US20170082283A1

US20170082283A1 - Flameless oxidation device, apparatus and method

Info

Publication number: US20170082283A1
Application number: US15/310,557
Authority: US
Inventors: Angus DUNCAN; Gerry HESSELMANN; Joachim G WÜNNING
Original assignee: WS Warmeprozesstechnik GmbH; Doosan Babcock Ltd
Current assignee: WS Warmeprozesstechnik GmbH; Altrad Babcock Ltd
Priority date: 2014-05-13
Filing date: 2015-05-11
Publication date: 2017-03-23
Also published as: WO2015173548A1; AU2015261330A1; GB201408459D0; KR20170042499A; EP3143330A1

Abstract

A device for the flameless oxidation of fuel includes a flameless oxidation burner, a first conduit to convey a fluid fuel phase to a first outlet and a direct primary jet including the fluid fuel phase outwardly therefrom. A second conduit is provided to convey a jacketing gas to a second outlet. The second conduit is disposed surrounding the first conduit so as to direct a jacketing jet of the jacketing gas outwardly therefrom surrounding the primary jet.

Description

The invention relates to a device for the flameless oxidation of fuel, for example comprising a flameless oxidation burner. The invention further relates to an apparatus for the flameless oxidation of fuel comprising one or more such devices, for example disposed to direct such fuel into a reaction chamber for flameless oxidation. The invention further relates to a method of flameless oxidation of fuel and to a method of operation of such a device or apparatus.
In the preferred case the invention relates to a device for the flameless oxidation of particulate solid carbonaceous fuel. In the preferred case the fuel is pulverous solid carbonaceous fuel and for example pulverised coal, and the invention is particularly discussed in that context. However the general principles of the invention may be applied to other solid carbonaceous fuel such as biomass, oil shales, petroleum, coke etc, and to other fuels including non-solid fuels.
In particular, but not exclusively, the invention relates to a combustion apparatus for the flameless oxidation of fuel to generate heat in a furnace chamber, for example for use in a power generation apparatus, and to a power generation apparatus incorporating such a combustion apparatus.
The heating of a furnace chamber with one or more burners designed for flameless oxidation of fuel within a reaction volume defined by the furnace chamber is known in the art. Burners adapted to heat a furnace chamber by means of a flameless oxidation of the fuel have advantages in many applications over burners that form flames. For example the distribution of generated heat over a large area of the furnace chamber provides for safe operation with a range of gaseous, liquid and solid fuels in hot combustion chambers. Emissions may be reduced, and for example the formation of nitrogen oxides may be suppressed.
Flameless oxidation is applied in many different applications. Flame formation and corresponding peak temperatures are suppressed by internal recirculation of host combustion products. It should be noted that the desirable internal local recirculation of hot exhaust gas combustion products is internal to the furnace, not external via a fan. This ‘internal recirculation’ is jet induced recirculation in the furnace, or ‘induced recirculation’. This may be distinguished from ‘external recirculation’ as recirculation of flue gases via a fan or other positive circulation device, or ‘forced recirculation’.
Since there is no need for flame stability, flameless oxidation is ideally suited for combustion of difficult fuels, even with changing composition.
Flameless oxidation burners are known for use with solid carbonaceous fuels such as coals. The fuel is in particulate and for example pulverous form and is conveyed as a primary fuel jet by means of a carrier gas. The gas carrier preferably comprises or includes a comburant gas, which is for example combustion air.
In most cases, flameless oxidation may be achieved by careful arrangement of free jets. Depending on boundary conditions, fuel and combustion air can be injected premixed, combined or delivered through separate jets.
However, tests with pulverised coal fuel in particular have shown that ignition can occur at the borders of the fuel jet where the fuel jet comes into contact early with hot locally recirculated exhaust gases which can then act as a pilot flame igniting a main flame. Pulverised coal is usually transported with a carrier gas capable of supporting combustion, for example combustion air. This air, in combination with a high reactivity of volatiles and high combustion chamber temperatures typically encountered lead to the unwanted self-ignition. This effect can be found to occur especially for high burner capacities, highly reactive fuels (such as hydrogen or volatiles of coal), high combustion chamber temperatures and low jet velocities.
It may be possible that this unwanted ignition could be suppressed by dilution of the combustion air with cold exhaust gas, or by substituting the carrier air with an inert gas. Neither of these solutions is satisfactory.
It is desirable that a system and method is developed which tends to suppress unwanted ignition and control the temperature development in front of burners and better support flameless oxidation, in particular for the flameless oxidation of pulverous solid fuel, such as pulverous carbonaceous fuel such as pulverised coal, without the need to recirculate large amounts of exhaust gas and without the need to substitute the carrier air by an inert gas.
