| JP10325525 | HOPPER STRUCTURE FOR INCINERATOR |
| JP07035302 | METHOD FOR WARMING ALWAYS MILL OF COAL FIRED BOILER |
| WO/2011/071339 | TOP-FEEDING DOUBLE-SWIRL TYPE GASIFIER |
| 1. A device, comprising: a biomass intake assembly; a pyrolysis reactor; an ejector system; and a gas burner, the biomass intake assembly is coupled to the pyrolysis reactor to enable movement of biomass from the intake assembly into the pyrolysis reactor, and the pyrolysis reactor is coupled to the gas burner through the ejector system, which facilitates movement of a producer gas from the pyrolysis reactor and a primary combustion gas from a source of primary combustion gas into the gas burner. 2. The device of claim 1, wherein the ejector system comprises a producer gas conduit providing fluid communication between the pyrolysis reactor and the gas burner, and a primary combustion gas conduit within the producer gas conduit which provides fluid communication between the source of primary combustion gas and the burner. 3. The device of claim 2, wherein: the source of primary combustion gas is a high speed blower; having a blower flow pressure; the producer gas conduit is a first tube, which has a first diameter and a straight section of tube having a first length; the primary gas conduit is a second tube, which has a second diameter and a second length, the second tube is mounted coaxially within the straight section of the first tube; the ejector system has a mixing length defined by the first length minus the second length; and, the pyrolysis reactor comprises a third tube having a third diameter. 4. The device of claim 3, wherein: the ratio of the second diameter of the second tube to the first diameter of the first tube ranges from about 0.1 to about 0.4; the ratio of the ejector mixing length to the second diameter of the second tube ranges from about 5 to about 15; the ratio of the diameter of the first tube to the diameter of the reactor tube ranges from about 0.25 to about 0.75; the blower pressure ranges from about 5 to about 50 in a water column; the ejector system has an air temperature ranging from about 200 to about 400 degrees C; and, the producer gas has a temperature ranging from about 350 to about 650 degrees C. 5. The device of claim 3, wherein the first, second, and third diameter, the blower flow pressure, and the mixing length are chosen to match an induced mass flow of producer gas to gas production rate in the pyrolysis reactor, and to provide sufficient air for stoichiometric combustion of producer gas in the gas burner. 6. A device according to claim 1, further comprising a char storage assembly which is coupled to the pyrolysis reactor to permit movement of char from the reactor to the char storage assembly. 7. A device according to claim 6, further comprising a conveyance mechanism for moving biomass from the intake assembly through the pyrolysis reactor and into the char storage assembly. 8. A device according to claim 7, wherein the conveyance mechanism is a motor- driven auger enclosed in a conveyance tube and the pyrolysis reactor comprises a segment of the conveyance device upstream from the char storage assembly and a heater. 9. A device, comprising: a) a char storage assembly optionally comprising a conveyance mechanism for moving char from a bottom end of the char storage assembly toward a top end of the char storage assembly; b) a biomass reactor assembly comprising: i) an intake assembly comprising a feed system for metering biomass feedstock connected to a receiving chamber through an airlock; a conveyance device for moving biomass from the receiving chamber to the char storage assembly, the conveyance device has an entry end and an exit end; ii) a pyrolysis reactor comprising a segment of the conveyance device upstream from the char storage assembly and a heater; the segment having a venting port for releasing producer gas; iii) a gas burner having a first port for receiving both producer gas and a primary combustion gas, and a second port removed from the first port for receiving secondary combustion gas; iv) an ejector for moving producer gas and primary combustion gas into the gas burner, the ejector comprising a first conduit with a first end and a second end and a second conduit mounted coaxially within the first conduit, wherein the first end of the first conduit is connected to the conveyance device at the venting port and the second end of the first conduit is connected to the gas burner at the first port; and, c) a source of combustion gas, having a third conduit for delivering the combustion gas; wherein, the second conduit is fluidly connecting to the third conduit through a first t-fitting, and a fourth conduit is fluidly connected at a first end to the third conduit through the first t-fitting and fluidly connected at a second end to the second port. 10. A method of separating char from producer gas, comprising: pyrolysizing biomass in a pyrolysis reactor having a venting port, and facilitating the movement of producer gas through the venting port using an ejector system comprising a first conduit and a second conduit, wherein: the first conduit has a straight section and a first end and a second end, the first end is coupled to the venting port; the second conduit has a first end and a second end, is coaxially mounted within the straight section of the first conduit, and the second conduit's first end is configured for coupling to a source of gas and the second conduit's second end terminates within the first conduit prior to the second end of the first conduit. 11. A method for producing renewable thermal energy and biochar, comprising introducing biomass into the device of claim 1 and operating the device of claim 1. 12. A method for producing renewable thermal energy and biochar, comprising using the device of claim 9 and operating the device of claim 9. 13. A method of producing renewable thermal energy and biochar, comprising: pyrolysing biomass in an anaerobic pyrolysis reactor to produce producer gas and biochar; facilitating the movement of producer gas through a vent in the pyrolysis reactor into a gas burner using an ejector system, thereby separating the producer gas from the biochar, wherein the ejector system comprises a producer gas conduit providing fluid communication between the pyrolysis reactor and the gas burner, and a primary combustion gas conduit within the producer gas conduit which provides fluid communication between a source of primary combustion gas and the burner. 14. A method of producing a carbon credit, comprising: producing biochar according to claim 13, moving the biochar into a char storage container, and optionally using at least a portion of the biochar as a soil amendment. 15. A device according to claim 1 or 9 wherein the intake assembly further comprises a pre-dryer. |
AND BIOCHAR CROSS REFERENCE TO RELATED APPLICATIONS
This application claims benefit of priority to U.S. Provisional Patent Application No. 61/431,329, entitled, "DEVICES FOR AND METHODS OF MAKING RENEWABLE THERMAL ENERGY AND BIOCHAR," filed January 10, 2011, which application is incorporated herein by reference in its entirety.
