WO2019166873A1

WO2019166873A1 - Method and apparatus for biomass torrefaction

Info

Publication number: WO2019166873A1
Application number: PCT/IB2019/000106
Authority: WO
Inventors: Darko GORICANEC
Original assignee: University of Maribor
Priority date: 2018-02-27
Filing date: 2019-03-01
Publication date: 2019-09-06
Also published as: WO2019166873A4; SI25600A

Abstract

The method and apparatus according to the invention in a preferred embodiment comprises a thermally insulated gas-tight chamber (10), further comprising two perforated endless conveyor belts (9) for transfer of biomass (4), wherein biomass torrefaction is utilized by recirculation of re-heated torrefaction gas and introducing the heat into said chamber (10) by means of forced convection heat transfer, wherein the heat is transferred by recirculated torrefaction gas and released directly to the biomass (4) dispensed on endless perforated conveyor belts (9) through the apertures on receiving surface of perforated endless conveyor belts (9). The target temperature of the torrefaction gas within the chamber (10) is established and maintained by waste heat utilization and by firing the torrefaction gas within primary heat releasing unit (16) comprising a gas burner (15) and incorporated heat exchanger. The biomass is preferably introduced and discharged from chamber (10) by means of a screw conveyor (2, 24), which essentially prevents ingress of air (i.e. oxygen) and loss of energy within the system.

Description

Title Of Invention : METHOD AND APPARATUS FOR BIOMASS

TORREFACTION

Technical Field

[0001 ] The main object of the invention relates to the methods and apparatus for biomass torrefaction. Torrefaction is a thermal pre-treatment of biomass at a temperatures between 200 to 300 ° C (low temperature pyrolysis) in an inert atmosphere (substantially oxygen free environment), where volatile products of biomass are released from biomass, mainly in the form of the gas. During this process, 70% of biomass is maintained as a solid product, containing 90% of the initial energy value. The product of such pre-treatment of biomass is a torrefacted biomass that has a higher energy density than raw biomass, it is not hygroscopic, it is biodegradable, it can be compressed and formed in briquettes or pellets, it is safe from self-ignition, which makes it easier to store and transport.

Background Art

[0002] The technical problem addressed in this patent application is the lack of a simplified method and cost effective apparatus for efficient torrefaction of the biomass, wherein the main disadvantage of torrefaction devices from state of the art is complex assembly and unsteady heat pre-treatment within the process of torrefaction which results in a lower overall efficiency.

[0003] The solution according to the W02013003599A3 discloses a system for torrefaction of biomass within reactor vessel, wherein biomass travels through the stack of tray assemblies in vertical direction, hence charging and discharging of device under pressure is highly complex due to pressurized reactor, which requires at least 3 bar gauge pressure.

[0004] Similarly, solution according to the W02007078199A1 comprises a reactor with drying and torrefaction chamber located downstream of the drying chamber when viewed in the direction of flow of the material, wherein the hot gas for torrefaction is introduced from side of the reactor, thus the heat treatment of the biomass is limited within the torrefying chamber of reactor.

[0005] Another solution according to the US20080223269A1 comprises endless conveyor belt, wherein the pre-heat treatment of biomass for torrefaction is limited to the conduction heat transfer provided by said endless conveyor belt.

Summary of Invention

[0006] The method and apparatus according to the invention in a preferred embodiment comprises a thermally insulated gas-tight chamber, further comprising two perforated endless conveyor belts for transfer of biomass, wherein biomass torrefaction is utilized by introducing the heat into said chamber by means of forced convection heat transfer to the biomass dispensed on perforated conveyor belts, where the target temperature of the torrefaction gas within the chamber is established and regulated by primary heat source (preferably flue gas burner with incorporated heat exchanger). The biomass is preferably introduced and discharged from chamber by means of a screw conveyor, which essentially prevents a flue gas leakage and loss of energy within the system.

[0007] In addition, the method and device according to the invention further comprises secondary means for increasing the robustness of process and for increasing the total efficiency of biomass torrefaction. Thus, device according to the invention may further comprise secondary heat sources, pipes, flaps, valves and channels for manipulation and regulation of gas flow (i.e. stream) within the chamber, prime mover (i.e. fan or blower) for increasing the gas flow with aim to increase the convection heat transfer within the chamber, means for redistribution of biomass on conveyor belts, means for separation and cleaning of conveyor belts, etc., which are explained in detail hereinafter.

