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Method and Device to Compact Biomass - Liu, Henry
Method and Device to Compact Biomass
United States Patent Application 20090188160
The biomass log fuel has not been commercialized due to difficulties in mass-producing the logs at low cost. The current invention solves this problem by introducing a three-step compaction process: pre-compaction, final compaction, and ejection. While a rotary feeder/compressor is used to perform pre-compaction, a ram driven by a toggle mechanism performs final compaction rapidly and efficiently. A press implementing the three-step compaction is designed and described. This invention should improve the cost-effectiveness of biomass solid fuel or feedstock.
Biomass materials such as yard waste, corn stover and switchgrass are compacted at high pressure to form dense “biomass logs” without binder or heat. Biomass logs serve as a solid fuel for heating buildings, and as feedstock for bio-reactors for liquefaction or gasification. Densifying the uncompacted fluffy biomass reduces space needed for storage, decreases the number of vehicles needed to transport biomass, and increases the energy density of fuel.
Liu, Henry (Columbia, MO, US)
Lin, Yuyi (Columbia, MO, US)
Harby, Donald Wade (Warrensburg, MO, US)
Haynes, Kirk Lawton (Columbia, MO, US)
12/022603
C10L5/40; C10L5/36
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OLADAPO, TAIWO
HENRY LIU (2601 MAGUIRE BLVD., COLUMBIA, MO, 65201, US)
1. A method and device to compact loose biomass materials, without using heat or binder, in three steps including: Step 1, during which loose biomass material in powdered or particulate form is fed by gravity into the top of a vertical hollow cylinder (mold) in which the biomass is pre-compacted to a density in the range of 20% to 60% of the final density of the log(solid cylinder or tablet) produced: Step 2, during which the pre-compacted biomass is further compacted to a density up to 20% higher than the final density of the biomass log produced; and Step 3 during which the compacted biomass is pushed out of the mold to become a biomass log.
2. A method and device as set forth in claim 1, in which the biomass is pre-compacted by a rotary feeder/compressor that not only feeds the biomass into the mold beneath it but also compresses (pre-compacts) the biomass.
3. A method and device as set forth in claim 2, in which compaction of the biomass in step 2 is done by a force-providing ram (piston or plunger) that produces sufficient force to bind the biomass particles permanently together to form an agglomerated dense log.
4. A method and device as set forth in claim 3 in which the peak pressure of compaction in stage 2 is in the range of 12,000 to 23,000 psi.
5. A method and device as set forth in claim 4, in which a toggle mechanism is used to amplify the force on the ram so that the ram can provide the 12,000 to 22,000 psi peak pressure needed for producing the biomass log.
6. A method and device as set forth in claim 1, in which the loose material to be compacted is not biomass but has properties similar to biomass, and can be compacted into logs by using the same process as for the biomass.
7. A method and device as set forth in claim 1, in which a binder is used to aid in the agglomeration of the biomass logs.
8. A method and device as set forth in claim 6, in which a binder is used to aid in the agglomeration of the biomass logs.
9. A method and device as set forth in claim 1, in which the loose biomass material is fed into the mold, in step 1, by a conveying system such as a conveyor belt, a screw conveyor or an extruder.
10. A method and device as set forth in claim 6 in which the loose non-biomass material is fed into the mold, in step 1, by a conveying system such as a conveyor belt, a screw conveyor or an extruder.
11. A method and device as set forth in claim 1, in which ejection of the log in step 3 is conducted by a force-providing ram that produces sufficient force to expel (eject) the compacted biomass log from the mold.
12. A method and device as set forth in claim 6, in which ejection of the log in step 3 is conducted by a force-providing ram that produces sufficient force to expel (eject) the compacted biomass log from the mold.
A related separate application, entitled “Method to feed biomass tablets and logs into burners,” (inventors Henry Liu and Yuyi Lin), USPTO Application Ser. No. 11/382,988, is pending.
This invention is the result of a research project, entitled “Biomass Log Fuel for Heating Farm Buildings”, supported by the U.S. Department of Agriculture (USDA), under its Small Business Innovation Research (SBIR) Phase I Program, Project No. 2007-00233. According to the Bayh-Dole Act of 1980. the rights to this invention belong to the Small Business Grantee (Freight Pipeline Company), whereas the USDA retains limited non-exclusive right.