In accordance with the invention in a first most general aspect a device for the flameless oxidation of fuel comprises:
a first conduit to convey a fluid fuel phase to a first outlet and direct a primary jet comprising the fluid fuel phase outwardly therefrom, for example via a suitable nozzle;
a second conduit to convey a jacketing gas to a second outlet;
wherein the second conduit is disposed surroundingly about the first conduit so as direct a jacketing jet of the jacketing gas outwardly therefrom surroundingly about the primary jet, for example via a suitable nozzle.
The second conduit is disposed surroundingly about the first conduit at least at their respective outlet ends, so that the second outlet is disposed surroundingly about the first outlet and is thereby disposed to direct a jacketing jet of the jacketing gas outwardly therefrom surroundingly about the primary jet exiting the first outlet. Conveniently however the second conduit may be disposed surroundingly about the first conduit for at least a substantial part of its length.
The jacketing gas is selected to be relatively less oxidising than, and to isolate the primary jet to some extent from early contact with, local hot recirculated exhaust gases, and is for example selected from a comburant gas, cold recirculated FGR, inert gas, or a mixture thereof.
More completely, the device comprises:
a first inlet to receive a supply of fuel, a first outlet and a first conduit disposed as a channel means to convey a fluid fuel phase from the first inlet to the first outlet;
a second inlet to receive a supply of jacketing gas, a second outlet and a second conduit disposed as a channel means to convey the jacketing gas from the second inlet to the second outlet.
Although reference is made for convenience to a first and second inlet in the singular this would be understood not only to encompass the plural in the generality but in particular should be understood to encompass, in the case where a supply comprising a mixture of gases is envisaged, a combined inlet to receive a supply comprising a mixture of a plurality of gases or plural inlets respectively to receive a supply comprising each such gas.
More completely yet, the device comprises:
a fuel supply in fluid communication with said first inlet;
a jacketing gas supply in fluid communication with said second inlet and for example a comburant gas supply in fluid communication with said second inlet and/or an exhaust gas supply in fluid communication with said second inlet and/or an inert gas supply in fluid communication with said second inlet.
As will be understood by the skilled person in this context, a comburant gas comprises a gas capable when so supplied to support oxidation of the fuel in an oxidation zone downstream of the fuel outlet during use, an exhaust gas comprises one or more recirculated exhaust products of such oxidation, and an inert gas in this context comprises a gas not capable of supporting oxidation of the fuel.
The purpose of the invention is to give better control over unwanted flame formation. It has been found that ignition can occur at the borders of the fuel jet where the fuel jet comes into contact early with hot local recirculated exhaust gases. This ignition of the fuel jet can then act as a pilot igniting a main flame. Suppression of this effect is desirable to ensure flameless oxidation. The use of a jacketed jet in the manner described in accordance with the invention helps to suppress such pilot flame formation, and hence the development of a main flame in the manner described, in that the jacketing gas is selected to be relatively less oxidising than, and thereby to isolate the primary jet to some extent from excessively early contact and ignition by, hot locally recirculated exhaust gases. The jacketing jet shields the fuel jet from high exhaust temperatures and from the oxygen within the reaction chamber, suppressing flame formation and tending to encourage flameless oxidation.
This solution suppresses unwanted ignition and enables better control of temperature development in front of a flameless combustion device, and in particular in front of a burner, without the need for external recirculation of large amounts of exhaust flue gas to the burner inlet. Where it is desired to use a carrier gas that supports combustion such as carrier air, it is not necessary to dilute or substitute such a comburant by an inert gas. The amount of necessary externally recirculated exhaust flue gas can be drastically reduced or eliminated completely.
Control of the composition and mass flow of the jacketing jet can provide an effective and inexpensive way to control the course of combustion. Individual control of individual burners can be effected in a much more ready manner than would be possible using a solution that involved changes to the fuel phase composition itself, for example by alternative solutions involving dilution of any comburant gas in the mixture, provision of inert gases etc.
The purpose of the invention is in particular to provide a system for the flameless oxidation of fuel comprising one or more devices such as above described, for example disposed to direct such fuel into a reaction chamber for flameless oxidation. The invention further relates to a method of flameless oxidation of fuel and to a method of operation of such a device or system.
Accordingly, in accordance with the invention in a second aspect an apparatus for the flameless oxidation of fuel comprises one or more devices in accordance with the first aspect of the invention. For example the apparatus comprises a reaction chamber and one or more such devices disposed to direct fuel and comburant into a reaction chamber for flameless oxidation.