FIELD
The specification generally relates to devices for producing renewable thermal energy, biochar, and/or carbon credits. The specification also generally relates to methods for producing renewable thermal energy, biochar, and/or carbon credits.
BACKGROUND
Development of renewable energy is receiving increased attention due at least in part to economic, energy security, and climate change concerns related to continued reliance on fossil fuels. Biomass (e.g. cellulosic plant matter) is one potential source of renewable energy. For example, thermal energy can be produced by biomass pyrolysis, which involves anaerobic heating of plant matter. At temperatures ranging from about 350 degrees C to about 700 degrees C, cellulose, hemicellulose, and lignin break down into volatile gases (syngas), condensable vapors (which condense to tars and bio-oil at room temperature), and a porous solid char
(biochar). The gases and vapors (together, "producer gas") can be premixed with air and combusted in a gas burner producing renewable thermal energy for firing conventional boilers, furnaces, dryers, or other thermal devices. SUMMARY
The specification relates to biomass pyrolysis devices, and methods of producing renewable thermal energy, biochar, and/or carbon credits. In some embodiments, the pyrolysis devices include a reactor in which producer gas is manufactured on a continuous basis, a burner in which the producer gas is combusted together with a combustion gas, and an apparatus for using high pressure combustion gas (such as air) to suck the producer gas from the reactor into the burner. In some
embodiments, the reactor and the burner are close-coupled to maintain the temperature of the producer gas, for example at a level suitable for combustion or compatible for use in the burner. In some embodiments, the methods involve using low grade biomass fuels in combination with biomass pyrolysis devices according to this disclosure to combust gas, which can be used, for example, in boilers.
According to some embodiments, the devices comprise a biomass intake assembly, a pyrolysis reactor, an ejector system, and a gas burner. In some embodiments, the devices also comprise a biomass pre-dryer. The intake assembly enables movement of biomass into the pyrolysis reactor. In some embodiments, the intake assembly enables continuous movement of biomass into the pyrolysis reactor in a controlled manner. The biomass undergoes pyrolysis in the reactor to form producer gas and char. The ejector system couples the reactor and the gas burner, and facilitates mixing of a primary combustion gas with the producer gas, as well as movement of the producer gas from the reactor into the burner. The primary combustion gas is typically pre-heated to a temperature that is compatible for mixing with the producer gas, for example to temperature sufficient to prevent or alleviate condensing the tar and oil fractions of the producer gas stream upon mixing.
According to some embodiments, the devices also include a char storage container which receives char from the reactor. In some embodiments char storage containers are used for temporary storage of the char and the devices include an assembly, for example a pneumatically-operated conveyance system, for removing the char from the char storage container into a second, more permanent char storage container. According to some embodiments, the ejector system comprises a producer gas conduit and a primary combustion gas conduit, the producer gas conduit provides fluid communication between the pyrolysis reactor and the gas burner, the primary combustion gas conduit provides fluid communication between a source of combustion gas and the gas burner, and the primary combustion gas conduit is located within the producer gas conduit, for example in coaxial alignment.
According to some embodiments, the device comprises an intake assembly, a thermal energy and char production unit (biomass reactor), and a char storage container interconnected by a conveyance mechanism for moving biomass through the device. The biomass reactor further comprises a pyrolysis reactor, a gas burner, a source of combustion gas, and an ejector system, and the device can further comprise an optional biomass pre-dryer. The device can also include an exhaust duct having a damper control for controlling the flow rate of combustion products around the device. The ejector system fluidly interconnects the pyrolysis reactor with the gas burner, and the source of combustion gas with the gas burner. In some embodiments, the ejector system comprises a producer gas conduit that fluidly connects the pyrolysis reactor with the gas burner, and a primary combustion gas conduit that fluidly connects the source of combustion gas with the gas burner. The primary combustion gas conduit is located at least partially within the producer gas conduit and, for example, in coaxial alignment with the producer gas conduit. In some embodiments, the gas burner is alternatively or in addition fluidly connected to the source of combustion gas by a secondary combustion gas conduit, and a suitable connection such as a t-fitting fluidly interconnects the combustion gas source with the primary combustion gas conduit (and hence the ejector system) and the secondary combustion gas conduit (and hence the gas burner). In some embodiments, the pyrolysis reactor and gas burner are close-coupled to maintain at least the producer gas and (in some embodiments also the combustion gas) at a temperature sufficient to prevent or alleviate condensation of tar and oil fractions of the producer gas. In some embodiments, the intake assembly includes a hopper or intermediate biomass feed metering system, an optional pre-dryer, an airlock, and a receiving chamber. The hopper or intermediate biomass feed metering system receives biomass, which is moved into the receiving chamber after passing through the airlock and optional pre-dryer. In some embodiments, a conveyance mechanism such as a motor-driven auger can be used to help move the biomass across the length of the hopper and optional pre-dryer toward the entryway of the airlock. According to some embodiments the airlock is a rotary airlock, but the airlock can be any device that restricts the flow of air with the biomass into the receiving chamber. According to some embodiments, the reaction chamber can also include a device for automatically shutting off further movement of biomass into the reaction chamber of the system when the device senses that the reaction chamber contains a predetermined amount of biomass.
In some embodiments, the pyrolysis reactor can simply be a segment of the conveyance mechanism located upstream from the char storage container, at least a portion of which is heated by a heating device. In some embodiments, the heating device can be an electrical resistance band heater, which contacts and wraps around the conveyance device. In some embodiments, the heating device can be, among other options, a burner that uses a gaseous fuel such as natural gas or propane or the biomass producer gas itself. In some embodiments, the pyrolysis assembly converts biomass into producer gas and biochar using a slow pyrolysis process. In some embodiments, an ejector is used to fluidly connect the pyrolysis reactor to the gas burner and both induce movement of producer gas from the pyrolysis reactor to the gas burner as well as enable a primary combustion gas such as air to mix with the producer gas prior to combustion in the burner. In some
embodiments, the ejector can include a first conduit fluidly linking the pyrolysis reactor to the gas burner and a second conduit passing longitudinally through the interior of the first conduit and fluidly linking the source of primary combustion gas to the gas burner.
