Method for conducting a pyrolysis process of woody biomass

Abstract

The invention relates to a method for conducting a pyrolysis process of woody biomass, the method being characterised in that it comprises the following steps: - a) mechanically grinding the woody biomass into particles smaller than 3 cm3 in size; - b) conveying the woody particles to a dryer; - c) heating the woody particles from the dryer in a horizontal trough pyrolysis reactor having an oxygen content of less than 15% and comprising a first input for the woody particles and a second input for heat-transfer beads, the reactor being configured to cause the woody particles to react so as to have a first outlet of a mixture of heat-transfer beads and pyrolysed woody particles, the residence time of which in the reactor is at least 20 seconds, and a second pyrolysis gas outlet; - d) heating the heat-transfer beads in a bead regenerator.

Description

Pyrolysis process for woody biomass Technical field of the invention

[0001] The present invention relates to a process for the pyrolysis of woody biomass. It applies, in particular, to the recovery of wood residues (branches, leaves, shavings, sawdust, etc.) with the aim of producing bioenergy and bioproducts and helping to reduce greenhouse gas emissions.

[0002] Some prior art documents also propose pyrolysis processes.

[0003] For example, publication document US2010163395 is known, which describes a process for the rapid pyrolysis of lignocellulose, comprising several steps: a) mechanically grinding lignocellulose particles into particles; b) drying and preheating lignocellulose particles; c) mixing the lignocellulose particles with heat transfer particles so as to provide a mixture; d) heating the heat transfer particles, prior to mixing, to a certain temperature; and e) heating, in a pyrolysis reactor so as to provide pyrolysis coke, pyrolysis condensate and pyrolysis gas.

[0004] However, the way of managing the heat carrier in terms of heating and management is not optimal.

[0005] The aim of the present invention is to provide the core of the reactor with optimal pyrolysis in order to ensure better homogeneity of the heat exchange and ensure an optimal pyrolysis reaction. Presentation of the invention

[0006] The present invention aims to overcome these drawbacks with a completely innovative approach.

[0007] More specifically, the invention aims to significantly improve the efficiency of the pyrolysis reaction and optimize the reaction extracts (biochar, condensates, combustion gases, etc.).

[0008] These objectives, as well as others which will appear subsequently, are achieved, according to a first aspect, using a process for pyrolysis of woody biomass, remarkable in that it comprises the following stages:- a) mechanically grinding woody biomass into woody particles smaller than 3cm 3;- b) conveying the woody particles to a dryer operating at a temperature of at least 80°C configured to have a humidity level of less than 10% of the woody particles at the outlet;- c) heating the woody particles from the dryer, in a horizontal trough pyrolysis reactor and having an oxygen level of less than 15% comprising a first inlet for the woody particles and a second inlet for heat-transfer beads, the heating is configured to establish a temperature inside the reactor of between 400°C and 660°C and configured to react the woody particles so as to have a first outlet of a mixture of heat-transfer beads and pyrolyzed woody particles whose presence time in the reactor is at least 20 seconds and a second outlet of the pyrolysis gas;- d) heating the heat transfer balls in a ball regenerator, prior to the heat transfer balls entering the reactor, to a temperature between 400°C and 650°C for at least 40 seconds.;

[0009] Thanks to these process elements, heat transfer to the woody biomass is increased, continuously and reliably.

[0010] The process aims to control not only the temperature of the heat transfer fluid, but also the heating time, in order to ensure that a temperature of 550°C to 660°C is reached in the center of the heat transfer fluid and not only on its surface.

[0011] This allows the heat transfer fluid to store as much thermal energy as possible, ensuring better heat transfer capacity to the biomass in the pyrolysis reactor. The process has been designed so that this targeted temperature of the beads at the reactor inlet can be maintained at all times, in a continuously moving environment.

[0012] It is also about maximizing the contact surface between the heat transfer fluid and the biomass, by reducing empty spaces when the biomass mixes with the heat transfer fluid.

[0013] The invention is advantageously implemented according to the embodiments and variants set out below, which are to be considered individually or in any technically effective combination.

[0014] In one embodiment, said method further comprises a step of separating the heat-transfer beads and the pyrolyzed wood particles by screening, said screening comprising two outlets, a first for the heat-transfer beads and a second for biochar.

