GB2187276A - Solid fuel combustion appliance - Google Patents

Abstract

A solid fuel combustion appliance comprises a primary combustion chamber 16, and a secondary combustion chamber 14 arranged at the rear of the primary chamber. The secondary combustion chamber has a downwardly opening inlet 15 to receive combustion products from the primary combustion chamber leading upwardly into a first passageway 17 and an outlet disposed adjacent the bottom of at least one second passageway 23 disposed rearwardly of the first passageway, and means 30 to 33 for supplying preheated air into the secondary combustion chamber, and the outlet of the second passageway communicates with an upwardly extending flueway (not shown) laterally adjacent the passageway 23. Both the top of the first passageway 17 and the top of the flueway have respective openings for the emission of combustion products from the appliance, and the appliance further comprises a slidable damper 29 for selectively opening and closing the top of the first passageway whereby when the top of the first passageway is open at least the greater part of the combustion products entering the inlet from the primary combustion chamber pass upwardly in the first passageway for emission directly from the open top thereof, whereas when the top of the first passageway is closed at least the greater part of the combustion products entering the inlet initially rise upwardly in the first passageway, subsequently change direction within the secondary combustion chamber to pass downwardly in the second passageway to the said outlet, and finally pass upwardly in the flueway for emission from the top thereof. <IMAGE>

Description

SPECIFICATION Solid fuel combustion appliance This invention relates to a solid fuel combustion appliance, and is an improvement in the appliance described and claimed in my copending Irish Patent Application 531/84 (corresponding to British Patent Application 8514221).

The above Patent Application discloses an open or closed fronted solid fuel combustion appliance with a secondary combustion chamber provided with a supply of pre-heated air.

The purpose of the secondary chamber is to effect a more complete combustion of gaseous combustion products produced by the primary combustion chamber, i.e. the firebox, in order to reduce the amount of smoke emitted by the appliance.

While the above appliance works quite satisfactorily when it has reached full temperature, it has been found that when first lit the appliance generates more smoke than is desired until such temperature is reached. This has been found to be due to the relatively high resistance of the secondary combustion chamber which delays a rapid warm-up.

Therefore, until a good fire, and a good draught, is established, it is necessary to have the combustion products of the fire discharging directly to the chimney and by-passing the secondary combustion chamber altogether.

It is an object of the present invention to mitigate this disadvantage.

Accordingly, the present invention provides a solid fuel combustion appliance, comprising a primary combustion chamber for containing a solid fuel to be burned, and a secondary combustion chamber arranged at the rear of the primary chamber, the secondary combustion chamber having a downwardly opening inlet to receive combustion products from the primary combustion chamber upwardly into a first passageway and an outlet disposed adjacent the bottom of at least one second passageway disposed rearwardly of the first passageway, the appliance further comprising means for supplying preheated air into the secondary combustion chamber, ana the outlet of the second passageway communicating with an upwardly extending flueway, both the top of the first passageway and the top of the flueway having respective openings for the emission of combustion products from the appliance, the appliance further comprising means for selectively opening and closing the top of the first passageway whereby when the top of the first passageway is open at least the greater part of the combustion products entering the inlet from the primary combustion chamber pass upwardly in the first passageway for emission directly from the open top thereof, whereas when the top of the first passageway is closed at least the greater part of the combustion products entering the inlet initially rise upwardly in the first passageway, subsequently change direction within the secondary combustion chamber to pass downwardly in the second passageway to the said outlet, and finally pass upwardly in the flueway for emission from the top thereof.

In use, when the fire is first lit the top of the first passageway is open, so that the greater part of the combustion products entering the secondary combustion chamber are emitted from the top of the first passageway and by-pass the second passageway and flueway. This is because the open-topped first passageway presents a much lower resistance to the combustion products than the alternative path via the second passageway and flueway. If desired, to increase the resistance of the path via the second passageway and flueway, the means (such as a slidable damper) which selectively opens and closes the top of the first passageway may operate so as to close the top of the flueway when the top of the first passageway is open, and vice versa.

