Pyrolysis Plants and Methods for Thermal Mineralization of Biomass and Production of Combustible Gases, Liquids and Biochar

Abstract

Methods and pyrolysis plants are described, comprising reactors for producing pyrolysis gas from biomass. The reactors comprise one or more reaction channels linked thermally with at least one heating circuit, which is configured to heat the reaction channels to a temperature that is high enough to gasify the biomass. The reactors comprise a feed section configured for feeding the biomass into the reaction channels. The pyrolysis plants comprise a gas accelerator configured for recirculating the gas that is present in the at least one reaction channel and for providing a gas flow velocity that is able to distribute the biomass in the reaction channel.

Claims

1. A pyrolysis plant comprising: a reactor for producing pyrolysis gas from biomass, the reactor comprising: one or more reaction channels linked thermally with at least one heating circuit configured to heat the one or more reaction channels to a temperature that gasifies the biomass; and a feed section configured for feeding the biomass into the one or more reaction channels; a gas accelerator configured for recirculating the pyrolysis gas that is present in the one or more reaction channels and for generating a gas flow velocity that is able to distribute the biomass in the one or more reaction channels; a carbon separator recirculating pyrolysis gas to a gas preheater from a top of the carbon separator; and a plurality of nozzles provided in the heating circuit, each nozzle configured to supply gas to the heating circuit.

2. The pyrolysis plant according to claim 1, wherein the heating circuit is configured to carry out heating by burning gas.

3. The pyrolysis plant according to claim 1, further comprising an oxygen minimizing device in fluid communication with the feed section, wherein the oxygen minimizing device is configured to keep an oxygen concentration of air, which is fed together with the biomass into the one or more reaction channels via the feed section, below a predefined level.

4. The pyrolysis plant according to claim 3, wherein the oxygen minimizing device is in fluid communication with a pipe that receives flue gas from the heating circuit.

5. The pyrolysis plant according to claim 3, wherein the oxygen minimizing device is connected to or integrated in a feed system configured for feeding the biomass into the one or more reaction channels, the feed system comprising: a silo for receiving, storing and supplying biomass; a metering screw mounted rotatably in a first screw channel; and a feed screw mounted rotatably in a second screw channel; wherein the feed system is pressurizable.

6. The pyrolysis plant according to claim 1, wherein the one or more reaction channels comprise one or more ejection sections configured to release a portion of the pyrolysis gas when a gas pressure exceeds a predefined level.

7. The pyrolysis plant according to claim 1, wherein the gas accelerator is a blower mounted and configured for providing a gas flow velocity that disperses the biomass in the one or more reaction channels.

8. A method for producing pyrolysis gas from biomass, the method comprising: providing a pyrolysis plant having: a reactor comprising: one or more reaction channels linked thermally with at least one heating circuit configured to heat the one or more reaction channels to a temperature that gasifies the biomass; and a feed section configured for feeding the biomass into the one or more reaction channels; a gas accelerator configured for recirculating the gas that is present in the one or more reaction channels and generating a gas flow velocity that is able to distribute the biomass in the one or more reaction channels; a carbon separator recirculating pyrolysis gas to a gas preheater from a top of the carbon separator; and a plurality of nozzles provided in the heating circuit, each nozzle configured to supply gas to the heating circuit; and providing a gas flow that disperses the biomass in the one or more reaction channels.

9. The method according to claim 8, wherein the gas flow is provided by a blower installed in the one or more reaction channels.

10. The method according to claim 8, wherein the biomass is transported around in the reactor by a carrier gas, which is produced in the one or more reaction channels, wherein the carrier gas is recirculated in the one or more reaction channels.

11. The method according to claim 10, further comprising maintaining a temperature of the carrier in a predefined temperature range.

12. The method according to claim 10, further comprising increasing a temperature of the carrier gas in a section of the one or more reaction channels.

13. The method according to claim 10, further comprising keeping an oxygen concentration of the gas that is fed into the feed section below a predefined level, which is lower than an oxygen concentration of atmospheric air.

14. The method according to claim 8, wherein the pyrolysis plant further comprises an oxygen minimizing device in fluid communication with the feed section, wherein the oxygen minimizing device is configured to keep an oxygen concentration of air, which is fed together with the biomass into the one or more reaction channels via the feed section, below a predefined level.

15. The method according to claim 14, wherein the oxygen minimizing device is in fluid communication with a pipe that receives flue gas from the heating circuit.

16. The method according to claim 15, further comprising a step of pressurizing the feed system by introducing flue gas and closing the oxygen minimizing device.

