GB2507346A

GB2507346A - Burner inlet assembly for generating a fluid pulse to assist in residue removal

Info

Publication number: GB2507346A
Application number: GB1219404.9A
Authority: GB
Inventors: Andrew James Seeley
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2012-10-29
Filing date: 2012-10-29
Publication date: 2014-04-30
Also published as: WO2014068275A1; TW201420967A; GB201219404D0

Abstract

A burner inlet assembly 200 is for generating a fluid pulse to assist in removal of accumulated deposits/residues (24 Fig 2) in a burner 10. The assembly includes a fluid accumulator/pressure vessel 16 chargeable with a pulse fluid from a fluid source 30 at a charging flow rate, and an actuator/valve 18 operable to discharge pulse fluid from the fluid accumulator through an outlet conduit (58 Fig 8) at a discharging flow rate in response to a change in an actuation signal for example from a controller 32. The discharging fluid flow rate is greater than the charging fluid flow rate, and the assembly generates the discharged fluid pulse through the outlet conduit to assist in deposits/residues removal. The assembly and method of use allows accumulated deposits/residues to be reduced in a burner which treats an effluent gas stream 12 to produce a treated gas stream 14. The accumulator/pressure vessel permits generation of fluid pulses without affecting the performance of the fluid source or the performance of any other parts connected thereto. The arrangement may also include a flow control orifice 34 and a purge line 38.

Description

BURNER INLET ASSEMBLY

FIELD OF THE INVENTION

The present invention relates to a burner inlet assembly and a method.

BACKGROUND

Burners are known and are typically used for treating an effluent gas stream from a manufacturing process tool used in, for example, the semiconductor or flat panel display manufacturing industry. During such manufacturing, residual pertluorinated compounds [PFCs] and other compounds exist in the effluent gas stream pumped from the process tools. PFCs and the other compounds are typically difficult to remove from the effluent gas stream and their release into the environment is undesirable because they are known to have relatively high greenhouse activity.

Known burners use combustion to remove the PECs and other compounds from the effluent gas stream. Typically, the effluent gas stream is a nitrogen stream containing PFCs and other compounds. In a burner, a fuel gas is typically mixed with the effluent gas stream and that gas stream mixture is conveyed into a combustion chamber together with a fuel gas and air mixture to affect flameless combustion, with the amount of air being sufficient to consume not only the fuel gas supply to the burner but also the combustibles in the gas stream mixture injected into the combustion chamber.

As the surface areas of the semiconductors being processed increases, the flow rate and range of compounds in the effluent gas also increases.

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 and effluent gas stream.

SUMMARY

According to a first aspect, there is provided a burner inlet assembly for generating a fluid pulse deliverable to assist in removal of residues in a burner, the burner inlet assembly comprising: a fluid accumulator chargeable with a pulse fluid from a fluid source at a charging flow rate; and an actuator operable, in response to a change in an actuation signal, to discharge pulse fluid from the fluid accumulator through an outlet conduit at a discharging flow rate, which is greater than the charging flow rate, to generate the fluid pulse.

The first aspect recognizes that a problem with increasing the flow rate and range of compounds in the effluent gas stream is that the inlet assemblies for burners can become clogged with deposits or residues which are typically provided by condensables within the effluent gas. Such deposits will impair the operation of the burner by restricting or impairing the flow of the effluent gas into a combustion i chamber or by influencing the chemistry of the combustion occurring within the burner.

Accordingly, a burner inlet assembly is provided. The assembly may generate a fluid pulse which may be delivered to assist in the removal of residues or deposits in a burner. The burner inlet assembly may comprise a fluid accumulator which may be charged at a charging flow rate with a fluid from a fluid source. The burner inlet assembly may also comprise an actuator which may discharge fluid from the fluid accumulator, through an outlet conduit, at a discharging flow rate.

The discharging flow rate may be higher than the charging flow rate to generate or create the fluid pulse.

By providing a fluid accumulator, an existing fluid source may be reused. This existing fluid source may then continue to supply fluid to other parts of any processing tools being used to process the effluent gas, such as the burner. This reuse is possible because the accumulator stores the pulse fluid to enable a fluid pulse to be generated. If the pulse fluid was not stored by the accumulator, then the fluid source would need to be capable of continuing to be able to supply adequate levels of fluid to other parts of the processing tools whilst concurrently generating the fluid pulses. If the fluid source was incapable of doing this, then those other parts of the processing tools may cease to operate correctly during the generation of the fluid pulses. By storing the pulse fluid in the fluid accumulator, it is possible to generate the required fluid pulses to reduce or remove accumulated deposits or residues without affecting the performance of the fluid source or the performance of any other parts of the processing tools.

Storing the pulse fluid in the fluid accumulator enables the pulse fluid to be released from the fluid accumulator through an outlet at a velocity or volume in which is greater than that would be possible if the pulse was generated directly from the fluid source itself. Accordingly, this arrangement enables a more effective fluid pulse to be generated which is better at removing residues or deposits than would be possible from a fluid pulse generated directly from the fluid source.

