Field

[001 ] The present invention relates to abatement apparatus including scraper cages, and to scraper cages for abatement apparatus. The present invention also relates to methods of assembling a combustion-type abatement apparatus.

Background

[002] Abatement apparatus remove components of a process gas stream, e.g. compounds of a semiconductor or flat panel display manufacturing process, so that the abated gas stream can be more safely released to the outside environment.

[003] In a combustion-type abatement apparatus, which use combustion to remove compounds from the process gas stream, the process gas is fed into the flame tube of a combustion chamber, by one or more inlet systems or manifolds, via nozzles. Typically, a combustion-type abatement apparatus will comprise multiple inlet systems, e.g. two, which are each configured to supply gas to the flame tube via multiple nozzles, e.g. six.

[004] A scraper cage, usually cylindrical in shape and comprising a set of elongate scraping blades bounded by rims at each end, is arranged within a flame tube and is configured to rotate reciprocally within the flame tube about its longitudinal axis, in use, to dislodge or remove process components, e.g. powder biproducts, which are deposited on the inner surface of the flame tube. In normal use, the scraper cage should not contact the wall of the flame tube (aside from where it is attached thereto). Typically, a process gas flows from a top end of the flame tube to a bottom end thereof, and a burner of the abatement apparatus is located above or towards a top end of the combustion chamber.

[005] The present inventors have, however, observed failures in the flame tubes of existing combustion-type abatement apparatus. [006] In particular, rupturing of flame tubes of abatement apparatus has been observed, i.e. holes occurring in the flame tubes between the chamber defined by the flame tube and the exterior of the flame tube.

[007] These issues have resulted in more frequent and prolonged downtime of abatement apparatus, and the need to repair or replace components thereof more frequently.

[008] The present invention aims to address these and other problems with the prior art.

Summary

[009] Accordingly, in an aspect, the present invention provides a combustion-type abatement apparatus including a burner, an outlet, a flame tube located substantially therebetween, and a scraper cage located within said flame tube with a clearance therebetween. The scraper cage has a burner end which is proximal to the burner of the abatement apparatus, and an opposing outlet end. The outlet end of the scraper cage is thus distal to the burner. The scraper cage is configured to rotate about a rotational axis. The clearance between the flame tube and the scraper cage increases towards the outlet end of the scraper cage.

[010] Thus, the clearance may increase along the length of the scraper cage being greatest toward the outlet end of the scraper cage. Typically, the minimum clearance between the scraper cage and the flame tube is proximal the burner end of the scraper cage. Typically, the maximum clearance between the scraper cage and the flame tube is proximal the outlet end of the scraper cage.

[011 ] The clearance may refer to a radial distance between an outer surface scraper cage and an opposing inner surface of the flame tube. Typically, the radial distance between a rotational circumference of the scraper cage and an inner surface of the flame tube. The rotational circumference referring to the circumference of an imaginary circle formed by the path of the outermost point of the scraper cage in a given plane tangential to the rotational axis of the scraper cage if the scraper cage were to complete full rotation about said rotational axis.

[012] Analysis by the present inventors revealed that the reported ruptures in flame tubes were the result of excessive corrosion. They have determined that this is a result of the protective coatings on the inner surfaces of walls, for example chromium oxide, being compromised. The underlying cause of this, however, has not been established until now.

[013] Several potential reasons for flame tube ruptures have been considered by the present inventors, including incorrect equipment (e.g. flame tube material not correct for combustion temperatures), errors in manufacture (e.g. assembly drawings not adhered to, or insufficient stack up tolerance causing scraper cage interference), or errors in operation (e.g. flame tube thinning over time, or excessive oxidation of the flame tube surface).

[014] Upon investigation, the present inventors have found that non-uniform heating within an abatement apparatus flame tube may cause uneven thermal load and thermal expansion of the components located therein, and in particular the scraper cage. Such uneven heating may occur, for instance, when only a portion, e.g. half, of the burners in the flame tube are ignited, particularly if the ignited burners are not evenly distributed about the axis of the scraper cage.

[015] Importantly, it has been found that known scraper cages may deform asymmetrically in these circumstances, due to uneven thermal load and expansion, and that this may lead to bending of the scraper cage and, ultimately, contact between the scraper cage and the flame tube.

[016] For instance, the scraper cage may comprise a plurality of scraper surfaces located on or forming part of one or more scraping blades, and one or more of the scraping blades may deform due to localised heating, causing that scraping blade or another scraping blade, or the outlet (downstream) end of the scraper cage (i.e. that end which is typically lowermost in the flame tube), to contact the protectively coated circumferential inner surface of the flame tube as the scraper cage rotates back and forth.

[017] Thus, it has been determined that contact between the scraper cage and flame tube as a result of non-uniform heating may compromise the protective coating of the flame tube, markedly accelerating corrosion of the flame tube.

[018] This leads to those failures described above, which are now addressed by the present invention.

[019] The apparatus of the present invention is advantageously configured so that the clearance between the flame tube and the scraper cage thereof is greatest towards the outlet end of the scraper cage. Thus, the present invention accommodates potential thermal expansion of the scraper cage within the flame tube, particularly towards the outlet end thereof. Therefore, the risk of compromising any protective coatings on an inner surface of the flame tube, which would lead to excessive corrosion and eventual rupture, is also minimised or avoided.

[020] Often, gases processed by abatement apparatus are strong oxidisers, and so the preservation of protective coatings such as chromium oxide on the inner surfaces of the flame tube is critical for the life of the flame tube and effective use of abatement apparatus.

[021 ] The structural strength and bending resilience of the scraper cage is also improved.

[022] As used herein, the term “outlet” refers to an exhaust or similar through which a process gas typically passes once it has passed through the flame tube, typically in a generally downward direction. In embodiments, the outlet may be a conduit through which a process gas passes towards further treatment in the abatement apparatus.

[023] In embodiments, when the scraper cage rotates, a circumferential inner surface of the flame tube may be radially furthest from an outermost radial surface of the scraper cage towards the outlet end of the scraper cage. [024] Typically, the flame tube and scraper cage of the abatement apparatus are substantially elongate, each having a longitudinal axis. Typically, the longitudinal axis of the flame tube and the longitudinal axis of the scraper cage are substantially coincident.