CURRENT U.S. CLASS: Class 425, subclass 344
This invention deals with compacting biomass materials, and hence should be in the fields of biomass utilization, compaction, and agglomeration.
A. Non-Patents.
[1] Liu, H. and Li, Y. (2000), “Compacting Biomass and Municipal Solid Wastes to Form an Upgraded Fuel”, Project Final Report submitted to U.S. Department of Energy under Contract No. DE-AC26-98FT40155, 82 pages,
[2] Liu, H.(2000), “Economic Analysis of Compacting and Transporting Biomass Logs for Co-Firing with Coal in Power Plants”, Report to U.S. Department of Energy under Contract DE-AC26-98FT40155, 52 pages.
[3] Li, Y. and Lin, Y. (2002), “Compacting Solid Waste Materials Generated in Missouri to Form New Products”, report to Missouri Department of Natural Resources under Contract No. 00038-1, 90 pages.
[4] Liu, H. and Li, Y. (2000), “Compacting Municipal Solid Waste into Logs for Combustion at Power Plants,” Proc. of Int. Sym. on Energy Engr. Begell House, N.Y., pp. 1420-1426.
[5] Li, Y., Hu, R., Wenzel, J. E. and Liu, H. (2000), “Turning Yard Waste into an Upgraded Biofuel,” Proc. of 25th Int, Tech. Conf. on Coal Utilization & Fuel Systems, pp. 107-114.
[6] Li, Y. and Liu, H. (1999), “High-Pressure Densification of Wood Residues to Form an Upgraded Fuel,” Biomass and Bioenergy, Vol. 19, No. 3, pp. 177-186
[7] Li, Y. and Liu, Y. (2000), “High-Pressure Binderless Compaction of Waste Paper to Form Fuel,” Fuel Processing Technology, Vol. 67, No. 1, pp. 11-21.
[8] Xue, K. (1999), “Research and Design of a 5.4-Inch Diameter Mold Rotary Press for Coal Log and Biomass Compaction”, M. S. Thesis, Mechanical & Aerospace Engineering, University of Missouri-Columbia, 101 pages. (Advisor: Dr. Yuyi Lin).
[9] Zhang, O. (2002), “Compacting Biomass Waste Materials for Use as Fuel”, Ph. D. Dissertation, Department of Civil and Environmental Engineering, University of Missouri-Columbia, 258 pages. (Adviser: Dr. Henry Liu).
[10] Liu, H. (2007), “Biomass Log Fuel for Heating Farm Buildings”. Small Business Innovation Research (SBIR) Phase I Program, U.S. Department of Agriculture (USDA), Project No. 2007-00233.
[11] Pietsch, W. (1997), “Granulate Dry Particulate Solids by Compaction and Retain Key Powder Particle Properties,” Chemical Engineering Progress, April, pp. 22-47.
B. Patents Cited:
5658357 August 1997 Liu, H. et al.
5879421 March 1999 Liu, H. et al.
5375690 April 2002 Gunnink, B. et al.
3996848 August 1975 Molitorisz, J.
3890413 June 1975 Peterson, W. M.
4371328 February 1983 Giles, D. D. & Osborn, R. W.
7264763 September 2007 Von Hass, G. & Kroll, D.
3706540 December 1972 Stanton, M. W.
4220453 September 1980 Holder, M. E.
3427960 February 1969 Napolitano, G. C.
C. Pending Patent Cited:
“Method to feed biomass tablets and logs into burners,” (inventors: Henry Liu and Yuyi Lin), USPTO Application Ser. No. 11/382,988, pending.
3. Brief History of the Invention
This invention is closely related to a research project completed in 2000 at the University of Missouri-Columbia (UMC), under the sponsorship of the U.S. Department of Energy. The UMC project, entitled “Compacting Biomass and Municipal Solid Waste to Form an Upgraded Fuel”, investigated the feasibility of using high pressure to compact various types of biomass materials in order to produce dense cylindrical-shaped objects called “biomass logs” [1]. In this patent, the term “log” refers to cylindrical solid objects of any length or size. The UMC project found that by using pressure of the order of 18,000 psi (124 MPa), most biomass materials, including but not limited to yard wastes (tree and bush trimmings, mowed lawn grass, fallen leaves), timber processing wastes (sawdust, tree barks, and mulches), agricultural wastes (cornstalks, corn cobs, and switch grass), and the combustible part of municipal solid wastes (waste papers, cardboard, waste wood as from discarded pallets, and discarded textile products), can all be compacted into biomass logs, without having to use either binder or heat. More than 30 types of biomass waste materials were successfully compacted into logs in the UMC project [1].
