GB2093960A - Ash/clinker removal arrangement for a coal-fired boiler system - Google Patents

Abstract

A coal-fired boiler, which has a pot type underfeed stoker, has coal fed to its retort 18 along a tube 21 by means of a rotatable conveyor screw 22. The retort is surmounted by tuyeres 40 which are connected by way of a plenum chamber 55 to a forced-draught means and which support an annular device 45 which encircles said tuyeres. The annular device 45 has a periphery over which ash and clinker, which are produced continuously by the fuel burnt in the retort, fall in the manner of water pouring over a weir. Said annular device comprises a continuous flange 47 which may be horizontal or which may be shaped as a frustum of a cone. The ash and clinker falls into an ash removal system which preferably comprises a pair of rotatable conveyor screws. <IMAGE>

Description

SPECIFICATION Ash/Clinker Weir for a Coal-fired Boiler System This invention relates to a coal-fired boiler system.

A coal-fired boiler (for example, for domestic use) is known which comprises a feed screw which, when rotated, feeds coal from a bunker into and through a tube into a retort around which there is disposed an air chamber which is connected to a conduit along which air is forced by a fan. The retort is so shaped that the coal being forced along the tube in a generally horizontal direction is forced to change direction and move upwardly. The retort itself is either surmounted by detachable tuyeres or is suitably apertured so as to provide air holes equivalent to the detachable tuyeres. Once ignited, the fuel bed burns continuously with unburnt coal being supplied from beneath the incandescent part of the fire, the ash and clinker spreading out substantially radially from the fire and falling into an ash pit or equivalent area.The feed screw rotating in the tube constitutes an underfeed stoker of the pot type.

In said known boiler, which has been marketed in the United Kingdom, one failure of the device was in connection with the removal of the ash and clinker. The tuyeres were encircled by a refractory hearth which was supported upon the top of the plenum chamber and the ash and clinker, where it spread radially beyond the tuyeres themselves, simply piled up on the hearth and over the fire bed. The boiler was provided with an openable door through which the clinker could be extracted but that is a time-consuming and unpleasant job; the clinker tends to be kept at a very high temperature by the fuel bed and has to be picked up by special tongs and can easily be dropped.Ash and clinker removal is also unpleasant and dirty to have to attend to because, unlike the automatic supply of coal from the bunker to the boiler for burning, the ashes and clinker have to be manually deposited in a dustbin (preferably of metal), the resultant dust settling all over everything.

Moreover, ash and clinker were inclined to build up over the fuel bed itself because they had nowhere to which to disperse. This had the effect of clogging the fuel bed and of damping the fire.

The principai object of the present invention is to improve this known system by providing means which will enabie the system to be self-cleansing as far as ash and clinker are concerned. A subsidiary object of the present invention is to provide said means in a number of different sizes, thereby enabling the fitter and/or the user to adjust the rate of self-cleaning of the boiler.

Accordingly the present invention consists in a coal-fired boiler system which has a pot type underfeed stoker and which comprises a rotatable conveyor screw driven to feed coal along a tube to a retort surmounted by tuyeres, said tuyeres being connected by way of a plenum chamber to means operable to produce a forced draught and also supporting and being encircled by a device having a periphery which acts as a weir by permitting continuously produced ash and clinker to fall off the device into an ash removal system.

The device is preferably a ring which includes a continuous flange extending radially outwardly from said tuyeres. Said flange may be horizontal, or shaped as a frustum of a cone with the portion thereof of greatest diameter lower than the portion thereof of least diameter or vice versa.

In a preferred embodiment of the device described in the preceding paragraph, the inner periphery of the ring is connected to one end of a right cylindrical sleeve whose other end is supported by three or more support elements provided at spaced locations around said tuyeres.

The ash removal system preferably comprises a pair or rotatable conveyor screws, placed one on each side of the duct through which the primary air passes to the tuyeres from a plenum chamber to which the air is supplied, said conveyor screws being parallel to the conveyor screw which feeds coal to the retort. Said pair of conveyor screws may be and preferably are contra-rotating and act to crush any clinker which may fall into them and to convey ash and crushed clinker to a discharge location outside the room in which the boiler is situated. It may be that ash formation will be the exception and clinker formation the rule, or vice versa, but the two clinker-crushing conveyor screws will be able to reduce any clinker to powder.

