METHOD AND SYSTEM FOR CONTINOUSLY TREATING BIOMASS MATERIAL

Abstract

A method for continuously treating biomass material includes: feeding the biomass material into a substantially vertically arranged pressurized vessel; adding steam to said pressurized vessel for hydrothermal treatment of the biomass material, wherein said adding steam comprises adding steam at a lower portion of the pressurized vessel; discharging the biomass material from a bottom portion of the pressurized vessel using a discharge device; withdrawing vapor from a top portion of the pressurized vessel, and adding said vapor to the discharge device; controlling differential pressure between said top portion of the pressurized vessel and said discharge device by controlling a flow of said vapor; and determining a minimum flow of steam needed to heat the biomass material in the pressurized vessel to a predetermined temperature, wherein said adding steam comprises adding steam at a flow that is higher than said minimum flow.

Claims

1.-15. (canceled)

16. A method for continuously treating biomass material comprising: feeding the biomass material into a substantially vertically arranged pressurized vessel; adding steam to said pressurized vessel for hydrothermal treatment of the biomass material, wherein said adding steam comprises adding steam at a lower portion of the pressurized vessel; discharging the biomass material from a bottom portion of the pressurized vessel using a discharge device; withdrawing vapor from a top portion of the pressurized vessel, and adding said vapor to the discharge device; controlling differential pressure between said top portion of the pressurized vessel and said discharge device by controlling a flow of said vapor; and determining a minimum flow of steam needed to heat the biomass material in the pressurized vessel to a predetermined temperature, wherein said adding steam comprises adding steam at a flow that is higher than said minimum flow.

17. The method according to claim 16, further comprising adding discharge steam from a source of steam to the discharge device, wherein said differential pressure is controlled by controlling the flow of said discharge steam.

18. The method according to claim 16, wherein said discharge device comprises a pressure sealing screw arranged at said bottom portion of the pressurized vessel, and a steam explosion device, wherein said vapor is added to said steam explosion device.

19. The method according to claim 18, wherein said steam explosion device comprises a discharge chamber connected to the pressure sealing screw to receive discharged biomass, and a blow valve arranged for steam explosion discharge of the biomass from said discharge chamber, wherein said vapor is added to said discharge chamber.

20. The method according to claim 16, wherein said adding steam comprises adding steam at or near said top portion of the pressurized vessel.

21. The method according to claim 16, wherein said adding steam comprises adding steam together with the biomass material by means of a mixing device arranged upstream of the pressurized vessel.

22. The method according to claim 16, wherein said adding steam comprises adding at least 50% of overall added steam at said lower portion.

23. The method according to claim 16, wherein said adding steam comprises adding steam at a flow being at least 50% higher than said minimum flow.

24. The method according to claim 16, wherein said controlling comprises controlling the flow using a valve arranged in a conduit connecting said top portion of the pressurized vessel and said discharge device.

25. The method according to claim 17, wherein: said controlling comprises controlling the flow using a valve arranged in a conduit connecting said top portion of the pressurized vessel and said discharge device; and said discharge steam is added to said discharge device indirectly by being added to said conduit.

26. The method according to claim 16, wherein said vapor comprises steam and/or VOC and/or inert gases.

27. A system for continuous hydrothermal steam treatment of biomass material, said system comprising: a substantially vertically arranged pressurized vessel; a discharge device configured to discharge the biomass material from a bottom portion of the pressurized vessel; a conduit connecting a top portion of the pressurized vessel with said discharge device, said conduit comprising a control valve for controlling a flow of vapor from said top portion to said discharge device; a pressure measurement device configured to measure differential pressure between said top portion of the pressurized vessel and said discharge device, at least one steam injection nozzle configured to inject steam into said pressurized vessel, each injection nozzle comprising a corresponding valve to control the steam flow, wherein at least one of said at least one steam injection nozzle is arranged at a lower portion of said pressurized vessel, and a control unit configured to control said control valve in response to differential pressure measurement data from said pressure measurement device, the control unit further being configured to determine a minimum flow of steam needed to heat the biomass material in the pressurized vessel to a predetermined temperature, and to control each valve of the at least one steam injection nozzle such that the total flow of steam into the pressurized vessel is higher than said minimum flow.

28. The system according to claim 27, further comprising at least one steam injection device configured to directly or indirectly provide discharge steam to the discharge device, wherein said control unit is configured to control said control valve and said steam injection device in response to differential pressure measurement data from said pressure measurement device.

29. The system according to claim 27, wherein said discharge device comprises a pressure sealing screw arranged at said bottom portion of the pressurized vessel, and a steam explosion device, wherein said conduit is connected to said steam explosion device.

30. The system according to claim 29, wherein said the steam explosion device comprises a discharge chamber connected to the pressure sealing screw to receive discharged biomass, and a blow valve arranged for steam explosion discharge of the biomass from said discharge chamber, wherein said conduit is connected to said discharge chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show presently preferred embodiments of the invention, wherein:

[0037] FIG. 1 shows a schematic illustration of an embodiment of the system according to the second aspect of the invention;

[0038] FIG. 2 shows a schematic illustration of another embodiment of the system according to the second aspect of the invention, and

[0039] FIG. 3 shows a flow chart of an embodiment of the method according to the first aspect of the invention.

DETAILED DESCRIPTION

[0040] FIG. 1 shows a schematic illustration of an embodiment of the system according to the second aspect of the invention.

