Patent Application
20140110242
This invention relates to the reduction of biomass to char. Embodiments of the invention provide methods and apparatus for reducing biomass to char.
Biomass such as straw, other crop residues, wood chips, and the like are readily available. It is often a problem to dispose of biomass. Various agricultural operations can produce significant amounts of biomass as byproducts. Biomass can be reduced to char by heating the biomass in a reduced-oxygen atmosphere. Char is a useful material that may, for example, be mixed into soil to improve the quality of the soil.
Various systems for processing biomass are known. Some of those systems are described in the following patents and patent applications:
There remains a need for cost effective and efficient systems for processing biomass to yield char. There is a particular need for such systems that are easily transportable to locations where biomass is available and/or locations where char may be useful. For example, there is a need for such systems that are transportable to farms which yield biomass byproducts so that biomass can be converted to char at the farm and the char can be used on the farm, thereby eliminating transportation of the biomass and char. There also remains a need for new cost effective and efficient systems for producing syngas or producer gas.
This invention has a number of aspects. These aspects may be applied to advantage in combination. However, these aspects may also have application individually and/or in combination with other existing apparatus and/or methods.
One aspect provides apparatus for thermal decomposition of biomass. The apparatus comprises a tubular reactor vessel that extends through a furnace. Hollow walls or paddles project inwardly from an outside wall of the tubular reactor. Openings in an outer wall of the tubular reactor vessel provide fluid communication between the interior of the furnace and spaces interior to the hollow walls or paddles. The openings are slit-shaped in some embodiments. Hot gases in the furnace can enter the interior spaces in the hollow walls or paddles by way of the openings. The hot gases heat the paddles from inside and the heat from the paddles may be transferred to biomass being processed.
In some embodiments the hollow walls or paddles extend transversely to a longitudinal centerline of the reactor vessel. The hollow walls or paddles may be spaced apart from one another along the reactor. In an example embodiment, the hollow walls or paddles alternate—with one hollow wall or paddle projecting inwardly from a first side of the reactor vessel, a next hollow wall or paddle projecting inwardly from a second side of the reactor vessel opposed to the first side of the reactor vessel, a next next hollow wall or paddle projecting inwardly from the first side of the reactor vessel, and so on. In other embodiments successive hollow walls or paddles project into the interior of the reactor vessel from different directions.
The hollow walls of paddles in some embodiments project inwardly past the longitudinal centerline of the reactor vessel such that, when the reactor vessel is viewed end-on, the hollow walls or paddles overlap with one another.
In some embodiments the hollow walls or paddles have arcuate inward edges. In some embodiments the hollow walls or paddles are at least generally planar. In some embodiments the hollow walls or paddles are substantially perpendicular to the longitudinal centerline of the reactor vessel.
The tubular reactor vessel may be supported for rotation in the furnace and the apparatus may comprise a drive coupled to rotate the reactor vessel about its longitudinal axis. In some embodiments the reactor vessel is inclined such that an input end of the reactor vessel is higher than an output end of the reactor vessel.
Another aspect provides apparatus for thermal decomposition of biomass which includes an airlock upstream from a heated reactor vessel. A supply of syngas or producer gas is connected to supply syngas or producer gas into the airlock. In some embodiments the airlock includes a reciprocating piston that pushes the biomass along a channel into the reactor. The syngas or producer gas may be introduced into a chamber behind the piston.
Introduction of syngas or producer gas may be coordinated with operation of the piston such that syngas is fed into the airlock when the piston is advancing. The coordination may be facilitated, for example, by an electronic controller (which may, for example comprise a programmable controller) controlling an electrically-controlled valve or by a mechanical system.
In some embodiments the airlock comprises a pair of gate or flap valves that can be closed to define a chamber between them and syngas is introduced into the chamber. Introduction of the syngas may be coordinated with operation of the airlock such that the syngas is admitted into the chamber while the chamber is closed. In some embodiments a vacuum pump is connected to extract gases from the chamber. By a combination of applying vacuum and/or introducing syngas or producer gas into the chamber the air content of the chamber may be significantly reduced. The vacuum pump may deliver gases withdrawn from the chamber to a burner.
Another aspect provides apparatus for thermal decomposition of biomass which includes an airlock upstream from a heated reactor vessel and a vacuum pump for removing air or other gases from the airlock. An outlet of the vacuum pump may communicate with a burner so that flammable gasses that pass through the vacuum pump are combusted before being released. A valve may be provided to control application of the vacuum to the airlock. In some embodiments, application of the vacuum is coordinated with operation of the airlock. For example, the airlock may comprise a chamber between a pair of valves for passing biomass. A controller, mechanical linkage or the like may cause application of the vacuum to the chamber while at least an inlet one of the valves is closed. For example, the vacuum may be applied for a few seconds after the inlet valve is closed.
