EP0073830B1

EP0073830B1 - Fuel combustor

Info

Publication number: EP0073830B1
Application number: EP82901239A
Authority: EP
Inventors: John A. Hardgrove; Charles L. Dailey; Hideo Iwata; Douglas B. Sheppard
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1981-03-17
Filing date: 1982-03-11
Publication date: 1988-01-13
Also published as: CA1181998A; NL8220118A; EP0073830A4; JPH0259362B2; DE3237454T1; ZA821798B; PL235462A1; WO1982003261A1; AU8331382A; IT8267327A0; JPS58500420A; IT1155634B; MX160386A; DE3237454C2; AU551776B2; IL65224A0; DK509582A; EP0073830A1

Abstract

A combustor and a corresponding method for its operation, wherein the fuel, which is pulverized coal in the illustrative embodiment, is first reacted with at least a portion of oxidizer gas flow directed to the head end (20) of the combustor. Combustion in the head end proceeds at a substantially lower stoichiometric ratio than the overall ratio for the combustor, which therefore operates at a relatively low temperature and high thermodynamic efficiency, while maintaining good slag removal characteristics. Of the several embodiments disclosed, one group has an oxidizer inlet (12) from which oxidizer gas splits into a component directed toward the head end, where the first phase of combustion takes place, head-end and a component directed toward the exit end (18), where a second phase of combustion takes place. In another group of embodiments, oxidizer is directed only toward the head-end, and the resultant exiting gas is rich in combustibles.

