IMPROVED FUEL SYSTEM FOR DIESEL TYPE ENGINES USING CARBONACEOUS AQUEOUS SLURRY FUELS

Abstract

The present invention provides an improved fuel injection system and related method for controlling fuel heating and circulation in diesel type engines configured to use carbonaceous aqueous slurry fuels. The fuel injection system comprises: at least one fuel injector including an injector nozzle through which fuel is atomised and a fuel injector pump for pressurising fuel for supply to the injector nozzle; and a controlled bleed valve fluidly connected to each fuel injector and positioned to allow a controlled amount of carbonaceous aqueous slurry fuel to flow from the fuel injector.

Claims

1. A fuel injection system of a diesel type engine configured to use carbonaceous aqueous slurry fuels, the fuel injection system comprising: at least one fuel injector including an injector nozzle through which fuel is atomised and a fuel injector pump for pressurising fuel for supply to the injector nozzle; and a controlled bleed valve fluidly connected to each fuel injector and positioned to allow a controlled amount of carbonaceous aqueous slurry fuel to flow from the fuel injector; wherein the controlled bleed valve comprises at least one of an electronically controlled bleed valve or a hydraulically controlled bleed valve.

2. (canceled)

3. A fuel injection system according to claim 1, wherein the controlled bleed valve is operated to allow flow from the fuel injector after the fuel injection pump draws fuel into the injector and before the fuel injector injects fuel through the injector nozzle.

4. A fuel injection system according to claim 1, wherein the controlled bleed valve is fluidly connected by the injector around or between the fuel injector pump and the injector nozzle.

5. A fuel injection system according claim 1, wherein the injector nozzle includes a flow valve for controlling flow through the injector nozzle and the controlled bleed valve is fluidly connected to the injector at or around said flow valve.

6. A fuel injection system according to claim 1, wherein the flow valve includes a valve seat, and the controlled bleed valve is fluidly connected to the injector at or around the valve seat of the flow valve.

7. A fuel injection system according to claim 1, wherein the flow valve comprises a needle valve.

8. A fuel injection system according to claim 1, wherein the controlled bleed valve is fluidly connected to the fuel injector pump.

9. A fuel injection system according to claim 8, wherein the fuel injector pump comprises a plunger pump including a cylinder and driven plunger for pumping fuel to the injector nozzle and the controlled bleed valve is fluidly connected to a pump volume in the cylinder between the plunger and a fuel inlet of the plunger pump.

10. A fuel injection system according to claim 1, wherein each controlled bleed valve is fluidly connected to a fuel recycle system.

11. A fuel injection system according to claim 10, further including a fuel delivery pump for pumping fuel to the fuel injector, and wherein the fuel recycle stream is fluidly connected between the outlet of the controlled bleed valve and an inlet of the fuel delivery pump.

12. A fuel injection system according to claim 10, further including a fuel circulation main, wherein the return from the fuel circulation main is fluidly connected to the inlet of the fuel delivery pump.

13. A fuel injection system according to claim 10, wherein the fuel recycle stream includes a connection to a waste stream into which flow can be selectively diverted to remove fluid from the fuel recycle stream.

14. (canceled)

15. A fuel injection system according to claim 1, further comprising a service tank into which fresh carbonaceous aqueous slurry fuel is feed, the service tank being fluidly connected to an inlet of the fuel delivery pump.

16-17. (canceled)

18. A fuel injection system according to claim 1, further including a fuel preconditioning system fluidly connected to the inlet of the injector system, the fuel preconditioning system including a fuel preheater for heating the fuel to a service temperature.

19-20. (canceled)

21. A fuel injection system according to claim 1, wherein the flow through the bleed valve is controlled by the flow duty of the bleed valve for a given fuel delivery pressure.

22-23. (canceled)

24. A diesel type engine configured to use carbonaceous aqueous slurry fuels comprising a fuel injection system comprising at least one fuel injector, each injector including: an injector nozzle through which fuel is atomised and a fuel injector pump for pressurising fuel for supply to the injector nozzle; and a controlled bleed valve fluidly connected to each fuel injector and positioned to allow a controlled amount of carbonaceous aqueous slurry fuel to flow from the respective injector, wherein the controlled bleed valve comprises at least one of an electronically controlled bleed valve or a hydraulically controlled bleed valve.

