Fluctuating fuel prices, unabated energy sustainability concerns, and waste energy byproducts generated in industry have created the opportunity to develop fuel flexible combustion systems. A combustion system's capability to handle multiple liquid fuels depends on the fuel injector. Most combustion applications have limited fuel flexibility mainly because of the strong dependence of the injector performance on physical and chemical properties of the fuel. Thus, an ideal fuel injector would perform robustly with minimal dependence on fuel properties. The most common fuel injection techniques are: pressure driven as in direct injection systems, and kinetic energy driven as in twin-fluid atomizers. Less commonly used techniques include centrifugal energy driven atomization as in rotating discs, and effervescent, flashing, electrostatic, vibratory, and ultrasonic atomizers.
Twin-fluid injectors utilize kinetic energy provided by a gas introduced in the injector system, mainly for the purpose of enhancing atomization of the liquid fuel. An air-blast (AB) injector is a typical example of a twin fluid atomizer. In AB atomization, atomizing air and liquid are supplied separately to the injector. Air is delivered and swirled on the outer periphery of the injected liquid fuel at a relatively large velocity to break up the ejected fuel and to disperse the resulting spray in the combustion zone. The primary driving force of liquid break up and droplet formation is by the shear forces formed because of the high relative velocities between the two phases. However, a major shortcoming of this technique is that in highly viscous liquids such as glycerol or straight vegetable oils, or other alternative and opportunity fuels, shear layer instabilities are suppressed, giving rise to less effective droplet break up or larger droplet diameters in the spray.
Another twin fluid injector is an effervescent atomizer (EA). In EA, a pressurized gas is injected into the bulk liquid fuel inside an atomizer body, upstream of a nozzle orifice from which the fuel-air mixture is ejected into the combustion zone. Bubbles formed by the injected gas are then expanded rapidly when the two-phase mixture is exposed to a low pressure zone at the orifice exit, breaking up the liquid into droplets. EA is reported to produce a spray with very fine droplets. However, this method has known drawbacks in that the spray angle is usually narrow and atomizing air must be pressurized to the fuel supply pressure. This pressurization can be difficult to accomplish and might require large amounts of power. In addition, the spray produced can exhibit undesirable unsteadiness related to two-phase mixing flow processes in the channel downstream of the mixing chamber.
Accordingly, an improved fuel-flexible combustion system is needed that yields low emissions, requires low power, is suitable for alternate liquid fuels including highly viscous processed or unprocessed fuels, and can be scaled to different heat release rates.
Various implementations include a fuel injector that includes an inner injector tube, an outer injector tube, a spacer ring, and an orifice plate. The inner injector tube includes an outlet portion defining an outlet and a choke portion. The choke portion is disposed below the outlet 10 D to 20 D, wherein D is the inner tube diameter. The outer injector tube is spaced radially apart from at least the outlet portion of the inner injector tube. The outer injector tube has an outer injector tube outlet disposed radially adjacent the outlet of the inner injector tube. The spacer ring includes an annular wall that defines a central axial opening and has an upper annular surface. The orifice plate defines a central opening that has an inlet side and an outlet side. The central opening defines a frustoconical cross-sectional shape as taken along a central axis extending through the central opening. An inner diameter of the inlet side is smaller than an inner diameter of the outlet side, and the inner diameter of the inlet side is substantially the same as an inner diameter of the outlet of the inner injector tube. And, the central opening of the orifice plate is co-axial with and spaced above the outlet of the inner injector tube.
In some implementations, the choke portion is a venturi constriction portion having an inner diameter that is smaller than the inner diameter of the outlet of the inner injector tube. In some implementations, the choke portion is a check valve.
In some implementations, the choke portion is integrally formed in the inner injector tub, and in other implementations, the choke portion is formed separately from the inner injector tube and disposed therein.
In some implementations, the choke portion is disposed 10 D to 20 D below an outlet of the inner injector tube.
In some implementations, the choke portion has an inner diameter of between 0.2 D and 0.4 D.
