EP1201993A1

EP1201993A1 - A waste material incineration process and apparatus

Info

Publication number: EP1201993A1
Application number: EP00123175A
Authority: EP
Inventors: Manop Piyasil; Somjit Piyasil
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-10-25
Filing date: 2000-10-25
Publication date: 2002-05-02

Abstract

A waste material incineration process comprising

a) supplying waste material to a first combustion chamber (13, 113)

b) heating the waste material in the first combustion chamber (13, 113) to cause thermal decomposition of the waste material, and

c) burning, in a second combustion chamber (18, 118), any inflammable gas or gases produced by the thermal decomposition; characterised in that

d) at least some of the heat produced during the burning of said gas or gases is used to heat the waste material in the first combustion chamber (13, 113).

Description

This invention relates to a waste material incineration process and to apparatus for the incineration of waste material.
The waste material to which this invention relates encompasses a range of unwanted materials such as are found in domestic and industrial waste, of the type which comprises a substantial proportion of combustible materials, and which are therefore suitable for disposal (or at least part-disposal) by burning or incineration.
Although a wide variety of processes and apparatus are known for the incineration of such materials, the various approaches proposed hitherto can - for the most part - be classified into one of two distinct categories.
One basic category of incinerators includes apparatus having only a single combustion chamber, in which the waste material is burned using a fuel/air mixture which is injected into the combustion chamber. This type of incinerator is commonly used at present, with relatively small such incinerators being used, for example, in a variety of factories and hospitals.
One drawback with this type of single combustion chamber incinerator is that the temperature which is attainable within the combustion chamber is rarely able to exceed 400-500°C or so, meaning that a number of polluting and poisonous gases remain un-combusted. Although a number of factors contribute to the low maximum temperature which is attainable, a principal cause is thought to be the evaporation of liquids which occurs from the waste material, as the evaporation process takes some of the heat energy away from the waste combustion process.
In an attempt to overcome this problem of incomplete combustion, a second category of incinerators uses two separate combustion chambers - a first chamber in which the waste material is burned, and a second chamber in which the released gaseous pollutants are burned, thus "cleaning" the products of the waste material incineration process.
However, such dual chamber incinerators require a continuous supply of combustible fuel to sustain the waste and gas burning processes, leading to inefficiency and an undesired use of fuel.
It is an object of the present invention to provide an improved waste material incineration process which overcomes or at least alleviates these problems, and to provide apparatus for the incineration of waste material which enables the invented process to be put into practice.
According to a first aspect of the present invention, there is provided a waste material incineration process comprising
a) supplying waste material to a first combustion chamber,
b) heating the waste material in the first combustion chamber to cause thermal decomposition of the waste material, and
c) burning, in a second combustion chamber, any inflammable gas or gases produced by the thermal decomposition; characterised in that
d) at least some of the heat produced during the burning of said gas or gases is used to heat the waste material in the first combustion chamber.
Preferably, at least part of the second combustion chamber is located within the first combustion chamber.
Said heat may be transferred from the second combustion chamber to the first combustion chamber through a wall of the second combustion chamber.
An inlet to the second combustion chamber may be generally concentric with the first combustion chamber.
Preferably, the second combustion chamber is provided with a barrier which serves, in use, to improve mixing of the gas or gases with air which is used during the burning.
The barrier may be provided by material surrounding an orifice which is located within the second combustion chamber, and the barrier may conveniently be generally annular.
Part of the second combustion chamber may be arranged generally helically within the first combustion chamber.
Preferably, the inlet to the second combustion chamber is located within part of the helix.
The air which is used during said burning preferably draws the inflammable gas or gases from the first combustion chamber towards the second combustion chamber.
The drawing may be caused by a venturi effect at the outlet end of an air supply.
Waste material may be supplied to the first combustion chamber using a screw feeder, the screw feeder being disposed within a feed conduit, the feed conduit having an open discharge end in communication with the first combustion chamber, the discharge end protruding beyond the free end of the screw.
One or more stirrers may be provided within the first combustion chamber, the or each stirrer preferably comprising a screw formation which is rotatable about an axis.
The axis of rotation is preferably generally vertical.