More completely in accordance with the invention in the second aspect an apparatus for the flameless oxidation of fuel comprises:
a reaction chamber having an internal reaction volume defined by one or more chamber walls;
at least one device in accordance with the first aspect of the invention extending through the wall and disposed to direct a primary jet comprising a fluid fuel phase into the reaction volume via its first outlet and to direct a jacketing jet comprising a jacketing gas into the reaction volume via its second outlet surroundingly around the primary jet.
The apparatus in accordance with the second aspect of the invention thus comprises one or more, and preferably a plurality of, flameless oxidation devices in accordance with the first aspect of the invention disposed in and through at least one wall extending into a reaction chamber. The devices direct a fuel jet and a jacketing jet in the manner above described into the reaction chamber. Each fuel jet (and its jacketing jet) is directed towards an oxidation zone downstream of the fuel outlet whereat in familiar manner it is intended that substantially flameless oxidation of the fuel will be supported in use. The reaction chamber may otherwise be conventional, and in particular for example supplies hot exhaust gas and/or comburant gas to the flameless oxidation zone in familiar manner. Thus the apparatus preferably further comprises a comburant gas supply conduit arranged to supply comburant to the oxidation zone and/or an exhaust gas supply conduit arranged to supply hot recycled exhaust gas to the oxidation zone. The comburant gas supply conduit is disposed to supply comburant gas supplied from an external source to the oxidation zone and is preferably provided with and fluidly connected to an external comburant gas supply source. The exhaust gas supply conduit is disposed to supply hot recycled exhaust gas exhausted from the reaction chamber to the oxidation zone and is preferably fluidly connected to an exhaust gas outlet of the reaction chamber via a recycle conduit.
A comburant gas supply conduit may comprise a part of the device of the first aspect of the invention, for example in that comburant gas is supplied via the second conduit of the device or via a further conduit of the device or otherwise by the device. Additionally or alternatively a separate comburant gas supply conduit may be provided.
A an exhaust gas supply conduit may comprise a part of the device of the first aspect of the invention, for example in that comburant gas is supplied via the second conduit of the device or via a further conduit of the device or otherwise by the device. Additionally or alternatively a separate exhaust gas supply conduit may be provided.
Preferably the apparatus in accordance with the second aspect of the invention comprises a combustion apparatus for the flameless oxidation of fuel to generate heat in a furnace chamber, for example for use in a power generation apparatus, and more completely in a further aspect there is provided a thermal power generation apparatus incorporating such a combustion apparatus as source of thermal energy.
Similarly, in accordance with the invention in a further aspect a method of flameless oxidation of fuel comprises the steps of:
directing a fluid fuel phase towards a flameless oxidation zone for example in a suitable reaction chamber, and for example by causing a fluid fuel phase to be conveyed via a first conduit to a first outlet letting into the reaction chamber, for example via a suitable nozzle;
causing a jacketing gas jet to be directed towards the said oxidation zone in a manner disposed surroundingly about the primary jet, for example by causing a jacketing gas to be conveyed via a second conduit to a second outlet letting into the reaction chamber, for example via a suitable nozzle, and disposed surroundingly about the first outlet;
supporting flameless oxidation of the fuel jet in the oxidation zone by control of conditions within the oxidation zone, and in particular for example by control of temperature in the oxidation zone and/or of supply of comburant gas to the oxidation zone and and/or of levels of hot exhaust gases in the reaction zone in familiar manner.
The general principle necessary for flameless oxidation of a fuel phase will be familiar to the person skilled in the art, and the invention assumes application of such principles. In general principle, comburant for example comprising exhaust gases from combustion from which some useful heat has been removed and/or preheated oxidant such as combustion air, and for example a mixture of the same, is kept at a temperature that is higher than the ignition temperature of the fuel phase, and the mixture of exhaust gas and combustion air is then brought together with the fuel, forming an oxidation zone in which a substantially flameless oxidation occurs in a reaction chamber.
The invention does not depart from these principles, but the jacketing jet of the invention acts to suppress undesirable ignition at the borders of the fuel jet where the fuel jet comes into contact early with the hot gases, tending to support more sustainable flameless oxidation.
The method of flameless oxidation of fuel for example comprises a method of operation of a device in accordance with the invention in the first aspect or system in accordance with the invention in the second aspect.