In some embodiments the gas burner in the biomass reactor assembly is capable of both primary combustion of a mixture of producer gas and primary combustion gas and secondary combustion of a secondary combustion gas. In some embodiments, the primary combustion gas and secondary combustion gas are provided by the same source, for example by a high speed blower, and a suitable connector such as a t-fitting having three openings is used to fluidly interconnect the blower with the ejector system to provide the primary combustion gas and to fluidly interconnect the blower with the gas burner to provide the secondary combustion gas. For example, a first opening of the t-fitting can connect to a conduit for conveying the primary and secondary combustion gas from the high speed blower or combustion gas blower. A second opening can connect to the outside of the burner head to provide secondary combustion gas, such as air, to, for example, a small annular opening or arrangement of circumferential holes around the periphery of the burner head. The third opening can connect to a conduit, which attaches to the ejector and provides primary combustion gas, such as air, into the ejector. The reactors can be sized to meet the heating needs of a given space, including home heating and larger commercial or industrial building heating. A portion of the thermal energy can also be diverted for heating the pyrolysis assembly. A portion or all of the producer gas can be diverted to feed a burner used to heat the pyrolysis assembly. A portion or all of the excess thermal energy can be used to dry the incoming biomass material.
The biochar can be temporarily stored in the char storage assembly, which is sealed to limit or prevent the entry of air into the biochar reactor and to avoid having the heated biochar spontaneously ignite. At appropriate intervals, the char storage assembly can be fully or partly emptied, for example into transportable storage containers. In some embodiments, the char storage assembly also includes a cooling unit for reducing the temperature of the char prior to emptying the char storage assembly. In some embodiments, biochar is removed from the char storage assembly only after the heater associated with the pyrolysis device has been allowed go cool to an appropriate temperature, or for example turned off for a period of time sufficient for the biochar to cool to an appropriate temperature. In some embodiments, the storage assembly can be emptied by a vacuum control device, which moves the char into transportable storage containers.
The specification also relates to methods for producing thermal renewable energy and biochar.
According to some embodiments, the process involves receiving a biomass feedstock, for example a low grade biomass feedstock, in a hopper; feeding the biomass feedstock through an airlock into a receiving chamber; moving the biomass through a pyrolysis reactor; heating the biomass as it moves along the pyrolysis reactor to convert it to producer gas and biochar; conveying the biochar from the pyrolysis reactor to a sealed storage container; venting the producer gas through a vent tube in the pyrolysis reactor, for example a vent tube on the top of the pyrolysis reactor, and into a gas burner; premixing the producer gas with a primary combustion gas such as air before delivery to the gas burner; and, supplying the primary combustion gas through a conduit mounted coaxially within the producer gas vent tube. In further embodiments, the process also involves preheating the combustion gas source prior to mixing with the producer gas, for example to a temperature sufficient to prevent or alleviate condensation of tar or oil fractions from the producer gas. In yet further embodiments, the process also involves supplying a secondary combustion gas at or downstream of the gas burner flame retention head.
In some embodiments, the biomass material is relatively uniform, relatively small in particle size, for example less than l/10 th the size of the reactor cross-section, and contains less than from about 20 to about 25% moisture. In some embodiments, the biomass is loose and non-uniform. In some embodiments, the biomass is in densified form, such as pellets or briquettes.
In some embodiments, the biomass is moved through the pyrolysis reactor by way of an auger or coreless rotating helix. In some embodiments, the residence time of the biomass in the pyrolysis reactor ranges from about 2 to about 15 minutes.
In some embodiments, the biomass feedstock is loaded into a pre-dryer prior to passing through the airlock. For example, the pre-dryer can extend across the unit and when biomass feedstock is moved by a conveyer mechanism across the pre- dryer to the airlock, it is dried by application of heat given off from the reactor and/or burner. The pre-dryer can have a perforated top or other means to allow moisture to escape. In some embodiments, the biomass is heated by external application of heat to the reactor tube such as by a resistance electrical heater, a microwave heater, or a gas burner using gas from an external supply or in a regenerative mode by using gases produced directly from the biomass material. In some embodiments, the biomass is heated internally through the auger. In some embodiments from about 30% to about 50% by mass of the original biomass remains as char following pyrolysis.
In some embodiments, the velocity and mass flow of secondary gas through the coaxially-mounted conduit is controlled to result in an essentially neutral or slightly negative pressure in the pyrolysis reactor relative to outside ambient pressure to minimize entry of air into the pyrolysis reactor through the airlock, biochar storage container, or elsewhere.
In some embodiments, the primary combustion gas is preheated to a temperature of at least about 200 degrees C, prior to mixing with the producer gas. In some embodiments, the primary combustion gas is preheated to a temperature sufficient to avoid condensing the tar and oil fractions of the hot producer gas stream on mixing.
In some embodiments, the process parameters include the biomass feed rate, the pyrolysis reactor gas pressure and outlet temperature, and the oxygen levels in the combustion exhaust.
The specification also relates to a method of separating char from producer gas produced in a biomass pyrolysis reaction. In some embodiments, the method involves pyrolyzing biomass in a pyrolysis reactor having a venting port, and facilitating the movement of producer gas through the venting port using a source of high pressure primary combustion gas to suck the producer gas from the reactor into the burner. In some embodiments, movement of the producer gas is
accomplished by an ejector system comprising a first conduit and a second conduit, wherein: the first conduit has a straight section and a first end and a second end, the first end is coupled to the venting port; the second conduit has a first end and a second end, is coaxially mounted within the straight section of the first conduit, and the second conduit's first end is configured for coupling to a source of gas and the second conduit's second end terminates within the first conduit prior to the second end of the first conduit.