Nevertheless, it is desirable that some combustion products be permitted to pass up the flueway when the top of the first passageway is open, so that the top of the flueway is preferably not completely blocked when the top of the first passageway is open. Furthermore, there may be a small opening or series of openings at the base of the flueway which permit combustion products to pass up the flueway directly from the primary combustion chamber. These measures are designed to allow a minor part of the combustion products to pass up the flueway even when the top of the first passageway is open, to permit the flueway to warm up in preparation for closing the top of the first passageway.

This latter occurs when the appliance has reached full temperature, so that the greater part and preferably substantially all the combustion products entering the secondary combustion chamber pass up the first passageway, down the second passageway, and finally up the flueway. This provides further time within the appliance to complete combustion.

The flueway preferably has its rear wall forming at least part of a wall of a heat exchanger containing water for heating by the appliance.

Preferably the at least one second passageway is disposed laterally to one side of the flueway, so that the rear wall of the second passageway also forms part of the wall of the heat exchanger. Most preferably, a pair of second passageways are provided, one laterally on each side of the flueway.

It will be appreciated that when the appliance has reached full operating temperature with the top of the first passageway closed, the configuration of the appliance is as claimed in claim 1 of the aforementioned Brit ish Patent Application.

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 side view of a solid fuel combustion appliance according to the invention, Figure 2 is a partially cut-away perspective view of part of the secondary combustion chamber at the rear of the appliance, omitting the front plate, Figure 3 is a perspective view of part of a second embodiment of the invention, Figure 4 is a cross-sectional view of an alternative damper arrangement to that of Figure 1, Figure 5 is a plan view of the sliding damper of Figure 4, and Figure 6 is a plan view of the pivotted damper of Figure 4.

Referring to the drawings, the appliance comprises an open fronted solid fuel boiler including a rear waterfilled heat exchanger 10 and a pair of forwardly extending side cheeks 11, only one of which is shown in Figure 1, i.e. the right hand cheek as viewed from the front. The appliance is fitted in conventional manner with an apertured grate 12 for supporting a solid fuel to be burned, and an ash tray 13 for collecting the solid combustion products which fall through the grate.

At its rear the appliance has a secondary combustion chamber generally indicated at 14.

The chamber 14 has a downwardly opening inlet 15 to receive combustion products from the primary combustion chamber 16 (i.e. ffirebed) upwardly into a first passageway or expansion chamber 1 7 formed between a front plate 18 and an intermediate plate 19, both of which extend fully between the cheeks 11.

The passageway 1 7 has a horizontal opening 20 at the top which extends across the full width of the appliance.

At the inlet 1 5 of the passageway 1 7 the front plate 18 has a hood 30 which extends across the width of the appliance and accomodates a heat resistant tube 31 which extends between a pair of air supply ducts 32, one on each side cheek 11. Each duct 32 supplies fresh air from the front of the appliance to each end of the tube 31, from where it is supplied into the secondary combustion chamber via apertures 33 distributed along the length of the tube. The air is pre-heated by the fire during its travel along the ducts 32 and along the tube 31. A downward extension 34 of the hood 30 promotes turbulence and mixing of the pre-heated air with the combustion gases before the latter enter the secondary combustion chamber.

A pair of second passageways 23 and a flueway 24 are defined by a pair of upright baffles 38 which extend front to rear fully across and divide the space between the intermediate plate 19 and the front wall 25 of the heat exchanger 10 into three compartments, the outermost compartments constituting the passageways 23 which are arranged laterally one on either side of the middle compartment which constitutes the flueway 24 (see also Figure 2). The wall 25 and plate 19 are common to the passageways 23 and flueway 24, which are all disposed rearwardly of the inlet 15 and first passageway 17.

The passageways 23 are closed at the top, as shown in Figure 2, whereas the flueway 24 has a horizontal opening 21 at the top. Furthermore, the plate 19 extends fully to the opening at the top of the flueway 24, whereas it stops short of the closed tops of the passageways 23 to form vertical openings 22 by which the top of the first passageway 17 can communicate with the tops of the second passageways 23.

