Flax Based Fuel Pellet and Method of Manufacture

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates generally to fuel pellets. Particularly, the present invention relates to a fuel pellet containing flax stem fibers in combination with a binder, preferably, vegetable oils or oilseeds, for use as an alternative heating source for pellet type residential and commercial heating appliances such as pellet stoves, pellet boilers, pellet furnaces, stoker type heating systems, furnaces, heating appliances and the like.

DESCRIPTION OF THE RELATED ART

In recent years, pellet burning heating appliances have increased in popularity. Such appliances generate heat for homes by burning small relatively solid pellets which are fed to the fire chamber at a predetermined rate from a storage container. To be optimally effective, the pellets should be capable of producing a significant BTU level of heat output, be clean burning, produce minimal ash residue, be capable of long term storage without rotting or otherwise degrading and be affordable as an alternative to other locally available fuels. The pellets range in size from the size of a corn kernel to about the size of a traditional lump of coal.

Known pellets are often made of hardwood sawdust residue obtained from sawmills and furniture factories. Such pellets are considered desirable, but it is difficult to provide adequate supplies since sources of such hardwood sawdust

are somewhat limited. The available seasonal supplies of hardwood pellets were exhausted by January 2006 in some parts of the country. Such sawdust pellets are formed by known methods which typically include mixing the sawdust with water or other binding agent, shaping them in pellet configuration and then drying and hardening the pellets. Wood fuel pellets are also undesirable as they create creosote when combusted. Creosote is unburned wood particles and condensed flue gases which deposit in the chimney. Creosote poses not only fire hazards but also health hazards as it is believed to be a carcinogen.

Another less efficient pellet type utilizes sawdust from coniferous softwood trees, but does not have the same high BTU output provided by hardwood pellets and also does not burn as cleanly; the amount of creosote and soot generated is much higher. Therefore, these pellets are typically less desirable than the hardwood pellets.

In recent years, it has become known to utilize corn kernels as pellets and to feed such kernels directly into the heating appliance. These pellets are workable but require special equipment to burn, namely, expensive corrosive- resistant stainless steel stoves and a stirring device in the fire chamber. Without such a stirring device, the kernels tend to form larger clinkers and cinder residue and tend to be less capable of steady, ongoing burning and pellet feeding without extra maintenance. In addition, fuel pellets including large amounts of corn provide less BTUs than wood based pellets.

The present invention addresses limitations and problems associated with the prior art.

SUMMARY OF THE INVENTION The present invention involves making a fuel pellet having principal ingredients being flax stem fiber material and a binder, preferably a vegetable oil or oilseed lubricant material. The fuel pellet of the present invention burns at a high temperature, generates little to no smoke, ash or creosote. In addition, the fuel pellets of the present invention can be stored for long periods without rotting or deteriorating. In preferred embodiments, the fuel pellet of the present invention includes at least about 60% by wt. flax stem fiber material; wherein the flax stem fiber material includes particles of different sizes; wherein at least about 60% of the particles are less than about a quarter of an inch in length; wherein the fuel pellet, when burned, produces less than about 4% ash residue. The present fuel pellets are made from waste material generally available at minimal cost that produces pellets that burn at a high temperature, generate little smoke and less than about 4% ash residue, and can be stored for long periods without deteriorating. The cost involved is often just the cost of bailing the unwanted flax straw and transporting the bailed flax straw to either a storage site or a processing site. Flax straw is remarkably durable over time. Growers are anxious to have it removed from their land as it can only be effectively disposed of by burning it, unless it is removed. Growers have found that flax straw is so resistant to decomposition, that it cannot be satisfactorily disposed of by plowing it into the soil. Preferred fuel pellets include at least about 60% by wt. flax stem

fiber; wherein at least about 60% of the particles are less than about a quarter of an inch in length. The fuel pellet is processed by first selecting or processing the flax stem fiber so that it has a moisture content of from about 5 to about 12%. The bulk flax stem fiber material is then processed in a hammermill or the like to reduce the size of the fiber particles. The processed flax is then extruded through a commercial pelletizing machine. The pellets are then cut and then dried.

Oilseeds or vegetable oil derived from oilseeds are preferably used as a binder and lubricant, but they also ease the flow of the flax stem fiber material through the pellet mill/extruder, thereby reducing the pressure created during the forming processes by lubricating the substrate material. Further, vegetable oil or oilseeds increase the BTU content of the finished product. The vegetable oil or oilseeds are added at a ratio of from about 1 to about 50% by wt., preferably no greater than 5% by wt., either by the addition of processed vegetable oils or by the addition of oilseeds added to the reduced flax straw or flax stem fiber material.