[0015] Thus, the screening includes a grid that allows the separation of heat-transfer beads and pyrolyzed wood particles. The grid is slightly inclined to allow, by gravity, the heat-transfer beads to roll and bounce on the grid, which detaches the pyrolyzed wood particles that fall through the grid by gravity.

[0016] In one embodiment, said method further comprises a step of conveying in a vertical conveyor the mixture of heat-transfer beads and pyrolyzed wood particles to the screening.

[0017] In one embodiment, in step b) the dryer is a rotary type dryer and operates with combustion gases.

[0018] In one embodiment, during step d) the ball regenerator consists of a main cylinder crossed by cylindrical tubes in which the heat-transfer balls pass.

[0019] In one embodiment, during step d) the tubes of the regenerator are positioned substantially vertically.

[0020] In one embodiment, during step d) the tubes of the regenerator are spiral.

[0021] In one embodiment, the heat transfer balls used in one of the steps of said method are made of metal, ceramic or hard material having a diameter greater than 3 mm. This dimension makes it possible to have a sufficient diameter to retain the heat and allows good restitution of this heat in the reactor.

[0022] In one embodiment, the heat transfer beads used in one of the steps of said method comprise at least two different diameters with a diameter ratio less than or equal to 0.5.

[0023] This mixture allows for better heat distribution and better overall performance.

[0024] In one embodiment, said method further comprises a step in which the pyrolysis gas from the reactor is conveyed into a condensation step configured to extract liquid phases.

[0025] In one embodiment, in step c) the pyrolysis reactor comprises a temporary storage zone for the pyrolysis gases, in which the storage zone is at least equal to 30% of the total volume of the reactor.

[0026] Thus the temporary storage area serves to eliminate the largest proportion of biochar in the fumes from the hood in order to allow time for the biochar dust to settle while the gases exit from the top. Brief description of the figures

[0027] Other advantages, aims and characteristics of the present invention emerge from the following description given, for explanatory and non-limiting purposes, with reference to the appended drawings, in which:

[0028] It represents, in the form of a flowchart, the steps implemented in a particular embodiment of the method which is the subject of the present invention.

[0029] Larepresente, in the form of a flowchart, steps implemented in another particular embodiment of the method which is the subject of the present invention.

[0030] The represents an example of a reactor according to a particular embodiment of the method which is the subject of the present invention.

[0031] This represents an example of reactor screening according to a particular embodiment of the method which is the subject of the present invention.

[0032] It represents an example of a reactor regenerator according to a particular embodiment of the method which is the subject of the present invention.

[0033] It represents, in the form of a flowchart, the steps implemented in the process.

[0034] This figure presents below the principle of the invention.

[0035] The recovered raw material, consisting mainly of residues from pruning and trimming operations (branches, leaves, shavings, sawdust, etc.), is delivered to a building by truck. The biomass is placed on a movable floor at the unloading dock.

[0036] In one example, the contents of the truck are unloaded directly onto the first skip in a series of three skips with a moving floor.

[0037] The woody biomass is then conveyed to a grinding stage 101.

[0038] The grinding stage is, for example, a classic hammer mill, adapted to the flow rate and size requirements of the wood. The size of the wood particles obtained is less than 3 cm. 3 .

[0039] The crushed biomass is then transferred to a so-called crushed biomass bin, from where it is sent to the drying step 102. The latter is carried out inside a rotary dryer.

[0040] The dryer operates at a temperature of at least 80°C and is configured to have a moisture content of less than 10% of the wood particles at the outlet.

[0041] The dryer is installed in a closed container, supplied with heat by combustion gases from a combustion chamber shown below.

[0042] Once dried, the biomass is transported to the dried biomass bin before being transferred to a thermolysis reactor. This latter bin is covered with a metal roof to preserve the quality of the product and reduce airborne losses.

[0043] In terms of environmental contamination prevention measures, it should be noted that all biomass is stored in metal bins and that these are placed on dry ground, such as a concrete slab, all entirely inside the building, sheltered from the weather and wind. It is therefore not planned to have biomass stored outside or that could pose an environmental issue.

[0044] Wood particle emissions are controlled through a series of cyclones, three for the shredder and one for the dryer. The particles captured by the cyclones are deposited in the appropriate bin and ultimately transferred to the pyrolysis reactor.

