Biochar Purification Unit

Abstract

The present inventive concept relates to a system for production and conditioning of high-quality biochar. The system comprises a gasification reactor adapted to transform biomass to syngas and biochar by a first thermochemical conversion and a biochar purification unit adapted to subject the biochar to a second thermochemical conversion and thereby prolonging conversion residence time. A first part of the biochar purification unit comprises a biochar inlet fluidly connected to the gasification reactor and a second part of the biochar purification unit, arranged downstream from the first part, comprises an inert gas inlet for purging the biochar within the biochar purification unit.

Claims

1. A system for production and conditioning of high-quality biochar, said system comprising: a gasification reactor adapted to transform biomass to syngas and biochar by a first thermochemical conversion; and a biochar purification unit adapted to subject said biochar to a second thermochemical conversion and thereby prolonging conversion residence time, wherein a first part of said biochar purification unit comprises a biochar inlet fluidly connected to said gasification reactor and a second part of said biochar purification unit, arranged downstream from said first part, comprises an inert gas inlet for purging said biochar within said biochar purification unit.

2. A system according to claim 1, wherein said gasification reactor is an entrained flow gasifier.

3. A system according to claim 1, said biochar purification unit is heated at least partly by external heating means, such as a heat-exchanger or an electric heater.

4. A system according to claim 1, wherein said biochar purification unit comprises an oxidant gas inlet located in said first part of said biochar purification unit.

5. A system according to claim 1, wherein said biochar purification unit comprises a gas outlet for syngas and purged gases located in said first part of said biochar purification unit.

6. A system according to claim 5, wherein said gas outlet is fluidly connected to said gasification reactor to enable feeding of syngas and purged gases back to said gasification reactor.

7. A system according to claim 1, wherein said biochar purification unit has a length between 1 to 8 meters, such as 3 to 6 meters.

8. A process for production and conditioning of high-quality biochar, said process comprising: i) providing a system according to claim 1, said system comprising a gasification reactor and a biochar purification unit; ii) in said gasification reactor, transforming biomass to syngas and biochar by a first thermochemical conversion; iii) feeding said biochar to said biochar purification unit to transform said biochar into partly purified biochar and syngas by a second thermochemical conversion; and iv) in said biochar purification unit, purging said partly purified biochar with inert gas to carry remaining hydrocarbon volatiles from said partly purified biochar.

9. A process according to claim 8, wherein said inert gas is selected from nitrogen (N.sub.2) or carbon dioxide (CO.sub.2).

10. A process according to claim 8, wherein said inert gas is caused to move in a countercurrent direction to a screw transportation direction of said biochar purification unit.

11. A process according to claim 8, comprising a step of feeding said syngas and purged gases back to said gasification reactor.

12. A process according to claim 8, comprising a step of feeding an oxidant into said biochar purification unit to promote said second thermochemical conversion.

13. A process according to claim 8, wherein the lambda value in said biochar purification unit is lower than the lambda value in said gasification reactor.

14. A process according to claim 8, wherein said first part has a lambda value of 0.1 to 0.2 and said second part has a lambda value of 0.

15. A process according to claim 8, wherein the residence time of said biochar in said biochar purification unit is from 2 to 20 minutes, such as 5 to 15 minutes or 10 to 12 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the following description, the present inventive concept is described with reference to a biochar purification system for production and conditioning of high-quality biochar.

[0040] FIG. 1a illustrates a system for production and conditioning of high-quality biochar according to at least one example embodiment of the inventive concept;

[0041] FIG. 1ab illustrates a system for production and conditioning of high-quality biochar according to at least one example embodiment of the inventive concept;

[0042] FIG. 2 illustrates a process for production and conditioning of high-quality biochar according to at least one example embodiment of the inventive concept.

DETAILED DESCRIPTION

[0043] FIG. 1a illustrates a system 10 for production and conditioning of high-quality biochar. The system 10 comprises a gasification reactor 12 and a biochar purification unit 14 fluidly connected to an outlet of the gasification reactor 12. The gasification reactor 12, which may be an entrained-flow gasification reactor 12, is adapted to transform biomass to syngas and biochar by a first thermochemical conversion. The biochar purification unit 14 is adapted to subject the biochar that exits the gasification reactor 12 to a second thermochemical conversion, thereby prolonging the conversion residence time. The biochar purification unit 14 is thus adapted to receive the biochar from the biochar reactor 12 and subject the biochar to further thermochemical conversion. The length of the biochar purification unit 14 may be in the interval between 1 to 8 meters, such as 3 to 6 meters.

[0044] The biochar purification unit 14 in FIG. 1a comprises a first part 20 and a second part 30. The first part 20 comprises a biochar inlet 22, a gas outlet 24, and optionally an oxidant gas inlet 26 for oxygen and/or air and the second part 30 comprises a biochar outlet 34 and an inert gas inlet 32.

[0045] In FIG. 1a, the first part 20 is located adjacent to the gasification reactor 12, e.g., towards a first end of the biochar purification unit 14, and the second part 30 is located remote from the gasification reactor 12, e.g., towards a second end of the biochar purification unit 14. Hereby a first end of the biochar purification unit 14 is located in the first part 20 and a second end of the biochar purification unit 14 is located in the second part 30. However, the biochar purification unit 14 according to the inventive concept may comprise more than two parts, such as a three or four parts. Hence, the second part 30 may not be located towards the second end of the biochar purification unit 14 as in FIG. 1a.

