RU2491435C1 - Method of decreasing harmful emissions from gas turbine with heat recovery - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: proposed method consists in stepwise compression of oxidiser with water injection, heating of compressed mix of oxidiser with water, stepwise expansion of working medium and combustion of organic fuel in combustion chambers ahead of mid expansion stages with oxidiser surplus factor smaller than unity while, in the final chamber, it is larger than unity. Consumption of oxidizer, water and fuel is controlled and temperature of mix expansion stages walls and their gas-dynamic channels as well as combustion temperature in the final combustion chamber are maintained. Water is injected to compressor inlet and outlet and between its stages in total amount of 20-40% of total consumption of working medium at exhaust stage. Oxidiser surplus factor in combustion chambers ahead of mix expansion stages and gas-dynamic channel is kept at not lower than 0.5 and temperature of mix expansion chambers walls and gas-dynamic channel may not be lower than 730 K. Catalytic combustion proceeds in outlet chamber at 1500-1100 K that is at temperature lower than that in downstream combustion chambers while oxidiser surplus factor equals or exceeds stoichiometric factor.

EFFECT: decreased harmful emissions of gas turbine, high efficiency of heat recovery and rules out sooting.

1 dwg

Description

The invention relates to the problem of the harmful effects of emissions from gas turbine units with heat recovery on the environment. It can be used in gas turbine plants operating on gaseous or liquid hydrocarbon fuel.

Known methods for reducing emissions of nitrogen oxides using additives of chemical reagents in the exhaust gases. These methods are complex and expensive, as they require the construction of large-sized cleaning devices and a significant consumption of chemicals. It is known that an increased air temperature at the entrance to the combustion chamber (800-850 K) due to heat recovery completely eliminates the possibility of using traditional diffusion combustion chambers due to excessively high emission of nitrogen oxides, as well as homogeneous combustion chambers due to the impossibility of reliable exclusion flame penetration into the zone of preparation of the fuel-air mixture. Therefore, it is proposed to use in GTU a fundamentally new process of fuel combustion - a catalytic process with heat recovery of exhaust gases. Catalytic combustion of hydrocarbon fuels can drastically reduce emissions of products of incomplete combustion (CO, HC) and nitrogen oxides. (Parmon V.N., Ismagilov Z.R., Favorsky O.N., Belokon A.A., Zakharov V.M. Bulletin of the Russian Academy of Sciences. 2007, Volume 77, No. 9, p. 820).

However, the maximum thermal and accordingly effective efficiency of the proposed gas turbines will depend not on the maximum allowable temperatures of the combustion products entering the gas turbine inlet, but on lower allowable temperatures determined by the materials of the composite catalytic elements of the combustion chamber, which is a significant obstacle to increasing the gas turbine's efficiency.

The closest technical solution to the proposed one is a method of converting thermal energy into work, which consists in stepwise compression of the oxidizing agent with water injection into an additional compressor, stepwise expansion of the working fluid and burning of organic fuel in the combustion chambers before the intermediate expansion stages with an oxidizer excess coefficient of less than 1, and before the latter - with an excess coefficient of oxidizing agent greater than 1. (see AS USSR SU 1560749 A1, 02C 3/00 dated 04/30/90. Bull. No. 16 - prototype)

The main disadvantage of this method is that in the latter, to the exhaust of the combustion chamber with conventional non-catalytic combustion, a more reduced combustion temperature is not supported in relation to the previous combustion chambers, which in combination with an unlimited value of the coefficient of excess oxidizer (> 1), especially for regenerative gas turbine plants, will not allow to obtain the currently required acceptable level of emissions of nitrogen oxides, carbon monoxide (CO) and unburned hydrocarbons (CH). In addition, any value of the coefficient of excess of the oxidizing agent less than unity in the previous combustion chambers and their gas-dynamic paths is also unacceptable without maintaining the necessary values of the temperature of the walls, the water content in the combustion products and the coefficient of excess of the oxidizing agent. Otherwise, soot formation will occur, which will complicate the application of this method.

The problem to be solved is a significant reduction in emissions of nitrogen oxides, carbon monoxide and unburned hydrocarbons in gas turbines with regenerative heating of a compressed mixture of air and water while ensuring high efficiency.

High thermal efficiency is achieved due to heat recovery, as well as by increasing the average thermodynamic temperature of heat supply and lowering the average thermodynamic temperature of heat removal, respectively, due to stepwise supply and removal of heat.

The solution to this problem is achieved by the fact that in the method of reducing harmful emissions from a gas turbine plant with heat recovery, which consists in stepwise compression of the oxidizer with water injection, heating the compressed mixture of the oxidizer with water, stepwise expansion of the working fluid and burning of organic fuel in the combustion chambers before the intermediate expansion stages with an excess coefficient of oxidizing agent less than 1, and in the latter - more than 1. What is new here is that by adjusting the flow rates of the oxidizing agent, water and fuel and maintaining allowable temperature values of the walls at the inlet and outlet of the compressor and between its stages, water is injected with a total flow rate of 20-40% of the total flow rate of the working fluid at the exhaust, while the oxidizer excess coefficient is not maintained in the combustion chambers in front of the intermediate expansion steps and in the gasdynamic path below 0.5 and the temperature of the walls of the intermediate stages of expansion and the gas-dynamic path not lower than 730 K, and in the outlet chamber a catalytic combustion process is carried out, providing a temperature of 1500-1100 K, lower temperature in the previous combustion chambers, and the coefficient of excess oxidizer as equal to stoichiometric or greater than stoichiometric.