In one embodiment, the burner inlet assembly comprises a flow restrictor operable to provide the pulse fluid from the fluid source to the fluid accumulator at the charging flow rate. Providing a flow restrictor helps to decouple the effects of the generation of the fluid pulse from the normal operation of the fluid source. In particular, providing a flow restrictor helps to minimise or prevent any reduction in pressure being experienced by the fluid source during the generation of the fluid pulse. This helps to ensure that the fluid source can continue to function and support the operation of other parts of the processing tools.

In one embodiment, the actuator couples the fluid accumulator with the outlet conduit near instantaneously in response to the actuation signal to generate the fluid pulse. Accordingly, the actuator may connect the fluid accumulator with the outlet conduits almost immediately to enable a well-defined fluid pulse to be generated.

In one embodiment, the fluid pulse has a near instantaneous change in flow rate through the outlet conduit from a decoupled flow rate when the outlet is decoupled from the fluid accumulator to the discharging flow rate when the outlet conduit is coupled with the fluid accumulator. Accordingly, the change in flow rate within the outlet conduits may occur almost immediately in order to generate a well-defined fluid pulse. Such a step-transition in flow rate helps to create a fluid pulse which imparts an abrupt force on any deposits or residues.

In one embodiment, the actuator comprises a valve having a minimal mass piston translatable between a decoupled position where the outlet conduit is decoupled from the fluid accumulator to a coupled position where the outlet conduit is in coupled with the fluid accumulator to generate the fluid pulse. Providing a piston which has minimal mass reduces the inertia of the piston and enables it to translate as rapidly as possible to enable an abrupt fluid pulse to be generated.

In one embodiment, the piston has a front face and a rear face and the pulse fluid i from the fluid accumulator is applied to the front face with a piston fluid applied to the rear face of the piston. Accordingly, control of the actuation of the piston may be effected by controlling the piston fluid applied to the rear face of the piston.

This provides a simple non-mechanical means for controlling the translation of the piston to generate the fluid pulse.

In one embodiment, an area of the rear face exceeds that of the front face and the pulse fluid from the fluid accumulator applied to the front face and the piston fluid applied to the rear face of the piston have substantially matching pressures.

By providing opposing ends of the piston with different surface areas, a piston fluid pressure which is no greater than that of the pulse fluid pressure within the accumulator can be used to retain the piston in the decoupled position, thereby enabling the accumulator to be charged with and to retain the fluid therein.

In one embodiment, the piston fluid applied to the rear face of the piston is provided by the fluid source. Accordingly, the pulse fluid from the fluid source may also be utilized to control the translation of the piston.

In one embodiment, the piston is tapered at least partially along its length. It will be appreciated that providing a taper provides for differing front and rear face areas. In embodiments, mentioned below, the tapering also provides a conduit through which a purge fluid may circulate around the actuator to help prevent deposits occurring.

In one embodiment, the piston is maintained in the decoupled position by the pressure of the piston fluid applied to the rear face of the piston.

In one embodiment, the piston is translatable to the coupled position by a reduction in the pressure of the piston fluid applied to the rear face of the piston compared to the pressure of the pulse fluid applied to the front face of the piston.

Reducing the pressure of the piston fluid on the rear face of the piston enables the pressure from the pulse fluid within the fluid accumulator to rapidly translate i the piston to the coupled position to generate the fluid pulse.

In one embodiment, the burner inlet assembly comprises a valve operable to vent the piston fluid applied to the rear face of the piston in response to the change in the actuation signal to translate the piston to the coupled position. Venting the piston fluid to, for example, atmosphere using a valve in response to the changing the actuation signal enables the pressure of the piston fluid at the rear of the piston to be rapidly decreased and an abrupt fluid pulse to be generated.

In one embodiment, the valve is operable to reapply the piston fluid to the rear face to translate the piston to the decoupled position in response to a change in the actuation signal. Accordingly, a further change in the actuation signal, such as restoring it to its previous level, may cause the valve to stop venting and instead to supply the piston fluid from the fluid source to the rear face of the piston to increase the pressure on the rear face of the piston to translate the piston to the decoupled position. Again, this provides for a simple translation of the piston using a minimal number of mechanical parts and reuses the fluid source.

In one embodiment, the burner inlet assembly comprises a controller operable to generate the actuation signal.

In one embodiment, the controller is operable to generate a plurality of the changes in the actuation signal to generate a corresponding plurality of fluid pulses. Accordingly, more than one change in the actuation signal may be generated in order to produce a number of fluid pulses. Typically, two fluid pulses have been found to be particularly effective at dislodging or removing in residues or deposits.

In one embodiment, the controller is operable to generate the plurality of the changes in the actuation signal to generate the corresponding plurality of fluid pulses where a time period between each fluid pulse exceeds a duration of each i fluid pulse. Accordingly, the length of the fluid pulses is typically shorter than the length of time between the generation of such fluid pulses. This is to enable the fluid accumulator to recharge between the production of each of the fluid pulses.

In one embodiment, the plurality of fluid pulses comprise a group of fluid pulses which is generated over an actuation period and wherein the controller is operable to generate groups of changes in the actuation signal to generate corresponding groups of fluid pulses where a time period between groups of fluid pulses exceeds the actuation period. Accordingly, groups of fluid pulses may be produced and those groups may be generated periodically. Typically, the period between the groups of fluid pulses may be much longer than the duration of the group of fluid pulses. This is because it is typically not necessary to continually supply the fluid pulses since deposits or residues can take a period of time to form. Hence, the groups of fluid pulses need only be generated when it is considered that that there are sufficient residues or deposits to remove.

