GB2193798A - Combustion apparatus - Google Patents

Abstract

A coal burner comprises a stoker portion (2) which feeds coal to, and extracts ash from, a combustion portion (3). The combustion portion (3) comprises a succession of concave grate sections (51 to 56) which define steps between adjacent sections, such that the coal travels through the grate and falls progressively down the steps. Venturi ports (58) and tuyere air ports (60) provide an air flow through the combustion portion (3), to promote movement of the coal both in an axial direction and with a circulatory motion. Optionally, the concave grate sections can be provided with pawls (77) which may be caused to project through apertures in the grate sections, so as to dislodge any fuel or fuel residues within the grate sections (Figs. 7, 8).

Description

SPECIFICATION Combustion apparatus This invention relates to combustion apparatus, and is especially concerned with solid fuel combusters and parts therefor. The invention has particular although not exclusive application to coal burners for small industrial and domestic use.

Soiid fuel burners have of course been known for very many years. However, they have generally not been easy to automate.

Automatic feed mechanisms, ignitors, and ash extractors have been devised, but these have generally been adapted to existing non-automatic plant, which can be somewhat expensive, and not in all cases successful.

One of the problems associated with the combustion of solid fuel is in ensuring complete combustion. Prior proposals have recognised the desirability of rotating or circulating the fuel in the combustion chamber. However, they have provided this in a very complicated manner, by rotating the combustion chamber itself. Apart from being complicated and expensive, such an arrangement is not inherently very reliable.

Preferred embodiments of the present invention aim to provide solid fuel combusters which are inherently designed for reliable, automatic operation, with a high efficiency of combustion, and being capabie of manufacture and maintenance in an economic manner.

Such preferred embodiments also aim to be compatible with many existing boilers.

More generally, according to a first aspect of the present invention, there is provided a grate for use in combustion apparatus, the grate comprising a succession of concave grate sections which define steps between adjacent sections, such that, in use, fuel may travel through the grate and fall progressively down the steps.

Preferably, the grate sections are disposed in a first series of sections in which each successive section is of greater diameter than the previous one.

Additionally or alternatively, the grate sections may be disposed in a second series of sections in which each successive section is of less diameter than the previous one. In a particularly preferred- arrangement, such a second series of grates follows on from said first series.

The grate sections are preferably formed with apertures for the throughflow of air or gas into the grate. Such apertures may be in the form of venturi ports. At least some of such apertures may be directed to assist movement of fuel through the grate.

Preferably, apertures are provided at the junctions between the grate sections, which apertures are arranged for the throughflow of air or gas in a direction to assist movement of fuel through the grate. Such apertures at the junctions may be in the form of tuyer ports.

Preferably, at least some of the aforementioned apertures are directed to assist circulation of fuel in the grate, in a direction transverse of its direction of travel through the grate.

Means may be provided for varying the relative dispositions of the grate sections and thereby varying the gradient of said steps.

According to a second aspect of the invention, there is provided a grate for use in combustion apparatus, the grate comprising a portion which supports fuel in use of the grate, a plurality of apertures formed in said portion, a plurality of members which project through said apertures, and means for so moving said members as to mechanically disturb fuel or fuel residue supported on said portion.

The invention also extends to a grate which is in accordance with both the first and second aspects of the invention.

According to a third aspect of the invention, there is provided combustion apparatus which comprises a combustion chamber and disposed therein, a grate in accordance with the first and/or second aspect of the invention.

Preferably, the combustion apparatus further comprises a refractory lining which lines the chamber, opposite the grate. Such a refractory lining is advantageously in the form of an arch.

The combustion apparatus preferably further comprises a fuel ignitor which is disposed at or adjacent a fuel entry point of the chamber.

The refractory lining is preferably of a type to maintain ignition of incoming fuel, after ignition has been initiated by said ignitor.

Preferably, the combustion apparatus further comprises feeding means for feeding fuel into the combustion chamber. Such feeding means may be in the form of a screw conveyor.

The combustion apparatus may further comprise a well for receiving ash exhausted from the grate, and extractor means for extracting ash from the well. Such extractor means may be in the form of a screw conveyor.

