WO2017212255A1

WO2017212255A1 - Burner

Info

Publication number: WO2017212255A1
Application number: PCT/GB2017/051643
Authority: WO
Inventors: Ik Soo Kim
Original assignee: Doosan Babcock Limited
Priority date: 2016-06-08
Filing date: 2017-06-07
Publication date: 2017-12-14
Also published as: GB201610007D0; GB2551166A; EP3469260A1; KR20190024958A

Abstract

A primary conduit for a burner is described having a primary conduit outlet; the primary conduit defining a primary conduit flow channel extending to the primary conduit outlet; wherein the primary conduit includes a primary conduit end pipe (3) proximal the primary conduit outlet (7) defining a flow channel having a linear flow direction from a first inlet end to a second outlet end corresponding to the primary conduit outlet and a primary conduit elbow pipe (1) upstream of and in fluid communication with the primary conduit end portion defining a flow channel having a deviating flow direction from a first inlet end to a second outlet end corresponding to the inlet end of the primary conduit end portion. The primary conduit has in its flow channel successively in a downstream flow direction: a first swirler formation (9a) comprising at least one swirler vane a first swirler location and a second swirler formation (9b) comprising at least one swirler vane at a second swirler location. A burner is described incorporating such a primary conduit.

Description

BURNER

The invention relates to a burner, and in particular a burner for the combustion of particulate carbonaceous fuel. In the preferred case the invention relates to a pulverous fuel burner such as a pulverous coal fired burner. For example the invention relates to a burner for use in a power generation apparatus and to a power generation apparatus including one or more such burners. At its most general concept, the invention relates to a primary air conduit arrangement for such a burner and to a burner incorporating the same.

Introduction

In general terms, a burner for combustion of particulate carbonaceous fuel may comprise a number of components, which may include:

· a primary conduit to supply the pulverous fuel and a conveying gas which may be a comburant gas (often known as "primary" air) to the burner outlet;

• a number of channels arranged for example concentrically around the primary conduit pulverous fuel supply, through which comburant gas and other gas may be supplied to support/ control/ modify combustion at the burner outlet; in a burner for the combustion of particulate carbonaceous fuel there will typically be two or more channels for the combustion air or other comburant gas and these are often known as "secondary" air, "tertiary" air, etc;

• a core conduit or core tube disposed axially centrally within an annular primary conduit to supply for example further comburant gas to support/ control/ modify combustion at the burner outlet, and/ or to locate supplementary equipment, such as igniters, light-up burners, flame monitoring sensors, etc;

• devices to induce a swirling motion into the gas flows for example in the secondary and tertiary (etc.) channels;

• devices to stabilise the flame, often placed on the end of the fuel supply pipe and sometimes known as the "flame-holder";

• devices placed inside the fuel supply pipe to control the fuel distribution at the outlet of that pipe; • supplementary equipment, such as igniters, light-up burners, flame monitoring sensors, etc., optionally installed in a separate tube, which may be located centrally within the fuel pipe where it is known as the "core" tube; the core tube may have its own air or other gas supply; alternatively supplementary equipment may be installed in other locations in the burner or close by.

Where "air" is used herein both with reference to the prior art and with reference to the invention the skilled person will readily appreciate that other oxygen containing comburant gases and mixtures may be substituted in the familiar way for example for oxyfuel firing including a comburant gas having a reduced nitrogen content relative to air, for example comprising mixtures of pure oxygen and/ or recycled flue gas and/ or air. References to a comburant gas will be understood to include mixtures of gases including gases capable of supporting combustion and other gases.

The present invention relates to a primary conduit for a burner as above described, adapted to supply pulverous fuel and a conveying gas to a primary conduit outlet corresponding to a burner outlet, which conveying gas is typically in use a comburant gas (often known as "primary" air); and to a burner incorporating the same.

The present invention relates to a primary conduit having a primary conduit inlet disposed to receive a supply of combustible pulverous fuel and a supply of comburant gas and a primary conduit outlet in the vicinity of which combustion of the fuel is supported during use; the primary conduit defining a flow channel extending from the primary conduit inlet to the primary conduit outlet to convey a mixture of fuel and a gas such as a comburant gas in use. The primary conduit is disposed annularly around a core conduit and may be provided with secondary and tertiary channels as above described. It is known by those knowledgeable in the art that there are a number of variant burner designs available for the combustion of particulate carbonaceous fuel. Implicit in the design of any burner is the requirement to ensure that there must be sufficient comburant gas to supply sufficient oxidant in any oxidant/ fuel mix and an even distribution of fuel in the oxidant to support the consistent combustion of the fuel and to maintain the stability of the flame. Alternative arrangements of burner design which are effective in creating an even distribution of fuel in the oxidant to support the consistent combustion of the fuel and to maintain the stability of the flame are desirable.

