Tempering air system for municipal solid waste fuel steam generator

Abstract

A steam generator includes a furnace configured and adapted to generate steam from heat transfer from furnace exit gases from the combustion of municipal solid waste fuel, where tempering air is used for at least two purposes. First, to prevent or minimize corrosion of heat transfer surfaces, specifically a plurality of platens and at least one superheater disposed within an upper portion of the furnace or backpass and second to push and exert a force on the hot flue gas to change the flow pattern and improve superheater metal temperatures.

1 . A steam generator comprising:
 a) a furnace configured and adapted to generate a stream of furnace exit gases from combustion of municipal solid waste;   b) at least one tempering air system disposed downstream of a combustion zone of the furnace, the tempering air system being configured and adapted to provide cooled furnace exit gases that contact a superheater; and   c) waterwall furnace platen disposed within the furnace upstream from the tempering air system and the superheater, the waterwall furnace platen being configured and adapted to lower furnace exit gas temperature by facilitating heat transfer between fluids within the waterwall furnace platen and furnace exit gases outside the waterwall furnace platen.   
     
     
         2 . A steam generator as recited in  claim 1 , wherein the tempering air system is disposed between the superheater and the waterwall furnace platen. 
     
     
         3 . A steam generator as recited in  claim 1 , wherein the tempering air system comprises a header having attached a plurality of nozzles that are configured to supply streams of air between the waterfall platens and the superheater. 
     
     
         4 . A steam generator as recited in  claim 3 , wherein a fluid communication with the header to supply ambient air to the nozzles. 
     
     
         5 . A steam generator as recited in  claim 1 , further comprising mechanical means operably connected to the waterwall furnace platens to vibrate the platen during operation and reduce residue build-up on exterior surfaces of the platen. 
     
     
         6 . A steam generator as recited in  claim 1 , wherein the at least one waterwall furnace platen header piping includes an expansion loop configured and adapted to accommodate for thermal expansion by flexing. 
     
     
         7 . A steam generator as recited in  claim 1 , wherein at least one superheater and waterwall furnace platen are in fluid communication with each other as part of a thermal hydraulic circuit. 
     
     
         8 . A method of retrofitting a municipal solid waste fuel steam generator to reduce corrosion of a superheater, the method comprising:
 a) providing an tempering air system configured and adapted to lower furnace exit gas temperature at a superheater in a municipal solid waste fuel steam generator by facilitating heat transfer between fluids within a waterwall furnace platen and furnace exit gases outside the superheater;   b) opening an access through an upper furnace roof of the steam generator and at least one furnace wall; and   c) operably connecting the tempering air system to a source of air.   
     
     
         9 . A method of retrofitting a municipal solid waste fuel steam generator as recited in claim  27 , further comprising:
 a) measuring temperatures within an existing municipal solid waste fuel steam generator; and   b) wherein the step of providing and configuring an tempering air system to reduce the measured temperatures, redistribute flue gas and to reduce corrosion of the superheater based on the temperatures measured in the existing municipal solid waste fuel steam generator.   
     
     
         10 . The method of  claim 9  further includes reconfiguring a nose arch within the steam generator by extending a length of the nose arch to further reduce the measured temperatures.