EP3204692A1

EP3204692A1 - Incineration of waste

Info

Publication number: EP3204692A1
Application number: EP15787907.3A
Authority: EP
Inventors: Ian HIBBIT; Neil Simpson
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2014-10-07
Filing date: 2015-10-07
Publication date: 2017-08-16
Also published as: WO2016055511A1; GB2531010A; GB201417679D0

Abstract

A method for incinerating waste comprising a first step of contacting, in a precombustion chamber (7), a first waste stream and oxygen- containing gas having insufficient oxygen for complete combustion to occur, thereby producing a partially combusted waste stream, and then contacting, in an incinerator chamber (13), the partially combusted waste stream and oxygen-containing gas, thereby causing the partially combusted waste stream to completely combust.

Description

Incineration of waste

The present invention relates to incineration of waste. More specifically, this invention relates to the incineration of liquid waste comprising nitrogen-containing compounds.

Landfills are often used as a way of disposing waste. However, the decreasing availability of land and environmental concerns relating to waste in a landfill adversely affecting air quality and contaminating groundwater has lead to waste incineration being used more frequently. Incineration is a process whereby undesirable compounds undergo thermal oxidation, and are destroyed. Various incinerators are available to incinerate waste with different properties including waste which is a solid, liquid or gas, and waste which needs to be combusted within a specific temperature range. Selecting the correct incinerator allows specialist waste to be treated accordingly.

Where waste contains nitrogen, care must be taken to ensure that the nitrogen does not oxidise producing nitric oxide (NO) and nitrogen dioxide (N0₂), hereafter referred to as ΝΟχ. Previously, the formation of NO_x could be avoided by limiting the residence time for incinerators burning nitrogen-containing compounds. However, new

environmental legislation has now been introduced which specifies minimum temperature and residence time requirements for incinerators, to ensure complete incineration of waste products. A problem with these new restrictions, however, is that some incinerators now produce unacceptable levels of NO_x. Accordingly, these incinerators can no longer be used or would require the exhaust gases to undergo further treatment such selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR).

There is therefore a need to provide novel and improved incinerators, which produce acceptable levels of NO_x compounds.

The inventors have also developed a novel method for incinerating waste, especially liquid waste.

In accordance with a first aspect of the invention, there is provided a method for incinerating waste, the method comprising:

a) contacting, in a pre-combustion chamber, a first waste stream and

oxygen-containing gas having insufficient oxygen for complete combustion to occur, thereby producing a partially combusted waste stream; and

b) contacting, in an incinerator chamber, the partially combusted waste stream and oxygen-containing gas, thereby causing the partially combusted waste stream to completely combust.

Advantageously, the method of the first aspect harnesses oxygen-staged incineration in which a waste stream is incinerated using the oxygen pre-combustion chamber, i.e. step (a) followed by a secondary oxygen-staged combustion (i.e. step (b). It will be appreciated that the pre-combustion chamber therefore acts as a primary combustion chamber, and that the incinerator chamber acts as a secondary or "main" chamber for the combustion of the first waste stream. The term "complete combustion" can mean that all of the carbon (C) in the waste stream has reacted to form carbon dioxide (C0₂) and all of the hydrogen (H) has reacted to form water (H₂0). Conversely, the term "partial combustion" can mean that at least some of the carbon (C) in the waste stream has reacted to form carbon monoxide (CO). Therefore, carrying out incineration using the method of the invention prevents any nitrogen, which may be present in the waste stream, from oxidising to form nitric oxide (NO) and nitrogen dioxide (N0₂).

Accordingly, the method of the first aspect solves the problem as to how to avoid unwanted NO_x compounds from being produced when incinerating nitrogen- containing wastes.

Accordingly, preferably the method comprises feeding the first waste stream

comprising nitrogen and nitrogen-containing compounds into the pre-combustion chamber. The first waste stream may comprise amines and/or amides. The first waste stream is preferably a fluid, and more preferably a liquid.

Preferably, the method comprises an initial step of atomising, in the pre-combustion chamber, the first waste stream with a fluid to produce an atomised waste stream. The atomisation step may be carried out at a temperature of between about 8oo°C and iioo°C.

