GB2160643A - Solid fuel combustion apparatus - Google Patents

Abstract

An apparatus for the secondary combustion of incompletely burned combustion products of a solid fuel combustion appliance comprises a second combustion chamber 5, 12, 12' having an inlet 2 open to receive the combustion products from the firebox 13 and an outlet 10' disposed rearwardly of and below the level of the inlet 2. A duct 4 is also provided to supply pre-heated air into the secondary combustion chamber. <IMAGE>

Description

SPECIFICATION Apparatus for the secondary combustion of incompletely burned combustion products This invention relates to an apparatus for the secondary combustion of incompletely burned combustion products of a solid fuel combustion appliance, in particular to promote the more efficient combustion of coal, peat, wood or lignite and the reduction of atmospheric pollution, in the form of smoke and other products of incomplete combustion, when such fuels are used in hand-fired heating or cooking appliances.

The increased use of solid fuels in recent years and the substantial difference in cost between smoke-producing and smokeless solid fuels has contributed substantially to air pollution in many urban areas. Some progress has been made with the development of smoke-reducing methods and appliances, but the object of the present invention is to provide more complete combustion than has previously been the case.

Accordingly, the present invention provides an apparatus for the secondary combustion of incompletely burned combustion products of a solid fuel combustion appliance, comprising a secondary combustion chamber having an inlet open to receive combustion products from the firebox of the appliance and an outlet disposed rearwardly of the inlet, the said combustion products initially rising upwardly from the said inlet and subsequently passing downwardly to the said outlet, the secondary combustion chamber further comprising means for supplying pre-heated air into the secondary combustion chamber.

The discharge of more completely burned high temperature gases at a low level within an appliance is of great importance because this permits greater vertical travel through or over the heat transfer surface which takes the heat to the point of use. The process of transferring heat from the combustion products must cool these products to the point where no further combustion can be sustained. Therefore it is a feature of the present invention that a secondary combustion chamber is used whereby the unburned gaseous products may be finally consumed in a very hot environment. This secondary combustion chamber is provided with a preheated air supply and in the preferred embodiment incorporates two expansion chambers of which the first is above the point of inlet of the preheated air.This expansion chamber is so arranged as to discharge the combustion products downwards, to a level below the original point of entry. A restriction at this point, followed by a further expansion chamber, ensures furher gas turbulence, completing the combustion process and depositing most of any carried-over ash. This ash falls onto an extension of the grate or firebars and may be readily removed. A preferred method of removal is by shaking the grate. In the preferred embodiment, therefore, the combustion products are not subjected to the cooling influence of a heat exchanger or boiler until they have passed through two expansion chambers, been subjected to two reversals of flow and been supplied with a pre-determined quantity of fresh heated air within the secondary combustion chamber.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional perspective view of an apparatus according to an embodiment of the invention, Figure 2 is a cross-sectional view of a closed fronted solid fuel combustion appliance incorporating the apparatus of Fig. 1, Figures 3a and 3b are side and plan views respectively of part of the appliance of Fig. 2, Figure 4 is a view similar to Fig. 2 of a second closed fronted appliance incorporating the apparatus of Fig. 1, and Figure 5 is a view similar to Fig. 2 of an open fronted appliance incorporating the apparatus of Fig. 2.

Fig. 1 shows a secondary combustion chamber located to the rear of a firebox in a solid fuel combustion appliance. The secondary combustion chamber includes a substantially vertical wall 5 and a hood 1 2 extending forwardly with clearance across the top of the wall 5 and downwardly partially towards the bottom of the wall. The secondary combustion chamber also includes a rear wall 12' extending downwardly from the rear of the hood 1 2.

Fuel resting on a grate 1 will transfer heat to any surrounding areas when it is burning. The smoke and products of combustion will be drawn by the chimney (not shown) into a restricted inlet 2 between the hood 1 2 and the wall 5 and upwards past an inlet 3 for pre-heated air. The pre-heated air enters via a duct 4 which is shown in this embodiment as being of tubular section. The duct 4 is incorporated in or supported by the top of the vertical wall 5 which forms the rear perimeter of the firebox as well as forming a vertical division fo the secondary combustion chamber. The assembly of the vertical wall and the air supply duct 4 receives a great deal of heat from the burning fuel and will do so even with a low fire, because the hottest point of the fire will always be close to the restricted inlet 2.

The air supply duct 4 is provided with a plurality of openings 6 and these are so arranged as to permit the passage of the optimum amount of air for efficient secondary combustion. The air for the duct 4 is derived from hollow side channels (not shown) which extend to the front of the appliance and feed the duct 4 from each end.

The combustion products, augmented by the pre-heated secondary air, pass upwards to a first expansion chamber 7 where turbulence and mixing is promoted by a change in direction of 180 degrees. A further space or extension of the secondary combustion chamber 8 terminates in a restricted mouth or outlet 9 which opens into a second expansion chamber 10. There is anothwer 1 80 degree change of direction prior to exit at outlet 10' of the second expansion chamber which permits the combustion products to move up across a heat exchanger 11. The second expansion chamber 10 has as its base or lower perimeter an extension of the grate 1. This is so arranged that the normal air gaps between the firebars are eliminated or substantially reduced so as to form a solid or almost solid base to the second expansion chamber 10.It is to be noted that the outlet 10' is disposed rearwardly of and below the level of the inlet 2. The side edges of the parts 5, 1 2 and 1 2' of the secondary combustion chamber are supported in this embodiment by the side walls of the firebox, and may be conveniently formed from castings in a suitable material such as chrome iron.