[025] In embodiments, the flame tube or scraper cage may be substantially cylindrical.

[026] In embodiments, the diameter of the scraper cage may be greater towards the burner end than towards the outlet end thereof. In other words, the scraper cage may be generally tapered.

[027] Additionally, or alternatively, an inner diameter of the flame tube may be greater towards the outlet end than towards the burner end of the scraper cage.

[028] In use, one area of the typically cylindrical flame tube may commonly be much hotter than another area because of the configuration of the inlets of the combustiontype abatement apparatus, and so the portion of the scraper cage in or near the hotter area of the flame tube will expand differently to the remainder of the scraper cage.

[029] The present inventors have determined that thermal expansion of a scraper cage in both the radial and axial directions occurs. In the abatement apparatus of the present invention, a decrease in the diameter of the scraper cage towards the outlet end and/or an increase in the inner diameter of the flame tube towards the outlet end, both resulting in an increase in the clearance between the flame tube and the scraper cage towards the outlet end of the scraper cage, reduces the likelihood of any deformation of the scraper cage resulting in contact between the scraper cage and the flame tube.

[030] In embodiments, the scraper cage may narrow in diameter along its length towards the outlet end such that an outermost radial surface of the scraper cage is radially furthest from the flame tube towards the outlet end. In embodiments, the scraper cage may narrow substantially uniformly towards the outlet end thereof. [031 ] In other words, the diameter of the scraper cage may be greater towards the burner end and smaller towards the outlet end when not in use as well as during use. Thus, particular use conditions may not be required in order to minimise the risk of contact between the scraper cage and the flame tube of the abatement apparatus.

[032] In embodiments, the scraper cage may include a plurality of scraper surfaces extending between the burner end and the outlet end. Wherein a radially outermost point on a scraper surface proximal the outlet end of the scraper cage is located radially inward of a minimum bounding circle formed about the outward facing scraper surfaces proximal the burner end of the scraper cage and/or wherein, in use, the greatest rotational circumference of the scraper surfaces is proximal the burner end of the scraper cage and the smallest rotational circumference of the scraper surfaces is proximal the outlet end of the scraper cage.

[033] For the purposes of the invention, the rotational circumference is the circumference of an imaginary circle formed by the path of the outermost point of the scraper surface in a given plane tangential to the rotational axis of the scraper cage if the scraper cage were to complete full rotation about said rotational axis.

[034] The minimum bounding circle being the smallest imaginary circle which can contain all of the scraper surfaces of the scraper cage in a given plane perpendicular to the longitudinal axis of the scraper cage.

[035] In embodiments, the scraper cage may narrow at an angle of around 5 degrees [-2 degrees I +5 degrees] between the burner end and the outlet end thereof.

[036] In embodiments, the scraper cage may be generally frustoconical in shape.

[037] In embodiments, the scraper cage may have a substantially trapezoidal longitudinal cross section. In embodiments, the scraper cage may have a longitudinal cross section substantially in the shape of an inverted isosceles trapezoid. [038] In embodiments, the scraper cage may be configured such that the diameter of the scraper cage is greater towards the burner end and smaller towards the outlet end only when the scraper cage is rotating, in use. Thus, in embodiments, the diameter of the scraper cage towards the burner end may be substantially the same as its diameter towards the outlet end when the scraper cage is not in use, i.e. is not rotating within a combustor flame tube.

[039] In embodiments, the scraper cage may be configured such that the forces acting on the scraper cage in use as it rotates within the flame tube cause the diameter of the scraper cage towards the outlet end to reversibly decrease compared to its arrangement when not in use. For example, bending or contraction of the scraper cage, or similar, may be in reaction to contact with compounds deposited on a radially inwardly facing wall the flame tube. In embodiments, the diameter of the scraper cage along substantially its whole length may decrease when the scraper cage rotates in use. The scraper cage may thus have at least a portion of resilient flexibility which allows the diameter of the scraper cage to reversibly change between use and nonuse states.

[040] In embodiments, the scraper cage may comprise one or more scraping blades which extend substantially between the burner end and outlet end of the scraper cage. In embodiments, the scraper cage may comprise a plurality of scraping blades.

[041 ] In embodiments, the or each scraping blade may comprise one or more scraper surfaces.

[042] In embodiments, the scraping blades may be substantially evenly spaced about the circumference of the scraper cage. A space between the scraping blades of the scraper cage, i.e. the interior of the scraper cage, may be fluidly connected to the exterior of the scraper cage.

[043] In embodiments, the or each scraping blade may be arranged such that an outermost surface of the or each scraping blade is radially furthest from the rotational axis of the scraper cage towards the burner end of the scraper cage. [044] In embodiments, the or each scraping blade may have a corresponding burner end and outlet end; and the or each scraping blade may be configured such that, in use, the rotational circumference of the scraper blade is greatest towards the burner end of the blade and shortest towards the outlet end of the blade.

[045] For the purposes of the invention, the rotational circumference is the circumference of an imaginary circle formed by the path of the outermost point of the scraping blade in a given plane tangential to the rotational axis of the scraping blade if the scraping blade were to complete full rotation about said rotational axis.

[046] In embodiments, the rotational axis of the or each scraping blade may be substantially parallel to the longitudinal axis thereof. In embodiments, the rotational axis of the or each scraping blade is not coaxial with the longitudinal axis thereof.

[047] In embodiments, the or each scraping blade may be substantially linear, i.e. straight, and angled inwardly, from the burner end towards the outlet end of the scraper cage, so that the diameter of the scraper cage narrows towards the outlet end thereof. In other words, the or each scraping blade may be inclined with respect to the longitudinal axis of the scraper cage and the degree of incline is substantially uniform between the burner end and the outlet end of the scraper cage.

