SYSTEM FOR THE TORREFACTION OF LIGNOCELLULOSIC MATERIAL
A pressurized torrefaction reactor vessel including: a rotatable shaft extending vertically down from a top of the vessel; scraper devices each at a different elevation within the vessel and mounted to the shaft; a tray associated with each one of the scraper devices such that the scraper device is immediately above a tray of the tray assembly; wherein the tray is an open mesh and impermeable to passage of biomass through the tray; each tray includes a discharge opening to transfer biomass from the tray and down to a tray of a lower one of the tray assemblies, and wherein the discharge opening in the lowermost tray assembly transfers the biomass to a pile of the biomass in the vessel, and a bottom discharge port of the vessel through which the torrefied biomass is discharged.
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This applications claims priority to U.S. Provisional Patent Application Ser. No. 61/502,116 filed Jun. 28, 2011, and is related to U.S. Provisional Patent Application Ser. No. 61/501,900 filed on Jun. 28, 2011. The entirety of these applications are incorporated by reference.BACKGROUND OF THE INVENTION
The present invention generally relates to methods for torrefaction of biomass material such as lignocellulosic material including wood and other biomass, and more particularly relates to a pressurized reactor vessel for the torrefaction of such material.
Torrefaction can be used to convert biomass, e.g., wood, to an efficient fuel having increased energy density relative to the input biomass. For example, wood generally contains hemicellulose, cellulose and lignin. Torrefaction removes organic volatile components from wood. Torrefaction may also depolymerize the long polysaccharide chains of the hemicellulose portion of biomass and produce a hydrophobic solid combustible fuel product with an increased energy density (on a mass basis) and improved grindability. Because torrefaction changes the chemical structure of the biomass, torrefied biomass may be burned in coal fired facilities (torrefied wood or biomass has the characteristics that resemble those of low rank coals) and can be compacted to high grade fuel pellets.
Torrefaction refers to the thermal treatment of biomass, usually in an oxygen deprived atmosphere at relatively low temperatures of 200 degrees Celsius (° C.) to 400° C., or 200° C. to 350° C., or temperatures outside the range used for the process known as pyrolysis. An oxygen deprived atmosphere may have a low percentage of oxygen as compared to the percentage of oxygen in atmospheric air. A torrefaction process is described in related U.S. Provisional Patent Application Ser. No. 61/235,114.
Unpressurized reactor vessels with multiple trays have been used for torrefaction, as is described in U.S. Patent Application Publication 2010/0083530 (the '530 application). The '530 application states that torrefaction should be performed in a reactor vessel operating at atmospheric pressure. By stating that it is advantageous to operate the vessel at atmospheric pressure, the '530 application teaches that vessels should not be operated at above-atmospheric pressures. See '530 application, para. 0061.
Pressurized reactor vessels with multiple trays have been used in pulp mills to delignify pulp by oxidation. Examples of a pulping reactor vessel with multiple trays are disclosed in U.S. Pat. Nos. 3,742,735 ('735 patent) and 3,660,225 ('225 patent). Multiple tray vessels allow pulp to cascade through the vertical arrangement trays in the reactor. The trays allow the pulp to cascade in discrete batches down through the vessel. An oxygen rich environment in the pulping reactor promotes delignification and bleaching of the pulp. The '735 patent and '225 patent do not suggest using a pulping reactor vessel having an oxygen deprived environment for torrefaction of wood or other biomass material.BRIEF DESCRIPTION OF THE INVENTION
A difficulty with unpressurized reaction vessels is their large size needed to handle the large volume of gas required to transfer a given amount of heat to the material to be torrefied. The mass of a gas per unit volume at atmospheric pressure is substantially less than the mass of gas per unit volume at a substantial pressure, such as above 20 bar gauge (290 psig). The volumetric flow rate of the gas impacts the pressure drop in the bed of material, piping, heat exchangers, and thus requires larger equipment and higher energy consumption to perform the same heating duty.
Pressurizing the gas increases the mass of the gas for a given volumetric flow rate. As compared to an unpressurized vessel, a pressurized reaction vessel may have a smaller volume due to the use of compressed gas. The ability of a gas to transfer heat to a biomass is proportional to the mass of the gas. The greater its mass, the faster a gas can heat the biomass.
As is well known in the art, pressurized reaction vessels require seals and other devices to keep the gas and materials in the vessel under pressure. Similarly, pressure transfer devices are required at the input to or in the feed systems for a pressurized vessel to pressurize the material being fed to the vessel. Further, pressurized reaction vessels require pressurized gases and conduits for the pressurized gases.
A novel reaction vessel has been conceived for torrefaction of biomass material having vertically stacked trays for drying and heating biomass using an oxygen deprived hot gas under substantial pressure. The stacked trays provide what amounts to as a moving bed for the biomass, in a relatively compact vertical reactor vessel. In addition, the vessel may be substantially smaller than a reaction vessel for torrefaction performed at atmospheric pressure. The oxygen deprived pressurized gas may be circulated through the vessel and through pressurized conduits that reheat the gas.
The vessel uniformly heats through each tray such that the material being torrefied is uniformly heated at each elevation in the vessel. To achieve uniform heating of the material on each tray the flow of oxygen deprived gas through the bed of material on each tray is regulated in a range of 1 to 6 kilograms (kg) of gas per kilogram of dry material being treated on the tray. The ratio of flowing oxygen deprived gas to dry material through the bed of material on each tray may be in another range, such as a range of 1 to 3.
