BIOMASS CONVERTER AND METHODS

A tubular reactor useful for converting biomass to char has walls projecting into its interior. The walls are hollow. Cavities in the walls are in fluid connection with the outside of the reactor by way of openings. The reactor may be deployed in a furnace chamber. Hot gases from the furnace chamber may enter the cavities through the openings to heat the walls from within. Biomass may be pyrolized as it passes along the reactor.

DETAILED DESCRIPTION

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.

FIG. 1illustrates an example biomass processing system10. System10has a biomass supply12such as a hopper, chute, intake or the like which can supply into system10biomass of any suitable type. For example, biomass supply12may comprise a hopper or the like equipped with a conveyor or other feed mechanism for feeding biomass from biomass supply12into subsequent parts of apparatus10. Details of the feed mechanism may be varied to accommodate different types of biomass. Before feeding biomass into subsequent parts of the apparatus10, feedstock may be classified to eliminate stones, metal, glass and other material that do not thermally break down. In some embodiments, biomass is chopped, shredded, mulched, macerated or otherwise broken down into small pieces before entering system10or by a suitable apparatus provided as part of system10.

In some embodiments, biomass supply12comprises 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 apparatus10to be adjusted and/or to permit the operation of the conveyor to be timed to coordinate with other aspects of the operation of apparatus10.

Biomass from biomass supply12is fed into a dryer14. Dryer14reduces the moisture content of the biomass. The biomass is then fed through an airlock16into a reactor18. Reactor18heats 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 reactor18. The pressure within the reactor18is controlled in a manner that produces a positive pressure pushing the producer gas out of reactor18. Material exits reactor18into a separator20which separates solids (e.g. char) from the gases exiting reactor18.

Solids may be received from separator20into a solids receptacle21. The solids may then be taken off to use for soil remediation or any other purpose to which they are suited.

Gaseous materials exiting reactor18(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 system22which may generate a supply of syngas. The syngas may be used for a range of purposes including, for example, running motors to drive apparatus10or 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 system22provides syngas to an engine24that runs on the syngas and drives a generator25to generate electrical power. The electrical power may be used to power apparatus10and/or used for other applications.

In some embodiments, as described more particularly below, some syngas from handling system22is directed into airlock16as indicated by line22A. The syngas helps to maintain an appropriate oxygen level within reactor18by one or a combination of steps assisting in purging air from incoming biomass and consuming oxygen within reactor18.

FIG. 2illustrates an example dryer14. Dryer14has an intake32which receives biomass from biomass supply12. Dryer14comprises an elongated cylindrical tube33containing paddles35. Paddles35are rotated about an axis of dryer tube33on a shaft37driven by a motor 38. Paddles35are angled so that, as they rotate they drive biomass along dryer tube33in direction36. In an example embodiment, dryer tube33is approximately 1½ to 2 meters long. Paddles35may, for example, be spaced apart by approximately 3 inches (7½ cm). Paddles35may, for example, be approximately 2 inches (5 cm) by 3 inches (7½ cm) in size.

Hot gases from elsewhere in apparatus10flow along dryer tube33. The hot gases preferably flow in a direction39countercurrent to the direction36in which biomass is moved along dryer tube33. The hot gases may comprise, for example, one or more of: flue gas from a furnace (such as furnace72described below, for example); gas heated directly or indirectly from cooling products of reactor18; exhaust gas from an engine or burner fueled by syngas or gas heated directly or indirectly from such exhaust gases; or the like. Exhaust stack31carries the heated mixture of gases that has passed through dryer tube33away.

Dryer tube33exits into a conveyor40which carries the biomass to airlock16for delivery into reactor18downstream from the airlock. In the illustrated embodiment, biomass is gravity-assisted in passing through airlock16and conveyor40is an elevator that lifts the biomass to a height sufficient that the biomass can be fed into the top of airlock16. In the illustrated embodiment, conveyor40is made up of an endless chain42carrying paddles43.

FIGS. 3 and 4show details of an exemplary airlock16. Airlock16comprises dump valves45A and45B. Biomass can be allowed to enter a chamber46between dump valves45A and45B by opening dump valve45A while dump valve45B is closed. Dump valve45A may then be closed. One of dump valves45A and45B may be kept closed at all times such that there is never an open path for gases and heat to escape from the inlet end of reactor18to the atmosphere and also so that there is never an open path for air to flow unobstructed into the inlet end of reactor18.