Preferably, the combustion apparatus comprises a grate which is provided or formed with apertures as aforesaid, and means is provided for creating a throughflow of air or gas through said apertures.

The combustion apparatus may advantageously be mounted on wheels for transport of the apparatus.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a simplified perspective view of a coal burner embodying the invention; Figure 2 is a longitudinal sectional view, in elevation, of the coal burner; Figure 3 is a longitudinal sectional view, in elevation, of primary and secondary burning zones of the burner; Figure 4 is a longitudinal sectional view similar to Figure 3, but in plan; Figure 5 is a sectional view taken on the line XX of Figure 4; Figure 6 is a sectional view taken on the line YY of Figure 4; Figure 7 is a simplified longitudinal sectional view, in elevation, of a modified coal burner; and Figure 8 is a cross-sectional view of the modified coal burner of Figure 7.

The illustrated coal burner 1 comprises a stoker portion 2 and a combustion portion 3.

As may be seen in Figure 2, the stoker portion 2 comprises a chassis 19 which is mounted on a set of wheels 4, which are adjustable in height, relative to the chassis 19.

The stoker portion 2 is adapted to receive coal which is fed to a reception point in the form of a hopper 5, from which the coal falls through a feed orifice 6 into a screw conveyor 7. The screw conveyor 7 comprises a worm 8 which is mounted within a coal feed tube 9, and is driven in rotation by an electric motor 10. The coal feed tube 9 terminates in a flange 11, at the periphery of the stoker portion 2.

In the lower region of the stoker portion 2, there is disposed another screw conveyor 12, which comprises a worm 13 which is disposed within an ash feed tube 14, and is driven in rotation by an electric motor 15. The ash feed tube 14 terminates in a flange 16, at the periphery of the stoker portion 2. An ash discharge orifice 17 is formed in the ash feed tube 12, and communicates with an ash outlet 18.

A forced draught fan 20 is mounted on the upper part of the stoker portion 2, and is arranged to intake ambient air and supply it under pressure to the combustion portion 3.

The combustion portion 3 similarly comprises a chassis 30, which is mounted on a set of wheels 31, which are also adjustable in height, with respect to the chassis 30.

The combustion portion 3 is composed of two parts-a primary burning zone 32 and a secondary burning zone 33. The two burning zones 32 and 33 have respective end walls 34 and 35 by means of which they are secured together. The secondary burning zone 33 also carries an ash well box 36.

The combustion portion 3 has a coal feed tube 37 terminating in a flange 38, which is secured to the flange 11, to align the two coal feed tubes 9 and 37 of the stoker portion and combustion portion respectively. The worm 8 of the screw conveyor 7 extends into the coal feed tube 37 of the combustion portion 3.

Similarly, the combustion portion 3 is also formed with an ash feed tube 40, which terminates in a flange 41 which is secured to the flange 16 of the ash feed tube 14 of the stoker portion. The worm 13 of the ash screw conveyor 12 extends into the ash feed tube 40 of the combustion portion 3. As may be seen in Figure 2, the ash feed tube 40 is provided with an ash feed orifice 42, within the ash well box 36.

As is shown particularly in Figures 3 to 6, the combustion portion 3 has a circular combustion chamber 45, within which there is disposed a concave stepped grate system 46 and, above this, a refractory lining 47 in the form of an arch. Association with the combustion chamber 45 is a lower chamber 48, which is supplied with air under pressure from the fan 20.

The grate system 46 comprises a succession of concave grate sections 51 to 56 which define steps between adjacent sections, such that, in use, coal travelling through the grate system 46 falls progressively down the steps.

The grate sections 51 to 53 form a first series, disposed in the primary burning zone 32, whilst the grate sections 54 to 56 form a second series, disposed in the immediately succeeding secondary burning zone.

Each of the grate sections 51 to 56 is formed with a plurality of venturi ports 58, some of which are shown in plan and some of which are shown in section, in Figure 4.

