Biochar production equipment

Abstract

Biochar production equipment (10) for producing biochar from a feedstock in the presence of minimal oxygen comprising: a lower chamber for the pyrolysis of the feedstock (12); one or more air inlets (

Description

The present invention relates to biochar production equipment. BACKGROUND TO THE INVENTION Biochar is formed by pyrolysis, i.e. by heating biomass to high temperatures in the presence of little to no oxygen. Biochar is commonly used in agriculture and horticulture for improving the soil quality. Biochar retains the porous structure of the biomass, which allows it to contribute to improved soil aeration and allow the retention of water, air and nutrients in the soil. It can also be used as a pH modifier for soil and other applications. Biochar production is used as a method of sequestering carbon from the atmosphere. The feedstock for biochar is usually plants and trees (i.e. organic biomass), which absorb carbon dioxide from the atmosphere as they grow. The organic biomass can then be turned into biochar, which fixes some of the carbon into a stable state, which can be buried. This process offsets carbon emissions, reducing the net amount of carbon dioxide that is released to the atmosphere, and thereby contributing to the reduction of global warming and climate change. Another use of biochar is the disposal of waste organic material such as wood chippings, or agricultural residues, which can be turned into biochar and sold. This can be an effective way of reducing the amount of waste that is burned, composted or goes to landfill, and instead provides an income stream from products that are otherwise wasted. Biochar is conventionally produced in biochar production equipment which comprises a cylindrical lower chamber where the biomass is heated to high temperatures in an atmosphere of reduced oxygen to produce biochar. Heating the biomass causes volatile gases such as methane to be produced. These gases are then removed to a separate part of the equipment, where they can be collected or combusted (not released). In some current designs, the augers transport feedstock through a heated chamber as it pyrolyzes. This method works well for smaller units, however they are problematic for scaling as the amount of feedstock that can be processed is limited by the length of the augers. The length of the augers is limited as the high temperatures that need to be maintained for pyrolysis can only be sustained on a relatively small scale. In other designs, feedstock may be fed into a circular chamber via a vertical auger, and then circular plates agitate the feedstock as it is heated, and transport it to the edge of the chamber as it pyrolyzes. However, this limits the amount of feedstock that can be processed. Large scale biochar production equipment can be produced to process a suitable quantity of feedstock, however it has to be built in situ. This can be inconvenient, with the biomass and biochar needing to be transported to and from the equipment. Furthermore, where biochar is being used to offset carbon emissions, the potential benefit in terms of fixing the carbon can be negated by transport emissions associated with moving the biomass across long distances. It is an object of the present invention to reduce or substantially obviate the aforementioned problems of scale and transportability. STATEMENT OF INVENTION According to the present invention there is provided biochar production equipment for producing biochar from a feedstock in a low oxygen environment comprising: a lower chamber for pyrolysis of the feedstock; one or more air inlets for providing oxygen for the combustion of pyrolysis gases, to heat the feedstock in the lower chamber and form the biochar; a feedstock inlet connected to the lower chamber for the feedstock to enter the lower chamber; a gas outlet for gases to exit the biochar production equipment; a solids outlet for removal of the biochar from the lower chamber; and a set of two or more plates disposed inside the lower chamber, in which the set of two or more plates comprise one or more reciprocating plates and in which each reciprocating plate moves along a linear axis for moving and agitating the feedstock as it is heated. The use of one or more reciprocating plates is advantageous over rotary oscillating plates because they allow a more efficient use of space. In particular, having one or more linearly reciprocating plates means that biochar production equipment can have a rectangular footprint and efficient design allowing for scaling whilst still allowing the equipment to be transported on the back of a lorry or in a shipping container. In contrast, though equipment with rotary oscillating plates can be housed in a rectangular container, it is not an efficient use of the space, and the capacity of the equipment is less for a given footprint. Additionally, the use of one or more reciprocating plates is advantageous because as plates move, they turn and agitate the feedstock as it is