Preferred features of each aspect of the invention as discussed in general principle below will accordingly be understood to apply to all aspects by analogy.
The device, apparatus and method in accordance with the invention operate in accordance with a principle that makes use of a jacketing gas which is selected to be relatively less oxidising than the hot recirculated exhaust gases typically present in a typical flameless oxidation reaction chamber. For example, the jacketing gas used in the method comprises, and a jacketing gas supply in the device comprises, comburant gas, exhaust gas, or a mixture of the two. The exhaust gas can be replaced by another relatively inert gas.
Suitable comburant gases for use with the device, apparatus and method in accordance with the invention are selected to support suitable flameless oxidation conditions for flameless oxidation of the primary jet, and will be familiar to those skilled in the art. A typical comburant gas comprises an oxygen-containing gas, and is for example air, simulated air, other oxygen-enriched gas including oxygen-enriched recycled flue gas etc. The composition of any comburant supply may be further modified for example by control of levels of other cases and for example reduction of nitrogen etc in familiar manner. A suitable comburant gas comprises combustion air in familiar manner.
The device/apparatus of the invention accordingly includes such a comburant gas supply and the method of the invention accordingly includes a step of supplying such a comburant gas.
The device of the invention comprises a first conduit disposed as a channel means to convey a fluid fuel phase to the first outlet, and direct a primary jet comprising the fluid fuel phase outwardly from the first outlet, for example via a suitable nozzle. The first outlet is configured to direct a primary jet comprising the fluid fuel phase outwardly from the first outlet and is for example shaped to produce a desired primary jet shape projecting outwardly beyond the first outlet. In a preferred case the first outlet is so configured in that it comprises a first nozzle shaped to direct a primary jet comprising the fluid fuel phase outwardly from the first outlet and shaped to produce a desired primary jet shape projecting outwardly beyond the first outlet.
Typically a desired primary jet shape diverges as it passes beyond the first outlet. For example a desired primary jet shape is generally conical as it projects beyond the first outlet (wherein conical should herein be interpreted generally as describing the divergent surrounding nature of the jet, and not in a strict mathematical sense as requiring a rigidly right circular cone shape for example). In a preferred case the first outlet comprises a first nozzle shaped to produce such a divergent and for example generally conical primary jet. The first nozzle for example comprises a nozzle outlet having a circular shape in a nozzle transverse direction (transverse to a fluid fuel phase flow direction in use) and is structured along a nozzle axial direction (a fluid fuel phase flow direction) to produce a divergent and for example generally conical primary jet and for example has a diverging profile in a nozzle axial direction.
In accordance with the method of the invention, the method in the preferred case comprises directing a primary jet having such a shape towards the flameless oxidation zone, for example by directing the fluid fuel phase through such a suitably configured first outlet and for example through such a suitably configured first nozzle.
The fluid fuel phase comprises a fuel suitable for flameless oxidation, which may be gaseous, liquid or solid. Suitable fuels include but are not limited to carbonaceous fuels such as fossil fuels, biomass, waste products etc.
The fluid fuel phase may comprise a mixture of fuel with a carrier gas, for example including comburant gas as above described and/or other gases such as inert gases (that is to say, gases with an inert role in the supporting of oxidation in a reaction zone). The fuel may for example be solid carbonaceous fuel in particulate and for example in pulverous form conveyed as a primary fuel jet by means of such a carrier gas. The fuel is for example pulverous coal.
Further conduit structures defining further outlets for additional gases to modify conditions in an oxidation region, for example including comburant gases, may be provided either as part of the device of the first aspect of the invention or separately as part of the apparatus of the second aspect of the invention.
Comburant gas may thus be provided as part of the mixture comprising the fluid fuel phase and hence via the first conduit and/or as part of the mixture comprising the jacketing gas and hence via the second conduit.
Additionally or alternatively comburant gas may be separately supplied via a third conduit disposed surroundingly about the jacketing gas jet directed about the second conduit. In this possible arrangement the jacketing jet also keeps the main comburant away from the primary jet and from the fuel for a certain time.
In such an embodiment the device comprises a third conduit to convey a comburant gas to a third outlet. The third conduit may be disposed surroundingly about the first and second conduits so as direct a comburant jet of the comburant gas outwardly therefrom surroundingly about the primary and jacketing jets, for example via a suitable nozzle. Alternatively a plurality of third conduits may be provided in the device arrayed surroundingly about the first and second conduits and configured to produce a corresponding plurality comburant jets projecting outwardly beyond the third outlet surroundingly about the jacketing jet.