After biomass has been received into chamber46and dump valve45A has been closed, the biomass can be allowed to fall from chamber46into an injection chamber47by opening dump valve45B. A reciprocating piston48moving in a channel49delivers biomass from injection chamber47into reactor18by way of a valve50such as a flap valve.

Biomass falls from injection chamber47into channel49which may, for example, comprise a cylinder that opens into injection chamber47through opening51. The biomass is then delivered along channel49and through flap valve50into reactor18by reciprocation of piston48. In a prototype embodiment, a feed tube which provides channel49has a diameter of approximately 3½ inches.

Piston48is driven by a piston rod53which passes through a seal54in the end of channel49. Piston48may be driven in any suitable way, for example by a hydraulic actuator, an electric actuator, a pneumatic actuator, a crank, or the like. Where piston48is driven by an actuator, apparatus10may comprise a suitable controller to cause piston48to operate in a manner coordinated with the operation of the valves of airlock16. The controller may, for example, comprise a programmable controller that may also be connected to control other aspects of the operation of apparatus10.

In some embodiments syngas is delivered to airlock16. The syngas may be admitted on regular intervals to airlock16by a solenoid valve that may be on a feed system timer, where the syngas is under operating pressure of a few psig and the airlock16is under atmospheric or vacuum pressure. The syngas can assist in maintaining appropriate conditions within reactor18. One process parameter that may be controlled by addition of syngas into airlock16is the oxygen content within reactor18. The syngas may be syngas generated from the biomass in reactor18that has been separated downstream. The syngas may be cooled prior to injecting it into airlock16.

Syngas is optionally introduced into chamber52behind piston48. In the illustrated embodiment, syngas is admitted into chamber52by way of delivery line55. Delivery of syngas into chamber52may be timed to the operation of airlock16such that syngas is delivered into chamber52prior to and/or during the operation of piston48to push biomass into reactor18. When the syngas is not being delivered into chamber52it may be diverted to a burner (for example, a burner used to heat reactor18). In the illustrated embodiment, the syngas may be delivered either into chamber52or diverted to a burner by way of a two-way valve56.

In some embodiments syngas is optionally also injected into chamber46. In the illustrated embodiment, syngas is delivered into chamber46by way of a delivery line57. In the illustrated embodiment, the syngas may be delivered either into chamber46or diverted to the burner by way of a two-way valve58. Delivery of syngas into chamber46may be timed to the operation of airlock16.

A vacuum line59may be provided to assist in removing air from chamber46. In the illustrated embodiment, vacuum line59is connected to a vacuum pump59A by way of a valve59B. Valve59B may be operated to withdraw gases from chamber46. Air may be purged from chamber46by admitting syngas by way of syngas line57while withdrawing gas by way of vacuum line59.

In some embodiments a controller, mechanical linkage or the like may cause application of the vacuum to chamber46while at least inlet valve45A is closed. For example, the vacuum may be applied for a few seconds after inlet valve45is closed. In some embodiments, chamber46is purged of oxygen by introducing one or more of: syngas, flue gas, and/or a backflow of gases from reactor18into chamber46and/or injector chamber47prior to and/or during application of the vacuum to chamber46.

FIG. 5illustrates an example method60for operating airlock16to admit biomass into reactor18. Method60begins by opening dump valve45A to admit biomass into chamber46in block62. In block64a vacuum is applied to chamber46. Application of the vacuum draws out air from chamber46. In block63, syngas is injected into chamber46. Blocks63and64may overlap so that, for a period, syngas is being injected into chamber46while gas is being removed from chamber46by a vacuum system. Gases that are removed from chamber46by the vacuum system may be delivered to a burner. The combined effect of applying a vacuum to chamber46and introducing syngas into chamber46purges chamber46of air, and thereby significantly reduces the oxygen content of chamber46.

In block65, dump valve45B is opened to allow the biomass contained within chamber46to fall into injection chamber47. In block66, piston48is advanced to drive biomass along channel49. The plug of biomass travelling along channel49pushes flap valve50open to allow the biomass to exit into reactor18. As this is occurring, additional syngas may be introduced into chamber52behind piston48. The introduction of the additional syngas prevents air from entering the system and also mixes syngas into the biomass being fed into reactor18. Oxidation of syngas in reactor18can further reduce the oxygen content within reactor18. In block67piston48is retracted. Blocks66and67may be repeated multiple times to deliver most or all of the biomass from chamber47into reactor18.

