GB2060162A - Improvements in the combustion efficiency of solid fuel burners - Google Patents

Abstract

The invention is a device for fitting in solid fuel burners such as open fires and wrap around boilers to improve the combustion efficiency. The device consists of a container (1) for a column of fuel and has an open bottom (3) forming an air inlet and a removable lid (2) forming an adjustable exhaust vent. The air inlet may be an opening (5) adjacent the bottom. <IMAGE>

Description

SPECIFICATION Improvements in the combustion efficiency of solid fuel burners The present invention relates to the improvement of the combustion efficiency of solid fuel burners.

In this specification the term "solid fuel burner" includes not alone solid fuel burners such as wraparound boilers which have one or more of their sides forming heat exchanger surfaces, for example, by hollow water carrying walls, but also open hearth fires, enclosed fire appliances such as stoves used for cooking and hot water supply.

As has been known for many years it is advantageous, and indeed for efficient combustion essential, to ensure that all the combustible gases given off by solid fuels and in particular coal, are burnt. Essentially, it is necessary to ensure the smokeless combustion of fuels wherein the combustible gases are consumed by providing sufficient air supply or by in some way returning the gases to the fire for combustion after having been initially driven off by pyrolysis of the fuel.

The technology of burning combustible gases given off by coal was well known in the nineteenth century and indeed prior to this. This technology was applied specifically to the fireboxes of locomotives prior to the 1 860's with a view to providing smokeless combustion. The application of secondary air for burning these gases was also well known at that time. Modern attempts at improving the combustion of such combustible gases, that is to say, by improving the methods of smokeless combustion have been primarily concerned with the burning of the gases by using a separate secondary air supply. Both downdraught and up-draught appliances utilising this principle are weil known.

However, the problem with such appliances is that they are generally very expensive to construct. Heretofore, no simple device has been proposed for improving the combustion efficiency of such solid fuel burners.

The present invention is directed towards providing such a device which will not only be simple to manufacture but can be readily easily used with existing fuel burners or alternatively incorporated into the fabric of conventional burners. It is also an object of the invention that such a device be relatively inexpensive to manufacture while at the same time providing substantially the same high combustion efficiencies of much more elaborate and expensive appliances.

According to the invention there is provided a device for fitting into a solid fuel burner to improve its combustion efficiency comprising a container for a column of unburnt fuel and for trapping combustible gases, said container having: top, bottom and side walls; an air inlet adjacent its bottom; and an exhaust vent.

The invention will be more clearly understood from the following description of some preferred embodiment thereof given by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a device according to the invention, Fig. 2 is a cross-sectional view of the device of Fig. 1, Fig. 3 is a cross-sectional view of the device of Fig. 1 fitted into an open-hearth fire, Fig. 4 is a cross-sectional view of a further device according to the invention, Fig. 5 is a cross-sectional view of a still further device according to the invention, Fig. 6 is a perspective view of another alternative construction of the device according to the invention, Fig. 7 is a plan view of a wrap-around boiler with the device of Fig. 6 fitted thereto, Fig. 8 is a cross-sectional view of the wraparound boiler incorporating the device of Fig. 6, Fig. 9 is a cross-sectional view of an enclosed fire appliance in which is mounted a modified form of the device of Figs. 1 to 3, Fig. 10 is a front view of a modified form of the device of Fig. 5, Fig. 11 is a cross-sectional view in the direction of the arrowsXl-Xl of Fig. 10, Fig. 1 2 is a front view of a modified form of the device of Figs. 6 to 8, Fig. 1 3 is a side view of the device of Fig. 12, Fig. 14 is a sectionai view in the direction of the arrows XIV--XIV of Fig. 12, with portions removed for clarity, and Fig. 1 5 is a cross-sectional view in the direction of the arrows XV-XV of Fig. 12.

Referring to the drawings and initially to Figs. 1 to 3 thereof, there is illustrated a container, indicated generally by the reference numeral 1, having a top wall formed by a lid 2, an open bottom 3 and side walls 4. A side air inlet 5 is provided in the side wall 4 adjacent the bottom 3.

The open bottom forms an additional air inlet while the lid 2, on removal or partial removal, forms an adjustable exhaust vent adjacent its top.

In use, the container 1 may be placed in a fire grate or, for example, a stove. Referring to Fig. 3, the device is shown mounted within a conventional fireplace, indicated generally by the reference numeral 17, having a grate 1 8. It will be appreciated that any of the devices according to the invention may be so placed in the fireplace 1 7.

The lid 2 is removed and fuel is packed into the container 1 filling it. When the fuel is fully packed into the container 1 a fire is lit at the bottom and air is drawn in through the side air inlet 5 and the open bottom 3. When the fuel is burning the lid 2 is placed in position so that there is only a slight draught. A substantially complete combustion of the fuel takes place and the heating efficiency is greatly improved.

