GB2495920A

GB2495920A - Solid fuel appliance with secondary combustion and a heat exchanger

Info

Publication number: GB2495920A
Application number: GB1118353.0A
Authority: GB
Inventors: Paul Allen Fealy; David James Saunders
Original assignee: Stovax Ltd
Current assignee: Stovax Ltd
Priority date: 2011-10-24
Filing date: 2011-10-24
Publication date: 2013-05-01
Anticipated expiration: 2031-10-24
Also published as: GB201118353D0; GB2495920A8; GB2495920B8; GB2495920B

Abstract

A solid fuel appliance (e.g. wood or multi-fuel stove 11) has air inlets 22,23; a water jacket heat exchanger 28-33 in a closed combustion chamber 18; tubes 34 delivering air to a secondary combustion region 38 within the combustion chamber between a primary combustion region 37 and the flue outlet 27; and deflector plates 25,26 creating an extended path for combustion product gases to a passage 31 through the heat exchanger. In another embodiment heat exchanger has a C-shaped portion (39, fig 2).

Description

IMPROVEMENTS RELATING TO A HEATING APPLIANCE

The present invention relates generally to a heating appliance and, particularly. to a solid fuel appliance. Such heating appliance may be a room-heating stove or an appliance having other functions, such as a cooker.

Solid fuel heating appliances provided with a heat exchanger or so-called boiler' are known as such. The heat exchanger is usually in the form at a tank or generally flat slab-like container located at the rear of Ihe combustion chamber to receive radiated heat from the combustion of fuel in use of the appliance. The heat transfer fluid, usually water, is circulated from the boiler to a tank for storage or to central heating radiators for room heating at other parts of the house.

One of the disadvantages of previously known solid fuel heating appliances with heat exchangers is the fact that the heat exchanger itself constitutes a heat sink thereby lowering the temperature of the walls of the combustion chamber where they are located reducing the effectiveness of the appliance as a heater. This also * detrimentally affects the combustion efficiency and makes it difficult to keep the * 20 emissions, particularly carbon monoxide, below desirable levels. *** . * * *

It is important in such appliances to achieve a good relationship between the heat transferred to the fluid in the heat exchanger and the heat transferred directly into the ** * * -room in which the appliance is located for appropriate control of the room temperature and the water temperature. Typically the target ratio is approximately 50% of the heat to be delivered to the heat exchanger and 50% to the surrounding environment. For this purpose the heat exchanger, in the form of a water jacket, is usually so designed as partly to surround the combustion chamber on at least three sides.

The present invention seeks to provide an improved solid fuel heating appliance with a configuration arranged more easily to meet the efficiency and emission targets whilst maintaining a good division of heat transfer between the surrounding environment and the heat transfer fluid.

According to the present invention, therefore, a solid fuel appliance having a body defining a combustion chamber, at least one primary combustion air inlet, a flue outlet for combustion products to exit the combustion chamber and a heat exchanger in the combustion chamber is provided with means for delivering secondary combustion air drown from outside the body to a delivery region located between a primary combustion region and the flue outlet in a position such that combustion product gases from the said delivery region pass over part of the heat exchanger on their way to the flue outlet.

The secondary combustion which takes place by re-ignition of the partly-burnt combustion products from the primary combustion of the fuel with the primary combustion air raises the temperature of the gases in the region by enabling a more 0**** * * complete combustion of the gases to take place and therefore increases the efficiency of combustion whilst, at the same time, reducing the emissions of carbon monoxide. ***. * . Oe* * 20 * *

In a preferred embodiment of the inventions the heat exchanger comprises a water jacket in the form of a generally slab-like water container occupying at least one side * of the combustion chamber of the appliance. Preterably, of course, the water jacket extends over a greater area, typically over three sides of the combustion chamber although, for improved performance, the heat exchanger may also have a component extending over the combustion chamber and between the combustion chamber and the flue outlet.

In such an embodiment of the invention the said part of the heat exchanger extending over the combustion chamber may be so shaped as to permit the passage of combustion product gases into the flue exit. This also improves the thermal contact between the combustion product gases and the heat exchange fluid in the heat exchanger. This upper port of the heat exchanger may be generally C-shape with two lateral arms one on each side of a central region which may be in general alignment with the flue outlet.

In an alternative embodiment the heat exchanger or at least the said upper part thereof may comprise a plurality of tubes for conveying a heat exchange fluid, typically water, through the combustion chamber.

