GB2227084A

GB2227084A - Stove with afterburner

Info

Publication number: GB2227084A
Application number: GB8929252A
Authority: GB
Inventors: Julian Charles Levick; Robert Leslie Tomlinson
Original assignee: CBR FABRICATIONS Ltd
Current assignee: CBR FABRICATIONS Ltd
Priority date: 1989-01-17
Filing date: 1989-12-28
Publication date: 1990-07-18
Anticipated expiration: 2009-12-28
Also published as: GB8900975D0; GB8929252D0; GB2227084B

Abstract

A waste wood burner comprises a fire box 2 for the combustion of wood in the presence of primary air that is connected to a duct which directs the gases products of combustion towards a chimney 6 and the duct is provided with a secondary air supply means such that combustion particles present in the products of combustion may be burned. <IMAGE>

Description

Wood Waste Burners This invention relates to wood waste burners.

In the furniture industry and other industries involved in the production of wooden articles a large quantity of offcuts and other wood waste is commonly produced and needs to be disposed of. This material has a high calorific value and so it is conventional to burn this waste matter and to use the resultant heat energy for process or space-heating.

There are, however, environmental constraints on the burning of wood because unaided this tends to produce a great deal of smoke.

Currently, in the U.K., legislation prohibits or at least restricts the use of combustion apparatus which produces high smoke emission.

Moreover, the wood burnt in these circumstances is often mixed with other materials such as various types of plastics material which when heated produce noxious if not toxic fumes. It is understood that smoke and fumes largely comprise particles of combustible but incompletely burned matter, and in order to conform with current legislation it has been proposed to reduce smoke emission from wood-burning stoves by introducing a fuel such as gas or oil into the gaseous combustion products, igniting the fuel, and thereby burning the smoke particles and fumes. The need to provide a supply of fuel, however, makes the burners more expensive to manufacture and less convenient to operate, and it is therefore an object of the invention to provide a wood burner which yields an acceptable low smoke emission without the need for a secondary fuel supply.

According to the invention we provide a waste wood burner comprising a fire-box for the combustion of wood in the presence of primary air and means defining a duct for directing gaseous products of combustion to a chimney, characterised in that the burner further comprises means for the introduction into said duct of secondary air wherein combustible particles present in the products of combustion may be burned.

The secondary air introduction means may comprise a pipe arranged transversely of the duct, said pipe having an air inlet port in fluid connection with an air blower and a plurality of air outlet ports.

Preferably the outlet ports are arranged to pass streams of secondary air into the duct both in the direction of flow of combustion products along the duct and in a contrary direction.

Preferably again, the burner comprises means defining a metal or other material edge spaced from the air outlet ports to act as a resistance bar for the combustion of the smoke particles in the secondary air.

The said edge may be provided by a strip of metal such as stainless steel or equivalent arranged vertically along the upper edge of the air pipe adjacent the air outlet ports.

This gives a "gas ring effect" to promote combustion by slightly retarding the passage of the products of combustion along the duct.

Embodiments of the invention will now be described, by way of example, and with reference to the accompanying drawings of which: Fig. 1 is a plan view of a wood waste burner equipped to deliver hot air; Fig. 2 is a sectional elevation of the burner of Fig. 1; Fig. 3 is a section on B - B of Fig. 2; Fig. 4 is a section on C - C of Fig. 2; Fig. 5 is a detailed side elevation of a secondary air inlet tube; and Fig. 6 is a plan view of the air inlet tube.

The burner shown in the figures comprises essentially a cylindrical fire-box 2 leading to a cylindrical flue 4 leading to a chimney 6 for the discharge of spent gasious products of combustion. The fire-box and flue are supported on a face 8 and encased within a rectangular housing 10.

The fire-box 2 has a plate 12 inclined downwardly from the front 14 of the burner to a grate 16.

In operation ash is deposited on the grate 16 and so there is provided a spy-hole 17, with an air jet, for monitoring the build-up of ash.

The cylindrical wall of the fire-box is cut away at 18, and a duct 20 leads from the aperture to an opening 22 in the housing 10 covered by a loading door 24 which is attached to a horizontal arm 26 pivoted to a port 28 whereby the door can be opened to allow wood to be introduced into the burner. The door is at other times kept closed by means of an electromagnetic door lock 30.

The rear of the fire-box is defined by a wall 32 of refractory material which at its lower edge defines a low arched throat 34 through which products of combustion of wood burning on the grate 16 can pass into the flue 4.

Below the grate 16 is an ash chamber 36 in which is a removable ash pan 38 which can be removed for emptying through a door 40 a primary air inlet port 42 is located in the door 40, and the later flow of air through the port is controlled by a hand wheel 44.

