NO328631B1 - Process for the preparation of fuel balls based on carbohydrate-containing biological raw material - Google Patents

Abstract

The invention comprises a process for the production of fuel spheres based on carbohydrate-containing biological raw material. The peculiarity of the process is that it comprises the following steps: - as a minimum component in a raw material mass for said fuel balls, to use at least one of the following types of residual mass: - beverage from alcohol production, - bagasse from sugar cane, - pulp from sugar beet, and - pulp from oil palm; - to arrange said raw material mass with a production moisture in the range 50-75% by weight; - to convert the raw material mass into spherical or approximately spherical units; and - drying the spherical units until they have a residual moisture content of a maximum of 12% by weight. The invention also comprises the use of carbohydrate-containing vegetable residues as a raw material for the production of fuel balls, wherein the raw material is selected from at least one of the following types of residues: - beverages from alcohol production, - bagasse from sugar cane, - pulp from sugar beet, and - pulp from oil palm.

Description

PROCEDURE FOR THE MANUFACTURE OF FUEL BALLS BASED ON CARBOHYDRATES CONTAINING BIOLOGICAL RAW MATERIALS

Field of the invention

The present invention relates to a method for producing a solid fuel, in the form of fuel balls, based at least on carbohydrate-containing vegetable residue. Such vegetable residue preferably consists of vegetable residues and/or waste from the food industry, agricultural activities and/or the wood processing industry.

According to the invention, residual mass from processing and/or processing of carbohydrate-containing vegetable material is used as raw material in the relevant fuel pellets. Such raw material can i.a. include bagasse from pressing sugar cane, liquor and other waste from alcohol production in breweries and/or distilleries, etc. Raw, undried bagasse will typically have a moisture content in the range of 45-55 percent by weight, while undried liquor often has a somewhat higher moisture content, typically in the range 60-70 percent by weight. With such a degree of moisture, these vegetable raw materials constitute poor fuel materials, even though they have a relatively high calorific value in a dried state. The word vegetable in this context is intended to include carbohydrate-containing raw materials from the entire plant kingdom, and from distinct tree species to distinct plant growths.

The fuel pellets in question are well suited as fuel in e.g. ordinary wood stoves and pellet stoves, but also in industrial heating systems that are adapted to such solid fuel. As a fuel, such balls can advantageously replace and/or complement ordinary wood pellets or the like.

The invention also relates to the use of specific carbohydrate-containing vegetable residues as raw material for the production of the fuel pellets in question.

The background of the invention

Biofuel in the form of pellets has become an increasingly common fuel for both domestic and industrial purposes. Most such fuel pellets are based on pure residual products from the wood industry, for example pure sawdust and/or wood chippings. This is a result of the fact that, in today's modern society, large quantities of wood are consumed for purposes other than heating. As a result, there are large quantities of residual wood that is easily available for the production of, among other things, wood pellets, wood briquettes and other designs of wood-based fuel products. Pure peat, or a mixture of peat and such residual wood, is also used to a certain extent for the production of such fuel products.

According to the current manufacturing method, such residual wood undergoes a relatively extensive, equipment-intensive, energy-intensive and therefore expensive process to arrive at the final fuel product, for example wood pellets. The same process is also used to produce pellets from peat, or from a mixture of peat and residual wood. This production process and its fuel product, especially wood pellets, are burdened with a number of technical, practical and economic disadvantages, which will be explained in more detail below.

There are, however, a number of other combustible raw materials that are used to little or no extent for the production of such processed solid fuel, even though these are often cheap, easily available and could be advantageously utilized for such purposes. Such other fuel raw materials can i.a. stem from trees, plants, shrubs, types of grass, fruits, vegetables, root vegetables, nuts, shells and the like, and they may well have an exotic origin. These fuel raw materials can i.a. include wood species, i.e. pure wood, which are not usually used for the production of wood pellets according to the aforementioned manufacturing process, and/or it may be types of residual wood that are considered inferior for this purpose. Current fuel raw materials can also include residual products from the wood processing industry and other industrial activities, for example recycled paper and cardboard. Alternative fuel raw materials can also be taken more or less directly from nature, for example in the form of peat, coal, coal dust, etc.

