US20120204482A1

US20120204482A1 - Moisture resistant biomass fuel compact and method of manufacturing

Info

Publication number: US20120204482A1
Application number: US13/453,999
Authority: US
Inventors: Robert Heimann
Original assignee: Enginuity Worldwide LLC
Current assignee: Enginuity Worldwide LLC
Priority date: 2010-01-29
Filing date: 2012-04-23
Publication date: 2012-08-16

Abstract

A method of processing a biomass fuel compact is provided that includes combining a composition of combustible biomass materials, comminuting the composition of biomass materials, adding an adhesive to the biomass materials to form a composite biomass, the adhesive having a starch and a hydroxide, forming the composite biomass into a shapeform, and heat treating the composite biomass shapeform at a base temperature sufficient to break O—H bonds, the base temperature being below a mean torrefication temperature of the composite biomass such that torrefaction of a substantial portion of the biomass materials does not occur.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 13/018,155, titled “Biomass Fuel Compact Processing Method” filed on Jan. 31, 2011, the contents of which are incorporated herein by reference in their entirety.

FIELD

The present disclosure relates to renewable energy sources, and in particular, resources that do not depend on fossil fuels and that reduce emissions of “greenhouse gas” carbon dioxide into the atmosphere. More specifically, the present disclosure relates to manufacturing processes for creating combustible biomass, or biofuel materials.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
With the recent emphasis on renewable energy sources, efforts have been made in the art to create so-called “biomass” materials, in which a combustible combination of waste, such as wood chips or sawdust, along with certain additives, are combined and processed to create an energy resource that can take the place of, or be combined with, for example, coal. A common biomass is the wood pellet, which is now subject to a standard developed by the Pellet Fuels Institute. More specifically, a “premium” oak species wood pellet provides 8810 BTU/lb, and a “standard” pine species wood pellet provides 9600 BTU/lb. Furthermore, both ash and chlorine content are provided by the standard.
Known biomass materials contain natural lignins, which are released with heat of the constituent materials in order to bind the materials together into a burnable mass. Natural lignins, for example from various wood sources, are complex natural polymers resulting from oxidative coupling of, primarily, 4-hydroxyphenylpropanoids. Additionally, other materials such as thermoplastic resins have been used to bind the constituent materials together.
However, these natural lignins and thermoplastic binders do not create a biomass that is durable for transport or other processing operations. Moreover, these biomass forms suffer from chronic crumbling and dust generation during production and downstream handling. Significant amounts of dust can become an explosive issue, and thus current binders in the art may ultimately cause safety hazards. As a further disadvantage of known binders, product uniformity is an issue, with irregular lengths and ragged cuts, which further add to the dust problem. As other materials without natural lignins are added, such as switchgrass, forest litter, paper waste, cane waste, corn stover, grass hay, and the like, product quality is reduced, and the dust issue often becomes more aggravated. Additionally, some of the known binders generate gases during the burning process that are environmentally undesirable, and in fact, some of the binders are not completely combusted during the burning process.
An additional handling issue with biomass fuel sources is moisture absorption. Due to their porous nature, biomass materials are prone to moisture absorption and subsequent degradation during transportation and storage. Additionally, bacteria can develop in biomass materials that contain moisture, which leads to the production of methane and thus a significant risk factor in transportation and storage. Efforts have been made to use additional binders and/or to further process the biomass fuel sources in order to provide moisture resistance. However, these efforts are often costly and require significant additional processing energy, thereby reducing the cost and environmental benefits of biomass as an alternative fuel source.

