A METHOD FOR THE PREPARATION OF A BIOMASS DOUGH, A BIOMASS DOUGH, A FUEL BRIQUETTE MADE OF A BIOMASS DOUGH, AND A METHOD FOR MANUFACTURING A FUEL BRIQUETTE

Field of the invention

The invention relates to a method for preparing a biomass dough, and a biomass dough. The invention also relates to a fuel briquette made of a biomass dough, and a method for manufacturing a fuel briquette.

Background of the invention

Baking is a method known in households and in food industry, such as in bakeries. In baking, what is most essential for the formation of a dough is that the dough mass becomes a solid elastic and stretchable mass. For example in the baking of bread, the gluten-forming property of gluten proteins included in wheat seeds is utilized for forming a dough of dry substances mixed together, when water is admixed to the dry substances and the dry substances are mixed together. The gluten proteins included in wheat flour form a mesh-like viscous structure in the baking process, binding the different ingredients together to form a solid dough mass.

However, the above-described baking method has not been utilized previously in the manufacture of products made for the purpose of energy production.

Summary of the invention

It is an aim of the present invention to disclose a method for preparing a biomass dough to be used as raw material for fuel briquettes, by applying the conventional baking method. It is also an aim of the invention to disclose a fuel briquette made of the biomass dough, to be used for the purpose of energy production in households and in industry.

To achieve this aim, the method for preparing a biomass dough according to the invention is primarily characterized in that the biomass dough is prepared by a baking method, in which method the raw materials of the biomass dough are mixed with a gluten-forming adhesive and are moistened, whereby the gluten proteins of the gluten-forming adhesive form a mesh-like structure that binds the raw materials of the dough to form a solid dough mass.

The biomass dough for the purpose of energy production according to the invention is, in turn, primarily characterized in that the biomass dough is made by a method according to any of the claims 1 to 9.

The invention is based on the idea that the conventional baking method is used for the preparation of a biomass dough and for the manufacture of final products to be made of the biomass dough for the purpose of energy production. In the manufacturing method according to the invention, the gluten-forming property of gluten proteins included in grain seeds, particularly wheat seeds, is utilized for forming a coherent dough of raw materials to be mixed together, when the raw materials are moistened and the ingredients are mixed together. The gluten proteins or gluten included in wheet flour form a mesh-like structure that binds the other ingredients of the dough, for example rough biomate- rial, together to form the dough mass.

The raw materials for the biomass dough do not need to be ground to fine powder, but thanks to the mesh structure formed by the gluten proteins, it is possible to use coarser raw material. Substances having different particle sizes can be mixed together without significantly affecting the properties of the final product. For example grain seeds, chaff, scales, straw, or other natural substances are used as raw materials for the biomass dough. By the method according to the invention, a biomass dough can be made of a dry, moist or wet mixture of raw materials.

In addition to the gluten-forming adhesive, it is possible to use another thickening ingredient for forming the dough, for example starch-

containing flour obtained from potato, sugar beet or corn, which also thickens the raw material mixture by becoming a paste when it is moistened. Furthermore, natural substances, such as tar or gelatin, can be used for forming a dough of the raw material mixture, because of their glueing and sticking properties. To thicken the raw material mixture, it is also possible to use artificially prepared fluid substances, or dry substances which make the raw materials thicken to a dough-like mass when they become moist or react with water. For thickening the raw materials of the biomass dough into a dough-like mass, it is also possi- ble to use fluid substances processed from natural raw materials, such as, for example, tarry liquid or black liquor solution, to thicken the raw materials of the dough mixture to a dough-like mass.

In the method for forming the biomass dough according to the inven- tion, it is also possible to use lignin-containing raw materials, for example straw or reed, as an ingredient to cause or to facilitate the formation of the dough, and thus to utilize the natural glueing property of lignin in the preparation of the biomass dough.

Thanks to the method according to the invention, it is possible to produce a burnable final product for the purpose of energy production, wherein the mesh-like structure of the gluten protein forms a dough of the raw materials used, a solid mass in which the gluten formed in the baking process binds, for example, sawdust, chaff, wood chips or grain seeds used as raw materials, when the ingredients of the biomass dough are mixed together.

