Patent Application
20060272557
A. Non-Patents:
(Note: Numerals in [ ] listed below correspond to the relevant non-patent literature discussed later this document.)
B. Patents Cited:
1. Brief History of the Invention
This invention is closely related to, but not a direct result of, a research project completed in 2000 at the University of Missouri-Columbia (UMC), under the sponsorship of the U.S. Department of Energy. The UMC project, entitled “Compacting Biomass and Municipal Solid Waste to Form an Upgraded Fuel,” Investigated the feasibility of using high pressure to compact various types of biomass materials in order to produce dense cylindrical-shaped objects called “biomass logs” or “biomass tablet” [1]. In this patent, the term “log” refers to cylindrical objects of a length greater than or equal to the diameter, and the term “tablet” refers to cylindrical objects of a length smaller than the diameter. The UMC project found that by using pressure of the order of 18,000 psi (124 Mpa), most biomass materials, including but not limited to yard wastes (tree and bush trimmings, mowed lawn grass, fallen leaves), timber processing wastes (sawdust, tree barks, and mulches), agricultural wastes (cornstalks, corn cobs, and switch grass), and the combustible part of municipal solid wastes (waste papers, cardboard, waste wood as from discarded pallets, and discarded textile products) can all be compacted into biomass logs or tablets, without having to use either binder or heat. More than 30 types of biomass waste materials were successfully compacted into logs or tablets in the UMC project [1].
The purpose of compacting biomass materials should be explained. Most biomass materials, such as waste papers, forestry waste, agricultural waste and yard waste, are very bulky (loose and fluffy) when first collected. They are costly to handle, store and transport, and cannot be burned efficiently in burners, boilers or furnaces. However, upon compaction at pressure of the order of 18,000 psi, the bulk density of the biomass increases by 4 to 15 times [1], resulting in a densified fuel (logs or tablets) that is efficient to transport, handle, store and combust. For instance, with a five times increase in density, the same tonnage of biomass material can now be transported by one instead of five trucks, and can be stored in one instead of five silos. Also, the intensity of the heat generated in any burner that uses biomass as the fuel, and the rate of chemical reaction of any reactor that uses biomass as the feedstock for gasification or liquefaction of the biomass, will greatly increase with the increased biomass density. Another advantage of compacting biomass at high pressure is the uniformity of the geometry, dimensions and density of the product—biomass logs. Having uniform shape, dimensions and density also renders the biomass fuel easy to handle, package and feed automatically by using specially designed machines.
It should be mentioned that the University of Missouri researchers of the biomass logs have published extensively their research findings in reports [1-3], conference proceedings [4, 5], technical journals [6, 7], and student theses [8, 9], but the University did not choose to apply for any U.S. or foreign patent. Now that the concept of compacting and making biomass logs and tablets has been published for several years, it is too late for the University or anyone else to apply for a patent on the method of producing biomass logs and tablets. However, neither the University of Missouri nor anyone else has published or invented any means or special device to feed the biomass logs and tablets into burners. Through unpublished work conducted by the Freight Pipeline Company, a special device to feed biomass and other carbonaceous fuel logs and tablets into burners has been invented and reduced to practice, which forms the object of this invention and patent application. In this patent application, the terms “biomass logs” and “biomass tablets” refer to biomass materials compacted or extruded into the shape of cylinders of circular or nearly circular cross sections. The term “burner” refers to any device that can burn biomass logs or tablets for any purpose—such as a “stove”, “furnace” or “fireplace” that can burn biomass logs or tablets for heating buildings, or a “boiler” at a power plant than can burn biomass logs or tablets, with or without co-firing with coal or another fossil fuel, for generating steam or electricity. The same device and method invented here for feeding biomass logs and tablets into burners are also applicable to feeding logs and tablets made of other carbonaceous materials such coal or petroleum coke.