The bottoms of the passageways 23 communicate with the bottom end of the centre flueway 24 around the bottom edges 26 of the baffles 38, the upward opening into the flueway 24 constituting a common outlet for both passageways 23 and hence of the secondary combustion chamber. It is to be noted that the bottom ends of the passageways 23 and the flueway 24 are separated from the firebed 16 by an access plate 27 and a firebrick 28.

A damper 29 (Figure 1) is provided across the full width of the appliance at the top or the passageway 17 and flueway 24, and this is slidable between the position shown in solid lines wherein it closes off or substantially closes off the opening 21 at the top of the flueway 24, and the position 29' shown in dashed lines wherein it closes off the opening 20 at the top of the passsageway 17.

Finally, a large pivotal damper 35 is provided at the top of the primary combustion chamber 16, and normally closes off the latter from the chimney 36. The operation of the appliance is as follows.

When the fire is first lit on the firebed 16 the damper 29 is slid to the position shown in solid lines in figure 1, i.e. opening the top of the passageway 17 and closing the top of the flueway 24. Accordingly, the passageway 17 provides a low resistance path for the gaseous products of combustion, so that the greater part of the gases are emitted directly from the opening 20 into the chimney 36 as shown by the arrow 39 (Figure 1). However, the damper 29 does not fully close off the opening 21 at the top of the flueway 24, and this together with the series of small openings 37 in the access plate 27 permits a minor part of the gases to escape up the flueway 24.

When the appliance has reached full temperature, the damper 29 is slid forward to the position 29' indicated in dashed lines in Figure 1, thereby closing off the opening 20 at the top of the passageway 17 and opening the top of the flueway 24. Now substantially all the combustion gases rising in the passageway 17 are forced to pass through the vertical openings 22 at the top of the passageways 23 and reverse direction, as shown by the arrows 40, to pass downwardly through the lateral passageways 23. Next, as shown by the arrows 41, the gases exit from the secondary combustion chamber 14 around the edges 26 of the baffles 38 to rise upwardly in the central flueway 24. Finally, the gases exit to the chimney 36 through the opening 21 at the top of the flueway 24, as shown by the arrow 42.

It is to be understood that the damper 35 would normally remain substantially closed, except for chimney sweeping and perhaps the first few minutes of ignition if the draft is poor.

Referring now to Figure 3, an alternative arrangement to the hood 30 and heat resistant tube 31 is shown. In Figure 3, only one side 11 of the appliance is shown but it is to be understood that the other side has a symmetrical arrangement.

In this case the air enters a plurality of apertures 50 into a vertical air duct 51 tormed at the front edge of each of the sides of the appliance. The air passes down each duct 51 and passes through an aperture 52 into a respective horizontal air duct 32 at each side of the appliance. The air emerges from each duct 32 via an aperture 53 into a removable hood 54. The air passes out of the hood 54 as shown by the arrows into the secondary combustion chamber at each side thereof.

The hoods 54 are positioned immediately below or just inside the opening of the secondary combustion chamber 14, i.e. at or just inside the opening of the first passageway 1 7 (not shown).

Referring back to Figure 1, the large pivotal damper 35 may be manually set at an optimum point to restrict air and combustion products passing to the chimney 36 via the front of the plate 18, while leaving a small opening to collect smoke that might otherwise emerge from the front of the fire and become a nuisance. It is desirable that this optimum open area should remain the same whether the top of the rear flueway 24 is open or not.

Therefore, an alternative arrangement is shown in Figures 4 to 6, which combines the functions of the sliding damper 29 and the pivotal damper 35.

A pivotal damper 60 is fitted towards the upper front of the appliance such that it is normally supported by a front pivot 61 while prevented from swinging downwards by the support of a sliding damper 62. However, it may be readily moved upwards to give access to the chimney 36 as shown by the dashed line position. An elongate slot or aperture 63 is cut in this damper 60, as shown in Figure 6. The free area of this aperture 63 corresponds with the optimum free-area opening from the primary combustion chamber to the chimney 36 and the width i-i is critical.

