WO2019171067A1

WO2019171067A1 - Abatement by combustion

Info

Publication number: WO2019171067A1
Application number: PCT/GB2019/050643
Authority: WO
Inventors: Andrew James Seeley; Duncan Michael PRICE; Gareth David Stanton; Christopher Andrew OSTERTAG-HILL; Laura ALCOCK; Alageswaren Reddi Balsamy RADIAR
Original assignee: Edwards Limited; Edwards Vacuum Llc
Priority date: 2018-03-09
Filing date: 2019-03-07
Publication date: 2019-09-12
Also published as: TW201938248A; GB201803860D0; GB2571793A

Abstract

An abatement method is disclosed. The method comprises: supplying an initial reaction zone of an abatement apparatus with non-stoichiometric amounts of initial reactants to perform an initial abatement reaction under non-stoichiometric conditions to produce a first reaction product at a concentration which is lower than a second reaction product; and supplying a subsequent reaction zone of the abatement apparatus with a subsequent reactant to perform a subsequent abatement reaction to lower the concentration of the second reaction product. In this way, the amount of individual reaction products produced can be better controlled than when operating the abatement apparatus under stoichiometric conditions. In particular, lower amounts of the first reaction product may be generated in the initial abatement reaction at a cost of generating greater amounts of a second reaction product. However, the amount of the second reaction product may then be subsequently decreased in a subsequent abatement reaction.

Description

ABATEMENT BY COMBUSTION

FIELD OF THE INVENTION

The field of the invention relates to an abatement method.

BACKGROUND

Abatement apparatus for performing abatement are known and are typically used for treating an effluent gas stream from a manufacturing processing tool used in, for example, the semiconductor or flat panel display manufacturing industry.

During such manufacturing, residual perfluorinated compounds (PFCs) and other compounds exist in the effluent gas stream pumped from the process tool. PFCs are difficult to remove from the effluent gas and their release into the environment is undesirable because they are known to have relatively high greenhouse activity.

Known abatement apparatus use combustion to remove the PFCs and other compounds from the effluent gas stream. Typically, the effluent gas stream is a nitrogen stream containing PFCs and other compounds. A fuel gas is mixed with the effluent gas stream and that gas stream mixture is conveyed into a

combustion chamber that is laterally surrounded by the exit surface of a foraminous gas burner. Fuel gas and air are simultaneously supplied to the foraminous burner to affect flameless combustion at the exit surface, with the amount of air passing through the foraminous burner seeking to be sufficient to consume not only the fuel gas supply to the burner, but also all the combustibles in the gas stream mixture injected into the combustion chamber.

Although techniques exist for processing the effluent gas stream, they each have their own shortcomings. Accordingly, it is desired to provide an improved technique for processing an effluent gas stream. SUMMARY

According to a first aspect, there is provided a method, comprising: supplying an initial reaction zone of an abatement apparatus with non-stoichiometric amounts of initial reactants to perform an initial abatement reaction under non- stoichiometric conditions to produce a first reaction product at a concentration which is lower than a second reaction product; and supplying a subsequent reaction zone of the abatement apparatus with a subsequent reactant to perform a subsequent abatement reaction to lower the concentration of the second reaction product.

The first aspect recognises that a problem with the operation with existing abatement apparatus is that the abatement is typically performed under generally stoichiometric conditions in order to minimise the amounts of reaction products generated during the abatement reaction. Whilst this minimises the total quantity of those reaction products produced, the first aspect recognises that some reaction products can be more harmful than others. Accordingly, a method is provided. The method may be a method of supplying or operating an abatement apparatus. The method may comprise the step of supplying, feeding or providing an initial or first reaction zone or part of the abatement apparatus with non- stoichiometric amounts, volumes, concentrations or flow rates of initial reactants to perform or support a first or initial abatement reaction within that zone under generally non-stoichiometric conditions. That is to say, the abatement reaction is conducted under conditions that are other than considered to be generally stoichiometric. Performing the reaction under those conditions produces reaction products where one reaction product is produced in a concentration, quantity or amount which is less than another reaction product. The method may comprise the step of supplying or operating a subsequent, second or further reaction zone or part of the abatement apparatus with a subsequent reactant to perform or support a subsequent or second abatement reaction which lowers the

concentration, quantity or amount of the second reaction product. In this way, the amount of individual reaction products produced can be better controlled than when operating the abatement apparatus under stoichiometric conditions. In particular, lower amounts of the first reaction product may be generated in the initial abatement reaction at a cost of generating greater amounts of a second reaction product. However, the amount of the second reaction product may then be subsequently decreased in a subsequent abatement reaction.