The special process to be patented here is a simple, practical and novel method to feed biomass and other carbonaceous tablets and logs into burners for burning. This new feeding method will facilitate the use of biomass energy and bringing down the cost of such use, thereby enabling the United States to use more biomass materials, which is a precious renewable energy resource largely unused and wasted at present. Increased use of biomass energy has the following benefits to the nation:
2. Different Methods to Densify Biomass
In general, there are four different methods to densify biomass raw materials. They are separately discussed as follows:
Briquetting—As described by Pietsch [10], briquetting is a century-old technology used mostly for agglomerating coal and charcoal fines. It forces materials to be compacted through the gaps of two parallel rotating drums to produce pillow-shaped agglomerates called “briquettes”. A major difference between briquetting and the biomass log technology developed at University of Missouri is the way pressure is applied to the material during compaction. While the latter applies pressure uniformly over the flat ends of the log or tablet (uni-axial compaction), the former compacts on curved surfaces which make pressure non-uniform. Consequently, the pressure applied to the rim of briquettes is much lower than that at the center of the briquettes. This makes it difficult to form strong briquettes without using considerable amount of binders or heat to aid in the agglomeration. It is not uncommonly to use 5 to 15% of binders to make coal briquettes. Without using binder or heat, biomass cannot be briquetted properly. In contrast, by compacting axially from the opposite flat ends, the pressure distribution across any biomass log or tablet is very uniform. This enables the formation of strong biomass agglomerates without having to use binder or heat. In comparison with the briquetting process, the biomass log process has the following advantages: (1) It produces strong products without using heat or binder; (2) it produces products in more precise and uniform shapes and density; (3) the quality of the product is more uniform and easy to control; and (4) it is more suitable for making large products (large logs and large tablets), thereby being more adaptable to mass production at low cost.
Extrusion—Extrusion is the processing in which materials are forced through a die or orifice, by using either an auger (screw), or a ram [10]. Extensive shear is generated, which together with the pressure, helps to agglomerate. While extrusion is widely used in the chemical and food industries, it cannot be used for binderless, room-temperature agglomeration of biomass. This is due to the fact that ordinary extruders cannot generate the high pressure required for binderless, room-temperature compaction of biomass, which is in the neighborhood of 18,000 psi [1]. Also, the extrusion process is very sensitive to the variation of raw material properties, such as moisture and particle size. A small variation of such material properties can often cause the extruder either to clog or to fail producing acceptable products. In contrast, the biomass log technology was found to be able to produce good quality products (logs or tablets) without clogging or other problems over a rather wide range of moisture, compaction pressure and particle size [1, 9]. This shows the superiority of the biomass log technology to extrusion for producing biomass logs and tablets. The only known commercial use of extrusion for biomass is the fuel logs used in fireplaces. Such fuel logs usually contain over 15% binder—the binder being either wax or an oil product. The first three of the four advantages cited above for biomass log process over briquetting also hold when comparing the biomass log process with the extrusion process.
Pelletizing—Pelletizing is a processes in which materials are forced through a pelletizer (pellet mill) which consists of a roller inside a perforated steel drum. The material drawn into the gap between the roller and the drum is forced through the perforations in a way similar to extrusion. Pelletizing is the most commonly used method for densifying biomass, and sawdust is the most common material used for making pellet fuel. However, to be successful in pelletizing, the biomass material is usually heated to over 140 degree Celsius (284 degree Fahrenheit) so that it will melt and release the lignin, which serves as the binder. Furthermore, the perforations of the pelletizer must be small, less than about 0.5-inch (13 mm) diameter, in order to form good pellets. All these lead to high energy consumption and high cost. According to the Pellet Fuel Institute [11], an organization representing manufacturers of the pellet fuel in North America, the average retail price of pellet fuel in North America is approximately $150 per ton. After subtracting the cost of material collection, packaging, transportation, storage and profits by retailers, the production cost of the pellet fuel is in the neighborhood of $30 per ton [12]. This is considerably higher than the anticipated production cost of manufacturing biomass logs as computed in the University of Missouri study [2]: $8 per ton for 5.5-inch diameter logs, and $14 per ton for 2-inch diameter logs. All the aforementioned four advantages of the biomass log method over the briquetting method also hold when comparing with the palletizing method.
The foregoing comparisons with competing technologies show that the biomass log technology is superior to all the existing technologies for compacting biomass.