Description

Background of the Invention

This invention relates generally to fuel combustors, and, more particularly, to a slagging combustor in which the fuel is pulverized coal. In the combustion and gasification of coal, non-combustible ash and mineral components cannot be allowed to accumulate within the combustion chamber, or serious operational problems will be experienced. In a slagging combustor, the temperature in the chamber is maintained high enough to allow the slag to be removed in liquid form by the action of shear forces and/or gravitational forces acting on the slag. This slagging capability will also have benefits related to operation of downstream equipment interacting with the product flowstream.
A slagging combustor may have different requirements, such as overall stoichiometry, imposed on it by the characteristics of a downstream process utilizing the products of combustion. However, regardless of these different requirements an ideal slagging combustor should have good slag recovery characteristics and should operate at a relattively low temperature, to minimize heat losses and maximize efficiency.
The degree of combustion of the coal in a slagging combustor will depend in part on the intended application of the gaseous products of combustion. For example, if the combustor is to be employed to produce gas for use as a fuel in a conventional power generation plant, or in chemical processes, the gases exiting from the combustion chamber should still be relatively rich in combustibles. Accordingly, if a coal combustor is to be used as such a gas generator, the combustion process should take place in a relatively fuel-rich environment. In terms of stoichiometry, a stoichiometric ratio as low as 0.3 might be desirable for subsequent combustion in a boiler or use as feed stock in a chemical process. If the gas were to be immediately employed in a combustion or heat exchange process, it might be desirable to provide a gas at a higher temperature, but with a lower equivalent heat value in the combustibles in the gas. This could be done by more completely combusting the coal in the slagging combustor, i.e. at a higher stoichiometric ratio.
By way of further example, the desired stoichiometry of a slagging combustor would be substantially different if the output gases were to be used in a magnetohydrodynamic (MHD) electric power generator. An MHD generator utilizes a high-temperature, high-velocity plasma which is passed through a magnetic field to generate electricity directly, without the use of rotating machinery. For such an application, the gaseous products from the slagging combustion stage may be lower in combustibles content and higher in temperature and heat content. The products of combustion may then be subject to further combustion after leaving the slagging combustor. Additional oxidizer, and sometimes additional fuel, may be added to the exiting gases for this purpose. Regardless of the end use to which the products of combustion are put, and the different requirements thereby placed on the combustor, the slagging combustor should still ideally provide good slag recovery and relatively low operating temperatures.
In any application of a coal combustor, the desired stoichiometry of the combustion process will depend on the requirements of the downstream application. Acceptable combustor operation and combustion product properties will also be dependent on the temperature and composition of the oxidizer gas, and the type and size of the coal particles. Selection of the appropriate parameters, to satisfy the requirements of the downstream application, typically involves a number of practical design trade-offs. For example, preheating the oxidizer gas to a higher temperature and thereby permitting reactions at a lower stoichiometric ratio might still meet the requirements of the downstream application, but would obviously require either the consumption of more energy in the preheating stage or the addition of a heat exchanger. The first of these alternatives may or may not comport with the overall energy requirements of the application, and the second may not even be feasible.
Furthermore, appropriate choice of the stoichiometric ratio in a slagging combustor is of critical importance to the rate of slag recovery. If the ratio is too low, temperatures will also tend to be low, and the slag may not liquify sufficiently to facilitate recovery. Conversely, if the ratio is too high, the temperature may be so high that a significant proportion of the slag is lost by vaporization. In theory at least, the effective slagging range has been thought to lie about 0.4 and up to 1.0 for the combustor as a whole. However, the stoichiometry desired to meet the requirements of the downstream application may not fall within this theoretical slagging range. For example, if the combustor is to act as a gas generator, a stoichiometric ratio as low as 0.3 might be preferred.
In any event, it will be appreciated that a coal combustor of this general type should ideally be capable of matching the overall combustor stoichiometry, and other characteristics of the slagging combustor, with the requirements of the downstream application of the combustor. Furthermore, the slagging combustor should provide a high rate of slag recovery, a relatively low heat loss, and therefore a relatively high thermal efficiency. In addition, there should be complete fuel utilization, i.e., no uncombined carbon should leave the combustor. In prior art combustors, it has not been possible to satisfy all of these objectives simultaneously. For example, good slag recovery, in conventional combustors, is not consistent with a relatively low temperature and low stoichiometric ratio.