In one embodiment, when the initial abatement reaction is optimised for an oxidization reaction, the subsequent abatement reaction is optimised for reduction, or vice versa.

In one embodiment, the initial abatement reaction abates an effluent stream during reaction of a first initial reactant with a second initial reactant under the non-stoichiometric conditions. Hence, the abatement reaction may treat an effluent stream.

In one embodiment, the non-stoichiometric conditions comprise reacting the first initial reactant with the second initial reactant at a first initial reactant/second initial reactant ratio which is greater than 1 .1 : 1 . Accordingly, the ratio of the first reactant to the second reactant may be selected to provide the first reactant in a quantity which is at least 10% more than its stoichiometric amount.

In one embodiment, the non-stoichiometric conditions comprise reacting the first initial reactant with the second initial reactant at a first initial reactant/second initial reactant ratio which is greater than 1 .3: 1 . Accordingly, the ratio of the first initial reactant to the second initial reactant may be selected to provide the first initial reactant in a quantity which is at least 30% more than its stoichiometric amount.

In one embodiment, the non-stoichiometric conditions produce the first reaction product at a concentration which is lower than under stoichiometric conditions. Accordingly, the initial abatement reaction may produce the first reaction product at a concentration, amount or quantity which is lower than would be produced under generally stoichiometric conditions. In one embodiment, the non-stoichiometric conditions produce the second reaction product at a concentration which is higher than under stoichiometric conditions. Accordingly, the initial abatement reaction may produce the second reaction product at a concentration, amount or quantity which is

disproportionately greater than would be produced under generally stoichiometric conditions.

In embodiments, running under these changed reaction conditions results in an absolute improvement in the emission of the first reaction product during the initial abatement reaction (for example, a 50% reduction such as from 20 ppm to 10 ppm); but at the cost of increasing the emission of the second reaction product by a disproportionately large amount (for example, a 500 - 5000% increase such as from 20 ppm to l OOOppm). However, the second reaction zone may then decrease the emission of the second reaction product.

In one embodiment, the abatement reaction comprises a combustion reaction. Accordingly, the abatement of the effluent stream may occur due to combustion.

In one embodiment, the first reaction product and the second reaction product comprise trace combustion products. Accordingly, the reaction products may be generated during combustion.

In one embodiment, the first reaction product comprises NOx and the second reaction product comprises CO.

In one embodiment, the supplying the initial reaction zone of the abatement apparatus provides an excess of the first initial reactant. Accordingly, the non- stoichiometric conditions may provide an excess or surplus of the first initial reactant. ln one embodiment, the excess of the first initial reactant provides one of a reducing and an oxidising environment within the initial reaction zone.

Accordingly, the initial abatement reaction may create either a reducing or an oxidising environment.

In one embodiment, the first initial reactant comprises one of a fuel and an oxidant. Hence, the first initial reactant may be either a fuel or an oxidant.

In one embodiment, the supplying the initial reaction zone of the abatement apparatus provides a depletion of the second initial reactant. Accordingly, the non-stoichiometric conditions may provide a depletion or scarcity of the second initial reactant.

In one embodiment, the depletion of the second initial reactant provides one of a reducing and an oxidising environment within the initial reaction zone.

Accordingly, the depletion or scarcity of the second initial reactant may create either a reducing or an oxidising environment.

In one embodiment, the second initial reactant comprises another of an oxidant and a fuel. Hence, the second initial reactant may be the other of an oxidant or a fuel.