In one embodiment, the burner inlet assembly comprises a plurality of the actuators, each coupled with the fluid accumulator and an associated outlet conduit. Accordingly, more than one actuator, each of which is associated with its own outlet conduit may be coupled with the fluid accumulator. This enables the fluid accumulator to be used to remove or reduce deposits in a variety of different locations.

In one embodiment, the controller is operable to generate an actuation signal for each actuator.

In one embodiment, the controller is operable to generate the actuation signals to generate fluid pulses from each associated outlet conduit at different times.

Accordingly, the group of fluid pulses may be generated by each actuator, with the time periods when these different groups of fluid pulses occurring at different times so that the fluid accumulator only generates groups of fluid pulses for one of the outlet conduits at the time. This enables a single fluid accumulator to be used by multiple actuators.

In one embodiment, the fluid accumulator is chargeable to a charge pressure, the fluid accumulator and the flow restrictor are configured to achieve the charge pressure between generation of the fluid pulses. Accordingly, the sizing of the fluid accumulator and flow restrictor may be set to enable the required fluid pulses to be generated when required.

In one embodiment, each outlet conduit is dimensioned to reduce dissipation of the fluid pulse. By sizing the outlet conduits in this way, the fluid pulse can be conveyed for delivery to the vicinity of any deposits or residues whilst minimizing any loss of power between the actuator and the point of impact on the deposits or residues.

One embodiment comprises a burner coupled with the outlet conduit of the burner inlet assembly, the outlet conduit delivering the fluid pulse to at least one of a nozzle, an inlet and a combustion chamber of the burner. Accordingly, the fluid pulses may be delivered to appropriate locations within the burner.

In one embodiment, the burner inlet assembly comprises a purge assembly operable to provide a purge fluid to each actuator. Providing a purge fluid to the actuator minimizes the likelihood of any deposits occurring on the actuator which may otherwise impair its operating performance.

In one embodiment, the purge assembly is operable to provide the purge fluid to the burner.

In one embodiment, the purge assembly provides as the purge fluid the fluid from the fluid source at a reduced pressure compared to that of the fluid source.

Providing the purge fluid at a reduced pressure minimizes the impact of providing such purge fluid on the fluid source.

According to a second aspect, there is provided a method of generating a fluid pulse deliverable to assist in removal of residues in a burner, the method comprising the steps of: charging a fluid accumulator with a pulse fluid from a fluid source at a charging flow rate; and in response to a change in an actuation signal received by an actuator, discharging pulse fluid from the fluid accumulator through an outlet conduit at a discharging flow rate which is greater than the charging flow rate to generate the fluid pulse.

In one embodiment, the step of charging comprising restricting flow to provide the pulse fluid from the fluid source to the fluid accumulator at the charging flow rate.

In one embodiment, the step of discharging comprises coupling, using the actuator, the fluid accumulator with the outlet conduit near instantaneously in response to the actuation signal to generate the fluid pulse.

In one embodiment, the fluid pulse has a near instantaneous change in flow rate through the outlet conduit from a decoupled flow rate when the outlet is decoupled from the fluid accumulator to the discharging flow rate when the outlet conduit is coupled with the fluid accumulator.

In one embodiment, the step of discharging comprises translating a valve having a minimal mass piston of the actuator between a decoupled position where the outlet conduit is decoupled from the fluid accumulator to a coupled position where the outlet conduit is coupled with the fluid accumulator to generate the fluid pulse.

In one embodiment, the piston has a front face and a rear face and the pulse fluid from the fluid accumulator is applied to the front face with a piston fluid applied to the rear face of the piston.

In one embodiment, an area of the rear face exceeds that of the front face and the pulse fluid from the fluid accumulator applied to the front face and the piston i fluid applied to the rear face of the piston have substantially matching pressures.

In one embodiment, the piston fluid applied to the rear face of the piston is provided by the fluid source.

In one embodiment, the piston is tapered at least partially along its length.

In one embodiment, the step of charging comprises maintaining the piston in the decoupled position by the pressure of the piston fluid applied to the rear face of the piston.

In one embodiment, the step of discharging comprises translating the piston to the coupled position by a reduction in the pressure of the piston fluid applied to the rear face of the piston compared to the pressure of the pulse fluid applied to the front face of the piston.

In one embodiment, the step of discharging comprises venting the piston fluid applied to the rear face of the piston using a valve in response to the change in the actuation signal to translate the piston to the coupled position.

In one embodiment, the step of charging comprises reapplying the piston fluid to the rear face using the valve to translate the piston to the decoupled position in response to a change in the actuation signal.

In one embodiment, the method comprises the step of generating the actuation signal using a controller.

In one embodiment, the method comprises the step of generating a plurality of the changes in the actuation signal to generate a corresponding plurality of fluid pulses.

In one embodiment, the method comprises the step of generating the plurality of the changes in the actuation signal to generate the corresponding plurality of fluid pulses where a time period between each fluid pulse exceeds a duration of each fluid pulse.

In one embodiment, the plurality of fluid pulses comprise a group of fluid pulses which is generated over an actuation period and wherein step of generating comprises generating groups of changes in the actuation signal to generate corresponding groups of fluid pulses where a time period between groups of fluid pulses exceeds the actuation period.