The reasons behind the lack of utilization of alternative fuel raw materials can be many and varied. For example, it may be that the resource possibilities have not been foreseen or investigated. The initiation and/or operation of such projects can also be hampered by poor finances, little interest and willingness to put in the effort, environmental considerations, political guidelines, etc. The finances and viability of such projects depend, among other things. of the nature and availability of the raw material in relation to the place of manufacture in question. Geographical distances, topography,

climate, infrastructure and available means of transport are therefore of great importance for such projects. Furthermore, there may be a lack of the necessary technology for extraction, production and production of the alternative biofuel in question. It could be, for example, that the technology does not exist or that it is insufficient, and/or that the technology is too expensive to acquire and/or use.

There is thus a need to provide technology that enables economically interesting utilization of alternative fuel raw materials for the production of new types and/or forms of solid fuel. The invention in question thereby seeks to provide a relatively simple and cost-effective method for the production of fuel pellets based on alternative, and preferably exotic, fuel raw materials. The invention is based on the utilization of mainly residues and/or waste from the processing and/or processing of carbohydrate-containing vegetable raw materials. Such residual mass preferably comes from the food industry, agricultural activities and/or the wood processing industry. There are extensive deposits of such residues and/or waste, and they occur in different types and extents depending on, among other things, geographical area and the type of business the residual mass comes from. Most such residues and/or waste are used to little or no extent as raw materials for the production of different types of solid fuel. These vegetable raw materials will be discussed in greater detail in what follows.

Known technique and disadvantages with this

It is known to use raw vegetable fibrous residue from the pressing of sugarcane, so-called bagasse, as fuel in e.g. steam boilers for the production of electricity. Bagasse is made up of the outer cellulose-containing fibers of sugar cane and is therefore a combustible material. However, as raw residual mass, bagasse has a typical residual moisture in the range of 45-55 percent by weight and therefore constitutes a poor fuel material in this state. As raw bagasse is largely regarded as problematic residual waste, open burning of large quantities of raw bagasse is carried out for no other purpose than to get rid of the waste. However, this causes problematic air pollution. In certain geographical areas, bagasse is also used as a raw material for the production of charcoal.

WO 2006/081645 describes the production of fuel pellets based on various biological residues, including bagasse.

Furthermore, DE 20 2006 013 363 describes the production of pellets or briquettes based on residual waste from plant materials, including residual waste from breweries and distilleries, such as hops from beer brewing and liquor from roasting.

Neither WO 2006/081645 nor DE 20 2006 013 363 suggests that the specified types of biological residual waste can be used for the production of fuel pellets of the type in question.

Furthermore, it is known to use coffee bean husks as solid fuel in, for example, kilns for the production of bricks.

Before anything else, there are a number of other carbohydrate-containing, vegetable residual materials, including those of exotic origin, which are considered only as waste, and which are burned and/or deposited as waste. Examples of such waste are stalks, stalks, straw, husks, husks, fiber bundles and the like from the processing and/or processing of various plants. This often causes air pollution and/or other types of environmental pollution, e.g. as a result of decomposition and rotting of the waste with associated pests and microbiological activity, which can also be harmful to health. Much of this residual waste is burned openly at or near the place of origin, but it is also burned directly in incinerators, for example in district heating systems or the like. Some such residual waste is also used for animal feed or in connection with animal husbandry, for example as litter.

Most known, however, is the production of fuel pellets based on (a) residual wood, (b) peat, or (c) a mixture of residual wood and peat, such as in the aforementioned, known process. According to this known process, clean wood is ground up into wood chips and/or wood flour which is dried in one or more stages, so that the ground wood pulp finally has a moisture content of approx. 5-10 percent by weight. This is an extensive process that requires a lot of energy, which is burdened with large dust nuisances, and which is thereby associated with the risk of ignition and fire. The ground and dried wood pulp is then fed into a pellet press and pressed under high pressure through a metal matrix (perforated plate). Cylindrical blanks are extruded from the metal matrix which break off, or are cut up, into short cylindrical rods. When the ground wood mass is pressed under high pressure through the metal matrix, the temperature in the wood mass increases. The increase in temperature causes the substance lignin to be released from the wood pulp. Lignin acts as a binder in the extruded rods when these are then cooled and turned into fuel pellets. Because of. this extrusion process gives the pellets a shiny and smooth cylinder surface, and they become hard and should thus be relatively dimensionally stable. Thereby, they should be better able to withstand the subsequent handling, packaging and transport to the user locations. An additional wood pellet hardness and moisture resistance can be achieved by boiling the wood pulp before it is fed into the pellet press. Thereby, the wood fibers in the wood pulp are broken and release additional lignin as a binder in the final wood pellets. The latter wood pellets are often referred to as brown wood pellets (as opposed to normal white wood pellets). For the production of wood pellets, wet wood pulp can also be used which is extruded as described above.

Such known fuel pellets are, as mentioned, also burdened with a number of technical and practical disadvantages which can be largely avoided by using fuel balls produced according to the present method. As mentioned above, such known fuel pellets are often in the form of short cylindrical rods which typically have a diameter of approx. 6-10 mm and a length of approx. 5-30 mm. Although the rods' cylindrical shape is a natural consequence of the manufacturing process, the cylindrical shape leads to a number of practical disadvantages. Cylindrical pellet rods usually have uneven, rough and chipped end surfaces, even if the cylinder surface is shiny and smooth. Irregular end surfaces constitute structural weaknesses which, when subjected to mechanical stress, easily lead to chipping and fragmentation of the pellets, thereby weakening their dimensional stability. This form of pellet weathering creates unwanted dust and microchips. In addition, the lignin binding in such pellets can be partly poor, which further assists pellet weathering and the associated formation of dust and microchips. In addition to weakening the structural integrity of the rod pellets, the formation of dust and microchips can also lead to partially dangerous and/or unfavorable conditions in connection with the firing process itself. Disintegration of pellets in connection with firing can i.a. inhibit the combustion process in that dust and microchips completely or partially prevent the supply of air to the combustion process. Dust and microchips also increase the possibility of a dust explosion in the incinerator and/or in associated equipment. For this reason, warns i.a. the pellet industry against allowing fuel pellets to come into contact with plastic and plastic objects, whereby static electricity can occur and cause a dust explosion. A cylindrical pellet design also inhibits the pellet feed to the incinerator. For this reason, feed chambers for such pellet incinerators are usually provided with a feed screw or similar feed device which forcibly feeds cylindrical rod pellets into the incinerator. The disadvantage of this, however, is that the incinerator's complexity and price increase, which is a direct consequence of the cylindrical pellet design. The above-mentioned, known process for producing fuel pellets, but also the cylindrical rod design of such pellets, is therefore associated with a number of significant problems.

Furthermore, the production and use of block-shaped fuel briquettes is burdened with many of the same technical and practical disadvantages as fuel pellets, and which can be largely avoided by using fuel pellets produced according to the present method. Such briquettes will typically have a cylindrical, rectangular or square design, which usually means that the briquettes also have uneven, rough and chipped side surfaces. Irregular side surfaces constitute structural weaknesses which, when subjected to mechanical stress, easily lead to chipping and fragmentation of the briquettes; this, like pellets. This disintegration weakens the shape stability of the briquettes and can lead to the formation of dust and microchips, so that partially dangerous and/or unfavorable conditions, including dust explosions and dust nuisances, can occur in connection with the firing process and the handling of the briquettes.

It is thus obvious that the known technique for the production of pellets and briquettes is extensive, equipment-intensive, energy-intensive, expensive and partly dangerous, which requires large-scale production to be economically interesting.

Vegetable raw materials for fuel pellets

In order to better define the invention, a more detailed description will be given in the following of raw materials that can be included in the fuel pellets in question, and which at least include carbohydrate-containing vegetable residue from the processing and/or processing of at least one carbohydrate-containing vegetable raw material . As potential additive material, chopped or ground wood, reeds, grass and similar vegetable material that does not constitute a residue from industrial processing and/or processing can also be used.