In one embodiment, the subsequent abatement reaction reacts a third reactant with the second reaction product to lower the concentration of the second reaction product. Accordingly, a third reactant may be provided which reacts with the second reaction product to lower its concentration, amount or quantity.

In one embodiment, when the initial abatement reaction provides a reducing environment within the initial reaction zone and the supplying the third reactant provides an oxidising environment within the subsequent reaction zone.

Accordingly, when the initial abatement reaction may be a reducing reaction, an oxidising reaction occurs within the subsequent reaction zone. In one embodiment, the supplying the third reactant provides an excess of oxygen.

In one embodiment, the third reactant comprises at least one of oxygen, ozone and an inorganic peroxide. The inorganic peroxide may be a hydrogen peroxide and/or a peroxide salt solution such as Na202 solution).

In one embodiment, when the initial abatement reaction provides an oxidising environment within the initial reaction zone and the supplying the third reactant provides a reducing environment within the subsequent reaction zone.

Accordingly, when the initial abatement reaction is an oxidising reaction then the subsequent reaction may be a reducing reaction.

In one embodiment, the supplying the third reactant provides an excess of hydrogen.

In one embodiment, the third reactant comprises a fuel. In one embodiment, this fuel may be a traditional hydrocarbon fuel such as methane, propane, acetylene or the like, or it may be a fuel containing inorganic elements such as silane, diborane, tetraethylorthosilicate, or the like.

In one embodiment, the initial reaction zone is located at a position within the abatement apparatus which is hotter than the subsequent reaction zone.

In one embodiment, the initial reaction zone is located upstream of the subsequent reaction zone.

In one embodiment, the initial reaction zone is located proximate a combustion chamber of the abatement apparatus. ln one embodiment, the initial reaction zone is located within the combustion chamber.

In one embodiment, the subsequent reaction zone is located within the

combustion chamber.

In one embodiment, the subsequent reaction zone is located downstream of the initial reaction zone.

In one embodiment, the initial reaction zone comprises the combustion chamber or a higher-temperature flame located within the combustion chamber, the combustion chamber being typically at least 100°C cooler than the hottest region of the flame.

In one embodiment, the subsequent reaction zone is located distal the

combustion chamber of the abatement apparatus.

In one embodiment, the subsequent reaction zone is cooler than the preceding zone. Typically, the temperate of the zone of the abatement apparatus are ordered as follows: flame (hottest) > radiant combustion zone > post combustion zone > post cooling > counter current wet scrubber (coolest) or radiant

combustion zone (hottest) > post combustion zone > post cooling > counter current wet scrubber (coolest). In embodiments, the flame is typically hotter than 1000°C at its hottest location; the combustion zone is in the range of 500°C to 1000°C; the post combustion zone and the transition into weir have a core temperature of 500°C - 750°C, with the temperature at their edge being < 100 °C due to the interaction with water curtain; the post quench zone is up to 150°C, but usually < 100°C due to practicality of liquid water as a coolant; the counter current wet scrubber has a temperature in the range of liquid water, but is typically 15°C to 75°C. ln one embodiment, the subsequent reaction zone is located downstream of a quench of the abatement apparatus.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 illustrates schematically the main components of an abatement apparatus according to one embodiment;

Figure 2 illustrates the operation of the abatement apparatus under stoichiometric conditions;

Figure 3 illustrates the operation of the abatement apparatus according to one embodiment;

Figure 4 illustrates schematically the main components of an abatement apparatus according to one embodiment; and

Figure 5 illustrates schematically the main components of an abatement apparatus according to one embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide an arrangement whereby an abatement apparatus is operated to decrease the amounts of reaction by-products that are produced during the abatement of an effluent gas stream with the abatement apparatus. Depending on the type of abatement required, existing abatement apparatus will typically be operated under generally stoichiometric conditions in order to try to minimise the amount of by-products produced. Embodiments instead typically perform an abatement reaction in one region or part of the abatement apparatus under non-stoichiometric conditions in order to decrease the amount or quantity of a first reaction by-product which is produced during that reaction. In particular, the amount of the first reaction by-product is lower than would be obtained under normal stoichiometric conditions. However, this typically causes a greater amount of a second reaction by-product to be produced during that reaction. In particular, the amount of the second reaction by-product is higher than would be obtained under normal stoichiometric conditions. The amount of the second reaction by-product is then decreased by a further abatement reaction occurring downstream in the abatement apparatus. This two-stage approach leads to the production of reaction by-products in amounts that are smaller than would be possible when operating the abatement apparatus under normal stoichiometric conditions.