U.S.-A-4,217,132 to Burge et al. proposes one solution to these problems by combining an axial and a tangential flow of oxidizing gas, so that the combustion of the fuel particles is essentially complete before the particles impinge on the walls of the combustion chamber. Although this technique is satisfactory in many respects, it fails to address the particular problems outlined above. In at least one respect, the Burge et al. patent is typical of prior art coal combustion techniques in that the oxidizer gas flows in a continuous pattern in which there is an axial velocity component directed from the head end to the exit end. No combustors operating on this principle combine good slag recovery, low heat loss and complete carbon burnout under all operating conditions of interest.
There is, therefore, a significant need for a coal combustor which can provide high thermodynamic efficiency and acceptably high rates of slag removal, and be adaptable to match the thermodynamic needs of a downstream process or application. The present invention satisfies this need.
According to the present invention, there is provided a fuel combustor comprising a combustion chamber having a head end and an opposite exit end, fuel inlet means for feeding particulate solid fuel into said chamber at said head end, oxidizer inlet means for feeding oxidizer into the chamber in a substantially tangential direction to produce high velocity rotational flow within the chamber, an outlet for exhausting combustion products from the exit end of said chamber, a slagging baffle between said ends and a slag tap for removing slag from said chamber; said com- 'bustor being characterised in that said oxidizer inlet means is located between said ends and is adapted to effect flow of a portion of the oxidizer toward said head end of said chamber and flow of the remainder of the entering oxidizer toward said exit end of the chamber in such proportions that said fuel and said oxidizer portion react within said head end of the chamber in a first phase of combustion at a relatively low stoichiometric ratio and a correspondingly low temperature to allow liquefaction of the slag content of the entering fuel with minimal vaporization, the rotational flow causing the liquid slag to be centrifuged onto the chamber wall for removal by said slag tap, the remainder of the entering oxidizer gas reacting with the combustion products of the first phase of combustion near said exit end of the chamber in a second phase of combustion to provide an overall stoichiometric ratio which is substantially higher than that of said first phase.
The present invention resides in a slagging coal combustor, having a head end and an exit end, in which oxidizer is introduced in such a manner that at least a portion of it flows away from the exit end and toward the head end, coal being introduced into the oxidizer flowing toward the head end, to provide an initial phase of combustion in the head end. Combustion in this first phase can take place at a stoichiometric ratio much less than that of the combustor as a whole.
Although conceived for the purpose of solving a problem experienced in coal combustors, the invention has application as well to combustors of other fuels. The essential elements of the invention in its broadest sense are means for introducing oxidizer in such a manner that a portion of it flows toward the head end, and means for injecting fuel into this oxidizer portion to provide the first phase of combustion in the head end.
Basically, and in general terms, the invention in its form as a pulverized coal combustor comprises a combustion chamber having a head end and an exit end, means for injecting pulverized coal into the head end, means for injecting oxidizer gas peripherally into the chamber, means for removing non-combustible slag from the chamber, and means located at the exit end to provide an exit for the essentially gaseous products of combustion. Most importantly, the means for injecting oxidizer gas and pulverized coal are so configured that a portion of the oxidizer gas stream flows toward the head end of the chamber and is there reacted with the coal fuel in the first phase of combustion. In one embodiment of the invention, gases from the first phase of combustion are further combusted with the remaining portion of the oxidizer gas, which flows toward the exit end of the chamber. In this embodiment, the stoichiometric ratio in the first phase of combustion in the head end, which is approximately one half of the overall ratio for the combustor, may, for example, be as low as 0.3 for some designs. Contrary to generally accepted practice with respect to effective slag removal, extremely good slag removal characteristics can be obtained in this low stoichiometric range.
When used for supplying high-temperature gases to an MHD generator, the combustor of the invention operates at an overall stoichiometric ratio selected to provide the best combination of slag recovery characteristics in the head end and exit gas conditions matching the requirements of the MHD generator. In a presently preferred embodiment, an overall ratio of approximately 0.6 is used, with a ratio of approximately 0.3 in the head end.
The oxidizer gas, when introduced tangentially into the combustion chamber, splits into two streams. One stream has an axial velocity component directed toward the exit end of the chamber while the other portion has an axial velocity component directed toward the head end, into which the fuel is injected. In one preferred embodiment of the invention, the two streams are approximately equal in volumetric flow rates. Because the fuel is initially combusted with a relatively low volume of oxidizer, first-phase combustion at the head end of the chamber takes place at a relatively low stoichiometric ratio. There is a correspondingly low reaction temperature and a relatively high efficiency, because of the reduced heat loss at the lower temperature. However, highly effective slag removal is obtained in these conditions. In short, the slagging stage is more efficient thermodynamically, and provides excellent slag recovery. Unburned gases from the first combustion phase then react with the remaining or exit-end stream of the oxidizer gas, and this second phase of combustion takes place at a higher stoichiometric ratio. For example, if the downstream application of the combustor is an MHD generator, the overall ratio can be approximately 0.6 to 0.9, with a corresponding head-end ratio of 0.3 to 0.45. Because of a relatively high temperature in the exit end, it may be made relatively shorter in length than is possible in a conventional combustor of the same type. This reduces the heat loss from the chamber and improves the overall thermodynamic efficiency of the combustor.