25. (canceled)

26. A method for controlling fuel heating and circulation in a diesel type engine using of carbonaceous aqueous slurry fuels, the diesel type engine including a fuel injection system according to claim 1, the fuel injector operating to inject fuel into a combustion chamber of the engine, the method including the steps of: operating the bleed valve to allow flow from the fuel injector between fuel injection events into the combustion chamber.

27. A method according to claim 26, wherein the controlled bleed valve is operated to allow flow from the fuel injector after the fuel injection pump draws fuel into the injector and before the fuel injector injects fuel through the injector nozzle.

28. (canceled)

29. A method according to claim 26, wherein the flow through the bleed valve is controlled by the flow duty of the bleed valve for a given fuel delivery pressure.

30. A method according to claim 26, wherein each controlled bleed valve is fluidly connected to a fuel recycle system, and during normal engine operation, the fuel recycle stream directs fuel from the bleed valves to the inlet of the fuel delivery pump.

31-36. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[0056] FIG. 1 provides a schematic of a fuel injection and recycle system according to one embodiment of the present invention providing about 5% return flow to a fuel delivery pump fluidly connected to an inlet of the engine containing at least one controlled bleed valve as illustrated in FIGS. 2 to 5.

[0057] FIG. 1A provides a cross-section of the diesel-type engine from the fuel injection system shown in FIG. 1 illustrating the location of the injector in that engine.

[0058] FIG. 2 provides a schematic drawing of one embodiment of a controlled bleed system according to the present invention configured for a hydraulically geared unit pump-injector with bleed flow taken from around the cut off or needle valve seat.

[0059] FIG. 3 provides a schematic drawing of one embodiment of a controlled bleed system according to the present invention configured for an ungeared unit pump-injector with bleed flow taken from around the cut off or needle valve seat.

[0060] FIG. 4 provides a schematic drawing of one embodiment of a controlled bleed system according to the present invention configured for a hydraulically geared unit pump-injector with bleed flow taken from the pump volume.

[0061] FIG. 5 provides a schematic drawing of one embodiment of a controlled bleed system according to the present invention configured for an ungeared unit pump-injector with bleed flow taken from the pump volume.

DETAILED DESCRIPTION

[0062] The present invention comprises a fuel injection system and related method for controlling fuel heating and circulation in diesel type engines using carbonaceous aqueous slurry fuels.

[0063] The fuel injection system (FIG. 1) of the present invention utilises electronically controlled bleed valves (V1 FIG. 1) on each injector 150 (see FIGS. 2 to 5) that can be used to regulate the circulating flow and timing of bleed flow from each injector. In contrast to heavy fuel oil, carbonaceous aqueous slurry fuels can be injected and burn well without the need for viscosity control by preheat thereby eliminating or reducing the need to ensure accurate temperature control under all conditions (e.g. during fuel change over where the separate slurry fuel system may be cooler than preferred).

[0064] Without wishing to be limited to any one theory, the inventors have discovered that carbonaceous aqueous slurry fuels generally behave adversely to high shear or cavitation conditions such as experienced through pressure relief valves and throttling valves. Problems include a particle decrepitation and particle agglomeration. These effects are increase significantly with increased temperature. Agglomeration is further increased by contamination of the circulating slurry from the use of seal oil to protect fuel injector pump plungers and valve spindles. The Inventors have found that this contaminated fuel need to be used as soon as possible to reduce the tendency for agglomeration (oil causes coal in coal-water slurries and bitumen in bitumen-water slurries to agglomerate). The current art of returning the circulating flow to the service tank will therefore lead to a build-up of destabilised slurry fuel which is likely to lead to blocking of fuel strainers and solid dropout in fuel lines (particularly at fittings and sudden increase in flow area).

[0065] It should be appreciated carbonaceous aqueous slurry fuels comprise an aqueous slurry or suspension type fuel that includes carbonaceous particles suspended in an aqueous medium. The carbonaceous particles may be sourced from any suitable carbonaceous source including, but not limited to a variety of coal, chars, bitumen, charcoal, wood, various hydrocarbons, and organic matter whether biological in nature or organic compounds etc. Preferably, the carbonaceous material is coal. Any type of coal may be used, for example anthracite, bituminous coal, or a brown or lignitic coal may be used. This is particularly advantageous as coal is readily available as a carbonaceous source. It is preferred that the carbonaceous source has low ash content, preferably less than 2 wt %, more preferably less than 1 wt %, most preferably less than 0.5 wt %. An example of one suitable type of carbonaceous aqueous slurry fuels is taught in International Patent Publication No. WO2015048843A1, the contents of which again should be understood to be incorporated into this specification by this reference.