Alternatively, an assembly incorporating the two expansion chambers with the 1 80 degree turn at the top and at the base, together with the vertical wall 5 and the duct 4 may be constructed using other suitable material such as moulded firebrick, or a composite assembly of firebrick and castings may be used.

Also, it will be understood that the heat exchanger 11 which represents a water cooled surface may be replaced by firebrick or other refractory material. These arrangements would further increase the secondary combustion of an incompletely burned combustion products.

Fig. 2 shows a section of a closed heating appliance incorporating the above apparatus, the secondary combustion chamber being arranged at the bottom rear of the primary combustion chamber 1 3 and extending partially to the top thereof. Air enters the primary combustion chamber 1 3 via a controlled air inlet 14 and the secondary combustion chamber is constructed as previously described.

The heat exchanger 11 is in this case the surface of a boiler with finned extensions to provide additional heating surface on the face of the boiler. The front of the vertical flueway incorporating the heat exchanger, is formed at the lower end by the rear wall 12' and at the upper end by a removable member which in this embodiment is a firebrick 1 5. A removable duct or chamber 1 6 fitted at the top of the combustion chamber 1 3 carries at its forward end a hinged flap 1 7 which is designed to fall open due to its own weight when the fuelling door 1 8 is opened. This ensures that there is direct access from the combustion chamber to the chimney whenever the door is opened for refuelling or for lighting.A rearward extension 1 9 of the duct or chamber 1 6 interrupts the flow of the combustion products leaving the heat exchanger 11 and forces them to pass under a further water-filled heat transfer surface before leaving via the flue 20.

Fig. 3(b) shows a plan view of the duct or chamber 1 6 showing how the flow of combustion products are baffled and driven sideways and forwards by the rearward extension 19. Removable side members 21 may be fitted to further increase the travel, and heat transfer, of the commbustion products, where a high chimney draught is available. They may be removed where the chimney draught is low.

Fig. 3(a) shows a side view of the duct 1 6 with the hinged flap 1 7 hanging open, as will be the case when the pressure exerted by the closed door, or by one or more inner extensions of the closed door, is removed.

Fig. 4 shows another embodiment where the heat exchanger incorporates two vertical flueways as might be used with a solid fuel cooker. In this case vertical flueway a discharges combustion products at a high temperature into a horizontal duct b, seen here in section, this duct being extended sideways to heat a hotplate and one or more ovens by the flow of heated gas. A second vertical flueway c is also open to the expansion chamber at its lower end. The flow of combustion products may be directed via a or c by the action of a damper d which opens or closes either chamber. A second damper e gives direct access from the combustion chamber to the chimney for lighting or for refuelling.

The present invention is not limited in its application to closed appliances only. It may be effectively used with a boiler behind an open fire having a controlled inlet for combustion air below the fire and a damper to divert the combustion products via the secondary combustion chamber or directly into the chimney. This is illustrated in Fig. 5 where an air inlet a admits air below the fire bars and a damper b controls the direction of the combustion products.

Claims (11)

1. An apparatus for the secondary combustion of incompletely burned combustion products of a solid fuel combustion appliance, comprising a secondary combustion chamber having an inlet open to receive combustion products from the firebox of the appliance and an outlet disposed rearwardly of the inlet, the said combustin products initially rising upwardly from the said inlet and subsequently passing downwardly to the said outlet, the secondary combustion chamber further comprising means for supplying pre-heated air into the secondary combustion chamber.

2. An apparatus according to claim 1, wherein the secondary combustion chamber comprises a first expansion chamber arranged above the said inlet which effects a substantially 180 change in direction of the combustion products, and a second expansion chamber arranged below the first expansion chamber which effects a further substantially 180 change in direction of the combustion products.

3. An apparatus according to claim 2, wherein at least part of the front surface of each expansion chamber is directly exposed to heat from the firebed.

4. An apparatus according to any preceding claim, wherein the secondary combustion chamber comprises an upright wall and a hood extending forwardly with clearance across the top of the wall and downwardly partially to the bottom of the wall, the said inlet being formed between the downwardly extending portion of the hood and the front surface of the wall, and the said outlet being formed behind and adjacent the bottom of the wall.

5. An apparatus according to claim 4, wherein the preheated air supply means is incorporated in or supported by the said vertical wall adjacent the top thereof.

6. An apparatus according to claim 4 or 5 when dependent on claim 2 or 3, wherein the upper part of the said upright wall extends into the first expansion chamber to effect the said 180 change of direction, and the lower part of the wall forms the front surface of the second expansion chamber, the downwardly extending portion of the hood forming the front surface of the first expansion chamber.

7. An apparatus according to any preceding claim, wherein the said outlet of the secondary combustion chamber is at the base of a substantially vertical flueway.

8. An apparatus according to claim 7, wherein the outlet is at the base of a pair of substantially vertical flueways which are provided with a damper to direct combustion products from the said outlet to either flueway.

9. An apparatus according to claim 7 or 8, wherein the or at least one of the flueways includes a heat exchanger.

10. An apparatus according to any preceding claim, wherein the outlet of the secondary combustion chamber is below the level of the inlet thereof.

11. An open or closed fronted combustion appliance incorporating an apparatus according to any preceding claim, the appliance including a primary combustion chamber fuelled from the front, and the secondary combustion chamber being arranged at the bottom rear of the primary chamber and extending partially towards the top thereof.

1 2. An apparatus according claim 1, substantially as described herein with reference to Figs. 1 to 3, Fig. 4 or Fig. 5 of the accompanying drawings.