Preferably, the heating of the waste material in the first combustion chamber is initially effected by burning a combustible fuel (diesel, for example) which is supplied to the first combustion chamber, said fuel being used until the flammable gas or gases is/are produced, such that the heating of the waste material may then continue using only the heat produced by the burning of said flammable gas or gases.
According to a second aspect of the present invention, there is provided a waste material incineration process comprising
a) supplying waste material to a first combustion chamber,
b) heating the waste material in the first combustion chamber to cause thermal decomposition of the waste material,
c) burning, in a second combustion chamber, any inflammable gas or gases produced by the thermal decomposition; characterised in that
d) at least some of the heat produced during the burning of said gas or gases is used to heat the waste material in the first combustion chamber, and in that
e) the heating of the waste material is initially effected by burning a combustible fuel which is supplied to the first combustion chamber, said fuel being used until the flammable gas or gases is/are produced, such that the heating of the waste material may then continue using only the heat produced by the burning of said flammable gas or gases.
The invention, in its second aspect, may comprise one or more of the features set out in relation to the first aspect of the present invention. Thus, the combustible fuel may be diesel.
According to a third aspect of the present invention, there is provided apparatus for the incineration of waste material comprising
a) a first combustion chamber for heating the waste material to cause thermal decomposition thereof,
b) a second combustion chamber for burning any inflammable gas or gases produced by the thermal composition,
c) at least part of the second combustion chamber being in thermal contact with the first combustion chamber such that at least some of the heat produced during the burning of said gas or gases may be used to heat the waste material in the first combustion chamber.
The invention, in its third aspect, may comprise one or more of the features and/or components described in relation to the first and/or second aspects of the present invention.
The invention will now be described in greater detail, but by way of example only, by reference to the accompanying drawings, of which
Figure 1 is a vertical cross-section of one embodiment of the invented apparatus;
Figure 2 is a schematic plan view of the apparatus of Figure 1,
Figure 3 is a vertical cross-section of a second embodiment of the invented apparatus and
Figure 4 is a schematic plan-view of the apparatus of Figure 3.
Referring first to Figures 1 and 2, an incinerator 10 comprises a housing 11 formed from a suitable heat and corrosion resistant metal, there being provided within an outer wall of the housing 11 a layer of insulation material 12. The incinerator 10 comprises a first combustion chamber 13 to which is supplied waste material to be incinerated, by a screw feeder 14 disposed within a supply conduit 15. As can be seen from Figures 1, 2 and 4, the supply conduit 15 has an open discharge end 16 which protrudes further into the first combustion chamber then the screw 17 of the screw feeder, thus ensuring that an amount of "packed" waste material is always present between the end of the screw 17 and the open discharge end 16 of the supply conduit. This quantity of "packed" waste material ensures that little or no back flow of flammable gases can occur through the screw feeder.
As can be seen from Figures 1 and 2, the first combustion chamber 13 is generally cylindrical in configuration, there being provided, generally concentric with the first combustion chamber, a second combustion chamber 18, the second combustion chamber 18 having an inlet 19 located towards a lower part thereof. Located within the inlet 19 is a generally annular barrier 20, the annular barrier defining a generally circular orifice 21, the purpose of which is described below.
Located within the first combustion chamber 13 are four stirrers generally indicated at 22, the stirrers each having a rotatable rod 23, to which are mounted screw configurations 24 which continually agitate the waste material which is supplied to the first combustion chamber by the screw feeder 14. Disposed around the inner wall 25 of the first combustion chamber 13 is an angled collar 26 which serves to guide the waste material away from the inner wall and towards a waste burning region generally indicated at 27. The waste burning region includes a somewhat conical grate 28 mounted above a support plate 29, the grate 28 serving to support part-burned waste material during the latter stages of combustion.
Located generally centrally of the grate 28 is an air inlet pipe 30a through which combustion air is supplied to the incinerator, in generally conventional manner. Air is also supplied to the system through a secondary air inlet pipe 30b, having outlets 32 (below the grate 28) and 33 (below an additional guide collar 34).
Air exiting the outlets 32 and 33 is effective to dislodge combusted or part-combusted material from the grate 28 and guide collar 34, causing it to fall to an ash collecting funnel 35 disposed towards the bottom of the incinerator.
The invented incineration process - and the operation of the associated apparatus - will now be described in detail.
