CH720175A2 - Pyrolysis plant with power modulation via a variable geometry - Google Patents

Abstract

The invention relates to a pyrolysis plant which converts woody biomass (17) into heat and biochar (19) in a continuous process. The process is preferably based on the direct current principle. It is considered to be an inventive novelty that this plant can implement a modulation of the output via a cross-sectional variation of the reaction zone (18) by moving the reaction zone (18) in a conical container (1), for example. For this purpose, the location and position of the reaction zone (18) are measured (16) and specifically influenced by control technology. In addition, the invention has a device (3, 11) for separating the solid from the gaseous products, which enables a high yield and at least reduces the entrainment of fine coal particles in the gas stream compared to previous processes without the use of a cyclone.

Description

[0001] A pyrolysis plant is described below which converts woody biomass into heat and biochar in a continuous process in cocurrent. This plant can implement a modulation of the power over a variable cross-section of the reaction zone by moving the reaction zone in a conical container, for example.

State of the art

[0002] Pyrolysis is a sub-step in gasifiers. Therefore, related gasifiers are considered first, with wood gasifiers being the most relevant.

[0003] WO001994026849A1 describes a gasifier in which the (partial) pyrolysis takes place in countercurrent and the subsequent gasification of the coal takes place in cocurrent. Both processes can take place spatially separated from one another. In the rotationally symmetrical reactor vessel, a stirrer with blades runs concentrically to dissolve any cavities that may occur in the fuel (the stirrer is not part of the protection claims).

[0004] DE202011002845U1 presents a process in which (high-temperature) pyrolysis of, for example, wood chips takes place in a standing hollow cylinder in the middle of which a pipe is concentrically inserted from above, which sucks the resulting combustible gases out of the lower part of the reactor and thus serves as a heat source for drying the fuel mass introduced from above. Furthermore, an agitator for distributing the fuel in the reactor immediately after it is introduced is mentioned here. In addition, a double lock for introducing the fuel into the reactor chamber is mentioned, in which both lock openings can never be open at the same time. The disadvantage is that the suction pipe takes up reaction volume and has a comparatively large mass during the start-up process that has to absorb thermal energy. This can cause long-chain hydrocarbons to condense on the surface and increase emissions in the start-up process. In addition, during continuous operation, the fuel that is close to the pyrolysis gas pipe is heated up and pyrolyzes sooner than fuel further away. This means that a horizontal reaction zone is not to be expected.

[0005] EP3241881A1 from Howäst GmbH describes a rust-free gasifier for low outputs (<60kW) that has a two-part vertical reactor chamber. The drying, pyrolysis and oxidation take place in the upper part, which has a larger diameter than the lower part, and the reduction of the coal takes place in the lower part. The lower part is connected to a horizontal "cross pipe" in which a conveyor screw carries away the coal that is left over from the gasification process. The ember bed of the reaction zone therefore rests on the turns of this screw. This means that a grate is not required. The patent specification points out that the cross section of the upper reactor chamber in which the pyrolysis takes place is crucial for the amount of gas produced. It is proposed to use different inserts with different diameters, also to respond to the different energy densities of different fuels such as pellets and wood chips [0026]. Furthermore, the lower part, in which the reduction takes place, is designed with an expanding cross-section, i.e. in the shape of a truncated cone. One side of the truncated cone is flattened to allow a transition to the cross pipe. This is intended to effectively prevent blockages in the screw and "hollow fires". Power modulation via the variable cross-section is not planned and the replacement of the various inserts with different diameters is only possible when the system is at a standstill.

[0006] DE102014004465B3 proposes a two-stage gasifier with a vertical reactor chamber. At the lower end, this has a device for discharging the "smoke-fuel gas mixture", which in a first embodiment is designed as a baffle plate, the position of which can be changed relative to the reactor chamber, thereby changing the cross-section through which the gas flows. In a second embodiment, an inflow element is used, via which the cross-section is also used to influence the flow rate of the gas. With both solutions, the thermal output can be influenced by changing the cross-section of the opening for the outlet of the gases in the lower section of the reactor chamber. The disadvantage is that this requires an additional actuator and solids can also escape from the reactor chamber through the same opening and are particularly stirred up by the movement.