In a preferred embodiment, the atomising fluid that is fed into the pre-combustion chamber comprises an oxygen-rich gas. The concentration of oxygen in the gas may comprise at least 25% oxygen, preferably at least 50% oxygen, and more preferably at least 75% oxygen. The oxygen-rich gas may comprise pure oxygen. However, in another embodiment, the atomising fluid that is fed into the pre- combustion chamber may comprise steam. In this embodiment, oxygen-rich gas is preferably fed into the pre-combustion chamber in order to produce the partially combusted waste stream.

Due to the effect of gravity acting on the atomised waste stream produced in step (a) of the method, it is good practice to initially feed the first waste stream into the pre- combustion chamber either horizontally or downwards (as opposed to upwards), or at an angle therebetween. Preferably, therefore, the first waste stream is not fed into the pre-combustion chamber in an upwards direction, and is preferably fed into the chamber at an angle of between o° and 90⁰ downwards from the horizontal (where o° is the horizontal plane, and 90⁰ is the vertical plane). More preferably, the first waste stream is fed into the pre-combustion chamber at an angle of between 5⁰ and 70⁰ downwards from the horizontal, even more preferably between io° and 50⁰ downwards from the horizontal, and most preferably between I9°and 25⁰ downwards from the horizontal.

Preferably, step (a) of the method is conducted at a temperature of between about 8oo°C and noo°C.

Preferably, the residence time of the reaction of step (a) is less than about 0.5 seconds, and is preferably between about 0.25 to 0.5 seconds. The term "residence time" is the time from the last injection of oxygen containing gas until gases in the chamber are vented. Accordingly, the residence time of the reaction of step (a) may refer to the time period between the last injection of the oxygen-containing gas in the pre-combustion chamber and the first injection of the oxygen-containing gas in the incinerator chamber.

Preferably, the method comprises controlling the amount of oxygen-containing gas that is fed into the pre-combustion chamber in step (a). For example, the method may comprise manually selecting the amount of oxygen-containing gas which is injected into the pre-combustion chamber in step (a). Preferably, however, the method comprises automatically controlling the amount of oxygen-containing gas which is injected into the pre-combustion chamber in step (a). The method preferably comprises sensing the temperature in the pre-combustion chamber and varying the amount of oxygen-containing gas which is fed into the pre-combustion chamber depending on the temperature in the pre-combustion chamber. It will be appreciated that as the temperature increases, the amount of gas fed into the chamber increases.

In one embodiment, the method may comprise the use of a plurality of pre-combustion chambers in order to carry out step (a), wherein the partially combusted waste produced by each pre-combustion chamber is fed into the incineration chamber.

Preferably, step (b) of the method comprises feeding the combustion gas into the incineration chamber, preferably using a forced gas fan. The combustion gas preferably comprises air. Alternatively, the combustion gas may be enriched with oxygen.

Preferably, the method comprises feeding an exhaust gas stream out of the incineration chamber.

Preferably, step (b) of the method is conducted at a temperature of between about 8oo°C and noo°C.

Preferably, the residence time of the reaction of step (b) is at least 0.5 seconds, and preferably is at least 2 seconds. The residence time of the reaction of step (b) may refer to the time period between the last injection of the oxygen-containing gas in the incinerator chamber and the step of feeding an exhaust gas stream out of the incineration chamber.

Preferably, the method comprises contacting, in the incineration chamber, the partially combusted waste stream with a second waste stream. Preferably, therefore, the method comprises feeding a second waste stream into the incineration chamber, such that it mixes with the partially combusted first waste stream. The second waste stream is preferably a fluid, more preferably a liquid or aqueous waste stream. Preferably, the concentration of nitrogen and nitrogen-containing compounds in the second waste stream is negligible, and preferably the second waste stream does not contain any nitrogen-containing compounds. Preferably, the second waste stream comprises waste of a low calorific value, for example contaminated water. Preferably, the second waste stream is fed downwards into the incineration chamber along a substantially vertical plane. Alternatively, the second waste steam is fed into the incineration chamber at an angle of between o° and 90⁰ downwards from the horizontal (where 0° is the horizontal plane, and 90⁰ is the vertical plane). In order to carry out the method of the invention, the inventors have produced a novel incineration apparatus.