It will be appreciated that the lid 2 must of necessity be loosely placed on the container 1 if the fire is to burn. Alternatively, if the lid is a tight fit it must always be slightly removed from the top of the container so as to provide an exhaust draught.

It will be noted that the cross-sectional area of the container increases from the top to the bottom preventing the jamming of fuel during combustion.

Referring to Fig. 4 there is illustrated another construction of device. This device comprises a frusto-conical container 11 having a lid 12, open bottom 13, and side wall 14. An air inlet 1 5 and an exhaust vent 1 6 are provided in the side wall 14. The air inlet 15 and exhaust vent 1 6 are opposite and equispaced circumferentially.

Advantageously, the lid is removed for ignition. In use, once the fire has been lit the lid 12 is placed firmly in position in an air tight manner. The fuel will burn on substantially cross-flow principles.

Essentially, there is a closed column of fuel above an ignited bed. Some of the unburnt fuel is heated sufficiently to drive off combustible gases and since the combustible gases are trapped in the column they must travel back down to the fire for ignition.

Referring to Fig. 5 there is illustrated a still further construction of device according to the invention. This device is essentially a modification of the two previous devices and combines the features of both. The device comprises a container 20 of frusto-conical shape having an open bottom 21, an air inlet 22 and an exhaust vent 23 which has an adjustable flap 24. The air inlet 22 and the exhaust vent 23 are opposite and equispaced circumferentially. The container 20 has a top cover 25 which may be removed for charging with fuel. Said top cover 25 has an additional adjustable exhaust vent 26. It will be appreciated that the device of Fig. 5 may be operated in one of two ways. It may be operated in the same manner as the embodiment of Fig. 1 with the exhaust vent 23 closed and the exhaust vent 26 opened.

Similarly with the exhaust vent 26 closed and the exhaust vent 23 opened it may operate in the same manner as the device of Fig. 4.

Referring to Figs. 6 to 8 there is illustrated a construction of the device which in use operates in a manner similar to the device of Fig. 4. This is particularly suitable for fitting into a wrap-around boiler so that portion of the boiler forms part of the side wall. Again it essentially comprises a container indicated generally by the reference numeral 30 having a lid 31 formed from a flat plate, an open bottom 32 and a side wall formed from a front plate 33 and two rearwardly diverging side plates 34. An air inlet 35 is provided. This container 30 as mentioned above is particularly suitable for mounting within a wrap-around boiler such as is illustrated in Figs. 7 and 8 which shows the container 30 fitted to a boiler indicated generally by the reference numeral 36.The apparatus operates in the same manner as described already with reference to Fig. 4 i.e. on cross-flow principles with the lid 31 closed.

Needless to say, for proper operation the combustible gases must not escape between the boiler and the side wall of the device. Thus, suitable coupling means will generally have to be provided in a manner which will be readily apparent to those skilled in the art.

Referring to Fig. 9 there is illustrated an enclosed fire appliance namely, a combined cooker and water heater, indicated generally by the reference numeral 40, having a pair of fuel inlets 41, a flue 42 and a controllable air inlet 43.

Incorporated in the fire appliance 40 is a device according to the invention similar to that described with reference to Fig. 1 except that it is of frusto-conical shape. The device has side walls 44, lid 45 and an air inlet 46. In use the device operates in the same manner. It will also be appreciated that any other form of the device might be used. It will be appreciated however; that when it is desired to use the stove for cooking that additional heat may be required. In this case the lid 45 will be opened more fully. A further fire is then lit at 47 adjacent the air inlet 46. This ensures that all the combustible gases are consumed.

Referring to Figs. 10 and 11 there is provided an alternative construction of the device which is essentially a modification of the device as illustrated in Fig. 5. There is provided a container, identified generally by the reference numeral 50.

The container is of frusto-conical shape having side walls 51, an air inlet 52 and an exhaust vent 53 which is opposite and equispaced circumferentially from the air inlet 52. The exhaust vent 53 is provided with an adjustable flap 54 to form an adjustable exhaust vent. Water inlet pipes 55 and outlet pipes 56 are provided which in use are connected into a hot water supply or central heating system. Safety steam vents (not shown) are also provided as is a combined lid and exhaust vent 57.

The operation of this device is substantially similar to the operation of the device of Fig. 5, however, it will be noted that because the side walls 51 are essentially hollow heat exchangers that this will reduce the wear of the side walls increasing the life of the device. Further, the use of hollow heat exchangers to form part of the device will of necessity increase the heat transfer efficiency of the burner in which it is placed.