The flow of the oxygen deprived gas through each of the trays may be continuous. The oxygen deprived gas is need not be totally devoid of oxygen. The gas is a heat transfer media that may add or remove heat from the material undergoing torrefaction. The gas flows through the material and the trays. The continuous flow of oxygen deprived gas through the material in the tray heats the material, provided that the gas is at a higher temperature than the material. The constant flow of gas may also cool the material where the torrefaction reaction, which is exothermic, causes the material to become hotter than the gas. If the material overheats, the torrefaction reaction may over-react. Accordingly, the continuous flow of gas regulates the temperature of the material in each tray to be about the same temperature as the gas.
The biomass material may have a total retention period for all of the trays in the reactor vessel of 15 to 60 minutes. This retention period may include trays in which the material undergoes torrefaction and lower trays in which the material is cooled after the reaction. The retention period in the reaction vessel may be selected based on the material processed in the vessel. For example, the total retention period in the vessel may be to 25 minutes for lignocellulose material, such as wood.
Each tray may have a pie-segment shaped opening through which biomass material falls to the tray at the next lower elevation in the vessel. The biomass material falls through the opening after traveling around the vessel and on the tray. A scraper may slide the material over the tray toward the opening. The rotational speed of the scraper is selected to provide the desired retention period on each tray. The retention period may be uniform for each of the trays in the vessel. The retention period may be selected based on the number of trays performing each of drying, torrefaction and cooling (optionally) of the biomass, and the period required to perform each of these processes.
A method has been conceived for torrefaction of biomass using a torrefaction reactor vessel having stacked trays including: feeding the biomass to an upper inlet of the vessel such that the biomass material is deposited on an upper tray of a vertical stack of trays in the reactor; as the biomass moves around the vessel on each of the stacked trays, heating and drying the biomass material with an oxygen deprived gas injected into the vessel under a pressure of 3 to 20 bar; cascading the biomass down through the trays by passing the biomass through an opening in each of the trays to deposit the biomass on a lower tray; discharging torrefied biomass from a lower outlet of the torrefaction reactor vessel, and circulating extracted gas from a lower elevation of the reactor and feeding the gas to an upper region of the vessel.
The oxygen deprived gas may include superheated steam, nitrogen and other non-oxygen gases, or oxygen lean gases suitable for the purpose of this invention. The biomass may be pressurized before being fed to the vessel with a pressure transfer device. The trays may be a mesh, screen or have perforations or slots and the heating and drying of the biomass includes passing the gas through the biomass and the trays. A scraper device may rotate to move the biomass material across the tray in an arch-shaped path. Alternatively, the trays may rotate while the scraper device and biomass do not rotate about the vessel. The opening in each tray may be a triangular shaped section extending from the shaft in the vessel to the wall of the vessel.
The gas may be injected into the vessel at multiple elevations wherein the gas is hotter when injected at a lower elevation than the gas injected at an upper elevation. At an elevation of the vessel below from which the gas is extracted, the biomass may continue to cascade down through the trays.
A method for torrefaction of lignocellulosic biomass using a torrefaction reactor vessel having stacked tray assemblies has been conceived comprising: continuously feeding the biomass to an upper inlet to the torrefaction reactor vessel such that the biomass material is deposited on an upper tray assembly of a plurality of tray assemblies stacked vertically within the reactor; as the biomass moves in the vessel while supported by a tray of each tray assembly, heating and drying the biomass material with a gas injected into the vessel, wherein the gas is substantially non-oxidizing of the biomass and is under a pressure of at least 3 bar gauge and at least a temperature in a range of 200° C. to 250° C., and cascading the biomass down through the trays by passing the biomass through an opening in each of the trays to deposit the biomass on the tray of the next lower tray assembly; discharging torrefied biomass from a lower outlet of the torrefaction reactor, and circulating gas extracted from the reactor vessel back to the reactor.
The trays of each of the tray assemblies have a mesh, screen or have perforations, and the heating and drying of the biomass includes passing the gas through the biomass and the trays. Any holes or openings in the tray assemblies may be cover by a finer mesh or screen material than the material used to form the tray assemblies. The gas entering each tray assembly may pass through a pipe at substantially a similar elevation as an extraction pipe which extracts gases from an immediately above tray assembly. In addition, each tray assembly may include a rotating scraper device above the tray and an extraction gas chamber below the tray.
The gas injected into tray assemblies for torrefaction may be hotter, e.g., by 5 to 60° C., than the gas injected to the tray assemblies for drying or cooling. Further, a void space, below all of the tray assemblies, in the bottom of the vessel may be a zone in which the biomass forms a pile. The void space may be used to complete the torrefaction of the biomass and cool the torrefied biomass before it is discharged from the vessel. The cooling gas injected into the cooling zone may be cooler than the gas injected to the cooling tray assemblies, wherein the cooling zone cools the torrefied biomass to below a temperature at which the biomass auto-combusts when exposed to the atmosphere and the cooling tray assemblies cool the torrefied biomass to stop or suppress the torrefaction reaction. It is possible for gas flows in the void to flow concurrent or countercurrent to the flow of the biomass material.