Hence, in a second aspect, there is provided a waste incineration apparatus

comprising: - a waste pre-combustion chamber;

feed means for feeding a first waste stream and an oxygen-containing gas to the pre-combustion chamber, wherein the pre-combustion chamber is configured to partially combust waste therein;

- an incineration chamber operably connected to the pre-combustion

chamber and configured to receive the partially combusted waste; and feed means for feeding combustion gas to the incineration chamber, such that the partially combusted waste is fully combusted. Preferably, the apparatus comprises a plurality of waste pre-combustion chambers, each being operably connected to the incineration chamber. Preferably, the pre- combustion chambers are arranged tangentially with respect to the incineration chamber. Accordingly, in some embodiments, the apparatus may comprise two, three, four or more pre-combustion chambers all connected to the incineration chamber.

Preferably, the feed means is configured such that the oxygen-containing gas atomises the waste stream. Preferably, the feed means comprises a first channel along which the waste stream is fed to the pre-combustion chamber, and a second channel along which the oxygen-containing gas is fed to the pre-combustion chamber. Preferably, the second channel is concentrically disposed around the outside of the first channel, or vice versa, and outlets of the first and second channels meet such that, in use, a waste stream exiting its outlet is atomised by oxygen-containing gas exiting its outlet. Preferably, the second channel comprises at least one insert which is configured to create a narrowed section therein at least adjacent to its outlet, which, in use, causes the oxygen- containing gas to be fed into the stream of liquid waste exiting the first channel.

Preferably, the waste feed means and the gas feed means are combined within a lance or atomiser. Preferably, the lance comprises an oxygen shroud configured to feed additional oxygen rich gas into the pre-combustion chamber. Preferably, the or each pre-combustion chamber is configured to feed the waste stream therein at an angle of between o° and 90⁰ downwards from the horizontal. More preferably, the or each pre-combustion chamber is configured to feed the waste stream into the pre-combustion chamber at an angle of between 5⁰ and 70⁰ downwards from the horizontal, even more preferably between io° and 50⁰ downwards from the horizontal, and most preferably between I9°and 25⁰ downwards from the horizontal.

The or each pre-combustion chamber may comprise at least one gas inlet port configured to inject additional oxygen rich gas into the or each pre-combustion chamber. Preferably, the apparatus comprises control means configured to control the

temperature of the or each pre-combustion chamber and/or the amount of oxygen- containing gas being fed thereto. In a preferred embodiment, the apparatus comprises at least one temperature sensor configured to measure the temperature in the or each pre-combustion chamber, and means for varying the flow of oxygen-containing gas into the or each pre-combustion chamber depending on the measured temperature.

The apparatus preferably comprises means for feeding the combustion gas into the incineration chamber, which is preferably a forced gas fan. The combustion gas is preferably air. Alternatively, the combustion gas may be enriched with oxygen.

Preferably, the apparatus comprises means for feeding an exhaust gas stream out of the incineration chamber.

Preferably, the apparatus comprises means for feeding a second waste stream into the incineration chamber. Preferably, the feed means is configured to feed the second waste stream into the incineration chamber along a substantially vertical plane. Alternatively, the feed means could be configured to feed the second waste steam into the

incineration chamber along an angle of between o° and 90⁰ downwards from the horizontal (where 0° is the horizontal plane, and 90⁰ is the vertical plane).

Advantageously, the partially combusted first waste stream will act as a fuel and cause contaminants contained in the second waste stream to combust.

The inventors believe that the pre-combustion chamber which allows partial combustion of the first liquid waste stream is an important aspect of the invention. Thus, in a third aspect, there is provided a waste pre-combustion chamber configured to be operably connected to a waste incineration chamber, the pre-combustion chamber comprising a combustion zone in which partial combustion occurs, waste feed means for feeding a waste stream to the combustion zone, gas feed means for feeding oxygen-containing gas to the combustion zone, wherein the gas feed means is configured to atomise the waste stream, and thereby produce a partially combusted feed stream in the combustion zone.

Preferably, the waste feed means comprises a first channel along which the waste stream is fed to the combustion zone. Preferably, the gas feed means comprises a second channel along which the oxygen-containing gas is fed to the combustion zone. Preferably, the second channel is concentrically disposed around the outside of the first channel, or vice versa, and outlets of the first and second channels meet such that, in use, a waste stream exiting its outlet is atomised by oxygen-containing gas exiting its outlet. Preferably, the second channel comprises at least one insert which is configured to create a narrowed section therein at least adjacent to its outlet, which, in use, causes the oxygen-containing gas to be fed into the stream of waste exiting the first channel. Preferably, the waste feed means and the gas feed means are combined within a lance or atomiser. Preferably, the lance comprises an oxygen shroud configured to feed additional oxygen rich gas into the pre-combustion chamber.

