The invention relates to a burner, and in particular a burner for the combustion of carbonaceous fuel. For example the invention relates to a burner for the combustion of particulate solid carbonaceous fuel such as pulverous coal or biomass, liquid fuel such as fuel oil, or gaseous fuel such as gaseous hydrocarbon. 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. In particular, the invention relates to a burner outlet shroud arrangement for such a burner and to a burner incorporating the same. In a possible case the invention relates to a pulverous fuel burner such as a pulverous coal fired burner.

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

• a primary conduit to supply a mixture of the 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 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 carbonaceous fuel such as solid 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.

Where it is desirable to reduce flame temperature and/ or emissions in a burner it is a known solution to make use of recycled flue gas. Flue gas recycle (FGR) principles can be applied across a range of burner designs from conventional through to flameless oxidation (FLOX) burners, and may be effective in suppressing flame temperature and in reducing emissions and in particular NOx formation.

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.

Alternative arrangements of burner design which are effective in reducing flame temperatures and/ or emissions from a burner are desirable.

Summary of the Invention

According to the invention there is provided a burner having a burner inlet for receiving a supply of 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 defining a primary flow channel extending along a burner axis to a primary conduit outlet for conveying a mixture of fuel and a primary gas such as a comburant gas;

a secondary conduit defining a secondary flow channel disposed about the primary conduit extending parallel to a burner axis to a secondary conduit outlet for conveying a secondary gas such as a comburant gas;

a burner shroud comprising a shroud outlet plate located at the burner outlet transverse to the burner axis, having a shroud central outlet and a plate formation extending outwardly from the shroud central outlet over and beyond the primary conduit outlet and the secondary conduit outlet;

a primary flow divider fluidly coupled to the shroud central outlet and configured thereat to divide the flow in the primary flow channel between a first primary subflow to the shroud central outlet and a second primary subflow diverted away from the shroud central outlet.

The invention is applicable to a range of burner designs of the general type having a primary conduit defining a primary flow channel extending along a burner axis and at least one secondary conduit defining a secondary flow channel disposed about the primary conduit, and further optionally as below described encompasses burners with tertiary or other higher conduits in familiar manner. It is distinctly characterised by the provision of a burner shroud, by the division of the primary stream containing fuel into two substreams, and by the creation thereby of two reaction zones downstream of the burner outlet. The effect of this design when appropriately configured can be to generate flue gas at the front of the burner, to produce an effect equivalent to flue gas recirculation and/or to enhance FGR recirculation.

In a burner in accordance with the invention, the burner includes a primary conduit defining a primary flow channel extending along the burner axis, and a secondary flow channel disposed around and fluidly isolated from the primary flow channel and defined by one or more secondary conduits disposed around the primary conduit. At a downstream end of the primary conduit proximal the burner outlet there is provided a primary flow divider which divides the flow in the primary flow channel between first and second streams. A first flow stream is directly coupled in fluid tight manner to the shroud central outlet, and thus a first portion of the primary flow passes directly through the central outlet. The shroud central outlet serves as a central burner outlet in use. The flow through the burner central outlet tends to create a first reaction zone in the combustion zone beyond the burner.

A second flow stream comprises a portion of the primary flow that is diverted away from the shroud central outlet, and diverted to impinge into and be deflected by a rear face of the plate formation extending outwardly from the shroud central outlet. The plate formation serves effectively as a baffle plate. Thus, the primary flow divider is configured to divides the flow in the primary flow channel between the first primary subflow and the second primary subflow and to direct the first primary subflow through the shroud central outlet and to divert the second primary subflow away from the shroud central outlet to impinge into and be deflected by a rear face of the plate formation outwardly away from the shroud central outlet.

Similarly, the secondary flow conduit is so disposed relative to the plate formation extending across it that flow from the secondary flow channel impinges on and is deflected by a rear face of the plate formation in the same manner. The second flow stream of the primary flow and the secondary flow are both diverted by the plate formation, acting as baffle plate, and tend to pass towards a perimeter thereof.

The plate formation is suitably configured, for example by the provision of suitable outlet means at or towards the perimeter thereof, to cause this deflected flow comprising a partitioned part of the primary flow and the secondary flow to pass beyond the burner at or towards the perimeter of the baffle plate, with a tendency thereby to create a second reaction zone in the combustion zone beyond the burner distinct from the first reaction zone.

The two reaction zones are for example created in the manner illustrated in figure 2 and described in more detail below.

In a convenient embodiment, the primary flow divider comprises an elongate annular structure coaxially located with but of smaller transverse extent than, and in the preferred case where both are cylindrical of smaller diameter than, the primary conduit, having an outlet end coupled in fluid tight manner with the shroud central outlet and an inlet end in fluid communication with the primary flow channel. Such an arrangement effectively divides the primary flow channel into two streams, comprising a first primary subflow through the central channel defined by the annular structure and directly to the shroud central outlet, and a second primary subflow passing between an external wall of the central annulus and an internal wall of the primary conduit, which then impinges upon and is diverted by a rear surface of the plate formation in the manner above described.