converted into biochar, which helps to form a uniform product. Pyrolysis is the process of heating material such as organic material (i.e. biomass) to thermally decompose the material in the absence of oxygen. The biochar-production equipment may be pyrolysis equipment. Reciprocating plates means that the plates move backwards and forwards (oscillate) in a straight line, i.e. along a linear axis. The biochar production equipment may comprise an upper chamber. The upper chamber may be disposed above the lower chamber. A gas outlet may be disposed above the upper chamber. The set of plates may comprise one or more stationary plates. The one or more reciprocating plates may reciprocate with respect to the one or more stationary plates, and the relative motion between them may cause the biomass and then biochar to be pushed down from plate to plate. In particular, as each reciprocating plate retracts with respect to an above stationary plate, the area of the reciprocating plate is reduced, and biochar / biomass is pushed off the front of the reciprocating plate. Likewise, as each reciprocating plate moves forward with respect to a below stationary plate, it pushes material off the below stationary plate. The set of plates may comprise alternating stationary and reciprocating plates. Each stationary plate may be disposed above and set back from a corresponding reciprocating plate. This means that as the reciprocating plate withdraws, the available surface area on a top of the reciprocating plate reduces as it is covered up by the above stationary plate, and hence a fraction of the material will fall off the reciprocating plate and onto the plate beneath, or in the case of a base plate, into the solids outlet. Each stationary plate may be disposed below a corresponding reciprocating plate. As the reciprocating plate moves forward, it pushes material that has landed on the below stationary plate off and onto the next plate. Each plate may be substantially rectangular. Each plate may abut its adjoining plates(s). In other words, each plate may be close to the plate above and / or below it. Therefore, the material can be swept off each plate by its adjoining plate. Each plate may have an edge perpendicular to its linear axis of movement, i.e. axis of reciprocation. The edge may be substantially linear, which prevents any biochar getting lodged or stuck in an edge of the plates, and instead allows it to tumble down from plate to plate. In other embodiments, the edge of the plate may be angled, or have protrusions or probes at the edge to assist with agitation. The set of plates may comprise a top plate. A separate upright element may be disposed above the top plate for pushing material onto the other plates. This may be referred to as a ‘ram’. The set of two or more plates may be stacked in a staggered configuration. This allows material to be pushed off each plate and onto the next one, and in this way, material falls down the plates as the biomass converts to biochar. Each set of plates may be configured to move the material (i.e. the feedstock biomass as it transforms to the biochar) such that a majority of the material may be on the set of plates for around 15 minutes. After around 15 minutes the biochar may drop into the solids outlet. The lower chamber may have a first side, and a second side. A first set of plates may be disposed on the first side of the lower chamber. A second set of plates may be disposed on the second side of the lower chamber. The solids outlet may be disposed between the sets of plates. The solids outlet may be disposed below an elongated gap between the first set of plates and second set of plates, to maximise the amount of material that can be processed. Two feedstock inlets may be provided. A first feedstock inlet may be provided above the first set of plates, and a second feedstock inlet may be provided above the second set of plates. Additionally, having the feedstock inlets provided above the plates means that material may be dropped across a large surface area. In contrast, where material may be supplied from beneath the plates, the feedstock that can be supplied by a vertically-oriented screw auger falls on a smaller surface area. Having two feedstock inlets and two sets of plates optimises the amount of material that can be processed, and ensures there may be a large surface area available to receive the feedstock and be exposed to the heat necessary for pyrolysis. The first set of plates and the second set of plates may be symmetrically disposed on either side of the lower chamber. The lower chamber may be under negative pressure. The upper chamber may also be under negative pressure. All the biochar production equipment bounded by the rotary valves may be under negative pressure. This prevents oxygen from moving to where the biomass is located on the plates as the negative exhaust pressure means all air and gas is pulled upwards and out of the lower chamber. A set of air inlets are provided by the first set of air inlet apertures