US20070251143A1

US20070251143A1 - Synthetic fuel pellet and methods

Info

Publication number: US20070251143A1
Application number: US11/789,921
Authority: US
Inventors: Jan K. Michalek; Theodore J. Thomas
Original assignee: Slane Energy LLC
Current assignee: Slane Energy LLC
Priority date: 2006-04-26
Filing date: 2007-04-25
Publication date: 2007-11-01
Also published as: WO2007127253A3; WO2007127253A2

Abstract

The present invention includes a synthetic fuel pellet, the pellet comprising a compressed agglomeration of: (a) coal fines; (b) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated; and (c) at least one binder, the binder adapted to form a pellet of the coal fines and the fibrous cellulosic material.

Description

PRIOR APPLICATION DATA

The present application claims the benefit of provisional patent application Ser. No. 60/795,401, the entire disclosure of all of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention is in the field of synthetic fuels, and relates generally to the production of non-traditional fuels, often referred to as synthetic fuels prepared from waste products such as coal fines and waste cellulosic materials. More particularly, this invention relates to the creation of such fuels using existing stockpiles of coal fines, coal dust, and other similar small particles of virgin coal.

DESCRIPTION OF THE PRIOR ART

For centuries coal has been mined as a source of fuel. During these years, numerous improvements have been made to increase mining efficiency and safety, and to improve the overall quality and purity of the end product. However, one drawback of coal mining is the by-product of coal fines that frequently end up abandoned into waste pits scattered throughout the countryside. These coal fines constitute up to 20% of the coal being mined, and are found in the waste stream generated by the initial washing and filtering of the coal from the mine. Although coal fines include particles as small as dust motes, the term can also include pieces of coal up to about one-half inch in diameter. This material has traditionally been abandoned to waste, deposited in the form of “coal tips,” because it has been economically inefficient to handle such sizes as they are brought to the point of being burned for their energy content. As a result, literally millions of tons of such material have been produced over the years, and currently lay dormant at or near mining sites. Not only does this non-use pose a great waste of valuable natural fuel resources, but it also poses a threat to the surrounding environment. In addition to respiratory hazards presented by the dust-sized particles, the large surface area associated with stockpiles of such particles poses a high risk for spontaneous combustion such as the type known as a dust explosion.
These environmental issues, together with the growing concern of the limited existing amount of natural fuel resources, has led to an increased interest in utilizing these dormant coal fines, as well as developing an alternative use of virgin coal.
Numerous processes have been proposed and implemented in the past for agglomerating particles. Most forms of agglomeration methods use either an organic binder such as lignosulfonate, petroleum pitch, latex or polymers, or an inorganic binder such as cement or bentonite. Binder choice depends principally on the cost of the binder and product quality required.
U.S. Pat. No. 44,994 to Cornell, issued over a century ago, teaches that coal dust can be pelletized by saturating it with a solution of starch, pressing it, or otherwise forming it into blocks or lumps, and drying it in the sun or by other suitable means. When these starch-based binders are used, the resulting green pellets must be dried to achieve acceptable fuel performance and reduce transportation costs. Also, starches and sulfates have no apparent ability to completely fuse the coal fines. Moreover, when rewetted, the bond weakens. Thus, pellets made with starch and sulphate binders are neither strong nor waterproof. Sulfates also add sulfur to the coal which produces undesirable sulfur oxides and stack gases, which is direct noncompliance with the clean air regulations.
U.S. Pat. No. 852,025 to Mashek discloses preparing coal for briquetting by drying and heating it, mixing an asphaltic binder material, then heating, cooling, and compacting the mixture. More recently, U.S. Pat. No. 5,752,993 to Eatough discloses a binder composition made up of tar, acid, a polymeric binder, water and, if necessary, a surfactant to aid in wetting the carbonaceous material. These asphaltic and tar binder compositions are well known in the art. However, they do not sufficiently prevent the bound material from absorbing water and they are not suitable for industrial use due to their soft and “gummy” characteristics. These binders produce a product that fouls the feed lines to furnaces by clogging the inlets. Neither can they be transported or stored without absorbing water and either degrading or decreasing in BTU content.
Many other natural and synthetic particles have been utilized as binders for coal fines. U.S. Pat. No. 5,244,473 to Sardessai discloses a binder for coal fines made from a phenolaldehyde resin mixed with a polyisocyanate in the presence of a catalyst. U.S. Pat. No. 5,089,540 to Armbruster discloses a binder for foundry molds made from an extra cured alkaline phenolic resin, which can be enhanced by conditioning the reclaimed sand with a solution containing an amine and a saline.
Likewise, U.S. Pat. No. 5,487,764 to Ford discloses the use of a binder composition made up of a styrene in a hygroscopic solvent (methyl ethyl ketone), polyvinyl acetate and water. Regrettably these prior art binders are derived from useful and often expensive raw materials such as natural and synthetic polymer, thereby adding significantly to the overall cost of the briquette and making their use cost prohibitive.
The use of such binders requires water. Unfortunately, the heating value of coal decreases as moisture content increases. Moreover, large amounts of water are associated with the fine coal either because it is being recovered from black water ponds or because the fines are slurried with the binder to achieve the desired coating. Regardless, water in the final product is undesirable as it is useless weight, increasing transportation costs and, as a result, decreasing the BTU content per ton. As a result, many examples of prior art have failed to produce synthetic fuels that have sufficient heating value.
Therefore, a need has remained for an inexpensive, yet reliable, coal binder that, when used to produce a fuel product, produces a strong, weather resistant, environmentally compliant fuel product.
The government has provided yet another incentive: a tax credit to those who create synthetic fuels. To qualify for this credit fuels must undergo a “significant chemical change.” The change is measured by comparing the synthetic fuel product to ingredients used to make it. Laboratory measurements of the feed stock coal, binders, additives and/or supplements are composited and compared to the synthetic fuel to verify that the chemistry of the synthetic fuel cannot be predicted from the ingredients. If the chemistry of the product is different than a mere mixture of the ingredients and the differences are statistically significant, the fuel may be deemed qualified. With the above binder shortcomings in mind it is apparent there is still need for improved binders and briquetting processes.
Attempts to utilize coals fines as fuel include the method disclosed in White (U.S. Pat. No. 5,916,826), which teaches a method of pelletizing and briquetting coal fines using bio-binders produced by liquefaction of biomass. Unfortunately, this process is extremely costly, primarily because of the required liquefaction process, which is carried out in an oxygen-free environment at elevated temperatures—between 450 degrees and 700 degrees F.—and elevated pressures, typically between 200 psi and 3,000 psi. The resulting liquid is then sprayed on coal fines that have themselves been heated to at least 250 degrees F., after which the coal and the liquid are allowed to react at about 300-400 degrees F. Although this method serves to alleviate certain environmental concerns, the high costs of reclaiming coal using this process undercuts the basic usefulness of the invention itself.