Preferably, the pre-combustion chamber comprises control means configured to control the temperature in the combustion zone and/or the amount of oxygen- containing gas being fed thereto. In a preferred embodiment, the pre-combustion chamber comprises at least one temperature sensor configured to measure the temperature in the combustion zone, and means for varying the flow of oxygen- containing gas into the zone depending on the measured temperature.

The inventors believe that they are the first to have ever used a pre-combustion chamber connected to a main incinerator to partially combust a first liquid waste prior to its complete combustion in the main incinerator chamber in order to limit the formation of NOx compounds.

Thus, in accordance with a fourth aspect, there is provided use of the pre-combustion chamber of the third aspect, for partially combusting a waste stream containing nitrogen-containing compounds prior to complete combustion of the waste stream in an incineration chamber.

All features described herein (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figures, in which:-

Figure l depicts a prior art incinerator for incinerating liquid waste;

Figure 2 depicts an incinerator for incinerating waste in accordance with the present invention;

Figure 3 is an enlarged view of the incinerator of Figure 2 showing a pre-combustion chamber; and

Figure 4 is a graph showing the concentration of hydrocarbons, carbon monoxide and oxygen in the flue gas, as well as the efficiency of the combustion reaction, as the concentration of oxygen increases.

Referring to Figure 1, there is shown a prior art system of an incinerator 1 which is used for incinerating liquid waste 2. The incinerator 1 comprises a main incinerator chamber 13, and an associated waste injector 3 for injecting the liquid waste 2 therein. The incinerator also includes a gas inlet 4 and an exhaust gas outlet 5. The liquid waste 2 is injected into the top 16 of the main incinerator chamber 13 via injector 3. As the liquid waste 2 falls into the incinerator 1, which is maintained at a temperature of about850 to 1200 °C, it encounters atmospheric gas 17 which is injected into the main incinerator chamber 13 through gas inlet 4. Accordingly, the liquid waste 2 undergoes a combustion reaction, which generates exhaust gas 18 which exits the main incinerator chamber 13 through exhaust 5. To ensure complete incineration of the liquid waste 2, the process is carried out at high temperatures with an excess of atmospheric gas 17.

A problem associated with the prior art incinerator 1 shown in Figure 1 is that if the liquid waste 2 contains nitrogen (N), then this is oxidised to form unwanted NO_x compounds. Previously, it was possible to overcome this problem by reducing the residence time of the materials in the main incinerator chamber 13. However, recent restrictions in environmental legislation now specify a minimum temperature and minimum residence time requirement for incinerators. Accordingly, when an incinerator l of the type depicted in Figure l complies with the minimum temperature and time requirements, undesirable NO_x compounds are often generated.

Accordingly, the inventors have developed a novel incinerator 6 for incinerating nitrogen rich fuel, which does not result in the production of NO_x compounds. Figure 2 depicts an embodiment of the incinerator 6 developed by the inventors. As in the known incinerator l shown in Figure l, the incinerator 6 includes a main incinerator chamber 13 and a waste injector 3 by which waste 2 is injected into chamber 13 where it is combusted. Also, as with the prior art incinerator 1, the novel incinerator 6 includes a gas inlet 4 and an exhaust gas outlet 5. However, in contrast to the known incinerator 1, the incinerator 6 of the invention includes a pre-combustion chamber 7, which is attached to one side 19 of the main incinerator chamber 13, and this pre-combustion chamber 7 is depicted in detail in Figure 3. While only one pre-combustion chamber 7 is illustrated, it will be understood that a plurality of pre-combustion chambers 7 could be installed tangentially to the main incinerator chamber 13.

Referring to Figure 3, the pre-combustion chamber 7 includes an open-ended box- shaped housing 30, which is connected to an upper corner of the main incinerator chamber 13, for example by welding. An elongate lance 8 extends out through an upwardly facing side of the housing 30, and is provided to atomise and initiate combustion of a waste stream 11 which flows therethrough. One end 22 of the lance 8 is connected to, and partially, extends into the housing 30 of the pre-combustion chamber 7, whereas the opposite end 32 of the lance 8 is connected to a waste feed 34. Extending through the centre of the lance 8, there is disposed a liquid waste channel 9 along which the waste stream 11 flows from feed 34. The waste channel 9 is itself surrounded by a concentric channel 10 along which steam or oxygen rich gas 12 is fed via inlet port 40. Oxygen rich gas 12 is preferable to steam.