SUMMARY

In one form of the present disclosure, a method of processing a biomass fuel compact is provided that comprises combining a composition of combustible biomass materials, comminuting the composition of biomass materials, adding an adhesive to the biomass materials to form a composite biomass, the adhesive consisting of a starch and a hydroxide, forming the composite biomass into a shapeform, and heat treating the composite biomass shapeform at a base temperature sufficient to break O—H bonds, the base temperature being below a torrefication temperature of the composite biomass such that torrefaction of the biomass materials does not occur. Various biomass fuel compacts manufactured according to the methods of the present disclosure are also provided.
In another form, a method of processing a biomass fuel compact is provided that comprises heat treating biomass materials of the biomass fuel compact at a base temperature sufficient to break O—H bonds, the base temperature being below a torrefication temperature of the biomass fuel compact such that torrefaction of the biomass materials does not occur.
In still another form, a method of processing a biomass fuel compact is provided that comprises heat treating biomass materials of the biomass fuel compact at a base temperature sufficient to break O—H bonds, the base temperature being below a mean torrefication temperature of the biomass fuel compact such that torrefaction of a substantial portion of the biomass materials does not occur.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a process flow diagram illustrating the various steps and forms of the manufacturing processes according to the teachings of the present disclosure;

FIG. 2 is a process flow diagram illustrating the various steps and forms of another manufacturing processes according to the teachings of the present disclosure;

FIG. 3 a is a photograph of a sample biomass fuel compact manufactured according to the teachings of the present disclosure;

FIG. 3 b is a photograph of a container filled with sample biomass fuel compact shapeforms defining sectors, and more specifically quadrants, manufactured according to the teachings of the present disclosure;

FIG. 4 is a perspective view of a biomass fuel compact manufactured according to the teachings of the present disclosure and having a shapeform defining a cylindrical sector in accordance with one form of the present disclosure; and

FIG. 5 is a photograph of an experimental test conducted on the quadrant shapeforms after passing through a conventional coal chute, illustrating a relatively even distribution without any binding, bridging, or lodging within the delivery chute.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
Referring to FIG. 1, manufacturing steps for processing a biomass fuel compact, and variations thereof, are shown. It should be understood that these steps may be carried out in order as shown, or alternately, in a different order. Therefore, the order of the steps illustrated should not be construed as limiting the scope of the present disclosure. In one form, the method of processing a biomass fuel compact comprises combining a composition of biomass materials. These biomass materials are essentially any combustible material, or combination of combustible materials. For example, these materials may include saw dust, cardboard and chipboard, grass, switchgrass, energy crops, hay, tree bark, sweetgum seed pods, pinecones, newsprint, wheat straw, duckweed, pine needles, mixed leaves, yard waste, agricultural waste, cotton waste, grape and wine offal, corn stover, crop stovers, peat, tobacco waste, tea waste, coffee waste, food processing waste, food packaging waste, nut meats and shells, chestnut hulls, pecan shells, animal waste, livestock waste, mammal waste, municipal solid waste, paper waste, pallets, and egg cartons, among others. Other combustible materials may also be employed, and thus these biomass materials should not be construed as limiting the scope of the present disclosure.
Next, these biomass materials may be comminuted, or crushed, to a particle size that is compatible with the specific process, and also with other additives and various processing steps, as set forth in greater detail below. The comminuted composition of biomass materials may next be dried, or alternately, the comminuted composition of biomass materials may be wet before entering a forming step, again depending on a variety of processing parameters. For example, if a tree or wood products were used as part of the biomass composition, then the comminuting step would take these materials down to a sawdust form. The comminution process may be carried out, for example, by tub grinders, horizontal grinders, hammer mills, burr mills, or shredders, among others. Each type of biomass material will have a different derived particle size from the comminuting step. Generally, particle size requirements are based on desired throughput rates. In one form of the present disclosure, a particle size that is about 20 to about 40%, and more particularly about 30%, of the die opening/diameter used to produce the desired shapeform. These particle sizes facilitate flow rates without excessive processing back-pressure.
If the biomass materials are dried before entering the forming step, a moisture content of about 8% to about 20%, and more specifically about 12%, is typical for many types of biomass materials. In one form of the present disclosure, the drying is performed by low cost solar collector troughs that concentrate solar energy and heat suitable thermal mediums such as oil, antifreeze, water, or a mixture thereof, for transmission of heat energy through liquid to air heat exchangers. Alternately, geothermal drying may be employed, alone or in combination with gas-fired or electric drying processes. Drying equipment may also be conventional grain drying batch hoppers, bins, or silos, or higher throughput horizontal dryers. Further still, heat may be transferred through a passive floor heating system. In yet another form, single or multiple desiccant beds may be employed to remove moisture from the drying air. It should be understood that these drying methods are merely exemplary and thus should not be construed as limiting the scope of the present disclosure.
An advantageous step of the present disclosure involves adding an adhesive to the biomass materials, wherein the adhesive comprises a starch and a hydroxide.
Advantageously, the biomass fuel compact is highly durable do to its inventive adhesive additive. Generally, the biomass fuel compact uses a Stein Hall type adhesive made from starch, or any other suitable material to replace the natural lignins as set forth above. In a Stein Hall adhesive, about 5% to 20% of the total starch content is gelatinized into a high viscosity paste called primary starch. The remainder of the starch (about 80% to 90%) stays ungelatinized and is called secondary starch. The starch may be one produced from wheat, oats, rice, corn, wheat middling, wheat waste or even wood and the like, but containing a gelatinized fraction that upon substantial drying will tightly bond the biomass composition.
Additionally, the adhesive additive includes a hydroxide. The hydroxide may be, for example, alkali metal hydroxides, alkaline earth hydroxides, sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, and caustic soda, among others. The synergistic combination of starch and hydroxide provide a highly durable biomass fuel compact, in which any number of constituent combustible materials may be used, without relying on any natural lignins or other undesirable binders.
In one form, the innovative adhesive is provided to bind the constituent biomass composition and also to form a substantially continuous shell around the exterior portion of the fuel compact. With this shell, the biomass fuel compact according to the present disclosure is highly durable and significantly reduces the traditional dust issues associated with biomass compositions, as set forth above.
In one exemplary composition of the present disclosure, the biomass fuel compact comprises, by percent weight, about 69-98% biomass composition, about 1-30% starch, and less than 1% hydroxide. Another composition is about 90-95% biomass and about 5-10% of the inventive adhesive additive.
Further additives are also provided by the present disclosure, which may include, by way of example, a silicate additive, (which may be a liquid or powder form), a viscosity additive, a preservative, and a BTU additive. The silicate additive is included to provide added weather resistance and hydrogen bonding of biomass particles. The silicate may include sodium, potassium, or lithium, or mixtures of these three in one form of the present disclosure. The viscosity additive may be a naturally occurring biomass such as duckweed reduced to a flour particle size, or rice hulls, or coal dust, or any other viscosity altering substance. The preservatives may include, by way of example, fungicides, biocides, or mixtures of these two, in one form of the present disclosure. In another form, the preservative may include sodium tetraborate or borax containing compounds at a concentration of about 1 to about 5%, and more particularly, about 1 to about 2%. Moreover, sodium silicate may be added to improve water repellency and act as a biocide, along with any oil, natural or petroleum based, used motor oil, or oil derivatives as the BTU additive.
The additives may also include materials that will benefit the combustion or emission profile of the biomass. When calcium hydroxide is used as a source of hydroxide, it may react to form calcium silicate, which scavenges sulfur dioxide and nitrous oxides in air emissions from combustion in flue gas. When lithium hydroxide is used, it may react and form lithium silicate, which forms a zeolite capable of sequestering carbon dioxide from combustion gases. Furthermore, it is contemplated that the addition of a mix of alkali metal or alkaline earth hydroxides may be beneficial to the emission of undesirable gases from combustion of the innovative compacts according to the teachings of the present disclosure.
Each of the viscosity additive and the BTU additive, in one form of the present disclosure, are combustible materials. The viscosity additive, in one form, is a naturally occurring biomass such as duckweed, rice hulls, and coal dust. Furthermore, by way of example, the BTU additive is an oil or an oil derivative, either natural or petroleum based, and either new, off specification, or waste oil.
In a further exemplary composition, the biomass fuel compact comprises about 50-95% biomass, about 5-50% starch, about 0.005-0.05% hydroxide, about 0.1-5% silicate additive, and about 0.1-2% viscosity additive or preservative. In should be noted that the BTU additive may comprise about 1 to about 40% of the final fuel compact composition. Further compositions according to the teachings of the present disclosure are set forth below in Table 1, with an exemplary target value for one biomass composition that comprises grass, corn stover, or a mixture thereof, according to the teachings of the present disclosure:

TABLE 1

Biomass	Starch	Hydroxide	Silicate	Viscosity	Preservative	BTU

Range	50-90%	1-50%	0.005-0.05%	0-5%	0-15%	0-2%	0-30%
Target	60	4	0.02	2.5	2	0.48	25

According to the various compositions of the present disclosure, an energy content of about 8,500 BTU/lb is achieved with the claimed biomass fuel compact.
After or during the introduction of additives, the composite biomass is formed into a shapeform. In one form of the present disclosure, the forming step is performed by an extrusion process. Other manufacturing processes may also be employed, including but not limited to compression molding, plunger molding, and die forming. Therefore, the extrusion process should not be construed as limiting the scope of the present disclosure. In one desired form of the present disclosure, the extruder premixes, extrudes, and cuts to length a composite biomass fuel compact at about 500 to about 30,000 pounds per hour.
In one form, the innovative adhesive is added at a throat portion of the extruder. Alternately, the adhesive is added in a hopper portion of the extruder. In still another form, the adhesive is added in a die portion of the extruder and is configured to coat an exterior surface area of the composition of biomass materials. The adhesive may be further divided within the processing step, wherein the starch is mixed with the biomass composition prior to forming, and the hydroxide is added during the forming. Alternately, the hydroxilazed, gelled starch is added between the throat and before the forming die. Additionally, steam may be used as a processing aid during forming in order to provide for better physical properties of the biomass composition and additives.
With plunger molding, in one form the adhesive is added between wads of the plunger. Alternately, the adhesive is added at a plunger input and is configured to coat an exterior surface area of the composition of biomass materials at an exit die.
It is further contemplated that a mechanical briquetting process, such as the Brik Series by Dipiu Macchine Impianti, Italy, or BHS Energy LLC, Wyoming, Pa., USA, may be employed in accordance with the teachings of the present disclosure.
The shapeform of the composite biomass may be any number of geometric configurations, including but not limited to pellets, briquettes, pucks, and the innovative corn kernel configuration as described in the copending application set forth above.
After the composite biomass is produced as a shapeform, it is partitioned into individual pieces. The individual pieces may be the same size, or of varying sizes/lengths. In one form, the individual pieces are compatible with any existing powerplants. These existing powerplants comprise, by way of example, combustion, power generation, gasification, ethanol, digestion, and steam generation plants.
In one form of the present disclosure, the processing is performed at lower temperatures such that an endothermic reaction of the biomass materials and adhesive results. These temperatures are in the range of about 200 to about 250° F. for an extrusion process, and similarly, about 25 to about 200° F. for other plunger or flywheel processes.
Moisture Resistance
Referring now to FIG. 2, another form of the present disclosure involves additional manufacturing steps in order to provide improved moisture resistance in the biomass fuel compact. More specifically, the method involves heat treating biomass materials of the biomass fuel compact at a base temperature sufficient to break O—H bonds, the base temperature being below a torrefication temperature of the biomass fuel compact such that torrefaction of the biomass materials does not occur. And in one form, the biomass materials are heat treated at a base temperature being below a mean torrefication temperature of the biomass fuel compact such that torrefaction of a substantial portion of the biomass materials does not occur.
By way of background, thermal and chemical treatment of biomass typically fall in the following temperature ranges:
Dehydration: about 382° F. (194° C.) to about 455° F. (235° C.);
Rectification: about 455° F. (235° C.) to about 482° F. (250° C.); and
Torrification: about 482° F. (250° C.) to 518° F. (270° C.). (It should be noted, however, that some sources indicate broadly that torrefaction occurs between 200° C. and 300° C.).
Further, biomass is generally comprised of hemicelluloses, cellulose, and lignin with each type varying in content for a particular biomass type as well as its response to thermal treatment.
According to the present invention, it has been determined that water adsorption characteristics are positively affected by heat treatment of the biomass in order to break O—H bonds. The response to low temperature treatment in the range of about 120° F. to about 455° F. using ovens and/or microwave energy-induced heating, or infrared (IR) induced heating, produced a weather/moisture resistant biomass fuel compact. Referring to FIG. 3 a, an example of such a biomass fuel compact that has been heat treated is illustrated and generally indicated by reference numeral 100. Various biomass materials were processed over a temperature range of 120° F. to 590° F. in an inert atmosphere in order to determine that the target temperature need not be as high as torrefication or even rectification for most biomass materials in order to provide a sufficient amount of moisture resistance. According to the present disclosure, a “base temperature” for the biomass materials is a lower temperature (about 120° F. to about 455° F. as set forth above) that produces a Maillard-like reaction, a non-enzymatic reaction that produces browning of some food stuffs, such as bread and coffee beans. Therefore, as used herein, a base temperature shall be construed to mean a temperature sufficient to break O—H bonds, the base temperature being below a mean torrefication temperature of the biomass fuel compact such that torrefaction of a substantial portion of the biomass materials does not occur.