In one embodiment, the method comprises the step of providing a plurality of the actuators, each coupled with the fluid accumulator and an associated outlet conduit.

In one embodiment, the method comprises the step of generating an actuation signal for each actuator.

In one embodiment, the step of generating comprises generating the actuation signals to generate fluid pulses from each associated outlet conduit at different times.

In one embodiment, the fluid accumulator is chargeable to a charge pressure and the method comprises the step of configuring the fluid accumulator and the flow restrictor to achieve the charge pressure between generation of the fluid pulses.

In one embodiment, the method comprises the step of dimensioning each outlet conduit to reduce dissipation of the fluid pulse.

In one embodiment, a burner is coupled with the outlet conduit and the method comprises the step of delivering the fluid pulse to at least one of a nozzle, an inlet and a combustion chamber of the burner.

In one embodiment, the method comprises the step of providing a purge fluid to each actuator.

In one embodiment, the method comprises the step of providing the purge fluid to the burner.

In one embodiment, the method comprises the step of providing as the purge fluid the fluid from the fluid source at a reduced pressure compared to that of the fluid source.

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. -12-

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 is a schematic drawing of a burner and burner inlet assembly of one embodiment; in Figure 2 is a schematic drawing of a burner and burner inlet assembly of Figure 1 showing deposits accumulated in a burner of the apparatus; Figure 3 is a schematic drawing of a burner and burner inlet assembly Figure 1 showing removal of the deposits; Figure 4 is a schematic drawing of a burner and burner inlet assembly of one embodiment; Figure 5 is a schematic drawing a of burner inlet assembly of one embodiment showing flow lines for a single discharge port; Figure 6 is a schematic drawing of a burner inlet assembly of one embodiment showing flow lines multiple discharge ports; Figure 7 is a perspective drawing of a burner inlet assembly of one embodiment; Figure 8 is a section taken along line VIll-VIll in Figure 7; and Figure 9 is enlarged view of part of the burner inlet assembly shown in Figures 7 and 8.

DESCRIPTION OF THE EMBODIMENTS

Overview Before discussing the embodiments in any more detail, first an overview will be provided. As mentioned above, the processing of effluent gases can lead to residues or deposits within a burner which can affect its performance. A burner inlet assembly is provided which generates fluid pulses which may be delivered to dislodge or reduce any such deposits or residues in order to improve the performance of the burner. An accumulator or fluid storage device is provided which is charged or filled with a pulse fluid from a fluid source which may already be utilized by processing tools, such as the burner. Storing the pulse fluid in the accumulator enables the fluid pulses to be generated without affecting the performance of the fluid source. If the accumulator was not provided, then the generation of such fluid pulses may cause a temporary loss of pressure from the fluid source which may impact on the performance of the processing tools. Using the accumulator enables the fluid pulses to be generated without such loss of pressure and also provides for greater control over the characteristics of these fluid pulses. Such fluid pulses comprise a temporary discharge of fluid which in results in an associated transient increase in pressure which travels as a wave having controlled characteristics to dislodge deposits.

A fluid-controlled piston may be provided which provides for pneumatic control of the actuator to generate the fluid pulses, which reduces the mechanical complexity of the actuator, improves its reliability and avoids the need for a further fluid source to control the piston. A purge arrangement may be provided which supplies a low-pressure and low-flow rate purge fluid to prevent any deposits or residues occurring within the burner inlet assembly. Furthermore, it is possible to utilize a common fluid accumulator which is used by multiple actuators to generate fluid pulses to be supplied to multiple outlet conduits in order that fluid pulses can be provided to multiple different locations of the burner or to multiple burners.

Burner and Burner inlet assembly -First Arrangement Figures 1 to 3, illustrate an arrangement of a burner and burner inlet assembly according to one embodiment. The burner 10 provides for combustive destruction of gas species in an effluent gas stream 12. A treated gas stream 14 is exhausted from the burner.

Coupled with the burner 10 is a burner inlet assembly 200. The burner inlet assembly 200 comprises a pressure vessel or accumulator 16 for containing a -14-fluid, preferably a gas, under pressure. The gas is preferably an inert gas such as nitrogen.

The pressure vessel 16 is arranged to be connected to a source of gas 30 for trickle charging the pressure vessel 16 with gas through a flow restricting, or charging, orifice 34. This arrangement is preferable for generating sufficient pressure and gas volume to apply the necessary force for blasting away the accumulated deposits from the inlet nozzle or other locations of the burner 10. In this regard, if the source of gas 30 were used to generate pulses of pressurised gas directly, rather than for charging the pressure vessel 16, the generation of a pulse would cause a temporary reduction in pressure at the source and divert gas from other pneumatically driven devices which are also connected to the source.

In this preferred arrangement, a relatively low trickle feed of pulse gas is conveyed from the source 30 for a longer duration without affecting the pneumatic pressure available to other pneumatic devices. By way of example, if the source of gas 30 is at 6 bar pressure then it would take approximately 20 seconds (indicated by t2 in Figure 1) to charge a pressure vessel of 1000 ml. In addition to the above advantages, the present arrangement avoids draining the source of gas 30 ifa valve arrangement 18 coupled with the pressure vessel 16 were to become damaged.