Flax is a plant with blue flowers and oil carrying seeds and is mainly an oilseed crop grown almost exclusively for its seeds. The seeds are typically harvested and later pressed to extract the oil. Flaxseed oil is quite desireable due to its high unsaturated fat content. It has multiple uses including the production of linseed oil and can be an ingredient in various food commodities. The flax plant is a relatively short stature, commonly reaching fully grown heights of 12" to 36". The stem fiber or straw left over from the

production of flax is both wiry and durable. The stalk residue remaining after harvesting of the flax is a serious problem for farmers because it is exceptionally resistant to decomposition/rotting. The flax staw is equally resistant to decomposition/rotting and is usually windrowed by growers and later burned just for disposal. As indicated above, flax straw is not easily disposed of by plowing it into the ground like corn stalks because of its resistance to decomposition. Attempts to plow flax straw into the ground often result in clogged harrows used to perform that task and the flax does not deteriorate easily or quickly as corn fodder and other crop fiber residues generally do. Flax straw is typically windrowed at he time of harvest and burned in fields by farmers in the fall. The burning presents environmental issues due to the release of heat/energy and carbon dioxide into the atmosphere without making appropriate use of the energy, as well as increased costs and risk to the farmer. Flax straw is preferred as the primary resource for making flax stem fiber material used in preferred embodiments of the present fuel pellets.

North Dakota produces approximately 300,000-750,000 acres of flax production per crop year. That amount is typically over 90% of the flax grown in the United States. Normal flax straw production varies, but is usually between 0.5 tons and 1 .5 tons per acre.

Flax stalk can be use to make certain specialized papers, such as linen paper and cigarette paper. The market for such paper is, however, quite limited, and typically seems to require less than about one percent of the flax stalk crop. Farmers find no market for the rest and have to destroy it.

The present invention relates to creating a fuel pellet from the flax stem fiber waste. The fuel pellet is preferably manufactured by first processing the flax stem fiber material. In preferred embodiments, the bulk flax stem fiber is run through a hammermill, a grinder or the like, with a suitable amount of water, optionally in the form of steam used to add moisture to the flax stem fiber material, to process the flax stem fiber. In preferred embodiments, the flax stem fiber material is reduced in particle size by as much as possible by means of hammermill processing to allow for more efficient processing, greater pellet density and better finished product cohession. The reduced flax straw material must then be assessed for moisture content, so as to determine the need to add or subtract moisture level for optimum extrusion results. The preferred moisture level for extrusion of the milled flax straw is preferably from about 5 to about 12%. The flax straw is fed into the intake chamber of an industrial pellet mill, in this case a California Pellet Mill (CPM) model 10OC, where the straw is drawn into the machine by means of a variable speed mechanical auger. If the addition of moisture is indicated, this increased moisture level is preferably achieved by the addition of steam. High temperature steam, preferably in excess of 500 degrees F, generally referred to as "dry steam", is believed to be more effective for the successful addition of moisture to flax straw, resulting in moisture penetration into the straw core and thus raising moisture levels without excess water on the surface of the stems and straw material, and resulting in better extrusion of the base product. If the flax straw has too much moisture content, a number of strategies can be employed to reduce the moisture content of the base product, including air drying of the base product, the addition of dry flax straw

or dry reduced flax straw, or the forced drying of the product by means of forcing heated air over the flax straw material.

A binder, preferably a lubricant is then added to the processed flax stem fiber as it is extruded through a commercial pelletizing machine (e.g. a California Pellet Mill (CPM ) Model 100C) to produce cut pellets, preferably having a density of at least about 40 lbs/ft ³ .

The resulting fuel pellets may be used in residential heating appliances such as pellet stoves, pellet boilers, pellet furnaces, and the like. Commercial applications of the present invention include, but are not limited to, commercial stoker type boilers, furnaces and heating appliances. The present invention may also be utilized in grain dryer type applications as well.