In a generally preferred embodiment of said boiler, the conveyor screw for the coal-feed and the pair of conveyor screws for clinker crushing and ash removal are driven by a D.C. motor through a gear box. The conveyor screws are rotated at rotational speeds falling within the range from 1/4 to 3 r.p.m., preferably at about 1 r.p.m.

In addition to the supply of primary air to the retort by way of the plenum chamber, secondary air is supplied to a conduit which directs said secondary air onto the fuel bed from above, said secondary air serving, in known manner, to burn any carbon monoxide produced by reduction of carbon dioxide through the incandescent zone of the fuel bed.

A preferred exemplary embodiment of a coal fired boiler system in accordance with the present invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is a view of the front of the boiler; Figure 2 is a vertical section on the median plane 0--0 of the boiler shown in Figure 1; Figure 3 is a section on the line M-M in Figure 1; Figure 4 is a section taken on the line N-N in Figure 1; Figure 5 is a section taken on the line K-K in Figure 4; Figure 6 is a scrap view looking in the direction indicated by the arrow L in Figure 4, part of the respective cover having been removed to show a porting arrangement for secondary air;; Figures 7 and 8 are two views (side and front) of a fuel tank which forms part of the boiler system; and Figure 9 is a section showing the ash/clinker removal system in front of the retort Referring to the drawings, a boiler 10, having the usual flue cleaning door 11 and an inspection door 12, has a D.C. motor 14 driving three conveyor screws by way of a gear box which is indicated generally by the reference numeral 13.

The shafts of the three conveyor screws are indicated in Figure 4 by the reference numerals 1 5, 16 and 17. The middle shaft 15 is the shaft of the coal-feed conveyor screw and the shafts 16, 1 7 are the shafts of the ash/clinker-crushing conveyor screws.

The shaft 1 5 extends from the gear box 1 3 through a retort 18 (Figure 2) and out through the back of the boiler into a coal bunker or tank 19 (Figure 7) in which it is supported for rotation in a V-shaped supporting channel 20. Said shaft 1 5 carries a small diameter helical flight or screw (not illustrated) whose function is simply to ensure that coal is fed or propelled towards the location at which the coal is constrained to enter a tube 21 mounted in the back of the boiler and connected at its front end to the retort 1 8. Said shaft 1 5 also carries a helical flight or screw 22 which is of a larger diameter than the firstmentioned helical flight or screw, the function of the screw 22 being to force the coal into the tube 21 and along said tube into the retort 18. Lastly, the shaft 1 5 also carries a helical flight or screw 23 of a hand opposite to that of the screw 22. The screw 23 is located within a tube 24 whose front end is mounted in the front of the boiler and whose rear end is connected to the retort 18. The screw 23 ensures that coal is not fed beyond the retort 18 along the tube 24 and into the gear box 1 3. The coal is therefore fed to the retort 1 8 from the tank 1 9 in a horizontal direction, and at the retort the coal moves in a generally upwards direction.

The shafts 1 6, 17 will now be described with reference to Figure 3 which illustrates the shaft 1 7; except as specified, the two shafts 1 6, 1 7 are identical in construction and operation and what is described in relation to shaft 1 7 is true for shaft 1 6. Thus, the shaft 1 7 extends through two tubes 25, 26 of which the tube 25 is mounted forwardly of the retort 18 and of which the tube 26 is mounted rearwardly of said retort. The rear end of the tube 25 and the front end of the tube 26 are in communication with an open trough which is of a configuration which can be determined by studying Figures 3 and 9 in conjunction with one another.A curved plate 27 is mounted in a sealed manner (e.g. by welding) on the respective parts of the boiler including the retort 18, and another plate 28 is mounted on said plate 27 and extends in a generally upwards direction therefrom. In fact, the two plates 27 and the two plates 28 together form the horizontally spaced troughs 29, the two plates 28 being joined to one another at their upper ends as indicated by the reference numeral 30. Thus,-the two inclined and conjoined plates 28 constitute a chute leading downwardiy into the respective troughs 29 for a purpose to be described hereinafter.At the rear of the boiler, the shaft 1 7 emerges from the tube 26 and is connected by a suitable form of universal joint (indicated by the reference numeral 31) to one end of an upwardly inclined shaft 32 (see Figures 2, 3, 7 and 8) which therefore acts as an extension of said shaft 17. The shaft 32 is enclosed within a tube 33 which extends upwardly through the fuel tank 19 to an appropriately dimensioned aperture 34 which is formed in that wall (the front wall) of the tank 19 which is farther away from the boiler. A chute 35 has one end thereof connected to said front wall covering said apertureiand has the other end thereof connected in a releasable manner to a bin 36 or to a bag 37.

