GB2093961A

GB2093961A - Solid fuel burners

Info

Publication number: GB2093961A
Application number: GB8200689A
Authority: GB
Original assignee: Bigwood Joshua & Son Ltd
Current assignee: Bigwood Joshua & Son Ltd
Priority date: 1981-01-09
Filing date: 1982-01-11
Publication date: 1982-09-08

Abstract

A solid fuel burner having a combustion chamber with a support for a fuel bed, for example a retort (10). The support is shaken to agitate the fuel and also causes ash to fall over the side of the support. The ash is collected in a receptacle (13) beneath the support and is conveyed away from by a pneumatic conveyor including a cyclone separator (18) which separates the ash and air, the ash being discharged into a cooling box (22) and the air being delivered to the combustion chamber through a duct (21). A number of different fuel bed supports and agitating means are described. <IMAGE>

Description

SPECIFICATION Solid fuel burners Description of invention This invention relates to solid fuel burners.

The invention has been developed in relation to solid fuel burners which are incorporated in boilers for heating water for central heating installations or to provide a supply of hot water or steam, such burners usually burning coal or coke, and the following description will therefore be confined to this application of the invention.

However, it is to be understood that there is no limitation in this regard since the invention is also applicable to solid fuel burners for other purposes, for example burners incorporated in furnaces, and which may burn coal or coke or other fuels such as straw or wood chippings.

According to a first aspect of the invention there is provided a solid fuel burner having a support for a fuel bed, wherein means are provided for shaking the support thereby, in use, to agitate the fuel in the bed.

Shaking of the support is preferably effected by vibrating or reciprocating it although other methods could be used, for example rocking the support.

Agitation of the fuel has the advantage that it produces a more efficient burning of the fuel than has hitherto been possible with conventional burners since the agitation allows air to come into contact with more fuel so that the amount of fuel which remains unburned is smaller.

Another advantage is that it prevents or at least minimises the formation of clinker in the fuel.

Yet a further advantage is that it can assist the separation from the fuel of ash and any clinker produced during burning of the fuel.

Preferably the support is formed so that the ash and clinker fall off the support on shaking thereof, and in this event a receptacle, for example in the form of a tray or hopper, is conveniently provided beneath the support to receive the ash and clinker discharged from the support. Pneumatic means are preferably provided for conveying the ash and clinker away from the receptacle.

The burner may be provided with means for reducing the size of any relatively large pieces of ash or clinker as they are discharged from support.

According to a second aspect of the invention there is provided a solid fuel burner having a support for a fuel bed from which, in use, ash is discharged, wherein there are provided means for collecting ash discharged from the support and pneumatic means for conveying the ash away from the collecting means.

Both aspects of the invention are applicable to burners of the type in which the support comprises a retort with an underfeed stoker and burners of the type in which the support is a chain grate or moving hearth conveyor.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic perspective view of one form of solid fuel burner embodying the invention; Figure 2 is a side view of another form of solid fuel burner embodying the invention; Figure 3 is a plan view of the burner shown in Figure 2; and Figure 4 is a side view partly in section of a further form of burner embodying the invention.

The solid fuel burner illustrated in Figure 1 of the drawings comprises a retort 10 of rectangular shape in plan and having a continuous side wall formed by tuyere blocks. The tuyere blocks are hollow so that there is a continuous passageway through the side wall which communicates with the interior of the retort through the tuyeres in the tuyere blocks. The bottom of the retort curves downwardly towards a fuel inlet 11 which contains an underfeed stoker in the form of a feed screw arranged to deliver fuel from a bunker (not shown) to the retort. The side wall of the retort projects above a surround 12, and the retort and the surround together form the bottom of a combustion chamber having a boiler mounted above the retort.The boiler is arranged to supply hot water or steam to, for example, a central heating installation and the hot gases from the combustion chamber, after heating the water in the boiler, are carried away through a flue (not shown).