[048] This configuration is particularly advantageous because, prior to thermal expansion of the scraper cage, the or each scraping blade is inclined with respect to the flame tube. In other words, a bottom end of the or each scraping blade may be positioned further from the flame tube than a top end of the scraping blade. Thus, as the scraper cage heats up, typically unevenly, i.e. one side of the scraper cage gets warmer than the other, thermal expansion causes the scraper cage to deform such that at least one said scraping blade is substantially parallel to the flame tube. For example, the thermal expansion of a first scraping blade may cause a second scraping blade, e.g. one which is substantially opposite to the first scraping blade, to become substantially parallel with the flame tube. This deformation characteristic improves removal of deposited compounds within the flame tube. [049] In embodiments, the or each scraping blade may be inclined by around 5 degrees [-2 degrees I +5 degrees]. In embodiments, the or each scraping blade may be inclined relative to the longitudinal axis of the scraper cage.

[050] In embodiments, the scraper cage may comprise a driveable rim at or towards the burner end and a closing rim at or towards the outlet end. The scraper cage may thus be formed collectively by the driveable rim, the closing rim and the or each scraping blade. In embodiments, the driveable rim and/or the closing rim may be permanently fixed to the or each scraping blade, or may be removably fixed thereto.

[051 ] In embodiments, the driveable rim may be attachable to the flame tube of the abatement apparatus, or another part of the abatement apparatus, to facilitate axial rotation of the scraper cage in use. In embodiments, the abatement apparatus comprises a drive for driving rotation of the scraper cage, in use. In embodiments, the closing rim may not be directly connected to the flame tube or another part of the abatement apparatus.

[052] As used herein, the term “axial rotation” refers to the scraper cage rotating about its longitudinal axis in a first, typically clockwise, direction and/or second, typically anticlockwise, direction. Preferably, the scraper cage is configured to rotate reciprocally between clockwise and anticlockwise directions. The rotational axis of the scraper cage may be generally coaxial with the longitudinal axis of the scraper cage.

[053] Typically, the scraper cage may be arranged to reciprocally rotate by approximately 50 to 60 degrees in each of the first and second directions. In embodiments, the scraper cage may be arranged to rotate substantially through 360 degrees. In embodiments, the scraper cage may be arranged to rotate substantially continuously in one direction. Typically, the minimum rotation angle will depend on the number of scraping blades present. Thus, the angle of rotational movement of the scraper blade may be expressed as 360 degrees divided by the number of scraping blades of the scraper cage, in order that substantially the entire circumference of the inwardly facing surface of the flame tube is scraped, in use. For example, the scraper cage may comprise two scraping blades and the scraper cage may be arranged to rotate substantially through at least 180 degrees. In another example, the scraper cage may comprise four scraping blades and the scraper cage may be arranged to rotate through at least 90 degrees.

[054] In embodiments, the scraper cage may be arranged such that, in use, it has an average rotational velocity of between around 5.2 radian per second (rad/s) to around 7.6 rad/s, more preferably around 6.4 rad/s.

[055] In embodiments, the scraper cage may be arranged such that, in use, it has a maximum rotational velocity of between around 10.4 rad/s to around 15.2 rad/s.

[056] In embodiments, the scraper cage may be arranged such that, in use, it rotates through substantially 60 degrees in around 0.13 to 0.21 seconds, more preferably in around 0.17 seconds.

[057] In embodiments, the closing rim may have a diameter which is smaller than the diameter of the driveable rim.

[058] In embodiments, the closing rim may have a diameter which is smaller by approximately 20mm or less, or by approximately 10mm or less than the diameter of the driveable rim, when the scraper cage rotates in use. In embodiments, the difference in diameter between the driveable rim and the closing rim may be around 5mm or less when the scraper cage rotates in use. In practise, the diameter of the outlet end of the scraper cage must be sufficiently less than the diameter of the scraper cage at the burner end so as to avoid contact with the flame tube.

[059] In embodiments, the or each scraping blade may have a substantially V-shaped transverse cross-section. Therefore, the or each scraping blade is more resilient to bending stresses and the like during use. In embodiments, the intersection of the or each V-shaped scraping blade may point substantially inwardly towards the longitudinal axis of the scraper cage. Thus, the or each scraping blade may comprise two scraper surfaces. In embodiments, the or each scraping blade may comprise two scraper surfaces, each of which is configured to scrape in a direction of rotation of the scraper cage. [060] In embodiments, the or each scraping blade may taper in width between the burner end and outlet end of the scraping blade, and thus between the burner end and the outlet end of the scraper cage.

[061 ] In embodiments, the width of the or each scraping blade may reduce at a region proximal to the burner end thereof, and the width of the or each scraping blade may be substantially constant between the outlet end thereof and the said proximal region.

[062] In embodiments, the or each scraping blade may be substantially curved. In other words, the or each scraping blade may be attached to the driveable rim in a first plane which intersects the longitudinal axis of the scraper cage, and may be attached to the closing rim of the scraper cage in a second, different plane which intersects the longitudinal axis of the scraper cage.

[063] In embodiments, the scraper cage may comprise a plurality of scraping blades which are arranged to form a substantially helical, i.e. spiral, arrangement.

[064] Typically, as described, the scraper cage is arranged to rotate in a first direction and in a second opposite direction, i.e. clockwise and anticlockwise about said longitudinal axis.

[065] In embodiments, the scraper cage may be configured such when the scraper cage rotates in the first direction, in use, the length of the scraper cage is shorter than when the scraper cage rotates in the second direction, or vice versa.

[066] In embodiments, the scraper cage may comprise a plurality of scraping blades which together form a substantially helical or spiral arrangement, and may be configured such that the length of the scraper cage changes as the scraper cages rotates, alternately, in clockwise and anticlockwise directions.

[067] In embodiments, the scraper cage may comprise a plurality of scraping blades which together form a substantially helical or spiral arrangement, and the scraper cage may be configured such that when it rotates in the first direction, in use, the diameter of the scraper cage, for example at a mid-region thereof, is greater than when the scraper cage rotates in the second direction, or vice versa. Thus, in embodiments, the scraper cage may be configured such that the clearance between the scraper cage and the flame tube is sufficient to avoid or minimise the risk of contact between the scraper cage and the flame tube when the scraper cage is at its greatest diameter.

[068] In embodiments, the scraper cage may further comprise one or more braces or struts arranged between the burner end and the outlet end. Advantageously, the or each brace minimises the risk that the or each scraping blade buckles during use.