The shafts 16,17 are parallel to one another and to the shaft 1 5 until they reach the respective universal joints 31; thereafter the shafts 32 and their enclosing tubes 33 converge until their upper ends are close together at the aperture 34.

The shafts 1 6, 1 7 are provided with helical flights or screws 38 (Figure 3) which feed ash/clinker from the respective troughs 29 into the respective tubes 26, rotation of the shafts 1 6, 17 and of the respective extension shafts 32 (which are provided with helical flights or screws 39) causing any clinker to be crushed into a fine condition and to be fed with any ash upwardly to the aperture 34, the chute 35 and bin 36 or bag 37.

The upper end of the retort 1 8 is surmounted by a plurality of separate tuyere elements 40 which are arranged in the form of a ring (see Figures 2 and 3) so shaped and constructed as to provide tuyeres 41 by way of which air is blown into the fuel bed which is indicated by the reference numeral 42. The retort 1 8 also has ports 43 through which blown air reaches the heated coal immediately under the incandescent part of the fire. Each tuyere element 40 has a radially outwardly projecting boss 44 integral therewith and a weir device 45, circular in plan configuration, sits on said bosses. The device 45 consists of a right cylindrical sleeve 46 connected to a horizontally disposed flange 47 which extends radially outwardly away from the elements 40 which it encircles. Minimal quantities of ash and the clinker which is formed by an underfeed stoker system are progressively pushed upwardly or outwardly until they fall off the edge 48; in doing so, said ash and clinker fall into the troughs 29 or onto one of the sloping plates 28 and thence into the respective trough 29.

A fan 49 driven by a motor 50 supplies air to each of two ducts 51,52. The duct 51 has a pipe 53 whose upper end is bent over so as to direct so-called secondary air downwardly towards the fire 42 in order to burn whatever carbon monoxide might be given off. The duct 52 is in communication with one end of a duct 54 which at its other end opens into a plenum chamber or wind box 55 which, in turn, communicates with a duct 56 by way of which ascending blown primary air reaches the ports 43 and the hollow elements 40 and the tuyeres41. Manually operable air-control flaps or dampers 57, 58 are provided near the fan: these are adjustable to regulate the draught.

The remainder of the boiler is of a construction which need not be described in detail. Suffice it to say that it has a two-pass heat exchanger, adjustable thermostat and any other desirable controls, safety devices and so on.

The motor 14 is reversible for the purpose of being able to clear any jams which may occur, such jams being possible in the feed of coal to the retort The tank 19 is provided with a hatch 59 which covers an access aperture 60 through which the jamming may be cleared.

The universal joints 31 will facilitate the fitting of the shafts 32 and their enclosing tubes 33 in a brick-built'or block-built fuel bunker if the buyer of the boiler system were to prefer such a bunker instead of a metal tank 19. Also, of course, the universal joints make it possible for said shafts/tubes 32, 33 to be upwardly inclined and convergent.

The extension of said shafts/tubes 32, 33 through the tank 1 9 or equivalent bunker ensures that all ash/clinker dust is completely cold by the time it reaches the upper ends of said tubes 33 and falls into the bin/sack 36, 37. In view of this, a dustbin of plastics material could be used or sacks of plastics material could be used or multi-wall paper sacks could be used. If any type of sack were to be used instead of a bin, the means of attachment of the neck of the sack to the lower end of the chute 35 could be made such (namely, of such strength) that the sack will simply drop off when it contains a predetermined weight of ash/clinker dust.

The screws 38 will crush any clinker into particles fine enough to be fed continuously along the tubes 26 and up the tubes 33.

The outside diameter of the device 45 (i.e. the distance between diametrically opposite points on the edge 48 of said.device) will determine the efficiency with which ash/clinker removal is carried out. Thus, a number of different sizes of device 45 can be provided, the smaller the outside diameter thereof the earlier the ash/clinker will fall off the weir. If it is found that the clinker pieces are prevented by their sizes from falling off the weir where said edge 48 is nearest to the boiler sides or where said edge is near to the pipe 53, the device 45 can be replaced by one of smaller diameter.