Other aspects of the invention provide methods for reducing biomass to char. Some such methods comprise passing biomass into a tubular reactor vessel that is heated by contact with hot gases surrounding the reactor. The method involves heating paddles or walls that project into the reactor by permitting the hot gases to enter chambers within the paddles or walls through openings. Some embodiments comprise rotating the tubular reactor and allowing the biomass to be moved through the tubular reactor at least in part by the force of gravity. In such embodiments the biomass may take a zig-zag path along the reactor as it spills over the puddles or walls.
The example aspects described above may be combined with one another in any combinations to yield further aspects. The disclosure describes a large number of additional features. Further embodiments may be arrived at by combining such aspect with any one or any combination of the additional features described in this disclosure. Other aspects provide methods and apparatus which include novel combinations and sub-combinations of the features described in this disclosure.
Further aspects and example embodiments are illustrated in the accompanying drawings and/or described in the following description.
The accompanying drawings illustrate non-limiting example embodiments.
Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. The following description of examples of the technology is not intended to be exhaustive or to limit the system to the precise forms of any example embodiment. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.
In some embodiments, biomass supply 12 comprises a charge bin from which biomass is delivered by a conveyor, such as a screw auger. The conveyor may have a variable-speed control to permit the speed with which biomass is introduced into the rest of apparatus 10 to be adjusted and/or to permit the operation of the conveyor to be timed to coordinate with other aspects of the operation of apparatus 10.
Biomass from biomass supply 12 is fed into a dryer 14. Dryer 14 reduces the moisture content of the biomass. The biomass is then fed through an airlock 16 into a reactor 18. Reactor 18 heats the biomass in an oxygen-reduced atmosphere to reduce the biomass to char and volatile gases (sometimes called ‘producer gas’). The producer gas is given off as the biomass decomposes under the conditions within reactor 18. The pressure within the reactor 18 is controlled in a manner that produces a positive pressure pushing the producer gas out of reactor 18. Material exits reactor 18 into a separator 20 which separates solids (e.g. char) from the gases exiting reactor 18.
Solids may be received from separator 20 into a solids receptacle 21. The solids may then be taken off to use for soil remediation or any other purpose to which they are suited.
Gaseous materials exiting reactor 18 (e.g. producer gas) are taken off and may be used for various purposes. For example, the gaseous materials may be taken off by a gas handling system 22 which may generate a supply of syngas. The syngas may be used for a range of purposes including, for example, running motors to drive apparatus 10 or other apparatus, generating electrical power (for example by running an engine to drive a generator or generating steam to drive a turbine or other steam engine), feeding a burner to generate heat or the like.
In the illustrated embodiment, gas handling system 22 provides syngas to an engine 24 that runs on the syngas and drives a generator 25 to generate electrical power. The electrical power may be used to power apparatus 10 and/or used for other applications.
In some embodiments, as described more particularly below, some syngas from handling system 22 is directed into airlock 16 as indicated by line 22A. The syngas helps to maintain an appropriate oxygen level within reactor 18 by one or a combination of steps assisting in purging air from incoming biomass and consuming oxygen within reactor 18.
Hot gases from elsewhere in apparatus 10 flow along dryer tube 33. The hot gases preferably flow in a direction 39 countercurrent to the direction 36 in which biomass is moved along dryer tube 33. The hot gases may comprise, for example, one or more of: flue gas from a furnace (such as furnace 72 described below, for example); gas heated directly or indirectly from cooling products of reactor 18; exhaust gas from an engine or burner fueled by syngas or gas heated directly or indirectly from such exhaust gases; or the like. Exhaust stack 31 carries the heated mixture of gases that has passed through dryer tube 33 away.
Dryer tube 33 exits into a conveyor 40 which carries the biomass to airlock 16 for delivery into reactor 18 downstream from the airlock. In the illustrated embodiment, biomass is gravity-assisted in passing through airlock 16 and conveyor 40 is an elevator that lifts the biomass to a height sufficient that the biomass can be fed into the top of airlock 16. In the illustrated embodiment, conveyor 40 is made up of an endless chain 42 carrying paddles 43.
After biomass has been received into chamber 46 and dump valve 45A has been closed, the biomass can be allowed to fall from chamber 46 into an injection chamber 47 by opening dump valve 45B. A reciprocating piston 48 moving in a channel 49 delivers biomass from injection chamber 47 into reactor 18 by way of a valve 50 such as a flap valve.