Coal injection into the first-phase combustion zone can be effected by a pintle nozzle disposed axially in the head end and directing fuel flow into that portion of the oxidizer gas flowing toward the head end. Alternatively, fuel can be injected through fuel inlets disposed peripherally around the chamber, to direct the flow into the head-end portion of the oxidizer gas flow.
Both horizontal and vertical configurations of the chamber are contemplated. In the horizontal configuration, the means for removing slag from the chamber includes a slag port disposed at the bottom portion of the cylindrical wall of the chamber. In the vertical configuration, the head end of the chamber is the lowermost end and the exit is the uppermost. The slag port is located at the head-end.
In terms of a novel method, the invention in its broadest terms comprises the steps of injecting oxidizer gas peripherally into a chamber having a head end and an exit end, in such a manner that a portion of the flow is directed towards the head end, injecting fuel, such as pulverized coal, into the head end in such a manner that combustion takes place initially at a relatively low stoichiometric ratio and low temperature, regardless of the end use of the gaseous products of combustion and regardless of the overall stoichiometry of the combustor, removing any non-combustible slag from the chamber, and allowing the essentially gaseous products of combustion to exit the chamber. More specifically, the steps of injecting oxidizer gas and injecting pulverized coal include injecting the oxidizer gas tangentially into the chamber at a point between the head end and the exit end of the chamber such that the oxidizer gas flow splits into two approximately equal portions having opposite axial components, and injecting the pulverized coal into the oxidizer gas portion flowing toward the head end, wherein a first phase of combustion occurs in the head end at a stoichiometric ratio of approximately one half of the overall stoichiometric ratio for the combustor.
It will be appreciated from the foregoing that the present invention represents a significant advance in the field of coal combustion and gasification. In particular, a novel coal combustor achieves good slag removal rates while attaining high thermodynamic efficiency, low heat loss and complete burning of carbon. Moreover, the combustor of the invention allows for convenient matching of its thermodynamic characteristics with those of a desired downstream process. Other aspects and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a simplified perspective view of a coal combustor embodying the present invention, including the slagging combustor and slag removal apparatus, and also showing an exit combustion stage which is not part of the invention;
FIG. 2 is a diagrammatic view of the slagging combustor;
FIG. 3 is a fragmentary sectional view of a pintle nozzle used to inject coal and, for MHD and other selected application, an additive material, into the combustor;
FIG. 4 is a diagrammatic view showing typical flow patterns of fuel, oxidizer gas and combustion products within the slagging combustor;
FIG. 5 is a diagrammatic elevational view showing the configuration of a first embodiment of the invention, having a tangential oxidizer inlet and a volute exit port;
FIG. 5a is an end view of the embodiment shown in Fig. 5, taken in the direction of the arrow 5a in Fig. 5;
FIG. 6 is a diagrammatic elevational view showing a second embodiment of the invention, having a tangential oxidizer inlet, a symmetric exit port and a shortened exit end portion;
FIG. 6a is an end view of the embodiment shown in Fig. 6, taken in the direction of the arrow 6a in Fig. 6;
FIG. 7 is a diagrammatic elevational view of a third embodiment of the invention similar to the second embodiment shown in Fig. 6 but having the slag tap located in the head end rather than the exit end;
FIG. 7a is an end view of the embodiment shown in Fig. 7, taken in the direction of the arrow 7a in Fig. 7;
FIG. 8 is a diagrammatic elevational view showing a fourth embodiment of the invention having a recessed volute oxidizer inlet, a symmetric exit port and a head-end slag tap;
FIG. 8a is an end view of the embodiment shown in Fig. 8, taken in the direction of the arrow 8a in Fig. 8;
FIG. 9 is a diagrammatic elevational view of a fifth embodiment of the invention having two slagging combustors, each with a recessed volute oxidizer inlet, and a head end with a fuel injector and a slag tap, the two combustors being matched to a common, centrally located exit port;
FIG. 10 is diagrammatic elevational view showing a sixth embodiment of the invention with a vertically oriented combustion chamber, a recessed volute oxidizer inlet, a symmetric exit port, peripheral coal injectors, and a head-end slag tap;
FIG. 10a is a plan view of the embodiment shown in Fig. 10.
FIG. 10b is a sectional view of the embodiment shown in Fig. 10, taken substantially along line 10b-10b in Fig. 10;
FIG. 11 is a diagrammatic elevational view of a seventh embodiment of the invention having a vertically oriented combustion chamber similar to that shown in Fig. 10, but including an inlet flow diverter to divert all of the inlet oxidizer flow to the head end of the chamber; and
FIG. 11a a is a sectional view of the embodiment shown in Fig. 11, taken substantially along line lla-lla in Fig. 11.