[0045] The next step is to heat the woody particles in a horizontal trough pyrolysis reactor 103 without oxygen.

[0046] The targeted pyrolysis reaction is initiated when the dried biomass is heated to a temperature of around 450°C in a low oxygen environment. The horizontal trough reactor consists of a cylinder into which a screw is inserted, where the biomass is mixed with steel heat transfer beads to optimize heat transfer and the thermolysis reaction.

[0047] Thus, the dried biomass from the dried biomass bin is conveyed by conveyor to the pyrolysis reactor. At the same time, heated steel heat transfer balls are also conveyed to the reactor to be mixed with the dried biomass.

[0048] Under the desired conditions, the pyrolysis reaction occurs and the biomass generates pyrolysis gases which are transferred to the condensation stage, detailed below.

[0049] At the end of the reactor, the biomass mixture reacts and the steel heat transfer balls are then recovered by a vertical conveyor; this is the mixture 104 composed of pyrolyzed wood particles and heat transfer balls.

[0050] Then, the biomass is separated from the steel balls by gravity through metal screens and then stored in bags to be marketed as biochar.

[0051] The steel balls resume the closed loop of heating-reaction-separation.

[0052] It represents, in the form of a flowchart, the steps implemented in the method according to another embodiment which specifies certain steps.

[0053] The unit incorporates the elements of the. At the reactor outlet, the pyrolysis gases are sent to a condensation stage 108. The pyrolysis gases are first routed to the oil quenching unit. The purpose of this equipment is to condense as much bio-oil gas as possible, which is also a marketable product and is temporarily stored in a double-walled, steam-heated stainless steel tank. In one example, it is located outside the building.

[0054] The gases that did not condense in the oil quench are then directed to the water quench, which primarily condenses water. This water, which contains acetic acid in particular, is known as wood vinegar. This product is intended for marketing and temporarily stored in a double-walled, steam-heated stainless steel tank. In one example, it is located outside the building.

[0055] The residual gases that have not condensed in the quenches, the renewable gases, are then transferred to the combustion chamber to generate part of the energy needed for the drying and reaction phases.

[0056] The mixture 104 composed of the pyrolyzed wood particles and heat-transfer beads is directed by a vertical conveyor to the screening step 106. Screening is a step of separating the heat-transfer beads and the pyrolyzed wood particles. The pyrolyzed wood particles and the heat-transfer beads are separated by gravity through metal grids, the beads remain above the grid while the pyrolyzed wood particles fall by gravity.

[0057] The pyrolyzed wood particles are stored in bags to be marketed as biochar.

[0058] The heat transfer beads after the screening step are sent to the regenerator step 107.

[0059] The ball regenerator consists of a main cylinder crossed by cylindrical tubes through which the heat-transfer balls pass. In one example, the tubes are positioned approximately vertically. In another example, the tubes have the shape of a spiral.

[0060] Lamontre shows an example of a reactor used in step c) of heating the wood particles.

[0061] The horizontal trough reactor is used for the pyrolysis of previously dried biomass. The biomass and heat transfer beads are introduced into the reactor through their respective inlets N1 and N2 at one end of the reactor. Using a screw driven by a motor M, the heat transfer beads and biomass are mixed and transported to the other end of the reactor. Throughout the reactor, the biomass is pyrolyzed using the energy transferred by the beads, which have been previously heated in a regenerator.

[0062] Pyrolysis produces biochar which will exit as N5 with the beads at a port at the end of the reactor. Syngas is recovered as N4.

[0063] A temporary storage area is created. The size of this temporary storage area is at least equal to one third of the total volume of the reactor.

[0064] Pyrolysis gases carry biochar dust with them. The temporary storage area, called the raised hood, serves to remove the largest proportion of biochar from the fumes in the hood to allow time for this dust to settle while the gases exit through the top of the hood.

[0065] A hot gas inlet N6 and a hot gas outlet N7 are positioned at the ends of the reactor.

[0066] Oil vapors are also produced and routed to a pyrolysis oil and wood vinegar recovery unit.

[0067] In addition to the biomass, according to another example, the portion of oil having a biochar concentration exceeding 1% in the pyrolysis oil (substrate) from the oil condensation unit is recycled to the reactor to be pyrolyzed again to N3.

