Method for heating a blast furnace stove

Abstract

A method for heating a blast furnace stove by combusting in a stable, visible flame a fuel with a lower heating value (LHV) of 9 MJ/Nm 3 or less in a combustion region, arranged in a combustion chamber in the stove, and causing the combustion gases to flow through and thereby heat refractory material in the stove, wherein the fuel is combusted with an oxidant comprising at least 85% oxygen, and combustion gases are caused to be recirculated into the combustion zone and thereby dilute the mixture of fuel and oxidant therein sufficiently for the flame not to damage the refactory material.

1 . A method for heating a blast furnace stove, comprising combusting a fuel with a lower heating value (LHV) of 9 MJ/Nm 3  or less in a combustion region in which there is maintained a stable, visible flame, arranged in a combustion chamber in the stove, and causing the combustion gases to flow through and thereby heat refractory material in the stove, wherein the fuel is combusted with an oxidant comprising at least 85% oxygen, and wherein combustion gases are caused to be recirculated into the combustion region thereby diluting the mixture of fuel and oxidant therein sufficiently for the flame not to damage the refactory material. 
     
     
         2 . The method of  claim 1 , wherein combustion gases are recirculated from a location inside the combustion chamber, but outside of the part of the combustion chamber occupied by the combustion region, and the oxidant is supplied to the combustion zone at high velocity through a lance, thereby entraining combustion gases into the combustion zone to achieve dilution of the flame. 
     
     
         3 . The method of  claim 2 , wherein the oxidant is lanced at a velocity of at least 200 m/s. 
     
     
         4 . The method of  claim 2 , wherein the oxidant is lanced at least at sonic velocity. 
     
     
         5 . The method of  claim 2 , wherein the lance has an orifice adjacent to a supply inlet for fuel, thereby entraining such fuel into the combustion region by ejector action. 
     
     
         6 . The method of  claim 1 , wherein the combustion is staged. 
     
     
         7 . The method of  claim 1 , wherein as a preliminary step an existing stove is refitted to perform the method, the refitting includes providing an existing burner in one or several high-velocity oxidant lances injecting said oxidant to supplement an existing burner, the existing burner being placed in communication with the recirculated combustion gases. 
     
     
         8 . The method of  claim 1 , wherein combustion gases that have flowed through the refractory material are caused to be recycled back into the combustion region. 
     
     
         9 . The method of  claim 8 , wherein the recycled combustion gases are premixed with said oxidant before entering the combustion region. 
     
     
         10 . The method of  claim 8 , wherein enough combustion gases are recycled so that the total oxygen percentage by volume of the inert part of the atmosphere in the combustion chamber, excluding counting the non-inert fuel components, does not exceed 12%. 
     
     
         11 . The method of  claim 1 , wherein an existing stove is as a preliminary step adjusted to perform said method by replacing an existing air burner with a fuel inlet and an inlet for recycled combustion gases, and the fuel is then combusted with said oxidant. 
     
     
         12 . The method of  claim 11 , wherein enough combustion gases are recycled to maintain the gas mass flow per time unit through the refractory material at a level which is at least the same as the gas mass flow per time unit which was used when the existing air burner was operated without recycling. 
     
     
         13 . The method of  claim 11 , wherein enough combustion gases are recycled to maintain the flame temperature at a level which is the same or lower, and a thermal energy transfer to the refractory material at a level which is the same or higher, as the flame temperature and the thermal energy throughput per time unit, respectively, which was used when the existing air burner was operated without recycling. 
     
     
         14 . The method of  claim 1 , wherein the fuel comprises blast furnace top gas. 
     
     
         15 . The method of  claim 14 , wherein the blast furnace top gas is from a blast furnace which is supplied with hot air by the stove. 
     
     
         16 . The method of  claim 1 , wherein the fuel comprises calorifically enriched blast furnace top gas. 
     
     
         17 . The method of  claim 1 , wherein the flame temperature is maintained below 1400° C. 
     
     
         18 . The method of  claim 17 , wherein the flame temperature is maintained below 1350° C.