Method of Co-Firing Coal or Oil with a Gaseous Fuel in a Furnace

Abstract

Methods for co-firing a fuel containing coal or oil that is injected into a burner in a furnace by injecting a gaseous fuel are disclosed. The gaseous fuel is injected in a manner so as not to consume air that would otherwise combine with the coal or oil in the primary flame. This can be accomplished by injecting the gaseous fuel at a higher or lower velocity than the coal or oil and combustion air are being injected. This can also be accomplished by directing the gaseous fuel being injected away from the primary flame created when the coal or oil burns.

We claim: 
     
         1 . A method for co-firing a fuel containing coal or oil that is injected into a burner in a furnace, the burner being provided with combustion air and the fuel wherein the combustion air burns in a primary flame within a primary combustion zone in the furnace, comprising injecting a gaseous fuel into the burner in a manner so that the gaseous fuel does not consume air that would otherwise combine with the fuel in the primary flame. 
     
     
         2 . The method of  claim 1  wherein the combustion air is injected into the burner at a selected velocity and the gaseous fuel is injected at a gaseous fuel injection velocity that is higher than the selected velocity. 
     
     
         3 . The method of  claim 2  wherein the gaseous fuel is injected at a velocity that is between ¼ and 20 times greater than the selected velocity. 
     
     
         4 . The method of  claim 1  wherein the combustion air is injected into the burner at a selected velocity and the gaseous fuel is injected at a gaseous fuel injection velocity that is lower than the selected velocity. 
     
     
         5 . The method of  claim 4  wherein the selected velocity is from 1.5 to 30 times the gaseous fuel injection velocity. 
     
     
         6 . The method of  claim 1  wherein the gaseous fuel is injected axially along a centerline of the coal or oil being injected. 
     
     
         7 . The method of  claim 1  wherein the gaseous fuel is injected circumferentially with the fuel. 
     
     
         8 . The method of  claim 1  wherein the gaseous fuel is injected without adequate stoichiometric air in a direction away from the primary flame and at a velocity which is 1.25 to 20 times a velocity at which the combustion air is being injected into the furnace. 
     
     
         9 . The method of  claim 1  wherein the burner has an igniter and the gaseous fuel is injected coaxially around the igniter. 
     
     
         10 . The method of  claim 1  wherein the gaseous fuel is injected above the primary combustion zone of the furnace. 
     
     
         11 . The method of  claim 1  wherein the gaseous fuel is injected in a manner so that over half of the gaseous fuel burns outside of the primary combustion zone. 
     
     
         12 . The method of  claim 1  wherein the gaseous fuel is methane. 
     
     
         13 . The method of  claim 1  also comprising measuring at least one of loss on ignition, levels of CO, O 2 , H 2 O, and NO and temperatures in the furnace while the gaseous fuel is being injected and adjusting a flow rate of the gaseous fuel based upon such measuring. 
     
     
         14 . The method of  claim 13  wherein the adjusting is based upon a multivariate analysis. 
     
     
         15 . The method of  claim 1  also comprising measuring at least one of coal flow into at least one burner, steam production, furnace temperature in at least one location in the furnace, O 2  levels in at least one location in the furnace, CO levels in at least one location in the furnace, and NOx levels in at least one location in the furnace before injecting the gaseous fuel. 
     
     
         16 . The method of  claim 1  also comprising measuring emissions of at least one of NO, SO 3 , CO, CO 2  and HCl from the furnace. 
     
     
         17 . The method of  claim 1  wherein the gaseous fuel is injected through converging sub-sonic nozzle. 
     
     
         18 . The method of  claim 1  wherein the gaseous fuel is injected through a divergent nozzle that produces a supersonic non-mixing core stream that later expands.