[0066] In the case where the carbonaceous particles are coal, it is preferred that the coal has undergone some form of pre-treatment. Pre-treatment may include removal of the bulk of the mineral ash contamination and in the case of the lower rank coals some form of densification and alteration of the surface properties to render the coal more hydrophobic to enable a fuel with a higher coal loading to be achieved. For example bituminous coal demineralisation can be achieved by selective agglomeration, flotation and cyclones. An example of one suitable injector nozzle, forming part of a blast atomiser type injector is taught in International Patent Publications WO2013142921A1 and WO2015048843A1 by the same applicant, the contents of which again should be understood to be incorporated into this specification by this reference.

[0067] Carbonaceous aqueous slurry fuels can be used to replace heavy fuel oil for diesel type engines, particularly for stationary electricity generation at greater than the 5 MW scale, and for large shipping. The fluid properties of coal water slurry fuels are significantly different to diesel and fuel oils, in particular the coal slurry have a much higher shear-thinning non-Newtonian viscosity, and both the coal particles and contaminant mineral particles are abrasive to low hardness steel, preventing the fuel from lubricating the fuel system. Coal water slurry fuels have been successfully demonstrated in adapted diesel type engines in a number of demonstration programsprovided hardened fuel system components were used, and the fuel had a sufficiently low viscosity.

[0068] Embodiments of the present invention can be configured to use a carbonaceous aqueous slurry fuel characterised as a type of micronized refined carbon fuel (MRC). Micronising involves fine milling a solid carbonaceous (carbon-containing) material to about 10 to 60 microns. Refining involves physically cleaning the carbonaceous material, so as to remove most of the mineral matter to produce a fuel with approximately 1 percent mineral content. The fine carbonaceous material and water are combined to produce an aqueous slurry/suspension containing 40 to 50% water.

[0069] It should be appreciated that the present invention is suitable for use in a directly injected combustion chamber of a compression ignition or diesel type engine. The particular engine may therefore comprise a conventional compression ignition or diesel type engine, or an engine improved, modified or otherwise derived from conventional compression ignition or diesel engines to operate using a fuel including carbonaceous particles suspended in an aqueous medium.

[0070] One example is a direct injection carbon engine (DICE)which is one type of a diesel type engine 112, which has been modified to enable combustion of water-based slurry of micronised refined carbon fuel (MRC) as shown in FIGS. 1 and 1A.

[0071] FIG. 1 provides a schematic of the one embodiment of the fuel injection system 100 according to the present invention that provides during bleed flow from 1 to 20%, preferably 3 to 10%, more preferably about 5% return flow to a fuel delivery pump 120 fluidly connected to an inlet of the engine 112 containing at least one controlled bleed valve V1 as illustrated in FIGS. 2 to 5. However, it should be appreciated (as described below) that in flushing mode that return flow may be up to 100%. Similarly, the bleed flow may also be adjusted to maintain system temperature. The illustrated fuel injection system 100 comprises a fuel circulation circuit that supplies fresh fuel from a service tank 110 to diesel type engine 112. The service tank 110 is connected to the engine through preconditioning circuit 114 which includes a fuel delivery pump 120, preheater 122 and fuel strainer 124. Pressure and temperature of the fuel in that circuit 114 is monitored using appropriate pressure and temperature sensors 125, 126, 127. A bleed flow of fuel from the injectors 120 in the engine 112 (see FIGS. 2 to 5 for further detail of the injectors 120) is recycled in normal operation to the preconditioning circuit 114 via fuel recycle stream 130. Flow meter 132 monitors the flow of fluid from the engine 112 via the bleed stream 135. Flow meter 138 monitors the flow of fluid being fed into the engine 112 via feed stream 139.