[069] In embodiments, at least one said brace, preferably the or each brace, may be in the form of a circumferential ring which is attached to an outer surface or an inner surface of the or each scraping blade. In embodiments, at least one said brace may be in the form of a supporting strut which is attached to an inner surface of one or more scraping blades. For example, a supporting strut may extend between opposing scraping blades of the scraper cage.

[070] In a further aspect, the invention provides a flame tube for a combustion-type abatement apparatus. The flame tube has a burner end and an outlet end and has a radially inwardly facing wall extending therebetween. The flame tube further comprising an exclusion zone extending radially inwardly from the inward facing wall of the tube, the exclusion zone extending radially inwardly to a greater extent proximal the outlet end of the flame tube and to a lesser extent proximal the burner end of the flame tube.

[071 ] The exclusion zone is a volume surrounding the inner surface of the burner tube which is free from other components of the abatement apparatus, when the burner tube is in-situ in the abatement apparatus, whilst the burner tube is at ambient temperature, e.g. when the abatement apparatus is not in use. In particular, any scraper cage may be outside the exclusion zone while inside the burner tube. The exclusion zone may be generally toroidal in shape, in particular a right-angled trapezoid toroid. [072] For the purposes of the invention ambient temperature may be about 21 °C. Unless otherwise stated, configurations disclosed herein refer to configurations at ambient temperature.

[073] The flame tube may house a scraper cage having a burner end and an opposing outlet end; wherein the outer diameter of the scraper cage narrows along its length towards the outlet end (e.g., it is tapered), and/or wherein the internal diameter of the flame tube extends along its length, such that the scraper cage does not enter the exclusion zone of the flame tube when the abatement apparatus is not in use.

[074] Thus, the flame tube may be configured such that, when the scraper cage is contained therein and rotates, the circumferential inner surface of the flame tube is radially furthest from an outermost radial surface of the scraper cage towards the outlet end of the scraper cage.

[075] In a further aspect, the present invention provides a scraper cage for a flame tube of combustion-type abatement apparatus. The scraper cage having a burner end, an outlet end, and a plurality of scraper surfaces extending therebetween, wherein a radially outermost point on a scraper surface proximal the outlet end of the scraper cage is located radially inward of a minimum bounding circle formed about the outward facing scraper surfaces proximal the burner end of the scraper cage and/or wherein, in use, the greatest rotational circumference of the scraper surfaces is proximal the burner end of the scraper cage and the smallest rotational circumference of the scraper surfaces is proximal the outlet end of the scraper cage.

[076] Wherein, for the purposes of the invention, the rotational circumference is the circumference of an imaginary circle formed by the path of the outermost point of the scraper surface in a given plane tangential to the rotational axis of the scraper cage if the scraper cage were to complete full rotation about said rotational axis.

[077] The minimum bounding circle being the smallest imaginary circle which can contain all of the scraper surfaces of the scraper cage in a given plane perpendicular to the longitudinal axis of the scraper cage. [078] Preferably, the scraper cage is configured such that, in use, when the scraper cage rotates, a radially outermost surface of the scraper cage is furthest from an inner circumferential surface of the flame tube towards the outlet end of the scraper cage.

[079] Preferably the longitudinal axis of the scraper cage and the rotational axis of the scraper cage are substantially coaxially aligned.

[080] In embodiments, the scraper cage may be configured such that, when the scraper cage rotates, the outermost radial surface of the scraper cage is radially furthest from the rotational axis of the scraper cage towards the burner end thereof.

[081 ] In embodiments, the scraper cage may narrow in diameter along its length towards the outlet end. In other words, the scraper cage may be generally tapered. In embodiments, the scraper cage may narrow substantially uniformly towards the outlet end.

[082] In embodiments, the scraper cage my narrow at an angle of around 5 degrees [-2 degrees I +5 degrees],

[083] In embodiments, the scraper cage may be substantially frustoconical in shape.

[084] In embodiments, the scraper cage may have a substantially trapezoidal longitudinal cross section. In embodiments, the scraper cage may have a longitudinal cross section substantially in the shape of an inverted isosceles trapezoid.

[085] In embodiments, the scraper cage may be configured such that the diameter of the scraper cage is greater towards the burner end and smaller towards the outlet end only when the scraper cage is rotating, in use. Thus, in embodiments, the diameter of the scraper cage towards the burner end may be substantially the same as its diameter towards the outlet end when the scraper cage is not in use, i.e. is not rotating within a combustor flame tube.

[086] The scraper cage may be configured such that the forces acting on the scraper cage in use as it rotates within a flame tube cause the diameter of the scraper cage towards the outlet end to reversibly decrease compared to its arrangement when not in use. For example, bending or contraction of the scraper cage, or similar, may be in reaction to contact with powder biproducts located on a radially inwardly facing wall the flame tube. In embodiments, the diameter of the scraper cage along substantially its whole length may decrease when the scraper cage rotates in use. The scraper cage may thus have at least a portion of resilient flexibility which allows the diameter of the scraper cage to reversibly change between use and non-use states.

[087] In embodiments, the scraper cage may comprise one or more scraping blades which extend substantially between the burner end and outlet end of the scraper cage. In embodiments, the scraper cage may comprise a plurality of scraping blades.

[088] In embodiments, the or each scraping blade may comprise one or more scraper surfaces.

[089] In embodiments, the plurality of scraping blades may be substantially evenly spaced about the circumference of the scraper cage. A space between the scraping blades of the scraper cage, i.e. the interior of the scraper cage, may be fluidly connected to the exterior of the scraper cage.

[090] In embodiments, the or each scraping blade may be arranged such that an outermost surface of the or each scraping blade is radially furthest from an inner circumferential surface of the flame tube towards the outlet end of the scraper cage.

[091 ] In embodiments, the or each scraping blade may be arranged such that an outermost surface of the or each scraping blade is radially furthest from the rotational axis of the scraper cage towards the burner end of thereof.