In such an embodiment the method additionally comprises causing a comburant gas jet to be directed towards the said oxidation zone in a manner disposed surroundingly about the jacketing jet, for example by causing a comburant gas to be conveyed via a third conduit to a third outlet letting into the reaction chamber, for example via a suitable nozzle, and disposed surroundingly about the second outlet.
The fuel may be gaseous, liquid or solid. In the case of solid fuel, the fuel is preferably particulate, and is for example a pulverous material, and is delivered entrained in a carrier gas such as above described. Suitable solid fuels include particulate and for example a pulverised coal (which term should be considered unless otherwise indicated herein to cover the range of materials so described including without limitation anthracite, bituminous coals, sub-bituminous coals and lignites), but other solid fuels including without limitation oil shales, biomass, petroleum, coke, comminuted solid combustible waste and the like might be considered.
A device/apparatus in accordance with the invention conveniently comprises a supply of a liquid fuel phase comprising a fuel or mixture as above described. A method in accordance with the invention conveniently comprises the step of delivery of a fuel or mixture as above described. Such a mixture may be supplied to the device/apparatus from a mixed supply, or components of the mixture may be separately supplied to and caused to mix within the device/apparatus in accordance with the invention.
The invention provides for a jacketing jet disposed generally around the primary fuel jet to tend to shield the primary fuel jet from high exhaust temperatures and from the oxygen in the exhaust gases so as to tend to suppress undesirable flame formation. The device of the invention accordingly comprises a second conduit to convey a jacketing gas to a second outlet wherein the second conduit is disposed surroundingly about the first conduit so as direct a jacketing jet of the jacketing gas outwardly therefrom surroundingly about the primary jet, for example via a suitable nozzle.
The second outlet is configured to direct a jacketing jet comprising a jacketing jet of the jacketing gas outwardly from the second outlet surroundingly about the primary jet and is for example shaped to produce a desired jacketing jet shape projecting outwardly beyond the second outlet about the primary jet. In a preferred case the second outlet is so configured in that it comprises a second nozzle shaped to direct a jacketing jet of the jacketing gas outwardly from the second outlet and shaped to produce a desired jacketing jet shape projecting outwardly beyond the third outlet.
The jacketing jet is suitably shaped to substantially envelop and for example entirely surround the primary jet. In a preferred geometry, the jacketing jet diverges outwards as it passes beyond the second outlet, and for example forms a generally conical jacket around the primary jet (wherein conical should herein be interpreted generally as describing the divergent surrounding nature of the jet, and not in a strict mathematical sense as requiring a rigidly right circular cone shape for example).
To effect this, a device in accordance with the invention is provided with a second outlet comprising a nozzle configured to produce such a jacketing jet shape, and for example shaped to tend to direct the jacketing gas into such a jacketing jet shape as it passes beyond the nozzle. In a preferred case the second outlet thus comprises a second nozzle shaped to produce such a divergent and for example generally conical jacketing jet. The second nozzle for example comprises a nozzle outlet having an annular shape transverse to a fluid fuel phase flow direction about the first outlet and is structured along a fluid fuel phase flow direction to produce a divergent and for example generally conical jacketing jet about the primary jet. The second nozzle for example comprises a nozzle outlet having an annular shape concentric with the primary outlet in a nozzle transverse direction (transverse to a fluid fuel phase flow direction in use) and is structured along a nozzle axial direction (a fluid fuel phase flow direction) to produce a divergent and for example generally conical jacketing jet and for example has a diverging profile in a nozzle axial direction.
In a particular preferred case for example, a device of the first aspect of the invention comprises an annular second outlet surroundingly disposed concentrically around a circular primary outlet and for example a nozzle of the second outlet comprises an annular nozzle surroundingly disposed concentrically around a nozzle of a first outlet.
In accordance with the method of the invention, the method in the preferred case comprises directing a jacketing jet in such a shape towards the flameless oxidation zone, for example by directing the jacketing gas through such a suitably configured second outlet and for example through such a suitably configured second nozzle.
In a possible embodiment a third conduit is provided for a comburant gas supply disposed to supply comburant gas surroundingly about the jacketing jet from a third outlet. Similar preferred features will apply by analogy. In particular in this embodiment the third outlet is configured to direct a comburant jet comprising comburant gas outwardly from the third outlet spaced apart from the first and second outlets surroundingly about the jacketing jet and is for example shaped to produce a desired comburant jet shape projecting outwardly beyond the third outlet. Optionally plural third conduits may be arrayed surroundingly about the first and second outlets for example having a corresponding plurality of third outlets configured to produce a corresponding plurality comburant jets projecting outwardly beyond each third outlet surroundingly about the jacketing jet.