[0072] As previously noted, the controlled bleed valve V1 is preferably be selected to provide fast opening and closing to enable full opening and closing cycles during the period between the end of one injection event and the beginning of another, and more preferably during the period between refilling of the fuel pump and the beginning of the next injection event. It should be appreciated that controlled bleed valve V1 can comprise any suitable bleed valve. A number of valve configurations would be suitable, including both inwards and outwards opening valves, which are either directly operated using a solenoid acting to pull open a spring loaded valve spindle, or indirectly using a small high speed servo hydraulic valve which controls hydraulic oil flow to either open or close the valve via a hydraulic piston attached to the slurry valve. A number of commercial actuation equipment are available, for example Moog brand actuation equipment, but in all cases the valve switching the slurry flow should be provided with hard valve surfaces such as tungsten carbide or ceramic inserts to resist abrasion and galling by the particles in the slurry, and have provision to protect any sliding valve spindles from slurry ingress. In embodiments, this can be advantageously provided by applying a high pressure sealing fluid to the valves spindle, in a similar manner to that provided to protect the other injector components in particular the pump plunger and cut off needle, and which would therefore be advantageously facilitated by incorporating the high speed slurry valve into the same unit injector assembly. In some embodiments, the controlled bleed valve V1 comprises a Moog brand electronically controlled valve/actuator, for example 72 series servo valves, which is preferably adapted for use with a carbonaceous aqueous slurry fuel as noted above.

[0073] Referring to FIG. 1, fresh fuel is supplied into the illustrated fuel injection system 100 via a service tank 110. The service tank 110 is typically a closed tank located proximate the engine 112 containing a reservoir of fuel for that engine 112. The service tank 112 is advantageously operated at a much lower temperature than that used for injection in the engine 112 which further reduces slurry destabilisation. The inventors consider that a service tank temperature of 25 to 40 C. will likely be suitable for most carbonaceous aqueous slurry fuels used in the engine 112. A valve V2 (FIG. 1) is provided to interrupt the flow from the service tank 110 and to enable pumping of flushing fluid 173 into the engine fuel system (as outlined below). This valve V2 could advantageously be a three-way valve or two separate valves.

[0074] The service tank 110 feeds fuel to the fuel delivery pump 120 of the fuel preconditioning circuit 114. The fuel delivery pump 120 can comprise any suitable pump including those known in the art for diesel engines, such as mechanical, hydraulic, inline, unit injectors or the like. The fuel preconditioning circuit 114 is used to condition the fuel to suitable properties (temperature, pressure, viscosity and the like) prior to being fed into the fuel injector system of the engine 112. As illustrated, the main fuel preheater 122 is located before fuel strainer 127 thereby allowing the strainer 127 to take advantage of the reduced viscosity of the preheated slurry. The fuel preheater 122 can comprise any suitable fuel preheating unit, including those known in the art for diesel engines which thermally heat the fuel to a selected temperature. Similarly, the fuel strainer 127 can comprise any suitable fuel filter or straining unit, including those known in the art for diesel engines. Fuel preheat should be varied according to the properties of the fuel and the return bleed flow to maximise the temperature of the injected fuel whilst minimising the average time that fuel is at elevated temperature. The preheater typically heats the fuel flowing therethrough to a temperature of between 50 to 150 C., preferably between 70 to 130 C. The acceptable time-temperature profile will be different for different fuels. The present invention differs considerably from current art by allowing close control of fuel delivery conditions to the engine to achieve best combustion and thermal efficiency (maximum fuel preheat) whilst substantially reducing the time-temperature at conditions that cause fuel destabilisation.

[0075] It should be appreciated that the components of the fuel preconditioning circuit 114 are well known in the art and can be selected from known components, for example as discussed in K. Nicol The direct injection carbon engine, IEA Clean Coal Centre report CCC/243, December 2014https://www.usea.org/sites/default/files/122014_The %20direct %20injection %20 carbon %20engine_ccc243.pdf, the contents of which should be understood to be incorporated into this specification by this reference.

[0076] The preconditioning circuit 114 is connected to feed stream 139 via valve V3 (FIG. 1). Valve V3 can be used to divert fuel flow from the fuel preconditioning circuit 114 to waste stream 174 that connects to a waste tank or flushing fluid recovery system 170 during system flushing or periods of abnormal operation to advantageously reduce the time for flushing. Valve V3 could advantageously be a three-way valve.