[0007] WO2019193098A1 discloses a single-stage gasifier with a vertical reactor chamber, which has an inclined grate in the lower part on which the fuel lies. This grate can be moved back and forth. The movement of the grate briefly changes the cross-sectional area of the reaction zone, which on the one hand is intended to cause cavities to collapse and on the other hand removes solids from the reactor vessel. A power modulation of this is not disclosed and does not seem to make technical sense.

[0008] Gasification is also used on a large scale for the disposal or significant volume reduction of urban organic waste. For example, GB1342457A presents a vertical reactor chamber in which waste is introduced at the top and the residual materials from the process (ash and coal) are discharged at the bottom. In GB1342457A, the combustible gas produced is extracted from the top of the reactor chamber in countercurrent, similar to the Imbert gasifier, and is used for thermal purposes, for example. Unlike the Imbert gasifier, however, the reactor chamber widens conically towards the top, presumably to reduce the flow rate of the combustible gas, thus increasing the residence time of the gas in the reactor chamber and thus improving the heat transfer to the waste it flows through. The gasifier has several temperature sensors that are arranged one above the other and extend into the reactor chamber to monitor the progress of the process. They are connected to control valves through which the oxygen-containing gases and water vapor are blown into the reactor vessel, which are used to regulate the oxidation of the waste. Unlike in the invention disclosed here, these sensors do not influence the position of the reaction zone, which is constant.

[0009] DE547555C presents a compact direct current carburetor for use in automobiles, which has a vertically aligned reactor chamber. A fire basket in the lower part of the reactor chamber is designed in a funnel shape, with an expansion of the cross-section towards the top. In order to respond to different fuel moisture levels and performance requirements, the reactor chamber provides the option of varying the cross-section of the narrowest point, which is located at the very bottom of the reactor chamber, using a throttle body that can be operated from the outside and while the carburetor is in operation. The throttle body is implemented using a hollow cylinder that is open at the bottom and closed at the top by a cone, but has smaller openings through which an oxygen-containing gas escapes into the reactor chamber. A smaller cone is rigidly attached to the hollow cylinder at the height of the fire basket, which limits the cross-section to the fire basket. Depending on the position of the hollow cylinder relative to the fire basket, the cross-section can now be varied, thus either influencing the performance of the carburetor or reacting to different fuel moisture levels. The disadvantage is that the fuel must be at least partially displaced and the cross-sectional variation occurs via moving parts.

[0010] Pyrolysis processes for the production of (process) heat and biochar in cylindrical or rotationally symmetrical containers are also known.

[0011] DE3126049A1 presents a pyrolysis process for waste materials in a horizontal, externally heated cylinder in which a screw conveyor or similar conveys the pyrolysis material through the reaction zone. The material is introduced and discharged via double locks. This principle has the disadvantage that the screw conveyor is a mechanical wearing part that is exposed to very high temperatures.

[0012] In EP1203802A1, a clean, combustible gas is to be used for later use in gas engines for power generation. Special features here include an air inlet at the top of the pyrolysis container and an entry of the oxidizing agent at another point slightly above a rotating grate. As an implementation example given (Example I), the gas is cooled with a water mist after leaving the reaction zone and filtered before it is oxidized. As a further embodiment (Example VI), it is mentioned that by reducing the supply of oxidizing agent and rotating the grate, biochar can be discharged before it is completely oxidized, with biochar yields of 25 - 30% being achieved. The disadvantage is that pulsed rotation of the grate probably produces a variable coal quality and continuous rotation can disrupt the pyrolysis process by mixing the reaction zone with fuel that is still cold or at least partially discharging it.

