The present invention relates to an improved thermal treatment device, for waste materials, in particular though not exclusively for biomass.

Extracting energy from organic or inorganic combustible wastes by waste to energy or pyrolysis style systems has become an important approach for disposing of, and reducing wastes that are either destined for landfill or are to be disposed of by some other economically and/or environmentally unsatisfactory method. Such wastes may contain dangerous pathogens and other contaminants, some of which can only be destroyed at elevated temperatures. At very high temperatures hydrocarbon structures are dissociated into free carbon and hydrogen, and in the presence of oxygen, they form carbon dioxide and water vapour. This exothermic oxidation process typically occurs in the secondary chamber of a pyrolysis device. The energy contained in the hot exhaust that is generated by such devices can be captured and converted to useful forms, such as hot water, steam or electricity.

Historically, common fuels such as wood, coal, natural gas, fuel oil, etc., have been used to heat water, produce steam and/or generate electrical power. Today, many wastes that are not suitable for recycling contain recoverable energy. These wastes include the remnants of plastic, paper and wood, as well as production farm animal manures, human bio-solids and many other such waste materials. As our production of wastes grows, almost exponentially, it is becoming increasingly obvious that more environmentally friendly and effective methods of waste reduction are required. Recovery of energy from such wastes has many benefits, three of them being: -

* the waste volume is significantly reduced;

* pathogens contained in certain parts of these wastes will be destroyed; and

* the recovered energy can be put to beneficial use.

If the recovery of energy from such materials were performed on a large scale it would reduce our use of fossil fuels and help to reduce our carbon footprint.

Most known typical incinerators use a so-called "brute force" method, based on the assumption that more heat input will cause more chemical reactions. In this type of incinerator the first burner in the primary chamber is aimed directly at the waste so as to cause direct burning of the waste. Unfortunately, there are drawbacks to this method. Firstly, the direct flame tends to physically agitate the waste, and as a result, cause a large amount of fly-ash to be included within the fumes from the burning waste. Secondly, this method does not provide sufficient heat intensity on an overall basis to properly volatilize all of the waste material. The ash that results is still black, which indicates that it is still composed largely of carbon and other incompletely combusted materials. Ash which contains large amounts of carbon is likely to contain undesirable material such as dioxins, furans and organo-chlorides, and other organic matter.

US 5,61 1 ,289 and 6. 1 16.168 in the name of Brookes, disclose an apparatus and method of an improved type of waste gasifier, using a so-called "hot hearth configuration" that overcomes some of the problems of associated with the "brute force" method.

Figures 1 and 2 show the basic "hot hearth configuration" for the known Brookes batch feed technology. The disclosure describes the apparatus and method of using the hot hearth to generate the hydrocarbon fume that is then directed into a secondary chamber where it is oxidized in an exothermic reaction. Some of the heat generated in the secondary chamber is transferred through the hearth to continue the volatilization process.

In further detail, referring to Figures 1 and 2, the waste incinerator 20 according to US 5,611,289 and 6, 1 16, 168 includes a primary chamber 30 arranged to receive a charge of waste 22 to be gasified and a main door 32 to permit selective access to the primary chamber 30. A low volume air inlet 34 is included to allow the inflow of small amounts of air or oxygen into the primary chamber 30. The floor 36 is strong enough to support the waste 22, but is also heat conductive to allow heat to enter the primary chamber 30 from below. A fume transfer vent 38 allows fluid communication with the primary chamber 30 so as to permit the escape of fumes from the primary chamber 30. A mixing chamber 40 is in fluid communication with the fume transfer vent 38 and thereby accepts the fumes from the primary chamber 30. A first portion of an afterburner chamber 42 is in fluid communication with the mixing chamber 40 where the fumes from the mixing chamber 40 are reacted. The afterburner turns a 90° corner to the second portion of the afterburner 46. A short length of the second portion of the afterburner portion 46 leads into a generally horizontal heat transfer chamber 52. The heat within the heat transfer chamber 52 rises through the roof of the heat transfer chamber 52, which is also the floor 36 of the primary chamber 30 so as to heat the primary chamber 30 and the waste 22. Using this arrangement, the waste 22 receives conductive and convective heat from the heat transfer chamber 30, which assists in the heating of the waste 22 in the primary chamber 30. The burner member 48 is situated at the top of the mixing chamber 40 and is orientated to project the heating flame downwardly through the mixing chamber 40 and into the first portion of the afterburner chamber 42. In use, this direct radiant heat assists in the heating of the waste 22. Additional features include; an oxygen inlet 49 to assist the burner member 48; a partition wall 50, 51 disposed between the primary chamber 30 and a temperature control means 56, including wires 57, 59 and thermocouple 58. Using a feedback system, the temperature controller 56 allows automatic adjustment of the heating flame.