In some implementations, the upper annular surface of the spacer ring defines a plurality of axial slots, and the spacer ring is disposed adjacent the outlet of the inner injector tube, the outer injector tube outlet, and the inlet of the orifice plate such that the central opening of the orifice plate and the outlet of the inner injector tube are co-axial with the central axial opening of the spacer ring. In a further implementation, the annular wall further defines a plurality of radially extending openings, and the radially extending openings are defined circumferentially between the axial slots and are spaced apart circumferentially around the annular wall. In some implementations, each axial slot has a height that is at least 0.2 D and a width that is twice the height of the slot, wherein the width is measured in a direction that is tangent to a circumference of the annular wall.
Various other implementations include a combustor assembly that includes a fuel injector, such as described above, and a swirler. The swirler is disposed radially outwardly and adjacent the outer injector tube outlet. The swirler includes a central hub, a first plurality of vanes extending therefrom a first angle greater than 0 degrees from a plane extending perpendicular to a central axis of the central hub, and a second plurality of vanes disposed radially outwardly of the first plurality of vanes and at a second angle greater than 0 degrees from the plane, wherein the swirler is in fluid communication with a gas supply plenum adjacent an inlet side of the swirler and a combustion housing adjacent an outlet side of the swirler.
In some implementations, the choke portion is disposed 10 D below the outlet of the inner injector tube.
In some implementations, the first and second plurality of vanes are disposed at an angle of 30 degrees relative to the plane.
The components in the drawings are not necessarily to scale relative to each other and like reference numerals designate corresponding parts throughout the several views:
According to various implementations, a combustor assembly is described that yields low emissions, requires low pumping power, is suitable for conventional and alternate liquid fuels, including highly viscous processed or unprocessed fuels, and can be scaled to different heat release rates. The combustor assembly according to certain implementations includes a FB injector.
A twin-fluid atomization technique known as Flow Blurring (FB) atomization was recently proposed by A.M. Gañán-Calvo. This technique is reported to produce finer droplets with up to fifty times the surface area to volume ratio and atomization efficiency of tenfold when compared to AB atomization.
The injector, according to various implementations, uses the FB atomization technique shown in
In some implementations, the space between the outlet of the inner injector tube and the orifice plate is precisely controlled by a spacer.
In addition, in some implementations, the combustor assembly also includes a swirler disposed radially adjacent an exit plane of the FB injector. The swirler may be a single, double, or multi-vane swirler. The swirler may include a plurality of angled vanes that cause gas, such as air, a combustible gas or a mixture of gases, to swirl upon exiting the swirler. The swirled gas assists with breaking up any remaining fuel streaks that exit the orifice plate, and assist in pre-vaporizing the fuel, which results in low emissions. Smaller applications may include a single vane swirler and larger applications may include a double swirler, according to some implementations.
Furthermore, according to various implementations, the combustor assembly may be used in small or large heat release rate environments. The combustor assembly is a dual fuel burner and as such it may use gaseous fuels and liquid fuels separately or both gaseous and liquid fuels at the same time. In addition, the dual fuel combustor assembly may have a smaller capacity, such as between 5 kWth and 10 kWth capacity (e.g., 7 kWth capacity) or a larger capacity, such as between 60 kWth and a 100 kWth capacity.
The orifice plate 203 defines a central opening having an inlet side 211 and an outlet side 213 along the axis A-A. The central opening includes a portion 215 defining a frustoconical-shaped opening and a portion 216 defining a cylindrical-shaped opening. The frustoconical portion 215 extends between an outlet side 213 of the plate 203 and the cylindrical portion 216 such that an inner diameter of the frustoconical portion 215 decreases along the axis A-A from the outlet side 213 to the cylindrical portion 216, and the cylindrical portion 216 extends between an inlet side 211 of the plate 203 to the frustoconical portion 215. An inner diameter of cylindrical portion 216 is smaller than the inner diameter at the outlet side 213 of the central opening and is substantially the same as the inner diameter D of the outlet 205 of the inner injector tube 201. The inlet side 211 of the orifice plate 203 is spaced axially above the outlet 205 of the inner injector tube 201 by a distance H, which is a quarter of the diameter D of the outlet 205 of the inner injector tube 201. The outlet side 213 of the central opening is within the dump plane 32 of the assembly 10.
