Patent ID: 6883443

Claim:
A method of reducing slagging and fouling in a furnace of a coal-fired steam boiler, the method comprising: a. diverting cooled flue gas from an output of a flue gas filter, wherein the flue gas filter is configured to clean the cooled flue gas by removing fly ash particulates and receive flue gas from an air preheater, the air preheater receiving the flue gas from the furnace; b. recirculating the cooled flue gas to one or more ports in an upper section of a firebox in the furnace; c. injecting the cooled flue gas into at least one of the one or more of the ports into the upper section of the firebox; and d. mixing the cooled flue gas with hot flue gas from the furnace, the hot flue gas having a higher temperature than the cooled flue gas, wherein the mixing reduces the higher temperature of the hot flue gas from the furnace to below a threshold temperature.