Description of the Preferred Embodiments

As shown in the drawings for purposes of illustration, the present invention is principally concerned with a pulverized coal combustor, and more particularly with a slagging coal combustor. In slagging coal combustors, the non-combustible ash and mineral components of the coal are removed in liquid form, so that these constituents do not remain in the gases produced by the combustor.
Designers of coal combustors in the past have striven for efficient slag removal, low heat loss, high thermodynamic efficiency, complete burning of carbon, and appropriate matching of the thermodynamic characteristics of the combustor with the requirements of downstream processes utilizing the products of combustion. Ideally, for example, a coal combustor should be adaptable to provide gas to an MHD generator, or to provide fuel gas for subsequent burning in boilers or in other chemical processes, and still should maintain a high rate of slag recovery and a high thermal efficiency. Prior coal combustors have traditionally employed an oxidizer flow pattern having an axial component directed towards the exit end, and have not been able to achieve the desired combination of ideal characteristics.
In accordance with the present invention, a coal combustor is provided with fuel and oxidizer injection means which cooperate in such a manner that combustion takes place initially in the head end of the combustor at a relatively low stoichiometric ratio, regardless of the end use of the gaseous products of combustion and regardless of the overall stoichiometry of the combustor. Extremely good slag recovery is provided at the relatively low local stoichiometric ratio in the head end, and heat losses are minimized, with a corresponding maximization of efficiency. A second combustion phase may optionally be provided to yield a higher overall stoichiometric ratio, for use in conjunction with an MHD generator, for example. If the second combustion phase is omitted, a relatively low overall stoichiometric ratio is then provided, such as when the combustor is operating as a synthesis gas generator.
As shown in Fig. 1, the apparatus of the invention includes a slagging coal combustor, indicated generally by reference numeral 10, and having a tangential oxidizer inlet 12 and an axial coal inlet 14. The combustor 10 comprises a generally cylindrical reaction chamber 16, shown as being disposed with its longitudinal axis horizontal, the cylinder having an exit end 18 through which the products of combustion leave the chamber, and a head end 20 into which the pulverized coal fuel is introduced. As shown in this illustrative configuration, the exit end 18 includes an exit assembly 22 usually referred to as the symmetrical type. As will be appreciated from Figs. 6a and 7a, a symmetrical exit is one in which the exit path followed by the products of combustion is symmetrical with respect to the axis of the combustor, i.e. the exit path extends from the center of the exit assembly, rather than being tangential or volute. The illustrative embodiment of Fig. 1 also includes a further exit combustion stage 24 into which further oxidizer and/or fuel may be introduced, through the inlet 26. This exit stage 24 is illustrative of a typical environment for the combustor, but is not essential to the present invention, since the slagging combustor will operate equally well without the exit stage.
As best shown in Fig. 2, unburned minerals or ash are removed as liquid slag from the chamber 16, through a slag port located low on the cylindrical wall of the chamber close to the exit end 18. The port is connected to a slag removal assembly 28, the details of which are not critical to the present invention. The entire chamber 16 and the oxidizer inlet 12 are cooled by a fluid, such as water, passed through coolant inlets 30 on top of the cylinder and emerging from coolant exits at the bottom, some of which are shown at 32. Cooling of the combustion chamber 16 produces a solidified layer of slag on the chamber walls. The solid layer of slag protects the chamber walls from erosion by liquid slag and by burning fuel particles, and also provides a relatively low conductivity insulating layer to reduce heat losses from the chamber. To provide better adhesion of the solidified slag layer to the chamber walls, the walls have a large number of upstanding pins affixed to them, as shown at 34 in Fig. 5. In one embodiment of the invention the pins 34 are approximately 1/8 inch (3.2 mm) in diameter and 1/4 inch (6.4 mm) long, welded to the chamber walls at approximately 3/4 inch (19.2 mm) spacing. The exit combustion stage 24 is used only in the event that it is required for matching the thermodynamic characteristics of the combustor with some downstream process, such as an MHD generator.
Fig. 2 shows in diagrammatic form the basic configuration of the slagging combustor. Oxidizer gas is introduced tangentially into the combustion chamber 16 through a rectangular port located between the head end 20 and the exit end 18. Fuel from the coal inlet 14 is dispersed along a generally conical spray having a substantial radial velocity component. In a presently preferred embodiment of the invention, a half angle of approximately 60° with respect to the central axis of the cylinder 16, is used. As best shown in Fig. 4, air from the oxidizer inlet 12 diverges into two separate paths, with respect to the axial component of flow of the oxidizer. That portion of the oxidizer flowing back towards the head end 20 will encounter fuel from the coal inlet 14, and combustion will take place in the head end at a stoichiometric ratio of approximately half the overall ratio for the entire combustor. Fuel particles leaving the nozzle 14 will be substantially heated as they traverse the head end to meet the oxidizer gas near the chamber walls. Thus, if the overall stoichiometric ratio is 0.58, as in an MHD generator application, the stoichiometric ratio in the first combustion phase in the head end will be approximately 0.29. For this MHD application, additional oxidizer is added in the inlet to the MHD generator (not shown).
Gases from the first phase of combustion will then move into a central region of the head end, near the axis, and will move generally along and near the axis and toward the exit end 18, where a further reaction will occur with the remaining portion of the oxidizer gas flowing towards the exit end. Combustion in this second phase of the combustor increases the overall stoichiometric ratio, such that the overall ratio is at the desired level. As shown in Fig. 4, there is also a small reverse core flow back through the exit port. It must be kept in mind, when referring to Fig. 4, that it represents only the axial and radial components of gas flow. Superimposed on this flow pattern is the rotational flow induced by the tangential introduction of the oxidizer gas. This rotational or cyclonic flow is important in that it provides a relatively long path over which burning of the fuel particles can take place and slag can be formed. The swirling action enhances fuel and oxidizer mixing, and directs entrained material outward to the wall surfaces.
An annular baffle 40 prevents, for all practical purposes, any flow of slag beyond the exit end 18 of the slagging combustor. Liquified slag, principally from the head end 20, flows towards the slag tap 28 under the effects of graviational force and shear force between the slag and the adjacent moving combustion gases. For the MHD and other selected applications of the combustor, an additive material may be injected axially with the coal fuel, as indicated at 41 in Fig. 2, to increase the electrical conductivity of the resultant exiting gases or to otherwise modify the exhaust gas species. Flow of the additive material has no significance in the present invention, however, except to the extent that it may be injected with sufficient velocity to avoid being captured in outflowing slag and to react with the hot exhaust gases.