In use, the liquid waste channel 9 is configured to pump the liquid waste 11 out of end 22 of the lance 8 into the pre-combustion chamber 7. Also, the oxygen channel 10 is configured to pump an oxygen rich gas 12 (preferably pure oxygen) out of end 22 of the lance 8, and directly into the pre-combustion chamber 7. As can be seen in Figure 3, at the end of the oxygen channel 10, which corresponds to end 22 of the lance 8 extending into the housing 30, angled inserts 20 and 21 are disposed, which create narrowed sections 36 in oxygen channel 10. These narrowed sections 36 that are created just before the point where the oxygen rich gas 12 is fed into the pre-combustion chamber 7 causes the gas 12 to be fed into the stream of liquid waste 11 exiting lance 8. This causes the oxygen rich gas 12 to atomise the liquid waste 11 as it exits lance 8.

In one embodiment, the lance 8 is fitted with an oxygen shroud 26 disposed circumferentially around the outside of the oxygen channel 10. Additional oxygen rich gas 27 can be injected via port 38 and along oxygen shroud 26 directly into the housing 30 of the pre-combustion chamber 7. Alternatively, in another embodiment (not shown), the pre-combustion chamber 7 may comprise at least one gas inlet port configured to inject the additional oxygen rich gas into the pre-combustion chamber 7. In both of these embodiments, the additional oxygen rich gas feed is introduced into the housing 30 at a site spaced apart from the site 36 where the liquid waste 11 is atomised by the gas 10.

The amount of oxygen rich gas 12 injected into the pre-combustion chamber 7 is carefully controlled to ensure that there is insufficient oxygen present for complete combustion of the liquid waste 11 to occur. The term "complete combustion" may mean that all the carbon (C) in the liquid waste 11 feeding through the lance 8 and into the pre-combustion chamber 7 has reacted to form carbon dioxide (C0₂) and all the hydrogen (H) in the liquid waste 11 has reacted to form water (H₂0). However, the conditions within the pre-combustion chamber 7 will cause the hydrogen (H) to form water (H₂0) as well as OH radicals, and the carbon (C) to partially combust to form carbon monoxide (CO). Due to the low concentration of nitrogen in the gas 12, and the excess of the liquid waste 11 compared to oxygen, the nitrogen in the liquid waste 11 does not oxidise to form undesirable NO_x, and instead forms inert nitrogen gas (N₂).

The pre-combustion chamber 7 operates at a temperature above the autoignition temperature of the liquid waste 11, which will be about 8oo-iioo°C. Since the pre- combustion reaction is occurring in conditions where there is an excess of the liquid waste 11, then increasing the concentration of oxygen will increase the temperature of the pre-combustion chamber 7, whereas decreasing the concentration of oxygen will decrease the temperature of the pre-combustion chamber 7. This is illustrated by the graph shown of Figure 4, where efficiency directly corresponds to temperature. Since the pre-combustion chamber will possess an excess of fuel 11, the conditions shown on the left hand side of the y-axis of the graph apply. Accordingly, the pre-combustion chamber 7 is provided with a temperature sensor 23 in the inside of the housing 30. The apparatus can be automated to monitor the temperature in the pre-combustion chamber 7, and vary the flow of the oxygen rich gas 12 therein depending on the temperature of the pre-combustion chamber 7.

Accordingly, if the temperature in chamber 7 detected by sensor 23 falls below a preset minimum value (e.g. the autoignition temperature of the liquid waste 11), the system increases the flow of oxygen rich gas 12 into the pre-combustion chamber 7.

Conversely, if the temperature of the pre-combustion chamber 7 rises above a preset maximum (e.g. 300°C above the autoignition temperature of the liquid waste 11), then the system decreases the flow of oxygen rich gas 12 into the pre-combustion chamber 7. This will allow the system to self-regulate the temperature in the pre-combustion chamber 7 by controlling the flow of the oxygen rich gas 12 into the pre-combustion chamber 7.

The liquid waste 11 is injected through lance 8 in a downwards direction into the pre- combustion chamber 7 at an angle of 22⁰ to the horizontal, shown as Θ in Figure 2. The reason for this is that 22⁰ is the natural spray expansion of a jet. Due to the effect of gravity acting on the spray, it is good practice to inject the liquid horizontally or downwards as opposed to upwards. The angle of 22⁰ therefore means that the top of the spray will initially be horizontal avoiding any of the liquid waste 11 being injected into the chamber 7 at an upwards angle. However, it will be appreciated that this is not essential, and in practice the liquid waste 11 could be injected into the pre-combustion chamber 7 at a wide range of angles.

