Continuous biomass pyrolysis device with separation of co-products by condensation and centrifugation

Abstract

Continuous biomass pyrolysis device with separation of co-products by condensation and centrifugation. The device according to the invention is a continuous pyrolysis device characterized in that it comprises the following steps: i) biomass drying step; ii) biomass pyrolysis step; iii) condensation and centrifugation step; iv) step of mixing carbon residues with wood vinegar; v) step of combustion of bio-oil in a burner; vi) step of combustion of biogas in an optional electric generator; vii) step of energy recovery in the form of heat in an optional Organic Rankine Cycle (ORC) machine. Figure for abstract: [Fig.1]

Description

Title of the invention: Continuous biomass pyrolysis device with separation of co-products by condensation and centrifugation Technical field

[0001] The present invention relates to a device for continuous pyrolysis of biomass with separation of co-products by condensation and centrifugation making it possible to obtain: a mixture of biochar and biopesticide capable of being used as a carbon sink, fertilizer and natural agricultural pesticide, a biogas capable of being used by an electric generator, heat capable of being used locally or by an organic Rankine cycle (ORC) machine, and finally a bio-oil with improved calorific value capable of being used by combustion to maintain the continuity of the pyrolysis reaction of the entire device mentioned above. Prior art

[0002] Continuous pyrolysis of biomass consists of subjecting it to high temperatures in the absence of oxygen to avoid any combustion reaction. Biomass is formed essentially of water, cellulose, hemicellulose and lignin. In the pyrolysis reaction, the biomass will therefore first dehydrate and then decompose as the temperature increases.

[0003] At the end of this process, two types of products are obtained: 1. Solid carbonaceous residues known by various names such as “biochar”, “agrichar”, “char”, “biochar”, “biocarbon”, “vegetable charcoal”, “green charcoal”, “coal”, “coke”, “pyrolytic coke”; 2. Condensable and incondensable gases, inseparable, which themselves allow three types of products to be obtained after treatment, the distribution of which depends on the temperature, the duration of pyrolysis and the biomass used: a. Non-condensable gases comprising mainly methane (CH4), dihydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2) known by various names such as “biogas”, “biogas”; “syngas”, “synthetic gas”, “synthesis gas”, “synthetic gas”, “manufactured gas”; b. An organic liquid phase known by various names such as “bio-oil”, “synthetic oil”, “bio-oil”, “synthetic oil”, “synoil”, “pyrolytic oil”, “pyrolytic oil”, “pyrolysis oil”, “pyrolysis bio-oil”, “pyrolytic bio-oil”; c. An aqueous liquid phase known by various names such as “wood vinegar”, “pyroligneous acid”, “pyroligneous acid”, “wood acid”, “liquid smoke”, “wood distillate”.

[0004] Generally speaking, existing continuous biomass pyrolysis devices can be used to produce biochar, biofuel, and sometimes even hydrogen or methane by an expensive process of steam cracking of non-condensable gases.

[0005] The most common existing continuous biomass pyrolysis devices use all of the condensable and non-condensable gases by combustion to maintain the continuity of the pyrolysis reaction of the entire device, inducing several limitations: on the one hand, the condensable gases contain a significant quantity of wood vinegar with very low calorific value, which greatly reduces the energy efficiency of the process; on the other hand, wood vinegar is a biopesticide that can be used in agriculture in the same way as biochar, and burning it thus reduces the potential sources of income.

[0006] The most advanced existing continuous biomass pyrolysis devices use non-condensable gases by combustion to maintain the continuity of the pyrolysis reaction of the entire device and treat the condensable gases via distillation columns or condensers in series at different temperatures to recover a high-quality bio-oil intended for use in the form of biofuel, inducing several limitations: on the one hand, the cost of treating condensable gases is significant in view of the equipment necessary for the production of biofuel, on the other hand, wood vinegar is a biopesticide usable in agriculture in the same way as biochar and treating it as waste thus reduces the potential sources of income.

[0007] In view of the above, a major challenge is to provide an optimized process for the conversion of biomass into biochar on an industrial scale that is inexpensive, energy efficient, of high capacity, and of positive impact on the environment. Summary of the invention

[0008] The device according to the invention makes it possible to overcome the limitations of the existing system previously mentioned by meeting the need for industrial-scale production of several thousand to tens of thousands of tonnes of biochar per year, with the objectives of cost, energy efficiency, capacity, and positive impact on the environment.

[0009] The continuous biomass pyrolysis device with separation of co-products by condensation and centrifugation comprises at least the following successive steps: 1. Biomass drying stage; 2. Biomass pyrolysis stage (dehydration, cellulose / hemicellulose decomposition, lignin decomposition) leading to the formation of two fractions: solid carbon residues on one side and condensable and non-condensable gases on the other; 3. Condensation and centrifugation stage leading to the formation of three fractions: biogas, bio-oil and wood vinegar; 4. Step of mixing the carbon residues with the wood vinegar; 5. Stage of combustion of bio-oil in a burner; 6. Biogas combustion stage in an optional electric generator; 7. Energy recovery stage in the form of heat in a machine Organic Rankine Cycle (ORC) as an option.

