TORREFACTION UNIT AND METHOD

Abstract

The torrefaction unit 1 comprises at least one multiple hearth furnace 2 which is heated by a heat transfer fluid 16 comprising hot water taken form a water space 21 of a steam drum 11. The heat transfer fluid 16 is guided through a water circuit 20 to a heating system 19 of the at least one multiple hearth furnace 2. This means the multiple hearth furnace 2 is heated to a torrefaction temperature indirectly by the use of hot water as heat transfer fluid 16. This is environmentally advantageous. The torrefaction gas 3 created by the torrefaction of material comprising biomass such as municipal solid waste is preferably partially oxidized in a partial oxidation reactor 23 for creating syngas. Preferably, a part of the thermal energy of the syngas is used in an evaporator 9 and/or a superheater 13 to heat water and/or steam and/or to evaporate water. The evaporated water is preferably guided to a steam space 22 of the steam drum 11 and can, thus, be used to heat the heat transfer fluid 16. The partial oxidation reactor 23 and the temperature of the heat transfer fluid 16 can be controlled independently allowing to one single partial oxidation reactor 23 for at least two multiple hearth furnaces 2.

Claims

1. A torrefaction unit (1) for the torrefaction of a material comprising biomass, comprising at least one multiple hearth furnace (2), said multiple hearth furnace (2) comprising a heating system (19) which can be flown through by a heat transfer fluid (16), characterized in that the heating system (19) is connected to a water circuit (20) by which water is heatable and conveyable through the heating system (19).

2. A torrefaction unit (1) according to claim 1, further comprising a partial oxidation reactor (23) including a burning chamber (4) being connected to the at least one multiple hearth furnace (2) for the partial oxidation of torrefaction gas (3) with oxygen creating a syngas (8).

3. A torrefaction unit (1) according to claim 2, wherein a single partial oxidation reactor (23) is connected to at least two multiple hearth furnaces (2).

4. A torrefaction unit (1) according to claim 1, further comprising a steam drum (11) having a steam space (22) and a water space (21), wherein the water circuit (20) is connected to the water space (21) of the steam drum (11).

5. A torrefaction unit (1) according to claim 4, wherein the water space (21) and the steam space (22) of the steam drum (11) are in fluid connection with an evaporator (9) which is heatable by syngas (8) generated by partial oxidation of torrefaction gas (3).

6. A torrefaction unit (1) according to claim 4, wherein the steam space (22) of the steam drum (11) is in fluid connection with a superheater (13) which is heatable by syngas (8) generated by partial oxidation of torrefaction gas (3).

7. A method for the torrefaction of a material comprising biomass, wherein the material is heated to a torrefaction temperature in at least one multiple hearth furnace (2), wherein the atmosphere in the at least one multiple hearth furnace (2) is controlled to provide a sub-stoichiometric amount of oxygen, characterized in that the at least one multiple hearth furnace (2) is heated by a heat transfer (16) fluid comprising water.

8. A method according to claim 7, wherein torrefaction gas (3) is generated by the torrefaction of the material, said torrefaction gas (3) being partially oxidized to generate a syngas (8).

9. A method according to claim 8, wherein the torrefaction gas (3) of at least two multiple hearth furnaces (2) is partially oxidized in a single partial oxidation reactor (23).

10. A method according to claim 7, wherein the heat transfer fluid (16) comprises water taken from a steam drum (11).

11. A method according to claim 10, wherein the heat transfer fluid (16) is guided in a water circuit (20) from the steam drum (11) through a heating system (19) of the at least one multiple hearth furnace (2) and back to the steam drum (11).

12. A method according to claim 10, wherein torrefaction gas (3) is generated by the torrefaction of the material, said torrefaction gas (3) being partially oxidized to generate a syngas (8), the syngas (8) being used to at least in part evaporate water (10) pro-vided from a water space (21) of said steam drum (11), wherein the at least partly evaporated water (10) is provided to a steam space (22) of said steam drum (11) after evaporation.

13. A method according to claim 10, wherein torrefaction gas (3) is generated by the torrefaction of the material, said torrefaction gas (3) being partially oxidized to generate a syngas (8), the syngas (8) being used to superheat steam (12) provided from a steam space (22) of the steam drum (11).

14. A method according to claim 7, wherein the atmosphere in the at least one multiple hearth furnace (2) is controlled to provide an oxygen content of less than 1 vol.-%.

Description

[0024] It should be noted that the individual features specified in the claims may be combined with one another in any desired technologically reasonable manner and form further embodiments of the invention. The specification, in particular taken together with the FIGURES, explains the invention further and specifies particularly preferred embodiments of the invention. Particularly preferred variants of the invention and the technical field will now be explained in more detail with reference to the enclosed figures. It should be noted that the exemplary embodiment shown in the FIGURES is not intended to restrict the invention. The figures are schematic and may not be to scale. The single FIGURE displays:

[0025] FIG. 1 a process scheme of the torrefaction unit.

[0026] FIG. 1 displays a torrefaction unit 1. The torrefaction unit 1 comprises in this example three multiple hearth furnaces 2 two of which are only displayed very schematically. In each multiple hearth furnace 2 a material comprising biomass is torrefied, i.e. heated within in an atmosphere which is substoichiometric regarding an oxidation of the material at temperatures of up to 300 C. and is preferably virtually free of oxygen, i.e. is having an oxygen content of less than 1 vol.-%. Each multiple hearth furnace 2 comprises several hearths 18. The material is applied to the uppermost hearth 18 and is conveyed around each hearth 18 and downwards from hearth 18 to hearth 18. The multiple hearth furnace 2 is heated to a torrefaction temperature, e.g. to about 300 C. This is performed by a heating system 19. The heating system 19 comprises ducts through which hot water is conveyed to heat the multiple hearth furnace 2 indirectly. The water is provided to the heating system 19 from a water circuit 20. The water is preferably boiler water, i.e. conditioned to reduce corrosion in a boiler water/steam cycle.