[092] In embodiments, the or each scraping blade may have a corresponding burner end and outlet end; and the or each scraping blade may be configured such that, in use, the rotational circumference of the scraper blade is greatest towards the burner end of the blade and shortest towards the outlet end of the blade. [093] For the purposes of the invention, the rotational circumference is the circumference of an imaginary circle formed by the path of the outermost point of the scraping blade in a given plane tangential to the rotational axis of the scraping blade if the scraping blade were to complete full rotation about said rotational axis.

[094] In embodiments, the rotational axis of the or each scraping blade may be substantially parallel to the longitudinal axis thereof. In embodiments, the rotational axis of the or each scraping blade is not coaxial with the longitudinal axis thereof.

[095] In embodiments, the or each scraping blade may be inclined by around 5 degrees [-2 degrees I +5 degrees],

[096] In embodiments, The scraper cage may comprise a driveable rim at or towards the burner end and a closing rim at or towards the outlet end. The scraper cage may thus be formed collectively by the driveable rim, the closing rim and the or each scraping blade.

[097] In embodiments, the driveable rim and/or the closing rim may be permanently fixed to the or each scraping blade, or may be removably fixed thereto.

[098] In embodiments, the driveable rim may be attachable to a flame tube of an abatement apparatus, or another part of an abatement apparatus, to facilitate axial rotation of the scraper cage in use. In embodiments, the closing rim may not be directly connected to a flame tube or another part of an abatement apparatus.

[099] In embodiments, the closing rim may have a diameter which is smaller than the diameter of the driveable rim.

[100] In embodiments, the closing rim may have a diameter which is smaller by approximately 20mm or less, or by approximately 10mm or less than the diameter of the driveable rim, when the scraper cage rotates in use. In embodiments, the difference in diameter between the driveable rim and the closing rim may be around 5mm or less when the scraper cage rotates in use. In practise, the diameter of the outlet end of the scraper cage must be sufficiently less than the diameter of the scraper cage at the burner end so as to avoid contact with a flame tube.

[101 ] In embodiments, the or each scraping blade may have a substantially V-shaped transverse cross-section. Thus, the or each scraping blade is more resilient to bending stresses and the like during use. In embodiments, the intersection of the or each V- shaped scraping blade may point substantially inwardly towards the longitudinal axis of the scraper cage. Thus, the or each scraping blade may comprise two scraper surfaces. In embodiments, the or each scraping blade may comprise two scraper surfaces, each of which is configured to scrape in a direction of rotation of the scraper cage.

[102] In embodiments, the or each scraping blade may taper in width between the burner end and outlet end of the scraping blade, and thus between the burner end and the outlet end of the scraper cage.

[103] In embodiments, the width of the or each scraping blade may reduce at a region proximal to the burner end thereof, and the width of the or each scraping blade may be substantially constant between the outlet end thereof and the said proximal region.

[104] In embodiments, the or each scraping blade may be substantially curved. In other words, the or each scraping blade may be attached to the driveable rim in a first plane which intersects the longitudinal axis of the scraper cage, and may be attached to the closing rim of the scraper cage in a second, different plane which intersects the longitudinal axis of the scraper cage.

[105] In embodiments, the scraper cage may comprise a plurality of scraping blades which are arranged to form a substantially helical, i.e. spiral, arrangement.

[106] Typically, as described, the scraper cage is arranged to rotate in a first direction and in a second opposite direction, i.e. clockwise and anticlockwise about said longitudinal axis. [107] In embodiments, the scraper cage may be configured such when the scraper cage rotates in the first direction, in use, the length of the scraper cage is shorter than when the scraper cage rotates in the second direction, or vice versa.

[108] In embodiments, the scraper cage may comprise a plurality of scraping blades which together form a substantially helical or spiral arrangement, and may be configured such that the length of the scraper cage changes as the scraper cages rotates, alternately, in clockwise and anticlockwise directions.

[109] In embodiments, the scraper cage may comprise a plurality of scraping blades which together form a substantially helical or spiral arrangement, and the scraper cage may be configured such that when it rotates in the first direction, in use, the diameter of the scraper cage, for example at a mid-region thereof, is greater than when the scraper cage rotates in the second direction, or vice versa. Thus, in embodiments, the scraper cage may be configured such that the clearance between the scraper cage and a abatement apparatus flame tube is sufficient to avoid or minimise the risk of contact between the scraper cage and the flame tube when the scraper cage is at its greatest diameter.

[110] In embodiments, the scraper cage may further comprise one or more braces or struts arranged between the burner end and the outlet end. Advantageously, the or each brace minimises the risk that the or each scraping blade buckles during use.

[111 ] In embodiments, at least one said brace, preferably the or each brace, may be in the form of a circumferential ring which is attached to an outer surface or an inner surface of the or each scraping blade. In embodiments, at least one said brace may be in the form of a supporting strut which is attached to an inner surface of one or more scraping blades. For example, a supporting strut may extend between opposing scraping blades of the scraper cage.

[112] In a further aspect, the present invention provides a flame tube scraping blade for cleaning the flame tube of a combustion-type abatement apparatus, the flame tube having a burner end and an outlet end; wherein the scraping blade has a corresponding burner end and outlet end, and one or more scraper surfaces extending therebetween; and wherein the scraping blade is configured such that, in use, the rotational circumference of the scraper blade is greatest towards the burner end of the scraping blade and shortest towards the outlet end of the scraping blade.

[113] For the purposes of the invention, the rotational circumference is the circumference of an imaginary circle formed by the path of the outermost point of the scraping blade in a given plane tangential to the rotational axis of the scraping blade if the scraping blade were to complete full rotation about said rotational axis.

[114] In embodiments, the rotational axis of the or each scraping blade may be substantially parallel to the longitudinal axis thereof. In embodiments, the rotational axis of the or each scraping blade is not coaxial with the longitudinal axis thereof. Typically, the scraper blade rotates about the rotational axis of the scraper.

[115] In embodiments, an outermost surface of the scraping blade may be radially closest to the rotational axis of the scraper cage towards the outlet end of the scraping blade. The outermost surface may be a scraper surface.

[116] Thus, the scraping blade may be arranged such that the outermost surface of the scraping blade is radially furthest from the rotational axis of the scraper cage towards the burner end of thereof.