[0041] Biomass A is fed to the container 1, from which the biomass is continuously conveyed with a screw feeder 2, to a conical screw 3 for feeding of it into a pressurized vessel 4, e.g. a reactor. The conical screw compresses the biomass to a gas-tight plug which seals the pressure of the vessel 4 to atmospheric. A conical screw is a preferred but not a mandatory solution of feeding material to the vessel 4. It may optionally be replaced with other technical solutions such as a rotary lock feeder or a lock hopper system. The vessel 4 is substantially vertically arranged. Biomass from the screw 3 falls by gravity inside the vessel 4 and piles up inside the vessel. The biomass pile slowly moves downwards as it is continuously emptied in the bottom of the vessel 4 with a discharge screw 6 as a treated biomass C.

[0042] Steam B is added to a lower portion of the vessel 4 by means of steam injection nozzle 5b. The steam flow is controlled by valve 5a. The steam heats the biomass inside the vessel 4.

[0043] Steam D is also added to an upper portion of the vessel 4 by means of at least one additional steam injection nozzle 13b and valve 13a. At least 50% of the steam is added using the lower steam injection nozzle. The total flow of steam B, D provided by nozzles 5b, 13b is controlled to be at least 1.5 times the minimum flow of steam needed to heat the biomass material in the pressurized vessel to a predetermined temperature. Optionally, the valves 5a, 13a are electrically controlled by control unit 12 to achieve the desired flows.

[0044] A discharge device is formed by discharge screw 6 arranged at the bottom portion of the vessel and a thereto connected steam explosion device 7a-b, 8. The discharge screw continuously empties the bottom of the reactor. The discharge screw is of the pressure-sealing type, i.e. is gas-tight just like the feeding screw 3 which means that no steam passes concurrently with biomass to the discharge chamber 7a of the steam explosion device, which further comprises a blow valve/discharge nozzle 8 in the chamber 7. The steam explosion device further comprises a transport screw 7b arranged in the discharge chamber to convey the biomass towards the blow valve/discharge nozzle 8.

[0045] Accumulated VOC/NCG and excess steam in the gas phase of vessel 4 are led from the top portion of the vessel to the discharge chamber 7a via a conduit 9 connecting a top portion of the pressurized vessel with the discharge device, said conduit being provided with an electrically controllable valve 10 for controlling the flow of vapor in the conduit. A pressure measurement device is provided, which device comprises two pressure sensors 11a, 11b, one arranged at the top portion of the vessel, and one in the discharge device. The valve 10 and pressure sensors 11a, 11b are electrically connected to a control unit 12 configured to control valve 10 in response to differential pressure measurement data from the pressure sensors.

[0046] Typical operating conditions are as follows: [0047] Temperature in reactor: 140-225? C. [0048] Pressure: corresponding pressure 2-30 bar (g) [0049] Residence time: 1 min-3 hours, preferably 3-20 minutes [0050] Delta pressure at discharge: 2-30 bar, preferably 2-15 bar or 2-10 bar.

[0051] FIG. 2 shows a schematic illustration of an embodiment of the system according to the second aspect of the invention. Container 101, screw feeder 102, conical screw 103, pressurized vessel 104, valve 105a, steam injection nozzle 105b, discharge screw 106, steam explosion device 107a-b, discharge nozzle 108, conduit 109, electrically controllable valve 110, pressure sensors 111a, 111b and control unit 112 correspond to the refs. 1-12 in FIG. 1.

[0052] The embodiment in FIG. 2 differs in that steam is solely injected into the vessel 104 at a lower portion of the vessel using nozzle 105b. A further difference is that a steam injection device 114b is provided which is connected to conduit 109 to provide (fresh non-recirculated) discharge steam E to the discharge chamber 107a via the conduit. The control unit 112 is configured to control not only the electrically controllable valves 110 (as in FIG. 1) but also electrically controllable 114a in response to differential pressure measurement data from said pressure measurement device.

[0053] The flow of steam provided by nozzle 105b is controlled to be about 2 times the minimum flow of steam needed to heat the biomass material in the pressurized vessel to a predetermined temperature. For example, assuming that a total of 7 ton of fresh steam per hour is to be added to the system, and that 3 ton/hour is required for heating of the biomass, then about 6 ton/hour is added via nozzle 105b at the bottom of the vessel, and 1 ton/hour is added to the discharge chamber 107a using nozzle 114a via conduit 109.

[0054] FIG. 3 shows a flow chart of an embodiment of the method according to the first aspect of the invention.

[0055] The method comprises continuously feeding 201 the biomass material into a substantially vertically arranged pressurized vessel, continuously adding 202 steam to the pressurized vessel for hydrothermal treatment of the biomass material, continuously discharging 203 the biomass material from a bottom or lower portion of the pressurized vessel by means of a discharge device, continuously withdrawing 204 vapor from a top or upper portion of the pressurized vessel, and adding the vapor 205 to the discharge device, determining differential pressure 206 between the top or upper portion of the pressurized vessel and the discharge device, and controlling the vapor flow 207 such that the differential pressure approaches a target value. For instance, if the differential pressure is larger than its target value, the vapor flow is increased and vice versa.

[0056] The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, steam may be injected at further positions in the vessel, for instance at a vertically intermediate position or using a mixer upstream of the vessel. Further, the steam explosion device may be configured differently, for example without a transport screw. Further, the vessel may be provided with a vent at its top portion for venting off accumulated VOC/NCG and steam which is not presently possible to add to the discharge device. The scope of protection is determined by the appended patent claims.