Uni-axial compaction—uni-axial compaction is the method used at the University of Missouri to compact biomass materials into logs and tablets. It uses a cylindrical mold and a piston of cylindrical cross section with the piston head (i.e., the part of the piston in contact with the biomass during compaction) slightly smaller than the inner diameter of the mold. By using biomass feedstock of an appropriate moisture and by using high pressure in the range of 15,000 to 20,000 psi (pounds per square inch), practically all biomass materials can be compacted into dense biomass logs or tablets without having to use binder or heat [1]. The logs and tablets produced are dense (having specific gravity slightly greater than one), and they are wear-resistant and impact-resistant. They can be easily handled, transported, stored, and burned. Depending on the type of biomass materials and moisture, the biomass logs have heating values between 7,000 and 8,500 Btu/lb. The optimum moisture for making biomass logs, depending on types of biomass, is 5% to 15% [1,9].
The DOE-sponsored project also conducted a detailed and rigorous investigation of the cost of production of biomass logs [2]. By performing life-cycle cost analyses, the cost of producing each ton of biomass logs for manufacturing facilities of various sizes (capacities) was calculated. The analysis covered two sizes of biomass logs (2-inch and 5.5-inch diameters), over the manufacturing capacity range of 135,000-675,000 tons/yr. The study showed that over the plant capacity range of 135,000 and 675,000 tons/yr., the unit cost for producing the large (5.5-inch-diameter) biomass logs is between $5.4 and $8.2 per ton, and the unit cost for producing the small (2-inch-diameter) biomass logs is between $12.4 and $14.2 per ton. These cost figures include not only capital and annual (operation and maintenance) costs but also taxes, insurance and a 15% above-inflation return-on-investment (ROI). They do not include the cost of raw material or feedstock. It was assumed that the biomass waste materials used for making the logs can be obtained free of charge because they would otherwise be headed for landfill. To be conservative, the avoided landfill tipping fee, usually above $30 per ton, was not included in the cost analysis. Due to the inclusion of 15% ROI, the cost figures cited above are the anticipated price of the fuel that would allow the producer to achieve above-inflation return of 15%, which is a healthy return on investment. If the producer were paid a portion of the avoided landfill tipping fee, the profit or return would be much higher.
Further study by Li and Lin [3], sponsored by the Missouri Department of Natural Resources (MDNR), showed that the biomass logs and tablets, without crushing or size reduction, burn well in stoker boilers of ordinary coal-fired power plants, and in fireplaces, furnaces, and wood stoves for heating buildings. However, the study found that at present there is a lack of a suitable device to feed the biomass logs and tablets into boilers, furnaces and fireplaces. Such a feeder must be developed before the biomass log technology can be used widely. This provided the incentive for the present invention.
3. Field of Invention
This invention deals with a method to inject or feed biomass and other carbonaceous logs or tablets into burners (furnaces, boilers, stoves or fireplaces) for use as the fuel for combustion. It is in the general areas of biomass and other solid fuel combustion and feeding.
4. Description of and Comparison with Prior Art
The most relevant prior art is the biomass compaction study conducted at University of Missouri-Columbia [1-9]. The University researchers invented and developed the biomass log/tablet fuel, but did not invent or develop any special equipment or method for feeding this type of fuel into burners. Description and comparison with other related prior arts are to be given next.
There are many patented processes for producing and burning biomass and other carbonaceous fuel or fuel elements. For instance, in 1997, U.S. Pat. No. 5,658,357, entitled “Process for forming coal compact without a binder,” was issued to H. Liu et al at University of Missouri-Columbia (UMC). The patent deals with a process that applies high pressure to coal particles inside a mold to produce water-resistant coal logs for pipeline transportation—the concept of coal log pipeline. This compaction method is essentially the same used by researchers of the UMC to produce the biomass logs and tablets sponsored by the DOE project mentioned before. The patent is different from the present patent in that it does not deal with how the coal logs are to be combusted or fed into burners.
Another U.S. patent (U.S. Pat. No. 5,879,421), entitled “Apparatus and method for forming an aggregate product from particulate material,” was issued to H. Liu et al. in 1999. The patent deals with using special mold shapes and back pressure during compaction to produce strong coal logs for pipeline transport. Again, it does not deal with the combustion of the coal logs or other products.
