Method of producing heat in a power station

Abstract

Method for producing thermal energy from a fuel containing hydrocarbons. According to the method, the fuel is burned in a combustion plant at an increased temperature, heat obtained from the combustion is recovered and the combustion's exhaust gases and soot particles are cleaned by catalytic exhaust-gas combustion. Fuel and air are fed to the invention's exhaust gases to form a gas mixture, which is brought to catalytic combustion performed at a temperature of more than 600° C. to reduce the nitrogen oxides and oxidize the carbon monoxide, hydrocarbons, and soot particles. The solution can be used to significantly reduce the level of the gas's NOx, and CO and VOC emissions. The thermal energy produced by the catalytic combustion process can also be used to produce heat, in which case the feed of fuel is divided between the combustion plant and the catalytic combustion process.

1 . A method for the catalytic cleaning, in reducing and oxidizing conditions, of the combustion gases containing nitrogen oxides and carbon monoxide, hydrocarbons and soot particles of energy plants which use fuels with a hydrocarbon content, wherein:
 fuel and air are fed to the exhaust gases to form a gas mixture, and   the gas mixture is brought to one or more-stage catalytic combustion performed at a temperature of more than 600° C. to reduce the nitrogen oxides and to oxidize the carbon monoxide, hydrocarbon, and soot particles.   
     
     
         2 . The method according to  claim 1 , wherein the emission level of the NOxs of the gas obtained from the catalytic combustion is 1 ppm or less and the level of CO and VOC emissions is at most 2 ppm. 
     
     
         3 . The method according to  claim 1 , wherein the catalytic combustion is performed in a catalyser, in which the temperature is maintained at 850-1000° C. 
     
     
         4 . The method according to  claim 1 , wherein the gas mixture is burned in a three-way catalyser using a stoichiometric oxygen/additional-fuel ratio in order to oxidize CO and VOC compounds that have remained unburned in the combustion plant and to reduce NOx emissions and oxidize soot particles. 
     
     
         5 . The method according to  claim 1 , wherein the gas mixture is burned in an oxidizing and reducing catalyser, first with a rich additional-fuel/oxygen mixture to reduce the nitrogen oxides and then with a lean additionalfuel/oxygen mixture to oxidize the CO and VOC compounds and the soot particles. 
     
     
         6 . The method according to  claim 4 , wherein the space velocity of the three-way catalyser is 50 000-150 000 l/h, preferably 60 000-100 000 l/h and the space velocities of the reducing and oxidizing catalyser are 60 000-200 000 l/h, preferably 70 000-150 000 l/h. 
     
     
         7 . The method according to  claim 1 , wherein catalytic combustion is performed in reducing and correspondingly oxidizing conditions in at least two stages. 
     
     
         8 . A method for producing thermal energy from a fuel containing hydrocarbons, wherein:
 the fuel is burned at an increased temperature in a combustion plant,   the heat available from combustion is recovered, and   the combustion's exhaust gases and soot particles are cleaned by catalytic exhaust-gas combustion,   
       and wherein:
 fuel and air are fed to the exhaust gases to form a gas mixture, and 
 the gas mixture is brought to catalytic combustion at a temperature of at least 600° C., preferably more than 600° C. to reduce the nitrogen oxides and oxidize the carbon monoxide, hydrocarbons, and soot particles. 
 
     
     
         9 . The method according to  claim 8 , wherein catalytic combustion is performed in reducing and correspondingly oxidizing conditions in one or more stages, particularly in at least two stages. 
     
     
         10 . The method according to  claim 8 , wherein the exhaust gases, fuel, and air are mixed evenly together in a nesting, perforated feed pipe and a static mixer to create a gas mixture. 
     
     
         11 . The method according to  claim 8 , wherein the gas mixture is brought to catalytic combustion in a three-way catalyser oxidizing and reducing catalyser. 
     
     
         12 . The method according to  claim 8 , wherein the gas mixture is burned in a three-way catalyser using a stoichiometric oxygen/additional-fuel ratio to oxidize the CO and VOC compounds left unburned in the combustion plant and to reduce the NOx emissions and oxidize the soot particles. 
     
     
         13 . The method according to  claim 8 , wherein the gas mixture is burned in an oxidizing and reducing catalyser first with a rich additional-fuel/oxygen mixture to reduce the nitrogen oxides and then with a lean additionalfuel/oxygen mixture to oxidize the CO and VOC compounds and the soot particles. 
     
     
         14 . The method according to  claim 13 , wherein the temperature in the catalyser is 850-1000° C. in at least reducing conditions or in both reducing and oxidizing conditions. 
     
     
         15 . The method according to  claim 13 , wherein the three-way catalyser's space velocity is 50 000-150 000 l/h, preferably 60 000-100 000 l/h, and the reducing and oxidizing catalyser's space velocities are 60 000-200 000 l/h, preferably 70 000-150 000 l/h. 
     
     
         16 . The method according to  claim 8 , wherein fuel is burned in a combustion plant, which is an oil or gas boiler, a gas turbine, a diesel power plant, or a similar energy plant. 
     
     
         17 . The method according to  claim 8 , wherein additional air and fuel are fed to the exhaust-gas burner and their feed is controlled by the temperature after the catalyser and linear oxygen sensors, according to the air/fuel ratio required by each catalyser. 
     
     
         18 . The method according to  claim 8  for producing thermal energy from a fuel with a hydrocarbon content, using combustion performed in at least two stages, 
       wherein:
 in the first combustion stage part of the fuel is burned in a combustion plant to produce heat and exhaust gas with a nitrogen- and oxygen-oxide content, 
 the heat and exhaust gas obtained from the first combustion stage are recovered separately, 
 in the second combustion stage the exhaust gas obtained from the previous combustion stage is fed with the second part of the fuel and air to form a gas mixture, and 
 the gas mixture thus obtained is burned catalytically to produce heat and to dissipate the nitrogen- and oxygen oxides, 
 
       when reducing conditions are maintained in at least one catalyst zone and combustion is performed in these conditions at a temperature of more than 600° C., after which the heat obtained from the second combustion stage is recovered. 
     
     
         19 . The method according to  claim 18 , wherein in the second combustion stage at least 10%, most suitably 15-80 mol-%, of the total amount of the fuel with a hydrocarbon content is burned. 
     
     
         20 . The method according to  claim 18 , wherein as much as about 60% additional thermal energy is produced for the primary energy source. 
     
     
         21 . The method according to  claim 18 , wherein the flue gases of the thermal energy plant are used as inert heat storage and transfer agents to keep the temperature of the catalytic combustion within a preselected temperature range. 
     
     
         22 . The method according to  claim 18 , wherein catalysers used in combustion are surfaced with stable metal oxides, particularly oxides, the cation of which is Al, Ce, Zr, L, or Ba, and to which are attached noble metals such as Pd, Pt, Rh, or their mixed oxides with base metals. 
     
     
         23 . The method according to  claim 18 , wherein the noble-metal catalysts are not toxic and do not create toxic compounds in reactions, as happens in traditional SCR catalysers. 
     
     
         24 . The method according to  claim 18 , wherein the thermal energy contained in the gases arising in combustion is recovered in at least one heat-exchange stage, when the thermal energy is transferred to water, air, or some other liquid or gaseous medium. 
     
     
         25 . The method according to  claim 1 , wherein the method produces recoverable thermal energy.