Method of producing energy at a pulp mill

Abstract

A method to produce energy at a pulp mill, including the steps of: combusting pulping process waste liquor in the furnace of a recovery boiler to generate flue gases, recovering the heat from the flue gases by producing saturated and/or partially superheated steam in the recovery boiler, gasifying wood, bark or wood wastes in a gasifier for producing a combustible gas, burning at least part of the combustible gas in a superheating boiler, and superheating the saturated and partially superheated steam in the superheating boiler to produce superheated steam.

What is claimed is:  
     
         1 . A method of producing energy at a pulp mill having a gasifer, a recovery boiler, and a superheating boiler, said method comprising: 
 a) combusting waste liquor from a pulping process in a furnace of the recovery boiler to generate flue gases;    b) recovering heat from the flue gases to produce saturated steam in the recovery boiler;    c) gasifying a solid wood-based material in a gasifier to produce a combustible gas,    d) burning at least part of the combustible gas in the superheating boiler, and    e) superheating the saturated steam in the superheating boiler to produce superheated steam.    
     
     
         2 . A method as recited in  claim 1 , wherein the steam is superheated to a temperature in a range of 450 to 600 degrees Celsius.  
     
     
         3 . A method as recited in  claim 1 , wherein the steam is superheated to a temperature in a range of 500 to 560 degrees Celsius.  
     
     
         4 . A method as recited in  claim 1 , wherein the steam is superheated to a temperature in a range of 530 to 560 degrees Celsius.  
     
     
         5 . A method as recited in  claim 1 , further comprising cleaning the combustible gas from step (c) before step (d).  
     
     
         6 . A method as recited in  claim 1 , wherein a sulfur-containing fuel is burned with the combustible gas in step d).  
     
     
         7 . A method as recited in  claim 6 , wherein the sulfur-containing fuel is a non-condensable gas generated by the pulp mill.  
     
     
         8 . A method as recited in  claim 1 , wherein the burning of the combustible gas is effected under overstoichiometric conditions.  
     
     
         9 . A method as recited in  claim 1 , wherein flue gases are generated in step d) and the flue gases flow into a furnace of the recovery boiler.  
     
     
         10 . A method as recited in  claim 9 , wherein the flue gases flow into the furnace of the recovery boiler to increase gas mixing in the furnace.  
     
     
         11 . A method as recited in  claim 1 , wherein burning of the combustible gas is under substoichiometric conditions, and flue gases are generated and flow into a furnace of the recovery boiler.  
     
     
         12 . A method as recited in  claim 9 , wherein the flue gases generated in step d) are mixed with flue gases generated in step a).  
     
     
         13 . A method as recited in  claim 1 , wherein a portion of the combustible gas is burned in a lime reburning process.  
     
     
         14 . A method as recited in  claim 1 , wherein the solid wood-based material is dried before gasification.  
     
     
         15 . A method as recited in  claim 1 , wherein the saturated steam produced in the recovery boiler is further partially superheated in the recovery boiler.  
     
     
         16 . A method as recited in  claim 1 , wherein the solid wood-based material is bark.