Each of the venturi ports 58 is disposed at an angle of approximately 60 degrees to the longitudinal axis of the combustion portion 3, to direct air flowing therethrough in such a direction as to assist movement of coal through the grate system 46. At the junctions between successive grate sections, there are defined tuyer air ports 60, which direct air flow in a direction substantially longitudinally of the combustion portion 3.

The first grate section 51 is provided with an end wall 61, affording an aperture 62 which communicates with the coal feed tube 37. Also formed in the end wall 61 are a plurality of air ports 63, for the inlet of air in a direction substantially longitudinally of the combustion portion 3.

At the upstream end of the combustion chamber 45, there is provided an ignitor port 63, in which there is disposed a fuel ignitor unit 64 (Figure 2). The ignitor unit 64 terminates in the vicinity of the first grate section 51, which affords an ignition zone.

The coal burner 1 operates as follows.

Firstly, coal is fed into the hopper 5, and thence into the screw conveyor 7, which conveys it to the ignition zone at the first grate section 51. At this point, when the burner 1 is first started up, the ignition unit 64 is operated, to ignite the coal entering the combustion chamber. Once the coal has ignited, and combustion is underway, the refractory lining 47 heats up, and is of such a type as to maintain ignition of incoming fuel by radiated heat, after ignition has been initiated by the ignitor unit 64. Such refractory linings are known per se. Once the refractory lining 47 is so operating, the ignitor unit 64 is turned off.

The fan 20 provides a forced draught of air, the effect of which is first felt in the ignition zone, where the air enters via the strategically placed ports 63, to facilitate ignition of incoming "green" coal. In addition to this, however, it will be appreciated that the forced draught of air continues through the various venturi ports 58 and tuyer ports 60.

As coal enters the combustion chamber 45, it is rotating, by virtue of the movement of the screw conveyor 7 by which it has been propelled. Due to the configuration of the stepped concave grate sections 51 to 56, the coal tends to continue in a circulatory motion, as it falls progressively down the steps of the grate system 46. Moreover, the draughts provided by the strategically positioned venturi ports 58 serve to maintain the coal in a circulatory motion, transverse of its general direction of travel. Both the venturi ports 58 and the tuyer ports 60 assist progression of the coal, longitudinally of the combustion portion 3.

In the primary burning zone 32, the first series of grate sections 51 to 53 progressively increase in diameter, to accommodate the increasing volume of combustion gases. In the secondary burning zone 33, the second series of grate sections 54 to 56 progressively decrease in diameter, to increase the exhaust velocity of the combustion gases, and to contain the progressively reducing volume of fuel and ash.

The configuration of the grate system 46 and the arrangement of the various air ports serve to ensure that the hot gases are expelled directly from the open mouth of the burner 1 into an adjacent boiler chamber (not shown), in the direction indicated by arrow A in Figure 2, without loss of heat transfer surface area.

Thus, it may be appreciated that the illustrated coal burner 1 affords a combustion apparatus which is not only capable of, but inherently adapted for continuous, automatic operation, whilst achieving a high efficiency of combustion. This is due in particular to the continuing circulatory movement that is afforded to the fuel within the combustion chamber, which overcomes an inherent tendency for the fuel particles to fuse together, due to the high temperature (e.g. of the order of 700 degrees Centigrade) prevailing in the ignition zone. Since this circulatory movement of the fuel in the combustion chamber is achieved without moving parts (with the exception of the feed and extraction screw conveyors 7 and 12, which are of a well proven and reliable construction), the coal burner 1 may be particularly reliable in operation, and simple and cheap to maintain.

Maintenance of the burner 1 is further facilitated, due to the mounting thereof upon wheels. If maintenance is required, the entire burner 1 can be wheeled away from its respective boiler, and readily broken down into its component parts comprising the stoker portion 2 and the combustion portion 3. The latter part can again readily be broken down into the primary burning zone 32 and the secondary burning zone 33.

In the modification illustrated in Figures 7 and 8, a coal burner 70 is generally similar to the previously described coal burner 1, having a succession of concave grate sections 71 to 75. In the modified coal burner 70, each of the grate sections 71 to 75 is formed with a plurality of apertures 76, through each of which extends a respective pawl 77, which is pivotally mounted upon a cradle 78. Secured to one end of the cradle 78 is a rack 79, which meshes with a drive pinion 80.