Biomass falls from injection chamber 47 into channel 49 which may, for example, comprise a cylinder that opens into injection chamber 47 through opening 51. The biomass is then delivered along channel 49 and through flap valve 50 into reactor 18 by reciprocation of piston 48. In a prototype embodiment, a feed tube which provides channel 49 has a diameter of approximately 3½ inches.
Piston 48 is driven by a piston rod 53 which passes through a seal 54 in the end of channel 49. Piston 48 may be driven in any suitable way, for example by a hydraulic actuator, an electric actuator, a pneumatic actuator, a crank, or the like. Where piston 48 is driven by an actuator, apparatus 10 may comprise a suitable controller to cause piston 48 to operate in a manner coordinated with the operation of the valves of airlock 16. The controller may, for example, comprise a programmable controller that may also be connected to control other aspects of the operation of apparatus 10.
In some embodiments syngas is delivered to airlock 16. The syngas may be admitted on regular intervals to airlock 16 by a solenoid valve that may be on a feed system timer, where the syngas is under operating pressure of a few psig and the airlock 16 is under atmospheric or vacuum pressure. The syngas can assist in maintaining appropriate conditions within reactor 18. One process parameter that may be controlled by addition of syngas into airlock 16 is the oxygen content within reactor 18. The syngas may be syngas generated from the biomass in reactor 18 that has been separated downstream. The syngas may be cooled prior to injecting it into airlock 16.
Syngas is optionally introduced into chamber 52 behind piston 48. In the illustrated embodiment, syngas is admitted into chamber 52 by way of delivery line 55. Delivery of syngas into chamber 52 may be timed to the operation of airlock 16 such that syngas is delivered into chamber 52 prior to and/or during the operation of piston 48 to push biomass into reactor 18. When the syngas is not being delivered into chamber 52 it may be diverted to a burner (for example, a burner used to heat reactor 18). In the illustrated embodiment, the syngas may be delivered either into chamber 52 or diverted to a burner by way of a two-way valve 56.
In some embodiments syngas is optionally also injected into chamber 46. In the illustrated embodiment, syngas is delivered into chamber 46 by way of a delivery line 57. In the illustrated embodiment, the syngas may be delivered either into chamber 46 or diverted to the burner by way of a two-way valve 58. Delivery of syngas into chamber 46 may be timed to the operation of airlock 16.
A vacuum line 59 may be provided to assist in removing air from chamber 46. In the illustrated embodiment, vacuum line 59 is connected to a vacuum pump 59A by way of a valve 59B. Valve 59B may be operated to withdraw gases from chamber 46. Air may be purged from chamber 46 by admitting syngas by way of syngas line 57 while withdrawing gas by way of vacuum line 59.
In some embodiments a controller, mechanical linkage or the like may cause application of the vacuum to chamber 46 while at least inlet valve 45A is closed. For example, the vacuum may be applied for a few seconds after inlet valve 45 is closed. In some embodiments, chamber 46 is purged of oxygen by introducing one or more of: syngas, flue gas, and/or a backflow of gases from reactor 18 into chamber 46 and/or injector chamber 47 prior to and/or during application of the vacuum to chamber 46.
In block 65, dump valve 45B is opened to allow the biomass contained within chamber 46 to fall into injection chamber 47. In block 66, piston 48 is advanced to drive biomass along channel 49. The plug of biomass travelling along channel 49 pushes flap valve 50 open to allow the biomass to exit into reactor 18. As this is occurring, additional syngas may be introduced into chamber 52 behind piston 48. The introduction of the additional syngas prevents air from entering the system and also mixes syngas into the biomass being fed into reactor 18. Oxidation of syngas in reactor 18 can further reduce the oxygen content within reactor 18. In block 67 piston 48 is retracted. Blocks 66 and 67 may be repeated multiple times to deliver most or all of the biomass from chamber 47 into reactor 18.
In an example embodiment, upper dump valve 45A opens and allows biomass to fall into chamber 46. Upper dump valve 45A is then automatically closed. Vacuum valve 59B is then opened for a period of time sufficient to withdraw a significant amount of air out of chamber 46. For example, valve 59B may open for 15 seconds. Piston 48 is then moved to a fully retracted position and lower dump valve 45B is opened to allow biomass to fall from chamber 46 into injection chamber 47. Lower dump valve 45B is then closed. Syngas valve 56 is then opened so that syngas is delivered to chamber 52 behind piston 48. Piston 48 is then advanced toward reactor 18.