Abatement Apparatus

Figure 1 illustrates schematically the main components of an abatement apparatus 10 according to one embodiment. The abatement apparatus 10 has an inlet head assembly 20 which is fluidly coupled with a source of an effluent gas stream 90 from a processing tool and typically with sources of a fuel (such as methane) and an oxidant (such as air). The inlet head assembly 20 is fluidly coupled with a downstream combustion chamber 30 of a radiant burner. The combustion chamber 30 is fluidly coupled with the sources of the fuel and the oxidant. The combustion chamber 30 is fluidly coupled with a downstream weir chamber 40. The weir chamber 40 generates a water curtain 50 which flows down an inner surface. The weir chamber 40 also generates a spray 60 which sprays across the inner surface of the weir chamber 40. The weir chamber 40 is fluidly coupled with a downstream sump 70. The sump 70 is fluidly coupled with a downstream packed tower 80. The sump 70 collects water from the weir chamber 40 and the packed tower 80. The sump 70 recirculates water to supply the weir chamber 40 and the packed tower 80. The packed tower 80 is filled with packing and water flows from an upper portion of the packed tower 80, over the packing and into the sump 70. An oxidant supplier 100 generates or supplies a controlled amount of an oxidant (such as ozone or peroxide) to the water in the sump 70. The treated effluent stream then vents via the outlet 130.

Operation

In operation, the effluent gas stream 90 is received by the inlet head assembly 20 and is typically pre-mixed with nitrogen and with oxygen. The resultant mixture is then typically further mixed with the fuel. This mixture is then injected into the combustion chamber 30 via inlets in the inlet head assembly 20. The inlets are typically provided with concentric annular injectors which surround the mixture entering the combustion chamber 30 with fuel. The wall of the combustion chamber 30 is typically porous and the mixture of fuel and oxygen is forced under pressure through the wall of the combustion chamber 30 and combusted within the combustion chamber 30.

Following ignition, the heat generated by the fuel and air mixture passing through the wall of the combustion chamber 30 and the flames generated at the inlets to the combustion chamber 30 raises the temperature within the combustion chamber 30 to typically around 700°C, rising to around 1500°C in the flame. The heat and the combustion by-products break down or abate compounds (such as PFCs) present in the effluent gas stream 90.

As illustrated in Figure 2, the ratio of fuel to oxygen (typically provided by air) in a typical existing abatement apparatus seeks to achieve stoichiometric combustion in order to minimise the amount of carbon monoxide and NOx produced as a by- product of the combustion reaction to the concentration Ci. That is to say, a typical existing abatement apparatus would provide two moles of oxygen for each mole of methane in order to achieve as close to stoichiometric conditions as possible, in order to minimise the amount of carbon monoxide and NOx which is produced as combustion by-products within the combustion chamber 30. However, as illustrated in Figure 3, in this embodiment the ratio of fuel to oxidant supplied to the combustion chamber 30 is adjusted to a non-stoichiometric ratio. In particular, the ratio of fuel to oxidant is changed to make the mixture fuel-rich and deplete oxygen. In particular, the ratio is adjusted to make the mixture at least 10% fuel-rich and preferably at least 30% fuel-rich. Making the combustion chamber 30 fuel-rich provides a reducing environment, which significantly decreases or diminishes the amount of NOx produced within the combustion chamber 30 to C2 (which is less than C1), but significantly increases the amount of carbon monoxide produced in the combustion chamber 30 to C3 (which is greater than C1), as shown in Figure 3.

As the effluent stream and combustion by-products exit the combustion chamber 30 and enter the weir chamber 40, the temperature of the gases cool to around 500°C. As mentioned above, the water within the sump 70 is dosed with an oxidant such as ozone or peroxide to produce an oxidising environment.