The flue 4 has an upwardly extending hollow baffle defined by wall 46 and refractory-lined wall 48. This is followed by a further, downwardly directed, hollow baffle defined by walls 50, 52. The baffles cause the products of combustion to follow a sinuous path, and provide large heat exchange surfaces as will be mentioned hereafter.

Following the baffle wall 52, the flue is closed with a circular end plate 54 in which, however, is provided a removable panel 56 for access. The portion of the flue between the walls 52 and 56 are connected to the chimney 6 which leads out of the housing 10. Below the chimney 6 the flue is penetrated by a number of heat exchange tubes most clearly seen in Fig. 4 which open at one end in the openings 58 in the circumferential wall of the flue, and at their lower ends bend at right angles and open in the end plate 54.

As has already been mentioned, the fire-box 2 and the flue 4 are essentially cylindrical, whilst the casing 10 is rectangular so that there is a void between the inner surface of the housing 10 and the outer surface of the fire-box and flue. Moreover the outer surface of the flue is increased by virtue of the hollow baffle walls and the tubes 57. These surfaces, which become heated by the hot flue gases transmit some of their heat to the air in the void, and this air is circulated through the void by means of a fan 60 located in a housing 62 behind the burner. The air from the fan 60 passes into the housing via an opening in the rear wall of the housing, and the air leaves the housing through an opening 64 above the fire-box.

Experience shows that wood is commonly incompletely burned in fire-boxes such as that described, and the burner of the invention accordingly also incorporates secondary air inlet means comprising a fan 66 connected by a duct 68 to an opening 70 in the side wall of the housing 10, which opening is controlled by a hand wheel 72 similar to the hand wheel 44 described in connection with the primary air inlet.

From the fan 66, an upwardly extending duct 74 leads to a Tshaped plenum chamber 76, the limbs of which are of substantially square section.

The plenum 76 shown in more detail in Figs. 5 and 6 has a horizontal head 78 which, as seen from Fig. 2, is arranged adjacent the refractory-lined wall 48 and behind the arched throat 34. At this point and depending on burning conditions in the fire-box, the gases leaving the fire-box through the throat 34 may be rich in smoke and it is highly desirable that this smoke shall not be emitted through the chimney 6.

It has been found, that by introducing air into the flue behind the throat 34, much of the smoke, which is made of unburnt particles of combustible material, may be burnt, increasing the heat output of the burner and reducing smoke emission. An ignition probe inlet is located behind the throat 34 and so, if required, gases may be ignited with a flame.

As can be seen in Figs. 5 and 6 the plenum has a series of holes 80 along the front edge, two spaced rows of holes respectively 82, 84 along the upper edge and a further row of holes 86 along a 450 bevelled edge 88. The holes 80, 82 and 84 are in line and the holes 86 are relatively staggered midway between the line on which the holes 80, 82 and 84 are positioned. Air issuing from the orifices 80 is directed substantially counter to the direction of flow of flue gases, whilst air from the openings 82, 84 and to some extent 86 is directed in the same direction as the flow of the flue gases.

As a further aid to the combustion of the smoke in the flue gases, a stainless steel strip 90, bent at right angles at its ends 92 is fixed vertically to the upper face of the plenum 78 between the rows 82 and 84 of air outlet holes. The upper edge 92 of the strip appears to provide a focus for the combustion of the smoke particles in the air issuing from the plenum, and it may also serve slightly to inhibit the flow of gases through the flue and thereby encourage combustion in the secondary air.

Claims

1. A waste wood burner comprising a fire-box for the combustion of wood in the presence of priminary air and means defining a duct for directing gases products of combustion to a chimney, characterised in that the burner further comprises means for the introduction into said duct of a secondary air supply wherein combustion particles present in the products of combustion may be burned.

2. A waste wood burner according to Claim 1 wherein the secondary air supply means comprises a pipe arranged transversel of the duct, said pipe having an air inlet port in fluid connection with an air blower and a plurality of air outlets ports.

3. A waste wood burner according to Claim 2 wherein the outlet ports are arranged to pass streams of secondary air into the duct both in the directional flow of combustion products along the duct and in a contrary direction.

4. A waste wood burner according to Claim 2 or 3 wherein a means defining a metal or other material edge is spaced from the air outlet ports to act as a resistance bar for the combustion of smoke particles in the secondary air.

5. A waste wood burner according to Claim 4 wherein the said edge maybe provided by a strip of metal such as stainless steel or equivalent arranged vertically along the upper edge of the air pipe adjacent the air outlet port.

6. A waste wood burner as substantially herein described.