[0013] AT522059B1 presents a method for producing biochar using direct countercurrent pyrolysis, whereby the method describes a heating system. The combustible gases pass from the pyrolysis container through a centrally arranged drive nozzle into the combustion chamber, where atmospheric oxygen is added. Exhaust gases from the combustion chamber are guided in a double wall around the pyrolysis container and partly into the pyrolysis container via a valve. The system also has a cooling device in the biochar discharge, in which, among other things, the biochar is quenched with water. It is proposed to use nutrient-containing media instead of water to biologically "charge" the biochar. The disadvantage of this system is that powerful fans are required to set the desired pressure differences and sometimes have to be used in the hot area, since gas backflow through the pyrolysis chamber is to be achieved and mixer nozzles are used. In addition, regular cleaning of the central propulsion nozzle is probably necessary, since the combustible gases usually entrain fine carbon particles and can condense out tars when mixed with (relatively cold) fresh air.

[0014] A separate category of plants for biochar production are vertically installed reactors ("shaft gasifiers" or "moving bed reactors") that have an internal heating system, e.g. DE102016006884A1 and EP3919586A1. The biomass is pyrolyzed in the absence of oxygen using the heating elements, which are introduced into the reactor vessel from the outside, and the combustible gases produced are released for later combustion. The advantage is that there is a good possibility of regulating the process and ensuring a consistent coal quality. The disadvantage is that significant amounts of external, usually electrical, energy must be supplied to the actually exothermic process. Another group of plants for the production of biochar are rotary kiln plants in which biomass is pyrolyzed in an oxygen-free or oxygen-reduced atmosphere at temperatures of 450°C - 650 °C, see e.g. DE202006017001U1 or DE102008012018B4. Due to the complex design of the rotary kilns, the high demands on the thermally, chemically and mechanically stressed material of the moving tube and the difficulty of disposing of the solid products, these plants are only economically interesting in a few special cases.

[0015] Screw conveyor pyrolysis systems can also be found in the patent literature. These are systems in which biomass is pyrolyzed by constant conveying through a screw conveyor, which is often arranged at an incline. There are direct pyrolysis processes, but also externally heated conveying systems (see, for example, the systems from Biomacon GmbH or Pyreg GmbH). An intermediate form is the process from Hertz Energietechnik GmbH, which is described in EP3358253A1. In this process, an oxidizing agent is first fed into the upper part of a screw conveyor that conveys at an angle upwards, which is then sucked out in the middle part of the screw conveyor. This enables an exothermic pyrolysis process without the supply of external energy (external energy is only required in the start-up process). This system also enables complete gasification of the biomass, whereby no more biochar is produced.

[0016] DE202014004445U1 shows a furnace that burns wood to ash. In this furnace, woody biomass is introduced into the hot zone via a conveyor mechanism such as a screw conveyor, where it is pyrolyzed and releases combustible gases that exit the conveyor mechanism and are immediately oxidized in the combustion chamber. If the biochar produced in the process is removed from the hot area in time, it does not burn completely and can then be cooled and used. This device would be suitable, at least in principle, for power modulation via the feed rate, even if this is not mentioned in the utility model specification.

[0017] US2020040268A1 presents a standing plant for generating heat and biochar, which has an actively rotating and actively height-adjustable grate. Biomass is placed on this grate and an oxygen-containing gas such as fresh air enters from below and flows through the fuel bed in countercurrent. The reactor chamber here has the cross-sectional variation over the height that is often found in this type. This cross-sectional variation is due to a different fuel density in the different reaction zones (drying, pyrolysis, oxidation and reduction) in the reactor chamber. On the rotating grate, a disk with a smaller diameter than the grate itself is attached around the center of rotation, into which a spiral is embedded. The purpose of this spiral is to transport the coal on the rotating grate to the outside, where the grate has penetrations through which the coal should fall. The biochar falls through holes in the grate and is conveyed by a screw conveyor to a valve, e.g. a rotary valve with only one flap, and is discharged.

[0018] US2004167367A1 shows a plant for producing biochar and a largely tar-free combustible gas. In this plant, the spatial position of the reaction zone (“level of the pyrolysis zone”) is recorded with at least one thermocouple and kept at a constant position by a control system during normal operation. In addition, a high temperature in the reaction zone of 800 °C to 1,000 °C is mentioned for pyrolysis. Another special feature here is that the thermal energy of the (unburned) combustible gas is transferred directly to water as part of the gas scrubbing process, in which the gas is fed into a water tank and “bubbles” upwards from below through the water.