[117] In embodiments, the scraping blade may be inclined by around 5 degrees [-2 degrees I +5 degrees],

[118] In embodiments, the scraping blade may have a substantially V-shaped transverse cross-section. Thus, the scraping blade is more resilient to bending stresses and the like during use. In embodiments, the scraping blade may be configured such that the intersection of the V-shaped scraping blade may point substantially inwardly towards the longitudinal axis of the scraper cage. Thus, the scraping blade may comprise two scraper surfaces. In embodiments, the scraping blade may comprise two scraper surfaces, each of which is configured to scrape in a direction of rotation of the scraping blade. [119] In embodiments, the scraping blade may taper in width between the burner end and outlet end thereof.

[120] In embodiments, the width of the scraping blade may reduce at a region proximal to the burner end thereof, and the width of the scraping blade may be substantially constant between the outlet end and the said proximal region.

[121 ] In embodiments, the scraping blade may be substantially curved. In other words, the scraping blade may be configured to attach to the driveable rim of a scraper cage in a first plane which intersects the longitudinal axis of the scraper cage, and may be attached to the closing rim of a scraper cage in a second, different plane which intersects the longitudinal axis of the scraper cage.

[122] In a further aspect, the present invention provides a combustion-type abatement apparatus comprising a flame tube in accordance with any preceding aspect, and/or a scraper cage in accordance with any preceding aspect, and/or a flame tube scraping blade in accordance with any preceding aspect.

[123] In a further aspect, the present invention provides a method of assembling a combustion-type abatement apparatus, comprising the step of installing a flame tube according to any preceding aspect and/or installing a scraper cage according to any preceding aspect and/or installing a flame tube scraping blade according to any preceding aspect.

[124] In embodiments, the method may further comprise the prior step of removing a flame tube and/or scraper cage and/or flame tube scraping blade of the abatement apparatus before installing a flame tube and/or scraper cage and/or flame tube scraping blade according to any preceding aspect.

[125] In a further aspect, the present invention provides a method of designing a combustion-type abatement apparatus comprising the steps of:

• determining the potential thermal expansion of a scraper cage of the abatement apparatus, in use; • modifying the scraper cage and/or the flame tube of the abatement apparatus such that the clearance between the scraper cage and the flame tube is greatest towards an outlet end of the scraper cage when the scraper cage rotates, in use.

[126] Thus, in the method of the present invention, the abatement apparatus is designed so that the clearance towards the burner end of the scraper cage is greater and the clearance towards the outlet end of the scraper cage is smaller, in use, to the extent that the outlet end of the scraper cage and the or each scraping blade of the scraper cage do not contact the flame tube of the abatement apparatus, in use.

[127] In embodiments, the method comprises modifying the diameter of the scraper cage such that the diameter of the scraper cage is greater towards the burner end than towards the outlet end thereof.

[128] In a further aspect, the present invention provides a method of designing a scraper cage for a combustion-type abatement apparatus comprising the steps of:

• determining the potential thermal expansion of a scraper cage, in use;

• modifying the scraper cage such that the clearance between the scraper cage and the flame tube of an abatement apparatus in which it is located is greatest towards an outlet end of the scraper cage when the scraper cage rotates, in use.

[129] In embodiments, the method comprises modifying the diameter of the scraper cage such that the diameter of the scraper cage is greater towards the burner end than towards the outlet end thereof.

[130] For the avoidance of doubt, features of aspects and embodiments described herein may be combined, and still fall within the scope of the present invention.

Brief Description of Figures [131] Preferred features of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[132] Figure 1 illustrates a schematic side on view of a scraper cage according to the present invention.

[133] Figure 2 illustrates a part-cutaway schematic perspective view of a flame tube including a scraper cage according to the present invention.

[134] Figure 3 illustrates a schematic perspective view of another scraper cage according to the present invention.

[135] Figure 4 illustrates a schematic perspective view of a further scraper cage according to the present invention.

Detailed Description

[136] Figure 1 shows a combustion-type abatement apparatus scraper cage of the present invention, which is referenced generally as 10.

[137] The scraper cage 10 is located within the flame tube 24 of the abatement apparatus (as shown in Figure 2). The scraper cage 10 is elongate and substantially vertically arranged. The scraper cage 10 is also substantially hollow. The abatement apparatus also includes a shroud (not shown) which surrounds the flame tube 24. In use, air passes between the shroud and flame tube 24 for temperature control.

[138] A burner (not shown) is usually positioned above or towards the uppermost end of the flame tube 24, and thus above the scraper cage 10, and a process gas flows into the burner end 42, i.e. the uppermost end, of the flame tube 24. The flame tube 24 has an opposing outlet end 44.

[139] A typical burner may comprise two inlet systems or manifolds which supply gas, each via three manifold branches leading to nozzles, to each longitudinal half of the flame tube. Usually, one of the two inlet systems is supplying significantly more gas than the other inlet system. There is therefore a non-uniform distribution of gas because there is a much greater proportion of gas supplied to one side of the flame tube than the other. For example, a first inlet manifold may supply around 400 standard litres per minute (SLM) at one side of the flame tube 24 while a second inlet manifold supplies 150 SLM at the other side of the flame tube 24. This causes a difference in gas flow and thus asymmetric heating within the flame tube 24.

[140] During use, powder biproducts typically deposit on an inner surface of the flame tube 24, and the scraper cage 10 is thus configured to rotate axially, back and forth, inside the flame tube 24 to dislodge those deposits in order that they continue to flow through the abatement apparatus and not build up and eventually clog the apparatus. A plurality of scraper surfaces 38 are configured to scrape deposits from the inner surface of the flame tube 24 as the scraper cage 10 rotates.

[141 ] The scraper cage is substantially cylindrical and has a burner end 12 and an opposing outlet end 14. The burner end 12 is that end of the scraper cage 10 which is typically proximal to the burner of the abatement apparatus and corresponds to the burner end 42 of the flame tube 24, and the outlet end 14 is distal therefrom.