Thus, the primary flow is effectively divided between a first stream which passes directly out of the shroud central outlet acting as a central burner outlet to a first reaction zone as illustrated in figure 2, and a second stream which mixes with the stream from the secondary flow channel, is deflected by the shroud plate, and forms second reaction zones in the manner illustrated in figure 2.

Optionally the burner comprises one or more tertiary conduits each defining a tertiary flow channel for conveying a tertiary gas such as a comburant gas. For example plural tertiary conduits are provided disposed around the primary and secondary. In such an embodiment the shroud outlet plate includes for each such tertiary conduit a shroud tertiary aperture fluidly communicating with the tertiary conduit to direct tertiary gas from the tertiary conduit to a combustion zone beyond the burner. In particular the shroud tertiary apertures are configured to direct tertiary gas to the first reaction zone as above defined.

A conduit may comprise any suitable arrangement defining and elongate flow channel. Each of the primary and secondary conduits and if applicable tertiary, higher order and core conduits may each 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, primary, secondary and where applicable 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 primary conduit may be provided along a burner axis, a secondary conduit may be disposed therearound, and tertiary or higher order conduits where present 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. A primary, secondary or higher order conduit may incorporate one or more swirler devices to induce a swirling motion into the gas flows within the conduit in use.

In a particular preferred case each tertiary conduit includes within its flow channel one or more swirler devices to induce a swirling motion into the gas flows within the conduit in use.

A secondary or higher order conduit may be provided with an outlet disposed to direct flow beyond the outlet away from a burner axial direction, so as to induce a swirling motion into the gas flow beyond the outlet.

In a particular preferred case each tertiary conduit is provided with an outlet disposed to direct flow beyond the outlet away from a burner axial direction, so as to induce a swirling motion into the gas flow beyond the outlet. Advantageously plural tertiary conduits are provided disposed about a burner axis and with outlet apertures co-operably disposed to direct flow beyond the outlet away from a burner axial direction so as to induce a swirling motion into the tertiary gas flow beyond the outlet. Advantageously each such conduit is additionally provided with one or more swirler devices to induce a swirling motion into the gas flow within the conduit, and this individual swirling motion in each stream complements the global swirling motion induced downstream. Advantageously, a primary conduit in accordance with the invention comprises a primary tube such as a cylinder, elongate in a burner elongate direction and thereby defining a burner axis, such that an internal surface of the primary conduit tube defines a primary flow channel. A downstream end of the primary conduit tube is then provided with a primary flow divider comprises an elongate annular structure coaxially located with but of smaller transverse extent than, and in the preferred case where both are cylindrical of smaller diameter than, the primary conduit tube, having an outlet end coupled in fluid tight manner with the shroud central outlet and an inlet end in fluid communication with the primary flow channel.

Such an arrangement divides the primary flow channel at the downstream end into two streams, comprising a first primary subflow through the central channel defined by the annular structure and directly to the shroud central outlet, and a second primary subflow passing between an external wall of the central annulus and an internal wall of the primary conduit tube, which then impinges upon and is diverted by a rear surface of the plate formation in the manner above described.

Advantageously an outwardly flared end portion of the flow divider may be provided to guide the second primary subflow outwardly as it impinges against the rear surface of the plate formation.

Advantageously, a secondary conduit in accordance with the invention comprises a secondary tube such as a cylinder, elongate in a burner elongate direction and coaxially located with and fluidly isolated from the primary conduit tube such that an external surface of the primary conduit tube and an internal surface of the secondary conduit tube define a secondary flow channel annularly about the primary flow channel.

Advantageously an outwardly flared end portion of the primary may be provided to guide the secondary flow outwardly as it impinges against the rear surface of the plate formation. Tertiary conduits such as tertiary conduit tubes may be provided. Typically plural tertiary conduits may be provided disposed around the burner beyond and fluidly isolated from the secondary conduit. The primary conduit to which the principles of the invention applies 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 fuel and conveying the same to a combustion site of a burner at the burner outlet. The primary conduit more completely includes a primary conduit inlet disposed to receive a supply of combustible 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.

The primary conduit is preferably in fluid communication at the primary conduit inlet with a supply of combustible fuel and a supply of comburant gas. Advantageously the burner of the invention is adapted for the combustion of carbonaceous fuel, for example particulate solid carbonaceous fuel such as pulverous coal or biomass, liquid fuel such as fuel oil, or gaseous fuel such as gaseous hydrocarbon. Advantageously the burner comprises a source of carbonaceous fuel to supply fuel to a burner inlet, and in particular at least to an inlet of the primary conduit.

In a possible case, 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 in such case, 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 a particulate carbonaceous fuel and in the preferred case is a pulverous solid 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 a front face view of a burner shroud of an example of a possible embodiment of the invention;

Figure 2 shows cross-sectional views of the vicinity of the burner outlet and burner shroud of the embodiment of figure 1 ;

Figure 3 illustrates the creation of two reaction zones downstream of the burner of the embodiment of figures 1 and 2.