Another U.S. patent (U.S. Pat. No. 6,375,690), entitled “Process for forming coal compacts and product thereof,” was issued to B. Gunnink et al. in 2002. The process deals with heating coal-water mixture to above 100 degree Celsius while the mixture is being compacted inside a mold to produce binderless coal logs. Again, the method deals with manufacturing rather than combusting coal logs.
In July 2004, a U.S. patent (U.S. Pat. No. 6,767,375), entitled “Biomass reactor for producing gas,” was issued to L. E. Pearson. The patent deals with an apparatus (reactor) for producing synthesis gas from a biomass feed in a closed, helical coil reactor fired by at least a natural gas fed burner. The biomass is fed into a mixing vessel pressurized by a transport gas such as natural gas which transports the biomass feed to the reactor coil. Feeding of the biomass into the mixing vessel is through a rotary valve, which is the standard feeding method used in pneumatic conveying of bulk solids. Such a feeding method is very different from the feeding method described in the present patent, which rolls the biomass logs and tablets into a burner.
In November 2004, a U.S. patent (U.S. Pat. No. 6,814,940), entitled “Process for pyrolyzing carbonaceous feedstocks,” was issued to J. Hiltunen. The patent deals with a process and an apparatus for pyrolyzing (thermal conversion of) biomass and organic wastes into a hydrocarbon liquid fuel. As in the case of conventional pyrolysis processes, biomass or organic waste feedstock is inject into the reactor by using a screw conveyor, which is very different from the present invention.
In March 2005, a U.S. patent (U.S. Pat. No. 6,863,878), entitled “Method and apparatus for producing synthesis gas from carbonaceous materials,” was issued to R. E. Klepper. The patent deals with a method and apparatus for producing synthetic gas from biomass or other carbonaceous materials, utilizing a controlled devolatilization reaction in which the temperature of the feed material is maintained at less than 450 degree Fahrenheit, until most available oxygen is consumed. Two types of feeder mentioned in the Claims of the patent are: a rotary feeder and a cyclone feeder. Both are conventional devices for feeding bulk solids, and hence are very different from the log/tablet feeder in the current invention.
In April 1982, a U.S. patent (U.S. Pat. No. 4,325,310), entitled “Boilers”, was issued to T. A. Babbage. The patent deals with an automatic boiler for combusting coal in power plants. The boiler has an internal hopper to store and feed coal into the fire bed. Coal is stored in the hopper and fed into the fire bed in bulk form. The system was designed to feed bulk solids having top size of 5/16 inch. It cannot feed biomass logs and tablets, which are generally much greater than 5/16 inch in diameter and length. Furthermore, the mechanism involved in feeding, which does not rely on the rolling of particles, is very different from the one to be patented herein.
In August 1988, a U.S. patent (U.S. Pat. No. 4,766,824), entitled “Burner especially for burning biomass,” was issued to E. Tenhunen. The patent deals with an improvement of the stoker boiler for handling biomass. Feeding is done by using an automatic stoker which is for feeding granular bulk solids (wood chips and peat) of relatively small (less than 1 inch) size, which is unsuitable for feeding biomass logs and tablets.
5. Distinct Features of Current Invention
The feeder in the current invention is different from all the known existing biomass and other carbonaceous material feeders for burners in two main respects: (a) it is a special feeder designed for feeding logs or tablets (i.e., fuel or feedstock elements of circular cross section) having uniform diameter, and (b) the feeder relies on gravity to roll the fuel elements, which is the most dependable and practical way to feed tablets or logs of uniform or approximately uniform size. Note that some degree of non-uniformity in the log (tablet) diameter and length is tolerated in using this feeder, as long as the logs (tablets) are cylindrical and roll easily down a slope under gravity.