Fig. 3 shows in sectional form a typical pintle nozzle structure. The pintle 14 is cylindrical in shape and has a number of annular elements defining an axial passage 42 for the additive material, two concentric annular passages 43 and 44 joined in fluid communication at the end of the pintle, as shown at 45, to provide a cooling fluid path, and a surrounding annular fuel passage 46. The annular fuel passage 46 terminates in conical exit port 48 extending in a continuous circle around the periphery of the pintle. Coal is ejected in a conical sheet from the exit port 48. An additional annular cooling passage 49 is provided between the fuel passage 46 and the outside surface of the pintle.
As shown in Figs. 5-11, the invention may be used in a variety of embodiments, depending on the needs of the associated downstream application. First, in Fig. 5, there is shown a basic configuration utilizing the principles of the invention. Included are the coal pintle nozzle for injection of coal 14, a tangential inlet 12, slag tap 28, and an exit shown at 22a. In this embodiment, and all others to be described, the coal could be alternatively injected by means of peripheral fuel inlet ports, such as those shown at 60 in Figs. 10 and 11. The only difference between the embodiment shown in Fig. 5 and that discussed with respect to Figs. 1-4 is that the exit 22a is a volute exit shown in more detail in Fig. 5a. In a volute exit, the radius of the exit assembly increases from a minimum value to a maximum value, and an exit duct merges tangentially with the assembly at its point of maximum radius. This is to be distinguished from the symmetrical exit (Fig. 6a), wherein an exit duct merges with a cylindrical exit assembly symmetrically, i.e., along a radius. In both types of exit, the object is to provide a uniform, non-swirling flow in the exit duct.
The embodiment shown in Figs. 6 and 6a differs from that of Fig. 5 in two respects. First, a simpler symmetrical exit 22b is shown. Secondly, and more importantly, the exit 22b is located much closer to the inlet, i.e., the overall length of the slagging stage is reduced. This reduction is made possible because the second phase of combustion, in the exit end 18 of the chamber 16, takes a relatively short time, since it involves only gaseous components at a high temperature, the solid fuel having been practically completely combusted in the head end. The more compact design of the Fig. 6 embodiment results in a further reduced heat loss and increased efficiency, while still maintaining good slag recovery.
The embodiment shown in Figs. 7 and 7a is similar to that shown in Fig. 6, except that the exit end combustion phase takes place in an even smaller volume, since the oxidizer inlet, referred to as 12c, is moved much closer to the exit end 18 of the chamber 16, as a consequence of locating the slag tap 28c at the head end. The coal injector has been accordingly lengthened and effectively moved towards the exit end with the inlet 12c. The head end volume is correspondingly increased by relocation of the slag tap, and, as in all of the embodiments shown, most of the slag removal function is taking place in the first phase of combustion, at the head end. In this manner, heat loss through the slag tap 28c is reduced, because of the lower temperature in the head end region. Placement of the slag tap 28c at the head end 20 also results in a higher slag removal efficiency, since there should be reduced slag volatilization because of the lower temperature of the head end. Moreover, the slag deposited on the head-end walls should be more easily convected toward the slag tap by the axial component of the inlet flow entering the head end 20.
The configuration shown in Figs. 8 and 8a represents a further refinement of the embodiment shown in Fig. 7. In particular, the tangential oxidizer gas inlet has been replaced by a volute inlet 12d, usually referred to as the recessed volute type. The same volume of oxidizer gas can be introduced through the volute inlet as through the tangential inlet, but with an effective reduction in axial length of the inlet, since the volute inlet duct can be larger, measured in a radial direction, than a tangential inlet to a cylinder of the same size. This shorter axial length can reduce heat losses from the combustor, and thereby increase efficiency. More importantly, however, the recessed volute 12d, shown in more detail in Fig. 8a, introduces the oxidizer gas in a more symmetrical fashion about the walls of the chamber 16. The oxidizer circulating in the volute spills over the volute edges in a fairly uniform way around the volute circumference, rather than spilling out into opposite axial directions in a limited region close to the tangential inlet opening. Stated another way, the volute inlet introduces oxidizer flow uniformly about the periphery of the chamber, rather than at an angularly limited region.
In the configuration shown in Fig. 9, there is a double-ended slagging combustor, in which two head ends 20 and 20' are disposed one on each side of a central exit region 50, there being two inlets 12e of the recessed volute type shown in the Fig. 8 configuration. There are also two slag taps 28e and two coal injectors 14 and 14'. The principal advantage of the configuration shown in Fig. 9 is further reduced heat loss, since the exit ends of the Fig. 8 configurations are eliminated. In the single-ended configuration of Fig. 8, there is substantial heat loss from the exit end 22a, but in the Fig. 9 configuration such losses are minimized by joining the exit ends at the central region 50.
Fig. 10 shows a vertically oriented combustion chamber 16 having a recessed volute inlet 12f, a symmetrical outlet 22f, coal injectors 60 disposed peripherally about the chamber 16 at a location slightly towards the head end 20f from the inlet 12f, and a slag tap 28f located in an axial orientation in the head end. The principle of operation is the same as that of the basic configurations already described. Coal is injected into the portion of the inlet flow proceeding towards the head end 20f of the chamber 16, and a first phase of combustion occurs at the head end at a relatively low stoichiometric ratio. A second stage of combustion can then occur in the exit end of the combustor before the products of combustion exit through the symmetrical exit 22f.
Any of the aforedescribed embodiments may be modified for operation as gas generators by including means for diverting the entire oxidizer gas flow towards the head end 20 of the combustor. For example, as shown in Figs. 11 and 11a, the vertically oriented embodiment of Fig. 10 is shown as having a head end 20g and a cylindrical baffle 62 disposed in the oxidizer inlet 12g to act as a flow diverter, ensuring that the oxidizer flow has an axial component directed only toward the head end, as shown by the arrows 64. The inlet flow is, of course, adjusted to provide a desired stoichiometric ratio for generating combustible gas. By this means, the second phase of combustion described above as occurring in the exit end of the combustor, is eliminated, and the overall stoichiometric ratio of the combustor is reduced to the same relatively low value that obtains in the head end. Exit gases are thereby provided with the thermodynamic properties characteristic of suitable fuel gas. It will be understood that any of the other configurations could easily be modified to include the flow diverter 62 shown in Fig. 11 for gas generator operation.
It will be appreciated from the foregoing that the present invention represents a significant advance in the field of coal combustors. In particular, the invention provides a slagging combustor operating with desirable slag removal characteristics at a relatively low stoichiometric ratio, and therefore providing for reduced heat losses and increased efficiency. Furthermore, the combustor is easily adaptable to match the requirements of various downstream processes, such as MHD generators or processes requiring synthetic fuel gas.

