Method for heating a blast furnace stove

Abstract

A method for heating a blast furnace stove having a combustion chamber with a combustion zone therein, includes causing combustion gases to flow through and be exhausted from refractory material in the stove for heating said material, supplying and adding an oxidant comprising an oxygen content of at least 85% into the combustion chamber for recirculating the combustion gases including said oxidant into the combustion zone, wherein the recirculating the combustion gases is from a location inside the combustion chamber, but outside an area of the combustion chamber occupied by the combustion zone, and the supplying the oxidant to the combustion zone is at high velocity through at least one lance, thereby entraining the combustion gases into the combustion zone, diluting a mixture of the fuel and the oxidant with the recirculated combustion gases, and flamelessly combusting said mixture in the combination zone.

What is claimed is: 
     
         1 . A method for heating a blast furnace stove including a combustion chamber having a combustion zone therein, comprising:
 combusting a fuel with a lower heating value (LHV) of not more than 9 MJ/Nm 3  in the combustion zone of the blast furnace stove,   causing combustion gases to flow through and be exhausted from refractory material in the blast furnace stove for heating said refractory material,   supplying and adding an oxidant comprising an oxygen content of at least 85% into the combustion chamber for recirculating the combustion gases including said oxidant into the combustion zone, wherein the recirculating the combustion gases is from a location inside the combustion chamber, but outside an area of the combustion chamber occupied by the combustion zone, and the supplying the oxidant to the combustion zone is at high velocity through at least one lance, thereby entraining the combustion gases into the combustion zone,   diluting a mixture of the fuel and the oxidant with the recirculated combustion gases, and   flamelessly combusting said mixture in the combustion zone.   
     
     
         2 . The method according to  claim 1 , wherein the supplying the oxidant through the at least one lance is at a velocity of at least 200 m/s. 
     
     
         3 . The method according to  claim 1 , wherein the supplying the oxidant through the at least one lance is at least at sonic velocity. 
     
     
         4 . The method according to  claim 3 , further comprising arranging an orifice of the at least one lance adjacent to a supply inlet for the fuel for entraining said fuel into the combustion zone by ejector action. 
     
     
         5 . The method according to  claim 4 , further comprising providing additional oxidant to the combustion chamber downstream of the supply inlet for the fuel for achieving staged combustion in the combustion zone. 
     
     
         6 . The method according to  claim 1 , further comprising supplementing an existing air burner for the blast furnace stove with at least one high-velocity oxidant lance for injecting said oxidant. 
     
     
         7 . The method according to  claim 1 , further comprising recycling the combustion gases flowing through the refractory material back into the combustion zone. 
     
     
         8 . The method according to  claim 7 , further comprising premixing the recycled combustion gases with said oxidant before entering the combustion zone. 
     
     
         9 . The method according to  claim 7 , wherein a sufficient amount of the combustion gases are recycled when total oxygen percentage by volume of an inert portion of an atmosphere in the combustion chamber, excluding non-inert fuel components, does not exceed 12%. 
     
     
         10 . The method according to  claim 7 , further comprising replacing an existing air burner in the blast furnace stove with a fuel inlet and an inlet for the recycled combustion gases, and combusting the fuel with said oxidant. 
     
     
         11 . The method according to  claim 10 , wherein a sufficient amount of the combustion gases are recycled to maintain a gas mass flow per time unit through the refractory material at a level which is at least the same as a gas mass flow per time unit used when operating the existing air burner without recycling. 
     
     
         12 . The method according to  claim 10 , wherein a sufficient amount of the combustion gases are recycled to maintain a flame temperature at a level which is not more than, and a thermal energy transfer to the refractory material at a level which is not less than, the flame temperature and the thermal energy throughput per time unit, respectively, which was used when the existing air burner was operating without recycling. 
     
     
         13 . The method according to  claim 1 , wherein the fuel comprises blast furnace top gas. 
     
     
         14 . The method according to  claim 13 , further comprising obtaining the blast furnace top gas from a blast furnace supplied with hot air from the blast furnace stove.