17. The method according to claim 14, wherein the oxygen minimizing device is connected to or integrated in a feed system configured for feeding the biomass into the one or more reaction channels, the feed system comprising: a silo for receiving, storing and supplying biomass; a metering screw mounted rotatably in a first screw channel; and a feed screw mounted rotatably in a second screw channel; wherein the feed system is pressurizable.

18. The method according to claim 8, wherein the one or more reaction channels comprise one or more ejection sections configured to release a portion of the pyrolysis gas when a gas pressure exceeds a predefined level.

19. The method according to claim 8, further comprising continuously mixing the biomass within the one or more reaction channels.

20. The method according to claim 8, further comprising separating biochar from the pyrolysis gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] The invention will be explained hereunder, referring to the appended drawings, where

[0087] FIG. 1 shows a schematic sectional view of a reactor according to an embodiment,

[0088] FIG. 2 shows a close-up view of a part of a reactor corresponding to the reactor shown in FIG. 1,

[0089] FIG. 3 shows a schematic view of a reactor according to an embodiment,

[0090] FIG. 4 shows a schematic diagram of a biomass feed unit according to an embodiment, and

[0091] FIG. 5 shows a schematic diagram of a filter system for withdrawing and separating biochar according to an embodiment.

DETAILED DESCRIPTION

[0092] By way of introduction, it should be noted that the appended drawings only illustrate non-limiting embodiments. A number of other embodiments will be possible within the scope of the present disclosure. In the following, equivalent or identical elements in the various embodiments will be designated with the same reference symbol.

[0093] FIG. 1 shows a schematic diagram of a reactor 2 according to an embodiment. The reactor 2 comprises a reaction channel 3, which is placed in a heat exchanger 4, which exchanges heat with the surrounding heating circuit 18. It is emphasized that FIG. 1 is a schematic view, and that the reactor 2 may in practice comprise many layers of reaction channels 3, which are surrounded by the surrounding heating circuit 18. In an embodiment, the reactor 2 comprises many layers of reaction channels 3 and heating circuits 18, provided in such a way that most of the reaction channels 3 are surrounded by heating circuits 18 with a view to minimizing heat loss to the surroundings and at the same time providing a large reaction volume.

[0094] In an embodiment, the reactor 2 only comprises one continuous reaction channel 3.

[0095] In contrast to the pyrolysis plants known hitherto, the comminuted biomass 30 is fed into reaction channel 3 of the reactor in a section that contains a carrier gas, which is recirculated through the reaction channel 3. The carrier gas will in practice be the pyrolysis gas that forms in the reaction channel 3. In an embodiment there is recirculation of the carrier gas as it leaves the reaction channel 3 by ejection as a result of the increase in pressure that occurs in the reaction channel 3, when more and more biomass 30 is gradually gasified.

[0096] Feed of comminuted biomass 30 may be affected by a metering screw 92′ (see FIG. 4). Recirculation of the carrier gas can be provided by a gas accelerator, which may for example be configured as a blower 20, which is placed inside the reaction channel 3. The blower 20 (see FIG. 3) generates a pressure gradient and therefore a gas flow velocity 11, which on the one hand makes it possible to maintain recirculation of the carrier gas and on the other hand ensures that the comminuted biomass 30 is distributed in the reaction channel 3 of the reactor. The biomass 30 is gasified and forms pyrolysis gas 28 under the conditions in the reaction channel 3, which thus constitutes the pyrolysis chamber of the reactor.

[0097] The reactor 2 is characterized in that it provides very rapid heating of the biomass 30 compared to conventional pyrolysis plants, where the biomass is introduced with a screw and then lies in a relatively thick layer. As the biomass in conventional installations is introduced in a manner in which a relatively thick layer of biomass forms on the reactor bottom, the heating of the biomass does not take place uniformly (as the biomass has an insulating effect and therefore it is far colder in the middle of the layer than in the uppermost part of the layer). Owing to this temperature gradient, moreover, the heating time is relatively long compared to the heating time in a reactor 2 according to the present disclosure. Put briefly, heating of the comminuted biomass 30 takes place many times more quickly and much more evenly in a reactor 2 according to the present disclosure than in conventional pyrolysis plant.

[0098] In an embodiment, the heating circuit 18 is heated with gas that is burned in a controlled environment, where the oxygen concentration is maintained in a predefined range, e.g. approx. 4%.