Claims

1. A fuel combustor comprising a combustion chamber (16) having a head end (20) and an opposite exit end (18), fuel inlet means (14) for feeding particulate solid fuel into said chamber at said head end (20), oxidiser inlet means (12) for feeding oxidiser into the chamber in a substantially tangential direction to produce high velocity rotational flow within the chamber, an outlet (22) for exhausting combustion products from the exit end of said chamber, a slagging baffle (40) between said ends and a slag tap (28) for removing slag from said chamber; said combustor being characterised in that said oxidiser inlet means (12) is located between said ends and is adapted to effect flow of a portion of the oxidiser toward said head end (20) of said chamber and flow of the remainder of the entering oxidiser toward said exit end (18) of the chamber in such proportions that said fuel and said oxidiser portion react within said head end (20) of the chamber in a first phase of combustion at a relatively low stoichiometric ratio and a correspondingly low temperature to allow liquefaction of the slag content of the entering fuel with minimal vaporisation, the rotational flow causing the liquid slag to be centrifuged onto the chamber wall for removal by said slag tap, the remainder of the entering oxidiser gas reacting with the combustion products of the first phase of combustion near said exit end of the chamber (18) in a second phase of combustion to provide an overall stoichiometric ratio which is substantially higher than that of said first phase.

2. A fuel combustor as claimed in claim 1, further characterised in that said oxidiser inlet means (12) is so located between said chamber ends that flow of said portion of the oxidiser gas occurs in generally counterflow relation to the flow of fuel and first phase combustion products through said chamber.

3. A fuel combustor as claimed in either claim 1 or claim 2, further characterised in that said oxidiser inlet means (12) is arranged to direct a major proportion of the entering oxidiser gas toward said head end (20).

4. A fuel combustor as claimed in either claim 1 or claim 2, further characterised in that said oxidiser inlet means (12) is arranged to direct approximately one half of the entering oxidiser gas flow to said head end (20) to give a stoichiometric ratio of the first phase of combustion of approximately one half of the overall ratio for said combustor.

5. A fuel combustor as claimed in any one of the preceding claims, further characterised in that said oxidiser inlet means (12) comprises a recessed volute type oxidiser inlet.

6. A fuel combustor as claimed in any one of the preceding claims, further characterised in that said outlet (22) opens axially through said chamber exit end.

7. A fuel combustor as claimed in any one of claims 1 to 5, further characterised in that said outlet (22) comprises a volute outlet opening tangentially from said chamber exit end.

8. A fuel combustor as claimed in any one of claims 1 to 5, further characterised in that said outlet (22) opens laterally from said chamber exit end.