The specification also relates to a method of producing carbon credits and the carbon credits produced thereby. In some embodiments, the method involves pyrolyzing biomass to produce producer gas and char, separating the biomass and char using an ejector system that induces flow of producer gas out of the pyrolysis reactor, and moving the remaining char into a char storage unit, and optionally removing the char from the storage unit and using it as a soil amendment or in another capacity wherein the entrained carbon creates a carbon credit. In some embodiments, the process represents a carbon negative cycle capable of creating carbon credits. For example, devices in accordance with the present disclosure generate char and producer gas from biomass. A portion of the carbon absorbed by the biomass during growth is present in the char and a portion is in the producer gas. Accordingly, only a portion of the carbon originating from the atmosphere is returned to the atmosphere, the remainder being sequestered in the char, which undergoes slow, limited or essentially no oxidation.
While the disclosure provides certain specific embodiments, the invention is not limited to those embodiments. A person of ordinary skill will appreciate from the description herein that modifications can be made to the described embodiments and therefore that specification is broader in scope than the described
embodiments. All examples are therefore non-limiting.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an embodiment of a biomass reactor assembly.
FIG. 2 is a transparency view of the biomass reactor assembly of FIG. 1.
FIG. 3 is a view of a portion of the interior components of an embodiment of the reactor assembly.
FIG. 4 is a top view of a portion of the components of an embodiment of the burner assembly.
FIG. 5 is a view from the intake end of the biomass reactor assembly embodiment of FIG. 1.
FIG. 6 is an end view of the burner assembly embodiment of FIG. 4.
FIG. 7 is a transparency view of another embodiment of a biomass reactor, wherein the reactor includes a pre-dryer.
FIG. 8 is a top view of the pre-dryer of the embodiment of FIG. 7. DETAILED DESCRIPTION
The specification discloses systems and processes for biomass pyrolysis and biochar production. The specification will describe certain non-limiting embodiments of the invention with reference to the drawing figures in which like reference numerals refer to like parts throughout.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. In the event that there is a plurality of definitions for a term herein, those in this section prevail unless stated otherwise.
Where ever the phrases "for example," "such as," "including" and the like are used herein, the phrase "and without limitation" is understood to follow unless explicitly stated otherwise.
The terms "comprising" and "including" (and similarly "comprises" and "includes") are used interchangeably and mean the same thing. Specifically, each of the terms is defined consistent with the common United States patent law definition of
"comprising" and is therefore interpreted to be an open term meaning "at least the following" and also interpreted not to exclude additional features, limitations, aspects, etc.
The term "about" is meant to account for variations due to experimental error and/or measurement error or limitations.
Where ever the terms "a" or "an" are used, "one or more" is understood, unless such interpretation is nonsensical in context. For example "a char storage assembly" means "one or more char storage assemblies". The term "biomass" should be interpreted expansively and includes for example, woody and agricultural feedstock, animal manure, and biosludge (sewage sludge). Although the device described herein is generally referred to for use with biomass, it is not limited to pyrolysis of biomass feedstock but can be used for pyrolysis of any compatible feedstock.
Referring now to the drawings, an embodiment of a biomass pyrolysis device 10 in accordance with the invention is shown in FIG. 1. The pyrolysis device 10 includes a thermal energy and char production unit 20 ("the unit 20"), a char storage assembly (unit) 60, an intake 50, and a power supply (not shown) and control panel 23. The intake 50 receives and empties biomass feedstock into the unit 20, wherein the biomass is converted to producer gas and biochar, the producer gas is separated from the biochar and combusted into thermal energy, and the biochar is conveyed into a char storage container 63. The unit 20, and particularly the reactor tube 35 (shown in FIG. 2) is sized according to the heating needs of the space being heated. In some embodiments, the unit 20 ranges in size from about 20,0000 Btu/hr to about 5,000,000 Btu/hr, which correspond to a biomass feed rate ranging from about 51b/hr to about 1500 lb/hr. In some embodiments, the unit 20 ranges in size from about 50,0000 Btu/hr to about 5,000,000 Btu/hr, which correspond to a biomass feed rate ranging from about lOlb/hr to about 1500 lb/hr. The control panel 23 can be used to control process parameters such as but not limited to biomass feed rate, reactor gas pressure and outlet temperature, and oxygen levels in the combustion exhaust. FIG. 1 also shows the pyrolysis device 10 attached to a boiler 70, which is heated by the generated thermal energy, and which distributes hot water around the space to be heated through a system of hot water radiators. The pyrolysis device 10 can be attached to any thermal device, including boilers, furnaces and dryers. FIG. 2 is a transparent perspective of the biomass pyrolysis device 10 of FIG. 1, enabling a view of some of the internal components of the unit 20 and char storage assembly 60. The unit 20 comprises an enclosure 27 containing an intake assembly 21, a reactor 30, and a gas burner 40. Insulation 11, 12 is provided around the reactor 30 and gas burner 40 respectively. The char storage assembly 60 can include a sealed barrel 63 equipped with a conveyance mechanism for moving biochar through the barrel 63. In the illustrated embodiment, the mechanism is an auger 62 and in an upward direction. A motor 64 is mounted on the barrel 63 and operably connected to the control panel 23 and auger 62. Alternatively, the biochar can be discharged from the end of the reactor tube into the top of the char storage chamber 60 under gravity.
