RU2287066C1 - Method to deliver steam into combustion chamber of steam-gas turbine plant - Google Patents

Abstract

FIELD: mechanical engineering; steam-gas turbine plants.

SUBSTANCE: invention relates to methods of delivery of steam into combustion chamber of steam-gas turbine plant designed for driving electric generators. Proposed method includes delivery of steam into primary and into secondary zones of combustion chambers, delivery of steam into primary zone is regulated by bypassing part of steam into secondary zone, and optimum temperature of flame is maintained in primary zone at all main operating modes of steam-gas plant. Steam is delivered into secondary zone directly into flame tube of combustion chamber without preliminary mixing with air delivered into secondary zone.

EFFECT: provision of low level of emission of nitrogen oxides, carbon monoxide and noncombusted hydrocarbons, stable and reliable operation of combustion chamber, increased power and efficiency of steam-gas turbine plant under all operating conditions within the range of main modes.

4 cl, 3 dwg

Description

The present invention relates to methods for supplying steam to the combustion chamber of a steam-gas turbine installation, for example, for driving electric generators.

Steam is supplied to the combustion chamber to improve the environmental performance of the installation and increase its power and efficiency. Reducing the emission of harmful substances (nitrogen oxides NOx, carbon monoxide CO, unburned CnHm hydrocarbons) is one of the most urgent problems to be solved when creating modern gas turbine units.

It is known that to reduce the emission of harmful substances, the combustion of a pre-mixed (homogeneous) air-fuel mixture (FA) is organized in a narrow range of flame temperature _Tm = 1750 ... 1900 K, where the generation of nitrogen oxides NOx, carbon monoxide CO and unburned hydrocarbons CnHm is quite low .

The flame temperature and the concentration of harmful substances NOx and CO depend on the coefficient α of excess air of the premixed air-fuel mixture in the primary combustion zone. In a traditional control system, the coefficient α in the combustion zone changes significantly with a change in the engine operating mode.

With a significant decrease in engine power, the air-fuel mixture becomes leaner (coefficient α increases) and the flame temperature decreases so much that combustion becomes ineffective (the completeness of fuel combustion decreases, the concentration of carbon monoxide CO increases) and the flame may break off.

Various methods are known for maintaining the optimum flame temperature. For example, by regulating the air flow into the combustion chamber according to US patent No. 5303542 of 11.16.1992 and changing the combustion area by sequentially connecting several fuel circuits according to the patent of the Russian Federation No. 2162953 of 02/10/2001. These methods are applicable when using an adjustable input a guide vane, air bypass valves from the compressor, several fuel circuits (manifolds, burners, dispensers) controlled by processors, which significantly complicates the engine control system.

An effective way to reduce the temperature of the flame and, accordingly, the emissions of nitrogen oxides NOx with exhaust gases is to inject steam into the combustion chamber. So, at a General-Electric LM-5000 gas turbine unit (USA), steam injection into a compressor, a combustion chamber, and a turbine ensured a decrease in NOx concentration in exhaust gases from 225 ppm to 25 ppm, an increase in power from 32.5 to 49.5 MW, and an increase in efficiency from 36 to 43%. At the same time, carbon monoxide “СО” emissions do not exceed 60 ppm, the norm for LM-5000.

However, a significant increase in steam consumption to further reduce NOx leads to an unnecessary decrease in flame temperature and an increase in emissions of carbon monoxide CO and unburned CnHm hydrocarbons, especially during throttle operation of the installation. This limits the possibility of increasing the capacity of gas turbines due to the injection of steam into the chamber.

Closest to the proposed invention is a method of supplying and controlling the flow of steam and water into the combustion chamber of stationary engines in order to increase engine power and ensure environmental performance (US patent No. 5054279 from 08.10.1991). It provides for the supply of steam and water to the primary and secondary zones. The amount of steam and water in the primary zone is regulated so that the total ratio of superheated steam to fuel is about 2.75 / 1 or to prevent flame failure. In the secondary zone, steam is supplied only for aircraft gas turbine engines through an air intake pipe for aircraft needs, is mixed with air flowing around the flame tube, and through all openings on it, the mixture enters. The specified method of controlling the flow of steam into the primary zone to fuel consumption (2.75 / 1) at reduced operating modes will inevitably lead to a decrease in combustion efficiency and an increase in emissions of carbon monoxide CO and unburned hydrocarbons CH. In addition, the steam supplied to the air flowing around the flame tube reduces the reliability, since:

- significant temperature gradients appear on the walls of the flame tube;

- condensation of steam in the annular channels between the flame tube and the housings is possible, especially at reduced modes, which is fraught with unstable operation of the chamber.

These factors limit the amount of steam that can be supplied to the chamber by the method specified in the patent, and therefore, the possibility of a significant increase in the power of gas turbines.

The technical result of the invention is to ensure, under all operating conditions of the installation, in the range of basic operating modes of a low level of emission of nitrogen oxides, carbon monoxide and unburned hydrocarbons, stable and reliable operation of the combustion chamber, a significant increase in the power and efficiency of a combined cycle gas turbine plant.

In order to achieve the indicated technical result in the proposed method for supplying steam to the combustion chamber of a combined cycle plant, comprising supplying steam to the primary zone of the combustion chamber and to the secondary zone of the combustion chamber, in accordance with the invention, the flow rate of steam into the primary zone is controlled by bypassing part of the steam into the secondary zone, and support optimal flame temperature in the primary zone at all the main operating modes of the combined cycle plant, while steam is fed into the secondary zone directly into the heat pipe of the combustion chamber premixing of the air supplied to the secondary stage.

