Heating device and method for its operations

Abstract

This invention relates to a heating device consisting of at least one burner for the combustion especially of a gaseous fuel, at least one radiant tube connecting to the burner, at least one fan generating a negative pressure or an excess pressure in the radiant tube, and at least one exhaust gas recirculation system with at least one exhaust gas recirculation passage through which an exhaust gas produced during the combustion of the primary fuel can be recirculated from the radiant tube to a transition zone from the burner into the radiant tube. In order to further develop a heating device of this type as well as a method for its operation the burner is adapted for being operated in at least two power stages and the exhaust gas recirculation system is controlled in dependence of the power stages of the burner in such a way that the volume flow of the recirculated exhaust gas is reduced with an increasing power stage of the burner.

What is claimed is: 
     
         1 . A heating device comprising at least two radiant tubes opposed to each other and each including a burner capable for combustion of a gaseous fuel, at least one fan generating a negative pressure or an excess pressure in the radiant tubes, each radiant tube having at least one exhaust gas recirculation system through which an exhaust gas that is produced during the combustion of the primary fuel can be recirculated from the radiant tube to a transition zone from the burner into the radiant tube, characterized in that the burners can be operated in at least two power stages and that the exhaust gas recirculation systems can be controlled in dependence of the power stages of the burners in such a way that the volume flow of the recirculated exhaust gas is reduced with an increasing power stage of the burner. 
     
     
         2 . The heating device of  claim 1 , wherein the radiant tubes are mutually parallel aligned. 
     
     
         3 . The heating device of  claim 1 , wherein the burners are arranged on the opposite ends of the opposed radiant tubes. 
     
     
         4 . The heating device of  claim 1 , wherein the exhaust gas recirculation systems can be controlled in dependence of the output of the burner of the radiant tube. 
     
     
         5 . The heating device of  claim 1 , wherein the exhaust gas recirculation systems of the radiant tubes can be controlled independently of each other. 
     
     
         6 . A method for operating a heating device in which a gaseous fuel is burned in at least one burner and in at least one radiant tube connecting to the burner a flame is produced which heats up the radiant tube, wherein a negative pressure or an excess pressure is generated in the at least one radiant tube through a fan, and wherein exhaust gas produced during the combustion of the fuel is recirculated from the radiant tube to a transition zone from the burner into the radiant tube through at least one exhaust gas recirculation system including at least one exhaust gas recirculation passage, characterized in that the burner is operated in at least two power stages and that the exhaust gas recirculation system is controlled in dependence of the power stages of the burner in such a way that the volume flow of the recirculated exhaust gas is reduced with an increasing power stage of the burner. 
     
     
         7 . The method of  claim 6 , wherein the burner is operated in a modulating fashion in power stages. 
     
     
         8 . The method of  claim 6 , wherein through the exhaust gas recirculation system a volume flow regulator for the volume flow of the recirculated exhaust gas is controlled. 
     
     
         9 . The method of  claim 8 , wherein through the volume flow regulator the output and the speed of the fan is controlled. 
     
     
         10 . The method of  claim 8 , wherein through the volume flow regulator a flap and/or sliding valve is controlled which is arranged in the exhaust gas recirculation passage and which is closed at a determined output of the burner. 
     
     
         11 . The method of  claim 6 , wherein the burner is operated in two power stages and that the exhaust gas recirculation system is activated in one power stage. 
     
     
         12 . The method of  claim 6 , wherein exhaust gases from a first radiant tube including a first burner are introduced through an exhaust gas recirculation system in an opposed second radiant tube which includes a second burner, whereas exhaust gases from the opposed second radiant tube are introduced in the first radiant tube through an exhaust gas recirculation system. 
     
     
         13 . The method of  claim 12 , wherein the exhaust gas recirculation systems are controlled in dependence of the output of the burners of the opposed radiant tubes. 
     
     
         14 . The method of  claim 12 , wherein the exhaust gas recirculation systems of the opposed radiant tubes are controlled independently of each other. 
     
     
         15 . The method of  claim 6 , wherein the exhaust gas recirculation systems are controlled through a measuring element by temperature, exhaust gas values, volume flow and the like are measured. 
     
     
         16 . The method of  claim 8 , wherein the volume flow regulator is electrically and/or thermally controlled. 
     
     
         17 . The method of  claim 8 , wherein the volume flow regulator is controlled simultaneously with an output regulator of the burner. 
     
     
         18 . The method of  claim 6 , wherein the power stages of the burner are controlled through a magnetic valve which has a number of switching steps corresponding to the number of power stages. 
     
     
         19 . The method of  claim 6 , wherein the switching steps of the magnetic valve are controlled through a temperature regulator. 
     
     
         20 . The method of  claim 6 , wherein the exhaust gas is conveyed by pressure differences between the end-side end of the radiant tube and the transition zone between the burner and the radiant tube. 
     
     
         21 . The method of  claim 6 , wherein in a first, higher power stage of the burner 0 to 30% by volume of the exhaust gas are recirculated into the transition zone between the burner and the radiant tube. 
     
     
         22 . The method of  claim 6 , wherein in a second, lower power stage of the burner from 20 to 60% by volume of the exhaust gas are recirculated into the transition zone between the burner and the radiant tube.