In use, the drive pinion 80 is driven alternately in opposite directions of rotation, so as to cause an elongate reciprocating movement of the rack 79 and the cradle 78 secured thereto. This reciprocating movement of the cradle 78 causes the pawls 77 to move up and down through their respective apertures 76, in dependence upon the momentary position of their respective pivot points on the cradle 78. It will be noted that the lengths of the apertures 76, in a direction axially of the coal burner 70, are sufficiently great as to allow each pawl 77 to bear against the forward or rearward edge of its respective aperture 76, depending upon the momentary position of its pivot point upon the cradle 78.

In use, the cradle 78 may be left in such a position that the pawls 77 are substantially withdrawn within their apertures 76 in the grate sections 71 to 75. When it is considered necessary to remove fuel or fuel debris from the grate sections, the pinion 80 is driven so as to cause reciprocating movement of the cradle 78, as mentioned above. Then, the pawls 77 bear against the fuel or fuel residue, to move the same upwardly and forwardly through the grate sections 71 to 75.

Some fuels can be more "difficult" to burn than others, in the sense that they may leave residue which is particularly likely to block the grate sections 71 to 75. If necessary, the drive pinion 80 may be operated continuously, such that the pawls 77 work continuously to assist propulsion of fuel and/or fuel residue throughout the coal burner 70. Alternatively, it may be necessary only to operate the pawls 77 when restarting the coal burner 70 after an "OFF" period. For example, during such an "OFF" period, a layer of clinker of the order of 1 cm thickness and 10 cm length (axially of the furnace) may build up, and require removal, before the furnace can be successfully restarted. Such clinker residue is usually very brittle, such that it tends to fragment easily, as soon as it is moved by the pawls 77.

The invention is not restricted to the details of the foregoing embodiment(s), The invention extends to any novel one, or any novel combination, of the features disclosed in this specification and/or drawings, or to any novel one, or any novel combination, of the steps of any method or process disclosed herein.

Claims (16)

1. A grate for use in combustion apparatus, the grate comprising a succession of concave grate sections which define steps between adjacent sections, such that, in use, fuel may travel through the grate and fall progressively down the steps.

2. A grate according to Claim 1, wherein the grate sections are disposed in a first series of sections in which each successive section is of greater diameter than the previous one.

3. A grate according to Claim 1 or 2, wherein the grate sections are disposed in a second series of sections in which each successive section is of less diameter than the previous one.

4. A grate according to Claims 2 and 3, wherein said second series follows on from said first series.

5. A grate according to Claim 1, wherein said sections are formed with apertures for the throughflow of air or gas into the grate.

6. A grate according to Claim 5, wherein at least some of said apertures are directed to assist movement of fuel through the grate.

7. A grate according to Claim 1, wherein apertures are provided at the junctions between said sections, which apertures are arranged for the throughflow of air or gas in a direction to assist movement of fuel through the grate.

8. A grate according to Claim 5, 6 or 7, wherein at least some of said apertures are directed to assist circulation of fuel in the grate, in a direction transverse of its direction of travel through the grate.

9. A grate according to Claim 1, including means for varying the relative disposition of the grate sections and thereby varying the gradient of said steps.

10. A grate for use in combustion apparatus, the grate comprising a portion which supports fuel in use of the grate, a plurality of apertures formed in said portion, a plurality of members which project through said apertures, and means for so moving said members as to mechanically disturb fuel or fuel residue supported on said portion.

11. A grate according to both Claim 1 and Claim 10.

12. Combustion apparatus comprising a combustion chamber and, disposed therein, a grate according to Claim 1, 10 or 11.

13. Combustion apparatus comprising a combustion chamber and, disposed therein, a grate according to any of Claims 2 to 9.

14. Combustion apparatus according to Claim 12, further comprising a refractory lining which lines the chamber, opposite the grate.

15. A grate for use in combustion apparatus, the grate being substantially as hereinbefore described with reference to the accompanying drawings.

16. Combustion apparatus substantially as hereinbefore described with reference to the accompanying drawings.