A problem however of the above disclosure is that the incinerator is fed with waste by a batch process. In other words, once the waste has been consumed, the incinerator has to be shut down to enable a new batch to be loaded. This is both time consuming and inefficient.

Figures 3 and 4 show a further invention by Brookes, WO 2008/034263, which discloses a continuous feed gasifier designed on the "hot hearth configuration", but with the ability to be fed waste on a continuous basis rather than having to batch feed the gasifier. This method eliminates the need to shut down and reload the gasifier after every batch load.

In the Brookes continuous feed gasifier, the method for transporting the waste across the hot hearth is with slowly turning augers. The waste particles must be 1 cm in size, or smaller, at least partially because the system relies on preventing air intrusion into the primary chamber through the loading hoppers by choking the inflow with the waste itself. The warm up burner is also positioned firing down from the top of the mixing chamber

As can be seen particularly in Figures 3 and 4, the sludge 152 (having a particle size not greater than 1 cm, and having a 20% to 100% solid content) is driven across the primary chamber 102 by augers 106. Typically, the speed at which the augers rotate is up to as much as 5 RPM, which allows for the complete volatilization of the waste. This disclosure allows a waste gasifier to be fed on a continuous basis, and overcomes certain problems associated with a batch feed process.

Unfortunately there are drawbacks to adapting an apparatus designed to be fed in batch mode, as in US 5,611,289 and 6,1 16, 168, to run on a continuous mode as in WO 2008/034263.

A problem with WO 2008/034263 is that the waste must have a particle size not greater than 1 cm. Since waste typically comes in sizes greater than 1 cm, additional expense is incurred through grinding larger particles into smaller ones. Additionally, as the primary chamber 102 is filled with waste, the air inlet 34 can be blocked by the waste itself.

A further problem is the positioning of the burner. In WO 2008/034263 the burner is positioned vertically at the top of the mixing chamber. The heat in the mixing chamber tends to rise into the burner housing which can shorten the life of the burner, requiring additional maintenance of the burner, or in some cases, requiring replacement of the burner. To prevent this from happening, the burner air is kept on so as to "cool" the burner. Unfortunately, this has the knock-on effect that the air entering the system is not completely controlled. This therefore leads to a certain lack of controllability over the combustion process.

The object of the present invention is to provide an improved thermal treatment device, which alleviates problems associated with known devices.

According to the invention there is provided a thermal treatment device comprising:- a primary chamber for receiving waste material to be combusted, the primary chamber having a hearth; a transport system arranged for transportation of waste material across the hearth; a mixing chamber in fluid communication with the primary chamber; a secondary chamber in fluid communication with the mixing chamber; and material introducing means for introducing waste material into the primary chamber; wherein the material introducing means comprises a valve for controlling air flow there-through. In this way, the device can more effectively deal with larger particle sizes, therefore reducing additional expense incurred through grinding larger particles into smaller ones. The hearth is preferably solid.

Preferably, the secondary chamber extends below the primary chamber. In this way heat can rise from the secondary chamber into the primary chamber.

Conveniently, the primary chamber includes a ceiling having a minimum height no less than 6 cm for every square meter of hearth. This is important for allowing a good flow of the fume that is volatilized off the waste. Further, the primary chamber preferably has a minimum ceiling height of 36 cm for hearths less than 6 meters in area.

Preferably, the mixing chamber includes an opening, allowing air to enter from an external source. This contributes to allowing the airflow to be controlled in the mixing chamber and secondary chamber. Conveniently, the external source of air is supplied by a secondary air fan. In this way, the supply of combustion air to the mixing chamber and secondary chamber is completely controllable, which is important for the combustion process.

Preferably, the secondary air fan houses a variable speed motor that is controlled by one or more feedback loops. This control feature helps to substantially remove the production of thermal NO _x .

