Micro-mixer/combustor

Abstract

A micro-mixer/combustor to mix fuel and oxidant streams into combustible mixtures where flames resulting from combustion of the mixture can be sustained inside its combustion chamber is provided. The present design is particularly suitable for diffusion flames. In various aspects the present design mixes the fuel and oxidant streams prior to entering a combustion chamber. The combustion chamber is designed to prevent excess pressure to build up within the combustion chamber, which build up can cause instabilities in the flame. A restriction in the inlet to the combustion chamber from the mixing chamber forces the incoming streams to converge while introducing minor pressure drop. In one or more aspects, heat from combustion products exhausted from the combustion chamber may be used to provide heat to at least one of fuel passing through the fuel inlet channel, oxidant passing through the oxidant inlet channel, the mixing chamber, or the combustion chamber. In one or more aspects, an ignition strip may be positioned in the combustion chamber to sustain a flame without preheating.

1 . A micro-mixer/combustor comprising:
 a fuel inlet and an oxidant inlet;   a mixing chamber downstream from the fuel and oxidant inlets, and in communication with the fuel and oxidant inlets, designed to mix fuel and oxidant received from the fuel and oxidant inlets, the mixing chamber having walls that converge towards each other downstream from the fuel and oxidant inlets, the walls forming a restriction at the downstream end of the mixing chamber restricting the flow of fuel and oxidant out of the mixing chamber;   a combustion chamber downstream from the restriction and in fluid communication with the mixing chamber through the restriction, the combustion chamber including walls that diverge from each other from the restriction, the combustion chamber being wider than the restriction at an end of the combustion chamber downstream from the restriction; and   an exhaust outlet downstream from the combustion chamber for exhausting combustion products from the combustion chamber.   
     
     
         2 . The micro-mixer/combustor of  claim 1 , wherein heat from the combustion products is used to provide heat to preheat at least one of fuel passing through the fuel inlet channel, oxidant passing through the oxidant inlet channel, the mixing chamber, or the combustion chamber. 
     
     
         3 . The micro-mixer/combustor of  claim 1 , further comprising an outer wall encasing the micro-mixer/combustor, the outer wall formed of a material having a low thermal conductivity sufficient to reduce heat loss and sustain a combustion flame in the combustion chamber. 
     
     
         4 . The micro-mixer/combustor of  claim 2 , wherein heat from the combustion products provides preheating to at least 100° C. 
     
     
         5 . The micro-mixer/combustor of  claim 1 , further including a catalytic ignition strip in the combustion chamber. 
     
     
         6 . The micro-mixer/combustor of  claim 5 , wherein the catalytic ignition strip is a platinum strip. 
     
     
         7 . The micro-mixer/combustor of  claim 1 , further comprising an outer wall and two inner walls, the inner walls positioned inside of the outer wall and spaced apart from the outer wall, the inner walls further positioned opposite and spaced apart from each other, the inner walls providing the walls forming the mixing chamber, restriction and combustion chamber, the spacing between the inner walls and the outer wall forming the exhaust outlet. 
     
     
         8 . The micro-mixer/combustor of  claim 7 , wherein at least one of the inner walls is formed of a thermally conductive material allowing heat from combustion products passing through the exhaust outlet to be transferred through the at least one inner wall to provide heat to preheat at least one of fuel passing through the fuel inlet channel, oxidant passing through the oxidant inlet channel, the mixing chamber, or the combustion chamber. 
     
     
         9 . The micro-mixer/combustor of  claim 8 , wherein the inner walls are positioned inside of the outer wall and spaced apart from the outer wall to form the exhaust outlet having at least two exhaust channels, an exhaust channel provided in the space between one of the inner walls and the outer wall and a second exhaust channel provided in the space between the second inner wall and the outer wall. 
     
     
         10 . The micro-mixer/combustor of  claim 9 , wherein at least one of the exhaust channels is on a side of an inner wall opposite at least one of the mixing chamber, restriction or combustion chamber. 
     
     
         11 . The micro-mixer/combustor of  claim 1 , wherein the micro-mixer/combustor provides a diffusion flame. 
     
     
         12 . A method of mixing and combusting a fuel and an oxidant, comprising:
 providing the micro-mixer/combustor of  claim 1 , the micro-mixer/combustor including an outer wall and two inner walls, the inner walls positioned inside of the outer wall and spaced apart from the outer wall, the inner walls further positioned opposite and spaced apart from each other, the inner walls providing the walls forming the mixing chamber, restriction and combustion chamber, the spacing between the inner walls and the outer wall forming the exhaust outlet, the exhaust outlet including an exhaust channel formed in a space between the outer wall and at least one of the inner walls and positioned on a side of the at least one inner wall opposite at least one of the mixing chamber, restriction or combustion chamber   
       wherein the at least one inner wall is formed of a thermally conductive material allowing heat from combustion products passing through the exhaust channel to be transferred through the at least one inner wall to provide heat to preheat at least one of fuel passing through the fuel inlet channel, oxidant passing through the oxidant inlet channel, the mixing chamber, or the combustion chamber;
 introducing fuel into the mixing chamber of the micro-mixer/combustor through the fuel inlet; 
 introducing oxidant into the mixing chamber of the micro-mixer/combustor through the oxidant inlet; 
 mixing the fuel and the oxidant in the mixing chamber; 
 passing the mixture of fuel and oxidant through the restriction into the combustion chamber; 
 combusting the mixture of fuel and oxidant in the combustion chamber; 
 exhausting combustion products resulting from the combustion of the mixture of fuel and oxidant out of the combustion chamber and through the exhaust channel, such that heat from the combustion products passing through the exhaust channel is transferred through the at least one inner wall and into at least one of the mixing chamber, restriction or combustion chamber to preheat the fuel, the oxidant and/or the mixture of the fuel and oxidant in the micro-mixer/combustor. 
 
     
     
         13 . The method of  claim 12 , wherein the combustion provides a stable diffusion flame. 
     
     
         14 . The method of  claim 12 , wherein the fuel, the oxidant and/or the mixture of the fuel and oxidant is heated to at least 100° C. 
     
     
         15 . The method of any of  claim 12 , wherein the outer wall is formed of a material having a low thermal conductivity sufficient to reduce heat loss and sustain a combustion flame in the combustion chamber. 
     
     
         16 . The micro-mixer/combustor of  claim 2 , further comprising an outer wall encasing the micro-mixer/combustor, the outer wall formed of a material having a low thermal conductivity sufficient to reduce heat loss and sustain a combustion flame in the combustion chamber. 
     
     
         17 . The micro-mixer/combustor of  claim 2 , further comprising an outer wall and two inner walls, the inner walls positioned inside of the outer wall and spaced apart from the outer wall, the inner walls further positioned opposite and spaced apart from each other, the inner walls providing the walls forming the mixing chamber, restriction and combustion chamber, the spacing between the inner walls and the outer wall forming the exhaust outlet. 
     
     
         18 . The micro-mixer/combustor of  claim 3 , further comprising an outer wall and two inner walls, the inner walls positioned inside of the outer wall and spaced apart from the outer wall, the inner walls further positioned opposite and spaced apart from each other, the inner walls providing the walls forming the mixing chamber, restriction and combustion chamber, the spacing between the inner walls and the outer wall forming the exhaust outlet. 
     
     
         19 . The method of  claim 14 , wherein the outer wall is formed of a material having a low thermal conductivity sufficient to reduce heat loss and sustain a combustion flame in the combustion chamber.