METHODS AND SYSTEMS FOR REDUCED NOx COMBUSTION OF COAL WITH INJECTION OF HEATED NITROGEN-CONTAINING GAS

Abstract

A stream of nitrogen-containing gas is heated and injected into a stream of coal and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, and conveying gas. Oxygen is injected into the stream of mixed nitrogen-containing gas, coal, and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, conveying gas, and oxygen. The mixed nitrogen-containing gas, coal, conveying gas, and oxygen are combusted in a combustion chamber.

1 . A system for burning coal with reduced NOx emissions, comprising: 
 a) a source of a mixture of coal and conveying gas;    b) a source of oxygen-containing gas;    c) a source of nitrogen-containing gas;    d) a heating device adapted and configured to heat nitrogen from said nitrogen-containing gas source;    e) a combustion chamber;    f) a burner disposed at a wall of said combustion chamber;    a burner operatively associated with a combustion chamber;    g) a fuel duct in fluid communication with said source of a mixture of coal and conveying gas, said fuel duct extending towards said burner; and    h) a nitrogen-containing gas injection element in fluid communication with said heating device and said fuel duct, said first injection element being adapted and configured to inject heated nitrogen-containing gas from said heating device into a stream of a mixture of coal and conveying gas and mix therewith inside said fuel duct.    
   
   
       2 . The system of  claim 1 , further comprising an oxygen-containing gas injection element in fluid communication with said source of oxygen-containing gas and said fuel duct, said oxygen-containing gas injection element fluidly communicating with said fuel duct downstream of where said nitrogen-containing gas injection element fluidly communicates with said fuel duct and upstream of or at said burner, said oxygen-containing gas injection element being adapted and configured to inject oxygen-containing gas from said oxygen-containing gas source into the stream of mixed heated nitrogen-containing gas, coal, and conveying gas.  
   
   
       3 . The system of  claim 1 , wherein said source of oxygen-containing gas and said source of nitrogen comprises an ASU.  
   
   
       4 . The system of  claim 1 , wherein said conveying gas comprises flue gas from said combustion chamber mixed with oxygen-containing gas from said oxygen source.  
   
   
       5 . The system of  claim 1 , wherein said heating device is adapted and configured to directly impart heat to nitrogen-containing gas from said nitrogen-containing gas source from a flame.  
   
   
       6 . The system of  claim 1 , wherein said heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from said nitrogen-containing gas source and heat from combustion of said coal and oxygen in said combustion chamber.  
   
   
       7 . The system of  claim 2 , wherein said conveying gas is flue gas from said combustion chamber mixed with oxygen-containing gas.  
   
   
       8 . The system of  claim 2 , wherein said heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from said nitrogen-containing gas source and heat from combustion of said coal and oxygen in said combustion chamber.  
   
   
       9 . The system of  claim 6 , wherein said heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from said nitrogen-containing gas source and heat from combustion of said coal and oxygen in said combustion chamber.  
   
   
       10 . The system of  claim 1 , wherein said conveying gas is air.  
   
   
       11 . The system of  claim 2 , wherein said oxygen-containing gas injection element fluidly communicates with said fuel duct at said burner.  
   
   
       12 . The system of  claim 1 , wherein said nitrogen-containing gas injection element fluidly communicates with said fuel duct at a peripheral portion of said fuel duct.  
   
   
       13 . The system of  claim 1 , wherein said nitrogen-containing gas injection element fluidly communicates with said fuel duct along a central axis of said fuel duct.  
   
   
       14 . The system of  claim 1 , wherein said oxygen element fluidly communicates with said fuel duct at a peripheral portion of said fuel duct.  
   
   
       15 . The system of  claim 1 , wherein said oxygen element fluidly communicates with said fuel duct along a central axis of said fuel duct.  
   
   
       16 . A method of combusting coal with reduced NOx emissions, comprising the steps of: 
 heating a stream of nitrogen-containing gas;    injecting the heated stream of nitrogen-containing gas into a stream of coal and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, and conveying gas; and    combusting the coal from the stream of mixed nitrogen-containing gas, coal, and conveying gas with oxygen-containing gas at a burner in the combustion chamber.    
   
   
       17 . The method of  16 , further comprising the step of injecting oxygen-containing gas into the stream of mixed nitrogen-containing gas, coal, and conveying gas upstream or at the burner.  
   
   
       18 . The method of  claim 16 , wherein the nitrogen-containing gas and oxygen are obtained from an ASU.  
   
   
       19 . The method of  claim 16 , wherein said step of heating a nitrogen-containing gas stream comprises directly imparting heat from a flame to the nitrogen stream.  
   
   
       20 . The method of  claim 16 , wherein said step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from a flame to the nitrogen-containing gas stream via a heat exchanger.  
   
   
       21 . The method of  claim 16 , wherein said step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from said step of combusting to the nitrogen-containing gas stream via a heat exchanger.  
   
   
       22 . The method of  claim 16 , wherein the stream of nitrogen-containing gas is heated to a temperature in the range of from about 1,000° F. to about 1,800° F.  
   
   
       23 . The method of  claim 16 , wherein injection of the heated stream of nitrogen-containing gas causes devolatilization of most of a volatile species content in the coal.  
   
   
       24 . The method  16 , wherein the conveying gas is air.  
   
   
       25 . The method of  claim 16 , further comprising the steps of: 
 collecting at least some of any flue gas produced from said step of combusting;    injection oxygen-containing gas into the collected flue gas to mix therewith; and    introducing the oxygen-containing gas oxygen and flue gas to the burner.    
   
   
       26 . The method of  claim 25  wherein oxygen-containing gas is injected into the collected flue gas in an amount such that an oxygen concentration in the mixed oxygen-containing gas and flue gas is from about 3% to about 20%.  
   
   
       27 . The method of  claim 17 , wherein said step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from said step of combusting to the nitrogen-containing gas stream via a heat exchanger.  
   
   
       28 . The method of  claim 17 , wherein the stream of nitrogen-containing gas is heated to a temperature in the range of from about 1,000° F. to about 1,800° F.  
   
   
       29 . The method  claim 17 , wherein the conveying gas is air.  
   
   
       30 . The method of  claim 17 , further comprising the steps of: 
 collecting at least some of any flue gas produced from said step of combusting;    injection oxygen-containing gas into the collected flue gas to mix therewith; and    introducing the mixed oxygen and flue gas to the burner.    
   
   
       31 . The method of  claim 27 , wherein the stream of nitrogen-containing gas is heated to a temperature in the range of from about 1,000° F. to about 1,800° F.  
   
   
       32 . The method of  claim 31 , further comprising the steps of: 
 collecting at least some of any flue gas produced from said step of combusting;    injection oxygen-containing gas into the collected flue gas to mix therewith; and    introducing the mixed oxygen-containing gas and flue gas to the burner.