The purpose of compacting biomass materials should be explained. Most biomass materials, such as waste papers, forestry waste, agricultural waste and yard waste, are very bulky (loose and fluffy) when first collected. They are costly to handle, store and transport, and cannot be burned efficiently in burners, boilers or furnaces. However, upon compaction at pressure of the order of 18,000 psi, the bulk density of the biomass increases by 4 to 15 times [1], resulting in a densified fuel (logs) that is efficient to transport, handle, store and combust. For instance, with a five times increase in density, the same tonnage of biomass material can now be transported by one instead of five trucks, and can be stored in one instead of five silos. Also, the intensity of the heat generated in any burner that uses biomass as the fuel, and the rate of chemical reaction of any reactor that uses biomass as the feedstock for gasification or liquefaction of the biomass, will greatly increase with the increased biomass density. Another advantage of compacting biomass at high pressure is the uniformity of the geometry, dimensions and density of the product—biomass logs. Having uniform shape, dimensions and density also renders the biomass fuel easy to handle, package and feed automatically by using specially designed machines.
It should be mentioned that the University of Missouri researchers of the biomass logs have published extensively their research findings in reports [1-3], conference proceedings [4, 5], technical journals [6, 7], and student theses [8, 9], but the University did not choose to apply for any U.S. or foreign patent for lack of a satisfactory way to mass-produce the biomass logs. Now that the concept of compacting and making biomass logs has been published for several years, it is too late for the University or anyone else to apply for a general patent on compacting biomass logs. However, neither the University of Missouri researchers nor anyone else has published or invented any means or special device to mass-produce the biomass logs in a cost-effective way, as is the subject of this invention through the USDA-sponsored research project [10]. In this patent application, the term “biomass logs” refer to biomass materials compacted or extruded into the shape of cylinders of circular or nearly circular cross sections of any length or diameter. A special method and device are invented here for efficient and cost-effective production of biomass logs. The same device and method invented here for manufacturing biomass logs are also applicable to manufacturing logs made of other fluffy or loose materials that need to be compacted (densified) in order to facilitate utilization.
The special process to be patented here is a simple, practical and novel method to mass-produce logs made of biomass and other cellulosic and carbonaceous materials. This new manufacturing method will facilitate the use of biomass energy and bring down the cost of such use, thereby enabling the United States to use more biomass materials, which is a precious renewable energy resource largely unused and wasted at present. Increased use of biomass energy has the following benefits to the nation:
It reduces the nation's reliance on fossil fuel for heating and generating electricity, thereby reducing air pollution and global warming.
It reduces the amount of biomass waste materials that enter the nation's landfills, thereby reducing the need for using additional land for landfills.
It results in reduced use of imported oil for heating buildings, thereby reducing the nation's reliance on imported oil.
4. Different Methods to Densify Biomass
In general, there are four different methods to densify biomass raw materials. They are separately discussed as follows:
Briquetting—As described by Pietsch [11], briquetting is a century-old technology used mostly for agglomerating coal and charcoal fines. It forces materials to be compacted through the gaps of two parallel rotating drums to produce pillow-shaped agglomerates called “briquettes”. A major difference between briquetting and the biomass log technology developed at University of Missouri is the way pressure is applied to the material during compaction. While the latter applies pressure uniformly over the flat ends of the log or tablet (uni-axial compaction), the former compacts on curved surfaces which make pressure non-uniform. Consequently, the pressure applied to the rim of briquettes is much lower than that at the center of the briquettes. This makes it difficult to form strong briquettes without using considerable amount of binders or heat to aid in the agglomeration. It is not uncommon to use 5 to 15% of binders to make coal briquettes. Without using binder or heat, biomass cannot be briquetted properly. In contrast, by compacting axially from the opposite flat ends, the pressure distribution across any biomass log or tablet is very uniform. This enables the formation of strong biomass agglomerates without having to use binder or heat. In comparison with the briquetting process, the biomass log process has the following advantages, (1) It produces strong products without using heat or binder; (2) it produces products in more precise and uniform shapes and density, (3) the quality of the product is more uniform and easy to control; and (4) it is more suitable for making large products (large logs and large tablets), thereby being more adaptable to mass production at low cost.