Detailed description of the preferred embodiment(s) Figures 1 and show a burner shroud embodying the principles of the invention at a burner outlet end of a burner, Figure 1 illustrating a front elevation of the shroud plate, and figure 2 respectively from left to right in side cross section first the entire plate and downstream end of the burner and then the burner outlet end in more detail and in simplified exploded representation. It should be emphasised that components in figure 2, and in particular the flow divider 1 1 and features associated with it, may be shown truncated for illustrative purposes.

A shroud 1 is shown in front view comprising a shroud plate 3 extending outwardly from a central outlet 5 on the burner axis that serves as a burner central outlet to supply a combustion zone downstream of the outlet in use. Spaced evenly around the central outlet 5 are four tertiary outlets 7 that communicate with tertiary air tubes 17 to supply tertiary air (TA) to the combustion zone. A primary conduit comprising a primary air tube 13 defines a primary flow channel extending along the burner axis to convey a mixture of fuel and primary air (PA). A secondary conduit comprising a secondary tube 15 disposed annularly around and coaxially with the primary tube defined a secondary flow channel for the supply of secondary air (SA).

An annular flow divider 1 1 sits in the primary tube at a downstream end. The main structure of the flow divider 11 is an elongate annular cylinder coaxially located within the primary tube and coupled in fluid tight manner to the outlet 5. The flow divider 11 is shown truncated for illustrative purposes and is likely in practice to be relatively more elongate. However it illustrates the function of the divider which acts to partition the primary air between two streams, a first stream that flows directly through the divider 5 and a second stream that flows between the outer wall of the divider 5 and the inner wall of the primary tube. This partition of the primary flow into two sub-streams (PA1 and PA2) is central to the invention.

The first flow stream that flows directly through the divider 5 passes out of the central outlet providing a fuel/ primary air mix (PA1) to a first reaction zone in the combustion zone downstream of the burner.

The rear face of the plate formation 3 otherwise extends across and occludes the outlet of the primary tube and the outlet of the secondary tube. It thus occludes and deflects the second stream of fuel/ primary air (PA2) and the secondary air (SA) respectively exiting the outlet of the primary tube and the outlet of the secondary tube. The deflection is further guided by respective flared end portions of the divider 5 and primary tube 13. The second flow stream of the primary flow and the secondary flow are both diverted by the plate formation, acting as baffle plate, and tend to pass towards a perimeter thereof. The plate formation is suitably configured, for example by the provision of suitable outlet means at or towards the perimeter thereof, to cause this diverted flow comprising a partitioned part of the primary flow and the secondary flow to pass beyond the burner at or towards the perimeter of the baffle plate, with a tendency thereby to create second reaction zones in the combustion zone downstream of the burner in the manner illustrated in more detail in figure 3.

The central partitioned stream of primary air/ fuel PA1 passes through the central aperture to Reaction Zone 1. The tertiary air supply TA is directed generally to provide additional supporting oxidant to this zone in familiar manner. The outer partitioned stream of primary air/ fuel PA2 and the secondary air SA are deflected by the plate to leave the burner peripherally of the plate and thereby form Reaction Zones 2. The effect of this design when appropriately configured can be in effect to generate flue gas at the front of the burner, to produce an effect equivalent to flue gas recirculation and/or to enhance FGR recirculation.

The tertiary outlets 7 are directional, being disposed to direct the outlet flow away from the burner axial direction in co-operative manner so as to impart a general swirling motion about the burner axial direction to the tertiary flow downstream of the burner outlet.

Advantageously each tertiary conduit is additionally provided with one or more swirler devices (not shown) to induce a swirling motion into the individual gas flow within the conduit, and this individual swirling motion in each stream complements the general swirling motion induced downstream by the off-axis directionality of the outlets.

Design considerations and optional features to control this effect will include the following.

> PA stream contains fuel and split into 2 streams, PA1 and PA2, to the reaction zone 1 and 2.

- PA can have swirler(s) to generate swirling flow - Inside of PA2 can have a fuel concentrator to control the fuel concentration

- PA2 can have bluff body(s) to stabilise the reaction zone 2.

> SA oxidant stream will inject along PA, but changing direction to the reaction zone 1 in order to react with the partial PA fuel, PA1.

- SA can have a swirler to generate swirling flow.

- SA pipe attached to PA2 can have a flame holder to stabilise the reaction zone 2.

> TA oxidant stream will directly interact with the fuel stream PA2 to form reaction zone 2.

- TA can be tilted to generate swirling flow.

- TA can be tilted to disturb PA2 directly or indirectly.

- Number of TA≥ 2

> Flue gas generated by the reaction zone 1 will provide their flue gas to the reaction zone 2.

> Burner Shroud will guide the reaction zone 1 formation.