The valve arrangement 18 is arranged to selectively discharge pressurised pulse gas contained in the pressure vessel 16 for generating a high velocity pulse of pressurised gas. For example, as shown in Figure 1, pulses 300 lasting approximately 2 seconds (indicated by ti) are generated. The valve arrangement 18 preferably comprises a fast acting high conductance valve to ensure that the force which can be generated by the pulse is not dampened. The valve arrangement 18 is controlled by a controller 32 which generates an actuation signal to open and close the valve arrangement 18 in order to couple the pressure vessel 16 with the burner 10.

As shown in Figure 2, the effluent gas stream may contain particle or residue forming gases, such as pyrophoric gases, for example silane, chloro-silane and organo-silane which produce by-products such as Si02 and Si3N4. Accordingly, locations in the burner 10 and particularly the inlet nozzles 22 of the burner are prone to blockage by the accumulation of particles or residue 24. However, it will be appreciated that deposits may occur at other locations.

As shown in Figure 3, a pulse guide 26 (which is a narrow annular passage surrounding the nozzle 11) guides the high velocity discharged pulses 28 from the pressure vessel 16 towards the inlet nozzle 22 for removing accumulated deposits from the burner. The pulse guide may additionally or alternatively be arranged to guide pulses of gas to other locations within the burner that are prone to the accumulation of deposits.

i If the burner 10 comprises a plurality of nozzles 22, the burner inlet assembly 200 may comprises a respective plurality of pulse guides 26 for guiding a discharged pulse towards each of the nozzles 22. Gas can be discharged from the pressure vessel 16 for cleaning the plurality of nozzles 22 simultaneously, although it is preferred to clean the nozzles 22 one after another since otherwise the force from one gas discharge would be distributed over all the nozzles 22. The valve arrangement 18 can therefore be arranged for sequentially connecting each pulse guide 26 to the pressure vessel 16 for receiving respective pulses of pressurised pulse gas.

The valve arrangement 18 is operably connected to a controller 32 for controlling the discharge of pressurized pulse gas at selected intervals from the pressure vessel. The controller 32 may be a programmable control unit, a general purpose processing device or a control unit integrated with another component of the abatement or processing apparatus and configured for controlling the discharge assembly.

A single pulse of pulse gas may be sufficient to dislodge the accumulation of deposits depending on the area affected by the accumulation and the density of accumulation. It has been found that two or three pulses in short succession yields good results. For example, if the pressure vessel 16 can be charged in 20 seconds, the controller 32 is configured to control generation of three pulses at second intervals.

Such a cleaning routine may be required at hourly intervals, although this is dependent on the rate of accumulation which is different between processes and the compositions of the gas stream. The controller 32 is therefore preferably configured to initiate a cleaning routine at appropriate intervals, for example once an hour during operation, as indicated by t3 in Figure 1.

Purge Assembly While the pressure vessel 16 is being charged with gas between pulses, process gas 12 has a propensity to leak upstream along the pulse guide 26/36 and into the valve arrangement 18. Since these process gases can cause corrosion or can cause deposits to form, it is desirable to purge the burner inlet assembly 200 at least during the period the pressure vessel 16 is being charged with pulse gas.

Figure 1 shows one purge arrangement in which some purge gas from the gas source 30 is used for purging the burner inlet assembly 200. This purge gas can be diverted to locations upstream and downstream of the valve arrangement 18, as shown by purge line 38. Preferably only a small flow of purge gas is used for purging the burner inlet assembly 200 and therefore the purge line 38 diverts purge gas downstream of flow restricting orifice 34. In one alternative arrangement, gas from a separate low pressure gas source (not shown) can be used for purging.

Burner and Burner inlet assembly -Second Arrangement Figure 4 shows a burner inlet assembly 200A which is similar to that shown in Figures 1 to 3 except that the pulse guide comprises a lance 36 located centrally along the nozzle 22. The high velocity pulse gas stream 28 discharged from pressure vessel 16 is conveyed along the lance 36 for dislodging material accumulating on the periphery of larger diameter nozzle 22. The lance is shown as terminating approximately at the exit point of the nozzle 22 into the burner 10, but it will be appreciated that it can terminate higher within the nozzle 22. It will also be appreciated that a similar purge arrangement to that mentioned above may be incorporated into the embodiment shown in Figure 4.

Burner inlet assembly -Third Arrangement in Figure 5 is a schematic diagram of a burner inlet assembly 200B with a single discharge outlet 86 coupled with an associated pulse guide, such as the annular channel 26 or lance 36 mentioned above. The burner inlet assembly 200B is connected to the source of gas 30 for supplying nitrogen gas at 6 bar. The pressure vessel 16 is connected by a first conduit 80 to the source of gas 30 via a i flow restricting orifice 34 which is arranged to restrict the flow of gas to 10 slm (standard litres per minute).

The source of gas 30 is also connected to a second conduit 82 for purging the burner inlet assembly 200B. The pressure of gas from the source of gas 30 is regulated by a controllable pressure regulator 88 to a pressure of 5 psi (0.34 bar).