[0046] The biochar that exits the gasification reactor 12 is fed to the biochar purification unit 14 through a biochar inlet 22 located at the first part 20 of the biochar purification unit 14, e.g., towards the first end, and exits the biochar purification unit 14 through a biochar outlet 34 provided the second part 30 of the biochar purification unit 14, e.g., towards the second end. In case the biochar purification unit 14 comprises more than two parts, the biochar outlet 34 may be located in another part than the second part 30, such as a third or fourth part. No matter how many parts the biochar purification unit 14 comprises, the biochar outlet 34 may preferably be located towards a second end of the biochar purification unit 14.

[0047] In the first part 20 of the biochar purification unit 14, the oxidant gas inlet 26 for oxygen and/or air is provided to enhance the second thermochemical conversion of the hot biochar as it enters the biochar purification unit 14.

[0048] In the second part 30 of the biochar purification unit 14, e.g., towards the second end, the inert gas inlet 32 is provided to purge remaining hydrocarbon volatiles from the biochar and thus provide biochar of high quality. The location of the inert gas inlet 32 in the second part 30, e.g., near the second end, allows the inert gas to flow in a counter current direction to the biochar. The syngas produced in the biochar purification unit 14 and the purged gases exit the biochar purification unit 14 through a gas outlet 24 located in the first part 20. In FIG. 1a, the biochar inlet 22 serves as gas outlet 24 and the syngas and purged gases are fed back to the gasification reactor 12. The outlet of the gasifier fluidly connected to the biochar inlet 22 allows the biochar produced in the gasification reactor 12 to be fed to the biochar purification unit 14 at the same time as the hydrocarbon volatiles and/or produced gases is fed back to the gasification reactor 12.

[0049] FIG. 1b illustrates the system 10 for production and conditioning of high-quality biochar in FIG. 1a with the difference that the system in FIG. 1b comprises a gas outlet 24 which is separated from the biochar inlet 22.

[0050] FIG. 2 illustrates a schematic flow chart describing a process for production and conditioning of high-quality biochar. The process comprises a step S1 of providing a system 10 for production and conditioning of high-quality biochar. The system 10 comprises a gasification reactor 12 and a biochar purification unit 14 fluidly connected to the gasification reactor 12. The gasification reactor 12 may be an entrained-flow gasification reactor 12.

[0051] Next, biomass is fed to the gasification reactor 12 in which the biomass is transformed, S2, into syngas and biochar by a first thermochemical conversion. The temperature of the first thermochemical conversion may typically be in the interval between 850? C. to 1200? C. The residence time of the biomass in the first thermochemical conversion may typically be in the interval between 1 to seconds.

[0052] The biochar produced in the gasification reactor 12 leaves the gasification reactor 12 and is fed to the biochar purification unit 14 in which the biochar is subjected to a second thermochemical conversion. The biochar is thus transformed, S3, by a second thermochemical conversion to fully converted biochar and syngas. The biochar may be fed to the biochar purification unit 14 through a biochar inlet 22 located at a first part 20 of the biochar purification unit 14, e.g., near a first end of the biochar purification unit 14.

[0053] The temperature of the biochar entering the biochar purification unit 14 is typically in the interval between 700? C. to 1200? C. This temperature is sufficiently high for the biochar to allow for the second thermochemical conversion in the biochar purification unit 14. The temperature of the second thermochemical conversion may typically be in the interval between 700? C. to 1200? C. However, in order to enhance the second thermochemical conversion, the process may comprise a step of feeding an oxidant into the biochar purification unit 14. The oxidant may be fed in the first part 20 of the biochar purification unit 14, adjacent the first end.

[0054] The lambda value in the biochar purification unit 14 is typically lower than the lambda value in the gasification reactor 12. In the biochar purification unit 14, the lambda value in the first part 20 is typically higher than the lambda value in the second part 30. In the first part 20, the lambda value may be 0.1 to 0.2 whereas the second part 30 may have a lambda value of 0.

[0055] The residence time of the biomass and the biochar in the second thermochemical conversion and biochar purification may be in the interval between to 20 minutes. The feeding velocity of the biochar trough the biochar purification unit 14 may be 0.002 to 0.07 m/s.

[0056] In the biochar purification unit 14, an inert gas is used to purge, S4, remaining hydrocarbon volatiles from the biochar. High-quality biochar is then produced. An inert gas inlet 32 may for this purpose be provided in the second part of the biochar purification unit 14, e.g., adjacent a second end of the biochar purification unit 14. The location of the inert gas inlet 32 allows the inert gas to flow in a countercurrent direction to the biochar. The inert gas may be fed in a pressure over atmospheric pressure, such as 0.3 to 1.5 bar over atmospheric pressure in order to remove the purged gases in the countercurrent direction to the biochar in the biochar purification unit 14. The inert gas and the hydrocarbon volatiles purged from the biochar may thus be caused to flow out of the biochar purification unit 14 at the first part 20, e.g., through the biochar inlet 22, and to be fed back to the gasification reactor 12.