ES2929593T3 - Burner assembly, method of operating said burner assembly and plant comprising said burner assembly - Google Patents

Abstract

A burner assembly for burning pulverized fuel including: a main duct (2) extending along a longitudinal axis (A) into which a flow of air and pulverized fuel flows in one direction (D); the primary conduit (2) being provided with an inlet (7) and an outlet (8); and a homogenizing device (26) housed inside the primary duct (2) and comprising a hollow body (37) substantially centered on the longitudinal axis (A) and provided with an outer surface (38) and an inner surface (39). ); at least one eddy (40; 41) arranged on the outer surface (38) and/or on the inner surface (39) to create a gradient between the tangential components of the air and fuel flow velocities flowing out of the hollow body (37) and inside the hollow body (37). (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Burner assembly, method of operating said burner assembly and plant comprising said burner assembly

technical field

The present invention relates to a burner assembly and to a method of operating said burner assembly. In particular, the present invention relates to a burner assembly configured to burn pulverized fuel such as, for example, pulverized coal or pulverized biomass.

The present invention also refers to a steam generation thermal plant comprising said burner assembly.

Background art

In the solid fuel combustion sector, there is a growing need to optimize combustion processes by reducing unburned fuel and excess air. However, this optimization must be carried out always keeping the levels of harmful emissions (such as, for example, CO and NOx) below the legal limits.

Some solutions are described in the documents WO2015/037589, US2010/123027 and US4924784. In particular, document WO2015/037589 illustrates the features of the preamble of claim 1.

Description of the invention

Therefore, an object of the present invention is to provide a burner assembly, which is capable of optimizing the combustion of solid fuels and, at the same time, of complying with the legal limits in terms of emissions.

In accordance with these objects, the present invention relates to a burner assembly for burning pulverized fuel, comprising:

• a primary duct extending along a longitudinal axis where a stream of air and fuel spray flows in one direction; the primary duct which is provided with an inlet and an outlet;

• a homogenizing device housed inside the primary conduit and comprising a hollow body substantially centered on the longitudinal axis and provided with an outer surface and an inner surface; at least one turbulence generator arranged on the outer surface and/or on the inner surface to create a gradient between the tangential components of the velocities of the air and fuel flows flowing out of the hollow body and into the body hole.

A further object of the present invention is to provide a method for operating a burner assembly according to claim 15.

Still a further object of the present invention is to provide a steam generation plant according to claim 16.

Brief description of the drawings

Additional characteristics and advantages of the present invention will be evident from the following description of a non-limiting embodiment thereof, with reference to the figures of the accompanying drawings, where:

- Figure 1 is a schematic sectional view, with parts removed for clarity, of the burner assembly according to the present invention;

- Figure 2 is a schematic perspective view, with parts in section and parts removed for clarity, of a burner assembly according to the present invention;

- Figure 3 is a schematic perspective view, with parts in section and parts removed for clarity, of a burner assembly according to the present invention according to a first embodiment;

- Figure 4 is a schematic perspective view, with parts in section and parts removed for clarity, of a burner assembly according to the present invention according to a second embodiment;

- Figure 5 is a schematic perspective view of a first detail of Figure 1;

- Figure 6 is a schematic perspective view of a second detail of Figure 1;

- Figure 7 is a schematic sectional view of a third detail of Figure 1;

- Figure 8 is a schematic perspective view of the third detail of Figure 1;

- Figure 9 is a schematic representation of the burner assembly according to the present invention including a velocity diagram.

Best Mode for Carrying Out the Invention

In Figure 1, reference numeral 1 indicates a burner assembly according to the present invention.

In particular, the burner assembly 1 is configured to burn pulverized solid fuel and is part of a steam generation thermal plant.

In the non-limiting example described and illustrated herein, the burner assembly 1 is configured to burn pulverized coal. The embodiments envision that the burner assembly 1 is configured to burn biomass (eg pellets, bones of various kinds and types, shells of various kinds and types, etc.), or to burn secondary solid fuel (SSC), etc.

In principle, the burner assembly 1 can burn any solid fuel that can be adequately pulverized.

The burner assembly 1 comprises a primary conduit 2, a secondary conduit 3, a tertiary conduit 5 and an inlet assembly 6.

The primary conduit 2 extends along a longitudinal axis A and is provided with an inlet 7 connected to the inlet assembly 6, and an outlet 8 facing the combustion chamber of the thermal plant (not shown for simplicity).

Outlet 8 and inlet 7 are preferably axial.