[0008]

Technical Problem

[0009] The technical problem addressed in this patent application is the lack of a simplified method and cost effective apparatus for biomass torrefaction, hence the main object of disclosed invention is to provide a simplified method for heating the biomass for torrefaction and cost effective apparatus for utilization of such a method by guided flow of heated torrefaction gas through the system of perforated endless conveyor belts and gas collector channel for utilization of forced convection heat transfer.

Solution to Problem

[0010] The method of biomass torrefaction according to the invention in preferential embodiment comprises the steps of:

[0011 ] -providing a thermally insulated and substantially gas-tight chamber for utilization of biomass torrefaction;

[0012] - providing at least one perforated endless conveyor belt with plurality of apertures and apparatus for mounting the endless belt on respective rollers, wherein the enclosed space on inner side of perforated endless belt is essentially limited with openings (apertures in function of nozzles), hence it is used as a pressure redistribution chamber for releasing the hot gas to the chamber through the apertures within the perforated endless belt;

[0013] - adding biomass to a substantially gas tight and thermally insulated chamber preferably by screw conveyor, wherein biomass is already prepared and comminuted to the fragments in appropriate size to be dispensed onto transportation means within said chamber;

[0014] - dispensing biomass onto transportation means in chamber, wherein said biomass is dispensed and redistributed on the perforated endless conveyor belt in substantially constant nominal thickness of loaded material;

[0015] - transporting the biomass through the chamber by means of at least one perforated endless conveyor belt, wherein the speed of transportation is regulated and defined by measuring the temperature of the gas released from the biomass dispensed on said conveyor belt;

[0016] - heating the interior of said chamber by means of forced convection heat transfer provided with incorporated fan and first heat releasing unit (i.e. heat exchanger connected to the gas burner), wherein the biomass dispensed on said conveyor belt is essentially heated up to the target torrefaction temperature (200- 300°C) by forced convection of torrefaction gases within the chamber, wherein preferably at least a portion of released torrefaction gas is used as primary fuel for said gas burner, wherein another fuel (i.e. LPG or gas fuel) may be used to initiate the process of pyro lysi s/to rref action in said chamber. For increasing the overall efficiency of disclosed method for biomass torrefaction, the process of heating may further comprise the preheating of ambient air for gas burner by utilization of waste heat recovery of flue gases from said gas burner, hence a secondary heat exchanger may be used to recover at least a portion of the flue gas heat with aim to increase the temperature of supply ambient air for gas burner;

[0017] - recirculation of gas within substantially gas tight chamber, wherein collector channel is used to collect at least a portion of released torrefaction gas, and at least a portion of collected torrefaction gas used as a fuel (i.e. fired) by first heat releasing unit for increasing the temperature of gas within substantially gas tight chamber, wherein the gas charging device (i.e. blower of fan) with inlet and outlet aperture is used to charge and release reheated hot torrefaction gas through the apertures of perforated endless conveyor belt with aim to increase the temperature of the biomass dispensed on conveyer belt by principle of forced convection heating to the required temperature level for substantially continuous process of biomass torrefaction, and wherein at least one heat releasing unit is used to increase the temperature of the recirculation gas before it is released through the apertures within said perforated endless conveyor belt;

[0018] - maintaining the biomass temperature on the target elevated temperature required for efficient torrefaction of biomass, wherein the heat generated by said first heat releasing unit is released into the chamber and transferred to the biomass dispensed on said perforated endless conveyor belts through the system of channels, tubes, pipes, flaps and valves, which guides and directs the flow of re heated torrefaction gas to the biomass through the perforated conveyor belts, on which the biomass is dispensed therein, and wherein the space between the mechanism of endless conveyor belt is used as a buffer (i.e. pressure redistribution chamber) for supplying the re-heated gas to the biomass through the perforated endless belt, with aim to increase the temperature of the biomass dispensed on upper side of said perforated endless belt to the target temperature required for biomass torrefaction, and wherein the primary heat source for re-heating the torrefaction gas is preferably situated within the chamber;