Another recent example of the attempt to use coal fines as fuel, Ford (U.S. Pat. No. 5,453,103; issued 1995), discloses a method of forming solid fuel pieces from coal fines by combining and mixing water, hydrochloric acid, a conditioner, and a polyvinyl acetate (PVA) emulsion and then compressing the resulting slurry into solid fuel pieces. Although this process is effective, its requirement of PVA, which must be separately created for this particular use, makes the Ford process economically and environmentally inefficient in comparison with a process founded entirely on the use of constituents that are already present, and which some of the constituents are not being devoted to any economical purpose. In other words, a process that consumed both coal fine waste and another hitherto waste element would be more desirable than the Ford process.
A process that does use as input primarily waste products from other industrial operations is revealed by Major (U.S. Pat. No. 6,013,116), which teaches a composition for binding coal fines into larger pieces, typically called briquets. The briquet-binder composition of Major can be produced using an asphalt base, sodium carbonate pulping liquor, and a surfactant. However, for optimal binding results, strength-increasing additives such as latex, vinyl derivatives, cellulose, cellulose derivatives, peat moss, starch, starch derivatives, and various pulps need to be added to the binder composition. (The addition of lignosulfate, cement, rubber, and plastics is also taught by Major.) Although this process does use various waste products of other industries in transforming coal fines into a more usable fuel source, the complexity of the binding material makes the process quite complex, thereby reducing the economic viability of the overall method.
An older process of reclaiming coal fines is disclosed in Dondelewski (U.S. Pat. No. 4,357,145; issued 1982). In Dondelewski, coal fines are combined with a liquid by-product of the pulp and paper industry, namely a liquid containing tall oil, tall oil pitch, or mixtures thereof (“tall oil mix”). Tall oil and tall oil pitch are by-products from the digestion of wood by the Kraft (sulfate) paper manufacturing process. In the Dondelewski method, the coal fines are first put into the form of a slurry by mixing them with water. After the slurry has been formed, it is fed to a conditioning tank where it is mixed with tall oil mix. In the conditioning tank, the tall oil mix adheres to and thus coats the surfaces of the individual coal particles, after which the slurry of now-coated coal particles and excess tall oil mix is introduced into a flotation cell, where the coated coal particles are separated from the excess tall oil mix and most of the water. Vacuum filters, vibratory screens and centrifuges may be used to remove excess liquid, a necessary step since most coal—consuming furnaces cannot tolerate high moisture content. Again, although the process of Dondelewski has as its feed stock predominantly industrial by-products, it is very process intensive, first requiring large vats to mix the coal slurry and tall oil mix, followed by further processing to remove excess water and tall oil mix followed by drying the end product. Thus, the method of Dondelewski does not satisfy the condition of using industrial by-products to produce a synthetic fuel that is economically competitive with the fuels that the synthetic fuel is intended to supplant, or which in general is in competition with it as a fuel source.
Another method is described by Pradeep Agarwal, et al. (U.S. Published Patent Application No. 20020014155; published 2002). This method involves agglomerating and processing carbonaceous fines by powdering the carbonaceous fines, mixing the powdered carbonaceous fines with an organic liquid creating a slurry, adding a predetermined amount of an aqueous electrolyte to the slurry creating agglomerated particles, settling the large agglomerated particles resulting in a settled mixture of agglomerated coal fines and reagent liquor, and separating the agglomerated coal fines from the reagent liquor.
Still another method is described by Donovan (U.S. Pat. No. 6,558,442; issued 2003) and includes a method of producing a synthetic fuel comprising the steps of: (a) preparing an emulsion comprising a tall-oil-mix and water, and (b) reacting the emulsion with coal fines of bituminous coal so as to obtain the synthetic fuel comprising emulsion-treated coal fines. An additional method is further disclosed by Donovan (U.S. Published Patent Application No. 20040049973; published 2004). This method produces a synthetic fuel by treating bituminous coal fines with a tall-oil mix that may include enhancer additives that either increase the chemical change capability of the tall-oil mix or reduce the cost of the tall-oil mix while maintaining the chemical change rate, and/or an additive of tar decanter sludge and light cycle oil. Enhancers include poly vinyl acetate (PVA) and/or ethyl vinyl acetate (EVA), glycol, lignosulfonate, beet sugar bottoms, corn bottoms, brewery bottoms, vegetable tall oil, vegetable oil, and/or spent frying oil.
U.S. Pat. No. 6,013,116 to Major et al. is directed towards inducing a chemical alteration in synthetic fuel in order to qualify for IRS Section 29 tax credits. However, Major et al. is primarily focused on utilizing a binder for improved structural integrity in fuel briquettes or pellets. Further, this invention relies primarily upon lignosulfonate as a binder. Lignosulfonate is a relatively inexpensive waste product of the paper-making industry. It generally has a high BTU value but since it adds sulfur to the fuel, its use results in higher SO_xemissions and the resulting need to purchase, rather than sell, priority air pollutant credits.
The foregoing references are hereby incorporated herein by reference.
Notwithstanding decades of development, the pelletization and of synthetic fuels produced from coal fines continues to be plagued by several problems.
The synthetic fuel pellets of the prior art remain subject to disintegration during handling and transport. This is often exacerbated by the fact that synthetic fuel pellets of the prior art containing cellulosic materials (whether provided in the form of powder, particulates or chips) absorb and retain moisture that hastens disintegration. One component of cellulose, hemicellulose, is especially susceptible to sorption and needs to be chemically converted or physically isolated to achieve waterproof briquettes. In addition, synthetic fuel pellets of the prior art are often produced using relatively expensive binders, such as epoxies, and/or must be produced using relatively high pressures and temperatures (typically above 10,000 pounds/square inch and typically above 400 degrees Fahrenheit), in order to form a satisfactory pellet by removing water and compacting the pellet material blend.
The presence of water in the pelletizing mixture, its efficient removal during processing, and the uptake of water in finished pellet remains a challenge to the production, transport and combustion of stable synthetic fuel pellets.
It is also desirable to be able to form synthetic fuel pellets without the minerals typically present when fibrous cellulosic material is obtained from pulp liquors from paper-making processes. Thus, the efficient and cost-effective removal of minerals and other non-combustibles from stable synthetic fuel pellets is an area still in need of improvement.
It is also desirable to be able to form synthetic fuel pellets with the most efficient use of binders, to reduce attendant expense while maintaining the energy value of the pelletized fuel. In this same regard, the production of synthetic fuel pellets typically requires high pressures and temperatures when binders such as lignin is used, or relatively expensive plastic binders to achieve a pellet of acceptable stability.
Accordingly, there remains a need for improvements to methods of making synthetic fuel pellets that better resists disintegration and moisture absorption, and which can be prepared more efficiently through lower energy investment.

