NOX reduction in multisolid fluidized bed combustors

Claim 1

A method of lowering nitrogen oxides to a desired level and minimizing sulfur dioxide in the reaction gases from the combustion of fuel in a multisolid fluidized bed having a lower dense fluidized bed of relatively large particles, an upper dispersed entrained bed of relatively fine particles recirculating through the dense fluidized bed and an entrained sulfur sorbent material therein, which comprises (A) operating a lower region of the multisolid fluidized bed under substoichiometric conditions such that NO x is reduced to the desired level, (B) operating an upper region of the multisolid fluidized bed above the substoichiometric lower region under oxidizing conditions to complete the combustion of the fuel, (C) maintaining a size difference between the relatively large particles and the relatively small particles such that substantially all of the former are at least about four times the size of substantially all of the latter, and (D) recycling a portion of the relatively fine particles through the lower region of the dense bed operating under substoichiometric conditions and a portion of the relatively fine particles from the entrained bed through substantially only the upper region which is operating under oxidizing conditions whereby to depress the temperature of such oxidizing region to a level conductive to sulfur capture by the sulfur sorbent material and to operate the lower region at as low a temperature as will support combustion.

Claim 2

A method of lowering nitrogen oxides to a desired level and minimizing sulfur dioxide in the reaction gases from the combustion of fuel in a multisolid fluidized bed having a lower dense fluidized bed of relatively large particles, an upper dispersed entrained bed of relatively fine particles recirculating through the dense fluidized bed and an entrained sulfur sorbent material therein, which comprises (A) operating a lower region of the multisolid fluidized bed under substoichiometric conditions such that NO x is reduced to the desired level, (B) operating an upper region of the multisolid fluidized bed above the substoichiometric lower region under oxidizing conditions to complete the combustion of the fuel, (C) maintaining a size difference between the relatively large particles and the relatively small particles such that substantially all of the former are at least about four times the size of substantially all of the latter, and (D) recycling a portion of the relatively fine particles through the lower region of the dense bed operating under substoichiometric conditions and a portion of the relatively fine particles from the entrained bed through substantially only the upper region which is operating under oxidizing conditions whereby to depress the temperature of such oxidizing region to a level conductive to sulfur capture by the sulfur sorbent material and to operate the lower region at as low a temperature as will support combustion.