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A biomass fuel combustor for use in the pressurized combustion comprising of biomass fule particles to produce a pressurized exhaust gas, the combustor comprising: a cyclonic combustion chamber having a combustion region and first and second fuel inlets, the first inlet being for the entry into the

A biomass fuel combustor for use in the pressurized combustion comprising of biomass fule particles to produce a pressurized exhaust gas, the combustor comprising: a cyclonic combustion chamber having a combustion region and first and second fuel inlets, the first inlet being for the entry into the chamber of gas and/or liquid secondary fuel for combustion in said combustion region and the second inlet being for the entry into the chamber of biomass fuel particles also for combustion in said combustion region, the chamber being so constructed and arranged that the heat generated by the secondary fuel combustion will, in use and at least during stan-up of the combustor, promote fragmentation of the incoming biomass fuel particles.

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1. A biomass fuel combustor for use in the pressurized combustion of biomass fuel particles to produce a pressurized exhaust gas for use in a direct cycle biomass-fired gas turbine system, the combustor comprising:a cyclonic combustion chamber having an upstream combustion region and a downstream co

1. A biomass fuel combustor for use in the pressurized combustion of biomass fuel particles to produce a pressurized exhaust gas for use in a direct cycle biomass-fired gas turbine system, the combustor comprising:a cyclonic combustion chamber having an upstream combustion region and a downstream combustion region, the downstream region being arranged to receive combustion products from the upstream region, the upstream region having first and second fuel inlets, the second inlet allowing the entry into the upstream region of biomass fuel particles for combustion and the first inlet allowing the entry into the upstream region of fluid secondary fuel for combustion in the upstream region at least during start-up of the combustor; wherein heat is supplied to the upstream region, thereby promoting fragmentation in the upstream region of the biomass fuel particles entering the upstream region via the second inlet, wherein the second inlet is positioned such that biomass fuel particles enter the upstream region via the second inlet with a tangential component to promote cyclonic motion of gases and biomass particles in the upstream region and wherein the downstream region of the combustion chamber is provided with a plurality of air injection openings arranged such that air enters the downstream region of the combustion chamber with a tangential component to promote cyclonic motion of gases and fragmented biomass particles in the downstream region of the combustion chamber, wherein the combustor further comprises a first outlet for the efflux from the combustion chamber of the hot pressurized combustion gas resulting from the biomass and/or secondary fuel combustion and also further comprises a dilution chamber downstream of said first outlet, said dilution chamber being provided with one or more third inlets for the supply to the dilution chamber of air to dilute the hot pressurized combustion gas. 2. A combustor as claimed in claim 1, wherein the combustor is so constructed and arranged that biomass fuel particle fragmentation takes place within 10 ms of said particles entering the upstream region of the combustor via the second inlet.3. A combustor as claimed in claim 2, wherein the combustion chamber is so constructed and arranged that both volatile and char burnout of the biomass fuel particles is complete within 100 ms of the particles entering the upstream region of the combustor via the second inlet.4. A combustor as claimed in claim 1, wherein the combustion chamber is substantially defined by a flame can.5. A combustor as claimed in claim 4, wherein the flame can is predominantly made of metal.6. A combustor as claimed in claim 4, wherein the flame can, at least in the region of the first and second fuel inlets, is unlined with refractory material.7. A combustor as claimed in claim 4, wherein the flame can is substantially enclosed by a wind box, to form a chamber between the exterior of the flame can and the interior of the wind box, whereby a supply of pressurized cooling air to said chamber cools the flame can.8. A combustor as claimed in claim 7, wherein the air injection openings are provided in the wall of the combustion chamber, opening into the wind box, so that the pressurized cooling air supplied to the chamber between the combustion chamber and the wind box enters the combustion chamber via said openings.9. A combustor as claimed in claim 1, wherein the first inlet forms part of a burner for the secondary fuel.10. A combustor as claimed in claim 9, wherein the burner is for fluid fossil fuel.11. A combustor as claimed in claim 1, wherein the first inlet is positioned relative