As an initial step, a combustible fuel such as diesel is supplied to the incinerator, being sent through a duct (not shown) and supplied to the open upper part 36 of the inlet pipe 30a. The fuel/air mixture is ignited in generally conventional manner, with the fuel/air mixture thus burning in the second combustion chamber 18, the temperature rising up to a maximum of about 800 to 900°C. The barrier 20 restricts the flow (i.e. increases its turbulence) of the fuel/air mixture, thus improving the mixing thereof, and thus allowing more complete combustion of the combustible fuel. As the temperature within the second combustion chamber increases, so does the temperature of the thermally conductive (e.g. metallic) wall 37 of the second combustion chamber 18, which in turn heats the first combustion chamber surrounding it.
Waste material is then supplied to the first combustion chamber 13 by the screw feeder 14, the material dropping into the first combustion chamber, down towards the grate 28, with the stirrers 22 being effective to continually agitate the material as the level of waste material builds up within the first combustion chamber 13.
Much of the heat produced in the second combustion chamber is transferred to the waste material, through the wall 37, causing thermal decomposition of the waste material in a pyrolysis-like manner. As is well known in the art, such decomposition results in the release of volatile - and harmful - gases, with this release increasing in line with the increasing temperature which exists in the second combustion chamber 18.
The temperature within the second combustion chamber is monitored by a temperature probe (not shown) so that the supply of combustible fuel may be cut off once the temperature has reached a certain level. This level is selected to be that at which a sufficient quantity of flammable gases are produced from the waste material for the combustion in the second combustion chamber 18 to consist purely of the burning of the waste gases.
From this point, the inflammable gases are entrained within the air flow exiting the air inlet pipe 30a, the flammable gases being sucked into gas conduits 38 having inlet openings 39 disposed just beneath the guide collar 26, which protects them from blockages. The underside of the guide collar 26 also acts as something of a gas trap, which enables a gas build-up to occur, thus increasing the concentration of the flammable gas in the vapour mixture which is entrained with the airflow.
Flammable gas is also drawn down towards the opening 39 of the gas conduit 38 through a number of vertically orientated ducts 40 which are disposed around the inner wall 25 of the first combustion chamber 13. The ducts are perforated to allow the passage of gas, although the perforations are sufficiently small so that solids from the waste material cannot pass therethrough, causing blockages to the gas conduits 38 which are disposed towards the bottom of the first combustion chamber 13.
The pyrolyised waste material eventually falls to the grate 28, at which point a final burning process takes place. Air is supplied to the underside of the grate 28 through an outlet 32 of a secondary inlet pipe 30b, this air serving not only to facilitate the final combustion of the waste materials but also to ensure that the burnt materials are dislodged from the grate, so that they fall down to the ash collecting funnel 35, for collection and subsequent disposal, in generally conventional manner. Air from the secondary air inlet pipe 30b is also discharged through an outlet 33 which prevents any build up of combusted or part-combusted material on the upper surface of the guide collar 34.
The incinerator shown in Figures 1 and 2 has a second combustion chamber 18 having an exhaust outlet 41 which emits the combusted/part-combusted flammable gases either to the atmosphere or to a further scrubbing apparatus, as appropriate.
However, the incinerator shown in Figures 3 and 4, which has corresponding parts numbered using the same nomenclature as is used in Figures 1 and 2, but with the addition of 100, whilst being very similar in construction, is somewhat larger. The increase in size allows the second combustion chamber 118 to extend around the innerside of the first combustion chamber 113 in a generally helical manner, with the exhaust in this case (141) being located in the first combustion chamber 113 at a lower point, indicated generally at 42 in Figure 3. By use of this helical construction, more use is made of the heat produced during combustion of the flammable gases, in that more of the heat is put back into the first combustion chamber 113 through the walls of the exhaust. As will be appreciated, this in turn improves the degree of heating of the waste material, allowing more flammable gases to be produced.
In summary, the invention provides a waste material incineration process and apparatus which makes use not only of the heat which is produced during combustion of the dangerous pollutant gases which are produced during heating of the incoming waste material, but which also eventually allows the process to be sustained without the need for any additional combustible fuel to be added to the system. This results not only in a much cleaner output, but also results in considerable cost savings in view of the reduced amount of combustible fuel which is required.
In the present specification "comprise" means "includes or consists of" and "comprising" means "including or consisting of".
The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