In use, the feed screw is operated to maintain a bed of fuel, for example coal, in the retort to a level such that it almost spills over the side wall of the retort, the operation of the feed screw being controlled by means sensing the temperature of the water in the boiler so that this temperature can be maintained at the required level by controlling the rate of feed of fuel to the retort and hence the rate at which fuel is burnt in the retort.

Air at a relatively low pressure is supplied to the passageway in the side wall of the retort by a blower (not shown) so that streams of air issue from the tuyeres in the tuyere blocks and thereby produce a forced underdraught to promote burning of the bed of fuel in the retort.

The formation of a clinker in the fuel bed during burning of the fuel is prevented, or at least minimised, by vibrating the retort 10 and hence shaking the fuel bed. This vibratioan also promotes burning of the fuel since the resultant agitation of the fuel allows air to enter the bed and come into contact with the particles and larger pieces of fuel.

The retort is vibrated by a vibrator arranged to vibrate the retort but not the surround 12. The retort is mounted on a support which in turn is supported independently of the surround by means of springs on a base. The support carries an electrical vibrating motor (not shown).

The vibration is such that the ash formed on top of the fuel bed during burning of the fuel is caused to flow outwardly over the side wall of the retort so that it is separated from the fuel and falls onto the surround 12.

The surround 12 is of rectangular shape in plan and comprises a tray 13, the bottom of which is shaped so that it slopes downwardly towards four outlets 14 at the respective corners. Mounted on top of the tray are a series of spaced parallel bars 1 5 so that the ash discharged from the retort falls through the gaps between these bars into the tray. The bars are in the form of rollers which are rotated by a motor (not shown) so that any large pieces of ash or clinker are broken up or crushed as they pass between the bars.

The ash falls towards the outlets 14 and is sucked out of the tray, together with hot gases from the combustion chamber, by a pneumatic conveyor, the hot gases being conveyed from the chamber through pipes 101 to the inlets.

This conveyor comprises two ducts 16 connected to the outlets 14 at the respective sides of the tray and merging into a single main duct 17. This main duct is connected to the inlet of a cyclone separator 18, the outlet of which is connected by a duct 1 9 to the suction side of a fan 20 driven by an electric motor. The delivery side of the fan is connected by a duct 21 to the combustion chamber of the burner.

The ash and hot gases are sucked out of the tray by the suction effect produced by the fan 20 and they are sucked into the cyclone separator 1 8 along with cool air from the atmosphere. The cyclone separator removes the majority of the ash (and any other solid matter) from the gases and the ash falls through a discharge opening into an ash cooling box 22. The cool air drawn into the cyclone with the combustion products mixes with the latter and assists burning of any remaining combustible material in the cyclone separator as well as partially cooling the ash.

The discharge opening of the cyclone separator is controlled by a slide valve 23 disposed between the opening and the inlet of the ash cooling box 22. The box also has an inlet 102 for cooling air, and a discharge pipe 24 extends through this inlet into the lower part of the box. When the ash in the cooling box has cooled sufficiently, it is sucked out of the box by applying suction to the pipe 24 by means of a fan (not shown), the ash being discharged from the boiler house to a collection point.

The gases extracted from the cyclone separator through the duct 19, together with any fine ash dust still left in the gases, are blown by the fan 20 through the ducts 21 into the combustion chamber The pneumatic ash extraction system is controlled automatically by a programmer linked to the boiler controls. The system will usually be operated periodically, for example for five minutes every hour.

The solid fuel burner illustrated in Figures 2 and 3 of the drawings comprises a boiler 30 having a combustion chamber with a support 31 for a bed of fuel in the chamber.

Disposed above the support is a combined fuel and air inlet comprising an inner tube 32 through which fuel, for example coal, is fed onto the support 31, and an outer tube 33 which defines with the inner tube an annular passageway through which air is blown onto the bed of fuel on the support to promote burning.