The shafts 16, 1 7 are contra-rotating in order to convey the ash/crushed clinker in the same direction.

The fan motor 50 may be a D.C. motor but, of course, both the motor 14 and the motor 50 could be A.C.

The weir device 45 need not be of the shape and configuration described herein and illustrated in the drawings. The weir device may be made of .any suitable heat-resistant material (for example, of metal, of ceramic material, of cast iron), and it could be made so as to be of basically triangular section in any part thereof as distinct from the angle section shape shown in the drawings.

Water is circulated in the region of the shafts 1 6,1 7 and respective troughs. This is best shown in Figure 9 in which the water jacket indicated by the reference numeral 65 will be seen to have been continued under the conveyor screws 16, 15, 17; therefore, the whole space beneath the plates 27 and the retort 18 and above the chamber 55 is cooled and the heat therefrom is utilised. Alternatively, that space could be filled with a refractory material instead of with water.

It will be noted that it is an important feature of the boiler system described above that the conveyor screws are supported within the various tubes of the ash removal system by the ash/crushed clinker. There are no bearings for the shafts 1 6, 1 7, 32 which are located within their respective tubes 26, 33; the packed ash/crushed clinker supports those shafts.

Claims (Filed on 26th Jan 1982) 1. A coal-fired boiler system which has a pot type underfeed stoker and which comprIses a rotatable conveyor screw driven to feed coal along a tube to a retort surmounted by tuyeres, seid tuyeres being connected by way of a plenum chamber to means operable to produce a forced draught and also supporting and being encircled by a device having a periphery which acts as a weir by permitting continuously produced ash and clinker to fall off the device into an ash removal system.

2. A system as claimed in Claim 1, wherein said-device is a ring which includes a continuous flange extending radially outwardly from said tuyeres.

3. A system as claimed in Claim 2, wherein said flange is horizontal.

4. A system as claimed in Claim 2,.wherein said flange is shaped a's a frustum of a cone with the portion thereof of greatest diameter lower than the portion thereof of least diameter, or vice versa.

5. A system as claimed in any one of Claims 2 to 4, wherein the inner periphery of the ring is connected to one end of a right cylindrical sleeve whose other end is supported by three or more support elements provided at spaced locations around said tuyeres.

6. A system as claimed in any one of the preceding Claims, wherein the ash removal system comprises a pair of rotatable conveyor screws, placed one on each side of a duct through which primary air passes to the tuyeres from the plenum chamber to which the air is supplied, said conveyor screws being parallel to the conveyor screw which feeds coal to the retort.