In some embodiments, the pyrolysis device 10 is designed to cooperate with existing boilers, or other thermal devices, to enable users to convert existing systems, for example oil- or propane-based systems, to biomass-based systems. As can be seen in Fig. 2 (better identified in Fig. 3), the unit 20 is configured with a flange 65 to connect to a pre-existing boiler unit. Typically, the connection point for pre-existing boilers is less than a foot off of the ground, and therefore the various components of the unit 20 are configured to enable the device 10 to connect to the boiler at that height. Although Figs. 1 and 2 depict the intake 50 as a funnel, other possibilities are contemplated, as long as there is an opening to permit entry of biomass into unit 20. In some embodiments, it is contemplated that in the same or similar way that propane and oil is bulk delivered by trucks, and used to fill propane and oil storage tanks which are connected to oil and propane-based heating systems by an automatic feed system, biomass such as in pellet form may also be bulk delivered by trucks, used to fill storage tanks on site which are connected to the biomass pyrolysis devices 10 by an automatic feed system.
Although the figures depict the device 10 as having the reactor 30 and gas burner 40 positioned in the same horizontal plane, alternative configurations are possible. For example the reactor 30 and gas burner 40 can be configured in the same vertical plane or at any angle in between. Similarly, although the figures depict the bottom of the char storage container 60 as being level with the bottom of the unit 20, the relative positions of the char storage container 60 and unit 20 can vary, for example the bottom of the char storage container 60 can be positioned lower than the bottom of the unit 20, and/or the conveyance mechanism connecting unit 20 and the char storage container 60 may be angled. In such a configuration, gravity may provide assistance in the movement of char within the char storage unit and/or biomass and/or char through the device 10.
FIG. 3 provides an interior view of some of the components of the biomass pyrolysis device 10. As is shown, in the illustrated embodiment, the biomass pyrolysis device 10 is equipped with an exemplary conveyance mechanism for moving biomass through the unit 20 into the char storage container 63. The conveyance mechanism
32 can be a mechanical rotary mechanism such as a rotary screw or auger 33 as shown. A motor 37 is mounted on or within the unit 20 and operably connected to auger 33 and control panel 23 (not shown in Fig. 3). As illustrated, the conveyance mechanism 32 is a motor 37-driven auger 33 enclosed in a tube 39. Although a single auger 33 is illustrated, multiple inter-twined augers can be used for conveying the biomass (and later the resultant char). Similarly, although an auger
33 is illustrated, any other suitable conveyance device can be used such as for example a coreless rotating helix. In addition, the conveyance mechanism may be equipped with a reversible motor to reverse the flow of biomass periodically down the reactor tube 39 thereby further mixing the biomass material and increasing the heat transfer to the biomass material. In any event the conveyance mechanism 32 should be enclosed to reduce or prevent the entry of air, and maintain an anaerobic reactor environment. As shown in FIG. 3, the auger 33 is enclosed within a tube 39, and where the auger 33 is exposed to other components of the pyrolysis device 10, the tube 39 is in sealed engagement with those components. Although the conveyance mechanism 32 is illustrated in a horizontal position, it could also be angled for example such that the force of gravity could assist in the movement of biomass (and biochar) through the system. As further shown in FIG. 3, the intake assembly 21 has an intermediate feed system 24 for metering the biomass feedstock. The feed system 24 is connected to a receiving chamber 29 via a feed airlock 28. The feed system includes a motor- driven auger (not shown) for moving biomass toward an entry to the airlock 28. Alternatively this auger tube may be mildly heated by the exhaust gases of the producer gas burner to evaporate moisture in the incoming biomass fuel. The motor 26 is mounted on the feed system 24 and operably connected to the feed- system auger (not shown) and control panel 23 (not shown in Fig. 3). The feed airlock 28 can be a rotary airlock as illustrated or it can be any device that can restrict the flow of air with the biomass into the receiving chamber 29. For example, a tapered screw auger rotating inside a similarly tapered tube and connected to the inlet of the reactor auger 33 can serve to restrict the airflow while the biomass is being fed. The feed airlock 28 may be operably connected to the control panel 23 (not shown in Fig. 3), optionally together with sensing and/or timing devices to control the functioning of the feed airlock 28, for example to prevent the reactor from building up too much pressure, and/or to control the feed rate, and/or stop the delivery of feed to the receiving chamber altogether. For example, the intake assembly 21 also includes a proximity switch 25 that stops conveyance of biomass into the receiving chamber when the receiving chamber contains a predetermined amount or level of biomass.
The unit 20, as also illustrated in Figs. 4 and 5, also includes a reactor 30, which, as shown, comprises a segment of the conveyance mechanism 32 ("the reactor tube 35") and a heater 34 for heating at least a portion of reactor tube 35 and biomass therein. The heater 34 can be an electrical resistance band heater as shown, or any other device capable of heating the biomass within the pyrolysis reactor 30. Some non-limiting examples of heaters include a microwave heater, a gas burner using gas from an external supply or in a regenerative mode using gases produced directly from the biomass material once the pyrolysis device has been running and producing those gases. In the embodiment shown, the reactor tube 35 is cut away at the receiving end to join with the open bottom end of the receiving chamber 29 to permit passage of biomass into the reactor 30. The receiving chamber 29 and reactor 30 can be in sealed engagement to prevent or limit the entry of air into the reactor 30. The unit 20 also includes an ejector system 48, a source of combustion gas 49(Fig. 2) and a gas burner 40. As shown, the ejector system 48 comprises a first conduit 43 (also referred to as a producer gas tube 43) at least partially enclosing a second conduit 46 (also referred to as an ejector tube 46). The first conduit 43 provides fluid communication between the reactor tube 35 and the gas burner 40. The second conduit 46 provides fluid communication between the first conduit 43 and source of combustion gas 49 (Fig. 2). As shown the first conduit 43 has a straight section connected to the gas burner 40 and the second conduit 46 is mounted in coaxial alignment with the straight section of the first conduit 43. The second conduit 46 terminates within the first conduit 43. This configuration can induce movement of producer gas from the reactor tube 35 to the gas burner 40, and the mixing of primary combustion gas with producer gas prior to entry into the gas burner 40.