The rearward-facing edge of the damper 60 has a clearance from the top edge of the front plate 18 which is the same distance as the dimension i-i. The sliding damper 62 is also provided with a slot or aperture 64 which corresponds with the dimension of the opening from the first passageway 17 such that when the damper 62 is pushed fully to the rear, as shown in Figure 4, the aperture 64 is directly above the opening from the front passageway, while when the damper 62 is pulled fully forward, as shown in dashed lines, leaving the opening 21 above the flueway 24 exposed, the rear portion 66 of the damper 62 closes the opening from the first passageway 17.

It will be seen from Figure 4 that when the sliding damper 62 is pushed fully to the rear the aperture 63 is open to the chimney 36 and that when it is pulled fully forward against stops (not shown) fitted in the damper 60 the similarly sized aperture 65 between the rear edge of the damper 60 and the top of the plate 18 is open to the chimney. In any intermediate position the sum of the two partopen apertures will have an area substantially constant and equal to the total optimum area.

The invention is not necessarily restricted to the heating of water, and the heat exchanger may be used to heat a volume of air which may be distributed by convection or with the assistance of a fan.

Although the above describes an open fronted solid fuel appliance, the invention is equally applicable to a closed fronted appliance.

Claims (8)

1. A solid fuel combustion appliance, comprising a primary combustion chamber for containing a solid fuel to be burned, and a secondary combustion chamber arranged at the rear of the primary chamber, the secondary combustion chamber having a downwardly opening inlet to receive combustion products from the primary combustion chamber upwardly into a first passageway and an outlet disposed adjacent the bottom of at least one second passageway disposed rearwardly of the first passageway, the appliance further comprising means for supplying preheated air into the secondary combustion chamber, and the outlet of the second passageway communicating with an upwardly extending flueway, both the top of the first passageway and the top of the flueway having respective openings for the emission of combustion products from the appliance, the appliance further comprising means for selectively opening and closing the top of the first passageway whereby when the top of the first passageway is open at least the greater part of the combustion products entering the inlet from the primary com bustion chamber pass upwardly in the first passageway for emission directly from the open top thereof, whereas when the top of the first passageway is closed at least the greater part of the combustion products entering the inlet initially rise upwardly in the first passageway, subsequently change direction within the secondary combustion chamber to pass downwardly in the second passageway to the said outlet, and finally pass upwardly in the flueway for emission from the top thereof.

2. An appliance as claimed in claim 1, wherein the means which selectively opens and closes the top of the first passageway is adapted to at least partially close the top of the flueway when the top of the first passageway is open, and vice versa.

3. An appliance as claimed in claim 1 or 2, wherein the means which selectively closes the top of the first passageway does not completely block the top of the flueway when the first passageway is open, and wherein the appliance further comprises one or more small openings at the base of the flueway which permit combustion products to pass up the flueway directly from the primary combustion chamber, whereby a minor part of the combustion products can pass up the flueway from the primary combustion chamber when the top of the first passageway is open.

4. An appliance as claimed in any preceding claim, wherein the flueway has its rear wall forming at least part of a wall of a heat exchanger containing a fluid for heating by the appliance.

5. An appliance as claimed in any preceding claim, wherein the at least one second passageway is disposed laterally to one side of the flueway, so that the rear wall of the second passageway also forms part of the wall of the heat exchanger.

6. An appliance as claimed in claim 5, wherein a pair of second passageways are provided, one laterally on each side of the flueway.

7. An appliance as claimed in any preceding claim, wherein the primary combustion chamber and the tops of the first passageway and flueway communicate with a common chimney, wherein the means which selectively closes the top of the first passageway comprises a first apertured damper slidable between a rear position wherein the top of the first passageway is open and a forward position wherein the top of the first passageway is closed, and wherein the top of the primary combustion chamber has a further apertured damper, the first and further dampers being so arranged that irrespective of the position of the first apertured damper between the front and rear positions the primary combustion chamber is open to the chimney over a substantially constant area.

8. An appliance as claimed in claim 1, substantially as described herein with reference to the accompanying drawings.