[0019] - regulating the flow of heated gas for heating the biomass on said perforated conveyor belts, wherein the flow of heated gas with highest temperature is dynamically directed in sections of conveyor belts by means of said flaps, valves, tubes, pipes and channels, wherein the lateral flow (i.e. stream) of gas on upper side of conveyor belt is controlled and essentially limited, hence manipulated by flaps, which guides and directs the released torrefaction gas into collector channel situated on upper side of conveyor belt. It is important to notice, that released torrefaction gas is preferably used as a primary fuel for said gas burner with aim to provide a first heat releasing unit for forced convection heating;

[0020] - regulating the speed of endless conveyor belt to increase the efficiency of biomass torrefaction, wherein the speed of biomass transportation is adapted to the measured temperatures of the released torrefaction gas on upper side of said conveyor belt, wherein the temperature is preferably measured in plurality of sections above conveyor belt in lateral direction, when viewed in the direction of flow of the material downstream of transportation conveyor belt, hence the speed of endless conveyor belt is adapted and the stream of the flow of re-heated gas is directed by flaps into the areas with highest temperature difference with aim to increase the torrefaction efficiency;

[0021 ] - discharging torrefied biomass, wherein the screw conveyor is preferably used with aim to increase the efficiency of method my minimizing the heat losses in system.

Advantageous Effects of Invention

[0022] The method and apparatus according to the invention is a cost effective solution for biomass torrefaction and preferably comprises a standalone, thermally insulated gas tight chamber, in which the series of endless belts are incorporated and used in cooperation with conveyor screws to carry and transfer the biomass through the drying process, heating process and torrefaction process. In addition, the method comprises the process of guided flow distribution, where guided flow of heated torrefaction gas is established by series of channels, pipes, tubes, flaps and valves which are used in cooperation with heat exchanger to heat up the biomass on perforated endless conveyor belts by means of forced convection heat transfer, wherein said flaps and collector channels are used to dynamically direct and deflect the flow of the heated torrefaction gas into the segments of endless conveyor belts (i.e. target areas) with higher temperature differences with aim to increase the efficiency of torrefaction process. It is important to notice, that heat for forced convection heating is preferably provided by primary heat releasing (i.e. heat exchanger) which is connected to gas burner, wherein preferential fuel for providing the heat is torrefaction gas released from biomass in chamber.

[0023] The method and apparatus according to the invention is explained in details hereinafter with reference to the accompanied drawings.

Brief Description of Drawings

[0024] Figure 1 shows a schematics of a preferred embodiment of the device according to the invention with depicted and marked: conical container (1 ), screw conveyor (2, 24), dispensing device (3), biomass (4), flaps (5), gas collector channel (6), valve (7, 21 ), lateral gas baffles (8), perforated endless conveyor belts (9), thermally insulated gas-tight chamber (10), electric motor (EM) drive of the fan or blower, exhaust (1 1 ), secondary heat exchanger (12), ambient (A) air supply (13), torrefaction gas supply line (14), gas burner (15), primary heat releasing unit (16), dust particle collector (17), biomass particle collector (18), belt cleaning units (19, 23), heating gas supply line (20), torrefaction gas flow (22), discharge of torrefied biomass (25).

[0025] Figure 2 shows a schematics of a simplified embodiment of the device according to the Figure 1 with depicted and marked: conical container (1 ), screw conveyor (2, 24), dispensing device (3), biomass (4), flaps (5), gas collector channel (6), valve (7), lateral gas baffles (8), perforated endless conveyor belt (9), thermally insulated gas-tight chamber (10), electric motor drive (EM) of the fan or blower, exhaust (1 1 ), secondary heat exchanger (12), ambient (A) air supply (13), torrefaction gas supply line (14), gas burner (15), primary heat releasing unit (16), dust particle collector (17), belt cleaning unit (19), heating gas supply line (20), torrefaction gas flow (22), discharge of torrefied biomass (25).