The regulated pressure selected is not restricted to 5 psi (0.34 bar) and other pressures may be used. A flow restricting orifice 84 restricts the flow of purge gas to 1 slm. Other trickle flows can be selected as required. A downstream end of the second conduit 82 is connected to a location which is downstream of the discharge valve 18 so that purge gas flowing through conduit 82 resists the passage of process gases upstream through the discharge outlet 86.

The pressure vessel 16 has a charging volume of 1000 ml and is charged for 20 seconds by the flow of gas shown by the solid arrow in Figure 5. Purge gas flows 3° through the second conduit 82 during charging of the pressure vessel 16. When the pressure vessel 16 is charged and it is determined that removal of deposits is required, the controller 32 activates the discharge valve 18 and a pulse of high pressure pulse gas is discharged along conduit 89 and through outlet 86 as indicated by the broken arrow. A single pulse may be sufficient to remove deposits however it has been found that discharging a plurality of consecutive pulses, ideally two or three, at 20 second intervals (i.e. the time required for charging the pressure vessel 16) is particularly effective at removing all deposits.

The cleaning process may be controlled to take place at hourly intervals dependent on the rate at which deposits accumulate and require cleaning.

The arrangement shown in Figure 5 may be used to clean different locations in a in burner by directing pulses from one location to the next location in sequence for example by manual or automatic moving of the pulse guide 26, 36.

Burner inlet assembly -Fourth Arrangement A burner inlet assembly 200C for cleaning multiple locations, or inlet nozzles, is i shown in Figure 6. The burner inlet assembly 200C comprises a plurality of discharge ports or outlets 90, 92, 94 and associated pulse guides 96, 98, 100 (e.g. the lances or annular passages mentioned above). It will be appreciated that any other number of discharge ports may be provided dependent on the number of locations within the burner which require cleaning.

The burner inlet assembly 200C is connected to a source of gas 30 for supplying nitrogen gas at 6 bar. A pressure vessel 40 is connected by a first conduit 64, 66 to the source of gas 30 via a flow restricting orifice 68 which is arranged to restrict the flow of gas to 10 slm (standard litres per minute). The source of gas 30 is also connected to a second conduit 64 for purging the burner inlet assembly 200C. The pressure of gas is regulated by a controllable pressure regulator 88 to a pressure of 5 psi (0.34 bar). The second conduit 64 divides into three further conduits 93 having flow restricting orifices 91 which restrict the flow of purge gas to 1 slm. Downstream ends of the second conduits 93 are connected to locations which are downstream of the discharge valves 50 so that purge gas flowing through the conduits 93 resist the passage of process gases upstream through the discharge ports 90, 92, 94.

The pressure vessel 40 may have a charging volume of 1000 ml similar to Figure above and is charged for 20 seconds by the flow of gas shown by the solid arrow in Figure 6. Purge gas flows through the conduits 64, 66, 93 during charging of the pressure vessel 40 to prevent the discharge valves 110, 112, 114 from being contaminated with process gas or debris.

When the pressure vessel 40 is charged at 6 bar and it is determined that removal of deposits is required (e.g. from a first nozzle of the burner), a controller 108 activates a first discharge valve 110 and a pulse of high pressure pulse gas is discharged through port go as indicated by the broken arrow referenced Si. A single pulse may be discharged or a plurality of consecutive pulses at 20 second intervals (i.e. the time required for charging the pressure vessel 40) may be required for cleaning for cleaning the nozzle. When it is determined that a second location, or nozzle, of the burner, requires cleaning the controller 108 activates a second discharge valve 112 and one or more pulses of high pressure pulse gas are discharged as indicated by the broken arrow referenced 52.

Similarly, when it is determined that a third location, or nozzle, of the burner, requires cleaning the controller 108 activates a third discharge valve 114 and one or more pulses of high pressure pulse gas are discharged as indicated by the broken arrow referenced S3. The cleaning process may be controlled to take place at hourly intervals dependent on the rate at which deposits accumulate and require cleaning.

In an alternative cleaning process, a first pulse Si, S2, S3 may be discharged to each of the nozzles in sequence followed by a second pulse to each of the nozzles in turn and then a third pulse to each of the nozzles in turn.

In a still further cleaning process, the controller 108 may activate all of the discharge valves 110, 112, 114 simultaneously for cleaning a plurality of corresponding locations in the burner at the same time. However, the charged volume of gas in the pressure vessel would then be split into three pulses and -20 -therefore the volume of the pulses generated would be smaller. This process may still be acceptable for cleaning light deposits or for frequent cleaning.

Burner inlet assembly -Fifth ArranQement Figures 7 to 9 illustrate a burner inlet assembly 200D. The same reference numerals will be used to describe those aspects of this embodiment which are common to the embodiment shown in Figure 6. Figure 7 is a perspective view of the burner inlet assembly 200D. Figure 8 is a section taken along a VI-VI in Figure 7 showing the top part of the burner inlet assembly 200D. Figure 9 is an enlarged view of the central portion of the burner inlet assembly 200D shown in Figure 8.

The burner inlet assembly 200D comprises a cylinder 40 made from a sufficiently strong material such as steel, stainless steel or aluminium to withstand high gas pressures when the cylinder 40 is fully charged. The cylinder 40 is closed at each end with end plates 42, 44 that are tied together with a tie rod 46 and fastened with suitable fasteners to form a charging volume 48. End plate 44 is of elongate form relative to the longitudinal axis of the cylinder and is machined for locating the required valves, passages and structures of the burner inlet assembly 200D. In the example shown, end plate 44 is machined to a polygonal profile with discharge valves 50 being located at respective sides of the profile.