This invention deals with a method to feed or inject cylindrical fuel elements (logs and tablets), made of biomass and other carbonaceous materials, into burners (furnaces, stoves, boilers and fireplaces) for combustion. The method takes advantage of the round shape and uniform geometry of the fuel elements in the fuel feeding (injection) process. The fuel elements are stacked inside a special feeder chamber that has a downward bottom slope, and then rolled by gravity into the burner for combustion. The feeder has a control mechanism that regulates the rate of feeding of the fuel elements into the burner. The feeder also has one-way valves or gates that allow the biomass logs and tablets to enter the burner, but prevent smoke and fire from entering the feeder. Due to the use of gravity for feeding, the feeder is simple, energy-efficient, and reliable.
As shown in
Invented here is a method and device to inject or feed cylindrical fuel elements (logs or tablets) that are made of biomass or other carbonaceous materials. The elements are fed into a burner, which may be a stove, boiler, furnace or fireplace, for combustion. The heat generated from such combustion can be utilized for producing hot water, heating buildings, producing steam, generating electricity, or other purposes.
The method takes advantage of the cylindrical shape and uniform dimensions of the fuel elements to be injected. It uses a specially designed injector or feeder to store and inject the fuel elements. Injection is done by the force of gravity and hence is simple, reliable and convenient. The principal part of the injector is a feed channel having a general downward slope towards the burner. Preliminary tests conducted by the inventors indicated that the minimum slope for causing biomass logs and tablets to roll on a metal plate or any other smooth and hard surface is about 5%, which is slightly less than 3 degrees. Thus, with a minimum channel floor slope of 3 degrees, cylindrical fuel elements inside the channel will roll down the slope by gravity and enter the burner as long as they are not blocked or physically restrained from moving. The preferred vertical profile of the feed channel is zig-zaged as shown in
Loading biomass fuel elements into the feeder is through the feeder inlet, 1, as shown in
Fuel elements, 3, are loaded inside the feeder channel, 4. The fuel elements may be made of any carbonaceous materials such as biomass, coal, petroleum coke, etc. that are compressed, extruded, or cast into cylindrical shapes of any practical diameter and length. The preferred material for making the feeder channel is sheet metal such as galvanized steel, although other suitable metallic and non-metallic materials may be used.
The motion and the rate of release of the fuel elements in the feeder channel are controlled by the stopper, 5, which either stops or allows the elements to move. The stopper can be made of various objects and shapes, and activated by various mechanisms. For instance, the stopper may be a simple bar or a rod (see
One-way valves or swing gates (part 6 in
Finally, the channel outlet, 8, may be simply the end of the channel, or may have an elbow of any angle to direct the exiting fuel elements down to the burner floor or the fuel bed. The outlet may either be stationary or mobile. A mobile outlet has an extendable arm which can reach different areas of the burner, so that the fuel elements can be distributed more uniformly in the burner. The same PLC that controls the stopper can be used to control the motion of the extendable arm. The mobile outlet is needed only for large burners where the fuel elements exiting from the channel may not reach certain areas of the burner, or where the burner does not use a moving grate.
Loading of the feeder involves periodic conveying or transporting fuel elements to the feeder, either by a conveyor or manually, depending on the size of application. For instance, for use at power plants, the quantity of fuel used is large and hence automatic conveyance of the fuel elements from the stockpile or silo to the injector is necessary. It can be done by using belt conveyors, auger conveyors, or other automated conveying systems. In contrast, for use in a fireplace or in a special stove for heating a residence or small building, the quantity of biomass logs or tablets used is small, and thus transporting to and loading of such fuel elements into the feeder can be done manually as needed, such as once a day.
The invented method and device described here for feeding logs and tablets made of carbonaceous materials will greatly facilitate the use of biomass for heating and energy generation, thereby causing more beneficial use of biomass materials, which in turn will reduce air pollution and the emission of greenhouse gases generated by using fossil fuel. Because biomass is a renewable energy resource supplied by trees, bushes and grass, whose growth converts carbon dioxide to oxygen through photosynthesis, use of biomass for heating and generating electricity is a carbon-dioxide-neutral process. It does not contribute to an increase in carbon dioxide in the atmosphere, and hence does not cause global warming. It is good for the nation and the planet earth. Although this invention was intended for feeding biomass fuel elements, the same method can be used to feed other solid fuels that are made into cylindrical-shaped elements.
| Number | Date | Country | |
|---|---|---|---|
| 60595094 | Jun 2005 | US |