which provide air for combustion and therefore to provide heat. The first set of air inlet apertures may be disposed above the plates. One or more fans may be provided to blow air into the air apertures. A further set of air inlets are provided by a second set of air inlet apertures for combustion of uncombusted gases. These allow any volatile and combustible gases that have not been used for combustion for heat at the first set of air inlet apertures, to be combusted before release to the atmosphere. For example, this allows gases like methane to be removed from the gas stream so they do not enter the atmosphere, where they would be damaging to the environment. Additionally, some additional heat can be provided by the combustion of these remaining combustible gases. The second set of air inlet apertures may be disposed above the first set of air inlet apertures. The hot volatile gases rise through the equipment and upwards through the upper chamber, and therefore the second set of air inlet apertures may be disposed above the first. A controller may be provided to control the ratio of air entering the first set of air inlet apertures to air entering the second set of air inlet apertures and therefore to control 5 the amount of heat provided to the feedstock. For example, providing more air to the first air inlet apertures can provide hotter temperatures for the feedstock. However if too much air is provided by the first set of air inlet apertures then the biomass will be exposed to too much oxygen and combust instead of pyrolyzing. Each feedstock inlet may be provided as a chute. Each chute may store feedstock which can then be fed into the lower chamber. A chute may be disposed above each set of plates. Quenching means such as water jets may be provided at the solids outlet for wetting and cooling the biochar. This may prevent the biochar from igniting when it is exposed to the air upon deposit from the equipment. The biochar production equipment may comprise transportation means such as a screw auger for transporting the product. The transportation means are provided below the plates. In this way, the biochar produced may be transported away from the biochar production equipment. An inlet rotary valve may be disposed below the feedstock inlet to isolate the lower chamber and upper chamber from the air, and to control the rate at which the feedstock is introduced. Isolating the equipment from the air means that the equipment can be held under reduced pressure, which is essential in maintaining the correct flow of air and gas within the equipment to convert the biomass to biochar, rather than combust or burn the biomass. The inlet rotary valve may feed a fixed volume of material, so the amount of material going into the biochar production equipment can be recorded. The biochar production equipment may comprise an outlet rotary valve for isolating the lower chamber and upper chamber from the air. The outlet rotary valve may be disposed at the end of the transportation means. The gas outlet may comprise ducting. The gas outlet, or the ducting, may comprise heat exchange means, for capturing heat to be used to dry biomass or otherwise. A gas monitor such as an oxygen monitor may be disposed at the gas outlet. This allows the amount of oxygen in the combusted gases be monitored, which can indicate what the conditions are inside the lower chamber (and if more air is required to maintain complete combustion of the gases). This may inform whether the inflow 6 of air into the first set of air inlet apertures and / or the second set of air inlet apertures should be adjusted. The lower chamber may be partially separated from the upper chamber by a divider. The divider may have an aperture. The secondary inlet apertures may be disposed around the divider aperture. Specifically, the secondary inlet apertures may be disposed on a surface of the divider aperture. The divider aperture may be centrally disposed on the divider. The divider aperture may be substantially circular in cross section. The divider may have a central, circular aperture. In some embodiments, the divider may be cooled by a flow of fluid. The fluid may be gas, or a liquid such as water or oil. The divider may be hollow. The hollow divider may be cooled by the flow of fluid. A footprint of the biochar production equipment may be less than 12 m by 3 m so it can be transported on the back of a lorry or fit in a shipping container. A footprint of the biochar production equipment may be less than 6 m by 3 m. The equipment may be partially dissembled, or some parts of the equipment may be removed from the equipment in order for the equipment to be of the transportable size. According to a second aspect of the invention, there is provided a method of manufacturing biochar from biomass using the biochar production equipment according to the first aspect of the invention, comprising the steps of: a) reducing the oxygen concentration inside the biochar production equipment; b) providing biomass to the feedstock inlet; c) heating the biomass to a temperature of around 400°C to 800°C; d) agitating and moving the biomass using the reciprocating plates as it turns to biochar; and e) collecting the biochar product. Any combination of steps (b), (c), (d) and (e) may happen simultaneously, as the equipment may be continuously operated. The second embodiment of the invention may comprise any features of the first embodiment of the invention. The biochar production equipment may be used more broadly as a waste or refuse to fuel plant, to generate heat, biochar or other fuel. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 is a perspective view of the biochar production equipment; Figure 2 is a cutaway view of the biochar production equipment of Figure 1; Figure 3 is a part of the cutaway view of the equipment shown in Figure 2; Figure 4 is a perspective view of the plates used in the biochar production equipment of Figure 1; Figure 5 is a part of the cutaway view of the biochar production equipment of Figure 1; Figure 6 is a part of the cutaway view of the biochar production equipment of Figure 1; and Figure 7 is a part of a cutaway view of another embodiment of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS Referring firstly to Figures 1 and 2, there is shown biochar production equipment 10. Though Figure 2 is a cutaway view of the equipment, features provided on the visible half of the equipment will be provided on the side of the equipment that is not shown. The biochar production equipment 10 has a lower chamber 12, in which feedstock is converted to biochar. The biochar production equipment 10 has an upper chamber 14 disposed above the lower chamber 12. A longitudinal length of the biochar production equipment 10 is greater than its transverse length, such that it has a substantially rectangular footprint. A first set of plates 30a, and a second set of plates 30b are disposed within the lower chamber 12. The plates 30 form a base of the lower chamber 12. The first and second set of plates 30 are substantially symmetrical to each other. Each set of plates 30 is staggered. Each plate 30 is disposed substantially horizontally. Reciprocating plates and stationary plates (42 and 44, shown in Figure 3) are provided in each set of plates 30. In this embodiment, there is an alternating arrangement of reciprocating plates 42 and stationary plates 44. Each reciprocating plate 42 reciprocates i.e. moves along a linear axis. The axis of reciprocating is substantially horizontal and is parallel to the linear axis of movement of the other reciprocating plates. A front edge 46 is defined on each plate. The front edge 46 is substantially straight and is perpendicular to the linear axis of movement of each plate in this embodiment. However, in other embodiments the edge 46 may be angled, have protrusions or be jagged. Each reciprocating plate 42 reciprocates between a first position and a second position. In the first position, the front edge of the reciprocating plate is substantially flush with the front edge of the stationary plate 44 beneath it. In the second position, the front edge 46 of the reciprocating plate 42 is behind the front edge of the stationary plate beneath it. In Figure 2, the set of plates 30 are shown in the first position. A top plate 24 is disposed at the top of the set of plates 30b. An upright element 26a is disposed on an upper surface of the top plate 24a. The upright element 26a is substantially perpendicular to the top plate 24a, so it can push material into the centre of the lower chamber 12. On each side of the equipment 10, the reciprocating plates 42 and top plate 24 are driven by pistons 28. In this embodiment, the plates are driven by hydraulic rams, but in an embodiment, they may be driven by electric motors. Inner walls (one of which is shown at 48) are disposed on either side of the sets of plates 30. The inner walls 48 are parallel to the linear axis of movement of the reciprocating plates 42. The first set of air inlet apertures (50, shown in Figure 3) are disposed on the inner wall 48. A gap 60 is provided between the first set of plates 30a and the second set of plates 30b for the biochar to fall into and be removed. Below the gap 60 is solids outlet 32. The gap 60 is elongated. In this embodiment, the gap 60 is narrower than a width of a plate. The gap 60 has parallel edges. The elongated gap 60 allows for the cooling of biochar with water spray jets. Transporting means 58 are part of the solids outlet 32, and are disposed below the gap 60. The gap 60 is parallel to the transporting means 58. A divider 36 is disposed between the lower chamber 12 and the upper chamber 14. An aperture 38 is disposed centrally in the divider 36 to allow gases to travel upwards into the upper chamber 14. The aperture 38 is substantially circular in cross section. The divider 36 has a thickness. The divider 36 is partly hollow and can therefore be cooled by a flow of liquid such as water. A second set of air inlets 40 are provided on an inner surface of