7. A system as claimed in Claim 6, wherein the conveyor screws of said pair of conveyor screws

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. communication with one end of a duct 54 which at its other end opens into a plenum chamber or wind box 55 which, in turn, communicates with a duct 56 by way of which ascending blown primary air reaches the ports 43 and the hollow elements 40 and the tuyeres41. Manually operable air-control flaps or dampers 57, 58 are provided near the fan: these are adjustable to regulate the draught. The remainder of the boiler is of a construction which need not be described in detail. Suffice it to say that it has a two-pass heat exchanger, adjustable thermostat and any other desirable controls, safety devices and so on. The motor 14 is reversible for the purpose of being able to clear any jams which may occur, such jams being possible in the feed of coal to the retort The tank 19 is provided with a hatch 59 which covers an access aperture 60 through which the jamming may be cleared. The universal joints 31 will facilitate the fitting of the shafts 32 and their enclosing tubes 33 in a brick-built'or block-built fuel bunker if the buyer of the boiler system were to prefer such a bunker instead of a metal tank 19. Also, of course, the universal joints make it possible for said shafts/tubes 32, 33 to be upwardly inclined and convergent. The extension of said shafts/tubes 32, 33 through the tank 1 9 or equivalent bunker ensures that all ash/clinker dust is completely cold by the time it reaches the upper ends of said tubes 33 and falls into the bin/sack 36, 37. In view of this, a dustbin of plastics material could be used or sacks of plastics material could be used or multi-wall paper sacks could be used. If any type of sack were to be used instead of a bin, the means of attachment of the neck of the sack to the lower end of the chute 35 could be made such (namely, of such strength) that the sack will simply drop off when it contains a predetermined weight of ash/clinker dust. The screws 38 will crush any clinker into particles fine enough to be fed continuously along the tubes 26 and up the tubes 33. The outside diameter of the device 45 (i.e. the distance between diametrically opposite points on the edge 48 of said.device) will determine the efficiency with which ash/clinker removal is carried out. Thus, a number of different sizes of device 45 can be provided, the smaller the outside diameter thereof the earlier the ash/clinker will fall off the weir. If it is found that the clinker pieces are prevented by their sizes from falling off the weir where said edge 48 is nearest to the boiler sides or where said edge is near to the pipe 53, the device 45 can be replaced by one of smaller diameter. The shafts 16, 1 7 are contra-rotating in order to convey the ash/crushed clinker in the same direction. The fan motor 50 may be a D.C. motor but, of course, both the motor 14 and the motor 50 could be A.C. The weir device 45 need not be of the shape and configuration described herein and illustrated in the drawings. The weir device may be made of .any suitable heat-resistant material (for example, of metal, of ceramic material, of cast iron), and it could be made so as to be of basically triangular section in any part thereof as distinct from the angle section shape shown in the drawings. Water is circulated in the region of the shafts 1 6,1 7 and respective troughs. This is best shown in Figure 9 in which the water jacket indicated by the reference numeral 65 will be seen to have been continued under the conveyor screws 16, 15, 17; therefore, the whole space beneath the plates 27 and the retort 18 and above the chamber 55 is cooled and the heat therefrom is utilised. Alternatively, that space could be filled with a refractory material instead of with water. It will be noted that it is an important feature of the boiler system described above that the conveyor screws are supported within the various tubes of the ash removal system by the ash/crushed clinker. There are no bearings for the shafts 1 6, 1 7, 32 which are located within their respective tubes 26, 33; the packed ash/crushed clinker supports those shafts. Claims (Filed on 26th Jan 1982)

1. A coal-fired boiler system which has a pot type underfeed stoker and which comprIses a rotatable conveyor screw driven to feed coal along a tube to a retort surmounted by tuyeres, seid tuyeres being connected by way of a plenum chamber to means operable to produce a forced draught and also supporting and being encircled by a device having a periphery which acts as a weir by permitting continuously produced ash and clinker to fall off the device into an ash removal system.

2. A system as claimed in Claim 1, wherein said-device is a ring which includes a continuous flange extending radially outwardly from said tuyeres.

3. A system as claimed in Claim 2, wherein said flange is horizontal.

4. A system as claimed in Claim 2,.wherein said flange is shaped a's a frustum of a cone with the portion thereof of greatest diameter lower than the portion thereof of least diameter, or vice versa.

5. A system as claimed in any one of Claims 2 to 4, wherein the inner periphery of the ring is connected to one end of a right cylindrical sleeve whose other end is supported by three or more support elements provided at spaced locations around said tuyeres.

6. A system as claimed in any one of the preceding Claims, wherein the ash removal system comprises a pair of rotatable conveyor screws, placed one on each side of a duct through which primary air passes to the tuyeres from the plenum chamber to which the air is supplied, said conveyor screws being parallel to the conveyor screw which feeds coal to the retort.

7. A system as claimed in Claim 6, wherein the conveyor screws of said pair of conveyor screws

are contra-rotating and act to crush any clinker which may fall into them and to convey ash and crushed clinker to a discharge location remote from that of the boiler.

8. A system as claimed in Claim 6 or Claim 7, wherein the conveyor screw for the coal-feed and the pair of conveyor screws for clinker crushing and ash removal are driven by a D.C. motor through a gear box.

9. A system as claimed in Claim 8, wherein said conveyor screws are rotated at rotational speeds falling within the range from 1/4 to 3 r.p.m., preferably at about 1 r.p.m.

10. A system as claimed in any one of the preceding Claims, wherein, in addition to the supply of primary air to the retort by way of the plenum chamber, secondary air is supplied to a conduit which directs said secondary air onto the fuel bed from above, said secondary air serving, in known manner, to burn any carbon monoxide produced by reduction of carbon dioxide through the incandescent zone of the fuel bed.

11. A coal-fired boiler system constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

12. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawings.