STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with United States government support by the CSREES Small Business Innovation Research program of the Department of Agriculture, grant numbers 2005-33610-15483 and 2006-33610-17595. The U.S. government has certain rights in the invention.

FIELD OF THE INVENTION

Our invention relates to harvesters, particularly balers, and provides a baling system engineered to predictably and reproducibly produce rectangular bales of woody biomass at optimum transportation densities, and more particularly to transportable baling chambers of sufficient strength to withstand the Poisson's ratio effect of woody biomass when compacted to such densities.

BACKGROUND OF THE INVENTION

Woody biomass is a core element of the world-wide strategy to replace imported oil and natural gas with renewable resources. Woody biomass has low bulk density, and so machinery has been developed to collect and compact woody biomass into transportable bundles, bales, modules, and containers. Pioneering research was undertaken in Scandinavia (Makela 1975; Danielsson 1977; Carlsson 1980; Sail 1981 ; Larsson 1981) and Canada (Sinclair 1981 ; Jones et al. 1981 a, 1981 b).

In the United States, Dr. Awatif Hassan at North Carolina State University early on investigated the energy consumption for a wood chip compaction system (Hassan 1976). Dr. William Stuart at Virginia Polytechnic and State University was among the early U.S.

developers of forest biomass balers (Stuart and Walbridge 1978). His baler was brought to the University of Washington in 1982 for testing by Dr. Peter Schiess (Schiess and Yonaka

1983) . Concurrently, James Fridley and Dr. Thomas Burkhardt at Michigan State University worked to adapt round agricultural balers to handle forest biomass (Fridley and Burkhardt

1984) . Both projects stopped when the price of oil began to fall and public interest in biomass energy waned.

Fortunately, much of that initial flurry of research was documented in conference proceedings and review articles (Sturos 1981 ; Guimier 1985). Guimier compared the potential of five existing systems (round agricultural baler, rectangular baler, garbage truck, garbage compactor, and cotton module builder). His team found that rectangular bales of the type made by recycling balers and large cotton modules showed the most promise.

Renewed interest in woody biomass as a fuel and feedstock during the 1990's stimulated a number of development programs around the globe. Baling, chopping, and intermodal bulk hauling are being concurrently developed, with each being an optimal solution for particular circumstances. Chopping and intermodal bulk hauling are particularly attractive for very short haul distances. However, once the haul distance exceeds about 35 miles (60 km), the need for high bulk density solutions becomes apparent.

Baling woody biomass to achieve high bulk density is being pursued by three technical approaches, again each approach being preferred for particular situations.

Timberjack, now John Deere Forestry, has commercialized a biomass bundling system that was developed in Finland to enable forest materials to be handled similar to logs. Dr.

Philippe Savoie's team in Canada has been developing round baling for woody biomass crops such as willow (Savoie 2006), and more recently with SuperTrak has adapted the round bale technology for use in forestlands to cut and collect understory saplings and brush. Round bales can be collected, transported and handled like round bales of hay. The third technology, rectangular balers is the subject of this patent application.

The present inventors have reported their progress under a federal contract from the USDA CSREES SBIR program to develop better methods to collect and transport woody biomass (Dooley 2006a; Dooley 2006b; Dooley 2006c; Lanning 2007; Dooley 2007; Lanning 2008; Dooley 2008; Dooley 2009). Our goal has been to engineer more efficient recovery and transport of woody biomass to second-generation bioenergy and biofuel plants.

SUMMARY OF THE INVENTION

We have elucidated the three rheological properties of woody biomass material requisite to predictably and reproducibly bale woody biomass at pre-selected optimum transportation densities while minimizing fossil fuel consumption during baling, handling, and transport.

First, we have empirically determined the baled bulk density (e.g., lb/ft ³ or kg/m ³ ) v. platen pressure (e.g., psi or kPa) curves for woody biomass at various moisture contents. These relationships indicate the target compression platen pressures that will compress woody biomass to predetermined transport densities.

Second, we have empirically determined that woody biomass material compacted to optimum transport densities has a Poisson's ratio effect of about 1 1%. This value is required to determine the minimum mechanical strength of baling chamber sidewalls, be they fixed or moveable, for producing woody biomass bales of optimum transport densities.

Third, we have observed that green woody biomass material compacted to optimum transport densities has a coefficient of friction against steel baling chamber walls of approximately 0.60. This value is necessary, in conjunction with both the target compression platen force and the Poisson's ratio, to determine the minimum platen pressure required to form and eject a compacted bale of woody biomass from the baling chamber.

These three discoveries permit one of ordinary skill to for the first time design and manufacture robust, lightweight and economical rectangular balers to produce woody biomass bales optimized for transport on conventional semi-trailer trucks to bioenergy and biofuel plants.

Accordingly, the invention provides a woody biomass baler having a baling chamber adapted to receive woody biomass material and a compression system adapted to compact the material into a rectangular bale in the baling chamber, wherein the baling chamber has a front wall that acts as a reciprocating compression platen corresponding in dimensions to the width W and height H of the bale, opposing upper and lower walls corresponding in dimensions to the length L and either of the W and H of the bale, and opposing sidewalls corresponding in dimensions to the L and the other of the W and H of the bale, wherein each chamber wall selected from among the upper wall, the lower wall, and each of the sidewalls can withstand a minimum distributed force perpendicular to the selected wall of at least (0.1 1 x P _p x A _w ), wherein 0.1 1 is the Poisson's ratio of woody biomass, P _p is the maximum pressure that the compression system can apply to the material, and A _w is the area of the selected wall.

In a representative embodiment, each of the selected chamber walls is designed and fabricated to withstand a distributed force perpendicular to the selected wall of between (0.1 1 x Pp x A _w ) and (0.5 x P _p x A _w x SF), wherein 0.5 is the Poisson's ratio of solid wood and SF is a safety factor calculated by dividing the baler manufacturer's predetermined design failure load of the compression platen by P _p . In representative embodiments, the compression system can apply at least one platen pressure between 26 psi (180 kPa) and 126 psi (870 kPa) to the woody biomass material. Preferably the compression system can apply at least one platen pressure between 46 psi (317 kPa) and 86 psi (593 kPa) to the woody biomass material in the baling chamber. Most preferably, the compression system can apply at least one platen pressure between 50 psi (345 kPa) and 71 psi (490 kPa) to the woody biomass material.

The woody biomass baler can include a loading system, e.g., a knuckle boom loader, adapted to introduce woody biomass material into the baling chamber, an ejection system adapted to move the bale from the chamber, and may incorporate a tying system adapted to automatically tie the bale of compacted woody biomass material.

The baling chamber may be open-ended or closed by a back wall corresponding in dimensions to the front wall. The back wall may be open or reversibly opened, in which case the ejection system should apply a force greater than or equal to (0.132 x P _p x )( h + w) to move the bale from the chamber through the open or opened back chamber wall, wherein / is the length of the chamber, h is the height of the compression platen, and w is the width of the compression platen.

At least one of the side walls may be reversibly opened, in which case the ejection system should apply a force greater than or equal to (P _p x w)(l 2h + 0.132/) to move the bale from the chamber through the opened sidewalk

For bale stability and stackability, either or both L/W and L/H should be equal to or greater than 1.5, and preferably equal to approximately 2.

BRIEF DESCRIPTION OF THE DRAWING

FIGURE 1 shows a perspective view of a representative woody biomass bale;

FIGURE 2A is a graph that contrasts the density v. platen pressure curves of woody biomass (at 45%wwb, 30%wwb, 15%wwb, and dry weight) and timothy hay (at 15%wwb);

FIGURE 2B is a graph that contrasts the density v. platen pressure curves of switchgrass (at 60%wwb, 45%wwb, 30%wwb, 15%wwb, and dry weight) and timothy hay (at 15%wwb); and

FIGURE 3 is a graph that contrasts the Poisson's ratio effects of woody biomass (0.1 1), timothy hay (0.17), and switchgrass (0.22) when baled at optimum transportation densities. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The terms "parallelepiped" and "rectangular" are used interchangeably herein to refer to a solid shape bounded by six substantially square or rectangular faces in which each pair of adjacent faces meets in a substantially right angle.

The term "bale" as used herein refers to a parallelepiped-shaped bundle of compacted and bound biomass. FIGURE 1 depicts a representative bale 10 of compacted biomass 12 bound with a plurality of loops of binding material 14. Dimension W is perpendicular to the plane created by the binding material that encircles the compacted biomass. Dimension H is perpendicular to W and in line with the binding material. Dimension L is perpendicular to the plane created by W and H. Binding material is parallel to L. Representative binding materials include wire, polypropylene twine, and banding straps. For stackability, bale compression is preferably along the L axis, most preferably with the biomass material disposed substantially along the W axis, transecting the binding material plane.

The term "cellulosic biomass" as used herein refers generally to encompass all plant materials compacted/compressed by baling for use as industrial feedstocks, including woody biomass, energy crops like switchgrass and hemp, and agricultural crop residues including corn stover.

The term "woody biomass" as used herein refers to all parts of trees, shrubs and woody plants useable as industrial feedstocks for fiber, bioenergy, and biofuels, including timber harvest slash and land clearing debris, small-diameter trees, shrubs and brush, dedicated energy crops like willow and poplar, tree service prunings, and residential green waste.

The terms "tall grass" and "tall grasses" as used herein refer to switchgrass

(Panicum viratum), miscanthus (particularly Miscanthus x giganteus), big bluestem

{Andropogon gerardii), Indian grass (Sorgastrum nutans), reed canary grass (Phalaris arundinacea), and other tall perennial grasses harvested as biomass feedstocks for ethanol production and biorefining.

The term "green weight" as used herein refers to the weight of freshly harvested woody biomass that has substantially the same moisture content, typically 40 to 55 percent wet-weight-basis (%wwb), as the stranding plants. The term "equilibrium weight" refers to the eventual weight of woody biomass that has dried in bales under ambient conditions to an equilibrium moisture content, typically 10 to 18 %wwb in the U.S. Pacific Northwest and less that 10 %wwb in drier regions. "Dry weight" as used herein refers to the weight of woody biomass after drying to constant weight at 221°F (105°C).

The term "semi-trailer truck" as used herein refers to an articulated rig consisting of a towing engine ("tractor") coupled to a single "semi-trailer" (a trailer without a front axle), or to a "double trailer" consisting of a semi-trailer coupled to either another semi-trailer or a "full trailer" (a trailer supported by front and rear axles), or to a 'triple trailer" consisting of a semi-trailer coupled to two full trailers. The trailers can be flatbed trailers, curtain siders, or box trailers. As used herein, the term "semi rig" refers to a tractor & semi-trailer

combination, commonly a 10-wheeled tractor coupled to an 8-wheeled trailer; and the terms "double rig" and "triple rig" refer to tractors pulling two and three trailers, respectively. The term "fleet" refers to a group of semi-trailer trucks owned or leased by a business or government agency.

The overall weight of a particular semi-trailer truck empty of cargo is referred to herein as "curb weight."

The term "cargo" as used herein refers to a plurality or multiplicity of parallelepiped bales of woody biomass that are loaded for transport on or in the one or more trailers of a semi-trailer truck. The term "payload" refers to the weight, volume, and density

characteristics of the cargo. The terms "payload weight" and "payload volume" refer to the weight and volume of the cargo, respectively.

The term "Gross Vehicle Weight (GVW)" as used herein refers to the total weight of a semi-trailer truck and everything aboard, including cargo. The U.S. federal maximum GVW for semi-trailer trucks is 80,000 pounds. Double and triple rigs must additionally comply with federal bridge protection regulations.

As used herein the terms "maximum transport volume" and "maximum transport weight" refer to the maximum volume and weight of cargo, respectively, that a particular semi-trailer truck can legally transport. The maximum transport weight is determined by subtracting the curb weight of the semi-trailer truck from the maximum allowable GVW of the truck. The term "optimal transport density" refers to the computed density

(weight/volume) of a cargo that has both the maximum legal transport volume and the maximum legal transport weight. Such an optimized cargo is said to "cube out" the legal payload of a semi-trailer truck.

In ordinary circumstances, a tractor-coupled semi-trailer will weigh about 35,000 pounds, leaving about 45,000 pounds of payload capacity. The cargo space available on or in a semi-trailer is normally 48 or 53 feet long and about 8 foot 4 inches wide and 8 foot 10 inches high. These general constraints give an optimal transport density range of 12.7 to 1 1.5 lb/ft ³ (203 to 184 kg/m ³ ). In practice, however, maximum transport weight and volume limits depend specifically on a particular semi -trailer truck's curb weight, trailer configuration, and travel route on national and state highways.

For example, the California State Department of Transportation has relatively strict regulations on weight and size limits for highway transportation vehicles. Semi-trailers are limited to 48 or 53 feet maximum length; and each trailer in a double trailer cannot exceed 28 feet 6 inches in length. For illustrative purposes, we describe an optimized bale size and density for cargo transport on a 48-foot semi-trailer in the State of California. Considering payload volume, a 14-foot maximum allowable load height leaves 8 to 9 feet of useable cargo space. We assume an 8-foot cargo height and an 8-foot loading width, leaving buffer spaces for pallets, tarps, and straps. The exemplary volume, then, of cargo that can be transported on a semi-trailer in California (without special permits) is 48 ft x 8 ft x 8 ft equaling 3072 cubic feet.

With this information we can determine appropriate bale sizes for truck transport of woody biomass on California highways. Table 1 lists several suitable bale configurations, sized for different businesses and woody biomass sources.

Table 1

For example, 54 woody biomass bales sized 64x48x32 inches will cube out the exemplary 3072 ft ³ payload volume of a 48-ft semi trailer. To maximize packing efficiency, bale configurations are preferably selected so that trailer dimensions are evenly divisible by bale dimensions. In this example the trailer length is divisible without remainder by the bale length dimension, and likewise trailer width by bale width, and trailer height by bale height.

Woody biomass bales should preferably have an L/W and/or L/H ratio(s) of at least 1.5, as we have observed that smaller ratios tend to produce egg-shaped bales rather than consistently stackable, rectangular bales. Most preferably, L/W and/or L/H ratio(s) of approximately 2 advantageously permit the bales to be stably interlocked on pallets or in stacks. We note that finished bale dimensions will increase by the amount of stretch in the chosen binding material, e.g., polypropylene twine stretches under load more than steel wire. Consequently the baling chamber walls (discussed below) can be dimensioned accordingly shorter, to accommodate the anticipated stretch of particular binding materials.

Considering payload weight, a typical semi rig payload legal in California is 44,000 to 48,000 pounds. Combining these volume and weight constraints gives an optimum transport density range of 14.3 to 15.6 lb/ft (229 to 250 kg/m ). Assuming a maximum payload weight of 45000 lbs, 54 woody biomass bales sized 64x48x32 inches with an average green density of 14.6 lb/ft ³ (234 kg/m ³ ) will cube out the truck. FIGURE 2 A indicates that green woody biomass can be compacted to a density of about 14.6 lb/ft ³ (234 kg/m ³ ) by a platen pressure force (i.e., baler system pressure applied to the platen times the area of the platen in inches) of about 50 psi (345 Kpa). However, transporting such green woody biomass bales over long distances would be far from optimal, as this green payload would contain some ten tons of noncombustible water. Drying the bales prior to long-haul transport significantly increases the energy content of the woody biomass payload, but to predictably cube out the truck with dried woody biomass the green woody biomass must be baled at predetermined higher initial densities, for example as shown in Table 2.

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In Table 2, row la summarizes the exemplary green bale cargo: fifty-four 64x48x32 inch bales of green woody biomass, compacted at about 50 psi (345 kPa) to about 14.6 lb/ft ³ (234 kg/m ³ ), will essentially cube out the maximum transport weight while filling about 86% of the available transport volume (3072/(48 x 8.3 x 9)). At an energy value of 9,000 Btu per dry weight pound, this green bale cargo has total energy value of about 222.75 million Btu.

Row lb indicates that green woody biomass (45%wwb) that is baled to about 17.8 lb/ft ³ (285 kg/m ³ ) at a platen pressure of about 61 psi (421 kPa), will dry down to the maximum payload weight at about 30%wwb. The resulting cargo has total energy value of about 283.5 million Btu.

Row lc indicates that drying green bales down to 15%wwb increases the total energy value of the cargo to 344.25 million Btu, provided the green biomass is initially baled at a proportionally higher density (-20.5 lb/ft or 328 kg/m , at about 71 psi or 490 kPa) to accommodate the greater water loss during dry down to the predetermined maximum payload weight.

In this manner, by selectively producing relatively dense green woody biomass bales for drying to predetermined optimum transport densities, especially by natural evaporation and transpiration under ambient conditions, the long-haul highway transportation and fuel costs per unit energy delivered can be greatly reduced and optimized.

Additional economies can accrue during the baling process by limiting the strength (weight) and power (weight, size, noise, and fuel consumption) of the baler, as explained below, to achieve but not unnecessarily exceed an optimized transport density range selected to accommodate particular biomass types and trailer truck configurations.

The experimental data reported herein was acquired in a laboratory-scale baler and confirmed using a full-size woody biomass baler that had the requisite minimum strength and power requirements disclosed herein.

Laboratory-scale baler materials and methods.

Prior to designing and fabricating the laboratory-scale baler, our literature review revealed insufficient prior data for the compression, expansion, and friction properties of compacted woody biomass needed to optimally design a woody biomass baler. By using a lab-scale baler rather than a full-scale machine, material and time were saved in testing and validating hypotheses. The scaling was modeled after the way forces and moments are scaled in homogeneous isotropic materials like steel and aluminum. Woody biomass under pressure can be approximated as an isotropic solid. The pressure-pressure relationships developed in the lab baler were incorporated as explained below into the full-scale prototype baler.

The lab- scale combined baling and infeed chamber measured 68.8 cm (27 inches) long, of which 49.5 cm (19.5 inches) was the enclosed baling chamber. The platen and end wall were 29.2 x 29.2 cm (1 1.5 x 1 1.5 inches).

The bulk of the lab baler structure was made from standard 1018 steel in the forms of 50 x 50 x 6.4 mm wall (2x2x1/4 inch) tubing and 50 x 50 x 6.4 mm (2x2x1/4 inch) angle. The volume of the bale chamber was encompassed by six sides. They consisted of three fixed sides, two sides that were part of the L shaped door, and the sixth side was formed by the compression platen. The bottom and right side both extended from the retracted platen to the end wall. While the corners of these sides were welded in place, the two rails of each side were formed by load beams that could sense force exerted perpendicular to the compression platen, either down or to the side. The opposite sides were formed by the door with the left side being full length, and the top being cut short to designate the infeed. The door was hinged along the lower left corner and clamped in two places opposite the hinge, one close to the infeed and one close to the end wall. The sides and ends of the chamber were slotted such that binding twine could be pushed or pulled around the bale in six places, three in each plane perpendicular to the platen motion. The platen and end wall each had nine evenly spaced posts to create the string passages around the ends of the completed bale. Hydraulic fluid was moved by a Haldex Barnes® Power Unit model number

140001 1, with a 1.5 kW (2 HP) motor capable of moving 95 cc per second (1.5 gpm) at up to 13.8 MPa (2000 psi). The compression cylinder was controlled by an open center, manual, monoblock valve. For safety, the valve was positioned such that the operator could not have hands in the infeed or baling chamber while operating the valve. Compression was facilitated by an 8.9cm (3.5") bore by 45.7cm (18") stroke 20.7 MPa (3000 psi) max cylinder.

Maximum force was 85.6 kN (19250 pounds) and the cylinder fully extended in 30 seconds (1.5cm or 0.6 inches per second). A pressure gauge and a pressure sensor were installed between the directional valve and the base of the cylinder, thus allowing the cylinder pressure to be monitored even when the flow from the pump stopped. A needle valve allowed a finely adjustable flow between the front and rear of the cylinder, and a ball valve allowed oil to escape from the front of the cylinder back to the tank when the direction control was in neutral. A second pressure gauge was located at the pump so pressure could be measured when the control was in reverse.

A wheel type linear position sensor was used to record the position of the platen while hydraulic pressure (from which paten pressure was calculated) and side force (from which Poisson's ratio effect was calculated) were measured. Sensors outputs were recorded simultaneously at 15 times per second.

Engineering constraints for rectangular woody biomass balers.

FIGURE 2A discloses the range of compression platen pressures requisite to compress woody biomass of various water contents to optimum transport densities. This information can be used in two ways. The water content of air-dried woody biomass, like old forest slash, can be determined to select an appropriate curve for correlating platen pressure with a predetermined optimum transport density. Alternatively, this information can be used to predict the weight loss resulting from drying green woody biomass bales to lower water contents. In either case pursuant to this disclosure the biomass baler's compression system can be routinely fabricated to target the corresponding range of platen pressures requisite to achieve a desired range of transport densities.

In practice, expected bale densities are subject to some variability due to the inherent heterogeneity of mixed woody biomass materials. Nevertheless, by mounting a conventional load cell under the baling chamber, the weight of the woody biomass going into a bale can be monitored during loading and flake formation, and the platen pressure adjusted to achieve a completed bale of targeted density. Acceptable variations in bale density will tend to average out when the bales are loaded into multiple-bale cargoes.

However, one cannot take such empirically determined platen pressure v. bulk density data and predict or calculate the minimum strength of a rectangular baling chamber sidewall, without also knowing or determining the Poisson's ratio of the material under compaction.

FIGURE 3 discloses that the woody biomass material exhibits a Poisson's ratio effect (PR) of approximately 1 1%. This physical property, which is substantially independent of water content, is required to determine the minimum mechanical strength (and hence weight) of a baling chamber for producing woody biomass bales at the requisite platen pressures. The distributed force on the back wall is equal to the force of the platen (P _p x A _p ), wherein P _p is the maximum pressure that the baler can apply by the compression platen, and A _p is the area of the platen wall. However, the force resisted (F _w ) by the other baling chamber walls must be at least equal to:

F _w = PR x P _p x A _w

wherein F _w is the distributed load against any one of the chamber walls selected from among the upper wall, the lower wall, and either one of the sidewalls of the rectangular baling chamber, P _p is the maximum pressure that the baler can apply by the compression platen, and A _w is the area of the selected wall. Substituting for the empirically determined Poisson's ratio value of compacted woody biomass, then:

F _w > 0.1 1 x P _p X A _w .

In conventional practice, baler manufacturers will add standard factors of safety to such calculated design constraints, as described in the literature, e.g., Shigley 1963. For example, a Poisson's ratio of 0.3 or 0.5, corresponding respectively to values reported for root wood (Dupuy et al. 2005) and solid lumber (Wood Handbook 2002), may be selected to calculate an estimated upper strength limit, and a market-driven safety factor (SF) may be added to the calculated result. SF is a predetermined design loading multiplier set by the baling chamber manufacturer to ensure that the operational loading is not greater than the design loading. In a representative embodiment, such a calculated upper limit for sidewall strength (0.3 x P _p x A _w ) is multiplied by the identical safety factor that the manufacturer chooses to use for the compression platen, in which case SF as applied to the sidewalls is calculated by dividing the predetermined design failure load of the compression platen by the maximum pressure that the baler can operationally apply by the compression platen (P _p ), such that the design upper limit of the sidewalls is (0.3 x P _p x A _w x SF).

Bale ejection requires that sufficient force be applied against the bale to overcome the total frictional forces (F _f ) that the compacted woody biomass applies to the chamber walls (typically steel) that contain the bale during ejection. We determined using our full-size baler that the coefficient of friction of compacted green woody biomass is approximately 0.60 and decreases as the water content of the biomass decreases. Optionally, coating the baling chamber walls with a low friction material will reduce the applicable F _f value.

For ejection through an open or opened back chamber wall, the bale applies frictional forces against the upper wall, the lower wall, and the two sidewalls. For side ejection, the ejection system must overcome the frictional forces against the platen, lower wall, back wall, and upper wall. Top or bottom ejection systems would be designed to overcome the frictional forces against the platen, back wall, and sidewalls.

The frictional force that the bale applies against any one of the chamber walls is expressed as F _f = F„ x C _f , where F _n is the normal force (calculated below) and C _f is the coefficient of friction of compacted woody biomass on the wall material.

Considering rear ejection, the pressure (P _w ) that the compacted bale applies against the upper, lower, and two sidewalls is equal to the platen pressure times the Poisson's ratio, or P _w = Pp x PR. Alternatively, P _w can be expressed as the normal force divided by the area of the wall, P _w = F _n / A _w .

Assume that the area of the upper and lower walls is L x W; and that of the sidewalls is L x H. Then for each sidewall, P _w = F _n /(L x H), which converts to F„ = P _w x L x H.

Substituting for P _w , then F _n = P _p x PR x L x H. Accordingly, for each sidewall:

F _f = F _n x C _f

Ff = P _p x PR x L x H x C _f .

Similarly, for the upper and lower walls:

Ff = P _p x PR x L x W x C _f .

In combination, then, the cumulative frictional forces during rear ejection are:

F _f total for rear ejection = 2(P _P x PR x L x H x C _f ) + 2(P _P x PR x L x W x C _f ). Pursuant to this disclosure, for woody biomass the Pp for optimum transport density is at least 50 psi (345 kPa), PR is 0.1 1 , and C _f is 0.6. Thus, the rear ejection system should control the compression platen to apply at least the following force to eject the bale through the back wall of the baling chamber:

F _f total for rear ejection = 2(P _P x 0.1 1 x L x H x 0.6) + 2(P _P x 0.1 1 x L x W x 0.6)

(0.132 x P _p x L x H) + (0.132 x P _p x L x W)

(0.132 x P _p x L)(H + W).

For side ejection, the platen and back wall are compacted to the platen pressure, and so for these "sides" of the ejected bale:

P _p = F _n / A _p , or F _n = P _p X W x H.

However, the Poisson's ratio effect still applies to the F _f values for the upper and lower walls, as calculated above. Thus, in combination:

F _f total for side ejection = 2(P _P x W x H x C _f ) + 2(P _P x PR x L x W x C _f )

2(P _P x W x H x 0.6) + 2(P _P x 0.11 x L x W x 0.6)

(1.2 x P _p x W x H) + (0.132 x P _p x L x W)

(P _p x W)(1.2H + 0.132L).

Similarly, top or bottom ejection must overcome the frictional forces against the platen, back wall, and sidewalls. Combining these forces in the manner calculated above, the F _f total for top or bottom ejection of a woody biomass bale compacted to optimum transport density equals at least:

F _f = 2(P _P x W x H x C _f ) + 2(P _P x PR x L x H x C _f )

2(P _P x W x H x 0.6) + 2(P _P x 0.1 1 x L x H x 0.6)

(1.2 x P _p x W x H) + (0.132 x P _p x L x H)

(P _p x H)(1.2W + 0.132L).

Most preferably, the baler compression system is configured to compact the woody biomass material with a force between 50 and 71 psi (345 and 490 kPa). This optimal range, for the most common case of delivery by highway-legal trucks, encompasses the exemplary dry-down strategies disclosed in the Table 2 above.

The baler compression system will typically incorporate one or more hydraulic cylinders to advance the platen and thereby compact the woody biomass material within the baling chamber. The hydraulic system is preferably adjustable by conventional controls to encompass all or a substantial part of this optimal range, in order to permit the operator to select an appropriate platen pressure to achieve a predetermined bale density, taking into consideration initial moisture content, expected dry-down period, and mode of transportation.

The invention accordingly permits an optimized woody biomass transport system including a fleet of semi-trailer trucks that are reversibly loaded at transport intervals with cargoes of parallelepiped bales of woody biomass, wherein the aggregate weight of the loaded bales is at least 80% of the aggregate maximum cargo weight capacities of the loaded semi-trailer trucks, and wherein the aggregate volume of the bales is at least 80% of the aggregate maximum cargo volume capacities of the loaded semi-trailer trucks. The trucks are preferably loaded to at least 85%, and most preferably to at least 90%, of their legal volume and particularly weight payloads. To further reduce transportation costs, the woody biomass bales should be dried before long-haul transport to average moisture contents of less than 30%, preferably less than 20%, and most preferably less than 15%wwb. In this manner, conventional semi-trailer trucks can be routinely loaded with woody biomass payloads having energy values of at least 200 million Btu, for economical transport over highway distances of several hundred miles.

One of ordinary skill in the art will readily understand and appreciate that the platen pressure v. bale density relationships disclosed in FIGURE 2A are just as useful, mutatis mutandis, to predictably and reproducibly produce bales of woody biomass at predetermined lower transportation densities for short haul or barge transportation, as well as at higher densities for long-haul transport by rail or ship. The cost of hauling the extra air content of low-density bales by barge or short-haul truck is relatively low, and that incremental cost may be more than offset by lower fossil fuel consumption in the baling process. Trains and ships have more constrained payload volumes than barges, and maximum higher payload weights than trucks, and so their cargoes can be cubed out at maximum payload by baling at higher platen pressures, in the substantially constant slope regions of the woody biomass curves disclosed in FIGURE 2A. Accordingly, to accommodate such alternative commercial carriers the compression system can be powered to propel the compression platen within a range of force between 26 psi (180 kPa) and 126 psi (870 kPa), and preferably between 46 psi (317 kPa) and 86 psi (593 kPa). Moreover, FIGURE 3 indicates that throughout the noted compression ranges the observed Poisson's ratio of 0.1 1 applies. Engineering constraints for rectangular tall grass biomass balers

In a related embodiment, our invention provides baling chambers of sufficient strength to withstand the Poisson's ratio effect of tall grass biomass when compacted to such densities.

We have elucidated the three rheological properties of tall grass biomass material requisite to predictably and reproducibly bale tall grass biomass at pre-selected optimum highway transportation densities while minimizing fossil fuel consumption during baling, handling, and transport.

First, we have empirically determined the baled bulk density (lb/ft ³ or kg/m ³ ) v. platen pressure (psi or kPa) curves for tall grass biomass at various moisture contents. These relationships indicate the target compression platen pressures that will compress tall grass biomass to predetermined transport densities.

Second, we have empirically determined that tall grass biomass material compacted to optimum transport densities has a Poisson's ratio effect of about 22%. This value is required to determine the minimum mechanical strength of baling chamber sidewalls, be they fixed or moveable, for producing tall grass biomass bales of optimum transport densities.

Third, we have observed that tall grass biomass material compacted to optimum transport densities has a coefficient of friction against steel baling chamber walls of approximately 0.40. This value is necessary, in conjunction with both the target compression platen force and the Poisson's ratio value, to determine the minimum platen pressure required to form and eject a compacted bale of tall grass biomass from the baling chamber.

These three discoveries permit one of ordinary skill to for the first time calculate the requisite strength of tall grass baling chamber walls, which in turn permits one to

manufacture robust, lightweight and economical rectangular balers to produce tall grass biomass bales at high densities optimized for transport on conventional semi-trailer trucks to biorefineries.

Accordingly, the invention provides a tall grass biomass baler having a baling chamber adapted to receive tall grass biomass material and a compression system adapted to compact the material into a rectangular bale in the chamber, wherein the baling chamber has a front wall that acts as a reciprocating compression platen corresponding in dimensions to the width W and height H of the bale, opposing upper and lower walls corresponding in dimensions to the length L and either of the W and H of the bale, and opposing sidewalls corresponding in dimensions to the L and the other of the W and H of the bale, wherein each chamber wall selected from among the upper wall, the lower wall, and each of the sidewalls can withstand a minimum distributed force perpendicular to the selected wall of at least (0.22 x P _p psi x A _w ) pounds, wherein P _p is the maximum pressure that the compression system can apply to the material and A _w is the area of the selected wall expressed in square inches. In a representative embodiment, the compression system can apply at least one platen pressure between 4 psi (27 kPa) and 30 psi (207 kPa) to the material.

FIGURE 2B discloses the range of compression platen pressures requisite to compress tall grass biomass of various water contents to predetermined transport densities. This information can be used in two ways. The water content of winter killed tall grass biomass can be determined to select an appropriate curve for correlating platen pressure with a predetermined optimum transport density. Alternatively, this information can be used to predict the weight loss resulting from drying green tall grass biomass bales to lower water contents. In either case the biomass baler's compression system can be routinely fabricated to target the corresponding range of platen pressures requisite to achieve a desired range of transport densities.

In practice, expected bale densities are subject to some variability but, by mounting a conventional load cell under the baling chamber, the weight of the tall grass biomass going into a bale can be monitored during loading and flake formation, and the platen pressure adjusted to achieve a completed bale of targeted density. Acceptable variations in bale density will tend to average out when the bales are loaded into multiple-bale cargoes.

FIGURE 3 discloses that tall grass biomass (switchgrass) exhibits a Poisson's ratio effect (PR) of approximately 22%. This physical property, which is substantially

independent of water content, is required to calculate the minimum mechanical strength of a baling chamber for producing tall grass biomass bales at the requisite platen pressures. The distributed force on the back wall is equal to the force of the platen (P _p x A _p ), but the force resisted (F _w ) by the other baling chamber walls must be at least equal to:

F _w = PR x P _p x A _w

wherein F _w is the distributed load against any one of the chamber walls selected from among the upper wall, the lower wall, and either one of the sidewalls of the rectangular baling chamber, P _p is the maximum pressure that the baler can apply by the compression platen, and A _w is the area of the selected wall. Substituting for the observed Poisson's ratio of compacted tall grass biomass, then:

F _w > 0.22 x Pp x A _w.

In conventional practice, baler manufacturers will add standard factors of safety to such calculated design constraints, as described in the literature, e.g., Shigley 1963. SF is a predetermined design loading multiplier to ensure that the operational loading is not greater than the design loading. In a representative embodiment, such a calculated upper limit for sidewall strength (0.22 x P _p x A _w ) may be multiplied by the same safety factor that the manufacturer chooses to use for the compression platen, in which case SF as applied to the sidewalls is calculated by dividing the predetermined design failure load of the compression platen by the maximum pressure that the baler can operationally apply by the compression platen (P _p ), such that the design upper limit of the sidewalls is (0.22 x P _p x A _w x SF).

Bale ejection requires that sufficient force be applied against the bale to overcome the total frictional forces (Ff) that the compacted tall grass biomass applies to the chamber walls (typically steel) that contain it during ejection. We determined that the coefficient of friction of compacted tall grass tall grass biomass is approximately 0.40 and decreases as the water content of the biomass decreases. Optionally, coating the baling chamber walls with a low friction material will reduce the applicable Ff value.

For ejection through an open or opened back chamber wall, the bale applies frictional forces against the upper wall, the lower wall, and the two sidewalls. For side ejection, the ejection system must overcome the frictional forces against the platen, lower wall, back wall, and upper wall. Top or bottom ejection systems would be designed to overcome the frictional forces against the platen, back wall, and sidewalls.

The frictional force that the bale applies against any one of the chamber walls is expressed as F _f = F _n x Cf, where F _n is the normal force (calculated below) and Cf is the coefficient of friction of compacted tall grass biomass on the wall material.

Considering rear ejection, the pressure (P _w ) that the compacted bale applies against the upper, lower, and two sidewalls is equal to the platen pressure times the Poisson's ratio, or P _w = P _p x PR. Alternatively, P _w can be expressed as the normal force divided by the area of the wall, P _w = F _n / A _w . Assume that the area of the upper and lower walls is L x W; and that of the sidewalls is L x H. Then for each sidewall, P _w = F _n /(L x H), which converts to F _n = P _w x L x H.

Substituting for P _w , then F„ = P _p x PR x L x H. Accordingly, for each sidewall:

F _f =F _n xC _f

F _f =P _p xPRxLxHxC _f .

Similarly, for the upper and lower walls:

F _f -P _p xPRxLx WxC _f .

In combination, then, the cumulative frictional forces during rear ejection are:

F _f total for rear ejection = 2(P _P x PR x L x H x C _f ) + 2(P _P x PR x L x W x C _f ).

Pursuant to this disclosure, for tall grass biomass the PR is 0.22, and C _f is 0.4. Thus, the rear ejection system should control the compression platen to apply at least the following force (in pounds, when L, W, and H are expressed in inches) to eject the bale through the back wall of the baling chamber:

F _f total for rear ejection = 2(P _P x 0.22 x L x H x 0.4) + 2(P _P x 0.22 x L x W x 0.4)

(0.176 x P _p x L x H) + (0.176 xP _p xLxW)

(0.176 xP _p xL)(H + W).

For side ejection, the platen and back wall are compacted to the platen pressure, and so for these "sides" of the ejected bale:

Pp = F _n / A _p , or F _n = Pp x W x H.

However, the Poisson's ratio effect still applies to the F _f values for the upper and lower walls, as calculated above. Thus, in combination:

F _f total for side ejection = 2(P _P x W x H x C _f ) + 2(P _P x PR x L x W x C _f )

2(P _P x W x H x 0.4) + 2(P _P x 0.22 x L x W x 0.4)

(0.8 x Pp x W x H) + (0.176 x P _p x L x W)

(P _p x W)(0.8H + 0.176L).

Similarly, top or bottom ejection must overcome the frictional forces against the platen, back wall, and sidewalls. Combining these forces in the manner calculated above, the F _f total for top or bottom ejection of a tall grass biomass bale compacted to optimum transport density equals at least:

F _f = 2(P _P x W x H x C _f ) + 2(P _P xPRxLxHxC _f )

2(P _P x W x H x 0.4) + 2(P _P x 0.22 x L x H x 0.4) (0.8 x P _p x W x H) + (0.176 x P _p x L x H)

(P _p x H)(0.8W + 0.176L).

Most preferably, the baler compression system is configured to compact the tall grass biomass material with a platen pressure between about 4 and 30 psi. This optimal range, for the most common case of delivery by highway-legal trucks, encompasses the exemplary dry- down strategies disclosed in the Table 3 below.

Table 3

In Table 3, row la summarizes the exemplary green bale cargo: fifty-four 64x48x32 inch bales of green switchgrass at 45% wwb, compacted to about 14.6 lb/ft (234 kg/m ), will essentially cube out the maximum transport weight while filling about 86% of the available transport volume (3072/(48 x 8.3 x 9)). At an energy value of 7,750 Btu per dry weight pound, this green bale cargo has a net energy value of about 192 million Btu.

Row lb indicates that green switchgrass (45% wwb) that is baled to about 17.8 lb/ft ³ , at a platen pressure of about 14 psi, will dry down to the maximum payload weight at about 30% wwb. The resulting cargo has a net energy content of about 244 million Btu.

Row lc indicates that drying green bales down to 15% wwb increases the net energy content of the cargo to about 296 million Btu, provided the green tall grass biomass is initially baled at a proportionally higher density (~20.5 lb/ft ³ , at ~ 22 psi) to accommodate the greater water loss during dry down to the predetermined maximum payload weight. Rows 2a, 2b, and 2c present similar calculations for late season switchgrass when baled at 30% or 12.5% wwb.

In this manner, by selectively producing relatively dense tall grass biomass bales for drying to predetermined optimum transport densities, especially by natural evaporation and transpiration under ambient conditions, the long-haul highway transportation and fuel costs per unit energy delivered can be greatly reduced and optimized.

Additional economies can accrue during the baling process by limiting the strength (weight) and power (weight, size, noise, and fuel consumption) of the baler to achieve but not unnecessarily exceed an optimized transport density range selected to accommodate particular biomass conditions and trailer truck configurations.

The baler compression system will typically incorporate one or more hydraulic cylinders to advance the platen and thereby compact the tall grass biomass material within the baling chamber. The hydraulic system is preferably adjustable by conventional controls to encompass all or a substantial part of this optimal range, in order to permit the operator to select an appropriate platen pressure to achieve a predetermined bale density, taking into consideration initial moisture content, expected dry-down period, and mode of transportation.

The invention accordingly permits an optimized tall grass biomass transport system including a fleet of semi-trailer trucks that are reversibly loaded at transport intervals with cargoes of parallelepiped bales of tall grass biomass, wherein the aggregate weight of the loaded bales is at least 80% of the aggregate maximum cargo weight capacities of the loaded semi-trailer trucks, and wherein the aggregate volume of the bales is at least 80% of the aggregate maximum cargo volume capacities of the loaded semi-trailer trucks. The trucks are preferably loaded to at least 85%, and most preferably to at least 90%, of their legal payloads. To further reduce transportation costs, the tall grass biomass bales should be dried before long-haul transport to average moisture contents of less than 30%, preferably less than 20%, and most preferably less than 15%. In this manner, conventional semi-trailer trucks can be routinely loaded with tall grass biomass payloads having energy values of at least 200 million Btu, for economical transport over highway distances of several hundred miles.

One of ordinary skill in the art will readily understand and appreciate that the platen pressure v. bale density relationships disclosed in FIGURE 2B are just as useful, mutatis mutandis, to predictably and reproducibly produce bales of tall grass biomass at predetermined lower transportation densities for short haul or barge transportation, as well as at higher densities for long-haul transport by rail or ship. The cost of hauling the extra air content of low-density bales by barge or short-haul truck is relatively low, and that incremental cost may be more than offset by lower fossil fuel consumption in the baling process. Trains and ships have more constrained payload volumes than barges, and maximum higher payload weights than trucks, and so their cargoes can be cubed out at maximum payload by baling at higher platen pressures, in the substantially constant slope regions of the tall grass biomass curves in FIGURE 2B. Moreover, FIGURE 3 indicates that throughout the noted compression ranges the observed Poisson's ratio of 0.22 applies.

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While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.