It is particularly vegetable residues and/or waste from the food industry, agricultural activities and/or the wood processing industry that are sought to be utilized in this invention. The reason for this is that such residual mass is often easily available and cheap, often free of charge, and that this residual mass is often regarded as unwanted and problematic waste.

Furthermore, it is particularly carbohydrates in the form of cellulose, hemicellulose, lignocellulose and the like that make up the combustible material in said residue. Such residual mass may also contain lignin, various vegetable oils, any residual substances in the form of simple sugars and starch, various proteins and minerals as well as ash substances, most of which also constitute combustible materials. Many of these substances, including lignin, sugar, starch, vegetable oil and/or proteins, act as glue in the mass they appear. This sizing material is used advantageously in the invention in question in that the main raw materials of the fuel balls, i.e. liquor, bagasse, pulp of sugar beet (also called sugar beet) and/or pulp of oil palm, contain such natural sizing materials. In their natural state, these main vegetable raw materials usually exist as relatively wet residual masses with moisture levels in the range of 40-70 percent by weight.

Relevant vegetable raw material mass can come from a number of carbohydrate-containing plants, trees, reeds, grasses, legumes, root vegetables, fruits and nuts. As examples of such crops, sugar cane (from the grass genus Saccharum), sugar beet (Beta vulgaris) and oil palm (from the family Arecaceae) have already been mentioned, but they can also include various types of cereals, potatoes, rice, maize, beans (including soybeans ), peanuts, rapeseed, canola, various types of berries and fruit, banana, coconut, bamboo, cassava (manioc), sorghum (from the Sorghum genus), cotton wool, flax, jute, hemp, ramie, millet, tea and tobacco. Such vegetable raw materials can originate from both agricultural activities, the food industry and the wood processing industry. Thus, the raw material mass in question can include appropriate, carbohydrate-containing raw materials from the entire plant kingdom, and from distinct types of wood, via various species of reeds and grass, to distinct plants, berries and vegetables. It is particularly vegetable raw materials on land that are of interest, but it is also conceivable to use vegetable raw materials originating in seas, rivers and/or lakes.

Thereby, the vegetable raw material mass can include both woody and non-woody raw materials and can include everything from distinctly fibrous materials (for example, various wood, paper, cardboard, bagasse) to distinctly non-fibrous materials (for example, liquor from alcohol production).

Materials with a fibrous or other integrity-promoting structure can advantageously be used as a reinforcing material in the relevant fuel balls. Such reinforcing material can i.a. include clean wood, residual wood, paper, cardboard from the wood processing industry. As an alternative or addition, such reinforcing material can include residual vegetable waste in the form of leaves, stalks, stalks, straw, fibers, fiber bundles, pods, capsules, flasks, and/or husks from agricultural and/or industrial activities. Such residual waste is often relatively dry and typically has a moisture content in the range of 8-15 percent by weight, in which condition this residual waste is well suited as fuel.

Suitable vegetable raw materials from agriculture and the wood processing industry are relatively obvious, while vegetable raw materials, including residues and/or waste, from the food industry may be less obvious. For this reason, examples will now be given of useful vegetable raw materials from the food industry.

Such vegetable raw materials include i.a. residues from sifting, grinding or other processing of grain or legumes, including the following categories: A. Bran, flour and other residues from grinding grain.

This category mainly consists of by-products from the milling of wheat, rye, barley, oats, maize, rice, grains of sorghum and buckwheat. A by-product is bran, which comprises the grain's outer shell with smaller remnants of the kernel attached and some flour. Another by-product is fine flour, which mainly consists of the finer parts of the shell that remain during sifting, as well as some flour.

B. Residues from sifting or other treatment of grain.

This category consists of residues from sifting the grain, but before grinding it, and usually includes the following components: - less malformed, crushed or crumbled grains of various grain types; - seeds from wild plants mixed with said cereal; and - fragments of leaves, stems, minerals, etc; - residues from cleaning silos, ship holds, etc., where these have largely the same composition as mentioned above; - husks removed from rice grains and the like during the grinding process; and - residues after dehusking, rolling, processing into flakes or pearl grains, cutting or coarse crushing of grain and the like. C. Residues and similar waste from grinding or other processing of legumes.