A waste material incineration process comprising

a) supplying waste material to a first combustion chamber (13, 113)

b) heating the waste material in the first combustion chamber (13, 113) to cause thermal decomposition of the waste material, and

c) burning, in a second combustion chamber (18, 118), any inflammable gas or gases produced by the thermal decomposition; characterised in that

d) at least some of the heat produced during the burning of said gas or gases is used to heat the waste material in the first combustion chamber (13, 113).
A waste material incineration process according to claim 1 wherein at least part of the second combustion chamber (18, 118) is located within the first combustion chamber (13, 113).
A waste material incineration process according to claim 1 or claim 2 wherein said heat is transferred from the second combustion chamber (18, 118) to the first combustion chamber (13, 113) through a wall (37, 137) of the second combustion chamber (18, 118).
A waste material incineration process according to any one of the preceding claims wherein an inlet (19, 119) to the second combustion chamber (18, 118) is generally concentric with the first combustion chamber (13, 113).
A waste material incineration process according to any one of the preceding claims wherein the second combustion chamber (18, 118) is provided with a barrier (20, 120) which serves, in use, to improve mixing of the gas or gases with air which is used during the burning.
A waste material incineration process according to claim 5 wherein the barrier (20, 120) is provided by material surrounding an orifice (21, 121) which is located within the second combustion chamber (18, 118).
A waste material incineration process according to claim 5 or claim 6 wherein the barrier (20, 120) is generally annular.
A waste material incineration process according to any one of the preceding claims wherein part of the second combustion chamber (18, 118) is arranged generally helically within the first combustion chamber (13, 113).
A waste material incineration process according to claim 8 wherein the inlet (19, 119) to the second combustion chamber (18, 118) is located within part of the helix.
A waste material incineration process according to any one of the preceding claims wherein the air which is used during said burning draws the inflammable gas or gases from the first combustion chamber (13, 113) towards the second combustion chamber (18, 118).
A waste material incineration process according to claim 10 wherein the drawing is caused by a venturi effect at the outlet end of an air supply (30a, 130a).
A waste material incineration process according to any one of the preceding claims wherein the waste material is supplied to the first combustion chamber (13, 113) using a screw feeder (14, 114), the screw feeder (14, 114) being disposed within a feed conduit (15, 115), the feed conduit (15, 115) having an open discharge end (16, 116) in communication with the first combustion chamber (13, 113), the discharge end (16, 116) protruding beyond the free end of the screw (17, 117).
A waste material incineration process according to any one of the preceding claims wherein one or more stirrers (22, 122) are provided within the first combustion chamber (13, 113).
A waste material incineration process according to claim 13 wherein the or each stirrer (22, 122) comprises a screw formation (24, 124) which is rotatable about an axis.
A waste material incineration process according to claim 14 wherein the axis of rotation is generally vertical.
A waste material incineration process according to any one of the preceding claims wherein the heating of the waste material in the first combustion chamber (13, 113) is initially effected by burning a combustible fuel which is supplied to the first combustion chamber (13, 113), said fuel being used until the flammable gas or gases is/are produced, such that the heating of the waste material may then continue using only the heat produced by the burning of said flammable gas or gases.
A waste material incineration process comprising:

a) supplying waste material to a first combustion chamber (13, 113),

b) heating the waste material in the first combustion chamber (13, 113) to cause thermal decomposition of the waste material,

c) burning, in a second combustion chamber (18, 118), any inflammable gas or gases produced by the thermal decomposition; characterised in that

d) at least some of the heat produced during the burning of said gas or gases is used to heat the waste material in the first combustion chamber (13, 113); and in that

e) the heating of the waste material is initially effected by burning a combustible fuel which is supplied to the first combustion chamber (13, 113), said fuel being used until the flammable gas or gases is/are produced, such that the heating of the waste material may then continue using only the heat produced by the burning of said flammable gas or gases.
A waste material incineration process according to claim 17, further comprising one or more of the features of claims 2 to 16.
Apparatus (10, 110) for the incineration of waste material comprising

a) a first combustion chamber (13, 113) for heating the waste material to cause thermal decomposition thereof,

b) a second combustion chamber (18, 118) for burning any inflammable gas or gases produced by the thermal decomposition,

c) at least part of the second combustion chamber (18, 118) being in thermal contact with the first combustion chamber (13, 113) such that at least some of the heat produced during the burning of said gas or gases may be used to heat the waste material in the first combustion chamber (13, 113).
Apparatus (10, 110) for the incineration of waste material according to claim 19, further comprising one or more of the features and/or components of claims 2 to 18.
A waste material incineration process substantially as hereinbefore described and/or shown in the accompanying drawings.
Apparatus (10, 110) for the incineration of waste material substantially as hereinbefore described and/or shown in the accompanying drawings.
Any novel feature or novel combination of features described herein and/or in the accompanying drawings.