The outer injector tube 202 is spaced apart radially outwardly from the inner injector tube 201 and defines a space 202a between an inner wall of the outer injector tube 202 and the outer wall of the inner injector tube 201 through which pressurized gas flows. The outer injector tube 202 includes an outlet portion 207 adjacent the outlet 205 of the inner injector tube 201. In particular, the outlet portion 207 is defined by the usually tapered portion 209 of the inner injector tube 201 and a portion of the orifice plate 203 that is adjacent the inlet side 211 of the central opening.
Pressurized liquid fuel flows through a liquid fuel inlet into the inner injector tube 201. In addition, pressurized gas flows through an atomizing gas inlet into the space 202a. This pressurized gas is forced through the outlet 207 and between the outlet 205 of the inner injector tube 201 and the inlet side 211 of the central opening of the orifice plate 203. The pressurized gas turns radially as it enters this space, and a stagnation point develops somewhere between the outlet 205 of the inner injector tube 201 and the inlet side 211 of the orifice plate 203. Thus, the pressurized, or atomizing, gas flow is bifurcated about the stagnation point, with part of the gas being directed upstream into the inner injector tube 201 and the rest flowing out through the orifice plate 203. The back flow gas that enters the inner injector tube 201 results in bubbling and turbulent two-phase mixing with the incoming liquid fuel. Exemplary pressurized gases may include air, steam, gaseous fuels such as natural gas or propane, nitrogen, and oxygen.
A spacer ring with a plurality of slots and/or holes is used to precisely control the geometry, and thus, bifurcation of the atomizing gas, between the outlet 205 of the inner injector tube 201 and the inlet 211 of the orifice plate. For example, as shown in
The upper surface 42 defines a plurality of slots 44, or axial depressions, that extend axially inwardly from the upper surface 42 and are spaced apart from each other. For example, the implementation shown in
The choke portion 206 creates an area of high pressure just downstream of the choke portion 206 to prevent the pressurized gas from flowing past it and potentially hindering or slowing the flow of the liquid fuel through the inner injection tube 201. In certain implementations, the choke portion 206 may include a venturi constriction portion having a reduced diameter as compared to the inner diameter of the inner injector tube 201 or a valve. In addition, the choke portion 206 may be integrally formed with the inner injector tube 201, such as by pinching the tube 201 radially inwardly at the location for the choke portion 206 or molding or otherwise forming the choke portion 206 within the inner injector tube 201.
Alternatively, the choke portion 206 may be formed separately and inserted into the inner injector tube 201. In one implementation where choke point is located 10 D to 20 D upstream of the outlet 205 of the inner injector tube 201, the diameter at the choked point can be 0.2 D to 0.4 D, the upstream converging length can be 2 D, and the downstream diverging length can be 4 D, where D is the diameter of the inner injector tube 201.
The swirler 25 is disposed circumferentially around and adjacent to the FB fuel injector 20 and swirls a primary gas and/or a gaseous fuel mixture into the combustion housing 30. In particular, as shown in
A primary gas-gaseous fuel mixture flows through an inlet side of the swirler 25 and out of an outlet side of the swirler 25 into the combustion housing 30. The primary gas and/or gas mixture exiting the swirler 25 assists with breaking up any non-atomized streaks of liquid fuel that may exit the outlet side 213. Substantially atomized fuel exiting the outlet side 213 of the orifice plate 203 vaporizes and mixes with the primary gas and/or gaseous fuel mixture, and then combusts within the housing 30. A portion of heat from the combustion also reaches upstream to preheat the primary gas and/or gas mixture products, which helps to quickly pre-vaporize the liquid fuel, allowing it to burn cleanly and resulting in low emissions.