This category includes e.g. whole corn on the cob that has been ground with or without the husk.

Such residual products from the food industry also include residual mass from the production of sugar and starch, as well as residual mass from breweries and distilleries.

Such residues may include the following categories:

D. Residues from starch production and similar residues (from corn, rice, potatoes, etc.).

This category mainly consists of stringy, protein-containing ingredients that are usually in the form of pellets or flour, but also in the form of cakes.

E. Sugar beet pulp (beet pulp).

Beet pulp is the product that remains after the sugar juice has been extracted from the root of the sugar beet (sugar beet). Such beet pulp can be present both in a wet and dried state.

F. Bagasse.

As mentioned, bagasse is a waste product that consists of the stringy (fibrous) pulp that remains from the sugar cane after it has been pressed and the sugar juice has been extracted. Bagasse is usually present in a wet state.

G. Other waste products from sugar processing ten 11 ing .

Such waste products include foam waste, filtration waste, etc.

H. Pulp of oil palm.

These are residual products, for example fibers and stringy bundles of residual pulp, from the processing of oil palms. Raw oil palm pulp can be oily and is often present in a relatively wet state, preferably with a moisture content in the range of 40-55% by weight. I. Beverage and other waste from breweries and / or distilleries.

This category includes e.g. drank from alcohol production in breweries and/or distilleries. Liquor is a gruel-like waste that remains after sugar and/or starch in the raw material in the brewing or roasting process has been converted into alcohol. There are different types of booze, which depends on the raw material used for alcohol production. Grain liquor (barley, rye, etc.) and corn is obtained during beer brewing and consists of the malt waste that remains after the wort has been extracted from the raw material. Drinks made from berries, fruit and the like (also known as wine lees) are obtained during the production of wine. It is also obtained from the distillation of grain, maize, rice, potatoes, seeds, etc. Such waste is also obtained from the distillation of sugar-beet molasses. This category also includes boiled hops. As mentioned, this drink is usually available in a wet state, but it can also be available in a dried state.

Said residual products from the food industry may also include oil cakes and other solid residues after the extraction of vegetable fats or oils from fatty or oily plants. It can thus be about residual products after the extraction of, for example, soya oil from soybeans, peanut oil from peanuts, rapeseed oil from rapeseed, or oil from oil-containing seeds, fruits and grain germs, including linseed, cottonseed, sesame seed, mustard seed, copra, rice bran, etc. Some however, such types of oil cakes and solid residues constitute valuable animal feed and may therefore be of less interest as a raw material in the fuel pellets in question.

The food industry can also be burdened with vegetable food raw materials, for example various grain products, which for one reason or another have been damaged, for example mould-infested, and which are therefore not suitable for human consumption and/or animal feed. Such vegetable raw materials can possibly also be used in the relevant fuel balls.

Purpose of the invention

The overall purpose of the invention is to provide a technology which enables a more versatile and cost-effective utilization of alternative raw materials for the production of solid fuel based at least on vegetable residues and/or waste, preferably from the food industry, agricultural activities and/or the wood processing industry. It is particularly bagasse, liquor, pulp from sugar beet and/or pulp from oil palm that are of interest as main raw materials.

A further object of the invention is to avoid or significantly reduce the above-mentioned disadvantages associated with known techniques for the production of fuel pellets, but also disadvantages associated with the design of such pellets.

How the objectives are achieved

Said purpose is achieved by features which are indicated in the following description, and on which the subsequent patent claims are based.

According to a first aspect of the invention, a method for producing fuel pellets based on carbohydrate-containing, biological raw material is provided. The method comprises the following steps: (A) as a minimum component in a raw material mass for the production of fuel units, to use at least one of the following types

residual mass:

- drank from alcohol production,

- bagasse from sugar cane,

- pulp from sugar beet, and

- pulp from oil palm; (B) arranging said raw material mass with a production humidity in the range of 50-75 percent by weight;

(C) converting the mass of feedstock into smaller units; and

(D) to dry the units until they have residual moisture on them

maximum 12 percent by weight. The peculiarity of the procedure is that

the one in step (C) includes:

- to extrude the raw material mass through a perforated plate to thereby form a strand of the raw material mass;

- dividing said string into units; and

- to pass said units of the string through a circumferentially rotating tube to thereby form spherical or nearly spherical units of the raw material mass, the spherical units forming said fuel balls.