Object of the invention

[0019] The biochar market has shown sustained and strong growth worldwide in recent years as it is used in more and more areas of application. However, the main application is still in agriculture, where biochar can increase yields as a soil improver without the use of additional fertilizers or other measures (Agroscope Science | No. 112 / 2021). In addition, the production of biochar is a method of chemically stabilizing the carbon dioxide contained in wood and thus permanently removing it from the atmosphere. Other possible uses of biochar include its use as a concrete aggregate or sand substitute in concrete, its use as a dye or after refinement in activated carbon filters.

[0020] In recent years, a large number of technical solutions have been proposed for producing biochar. The production of biochar generates large amounts of waste heat, which is usually used for heating purposes or as process heat. Until now, these systems had in common that they were not or only poorly suited to modulating the thermal output, which is why the waste heat from these systems cannot be used in monovalent heating systems. For example, the waste heat from state-of-the-art systems is used primarily in heat networks or - at least in the summer months - for less economical applications, or it must be supplemented by other heating systems.

[0021] The following invention therefore aims to implement a plant for the production of heat and biochar with the possibility of a wide power modulation with a constant, high quality of the products produced in a continuous process.

Brief description of the invention

[0022] The pyrolysis plant according to the invention converts fuels such as wood chips or wood pellets in a pyrolysis container into a combustible gas and a carbon-containing solid such as biochar as well as liquid substances such as pyrolysis oil. An autothermal direct current gasification is used in which gases and fuel are passed from top to bottom through a reactor or pyrolysis container. The combustible gas is oxidized in a combustion chamber with, for example, fresh air and the heat generated can be transferred in a heat exchanger to a heat carrier such as heating water or used directly as process heat.

List of drawings

[0023] Fig. 1 shows an embodiment in which important components are numbered, to which reference is made in the text. Fig. 2 shows the core elements of the invention in an exemplary manner and with reduced complexity and shows the same numbering as Fig. 1 for selected components. In addition, Fig. 2 also shows a fuel (17), a reaction zone (18) and a carbonized fuel or coal (19).

[0024] Both figures show sectional views of the construction, with the cutting plane set in the middle of the system.

Detailed description of the invention

[0025] A continuous process provides a pyrolysis container (1) which is supplied with fuel and oxidizing agent from above from a storage container and discharges the products (including biochar and a combustible gas) from below. An exothermic pyrolysis of the fuel (17) takes place in this container under substoichiometric conditions, i.e. under oxygen deficiency. This container has a variable cross-section over its height, for example in the shape of a cone (1). The position of the pyrolysis reaction zone (18), in which the fuel is pyrolyzed to coal (19), can be varied therein and thus its extent can be changed. The variation in the position of the reaction zone occurs through a variable discharge (or input) speed of biochar or through a variable input (or output) speed of fuel (depending on the orientation of the container). This results in a changed conversion performance or gas generation performance with otherwise constant process parameters such as reaction temperature and residence time of the fuel in the reaction zone. The required amount of oxidizing agent is fed in proportionally through an opening (14) with an adjustable cross-section in the upper part of the system. The advantage is that constant properties of the products can be expected despite variable performance. The pyrolysis container is operated, for example, with the help of an induced draft fan, preferably under negative pressure so that no gases escape from the process space in the event of any leaks. The necessary oxidizing agent is also sucked into the combustion chamber via the opening (14). Operating the system under positive pressure is also conceivable. The combustible gases are sucked out of the middle of the pyrolysis container. For this purpose, a small truncated cone (11) is attached to the lower part of the pyrolysis container, which widens towards the bottom and from which a horizontal gas pipe (3) branches off to the side. As a result, the combustible gases rise directly above the coal shaft (9) in the middle of the pyrolysis tank, which separates the two products. In contrast to DE202011002845U1, the extraction device here is largely covered by fuel or coal, which means that the process space is not unnecessarily reduced and the gas is not unnecessarily cooled when the system is started up when the material is still cold.