Summary of the Invention

According to the invention there is provided a primary conduit for a burner having a primary conduit outlet in the vicinity of which combustion of the fuel is supported during use; the primary conduit defining a primary conduit flow channel extending to the primary conduit outlet to receive and convey a mixture of fuel and a gas such as a comburant gas in use;

wherein the primary conduit includes a primary conduit end pipe proximal the primary conduit outlet defining a flow channel having a linear flow direction from a first inlet end to a second outlet end corresponding to the primary conduit outlet and a primary conduit elbow pipe upstream of and in fluid communication with the primary conduit end pipe defining a flow channel having a deviating flow direction from a first inlet end to a second outlet end corresponding to the inlet end of the primary conduit end pipe;

wherein there are located within the primary conduit end pipe in the annular flow channel about the core conduit successively in a downstream flow direction:

a first swirler formation comprising at least one swirler vane a first swirler location; a second swirler formation comprising at least one swirler vane at a second swirler location.

The change of direction as the fuel and gas mix passes through the elbow pipe may create undesirable flow concentration effects. The invention seeks to mitigate these as pulverous fuel flows into the end pipe and to the outlet by creating pulverous fuel and comburant flow distributions and concentrations that improve combustion performance.

It achieves this by providing in combination at least first and second swirler formations as above described. Each swirler vane comprises in familiar manner an elongate vane formation disposed at an angle to a primary conduit end pipe axial direction to present a leading edge into the primary conduit flow channel. Each swirler vane thereby defines a pressure face and a rear face and presents the pressure face to a flow in the primary conduit flow channel in use, whereby flow is deflected.

A suitable swirler vane angle is between 20° and 60°.

A swirler vane is positioned and configured such that said deflection tends to impart a rotary motion to the flow as so deflected. For example a swirler vane comprises a progressively curved vane formation presenting a leading edge and a progressively curved pressure face to the flow in the primary conduit flow channel in use.

A swirler vane may comprise an elongate vane formation of suitable cross-sectional shape which for example include L-shaped, rectangular, triangular, C-shaped, U- shaped etc.

The first and second swirler formations are disposed to generate a more swirled flow towards the outside of the primary conduit flow channel to obtain more uniform distribution in the particle flow as it enters the end pipe from the elbow pipe.

One, other or both of the first and second swirler formations preferably comprises a plural set of swirler vanes. Advantageously, each swirler vane in such a plural set is geometrically congruent in shape excepting that they may be curved in an opposite sense.

Advantageously a plural set of swirler vanes comprises one or more pairs of swirler vanes. Advantageously each swirler vane of the pair is angled disposed at an angle to a primary conduit end pipe axial direction at the same angle but in the opposite sense. Advantageously each swirler vane of the pair is geometrically congruent in shape excepting that where the vanes have a progressive curve they are curved in an opposite sense.

Advantageously a plural set of swirler vanes comprises two pairs of swirler vanes as above described. A first pair may be located at an opposite position by 180 degrees to a second pair. For example a first pair may be in an uppermost part of the primary conduit end pipe above an elongate axis of the end pipe and a second pair may be in a lowermost part of the primary conduit end pipe below the an elongate axis of the end pipe. A first swirler formation is located a first swirler location in that a leading end thereof is presented at a first position in the primary conduit flow channel, the first swirler formation extending along the primary conduit flow channel for a first length to a downstream end thereof. For example a leading end is a leading edge of one or more vane formations as above described that make up the first swirler formation and a downstream end is a trailing edge thereof. Similarly a second swirler formation is located a second swirler location downstream of the first in that a leading end thereof is presented at a second position in the primary conduit flow channel, the second swirler formation extending along the primary conduit flow channel for a second length to a downstream end thereof. For example a leading end is a leading edge of one or more vane formations as above described that make up the first swirler formation and a downstream end is a trailing edge thereof.