Thus, the invention also relates to a fuel briquette made of a biomass dough according to the invention. The fuel briquette according to the invention is primarily characterized in that the fuel briquette is a product compressed of a biomass dough made by the method according to any of the claims 1 to 9, and cut to a fixed length, intended to be burnt for the purpose of energy production. The fuel briquette is made by a method which is, in turn, characterized in that the biomass dough is compressed to such an extent that the final product is solid during its packing, transportation and feeding into a furnace.

The invention makes it possible to use grain and other natural materials as raw materials for energy production in the form of such a cohesive physical end product that can be used for energy production, for example in conventional furnaces and fireplaces intended for heating with wood. By means of the invention it is also possible to manufacture an inflammable fuel briquette of natural raw materials. By means of the invention, it is possible to produce an end product to be used for energy production, which can be consumed for the purpose of energy production even by primitive technology. By means of the invention, it is possible to produce a burnable fuel briquette without exactly specified physico-chemical and technical requirements, for example, for the moisture content of the raw material and for the technical equipment used in the manufacture. Instead of exact technical requirements, it is sufficient that the biomass has formed into a dough in such a way that the end product is cohesive for the time of its packing, transportation and feeding into a furnace. It is possible to vary the composition and compactness of the biomass dough used as the raw material for the final product to a great extent, and in this way to adjust the cohesive property of the final product.

According to the invention, the raw material options for the biomass dough and for the fuel briquettes to be made of it are very flexible, because, in practice, any burnable material can be used for preparing the biomass dough. For the same end product intended to be burnt for the purpose of producing energy, it is possible to use a variety of different raw materials, which makes it possible to optimize both the burning result and the energy production capacity of the end product. In practice, it is possible to optimize the burning properties of the fuel briquette to be produced for a given apparatus, to be optimal for said apparatus. Another advantage of the invention is the fact that different raw materials can be introduced in the end product during the production process, including, for example, raw materials that intensify the burning of each other, so that there is hardly any need to change the production process itself, because there are hardly any mutual dependency relations between the raw materials entered in the pro-

duction process, which would relate to or limit the production process, except for the substances that bring about the dough formation.

The fuel briquette made of the biomass dough can be compressed to reduce bulkiness, to minimize the costs on package, storage and transportation, as well as to remove extra moisture from the end product. For example, a resin adhesive can be sprayed or applied onto the surface of the form-cut or form-pressed fuel briquette to secure the cohesion of the end product, to facilitate its ignition or to boost its burning.

An advantage of the invention is that the production principle is simple and the technology used has a low level of complexity, and the production process, as such, is independent of the level of the technology used. For the production of the dough-like biomass and the fuel briquettes made of it, it is possible to utilize agricultural machinery and equipment already available on farms, even without any technical conversions. The invention reduces the dependence of agricultural producers on the chain of food production, because the invention gives a farm operator an option for an alternative line of business, and furthermore, it provides the farm operator applying the invention with a means to balance economical risks relating to agricultural production, among other things, by reducing the risk effect caused by weather conditions at harvest time.

The fuel briquettes according to the invention can be used in conventional furnaces of households which have been normally heated with wood, or in special furnaces operating at a better efficiency, and in combustion plants. The fuel briquettes can also be burnt in large industrial furnaces for producing, for example, district heat or heat energy required for industrial production. The product can also be utilized by hikers, for whom particularly a fuel briquette that contains tar or another inflammable ingredient or a special ignition wick is an easy means to produce heat energy at a camp fire.

Description of the drawings

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 is a chart illustrating the process for producing a biomass dough and a fuel briquette according to the invention,

Fig. 2 shows a production apparatus for preparing biomass dough, and

Fig. 3 shows a production apparatus for making fuel briquettes of a biomass dough.

Detailed description of the invention

A mealy gluten-forming adhesive and a coarser burnable material, or a mixture of materials, which may contain coarser and fine-powdered burnable raw materials, are used as the raw materials for the biomass dough.

As an adhesive for the biomass dough, flour or fine-crushed grain is used, which has been obtained from grain seeds, particularly wheat, and which contains gluten protein to make the raw materials form a dough when the raw material mixture is moistened and this mixture is stirred for a sufficiently long time. The formation of the dough of the raw materials is caused by the gluten protein contained in the mealy adhesive, which produces a mesh-like gluten structure in the baking process. The mesh-like structure binds the coarser materials to the dough- like mass. The mixture of the raw materials is moistened, for example, by introducing water or another fluid substance, such as black liquor solution or tarry liquid, into the mixture, or moisture is introduced in the form of water vapour into the mixture.