SUMMARY OF THE INVENTION

One of the principal novel features of this invention is the use of disintegrated fibrous cellulosic materials (such as those of a character obtained from mechanical or pneumatic comminution or shearing processes, and/or from thermomechanical pulping) in a manufacturing process which may use conventional production equipment to make strong and water-insoluble/resistant products from a variety of particulate feedstocks, including finely-divided lignocellulosic fiber and particles, or fines, of chemically-inert materials. Of particular commercial interest is ability to produce synthetic fuel from coal fines without the use of higher amounts of binder and without the input of large amounts of energy normally required to compress and dewater particulate mixtures to produce synthetic fuel pellets.
The present invention includes a synthetic fuel pellet, the pellet comprising a compressed agglomeration of: (a) coal fines; (b) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated; and (c) at least one binder, the binder adapted to form a pellet of the coal fines and the fibrous cellulosic material.
The synthetic fuel pellet of the present invention may be described as a pellet comprising a compressed agglomeration of: (a) coal fines; (b) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated; and (c) at least one binder, the binder preferably adapted to render the fibrous cellulosic material substantially waterproof and to form a pellet of the coal fines and the fibrous cellulosic material.
The present invention also includes pelletizable mixture for making a synthetic fuel pellet, said pellet mixture comprising: (a) coal fines; (b) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated; and (c) at least one binder, the binder preferably adapted to render the fibrous cellulosic material substantially waterproof and to form a pellet of the coal fines and the fibrous cellulosic material.
The present invention also includes a method of preparing a synthetic fuel pellet, comprising the steps of: (1) bringing into contact a mixture of: (i) coal fines; (ii) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated; and (iii) at least one binder, the binder adapted to render the fibrous cellulosic material substantially waterproof and to form a pellet of the coal fines and the fibrous cellulosic material; and (b) compressing the mixture for sufficient time to form a pellet.
Also part of the present invention is a pelletizable blend system for pelletizing/briquetting a mixture of coal fines and biomass, comprising the following: (1) water, to distribute binder materials, to provide surface tension for initial binding, to bring the final binder to the surface, and to provide steam for biomass steam distillation; (2) an initial binder (over 50 binders are known in the literature) to provide initial handling strength to the pellet as it dries; pressure to densify the pellet; and (3) a polymerizing binder, to provide final strength to the binder and resistance to water dissolution, such that a heat treatment, providing biomass distillation, surface activation, and polymerization.
While any method of addition and blending may be used, it is preferred that at least one binder is first admixed with the fibrous cellulosic material prior to forming the pellet mixture by the addition of the coal fines.
The present invention also preferably includes a method of preparing a synthetic fuel pellet, the method comprising the steps of: (a) bringing into contact a mixture of: (i) coal fines; (ii) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated by pneumatic or mechanical fibril disintegration; preferably wherein the coal fines are present in an amount in the range of from about 70 to about 90 percent by weight of the mixture; and wherein the fibrous cellulosic material is present in an amount in the range of from about 10 to about 30 percent by weight of the mixture; and (iii) at least one binder, the binder adapted to render the fibrous cellulosic material substantially waterproof and to form a pellet of the coal fines and the fibrous cellulosic material; and compressing the mixture for sufficient time to form a pellet.
Preferably, pellets of the present invention are formed with compression pressures below about 10,000 pounds per square inch, and/or at forming temperatures of less than about 400 degrees Fahrenheit.
The heat treatment is also one aspect of the preferred embodiment of the present invention. While others heat treat for thermosetting, and/or for melting of lignins and even of coal, the heat treatment of the present invention preferably converts most of the briquette water into steam. This has the effect of performing a steam reduction of the biomass, extracting light volatiles and steam-melting high boiling point oils. In addition, at proper temperatures, the steam hydrolyzes hemicellulose (to wood sugars), eliminating much of the cellulose water sorption potential. While not limited to the theory of operation, this process is believed also to activate surface sites on coal and on biomass, creating active hydroxyl sites on both coal and wood (i.e., cellulosic material) to allow and promote binding to the second binder.
The temperature range preferably is set low enough to avoid significant decomposition of the second binder while allowing the steam reduction and surface activation to occur. A temperature range for PVA is 350-400 F.