[0099] The heating circuit 18 is provided with nozzles 40, which are configured for supplying gas to the heating circuit 18. As a result, it is possible on the one hand to control the amount of gas that is fed into the heating circuit 18 and on the other hand the distribution of the gas (i.e. where the gas is introduced). The aim is for the nozzles 40 to be installed in such a way that the gas is distributed evenly by being introduced in a row of feed zones (corresponding to the placement of the nozzles). In this way it is possible to avoid local overheating (hot spots). In an embodiment the nozzles 40 are installed in such a way that there is a mutual distance between adjacent nozzles 40 of 50-200 cm. In an embodiment, all the nozzles 40 are configured for introducing gas simultaneously. In an embodiment, all the nozzles 40 are configured for introducing gas with the same flow (feed rate). It may be advantageous if the nozzles 40 supply pyrolysis gas 28 that is produced in the reaction channel 3.

[0100] On the left side of the section of the reaction channel 3 shown, there is a relatively high concentration of biomass 30. On the right side of the section of reaction channel 3 shown, there is on the other hand a lower concentration of biomass 30, while conversely there is a higher concentration of pyrolysis gas 28 and biochar (carbon) 105. This is because the biomass 30 has been converted to pyrolysis gas 28 and biochar (carbon) 105, respectively.

[0101] FIG. 2 illustrates a close-up view (sectional view) of a part of a reactor corresponding to the reactor shown in FIG. 1. The reactor comprises a heat exchanger 4, which is in thermal contact with an adjoining heating circuit 18, which consists of a channel that extends parallel to the heat exchanger 4. In the heat exchanger 4, a reaction channel 3 is provided, into which comminuted biomass 30 is fed, which is gasified when a sufficiently high temperature (typically above 800° C.) is provided, and at the same time the oxygen content is kept low.

[0102] In FIG. 2, gasification of biomass 30 has occurred, which is thus converted to pyrolysis gas 28 in the reaction channel 3. The comminuted biomass 30 is distributed in the reaction channel 3 by a blower 20 (see FIG. 3), which provides a flow velocity 11 of a magnitude that ensures that the biomass 30 is distributed in the reaction channel 3. The flow velocity 11 further ensures that the carrier gas (by which the biomass 30 is transported) is recirculated in the reaction channel 3. The flow velocity 11 is selected in such a way that the biomass 30 used can be distributed in the reaction channel 3. If it is a question of for example comminuted straw, the required flow velocity 11 will for example be less than the flow velocity that is required to ensure that comminuted biomass 30 with a far higher density (e.g. poultry manure) is distributed in the reaction channel 3. In an embodiment, the flow velocity 11 is selected in the range 10-100 m/s, or 20-60 m/s, or 30-50 m/s.

[0103] In an embodiment, the oxygen concentration in the reaction channel 3 is kept low by injecting flue gas (from the burnt gas in the heating circuit 18) into the reaction channel 3. The heating of the heating circuit 18 can be controlled by regulating the gas flow velocity 15. As is the case for the reactor 2 shown in FIG. 1, the reactor in FIG. 2 is illustrated schematically. It will thus be possible to provide the reactor with several reaction channels 3, which are surrounded by heating circuit 18.

[0104] The reactor is characterized in that it can be started and stopped in a flexible manner, as the gasification of biomass 30 in the reaction channel 3 takes place when the oxygen content in the reaction channel 3 is kept at a low level simultaneously with the temperature in the reaction channel 3 being suitably high. It is thus possible to stop the production of pyrolysis gas very quickly by adjusting the feed of biomass 30.

[0105] In the same way as illustrated in FIG. 1, a plurality of nozzles 40, spaced apart, is provided in the heating circuit 18. The nozzles 40 are configured for supplying gas to the heating circuit to provide heating. By using the nozzles to feed gas into the heating circuit 18, it is possible to control both the amount of gas that is fed into the heating circuit 18 and the distribution of the gas feed. To prevent overheating of the heating circuit 18, the aim is to instal the nozzles 40 in such a way that the gas that is introduced via the nozzles is distributed evenly along the heating circuit.

[0106] On the left side of the section of the reaction channel 3 shown, there is a higher concentration of biomass 30 than in the right-hand part of the section of the reaction channel 3 shown. On the right-hand side of the section of the reaction channel 3 shown, there is a higher concentration of pyrolysis gas 28 and biochar (carbon) 105 than in the left side of the section of the reaction channel 3 shown, because the biomass 30 has been converted to pyrolysis gas 28 and biochar (carbon) 105, respectively.