[0026] In addition to the horizontal gas pipe (3), one or more other pipes or struts, e.g. (13), can be attached to the truncated cone, which are connected to the wall of the pyrolysis chamber. It is also conceivable that the gas pipe is not led out of the pyrolysis container horizontally, but at a different angle. This device(s) ensures that when the solid products are discharged through the spiral arm (12), the fuel or coal above this device(s) does not rotate, which could disrupt the pyrolysis process and dissolve the reaction zone.

[0027] Depending on the fuel used, struts, arms, etc. can be attached to the axis (2) of the spiral arm, which protrude approximately radially from the axis and thus distribute the fuel evenly in the pyrolysis chamber. These struts, which are not shown in the embodiment in Fig. 1, can in particular be provided with paddles or other devices and can also have one or more bends, for example to cause cavities in the fuel to collapse.

[0028] The coal discharge from the pyrolysis tank is carried out via a spiral arm (12) on the floor of the pyrolysis chamber and a concentrically arranged coal shaft (9). The spiral arm (12) is driven by an axle (2) in the middle of the pyrolysis tank, which exits from the top of the pyrolysis tank. In another embodiment, this spiral arm is driven by means of an angle gear through the pipe (13), whereby advantageously no axle (2) is necessary in the inlet in the upper part of the pyrolysis tank, which advantageously increases the cross-section in the inlet.

[0029] A discharge (6) for the solid products can be connected to the coal shaft, which can have one or more cooling devices (15) for cooling the products. It is expedient to feed the heat energy extracted from the products back into the system in another way. In another embodiment, it is also conceivable that the coal is conveyed directly after the coal shaft into a gas-tight intermediate storage facility. It is also conceivable that the coal is crushed in the coal discharge, for example in the coal shaft or within the cooling device, which, among other things, increases the bulk density of the coal and thus requires less storage volume. The coal discharge is designed to be gas-tight, i.e. it has a lock (5) for continuous discharge. However, in at least another embodiment, a gas-tight container is connected to the discharge in a gas-tight manner, which receives the coal and is only opened when the system is switched off.

[0030] The combustible gases are burned in a downstream combustion chamber (10). This combustion chamber is designed in such a way that mixing of the combustible gases with oxidizing agents, for example from fresh air, is facilitated. In order to make optimum use of the waste heat from the combustion chamber, it is proposed that the housing be surrounded by heating water as completely as possible, or at least its outer surface. To prevent the oxidation area from being cooled too much, which would have a detrimental effect on the exhaust gas quality, an insulating layer between the combustion chamber and the heating water is recommended.

[0031] To start the system, the pyrolysis chamber is first filled with fuel from above through a gas-tight lock (4) and closed at the bottom with a rotating grate (7). Directly above the rotating grate there is a glow plug (8) in the middle, which is covered with fuel by briefly operating the discharge (12). The pyrolysis process is started by switching on the glow plug and supplying an oxidizing agent. In an advantageous embodiment, the rotating grate is welded to the conveyor screw of the discharge (6) and the angle of rotation is recorded by a sensor in order to position the screw with the rotating grate in a suitable alignment. Note: In Fig. 1, the rotating grate (7) is shown in section in the open position.

[0032] The pyrolysis plant has the pyrolysis container (1), at least one sensor for determining a position of a reaction zone in the pyrolysis container and at least one control and/or regulating unit which is provided for moving a reaction zone in a targeted manner over a geometry which is not constant along the transport direction of the fuel in order to modulate the power, and thus to change the extent of the reaction zone depending on the position.