An important aspect of the present invention is the fuel pellet's low carbon dioxide emission and its effect under the Kyoto Protocol. Countries that ratify this protocol commit to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases. Under the Kyoto Protocol, each country ratifying the agreement is allotted a certain amount of carbon credits to be divided amongst that country's companies. Each company must either stay within their allotted amount of carbon emissions (carbon credits) or must purchase carbon credits from another party who will not use all of their carbon credits. This scenario has formed a new form of investment and emissions trading. Companies able to decrease their carbon emissions have the

incentive to do so not only to ensure they stay within their allotment but also to save carbon credits for selling. One such member of the Kyoto Protocol is Canada. Canada's proximity to North Dakota, an abundant source of flax material, makes the fuel pellets of the present invention not only an environmentally and convenient source of fuel but also a valuable investment for the trading of carbon credits.

These and various other advantages and features of novelty which characterize the present invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages and objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention involves a fuel pellet and method of making a fuel pellet having principal ingredients being flax stem fiber material and a binder, preferably vegetable oil and/or oilseeds or a combination thereof. Flax stem fiber material for the preferred fuel pellet is selected from clean fields presenting minimal weed infiltration. The selected flax stem fiber material can be allowed to dry down in the windrows in the field to an intended moisture content, which is preferably between about 8% and about 12%. The flax stem fiber material can then be baled into large round bales using readily available farming equipment. The bales can then be transported to a processing plant.

In preferred embodiments, the flax stem fiber material is reduced to smaller straw fibers or stem portions or even ground to powder consistency before extrusion. Such processing can be completed with a hammermill to reduce the flax stem fiber material to particle size. In this case, a Mighty Giant diesel powered hammermill model 4002, manufactured by Jones Manufacturing of Beemer, Nebraska and equipped with 1 " hammers and a 2" screen, was utilized to reduce the particle size of the flax straw as much as possible. Preferably, the flax stem fiber material is processed with a suitable amount of water, optionally in the form of steam, to ease the processing. In preferred embodiments, the particle size will be no larger than from about 1 .5 to about 2 inches. To accomplish this, the use of a small hammer size and screen is preferable. In preferred embodiments, the hammermill will be a Mighty Giant Hammermill, from Jones Manufacturing, Beemer, Nebraska, model No. 4002 , preferably equipped with half inch hammers and a 1 inch screen. Small hammers and a smaller screen may also be used in alternative embodiments. The preferred range of particle sizes for the processed flax stem fiber material used to make the present pellets is from about 50 to about 90% by wt., preferably from about 60 to about 80% less than about a quarter of an inch in length and from about 5 to about 20%, preferably from about 10 to about 15% greater than about a half of an inch in length; wherein the particles preferably also include from about 0.1 to about 10% particles having a particle size of greater than about 1 inch in length and preferably include from about 10 to about 20% particles having a particle size of greater than about one-half of 1 inch in length and preferably include from about 0.1 to about 30% particles

having a range of particle sizes from about one-quarter of 1 inch or greater and about 1 and one-half an inch or less in length.

The processed flax stem fiber material is then blended with a binding agent, which consists of find particulate cereal grain flour byproducts which can be leftover from the industrial milling of flour products, typically consisting of wheat, barley, corn, oats or other cereal grains. The binder is preferably added at concentrations of from about 1/500 (0.002) to about 5% by wt., but can be added in percentages of up to about 50% by wt. The preferred binder is No. 2 Clear produced from the milling of spring wheat. The binder, No. 2 Clear is available from Minot Milling, Minot, ND. It will be appreciated that other binders may also be used, however, No. 2 Clear is preferred. Another preferred ingredient, oilseeds or vegetable oil derived from oilseeds, can be added to ease the pressure of forming or extruding processes by lubricating the pressure forming process, and also by acting as a lubricant and binder for the final fuel pellet product. Further, vegetable oil or oilseeds increase the BTU content of the finished product. The vegetable oil and/or oilseeds are preferably added at a ratio of from about 1/500% to about 5% by wt., but could be used at ratios of 50% by wt. or more. The lubricant can be either the addition of processed vegetable oils or the addition of oilseeds to the processed flax, whereupon the vegetable oils contained within the seeds are liberated into the mixture during the pressure forming process into the final pressure formed or pelletized product. The vegetable oils or oilseeds can be derived from flax, canola, soybeans, corn, sunflower, safflower, crambe, or any other vegetable based oil product or seed.

The processed flax and lubricant mixture is then extruded through a commercial pelletizing machine, cubing equipment or the like. The processed flax is preferably of relatively low moisture content in order to process the material through the extrusion equipment, preferably containing from about 5 to about 12% moisture content. This level of moisture content can be achieved by drying operations or by adding moisture via steam, preferably "dry steam", or a hot water spray.