Six discharge valves are shown located at six sides of the profile. The pressure regulator 88 is located at a seventh side of the profile.

The end plate 44 comprises a high pressure gas inlet 56 for connection to a source of gas 30 and a plurality of gas outlets 58 for discharging pulses of high pressure pulse gas to respective pulse guides 26, 36. Each outlet 58 is associated with a corresponding valve 50.

Gas from source of gas 30 is used for charging the charging volume 48, for purging the apparatus and for operating the valves 50, as will now be described in more detail. -21 -

As can be seen in Figure 8, a conduit 62 extends generally axially from gas inlet 56. Flow restricting orifice 68 (see Figure 9) communicates with conduit 62 and is sized to restrict the flow of gas passing through it to 10 slm. The orifice 68 is formed in an end of a generally cylindrical part 69 located in the end plate 44. An array of openings 71 are formed about a circumference of the cylindrical part 69 and communicate with the orifice 68 through a central hollow portion 73 of the cylindrical part 69. The end plate 44 is formed with a bore 75 having a larger diameter than that of the cylindrical pad 69 and gas conveyed through openings 71 passes along the bore 75 and into the charging volume 48 of the cylinder 40.

A radially extending conduit 64 communicates with conduit 62 and conveys gas from the source of gas 30 to the pressure regulator 88. The pressure regulator 88 regulates the gas from a pressure of for example 6 bar to 5 psi (0.34 bar).

The pressure regulator 88 is an off the shelf component and will not be described in detail.

A generally axially extending conduit 66 conveys purge gas at the regulated pressure to an annular purge gallery 81 via a radially extending conduit 83. In this embodiment, the purge gallery 81 is formed by an annular channel formed in an outer circumference of the end plate 44. 0-rings 85, 87 are located on axial sides of the purge gallery 81 and resist leakage seal of purge gas from the purge gallery 81.

The purge gallery 81 is arranged to convey low pressure purge gas to each of the valves 50. In this regard, a plurality of radially extending conduits 89 convey purge gas from the purge gallery 81 through flow restricting orifices 91 to axially extending conduits 93. The flow restricting orifices 91 reduce the flow of purge gas to the valves SOto 1 slrn. Only one valve is shown in Figure 8 and it will be appreciated that a corresponding arrangement of conduits 89, 93 and orifices 91 is provided for guiding purge gas to each of the other valves 50.

-22 -The valves 50 comprise a minimal mass piston 95 which is shaped to allow the flow of pulse gas from the axially extending conduits 93 to the discharge outlets 58 when the piston 95 is in a closed condition. In this regard, the piston has a chamfered end 97 which forms, with a valve bore 99, a route for the flow of purge gas around the piston 95 to the discharge port 58.

Although not shown in this embodiment, a second inlet may be provided for connection to a low pressure source of gas for purging the volume inside the end plate 44 and the pulse guides downstream of the end plate.

A plurality of radially extending conduits 101 conveys piston gas from the source of gas 30 to respective valves 50 for pneumatically operating those valves 50.

The valves 50 are fast acting and high conductance, and in a preferred arrangement, utilise a pilot actuated solenoid valve 50A controlling a main valve part comprising a valve seat 103 closed by the piston 95. The piston 95 is mounted for movement in the bore 99 and is held in a closed position by the pneumatic pressure acting on a rear face 105 of the piston 95. This pneumatic pressure is caused by piston gas flowing via conduits 101 and 107 and the deactivated solenoid valve 50A. When the solenoid valve 50A is activated, piston gas is no longer conveyed via the conduits 101 andlO7 to the rear face 105 of the piston 95, but instead the pressure acting on the rear face 105 of piston 95 is vented rapidly to atmosphere via conduit 107 to the solenoid valve 50A and an exhaust conduit (not shown) and the high pressure in the charging volume acts on the front end face 109 of the piston. The volume of high pressure piston gas acting on the rear face 105 of the piston 95 is small in relation to the volume contained in the charging volume 48, thus the discharge of pressure in this region is fast compared to the speed of movement of the (low mass) piston 95 in the bore 99 since this action is limited by the inertia of the piston 95, not the speed at which the pneumatic pressure discharge precedes it. The high pressure in the charging volume 48 acting on the end face 109 of the piston 95 causes it to move rapidly in the bore 99, thereby causing the contents of the charging volume 48 to discharge as a pulse, via conduits 111, 58 to the burner location(s) to be cleaned.

On deactivating solenoid valve 50A, the fluid pressure applied to the rear face of piston 95 causes the piston 95 to move along the bore 99, acting against the seat 103, closing the passage 111, allowing the pressure to build in the charging volume 48. Once charged, the cycle can be repeated. In one alternative arrangement a normally closed pilot solenoid valve could be used, although the electric logic would need to be reversed.

When the valve 50 is opened, pulse gas flows from the charging volume 48 through the bore 75 in the end plate 44 and into one or more conduits 111, depending on which of the pilot valves has been opened. Gas passing through an open valve 50 is conveyed to its associated outlet 58 for discharging along a pulse guide for cleaning a location in the burner.