The support 31 comprises a frusto-conical hopper 34 having a vertical upper wall 35 connected to it by an outwardly projecting flange around the upper edge of the hopper which is secured to a similar flange around the lower edge of the vertical wall. Mounted in the upper part of the hopper is a generally flat grate 36 of square shape in plan, the corners of the grate being welded to the hopper.

A screen 37 of reticulate or perforate form, for example of wire mesh as illustrated or a metal grille, is provided between the edges of the grate 36 and the side wall of the hopper, the outer edges of the screen being clamped between the connecting flanges of the hopper and the vertical wall 35.

The grate 36 comprises four porous tiles 38 which support the firebed and through which air can pass into the firebed from a chamber 39 forming part of the grate and connected by a pipe 40 to the delivery side of a fan (not shown). The tiles are heat resistant and may be formed from perforated stainless steel, slotted sheet, wire, compacted swarf, strip or a sandwich combination of any of these materials.

The bottom of the hopper 34 has an outlet which is connected by a duct 41 to the inlet of a cyclone separator 42. The outlet of the separator is connected by a duct 43 to the suction side of a fan 44 which is driven by an electric motor. The delivery side of the fan is connected by a pipe 45 to the combustion chamber of the boiler.

The cyclone separator 42 has a discharge opening in communication with an ash cooling box 46 which is the same in construction and operation as the ash cooling box 22 in the embodiment shown in Figure 1.

The whole assembly of the hopper 34 and the grate 36 is mounted on a frame 47 which is supported by springs 48 on a fixed base 104 and carries an electrical vibrating motor 49.

In operation, fuel discharged from the tube 32 falls onto the grate 36 and forms a bed B supported by the grate. The bed having been ignited, burning of the fuel is promoted by the air blown onto the bed through the tube 33 and the air blown into the chamber 39 beneath the grate through the pipe 40, this air passing through the porous tiles 38 into the bed.

The assembly of the hopper and the grate are vibrated by the vibrating motor 49 and the resultant shaking of the bed B causes the fuel to be agitated to allow the air to circulate through it and also causes the ash produced on burning of the fuel to fall over the edge of the grate through the wire mesh 37 into the hopper 34. The wire mesh prevents large pieces of material entering the pneumatic conveyor system which conveys the ash away from the hopper.

The suction effect created in the duct 41 by the fan 44 sucks the ash which collects in the bottom of the hopper, and with it hot gases from the combustion chamber, into the cyclone separator 42 where the majority of the ash is separated from the gases. The separated ash falls into the ash cooling box 46 and, after cooling, is sucked out of the box through a pipe 50 corresponding to the pipe 24 in the Figure 1 embodiment. The gases with any fine dust remaining in them are sucked out of the separator and blown through the duct 45 into the combustion chamber.

The embodiment shown in Figure 4 comprises a retort 60 of generally the same form as the retort of the embodiment illustrated in Figure 1. In this case, however, the retort has wheels 61 arranged to run on a carriage 62 which also has wheels 63 and is supported by a fixed track 64.

The carriage 62, together with the retort 60 forms the bottom of a combustion chamber 65, the top of which is closed by a boiler, disposed above the retort. Fuel is supplied to the retort through a pipe 66, one end of which is received with a close sliding fit in the fuel inlet 67 of the retort and the other end of which is also a close sliding fit in a discharge opening 68 of a hopper 69. This hopper is supported on the track 64 by a lockable wheel 70 and tie bars 71 are connected between the wheel mounting and the carriage 62.

The retort 60 is reciprocable in the directions of arrows A between stops 72 on the carriage 62 to agitate the fuel in the retort. For this purpose, drive means 73 are provided outside the combustion chamber. These drive means are also arranged to reciprocate the pipe 66 in the directions of arrows B relative to the hopper 69 and to a fixed ram 74 so that on each stroke in one direction, a quantity of fuel from the hopper enters the gap between the ram and the body of fuel already in the pipe and on each stroke in the other direction the fuel is pushed by the ram along the pipe whereby more fuel is introduced into the retort.

