GB2078933A

GB2078933A - Solid fuel fired heaters

Info

Publication number: GB2078933A
Application number: GB8115185A
Authority: GB
Original assignee: Trianco Redfyre Ltd
Current assignee: Trianco Redfyre Ltd
Priority date: 1980-05-30
Filing date: 1981-05-18
Publication date: 1982-01-13
Also published as: GB2078933B

Abstract

A solid fuel fired heater includes a combustion chamber 11, means for admitting primary combustion air into an upper region of the combustion chamber, a flue 14, and one or more exhaust gas ducts 15 each having an opening to a lower region of the combustion chamber 11 and discharging to the flue 14. The or each exhaust gas duct 15 is defined by one or more unitary constructions of refractory material having a back wall, and a pair of side walls supporting a front wall towards the combustion chamber with its base in upwardly staggered relationship to the base of the back wall to define the mouth of the exhaust gas duct. Manifold means are provided in the front wall 15A to direct secondary combustion air through a first set of ports 15C to the firebed and through a second set of ports 15D into the exhaust gas duct. <IMAGE>

Description

SPECIFICATION Solid fuel fired heaters The invention relates to solid fuel fired heaters.

Where there is a requirement to minimise smoke emission within the requirements of the Clean Air Act from solid fuel heaters it is necessary to burn only 'smokeless' fuel. Such fuel can be very expen sive and in some regions in short supply. Various heaters have already been proposed, see for exam ple in U.K. Patent Specification 1,472,591, of the kind which use ordinary bituminous house coal and satisfy the requirements of the Clean Air Act by arranging the primary air to pass downwardly through the fire bed, the volatiles released from the fuel, which tend to cause unacceptable smoke emission in otherwise conventional heaters, are urged by the primary air into the fire bed when they are burned-off by secondary air.

The present invention relates to solid fuel fired heaters of the kind referred to, suitable for use with ordinary bituminous house coal.

According to one aspect of the present invention there is provided a solid fuel fired heater including a body, a combustion chamber enclosed in the body, an aperture in the body for admitting primary combustion air into an upper region of the combus tion chamber, a flue for leading exhaust gases from the combustion chamber and one or more exhaust gas ducts each having an opening to a lower region of the combustion chamber and discharging to the flue, wherein the or each exhaust gas duct is defined by one or more unitary constructions of refractory material having a back wall towards the body and a pair of side walls supporting a front wall towards the combustion chamber with its base in upwardly staggered relationship to the base of the back wall to define the mouth of the exhaust gas duct, manifold means in the front wall communicating with gas flow passages in the body to direct secondary combustion air through a first set of ports to the firebed to maintain quiescent combustion thereof and through a second set of ports into the exhaust gas duct to burn offvolatiles released from the fuel.

According to another aspect of the invention, there is provided a solid fuel fired heater including a body, a combustion chamber enclosed in the body, a doorway in an upper region of the body for admis sion of fuel to the combustion chamber, a fuel charging door normally closing off the doorway, an aperture in the body for admitting primary combus tion air into an upper region of the combustion chamber from which it normally flows as a down draught through the firebed, a flue for leading exhaust gases from the combustion chamber, one or more exhaust gas ducts each opening to a lower region of the combustion chamber and discharging to the flue, and manifold means in said duct or ducts communicating with gas flow means in said body for discharge of secondary combustion airthrough a first set of ports to the firebed to maintain quiescent combustion thereof and through a second set of ports with the exhaust gas duct to burn off volatiles released from the fuel, the upper region of the combustion chamber communicating directly with the flue via a by-pass aperture in the roof of the combustion chamber and a damperflap operable to close off the aperture when the door is closed for normal operation and to open the aperture when the door is open so that a gas updraught from the bed can flow through the by-pass aperture to the flue.

According to a third aspect of the invention there is provided a solid fuel heater including a body, a combustion chamber enclosed in the body, a doorway in an upper region of the body for admission of fuel to the combustion chamber, a fuel charging door normally closing off the doorway, an aperture in the body for admitting primary combustion air into an upper region of the combustion chamber from which it normally flows as a downdraught through the firebed, one or more exhaust gas ducts each opening to a lower region of the combustion chamber and discharging to the flue, and manifold means in said duct or ducts communicating with gas flow means in said body for discharge of secondary combustion air through a first set of ports to the firebed to maintain quiescent combustion thereof and through a second set of ports into the exhaust gas duct to burn off volatiles released from the fuel, the upper region of the combustion chamber being communicable directly with the flue via a by-pass aperture in the roof of the combustion chamber and a flap arranged to close-off said aperture whenever the door is closed and to obscure the top of the doorway whenever the door is open.

Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which; Figure 1 is a cut away side view of the heater; Figure 2 is a front elevation, partly cut away, of an exhaust gas duct or "choke" on an enlarged scale; Figure 3 is an underneath view of the choke; Figure 4 is a vertical section of the choke; Figure 5 is a cut-away side view of a second embodiment of the heater; and Figure 6 is an enlarged detail of Figure 5 within circle A showing the working relationship between a fuel charging door and a damper flap forming part of the heater.

Referring to the drawings, in Figure 1, a heater body 10 has a combustion chamber 11. An aperture 12, controlled by a thermostat 13, is provided for allowing primary air to enter the top of the combustion chamber 11 via one or more vertical ducts extending either side of a doorway. This tends to avoid emission of flue gases and smoke out of the aperture 12. By discharging primary air at a higher level even distribution of the primary air over the whole fire bed is achieved. Flueways 14 within a waterjacket allow exhaust gases to pass from the bottom of the combustion chamber 11 via a choke or chokes 15, arranged side by side into a chimney 16.

The chokes are supported by a platform 17 welded to the inside of the body 10. Each choke (better seen in Figures 2 to 4) comprises a unitary construction of refractory material in which the space between a front hollow wall 1 SA and a rear wall 1 SB provides an opening for exhaust gases to pass through the choke into the flueways 14. Secondary air is supplied to flow into the hollow front wall 15A to be expelled through series of ports 15C and 15D and directed into the combustion chamber 11 and opening re spectively to supply secondary air to the firebed to maintain slumbering combustion and to introduce air into the stream of exhaust gas.The walls ISA and 15B of the choke are connected at each end by side walls 15E and 15Fwhich form part of the unitary construction.

The flueways 14 are routinely cleaned by inserting a scraper through a top opening 30 and deposits scraped down the flue are readily re-burned in the chokes 15.

In use, primary air passes through the aperture 12.

The flow of air is controlled by the thermostat 13.

Primary air passes generally from the top of the combustion chamber 11 downwards towards the fire bed. The primary air carries with it volatiles, which are distilled from the burning fuel, into the region of the fire bed. A by-pass behind the plate 26 is provided for some of the primary air to pass directly into the lower part of the fire bed. The by-pass air carries some of the volatiles which roll off the top of the fire bed. Exhaust gases from the fire bed pass through the chokes 15 into the flueways 14.

Secondary air passes into the hollow part 15A of each choke 15 and is expelled through the ports 15C and 15D. The ports 15C provide air required during slumbering conditions of the heater and ports 15D provide air which assists in the complete combustion of any unburnt volatiles entering the choke. The secondary air is warmed by the chokes 15 and the velocity effect created by secondary air jets causes a very intense and turbulent combustion zone to ensure optimum burn off of volatiles.

Atop capping within the choke defines a narrow vertically directed exit slot 15G leading to the flue 14 and between inlet 15H and exit 15G there is provided a primary expansion chamber 151. Thus the flue gases are retarded within chamber 151 where there is considerable turbulence which promotes mixing of the secondary air with the exhaust gas, so that a major proportion of the volatiles are burnt off before the exhaust gas enters the flueway 14. The exit slot 15G has parallel sides to straighten the discharge of gas so that it has the effect of a vertical jet which is distributed evenly between a pair of ways 14A and 14B into which the upper region of the flue 14 is divided. At the lower end of the ways 1 4A and 1 4B there is a secondary expansion chamber 14C which allows free expansion ofthe gas stream from the choke 15.The result is that the gases dwell in the chamber 14C for a short period within which they can give up their heat by radiation. When the rising stream of exhaust gas enters ways 14A and 14B there is a reduction in cross-sectional area and the gas stream is accelerated, and this results in an efficient scrubbing action against the walls of ways 14A, 14B which gives efficient heat transfer.

Each choke, as better seen in Figure 2, is shaped and formed so thatthe front wall 15A is well supported so that even if the front wall 15A fractures in use, it remains generally in position due to the cantilever effect provided by the side walls 15E and 15F and does not collapse. In an earlier proposal where the choke was not of unitary construction and included a hollow part extending across the width of the heater supported only at its ends, any fractures tended to cause the heater to become immediately unserviceable. In the described heater, two chokes are provided to reduce the vulnerability even further to fractures but embodiments of the invention may be provided with one unitary construction choke or more than two separate unitary construction chokes as desired.

A door 18 is supported by a vertical hinge (not shown) on the front of the body 10.Acounter- balanced hinged flap 24 is provided above the door; 18 to allow air to pass directly to the chimney 16 to help balance any sudden changes of pressure in the heater caused for example by gusts of wind. The flap 24 provides draught stabilisation and ensures that the draught to the fire is maintained in a steady state enabling most economic burning at all fire rates. In the Figure 5 embodiment a plate 25 extending over a by-pass aperture 22 (to be described below) serves to ensure mixing of the air entering past the flap 24 takes place away from the aperture 22 and towards the top oftheflueway 14.