divider aperture 38, i.e., above the first set of air inlet apertures. These are provided to provide air for combusting any remaining flammable gases before they exit from the equipment 10. The flow of air into the first air inlet apertures relative to the flow of air into the second air inlet apertures 40 can be controlled in order to control the temperature inside the lower chamber 12, and to allow control over the position of combustion of pyrolysis gases. An upper chamber refractory wall 52 forms an edge of the upper chamber 14. An outer refractory wall 54 forms an edge of the biochar production equipment 10. The refractory walls 52, 54 are made of material that is resistant to the high temperature inside the biochar production equipment 10. A gas outlet 22 is disposed above the upper chamber 14, for allowing release or collection of fully combusted gases. The gas outlet 22 is disposed horizontally across a top of the upper chamber 14. The gas outlet 22 may comprise ducting. The gas outlet or ducting may comprise heat exchange means for capturing heat to be used to dry biomass or otherwise. The heat exchange means may transfer the heat in the combusted or released gases using water, oil, air or another substance. A gas monitor such as an oxygen monitor (not shown) is disposed at the gas outlet 22 to allow the amount of oxygen to be monitored, which can indicate the combustion conditions inside the lower chamber and inform whether the inflow of air into the first air inlet apertures (not shown) and second air inlet apertures 40 should be adjusted. An exhaust fan (induced draft fan) is provided (not shown) to maintain a negative pressure in the lower chamber and upper chamber 14. The fan is disposed after the heat exchange means and ahead of the part of the gas outlet which vents the gases to atmosphere. That is to say, the fan is disposed between the heat exchange means and the part of the gas outlet which vents gases. The fan ensures air introduced at the first or second air inlet apertures flows upwards and away from the flammable feedstock, to avoid unwanted combustion of the feedstock. Solids outlet 32 is disposed beneath the sets of plates 30 for removing the biochar product. The solids outlet 32 comprises two upper walls (one of which is shown at 64a), and two lower walls (one of which is shown at 66a). Each upper wall 64 is disposed below a set of plates 30. The upper walls 64 are substantially perpendicular to the plates 30. The upper walls 64 are parallel to each other. The lower walls 66 are sloped. Quenching means 34 such as water jets are provided on the solids outlet 32 for wetting and cooling the biochar to prevent it igniting on contact with air. Transportation means 58 such as a screw auger are part of the solids outlet 32 and transport the solid product away from the lower chamber 12. The screw auger is a device with a helical shaft for moving loose material. In this embodiment, the transportation means 58 is positioned at a slight incline, so the biochar moves upwards. An outlet rotary valve (not shown) is disposed at the end of the transportation means 58 to isolate the lower chamber 12 and upper chamber 14 from the air. A first chute 16a and a second chute 16b are provided on either side of the lower chamber 12 to hold a supply of feedstock, one chute 16 above each set of plates 30. Each chute 16 comprises four walls. A first wall and third wall of each chute 16 are longer than the second and fourth wall. The first wall of each chute 16 is sloped to enable the feedstock to slide downwards towards the lower chamber 12. In alternative embodiments, the first wall may instead be vertical. Each chute 16 has an open top to receive the feedstock and each chute 16 has an open base to allow 11 feedstock to fall or be fed into the lower chamber 12. In other embodiments, the open top of the chute 16 may be covered and closed, for example, covered by a supply auger. Each chute 16 is substantially shaped as a half of a trapezoidal prism, i.e. a trapezoidal prism halved along a longitudinal axis. An inlet rotary valve 18 is disposed below each chute 16 to seal the lower chamber 12 from the air and control and enable monitoring of the rate of biomass entering the lower chamber 12. The inlet rotary valve 18 is disposed along a length of each chute 16, and a surface of the valve 18 is flush with a base of each chute 16. The inlet rotary valves 18 are rotatable around a central, longitudinal axis. The outer surface of each inlet rotary valves 18 is substantially cylindrical in shape. The inlet rotary valves 18a have a sector, in particular a quarter sector, removed to form a transporting portion. The transporting portion is of a set volume, to receive a fixed amount of material. Each inlet rotary valve 18 has a controller (not shown) for controlling the rotation speed of the inlet rotary valve 18 to allow the flow of feedstock into the lower chamber to be controlled and recorded. A conveyor (not shown) is disposed above each chute 16, to provide feedstock