In a preferred case the or each third outlet is so configured in that it comprises a third nozzle shaped to direct a comburant jet of the comburant gas outwardly from the third outlet and shaped to produce a desired comburant jet shape projecting outwardly beyond the third outlet. In a preferred geometry, the comburant jet diverges outwards as it passes beyond the third outlet, and for example forms a generally conical shape. In a preferred case the third outlet thus comprises a third nozzle shaped to produce such a divergent and for example generally conical comburant jet.
In a particular preferred case for example, a device of the first aspect of the invention comprises concentrically disposed a central circular first outlet and for example first nozzle, a second annular outlet and for example annular nozzle surroundingly disposed about the first, and an array of at least two third outlets, and for example third nozzles, disposed about the second outlet.
In a preferred embodiment, the device of the first aspect of the invention comprises an elongate structure having first and second (and where applicable further) inlets at or towards an inlet end, and first and second (and where applicable further) conduits extending to outlets at or towards an outlet end. The device is for example an elongate burner.
A system of the second aspect of the invention preferably comprises plural such burners for plural burner firing.
In accordance with the foregoing discussion, comburant gas to support flameless oxidation in the oxidation zone may be supplied for example as part of the jacketing gas supply and/or as a carrier gas for the fuel phase. Additionally or alternatively, comburant gas may be supplied by one or more additional comburant gas supplies letting into the reaction volume. Thus, in a preferred embodiment, an apparatus in accordance with the second aspect of the invention further comprises at least one additional comburant gas supply device comprising a conduit defining a fluid channel to convey a comburant gas to a comburant gas outlet and direct a jet of comburant gas outwardly therefrom, the additional comburant gas supply device extending through the wall of the chamber and disposed to direct a comburant gas supply into the reaction volume via a comburant outlet. The comburant outlet is for example disposed generally in the vicinity of and suitably laterally spaced from the first and second outlets of the flameless oxidation device. In a typical arrangement, a flameless oxidation device in accordance with the first aspect of the invention may be provided with a plurality of such additional comburant supply devices disposed suitably around it.
A typical comburant gas such as combustion air may be preheated prior to injection into a reaction chamber/combination into a fuel phase as the case may be. To preheat the combustion air, exhaust gases from combustion, from which useful heat has already been removed, may typically be used. Additionally or alternatively it would be possible to use waste heat from other processes for preheating the comburant.
An apparatus to put this principle into practice in conjunction with a device of the invention may therefore include a suitable comburant preheater, for example disposed to preheat comburant such as combustion air by transfer of recovered heat from exhaust gases from combustion, and a method may include a step of preheating comburant gas such as combustion air by transfer of recovered heat from exhaust gases from combustion.
A typical comburant gas such as combustion air may be mixed with exhaust gases from combustion prior to injection into a reaction chamber/combination into a fuel phase as the case may be. An apparatus to put this principle into practice in conjunction with a device of the invention may therefore include a suitable exhaust gas recirculation system disposed to mix comburant such as combustion air with exhaust gases from combustion, and a method may include a step of mixing comburant gas such as combustion air with exhaust gases from combustion prior to injection into a reaction chamber/combination into a fuel phase as the case may be.
It is a particular advantage of the invention that control of oxidation conditions can be effected in individual devices by means of control of the jacketed jet mass flow, composition and temperature. Accordingly, in accordance with the preferred embodiment, a device of the invention comprises means to control the mass flow of and/or means to control the composition of and/or means to control the temperature of the jacketing gas supply. By analogy the method of invention comprises supplying jacketing gas with a controlled and varied mass flow and/or composition and/or temperature to control and vary oxidation conditions.
In a preferred case, the mass flow is controlled so that the velocity of the jacketing jet is similar to or lower than the velocity of the fuel jet.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side view of a prior art flameless oxidation burner to which the principles according to the invention could be applied, and illustrates the problem arising in particular with pulverised coal firing;