[0027] By the torrefaction, volatiles of the material are released comprising water, carbon monoxide, carbon dioxide, smaller oxygenated hydrocarbons and tars. The remaining solid material taken from of the multiple hearth furnace 2 is improved regarding its grindability and can be used in different processes. A further product of the torrefaction process is, thus, a torrefaction gas 3 comprising the volatiles. Preferably, the torrefaction gas 3 is provided via a burner 4 to burning chamber 25 for partial oxidization with oxygen from an oxygen comprising gas 5, preferably pure oxygen. Auxiliary fuel 26 can be provided to the burner 4 as well, in particular for starting up. A control line is depicted as a dashed line by which valves regulating the flow of auxiliary fuel 26 and/or superheated steam 14, in particular based on the pressure in a steam space 22 of the steam drum 11, are controllable.

[0028] One product of this partial oxidation is syngas which is quenched with cooler quenching syngas 7 in a quenching chamber 6 resulting in a cooled syngas 8 which is provided to an evaporator 9. Solids or melted solids in the syngas are solidified due to the quenching process and are preferably removed from the syngas.

[0029] The cooled syngas 8 after quenching has a temperature of e.g. 730 C. to 770 C. A part of the thermal energy of the cooled syngas 8 is used to at least partly evaporate water 10. Said water 10 is provided from a water space 21 of a steam drum 11 and is returned to a steam space 22 of the steam drum 11. Steam 12 from the steam space 22 of the steam drum 11 is guided via a superheater 13 to superheat the steam 12 using thermal energy from the cooled syngas 8 generating superheated steam 14 which can be used in at least one steam consumer (not shown) in which the steam is used e.g. to drive a turbine, to feed a dryer etc. The superheated steam 14 has a temperature of e.g. 340 C. to 360 C. and a pressure of 130 bar to 150 bar. Downstream of the superheater 13 the cooled syngas 8 can be further used e.g. for synthesizing longer chemical molecules, e.g. methanol or the like. Boiler feedwater 15 can be used to provide the steam drum 11 with liquid water. Boiler feedwater 15 has preferably a conductivity of less than 5 S/cm [mikrosiemens per centimeter]. Boiler feedwater 15 is preferably conditioned for anti-corrosive properties, preferably by providing ammonia to the boiler feedwater 15.

[0030] The steam drum 11 is part of the water circuit 20. Heat transfer fluid 16 comprising hot boiler water from the water space 21 of the steam drum 11 is conveyed by a pump 17 through the ducts of the water circuit 20 to heating system 19 of at least one multiple hearth furnace 2.

[0031] The steam drum 11 is controlled such that the heat transfer fluid 16 is taken from the water space 21 as liquid and has preferably a temperature from 335 C. to 345 C. when exiting the steam drum 11. The heat transfer fluid 16 is guided through respective heating ducts of the heating system 19 in the walls of the at least one multiple hearth furnace 2, preferably in the ceilings of respective stages of the multiple hearth furnaces 2, to heat the interior of the multiple hearth furnace 2 to the torrefaction temperature. After having heated the multiple hearth furnace 2 the heat transfer fluid 16 is returned to the steam drum 11 via the water circuit 20. Usually, the temperature of the heat transfer fluid 16 downstream the multiple hearth furnace 2 is reduced by 15 C. to 25 C. compared to the temperature of the heat transfer fluid 16 upstream of the multiple hearth furnace 2.

[0032] Preferably, the steam space 22 of the steam drum 11 is connectable to a steam grid 24. This allows to use steam from an external source to start-up the steam drum 11, if necessary.

[0033] The torrefaction unit 1 comprises at least one multiple hearth furnace 2 which is heated by a heat transfer fluid 16 comprising hot water taken form a water space 21 of a steam drum 11. The heat transfer fluid 16 is guided through a water circuit 20 to a heating system 19 of the at least one multiple hearth furnace 2. This means the multiple hearth furnace 2 is heated to a torrefaction temperature indirectly by the use of hot water as heat transfer fluid 16. This is environmentally advantageous. The torrefaction gas 3 created by the torrefaction of material comprising biomass such as municipal solid waste is preferably partially oxidized in a partial oxidation reactor 23 for creating syngas. Preferably, a part of the thermal energy of the syngas is used in an evaporator 9 and/or a superheater 13 to heat water and/or steam and/or to evaporate water. The evaporated water is preferably guided to a steam space 22 of the steam drum 11 and can, thus, be used to heat the heat transfer fluid 16. The partial oxidation reactor 23 and the temperature of the heat transfer fluid 16 can be controlled independently allowing to one single partial oxidation reactor 23 for at least two multiple hearth furnaces 2.

REFERENCE NUMERALS

[0034] 1 torrefaction unit [0035] 2 multiple hearth furnace [0036] 3 torrefaction gas [0037] 4 burner [0038] 5 oxygen comprising gas [0039] 6 quenching chamber [0040] 7 quenching syngas [0041] 8 cooled syngas [0042] 9 evaporator [0043] 10 water [0044] 11 steam drum [0045] 12 steam [0046] 13 superheater [0047] 14 superheated steam [0048] 15 boiler feedwater [0049] 16 heat transfer fluid [0050] 17 pump [0051] 18 hearth [0052] 19 heating system [0053] 20 water circuit [0054] 21 water space [0055] 22 steam space [0056] 23 partial oxidation reactor [0057] 24 steam grid [0058] 25 burning chamber [0059] 26 auxiliary fuel