Coal Fines

The coal fines used in accordance with the present invention may be obtained from any commercial source, such as from on-going or past coal mining operations.

Binders

While over 50 binders have been identified in the literature, none offer a complete solution to the binding of coal and coal mixtures. Some users attempt blends of binders in order to achieve a good result. One of the aspects of the present invention uses a mix of binders to achieve different ends at stages of the binding process. The initial binder can be any of a broad range of binding materials known to provide immediate structure to the briquette, thus allowing time for the successor binder to activate. Sometimes, simple is best: wheat flour provides an adequate initial binder, and concentrations can range from 0-5% by weight. Less than 1% by weight wheat flour is sufficient.
Water is typically necessary for binding. Total water additions of 0-25% may be provided, and experience shows that the pellet needs to have 8-10% water for distribution, and 15% water results in water extrusion. The correct water addition provides just sufficient water for a surface “ooze”, and the present invention disclosed here is for the process that preferably creates a surface weeping of expressed binder, although less or more can be used.
Pressure densification is an essential part of any briquetting process. Pressures used in briquefting typically range up to 25,000 pounds per square inch. While practicable briquettes may be formed below 500 psi, the process of the present invention allows for the creation of high stability briquette below 10,000 psi, typically in the 5000 to 10,000 psi range.
A second binder, providing final strength and water resistance, may also be used in accordance with the present invention. There are several binders known to polymerize under heat and pressure, and/or over time. It is preferred that the second binder, operating in conjunction with the first binder, provides a different form of binding. Examples of a second binder would include thermoset plastics such as aqueous solutions of PVA, two part reactives such as aqueous solutions of PMMA and a hardener, and polymerizing blends of agricultural products such as linseed oil. Ideally, the second binder will polymerize to hydroxyl groups and is water soluble before polymerization, and insoluble after. PVA is one such binder with the additional advantages of being relatively safe.
The binders that may be used include other plastics, such as polyethylene, starch, petroleum by-products and bioplastics. The binder may also comprise nylon.
Another aspect of the present invention is that synthetic fuel pellet may be produced with a binder that is substantially free of epoxy resins, where the elimination of epoxy resins is desired.
The amount of binder may vary with the binder type.