Conveniently, the thermal treatment device includes a warm-up burner. This allows for it to warm to the correct operating temperature, particularly the mixing chamber and secondary chamber.

Preferably, the warm-up burner has a substantially horizontally orientated output orifice. This helps to avoid damaging the warm-up burner, as hot rising gases will not naturally rise into the burner components.

Conveniently, the warm-up burner is positioned such that its output is below the primary chamber. In this way, the output is directed under the primary chamber.

Preferably, the warm-up burner is orientated such that the flame projection from the warm-up burner is directed at the secondary chamber. This allows the heat output to rise from the secondary chamber, through the hearth, towards the primary chamber.

Preferably, the warm-up burner is recessed from an inside wall of the apparatus. This prevents damage to the warm-up burner from hot gases, and also flying debris such as fly-ash etc.

Preferably, the warm-up burner has an isolation valve that can separate it from the device. This allows the warm-up burner to be switched on when required, and off, when not required.

Conveniently, the thermal treatment device includes an opening for introducing waste into the primary chamber. This allows the device to run in continuous mode. That is, waste can fed into it continuously.

Preferably, the material introducing means additionally comprises: a loading hopper, having an open top; and a feeding hopper, for receiving a quantity of waste from the loading hopper. This allows waste to be continuously fed into the device. Conveniently, the loading hopper has sides that project outwards towards a common edge of the open top. This allows the loading hopper to act as a funnel, guiding the waste into the feeding hopper.

Conveniently, a valve separates the loading hopper from the feeding hopper.

Preferably, the thermal treatment device includes an opening for collection of ash from the primary chamber. This allows ash to be continuously collected from the device.

Conveniently, the device includes an ash hopper. This allows ash to be conveniently stored.

Preferably, the ash hopper is substantially air tight. This prevents rogue air from entering the primary chamber through the ash hopper.

Conveniently, the ash hopper includes a cooling jacket placed around its distal end to cool the ash. This helps to cool the ash before it goes into the ash container.

Preferably, the ash hopper includes a vacuum fan to maintain a negative pressure in the ash hopper, with respect to the primary chamber. This helps to reduce the fly ash that might travel through the opening into the mixing chamber.

Conveniently, the thermal treatment device may include an air valve positioned on an outer side wall of the primary chamber. This allows for minimal air to be introduced into the primary chamber.

Preferably, the primal chamber air inlet includes a valve that is controlled automatically using a temperature feedback loop. This allows the temperature profile of the primary chamber to be readily controlled.

Conveniently, the ai valve can be at least substantially closed. This allows the air flow to the primary chamber to be restricted based on sudden surges in the primary chamber temperature profile.

Preferably, the thermal treatment apparatus is auto-thermic. This allows for the temperature profile in the device to become self-sustaining, and therefore the warm-up burner can be switched off.

Conveniently, the use of an air tight feed hopper allows for the waste particle size to be up to 8 cm. Preferably, the apparatus includes a draft fan. This draws the hot exhaust generated in the secondary chamber through the heat recovery unit and other equipment such as filtration or abatement equipment.

Conveniently, the draft fan has a variable speed motor. This allows the draft to be held stable at the exit of the secondary chamber.

Preferably, the variable speed motor is controlled by one or more draft monitoring sensors. Controlling the draft has the effect of stabilising the processes in both the primary and secondary chamber.

According to a further aspect of the present invention there is provided thermal treatment device comprising: -a primary chamber for receiving waste material to be combusted, the primary chamber having a hearth; a transport system arranged for transportation of waste material across the hearth; a mixing chamber in fluid communication with the primary chamber; a secondary chamber in fluid communication with the mixing chamber; material introducing means for introducing waste material into the primary chamber; and a warm-up burner having a substantially horizontally orientated output orifice. In this way, damage to the warm-up burner is avoided, as hot rising gases will not naturally rise into the burner components.

Conveniently, the hearth is a solid hearth.

Preferably, the warm-up burner is positioned such that its output is below the primary chamber. In this way, the output is directed under the primary chamber.

Conveniently, the warm-up burner is orientated such that the flame projection from the warm-up burner is directed at the secondary chamber. This allows the output to rise from the secondary chamber, through the hearth, towards the primary chamber.