[0033] During normal operation, the system's performance is regulated according to the power requirement of the heat sink (usually a hot water buffer tank). For this purpose, the position of the reaction zone is determined and specifically influenced by the at least one sensor (16). If the amount of combustible gas produced is to be increased, the reaction zone is moved to an area of the pyrolysis chamber in which its cross-section is larger. Conversely, if the amount of gas is to be reduced, the reaction zone is moved to an area with a smaller cross-section. At the same time, the amount of oxidizing agent supplied is advantageously adjusted proportionally to the cross-section of the reaction zone, for example via a continuously adjustable valve. In the embodiment in Fig. 1, the cross-section of the reaction zone is increased by discharging biochar, causing the reaction zone to slide downwards. On the other hand, the cross-section of the reaction zone is reduced by stopping the discharge and allowing the reaction zone to move upwards through the fuel.

[0034] To shut down the plant, the supply of fuel is stopped, which means that after a certain time, when the reaction zone has moved upwards, it runs out of fuel. When gas production ceases, the supply of oxidizing agent to the pyrolysis chamber is stopped and the biochar is discharged.

[0035] In order to transport the oxygen-containing gas, e.g. fresh air, into the pyrolysis chamber and to remove the resulting combustible gases from the pyrolysis chamber, it is recommended to use a blower that can generate a pressure lower than the ambient atmospheric pressure in the pyrolysis chamber and in a possible downstream combustion chamber. However, it is also conceivable to blow the oxygen-containing gas into the pyrolysis chamber through a blower, which would create a pressure there that would be higher than the ambient atmospheric pressure.

[0036] In Fig. 1 a cross-section of the invention is shown in a specific embodiment. This embodiment is only for illustrating the invention and does not limit it to the possibility of adopting other embodiments.

Claims (11)

1. Pyrolysis plant for generating heat and biochar from biomass, with at least one pyrolysis container (1), with at least one sensor (16) for determining a position of a reaction zone in the pyrolysis container (1) and with at least one control and/or regulating unit which is provided for moving a reaction zone in a targeted manner over a geometry of the pyrolysis container which is not constant along the transport direction of the fuel in order to modulate the power, and thus to change the extent of the reaction zone depending on the position. 2. Pyrolysis plant according to claim 1, characterized by a spiral discharge for conveying the biochar from the pyrolysis container (1), wherein the bottom of the pyrolysis container (1) consists of a solid plate which has a hole only in its center, through which gases can be discharged through a hollow cone covering the hole at a certain distance and through which the biochar can be conveyed. 3. Pyrolysis plant according to claim 1, characterized in that the at least one sensor is provided to monitor a position and location of the reaction zone in the pyrolysis container (1) in real time and the control and/or regulating unit is provided to control a position and location of the reaction zone in the pyrolysis container (1) in real time. 4. Pyrolysis plant according to claim 1, characterized in that the control and/or regulating unit is provided to adapt a mass flow of oxidizing agent, preferably fresh air, in real time to the position and location of the reaction zone. 5. Pyrolysis plant according to claim 1, characterized by a spiral arm (12) and a coal shaft (9) embedded centrally in a flat bottom of the pyrolysis container (1), wherein the spiral arm (12) and the coal shaft (9) are provided for discharging coal over the surface of the pyrolysis container (1). 6. Pyrolysis plant according to claim 1, characterized by a spiral discharge for conveying the biochar from the pyrolysis container (1), wherein at least one chicane of any shape protruding from the axis of the spiral discharge is attached to the axis for uniform distribution of the fuel. 7. Pyrolysis plant at least according to claim 5, characterized by a cooling device (15) which is arranged in a coal discharge, in particular in the coal shaft (9), and is intended for cooling the solid products. 8. Pyrolysis plant according to claim 1, characterized by a device for comminuting the biochar, which is arranged in a coal discharge, in particular in a coal shaft (9). 9. Monovalent heating system for a building with a pyrolysis plant according to one of the preceding claims. 10. A method for generating heat and biochar from biomass by means of a pyrolysis plant according to one of the preceding claims, characterized in that, for power modulation, a reaction zone is deliberately moved over a geometry that is not constant along the transport direction of the fuel and the extent of the reaction zone is thus changed depending on the position. 11. The method according to claim 10, characterized in that the position and location of the reaction zone in the pyrolysis container (1) is monitored and controlled in real time via sensors.