Gases extracted from the tray assemblies and the cooing zone may be circulated back to the vessel by blowers or compressors. The gases to be circulated may pass through a cyclone, condenser or filter to separate particles and condensable byproducts before the gas flows to the compressor or blower. The gases circulated back to the torrefaction tray assemblies may be heated before being injected to the torrefaction tray assemblies. A portion of the gases extracted from the tray assemblies may be directed to a combustor to generate heat energy to be added to the gases circulated back to the torrefaction tray assemblies, or for other process steps.
A pressurized torrefaction reactor vessel has been conceived comprising: a vessel wall extending substantially vertically; a rotatable shaft extending vertically down through a top of the vessel; scraper devices each at a different elevation within the vessel and coaxial to the shaft; tray assemblies wherein each tray assembly is associated with one of the scraper devices such that the scraper device is immediately above a tray of the tray assembly; at least one of the tray assemblies includes the tray, a gas extraction passage below the tray, and a gas injection passage above the tray, wherein the tray is an open mesh or otherwise permeable to gas flow and impermeable to passage of biomass through the tray; each tray includes a discharge opening to transfer biomass from the tray and down to a tray of a lower one of the tray assemblies, and wherein the discharge opening in the lowermost tray transfers the biomass to a pile of the biomass in the vessel; a plurality of gas extraction openings in the vessel wall, wherein at least one of the gas extraction openings is aligned with the gas extraction passage and another one of the gas extraction openings is at an elevation below the lowermost tray assembly and above the pile of the biomass, and a bottom discharge port of the vessel through which the torrefied biomass is discharged.
The upper inlet 14 to the pressurized vessel may be coupled to a continuous feed, pressure isolation device, such as a conventional rotary valve or plug screw feeder, to feed the biomass into the pressurized vessel from a source of biomass at atmospheric pressure. The vessel 10 operates in a gas phase in which the dried biomass remains dry in the vessel.
The biomass may be fed to the inlet 14 to the vessel at a temperature of ambient temperature or, if a dryer 21 preheats the biomass, at 80° C. to 120° C., or higher, before entering the vessel. The biomass is heated in the vessel by a pressurized, hot and oxygen starved or deprived gas. The gases entering the vessel may be at a temperature in a range of 200° C. to 600° C. and may particularly be in any of the ranges of 250° C. to 400° C., 250° C. to 300° C., and 300° C. to 380° C.
The biomass enters the pressure treatment vessel through the upper inlet 14, which may be a single inlet orifice or an array of inlet orifices in the top or upper portion of the vessel. The biomass may have been previously dried before entering the vessel or the biomass may be dried in an optional drying zone (trays) 15 in an upper region of the vessel. Below the drying zone, the biomass enters a torrefaction zone 41 (trays and optionally a chamber below the trays).
Immediately below the upper inlet in the vessel 10 may be a chute that receives the biomass from the inlet and directs the biomass to a trailing section portion of the upper tray of a drying tray assembly 16. The trailing section is adjacent a discharge opening 64 (
The open sections 64 (also referred to as “openings”) of each tray preferably are not vertically aligned with the openings 64 in the trays immediately above and below the tray. If the openings were vertically aligned, the biomass may fall from one open section and immediately through the open section in the underlying tray without resting on the support surface of the underlying tray.
The opening sections 64 may be vertically staggered such that each opening is over a trailing region of the upper section of the tray immediately below the opening. The trailing region of a tray is adjacent and behind the open section in the direction of rotation of the scraper device 56. By aligning an open section 64 above a trailing region on a lower tray, the biomass falls through the open section and onto the trailing region. As the scraper turns, the biomass slides across the entire upper surface of the tray in an arc-shaped path from the trailing region to the opening section. Maintaining the biomass on the upper surface of each tray maximizes the retention period of the biomass on tray and, thus, allows the biomass to be heated and dried (in an upper tray and undergo torrefaction (in a lower tray).
Immediately below the optional drying tray assembly(ies) 16 are arranged one or more torrefaction tray assemblies 18 on which the dried biomass material is subjected to conditions which cause the torrefaction reaction. Below the torrefaction tray assemblies are arranged optional cooling tray assembly(ies) 20. The structure of each of the tray assemblies 16, 18 and 20 may be substantially similar. Each tray assembly is effectively a moving bed on which the biomass is exposed to a flow of the oxygen deprived gas.
The flow of heated gas into, through and from the pressure reaction vessel may be configured to promote the flow of hot, pressurized gases through the tray assemblies in the upper elevations of the vessel where the biomass is being heated to the desired temperature for torrefaction. As shown in
The oxygen deprived gases flowing to multiple elevations in the vessel may be at temperatures and compositions that vary for each of the tray assemblies. For example, the hot gas 86 introduced to the uppermost elevation of the vessel may be at a temperature slightly, e.g., 10° C. to 40° C., hotter than the temperature, e.g., 100° C., of the dried biomass 12 being fed to the vessel. The hot gases introduced at succeeding lower elevations of the vessel may be increasingly hotter to be slightly above the temperature of the biomass in the vessel that is proximate to the injected hot gas. By injecting the gas at temperatures slightly above the biomass being heated by the gas, the efficiency of heating can be increased as compared to injecting gas at a single temperature which may be substantially hotter than the incoming biomass to the vessel. Alternatively, the gases injected for drying and torrefaction may be at substantially similar temperatures and compositions, and the gases for cooling the biomass may be recirculated gases extracted from other cooler elevations in the vessel. For example the exhaust gas from the drying trays will be cooler than that from the torrefaction levels and will be below temperatures required for torrefaction.