Advantageously the first and second swirler formations are disposed to overlap, in that the second position of the leading end of the second swirler formation is part way along the length of the first formation between a leading end and a downstream end thereof as above defined. It is for example at the mid point of the length of the first formation.

In a possible embodiment the primary conduit end pipe is disposed coaxially about a core conduit, the core conduit defining a core flow channel for conveying a further gas flow such as a further comburant gas flow to a core conduit outlet, and so disposed that the primary conduit end pipe defines an annular flow channel about the core conduit. Other structures adapted further to modify the flow may be provided in the primary conduit, in particular downstream of the swirler formations.

Optionally a first particle diffuser may be provided comprising an axially mounted bullet formation, which bullet formation includes progressively in a downstream flow direction a first wall portion that flares in radially outwardly extending manner to provide a progressively increasing occlusion of the primary conduit flow channel, and a second wall portion that taper in radially inwardly extending manner to provide a progressively decreasing occlusion of the primary conduit flow channel. This provides the advantage that the bullet formation presents an occlusion that interacts with the flow generated by the swirler formations to stabilise the distribution as it flows towards the burner exit.

Optionally the bullet formation may include an untapered cylindrical third wall portion intermediate between the first and second wall portions.

Optionally the bullet formation may be mounted so as to be translatable axially to and fro along the burner. This provides the advantage of enabling control in use of the distribution of particles in the pulverous flow.

In an embodiment comprising a core conduit, the first particle diffuser may be mounted about the core conduit for example on an outer surface of the core conduit. The bullet formation may be mounted to be slideably axially along the core conduit and thus axially to and fro along the burner

The first swirler formation is preferably located in the primary conduit end pipe generally at or shortly downstream of the point of communication between the primary conduit end pipe and the primary conduit elbow pipe and for example is located downstream of the point of communication between the primary conduit end pipe and the primary conduit elbow pipe by no more than a length equivalent to the transverse extent and for example the diameter of the primary end pipe. Optimally the first swirler formation is located closer to the point of communication between the primary conduit end pipe and the primary conduit elbow pipe, for example spaced therefrom by no more than 20 % and optimally at about10% of a primary conduit end pipe diameter.

The second swirler formation is located further downstream of but preferably overlaps with the first swirler formation. The bullet formation where present is located further downstream of and preferably beyond the second swirler formation. The invention seeks to create pulverous fuel and comburant flow distributions and concentrations at the primary conduit outlet that improve combustion performance. It achieves this by providing in combination first and second swirler formations and other optional structures such as a bullet formation as above described.

The primary conduit to which the principles of the invention applies otherwise typically comprises in familiar manner a continuous flow channel for receiving a supply of a gas such as a comburant gas and a supply of combustible pulverous fuel and conveying the same to a combustion site of a burner, which has at least a primary conduit end pipe extending along a burner axis to the burner outlet to define a linear flow direction parallel to the burner axis, and an elbow portion immediately upstream of the primary conduit end pipe to define a deviating flow direction changing in direction from an upstream flow direction upstream of the elbow portion to a downstream flow direction downstream of the elbow portion and in the end pipe.

A core conduit optionally extends through the end pipe coaxially with the end pipe on a burner axis so that an outer surface of the core conduit and an inner surface of the end pipe define an annular primary flow channel, and so that an inner surface of the core conduit defines a fluidly isolated core flow channel, in generally familiar manner.

The primary conduit end pipe preferably has a length at least three times its transverse extent and in the typical case where the primary conduit end pipe is cylindrical at least three times its diameter. The primary conduit more completely includes a primary conduit inlet disposed to receive a supply of combustible pulverous fuel and a supply of a gas such as a comburant gas and a primary conduit outlet in the vicinity of which combustion of the fuel is supported during use; the primary conduit defining a primary conduit flow channel extending from the primary conduit inlet to the primary conduit outlet to convey a mixture of fuel and a gas such as a comburant gas in use; with the primary conduit elbow pipe and end pipe to which the invention principally relates being located in a downstream portion of the primary conduit consecutively adjacent towards the outlet. The primary conduit is preferably in fluid communication at the primary conduit inlet with a supply of combustible pulverous fuel and a supply of comburant gas.

In a more complete aspect, a burner is provided having a primary conduit as above described.

