DE112004000994T5 - Method of obtaining ultra-low NOx emissions from gas turbines operating at high turbine inlet temperatures - Google Patents

Abstract

A method of decreasing NOx combustion, wherein the kinetic rate of NOx formation at a given combustion temperature is reduced, comprising the following steps:
a. Providing a supply of fuel to a gas turbine combustor (14);
b. Obtaining a supply of ambient air in sufficient quantity to form a fuel / air mixture having an equivalence ratio greater than about 0.55 when mixed with the fuel;
c. Obtaining a supply of cooled combustion gases in a sufficient amount so that when mixed with the air, the oxygen content of the resulting air mixture is less than 18 percent;
d. Mixing the air with the cooled combustion gases; and
e. Supplying the air mixture to the burner (14).

Description

BACKGROUND THE INVENTION

Field of the invention

The The present invention relates to a method for improving the thermal efficiency of gas turbine systems by enabling higher firing temperatures without unacceptable generation of NOx. Especially, the present invention a method for obtaining low, single decay NOx emission levels gas turbines with high turbine inlet temperatures. Especially The present invention is in combined cycle gas turbine systems directed to a method which involves using a higher pressure ratio, Gas turbines with higher efficiency without sacrificing or dispense with steam cycle performance, thereby an increased System performance is created.

description of the prior art

With the present knowledge of the importance of improving Gas turbine systems to reduce fuel costs and also to Reduction of emissions of greenhouse gases has a continuous Trend for operating such systems given higher turbine inlet temperatures. This results in combustor exit temperatures being so excessively high, that a limit for achievable NOx emission levels is arranged on the required combustor service times. Thus, essentially all gas turbine systems that are typically associated with a turbine inlet temperature of more than 2200 ° F, known in the art as "F-class" machines, even those with dry low NOx combustion systems now require efficiency consuming post-treatment to reduce NOx emissions to less than about 3 ppm to reach. With emission levels of 2 ppm or lower, the rising, there is a separation between the need for lower NOx emissions and the need for reduced emissions of Greenhouse gases.

It It is well known in the art that combined cycle gas turbine / steam turbine systems higher Efficiency earnings bring as either simple circulatory gas turbines or stand-alone Steam turbine power plants, especially when such combined cycle systems operate with exhaust gas temperatures of gas turbines of at least about 1000 ° F, typically more at 1100 ° F. A use of gas turbines with higher efficiency with pressure ratios from much bigger than 20: 1 is common unfavorably without increases in turbine inlet temperature, around a maintain sufficiently high exhaust gas temperature. Therefore, there is one Need for Gas turbine combustors that are capable of ultra-low NOx emissions the higher one to achieve required combustion chamber outlet temperatures. Because the Efficiency of typical high performance gas turbines at ambient temperatures below is reduced to the design point, there is still a need for a Method of enabling improved performance at low ambient temperatures.

It It has now been found that NOx emissions below 3 ppm are also at Combustion temperatures over those can be achieved well, the for the highest Inlet temperature gas turbines are now available. By mixing of cooled Turbine exhaust with fresh air will intake air with reduced Oxygen content supplied to the turbine compressor. Advantageously, the Temperature of the air supplied to the compressor to a previously controlled value, regardless of how low the ambient air temperature can be, being the turbine so allows is operated at maximum efficiency, regardless the environmental conditions. When maximum performance is required, The intake air temperature can at some sacrifice in performance be reduced.

DESCRIPTION THE INVENTION

The The present invention is a method and an apparatus for the Achieving ultra-low NOx combustion emissions, even at the highest Combustion temperatures for existing gas turbines are required, which the use of Exhaust gas recirculation (EGR) or exhaust gas recirculation have.

In In the present invention, the term "air" refers to a gas which the oxidizing agent contains oxygen. For clarity of presentation The invention is the more common Fuel / air terminology ("fuel / air mixture") used, but the The invention is not to be considered as limited therein.

The term "equivalence ratio" is used to refer to the proportions of fuel and air in the fuel / air mixture The "equivalence ratio" is the ratio of the current air / fuel ratio to the stoichiometric air / fuel ratio, in which the stoichiometric coefficients calculated for the reaction which gives complete oxidation products CO ₂ and H ₂ O. An equivalence ratio greater than 1.0 defines a fuel rich air / fuel mixture, and an equivalence ratio less than 1.0 defines a fuel lean or lean fuel / air mixture.

As recognized in the art, have hydrocarbon fuels a limited range of fuel / air ratios within, within which a flame can spread. The rich or fat flammability limit for combustion is the highest equivalence ratio for flame combustion, and in a similar way Way, the lean flammability limit is the lowest. As known Typically, this limit typically increases with an increase the temperature or pressure of the fuel / air mixture and narrow with a reduction in oxygen concentration. Catalytic combustion, as for example the method of U.S. Patent No. 6,358,040 is different from conventional flame combustion and not on equivalence ratios within the normal flammability limits of flame combustion limited and is thus in the process of the present invention prefers.

In The present invention provides fresh intake air with cooled combustion gases mixed in sufficient quantity to increase the oxygen content to reduce the resulting mixture, preferably to at least eighteen Mole percent, more preferred is about fifteen Mole percent or less. Sufficient oxygen must be present Be sure to mix with fuel at the burner inlet temperature to reach with the required flame temperature. Advantageously, the Combustion products contain less than one percent residual oxygen. To a complete Combustion of fuel, it is preferable that the combustion is a poor fuel ratio with an equivalence ratio of greater than approximately 0.55, and more preferably greater than about 0.6.