In one form of the present disclosure, coarse ground biomass is heat treated up to about 455° F. to dehydrate in conventional dryers. In one form, this is accomplished in two steps. First, in a rotary kiln, such as a triple-pass dryer for effluent drying down to about 5-10% moisture content. A second step can be in a conventional oven, microwave or the like with an inert atmosphere such as carbon dioxide, followed by a final size and particle reduction to suit the follow-on compaction equipment. A higher temperature heat treatment of about 250° F.-450° F. in a carbon dioxide atmosphere enhances cell disruption to release intersticial moisture, thereby rendering the biomass friable. It should be understood that at temperatures in the lower portion of the range of the present disclosure (near about 120° F.), it is possible to sufficiently heat treat the biomass materials in an environment that is not inert. Therefore, an inert heat treating environment should not be construed as limiting the scope of the present disclosure.
One form of the present disclosure uses a high wattage microwave, for example from about 90 to about 3,200 watts, to perform the heat treatment. However, certain biomass materials are transparent to microwave energy. These include most grasses, and grain stover. Therefore, by the addition of a few percent of microwave receptors, such as woody biomass, nut shells, coffee grounds or the like, the biomass composition can be properly heat treated according to the teachings of the present disclosure. In one form, the microwave heat treatment is continuous with the other processing steps of combining, comminuting, adding the adhesive, and forming the composite biomass, among other possible processing steps. As a continuous process, the biomass materials are passed through a sealed microwave environment without an interruption of opening and closing the microwave environment.
Referring now to FIGS. 3 b and 4, a novel shapeform 120 is provided by the present disclosure. As shown, the shapeform 120 is a sector, and in one form is ¼ of a cylindrical puck (shown in FIG. 3 a) to define a quadrant. This quadrant form is relatively simple to manufacture by cutting the cylindrical puck of FIG. 3 a into equal quarters. It should be understood, however, that this shapeform and variations/derivative thereof may be manufactured by other processes such as molding or grinding, by way of example, and thus partitioning the cylindrical puck as set forth above should not be construed as limiting the scope of the present disclosure.
Referring to FIG. 5, the quadrant shapeform was tested in a conventional coal chute to determine how well it would distribute in a holding area or combustion floor and if it was susceptible to binding, bridging, or lodging within the delivery chute on its way to a destination. In this test, the quadrant shapeform was dropped through a coal chute, through fuel distribution ports, and to the floor of a solid fuel boiler. A batch of conventional coal (shown as black pieces on floor of holding area) was first distributed within the holding area in order to compare its distribution with the novel quadrant shapeform (shown as the lighter pieces on floor of holding area) of the present disclosure. As shown, the quadrant shapeform exhibited an excellent and relatively even distribution within the holding area that was comparable to the coal distribution. Therefore, the quadrant shapeform demonstrated suitability to be used within existing coal processing equipment, thereby providing further benefits from the biomass compact according to the teachings of the present disclosure.
In another form of the present disclosure, an oil coating is applied to at least a portion of the composite biomass shapeform after heat treating. This oil coating may be sprayed onto, or the biomass may be dipped into a bath of oil, by way of example. The oil coating is provided in order to further improve the moisture resistance of the biomass fuel compact, and to increase its BTUs when fired. The oil may be used restaurant waste, used motor oil, or hydraulic fluids, by way of example.
It should be noted that the disclosure is not limited to the embodiment described and illustrated as examples. A large variety of modifications have been described and more are part of the knowledge of the person skilled in the art. These and further modifications as well as any replacement by technical equivalents may be added to the description and figures, without leaving the scope of the protection of the disclosure and of the present patent. For example, the combining and comminuting steps as shown in FIG. 2 may be performed in either order, and the heat treating may occur on the raw biomass materials prior to adding the adhesive as shown. Further, the adhesive need not be the starch and hydroxide as set forth herein, or an adhesive may be omitted all together while remaining within the scope of the present disclosure.