A plate 26 mounted within the combustion chamber 11 and below the door 18 has a slot or series of apertures 27. Some of the primary air flowing from the top of the combustion chamber 11 together with volatiles can therefore by-pass the unburned fuel by flowing behind the plate 26 and be directed into the lower incandescent portion of the fire bed.

The fire bed is supported by a grate 28 at the bottom of the combustion chamber 11. The grate consists of a plurality of fire bars which can be jolted in conventional manner by an external lever with the door 18 closed. There is no ash pan; ash is allowed to fall onto a series of ribs 29 in the bottom of the heater and the accumulated ash provides heat insulation. An ash scoop is used to remove excess ash as required but a residue of ash is left between the ribs 29 to continue to provide heat insulation.

A by-pass opening 22 is provided which allows flue gases to pass from above the fire bed directly to the chimney 16. It extends across substantially the whole width of the combustion chamber but is relatively narrow as shown so as to produce a directed flow of rising gas. A manual operating lever extends from the aperture 22 to a handle 31 at the front of the heater so that when an outer hinged cover 32 is opened the aperture 22 can be opened by pulling the handle 31 to the phantom postion 31': In use, the door 18 is opened to charge the heater with fuel after the aperture 22 is opened. The door 18 is then closed and the handle 31 pushed to close the aperture 22. However, the handle 31 is so positioned that if it is not pushed in or pushed home by the operator, the handle is automatically pushed in or home by closure of the outer cover 32 so preventing the heater being operated with the aperture 22 in an open condition. In another arrangement this could be pushed by hand.

It will be noted that the aperture 22 is automatical lymaintained in its closed condition during normal operation of the heater and so prevents unlawful or unacceptable emission of smokey gases from the chimney 16 for time periods other than short periods during re-charging of the heater with fuel.

The embodiment of Figures 5 and 6 is generally similar, but a choke 15 without the primary expan sion chamber 151 discharges into an undivided flueway 14. A door 18 is supported by a vertical hinge (not shown) on the front of the body 10 and is provided with a probe 19. In the closed door position, the probe 19 presses against a panel 20 on a a hinged flap 21 to urge the flap 21 to close the by-pass aperture 22 in the roof of the combustion chamber 11. The flap 21 has a protrusion 23 extending downwards into a slot (not shown) in the probe 19 which is arranged so that when the door 18 is opened, the end of the slot engages the protrusion 23 to force the flap 21 away from the aperture 22.

Opened the flap 21 will fall down but if there is any stiction, the interaction of the slot and the protrusion 23 will overcome such stiction and cause the flap 21 to separate from the aperture 22. When the heater has to be re-charged, the door 18 is opened and the flap 21 falls down to cover the upper part of the doorway. Occasionally, there is a tendency for the flap 21 to stick in its upper position blocking-off the aperture 22. To overcome this the probe 19 has a slot (not shown) which engages the protrusion 23 and forcestheflap down as required. During operation of the heater, as the door 18 is opened there is a reduction in downdraught. As a result, smoke is carried upwards towards the doorway. The flap 21 steers this smoke away from the doorway, through the aperture 22 and into the chimney 16 during the short time the door is open. Fuel may then be fed through the doorway and into the combustion chamber 11. The flap 21 is free to be pushed out of the way of the fuel by the fuel as it enters through the doorway.

Claims

1. A solid fuel fired heater including a body, a combustion chamber enclosed in the body, an aperture in the body for admitting primary combus tion air into an upper region of the combustion chamber, a flue for leading exhaust gases from the combustion chamber and one or more exhaust gas ducts each having an opening to a lower region of the combustion chamber and discharging to the flue, wherein the or each exhaust gas duct is defined by 1 one or more unitary constructions of refractory material having a back wall towards the body and a pair of side walls supporting a front wall towards the combustion chamber with its base in upwardly staggered relationship to the base of the back wall to define the mouth of the exhaust gas duct, manifold means in the front wall communicating with gas flow passages in the body to direct secondary combustion air through a first set of ports to the firebed to maintain quiescent combustion thereof and and through a second set of ports into the exhaust gas duct to burn off volatiles released from the fuel.

2. A solid fuel fired heater according to Claim 1 wherein the exhaust gas duct is arranged to choke the flow of gas to the flue so that burn-off of volatiles predominantly takes place in the exhaust gas duct.