The said means for delivering secondary combustion air into the combustion chamber may comprise one or more ducts having one or more exit openings at an upper level within the combustion chamber whereby to define the said delivery region. In a preferred embodiment of the invention there are two such ducts one at each side of the combustion chamber, joined by a hollow transverse duct having a plurality of outlet openings spaced across the width of the combustion chamber. In use of the * ., * appliance, then, the said delivery region constitutes in effect a region where secondary *..

combustion takes place by re-ignition of the partly burnt combustion products from the *.a... *

primary combustion of the fuel. ** * * * *** 0 *

* CV In order further to improve the efficiency of the appliance there may be provided a deflector or baffle between the primary combustion region and the flue outlet, acting in use to extend the path of combustion product gases between the primary combustion region and the flue outlet, and the exit opening or openings from the said secondary combustion air delivery duct or ducts is or are located on the side of the deflector plate remote from the flue outlet whereby, in use, secondary combustion occurs in the said secondary air delivery region and the heated combustion product gases are then caused by the deflector to flow over the upper part of the heat exchanger on their way to the flue outlet.

Preferably the inlet openings to the said secondary air delivery ducts are located at a low level in the body of the appliance, and preferably at an under surface thereof, whereby the ducts pass through or alongside the primary combustion region such that, in use, the secondary combustion air delivered thereby is heated within the ducts on its way to the delivery region without substantially reducing the heat transter to the heat exchanger.

The appliance may be designed as a wood burning stove or as a so-called multi-fuel stove capable of burning coal or coal products as an alternative to wood. For this purpose the appliance may have a grate for supporting solid fuel above the level of a lower primary combustion air inlet so that, in use, this lower ptimary air con flow upwards through the openings in the grate and infuse the fuel to support combustion thereof.

Typically the appliance may have a glazed fuel-loading door and the body may further have an upper combustion air inlet for creating a down wash of combustion air * over the inner fact of the fuel-loading door in use of the appliance.

* ** a a * * 20 ** Two embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompandng drawings, in which: r.a. -Figure 1 is a transverse section through a multi-tuel room-heating stove provided with a heat exchanger for supplying a central heating system; and -Figure 2 is a schematic perspective view of a water jacket for the heat exchanger ot a second embodiment ot the invention.

The drawing illustrates a solid fuel stove generally indicated 11 having a generally box-like body with a rear wall 12, floor plate 13. top plate 14 and a glazed door 15 hinged to side walls (not shown). The floor plate 13 is carried on front and rear legs 16, 17 so that the floor plate 13 itself is spaced from the ground.

The interior of the stove 11 comprises a combustion chamber generally indicated 18 detined at the bottom by a grate 19, for supporting the fuel. Below the grate, 19, is an ash space 20, in which an ash pan 21, is located.

Air is allowed into the stove 11, via lower and upper air inlets 22, 23 respectively, the former being located below the grate 19 and allowing air into the ash chamber 20 from where it can flow up through the fuel located on the grate 19. Primary combustion air entering through the upper opening 23 can pass through a regulator generally indicated 24 from where it flows downwardly over the inner face of the glazed door 15.

The regulator 24 is adjustable to determine the rate of flow of primary combustion air through the upper inlet 23. Although not shown, a further regulator for controlling the rate of flow of primary combustion air at the lower inlet 22 is also provided.

Within the combustion chamber l8is located an inclined detlector plate 25 to which is connected an upper generally horizontal baffle 26 spaced slightly trom the top plate 14 * to allow combustion product gases to flow round the baffle 26 through the narrow * *.*..

* 20 space between its front edge and the primary air inlet control adjustor 24 on its way to aflueoutlet27. **..* * .

A heat exchanger in the form of a water jacket generally indicated 28 comprises a rear panel 29, side cheeks 30 (only one of which is visible in the drawing), and an upper part 300 having a passage 31 therethrough tor a purpose which will be described in more detail below. The water jacket 28 has an inlet 32 at a lower level approximately at the level of the grate 19, and an outlet 33 in line with the upper part 30 thereof.

Welded to the inner port of the rear panel 29 of the water jacket 28 are two cranked tubes 34, one at each side of the combustion chamber. These tubes 34 each hove a lower inlet opening 35 passing through the floor plate 13 of the stove and upper outlets in communication with a transverse tube 36 located just under the baffle 26. The tube 36 has a plurality of opening 36a in its side wall to provide outlets across the width of the combustion chamber 18.