In some embodiments, the ejector system 48 is designed to continuously remove the producer gas generated by pyrolysis of the biomass fuel in the reactor tube 35 and deliver it to the inlet of the gas burner 40. In the process, the reactor tube 35 is maintained at a pressure designed to minimize the flow of outside air or internal gases through the airlock 28. For example, the pressure can be neutral
(atmospheric) pressure or slightly below atmospheric pressure. The pumping fluid can be the combustion gas or air delivered by the high pressure blower 49 (Fig. 2). This pumping fluid (e.g. combustion gas or air) is first preheated as it is moved through a heat exchanger coil 44 or other similar device that extracts excess heat from the reactor tube 35. A producer gas tube 43 connects the reactor tube 35 to the inlet of the gas burner 40 in a gas tight manner. The ejector air tube 46 is mounted coaxially inside the straight section of the producer gas tube 43. When the pumping fluid (e.g. combustion gas or air) is forced through the ejector tube 46 it leaves as a jet with a given velocity. The friction of this jet causes turbulent mixing of the jet with its surrounding fluid (producer gas) which is then pulled along with the jet of combustion gas or air. The jet velocity and tube diameter (i.e. mass flow) along with downstream mixing length and duct configuration (bellmouth and diverging diffuser tube) determine the subsequent induced flow and suction pressure in the surrounding fluid. The design of the blower flow characteristic (flow vs pressure vs rpm) and the relative sizing of the ejector tube 46 and the producer gas tube 43 and the mixing length and configuration downstream of the exit of the ejector tube 46 are carefully sized in order to match the induced mass flow of producer gas to the gas production rate in the reactor tube 35 (i.e. neutral pressure), and to provide sufficient pumping fluid (e.g. combustion gas or air) for
stoichiometric combustion of the producer gas in the downstream gas burner 40. Non-limiting examples of the relative sizing range of these components and the flow conditions to provide the desired function include:
Diameter of producer gas tube/diameter reactor tube ranges from about 0.25 to about 0.75;
Diameter ejector tube / diameter producer gas tube ranges from about 0.1 to about 0.4;
Ejector mixing length / ejector tube diameter ranges from about 5 to about
15;
Blower pressure ranges from about 5 to about 50 in water column;
Ejector gas temperature ranges from about 200C to about 400C; and
Producer gas temperature ranges from about 350C to about 650C.
The gas burner 40, as shown in FIGS. 4 and 5, can include a spark plug or other similar device 45 to ignite the flame. The gas burner 40, as shown, includes a venturi section 47 in fluid communication with the reactor 30. As shown, the venturi section 47, is connected by the producer gas conduit 43 through a port in the gas burner 40 to a venting port 66 on the top of the reactor 30. The gas burner 40 may also have a second port through which the secondary combustion gas can be delivered to accomplish secondary combustion. The gas burner 40 is in fluid communication with a blower 49 which generates combustion gas or air for both primary and secondary combustion and for inducing flow of the producer gas from the reactor 30 to the burner 40. The gas burner 40 is connected to the blower through a conduit, which has a first portion 52 and a second portion 53 connected together by a t-fitting 42. The ejector tube 46 is also connected to the blower through the second conduit portion 53 and t-fitting 42. Conduit 53 may optionally serve as a heat exchange conduit and be wrapped around reactor tube 35 in heat exchange relation to permit the combustion gas or air within the conduit 53 to be heated by the hot contents of the reactor tube 35. The combustion gas or air can also be heated by any other suitable means such as by the separate burner used also for heating the reactor tube.
As shown in Fig. 3, the char storage unit 60 is connected to the reactor 30 by a second or continuing segment of the conveyance mechanism 32. In the illustrated embodiment, the conveyance mechanism 32 extends into the center of a sealed barrel 63. The char storage unit 60 also includes a second conveyance device 61, also shown as a single motor 64-driven auger 62 for moving the char in an upward direction. The storage unit 60 is generally for temporary storage of the biochar.
In some embodiments, the storage unit 60 includes a device for transferring at least a portion of the biochar to another container. The device may be a vacuum operated device that transfers the biochar pneumatically to a transportable storage container after the biochar has cooled sufficiently to prevent any likelihood of spontaneous ignition, for example while the reactor is in shut down mode. For example, a vertical steel tube can be mounted in the top lid of the char storage container 63. The steel tube can extend to a point near the bottom of the container 63. The tube can be in the form of a Tee or other such configuration at the inlet (bottom of the storage container 63) to enable more extensive removal of the biochar from the flat bottomed container. The outlet of this vertical tube is connected to a larger more permanent storage bin, preferably located outside of the building, by a flexible tube. The outside storage bin can be emptied periodically into a transportation vehicle for delivery to a consolidation site for subsequent sale and distribution into the appropriate market. The outside storage bin contains a vacuum system for sucking the biochar material out of the sealed container next to the reactor/boiler system and through the flexible connecting tube. In some embodiments, the vacuum system would be triggered by a proximity level sensor and a temperature sensor in the sealed container and would only be operable when the reactor is in shut down mode and the biochar is cool. FIG. 7 illustrates an embodiment of a biomass pyrolysis device 100 including a pre- dryer 110. The pre-dryer is equipped with a mechanism for moving biomass across the pre-dryer to the intake assembly 21. The mechanism can be a motor 150-driven auger 160. In the illustrated embodiment, the pre-dryer is heated (causing removal of moisture from the biomass) by thermal energy created by the device 100 when biomass is pyrolyzed in the reactor tube 30 and/or combusted in the burner. The pre-dryer 110 may have a perforated top 111, as shown in Fig. 8, or other suitable means to enable moisture to escape.