The extruded pellets are preferably cut with a cutter on the extrusion equipment to about VA" to about 5/16" although numerous sizes of pellets may be produced in accordance with the teachings of the present invention. The extruded pellets typically exit the extrusion equipment having a temperature of about 200-300 degrees so it is then preferable to cool the pellets with an industrial cooler/drier to increase the pellet hardness and durability, and reduce the friability. The preferred moisture content of the final pellet is from about 4% and about 14%, which additionally avoids potential spoilage during extended storage. The pellet product can then additionally be processed through industrial screening equipment to separate fines or particulate matter from the end product as desired.

In preferred embodiments, as referenced above, the flax stem fiber material is first reduced in particle size by as much as possible by means of hammermill processing. The reduced flax straw material must then be assessed for moisture content, so as to determine the need to add or subtract moisture level for optimum extrusion results. The preferred moisture level for extrusion

of the milled flax straw is from about 5 to about 12%. The flax straw is fed into the intake chamber of an industrial pellet mill, in this case a CPM model 100C, where the straw is drawn into the machine by means of a variable speed mechanical auger. The rotation of the intake auger must be regulated as the material conditions indicate, but is preferably at a rotational speed of 10 to 20 RPM for a low density material such as flax stem fiber material. The flex stem fiber material is then delivered to a middle mixing and conditioning chamber that is integral to the CPM model 100C in this case. The middle conditioning chamber is equipped with mixing paddles that revolve at a high fixed speed of about 2,000 RPM. This chamber is equipped with ports that allow the injection of additives or the injection of steam or hot water. The moisture content of the base straw product is believed to be critical for the successful extrusion of the flax pellets. If the addition of moisture is indicated, this increased moisture level is preferably achieved by the addition of steam. High temperature steam, far above the boiling point of water, preferably in excess of 500 degrees F, generally referred to as "dry steam", is believed to be more effective for the successful addition of moisture to flax straw, resulting in moisture penetration into the straw core and thus raising moisture levels without excess water on the surface of the stems and straw material, and resulting in better extrusion of the base product. If the flax stem fiber material has too much moisture content, a number of strategies can be employed to reduce the moisture content of the base product, including air drying of the base product, the addition of dry flax stem fiber material or dry reduced flax straw, or the forced drying of the product by means of forcing heated air over the flax stem fiber material. Binder agents, such as Wheat Clear No. 2, can be injected at a rate

preferably from about 0.1 % to about 0.2% by wt., and plant based vegetable oils, preferable at a rate of 0.2% to 0.4% by wt., are added to the mixture to increase cohesion, durability, and lubricity of the product. As an alternative, a wide variety of binder agents may be effectively incorporated in the range of from about 0.01 % to about 5% by wt. and up to a range of from about 0.001 % to about 10% by wt., and plant based vegetable oils may be effectively incorporated in the range of from about 0.01 % to about 5% by wt. and up to a range of from about 0.001 % to about 10% by wt., to result in an efficiently extruded end product.

In preferred embodiments, the present fuel pellets are made primarily of flax stem fibers, however, other burnable plant material may also be included. The flax stem fiber is very clean burning and leaves little ash and no creosote residue, which is an important feature as a low residue product will require less maintenance. For that reason, fuel pellets of the present invention including at least about 40%, preferably about 65%, more preferably about 85%, even more preferably about 95% and most preferably about 99.9% by wt. flax stem fiber are also desirable products for fuel pellet users seeking renewable fuels.

A flax based fuel pellet of the present invention comprising approximately 99.99% by wt. flax and approximately .003% by wt. fax seeds and 0.0001% by wt. #2 clear binder was tested by Minnesota Valley Testing Laboratories, Inc. in November 2007. Table 1 below illustrates the results of the testing as well as published testing results of other various known fuels. Testing

methods for the fuel pellet of the present invention include Moisture E871 , Ash E1 102, Sulfur D4239, BTU/lb. E71 1 and Sodium Pellet Institute Specifications. Methods for the remaining tests include Moisture ASTM D3173; Ash ASTM D3174; BTU/lb: ASTM D1989; Sulfur: ASTM D4293 Calculated value using ASTM Standard D3180-89.

Table 1.