The number of tray assemblies for drying, torrefaction and cooling may depend on various factors, including whether an optional drying device 21 is used to dry the biomass before the material enters the vessel 10, and the extent to which the torrefaction and cooling zones 22, 24 or cooling screw 68 (
By way of example, the total number of tray assemblies may be a number (N) and in a range of 5 to 15. The number of drying tray assemblies 16 (DTA) may be zero, one (such as shown in
DTA=N*L, where L is in a range of 0.2 to 0.3.
The number of cooling tray assemblies 20 (CTA), if any, may be two, such as is shown in
CTA=N−(N*M), where M is in a range of 0.7 to 0.8.
The number of torrefaction tray assemblies 16 (TTA) may be greater than each of DTA and CTA, such as the four TTAs shown in
The number of tray assemblies in a vessel and the proportions of drying, torrefaction and cooling tray assemblies will depend on the design requirements for the vessel. For example, the total number of tray assemblies in the vessel 10 may be in any of the ranges of 4 to 20 and 6 to 15. The proportion of drying tray assemblies and of cooling tray assemblies may each be in a range of 15 to 30 percent (%) of the total number of tray assemblies. The proportion of tray assemblies for torrefaction may be in a range of 70 to 40% of the total number of tray assemblies. These ranges are exemplary and do not define limits on the numbers of tray assemblies. For example, the vessel may have no drying tray assemblies and no cooling tray assemblies, and have all tray assemblies for torrefaction.
The torrefaction reaction may occur in the middle tray assemblies. The ranges of the middle tray assemblies where torrefaction occurs may be any of 15 to 85%, 30 to 60% and 15 to 100% of the total number of tray assemblies. Where torrefaction occurs is most or all of the tray assemblies, the drying of the biomass may occur fully or partially in a dryer external to and upstream of the vessel, and the optional cooling may occur in the pile of the torrefied biomass in a lower region of the vessel or in a cooling screw near the discharge of the vessel.
The inlet nozzles and extraction nozzles are numbered in
The supply of biomass 12 may provide, such as lignocellulose material that has been chipped or cut to have chip dimensions of a length between 10 to 50 millimeters (mm), a width of 10 to 50 mm, and a thickness of 5 to 20 mm. The chip thickness may be in other ranges, such as 20 to 30 mm, 15 to 25 mm, and 3 to 10 mm. These chip dimensions may be most suitable for wood. Other chip dimensions may be suitable depending on the type of wood or the non-wood material being used for the biomass.
Below the stack of tray assemblies 16, 18 and 20, the vessel 10 may have a torrefaction zone 22 and an optional lower cooling zone 24. The torrefaction zone 22 and lower cooling zone 24 may be hollow regions of the pressure reactor vessel below the lowest tray 20 and may span the lower one-half or lower two-thirds of the height of the pressure vessel. The pressure vessel may have dimensions, such as diameter and height, based on the desired operational conditions, such as the composition of the biomass material and the volumetric rate of biomass to flow through the vessel. In general, for industrial scale units, the pressure vessel may have a height of over 100 feet (33 meters) and a diameter of over 9 feet (3 meters).
The lower cooling zone 24 of the pressure reactor vessel may include a convergence section, such as one-dimensional convergence, to provide uniform movement of the biomass through the bottom of the vessel and to a bottom discharge port 26. The convergence section may be a DIAMONDBACK® convergence section sold by the Andritz Group and described in U.S. Pat. Nos. 5,500,083; 5,617,975 and 5,628,873.
The lower zone 24 of the pressure reactor vessel may be maintained at a cooler temperature than the tray assemblies used for torrefaction. The lower zone 24 may contain a pile of torrefied biomass material which has been treated in the tray assemblies and drop down into the lower zone.
The temperature in the lower zone 24 may be below 265° C., 240° C. or 200° C., in addition or alternatively, the temperature in the lower zone 24 may be at least 15° C. to 40° C. lower than the maximum temperature of the hot gases entering the torrefaction tray assemblies. To control and maintain the temperature in the lower zone cooling gas may be inject to the upper section of the lower zone such as into the injection nozzle 92 (
As shown in
The pressure vessel 10 may have an access and observation port 30 which, when open, provides access to the cooling and convergence zones of the vessel. The access and observation port is generally closed during operation of the vessel. The observation port may include a clear window to provide for viewing of the interior of the vessel. Other observation ports, with clear windows or sight glasses, may be located in the vessel at locations other than at the access and observation port 30.
Immediately below the tray 40 is a solid annular bottom plate 44 that forms a bottom to a gas passage 52 between the tray 40 and the plate 44. The gas passage is for gases drawn through the biomass and tray to be exhausted to the extraction nozzles 36 that are mounted to the wall 42 of the vessel at elevations corresponding to the gas passage between the tray and bottom plate 44. Baffle plates 46, 48 and 50 may be mounted on the bottom plate 44 and extend upward through the gas passage to the tray 40. The baffle plates direct gases towards the inlets to the extraction nozzles 36. The baffle plates may include short 46 and long 48 radially extending plates, and a circular wall plate 50 that forms and end wall for the gas passage. The long 48 radial plates divide the gas passage into triangular shaped screen segments. By way of example, each tray may have four to eight screen segments. In addition to the tray 40 being formed of pie-shaped segments, the plate 44 may also be pie-shaped segments and the long radial plates 48 may form sidewalls to each of these segments.