The secondary conduit 3 extends around at least a part of the primary conduit 2 and is coaxial with the primary conduit 2. In particular, the secondary conduit 3 extends around an outlet part 9 of the primary conduit 2, which includes the outlet 8.

Tertiary duct 5 extends around secondary duct 3 and is coaxial with primary duct 2 and secondary duct 3.

In use, a pulverized fuel-air mixture flows in the primary conduit 2 in a direction D from the inlet assembly 6. The inlet assembly 6 receives a pulverized fuel-air mixture from a dryer mill (not shown for simplicity). ).

Air, usually defined in technical jargon as "secondary air", flows in secondary duct 3, while air, normally defined in technical jargon as "tertiary air", flows in tertiary duct 5.

With reference to Figures 1 and 2, the inlet assembly 6 is provided with an elbow conduit 10 and at least one inclined part 13.

The first elbow conduit 10 is coupled to the inlet 7 of the primary conduit 2.

The inclined part 13 is arranged upstream of the first bend conduit 10 along the flow direction of the flow in the inlet assembly 6.

The first elbow duct 10 is provided with a rear wall 11. The rear wall 11 is preferably transverse to the longitudinal axis A. In particular, the rear wall 11 forms an angle p with the longitudinal axis A facing the inlet 7. Preferably , the angle p is greater than 90°, more preferably greater than 120°.

In the non-limiting example described and illustrated herein, the first elbow conduit 10 defines a bend of approximately 90°.

Preferably, the inclined part 13 is directly coupled to the first elbow conduit 10.

An embodiment, not shown, provides for an intermediate duct, preferably substantially rectilinear, to be arranged between the first angled duct 10 and the inclined part 13.

The inclined part 13 is configured to divert the flow of air and fuel in such a way that the flow itself has a velocity component opposite to the direction D.

In other words, the flow of air and fuel spray flowing in the inclined part 13 is deflected in a direction substantially opposite to the direction D.

The inclined part 13 is defined by a first wall 16 provided with a first outer lateral surface 17 facing the primary duct 2, and a second wall 18 provided with a second outer lateral surface 19 not facing the primary duct 2.

The inclined part 13 is configured in such a way that at least the first wall 16 helps to divert the flow of air and sprayed fuel. In particular, the first wall 16 is inclined with respect to the longitudinal axis A.

In particular, the first wall 16 is inclined so as to form with the longitudinal axis A an angle a facing the elbow conduit 10, preferably less than 60°.

In the non-limiting example described and illustrated herein, the second wall 18 also helps deflect the flow of air and fuel spray. In particular, the second wall 18 is also inclined with respect to the longitudinal axis A.

Preferably, the first wall 16 and the second wall 18 have the same inclination with respect to the longitudinal axis A. An embodiment, not shown, provides for the second wall 18 to have a different inclination from that of the first wall 16 with respect to the longitudinal axis A.

Basically, in the non-limiting example described and illustrated herein, the inclined part 13 substantially defines a further elbow conduit of the inlet assembly 6.

Preferably, the inclined part 13 has a constant pitch section. Therefore, the extension axis B of the inclined part 13 forms with the longitudinal axis A an angle facing the primary conduit 2 substantially identical to the angle a.

The inclined part 13 is arranged between a coupling part of the elbow conduit 10 and an inlet part 22 of the inlet assembly 6, connected to the dryer mill (not shown for simplicity).

The coupling part 20 and the input part 22 are preferably configured to extend substantially along respective axes C, D orthogonal to the longitudinal axis A.

Preferably, the distance between the axes C and D is equal to the diameter of the inclined part 13.

Preferably, the coupling part 20 and the input part 22 also have a constant pitch section.

The burner assembly 1 also includes a baffle element 25, a turbulence generating device 27, a stabilizing device 28 and a lance 30 (optional), a part of which extends inside the primary duct 2 along the axis longitudinal a.

In the non-limiting example, the lance 30 is an oil lance. An embodiment, not shown, provides for the lance 30 to be fueled by gas or diesel.

In detail, the lance 30 is housed in a lance-carrying tube 31 which extends along the longitudinal axis A. With reference to Figure 1 and Figure 2, the deflector element 25 is housed, at least in part, in the conduit in elbow 10 of the inlet assembly 6.

In particular, the baffle element 25 is housed in a coupling portion 23 of the elbow conduit 10, which is coupled, in use, to the inlet 7 of the primary conduit 2.

The deflector element 25 is provided with at least one axial part 32.

In the non-limiting example described herein, the axial part 32 includes two axial fins 34 (as best seen in Figure 2), which extend on opposite sides of the longitudinal axis A.

