RU2137936C1 - Method for controlling amount of nitrogen oxides exhausted from gas-turbine engine - Google Patents

Abstract

FIELD: pollution control of environment. SUBSTANCE: method for controlling NOx emission from gas-turbine engines of primarily ground and marine power plants involves combustion of rich and lean fuel-air mixtures in flame tube to form primary zone rich in fuel, lean-fuel burning zone and fast thinning zone for rich mixture combustion products between them. Steam or water mixed up with air is admitted to fast thinning zone for rich mixture combustion products. EFFECT: reduced emission of nitrogen oxides and reduced water flowrate. 2 cl, 3 dwg

Description

 The invention relates to the field of gas turbine engines, mainly onshore and offshore power plants running on liquid or gaseous fuels with water injection into the combustion chamber.

 A known method of controlling emissions of nitrogen oxides NOx by injecting water directly into the primary combustion zone of the combustion tube of the combustion chamber [1].

 The disadvantage of this method is the increase in specific fuel consumption as a result of heat loss during the conversion of water to steam, the unpredictable dependence of the reduction of nitrogen oxides NOx on preliminary preparation and mixing of fuel with air and water, as well as increased water consumption.

 Closest to the claimed one is a method for controlling emissions of nitrogen oxides NOx of a gas turbine engine, which consists in burning a rich and poor air-fuel mixture in a combustion pipe with the formation of a fuel-rich primary zone, a poor combustion zone, and between them - zones of rapid dilution of the combustion products of the rich mixture with air compressed in the compressor [2].

 The disadvantage of this method is the incomplete use of the ability to reduce emissions of nitrogen oxides NOx, mainly in land and offshore power plants running on liquid or gaseous fuels with water injection into the combustion chamber.

 The technical problem to which the claimed invention is directed is to reduce the emission of nitrogen oxides NOx of a gas turbine engine due to the increased heat capacity of water vapor or water, as well as to reduce water consumption.

 The essence of the technical solution lies in the fact that in the method for controlling the emission of nitrogen oxides NOx of a gas turbine engine, which consists in burning a rich and poor air-fuel mixture in the combustion chamber with the formation of a fuel-rich primary zone, a zone of poor combustion, and between them a zone of rapid dilution of combustion products rich mixture, according to the invention, in the zone of rapid dilution of the combustion products of the rich mixture serves water vapor or water. Water vapor or water is fed into the dilution zone of the combustion products of the rich mixture in a mixture with air.

 When water vapor or water is supplied to the zone of rapid dilution of the combustion products of the rich mixture, the flame temperature in the zone of rapid dilution and lean combustion decreases, which leads to a decrease in the rate of formation of NOx, which exponentially depends on the flame temperature.

 A significant dependence of the rate of formation of nitrogen oxides NOx on the temperature of the gases formed after combustion of the air-fuel mixture is known, for example, from formula (6) p. 62, see [3].

 In FIG. 1 is a longitudinal sectional view of the upper part of a tubular-annular combustion chamber along one of the flame tubes with a fuel-rich primary zone I, a poor combustion zone II and a zone of rapid dilution of combustion products III.

 In FIG. 2 - section AA is shown along the flame tubes in the circumferential direction of the combustion chamber.

 In FIG. 3 - shows a graph of the flame temperature Tm. depending on the coefficient of excess oxidizer α and the method of burning fuel, where a is diffusion combustion, b is the combustion of the mixture with air supply to the quick dilution zone (water flow rate Gb = 0), c is the combustion of the mixture according to the claimed invention, with water supply to the zone rapid dilution of combustion products.

 The method is as follows. When starting a gas turbine, fuel, for example, compressed natural gas 1, is fed into the combustion chamber through nozzles 2, then mixed with the air stream 3 in the inner cavity 4 of the flame tubes 5. In this case, the components of the mixture ignite from the spark plug (not shown in Fig. 1) , forming a torch 6 of diffusion combustion of the fuel-rich primary zone I, α = 0.5 - 0.7, where α is the coefficient of excess oxidizer, equal to the ratio of the actual amount of air to the theoretically necessary for complete combustion of the fuel. In the fuel-rich primary zone I (α = 0.5 - 0.7), the temperature of the combustion products is lowered (~ 750 K) as a result of eliminating the mixing of air on the inner walls of 7 flame tubes 5. Moreover, the other part 8 of the air stream 3 and water 9 supplied through the pipeline 10 to the quick dilution zone 3, for example, through the hollow racks 11 of the mixer 12, is directed through the holes 13 in the racks 11 and the holes 14 of the mixer 12 to the front of the diffusion torch 6 of the fuel-rich primary zone I, where water is converted into water vapor in mixtures with air. Zones of kinetic combustion of fuel microparticles, resulting from the interaction of unburned fuel of zone I with the air supplied by part 8 of the air stream 3, are more effectively cooled by water vapor mixed with air. In this case, the maximum local temperature of the combustion products, i.e. microparticles of fuel, decreases mainly from 2400 to 750 K, which greatly reduces the emissions of nitrogen oxides NOx of a gas turbine engine, mainly from 150 rp to 9 rp. Using the proposed method of regulation reduces water consumption and reduces specific fuel consumption due to the intensification of mixing processes precisely in zone III of rapid dilution of the combustion products of the fuel-rich primary zone, and in the poor combustion zone, and not by supplying water or water vapor to the primary zone I together with the fuel aerosol, as in the known method.

 Thus, the inventive method can reduce emissions of nitrogen oxides NOx not by reducing the residence time of the combustion products in the zone of maximum local temperatures, as in the known method, but by reducing the temperature of the flame in the zone of rapid dilution III and poor combustion II.

Sources of information:
1. Energy machines N 3 1979, p. 56, FIG. 22, in the article by D. McKnight "Development of a compact combustion chamber of a gas turbine engine with an increased resource and an acceptable level of emissions", UDC 621.438.

 2. UK patent N 2086031, CL F 23 R 3/34, dated 05/06/82, the prototype.

 3. "The formation and decomposition of pollutants in the flame," N.A. Chigir et al., M., Mechanical Engineering, 1981, UDC 621.43.019.9.

Claims (1)

A method of reducing the emission of nitrogen oxides NO _{x of a} gas turbine engine, which consists in burning a rich and poor air-fuel mixture in the combustion tube to form a fuel-rich primary zone, a poor combustion zone, and between them, a zone of rapid dilution of the combustion products of the rich mixture, characterized in that water vapor or water is supplied to the zone of rapid dilution of the combustion products of the rich mixture.

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