Similar to the embodiment of FIG. 2, the device 100 includes an enclosure 27 containing an intake assembly 21, a reactor 30, and a gas burner 40. A biochar removal system 120 is equipped with a mechanism from removing biochar from the reactor 30 outside the device 100, for example to a char storage unit (not shown). The char moves through an airlock 130 prior to entering the storage unit. The device 100 may be connected to a boiler (not shown) at the gas exhaust 140.
The device 100 also includes a conveyance mechanism 32, which can be a mechanical rotary mechanism such as a rotary screw or, as is illustrated, a motor 37-driven auger 33 enclosed in a tube 39. The conveyance mechanism 32 moves biomass delivered to it through an airlock 28 in the intake assembly 21. The conveyance mechanism 32 also functions as a reactor tube 30, which is heated by combustion of gas in the burner 40 and/or a heating system such as a gas-fired heating system 170. The gas-fired heating system 170 can be used to provide heat to the system on start-up.
Char moving out of the combustion chamber 40 is conveyed by the removal system 120 which has a motor-driven auger (partially visible) 180.
The device 100 also includes an ejector system 48 and a source of combustion gas
49. The ejector system 48 is similar to that described in connection with the embodiment of FIGS. 1 and 2, operating on the same principle that high pressure combustion gas can be used to suck producer gas into the gas burner 40, and will not be further described. In some embodiments, approximately 80% of the thermal energy generated by the device 100 goes to the boiler (not shown) and about 20% of the generated thermal energy is used by the device 100 itself, for example to heat the pre-dryer, reactor tube 30 and/or maintain the temperature of the producer and/or combustion gases.
Device 100 also includes a movable baffle 190 to help regulate the temperature of the reactor tube 30. When the baffle 190 is closed, gases can move vertically over the reactor tube 30 and if open can bypass the reactor rube 30.
In operation, biomass feedstock is introduced into the device 10 through an intake
50. The biomass material can be any type and grade of woody or agricultural cellulosic residue in loose or densified form, including animal manures or biosolids (dried sewage sludge) for instance. In some embodiments, the biomass is low grade biomass including: agricultural residues such as from corn, hay, corn stover; animal manure such as poultry litter; and/or biosolids such as dried sewage sludge. In some embodiments, the biomass material contains no more than about 25% moisture on a wet matter basis at the point where it enters the inlet assembly to the reactor. In some embodiments, the biomass material contains no more than from about 20% on a wet matter basis at the point where it enters the inlet assembly to the reactor. In some embodiments the moisture level of the biomass material is chosen to maintain suitable operability of the gas bas burner, for example the moisture levels are chosen to limit the amount of moisture levels in the producer gas to a level at which the producer gas can still ignite and maintain a stable producer gas flame. In some embodiments, the biomass material is relatively uniform in size and has a particle size cross-section of about l/10 th or less that of the cross-sectional size of the pyrolysis reactor. Larger particle sizes may need to be prescreened or size reduced if they tend to hold up a smooth flow through the inlet feed system. In the embodiment shown in FIG. 1, the biomass material may have a diameter of l/10 th or less the diameter of the reactor tube 35.
According to some embodiments, biomass is moved through the device 10 through a combination of gravity and motor-driven augers. Initially, gravity feeds the biomass through the intake 50 into the hopper 24. A motor 26-driven auger (not shown) within the intermediate feed system or hopper 24 moves biomass above the entrance to the feed airlock 28. (In the embodiment of FIG. 7, a motor-driven auger moves the biomass across the burner to dry the biomass before moving into the airlock.) The biomass drops down into the receiving chamber 29 through the feed airlock 28, which restricts the flow of air with the biomass into the receiving chamber 29 and therefore the reactor 30. The operation of the motor 26 and airlock 28 can be programmed or manually controlled by user input at the control panel 23 to provide the desired and constant flow of biomass material to the reactor. In addition, various sensors and timers can be strategically integrated in the system to automate control of the system. In some embodiments, the intake assembly 21 is equipped with an automatic shut off device 25, which prevents further delivery of biomass into the receiving chamber 29 upon sensing a pre-determined level of biomass in the receiving chamber using a remote proximity switch. In some embodiments, the speed of the auger can range from about 0.5 to about 5 rpm and the auger pitch can range from about 0.5 to about 2 times the auger diameter. In some embodiments, the speed and size of the auger are chosen to ensure a residence time of from about 2 to about 15 minutes for the biomass in the heated section of the reactor tube. The airlock 28 is controlled to provide biomass to the receiving chamber 29 at this desired rate.
The biomass material is slowly fed through the reactor tube 35 by way of a motor 37-driven auger 33 or a rotating coreless helix. The biomass material is heated and volatilized as it moves through at least a portion of reactor tube 35 by the external application of heat to the reactor tube 35 or internally through the auger shaft (not shown). As shown in Fig. 2, the reactor tube 35 is insulated 11 on the outside. In some embodiments, the insulation 11 surrounding the reactor tube 35 and band heater 34 assists to ensure that most of the heat is directed to heat up the biomass material moving inside the reactor tube 35. Various parameters may be controlled to optimize the pyrolysis reaction in the reactor 35, including the heat output of the band heater or gas burner 34, and the feed rate of the biomass in the reactor tube 35. The feed rate and residence time of the biomass fuel in the reactor 30 can be controlled by the speed of the auger 33. In some embodiments, the motor 37-driven auger 33 moves the biomass through the reaction tube to achieve a residence time for the biomass while it is being heated and undergoing volatilization during pyrolysis ranging from about 2 to about 15 minutes. The residence time and maximum temperature achieved by the biomass may determine the quality of the biochar, particularly the porosity of the char. In some embodiments, an optimum maximum temperature range is typically from about 450C to about 550C. The optimum residence time depends on the average particle size of the biomass and the rate of heat transfer to the biomass.