Claims

1. A method of processing a biomass fuel compact comprising:

combining a composition of combustible biomass materials;

comminuting the composition of biomass materials;

adding an adhesive to the biomass materials to form a composite biomass, the adhesive comprising a starch and a hydroxide;

forming the composite biomass into a shapeform; and

heat treating the composite biomass shapeform at a base temperature sufficient to break O—H bonds, the base temperature being below a torrefication temperature of the composite biomass such that torrefaction of the biomass materials does not occur.

2. The method according to claim 1 further comprising applying an oil coating to at least a portion of the composite biomass shapeform after heat treating.

3. The method according to claim 1, wherein the heat treating is performed in an inert environment.

4. The method according to claim 1, wherein the heat treating is performed in a microwave apparatus.

5. The method according to claim 4, wherein the composite biomass shapeform is heat treated by the microwave apparatus in a continuous process.

6. A biomass fuel compact manufactured according to the method of claim 4, wherein the combustible biomass materials include at least a portion of microwave receptors.

7. The method according to claim 1, wherein the heat treating is performed in a temperature range of about 120° F. to about 455° F.

8. A biomass fuel compact manufactured according to the method of claim 1.

9. The biomass fuel compact according to claim 8, wherein the shapeform defines a cylindrical sector.

10. The biomass fuel compact according to claim 9, wherein the cylindrical sector is a quadrant.

11. A method of processing a biomass fuel compact comprising heat treating biomass materials of the biomass fuel compact at a base temperature sufficient to break O—H bonds, the base temperature being below a torrefication temperature of the biomass fuel compact such that torrefaction of the biomass materials does not occur.

12. The method according to claim 11, wherein the heat treating is performed after the biomass fuel compact is formed into a shapeform.

13. The method according to claim 11, wherein the heat treating is performed on the biomass materials before the biomass fuel compact is formed into a shapeform.

14. The method according to claim 11 further comprising adding an adhesive to the biomass materials to form a composite biomass, the adhesive comprising a starch and a hydroxide, wherein the composite biomass is further processed into a shapeform.

15. The method according to claim 11 further comprising applying an oil coating to at least a portion of the biomass fuel compact after heat treating.

16. The method according to claim 11, wherein the heat treating is performed in an inert environment.

17. The method according to claim 11, wherein the heat treating is performed in a microwave apparatus.

18. The method according to claim 17, wherein the biomass fuel compact is heat treated by the microwave apparatus in a continuous process.

19. A biomass fuel compact manufactured according to the method of claim 17, wherein the biomass materials include at least a portion of microwave receptors.

20. The method according to claim 11, wherein the heat treating is performed in a temperature range of about 120° F. to about 455° F.

21. A biomass fuel compact manufactured according to the method of claim 11.

22. The biomass fuel compact according to claim 21 having a shapeform defining a cylindrical sector.

23. The biomass fuel compact according to claim 22, wherein the cylindrical sector is a quadrant.

24. A method of processing a biomass fuel compact comprising heat treating biomass materials of the biomass fuel compact at a base temperature sufficient to break O—H bonds, the base temperature being below a mean torrefication temperature of the biomass fuel compact such that torrefaction of a substantial portion of the biomass materials does not occur.