As piston 48 completes its travel, biomass being pushed in front of piston 48 through channel 49 is pushed into reactor tube 70 via flapper valve 50. At the end of the stroke, syngas valve 56 is closed. Upper dump valve 45A is then opened and simultaneously piston 48 is retracted back towards its fully retracted position. The cycle then repeats.
As shown in
The burner which heats the furnace 72 may burn any of a wide variety of fuels. For example, in some embodiments, the burner comprises one or more of a wood burner, a gas burner, an oil burner, or the like. The burner may burn solid fuels such as wood (in any suitable form, for example, logs, chips, shavings, sawdust, hog fuel, or pellets). In some embodiments, syngas is fed into the burner and at least some of the heat developed by the burner is developed by way of the combustion of syngas.
Baffles 77 in upper compartment 76 cause hot gases from burner compartment 74 to make intimate contact with reactor tube 70 as they pass through upper chamber 76 to an outlet (not shown in
Reactor tube 70 is inclined at a descending angle so that biomass which enters through flap valve 50 is carried down through reactor tube 70 by the action of gravity. Flap valve 50 acts as a check valve to prevent the backflow of gases from reactor 18 into feed channel 49.
The angle of inclination, θ, of reactor tube 70 may, for example, be on the order of 5 to 25 degrees. In a preferred embodiment, reactor tube 70 is sloped downward at a 20% (a one in five grade corresponding to an angle θ of approximately 11 degrees). Reactor tube 70 is rotated as the biomass passes through it. The rotation may be fairly slow. In one embodiment the reactor tube 70 rotates at a rate of less than 2 rpm. For example in one embodiment reactor tube 70 rotates at approximately ½ rpm.
The rotation of reactor tube 70 causes the biomass to tumble as it passes through the reactor tube. In the illustrated embodiment, rotation of reactor tube 70 is driven by a drive system 78 (not shown). Drive system 78 may, for example, comprise an electric motor and a speed-reducing transmission. The transmission may comprise one or more of a chain drive, gear reducer, gear drive, roller drive or the like, for example. The length of reactor tube 70 may vary depending on the diameter of tube 70 and the resistance time of biomass inside reactor tube 70, which in turn is dependent on the feed rate of biomass into reactor 18. More biomass input feed per unit time would require a reactor tube 70 having a larger diameter and/or a faster turning speed to ensure the biomass feed is relatively spread evenly for efficient heating. In some preferred embodiments, the residence time of biomass inside reactor tube 70 is, at least 15 minutes. For example, the residence time may be in the range of 20 to 25 minutes.
Reactor tube 70 has walls 79 that project into its interior. Each wall 79 is hollow and has at least one opening 80 which opens into the interior of furnace 72. Hot gases from furnace 72 can enter openings 80 and heat walls 79 from the inside. Walls 79 in some embodiments are spaced a apart and are arranged in an alternating pattern while projecting into the interior of reactor tube 70. Walls 79 may, for example, be spaced apart from one another by 6 inches (15 cm) in the direction along the longitudinal axis of reactor 70. In some embodiments, walls 79 are unequally spaced apart along the longitudinal axis of reactor 70. In particular, it can be advantageous for walls 79 to be spaced farther apart near the entrance of reactor 70 and to be spaced more closely toward the exit from reactor 70. Near the entrance to reactor 70 entering biomass may have a moisture content high enough to make the biomass tend to stick together so that it flows over walls 79 with more difficulty than the drier biomass found closer to the exit from reactor 70. Providing more widely-spaced walls 79 near to the entrance to reactor 70 facilitates passage of the biomass along the initial part of reactor 70.
Some or all of walls 79 in some embodiments each project slightly more than half of the diameter of reactor tube 70 into reactor tube 70 and, in some embodiments extend at least 20% of their overall height past the centerline of reactor tube 70 (see e.g.
In some embodiments, walls 79 may be on opposite sides of reactor tube 70 or may have a more offset arrangement. In some embodiments, walls 79 are non-planar. For example, walls 79 may be curved about axes of curvature that extend transverse to reactor tube 70. In such embodiments the curvature may be such that center portions of walls 79 project toward the upstream or downstream end of reactor tube 70.
Heated walls 79 both transfer heat into biomass passing through reactor tube 70 and act as mechanical lifts which mix and separate the biomass as it passes through the rotating reactor tube 70. Heated walls 79 may be, for example, approximately 1½ to 3 centimeters in thickness.