to the cyclonic combustion chamber such that in use, the flame produced by combustion of the secondary fuel is generally tangential to the longitudinal axis of the chamber.12. A combustor as claimed in claim 11, wherein the first and second inlets are generally diametrically opposite one another.13. A combustor as claimed in claim 1, wherein the first inlet is generally coaxial with the longitudinal axis of the combustion chamber.14. A combustor as claimed in any claim 1, wherein the combustor is provided with a first outlet for receiving the efflux from the combustion chamber of the hot pressurized combustion gas resulting from the biomass and/or secondary fuel combustion.15. A combustor as claimed in claim 1, wherein said one ore more third inlets are provided and are arranged to introduce air into the dilution chamber to reduce the cyclonic motion and temperature of the hot pressurized combustion gas passing therethrough.16. A combustor as claimed in claim 1, wherein the combustion chamber is provided with an outlet for the removal of ash.17. A direct cycle biomass-fired gas turbine system, comprising: a biomass fuel combustor as claimed in claim 1; anda gas turbine including a turbine section, arranged to receive and be driven by the hot pressurized combustion gas resulting from said biomass combustion, and a compressor section. 18. A system as claimed in claim 17, wherein the gas turbine is so constructed and arranged that, when operated in a recuperated cycle at a turbine section gas inlet pressure in the range of 3-7 times atmospheric pressure, the gas turbine will work at maximum efficiency.19. A system as claimed in claim 17, wherein the turbine section comprises a stator and a rotor that are tolerant to ash present in the hot pressurized combustion gas, with passages between the blades of the stator and the rotor being configured so as to minimize deposition and impaction of ash particles of the size present in the hot pressurized combustion gas.20. A system as claimed in claim 17, wherein the turbine section is of the radial flow type.21. A system as claimed in claim 17, wherein the gas turbine is derived from an adapted automotive, marine or similar turbocharger.22. A system as claimed in claim 17, wherein the gas turbine is so constructed arid arranged as to work at high efficiency at a turbine section inlet gas temperature of less than 900° C.23. A system as claimed in claim 17, wherein the turbine section is arranged to receive the hot pressurized combustion gas directly from the combustor.24. A system as claimed in claim 17, wherein the gas turbine includes a drive shaft connecting its turbine and compressor sections.25. A system as claimed in claim 24, wherein the gas inlet to the turbine section is not coaxial with the axis of said shaft.26. A system as claimed in claim 24, wherein the turbine includes only a single said drive shaft.27. A system as claimed in claim 24, wherein the gas inlet to the turbine section is generally tangential to sad axis.28. A system as claimed in claim 17, wherein said turbine section includes a single turbine stage.29. A system as claimed in claim 28, wherein said turbine section includes a radial inflow turbine wheel.30. A system as claimed in claim 17, wherein said compressor section includes a single compressor stage.31. A system as claimed in claim 30, wherein the compressor section includes a centrifugal compressor wheel.32. A system as claimed in claim 17, wherein at least one of said turbine and compressor sections is multi-staged.33. A method of pressurized combustion of biomass fuel to produce power, the method comprising:providing a system as claimed in claim 17; combusting biomass fuel under pressure in the combustor to produce hot pressurized combustion gas; expanding said hot pressurized combustion gas through the turbine section of the gas turbine to produce a power output. 34. A method as claimed in claim 33, further comprising supplying a secondary gas and/or liquid fuel to the combustion chamber of the combustor.35. A method of pressurized combustion of biomass fuel in a biomass fuel combustor to produce a pressurized exhaust gas for use in a direct cycle biomass-fired gas turbine system, the method comprising:providing a biomass fuel combustor having a cyclonic combustion chamber; supplying fluid secondary fuel to an upstream combustion region of said combustion chamber; combusting said secondary fuel in said upstream region of said combustion chamber; supplying biomass fuel particles to said upstream region of said combustion chamber with a tangential component to promote cyclonic motion of gases and biomass particles in said upstream region; at least during start-up of the combustor fragmenting said supplied biomass fuel particles in said upstream region using the heat generated by the combustion of said secondary fuel in said upstream region; passing the fragmented biomass particles from said upstream region to a downstream region of said combustion chamber; adding air into said downstream region with a tangential component to promote