Description of Embodiments

Examples

[0026] In preferential embodiment device according to the invention comprises a screw conveyor (2) for introducing the biomass (4) into the gas-tight chamber (10), wherein the biomass (4) is dispensed and arranged in substantially constant nominal thickness on perforated endless conveyor belt (9) by means of dispensing device (3). Once the device starts to operate, the primary heat releasing unit (16) starts to release the heat within the chamber (10) by mechanism of forced convection heating, wherein at least one fan or blower in cooperation with heat exchanger is used for recirculation of gas within said chamber (10), hence for forced convection heating of biomass (4) by torrefaction gas within the chamber (10). It is important to notice, that primary heat releasing unit (16) in preferential embodiment comprises at least one heat exchanger connected to its heat source, preferably cost effective gas burner (15), which substantially fires (i.e. burns) the torrefaction gas supplied by torrefaction gas supply line (14), however, another fuel (i.e. LPG or gas fuel) or heat source may be used to initiate the process of pyrolysis/torrefaction in said chamber (10). Hence, when the target temperature of biomass (4) for mild pyrolysis is reached (i.e. 200-300°C), the biomass (4) starts to effectively release the torrefaction gas by principle of biomass torrefaction, thus the source for firing the fuel by gas burner (15) is preferably switched to the torrefaction gas supply line (14). In preferential embodiment, an apparatus according to the invention further comprises at least one collector channel (6), situated above the perforated conveyor belt (9), where released torrefaction gas is collected and guided to the inlet duct of the fan for recirculation of the torrefaction gas within the chamber (10), wherein at least a portion of collected torrefaction gas is preferably supplied to the gas burner (15) with aim to provide a fuel for primary heat releasing unit (16) (i.e. gas burner with incorporated heat exchanger), where recirculated torrefaction gas is essentially reheated to the target temperature required for efficient biomass (4) torrefaction. It is important to notice, that the torrefaction gas within the chamber (10) is recirculated by means of fan, hence at least one fan is used to charge the outlet duct and heating gas supply line (20) with torrefaction gas, wherein the reheated torrefaction gas is pressurized preferably by fan in the area of outlet duct, transferred (i.e. guided) to the inner space of endless conveyor belt (9) by means of gas flow transportation (i.e. ducts, pipes, channels, valves (7, 21 ), and other supporting equipment of heating gas supply line (20)), and finally released back to the chamber (10) through the plurality of apertures within perforated endless conveyor belt (9), hence the biomass (4), dispensed on perforated endless conveyor belt (9), is essentially heated by flow of hot torrefaction gas being used for forced convection heating and utilization of biomass

(4) torrefaction.

[0027] For increased efficiency and robustness of disclosed method for biomass (4) torrefaction, the apparatus according to the invention may further comprise flaps

(5), valves (7,21 ), pipes, tubes, manifolds, ducts, channels and other means for torrefaction gas flow transportation and manipulation, wherein lateral gas baffles (8) are preferably used to effectively collect the released torrefaction gas above the conveyor belt (9), hence to prevent the lateral movement of released torrefaction gas due to the relative movement of biomass (4) (i.e. transportation of biomass 4 on rotated perforated endless conveyor belts (9)). Similarly, when the required boundary conditions for biomass torrefaction in the chamber (10) are established, the system regulation is used to switch the fuel source for gas burner (15) and to adapt the speed of screw conveyor (2, 24), speed of conveyor belts (9), power of gas burner (16), speed of fan, and power or state of pumps, valves (7, 21 ) and flaps with aim to establish and maintain the working point of apparatus with maximum efficiency for biomass torrefaction. With aim to increase the robustness of disclosed method and apparatus, the device according to the invention further comprises the means for cleaning the apertures of perforated conveyor belt (9), wherein simple brush type belt cleaning units (19, 23) or compressed gas may be used to remove the particles and dust residuals of biomass from apertures of perforated endless conveyor belt (9), wherein additional dust particle collector (17) or biomass particle collector (18) may be employed to remove the biomass residuals from the chamber in a controlled manner. With aim to increase the efficiency of disclosed method, the apparatus according to the invention further comprises means for waste heat source utilization, where exhaust (1 1 ) flue gas is preferably used for preheating the ambient (A) air supply (13) for gas burner (15) by additional secondary heat exchanger (12).