In step (B), the raw material mass can advantageously be arranged with a production humidity in the range of 60-70 percent by weight.

In step (C), the circumferentially rotating tube can, if necessary or desired, also be rotated back and forth around a rotation axis transverse to the tube, so-called double rotation. Such double rotation means that the ends of the tube are moved alternately up and down at the same time as the tube rotates around its longitudinal axis. Thereby, said raw material units are kneaded until they become spherical or nearly spherical.

Although any suitable size can be used, said string of raw material mass can advantageously be divided into units with transverse dimensions and lengths in the range of 5-25 mm, and preferably in the range of 10-15 mm. Furthermore, it is advantageous if the transverse dimensions and length of the unit are approximately the same, which facilitates the kneading of the raw material units in the rotating tube.

In step (C), the raw material mass can advantageously be extruded through a perforated plate with circular holes. Said string of raw material mass, and thereby units thereof, thereby acquire a circular cross-section, which further facilitates the transformation of the raw material units into spherical units.

In step (D), i.e. in the final drying process, the spherical units of the raw material mass can advantageously be dried in a

drying silo, for example a drying silo of the same type used for drying grain. In this context, fuel pellets with a diameter of 10-15 mm have proven to be the most favorable for achieving rapid and cost-effective drying of these. Under

in favorable weather conditions, ordinary air can be used in the drying process, but the supply of hot air may also be necessary in less favorable conditions.

The spherical units of the raw material mass are preferably dried until they have a residual moisture of a maximum of 10 percent by weight.

In step (A) of the method, as mentioned, one or more of the aforementioned types of vegetable residue can be used appropriately in the raw material mass. If necessary or desired, the raw material is cut up and/or ground to the desired size and/or shape for the further production of fuel pellets from the raw material mass.

All of the aforementioned types of residual mass that are included in the raw material mass contain natural adhesives (cf. discussion of these above) which are advantageously used in that they effectively bind the raw material mass together both in connection with the production of the fuel pellets in question, but also in connection with the subsequent handling , transport and firing with the balls.

Incidentally, the fuel balls in question do not have to have a completely spherical shape, and they may just as well have a somewhat irregular ball shape, for example an oval ball shape.

Fuel pellets based on alcohol have been measured with a calorific value of approx. 19.5 MJ/kg, while fuel pellets based on bagasse have been measured with a calorific value of approx. 17.0 MJ/kg. All in all, known wood pellets have a typical calorific value in the range of 14.4-18.8 MJ/kg. This clearly shows that the fuel raw material in question can exhibit similar calorific values.

In addition to these types of residual mass, other vegetable materials can also be included in the raw material mass, including such vegetable raw materials that are discussed in greater detail above.

Thus, in step (A) of the method, reinforcing vegetable material can be advantageously used in the raw material mass for the fuel pellets in question. This reinforcing material forms a reinforcing structure in the raw material mass and thereby in the fuel balls. This structure can take the form of a reinforcing braid or the like which, together with the aforementioned, natural glue in the raw material mass, serves to bind together and reinforce the fuel pellets. The balls thereby get a continuous, smooth and strong surface which exhibits a far greater structural integrity than for cylindrical stick pellets. Such a reinforcing structure is useful both for the formation and drying of such fuel balls, but it is also useful in connection with the subsequent handling, transport and firing with the balls. The reinforcement effect has proven to be particularly useful in connection with the final drying of the spheres, as the reinforcement helps to prevent cracking of the spheres when they dry and shrink somewhat. Such a natural, reinforcing structure can thus be useful in that it helps to prevent disintegration of the fuel balls during their overall life cycle.