The baffle plates also provide support for the screen or grating of the tray 40. The circular wall plate may have open slots to allow gases to flow to the inlet to the extraction nozzle 36 and to allow the pipe for the injection nozzle 34 to pass from the wall of the vessel through the bottom plate 44 and open to the next lower tray assembly.
The trays 40 may be supported by the inner surface of the wall 42 of the pressurized treatment vessel 10. The wall 42 may include hangers, ridges or other support surfaces on which rest the outer rim of each tray. The trays may be removed, replaced and repositioned in the vessel by opening the vessel and sliding the trays in and out of the vessel.
Alternatively, the trays, rotating scrapers and shaft may be constructed as a cartridge assembly and primarily supported from the top head plate of the vessel. A cartridge assembly could be inserted and removed from the vessel as a whole. Anti-rotation clips or pieces may be affixed to the vessel walls for the purpose of preventing the cartridge assembly from rotating within the vessel.
The biomass flowing through the chute 116 drops into an optional lower portion 80 of the vessel. The biomass may form a pile in the lower portion which temporarily retains the biomass in the lower portion. While in the pile, the biomass continues to undergo the torrefaction reaction. The torrefied biomass is discharged from an outlet 116.
As an alternative to a rotating scraper device, the trays may rotate with the shaft. A stationary scraper device may be in a fixed position and may include radial arms extending over the tray.
The injection nozzles 34 may extend through the gas passage and have an outlet 53 that extends through the bottom plate 44. The outlet 53 discharges gas into the biomass passage 54 formed between a bottom plate 44 of one tray assembly and the tray 40 of tray assembly immediately below the bottom plate. The biomass passage is a volume in the vessel 10 which receives the biomass. The number of injection nozzles 34 for each tray may be uniform and selected based on operational requirements of the vessel. The selection of the number of the nozzles may be sufficient to provide uniform gas flow, at a uniform flow distribution and gas temperature, through the biomass material on the tray. For example, six to eight injection nozzles may be used to provide uniform gas flow to each tray.
The injection nozzles 34 may be configured to supply 1 to 4 kilograms (kg) of gas per kilogram of biomass on the tray. The volume of gas supplied by the injection nozzles may also be in ranges of 1 to 6 kg, 1 to 12 kg or 1 to 24 kg of gas to kg of biomass.
The injection nozzle may be fabricated with the tray 40, bottom plate 44 and baffle plates 46, 48 and 50. For example, each pie shaped segment of tray, bottom plate, baffle plates and injection nozzle may be prefabricated and installed on a support structure, e.g., radial spokes, in the vessel. Further, these prefabricated tray assembly segments or prefabricated tray assemblies may be installed in the vessel by removing the top plate 38 and lowering the prefabricated assemblies down into the vessel to the appropriate elevations, wherein the assemblies are to be positioned. Once positioned, the injection nozzle is coupled to a nozzle opening in the sidewall 42 of the vessel 10. Similarly, once the tray assembly has been positioned in the vessel, an opening in the outer baffle plate 50 is aligned with an extraction nozzle 36 mounted to the sidewall 42 of the vessel.
Below each tray may one or more gas extraction nozzles 36 arranged at substantially the same elevation on the outer wall of the vessel and separated by uniform angles around the vessel. The number of gas extraction nozzles may be the same as or different from the gas injection nozzles. For example, one, two or three gas extraction nozzles may be below each tray or alternatively one for each tray segment. The gas injection nozzles 34 may be of a smaller diameter than the gas extraction nozzles, especially if the oxygen deprived gas expands as it enters the vessel. The gas inlet manifolds for the nozzles 34, 36 may be thick walled pipes or fabricated from steel. With respect to each tray, gas enters the vessel through the gas injection nozzles 34, passes through the biomass material on the tray, the tray and is discharged from the vessel through the extraction nozzles 36.
The scraper device 56 may be prefabricated and installed by sliding the device down into the vessel. The center collar may be welded or otherwise affixed to the shaft. The diameter of the scraper bar may conform to the inner diameter of the vessel with a small clearance. The center collar may be fixed to the shaft 32, such that the scraper device rotates with the shaft. The height of the scraper device 56 may be nearly the same as the height of the biomass space 54, or may be about the desired thickness of the biomass 66 on the tray, as shown in
The rotation of the shaft 32 rotates a scraper device 56 immediately above each of the trays 40. The biomass fills or partially fills the volume between the spokes 60 of the scraper device. The rotation of the scraper device over its respective the tray moves the biomass material across the tray. As the biomass material moves across the tray, the material is exposed to a constant flow of the oxygen deprived gas at a uniform temperature. The gas enters the vessel through gas injection nozzles 34 that has an opening at the outer wall of the vessel or an opening 53 in the bottom plate 44 above the tray and biomass space 54. The opening 53 in the bottom plate may be a single discharge port, or a gas distribution manifold 55 with an array of gas discharge ports arranged above the biomass on the tray. The opening may also be flared to assist with disbursing the oxygen deprived gas over the biomass on the tray. The gas distribution manifold 53 may be an arrangement of pipes and pipe fittings with nozzles, and fabricated with the tray assembly. The opening or gas distribution manifold may be arranged to uniformly distribute gas over the biomass on the entire tray. To achieve uniform gas distribution, multiple injection nozzles may be arranged around the wall of the vessel, such as at least one nozzle for each tray segment.
