a fluidized bed combustor, which has a combustion stage with a fluidized bed of particles, comprising the steps of continuously:

(a) supplying nitrogen containing fuel and an oxygen containing gas for combustion of the fuel into the fluidized bed of the combustor to produce flue gases which contain particles;
(b) maintaining a temperature of about 700.degree.-1000.degree. C. in the combustion stage;
(c) supplying a Ca-based sulfur absorbing sorbent to the fluidized bed for reducing sulfur emissions in the flue gases;
(d) without separate removal of the particles from the flue gases effecting vigorous and intimate mixing of the particles and flue gases by increasing the velocity of the flue gases before leaving the combustion stage, and then decreasing the velocity from the increased level;
(e) introducing an N.sub.2 O decomposing catalyst into the flue gases and particles immediately after increasing and decreasing of the velocity thereof;
(f) mixing the N.sub.2 O decomposing catalyst with the flue gases and particles to effect decomposition of the N.sub.2 O;
and
(g) discharging the flue gases with particles and decomposed N.sub.2 O therein from the combustor.

5 more elements

Dependencies are inferred from the claim text.

Reducing Z.sub.20 emissions

Life of this patent

Reducing Z.sub.20 emissions

Life of this patent

Abstract

Claims21