Referring to Figs. 12 to 1 5 there is illustrated a further device according to the invention which is essentially a modification of the device illustrated in Figs. 6 to 7. The device comprises a container indicated generally by the reference numeral 60 having a lid 61 formed from a flat plate, an open bottom 62 and a side wall formed from a hollow water carrying front heat exchanger 63 and two rearwardly projecting side heat exchangers 64. An air inlet 65 is provided. Water inlets 66 and water outlets 67 are provided. as are safety steam vents (not shown).

The operation of the apparatus is as described already with reference to the device illustrated in Figs. 10 and 11. There should be reduced wear and deterioration of the device together with increased heat exchange efficiencies. It will be appreciated that while this embodiment has been shown as a separate embodiment that it would be relatively easy to incorporate the side heat exchanger 64 into a boiler making one composite unit.

The device, needless to say, may be attached and connected to a boiler in any suitable manner.

Such modifications to the device will be readily apparent to those skilled in the art and will be necessary depending on the type of boiler to which it is fitted and the use to which the boiler is put.

In all cases it is generally desirable to ensure that the container has a shape that will allow the fuel to flow freely. Thus, parallel sided containers are not particularly advantageous as there is always the problem of the fuel, particularly coal, caking.

Generally in the cross flow device the exhaust vent and air inlet should be opposite and equispaced around its periphery.

While our experiments to date have not shown how the various forms of the apparatus according to the present invention operate or why they should be more efficient in operation than the boilers heretofore proposed there are certain possible explanations for this.

The following explanation of what we believe to be the manner in which the apparatus and process works must be appreciated as to a certain extent being merely conjecture. The experiments that we have conducted to date have not been completed and accordingly the following theory has not been fully verified. It is, however, given as it may be of some assistance.

In cross-flow devices a closed column or container stores fuel above an ignited bed. Some of the unburnt fuel is heated sufficiently to drive off certain of the combustible gases and since these combustible gases or volatiles are trapped in the column they must eventually travel downwards to the fire for ignition by the fire. Thus, essentially all the combustible volatiles are burnt by being trapped and being returned to the fire in somewhat the same manner as the more elaborate down-draught boiler.

When a unit such as illustrated in Figs. 1 to 3 is used some form of top lid or vent must be provided. It is necessary to have the lid partially open to provide a draught. Some of the combustible gases or volatiles will undoubtedly escape out past the lid at the top. However, most of these gases appear to be driven back down into the fire for combustion. As the present moment it is not possible to state why this happens however, it appears that the mass of fuel contributes to the delay of the upward travel of the gases forcing them back down into the fire bed for ignition.

Lastly, when a device such as illustrated in Fig. 9 is placed in an enclosed fire appliances, it operates under normal conditions as described above.

However, when it is desired to use the appliance for peak demand it will obviously be necessary to open the lid at the top of the column so that a considerable amount of the combustible gases or volatiles would normally escape. When this situation arises, as described, a secondary fire is lit beside the unit to meet this peak demand. As far as can be ascertained this secondary fire burns the combustible volatiles from the unit or column, that is to say, from the primary fire. This takes place at the upper level of the fire box of the enclosed fire appliance. Further, it appears that combustible gases from the secondary fire pass through the burning volatiles of the primary fire and are themselves ignited.

While the embodiments described above have all referred to the use of coal, other fuels such as turf and wood may also be used.

In all cases it is essential that there be a column of unburnt fuel above the fire.

Claims (11)

1. A device for fitting into a solid fuel burner to improve its combustion efficiency comprising a container, for a column of unburnt fuel and for trapping combustible gases, said container having: top, bottom and side walls; an air inlet adjacent its bottom; and an exhaust vent.

2. A device as claimed in claim 1 in which the exhaust vent is provided by a removable lid forming its top wall.

3. A device as claimed in claim 1 in which the exhaust vent and air inlet are provided in the side wall, said vent and inlet being opposite and equispaced around its periphery.

4. A device as claimed in claim 3 in which there is an additional adjustable exhaust vent adjacent its top wall.

5. A device as claimed in any preceding claim in which the container is open bottomed.

6. A device as claimed in any preceding claim in which the cross-sectional area of the container increases from the top to the bottom.

7. A device as claimed in any preceding claim in which portion of the walls of the container are hollow heat exchangers.

8. A device as claimed in any preceding claim in which part of the side wall of the container is formed by the burner when the device is fitted thereto.

9. A device as claimed in any of claims 1 to 7 which forms an integral part of the burner.

10. A device for fitting into a solid fuel burner to improve its combustion efficiency, substantially as described herein with reference to the drawings.

11. A burner incorporating a device as claimed in any preceding claim.