A pressure gauge 54 is located at one side of the end plate 44. The pressure gauge 54 is a transducer which senses the pressure in the charging volume 48 upstream of one or more of the discharge valves. This pressure sensing allows the condition of the assembly to be monitored, for example to check that the discharge valves are sealing correctly in their deactivated conditions or that a required discharge pressure has been achieved in the charging volume.

A discharge pulse is characterised by its pressure and volume which together influence the efficient removal of deposits from locations within the burner. The pressure of the pulse equates generally to the force which is applied to the accumulated deposits whilst the volume of the pulse equates generally to the period of time over which force is applied to the accumulation. A larger pressure applies a greater cleaning force and a larger volume applies force over a longer duration. However, the desirability for a high pressure and large volume pulse must be balanced by the requirement to charge the pressure vessel 40 with gas and maintain it within the vessel at pressure. The pressure which can be attained in a pressure vessel 40 is dependent on such factors as the pressure available from the source of gas 30. Also, the usage of significant amounts of gas from the source of gas 30 may deprive other pneumatic devices driven from the source. It -24 -has been found that a charging volume of 1000 ml at a discharge pressure of approximately 6 bar is suitable for cleaning typical accumulations of deposits at locations in a burner. Other pressures and volumes may be required in conditions of light or heavy depositing and those skilled in the art will be able to select a suitable pressure and volume by routine testing.

It will be appreciated from the description above that the embodiments provide a convenient arrangement and process for cleaning locations of a burner prone to accumulating deposits. Cleaning can be performed without taking the burner off-line and therefore improves abatement efficiency. Cleaning can be performed at regular intervals (such as each hour) or the accumulation of deposits can be monitored and cleaning initiated when it is required. In one arrangement, a sensor can be provided to monitor accumulation. The sensor outputs a signal to the control to initiate cleaning when sufficient deposits are sensed.

As mentioned above, it will be appreciated that each of the pulse fluid, the piston fluid and the purge fluid may be provide by the same fluid source thereby providing a simplified arrangement.

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.

Claims

-25 -CLAIMS1. A burner inlet assembly for generating a fluid pulse deliverable to assist in removal of residues in a burner, said burner inlet assembly comprising: a fluid accumulator chargeable with a pulse fluid from a fluid source at a charging flow rate; and an actuator operable, in response to a change in an actuation signal, to discharge pulse fluid from said fluid accumulator through an outlet conduit at a discharging flow rate which is greater than said charging flow rate to generate said fluid pulse.
2. The burner inlet assembly of claim 1, wherein said actuator couples said fluid accumulator with said outlet conduit near instantaneously in response to said actuation signal to generate said fluid pulse.
3. The burner inlet assembly of claim 1 or 2, wherein said actuator comprises a valve having a minimal mass piston translatable between a decoupled position where said outlet conduit is decoupled from said fluid accumulator to a coupled position where said outlet conduit is coupled with said fluid accumulator to generate said fluid pulse.
4. The burner inlet assembly of claim 3, wherein said piston has a front face and a rear face and said pulse fluid from said fluid accumulator is applied to said front face with a piston fluid applied to said rear face of said piston.
5. The burner inlet assembly of claim 4, wherein an area of said rear face exceeds that of said front face and said pulse fluid from said fluid accumulator applied to said front face and said piston fluid applied to said rear face of said piston have substantially matching pressures.

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6. The burner inlet assembly of any one of claims 3 to 5, wherein said piston is maintained in said decoupled position by said pressure of said fluid piston applied to said rear face of said piston.
7. The burner inlet assembly of any one of claims 3 to 6, wherein said piston is translatable to said coupled position by a reduction in said pressure of said piston fluid applied to said rear face of said piston compared to said pressure of said pulse fluid applied to said front face of said piston.
8. The burner inlet assembly of any preceding claim, comprising a controller operable to generate said actuation signal.
9. The burner inlet assembly of claim 8, wherein said controller is operable to generate a plurality of said changes in said actuation signal to generate a corresponding plurality of fluid pulses.
10. The burner inlet assembly of claim 9, wherein said plurality of fluid pulses comprise a group of fluid pulses which is generated over an actuation period and wherein said controller is operable to generate groups of changes in said actuation signal to generate corresponding groups of fluid pulses where a time period between groups of fluid pulses exceeds said actuation period.
11. The burner inlet assembly of any preceding claim, wherein each outlet conduit is dimensioned to reduce dissipation of said fluid pulse.
12. The burner inlet assembly of any preceding claim, comprising a purge assembly operable to provide a purge fluid to each actuator.
13. The burner inlet assembly of claim 12, wherein said purge assembly provides as said purge fluid said fluid from said fluid source at a reduced pressure compared to that of the fluid source.

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14. A method of generating a fluid pulse deliverable to assist in removal of residues in a burner, the method comprising the steps of: charging a fluid accumulator with a pulse fluid from a fluid source at a charging flow rate; and in response to a change in an actuation signal received by an actuator, discharging pulse fluid from the fluid accumulator through an outlet conduit at a discharging flow rate which is greater than the charging flow rate to generate the fluid pulse.
15. A burner inlet assembly as hereinbefore described with reference to the accompanying drawings.
16. A method as hereinbefore described with reference to the accompanying drawings.