As the gas moves through the biomass and the tray, the scraper device rotates to move the biomass in an arc shaped path through the tray assembly. The biomass moves through the tray assembly and is discharged through an opening 64, shown in
Gases flow down through the bed and tray, and enter the gas passage 52. The gases exhaust from the gas passage through the extraction nozzles 36 arranged radially around the wall of the vessel and at each segment of the tray. The gas extraction nozzles 36 may be arranged to promote the uniform flow of gases through the biomass on the tray. The number of gas extraction nozzles may be fewer than the number of gas injection nozzles 34.
Cooling gases may be injected in the lower(s) trays, cooling zone, chip tube or chip screw to cool the torrefied biomass prior to discharge from the reactor. The cooling gases may be used to stop or slow the torrefaction reaction and to make the torrefied biomass safe and suitable for an oxygen atmosphere outside of the vessel. For example, cooling to stop or slow the torrefaction reaction may occur to make the biomass suitable for an oxygen atmosphere may occur in the cooling zone 22 or in pressurized cooling devices downstream of the vessel. The cooling to stop or slow the torrefaction reaction may require cooling gases that are 10 to 30 degrees Celsius cooler than the gases injected in the torrefaction tray assemblies to promote the torrefaction reaction. The cooling gases to make the torrefied biomass safe for an oxygen atmosphere may be cooler by an additional 10 to 30 degrees Celsius, or 10 to 50 degrees Celsius, or 10 to 80 degrees Celsius, or 10 to 100 degrees Celsius, or 20 to 120 degrees Celsius from the cooling gases added to the cooling tray assemblies.
Gases from the cooling zone 24, such as in the convergence section, may be withdrawn through a screen 65 in a sidewall of the vessel, as is shown in
The cooled torrefied biomass passes through a pressure transfer device 70, such as a rotary valve. The pressure of the torrefied biomass downstream of the pressure transfer device may be at atmospheric. From the pressure transfer device, the torrefied biomass is moved to other processes such as using a screw conveyor 72.
Before the torrefaction reaction occurs in the vessel, such as in the lower trays 18, the biomass may be dried and heated in an oxygen deprived environment at a temperature of 200° C. to 400° C. The biomass may be dried and heated in a separated dryer that acts on the biomass before it reaches the vessel 10. In addition or alternatively, the biomass may be dried in an upper drying zone of the vessel 10, which may include one or more of the tray assemblies. The biomass may be directly heated with an oxygen deprived gas, e.g., super-heated steam, nitrogen or a mixture of both, injected into the top of the vessel or dryer.
The volume of hot oxygen deprived gas needed for the vessel is dramatically reduced in a pressurized reaction vessel 10 as compared to a vessel operating at atmospheric pressure. Pressurizing the treatment vessel 10 the volume of hot gas needed to heat the biomass is decreased by a factor of two (2) to thirty-five (35) as compared to a vessel at atmospheric pressure. The reduction factor for the vessel depends on the pressure in the vessel.
Because of the reduced volume of hot gas needed in the pressurized reactor, the volume and hence the size and cost of the vessel 10 may be significantly reduced as compared to a vessel operating at atmospheric pressure. A pressurized vessel in which a hot gas is injected provides effective and economical heat transfer from the gas to the biomass in the vessel.
The vessel 10 may be pressurized by injecting an oxygen deprived gas, e.g., oxygen starved gas, at a pressure of up to 35 bar gauge (barg), such as in a range of 3 barg to 35 barg. The pressurized vessel 10 operates in an oxygen deprived gas environment in which a heated pressured gas circulates through the vessel to directly heat the biomass and promote a torrefaction reaction with the biomass.
The hot, oxygen deprived gas may be steam, e.g., super-heated steam, nitrogen or carbon dioxide and may contain in lesser quantities gaseous byproducts from the torrefaction reaction. Further, the hot gas may be injected into the biomass in the feed system (not shown) such as in the inlet downstream of a pressure isolation device or downstream of a high pressure transfer device. If there is a high pressure transfer device, a pressure isolation device may be unnecessary at the inlet to the vessel 10.
In the drying and torrefaction tray assemblies, the hot gas flows through the biomass in the vessel 10 and directly heats the biomass to a temperature that promotes a torrefaction reaction in the material, such as a range of 240° C. to 300° C. The hot gas and any gas generated in the reactor are exhausted from the reactor at various elevations through extraction nozzles 36. The gas may exhaust from the vessel at a temperature of about 250° C. to 280° C. The gases used for drying may be cooler than the gases used for torrefaction. The gases for drying may be gases extracted from the torrefaction tray assemblies, and using a blower are circulated to the drying tray assemblies without adding additional heat to the gases. Gases that are circulated back to the torrefaction trays may be heated in a heat exchanger before being returned to the torrefaction tray assemblies.