[0010] The process differs fundamentally from the prior art in that it comprises a step of mixing the carbon residues with wood vinegar for agricultural purposes.

[0011] Advantageously, since wood vinegar is already used in agriculture as a natural pesticide, the mixture of biochar and biopesticide can now be marketed as a carbon sink, fertilizer and natural agricultural pesticide.

[0012] Advantageously, wood vinegar makes it possible to lower the temperature of the biochar during mixing, thereby reducing the energy consumption associated with its cooling.

[0013] Advantageously, wood vinegar makes it possible to stabilize and humidify the biochar, greatly reducing its storage constraints since no fire extinguishing system, temperature control or storage in an oxygen-poor atmosphere is necessary.

[0014] The method differs from the prior art in that it also includes a condensation and centrifugation step which does not require distillation columns or condensers in series at different temperatures.

[0015] Advantageously, the use of bio-oil in a burner greatly reduces the processing and refining constraints compared to use in the form of biofuel and makes it possible to reduce the costs of the process by using a single condenser operating at a single temperature.

[0016] Advantageously, the use of bio-oil in a burner makes it possible to maintain the pyrolysis reaction of the entire device and then makes the biogas available for sale or for electricity production purposes with an optional electric generator, which improves the revenues of the process.

[0017] Advantageously, the use of bio-oil on site greatly reduces storage and transport constraints compared to use in the form of biofuel and makes it possible to reduce process costs.

[0018] The continuous biomass pyrolysis device with separation of co-products by condensation and centrifugation which is the subject of the invention has several advantages: 1. Device deployable on an industrial scale; 2. Inexpensive device; 3. Energy efficient device; 4. Large capacity device; 5. Device having a positive impact on the environment.

[0019] Other characteristics and advantages of the invention will emerge from the additional description which follows.

[0020] It goes without saying that this additional description is given only as an illustration of the subject of the invention and must in no case be interpreted as a limitation of this subject. Brief description of the figures

[0021] The accompanying drawings illustrate the invention.

[0022] [Fig.l] schematically illustrates the different stages of a continuous pyrolysis device making it possible to obtain hot water and biogas as co-products.

[0023] [Fig.2] represents a variant of [Fig.l] with the addition of an electric generator making it possible to obtain hot water and electricity as co-products.

[0024] [Fig.3] represents a variant of [Fig.l] with the addition of an electric generator and an organic Rankine cycle (ORC) machine allowing to obtain a maximum of electricity as co-products. Detailed description of the figures

[0025] We refer to [Fig.l] which schematically illustrates the different stages of the continuous pyrolysis of biomass with separation of co-products by condensation and centrifugation which initially produces a mixture of biochar and biopesticide, biogas and hot water, then possibly as an option electricity using an electric generator using the biogas if we refer to [Fig.2] and finally as an option a maximum of electricity using an organic Rankine cycle (ORC) machine using hot water if we refer to [Fig.3].

[0026] With reference to these figures, the continuous biomass pyrolysis device with separation of co-products by condensation and centrifugation according to the invention comprises a hopper silo (2) for storing the biomass, the latter being able to be wet or almost dry.

[0027] Under the hopper, a screw conveyor (3) allows continuous and uniform feeding of a rotary dryer (4) which can be doubled if the biomass humidity level exceeds 30%.

[0028] The biomass thus dried to a humidity level of less than 15% is inserted via a screw conveyor (5) directly into the inner part of the rotary pyrolyzer (6) which is heated to a high temperature by the outer part of the rotary pyrolyzer (16) in which the combustion gases circulate.

[0029] The gradual rise in temperature in the inner part of the rotary pyrolyzer (6) will first completely dehydrate the biomass, before gradually degrading the cellulose and hemicellulose, then finally degrading the lignin. This dehydration and thermal decomposition of the biomass in the absence of oxygen makes it possible to obtain solid carbonaceous residues on one side and condensable and incondensable gases on the other (24).

[0030] The solid carbonaceous residues or biochar are then transported in a cooling screw conveyor (7) whose walls are in contact with a cold water inlet (38) and a warm water outlet (39) to a humidifying screw mixer (8) in which the biochar is mixed with the wood vinegar (31) in order to produce a natural agricultural fertilizer and pesticide. This mixture of biochar and biopesticide (9) can then be directly stored in the open air or packed in bags on a pallet.

[0031] The fresh air (10) required for the combustion of the bio-oil (28) is preheated in an air / air heat exchanger (11) to maximize the energy consumption of the device. This preheated fresh air circulates in an insulating sheath to an induced draft fan (13) which supplies the heavy oil burner (14).