As illustrated in
Reactor tube 70 may be sealed at its ends to prevent the ingress of air. In an example embodiment, the upper end of reactor tube 70 is sealed by an annular packing attached to a tube through which channel 49 extends. The packing seals against the inside of reactor tube 70 while allowing rotation of reactor tube 70. Tube support rollers may be attached to the packing or to a separate support to permit smooth rotation of reactor tube 70. The lower end of reactor tube 70 may be sealed to a non-rotating reactor receiver by a packing gland which bears against the external surface of reactor tube 70. In some embodiments, reactor tube 70 may be tapered so it becomes larger towards the outlet of reactor tube 70.
In some embodiments, a grinder is provided at the output of reactor tube 70. The grinder may grind chunks of charcoal produced by the pyrolisis of biomass in reactor tube 70 into smaller granular particles. In some embodiments the particles are smaller than about 0.5 cm. The particles may, for example, have diameters in the range of 0.1 to 0.3 cm. The particles are then separated from the gases exiting reactor 18 in separator 20.
In some embodiments, separator 20 comprises a cyclone separator. Superheated steam may be injected at a base of a riser in the separator to assist in lifting and spinning particles within the separator such that solids are separated from gases exiting reactor 18.
An airlock, such as a rotary airlock, may be provided to receive and pass solid particles separated by the cyclone separator without providing an opening through which significant amounts of gases can escape. The particles may optionally be cooled by a fine water mist or the like as they pass through the exit of the airlock on their way into solids receptacle 21.
Gas handling system 22 may treat the gases passed by separator 20 in any of a wide range of ways. In some embodiments, the gases are treated to crack heavy fractions (e.g. tars), cooled and filtered. For example, gas handling system 22 may comprise catalytic decomposition stages in which fractions of the producer gas from reactor 18 are decomposed catalytically. In such embodiments, a reheater may reheat the producer gas from approximately 400° C. to approximately 700° C. prior to passing the heated producer gas into a catalyst vessel.
The catalyst vessel contains a catalyst for assisting in the catalytic decomposition of tar molecules. The catalyst may, for example, comprise a mixture containing charcoal and/or dolomite. Superheated steam may optionally be injected into the producer gas in or just upstream from the catalyst vessel. The steam assists in the catalytic decomposition of heavier molecules in the syngas.
In an example embodiment a steam generator cools syngas exiting the catalyst vessel and, at the same time, produces saturated steam. The saturated steam may be heated in a steam superheater, which may be located, for example, in the burner section of furnace 72. The superheater may, for example, heat the steam from approximately 140° C. to approximately 400° C.
Syngas exiting the steam generator may be further cooled to ambient temperature or near ambient temperature by a syngas-to-air heat exchanger. The air side of the heat exchanger may be cooled by a forced air draft. The cooled syngas may be filtered to remove entrained dust or other particulates. The filtered and cooled syngas may then be supplied to drive an engine or to fuel a burner or the like. In some embodiments, an engine driven by combustion of the syngas directly drives motion of various components of apparatus 10. In other embodiments electricity generated by a syngas-driven generator is used to drive motion of some or all components of apparatus 10. In other embodiments steam generated in cooling syngas and/or burning syngas is used to drive motion of some or all components of apparatus 10.
Air heated by the cooling of syngas in the syngas-to-air heat exchanger may be used to provide a supply of heated air to one or more of: the main burner of furnace 72; biomass dryer 14; and a flare stack in which any surplus syngas may be burned off safely.
One advantage of apparatus as described herein is that some embodiments may be dimensioned and arranged so that a biomass processing apparatus as described herein may be provided on a single trailer. This can be convenient as the trailer may be taken to a farm or other area where biomass is present and the biomass may be processed at that location. This is particularly convenient in the case where it is desired to use char produced by the apparatus at the same location. For example, straw from a field on a farm, corn husks and stalks or other vegetable matter may be processed in apparatus 10 to yield char which may then be integrated into the soil at the farm. The apparatus 10 may be then taken to another location.
One possible arrangement for the components of apparatus 10 on a trailer 100 is illustrated in
Unless the context clearly requires otherwise, throughout the description and the claims:
Words that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present) depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.
While processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed simultaneously or in different sequences or at different times.
Where a component (e.g. an assembly, device, member, controller, valve, tube, motor, filter etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.
Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.
It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.
This application claims priority from U.S. Application No. 61/715,796 filed 18 Oct. 2012. For purposes of the United States, this application claims the benefit under 35 U.S.C. §119 of U.S. Application No. 61/715,796 filed 18 Oct. 2012 and entitled BIOMASS CONVERTER AND METHODS which is hereby incorporated herein by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61715796 | Oct 2012 | US |