Preferably, the warm-up burner is recessed from an inside wall of the apparatus. This prevents damage to the warm-up burner from hot gases, and also flying debris such as fly- ash etc.

Conveniently, the warm-up burner has an isolation valve. This allows the warm-up burner to be switched on when required, and off, when not required.

According to a further aspect of the present invention there is provided a method of combusting waste material in a thermal treatment device having primary, mixing and secondary chambers, the method comprising the steps of:- introducing waste material via a material introducing means into the primary chamber; moving the waste material across a hearth of the primary chamber; directing fume from the waste material to a secondary chamber via a mixing chamber, the secondary chamber; and controlling air flow through the material introducing means by way of a valve. In this way, the device more effectively deals with larger particle sizes, therefore reducing additional expense incurred through grinding larger particles into smaller ones.

According to a further aspect of the present invention there is provided a method of combusting waste material in an thermal treatment device having primary, mixing and secondary chambers, the method comprising the steps of:- introducing waste material via a material introducing means into the primary chamber; moving the waste material across a hearth of the primary chamber; directing fume from the waste material to a secondary chamber via a mixing chamber, the secondary chamber; and directing an output from a warm-up burner towards the second chamber, the warm-up burner having an output orifice which directs said output substantially horizontally. In this way, the method helps to avoid damaging the warm- up burner, as hot rising gases will not naturally rise into the burner components.

To help understanding of the invention, specific embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a sectional side elevation view of a first prior art gasifier;

Figure 2 is a plan view of the first prior art gasifier;

Figure 3 is a sectional side elevation of a second prior art gasifier;

Figure 4 is a plan view of the second prior art gasifier;

Figure 5 is a front view of a waste thermal treatment device according to the present invention;

Figure 6 is a side elevation view on "A" of a waste thermal treatment device according to the present invention;

Figure 7 is a side elevation view on "B" of a waste thermal treatment device according to the present invention;

Figure 8 is a diagram of a typical heat recovery assembly according to the present invention; and Figure 9 is reversed configuration of the waste thermal treatment device according to the present invention.

Primary chamber & Hearth

Referring to Figures 5 to 8, a thermal treatment device, 200 is provided comprising a horizontally disposed primary chamber 204, arranged to receive a continuous charge of waste 230 to be combusted. The waste 230 may include the remnants of plastic, paper and wood, as well as production farm animal manures, human bio-solids and many other such waste materials, i.e. biomass. In the preferred embodiment, the shape of the primary chamber 204 is generally rectangular, although any alternative suitable shapes may be adopted. The primary chamber 204 includes a, preferably solid, hearth 207 which is made of suitable material so as to support the weight of the waste 230. which maybe several tonnes. The hearth 207 is heat- conductive so as to allow heat to transfer into the primary chamber 204 from below. The hearth 207 may extend the full length of the floor of the primary chamber 204, as in the preferred embodiment, or it may encompass one or more sections of the primary chamber 204. The hearth 207 also forms at least a portion of a heat transferring ceiling of the secondary chamber 208.

The minimum 'X' height of the ceiling in the primary chamber 204 is important for allowing a good flow of the fume 216 that is volatilized off the waste 230. It has been found that the minimum height should be no less than 6 cm for every square meter of hearth 207 area to allow for proper flow characteristics of the fume 216 in the primary chamber 204. However, for small devices, when the hearth 207 is less than 6 square meters, the height should not be less than 30 cm.

On the upper surface o the hearth 207 is provided a waste transport system 206, which allows waste 230 to be transferred across the hearth 207. Waste 230 enters the hearth 207 through the opening 227. The waste transport system 206 may comprise any suitable system for moving material across the hearth and may include for example; a ram system, consisting of one or more rams; an auger system, consisting of one or more augers; or a drag chain conveyor system. The speed in which the transport system 206 operates is important to the thermal treatment apparatus's efficient operation, so as to ensure that the waste 230 is fully volatilized. As the waste 230 is volatilized, a hydrocarbon fume 216, the fume being a fluid, is generated that travels through the opening 205. The waste residual continues across the hearth 207, until it reaches the state where it is free of volatiles and has become ash that is almost free of carbon. That is, the transport system 206 also enables ash 231 from the primary chamber 204 to be transported for collection through the opening 228.