Fibrous Cellulosic Materials

The fibrous cellulosic material is of a character such that the fibers are substantially disintegrated, meaning that the native binding of the individual fibers have been substantially disrupted, and/or lignan has been substantially removed.
One of the features of the present invention is that the fibrous cellulosic material is subjected to pneumatic or mechanical fibril disintegration, such as through air shear such that the disintegrated fibers are substantially dried in the process. One of the advantages of this process is that it may be carried out on standard paper fiber obtained from pulp liquor, in which case the pulp fiber becomes dried as well as disintegrated, increasing operational efficiency. The drying of the fiber also removes the minerals resident in the pulp liquor, which reduces the amount of non-combustibles in the synthetic fuel pellet. These non-combustibles include minerals such as sodium compounds and sulfites that can lead to the formation of ash upon combustion.
This may be achieved through the use of air shear techniques, such as using the kinetic disintegration technology, conducted commercially by AGES of Canada or First American Scientific Corporation of Bakersfield, California. Methods and apparatus relating to comminution of fibrous materials are described for instance in U.S. Pat. Nos. 5,839,671 and 6,024,307, hereby incorporated herein by reference. The fibrous cellulosic material is obtained by subjecting wood chips or other acceptable source of cellulosic material, such as that derived from waste digesters, to pneumatic shear so as to disintegrate the cellulosic fibers. This may be done by obtaining the mechanical or pneumatic shear-treated material commercially, such as the kinetic disintegration technology commercially available from Alternative Green Energy Systems Inc. (AGES) of Canada or First American Scientific Corporation of Bakersfield, Calif. Examples of devices capable of performing this method are the KDS Model 250 and KDS Model 3000 (in development), commercially available from First American Scientific Corporation of Bakersfield, Calif. Another source of the desired fibers is that of thermomechanically processed pulp. While virgin pulp is not an economic source, recycled pulp, such as that extracted in the autoclave processing of municipal waste, is.
In the alternative, the fibrous cellulosic material is subjected to similar mechanical disintegration followed by drying through a secondary process in accordance with methods and equipment known and used in the art for drying fibrous and particulate materials.
This may also be accomplished through the use of opposing jet streams of air, or event through other techniques that hereafter may be developed, such as application of vacuum to cause expansion and/or explosive disruption of the fibrous cellulosic material. Any method may be used to render the cellulosic fibers into a disintegrated state.
Typically the fibers of the fibrous cellulosic material have been subjected to pneumatic or mechanical fibril disintegration prior to being incorporated into the compressed agglomeration.
It is preferred to use the fibrous cellulosic material in an amount of from about 10 to about 30 percent by weight, preferably from about 20 to about 30 percent by weight, and most preferably about 25 percent by weight of the total weight of the pellet blend, although the percentage may be as high as 33 percent by weight.
It is preferred to use the coal fines in an amount of from about 70 to about 90 percent by weight, preferably from about 70 to about 80 percent by weight, and most preferably about 75 percent by weight of the total weight of the pellet blend.
The fibrous cellulosic material may also be obtained from pulp material as is typically obtained in paper making operations, as well as recycled pulp, and cellulose fibers extracted from the autoclave processing of municipal wastes.
Although not limited to the theory of operability of the invention, it is believed that such fibril disintegration also has the effect of exposing unoxidized surfaces of the fibrils, such as through the rupture of cellular walls, such that these surfaces may be more highly interactive with the binder component. The rupture of the cellular walls also reduces the tendency of the material to retain water and swell. It is also believed that the fibrous cellulosic material subjected to kinetic disintegration as described herein allows individual unagglomerated fibrils to be more effectively wetted by the binder. This also has the effect of reducing the inclination toward separation of the coal fines and fibrous cellulosic material as the components are blended into a mixture to be pelletized.
While not limited to the theory of the invention, the modified fibrous cellulosic material of the present invention is believed to be better able to interact with a binder or other substance, such that the fibrous cellulosic material acts similar to an encapsulant
Accordingly, another aspect of the present invention is that the disintegrated fibrous cellulosic material is able to act in the manner of an encapsulant by forming a matrix around the coal fines to form a more stable pellet. The disintegrated fibrous cellulosic material may also be able to react chemically with the binder or other chemical species to form stronger attachments within that matrix.
It is also preferred that the fibrous cellulosic material is comprised substantially completely of disintegrated or unagglomerated fibers; i.e. is substantially free of particulate cellulosic material or cellulosic material chips wherein the fibers remain bound by their native cross-linking.
Typically, the fibrous cellulosic material used in accordance with the present invention has an average fiber length in the range of from about 0.5 to about 4.0 millimeters.
The synthetic fuel pellet of the present invention will typically be made using a fibrous cellulosic material having moisture content less than about 12%, preferably less than about 5%, prior to being incorporated into the compressed agglomeration.