Product Testing As Is I Dry

Matter

Flax based fuel pellet of

Moisture 5.42% the present invention BTU/lb I 7807 8254

Ash % 3.50% 3.70%

Sulfur % 0.10% I 0.11%

Moisture I 12.25%

BTU/lb 6934 7729

Alfalfa

Ash % 7.94% 9.06%

Sulfur % 7.94% I 9.06%

Moisture 6.02%

BTU/lb 7786 8501

Aspen

Ash % I 2.48% 2.67% Sulfur % 0.02% 0.02%

Moisture 12.06% BTU/lb 7199 8097

Corn Gluten Feed

Ash % 3.78% 4.30% Sulfur % 0.33% I 0.375%

Moisture I 13.43% BTU/lb 6924 8100

Corn Shelled

Ash % 1.13% I 1.23%

Sulfur % I 0.11% 1 0.11%

Moisture 12.49%

BTU/lb 7398 8480

Corn - High Oil

Ash % 1.17% I 1.34%

Sulfur % 0.095% 1 0.11%

Moisture 13.09%

BTU/lb 7073 8113

Corn - Waxy

Ash % 1.26% I 1.44%

Sulfur % 0.12% I 0.135%

Moisture I 7.12%

BTU/lb 7369 7911

Corn Cob

Ash % I 2.16% 2.32% Sulfur % 0.04% I 0.04%

Moisture I 9.14% BTU/lb 7057 7768

Corn Stover/Stalks

Ash % I 6.81% 7.64% Sulfur % 0.035% 0.04%

Moisture 9.27%

Dried Distillers Grain BTU/lb 8459 9422 w/solubles

Ash % I 4.16% I 4.13%

Sulfur % I 0.40% 0.45%

Moisture J 13.35%

Dried Distillers Grain BTU/lb 8473 9848 without solubles

Ash % 1.96% I 2.24%

Sulfur % 0.34% I 0.40%

Moisture 7.08%

BTU/lb 7955 8573

Hardwood Pellets

Ash % 0.34% 0.36%

Sulfur % 0.01% I 0.01%

Moisture I 12.49%

BTU/lb 7143 8242

Oats

Ash % 3.17% 3.58%

Sulfur % 0.135% I 0.16%

Moisture I 10.25%

BTU/lb 8783 10230

Soybeans

Ash % 5.19% 6.22% Sulfur % 0.29% 0.33%

Moisture 11.38% BTU/lb 6660 7570

Soybean Hulls

Ash % I 4.17% 4.22% Sulfur % 0.07% 0.08%

Moisture 8.26% BTU/lb 6839 7375

Straw - Wheat

Ash % I 10.40% 11.33%

Sulfur % 0.07% 0.075%

Moisture ; 6.91% BTU/lb 7153 7626

Straw - Oat

Ash % 7.90% I 8.49%

Sulfur % 0.05% 0.055%

Moisture I 9.70%

BTU/lb 6597 7345

Sugar Beet Pulp

Ash % 3.80% I 4.31%

Sulfur % 0.14% I 0.16%

Moisture 8.65%

BTU/lb 8474 9654

Sunflower Hulls

Ash % 2.86% I 3.13%

Sulfur % 0.14% I 0.15%

Moisture I 12.58%

BTU/lb 7228 8415

Wheat Middlings

Ash % 5.18% 6.00% Sulfur % 0.15% I 0.17%

Moisture 10.38% BTU/lb 7159 8063

Wheat (Hard Red Spring)

Ash % 2.08% 2.28% Sulfur % 0.20% 0.22%

As illustrated in the table above, the flax based pellet of the present invention is highly competitive with other known sources of fuel. A few of the main aspects in which the flax based fuel pellets of the present invention surpass

what is known are both the environmental aspects and the economical aspects. Unlike known fuel pellets, mainly typically consisting of wood products, the fuel pellets of the present invention are energy of a renewable and abundant source. The inventor has found that many farmers are willing to give their flax residue for free to someone who will remove the waste product for them. Fuel sources such as hardwood, corn cobs and dried distillers grain are extraordinarily expensive in comparison. In addition, many of the fuel sources listed present storage problems as they will begin deteriorating in a matter of days making handling and storage almost impossible. As the price for known energy sources increases and they become more scarce, an alternative source of fuel that meet supply demands is needed. A pellet made primarily from flax residue burns at a high temperature, generates little smoke, little ash, and no toxic creosote residue. In addition, it can be stored for long periods without rotting or deteriorating. Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.