Feeding arrangement

The thermal treatment device 200 also includes a waste material feeding arrangement 229, which includes a loading hopper 201, an isolation valve 202, and a feeding hopper 203, allowing for waste material 230 to be fed into the device 200. The isolation valve 202 may be a valve such as a sliding gate valve or rotary valve.

Waste 230 is fed into the loading hopper 201, which has an open top 237 to accept the waste 230, and then as required, fed into the feeding hopper 203 from the loading hopper 201. The sides 238 of the loading hopper project outwards towards a common edge of the open top 237 so as to act a funnel, guiding the waste 230 into the loading hopper 201. An isolation valve 202 is provided between the loading hopper 201 and the feeding hopper 203, so as to control communication between the loading hopper 201 and the feeding hopper 203. This arrangement allows the quantity of waste 230 entering the primary chamber 204 to be controlled. The waste 230 from the feeding hopper 203 is carried across the hearth 207 by the transport system 206.

The isolation valve 202 also controls the air flow through the feeding arrangement 229. With the feed hopper isolation valve 202 closed, the feeding hopper 203 is at least substantially air tight. This prevents rogue air from entering the primary chamber 204, and unbalancing the primary chamber 204 temperature profile and volatilization process. Rogue air can cause an uncontrolled rise in temperature in the primary chamber 204.

The use of an air tight feed hopper 203 with an isolation valve 202 allows for the waste

230 particle diameter to be up to 8 cm. This is because the prevention of air leakage into the primary chamber 204 from the feed side of the hearth 207 is not dependent on the waste 230 being the restriction for air intrusion, as with the earlier prior art arrangements.

As the feeding hopper 203 can be made at least substantially air tight by closing the isolation valve 202, this also gives the benefit of preventing rogue air from entering the primary chamber 204 if the waste bridges in the feed hopper 203. This prevents excessive temperature surges in the primary chamber 204 if the feed hopper 203 has been drained due to bridging, or clogging of the waste in the hopper 203. Similarly, the isolation valve 202 is of great benefit if there is a malfunction such as an electrical failure or a problem with the waste transport system 206. The isolation valve 202 will prevent excessive heat in the primary chamber 204 and additionally prevent heat and noxious fumes from escaping out through the feed hopper 203.

The residual ash 231 is pushed into the ash hopper 210 through an opening in the primary chamber 204. The feed rate of ash 231 into the ash hopper 210 is variable and will depend on the speed of the waste being introduced into the primary chamber via waste transport system 206. The time required to fully volatilize the waste 230 will depend on its composition and size of the waste 230. Adjustment of speed of the transport system 206 and the rate at which the waste 230 is introduced to the hearth 207 through the feed hopper 203 can be adjusted according to the composition and size of the waste.

The ash hopper 210 is also designed to be at least substantially externally air tight, i.e. air tight with respect to the outside air. This prevents rogue air from entering the primary chamber 204 through the opening 228 via the ash hopper 210. This stops rogue air from unbalancing the primary chamber 204 temperature profile and the volatilization process. It also stops rogue air from carrying fly ash through the opening 205 into the mixing chamber 220.

Conveniently, a cooling jacket 219 can be placed around the distal end of the ash hopper 210 to help cool the ash 231 before it goes into the ash container. This is important to prevent red hot cinders. The cooling jacket may contain fluid such as water, oil, or air.

Additionally, a vacuum fan 211 can be installed on the ash hopper 210 to maintain a slightly negative pressure in the ash hopper 210 in relation to the pressure in the primary chamber 204. This arrangement will cause fly ash to tend to move into the ash hopper.

Opening 205

An opening 205 is located at the back of primary chamber 204, which is positioned near the top of the primary chamber 204. The opening 205 is in fluid communication with the mixing chamber 220 so as to permit the escape of ^" the fume 216 when the waste 230 is being volatilized. The opening 205 allows fluid to be transferred from the primary chamber 204 to the secondary chamber 208. The fume 216 will generally consist of gases containing molecules having hydrogen, carbon and oxygen atoms therein, with a portion of the molecules having carbon and hydrogen bonded together, so-called "hydrocarbons".