[0077] The illustrated engine 112 (FIGS. 1 and 1A) can comprise any engine capable of running using a carbonaceous aqueous slurry fuel, such as a direct-injection, compression ignition or diesel type engine. In preferred forms, the engine comprises a modified diesel type engine, such as a diesel type engine having a blast injector. It can be advantageous to use a blast atomiser injector as it directly applies the kinetic energy intensity to atomise high solids content fuel that is highly viscous with a wide size distribution, containing both a high proportion of fine material as well as a larger top size. The direct application of kinetic energy from the blast fluid circumvents frictional energy losses within the fuel allowing more atomization energy to be used efficiently (i.e. to overcome surface tension effects.) The much lower fuel velocity and larger fuel passages minimize frictional losses handling the fuel as well as admit a larger maximum size of fuel particle than would otherwise be possible. An example of one suitable blast atomiser injector is taught in International Patent Publications WO2013142921A1 and WO2015048843A1 by the same applicant, the contents of which should be understood to be incorporated into this specification by this reference.

[0078] FIG. 1A provides a cross-sectional view of an example two-stroke DICE engine 112 that can incorporate the fuel injection system of the present invention. Examples of these engines are taught in Wibberley L J (2013) Coal base-load power using micronised refined coal (MRC). Energy Generation, pp 35-39 (January-March 2011) the contents of which should be understood to be incorporated into this specification by this reference. This engine is a diesel type engine modified to have a direct fuel injector 150 similar to those illustrated in FIGS. 2 to 5. As shown in FIG. 1A, the fuel injector 150, and more particularly the injector nozzle 152 is situated above the piston housing 151 and has a fluid connection to fuel injector pump 155.

[0079] FIGS. 2 to 5 illustrate four different embodiments of fuel injector 150 of the engine 112 including fluidly connected controlled bleed valves V1. It should be appreciated that whilst electronically controlled bleed valves V1 are used in the illustrated embodiments, other types of controlled bleed valves such as hydraulically controlled bleed valves could equally be used without departing from the spirit or scope of the invention.

[0080] In each of the illustrated embodiments in FIGS. 2 to 5, the illustrated fuel injector system 118 comprises a fuel injector 150 which has an injector nozzle 152 through which fuel is atomised and a fuel injector pump 154 for pressurising fuel for supply to the injector nozzle 152. The injector nozzle 152 includes a flow valve, typically a needle valve (not illustrated) for controlling flow through the injector nozzle 152. The flow valve typically includes a valve seat (not illustrated). The illustrated fuel injector pump 154 comprises a plunger pump including a cylinder and driven plunger 155 for pumping fuel to the injector nozzle 152.

[0081] In each of the illustrated embodiments in FIGS. 2 to 5, a controlled bleed valve V1 is then fluidly connected to each fuel injector 150 in a position which allows a controlled amount of carbonaceous aqueous slurry fuel to flow from the fuel injector 150 to the fluidly connected fuel recycle stream 130 (FIG. 1). The bleed valve V1 is operated to allow flow from the fuel injector 150 into the recycle stream 130 after the fuel injection pump 155 draws fuel into the injector 152 and before the fuel injector 150 injects fuel through the injector nozzle 152. This allows the injector 150 to operate normally to draw the requisite amount of fuel into the injector 150 and expel/atomise that fuel through the injector nozzle 152. The bleed flow is preferably controlled by the duty of the bleed valve V1 for a given fuel delivery pressure. During normal operation of the engine 112, the bleed flow is redirected via the recycle stream 130 to the inlet of the fuel low pressure delivery pump(s) 120 (FIG. 1) to avoid contaminating the service or day tank(s) with hot degraded/contaminated fuel and/or to reduce the time before hot degraded fuel is injected into the engine 112. The bleed return from the controlled bleed valve V1 to the fuel delivery pump 120 can be around 1 tph.

