Method For The Selective Catalytic Reduction Of Nitrogen Oxides In Combustion Flue Gases And System For Implementing It

Abstract

The present invention relates to limiting emissions of nitrogen oxides into the environment. In particular, the present invention relates to an improved process for the catalytic reduction of nitrogen oxides to nitrogen

1 - 15 . (canceled) 
     
     
         16 . A process for treating a feed in a furnace comprising: at least one air preheat circuit, a radiant section, a convection section located downstream of said radiant section, and a flue gas duct that passes through said convection section and in which said air preheat circuit is located, said process comprising:
 releasing heat via the combustion of a liquid or gaseous fuel in the presence of air preheated in said at least one air preheat circuit, wherein said preheat circuit passes through the convection section one or more times, thereby resulting in the creation of a flue gas containing nitrogen, discharging said flue gases into said flue gas duct through the convection section; and   reducing said nitrogen oxides in the flue gases by means of selective catalytic reduction, said selective catalytic reduction comprising the injection, in the convection section in which at least one catalyst is present, of a mixture of hot air and of ammonia, wherein the hot air of said mixture is directly withdrawn from said at least one air preheat circuit being used to feed the furnace with preheated air.   
     
     
         17 . The process of  claim 16 , wherein the furnace is supplied with preheated air via a single air preheat circuit, and that the hot air used during the selective catalytic reduction of the nitrogen oxides is withdrawn directly from said single air preheat circuit. 
     
     
         18 . The process of  claim 16 , wherein the furnace is supplied with preheated air via two air preheat circuits, and that the hot air used during the step of selective catalytic reduction of the nitrogen oxides is withdrawn directly from at least one of said two air preheat circuits. 
     
     
         19 . The process of  claim 16 , wherein the hot air used during the selective catalytic reduction of the nitrogen oxides is withdrawn directly from the at least one air preheat circuit, either at the outlet of the first passage of said at least one air preheat circuit in the convection section, or at the outlet of the second passage of said at least one air preheat circuit in the convection section of the flue gases, or at the outlets both of the first and of the second passage of said at least one air preheat circuit in the convection section. 
     
     
         20 . The process of  claim 16 , wherein the injection of the mixture of hot air and of ammonia takes place in at least one location of the convection section, upstream of the catalyst, which is held in the combustion flue gas duct by a support. 
     
     
         21 . The process of  claim 16 , wherein the at least one air preheat circuit is supplied with fresh air using at least one fan. 
     
     
         22 . The process of  claim 16 , in which the treatment of the feed is a preheating and/or heating and/or vaporization and/or superheating treatment of fluids in a petrochemical process furnace. 
     
     
         23 . The process of  claim 16 , in which the treatment of the feed is a reforming treatment of a hydrocarbon feed in the presence of steam in a steam reforming furnace. 
     
     
         24 . An installation for treating a feed in a process furnace comprising at least:
 a process furnace that enables the treatment of a feed, comprising means of feeding with fuel, and with preheated air;   an air preheat circuit that supplies the furnace with preheated combustion air passing through the convection section one or more times;   a convection section resulting in the flue gases produced during the combustion of fuels in the radiant section of the process furnace, in which at least one catalyst for the selective reduction of nitrogen oxides is present, preferably held in said duct using a support means;   a hot air/ammonia mixer supplied with hot air by said at least one air preheat circuit; and   an injector connected to said mixer, enabling the injection of said mixture of hot air and of ammonia into the flue gases in said convection section, preferably upstream of the catalyst.   
     
     
         25 . The installation of  claim 24 , wherein the process furnace is supplied with preheated air via a single air preheat circuit, and that the hot air supplying the at least one hot air/ammonia mixer is withdrawn directly from said single air preheat circuit. 
     
     
         26 . The installation of  claim 24 , wherein the process furnace is supplied with preheated air via two air preheat circuits, and that the hot air supplying the at least one hot air/ammonia mixer is withdrawn directly from at least one of said two air preheat circuits. 
     
     
         27 . The installation of  claim 24 , wherein the at least one hot air/ammonia mixer is supplied with hot air via a withdrawal from the air preheat circuit(s), either at the outlet of the first passage of the preheat circuit in the convection section, or at the outlet of the second passage of the preheat circuit in the convection section of the flue gases, or both at the outlet of the first and of the second passage of the preheat circuit in the convection section. 
     
     
         28 . The installation of  claim 24 , wherein the at least one air preheat circuit is supplied with fresh air using at least one fan. 
     
     
         29 . The installation as of  claim 24 , in which the furnace is a petrochemical process furnace capable of preheating and/or heating and/or vaporizing and/or superheating petrochemical process fluids. 
     
     
         30 . The installation of  claim 24 , in which the furnace is a steam reforming furnace capable of reforming a hydrocarbon feed.