For example, at least one of the following types of vegetable material can be used as reinforcing vegetable material: - pure wood, for example wood species that are not normally used for the production of wood pellets and the like; - residual wood, for example types of residual wood that are considered inferior for the production of wood pellets and the like; - cellulose-containing residual material from the wood processing industry, for example milled cellulose in the form of paper, cardboard and the like, and preferably clean, recycled cellulose products; - unprocessed fibrous residual material from at least one of the food industry and agricultural activities, including at least one of leaves, stems, stalks, straw, fibres, fiber bundles, pods, capsules, cobs, husks, bran and grain cleaning from associated vegetable crops.

In this context, for example, readily available wood species that grow near the production site, or wood species that are not normally used for the production of wood pellets, can be used. Types of residual wood that are considered inferior for this purpose can also be used, for example bark and sapwood.

Furthermore, bagasse and pulp from sugar beet and oil palm often contain such unprocessed fibrous residual material. Such residual material can thereby replace other reinforcing material of the above types.

Thus, in one embodiment of the method, the following vegetable raw material mass can be used:

- 50-70 percent by weight of said types of residual mass; and

- 30-50 percent by weight of said reinforcing vegetable material, for example ground paper and/or cardboard.

Thereby, the following can be used in the vegetable raw material mass, for example: - 50-70 percent by weight, and preferably 55-65 percent by weight, of said types of residual mass; - 10-30 percent by weight, and preferably 15-25 percent by weight, of at least one of said pure wood and said residual wood, for example ground wood chips of birch or the like; and - 10-30 percent by weight, and preferably 15-25 percent by weight, of at least one of said cellulose-containing residual material and said unprocessed, fibrous residual material, for example dried grass of the Phalaris type, also referred to as beach reed.

In the raw, undried state, the above-mentioned types of vegetable residue (drank, bagasse, sugar beet pulp and oil palm) have a moisture content typically in the range of 40-75 percent by weight, as mentioned above. The residual mass can advantageously be taken directly from the place of origin in such a raw, undried state and stored in this state at or near the production site for the fuel pellets in question. Although such an initially moist residual mass is preferable, the method does not require that such a moist residual mass is used.

According to step (B) in the method, the raw material mass is prepared with a production humidity in the range of 50-75 percent by weight. How the raw material mass is arranged with this production humidity depends on the desired production humidity and the said residual mass's initial moisture level. If said residual mass has a lower degree of moisture than the desired production moisture, water and/or other moist vegetable material is added until the correct production moisture is achieved. If said residue has a higher moisture content than the desired production moisture, vegetable material with a lower moisture content than the residue's moisture content is added until the correct production moisture is achieved. Such drier vegetable material can advantageously be made up of the above-mentioned residual waste, which typically has a moisture content in the range of 8-15 percent by weight, and which is often also fibrous and thereby reinforcing the balls' raw material mass.

According to a second aspect, the invention also includes the use of carbohydrate-containing vegetable residue as raw material for the production of fuel pellets according to any embodiment of the above-mentioned method. This means that the raw material in this application is selected from at least one of the following types of residual mass:

- drank from alcohol production,

- bagasse from sugar cane,

- pulp from sugar beet, and

- pulp from oil palm.

Advantages of the invention

By using the present method, the above-mentioned problems and disadvantages with the known technique can be largely avoided.

Firstly, major dust nuisances and the danger of ignition and fire, which the above-mentioned, known process for the production of fuel pellets and fuel briquettes are fraught with, are avoided or significantly reduced, which results from the fact that the wood is ground up and dried in large drying ovens before it ground wood is designed as pellets or briquettes. This follows from the fact that the present method makes use of a vegetable raw material mass which is adjusted to a production moisture in the range of 50-75 percent by weight before the raw material mass is converted into spherical or nearly spherical units. The raw materials are thereby processed in a cold state, so that drying in drying ovens and the like is not necessary. This is a significantly cheaper and safer way of treating the raw material mass than the aforementioned, known production process for fuel pellets or fuel briquettes can demonstrate.