Primary chamber Air valve

The primary chamber 204 includes an air valve 214. Optionally, more than one air valve 214 may be fitted to the primary chamber. The air valve 214 is positioned so as to not be blocked or chocked by the waste 230 in the primary chamber 204. In a preferred embodiment the air valve 214 is positioned on an outer side wall of the primary chamber 204, allowing fluid communication with the primary chamber 214. Minimal air may be allowed into the primary chamber 204 through air valve 214. The valve 214 can be automatically controlled with the ability to close at least substantially completely should this be required. For example during sudden surges in the primary chamber 204 temperature profile, or if the waste 230 characteristics are variable and change from time to time. Preferably the air valve 214 is controlled using a temperature feedback loop, so as to control the opening and closing of the valve 214. Previous prior art had air inlet valves that were manually operated and not capable of being fully closed.

Mixing chamber

A vertically disposed mixing chamber 220 is in fluid communication with the primary chamber 204 so as to accept the fume 216 from the primary chamber 204. The mixing chamber 220 includes an opening 232 to allow fluid to enter from an external source, such as supplied by a secondary air fan 212. As the fume 216 enters the mixing chamber 220 it begins oxidising as it mixes with the fluid supplied by the secondary air fan 212. The oxidation begins in the mixing chamber 220 and continues into the secondary chamber 208.

Secondary air fan

The secondary air fan 212 houses a variable speed motor 232 that is controlled by one or more feedback loops, in most cases; two feedback loops 233 and 234 are provided. The first control loop is the temperature feedback loop 233 which is directed towards the secondary chamber 208, and the second control loop is the oxygen feedback loop 234, also directed towards the secondary chamber 208. Feedback loop 233 may include a sensor in the form of an electrical thermometer to measure the temperature within the secondary chamber 208, and feedback loop 234 may include a sensor in the form of a Lambda sensor to measure oxygen content within the secondary chamber 208. Both such sensors measure electrical resistance. The primary control is the secondary chamber 208 temperature feedback loop 233 and the secondary control is secondary chamber 208 oxygen feedback loop 234, the excess oxygen level which is always brought to the lowest level possible with the minimum being approximately 3%. This control feature helps to reduce the production of mono-nitrogen oxides including NO and N0 ₂ , so-called NO _x gases.

Secondary chamber

The secondary chamber 208 is in fluid communication with the mixing chamber 220, both of which are connected by a 90° corner 235. The secondary chamber 208 is arranged to accept fluid from the mixing chamber 220. The secondary chamber extends below the primary chamber. An upper portion of the ceiling of the secondary chamber 208 includes the hearth 207, enabling heat from the secondary chamber 208 to transfer to the primary chamber 204.

Warm-up burner

A warm-up burner 213 is situated at the lower back wall of the mixing chamber 208 and is orientated horizontally so as to project a substantially horizontal heating flame below the hearth 207. The warm-up burner 213 supplies supplementary heat to the thermal treatment apparatus 200, and in most cases, brings the mixing chamber 220 and the secondary chamber 208 to the proper operating temperature. Once the waste 230 is introduced into the primary chamber 204 through the opening 227, is transported across the hearth 207 by transport system 228, and volatilization is underway, the device 200 becomes autothermic, that is, the reactions are exothermic to an extent that the generated heat sustains further reactions. Once this happens, the warm-up burner 213 can be shut down. Control of the warm-up burner 213 is provided using isolation valve 218, which when shut, prevents uncontrolled air from entering the secondary chamber 208. This means that the secondary air fan 212 provides the only, completely controllable supply of combustion air to the mixing chamber 220 and secondary chamber 208, which is important for the controllability of the oxidation process. This helps to improve the secondary chamber oxidation efficiency and helps in the reduction of mono- nitrogen oxides including NO and NO:, so-called NO _x gases.

Since the device operates in an "auto-thermic" mode for a significant portion of its operating time, the warm-up burner 213 remains switched off after warm-up has taken place. As the warm-up burner 213 is located in a recessed horizontal, lower back wall location, aimed below the hearth 207, and can be isolated by using valve 218 this arrangement reduces the exposure of the hot gases that rise in the mixing chamber to the warm-up burner, thus reducing the likelihood of damage to the warm-up burner.