To further improve the environmental performance, the steam supplied to the primary zone of the combustion chamber is pre-mixed with fuel in the mixer, and the steam transferred to the secondary zone is taken to the mixer.

The flow rate of steam into the primary zone of the combustion chamber is controlled by the signals of the concentration sensors of nitrogen oxides and carbon monoxide at the exhaust of the installation.

The proposed method is illustrated in figure 1, which shows a diagram of the supply of pre-mixed with fuel steam into the combustion chamber.

The method is as follows.

In the general case, the steam supplied to the combustion chamber of a combined cycle plant is distributed into the primary and secondary zones of the chamber. Steam is supplied to the secondary zone through nozzles directly to the combustion tube’s heat pipe without first mixing with air supplied to the secondary zone through openings in the flame tube.

Steam flow into the primary zone is regulated by a throttle valve, bypassing part of the steam into the secondary zone, and the optimal flame temperature in the primary zone is maintained at all main operating modes of a combined cycle plant. The regulation of the flow of steam into the primary zone of the chamber is carried out according to the signals of the concentration sensors of nitrogen oxides and carbon monoxide. The sampler is installed, for example, on the exhaust of the installation. If the “Nox” is greater than the established norm, the steam bypass into the secondary zone is reduced. If "WITH" is more than normal - steam bypass is increased. With a decrease in the operation mode of the installation in terms of power, the steam consumption in the mixer and, accordingly, in the primary zone of the combustion chamber is reduced by increasing its bypass into the secondary zone. With an increase in the mode, on the contrary, the steam consumption in the primary zone is increased by a decrease in its bypass into the secondary zone.

In the case of preliminary mixing of steam with fuel (Fig. 1), steam is supplied through a pipeline 1 through a controlled throttle valve 2 to a mixer 4, and fuel is supplied there through a pipeline 5. From the mixer 4, pre-mixed fuel through the burners 6 is fed into the primary zone 7 of the combustion chamber 10. Through a controlled throttle valve 3, steam is supplied through special nozzles 8 directly to the secondary zone 9 of the combustion chamber 10. Moreover, the vapor is not mixed with air 12 entering the primary zone 7 of the combustion chamber 10, for cooling the flame tube 11 and into the secondary zone 9.

без перепуска (11) и с перепуском (12) пара во вторичную зону по зависимости 13. Из этого примера следует, что, выбирая перепуск пара по зависимости типа 13 можно обеспечить постоянство оптимальной температуры пламени (12) в эксплуатационном диапазоне (14) режимов работы установки.Figure 2 shows the calculated dependences of the combustion temperature in the primary zone of the chamber on the mode of operation of the installation by power

without bypass (11) and with bypass (12) of steam to the secondary zone according to dependence 13. From this example it follows that, by choosing steam bypass according to type 13, it is possible to ensure constant optimum flame temperature (12) in the operating range (14) of operating modes installation.

без перепуска (15, 16) и с перепуском (17, 18) пара во вторичную зону камеры сгорания. Из сравнений этих зависимостей следует, что, например, на режиме

концентрация «СО» при перепуске пара во вторичную зону уменьшается с 150 мг/нм³ до 50 мг/нм³, т.е. в 3 раза. Концентрация NOx при этом возрастает с 20 мг/нм³ до 50 мг/нм³, но не превышает допустимую норму, обеспечиваемую на номинальном режиме.Figure 3 shows the calculated dependences of the concentrations of NOx and CO on the operation mode of the installation in terms of power

without bypass (15, 16) and with bypass (17, 18) of steam into the secondary zone of the combustion chamber. From comparisons of these dependencies it follows that, for example, in the mode

the concentration of "CO" when passing the vapor into the secondary zone decreases from 150 mg / nm ³ to 50 mg / nm ³ , i.e. 3 times. The concentration of NOx in this case increases from 20 mg / nm ³ to 50 mg / nm ³ , but does not exceed the permissible rate provided in the nominal mode.

A steam-gas-turbine unit developed using the proposed method provides a power of N = 135 MW with a base value of N = 30 MW with an efficiency of more than 42%, without the use of a special steam turbine. The amount of steam supplied to the combustion chamber is 4.5 times the amount of fuel.

Thus, the proposed method for supplying steam to the combustion chamber of a steam-gas turbine installation can significantly reduce the emission of carbon monoxide with exhaust gases at the throttle operating modes of the installation in the operating range, ensure stable combustion, reduce the concentration of nitrogen oxides, increase the power and efficiency of the installation.

Claims (3)

1. The method of supplying steam to the combustion chamber of a combined cycle plant, comprising supplying steam to the primary zone of the combustion chamber and to the secondary zone of the combustion chamber, characterized in that the flow rate of the vapor into the primary zone is controlled by bypassing part of the vapor into the secondary zone and the optimum flame temperature is maintained in the primary zone in all the main operating modes of the combined cycle plant, while the steam in the secondary zone is fed directly into the flame tube of the combustion chamber without first mixing with the air supplied to the secondary zone. 2. The method according to claim 1, characterized in that the steam supplied to the primary zone of the combustion chamber is pre-mixed with fuel in the mixer, and the steam entering the secondary zone is taken to the mixer. 3. The method according to claim 1 or 2, characterized in that the regulation of the flow of steam into the primary zone of the combustion chamber is carried out according to the signals of the concentration sensors of nitrogen oxides and carbon monoxide at the exhaust of the installation.

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