Preferably, the axial fins 34 extend in the same plane that passes through the longitudinal axis A. Preferably, the axial fins 34 extend in a plane that passes through the longitudinal axis A and is orthogonal to the axis C of extension of the coupling part 20 of the conduit at elbow 10.

Preferably, the axial fins 34 are substantially identical.

Preferably, the deflector element 25 is substantially in contact with the rear wall 11. In the non-limiting example described and illustrated herein, the deflector element 25 is arranged in such a way that the axial fins 34 are also in substantial contact with the rear wall 10.

Preferably, the axial length of the axial fins 34 is determined as a function of the diameter of the inclined part 13.

Preferably, the deflector element 25 is provided with a seat 35 extending along the axis A and configured to house at least a part of the lance support tube 31.

In use, baffle 25 diverts flow entering primary conduit 2 from inlet assembly 6. Turbulence generating device 27 is housed within primary conduit 2 and substantially centered on longitudinal axis A.

The turbulence generating device 27 is configured to rotate the inlet flow to convey the pulverized fuel towards the inner wall of the primary conduit 2.

With reference to Figure 5, the turbulence generating device 27 comprises a main body 47, which extends along the longitudinal axis A, and a plurality of blades 49, which are attached to an outer surface 48 of the main body 47 and They are evenly distributed around the longitudinal axis A.

The main body 47 is preferably provided with a substantially central axial cavity 50, designed to house the lance support tube 31.

The outer surface 48 of the main body 47 comprises a first frustoconical part 51, a second frustoconical part 52 and a cylindrical part 53 arranged between the first frustoconical part 51 and the second frustoconical part 52. The first frustoconical part 52 The frustoconical part 51 faces the inlet 7 of the primary duct 2, while the second frustoconical part 52 faces the outlet 8 of the primary duct 2. The first frustoconical part 51 has a radius that increases along the direction D, while the second frusto part 52 has a radius that decreases along the direction D.

Preferably, the second truncated cone part 52 has an inclination with respect to the axial direction at least 3 times greater than the inclination with respect to the axial direction of the first truncated cone part 51. The plurality of blades 49 are attached to the cylindrical part 53.

According to an embodiment shown in Figure 3, the turbulence generating device 27 is replaced by a homogenizing device 26 housed inside the primary conduit 2 downstream of the deflector 25 along the direction D.

With reference to Figure 6, the homogenizing device 26 comprises a hollow body 37, which is substantially centered on the longitudinal axis A and provided with an outer surface 38 and an inner surface 39. The flow of air and pulverized fuel flows inwards and towards the outside of the hollow body 37.

The homogenizing device 26 is provided with at least one turbulence generator arranged on the outer surface 38 and/or on the inner surface 39 to create a gradient between the tangential components of the air and fuel flow velocities flowing out of the hollow body 37 and flowing into the hollow body 37.

Preferably, the tangential component of the velocity of the air and fuel flow flowing out of the hollow body 37 is opposite to the tangential component of the velocity of the air and fuel flow flowing into the hollow body 37.

In the non-limiting example described and illustrated herein, the homogenizing device 26 comprises an outer swirler 40 coupled to the outer surface 38 of the hollow body 37 and an inner swirler 41 coupled to the inner surface 39 of the hollow body. 37.

Preferably, the homogenizing device 26 is attached to the lance support tube 31.

Preferably, the hollow body 37 is cylindrical.

In detail, the outer swirler 40 is configured to give the flow a first tangential velocity component and the inner swirler 41 is configured to give the flow a second tangential velocity component different from the first tangential velocity component.

Preferably, the first tangential velocity component is opposite to the second tangential velocity component.

In the non-limiting example described and illustrated herein, the outer swirler 40 is configured to rotate the flow in the V1 direction. Meanwhile, the inner swirler 41 is configured to rotate the flow in the V2 direction opposite to the V1 direction.

The outer turbulence generator 40 comprises a plurality of outer fins 43, which protrude from the outer surface 38 of the hollow body 37.

Preferably, the outer fins 43 extend orthogonally from the outer surface 38 and are arranged parallel and equidistant from each other along the outer surface 38.

Preferably, the outer wings 43 are arranged along a direction transverse to the longitudinal axis A.

Similarly, the inner turbulence generator 41 comprises a plurality of inner fins 45, which protrude from the inner surface 39 of the hollow body 37.

Preferably, the inner fins 45 extend orthogonally from the inner surface 39 and are arranged parallel and equidistant from each other along the inner surface 39.