[0082] The controlled bleed valve can be fluidly connected to the injector at any suitable location. As shown in FIGS. 2 and 3, the controlled bleed valve V1 can be fluidly connected to the injector 150 at or around the valve seat of the flow valve of the injector nozzle 152. Fluidly connecting the controlled bleed valve V1 to the cut off valve seat advantageously eliminates settling in any dead volume proximate the valve seat and maximises the efficiency (completeness) of any flushing action. FIGS. 2 and 3 show schematics of this embodiment using geared and ungeared hydraulically actuated injectors 150. FIG. 2 shows an embodiment where the fuel injector pump 154 is a hydraulically geared unit pump-injector 150A and the bleed valve V1 is connected around the cut off or needle valve seat of the injector nozzle 152. FIG. 3 shows an embodiment where the fuel injector pump 154 is an ungeared unit pump-injector and the bleed valve V1 is connected around the cut off or needle valve seat of the injector nozzle 152. These preferred arrangements take the bleed flow from around the cut off valve seat (i.e. needle valve seat) to eliminate settling in this dead volume and to maximise the efficiency (completeness) of flushing.

[0083] In other embodiments, the controlled bleed valve V1 is fluidly connected to the fuel injector pump 154 and therefore take the bleed flow for the recycle stream 130 from the pump volume of the fuel injector pump 154. FIG. 4 and show schematics of this embodiment using geared and ungeared hydraulically actuated injectors 150. FIG. 4 shows an embodiment where the fuel injector pump 154 is a hydraulically geared unit pump-injector 150A and the bleed valve V1 is connected to the pump volume of the fuel injector pump 154. FIG. 5 shows an embodiment where the fuel injector pump 154 is an ungeared unit pump-injector and the bleed valve V1 is connected to the pump volume of the fuel injector pump 154. It is envisaged that this arrangement would be advantageously used for injectors with smaller cross sections by raising the position of the bleed conduit.

[0084] The pressure drop of the bleed flow from the injector 150 is advantageously controlled by the pressure drop in in the conducting channels in the injector 150 both before and after the electronically controlled bleed valve V1 to reduce the shear intensity experienced by the bleed flow as compared to a similar flow passing over throttling valves.

[0085] A bleed flow of fuel from the injectors 120 in the engine 112 (see FIGS. 2 to 5 for further detail of the injectors 120) is recycled in normal operation to the preconditioning circuit 114 via fuel recycle stream 130. During flushing the fuel recycle stream 130 is connected to waste diversion stream 175 via operation of valve V4 (FIG. 1). Valve V4 can therefore be used to divert fuel flow from the fuel recycle stream 130 to a waste tank or flushing fluid recovery system 171 during system flushing or periods of abnormal operation to advantageously reduce the time for flushing. This valve V4 could advantageously be a 3-way valve.

[0086] During fuel system flushing the electronically controlled bleed valves V1 can be advantageously operated with an extended duty cycle, including continuously open, to provide rapid system flushing. To ensure complete flushing the injector can be advantageously operated for several cycles preferably at the end of the fuel system flushing period. This method will flush the injector passages below the cut of valve (i.e. needle valve) including the cut off valve seat and injector atomiser nozzles 152. During the flushing cycle, valves V2 is operated to feed flushing fluid 173 and valve V3 and/or V4 are operated to remove waste fluid from the fuel injection system 100 and the overall circuit. This allows the engine 112 and in particular the fuel injection system 100 to be regularly flushed and cleaned to remove any sludge or deposits in that system. Additionally, this provides the ability to flush the fuel system and comprising fuel injection system 100 for shut-down.

[0087] Whilst not illustrated, if a circulation main is desirable and used in the fuel injection system, the return from this main should be to the inlet of the low pressure fuel delivery pump(s) 120 and not the service tank 110. This eliminates mixing hot fuel with the cooler fuel in the service tank 110 and reduces the tendency for fuel destabilisation.

[0088] It is to be appreciated that the fuel injection system 100 and engine 112 can be used in a variety of applications, including as a stationary power generation engine, and a transportation engine, such as an engine in an ocean going vessel.

[0089] For ocean going vessels, the use of carbonaceous slurry fuels can advantageously address sulfur emissions limits for ocean vessels which in many jurisdictions have been restricted to use fuel oil on board with a sulphur content of no more than 0.5%, and in some cases of now more than 0.10%. The sulfur content of carbonaceous slurry fuels, particularly micronized refined carbon fuel (MRC) can be tailored to meet this specific sulfur content restriction. An engine such as disclosed in relation to the present invention, that uses such fuel can therefore assist in meeting these requirements.

[0090] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0091] Where the terms comprise, comprises, comprised or comprising are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.