A portion of the exhausted gas is removed from the vessel for use outside of the torrefaction system. Another portion of the exhausted gas is indirectly heated in a heat exchanger 84 (or other heat transfer device) and returned to the gas input manifold 24 at the top of the vessel 10. The heat exchanger 34 may add heat energy to heat the exhausted gas from about 250° C. to 300° C. to 380° C., for example. Reheating and recirculating the exhausted gas reduces the amount for additional pressurized heated oxygen deprived gas required to be supplied to the gas input manifold of the vessel.
The exemplary process flow in
The oxygen deprived gas shown in the process flows of
A portion of the gases may be removed from the system as bleed off gases 90. The portion may be the just gases from the lowest one or few torrefaction tray assemblies, all of the torrefaction tray assemblies, a middle set of torrefaction tray assemblies, or just gases removed from the drying tray assembly(ies). The bleed off gases may be selected to have a high concentration of torrefaction reaction byproducts to be removed and later combusted or otherwise processed. Alternatively, bleed off gases may be selected based on having a low concentration of torrefaction reaction byproducts to be used in combustion or other processes.
The oxygen deprived gases are circulated through the vessel 10 and heat exchanger 84. Blowers 74, 76 and 78 provide a motive force to circulate the gases. The hot gases from the torrefaction tray assemblies may flow through the high temperature blowers 76 and 74 and the heat exchanger 84, before being returned to the torrefaction tray assemblies 18 and, optionally, to the top inlet 86 of the vessel. Multiple blowers 74, 76 may be used to provide the needed flow rate to circulate gases through the many torrefaction tray assemblies. Valves 80 between the blowers 74, 76 may remain open to allow high temperature gases to flow in parallel through these blowers. Valves 82 may be closed to prevent the hot gases flowing through the high temperature blowers 74, 76 from mixing with the low temperature gases flowing through the low temperature blower 78. The valves 80, 82 may be set as opened or closed depending on the rate of hot gases extracted from the vessel as compared to the rate of cooler gases extracted from the vessel.
Relatively cooler oxygen deprived gases are extracted from the cooling tray assemblies 20, the cooling zone 22 of the vessel (such as through screen 65) and, optionally from the drying tray assembly 16, and flow through piping separate from the piping used for the hotter oxygen deprived gases extracted from the torrefaction tray assemblies. The cooler gases are removed through extraction nozzles 36 by a low temperature blower 78 which pushes the gases back to the vessel where they enter through injection nozzles 34 to the cooling tray assemblies 20, and optionally to the top of the cooling zone 22 through a nozzle 92 aligned with the bottom tray assembly.
The bleed off gases provide a means to remove primary byproducts of the torrefaction reaction occurring in the vessel 10. These primary byproducts may include acetic acid, carbon monoxide, carbon dioxide, formaldehyde, formic acid, water, lignin fragments, and other lesser components. The primary byproducts are generally gaseous at the temperature and pressure at which the torrefaction reaction occurs in the vessel. Some of the byproducts may be in aerosol or fine char form carried by in the bleed off gases. Similarly, fine particles of lignocellulose material from the biomass may flow with the gas as it passes through the screens in the trays and the vessel and be carried by the bleed off gases out of the system.
The primary byproducts may combine and condense to form tar like substances. If allowed to condense in the vessel and downstream process components, the tar like substances can deposit on the surfaces of the vessel and components, particularly on the interior surfaces of piping and heat exchangers.
The gases being circulated through the reactor vessel 10 and heat exchanger 84 may be treated to remove reaction byproducts from the circulating gases. The system for circulating the gases through the vessel 10 and heat exchanger 84 may include separation devices 96 for removing the reaction byproducts. Separation devices 96 may be a condensation device which cools the gases to cause the byproducts to be condensed to a liquid and removed, before the gases are reheated in the heat exchanger. Other examples of separation devices 96 include devices that oxidize the byproducts, catalytically convert the byproducts, filter the byproducts from the gas flow and flow separators, such as cyclones that use centrifugal forces to separate particles from the gas stream. These separation devices may be used singularly or in combination in the system. The byproducts separated by these components may be further processed by being separated, concentrated or purified into usable products. The bleed off gases 90 remove the primary byproducts from the vessel while these byproducts are in gaseous form. As shown in
The bleed off gases 90 may flow to the combustor where the gases may be mixed with a natural gas, or other gaseous fuel, and combusted. Combustion would release heat energy from the byproducts which would be used to reheat the circulating gases in the heat exchanger 84. The heat from combustion could also be used to dry and heat the biomass in the optional dryer 21.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
1. A pressurized torrefaction reactor vessel comprising:
- a vessel wall extending substantially vertically;
- a rotatable shaft extending vertically down through a top of the vessel;
- scraper devices each at a different elevation within the vessel and coaxial to the shaft;
- tray assemblies wherein each tray assembly is associated with one of the scraper devices such that the scraper device is immediately above a tray of the tray assembly;
- at least one of the tray assemblies includes the tray, a gas extraction passage below the tray, and a gas injection passage above the tray, wherein the tray is an open mesh or otherwise permeable to gas flow and impermeable to passage of biomass through the tray;
- each tray includes a discharge opening to transfer biomass from the tray and down to a tray of a lower one of the tray assemblies, and wherein the discharge opening in the lowermost tray transfers the biomass to a pile of the biomass in the vessel;
- a plurality of gas extraction openings in the vessel wall, wherein at least one of the gas extraction openings is aligned with the gas extraction passage and another one of the gas extraction openings is at an elevation below the lowermost tray assembly and above the pile of the biomass, and
- a bottom discharge port of the vessel through which the torrefied biomass is discharged.