Secondly, the mentioned handling and use-related weathering that known fuel pellets and fuel briquettes are plagued with is avoided by the fact that the fuel balls in question have a continuous, smooth and strong surface that exhibits a far greater structural integrity than cylindrical rod pellets and block-shaped fuel briquettes can exhibit.

Thirdly, the fuel pellets in question have the beneficial effect that they can easily be fed from a feed chamber into an incinerator by the fact that, due to its shape, rolls with the help of gravity. In contrast to known pellet stoves, the incinerator therefore does not need to be provided with a feed device, for example a feed screw, in order to feed the solid fuel into the stove. An incinerator for the fuel pellets in question can therefore be of a simpler and cheaper construction than a pellet stove.

Finally, the relevant fuel pellets, due to of its spherical shape, also easier to dry than rod-shaped pellets and block-shaped briquettes. The reason for this is that the drying medium, which will usually consist of air, flows more easily through a mass consisting of spheres than a mass consisting of rod-shaped pellets or block-shaped briquettes.

Claims (14)

1. Method for the production of fuel pellets based on carbohydrate-containing, biological raw material, where the method comprises the following steps: (A) as a minimum component in a raw material mass for the production of fuel units, to use at least one of the following types of residual mass: - liquor from alcohol production, - bagasse from sugar cane, - pulp from sugar beet, and - pulp from oil palm; (B) arranging said raw material mass with a production humidity in the range of 50-75 percent by weight; (C) converting the mass of feedstock into smaller units; and (D) drying the units until they have a residual moisture of a maximum of 12 percent by weight, characterized in that the method, in step (C), comprises: - extruding the raw material mass through a perforated plate to thereby form a strand of the raw material mass; - dividing said string into units; and - passing said units of the string through a circumferentially rotating tube to thereby form spherical or nearly spherical units of the raw material mass, the spherical units forming said fuel balls. 2. Method according to claim 1, characterized in that the circumferentially rotating tube is also rotated back and forth around a rotation axis transverse to the tube, so-called double rotation. 3. Method according to claim 1 or 2, characterized in that said strand of raw material mass is divided into units with transverse dimensions and lengths in the range of 5-25 mm. 4. Method according to claim 3, characterized in that the string of raw material mass is divided into units with a transverse dimension and length in the range of 10-15 mm. 5. Method any one of claims 1-4, characterized in that the raw material mass is extruded through a perforated plate with circular holes, whereby said string of raw material mass, and thereby units thereof, acquire a circular cross-section. 6. Method according to any one of claims 1-5, characterized in that the spherical units of the raw material mass are dried in a drying silo. 7. Method according to any one of claims 1-6, characterized in that the spherical units of the raw material mass are dried until they have a residual moisture of a maximum of 10 percent by weight. 8. Method according to any one of claims 1-7, characterized in that the raw material mass is prepared with a production humidity in the range of 60-70 percent by weight. 9. Method according to any one of claims 1-8, characterized in that reinforcing vegetable material is also used in the raw material mass, this reinforcing material forming a reinforcing structure in said fuel pellets. 10. Method according to claim 9, characterized in that at least one of the following types of vegetable material is used as reinforcing vegetable material: - pure wood; - residual wood; - cellulose-containing residual material from the wood processing industry; - unprocessed fibrous residual material from at least one of the food industry and agricultural activities. 11. Method according to claim 9 or 10, characterized in that the raw material mass is used: - 50-70 percent by weight of said types of residual mass; and - 30-50 percent by weight of said reinforcing vegetable material. 12. Method according to claim 11, characterized in that the raw material mass uses: - 50-70 percent by weight of said types of residual mass; - 10-30 percent by weight of at least one of said pure wood and said residual wood; and - 10-30 percent by weight of at least one of said cellulose-containing residual material and said unprocessed, fibrous residual material. 13. Method according to claim 12, characterized in that the raw material mass uses: - 55-65 percent by weight of said types of residual mass; - 15-25 percent by weight of at least one of said pure wood and said residual wood; and - 15-25 percent by weight of at least one of said cellulose-containing residual material and said unprocessed, fibrous residual material. 14. Use of carbohydrate-containing vegetable residue as raw material for the production of fuel pellets according to any one of claims 1-13.