FIG. 2 is sectional side view of a flameless oxidation burner in accordance with an embodiment of the first aspect of the invention;

FIG. 3 is a partial section of a flameless oxidation chamber in accordance with a second aspect of the invention incorporating such a flameless oxidation burner and with a simple schematic representation of a possible fuel and gas supply system.

The simple schematic system shown in FIG. 1 shows a typical flameless oxidation system that includes a central fuel jet supply conduit to supply a fuel jet 1, which may contain oxygen and for example carrier combustion air, and spaced further supply conduits to deliver additional jets 3 which supply additional combustion air or air plus recycled flue gas to the combustion zone. Also in familiar manner, hot recirculated exhaust gas 2 is introduced in advance of an intended flameless reaction zone. The combustion air or air plus recycled flue gas is typically preheated and the induced exhaust gas maintains temperature in a reaction zone in the reaction chamber above the desired ignition temperature of the fuel phase and may additionally provide some further oxygen to support oxidation of the fuel.
The condition illustrated in FIG. 1 is the condition that the invention seeks to suppress, in which ignition can occur at the borders of the fuel jet in advance of the intended flameless reaction zone which can then cause ignition of a main flame instead of a flameless oxidation in the intended flameless reaction zone. This problem is particularly encountered in the use of pulverised coal as fuel, when transported by carrier air, where the oxygen in the carrier air in combination with the high reactivity of volatiles and the high combustion chamber temperatures can lead to unwanted self-ignition, but the problem is not limited to such fuel, and nor is the solution offered by the invention so limited.
As illustrated in FIG. 1, the effect of early contact with the hot recirculated exhaust gas 2 in advance of a intended flameless reaction zone can be to cause undesirable initial ignition of flames 4 at the border of the fuel jet (and in the particular case at the border of the fuel/combustion air jet). These flames 4 may then ignite a main flame 5 producing unwanted flame combustion of the fuel instead of the desired flameless oxidation.
FIG. 2 illustrates a comparable situation where the primary fuel jet has been modified in accordance with the principles of the invention. Again a simple schematic is shown including a primary fuel jet 1 which may contain oxygen such as carrier air, and is for example pulverised coal entrained in a suitable carrier gas such as carrier combustion air, and optional additional conduits deliver secondary additional jets 3 to supply for example combustion air or air plus recycled flue gas. The combustion air or air plus recycled flue gas is typically preheated and the internally recirculated exhaust gas 2 again maintains temperature in a reaction zone in the reaction chamber above the desired ignition temperature of the fuel phase and may additionally provide some further oxygen to support oxidation of the fuel.
In this case, an additional annular conduit surrounds the central conduit which supplies the fuel/air jet 1, and this supplies a jacketing jet 6 containing air, exhaust or a mixture of both (optionally with additionally or substitutionally provided other oxidatively inert gas), shielding the fuel/air jet from high exhaust temperatures and from the oxygen in the secondary air jets and in the exhaust gas, and thus suppressing flame formation at the border of the fuel/air jet.
Suppression of such initial flame formation at the border of the fuel/air jet controls oxidation conditions more effectively, prevents ignition of a main flame as illustrated in FIG. 1, and instead supports flameless oxidation in the flameless oxidation region 7.
FIG. 3 is a partial section of a flameless oxidation chamber in accordance with a second aspect of the invention incorporating such a flameless oxidation burner and with a simple schematic representation of a possible fuel and gas supply system.
A chamber wall 12 (shown as partial section of one side only) defines a reaction volume generally designated 13. A single burner 11 in accordance with the embodiment of FIG. 2 is shown let into the wall. A single burner is shown for simplicity. In a practical system multiple burners will usually be provided. The burner is structured in general as shown in FIG. 2 to deliver a central jet comprising fuel which may be entrained in a suitable carrier gas such as carrier combustion air jacketed by the jacketing jet, and optional secondary additional jets 3 to supply for example additional combustion air or air plus recycled flue gas to a flameless reaction zone generally designated 14. A hot recirculated exhaust gas conduit 2 supplies exhaust gas from an exhaust outlet of the chamber (omitted for clarity) in advance of the intended flameless reaction zone in familiar manner to control conditions and encourage flameless oxidation.
The system is distinctly characterised by the provision of a jacketing jet about the fuel jet. The jacketing gas of the jacketing jet is selected to be relatively less oxidising than, and to isolate the primary jet to some extent from early contact with, these hot recirculated exhaust gases, and is for example selected from a comburant gas, cold recirculated FGR, inert gas, or a mixture thereof. A simple schematic of a fuel and gas supply arrangement to effect this is provided in FIG. 3.
A source of fuel 22 which is for example in the preferred pulverised coal embodiment of the invention a coal pulveriser or silo supplies fuel which is for example pulverised coal entrained in carrier air via a supply conduit 24 to the central conduit of the burner of FIG. 2 and thus supplies the primary fuel jet 1.
The schematic representation also provides for completeness a source of cold recycled flue gas 17 supplied by the recycle conduit 18 from a flue outlet (omitted for clarity), a secondary comburant supply 16 which supplies comburant gas for example combustion air, and a source of oxidatively inert gas 15.
A jacketing gas supply control system 32 is in fluid communication with the sources 15, 16 and 17 and includes at least a selective flow control system whereby a jacketing gas comprising air, exhaust or a mixture of both optionally with additionally or substitutionally provided other oxidatively inert gas, is supplied via the supply conduit 34 to the annular conduit of the burner of FIG. 2 and thus supplies the jacketing jet 6.
A secondary comburant gas supply control system 42 is in fluid communication with the sources 16 and 17 and includes at least a selective flow control system whereby a comburant gas comprising air, exhaust or a mixture of both is supplied via the supply conduit 44 to the optional additional conduits of the burner of FIG. 2 and thus supplies the additional jets 3. A heater 43 may preheat the comburant gas to further control conditions at the flameless reaction zone and encourage flameless oxidation.