3. A solid fuel fired heater according to Claim 2, wherein the exhaust gas duct diverges from its mouth to define a secondary combustion chamber and its upper regions of the duct define a flue outlet from said secondary combustion chamber of restricted size.

4. A solid fuel fired heater according to any preceding claim wherein the flue comprises first and second ways extending vertically from the duct, and the flue outlet from the duct is arranged to discharge the exhaust gas in a vertical stream so that it is distributed evenly between said ways.

5. A solid fuel heater according to any preceding claim wherein the flue passes through a water chamber in the body so that exhaust gas heat is transferred to the water.

6. A solid fuel fired heater according to any preceding claim wherein the combustion chamber has a fuel charging door and a roof, an aperture in the roof through which gas can pass directly into the flue and a damper flap arranged to close-off the aperture whenever the door is closed.

7. A solid fuel fired heater according to Claim 6 further comprising an outer cover hinged to the body which can be opened to reveal the fuel charging door, an operating handle connected to the damper flap being arranged so that in its damper flap open position it interferes with a formation on the outer cover when the outer cover is in its normal closed position whereby the outer cover can only be closed with the damper flap in its closed position.

8. A solid fuel fired heater according to Claim 6 or 7 wherein an anti-smoke flap connected at its top end to the body inside the fuel charging door by hinge means normally obscures the top of the doorway so that when the charging door is opened discharge of smoke into the surroundings is impeded but the flap is free to move towards the combustion chamber when the door is open to facilitate the entrance of fuel into the combustion chamber.

9. A solid fuel heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. A solid fuel fired heater including a body, a combustion chamber enclosed in the body, a doorway in an upper region of the body for admission of fuel to the combustion chamber, a fuel charging door normally closing off the doorway, an aperture in the body for admitting primary combustion air into an upper region of the combustion chamber from which it normally flows as a downdraught through the firebed, a flue for leading exhaust gases from the combustion chamber, one or more exhaust gas ducts each opening to a lower region of the combustion chamber and discharging to the flue, and manifold means in said duct or ducts communicating with gas flow means in said body for discharge of secondary combustion air through a first set of ports to the firebed to maintain quiescent combustion thereof and through a second set of ports with the exhaust gas duct to burn off volatiles released from the fuel, the upper region of the the combustion chamber communicating directly with the flue via a by-pass aperture in the roof of the combustion chamber and a damper flap operable to close off the aperture when the door is closed for normal operation and to open the aperture when the door is open so that a gas updraught from the bed can flow through the by-pass aperture to the flue.

11. A solid fuel fired heater according to Claim 10 further comprising an outer cover hinged to the body which can be opened to reveal the fuel charging door, an operating handle connected to the damper flap being arranged so that in its damper flap open position it interferes with a formation on the outer cover when the outer cover is in its normal closed position whereby the outer cover can only be closed with the damper flap in its closed position.

12. A solid fuel fired heater according to Claim 10 or 11 wherein an anti-smoke flap connected at its top end to the body inside the fuel charging door by hinge means normally obscures the top of the doorway so that when the charging door is opened discharge of smoke into the surroundings is impeded but the flap is free to move towards the combustion chamber when the door is open to faciliate the entrance of fuel into the combustion chamber.

13. A solid fuel fired heater as claimed in claim 12 wherein the by-pass aperture extends substantially the full width of the combustion chamber and is relatively narrow compared to its length.

14. A solid fuel fired heater including a body, a combustion chamber enclosed in the body, a doorway in an upper region of the body for admission of fuel to the combustion chamber, a fuel charging door normally closing off the doorway, an aperture in the body for admitting primary combustion air into an upper region of the combustion chamber from which it normally flows as a downdraught through the firebed, one or more exhaust gas ducts each opening to a lower region of the combustion chamber and discharging to the flue, and manifold means in said duct or ducts communicating with gas flow means in said body for discharge of secondary combustion airthrough a first set of ports to the firebed to maintain quiescent combustion thereof and through a second set of ports into the exhaust gas duct to burn off volatiles released from the fuel, the upper region of the combustion chamber being communicable directly with the flue via a by-pass aperture in the roof of the combustion chamber and a flap arranged to close-off said aperture whenever the door is closed and to obscure the top of the doorway whenever the door is open.

15. A solid fuel fired heater according to Claim 14, in which said door is provided with a probe attached to the door arranged to move the flap to close-off said aperture as the door is closed.

16. A solid fuel fired heater according to Claim 14 or Claim 15 in which said flap is connected to the body by hinge means and free to move towards said combustion chamber when the door is open to facilitate the entrance of fuel into the combustion chamber.

17. A solid fuel fired heater according to Claim 16, in which the flap is provided with a protrustion arranged to be engaged by said probe such that said flap can be positively urged away from the aperture in the roof by opening the door.