In this more complete aspect there is provided a burner having a burner inlet for receiving a supply of combustible pulverous fuel and a supply of comburant gas and a burner outlet in the vicinity of which combustion of the fuel is supported during use; said burner comprising:

a primary conduit for conveying a mixture of fuel and gas such as comburant gas in accordance with the above described first aspect.

The burner thus includes a primary conduit with primary end pipe that defines a flow channel for conveying a mixture of fuel and gas such as comburant gas disposed about the core conduit, for example coaxially.

The invention is characterised by the provision within the primary conduit of first and second swirler formations and a bullet formation as above described, to create pulverous fuel flow and comburant distributions and concentrations that improve combustion performance.

Subject to these basic features, a burner of the invention admits additional elements to supply material to the burner outlet and/ or to support combustion and flame stability at the burner outlet and/ or to facilitate mixing of one or more flow streams.

In particular optionally the burner may further comprise at least one further conduit, for example one or more secondary conduits and optionally one or more tertiary or higher order conduits comprising further flow channels for the supply of further gases such as further comburant gases to the combustion site at the burner outlet. Typically such a further conduit is disposed about the primary conduit, for example coaxially therewith. Optionally such a further conduit may comprise a swirl generation device to impart a swirl to the flow of gas therein. A conduit may comprise any suitable arrangement defining and elongate flow channel. Each of the core, primary and if applicable secondary, tertiary and higher order conduits may comprise one or more elongate structures defining elongate flow channels. Where a conduit comprises plural flow channels they are for example generally parallel. In a familiar design, core, primary, secondary and tertiary or higher order conduits may be disposed about each other for example axially to define axial flow in a burner elongate direction. For example, a core conduit may be provided along a burner axis, a primary conduit may be disposed therearound, a secondary conduit disposed further therearound, and tertiary or higher order conduits disposed further therearound to define parallel axial flow channels in a burner elongate direction. Such an arrangement will be familiar.

Typically for example concentric and/ or coaxial tubes such as concentric and/ or coaxial cylinders may define annular flow regions or sectors thereof for the primary, secondary and higher order conduits. For example, annular flow channels comprising single or plural annular sectors may make up the primary flow, secondary flow and tertiary flow as desired.

Preferably, the burner of the invention is adapted for the combustion of particulate carbonaceous fuel and in the preferred case is a pulverous fuel burner. Preferably, the burner comprises a source of particulate carbonaceous fuel to supply fuel to a burner inlet, and in particular at least to an inlet of the primary conduit.

Preferably, the pulverous fuel burner is a pulverised coal burner, for example a burner for pulverised bituminous coal or dried pulverised lower rank coal. Consequently preferably the pulverous fuel is pulverised coal, for example pulverised bituminous coal or dried pulverised lower rank coal. Alternatively, the burner of the invention may be adapted for the combustion of pulverous carbonaceous fuel such as biomass, pulverous carbonaceous waste material, etc.

In a more complete aspect of the present invention, there is provided a combustion apparatus comprising:

a combustion chamber; and

at least one and preferably a plurality of burners as hereinbefore described located so as to define combustion sites within the combustion chamber. Preferably the combustion apparatus comprises a boiler for generating steam.

Preferably the fuel used is particulate carbonaceous fuel and in the preferred case is a pulverous fuel, most preferably pulverised coal.

Brief Description of the Drawings

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

Figure 1 shows an example of a possible embodiment of the invention;

Figure 2 illustrates design/ dimension considerations for the embodiment of figure 1. Detailed description of the preferred embodiment(s)

Figure 1 shows an example of a possible embodiment of the invention in which a primary air elbow pipe 1 leads via a primary air end pipe 3 to a burner outlet 7. The elbow pipe defines a 90 degree change in flow direction and the end pipe provides a linear axial flow direction to the burner outlet that has a length of at least three times its diameter. These together form the downstream part of a primary conduit disposed to convey a supply of combustible pulverous fuel and a supply of comburant gas to the primary conduit outlet in the vicinity of which combustion of the fuel is supported during use. The primary conduit is disposed annularly around a core conduit 5 for the supply of core air to the burner outlet. Other conduits (not shown) may be included in familiar manner in a complete burner design.

The primary flow channel defined by the primary conduit includes moving progressively downstream first 9a and second 9b sets of swirler vanes and a bullet formation 15 projecting outwardly from the outside surface of the core conduit. Each is axially mounted about the burner axis. The bullet structure may be mounted about the core conduit so as to be translatable axially along the burner.