[142] Each of the burner end 12 and the outlet end 14 of the scraper cage 10 comprises a rim - a driven rim 18 at the burner end 12, and a closing rim 20 at the outlet end 14 - which surrounds and binds to a plurality of scraping blades 16 which extend therebetween. The scraper cage 10 of Figure 1 includes six scraping blades 16, each having two scraper surfaces 38, but it is envisaged that a greater or fewer number of scraping blades 16 may be present in other embodiments or that each scraping blade may comprise a greater or lesser number of scraper surfaces. In Figure 1 , the scraping blades 16 are substantially evenly spaced about the circumference of the scraper cage 10.

[143] The driven rim 18 and closing rim 20 are attached to each of the scraping blades 16 by suitable means, for example by welding, screws, rivets or the like.

[144] The scraper cage 10 is configured so that when it is rotating, in use, the diameter of the scraper cage 10 is smaller towards the outlet end 14 than towards the burner end 12. The scraper cage 10 is also configured so that the diameter of the scraper cage 10 is smaller towards the outlet end 14 than towards the burner end 12 when the scraper cage 10 is not in use. In other words, the scraper cage 10 is generally tapered. A clearance between the flame tube 24 and the scraper cage 10 is thus greater towards the outlet end of the scraper cage 10 than towards the burner end thereof.

[145] In the figures, a radially outermost point on a scraper surface 38 proximal the outlet end 14 of the scraper cage 10 is located radially inward of a minimum bounding circle formed about the outward facing scraper surfaces proximal the burner end 12 of the scraper cage 10.

[146] In use, the greatest rotational circumference of the scraper surfaces 38 is proximal the burner end 12 of the scraper cage 10 and the smallest rotational circumference of the scraper surfaces 38 is proximal the outlet end 14 of the scraper cage 10.

[147] In the scraper cage 10 of Figure 1 , each of the scraping blades 16 is angled inwardly towards the longitudinal axis of the scraper cage 10 such that the diameter of the scraper cage 10 decreases from the burner end 12 towards the outlet end 14. The diameter and circumference of the closing rim 20 are smaller than the diameter of the driven rim 18. The diameter of the scraper cage 10 tapers substantially uniformly between the burner end 12 and the outlet end 14. The scraper cage 10 is thus substantially frustoconical in shape, with its largest diameter being towards the burner end 12 and smallest diameter being towards the outlet end 14.

[148] In use, the configuration of the scraper cage 10 of Figure 1 minimises the risk that the outlet end 14 does not come into contact with the radially inwardly facing wall 40 of the flame tube 24 as the scraper cage 10 rotates. In particular, the configuration of the scraper cage 10 ensures that it does not contact the radially inwardly facing wall 40 of the flame tube 24 even as the flame tube 24 and scraper cage 10 heat up and regions of the scraper cage 10 expand to a greater or lesser extent than other regions of the scraper cage 10. Thus, protective coatings on the radially inwardly facing wall of the flame tube 24, for example chromium oxide, are not compromised. [149] The scraper cage 10 further comprises a brace 34 in the form of a circumferential ring, which is attached (typically welded) to each of the scraping blades 16 approximately half way along the length of the scraper cage 10. The brace 34 is configured to minimise the risk of the scraping blade 16 deforming or buckling, in use, when subjected to the high temperatures associated with combustion-type abatement.

[150] The scraper cage 10 is hollow and, in use, gas is free to flow from the exterior of the scraper cage 10 through the ‘interior’ thereof, i.e. that space which is formed by the driven and closing rims 18, 20, the scraping blades 16 and brace 20.

[151 ] The burner end 12 of the scraper cage 10 comprises a bracket 22 which is configured to attach the scraper cage 10 to the flame tube of the abatement apparatus. The bracket 22 comprises several attachments which attach the scraper cage 10 to the flame tube 24. No other part of the scraper cage 10 is typically attached to or in contact with the flame tube 24. The bracket 22 is configured so that the driven rim 18 is free to rotate, as described.

[152] The abatement apparatus typically includes an actuator (not shown) which confers a force to the driven rim 18, causing the scraper cage 10 to rotate, in use. Typically the actuator provides a linear force to the scraper cage which, via the mechanism of the actuator, causes rotation of the scraper cage 10.

[153] Referring to Figure 2, the scraper cage 10 is configured to rotate alternately within the flame tube 24 in a clockwise direction by about 50 to 60 degrees, and then in an anticlockwise direction to substantially the same degree. However, if the scraper cage 10 were to comprise fewer scraping blades or more scraping blades, the angle of rotation of the scraper cage may be correspondingly greater or smaller in order that substantially the entire circumference of the radially inwardly facing wall 40 of the flame tube is scraped, in use. The flame tube 24 comprises a burner end 42 and an outlet end 28. The scraper cage 10 rotates about a longitudinal axis, shown by dashed line ‘A’, which passes through the centre of the elongate scraper cage 10. The longitudinal axis of the scraper cage is substantially coincident, i.e. coaxial, with the longitudinal axis of the flame tube 24. [154] The scraper cage 10 rotates at an average velocity of between 5.2 radian per second (rad/s) and 7.6 rad/s. Thus, the scraper cage 10 typically rotates through 60 degrees in around 0.13 to 0.21 seconds, and most typically in 0.17 seconds.

[155] As described, air passes between the shroud and flame tube 24 to control temperature. That air typically flows in a generally downward direction while circumventing the flame tube 24, and then enters the flame tube 24 via louvers 26 located towards the outlet end 28 of the flame tube 24.

[156] The scraper cage 10 has a substantially frustoconical shape, and a longitudinal cross section thereof is substantially in the shape of an inverted isosceles trapezoid. Therefore, the clearance between the scraper cage 10 and the flame tube 24 is greater towards the outlet end 14 than towards the burner end 12 of the scraper cage 10 in order to accommodate thermal expansion of the scraper cage 10 at the outlet end 14 which might otherwise cause the outlet end 14 of a mid-region of the scraper cage 10 to contact the flame tube 24.

[157] In other words, the flame tube 24 comprises an exclusion zone which extends radially inwardly from the radially inward facing wall 40 of the flame tube 24. The exclusion zone extends radially inwardly to a greater extent proximal the outlet end 28 of the flame tube 24 and to a lesser extend proximal the burner end 42 of the flame tube 24. The configuration of the scraper cage 10 is such that the scraper cage 10 does not enter the exclusion zone of the flame tube when the abatement apparatus is not in use, ideally also when the abatement apparatus is in use.