[0107] FIG. 3 shows a schematic view of a reactor 2 according to an embodiment. The reactor 2 comprises a heat exchanger 4, which is in thermal contact with a heating circuit 18. It is one continuous heat exchanger 4, even if it is shown as two parts in FIG. 2. In an embodiment, the heat exchanger 4 and the surrounding heating circuit 18 are configured as described with reference to FIG. 1 and FIG. 2. Thus, in heat exchanger 4 there is a reaction channel 3, which forms a circuit, in which it is possible to provide recirculation of a carrier gas. The carrier gas is the pyrolysis gas that is produced in the reaction channel.

[0108] The reactor 2 comprises a feed section 6 for introducing comminuted biomass, which may for example be comminuted straw. Feed may advantageously be provided using a feed system as shown in FIG. 3.

[0109] An air blower 20 is installed in the reaction channel for recirculating carrier gas and distributing the biomass that is introduced via the feed section 6. Before the feed section 6, a gas preheater 10 is provided, the purpose of which is to increase the temperature of the carrier gas that is injected into the reactor 2 by the blower 20.

[0110] The function of the established heating circuit 18 (indicated with arrows) is to supply heat to the biomass in the reaction channel in the heat exchanger 4. The heat is supplied to the heating circuit 18 by recirculating hot combustion gas with a blower 8. Moreover, the necessary amount of gas and oxygen is added to maintain the desired heat production, which is required to provide pyrolysis production in the reaction channel.

[0111] Alternatively, the necessary amount of gas may be added to the recirculated combustion gas, while oxygen is supplied stepwise by a combustion air blower 14. The purpose of the vigorous recirculation and stepwise combustion is to increase heat transfer and prevent local overheating (hot spots) with the risk of burn-through of the reactor 2.

[0112] The reactor 2 comprises an air preheater 21, which heats the air from the combustion air blower 14. The heating circuit 18 is connected to the blower 8 that recirculates the hot combustion gas. The heating circuit 18 is further connected to the air preheater 21, so that the flue gas 12 is used for heating the injected air by heat exchange in the air preheater 21. The air preheater 21 is thus configured as a heat exchanger, which provides heating of the air that is introduced by the blower 14.

[0113] The reactor 2 may optionally comprise a heater 16, which generates the thermal energy for the heating circuit 18. The heater 16 may heat by electricity or by combustion of a fuel (gas, liquid or solid).

[0114] The reactor 2 comprises a preheater 10, the purpose of which is to raise the temperature of the recirculated carrier gas leaving the blower 20. This ensures that the temperature of the carrier gas is high enough for the pyrolysis process to take place as soon as the biomass is fed into the reaction channel.

[0115] The reactor 2 comprises a carbon separator 22, the uppermost part of which is connected to the outlet of the heat exchanger 4. The carbon separator 22 comprises a carbon outlet 24 and a pyrolysis gas outlet for withdrawal of pyrolysis gas 28. The pyrolysis gas 28 is withdrawn by ejection through the pyrolysis gas outlet, which is provided in the lowest part of the carbon separator 22. The pyrolysis gas 28 formed is led away via a pipe system (not shown) to a scrubbing process.

[0116] From the top of the carbon separator 22, the pyrolysis gas is recirculated further to the gas preheater 10.

[0117] A row of nozzles 40 is installed in the heating circuit 18. The nozzles 40 are installed and configured to be able to supply gas to the heating circuit 18 in such a way that the amount of gas that is fed into the heating circuit 18 and distribution of the gas in the heating circuit 18 may take place in such a way that the gas is distributed evenly in the heating circuit 18. It is thereby possible to avoid local overheating (hot spots) in the heating circuit 18. It is, moreover, advantageous for the nozzles 40 to ensure that the magnitude of temperature gradients in the heating circuit is minimized.

[0118] FIG. 4 shows a schematic diagram of a biomass feed unit 30 according to an embodiment. The purpose of the unit is to minimize the concentration of oxygen that is present in the biomass 30 that is fed into the reactor. A silo 97 is provided, equipped with an upper inlet 104, which in normal conditions is kept closed with a valve 103. This valve 103 is configured to be brought into an open configuration when biomass 30 is filled in the silo 97. In the lower part of the silo 97, an outlet is provided, which in normal conditions is kept open with valve 102. This valve 102 is configured to shut off the outlet when biomass 30 is filled in the silo 97.

[0119] Advantageously, a sensor (not shown) may be fitted, which measures the amount of biomass 30 in the silo 97. Measurements from this sensor may be used for controlling filling of biomass 30 in the silo 97.