Advantages

One of the advantages of the present invention is that synthetic fuel pellet may be produced with acceptable stability by using reduced amounts of binder as compared to prior formulations. Higher amounts of binder may be used, as desired. Typically, the synthetic fuel pellet may be produced with acceptable stability by using binder in a range from about 2 to about 20 percent by weight of the overall coal fines/fibrous cellulosic material/binder mixture, typically depending upon the type of binder. For instance, starch binders typically are present in higher amounts while plastic binders are effective in lower amounts. For instance, wheat starch binders are typically required in greater amounts, while plastic binders require lesser amounts.
Still another aspect of the present invention is that the synthetic fuel pellet is produced by using at least one binder that is adapted to render the disintegrated fibrous cellulosic material substantially waterproof or water resistant. One of the aspects of using disintegrated fibrous cellulosic material is that the binder component is able to wet the disintegrated fibrous cellulosic material sufficiently to render it substantially waterproof or water resistant. This in turn leads to the production of a synthetic fuel pellet that resists moisture uptake and the attendant tendency to disintegrate when exposed to moisture.
One of the advantages of the present invention is that the mixture resists separation once the coal fines, fibrous material and binder are combined prior to being pelletized.
It is preferred that the percent by weight ratio of the coal fines to that of the fibrous cellulosic material be in the range of from about 10 to 1 to about 2 to 1, although other ratios may be used.
Another advantage of the present invention is that it allows for reduced binder necessary to produce an acceptably dimensionally stable pellet, decreasing the overall cost of producing a fuel pellet, and increasing the amount of coal fines and cellulosic fibers that may be incorporated proportionately.
The present invention also includes a method of obtaining energy from combusting a fuel pellet, the method comprising the steps of obtaining a synthetic fuel pellet, the pellet comprising a compressed agglomeration of: (a) coal fines; (b) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated; and (c) at least one binder, the binder adapted to render the fibrous cellulosic material substantially waterproof and to form a pellet of the coal fines and the fibrous cellulosic material; and combusting the pellet so as to release energy thereby.
Another feature of the present invention is that the fibrous cellulosic material may be subjected to air shear such that the disintegrated fibers are substantially dried in the process. One of the advantages of this process is that it may be carried out on standard paper fiber obtained from pulp liquor, in which case the pulp fiber becomes dried as well as disintegrated. The drying of the fiber also removes the minerals resident in the pulp liquor, which reduces the amount of non-combustibles in the synthetic fuel pellet. In the alternative, the fibrous cellulosic material may be subjected to similar mechanical disintegration followed by drying through a secondary process in accordance with methods and equipment known and used in the art for drying fibrous and particulate materials. Another aspect of the invention is that the fibrous cellulosic material prepared in accordance with the present invention allows the fibrous cellulosic material to more effectively interact with the coal fines and binder.
With respect to the reactant, one of the pathways to a synthetic coal consists of using cellulosic fibers to serve as a matrix holding the coal fines (as opposed to “gluing” the mass together, or imbedding the mass in a matrix). Permanent and non-water soluble cross-linkages can be created with methylol compounds, such as dimethyloldihydroxyethyleneurea (DMDHEU) in the presence of heat and Lewis acid catalysts, such as ZnCl₂or MgCl₂. The N-methylol compounds react readily with the hydroxyl groups of adjacent cellulose chains, forming the desired crosslinks. Other classes of insoluble hydroxyl group cross-linkers may be used, of which there are numbers of examples, such as those used in permanent press processes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the foregoing summary, the following describes a preferred embodiment of the invention which is presently considered to be the best mode thereof.
To prepare a synthetic fuel pellet in accordance with one embodiment of the present invention, a mixture of: (a) coal fines; (b) a fibrous cellulosic material wherein the fibers of the fibrous cellulosic material have been substantially disintegrated; and (c) at least one binder, the binder adapted to form a pellet of the coal fines and the fibrous cellulosic material.
The fibrous cellulosic material is obtained by subjecting wood chips or other acceptable source of cellulosic material, such as that derived from waste digesters, to pneumatic shear so as to disintegrate the cellulosic fibers. This may be done by obtaining the mechanical or pneumatic shear-treated material commercially, such as the kinetic disintegration technology commercially available from Alternative Green Energy Systems Inc. (AGES) of Canada or First American Scientific Corporation of Bakersfield, Calif. Examples of devices capable of performing this method are the KDS Model 250 and KDS Model 3000 (in development), commercially available from First American Scientific Corporation of Bakersfield, Calif. Another source is municipal waste autoclaving, such as is commercially available from Estech USA LLC of Canal Winchester, Ohio.
The fibrous cellulosic material is typically first mixed with the cellulose binder in a suitable industrial charger as is known and used in the art. Mixing is continued until a uniform slurry is formed.
The coal fines are obtained from on-going or past coal mining operations, such as from waste ponds. The coal fines are collected and permitted to dry before being incorporated into the slurry. The coal fines are admixed to form a mixture with the coal fines binder that is prepared to be pelletized.
The mixture may be formed into pellets using machinery and methods known and used in the art, or which hereafter may be developed.
The pellets are articles of commerce that can be easily transported by rail or shipped from the palletizing operation to combustion chambers, such as for energy generation at electric generating plants. Because electric generating plants are often geographically separated from the mining operations, the pellets must be durable to provide stability during transport. The pellets are typically crushed just prior to feeding the combustion chamber.

EXAMPLES

Coal Fines Binder Step.

It is essential that the binder be non-water-soluble. While there are numerous such binders commercially available, one of the less expensive options appears to be that of a highly-hydrolyzed grade of polyvinyl alcohol (PVOH) such as Elvanol 90-50 (commercially available from Dupont). This material provides a high degree of cold-water insolubility, and its use as a binder is well known.
Experimentation with PVOH show that water resistant briquettes can be made with PVOH alone, with addition rates in the range of 0.1-1% (solids ratio), and preferably in the range of 0.1-0.4%.
PVOH also crosslinks with a number of materials, and experiments with crosslinkers have shown that the PVOH does indeed insolubilize, but the crosslinked material has a tendency to gel. Various crosslinkers were tested, ranging from aldehydes to metals. Invariably, as gelation occurs, the structural integrity of the briquette diminishes.
Testing has confirmed that gelation does not occur in alkaline environments. As an example, briquettes were formed with PVOH (using 90-50 Elvanol as an example) at 0.4% addition, and a glyoxol-based crosslinker (Curesan, from BASF), at 0.1% addition. Sufficient alkalinity was added to raise the pH above 8 (with sodium hydroxide), and briquettes were formed at room temperature at about 9000 psi. The briquettes were heated to accelerate drying to ˜200 F. Upon drying, the PVOH and Curesan react and cure. The resulting briquettes were both physically durable and waterproof. The alkaline insolubility of PVOH and coal is described in U.S. Pat. No. 6,709,472, which is hereby incorporated herein by reference.