In the illustrated embodiment each of the first 9a and second 9b sets of swirler vanes comprises a set of four vanes disposed as two pairs. A first pair is shown above and a second pair is shown below. Each vane in a pair is angled to present a leading edge and facing pressure surface into an axial flow direction in the end pipe, with the two members of the pairs being essentially identical except in that they are configured to be mirrored pairs when viewed from the axial direction. That is, each member of the pair is angled to a pipe axial direction at the same angle but in the opposite sense. In the event that the vanes have a progressive curve they are likewise curved in an opposite sense.

The first swirler formation is preferably located in the primary conduit end pipe shortly downstream of the point of communication between the primary conduit end pipe and the primary conduit elbow pipe so as to define a first vane start point 1 1a where the leading edges of the first vanes are positioned. The second swirler formation is located further downstream of the first so as to define a second vane start point 1 1 b where the leading edges of the second vanes are positioned. In this embodiment the second start point is in the middle of the length of the first vane set so that the two sets overlap. The bullet formation is located further downstream of and beyond the second swirler formation.

The swirler vanes tend to generate swirling flow outer side only to obtain more uniform particle distribution and stabilise the flow in the PA end tube. The illustrated embodiment shows two sets of 4 vanes + 4 vanes but the starting points are different so that the 2^nd set starts middle length of 1^st set swirler. Other different sets have been examined, as inset image (Type A & B). Two sets break the flow more efficiently and the swirling motion is maintained by the 2^nd set swirler. The bullet then acts to re-distribute the particles and stabilise flow. It can be moveable to up/down to control the mixing and flow.

The flow pattern is illustrated and suitable design parameters considered with reference to Figure 2.

Flow generally changes from the elbow pipe bent flow to straight flow in the PA end pipe. Two general representative flows are shown. The Swirler vane arrangement generates an outer swirling flow "A" and a straightened inner flow "B". A protective sleeve 17 for the core pipe/ bullet and a protective liner 19 for the inside surface of the end pipe may be provided. Suitable design parameters are as follows.

Non swirler area "B" ratio to PA area "C" (Protective Sleeve inner diameter)

- 40%< B/C<70%

- Recommend 50%< B/C<60%

- Therefore swirler height can be obtained.

• Thickness of Swirler vane:

- 40mm used in here

- Depending on erosion, the thickness can be varied.

· Swirler Vane Angle

- 20°<Swirler Vane<60°

- Recommend 45°

- Smaller angle leads longer vane length

• PA Pipe length "L"

- L≥1.5 x 0PA

- Recommend L≥ 3 x 0ΡΑ

Elbow bend radius "R"

- R > C/2

- Used in here R=C

· 10% < Bullet Blockage <40%

- Recommend 20%

(60% < Area Ratio E/C < 90%)

• Bullet Location "K", K≥0mm

- Recommend K~100mm from the Swirler end.

These and other combinations and variations on the principles of the invention may be optimised to mitigate undesirable flow concentration effects due to the change of direction as the fuel and gas mix passes via the elbow pipe into the end pipe creating pulverous fuel and comburant flow distributions and concentrations at the end pipe outlet that improve combustion performance.

Claims

1. A primary conduit for a burner having a primary conduit outlet; the primary conduit defining a primary conduit flow channel extending to the primary conduit outlet;

wherein the primary conduit includes a primary conduit end pipe proximal the primary conduit outlet defining a flow channel having a linear flow direction from a first inlet end to a second outlet end corresponding to the primary conduit outlet and a primary conduit elbow pipe upstream of and in fluid communication with the primary conduit end pipe and defining a flow channel having a deviating flow direction from a first inlet end to a second outlet end corresponding to the inlet end of the primary conduit end pipe;

a first swirler formation comprising at least one swirler vane a first swirler location;

a second swirler formation comprising at least one swirler vane at a second swirler location.

2. A primary conduit in accordance with claim 1 wherein each swirler vane comprises an elongate vane formation disposed at an angle to a primary conduit end pipe axial direction to present a leading edge into the primary conduit flow channel and thereby defines a pressure face and a rear face and presents the pressure face to a flow in the primary conduit flow channel.