to the chute and hence the lower chamber 12. The conveyor may be, for example, a screw conveyor, chain dray conveyor or belt conveyor. Jacks 20a are provided on the biochar production equipment 10, which are height-adjustable legs which can raise and lower the equipment. Figure 3 shows additional detail of the lower chamber 12. In particular, the detail of the first set of air inlets 50 is shown. The first set of air inlet apertures 50 are provided in two horizontal rows on inner wall 48. In alternative embodiments, only a single horizontal row of apertures 50 may be provided. Each aperture 50 is substantially circular in cross section. The row of apertures is parallel to the axis of reciprocation of the sets of plates 30. The gas released from the biomass is mixed and partially burnt with the air from the air inlet so that material can be heated evenly Figure 4 shows the first set of plates 30a and second set of plates 30b of the present invention without the rest of the structure of the biochar production equipment 10. As described previously, reciprocating plates 42 alternate with stationary plates 44. In 12 this figure, each set of plates 30 are shown in a position between the first position and the second position. The top plate 56 and the upright element 26 are also shown. Figure 5 shows the detail of the second set of air inlet apertures 40. The second set of air inlet apertures 40 are disposed around the aperture 38 of the divider 36. Each of the second set of air inlet apertures 40 have a substantially rectangular cross section. The second set of air inlet apertures 40 are disposed at regular intervals around aperture 38. The first set of air inlet apertures 50 can also be seen, which are disposed in the inner wall 48. Figure 6 shows the rotary valve 18a and pistons 28a in more detail. One piston is connected to upright element 26a. Another piston is connected to reciprocating plates 42. The arrangement is substantially symmetrical and is provided likewise on the other side of the equipment. Figure 7 shows an alternative embodiment of the biochar production equipment 110 and is a cutaway view through a different vertical cross section. Refractory wall 152 forms an outer edge of the upper chamber 114. Refractory wall 153 forms an outer edge of the lower chamber 112. Water jets 134 are disposed below the set of plates 130. Each water jet 134 is oriented such that the waterjet is substantially horizontal. The waterjets 134 cool biochar that falls off the reciprocating plates 130. In use, the biochar production equipment 10 is operated as follows. The biochar production equipment 10 processes feedstock and converts it to biochar. The feedstock provided is dry biomass. The dry biomass may have a moisture content of up to 20%. The size of the biomass is preferably smaller than the distance between the first position and the second position of a plate (around 30mm). The lower chamber 12 and upper chamber 14 are kept at reduced pressure relative to atmospheric pressure to ensure there is minimal oxygen in the biochar production equipment through gas and air flows out of the unit, which is essential to ensure that the feedstock is converted to biochar. The arrows marked on Figure 2 indicate how the biomass, and the resulting products (i.e., the biochar and the gases) move through the biochar production equipment 10. Arrows 1a and 1b indicate the path of the biomass into the lower chamber 12, on either side. On each side of the equipment, the biomass passes through the chute 16 and through the inlet rotary valve 18 which controls the entry of the biomass onto the plates 30 in the lower chamber 12. The inlet rotary valve 18 also provides a seal to prevent or hinder air entering the lower chamber 12. As the inlet rotary valve 18 rotates, the transporting portion is open to the biomass in the trough 16, which the inlet rotary valve picks up. As it rotates further, the transporting portion faces downwards and is open to the lower chamber 12, at which point the biomass drops out of the inlet rotary valve 18 and into the lower chamber 12. The biomass drops out of the inlet rotary valve 18 onto the top plate 24a. Top plate 24a has an upright element 26a disposed above it. The upright element 26a pushes material over the top of the top plate 24a, under the refractory wall 54 and into the lower chamber 12 where it can be heated and converted to biochar. The motion of the upright element 26a is synced with the rotations of the inlet rotary valve so biomass falls onto the plate in front of the upright element 26a. Arrow 2 indicates the path of the solids on one side of the lower chamber 12. The solids move similarly on the other side of the lower chamber 12. The solids are moved down the corresponding set of plates 30 by the motion of the plates 30, and into the solids outlet 32. As the biomass falls down the set of plates 30, it is heated by combusted pyrolysis gases in the lower chamber. The combustion of the pyrolysis gases is facilitated by air inlet apertures 