Cellulose binder

Several reaction pathways are available to produce “waterproof” cellulose. One pathway teaches that waterproof cellulose composites can be created using a thermoset binder extracted from (wood) cellulose by prescribed steam treatments: the steam hydrolyzes cellulose components which, after concentration, can be utilized as a glue or binder by thermosetting with heat and pressure.
Another pathway utilizes a Maillard reaction to bind “particulated” cellulose, such as that found in the preferred feedstocks of this patent. U.S. Pat. No. 5,582,682 to Ferretti (hereby incorporated herein by reference) regarding forming cellulose composites, teaches that the Maillard reaction resin is compatible with the surface of cellulose, and the particulation increases the binding site population with which the resin reacts. This patent also describes the ammoniation/protein (starch) binder for cellulose.
Indeed, experimentations have demonstrated that a water insoluble material can be formed from fibers derived from the autoclave processing of municipal waste (previously cited). In one experiment, a 50 gram sample of fiber (available from Estech USA LLC of Canal Winchester, Ohio) was combined with 50 grams of 2% ammonia (a commercial home product) and 20 grams of soy protein isolate, briquetted at under 100 psi, and heated cause the briquette core to rise to 350 F. The resulting briquette was porous, but insoluble.

Combined Binder

A synthetic coal briquette was made using techniques identical or similar to those outlined above. 70 grams of coal, along with its binder, and 30 grams of cellulose, along with its binder, were combined and briquetted using standard briquetting techniques at a pressure of about 10,000 psi. The resulting briquette was heated briefly to 350 degrees F. While not wishing to be bound by theory, prior work with the coal/PVOH system has shown that heating a stronger briquette, and indeed, the resulting synthetic fuel briquette was strong and did not dissolve after in 24 hours in water.
Additional information regarding the formulation and production of synthetic fuel pellets is provided in the following patents and published patent applications which are hereby incorporated by reference:


Patent/Publication Number	Title

3,954,443	Aluminum process
4,025,596	Method for pelletizing finely divided solids
4,152,119	Briquette comprising caking coal and
	municipal solid waste
4,219,519	Method for agglomerating carbonaceous
	fines
4,225,457	Briquette comprising caking coal and
	municipal solid waste
4,234,320	Process for the agglomeration of solids
4,243,393	Coal article
4,357,145	Carbonaceous pellets and method of
	making
4,369,054	Fiber/slag composition
4,385,995	Method of recovering and using fine coal
4,395,265	Fuel pellets
4,396,396	Deashing of coal by the oil agglomeration
	process
4,398,917	Process for the preparation of fuel pellets
4,405,331	Refuse derived fuel and a process for the
	production thereof
4,417,899	Self-bursting coal pellets and a method of
	making them
4,483,840	Synthetic carbonaceous granules having
	high mechanical characteristics
4,494,962	Fuel Product
4,497,661	Formed briquettes, process for forming the
	same and process for utilizing the same in
	the manufacture of metals
4,501,593	Process for the production of
	agglomerated fuels
4,529,439	Energy conservation during the smelting of
	ores
4,615,712	Fuel agglomerates and method of
	agglomeration
4,670,240	Energy conservation during the smelting of
	ores
4,681,597	Method for agglomerating powdered coal
	by compaction
4,720,346	Flocculation processes
4,741,278	Solid fuel and a process for its combustion
4,802,890	Agglomeration of coal fines
4,828,573	Method of manufacturing a pelletized fuel
4,830,637	Preagglomeration of fine coal before
	thermal dryer in a preparation plant
4,943,378	Flocculation processes
4,981,494	Water-resistant fuel agglomerate, process
	for preparing it and composition of matter
	employed in the process
5,171,781	Polymeric compositions
5,242,470	Pelletizing coal or coke with starch
	particles
5,298,040	Process for the preparation of a water-
	resistant fuel agglomerate
5,371,194	Biomass derived thermosetting resin
5,411,560	Method of producing binderless pellets
	from low rank coal
5,421,838	Binding composition for the preparation of
	a novel agglomerate based on finely
	divided materials, process using the said
	composition and thus obtained
	agglomerate
5,429,645	Solid fuel and process for combustion of
	the solid fuel
5,431,702	Waste conversion process and products
5,562,743	Binder enhanced refuse derived fuel
5,589,118	Process for recovering iron from iron-
	containing material
5,658,357	Process for forming coal compact without
	a binder
5,685,153	Efficient utilization of chlorine and/or
	moisture-containing fuels and wastes
5,698,007	Process for agglomerating particulate
	material
5,711,768	Sewage sludge disposal process and
	product
5,738,694	Process for recovering iron from iron-
	containing material
5,743,924	Pelletized fuel composition and method of
	manufacture
5,752,993	Blast furnace fuel from reclaimed
	carbonaceous materials and related
	methods
5,797,972	Sewage sludge disposal process and
	product
5,807,420	Process for reduction of iron with solid fuel
	objects as amended by exam
5,916,826	Pelletizing and briquetting of coal fines
	using binders produced by liquefaction of
	biomass
5,922,261	Process for recovering iron from iron-rich
	material
6,013,116	Briquette binder composition
6,015,527	Facility for producing reduced iron
6,071,325	Binder composition and process for
	agglomerating particulate material
6,099,770	Method of and apparatus for dewatering
	and pelletizing particulate fuel
6,165,238	Fuel pellet and method for its production
6,214,064	Process for making a fuel product from
	coal fines and sewage sludge
6,284,017	Method and facility for producing reduced
	iron
6,375,447	Apparatus for dewatering and pelletizing
	particulate fuel
6,384,126	Binder formulation and use thereof in
	process for forming mineral pellets having
	both low and high temperature strength
6,451,092	System and process for agglomeration
	and processing of carbonaceous fines and
	dust
6,506,223	Pelletizing and briquetting of combustible
	organic-waste materials using binders
	produced by liquefaction of biomass
6,530,966	Coal binder compositions and methods
6,558,442	Synthetic fuel production method
6,685,761	Method for producing beneficiated titanium
	oxides
6,692,544	Municipal waste briquetting system and
	method of filling land
6,709,472	Insolubly bound particulate products
6,786,949	Method and apparatus for using a pre-jel
	for producing self-reducing agglomerates
20010013197	Pelletizing and briquetting of combustible
	organic-waste materials using binders
	produced by liquefaction of biomass
20020014155	System and process for agglomeration
	and processing of carbonaceous fines and
	dust
20020020109	Synthetic fuel production method
20020050094	Synthetic fuel and methods for producing
	synthetic fuel
20020170388	Method for using a pre-jel for producing
	self-reducing agglomerates
20030041509	Synthetic fuel comprising coal dust, water
	and a reactive organic compound, and a
	process for making such synthetic fuel
20040010968	Synthetic Fuel Production Method
20040049973	Synthetic fuel production method
20050132643	Methods for binding particulate solids
20050183544	Method for producing mineral ore
	agglomerates using a hemicellulose binder
	and associated products
20050274224	Method and apparatus for carrying out a
	metallurgical process