Claims

1. A device for the flameless oxidation of fuel comprising:

a first conduit to convey a fluid fuel phase to a first outlet and direct a primary jet comprising the fluid fuel phase outwardly therefrom;

a second conduit to convey a jacketing gas to a second outlet;

wherein the second conduit is disposed surroundingly about the first conduit so as direct a jacketing jet of the jacketing gas outwardly therefrom surroundingly about the primary jet.

2. A device in accordance with claim 1 comprising:

a first inlet to receive a supply of fuel in a fluid phase, a first outlet and a first conduit disposed as a channel means to convey the fuel in a fluid phase from the first inlet to the first outlet;

a second inlet to receive a supply of jacketing gas, a second outlet and a second conduit disposed as a channel means to convey the jacketing gas from the second inlet to the second outlet.

3. A device in accordance with claim 2 comprising:

a fuel supply in fluid communication with said first inlet;

a jacketing gas supply in fluid communication with said second inlet.

4. A device in accordance with claim 3 wherein the jacketing gas supply comprises a supply in fluid communication with said second inlet of one or more gases selected from: a comburant gas; an exhaust gas; an inert gas.

5. A device in accordance with claim 3 wherein the fuel supply comprises a supply in fluid communication with said first inlet of pulverous coal in a carrier gas.

6. A device in accordance with claim 1 comprising an annular second outlet surroundingly disposed concentrically around a circular first outlet.

7. A device in accordance with any preceding claim 1 further comprising a third conduit to convey a comburant gas to a third outlet.

8. A device in accordance with claim 7 comprising a third conduit disposed surroundingly about the first and second conduits so as direct a comburant jet of the comburant gas outwardly therefrom surroundingly about the primary and jacketing jets.

9. A device in accordance with claim 7 comprising a plurality of third conduits arrayed surroundingly about the first and second conduits having a corresponding plurality of third outlets configured to produce a corresponding plurality comburant jets projecting outwardly beyond each third outlet surroundingly about the jacketing jet.

10. A device in accordance with claim 9 comprising concentrically disposed: a central circular first outlet, a second annular outlet surroundingly disposed about the first outlet, and an array of at least two third outlets, disposed about the second outlet

11. An apparatus for the flameless oxidation of fuel comprising:

a reaction chamber having an internal reaction volume defined by one or more chamber walls;

at least one device in accordance with claim 1 extending through the wall and disposed to direct a primary jet comprising a fluid fuel phase into the reaction volume via its first outlet and to direct a jacketing jet comprising a jacketing gas into the reaction volume via its second outlet surroundingly around the primary jet.

12. An apparatus in accordance with claim 11 wherein the at least one device comprises an oxidation device to direct a fuel jet and a jacketing jet towards an oxidation zone in the reaction chamber, and wherein the apparatus further comprises a comburant gas supply conduit arranged to supply comburant to the oxidation zone and/or an exhaust gas supply conduit arranged to supply hot recycled exhaust gas to the oxidation zone.

13. An apparatus in accordance with claim 12 wherein the oxidation device comprises a plurality of comburant gas supply conduits disposed surroundingly around the first and second conduits of the oxidation device.

14. An apparatus in accordance with claim 13 comprising a combustion apparatus for the flameless oxidation of fuel to generate heat in a furnace chamber.

15. A method of flameless oxidation of fuel comprising the steps of:

directing a fluid fuel phase towards a flameless oxidation zone in a reaction chamber;

causing a jacketing gas jet to be directed towards the said oxidation zone in a manner disposed surroundingly about the primary jet;

supporting flameless oxidation of the fuel jet in the oxidation zone at least by supplying to the oxidation zone one or both of comburant gas and hot exhaust gas.

16. A method in accordance with claim 15 wherein the steps of directing a fluid fuel phase towards a flameless oxidation zone and causing a jacketing gas jet to be directed towards the said oxidation zone are respectively performed by causing a fluid fuel phase to be conveyed via a first conduit to a first outlet letting into the reaction chamber, and causing a jacketing gas to be conveyed via a second conduit to a second outlet letting into the reaction chamber disposed surroundingly about the first outlet.

17. A method in accordance with claim 15 wherein the jacketing gas comprises one or more gases selected from: a comburant gas; an exhaust gas; an inert gas.

18. A method in accordance with claim 15 wherein the fluid fuel phase is pulverous coal in a carrier gas.