For larger scale industrial applications, such as for burners having a capacity of over 60 kWth, the swirler of the combustor assembly may include an enlarged, or double swirler, such as is shown in
Furthermore, dual fuels (combined liquid fuel-gaseous fuel operation) may be selected to yield fuel flexibility and/or more power. This increase in capacity is achieved because the gaseous fuel supply system is independent of the liquid fuel injector design.
When scaling the fuel injector assembly for small or large combustion applications, the scaling may be based on constant velocity scaling criterion. This criterion ensures that the residence time inside the combustion chamber is independent of the HRR. Thus, to keep the flow velocities within an acceptable or optimal range (e.g., flow velocities are within 50% of each other for various capacities), several cross sectional areas may be increased by a certain factor. For example, when increasing the capacity of a combustion system from 7 kW capacity to 60 kW capacity, several cross sectional areas may be increased by an average factor of around 9. For example, most circular diameters may be increased by a factor of around 3. For areas in which there may be a limit on maximum allowable dimension, care is taken to ensure that the flow velocity does not exceed the acceptable range, and proportionate dimension may be added to counter the effects of increases in velocity. These modifications may be implemented on the fuel injector, swirler, dump plane, combustion enclosure, and the upstream mixing tube. The length of the burner housing 30 is nearly the same for different scale combustion systems.
The combustor assembly may be used for combusting diesel, straight vegetable oil, and glycerol fuels, for example. However, other fuels may be used with this combustor assembly, such as bunker oil, minimally processed crude oil, fuels produced from algae, liquid chemical waste, conventional fuels, high viscosity fuels, alternative fuels, biofuels, and opportunity and waste fuels. In addition, this combustor assembly may use alternative gases such as steam, natural gas, and propane for the atomizing gas and/or various gaseous fuels for the primary gas flow through the swirlers.
The combustor assembly according to various implementations of the invention produces smaller droplets of fuel as compared to the AB technique and has the capability of burning fuels of very high viscosity, including straight vegetable oil (VO) and glycerol with low emissions. Since the injector tube outlet diameter and orifice exit diameter are large, the injector is not subjected to clogging by fuel contaminants or by fuel oxidation caused by heating of the fuel.
Fuel flexible, clean combustion has distinct importance for solving some of the environmental and economic concerns associated with alternative, waste, and minimally processed liquid fuels. For example, crude glycerol is generated as a byproduct of biodiesel production. Crude glycerol is considered as waste because, despite its significant energy content of 16 MJ/kg, it is very difficult to atomize and burn with traditional injectors. Thus, in its crude form, it has been of limited use. However, a combustor assembly according to various implementations, such as those described above, may allow the crude glycerol to be combusted for heat generation.
Thus, various implementations of the above described combustor assembly address several concerns that arise when applying air with the FB atomization technique to produce liquid fuel spray in combustion systems. In particular, the choke prevents back flow air entering the fuel tube from flowing too far down the fuel tube and blocking the fuel from flowing through the fuel tube, especially during the transients. In addition, the swirler prevents streaks of fuel in the combustion zone, which may be of particular concern when the fuel is highly viscous. These streaks of fuel do not burn as cleanly as droplets. Furthermore, the above described systems may be scalable for small scale to large scale industrial applications. Finally, the above described implementations of the spacer ring decrease the atomizing gasflow rate through the injector, which reduces the power consumption.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The implementation was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various implementations with various modifications as are suited to the particular use contemplated.
This application claims priority to U.S. Provisional Patent Application No. 62/321,288, filed Apr. 12, 2016, and entitled “COMBUSTOR ASSEMBLY FOR LOW-EMISSIONS AND ALTERNATE LIQUID FUELS,” the entire disclosure of which is incorporated herein by reference.
This invention was made with government support under grant no. DE-EE0001733 awarded by the Department of Energy. The government has certain rights in the invention.
Number | Date | Country | |
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62321288 | Apr 2016 | US |