When fuel, in the form of logs or coal, is place on the grate 19 and ignited. combustion is supported by primary combustion air entering through the lower inlet 22 and the upper inlet 23, and takes place in the immediate vicinity of the fuel in a primary combustion region generally indicated by the broken line 37. The combustion process heats the tubes 34 and the draught from the hot gases travelling upwards through the flue 27 causes a pressure reduction within the combustion chamber 18 encouraging secondary combustion air to be drawn in through the inlets 35 at the bottom of the tubes 34 and to exit, heated, through the outlets 36a into a secondary combustion region identified by the broken line 38 within the combustion chamber 18. The heated secondary combustion air in this region reignites any partly-burned combustion product gases resulting from combustion of the fuel in the primary combustion region 37 and these gases then flow, as shown by the arrows A around the front edge of the baffle 26, S.....

* 20 between this andthe upper limb 30 of the water jacket 28. through the passage 31 and *". into the flue collar 27. * S

Radiated heat from both the primary combustion region 37 and the secondary combustion region 38 within the combustion chamber 18 heats the water in the water jacket 28 and this may be pumped or may be driven by convection out through the outlet 33 to its ultimate destination, which may be ci hot water tank for domestic hot water or a central heating network, passing through one or more radiators before being delivered back to the inlet 32.

Because of the elevated temperatures reached in the secondary combustion region 38 and the addiliond combustion air delivered through the openings 36a in the tube 36 the exhaust gases are more completely burned and therefore the particulate matter and carbon monoxide content are both reduced. By having the water jacket on three sides and the top of the combustion chamber a good thermal contact between the heat exchange fluid and the combustion products within the combustion chamber is achieved so that a high thermal efficiency in the transfer ot heat to the heat transfer fluid is achieved. The opening or passage 3] in the upper part of the water jacket allows the hot combustion product gases to contact the water jacket intimately and provide a good thermal contact with the heat transfer fluid therein.

In an alternative embodiment, illustrated in Figure 2, the upper part 30 of the heat exchanger 28 is generally C-shape with a central bight portion 39 to allow the passage at combustion product gases to the flue. This configuration is easier to manufacture than the embodiment of Figure 1. a