9. A fuel combustor as claimed in any one of claims 2 to 8, further characterised in that said oxidiser inlet (12) is situated closer to said head end (20) than to said baffle (40) and in that said slag tap (28) is located adjacent said baffle (40).

10. A fuel combustor as claimed in any one of claims 2 to 8, further characterised in that said oxidiser inlet (12) is situated approximately midway between said head end (20) and said baffle (40), and in that said slag tap (28) is located adjacent said baffle (40).

11. A fuel combustor as claimed in any one of claims 2 to 8, further characterised in that said oxidiser inlet (12) is situated closer to said baffle (40) than to said chamber head end (20), and in that said slag tap (28) is located adjacent said chamber head end (20).

12. A fuel combustor as claimed in any one of the preceding claims, further characterised by a second combustion chamber having an exit end opening to said exit end of said first mentioned combustion chamber and an opposite head end, second fuel and second oxidiser inlet means for feeding particulate solid carbonaceous fuel into the head end of said second chamber and feeding oxidiser gas into the latter chamber to produce high velocity flow therein, an outlet for exhausting combustion products from the exit end of said second chamber, a slag tap for removing slag from said second chamber, and said second chamber inlet means effects flow of at least a portion of the entering oxidiser gas toward said head end of said second chamber and flow of any remainder of the entering oxidiser gas toward said exit end of the second chamber in such proportions that said oxidiser gas portion and the entering fuel react within said head end of the second chamber in a first phase of combustion at a relatively low stoichiometric ratio and a correspondingly low temperature to allow liquefaction of the slag content of the entering fuel with minimal vaporisation, and the liquid slag being centrifuged onto the chamber wall for removal via said slag tap, the remainder of the entering oxidiser gas reacting within said exit end of the second chamber with the combustion products of the first phase of combustion in a second phase of combustion to provide the second combustion chamber with an overall stoichiometric ratio which is substantially higher than the first phase stoichiometric ratio in the second chamber.

13. A fuel combustor as claimed in any one of the preceding claims, further characterised in that said combustion chamber is vertically disposed with its exit end uppermost and its head end lowermost.

14. A fuel combustor as claimed in any one of the preceding claims, further characterised in that said fuel inlet means comprises a plurality of fuel inlet ports spaced circumferentially around the head end of said combustion chamber.

15. A fuel combustor as claimed in any one of the preceding claims, further characterised in that said slag tap is centrally located at the bottom of said combustion chamber.

16. A fuel combustor as claimed in any one of the preceding claims, further characterised by means affixed to the walls of said combustion chamber to enhance adhesion of solidified slag thereto.

17. A fuel combustor as claimed in any one of the preceding claims, further characterised by the oxidiser inlet means being adapted to give an overall stoichiometric ratio which is sufficiently high to effect substantially complete gasification of the fuel which the combustion temperatures are sufficiently low to avoid vaporisation of liquid slag.

18. A combustion method comprising feeding particulate solid carbonaceous fuel and oxidiser into a reaction chamber having a head end and an opposite exit end in a manner to produce high velocity rotational flow within the chamber, exhausting combustion products from the exit end of the chamber, and removing slag from the chamber; said method being characterised by the steps of feeding said fuel to enter at the head end of the chamber, feeding said oxidiser to an inlet between said ends and distributing it such that a first portion of the entering oxidiser flows toward said head end of the chamber and the remainder of the oxidiser flows toward said exit end of the chamber in such proportions that said first portion reacts within said head end of the chamber with the entering fuel in a first phase of combustion at a relatively low stoichiometric ratio and a correspondingly low temperature such that the slag content of the fuel is liquified with minimal vaporisation and the liquid slag is centrifuged onto the chamber wall for removal from the chamber, and said remainder of the entering oxidiser reacts with the first phase combustion products in a second phase of combustion near said exit end of the chamber to provide an overall stoichiometric ratio which is substantially higher than that of said first phase.

19. A method as claimed in claim 18, further characterised in that the oxidiser is injected tangentially into the combustion chamber between the head end and the exit end, in such a manner that the entering oxidiser flow splits to create said first oxidiser portion which flows toward said head end and said remainder portion which flows toward said exit end.

20. A method as claimed in either claim 18 or claim 19, further characterised in that the oxidiser feed is such that the first phase of combustion occurs at a stoichiometric ratio approximately one half of the overall ratio for the combustor.

21. A method as claimed in either claim 18 or claim 19, further characterised in that substantially all of the entering oxidiser is directed toward the head end of said chamber.