cyclonic motion of gases and fragmented biomass particles in said downstream region; completing combustion of said fragmented biomass particles in said downstream region; and diluting with air a hot pressurized combustion gas produced by combustion of the biomass particles and/or secondary fuel. 36. A method as claimed in claim 35, wherein said combustion of said biomass particles produces hot pressurized combustion gas, which gas is expanded through the turbine section of a gas turbine to produce a power output.37. A method as claimed in claim 35, wherein the secondary fuel is used for start-up of said method, for supporting sustained ignition of the biomass fuel in the combustion chamber of the combustor and for responding to variations in the demand for pressurized exhaust gas.38. A method as claimed in claim 35, wherein on start-up of the process only secondary fuel is supplied to the combustion chamber, with feeding of the biomass fuel being commenced only after combustion in the chamber has been established with the secondary fuel.39. A method as claimed in claim 35, wherein at start-up, as the rate of feed of biomass fuel to the combustor is increased, the rate of supply of secondary fuel is reduced.40. A method as claimed in claim 35, wherein the rate of supply of secondary fuel is varied in response to variations in turbine shaft speed and power output demand.41. A method as claimed in claim 36, wherein the hot pressurized combustion gas is supplied to the turbine section at a temperature of approximately 700° C.-900° C.42. A method as claimed in claim 36, wherein the hot pressurized combustion gas is supplied to the turbine section at a pressure of approximately 3-7 times atmospheric pressure.43. A method as claimed in claim 36, wherein the hot pressurized combustion gas is supplied to the turbine section at a temperature below the ash fusion temperature of the biomass fuel.44. A method as claimed in claim 43, wherein the ash fusion temperature is greater than 800° C.45. A method as claimed in claim 35, wherein the pressure in the combustor is in the range of approximately 3-7 times atmospheric pressure.46. A method as claimed in claim 36, wherein the turbine section is tolerant to deposition, erosion and corrosion from the exhaust gas.47. A method as claimed in claim 35, wherein the biomass fuel is supplied to the combustion chamber of the combustor from a fuel supply at atmospheric pressure through a valve operated to maintain the higher pressure in the combustion chamber.48. A method as claimed in claim 35, wherein air is supplied to the combustion chamber at a rate approximately twice that necessary for stoichiometric combustion.49. A method as claimed in claim 35, wherein the heat release rate of the combusted biomass fuel is greater than 5 MW/m3 of biomass fuel.50. A method as claimed in claim 49, wherein the heat release rate is such that both volatile and char burnout of the biomass fuel is complete within 100 ms.51. A method as claimed in claim 35, wherein the mean temperature at the outlet from the combustion chamber of the combustor is typically between 1100° C. and 1500° C.52. A method as claimed in claim 35, wherein the temperature of the hot pressurized combustion gas exiting the dilution chamber is typically between 700° C. and 900° C.53. A method as claimed in claim 35, wherein ash is removed by passing the hot pressurized combustion gas through a filter between the combustor and the gas turbine.54. A method as claimed in claim 35, wherein the system can run and produce full power when solely fuelled by the secondary fuel.55. A method as claimed in claim 35, wherein the gas turbine is used to generate electrical power.56. A method as claimed in claim 35, wherein the compressor section of the gas turbine is used to compress air, at least some of the compressed air so produced being supplied to the combustor with the biomass fuel.57. A method as claimed in claim 56, wherein said compressed air is also used to cool the combustor.58. A method as claimed in claim 35, further comprising taking the expanded waste gas from the turbine section's exit and using said waste gas to heat compressed air output by the gas turbine's compressor section and/or in a heat recovery heat exchanger as part of a CHP system and/or for direct use as part of a drying system.59. A method as claimed in claim 35, wherein the ash particles produced by the biomass particle combustion are of a sufficiently small size that they will pass through the turbine section without significant deposition, erosion or corrosion damage to the blades of the turbine section.60. A method as claimed in claim 59, wherein the ash particles produced by the biomass particle combustion have a mean size of <1 micron.61. A process as claimed in claim 35, wherein the biomass fuel particles fragment within 10 ms of the particles entering the combustion chamber of the combustor.62. A process as claimed in claim 61, wherein the particles fragment to a mean size of <<1 mm.63. A combustor as claimed in claim 9, wherein the burner is for fluid bio-fuel.