recovery process and system for a pulp mill

Abstract

A method for burning chlorine-containing liquors in a chemical recovery boiler at a pulp mill, wherein the recovery boiler includes spent liquor sprayers for feeding spent liquor and a number of combustion air levels including: increasing a combustion temperature in the recovery boiler in a burning zone where a chlorine-containing liquor or a chlorine-containing effluent is burned; while burning the liquor or effluent, volatilizing the chlorine in the liquor or effluent to produce chloride-containing salts in flue gases in the boiler, and removing the chloride-containing salts from the flue gases.

1 . A method for burning chlorine-containing liquors in a chemical recovery boiler at a pulp mill comprising:
 increasing a combustion temperature in a burning zone of the recovery boiler, where a chlorine-containing liquor or a chlorine-containing effluent is burned;   while burning the liquor or effluent, volatilizing the chlorine in the liquor or effluent to produce chloride-containing salts in flue gases in the boiler, and   removing the chloride-containing salts from the flue gases.   
   
   
       2 . The method of  claim 1  wherein over 30 percent, as calculated from as fired liquor chlorine concentration, is volatilized into the flue gases. 
   
   
       3 . The method of  claim 1  wherein over 40 percent of chlorine from as fired stream chlorine concentration is volatilized into the flue gases. 
   
   
       4 . The method of  claim 1  wherein the pulp mill includes a bleach plant using chlorine dioxide, and the bleach plant has at least one chlorine dioxide stage, and chlorine-containing effluent flow from the bleach plant is concentrated and burned in the recovery boiler. 
   
   
       5 . The method of  claim 1  wherein the chlorine-containing liquor is a spent liquor. 
   
   
       6 . The method of  claim 5  further comprising mixing a bleaching effluent with the spent liquor before supplying the chlorine-containing liquor to the recovery boiler furnace. 
   
   
       7 . The method of  claim 5  further comprising superheating steam from a superheater of the recovery boiler in a separate combustion chamber of the boiler. 
   
   
       8 . The method of  claim 5  wherein the recovery boiler is provided with at least two separate combustion chambers, said method further comprises burning a chlorine-containing stream in one of the two separate combustion chamber, and superheating steam from a superheater of the recovery boiler in another of the two separate combustion chambers. 
   
   
       9 . The method of  claim 1  wherein the recovery boiler is provided with an integrated combustion chamber, and the chlorine-containing liquor is burned in the integrated combustion chamber. 
   
   
       10 . The method of  claim 1  further comprising increasing an oxygen concentration in the burning zone to increase the combustion temperature. 
   
   
       11 . The method of  claim 10  wherein the oxygen concentration is increased by adding oxygen-enriched air to a location adjacent to where the liquor or effluent is fed to the boiler. 
   
   
       12 . The method of  claim 10  wherein the oxygen concentration is increased by raising an oxygen content of combustion air supplied to the burning zone. 
   
   
       13 . The method of  claim 10  wherein the oxygen concentration is increased by supplying oxygen directly to the burning zone. 
   
   
       14 . The method of  claim 10  wherein oxygen-enriched air is added to a combustion chamber of the boiler. 
   
   
       15 . The method of  claim 10  wherein the oxygen-enriched air is added through at least one secondary air level of the recovery boiler furnace. 
   
   
       16 . The method of  claim 1  wherein a high dry-solids content of the liquor or effluent contributes to the increase the combustion temperature. 
   
   
       17 . The method of  claim 1  wherein the combustion temperature is increased by setting a combustion firing intensity in the burning zone. 
   
   
       18 . The method of  claim 1  wherein the combustion temperature is increased by adjusting a distribution of combustion air in the recovery boiler.