Accordingly, carbon monoxide within the gas stream flowing through the weir chamber 40 reacts with the dosed water curtain 50 and wet scrubber 60. The temperature of the gas stream after the wet scrubber 60 has typically dropped to between 40 and 70 degrees Celsius. Carbon monoxide also reacts with the dosed water in the sump 70 and with the dosed water as it bubbles through the packed tower 80. The temperature of the gas stream as it exits the packed tower 80 will typically be around the same temperature as the water, typically around 20°C.

The presence of an oxidant in the dosed water converts the carbon monoxide into carbon dioxide. Accordingly, by the time the gas stream exits the packed tower 80, the amount of carbon monoxide has been decreased by the oxidising environment created after the combustion chamber 30 to around C2 (which is less than Ci).

Through this approach, the amount of carbon monoxide and NOx present in the effluent stream when it exits the packed tower 80 is significantly lower than the amounts present when operating an existing abatement apparatus under stoichiometric conditions.

A control system 110 measures the amount of carbon monoxide and/or NOx exiting the abatement apparatus 10 using sensors couple with the outlet 130.

The control system 11 uses that information to adjust the ratio of fuel to oxygen in the combustion chamber 30 and/or the amount of oxidant in the water to control the amount of carbon monoxide and/or NOx exiting the abatement apparatus 10.

Abatement Apparatus - Alternative Embodiment

Figure 4 illustrates schematically the main components of an abatement apparatus 10’ according to one embodiment. The abatement apparatus 10’ has an inlet head assembly 20’ which is fluidly coupled with a source of an effluent gas stream 90’ from a processing tool and typically with sources of a fuel (such as methane) and an oxidant (such as air). The inlet head assembly 20’ is fluidly coupled with a downstream combustion chamber 30’ of a radiant burner. The combustion chamber 30’ is fluidly coupled with the sources of the fuel and the oxidant. The combustion chamber 30’ is made of two sections. In particular, there is provided pair of foraminious, inwardly-fired combustors of which the first or upstream burner 30A is supplied with a fuel-rich mixture of methane and air so as to generate a hot reducing environment for the destruction of N2O without producing significant NOx. A second or downstream burner 30B’, placed in series or downstream of the upstream burner 30A’, is operated in a fuel-lean manner to oxidise any unburned methane and carbon monoxide. Although in this embodiment, the two sections are separate burners or combustors, they could be provided as a single burner or combustor supplied with the appropriate different ratios of fuel-air mixture (such as via separate plenums feeding the respective burners). The combustion chamber 30’ is fluidly coupled with a downstream weir chamber 40’. Operation

In operation, the effluent gas stream 90’ is received by the inlet head assembly 20’ and is typically pre-mixed with nitrogen and with air. The resultant mixture is then typically further mixed with the fuel. This mixture is then injected into the combustion chamber 30’ via inlets in the inlet head assembly 20’. The inlets are typically provided with concentric annular injectors which surround the mixture entering the combustion chamber 30’ with fuel.

The wall of the upstream burner 30A’ is porous and the mixture of fuel and oxygen is forced under pressure through its wall and combusted within the upstream burner 30A’. In this embodiment, the mixture of fuel and air is 18 standard litres per minute (SLM) of methane with 115 SLM of air.

As was illustrated in Figure 3, in this embodiment the ratio of fuel to oxidant supplied to the upstream burner 30A’ is adjusted to a non-stoichiometric ratio. In particular, the ratio of fuel to oxidant is changed to make the mixture fuel-rich and depleted in oxygen. Making the upstream burner 30A’ fuel-rich provides a reducing environment, which significantly decreases the amount of NOx produced within the upstream burner 30A to C2 (which is less than C1 ), but significantly increases the amount of carbon monoxide produced in the upstream burner 30A to C3 (which is greater than C1 ), as shown in Figure 3.