a..... * . a ****. * . *.** * * ***. * a a. * * * S.. S* * a a * **

Claims

<claim-text>CLAIMS1. A solid tueF appliance having a body defining a combustion chamber, at least one primary combustion air inlet, a flue outlet tor combustion products to exit the combustion chamber and a heat exchanger in the combustion chamber, having means tor delivering secondary combustion air drawn from outside the body to a delivery region located between a primary combustion region and the flue outlet in a position such that hot combustion product gases from the said delivery region pass over part of the heat exchanger on their way to the flue outlet.</claim-text> <claim-text>2. A solid fuel appliance as claimed in Claim 1, in which the heat exchanger comprises a water jacket in the form ot a slab-like water container occupying at least one side ot the combustion chamber of the appliance.</claim-text> <claim-text>3. A solid fuel appliance as claimed in Claim 2, in which the water jacket extends over three sides of the combustion chamber.</claim-text> <claim-text>4. A solid fuel appliance as claimed in any of Claims 1 to 3 in which the heat * exchanger has an upper part extending over the combustion chamber between * 20 the chamber and the flue outlet. * * * *</claim-text> <claim-text>5. A solid fuel appliance as claimed in Claim 4, in which the said upper part of the heat exchanger extending over the combustion chamber has at least one : . passage therethrough for combustion product gases.</claim-text> <claim-text>6. A solid fuel appliance as claimed in Claim 4, in which the said upper part of the heat exchanger is generally C-shape.</claim-text> <claim-text>7. A solid fuel appliance as claimed in Claim 1, in which the heat exchanger comprises a plurality of tubes for conveying a heat exchange fluid through the combustion chamber.</claim-text> <claim-text>8. A solid fuel appliance as claimed in any preceding Claim, in which the said means tar delivering secondary combustion oir into the combustion chamber comprises one or more ducts having one or more exit openings at an upper level within the combustion chamber whereby to define the said delivery region.</claim-text> <claim-text>9. A solid fuel appliance as claimed in Claim 8. having a deflector between the primary combustion region and the flue outlet acting to extend the path of combustion product gases between the primary combustion region and the flue outlet, and the exit opening or openings from the said secondary combustion air delivery duct or ducts are located on the other side of the deflector plate from the flue outlet whereby in use secondary combustion occurs in the said secondary air delivery region.</claim-text> <claim-text>10. A solid fuel appliance as claimed in Claim 8 or Claim 9, in which the inlet * : openings to the said secondary air delivery ducts are located at a low level in S.....* 20 the body of the appliance. * S *555</claim-text> <claim-text>11. A solid tuel appliance as claimed in any of Claims 8, 9 or 10, in which the secondary air delivery means comprise a plurality of tubes each open at one end beneath the body of the appliance and communicating with one another by means of a transverse delivery duct at the other end, beneath a deflector plate within the combustion chamber.</claim-text> <claim-text>12. A solid fuel appance as claimed in any preceding claim, having a grate for supporting solid fuel above the level of a lower primary combustion air inlet.</claim-text> <claim-text>13. A solid fuel appliance as claimed in any preceding claim, in which the body also has an upper primary combustion air inlet br creating a downward flow of air over the inner face of a fuel-loading door in use of the appliance.</claim-text> <claim-text>14. A solid fuel appflance substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings. * . * * * *e* . * * e*ø * * 4. S ** S. S *S SJOAMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWSCLAIMS1. A solid fuel appliance having a body defining a closed combustion chamber, at least one primary combustion air inlet, a flue outlet tar combustion products to exit the combustion chamber, a heat exchanger in the combustion chanter, means for delivering secondary combustion oir drown from outside the body to a secondary combustion region located within the combustion chamber between a primary combustion region and the flue outlet, in which a deflector is located between the said secondary combustion region and the flue outlet to define on extended path for combustion product gases between the secondary combustion region and the flue outlet.
2, A solid fuel appliance as claimed in Claim I, in which the heat exchanger comprises a water iocket having a chamber between the said deflector and the said flue outlet, The chamber having a major surface defining one side of the path of the flue gases from the secondary combustion region the flue exit.
3. A solid fuel appliance as claimed in Claim 1 or Claim 2, in which the said water jacket further comprises a chamber lying at least to one side of the combustion * . . * *4 chamber of the appliance. * . S* 4. A solid Fuel appance as claimed in Claim 2 or Claim 3. in which the said water jacket extends over three sides of the combustion chamber. * S. * S * S.5. A solid fuel appliance as claimed in any of Claims ito 4 in which the said upper chamber of the heal exchanger extends aver the combustion chamber between the secondary combustion regions and the flue outlet.6. A solid fuel appliance as claimed in Claim 4, in which the said upper chamber of the heat exchanger has at east one passage therethrough for combustion product gases.7. A sohd fuel appliance as claimed in Claim 4;in which the said upper chamber of the heat exchanger is generally C-shape.8. A solid fuel appliance as claimed in Claim 1, in which the heat exchanger comprises a plurality of tubes for conveying a heat exchange fluid through the combustion chamber.9. A solid fuel appliance as claimed in any preceding Claim, in which the said means for delivering secondary combustion air into the combustion chamber compdses one or more ducts having one or more exit openings at on upper level within the combustion chamber whereby to deine the said delivery region.10. A solid fuel appliance as claimed in Claim B or Claim 9, in which the inlet openings to the said secondary air delivery ducts are located at a low level in the body of the appliance. * * S11. A solid fuel appliance as claimed in any of Claims 6. 9 or 10, in which the * . S secondary air delivery means camprse a plurality at tubes each apen at ace end S..beneath the body cf the appliance and communicating with one another by 25 means of a transverse delivery duct at the other end, beneath a deflector plate * ** within the combustion chamber.12. A solid fuel appliance as claimed in any preceding claim, having a grate for supporting solid fuel above the level of a lower primary combustion air inlet.13. A solid fuel appliance as claimed in any preceding claim, in which the body also has an upper primary combusJion air inlet for creating a downward flow of air over the inner face of a fuek$ooding door in use of the appliance.
4. A solid fuel appliance subsianlially as hereinbefore described with reference Ia, and as shown in, the accompan1ng drawings. * * . * **S*5**** * S... * S ** *S S..S * *5 S S * * S. *5 * 5 * a.</claim-text>