The pyrolysis reaction generally occurs over the temperature range of from about 300C to about 800C at atmospheric pressure. After pyrolysis, between about 30% to about 50% by mass of the original biomass remains as char depending upon the amount of carbon, ash and moisture in the original biomass material. The char continues to be moved by the auger 33 to the end of the reactor tube 35 and then into a sealed (no air) container 63, where it cools before removal to prevent any spontaneous ignition. Char produced by this process has value as a soil amendment, as a filter medium, for carbon sequestration, or as fuel.
As shown, the producer gas (syngas plus condensable vapors) is continuously vented through the top of the reactor tube 35 through a venting port and into producer gas conduit 43 where it is premixed with a primary combustion gas (e.g. air) before delivery to the gas burner 40. In other embodiments, the gas burner may be in any orientation relative to the reactor tube 35, for example above, beside or below the reactor tube 35 and consequently the producer gas may be vented from the top, the bottom or the side of the reactor tube 35 into the gas burner 40.
Regardless of the orientation, as shown in the embodiment of FIG. 3, the gas burner 40 is "close coupled" to the reactor tube 35 to maintain the gas stream at an appropriate temperature, such as for example to eliminate or reduce any
condensing of the tar and oils fractions in the gas stream, which can occur if the temperature falls below the dew point of these fractions, for example at
temperatures of about 200 degrees C or less. In some embodiments, the producer gas/air mixture temperature is maintained above about 350C but below the ignition temperature of about 650C. The air for premixing with the producer gas is supplied by a high pressure blower through a small ejector tube 46 that is mounted cooaxially within the producer gas vent tube 43. Another view of this arrangement is shown in Fig. 6. The higher velocity air jet acts as an ejector and induces flow of the producer gas where it creates turbulent mixing of the two flows before entering the venturi section 47 of the gas burner 40. The relative diameters of these 2 tubes and the downstream mixing length determines the amount of induced flow (and negative pressure) of the producer gas. The ejector flow creates a slightly negative pressure within the reactor tube 35 offsetting the positive pressure created by the volatilization of the biomass within the reactor 30. Careful balance of these two pressures by design of the air ejector permits the creation of an essentially neutral or slightly negative pressure relative to ambient within the reactor tube 35 thereby minimizing entry of air into the reactor tube 35 through the rotary airlock 28 or elsewhere.
Measurement of this differential pressure can be used to control the speed of the blower which provides combustion air to the ejector nozzle, thereby actively maintaining a neutral pressure.
The primary combustion gas which is premixed with the producer gas is preheated, either using the process heat or by heat from other sources or devices preferably to a temperature above which the tar and oil fractions of the hot producer gas stream will not condense on mixing. The temperature should therefore preferably be greater than the dew point of the producer gas, for example the temperature can be 200 degrees C or greater. Condensation of the producer gas could cause the air and gas passages to become blocked. As shown, the secondary gas is heated by having it flow through a conduit 53 which is in a heating exchange relationship with the reactor tube 35.
A second stream of combustion gas (e.g. air) is also supplied by the same blower (either prior to or after preheating) and injected into the burning gas stream at or downstream of the gas burner flame retention head for secondary combustion. Since the producer gas is a low calorific value gas (relative to natural gas or propane) and may contain additional moisture from the biomass material, a high temperature mesh screen or other similar proprietary devices attached to the burner head can help increase port loading and thereby improve flame stability over the range of the operating conditions. In Fig 6, a spark ignitor 45 or other suitable hot surface or flame ignitor is located in close proximity to and downstream of the burner flame retention head to provide ignition of the premixed producer gas. The ignitor or other suitable device provides continuous proof of flame following satisfactory ignition of the flame. This signal is used to reignite or safely shut down the system in the event of flame-out. In some embodiments, the control parameters include the biomass feed rate, the reactor gas outlet temperature and pressure differential, and the oxygen levels in the combustion exhaust. The biomass feed rate can be derived from calibration curves for specific materials and adjusted by a variable duty cycle to the drive motor to follow load demand. The reactor gas outlet temperature can be measured by thermocouple or thermistor and used to adjust the process heat input. High and low limits can initiate system shutdown. A lambda sensor (which measures the oxygen needed for good combustion) in the combustion exhaust can be used to adjust the blower speed for optimum combustion. Start up and shutdown procedures can be developed and implemented for safe and low emissions operation. Following boiler demand and for a first time or cold start up or after emptying the system of biomass fuel, the feed system can first be activated to provide sufficient fuel to fill the heated section of the reactor tube. The feed system is turned off and the heater and blower turned on. (For subsequent warm startups the feed system and heater/blower are initiated together). When the reactor reaches a predetermined minimum
temperature, typically 400C, the feed system can turn on again (if not already running) and the ignitor can be initiated until proof of flame is detected. Fine tuning of the blower speed within certain limits can be driven by differential pressure (primary) and lambda sensor (secondary) during operation. After the boiler outlet water temperature is satisfied a reactor shut down procedure can be initiated. The feed system and reactor heater can be shut off. The blower speed can follow a programmed ramp down over about 5 minutes in order to match the reducing flow of producer gas. After the flame is no longer detected the blower can be shut off.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concepts thereof. For example, the pyrolysis device may also include a pretreatment assembly prior positioned prior to the reactor (and/or prior to the intake assembly) to reduce the size of the biomass feedstock. As another example, the pyrolysis device may include a damper control in the exhaust duct to control the flow rate of combustion products around the reactor. It is understood, therefore, that this disclosure and the inventive concepts are not limited to the particular embodiments disclosed, but are intended to cover modifications within the spirit and scope of the inventive concepts including as defined in the appended claims. Accordingly, the foregoing description of various embodiments does not necessarily imply exclusion. For example, "some" embodiments or "other" embodiments may include all or part of "some", "other," "further," and "certain" embodiments within the scope of this invention.
WHAT IS CLAIMED IS:
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