The retort 60 has a shorter stroke than the pipe 66, for example 1 inch compared with 6 inches, and to achieve this, the drive means 73 are coupled directly to the pipe and through a slide or link connection to the retort. The drive means are operated continuously when the burner is operative, to provide a continuous supply of fuel to the retort and constant agitation of the fuel in the retort to promote burning.

The inlet of the hopper 69 is connected via a gate valve 75 to a cyclone separator 76 having a fan 77 arranged to convey fuel pneumatically from a supply to the separator. The separator separates the fuel from the conveying air and when a quantity of fuel has collected in the separator, the gate valve is opened to discharge it into the hopper. Opening of the gate valve at regular intervals therefore provides a continuous supply of fuel to the hopper. The separator and the hopper are supported by a framework 103.

The carriage 62 if formed around the retort with a pan arranged so that the ash and clinker discharged from the retort 60 over its side wall as a result of the reciprocation of the retort and the feeding of fresh fuel into the latter, fall into the pan. Provided above the pan around the retort is a grille arranged so that the ash and clinker discharged from the retort fall through the gapsin the grille. The grille comprises two rectangular end sections rigidly secured to the respective ends of the retort and of the same width as the latter, and two rectangular side sections which are carried by the carriage 62 and extend along, and close to, the sides of both the retort and the end sections.The end sections therefore move with the retort on reciprocation thereof, for example at a stroke of 1 inch, and the side sections move with the carriage relative to the retort and the end sections on reciprocation of the carriage, for example at a stroke of 6 inches. The side sections carry scrapers 78 which are connected to the sections by linkages permitting movement of the scrapers up and down and longitudinally relative to the sections.

The pan is shaped so that any ash or clinker falling over the ends of the retort and through the end sections is directed towards the sides of the pan. Any ash falling over the sides of the retort passes through the side sections into the sides of the pan and any relatively large pieces of clinker are moved by the scrapers along the side sections towards their ends adjacent to the feed pipe 66 whereupon the clinker falls over said ends of the sections into two deeper parts of the pan at the adjacent two corners thereof. The pan is shaped so that the ash and clinker directed into the sides thereof also passes into these deeper parts which form collection points.

The scrapers are arranged to move in a rectangular path, performing their scraping action as they move in one direction along the lower part thereof, being raised at the end of this movement by their engagement with cams 79, then moving back in the raised position and finally being lowered by their engagement with cams 80.

Extending downwardly into the two deeper corner parts of the pan are two pipes 81 connected to a pneumatic conveyor which may be of the same form as that shown in Figure 1 and which sucks the ash and clinker out of the pan.

The unit comprising the carriage 62 with the retort 60 and the hopper 69, being supported on wheels 63, 70, can be moved to withdraw the carriage from the retort for cleaning and maintenance purposes.

The hopper 69 is diconnectable from the cyclone separator 76 to facilitate such movement.

With the carriage in its operative position as shown in Figure 3, the wheel 70 is locked, and a seal 82 seals off the collection points from the interior of the combustion chamber so that the combustion gases are not sucked into the pneumatic conveyor.

Claims

1. A solid fuel burner having a suppport for a fuel bed, wherein means are provided for shaking the support thereby, in use, to agitate fuel in the bed.

2. A burner as claimed in Claim 1 wherein the said means are adapted to shake the support by vibrating or reciprocating it.

3. A burner as claimed in Claim 1 or 2 wherein the support is formed so that ash and any clinker produced during burning of the fuel fall off the support.

4. A burner as claimed in Claim 3 wherein a receptacle is provided beneath the support to receive the ash and clinker discharged from the support.

5. A burner as claimed in Claim 4 wherein pneumatic means are provided for conveying the ash and clinker away from the receptacle.

6. A burner as claimed in Claim 3, 4 or 5 wherein means are provided for reducing the size of any relatively large pieces of ash or clinker as they are discharged from the support.

7. A burner as claimed in Claim 3, 4 or 5 wherein means are provided for separating any relatively large pieces of ash or clinker from the ash or clinker as it is discharged from the support.