Preferably, the inner fins 45 are arranged along a direction transverse to the longitudinal axis A. Preferably, the plurality of inner fins extends into the interior of the hollow body 37 as far as the lance support tube 31. At least one of the inner fins 45 have one end coupled to the lance support tube 31 and one end coupled to the inner surface 39 in order to fix the homogenizing device 26 to the lance support tube 31.

One embodiment, not shown, provides that the inner ends of the inner fins 45 can be coupled to a tubular part that, in use, will fit into the lance support tube 31.

According to an embodiment shown in Figure 4, the burner assembly 1 includes the homogenizing device 26 and the turbulence generating device 27, both housed inside the primary conduit 2.

Preferably, the homogenizing device 26 is accommodated downstream of the baffle element 25 and upstream of the turbulence-generating device 27 along the direction D.

With reference to Figures 2, 7 and 8, the stabilizing device 28 is arranged at the outlet 8 of the primary conduit 2.

The stabilizer device 28 comprises an annular element 55 centered on the longitudinal axis A and provided with an inner surface 56 and an outer surface 57, and a plurality of cooling fins 59 attached to the outer surface 57 and facing the secondary duct 3 .

The cooling fins 59 are distributed substantially evenly around the longitudinal axis A and arranged equidistantly.

Preferably, the cooling fins 59 are arranged transverse to the longitudinal axis A.

More preferably, the cooling fins 59 are configured to divert the secondary airflow without changing its tangential component.

The annular element 55 is provided with an inlet 61 coupled to the primary conduit 2, and an outlet 62 facing the combustion chamber (not shown).

The inner surface 56 of the annular element is substantially cylindrical and preferably has a diameter d2 substantially identical to the diameter d1 of the primary conduit 2.

Preferably, the stabilizer device 28 also comprises a toothed ring 65 disposed along the inner surface 56 near the outlet 62.

The toothed ring 65 can be arranged flush with the outlet 65 or in a slightly rearward position (as shown in the examples of Figures 1, 7 and 8).

The toothed ring 65 is provided with a plurality of radially arranged and evenly distributed teeth 66.

The outer surface 57 of the annular element 55 comprises at least a first truncated cone part 68 and a second truncated cone part 69, which are preferably contiguous.

Preferably, the outer surface 57 also comprises a cylindrical part 70 coupled to the second frustoconical part 69. In other words, the second frustoconical part 69 is disposed between the first frustoconical part 68 and the cylindrical part 70. The cylindrical part 70 is close to the inlet 61 of the annular element 55, while the first truncated cone part 68 is close to the outlet 62 of the annular element 55.

The inclination 81 of the first frustum part 68 and the inclination 82 of the second frustum part 69 with respect to a direction parallel to the longitudinal axis A are different.

In particular, the inclination 81 of the first frustum part 68 is greater than the inclination 82 of the second frustum part 69 with respect to a direction parallel to the longitudinal axis A.

In addition, the first frustum part 68 and the second frustum part 69 have a radius that increases in the flow direction D.

In this way, an annular face 72 is defined at the outlet, the face of which preferably extends along a plane orthogonal to the longitudinal axis A.

In use, the fuel dust-air mixture is fed to inlet assembly 6.

The conformation of the inlet assembly 6 causes a diversion of the flow of air and fuel dust such as to concentrate the fuel dust in a given area of the primary conduit 2. In the non-limiting example described and illustrated herein, the conformation of the inlet assembly 6 causes a diversion of the flow of air and fuel dust such as to concentrate the fuel dust near the rear wall 11 of the elbow duct 10 of the inlet assembly 6.

In the primary conduit 2, the succession of the deflector element 25 and the turbulence-generating element 27 help to generate a flow that enters the stabilizer device 28 in which the fuel dust is homogeneously concentrated in a peripheral annular ring. In this way, the annular ring with a high concentration of fuel dust impacts on the toothed ring 65, which slows down the fuel dust and transports it along the axis of the duct 2.

In addition, the special conformation of the stabilizer device 28 causes the generation of a flame provided, near the outlet 62, with a recirculation area with low air content and high fuel content in which, advantageously, volatiles are released.

The ring gear 65 slows down the flow rich in fuel and directs it along the axis of the duct 2, while the arrangement of the two frustum parts 68 and 69 facilitates the creation of recirculation areas with low air content. The primary air, in fact, is concentrated in the axial area, while the secondary air is diverted by the two truncated cone parts 68 and 69 away from the axial area.

In particular, the toothed ring 65 forces the carbon particles to slow down below the fuel explosion velocity. This causes ignition to occur substantially in the ring gear 65, and the resulting hot exhaust gases are conveyed to recirculation areas. Recirculation of hot gases automatically maintains ignition of fresh fuel entering the chamber despite the presence of a low oxygen area.