The liquid waste 11 will undergo the pre-combustion reaction as it passes into and through the pre-combustion chamber 7. The partially combusted liquid waste 25 will then continue into the main incinerator chamber 13. As shown in Figure 2, the main incinerator chamber 13 is provided with a gas injector 14, which is configured to inject atmospheric air 17 therein. The gas injector 14 is fitted with a forced draft fan 24, which facilitates gas injection. The injection of atmospheric air 17 into chamber 13 causes the partially combusted liquid waste 25 exiting the pre-combustion chamber 7 to combust completely. The main incinerator chamber 13 is also provided with a waste injector 3 for injecting aqueous waste 15 therein. The aqueous waste stream 15 will have a low calorific value and does not contain nitrogen. The partially combusted liquid waste 25 mixes with the aqueous waste 15 and acts as a fuel, causing the contaminants within the aqueous waste 15 to combust. Exhaust gas 18 exits the incinerator chamber 13 through exhaust 5.

Advantages of the modified incinerator 6 of the invention reside in the presence of the pre-combustion chamber 7, which allows partial combustion of the liquid waste stream 11 containing nitrogen prior to complete combustion in the main incinerator chamber 13, thereby preventing the formation of unwanted NO_x compounds. Additionally, the incinerator 6 allows the liquid waste 11 containing nitrogen to act as a fuel, and thereby combust any contaminants in a second low calorific aqueous waste stream 15. Another advantage is the provision of a feedback loop capable of controlling the temperature of the pre-combustion chamber 7 by controlling the flow of oxygen 12 into the pre- combustion chamber 7.

Claims

A method for incinerating waste, the method comprising:

contacting, in a pre-combustion chamber, a first waste stream and oxygen- containing gas having insufficient oxygen for complete combustion to occur, thereby producing a partially combusted waste stream; and

contacting, in an incinerator chamber, the partially combusted waste stream and oxygen-containing gas, thereby causing the partially combusted waste stream to completely combust.

A method according to claim l, wherein the method comprises feeding the first waste stream comprising nitrogen and nitrogen-containing compounds into the pre-combustion chamber.

A method according to either of claims l or 2, wherein the first waste stream comprises amines and/or amides and the first waste stream is preferably a fluid, and more preferably a liquid.

A method according to any preceding claim, wherein the method comprises an initial step of atomising, in the pre-combustion chamber, the first waste stream with a fluid to produce an atomised waste stream.

A method according to any preceding claim, wherein the atomising fluid that is fed into the pre-combustion chamber comprises an oxygen-rich gas.

A method according to any preceding claim, wherein the concentration of oxygen in the gas comprises at least 25% oxygen, and preferably wherein the oxygen-rich gas comprises pure oxygen.

A method according to any of claims 1 to 4, wherein the atomising fluid that is fed into the pre-combustion chamber comprises steam, and wherein oxygen-rich gas is fed into the pre-combustion chamber in order to produce the partially combusted waste stream. 8. A method according to any preceding claim, wherein the first waste stream is fed into the chamber at an angle of between o° and 90⁰ downwards from the horizontal, or between 5⁰ and 70⁰ downwards from the horizontal, or between io° and 50⁰ downwards from the horizontal, or between i9°and 25⁰ downwards from the horizontal.

A method according to any preceding claim, wherein step (a) of the method is conducted at a temperature of between about 8oo°C and iioo°C.

A method according to any preceding claim, wherein the method comprises controlling the amount of oxygen-containing gas that is fed into the pre- combustion chamber in step (a).

A method according to claim 10, wherein the method comprises manually selecting the amount of oxygen-containing gas which is fed into the pre- combustion chamber in step (a).

A method according to claim 10, wherein the method comprises

automatically controlling the amount of oxygen-containing gas which is fed into the pre-combustion chamber in step (a) by sensing the temperature in the pre-combustion chamber and varying the amount of oxygen-containing gas which is fed into the pre-combustion chamber depending on the temperature in the pre-combustion chamber.

A method according to any preceding claim, wherein the method comprises the use of a plurality of pre-combustion chambers in order to carry out step (a), wherein the partially combusted waste produced by each pre- combustion chamber is fed into the incineration chamber.