The effluent stream and combustion by-products exit the upstream burner 30A and enter the downstream burner 30B’. The wall of the downstream burner 30B’ is porous and the mixture of fuel and air is forced under pressure through its wall and combusted within the downstream burner 30B’. In this embodiment, the mixture of fuel and air is 18 standard litres per minute (SLM) of methane with 290 SLM of air. Making the downstream burner 30B’ fuel-lean provides an oxidising environment, which significantly decreases the amount of carbon monoxide produced. Accordingly, carbon monoxide within the gas stream flowing through the downstream burner 30B’ reacts with the excess oxygen in the downstream burner 30B’. Accordingly, by the time the gas stream exits the downstream burner 30B’, the amount of carbon monoxide has been decreased by the oxidising environment created by the downstream burner 30B’ to around C2 (which is less than C1 ).

Through this approach, the amount of carbon monoxide and NOx present in the effluent stream when it exits the abatement apparatus 10’ is significantly lower than the amounts present when operating an existing abatement apparatus under stoichiometric conditions.

A control system (not shown) measures the amount of carbon monoxide and/or NOx exiting the abatement apparatus 10’ using sensors couple with its outlet.

The control system uses that information to adjust the ratio of fuel to oxygen in the upstream burner 30A and/or downstream burner 30B’ to control the amount of carbon monoxide and/or NOx exiting the abatement apparatus 10’.

Abatement Apparatus - Further Embodiment

Referring to Figure 5, an abatement apparatus (in this example a radial burner) 10”, comprising a co-axial injector 11”, is shown for removing noxious

substances from an effluent stream 90”. The abatement apparatus 10” comprises a combustion region in which a fuel gas 34” can be burnt for combusting the effluent stream 90”. In this arrangement the combustion region is formed by a combustion chamber 30” surrounded by a generally cylindrical wall 32”. The wall 32” is porous to allow passage of fuel gas through it into the combustion chamber 30” for burning on the inner surface of the wall 32”. Fuel gas 34” is introduced to an outer chamber 36” through inlet 38” and passes through the wall 32”. The wall 32” may form a right circular cylinder, elliptic cylinder, parabolic cylinder, or hyperbolic cylinder such that the wall 32” forms a surface on which fuel gas 34” can burn radiating hear radially inwardly and combusting the effluent stream 90” producing a flame 42”. The fluid stream 90” containing at least one noxious substance is introduced into the combustion chamber 30” through an inlet 48” and is combusted by contact with a hot reaction zone near the surface of the wall 32”. In this embodiment the ratio of fuel to oxidant of the fuel gas 34” supplied to the upstream burner outer chamber 36” is adjusted to a non-stoichiometric ratio. In particular, the ratio of fuel to oxidant is changed to make the mixture fuel-rich and deplete oxygen. Making the fuel gas 34” fuel-rich provides a reducing

environment, which significantly decreases the amount of NOx produced within the upstream portion of the combustion chamber 30” to C2 (which is less than C1 ), but significantly increases the amount of carbon monoxide produced in the upstream portion of the combustion chamber 30” to C3 (which is greater than C1 ), as shown in Figure 3.

A weir chamber 40” produces a weir of cold liquid 46” (typically water) for dissolving constituents of the combusted fluid stream and for washing away particulate matter. The cold liquid 46” also cools fluid exhausted from the combustion chamber 30” so that it can be conveniently disposed.

The injector 11” is shown in simplified form in Figure 5 and is located below the wall 32” and between the combustion chamber 30” and the weir chamber 44”. In use the injector 11” injects oxygen (or an oxygen-rich fuel mixture) as an annular flow 12” although only a semi-circular portion of which is shown in Figure 5. The flow 12” provides an oxidising environment, which significantly decreases the amount of carbon monoxide produced. The flow 12” can also act as a pilot to ignite the fuel gas 34” in the combustion chamber 30”. Accordingly, carbon monoxide within the gas stream flowing through the flow 12” reacts with the excess oxygen in the flow 12”. Accordingly, by the time the gas stream exits the injector 11”, the amount of carbon monoxide has been decreased by the oxidising environment created by the flow 12” to around C2 (which is less than C1 ). In experiments, 20 SLM of oxygen is provided through the injector 11” and leads to a reduction in NOx with a slight positive effect on CF_4.