Extrusion—Extrusion is the process in which materials are forced through a die or orifice, by using either an auger (screw), or a ram [10], Extensive shear is generated, which together with the pressure, helps to agglomerate. While extrusion is widely used in the chemical and food industries, it cannot be used for binderless, room-temperature agglomeration of biomass. This is due to the fact that ordinary extruders cannot generate the high pressure required for binderless, room-temperature compaction of biomass, which is in the neighborhood of 18,000 psi [1]. Also, the extrusion process is very sensitive to the variation of raw material properties, such as moisture and particle size. A small variation of such material properties can often cause the extruder either to clog or fail to produce acceptable products. In contrast, the biomass log technology was found to be able to produce good quality products (logs or tablets) without clogging or other problems over a rather wide range of moisture, compaction pressure and particle size [1, 9]. This shows the superiority of the biomass log technology to extrusion for producing biomass logs and tablets. The only known commercial use of extrusion for biomass is the fuel logs used in fireplaces. Such fuel logs usually contain over 15% binder—the binder being either wax or an oil product. The first three of the four advantages cited above for biomass log process over briquetting also hold when comparing the biomass log process with the extrusion process.
Pelletizing—Pelletizing is a processes in which materials are forced through a pelletizer (pellet mill) which consists of a roller inside a perforated steel drum. The material drawn into the gap between the roller and the drum is forced through the perforations in a way similar to extrusion. Pelletizing is the most commonly used method for densifying biomass, and sawdust is the most common material used for making pellet fuel. However, to be successful in pelletizing, the biomass material is usually heated to over 140 degree Celsius (284 degree Fahrenheit) so that it will melt and release the lignin, which serves as the binder. Furthermore, the perforations of the pelletizer must be small, less than about 0.5-inch (13 mm) diameter, in order to form good pellets. All these lead to high energy consumption and high cost. At present (2008), the average retail price of pellet fuel in the U.S. is approximately $225 per ton. After subtracting the cost of material collection, packaging, transportation, storage and profits by retailers, the production cost of the pellet fuel is in the neighborhood of $50 per ton. This is considerably higher than the anticipated production cost of manufacturing biomass logs as computed in the University of Missouri study conducted in 2000[2] $8 per ton for 5.5-inch diameter logs, and $14 per ton for 2-inch diameter logs All the aforementioned four advantages of the biomass log method over the briquetting method also hold when comparing with the pelletizing method.
The foregoing comparisons with competing technologies show that the biomass log technology is superior to all the existing technologies for compacting biomass.
Unitaxial compaction—Uni-axial compaction is the method used at the University of Missouri to compact biomass materials into logs and tablets. It uses a cylindrical mold and a piston of cylindrical cross section with the piston head (i.e., the part of the piston in contact with the biomass during compaction) slightly smaller than the inner diameter of the mold. By using biomass feedstock of an appropriate moisture and by using high pressure in the range of 15,000 to 20,000 psi (pounds per square inch), practically all biomass materials can be compacted into dense biomass logs or tablets without having to use binder or heat [1]. The logs and tablets produced are dense (having specific gravity slightly greater than one), and they are wear-resistant and impact-resistant. They can be easily handled, transported, stored, and burned. Depending on the type of biomass materials and moisture, the biomass logs have heating values between 7,000 and 8,500 Btu/lb. The optimum moisture for making biomass logs, depending on types of biomass, is 5% to 15% [1,9].