A method according to any preceding claim, wherein step (b) of the method comprises feeding the combustion gas into the incineration chamber, preferably using a forced gas fan.

A method according to any preceding claim, wherein the combustion comprises air. 16. A method according to any preceding claim, wherein step (b) of the method is conducted at a temperature of between about 8oo°C and iioo°C. A method according to any preceding claim, wherein the method comprises feeding an exhaust gas stream out of the incineration chamber.

A method according to any preceding claim, wherein the method comprises contacting, in the incineration chamber, the partially combusted waste stream with a second waste stream.

A method according to claim 18, wherein the method comprises feeding a second waste stream into the incineration chamber, preferably along a substantially vertical plane, such that it mixes with the partially combusted first waste stream.

A method according to either claim 18 or 19, wherein the second waste stream is preferably a fluid, more preferably a liquid or aqueous waste stream.

A method according to any of claims 18 to 20, wherein the concentration of nitrogen and nitrogen-containing compounds in the second waste stream is negligible, and preferably the second waste stream does not contain any nitrogen-containing compounds.

A waste incineration apparatus comprising: - a pre-combustion chamber;

an incineration chamber operably connected to the pre-combustion chamber and configured to receive the partially combusted waste; and feed means for feeding combustion gas to the incineration chamber, such that the partially combusted waste is fully combusted.

A waste incineration apparatus according to claim 22, wherein the apparatus comprises a plurality of waste pre-combustion chambers, each being operably connected to the incineration chamber and the waste pre- combustion chambers are optionally arranged tangentially with respect to the incineration chamber.

24. A waste incineration apparatus according to either claim 22 or 23, wherein the feed means is configured such that the oxygen-containing gas atomises the waste stream.

25. A waste incineration apparatus according to claim 24, wherein the feed means comprises a first channel along which the waste stream is fed to the pre-combustion chamber, and a second channel along which the oxygen- containing gas is fed to the pre-combustion chamber and the second channel is concentrically disposed around the outside of the first channel, or vice versa, and outlets of the first and second channels meet such that, in use, a waste stream exiting its outlet is atomised by oxygen-containing gas exiting its outlet.

26. A waste incineration apparatus according to claim 25, wherein the second channel comprises at least one insert which is configured to create a narrowed section therein at least adjacent to its outlet, which, in use, causes the oxygen-containing gas to be fed into the stream of liquid waste exiting the first channel.

27. A waste incineration apparatus according to any one of claims 22 to 26, wherein the waste feed means and the gas feed means are combined within a lance.

28. A waste incineration apparatus according claim 27, wherein the lance

comprises an oxygen shroud configured to feed additional oxygen rich gas into the pre-combustion chamber.

29. A waste incineration apparatus according to any one of claims 22 to 28, wherein the or each pre-combustion chamber comprises at least one gas inlet port configured to inject additional oxygen rich gas into the pre- combustion chamber. A waste incineration apparatus according to any one of claims 22 to 29, wherein the apparatus comprises control means configured to control the temperature of the pre-combustion chamber and/or the amount of oxygen- containing gas being fed thereto, preferably wherein the apparatus comprises at least one temperature sensor configured to measure the temperature in the pre-combustion chamber, and means for varying the flow of oxygen-containing gas into the pre-combustion chamber depending on the measured temperature.

A waste incineration apparatus according to any one of claims 22 to 30, wherein the apparatus comprises means for feeding the combustion gas, which is preferably air, into the incineration chamber, wherein the means for feeding the combustion gas is preferably a forced gas fan.

A waste incineration apparatus according to any one of claims 22 to 31, wherein the apparatus comprises means for feeding a second waste stream into the incineration chamber, and preferably, wherein the feed means is configured to feed the second waste stream into the incineration chamber along a substantially vertical plane.

A waste pre-combustion chamber configured to be operably connected to a waste incineration chamber, the pre-combustion chamber comprising a combustion zone in which partial combustion occurs, waste feed means for feeding a waste stream to the combustion zone, gas feed means for feeding oxygen-containing gas to the combustion zone, wherein the gas feed means is configured to atomise the waste stream, and thereby produce a partially combusted feed stream in the combustion zone.

Use of the pre-combustion chamber according to claim 33, for partially combusting a waste stream containing nitrogen-containing compounds prior to complete combustion of the waste stream in an incineration chamber.