8. A burner as claimed in any one of the preceding claims wherein the support comprises a generally flat support having disposed above it means for discharging fuel on to the support to maintain a bed of fuel thereon.

9. A burner as claimed in Claim 8 when dependant on Claim 4 wherein the receptacle comprises a hopper, the support being disposed in the upper part of the hopper with its edge spaced from the side wall of the hopper so that ash and clinker can fall over the edge into the hopper.

10. A burner as claimed in Claim 9 wherein a screen of reticulate or perforate form is provided between the edge of the support and the side wall of the hopper to separate any relatively large pieces of ash or clinker from the ash and clinker falling over the edge of the support into the hopper.

11. A burner as claimed in Claim 8, 9 or 10 wherein the support closes the upper part of a chamber connected to a source of air under pressure and is formed so that air can pass through it from the chamber into the fuel bed thereby to promote burning of the fuel.

12. A burner as claimed in any one of claims 1 to 7 wherein the support comprises a retort defining an open-topped chamber for holding a fuel bed, an underfeed stoker being provided for supplying fuel to the underside of the bed.

13. A burner as claimed in Claim 12 when dependant on Claim 4 wherein the receptacle comprises a tray arranged to receive the ash and any clinker which falls over the side wall of the retort.

14. A burner as claimed in Claim 13 wherein the tray is formed to direct the ash and clinker towards one or more locations for discharge from the tray.

1 5. A burner as claimed in Claim 13 or 14 wherein a number of spaced bars are provided around the retort so that ash and clinker falling from the retort into the tray passes through the gaps between the bars, the bars being rotatable to break up or crush any relatively large pieces of ash or clinker.

16. A burner as claimed in Claim 12, 13, 14, or 1 5 wherein the retort is provided with wheels and is coupled to drive means arranged to reciprocate the retort.

1 7. A burner as claimed in Claim 16 wherein the wheels of the retort run on a carriage which also has wheels running on a fixed track, the drive means also being arranged to reciprocate the carriage.

1 8. A burner as claimed in Claim 1 7 wherein the underfeed stoker is connected to a fuel supply hopper which is movable with the carriage.

19. A burner as claimed in Claim 18 wherein pneumatic means are provided for supplying fuel to the hopper.

20. A burner as claimed in Claim 1 6, 17, 18 or 19 wherein a grille is provided around the retort so that ash and clinker falling from the retort into the tray pass through the grille, scrapers being provided for clearing any relatively large pieces of ash or clinker from the grille.

21. A solid fuel burner having a support for a fuel bed from which, in use, ash is discharged, wherein there are provided means for collecting ash discharged from the support and pneumatic means for conveying the ash away from the collecting means.

22. A burner as claimed in Claim 21 wherein the collecting means comprises a receptacle disposed beneath the support and arranged to receive the ash discharged from the support, the receptacle having at least one outlet connected to the pneumatic means.

23. A burner as claimed in Claim 5 or 22 wherein the pneumatic means is adapted to suck the ash from the receptacle.

24. A burner as claimed in Claim 5, 22 or 23 wherein the pneumatic means includes means for separating ash from the air conveying the ash from the receptacle.

25. A burner as claimed in Claim 24 wherein the separating means comprises a cyclone separator having an inlet connected to the outlet or outlets of the receptacle and an outlet connected to the suction side of a fan.

26. A burner as claimed in Claim 24 or 25 wherein the separating means is arranged to discharge the separated ash into means for cooling the ash.

27. A burner as claimed in Claim 24, 25 or 26 wherein the separating means is arranged to deliver the air from which the ash has been separated, to a combustion chamber containing the fuel bed.

28. A solid fuel burner substantially as herein described with reference to and as illustrated in Figure 1 our Figure 2 and 3 or Figure 4 of the accompanying drawings.

29. Any novel feature or novel combination of features herein described and/or illustrated in the accompanying drawings.