In an example embodiment, upper dump valve45A opens and allows biomass to fall into chamber46. Upper dump valve45A is then automatically closed. Vacuum valve59B is then opened for a period of time sufficient to withdraw a significant amount of air out of chamber46. For example, valve59B may open for 15 seconds. Piston48is then moved to a fully retracted position and lower dump valve45B is opened to allow biomass to fall from chamber46into injection chamber47. Lower dump valve45B is then closed. Syngas valve56is then opened so that syngas is delivered to chamber52behind piston48. Piston48is then advanced toward reactor18.

As piston48completes its travel, biomass being pushed in front of piston48through channel49is pushed into reactor tube70via flapper valve50. At the end of the stroke, syngas valve56is closed. Upper dump valve45A is then opened and simultaneously piston48is retracted back towards its fully retracted position. The cycle then repeats.

As shown inFIG. 6, reactor18comprises a tube70that passes through a furnace72. Reactor tube70may, for example, have a diameter in the range of 25 to 75 cm. In the illustrated embodiment ofFIG. 6, furnace72comprises two parts, a burner compartment74in which a fuel is burned to heat furnace72and an upper compartment76through which reactor tube70passes.

The burner which heats the furnace72may 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.

Baffles77in upper compartment76cause hot gases from burner compartment74to make intimate contact with reactor tube70as they pass through upper chamber76to an outlet (not shown inFIG. 6). In some preferred embodiments, the temperature in the reactor tube70may maintained in excess of 400° C. For example, the temperature in reactor tube70may be maintained in the range of 450 to 500° C. The operating pressure in reactor tube70may, for example, be approximately 35 to 50 kPa. The reactor temperature may be controlled by a temperature controller that is connected to a sensor monitoring the temperature of gases inside or exiting reactor tube70. The temperature controller may comprise, for example, a PID controller. The controller may, for example, control the temperature in reactor70by adjusting fuel and combustion air valves that control combustion in furnace72according to the deviation of temperature measured by the temperature sensor from a set point. In some embodiments, the hot gases exiting upper chamber76are carried from the outlet to dryer14where they pass countercurrent through dryer tube33to assist in drying the biomass passing through dryer tube33.

Reactor tube70is inclined at a descending angle so that biomass which enters through flap valve50is carried down through reactor tube70by the action of gravity. Flap valve50acts as a check valve to prevent the backflow of gases from reactor18into feed channel49.

The angle of inclination, θ, of reactor tube70may, for example, be on the order of 5 to 25 degrees. In a preferred embodiment, reactor tube70is sloped downward at a 20% (a one in five grade corresponding to an angle θ of approximately 11 degrees). Reactor tube70is rotated as the biomass passes through it. The rotation may be fairly slow. In one embodiment the reactor tube70rotates at a rate of less than 2 rpm. For example in one embodiment reactor tube70rotates at approximately ½ rpm.

The rotation of reactor tube70causes the biomass to tumble as it passes through the reactor tube. In the illustrated embodiment, rotation of reactor tube70is driven by a drive system78(not shown). Drive system78may, 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 tube70may vary depending on the diameter of tube70and the resistance time of biomass inside reactor tube70, which in turn is dependent on the feed rate of biomass into reactor18. More biomass input feed per unit time would require a reactor tube70having 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 tube70is, at least 15 minutes. For example, the residence time may be in the range of 20 to 25 minutes.

Reactor tube70has walls79that project into its interior. Each wall79is hollow and has at least one opening80which opens into the interior of furnace72. Hot gases from furnace72can enter openings80and heat walls79from the inside. Walls79in some embodiments are spaced a apart and are arranged in an alternating pattern while projecting into the interior of reactor tube70. Walls79may, for example, be spaced apart from one another by 6 inches (15 cm) in the direction along the longitudinal axis of reactor70. In some embodiments, walls79are unequally spaced apart along the longitudinal axis of reactor70. In particular, it can be advantageous for walls79to be spaced farther apart near the entrance of reactor70and to be spaced more closely toward the exit from reactor70. Near the entrance to reactor70entering biomass may have a moisture content high enough to make the biomass tend to stick together so that it flows over walls79with more difficulty than the drier biomass found closer to the exit from reactor70. Providing more widely-spaced walls79near to the entrance to reactor70facilitates passage of the biomass along the initial part of reactor70.