Industrial Applicability

[0028] A method and apparatus for biomass torrefaction is preferably utilized as a stand-alone unit with all vital components integrated into a container for ease of transportation to the target destination, hence disclosed method and apparatus is designed as a simple and cost effective device intended to be used for conversion of biomass to the renewable energy source with higher biochemical and physical stability, wherein the heat required for biomass torrefaction dispensed on the perforated endless conveyor belt 9 is introduced into the chamber 10 by mechanism of forced convection heat transfer by primary heat releasing unit 16. In the foregoing description those skilled in the art will readily appreciate that modification may be made to the invention without departing from the scope of the invention, were device according to the invention may comprise plurality of perforated endless conveyor belts (9), fans, gas burners and heat exchangers or other heat sources in parallel and or serial connections, wherein such modification are to be considered as included in the following claims, unless these claims expressly state otherwise.

Reference Signs List

[0029] Conical container (1 ),

[0030] Screw conveyor (2, 24),

[0031 ] Dispensing device (3),

[0032] Biomass (4),

[0033] Flaps (5), [0034] Gas collector channel (6),

[0035] Valve (7, 21 ),

[0036] Lateral gas baffles (8),

[0037] Perforated endless conveyor belts (9),

[0038] Thermally insulated gas-tight chamber (10), [0039] Electric motor (EM) drive of the fan or blower, [0040] Exhaust (1 1 ),

[0041 ] Secondary heat exchanger (12),

[0042] Ambient (A) air supply (13),

[0043] Torrefaction gas supply line (14),

[0044] Gas burner (15),

[0045] Primary heat releasing unit (16),

[0046] Dust particle collector (17),

[0047] Biomass particle collector (18),

[0048] Belt cleaning units (19, 23),

[0049] Heating gas supply line (20),

[0050] Torrefaction gas flow (22),

[0051 ] Discharge of torrefied biomass (25).

Reference to Deposited Biological Material

[0052] /

Sequence Listing Free Text

[0053] /

Citation List

[0054] / Patent Literature

[0055] PTL1 : WO2013003599A3 [0056] PTL2: W02007078199A1 [0057] PTL3: US20080223269A1

Non Patent Literature

[0058] /

Claims

[Claim 1 ] A method for torrefaction of biomass (4) comprising the steps of: providing a thermally insulated and substantially gas-tight chamber (10) with at least one perforated endless conveyor belt (9) with plurality of apertures on receiving surface; adding a biomass (4) to said chamber (10), wherein said biomass (4) is dispensed on receiving surface of said perforated endless conveyor belt (9); transporting the biomass through the chamber (10) by said perforated endless conveyor belt (9); heating the interior of said chamber (10) by forced convection heat transfer, wherein at least one prime mover is used for recirculation of gas within said chamber (10) and at least one primary heat releasing unit (16) is used to gradually increase the temperature of the biomass (4) by recirculation of gas within said chamber (10) for utilization of torrefaction process characterized in that, at least a portion of heated gas is recirculating within the chamber (10), wherein at least a portion of recirculated gas is forced to flow through the apertures of perforated endless conveyor belt (9), hence at least a portion of the heated gas provided by said primary heat releasing unit (16) is forced to flow through the biomass (4) dispensed on said perforated endless conveyor belt (9), thus at least a portion of the heat introduced by primary heat releasing unit (16) is transferred within the chamber (10) by recirculation of gas and released to the biomass (4) dispensed on said perforated endless conveyor belt (9) for biomass (4) torrefaction process utilization.

[Claim 2] A method as in claim 1 characterized in that:

said heating process comprises a combustion process, wherein fuel is burned in a gas burner (15) with aim to provide a source of heat for primary heat releasing unit (16).

[Claim 3] A method as in claim 2 characterized in that:

said combustion process burns the fuel in form of torrefaction gas, wherein said source of fuel in form of torrefaction gas is preferably released and collected within said process of biomass torrefaction, and wherein said torrefaction gas is supplied by torrefaction gas supply line (14) and burned by gas burner (15).

[Claim 4] A method as in claim 2 characterized in that:

said combustion process comprises external source of fuel in form of LPG or liquid gas with aim to initiate the process of biomass torrefaction, hence external source of fuel is used by gas burner (15) with aim to provide a heat for primary heat releasing unit (16), at least until the biomass torrefaction process within the chamber (10) is fully established.

[Claim 5] A method as in claim 1 characterized in that:

said process of gas recirculation within said chamber (10) comprises the process of collecting the torrefaction gas, which is essentially released from biomass (4) being dispensed on perforated endless conveyor belt (9) within said process of biomass torrefaction, wherein collected torrefaction gas is guided by collector channel (6) to the inlet duct of said prime mover and furthermore, said torrefaction gas is reheated by primary heat releasing unit (16) for utilization of substantially continuous biomass torrefaction process.