2. The pressurized vessel of claim 1 wherein the tray assemblies and scraper devices are interleaved and stacked vertically along the shaft of the vessel.
3. The pressurized vessel of claim 1 wherein the trays are formed of at least one of a perforated steel mesh or a drilled steel plate.
4. The pressurized vessel of claim 1 wherein perforations in the tray are drilled holes or laser cut holes or slots.
5. The pressurized vessel of claim 4 wherein the holes or slots in the tray having an increasing cross-sectional area in a downward direction.
6. The pressurized vessel of claim 5 wherein the slots or holes each have a constant cross-sectional upper region and a lower region of the increasing cross-sectional area.
7. The pressurized vessel of claim 4 wherein an upper rim of the holes or slots is beveled at least along a trailing portion of the rim.
8. The pressurized vessel of claim 1 wherein at least one of the tray assemblies includes a solid bottom plate.
9. The pressurized vessel of claim 8 wherein the gas injection passage for the one of the tray assemblies extends between the tray and a solid bottom plate of the next higher tray assembly.
10. The pressurized vessel of claim 8 wherein a gas distribution manifold penetrates or is mounted to the bottom plate and is coupled to the gas injection passage.
11. The pressurized vessel of claim 10 wherein the gas distribution manifold is at least one of a fabricated metal structure and includes a pipe fitting.
12. The pressurized vessel of claim 10 wherein the gas distribution manifold includes at least one nozzle which distributes gas above the biomass on a tray of a lower tray assembly.
13. The pressurized vessel of claim 10 wherein the gas distribution manifold includes a plurality of nozzles directing gas to flow uniformly over the biomass on a tray of the next lower tray assembly.
14. The pressurized vessel of claim 1 wherein each tray is an annular array of pie shaped tray segments, and the discharge opening is a pie shaped opening in the annular array.
15. The pressurized vessel of claim 1 further comprising baffle plates extending radially in the gas extraction passage.
16. The pressurized vessel of claim 15 wherein the baffle plates include plates extending vertically and attached to tray and bottom plate of the tray assembly.
17. The pressurized vessel of claim 14 each pie shaped tray assembly has side plates extending vertically between the tray and the bottom plate.
18. The pressurized vessel of claim 1 further comprising at least one cleaning nozzle directed to at least one the trays, wherein the cleaning nozzle directs a pressurized fluid flow against the perforations, slots, holes or mesh of the tray.
19. The pressurized vessel of claim 18 wherein the cleaning nozzles are mounted to a lower edge of a blade of the scraper device.
20. The pressurized vessel of claim 1 wherein a gas injection passage connects to at least one gas injection port in the wall of the vessel.
21. The pressurized vessel of claim 1 wherein there is one of the gas extraction openings for each segment of the tray assembly associated with the extraction openings.
22. The pressurized vessel of claim 16 wherein the scraper device includes blades extending from the shaft towards the wall of the vessel, and the blades are arranged angularly around the shaft.
23. The pressurized vessel of claim 1 where the scraper device rotates with the shaft, and the rotation of the scraper devices moves the biomass over the tray immediately below the scraper device.
24. The pressurized vessel of claim 22 where the scraper device includes a central hub affixed to the shaft, and the blades of the scraper device extend outward from the hub.
25. The pressurized vessel of claim 22 wherein the blades have radially outward ends connected to a collar, wherein said collar is proximate to the wall of the vessel.
26. The pressurized vessel of claim 22 wherein each of the blades has a lower edge which in a range of 3 to 5 millimeters (mm) of the tray immediately below the blade.
27. The pressurized vessel of claim 22 wherein the blades are each inclined from zero to 20 degrees in the direction of rotation of the scraper device with respect to a radial line corresponding to the blade.
28. The pressurized vessel of claim 22 wherein the blades are curved or swept in a direction of rotation of the scraper device.
29. The pressurized vessel of claim 22 wherein at least one of the blades of the scraper device includes a radial slot receiving a high pressure passage, wherein the passage includes nozzles to direct a gas against the tray below the blade or suction ports to apply a suction to the tray.
30. The pressurized vessel of claim 1 wherein the area below the trays includes a torrefaction reaction zone and a cooling zone below the torrefaction reaction zone.
Filed: Jun 28, 2012
Publication Date: May 2, 2013
Applicant: ANDRITZ INC. (Glens Falls, NY)
Inventors: Andrew EYER (Gansevoort, NY), Bertil STROMBERG (Diamond Point, NY), Joseph Monroe RAWLS (Alpharetta, GA), Brian F. GREENWOOD (Cumming, GA), John WESTON (Queensbury, NY), Michael SESTRICH (Alpharetta, GA), Nachiketa NANDY (Alpharetta, GA), John BOLLES (Queensbury, NY), Jay MIELE (Milton, GA)
Application Number: 13/536,627
International Classification: C10B 49/04 (20060101);