[0068] Alternatively, a jacket is installed around the reactor to circulate hot gas from the outlet of the bead regenerator. This is to keep the walls of the reactor warm.

[0069] This represents an example of sieving during the separation stage of heat-transfer beads and pyrolyzed wood particles.

[0070] A separation grid made of parallel metal bars is used to separate the beads and biochar coming from the pyrolysis reactor at inlet T1. The space between the bars allows the biochar to flow by gravity or with the help of a pressure variation device at T2 through the grid and the beads to roll towards the regenerator inlet at T3. This separation grid is inserted into a pipe. In one example, the grid is inclined at least 25° from the horizontal, which allows the heat-transfer beads to roll and bounce on the grid while allowing pyrolyzed woody particles to detach from the heat-transfer beads.

[0071] In one example, the separator is chambered with hot flue gas from the regenerator to maintain gas temperature stability in the reaction loop equipment, avoiding temperature differences that can create condensation or affect the chemical composition of bioproducts.

[0072] Lamontre shows a regenerator used in step d) of heating the heat transfer balls.

[0073] The heat transfer bead regenerator transfers thermal energy to the beads which will serve as energy heat carriers to the biomass in the pyrolysis reactor.

[0074] Once the energy from the balls has been transferred, they are returned to the start of the regenerator to be reheated again.

[0075] The regenerator consists of a shell and tube heat exchanger with balls slowly descending through the tubes. The regenerator consists of a main cylinder positioned substantially vertically and crossed by cylindrical tubes positioned substantially vertically inside the cylinder through which the heat transfer balls pass. The balls to be heated enter at R1 and exit at R2.

[0076] The speed of the balls is controlled by a rotary valve, guillotine and / or double flap and / or rotary feeder and / or lock and / or butterfly valve etc...at the bottom of the regenerator.

[0077] The tubes are heated by high-temperature combustion gas from the shell side. It enters through an inlet R3 and exits through an outlet R4.

Claims

A process for pyrolyzing woody biomass, characterized in that it comprises the following steps: - a) mechanically grinding woody biomass into woody particles smaller than 3cm 3;- b) convey the wood particles to a dryer operating at a temperature of at least 80 °C configured to have a moisture content of less than 10% of the wood particles at the outlet; - c) heat the wood particles from the dryer in a horizontal trough pyrolysis reactor with an oxygen content of less than 15% having a first inlet for the wood particles and a second inlet for heat-carrying beads, the heating is configured to establish a temperature inside the reactor between 400°C and 660°C and configured to react the wood particles so as to have a first output of a mixture of heat-carrying beads and pyrolyzed wood particles whose presence time in the reactor is at least 20 seconds and a second output of the pyrolysis gas;- d) heat the heat transfer beads in a bead regenerator, prior to the entry of the heat transfer beads into the reactor, to a temperature between 400°C and 650°C for at least 40 seconds.; A process according to claim 1, wherein said process further comprises a step of separating the heat-carrying beads and the pyrolyzed wood particles by sieving, said sieving comprising two outlets, a first for the heat-carrying beads and a second for biochar. A process according to claim 2, wherein said process further comprises a step of conveying the mixture of heat-carrying balls and pyrolyzed wood particles in a vertical conveyor towards the sieving. A method according to claim 1, wherein in step b) the dryer is a rotary type dryer and operates with combustion gases. Method according to claim 1, wherein in step d) the ball regenerator consists of a main cylinder through which cylindrical tubes pass the heat-carrying balls. A method according to claim 1, wherein in step d) the tubes of the regenerator are positioned substantially vertically. A method according to claim 1, wherein in step d) the tubes of the regenerator are spiraled. A method according to claim 1, wherein the heat-carrying balls used in one of the steps of said method are made of metal, ceramic or hard material having a diameter greater than 3 mm. A method according to claim 8, wherein the heat-carrying balls used in one of the steps of said method comprise at least two different diameters with a diameter ratio less than or equal to 0.

5. A process according to claim 1, wherein said process further comprises a step in which the pyrolysis gas from the reactor is conveyed to a condensation step configured to extract liquid phases. A method according to claim 1, wherein in step c) the pyrolysis reactor includes a temporary storage zone for pyrolysis gases, in which the storage zone is at least equal to 30% of the total volume of the reactor.

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