The DOE-sponsored project also conducted a detailed and rigorous investigation of the cost of production of biomass logs [2]. By performing life-cycle cost analyses, the cost of producing each ton of biomass logs for manufacturing facilities of various sizes (capacities) was calculated. The analysis covered two sizes of biomass logs (2-inch and 5.5-inch diameters), over the manufacturing capacity range of 135,000-675,000 tons/yr. The study showed that over the plant capacity range of 135,000 and 675,000 tons/yr., the unit cost (in Year 2000 U.S. dollars) for producing the large (5.5-inch-diameter) biomass logs was between $5.4 and $8.2 per ton, and the unit cost for producing the small (2-inch-diameter) biomass logs was between $12.4 and $14.2 per ton. These cost figures included not only capital and annual (operation and maintenance) costs but also taxes, insurance and a 15% above-inflation return-on-investment (ROI). They do not include the cost of raw material or feedstock. It was assumed that the biomass waste materials used for making the logs could be obtained free-of-charge because they would otherwise be headed for landfill or left in the field to decay and generate greenhouse gas. To be conservative, the avoided landfill tipping fee, usually above $30 per ton, was not included in the cost analysis. Due to the inclusion of 15% ROI the cost figures cited above were the anticipated price of the biomass log fuel that would allow the producer to achieve above-inflation return of 15%, which is a healthy return on investment. If the producer were paid a portion of the avoided landfill tipping fee, the profit or return would be even higher.
Further study by Li and Lin [3], sponsored by the Missouri Department of Natural Resources (MDNR), showed that the biomass logs, without crushing or size reduction, burn well in stoker boilers of ordinary coal-fired power plants, and in fireplaces, furnaces, and wood stoves for heating buildings. However, the study found that there was no commercially available machine suitable for mass-producing biomass logs. This provided the incentive for a US Department of Agriculture sponsored study [10], focused on designing and developing a low-cost machine for on-farm mass-production of biomass logs. The study gave birth to the current invention.
5. Description of and Comparison with Prior Art
This invention is related to the biomass compaction study conducted at University of Missouri-Columbia [1-9]. The University researchers invented and developed the biomass log fuels but did not invent or develop any special equipment or method for mass-producing the logs. Description and comparison with other related prior arts are to be given next.
There are many patented processes for producing biomass and other carbonaceous fuel or fuel elements. For instance, in 1997, U.S. Pat. No. 5,658,357, entitled “Process for forming coal compact without a binder,” was issued to H. Liu et al at University of Missouri-Columbia (UMC). The patent deals with a process that applies high pressure to coal particles inside a mold to produce water-resistant coal logs for pipeline transportation—the concept of coal log pipeline. This compaction method is essentially the same used by researchers of UMC to produce the biomass logs and tablets sponsored by the DOE project mentioned before. The patent is different from the present patent in that it does not deal with how the coal logs are to be mass-produced.
Another U.S. Pat. No. 5,879,421, entitled “Apparatus and method for forming an aggregate product from particulate material,” was issued to H. Liu et al. in 1999. The patent deals with using special mold shapes and back pressure during compaction to produce strong coal logs for pipeline transport Again, it does not deal with methods or devices for mass-production of coal logs or other products.
Another U.S. Pat. No. 6,375,690, entitled “Process for forming coal compacts and product thereof,” was issued to B. Gunnink et al. in 2002. The process deals with heating coal-water mixture to above 100 degree Celsius while the mixture is being compacted inside a mold to produce binderless coal logs. Again, the method deals with compaction method rather than manufacturing or mass production of coal logs.
U.S. Pat. No. 3,996,848 entitled “Rotary compacting machine for fibrous material” was issued to Joseph Molitorisz in 1976. Molitorisz used rollers to compress loose fibrous material (hay) into a large cylindrical core (bale) which was cut into individual rolls. The present invention does not use rollers for compression nor does it use a cutting mechanism for the logs or use chemical additives as preservatives.
U.S. Pat. No. 3,890,413 entitled “Apparatus and method for compacting particulate materials” was issued to William M. Peterson in 1974. This machine was designed for compacting powder. It has a plurality of die cavities which have corresponding punches on a head, each punch being connected with a piston in a hydraulic cylinder on the head. The cylinders communicate with each other and with a hydraulic accumulator cylinder which permits the punches individually to shift axially and compensate for cavity-to-cavity variations in the amount of powder fill. This patent differs in many ways from the present patent due to its emphasis on compressing powder. It does not incorporate the two-stage compaction, toggle mechanism or turret system as in the present invention.
