Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-03-02
2001-11-06
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S737000, C060S039463, C239S402000, C239S403000, C239S424000, C431S181000
Reexamination Certificate
active
06311473
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a fuel injection apparatus and method for pre-mixing fuel and air for combustion in a turbine combustion system.
BACKGROUND OF THE INVENTION
In a typical turbine engine, air is compressed, then mixed with fuel, and the resulting mixture is ignited in a combustor, so that the expanding gases of combustion can rapidly move across and thus rotate the turbine blades. The fuel can be liquid (e.g., Diesel Fuel #2) or gaseous (e.g., methane) or both, and the turbine can be an axial flow or a radial in-flow type. Such turbine engine can be used for industrial power or moving an airplane or ground vehicle. Variable or fixed turbine vanes direct the expanded gases from the combustor to the rotatable turbine blades.
Air polluting emissions are an undesirable bi-product of turbine engines. The primary air pollution emissions produced by turbines burning conventional hydrocarbon fuels are oxides of nitrogen (NO
x
), carbon monoxide (CO) and unburned hydrocarbons. It is well known that oxidation of molecular nitrogen in air-breathing engines is dependent upon the flame temperature in the reaction zone. The rate of chemical reactions forming oxides of nitrogen is an exponential function of temperature. Consequently, if the flame temperature is controlled to a low level, thermal NO
x
production will be reduced.
A typical and preferred method of controlling the temperature of the reaction zone of a turbine combustor below the level at which thermal NO
x
is formed consists of pre-mixing the fuel and air to a lean mixture prior to combustion. The mass of the excess air present in the reaction zone of a lean, pre-mixed combustor absorbs heat and reduces the temperature rise of the products of combustion to a level where NO
x
production is substantially reduced. However, the fuel/air mixture strength should be somewhat higher than the lean flammability limit in order to prevent or eliminate combustion oscillations. It is generally known that lean, pre-mixed combustors tend to be less stable than more conventional diffusion flame combustors and do not provide adequate turn down for operation over the entire load range of the turbine. Stability for operation over all load conditions required for turbine operations, with minimum emissions of air pollutants in the turbine exhaust, is an ongoing challenge in the industry.
For liquid fuel turbine engines, another challenge is that it is desirable to pre-vaporize the fuel prior to entry into the combustion chamber. Pre-vaporizing the liquid fuel maximizes the combustion efficiency of the engine and minimizes pollution and stability problems. However, it is believed that in even the most efficient systems, full pre-vaporization of the fuel has not been achieved, that is, the fuel is not completely pre-mixed at the molecular level with the air prior to combustion. Consequently, flame temperature and NO
x
formation rates are higher than what is believed achievable in fully pre-mixed, pre-vaporized systems. Steam and/or water are many times injected into the. combustor primary zone to reduce and control formation of the oxides of nitrogen. However, the additional requirement of a steam and/or water injection system greatly increases the capital operating and maintenance costs of the turbine.
Another method of NO
x
control is with the use of catalytic combustors. This technique also raises capital, operating and maintenance costs issues with the turbine. There are also technological issues, such as material and structural integrity of the catalyst under high temperature and thermal cycling conditions, which must be resolved. It is also believed that the use of catalytic combustion has not been successfully demonstrated for oil fired combustion turbines.
As such, it is believed that there is a demand in the industry for an improved fuel injection apparatus for a turbine combustion system, where the system has clean and stable operation, and which does not require secondary control of NO
x
formation.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a novel and unique fuel injection apparatus for a turbine combustion system which vaporizes the liquid fuel and thoroughly and completely mixes liquid fuel with air prior to ignition in the combustion chamber for clean, stable combustion. The apparatus does not require secondary systems for the control of NO
x
emissions.
According to the present invention, the fuel injection apparatus includes one or more liquid fuel dispensing nozzles at an upstream end of the injector housing. Gaseous fuel nozzles can also be provided. At least one, and alternatively two (or more) radial inflow swirlers are longitudinally spaced apart from one another downstream from the fuel dispensing nozzles. The radial inflow swirler(s) direct air radially inward in a swirling motion to cause the fuel streams to swirl and thoroughly mix with air in the housing. The axial staging of the radial inflow swirlers reduces droplet dispersion towards the walls of the injection apparatus. Since the swirling flow is introduced incrementally along the injector housing, the swirl number of the air entering the housing increases from the base of the housing to its exit. Liquid fuel is introduced at the base of the housing in regions of low swirl intensity thereby minimizing droplet lateral dispersion and deposition on the walls of the housing. Most of the swirl is introduced towards the exit of the injection apparatus where the mean droplet size has decreased substantially as a result of droplet vaporization. It is to be noted that small droplets are less affected by the centrifuging action of the swirling flow field thereby reducing fuel flux towards the injection apparatus walls.
The liquid fuel nozzles have a macrolaminate structure and are configured to provide fine, conical sprays of fuel. The liquid fuel nozzles and gaseous fuel nozzles are supported at an annular arrangement substantially perpendicular to the longitudinal axis of the housing, with the gaseous fuel nozzles in alternating circumferential relation with the liquid fuel nozzles.
The annular arrangement of gaseous fuel nozzles includes a series of such nozzles between each of the liquid fuel nozzles. The series of gaseous fuel nozzles are arranged in radial spokes projecting outwardly from the longitudinal axis of the housing between the liquid fuel nozzles. The fuel passages in the gaseous fuel nozzles disposed radially further away from the longitudinal axis of the housing are larger to optimize the distribution of gaseous fuel in the housing.
An outer annular flow passage surrounds the nozzles to direct air in a cylindrical sheet around the fuel streams. Individual annular flow passages also surround each of the liquid fuel nozzles. The air flows vaporize the liquid fuel spray as it passes downstream through the housing. The air flows also provide momentum to carry the liquid and gaseous fuel through the housing and penetrate the swirling air provided by the swirlers, and prevent fuel accumulation along the walls of the housing.
An inner air passage is supported centrally in the housing to direct air in the downstream direction centrally of the fuel streams. The inner air flow prevents recirculating zones in the upstream end of the housing and also assists in vaporizing and providing momentum to the fuel.
After the vaporized fuel and air are thoroughly and completely mixed in the housing and are traveling in a swirling motion, the mixture passes into the combustor where the mixture is ignited to rotate the turbine blades.
A method is also provided for pre-mixing fuel within an injector for a turbine engine, including i) spraying liquid fuel through one or more nozzles in the housing; ii) vaporizing the fuel air as the fuel passes downstream through the housing; iii) thoroughly and completely mixing the vaporized fuel with swirling air such that the mixture is traveling in a swirling motion; and iv) directing the swirling mixture into a combustion chamber of the turbine for clean, stable combustion.
Gaseous fuel c
Benjamin Michael A.
Mansour Adel B.
Hunter Christopher H.
Kim Ted
Parker-Hannifin Corporation
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