In this regard, a problem with vertical warm-up burner arrangements in the prior art is that hot gases can rise in the mixing chamber into the burner housing causing damage to the burner. A solution is to "cool" the burner by feeding air through it when it was not in use. Whilst the burner was cooled, uncontrolled air was introduced into the thermal treatment apparatus, allowing for uncontrolled reactions. Moving the location and orientation of the burner addresses these problems, and thus, air does not need to be forced through the burner to "cool" it. Additionally, in situations such as electrical failure or secondary air fan 212 malfunction, whereby the temperatures in the thermal treatment apparatus 200 may exceed those of normal operating conditions, the warm-up burner 213 is less likely to be damaged by backlash heat in the location disclosed in this invention.

Should the temperature in the thermal treatment apparatus 200, such as the temperature in the secondary chamber 208 drop to a lower than acceptable level, the warm-up burner 213 can be restarted by opening the isolation valve 218. Similarly, once the temperature has increased, and reached normal operating conditions, the warm-up burner 213 can be shut down and the isolation valve 218 closed.

Partition wall

A partition wall 236 is positioned between the mixing chamber 220 and the primary chamber 204, and defines the bottom limit of the opening 205. The partitioning wall 236 is positioned and dimensioned to block a flame from the warm-up burner 213 from entering the primary chamber 204. In this manner, the heating flame does not directly heat the waste material in the primary chamber 204, and therefore, does not abruptly overheat a localized area of waste. The partition wall 236 is variable in height for example by way of subtraction or addition of bricks, so as to allow "fine tuning" of the cross sectional area of the vent 205.

Separation wall

A separation wall 209 is provided underneath the hearth 207 with both faces of the wall in communication with the secondary chamber 208. This wall acts to guide the hot exhaust under the hearth 207, ensuring that the gases move towards one of the optional exhaust ducts 217. The wall 209 ensures that the hot exhaust gases are in communication with the hearth 207.

Exhaust ducts and heat recovery unit The exhaust ducts 217 deliver the hot exhaust to a heat recovery unit 221. The controllable induced draft fan 222 controls the draft or suction in the thermal treatment apparatus 200 and pulls the exhaust through a heat recovery unit 221 and abatement 226. To maintain a good stability, that is, to hold the draft stable at the exit of the secondary chamber, the induction fan can have a variable speed motor that is controlled by a feedback loop from a draft monitoring sensor or manometer. Controlling the secondary chamber draft has the effect of stabilizing the processes in both the primary chamber and the secondary chamber which are inexorably linked through the opening from the primary chamber to the mixing and secondary chamber.

Further configuration

As shown in Figure 9, the configuration of the thermal treatment apparatus can be reversed for certain waste applications. That is the positioning of the feed hopper and the ash hopper may be reversed with respect to the opening 205. In this arrangement the feed hopper is located on the same side where the mixing chamber is. With certain waste, this is advantageous as the fly ash that is generated will have a more difficult transition to reach the opening 205 into the mixing chamber. Typically, such wastes would be dry and dusty and prone to producing excessive fly ash.

Operation

In operation, shredded or granulated waste up to 8 cm in particle diameter is fed into the open loading hopper 201 and then, as needed, fed into the sealed feed hopper(s) 203 using an isolation valve 202. A system for transporting the waste 206 across the primary chamber 204 hearth 207, such as a ram, drag chain, auger, etc., moves the waste across the hot hearth 207 at a rate that allows the waste to volatilize, generating a hydrocarbon fume 216 that travels through the opening 205. The un-evaporated solid residual continuing across the hearth 207 reaches the state where it is free of volatiles and has become ash that is almost free of carbon. The ash residual is pushed into the ash hopper 210 and then directed to an ash container. The feed rate of the waste by 206 is variable and will depend on the waste being introduced into the primary chamber 204. The time required to properly volatilize the waste will depend on its chemical composition and the size of the waste particles.

It is important to note that the hearth 207 is heated from below by the exothermic oxidation activity in the secondary chamber 208. Part of the hearth 207 may reach the set point temperature of the secondary chamber 208 which is usually a minimum of 850 C. This conductive heat coming through the hearth 207 is what continues the volatilization of the waste in the primary chamber 204. This effect makes the device very energy efficient.