U.S. Pat. No. 4,371,328, entitled “Apparatus for making composition logs by compressing particles,” was issued to Duane D. Gules and Richard W. Osborn in 1983. Differences include a heater, cooler and drain for the hydraulic fluid, not included in the present invention. Also, it does not incorporate the toggle mechanism for amplifying force, and the rotary feeder/compressor for pre-compaction, which are unique for the present invention. The reason for such differences is that Giles and Osborn's invention is designed for compressing uranium oxide, rather than biomass which has very different characteristics.
U.S. Pat. No. 7,264,763, entitled “Method and apparatus for the manufacture of compacts,” was issued to Gernot von Haas and Detlef Kroll in 2004. They invented a method for manufacturing compacts from lignocellulose material for burning in hearths. One difference is that they used a multi-platen press and heat the mold above 100° C. The ram and press table must also be heated. No heat is required in the present invention. The end product is a pellet—much smaller than the biomass log made by the Liu apparatus. Another difference is that there is no turrets no precompaction, and no toggle mechanism.
Another U.S. Pat. No. 3,706,540, entitled “Artificial fuel log machine,” was issued to Milton W. Stanton in 1970. This machine was designed to compress a fuel log from compressed waste paper sprayed with oil. There was no turret and the end product was a rectangular log the size of a loaf of bread. Pipes in the machine sprayed flammable waste crank oil into the paper to improve combustion capabilities. One chamber wall moves inward toward the end wall which releases end product onto conveyor belt, other differences include no pre-compaction and no toggle mechanism.
U.S. Pat. No. 4,220,453, entitled “Process for producing artificial fire logs,” was issued to Morris E. Holder in 1980. The goal was to make artificial fire logs from wood material and a binder (resin). The patent differs from the present invention in that it uses binder and heat, it has no pre-compaction, and it uses no toggle mechanism.
U.S. Pat. No. 3,427,960, entitled “Compacting machine” and issued to G. C. Napolitano in 1966, was designed to make fire logs from sawdust and binder. A drum with 3 compression chambers (each open at both ends) and having an inlet opening toward the outside of the drum compressed as the drum was rotated stepwise. The patent differs from the present invention in several ways, including it has no precompaction step, and there is no toggle mechanism,
6. Distinct Features and Merits of Current Invention
The current invention is innovative in solving a difficult problem in compacting biomass to form logs. The problem stems from the fluffiness of biomass raw materials, and the high compaction pressure required for binderless agglomeration at room temperature. Due to its fluffiness, loose biomass raw materials such as dry leaves or dry grass must often be densified many times so that its density will approach 1.0 g/cc (or 1,000 kg/m3) before it can agglomerate or form logs. To reach such bulk density for agglomeration often requires very high compaction pressure, close to 20,000 psi (138 MPa), and very long stroke of compaction—about 3 ft for a log having a length of only 3 inches. Using 20,000 psi to compact a 6-inch-diameter biomass log will require a large force (load) of 283 tons. Any hydraulic press that can generate such a large force and has a long stroke of 3 ft will be very expensive, and the machine speed will be very slow. This invention solves this problem by compacting the biomass in two stages first using a rotary feeder to prep compact (reduce the volume of the biomass raw materials several times), and then using a press (such as a hydraulic press) to perform final compaction of a somewhat compacted material. Using such a two-stage compaction, with the second stage aided by a toggle mechanism to amplify the force of the press many times during the final part of compaction when the force needed is big, makes this invented method highly practical and cost-effective.
This invention solves the challenging task of compacting fluffy biomass materials, which requires very little force of compaction initially during a compaction stroke, but requires increasingly large force as the material is more and more compact (dense), and finally requires a very large force (high pressure of compaction) as the density of the biomass being compacted approaches the final density of the logs produced, generally in the neighborhood of 1 g/cc (within 10% of that). Such compaction, if to be done in a single stroke, will require a press that has both very large force and large stroke. Such a press will be very expensive, and besides, it will act slowly, due to the long time needed to traverse a long stroke. Therefore, it is not practical to compact such biomass materials in one stage. It is far better to compact in two stages, with each stage using a different means or equipment for compaction.