[158] In Figure 2, the clearance between the scraper cage 10 and the flame tube 24 at the outlet end 14 is approximately 10mm. For example, at a combustion temperature around 1200°C, it is expected that the scraper cage may expand axially by approximately 6mm. Thus, a 10mm clearance between the flame tube and scraper cage 10 at the outlet end 14 accommodates axial growth of the scraper cage 10 by around 6mm without risking contact between the scraper cage 10 and flame tube 24. Of course, the clearance between the scraper cage 10 and the flame tube 24 will be dependent on the dimensions thereof, e.g. a smaller abatement apparatus having a smaller scraper cage and flame tube may require a smaller clearance between the two components, and vice versa.

[159] A plurality of openings 36 allow a process gas to flow through the scraper cage.

[160] Referring back to Figure 1 , the tilt angle, <t>, of each scraping blade 16 is such that the difference in diameter between the burner end 12 of the scraper cage 10 and the outlet end 14 thereof is sufficient to avoid the described unwanted contact. In Figure 1 , the tile angle, <t>, is around 5 degrees.

[161 ] Staying with Figure 1 , the diameter of the driven rim 18 is around 295mm and the diameter of the closing rim 20 is around 280mm. The length of the scraper cage 10 is around 500mm, including the bracket 22.

[162] In practise, as explained, the size of the scraper cage 10 and, in particular, the tilt angle of each scraping blade 16, and the diameters of the burner end 12 and outlet end 14 of the scraper cage 10 are such that contact between the scraper cage 10 and the flame tube 24 anywhere other than the bracket 22 is avoided, in use. This will depend, amongst other things, on the dimensions of the flame tube.

[163] In Figures 1 and 2, each scraping blade 16 is linearly arranged between the driving rim 18 and closing rim 20, and is angled inwards towards the closing rim 20.

[164] Each scraping blade 16 has a substantially V-shaped transverse cross-section, i.e. in a plane substantially perpendicular to the longitudinal axis of the scraper cage 10. Each scraping blade 16 is arranged such that the corner, i.e. the intersection, of the V-shaped blade is pointed inwardly towards the centre of the scraper cage 10. Thus, each scraping blade 16 comprises two scraper surfaces 38, each scraper surface 38 corresponding to an outwardly facing edge of the V-shaped scraping blade 16.

[165] Each scraping blade has a corresponding burner end, such as 30, and a corresponding outlet end, such as 32. Each scraping blade 16 is configured such that, in use, the rotational circumference of each scraping blade 16 is greatest towards the burner end 30 of the scraping blade 16 and is shortest towards the outlet end 32 of the scraping blade 16.

[166] In Figure 1 , the width of each scraping blade 16 at the burner end is around 45mm, and the width of each scraping blade 16 at the outlet end is around 40mm. Each scraping blade 16 tapers from around 45mm in width at the burner end to around 40mm in width at a point which is approximately 5mm from the burner end. The length of each scraping blade 16 in Figure 1 is around 400mm.

[167] In Figure 1 , each extension of each V-shaped scraping blade 16 extends around 20mm from the corner of the blade 16. The angle subtended by each extension of a scraping blade is approximately 120 degrees.

[168] Turning to Figure 3, there is shown a further scraper cage 10 according to the present invention. The scraper cage 10 of Figure 3 is similar to that shown in Figure 1 , except that the scraping blades 16 in Figure 3 are curved and together form a substantially helical arrangement.

[169] In Figure 3, each scraping blade 16 is attached to the driven rim 18 in a first plane intersecting the longitudinal axis of the scraper cage 10, and is attached to the closing rim 20 in a second plane intersecting the longitudinal axis of the scraper cage, wherein the second plane is different to the first plane. In the scraper cage 10 of Figure 3, the second plane is around a sixth of a turn about the circumference of the scraper cage 10 relative to the first plane.

[170] The flexibility of each scraping blade 16 is such that the length and width of the scraper cage 10 changes as it rotates, in use, due to the forces applied to the scraper cage 10.

[171 ] The scraper cage 10 of Figure 3 is configured such that, when the scraper cage 10 rotates in a first, clockwise direction, the length of the scraper cage 10 lengthens, and when the scraper cage 10 rotates in a second, anticlockwise direction, the length of the scraper cage 10 shortens. [172] Also, given the change in length of the scraper cage 10 as it rotates, back and forth, between a clockwise direction and an anticlockwise direction, the diameter of the scraper cage 10 also changes. More specifically, when the scraper cage rotates in the first, clockwise direction, the diameter of the scraper cage 10 decreases, and when the scraper cage 10 rotates in the second, anticlockwise direction, the diameter of the scraper cage 10 increases. The diameter of the scraper cage 10 changes, most noticeably, at a mid-region thereof, i.e. where the scraper cage 10 is most flexible at a point roughly equidistant from the driven rim 18 and the closing rim 20. Hypothetically, if the scraping blades were to be oppositely arranged, the scraper cage 10 would increase in length and decrease in diameter when the scraper cage 10 rotates in an anticlockwise direction.

[173] In Figure 4, which shows a further scraper cage 10 in accordance with the present invention, the scraper cage 10 comprises two braces 34. The braces 34 restrict the extent to which the scraper cage changes in length and diameter, in use, and improve the resilience of the scraper cage 10 against deforming or buckling. In the scraper cage 10 of Figure 4, each brace 34 is attached to each scraping blade 16 at an outer surface thereof.

[174] It will be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims.

Reference Key

10 Scraper cage

12 Burner end of scraper cage

14 Outlet end of scraper cage

16 Scraping blade

18 Driven rim

20 Closing rim

22 Bracket

24 Flame tube

26 Louver

28 Outlet end of flame tube

30 Burner end of scraping blade

32 Outlet end of scraping blade

34 Brace

36 Opening

38 Scraper surface

40 Radially inwardly facing wall

42 Burner end of flame tube

44 Outlet end of flame tube