In a preferred method of the present invention is the Intake air with cooled combustion product gas mixed before entering the compressor of a gas turbine. optional can they cooled Combustion gases are compressed separately and then with compressed Air are mixed, leaving the compressor of the gas turbine. To Compressing the compressed air mixture is mixed with fuel and burned, creating hot combustion products arise relaxed in the turbine to power and hot Generate exhaust gas. The exhaust gas is then conveyed to a heat recovery unit. typically, owns the heat recovery unit a steam boiler, in which case the steam is used for heat or further into a steam turbine for additional power generation promoted can be. Part of the chilled Combustion product gases from the heat recovery unit, typically at a temperature of about 100 degrees Celsius, can be used to fresh air intake to dilute. This has the advantage of increasing the burner inlet temperature and an improvement in combustion stability. Preferably, combustion product gases however, so cooled to a temperature below about 50 degrees Celsius, like for example, in a run of a water spray tower or a second heat exchanger, before they are mixed with the fresh air that is the compressor supplied becomes.

Around To maximize turbine efficiency is the temperature of the turbine recirculated exhaust gas such that when mixed with the ambient air, the Temperature of the gas turbine supplied supplement close to the design value the gas turbine is located. The temperature of the inlet mixture to the Compressor can be easily controlled or regulated by a controlled amount of exhaust around the second radiator passed through a bypass. To a mass flow through the To maximize compressors (and thus maximize performance) should the temperature of the recirculated exhaust gas as close as possible are at the ambient air, which is supplied to the gas turbine, or lower. Advantageously, a combustion is stabilized, by using a catalytic burner.

It is significant that a stable to fuel poor combustion in a gas turbine burner also with a reduction in oxygen content can be achieved, which is sufficient to the kinetic rate of NOx formation during to reduce fuel-lean combustion.

SHORT DESCRIPTION THE DRAWINGS

1 FIG. 12 is a schematic drawing of a typical combined cycle gas turbine system of the present invention. FIG.

2 and 3 represent respective plots of calculated NOx emissions for a typical premixed combustion of fuel and air with and without use of EGR (Exhaust Gas Recirculation) of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

1 provides a schematic of a typical combined cycle gas turbine system 10 of the present invention. As in 1 shows a combined cycle gas turbine system 10 a compressor 11 on what compressed air a burner 14 through a flow path 22 supplies. fuel 13 enters the burner 14 through Strö mung path 23 it being preferred that it be premixed with the compressed air prior to combustion. Hot combustion products become a turbine 12 via flow path 32 promoted. turbine 12 and steam turbine 18 turn and a power generator or power generator 16 , Exhaust gases from turbine 12 become a heat recovery boiler 20 via flow path 33 fed. With the steam generated is steam turbine 18 via flow path 40 fed. The cooled exhaust gases 37 pass through flow path 34 out, with a part of an additional cooler 50 via flow path 35 for returning to the inlet of the compressor 11 via flow path 36 is supplied. cooler 50 has a heat exchanger, which further comprises a coolant 38 has. fresh air 40 for combustion, the recirculated exhaust gases in flow path 36 via flow path 21 added, and both flows mix before entering the compressor 11 , Advantageously, burner 14 a catalytic burner as described, for example, in U.S. Patent No. 6,358,040.

2 represents the calculated NOx emissions for a typical premixed combustion of fuel and air with and without use of providing EGR into the fresh combustion air inlet 2 For example, NOx formation at a combustion temperature of 2750 ° F is reduced from more than 5 ppm to 3 ppm by using EGR to lower the oxygen content of the intake air to 15 percent. Plug flow residence time is 30 milliseconds. The oxygen content can be further reduced, resulting in lower NOx emissions. Oxygen levels of intake air as low as about 11 percent are feasible. 3 represents the calculated NOx comparison for a similar burner with a plug flow residence time of only fifteen milliseconds 3 is shown, the NOx reduction of EGR also applies to burners with reduced residence time.

Summary

A method for burning comprises the following method steps: provision of fuel ( 13 ) for a burner ( 14 ) a turbine; Feeding air ( 21 ) for forming a fuel / air mixture with an equivalence ratio greater than 0.55; Supplying cooled combustion gases ( 37 ) and mixing with the air such that the mixture oxygen is less than 18%; and supplying the mixture to the burner ( 14 ).

Claims (10)

A method of reducing NOx combustion, wherein the kinetic rate of NOx formation at a given combustion temperature is reduced, comprising the following steps: a. Providing a supply of fuel to a gas turbine combustor ( 14 ); b. Obtaining a supply of ambient air in sufficient quantity to form a fuel / air mixture having an equivalence ratio greater than about 0.55 when mixed with the fuel; c. Obtaining a supply of cooled combustion gases in a sufficient amount so that when mixed with the air, the oxygen content of the resulting air mixture is less than 18 percent; d. Mixing the air with the cooled combustion gases; and e. Feeding the air mixture to the burner ( 14 ). Method according to claim 1, characterized in that that the fuel / air mixture a fuel-poor equivalence ratio greater than approximately 0.6. A method according to claim 1, characterized in that the air mixture in a compressor ( 11 ) a gas turbine ( 12 ) before it enters the burner ( 14 ) entry. Method according to claim 1, characterized in that that the air and the cooled Combustion gases are compressed prior to mixing. Method according to claim 1, characterized in that that the cooled Combustion gases have a temperature of less than about 150 degrees Celsius. Method according to claim 1, characterized in that the compressor ( 11 ) of the gas turbine ( 12 ) is installed in a combined cycle gas turbine. Method according to claim 1, characterized in that that the fuel with the air mixture before burning before is mixed. Method according to claim 1, characterized in that the burner ( 14 ) is a catalytic burner. A method according to claim 3, characterized in that the temperature of the mixture which the compressor ( 11 ) is maintained at a predetermined value. A method according to claim 1, characterized in that the amount of ambient air supplied is controlled to reduce the oxygen concentration in the combustion gases below about ei per cent.