Based on this invention, we use a rotary feeder to provide initial or prep compaction, and then use a hydraulic press aided by a toggle mechanism, to do the final compaction. This makes both the pre-compaction and the final compaction practical and cost-effective. This invention also includes the design of a special revolving compactor (machine) to accomplish the aforementioned two-stage compaction. The compactor uses three vertical molds to accomplish three steps of biomass compaction: (1) pre-compaction, (2) final compaction, and (3) ejection of logs. The three molds are arranged around the circumference of a circle, 120° apart. They revolve in steps of 120°, so that the materials in each mold will go through two stages of compaction in steps 1 and 2, and then will be ejected from the mold in step 3 to form a compacted biomass log.
A preferred embodiment of the current invention is shown in FIG. 1, which illustrates a rotating machine (revolver or turret) for biomass compaction based on the 3-step process discussed before. The three steps are accomplished by using a turret that consists of three vertical cylinders with their tops connected to an upper disc and their bottom to a lower disc, with the three cylinders spaced around the circumference of the discs at 120° away from each other. In FIG. 1, part 1 is a hopper placed above one of the three cylinders located in station the initial location of the mold. Biomass raw material (loose material) is brought continuously into the hopper by a conveying system such as a conveyor belt or a screw conveyor not shown in the drawing. The biomass loose material dropped in the hopper is pushed down into the vertical cylinder (mold) by a rotary feeder/compressor shown as part 2. The rotating feeder/compressor performs the pre-compaction of the biomass in the mold. Part 3 is the pre-compacted biomass in the mold.
Initially, the pre-compaction mold is parted at station 1. As soon as the pre-compaction has reached a preset amount, as for instance detected by a sensor that measures the torque of the shaft of the rotary feeder/compressor, the turret (part 4) rotates 120°. This brings the mold that contains the pre-compacted biomass (part 3) to station 2, which is 120° from station 1. The pre-compacted biomass material receives final compaction in station 2. Part 5 is the revolving upper disc of the turret to which the tops of all three molds are rigidly attached, and part 6 is the stationary lower disc containing a hole in the 240° position. The hole is to allow release (ejection) of the compacted biomass from the mold. Part 7 is the biomass in the mold in station 2 after final compaction. Part 8 is the biomass ejected from the mold parked at station 3, which is 240° from station 1.
Part 9 is the toggle link connected to the ram (part 23) that amplifies the force on the ram for final compaction of the biomass in station 2. Part 10 is the hydraulic cylinder No. 1 for final compaction. As the hydraulic cylinder moves horizontally to press the toggle link, the ram (part 23) moves vertically. Part 11 is the tension link to support the hydraulic cylinder No. 1. Part 12 is a low-pressure hydraulic cylinder for ejection of the compacted biomass log (part 8). Part 13 is the hydraulic lines (hoses or tubes to convey the hydraulic fluid). Part 14 is the hydraulic motor, chain or gear for rotating the turret.
Part 15 is the center post supporting the turret. Part 16 is the bottom bracing. Part 17 is a set of four pillars to support this heavy machine Part 18 is the stationary top plate to support the system. Part 19 is a PLC (programmable logic controller) for automatic control of the system. Part 20 is the hydraulic pump that drives the hydraulic fluid through the hydraulic system. Part 21 is the PTO (power-take-off) of a tractor that can be used to drive the system. Alternatively, the hydraulic pump may be driven by an electric motor connected to a regular household or building power outlet, or connected to a generator. Part 22 represents the four legs of the machine. Part 23 is the compaction piston (ram) for final compaction in the 180° position. Part 24 is a small hydraulic cylinder for locating the position of the turret. Finally, part 25 shows the studs for supporting the system (compactor)=—the top studs support the top plate (part 18), and the bottom studs to support the bottom plate (part 26).
FIG. 2 shows the basic design of the rotary feeder/compressor. It consists of two basic parts: 2a, which is the rotating part of the feeder/compressor, and 2b which is the stationary part. While the rotating part is to feed and compress the biomass material entering the mold, the stationary part is to prevent the rotating vanes from bringing the biomass material back into the hopper, namely, to prevent short-circuiting.