[0032] A combustion chamber (15) is used to homogenize the temperature of the combustion gases which are introduced into the outer part of the rotary pyrolyzer (16) and will thus heat the inner part of the rotary pyrolyzer (6).

[0033] The high temperature exhaust (17) of the rotary pyrolyzer can be used in the rotary dryer (4) either directly, or diluted with fresh air, or used indirectly with an air / air heat exchanger depending on the biomass, its humidity and the risk of fire.

[0034] The residual temperature of this exhaust flow is used in the heat exchanger (11) previously mentioned before being treated in a cyclone (18) to remove fine particles. The pressure difference of the assembly is compensated by an induced draft fan (19). This exhaust flow is then directed towards a water purifier (20) or "water scrubber" in English.

[0035] Before the discharge of the treated air (23) into the atmosphere, the exhaust flow passes through a UV catalytic treatment (21) followed by filtration in an activated carbon filter (22).

[0036] The condensable and non-condensable gases (24) mentioned above are then directed to a single indirect water condenser (25) operating at a single temperature to give non-condensable gases on one side (32) and a bio-oil and wood vinegar mixture (26) on the other. Cooling is provided by a warm water inlet (39) and a hot water outlet (40). Extremely viscous tars can sometimes be deposited on the walls of the indirect water condenser (25) impairing its efficiency. If necessary, recirculation of the wood vinegar (26) in the form of sprays directly into the indirect water condenser (25) is to be provided and allows these extremely viscous tars to be better evacuated.

[0037] This bio-oil and wood vinegar mixture (26) is then treated in a plate separator (27) allowing easy collection of the tiny residual solids while efficiently separating the bio-oil (28) on one side and the wood vinegar (31) on the other. A storage tank (29) which can optionally be heated depending on the viscosity of the bio-oil (28) serves as a buffer with the heavy oil burner (14) then fed by a heated feed pipe (30).

[0038] The non-condensable gases (32) mentioned above are then treated in a cyclone (33) to remove fine particles. The pressure difference of the assembly is compensated by an induced draft fan (34) which then directs these gases towards a water purifier (35) or "water scrubber" in English.

[0039] Before using this biogas (37), a passage through an activated carbon filter (36) makes it possible to eliminate all residual impurities.

[0040] Optionally, this biogas (37) can be used in an electric generator (41) specially designed for biogas with low heat capacity, the main characteristic of which is the relatively low rotation speed. The injection of electricity (42) is then done on the local three-phase network.

[0041] Also optionally, the hot water (40) can be used in an organic Rankine cycle (ORC) machine (43) which certainly has a lower efficiency than the electric generator (approximately 0.11 vs. 0.44) but has the advantage of maximizing the electricity production of the entire device, this electricity (44) also being injected into the local three-phase network. Numbered list

[0042] Numbered list: 1. Biomass 2. Hopper silo 3. Screw conveyor 4. Rotary dryer 5. Screw conveyor 6. Rotary pyrolyzer (inner part) 7. Cooling screw conveyor 8. Wetting screw mixer 9. Biochar and biopesticide mixture 10. Fresh air 11. Heat exchanger 12. Insulating sheath 13. Induced draft fan 14. Heavy oil burner 15. Combustion chamber 16. Rotary pyrolyzer (external part) 17. High temperature exhaust 18. Cyclone 19. Induced draft fan 20. Water purifier 21. UV catalytic treatment 22. Activated carbon filter 23. Treated air 24. Mixture of condensable and non-condensable gases 25. Indirect water condenser 26. Organic oil and wood vinegar mix 27. Plate separator 28. Bio-oil 29. Storage tank 30. Heated feed pipe 31. Wood vinegar 32. Non-condensable gases 33. Cyclone 34. Induced draft fan 35. Water purifier 36. Activated carbon filter 37. Biogas 38. Cold water 39. Warm water 40. Hot water 41. Electric generator 42. Three-phase electricity 43. Organic Rankine Cycle (ORC) machine 44. Three-phase electricity

Claims

1.

2.

3. Claims Method according to the invention characterized in that it comprises the following steps:

1. Biomass drying stage; 2. Biomass pyrolysis stage (dehydration, cellulose / hemicellulose decomposition, lignin decomposition) leading to the formation of two fractions: solid carbon residues on one side and condensable and non-condensable gases on the other; 3. Condensation and centrifugation stage leading to the formation of three fractions: biogas, bio-oil and wood vinegar; 4. Step of mixing the carbon residues with the wood vinegar; 5. Stage of combustion of bio-oil in a burner; 6. Biogas combustion stage in a generator electric optional; 7. Energy recovery step in the form of heat in an optional Organic Rankine Cycle (ORC) machine. Method according to the

1. characterized in that it comprises a step of mixing the carbon residues with the wood vinegar leading to an all-in-one product (carbon sink, fertilizer and natural agricultural pesticide). Process according to any one of the preceding claims, characterized in that it also comprises a condensation and centrifugation step not requiring distillation columns or condensers in series at different temperatures.

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