[Claim 6] A method as in claim 5 characterized in that:

said process of gas recirculation comprises the process of supplying the reheated torrefaction gas through the heating gas supply line (20) to the inner space of said perforated endless conveyor belt (9), where the hot torrefaction gas is released for utilization of forced convection heating, and wherein the hot torrefaction gas is introduced to the biomass (4) being dispensed on the endless conveyor belt (9) through the apertures within the receiving surface of perforated endless conveyor belt (9).

[Claim 7] A method as in claim 6 characterized in that:

said process of gas recirculation comprises the process of gas pressure redistribution, wherein the inner space of said perforated conveyor belt (9) is used as a pressure redistribution chamber with aim to redistribute the hot torrefaction gas delivered by heating gas supply line (20) between the apertures of perforated endless conveyor belt (9) before said hot torrefaction gas is released through the apertures of said perforated endless conveyor belt (9) for forced convection heating of the biomass (4) being dispensed on outer surface of perforated endless conveyor belt (9).

[Claim 8] A method as in claim 6 characterized in that:

said process of gas recirculation comprises the process of torrefaction gas flow manipulation, wherein the temperature of the torrefaction gas is measured after the torrefaction gas is released from biomass (4) dispensed on the receiving surface of perforated endless conveyor belt (9) and before said torrefaction gas enters into the collecting channel (6), hence the state or position of regulation means comprising the flaps, valves, electric drives and prime mover is adapted to the required level and efficiency of biomass torrefaction process.

[Claim 9] A method as in claim 6 characterized in that:

said process of gas recirculation comprises the process of collecting the released torrefaction gas, wherein the lateral flow of torrefaction gas released from the biomass (4) being dispensed on the perforated conveyor belt (9) is limited by plurality of lateral gas baffles (8) which deflects the torrefaction gas flow (22) to the collector channel (6).

[Claim 10] A method as in claim 3 and 4 characterized in that:

said method further comprises the process of waste heat source utilization, wherein the heat of flue gas from gas burner (15) exhaust (11 ) system is utilized for preheating of ambient air (A) supplied to said gas burner (15) for combustion process utilization with aim to provide a heat source for primary heat releasing unit (16).

[Claim 11 ] A method as in claim 1 characterized in that:

said method further comprises the process of biomass (4) transportation, wherein at least one perforated endless conveyor belt is used to transfer the biomass (4) through the chamber (10) for biomass torrefaction process utilization.

[Claim 12] A method as in claim 11 characterized in that:

said biomass (4) transportation process comprises plurality of endless conveyor belts (9) in serial and/or in parallel connection.

[Claim 13] A method as in claim 1 characterized in that:

said process of adding a biomass (4) to said chamber (10) is utilized by screw conveyor (2), wherein the biomass (4) is substantially dispensed by dispensing device (3) onto the receiving surface of said perforated endless conveyor belt (9).

[Claim 14] A method as in claim 1 characterized in that:

said method further comprises the process of collecting the biomass torrefaction dust, wherein said biomass torrefaction dust is collected in biomass torrefaction dust collector (17).

[Claim 15] A method as in claim 1 characterized in that:

said method further comprises the process of collecting the biomass torrefaction particles, wherein said biomass torrefaction particles are collected in biomass torrefaction particle collector (18).

[Claim 16] A method as in claim 1 characterized in that:

said method further comprises a process of biomass (4) discharge, wherein the torrefied biomass is discharged from chamber (10) by screw conveyor (24), and wherein the biomass (4) containing substantially at least 90% of the initial energy value is compressed and formed in briquettes or pellets.

[Claim 17] A method as in claim 1 characterized in that:

said method further comprises the process of cleaning the apertures of perforated endless conveyor belt (10).

[Claim 18] A method as in claim 1 characterized in that:

said torrefaction process is the process of low temperature pyrolysis being utilized between 200°C and 300°C.

[Claim 19] A method as in claim 1 characterized in that:

said torrefaction process is the process of low temperature pyrolysis being utilized in substantially oxygen free environment within the substantially gas-tight chamber (10).