It will be appreciated that features of the three embodiments may be combined. For example, components of the upstream burner 30A / downstream burner 30B arrangement may be combined with components of the weir chamber 40 / sump 70 / packed tower 80 arrangement and/or combined with components of the injector 1 1” arrangement.

It will be appreciated that although the above embodiment describes an abatement reaction involving combustion of fuel and an oxidant and the creation of combustion by-products, this technique is applicable to other reactions where an excess of one by-product is created in order to minimise the creation of another by-product, and that the amount of the excess by-product is decreased in a subsequent reaction elsewhere in the abatement apparatus.

Embodiments provide a method for optimising the abatement of process gases while maintaining low emissions of NOx, carbon monoxide, hydrogen and other legislated or unwanted by-products. It is increasingly required to produce abatement equipment which continues to achieve high performance on process gases (CF₄, N2O, SiH₄, SF6, NF3) while needing to achieve very low

concentrations of legislated combustion gases such as CO, CH₄, NOx. In particular, it is increasingly required to provide extremely low emissions targets on typical combustion gases such as: CO - requires to be oxidised to CO2; NO - reduced to N2; NO2 - reduced to N2; CH₄ - oxidised to water and CO2; C2hl₄ - oxidised to water and CO2; H2 - oxidised to water; N2O - reduced to N2. These gases require two distinct environments to minimise their formation or to optimise their destruction.

Accordingly, the intention of embodiments is to generate two distinct reaction zones within the abatement system. In particular, embodiments provide two distinct environments within the abatement apparatus, a primary zone which is reducing or oxidising and a secondary post combustion zone which is

complementary to the first zone. In one embodiment, there is a reducing combustion zone and oxidising post combustion zone. In another embodiment, there is an oxidising combustion zone and a reducing post combustion zone. In one embodiment, the abatement combustion system is setup with oxidant / fuel (/ hydrogen) injects within the nozzle, this mixture is intended to minimise the formation of oxygen-containing side products such as NO, NO2, N2O; however in a reducing environment compounds such as CO will be generated. The post combustion / wet stage of the abatement system is set up as an oxidising environment, this could mean hydrogen peroxide dosing in the water or ozone dosing in the air; both these have been shown to efficiently oxidise CO.

In another embodiment, the abatement combustion system is setup with an oxidising flame; the post combustion / wet stage is setup with a reducing flame.

Embodiments provide a means of abating nitrous oxide which involves two-stage destruction of the target gas by reduction in a upper burner operated in a fuel-rich environment followed by oxidation of unburned fuel and carbon monoxide in a lower burner running fuel-lean. This avoids the generation of NOx which accompanies current methods of N2O abatement.

As mentioned above, the abatement of N2O at high (>95%) efficiency in current inwardly-fired combustors leads to high NOx and CO/CH₄ emissions.

Experiments have demonstrated that pre-mixing N2O into a fuel-rich CH₄-air mixture and burning the mixture within the burner pad, with excess air added via the inlet nozzle achieves high DRE and low NOx and CO/CH₄ emissions. This is not production worthy as any particulate matter would block the burner pad.

Embodiments involve creating a fuel-rich zone ahead of a lean zone and injecting the process gas into the fuel-rich zone.

Embodiments provide a plurality of zones with dramatically different combustion conditions which can be exploited to drive the chemical reactions which occur in each region to decrease the generation of undesirable by-products. In embodiments, the upper burner could be run at different firing rates but with the stoichiometry the same to avoid powder build up. Alternatively, the upper burner could be run fuel-lean and the lower one fuel-rich. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

10; 10’; 10” abatement apparatus 1 1 injector

12 flame

20; 20’ inlet head assembly

30; 30’; 30” combustion chamber 30A’ upstream burner

30B’ downstream burner

32” wall

34” fuel gas

36” outer chamber

38” inlet

40; 40’; 40” weir chamber 42” flame

46” liquid

48” inlet

50 water curtain

60 spray

70 sump

80 packed tower

90; 90’; 90” effluent gas stream 100 oxidant generator 1 10 control system 130 outlet

Claims

1. A method, comprising:

supplying an initial reaction zone of an abatement apparatus with non-stoichiometric amounts of initial reactants to perform an initial abatement reaction under non-stoichiometric conditions to produce a first reaction product at a concentration which is lower than a second reaction product; and

supplying a subsequent reaction zone of said abatement apparatus with a subsequent reactant to perform a subsequent abatement reaction to lower said concentration of said second reaction product.

