Nitrogen oxides combustion turbines

PGM catalyst technology can also be appHed to the control of emissions from stationary internal combustion engines and gas turbines. Catalysts have been designed to treat carbon monoxide, unbumed hydrocarbons, and nitrogen oxides in the exhaust, which arise as a result of incomplete combustion. To reduce or prevent the formation of NO in the first place, catalytic combustion technology based on platinum or palladium has been developed, which is particularly suitable for appHcation in gas turbines. Environmental legislation enacted in many parts of the world has promoted, and is expected to continue to promote, the use of PGMs in these appHcations. 

Methanol contains no sulfur and produces very little nitrogen oxide pollutants when burned, making it a very clean combustion fuel. At a power generating facility, it could be used as a supplemental fuel for gas turbines to meet peak electricity generation requirements, or it could be sold over the fence to commercial fuel and chemical companies. A commercial-scale power facility might generate 200 to 350 MW of electricity, while also producing 150 to 1000 tons per day of methanol. 

Sulfur compounds pose a dual problem. Not only do their combustion products contribute to atmospheric pollution, but these products are also so corrosive that they cause severe problems in the operation of gas turbines and industrial power plants. Sulfur pollution and corrosion were recognized as problems long before the nitrogen oxides were known to affect the atmosphere. For a time, the general availability of low-sulfur fuels somewhat diminished the general concern... 

Catalytic combustion is an environmentally-driven, materials-limited technology with the potential to lower nitrogen oxide emissions from natural gas fired turbines consistently to levels well below 10 ppm. Catalytic combustion also has the potential to lower flammability at the lean limit and achieve stable combustion under conditions where lean premixed homogeneous combustion is not possible. Materials limitations [1,2] have impeded the development of commercially successful combustion catalysts, because no catalytic materials can tolerate for long the nearly adiabatic temperatures needed for gas turbine engines and most industrial heating applications. 

MW of power. Utilization of DME for power generation offers tremendous environmental benefits, in terms of CO SO and NO emissions. It burns in conventional gas turbines without modifications to the turbine or the combustors. Emissions produced by combustion of conventional fuels in gas turbines include nitrogen oxides, carbon monoxide, unburned hydrocarbons, and sulfur oxides. Dimethyl ether produces no sulfur oxide emission, as the fuel is sulfur free. It generates the least amount of NO CO, and unburned hydrocarbons as compared with natural gas and distillate, and lower CO2 emissions than the distillates. 

Methanol is a clean-burning liquid that can be used to power electricitygenerating turbines or as a fuel for automobiles and other vehicles. It can also be a feedstock for a variety of chemicals 14). Though most methanol is produced from natural gas, it can be produced from syngas derived from other feedstocks. Methanol contains no sulfur and produces very little nitrogen oxide pollutants when burned, making it one of the cleanest combustion fuels. 

Catalytic combustion is a process in which a combustible compound and oxygen react on the surface of a catalyst, leading to complete oxidation of the compound. This process takes place without a flame and at much lower temperatures than those associated with conventional flame combustion [1, 2], Due partly to the lower operating temperature, catalytic combustion produces lower emissions of nitrogen oxides (NOv) than conventional combustion. Catalytic combustion is now widely used to remove pollutants from exhaust gases, and there is growing interest in applications in power generation, particularly in gas turbine combustors. 

Natural gas provides an attractive source of energy for various purposes. For instance, it is used to fire gas turbine combustion chambers [1] and more recently has been reported as an alternative fuel for automotive applications [2]. The main advantages are lower levels of particulate matter and nitrogen oxides in lean bum combustion [3]. The high H/C ratio reduces the net carbon dioxide emissions, when compared to other fossil fuels. 

On the debit side, the increased operating temperatures could lead to higher nitrogen oxide emissions (see Section 3.2.2.4). Moreover, hydrogen does not lead to any reduction in noise, which is a major drawback to the use of turbines in populated areas. Hydrogen offers a further advantage over petrochemical fuels in that no sulfur pollutants result from its combustion. 

The 1992 U.S. emissions of anthropogenic nitrogen oxides (NOx) are estimated at 23 million tons. Of this amount, approximately 45% were from transportation sources (cars, trucks, etc.) and the remainder from stationary sources. Examples of stationary source emitters include power plants (53%), internal combustion engines (20%), industrial boilers (14%), process heaters (5%), and gas turbines (2%). Total NOx emissions are estimated to have increased 5% since 1983. Stationary sources have accounted for the majority of the increase emissions from mobile sources have remained relatively constant. Approximately 51% of the total NOx emissions are a result of combustion in stationary-sources applications [1]. 

The combustion gases, residual char, and fly ash pass into a boiler chamber where burnout is completed and there are various stages of heat exchange and heat recovery, producing steam to drive the turbine and generator. As a result of the intense combustion conditions, nitrogen oxide (NOx) formation tends to be considerably higher than in a pulverized coal combustor. 

High levels of nitrogen removal are also possible. Some of the coal-nitrogen is converted to ammonia which can be almost totally removed by commercially available processes. Nitrogen oxide formation can be held to allowable levels by staging the combustion process at the turbine or by adding moisture to hold down flame temperature. 

Monolithic catalysts (or honeycombs) have received much attention ever since they were first applied in automotive catalytic converters [1]. An increasing interest in the use of monolithic reactors for other applications has also been noticed during recent years [2]. One application which particularly profits from the opportunities offered by the honeycomb structure is catalytic combustion for use in advanced gas turbines [3]. In a catalytic combustor, a premixed lean fuel-air mixture is ignited by the catalyst which results in complete combustion at maximum temperatures far lower than possible in conventional gas-phase combustors. Hence, the thermal formation of nitrogen oxides can almost completely be circumvented. This fact has promoted large R D programs in catalytic combustion during recent years. 

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