50, which allow the introduction of air and hence oxygen for combustion. The biomass is heated to around 400°C and 800°C depending on the material and desired properties of the biochar. These temperatures are sufficient to thermally decompose and convert the biomass into biochar. Though heating is provided by combustion of gases released from the biomass when the equipment is up and running, initial heating is provided by the direct combustion of the biomass. When the equipment is up to temperature, the oxygen level is reduced so the biomass pyrolyzes rather than combusts. As the biochar falls into solids outlet 32, it is cooled by waterjets 34. The biochar is then removed along a screw auger 58. The solids outlet 32 is sealed by an outlet rotary valve, which can allow biochar to be collected without significant amounts of air entering the lower chamber 12. Each reciprocating plate 42 moves between a first position and a second position. In the first position, the front edge of the reciprocating plate is substantially flush with the front edge of the stationary plate 44 beneath it. In the second position, the front edge 46 of the reciprocating plate 42 is behind the front edge of the stationary plate. In Figures 2 and 3, each reciprocating plate 42 is shown in the first position. Material disposed on top of a reciprocating plate 42, is pushed off as the plate retracts to the second position, as the available area on top of the reciprocating plate 42 decreases. Material is therefore pushed onto a stationary plate 44 beneath the reciprocating plate 42. As the reciprocating plate 42 moves back into the first position, it sweeps the fallen material onto the next reciprocating plate, and the process continues. The material that is not near the edge of the plate will remain for a few cycles of reciprocation, and in this way the material is slowly agitated and turned as it falls between the plates. Waterjets 34 cool and quench the solids that pass through solids outlet 32 to prevent the solids from igniting when they subsequently come into contact with the air. The plates move at a rate that ensures the biomass spends around 15 minutes travelling across a set of plates. Different types of biomass will need different retention times to fully convert to biochar, in which case the plates can be slowed down or sped up accordingly. Arrow 3 indicates the progress of the gases upwards into the upper chamber. Some of these gases will be combusted as they move upwards past the first air inlets 50. Some of the remaining flammable gases will be combusted as they pass through the second set of air inlet apertures 40 in the aperture 38 in the divider 36. Inert or nonflammable gases (for example, carbon dioxide) that are produced on heating the biomass will just travel up through the lower chamber 12 and upper chamber 14 without being combusted. Flammable gases such as methane are released from the biomass as it is heated. Fans (not shown) force air into air inlet apertures 40, 50 at the required rate. Introduction of air through the air inlet apertures allows controlled combustion of some of these released gases. The heat released from the combustion is used to continue heating the biochar, and in this way, once running, the system can continue without additional heating being provided. Oxygen is the limiting reagent in the combustion. Initially, biomass is fully combusted in ample air to get the unit up to temperature, before the amount of air being provided by the first set of air inlets is reduced to cause the biomass to pyrolyze instead of combusting. The second set of air inlets 40 operate similarly to the first set of air inlet apertures, and are primarily used to combust any uncombusted gases that have not been combusted by the first set of air inlet apertures. In this way, any gases such as methane can be combusted and turned into more inert products such as carbon dioxide, which is safer to release. The second set of air inlets 40 may also provide air for additional combustion and therefore heat. The air is swirled inside divider 36 so that air entering from each second set of air inlet apertures 40 has a tangential component to its flow. The relative flow of air going into the first air inlets 50 and second air inlets 40 respectively can be controlled. Controlling the flow of air into the first air inlets can allow the temperature to be controlled. Controlling the flow of air into the second set of air inlets 40 can allow the correct amount of air for the combustion of remaining uncombusted gases. Arrow 4 shows the path of the combusted gases out of the upper chamber 14, through the gas outlet 22. There may be heat recovery means provided beside or as part of the gas outlet 22 to recapture some of heat, which can then be used to dry biomass, for example. The equipment 10 operates on a continuous basis, rather than operating as a batch process. The embodiments described above are provided by way of example only. Various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.