The current invention uses a two-stage compaction process to produce biomass logs from fluffy (loose) biomass materials such as leaves, grass, corn stovers, bushes, etc. In stage 1, the fluffy biomass material is fed into a mold (vertical cylinder) on the top of which is mounted a rotary feeder that continuously pushes the biomass into the mold, causing pre-compaction. The feeder will pre-compact the material to a density 20% to 60% of the final density of the log. After this initial stage of compaction, the biomass material in the mold is now ready for final compaction which can be done more easily due to the much shorter biomass column in the mold caused by pre-compaction. To further aid in rapid and efficient final compaction, a toggle mechanism, such as that used for holding and opening injection molds, is used here. The toggle mechanism is most suited for this type of compaction because it matches the load-versus-displacement curve for the compaction of fluffy biomass materials—large displacement with little force initially, and small displacement with large force towards the end of compaction. By using the toggle mechanism, final compaction is rapid, and only a small force is needed to push and pull the toggle arms. It is a highly efficient way to compact biomass at low cost. Details of this process is explained below by considering the operation of the preferred embodiment illustrated in FIGS. 1 and 2, and briefly described in the previous section on drawings.
Using a machine shown in FIG. 1, fluffy biomass material is conveyed to and fed into a hopper (part 1). There is a rotary feeder/compactor (part 2) mounted on the bottom of the hopper, to push the biomass material into the cylinder (mold) beneath it, causing pre-compaction. The cylinder at this initial location is said to be parked at station 1. The degree of pre-compaction needed at this stage is determined by a sensor. As soon as the sensor detects that pre-compaction has reached a given critical value, the sensor stops the rotary feeder/compressor, and advances the revolver (turret) by 120° for final compaction in station 2. The sensor can be any of the following types, (a) a torque sensor that measures the torque on the shaft of the feeder/compactor, (b) a pressure sensor that measures the pressure exerted by the pre-compacted biomass material in the mold, (c) a density sensor that senses the density of the pre-compacted biomass material in the mold, (d) a strain gage that measures the hoop tension of the mold during pre-compaction, or any other practical means of sensing.
As soon as the cylinder containing the pre-compacted biomass has been rotated to reach station 2, which is 120° from station 1 the PLC (programmable logic controller) activates the hydraulic cylinder No. 1, which in turn drives the compaction ram (part 23) via the toggle links. By using the toggle, the hydraulic cylinder needs only to provide a small force, which will be fast and low-cost. Note that the toggle behaves like a lever with a variable arm length. Initially, when the toggle arm (link) is horizontal, the force is not amplified. However, as the arm tilts more and more, a larger and larger amplification of force is accomplished. Finally, when the arm is in its most extended position—almost horizontal the force is amplified many times. What is nice in using the toggle mechanism is that its force versus travel distance can be designed to match that of most biomass materials, so that effective compaction of the biomass can be done with a small hydraulic cylinder No. 1, which greatly reduces equipment cost, and makes compaction fast. In lieu of the hydraulic cylinder, one can also use a pneumatic cylinder, a linear electric motor (i.e. linear induction motor), or other means for providing a linear force to push and pull the toggle links.
Next, as soon as the final compaction has been completed in station 2, and the ram (piston) in the mold has been retrieved from the mold, the PLC will advance the mold containing the biomass to station 3 for ejection. The sensor used for directing the PLC to rotate the mold from station 2 to station 3 can be a photocell or proximity sensor which senses that the piston has retrieved beyond a certain location, or any other sensor that responds to the state that the piston is outside the mold, and can be programmed to direct the PLC to act.
As soon as the mold containing the biomass has reached station 3, the PLC activates the low-pressure hydraulic cylinder No. 2, which extends its ram rapidly to expel (eject) the log from the mold. The ejected log, part 8, drops from the machine onto a conveying system to bring the manufactured logs to a storage place, a bin, a silo, or a receiving vehicle.
Although the above discussion mentions biomass, the machine can also compact any other fluffy material in a similar manner. So, the application of this process/device is not limited to biomass. Also, it is not necessary to use a revolving press discussed before to carry out the two-stage or three-step compaction. The revolving press is simply a preferred embodiment or mechanical device to carry out the two-stage compaction. For instance, it is quite feasible to have three or more molds arranged in series along a straight line as in an assembly line, with the molds being transported from station 1 to stations by a conveyer or chain set, and then transported back to station 1 after the biomass log is ejected from the mold. Also, it is possible to have more than one set of molds in a single machine, so that biomass logs can be simultaneously produced. Furthermore, the hydraulic presses used in final compaction and in ejection of the logs can be replaced by other means for producing linear force, such as pneumatic cylinders, linear motors, solenoids, etc.
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