The proposed method prevents the formation of nitrogen oxides, carbon monoxide and unburned hydrocarbons, in excess of the permissible emission standards, despite the presence of heat recovery, due to the ability to maintain almost any low temperature level in the last (exhaust) combustion chamber, acceptable for catalytic combustion.

It is known that both elevated temperature and excess oxygen, for ordinary non-catalytic combustion, significantly increase the level of formation of nitrogen oxides. If, to reduce the level of formation of nitrogen oxides, it is advisable to reduce the coefficient of excess of the oxidizing agent as much as possible, then from the point of view of soot formation, this decrease must be limited. The proposed method allows to eliminate soot formation, maintaining acceptable values of the coefficient of excess oxidizing agent and the temperature of the walls of the gas-dynamic tract according to the content of water vapor in the combustion products.

Figure 1 shows a diagram of a gas turbine installation that implements a method of reducing harmful emissions from a gas turbine installation with heat recovery,

The circuit includes a compressor 12, consisting of compression stages 1 and mixing chambers 2, in which isobaric cooling of air occurs due to evaporation of atomized water, expansion stages of gas turbines 3, 5, 7, a regenerative heat regenerator 9, regulating the flow rate of the valve 11 and an electric generator 10, kinematically connected with the steps of gas turbines and a compressor.

The method is as follows. Using a compressor 12 compresses the mixture of water with air. The water sprayed with the nozzles is fed into the mixing chambers 2, then the compressed mixture is supplied to the regenerator 9, after the regenerator - to the combustion chambers 3, 5, 7. Fuel is supplied to the combustion chambers 3 and 5, in addition to the mixture of water and air. Using control equipment 11 in the combustion chambers 3 and 5, in accordance with the content of water vapor and the temperature of the walls of the gas-dynamic path, the allowable coefficient of excess oxidizer is less than 1, excluding soot formation. In combustion chambers 3 and 5, the maximum permissible temperature is maintained. After expansion in the stages of gas turbines 4 and 6, the products of incomplete combustion enter the combustion chamber 7, where also with the help of control equipment 11 the combustion temperature is maintained in the range of 1500-1100 K, lower than in the combustion chambers 3 and 5, and the oxidizer excess coefficient is equal to stoichiometric or more stoichiometric, carrying out catalytic afterburning of fuel. From the stage of the gas turbine 8, the combustion products enter the regenerator, where a compressed mixture of water and air is heated, and then the cooled combustion products are released into the atmosphere. All the obtained expansion work is converted into electrical energy using an electric generator 10. To illustrate the applicability of the proposed method, a numerical simulation of the process for the above scheme was carried out.

The fuel is synthesis gas obtained from Berezovsky coal by means of its air gasification with H ₂ O. Synthesis gas, after “hot” cleaning in a cyclone and in a “hot” filter, has a temperature of 870 K. The oxidizer excess coefficient and, accordingly, the temperature in the 3 combustion chamber is 0.61 and 1600 K, in the 5th combustion chamber - 0.59 and 1600 K, in the 7th combustion chamber - 1.1 and 1489 K. The relative water consumption is 20.4%. Pressure, respectively, in 3, 5. 7 combustion chambers - 7.0 MPa, 2.433 MPa, 0.846 MPa. The internal efficiency of turbines and compressors is taken equal to 0.85. The calorific value of coal is 26127 KJ / kg. For these parameters, the calculated value of the plant efficiency was 0.536 at an exhaust temperature of 443.4 K. The catalytic combustion chamber 7 can be equipped, for example, with a high-temperature catalyst proposed by the authors of the Institute of Catalysis named after G.K. Boreskov SB RAS see Patent No. 2185238 of 07.20.2002. Depending on the calorific value of the fuel and the permissible temperature of the turbine blades, the number of combustion chambers and, accordingly, expansion steps, for the proposed method, can be arbitrary, but not less than two.

Claims (1)

A method of reducing harmful emissions from a gas turbine unit with heat recovery, which consists in stepwise compression of the oxidizer with water injection, heating the compressed mixture of the oxidizer with water, stepwise expansion of the working fluid and burning of organic fuel in the combustion chambers before the intermediate expansion stages with an excess coefficient of the oxidizer of less than one, and in the last chamber - more than one, characterized in that by regulating the flow rate of the oxidizing agent, water and fuel and maintaining acceptable wall temperature values weft expansion steps and their gas-dynamic paths, as well as the combustion temperature in the last combustion chamber, water is injected at the compressor inlet and outlet and between its steps with a total flow rate of 20-40% of the total working fluid flow rate at the exhaust, while in the combustion chambers by the intermediate expansion steps and in the gas-dynamic path, the oxidant excess coefficient is maintained not lower than 0.5 and the wall temperature of the intermediate expansion steps and the gas-dynamic path is not lower than 730 K, and in the outlet chamber a catalytic combustion process, providing a temperature of 1500-1100 K, is lower than the temperature in the previous combustion chambers, and the oxidizer excess coefficient is equal to either stoichiometric or greater than stoichiometric.