Claims

1. A synthetic fuel pellet, said pellet comprising a compressed agglomeration of:

a. coal fines;

b. a fibrous cellulosic material wherein the fibers of said fibrous cellulosic material have been substantially disintegrated; and

c. at least one binder, said binder adapted to form a pellet of said coal fines and said fibrous cellulosic material.

2. A synthetic fuel pellet according to claim 1 wherein said at least one binder comprises a plasticized organic material.

3. A synthetic fuel pellet according to claim 1 wherein said at least one binder comprises nylon.

4. A synthetic fuel pellet according to claim 1 wherein said at least one binder comprises polyvinyl alcohol.

5. A synthetic fuel pellet according to claim 4 wherein said polyvinyl alcohol is present in said pellet in the range of from about 0.1% to about 1% of solids.

6. A synthetic fuel pellet according to claim 1 wherein at least one binder is substantially free of epoxy resins.

7. A synthetic fuel pellet according to claim 1 wherein at least one binder is adapted to make said fibrous cellulosic material substantially waterproof.

8. A synthetic fuel pellet according to claim 1 wherein said binder includes a thermoset binder derived from steam treatment of cellulose.

9. A synthetic fuel pellet according to claim 1 wherein said binder includes a Maillard reaction resin.

10. A synthetic fuel pellet according to claim 1 wherein said at least one binder comprises polyvinyl alcohol, and a binder selected from the group consisting of Maillard reaction resins and thermoset binders derived from steam treatment of cellulose.

11. A synthetic fuel pellet according to claim 1 wherein the percent by weight ratio of the coal fines to the fibrous cellulosic material is in the range of from about 10 to 1 to about 2 to 1.

12. A synthetic fuel pellet according to claim 1 wherein said coal fines are present in an amount in the range of from about 70 to about 90 percent by weight of said pellet.

13. A synthetic fuel pellet according to claim 1 wherein said fibrous cellulosic material is present in an amount in the range of from about 10 to about 30 percent by weight of said pellet.

14. A synthetic fuel pellet according to claim 1 wherein said fibrous cellulosic material has an average fiber length in the range of from about 0.5 to about 4.0 millimeters.

15. A synthetic fuel pellet according to claim 1 wherein the fibers of said fibrous cellulosic material have been has been subjected to pneumatic or mechanical fibril disintegration prior to being incorporated into said compressed agglomeration.

16. A synthetic fuel pellet, said pellet comprising a compressed agglomeration of:

a. coal fines;

c. at least one binder, said binder adapted to render said fibrous cellulosic material substantially waterproof and to form a pellet of said coal fines and said fibrous cellulosic material.

Method of Making Synthetic Fuel Pellet

17. A method of preparing a synthetic fuel pellet, said method comprising the steps of:

a. bringing into contact a mixture of:

i. coal fines;

ii. a fibrous cellulosic material wherein the fibers of said fibrous cellulosic material have been substantially disintegrated; and

iii. at least one binder, said binder adapted to render said fibrous cellulosic material substantially waterproof and to form a pellet of said coal fines and said fibrous cellulosic material; and

b. compressing said mixture for sufficient time to form a pellet.

18. A method according to claim 18 wherein said compression is at a pressure below about 10,000 pounds per square inch.

19. A method according to claim 18 wherein said compression is carried out at a temperature below about 400 degrees Fahrenheit.

20. A method according to claim 18 wherein said at least one binder is first admixed with said fibrous cellulosic material prior to forming said mixture by the addition of said coal fines.

21. A method of preparing a synthetic fuel pellet, said method comprising the steps of:

a. bringing into contact a mixture of:

i. coal fines;

ii. a fibrous cellulosic material wherein the fibers of said fibrous cellulosic material have been substantially disintegrated by pneumatic or mechanical fibril disintegration;

wherein said coal fines are present in an amount in the range of from about 70 to about 90 percent by weight of said mixture; and

wherein said fibrous cellulosic material is present in an amount in the range of from about 10 to about 30 percent by weight of said mixture; and

b. compressing said mixture for sufficient time to form a pellet.

Pelletizable Mixture Precursor

22. A pelletizable mixture for making a synthetic fuel pellet, said pellet mixture comprising:

a. coal fines;

at least one binder, said binder adapted to form a pellet of said coal fines and said fibrous cellulosic material.