2. The method of claim 1 , wherein said initial abatement reaction abates an effluent stream during reaction of a first initial reactant with a second initial reactant under said non-stoichiometric conditions.

3. The method of claim 1 or 2, wherein said non-stoichiometric conditions comprise reacting said first initial reactant with said second initial reactant at a first initial reactant/second initial reactant ratio which is greater than 1 .1 : 1 .

4. The method of any preceding claim, wherein said non-stoichiometric

conditions comprise reacting said first initial reactant with said second initial reactant at a first initial reactant/second initial reactant ratio which is greater than 1.3:1.

5. The method of any preceding claim, wherein said non-stoichiometric

conditions produce said first reaction product at a concentration which is lower than under stoichiometric conditions.

6. The method of any preceding claim, wherein said non-stoichiometric conditions produce said second reaction product at a concentration which is higher than under stoichiometric conditions.

7. The method of any preceding claim, wherein said abatement reaction

comprises a combustion reaction.

8. The method of any preceding claim, wherein said first reaction product and said second reaction product comprise combustion products.

9. The method of any preceding claim, wherein said first reaction product comprises NOx and said second reaction product comprises CO.

10. The method of any preceding claim, wherein said supplying said initial reaction zone of said abatement apparatus provides an excess of said first initial reactant.

11. The method of claim 10, wherein said excess of said first initial reactant provides one of a reducing and an oxidising environment within said initial reaction zone.

12. The method of any preceding claim, wherein said first initial reactant

comprises one of a fuel and an oxidant.

13. The method of any preceding claim, wherein said supplying said initial reaction zone of said abatement apparatus provides a depletion of said second initial reactant.

14. The method of claim 13, wherein said depletion of said second initial

reactant provides one of a reducing and an oxidising environment within said initial reaction zone.

15. The method of any preceding claim, wherein said second initial reactant comprises another of an oxidant and a fuel.

16. The method of any preceding claim, wherein said subsequent abatement reaction reacts a third reactant with said second reaction product to lower said concentration of said second reaction product.

17. The method of claim 16, wherein when said initial abatement reaction provides a reducing environment within said initial reaction zone and said supplying said third reactant provides an oxidising environment within said subsequent reaction zone.

18. The method of claim 16 or 17, wherein said supplying said third reactant provides an excess of oxygen.

19. The method of any one of claims 16 to 18, wherein said third reactant comprises at least one of oxygen, ozone and peroxide.

20. The method of any one of claims 16 to 19, wherein when said initial

abatement reaction provides an oxidising environment within said initial reaction zone and said supplying said third reactant provides a reducing environment within said subsequent reaction zone.

21. The method of any one of claims 16 to 20, wherein said supplying said third reactant provides an excess of hydrogen.

22. The method of any one of claims 16 to 21 , wherein said third reactant comprises a fuel.

23. The method of any preceding claim, wherein said initial reaction zone is located at a position within said abatement apparatus which is hotter than said subsequent reaction zone.

24. The method of any preceding claim, wherein said initial reaction zone is located upstream of said subsequent reaction zone.

25. The method of any preceding claim, wherein said initial reaction zone is located proximate a combustion chamber of said abatement apparatus.

26. The method of any preceding claim, wherein said initial reaction zone is located within said combustion chamber.

27. The method of any preceding claim, wherein said subsequent reaction zone is located within said combustion chamber.

28. The method of any preceding claim, wherein said subsequent reaction zone is located downstream of said initial reaction zone.

29. The method of any preceding claim, wherein said subsequent reaction zone is located distal said combustion chamber of said abatement apparatus.

30. The method of any preceding claim, wherein said subsequent reaction zone is located downstream of a quench of said abatement apparatus.