3. A primary conduit in accordance with claim 1 or claim 2 wherein each swirler vane comprises a progressively curved vane formation presenting a leading edge and a progressively curved pressure face to a flow in the primary conduit flow channel.

4. A primary conduit in accordance with any preceding claim wherein each swirler vane comprises a vane formation at a vane angle of between 20° and 60° to a primary conduit end pipe axial direction.

5. A primary conduit in accordance with claim 4 wherein each swirler vane comprises a vane formation at a vane angle of about 45° to a primary conduit end pipe axial direction.

6. A primary conduit in accordance with any preceding claim wherein one, other or both of the first and second swirler formations comprises a plural set of swirler vanes.

7. A primary conduit in accordance with claim 6 wherein each swirler vane in a plural set is geometrically congruent in shape excepting that some may be curved in an opposite sense.

8. A primary conduit in accordance with claim 6 or 7 wherein a plural set of swirler vanes comprises one or more pairs of swirler vanes.

9. A primary conduit in accordance with claim 8 wherein each swirler vane of the pair is angled disposed at an angle to a primary conduit end pipe axial direction at the same angle but in the opposite sense.

10. A primary conduit in accordance with claim 8 or 9 wherein each swirler vane of the pair is geometrically congruent in shape excepting that where the vanes have a progressive curve they are curved in an opposite sense.

1 1. A primary conduit in accordance with one of claims 8 to 10 wherein the plural set of swirler vanes comprises exactly two pairs of swirler vanes with a first pair located at an opposite position by 180 degrees a second pair.

12. A primary conduit in accordance with any preceding claim wherein the first swirler formation is located a first swirler location in that a leading end thereof is presented at a first position in the primary conduit flow channel, the second swirler formation is located a second swirler location downstream of the first in that a leading end thereof is presented at a second position in the primary conduit flow channel downstream of the first position, and the first and second swirler formations are disposed to overlap, in that the second position of the leading end of the second swirler formation is part way along a length of the first formation between a leading end and a downstream end thereof.

13. A primary conduit in accordance with any preceding claim wherein the primary conduit end pipe is disposed coaxially about a core conduit, the core conduit defining a core flow channel for conveying a further gas flow such as a further comburant gas flow to a core conduit outlet, and so disposed that the primary conduit end pipe defines an annular flow channel about the core conduit.

14. A primary conduit in accordance with any preceding claim further comprising an axially mounted bullet formation, which bullet formation includes progressively in a downstream flow direction a first wall portion that flares in radially outwardly extending manner to provide a progressively increasing occlusion of the primary conduit flow channel, and a second wall portion that taper in radially inwardly extending manner to provide a progressively decreasing occlusion of the primary conduit flow channel an untapered cylindrical third wall portion intermediate between the first and second wall portions.

15. A primary conduit in accordance with any preceding claim wherein the bullet formation includes an untapered cylindrical third wall portion intermediate between the first and second wall portions.

16. A primary conduit in accordance with any preceding claim wherein the bullet formation is mounted so as to be translatable axially along the burner.

17. A primary conduit in accordance with any preceding claim wherein the primary conduit end pipe has a length at least three times its transverse extent.

18. A primary conduit in accordance with any preceding claim further comprising a primary conduit inlet disposed to receive a supply of combustible pulverous fuel and a supply of a gas such as a comburant gas; the primary conduit defining a primary conduit flow channel extending from the primary conduit inlet to the primary conduit outlet to convey the mixture of fuel and gas to the outlet, wherein the primary conduit elbow pipe and end pipe are located in a downstream portion of the primary conduit consecutively adjacent towards the outlet.

19. A primary conduit in accordance with claim 18 in fluid communication at the primary conduit inlet with a supply of combustible pulverous fuel and a supply of comburant gas.

20. A burner having a burner inlet for receiving a supply of combustible pulverous fuel and a supply of comburant gas and a burner outlet in the vicinity of which combustion of the fuel is supported during use; said burner comprising a primary conduit in accordance with any preceding claim.

21. A burner in accordance with claim 20 further comprising at least one further conduit, for example one or more secondary conduits and optionally one or more tertiary or higher order conduits comprising further flow channels for the supply of further gases such as further comburant gases to a combustion site at the burner outlet.

22. A burner in accordance with claim 20 or 21 adapted for the combustion of particulate carbonaceous fuel such as pulverised coal.