Claims

1. Biochar production equipment for producing biochar from a feedstock in a low oxygen environment, comprising:a lower chamber for pyrolysis of the feedstock;one or more air inlets for providing oxygen for the combustion of pyrolysis gases, to heat the feedstock in the lower chamber and form the biochar;a feedstock inlet connected to the lower chamber for the feedstock to enter the lower chamber;a gas outlet for gases to exit the biochar production equipment;a solids outlet for removal of the biochar from the lower chamber; anda set of two or more plates disposed inside the lower chamber, in which the set of two or more plates comprise one or more reciprocating plates, and in which each reciprocating plate moves along a linear axis for moving and agitating the feedstock as it is heated.

2. Biochar production equipment as claimed in claim 1, in which the biochar production equipment comprises an upper chamber, the upper chamber being disposed above the lower chamber, and in which the gas outlet is disposed above the upper chamber.

3. Biochar production equipment as claimed in claim 1 or claim 2, in which the set of plates comprises one or more stationary plates.

4. Biochar production equipment as claimed in claim 3, in which the set of plates comprises alternating stationary and reciprocating plates.

5. Biochar production equipment as claimed in any preceding claim, in which each plate abuts its adjoining plate(s).

6. Biochar production equipment as claimed in any preceding claim, in which each plate has an edge perpendicular to the linear axis of movement, the edge being substantially linear.

7. Biochar production equipment as claimed in any preceding claim, in which each set of plates comprises a top plate, in which the top plate comprises an integral or separate upright element disposed above the top plate for pushing material onto the other plates.

8. Biochar production equipment as claimed in any preceding claim, in which the set of two or more plates are stacked in a staggered configuration.

179. Biochar production equipment as claimed in any preceding claim, in which the lower chamber has a first side, and a second side, and in which a first set of plates is disposed on the first side of the lower chamber, and a second set of plates is disposed on the second side of the lower chamber.

10. Biochar production equipment as claimed in claim 9 in which two feedstock inlets are provided, a first feedstock inlet being above the first set of plates, and a second feedstock inlet being above the second set of plates.

11. Biochar production equipment as claimed in claim 9 or claim 10, in which the first set of plates, and the second set of plates, are symmetrically disposed on either side of the lower chamber.

12. Biochar production equipment as claimed in any preceding claim, in which the lower chamber and upper chamber are under negative pressure.

13. Biochar production equipment as claimed in any preceding claim, in which a set of air inlets are provided as a first set of air inlet apertures, the first set of air inlet apertures being disposed above the plates for heating material on the plates.

14. Biochar production equipment as claimed in claim 13, in which a further set of air inlets are provided as a second set of air inlet apertures for combustion of uncombusted gases, in which the second set of air inlet apertures is disposed above the first set of air inlet apertures.

15. Biochar production equipment as claimed in claim 14, in which a controller is provided on the biochar production equipment to control the ratio of air entering the first and second set of air inlet apertures to control the amount of heat provided to the feedstock.

16. Biochar production equipment as claimed in any preceding claim, in which each feedstock inlet is provided as a chute.

17. Biochar production equipment as claimed in any preceding claim, in which quenching means such as water jets are provided at the solids outlet for wetting and cooling the biochar.

18. Biochar production equipment as claimed in any previous claim, in which the biochar production equipment comprises transportation means such as an auger for transporting the product.

19. Biochar production equipment as claimed in any preceding claim, in which an inlet rotary valve is disposed below the feedstock inlet to isolate the lowerchamber and upper chamber from the air, and to control the rate at which the feedstock is introduced.

20. Biochar production equipment as claimed in any preceding claim, in which the biochar production equipment comprises an outlet rotary valve for isolating the lower chamber and upper chamber from the air, disposed at the end of the transportation means.

21. Biochar production equipment as claimed in any preceding claim, in which the gas outlet comprises ducting, the ducting and / or the gas outlet having heat exchange means, for capturing heat to be used to dry biomass or otherwise.

22. Biochar production equipment as claimed in any preceding claim, in which a gas monitor such as an oxygen monitor is disposed at the gas outlet.

23. Biochar production equipment as claimed in any preceding claim, in which the lower chamber is separated from the upper chamber by a divider with an aperture, in which the secondary inlet apertures are disposed around the divider aperture.

24. Biochar production equipment as claimed in any preceding claim, in which a footprint of the biochar production equipment is less than 12 m by 2.5 m so it can be transported on the back of a lorry, or fit in a shipping container.

25. A method of making biochar from biomass using the biochar production equipment of any of claims 1 to 24 comprising the steps of:a. reducing the oxygen concentration inside the biochar production equipment;b. providing biomass to the feedstock inlet;c. heating the biomass to a temperature of around 400°C to 800°C;d. agitating the biomass using the reciprocating plates as it turns to biochar; ande. collecting the biochar product.

Images