Some or all of walls79in some embodiments each project slightly more than half of the diameter of reactor tube70into reactor tube70and, in some embodiments extend at least 20% of their overall height past the centerline of reactor tube70(see e.g.FIGS. 9A and 9B). Thus, as viewed, looking along the length of reactor tube70from one end, walls79overlap with one another along the longitudinal centerline of reactor tube70. In some embodiments, walls79may be perpendicular to the centerline of reactor tube70or tilted on an angle.

In some embodiments, walls79may be on opposite sides of reactor tube70or may have a more offset arrangement. In some embodiments, walls79are non-planar. For example, walls79may be curved about axes of curvature that extend transverse to reactor tube70. In such embodiments the curvature may be such that center portions of walls79project toward the upstream or downstream end of reactor tube70.

Heated walls79both transfer heat into biomass passing through reactor tube70and act as mechanical lifts which mix and separate the biomass as it passes through the rotating reactor tube70. Heated walls79may be, for example, approximately 1½ to 3 centimeters in thickness.

FIG. 7illustrates how walls79, in one embodiment, cause biomass within reactor tube70to follow a sinuous path71as reactor tube70rotates and the biomass spills over one wall79to be caught by the next wall79as the biomass makes its way downward along reactor tube70.

FIG. 8shows a possible cross-section of a reactor tube70and illustrates how walls79projecting inwardly from opposing sides of reactor tube70may overlap with one another.

As illustrated inFIGS. 9A and 9B, hollow walls79may have various configurations.FIG. 9Aillustrates a configuration where hollow walls79are flat-topped. In some embodiments, the cross section of the top edge of hollow walls79may be rounded, square, or may take other shapes. In some preferred embodiments, the edges of hollow walls79are arcuate.FIG. 9Billustrates a configuration where hollow walls79have arcuate edges projecting into the interior of reactor tube70. In the embodiment ofFIG. 9B, arcuate edges82have a radius of curvature similar to that of reactor tube70. In this example embodiment, the areas of overlap between hollow walls79projecting from opposing sides of reactor tube70are lenticular-shaped when viewed end-on (i.e. along the longitudinal center line of reactor tube70).

Reactor tube70may be sealed at its ends to prevent the ingress of air. In an example embodiment, the upper end of reactor tube70is sealed by an annular packing attached to a tube through which channel49extends. The packing seals against the inside of reactor tube70while allowing rotation of reactor tube70. Tube support rollers may be attached to the packing or to a separate support to permit smooth rotation of reactor tube70. The lower end of reactor tube70may be sealed to a non-rotating reactor receiver by a packing gland which bears against the external surface of reactor tube70. In some embodiments, reactor tube70may be tapered so it becomes larger towards the outlet of reactor tube70.

In some embodiments, a grinder is provided at the output of reactor tube70. The grinder may grind chunks of charcoal produced by the pyrolisis of biomass in reactor tube70into 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 reactor18in separator20.

In some embodiments, separator20comprises 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 reactor18.

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 receptacle21.

Gas handling system22may treat the gases passed by separator20in 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 system22may comprise catalytic decomposition stages in which fractions of the producer gas from reactor18are 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 furnace72. 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 apparatus10. In other embodiments electricity generated by a syngas-driven generator is used to drive motion of some or all components of apparatus10. In other embodiments steam generated in cooling syngas and/or burning syngas is used to drive motion of some or all components of apparatus10.

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 furnace72; biomass dryer14; 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 apparatus10to yield char which may then be integrated into the soil at the farm. The apparatus10may be then taken to another location.

One possible arrangement for the components of apparatus10on a trailer100is illustrated inFIG. 10. Reference numbers inFIG. 10are the same as the reference numbers used above for components and assemblies of similar function. Details of construction of any of these components and assemblies may be but are not necessarily the same as are shown in the other drawings.

FIG. 10also shows a line101carrying producer gas to destinations including a flare102, furnace72and a gas heater104. Gas heated by gas heater104is carried by line106to a catalytic reactor108, a gas cooler110, a gas chiller112and a gas filter114. Gas filtered by filter114may be supplied as fuel for an engine or burner or taken off for some other use.

FIG. 10also shows an air line120carrying air that has been pre-heated by gas chiller112to furnace72and drier14and a line122carrying flue gas from furnace72to drier14.

INTERPRETATION OF TERMS

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.