In this way, a very high flame stability is obtained, which allows operation with reduced loads. In fact, in the absence of controlled explosion and recirculation of hot fumes, the flame would go out at low loads.

Basically, with reference to the axial velocity schematic diagram shown in Figure 9, the burner assembly 1 according to the present invention causes the generation of a substantially toroidal recirculation volume VR with low air content, surrounded by an area ZO with a concentration higher oxygen.

In the VR recirculation volume, high temperature under low oxygen conditions causes the release of carbon volatile matter. In this way, the formation of nitrogen oxides (NOx) from nitrogen (N2) bound to the fuel is hindered and the reduction of nitrogenous compounds (NO2, NO, N2O, N2O) to N2 is promoted. In the recirculation volume VR, the fuel flow is withdrawn in a recirculation motion instead of immediately exiting the combustion chamber. Therefore, the residence time of the fuel in the combustion chamber increases. This facilitates completion of combustion and therefore reduces unburned materials.

This solution allows recirculation even with reduced loads. This leads to a strong reduction of unburnt materials at reduced loads.

This results in a significant improvement in combustion efficiency.

The presence of the homogenizing device 26, although optional, improves the homogeneity and segregation of the fuel dust in the peripheral annular ring, resulting in further improved combustion efficiency.

Finally, it is clear that modifications and variations can be made to the burner assembly and method described herein without departing from the scope of the appended claims.

Claims (16)

1. A burner assembly for burning pulverized fuel including: • a primary duct (2) extending along a longitudinal axis (A) where a flow of air and fuel spray flows in a forward direction (D); the primary duct (2) which is provided with an inlet (7) and an outlet (8); • a homogenizing device (26) housed inside the primary duct (2) and comprising a hollow body (37) substantially centered on the longitudinal axis (A) and provided with an outer surface (38) and an inner surface (39). ); the burner assembly being characterized in that the homogenizing device (26) comprises at least one turbulence generator (40; 41) arranged on the outer surface (38) and/or on the inner surface (39) to create a gradient between the tangential components of the velocities of the flow of air and pulverized fuel flowing out of the hollow body (37) and into the hollow body (37). The burner assembly according to claim 1, wherein the tangential component of the velocity of the air flow and pulverized fuel flowing out of the hollow body (37) is opposite to the tangential component of the velocity of the air flow and fuel pulverized fuel flowing into the hollow body (37). The burner assembly according to claim 1, wherein the homogenizing device (26) comprises an external swirler (40), coupled to the external surface (38) of the hollow body (37) and configured to give the flow a first tangential velocity component, and an inner turbulence generator (41), coupled to the inner surface (39) of the hollow body (37) and configured to give the flow a second tangential velocity component different from the first tangential velocity component . The burner assembly according to claim 3, wherein the outer swirler (40) is configured to rotate the flow in a first direction (V1) and the inner swirler (41) is configured to rotate the flow in a second direction (V2) opposite to the first direction (V1). The burner assembly according to claim 3 or 4, wherein the outer swirler (40) comprises a series of outer fins (43), which protrude from the outer surface (38) of the hollow body (37). The burner assembly according to claim 5, wherein the outer fins (43) extend orthogonally from the outer surface (38) and are arranged parallel and equidistant from each other along the outer surface (38). The burner assembly according to claim 5 or 6, wherein the outer fins (43) are arranged along a direction transverse to the longitudinal axis (A). The burner assembly according to any of claims 3 to 7, wherein the internal swirler (41) comprises a plurality of internal fins (45), protruding from the internal surface (39) of the hollow body (37) . The burner assembly according to claim 8, wherein the inner fins (45) extend orthogonally from the inner surface (39) and are arranged parallel and equidistant from each other along the inner surface (39). The burner assembly according to claim 8 or 9, wherein the inner fins (45) are arranged along a direction transverse to the longitudinal axis (A). The burner assembly according to any of the preceding claims, wherein the hollow body (37) is cylindrical. The burner assembly according to any of the preceding claims, comprising a turbulence generating device (27) housed within the primary duct (2) and substantially centered on the longitudinal axis (A). The burner assembly according to claim 12, wherein the homogenizing device (26) is arranged between the inlet (7) and the turbulence generating device (27). The burner assembly according to any of the preceding claims, comprising at least one baffle element (25) arranged upstream of the homogenizing device (26) along the direction of advance (D). 15. A method for operating a burner assembly according to any of the preceding claims, comprising the step of supplying a mixture of air and pulverized fuel to the burner assembly (1). A steam generating plant comprising a burner assembly (1) according to any of claims 1 to 14.