[0120] To the left of the silo 97, a feed system is provided for introducing flue gas 98 with low oxygen content. This flue gas 98 may advantageously be derived from burning of the gas, which generates the heat that heats the reaction channels of the reactor by heat exchange with the heating circuit. The first valve 90 regulates supply of flue gas 98 to the silo 97. The second valve 90′ is a pressure reducing valve, which ensures that the silo 97 is pressurized with a pressure that is within a predefined range. Thus, an excess pressure (relative to the surroundings) is created in the silo 97. This excess pressure prevents atmospheric air entering the silo 97. It is thus possible to reduce the oxygen content in the silo 97. This minimizes the oxygen concentration in the gas that is fed together with the biomass 30 into the reaction channel.

[0121] The silo outlet opens out into a screw channel, in which there is a metering screw 92′, which is driven by an electric motor 100′. The activity (rotary speed) of the metering screw 92′ is decisive for how much biomass 30 is metered.

[0122] A flap 99 is provided, which opens when biomass 30 is propelled forwards towards the flap 99. The biomass 30 that passes through the flap 99 drops down into a lower screw channel, which houses a feed screw 92, which is driven by an electric motor 100. The activity of the metering screw 92′ determines how much biomass 30 is fed into the reactor (see FIGS. 1-3). The feed screw 92 is surrounded by a double-walled jacket 95, which is heated with hot pyrolysis gas 28 from a pipeline 142, which is the gas outlet from the filter system shown in FIG. 5. In this way, the screw 92 and the biomass 30 that the screw 92 propels into the reactor are heated. The heating of the feed screw 92 may alternatively be provided with flue gas from burning of gas in the heating circuit.

[0123] FIG. 5 shows a schematic view of a filter system for withdrawing and separating biochar according to an embodiment. The filter system comprises a first filter 106 and a second filter 106′, each comprising filter elements configured for filtration of carbon 105. Ceramic filter sticks may be used advantageously. The two filters 106, 106′ are placed in parallel and open out into a screw channel, which houses a screw 96, driven by an electric motor 101.

[0124] The screw channel opens out into a conveyor tube 120, which is connected to the blower 124, which blows carbon 105 into a cyclone 130 via a transport section 122. The transport section 122 is connected to a cooler 126, which may be placed advantageously in the open air. The cooler 126 is depicted as a tubular cooler 126, which cools the hot carbon 105 to prevent fire. It is thus possible to provide efficient cooling in a simple manner.

[0125] The cooler 126 is connected to the cyclone 130, which is configured to lead carbon 105 down into a carbon silo 128, which comprises an inlet and an outlet, each of which is equipped with a valve for opening and closing the carbon silo 128. A pipeline 132 is connected to the carbon silo 128. A system for supplying flue gas 98 is connected to this pipeline 132.

[0126] A gas supply unit 110, which may be configured as a gas holder, is placed above the filters 106, 106′. This gas supply unit 110 forms a part of the “backflush system” of the filter system, which operates by injecting gas from above and down into the filters 106, 106′, which provides cleaning of the filters 106, 106′. The “backflush system” of the filter system comprises a pipeline 142 configured for leading gas away. The “backflush system” of the filter system further comprises a first valve 116 for regulating the gas flow to the first filter 106 and a second valve 116′ for regulating the gas flow to the second filter 106′.

REFERENCE NUMBERS

[0127] 2 Reactor [0128] 3 Reaction channel [0129] 4 Heat exchanger [0130] 6 Feed section [0131] 8 Blower (combustion recirculation) [0132] 10 Preheater [0133] 11 Flow velocity [0134] 12 Discharge [0135] 14 Blower (combustion air) [0136] 15 Gas flow velocity [0137] 16 Heater [0138] 18 Heating circuit [0139] 20 Blower (gas recirculation) [0140] 21 Heat exchanger [0141] 22 Carbon separator [0142] 24 Carbon outlet [0143] 26 Gas (for the scrubbing process) [0144] 28 Pyrolysis gas [0145] 30 Biomass (e.g. straw) [0146] 40 Nozzle [0147] 90, 90′ Valve [0148] 92, 92′ Screw [0149] 95 Double-walled jacket [0150] 96 Screw [0151] 97 Silo [0152] 98 Flue gas [0153] 99 Flap [0154] 100, 100′, 101 Motor [0155] 102 Valve [0156] 103 Valve [0157] 104 Inlet [0158] 105 Carbon [0159] 106, 106′ Filter [0160] 110 Gas supply unit [0161] 116, 116′ Valve [0162] 120 Conveyor tube [0163] 122 Transport section [0164] 124 Blower [0165] 126 Cooler [0166] 128 Carbon silo [0167] 130 Cyclone [0168] 132 Pipeline [0169] 142 Pipeline (gas outlet)