With the feed hopper 203 isolation valve 202 closed, the feed hopper 203 is at least substantially air tight. This prevents rogue air from entering the primary chamber 204 and unbalancing the primary chamber 204 temperature profile and the volatilization process. Such rogue air can cause an uncontrollable rise in the primary chamber 204 temperature. The air tight feed hopper 203, with the isolation valve 202 closed, also gives the benefit of preventing rogue air from entering the primary chamber 204 if the waste material bridges in the feed hopper 203. This also prevents excessive temperature surges in the primary chamber 204 if a feed hopper 203 has been drained due to bridging, or clogging of the waste in the hopper. The feed hopper 203 isolation valve 202 is also of great benefit if there is a malfunction in the system such as an electrical power failure, a problem with the waste feed conveyor, etc. The isolation valve 202 will prevent excessive heat in the primary chamber 204 and prevent heat and noxious fumes from escaping out through the feed hopper(s) 203.

The ash hopper 210 is also designed to be at least substantially air tight on the external side so that rogue air cannot enter the primary chamber 204 through the ash hopper 210. His has two benefits; first, it stops rogue air from unbalancing the primary chamber 204 temperature profile and the volatilization process; and second, it stops rogue air from dragging fly ash through the opening 205 into the mixing chamber 220. A cooling jacket 219 can be placed around the ash bed to help cool the ash before it goes to the ash container. Also, a vacuum fan 21 1 can be used to keep the pressure in the ash hopper 210 slightly negative in relation to the pressure in the primary chamber 204. This will help reduce the fly ash that might travel through the opening 205 into the mixing chamber 202.

Minimal air may be allowed into the primary chamber 204 through air valves 214, but these valves must be automatically controlled with the ability to close completely if required, based on sudden surges in the primary chamber 204 temperature profile. This can happen when the waste characteristics are variable and change from time to time.

The hydrocarbon fume 216 generated from the waste in the primary chamber 204 enters the mixing chamber 220 through the opening 205 and begins oxidizing as it mixes with the air supplied by the secondary air fan 212. The oxidation process starts in the mixing chamber 220 and continues into the secondary chamber 208. Note that the warm up burner 213 has been disengaged at this point and the burner gate valve or isolation valve 218 has been closed. The separation wall 209 guides the hot exhaust under the hearth 207 and around the separation wall 209 and out one of the optional exit ducts 217 that will deliver the hot exhaust to a heat recovery unit 221 under the pull draw of the Induced Draft fan 222.

Initially, the warm up burner 213 is used to warm up the mixing chamber 220 and the secondary chamber 208 to the proper operating temperature. Once the waste is introduced into the primary chamber 204 and volatilization is underway the device becomes auto-thermic, that is, the temperature profile in the device becomes self-sustaining and no auxiliary burner input is needed. At that point the warm up burner 213 is shut down and the burner isolation gate valve 218 is closed to prevent uncontrolled air from entering the secondary chamber 208. This means the secondary air fan 212 provides the only, and completely controllable, supply of combustion air to the mixing chamber 220 and the secondary chamber 208. This is important for the controllability of the oxidation process.

The location of the warm up burner 213 is much different from that shown in the earlier prior art devices. Because this device operates in an auto-thermic mode for essentially all of its operating time, the warm up burner 213 can be mounted in this preferred, lower back wall location, orientated to aim below the hearth. A gate valve 218 can be used to isolate the burner when it is not in use. This arrangement eliminates the need to constantly feed air through the burner 213 to keep it cool. The advantageous result, as indicated above, is that the secondary air fan 212 completely controls the air input into the secondary chamber 208. If the warm up burner 213 is located above the mixing chamber 220, as in the prior art, the hot gases will rise into the burner housing unless the burner air is always on. Even if an isolation valve is used to attempt to isolate the burner, the valve will risk being damaged due to the very high heat that rises from the mixing chamber. In situations such as an electrical power failure or draft fan malfunction, etc., the side mounted warm up burner 213 of the current embodiment is much less likely to be damaged by backlash heat.

The warm up burner 213 can be re-started briefly if the temperature in the econdary chamber drops lower than acceptable (dropping below the required set point) simply by opening the burner isolation gate 218 and re-firing the burner 213. Once the secondary chamber 208 temperature has safely recovered the warm up burner 213 can be shut down and the burner isolation gate 218 will be closed.

The hot or energy bearing exhaust generated by the oxidation of the hydrocarbons in the secondary chamber 208 travels to one of the optional exit ducts 217 and hence to the heat recovery unit 221. The controllable Induced Draft fan 222 controls the draft or suction in the device 220 and pulls the exhaust 217 through the components 221 and 226.