It is possible to use any natural burnable materials as the raw material for the dough. In particular, parts of a grain crop are used, such as

seeds, chaff, scales or straw. Other suitable raw materials include, for example, reed canary grass, reed, hay, sawdust, cuttings, peat, moss, bark, leaves, logging waste, organic debris, wood chips, and conifer needles. It is also possible to use a mixture of any of the above-men- tioned materials as the raw material.

In the manufacture of the biomass dough, it is possible to use dry, moist or wet biomass as the raw material. The gluten-forming adhesive used in the biomass dough is flour, mixed flour, crushed grains, flakes, malt, corn or crush made of grain seeds, particularly wheat.

In addition to the adhesive that contains the gluten protein, it is also possible to use another ingredient to make the dough thicker, such as starch-containing flour from potato, sugar beet or corn, which thickens the raw material mixture by becoming a paste when it is moistened, or substances having glueing or sticking properties, such as gelatin, egg, or tar. For forming the dough, it is also possible to use as an additive a fluid substance that thickens the raw materials of the biomass dough to a dough-like mass, such as, for example, tarry liquid or black liquor, which contains lignin. As an artificial cohesive substance, it is possible to use, for example, thickeners that are used in food industry, such as pectin. Besides those substances mentioned above, dough formation can also be caused by another artificially made fluid or dry substance, for example a chemical.

In the biomass dough, the raw materials constitute a solid elastic mass, thanks to the gluten proteins. In addition to the dough formation caused by the gluten protein, an essential process causing the formation of the dough from the raw materials of the biomass dough is the mixing of the damp, wet or moistened lignin-containing biomass with the other raw materials of the biomass dough. The lignin binds the raw materials of the biomass dough to a solid cohesive mass, when lignin in liquid form or moist lignin-containing material, for example straw material moistened with water vapour, is mixed together with the other raw materials selected for said biomass dough.

In the preparation of the biomass dough, it is possible to use, for example, gluten protein and lignin together as the ingredients to cause dough formation. In addition to lignin and gluten protein, a chemical can be used as an ingredient to cause dough formation.

The raw material used for preparing the biomass dough, for example straw material, can be moist with water at the stage when it is introduced to the dough vessel, or it can be moistened first in the process of preparing the biomass dough. The moistening can be implemented, for example, with a chemical in liquid form, which brings out the natural glueing property of lignin in the straw material. The raw materials for preparing the biomass dough can be mixed with a liquid substance, for example a solution of black liquor, which contains lignin in liquid form. The chemical additive added to the moist straw material may be such that it efficiently replaces water from the raw material mass. The applied chemical additive may also be such that, as a result of adding said chemical, the water contained in the raw material mass is efficiently replaced with said chemical, which reduces the drying time of the final product, reduces the time of its application for the purpose of energy production, and thereby improves the properties of the final product.

In the process of preparing the biomass dough, the straw material can be mixed or fluffed up so that the substance bringing out the glueing property of lignin can come better into contact with the surface of the straw material. The substance that brings out the glueing property of lignin can be added to the straw material simultaneously with or separately from the mixing or fluffing up of the straw material.

If a chemical substance is used in the preparation of the biomass dough to release lignin from the straw material or to secrete lignin onto the surface of the straw material so that the glueing property of lignin could be utilized for the formation of the biomass dough, the dough-like mixture formed of the raw materials of the biomass can be neutralized by adding a substance, for example lime, to the raw material mixture, to cause a change in the desired direction in the pH value of the dough

mixture. With this procedure, the biomass dough or the raw material mixture used for its preparation can be neutralized already at the stage of the dough formation. There is reason to carry out the above-mentioned neutralization in the production of the biomass dough or the fuel briquettes to be made of it, if the pH value of the biomass dough is changed by the substances used in the production process and becomes disadvantageous for the apparatus for producing the biomass dough or the fuel briquettes, or for the usability of the fuel briquettes to be made, in view of the handling of the fuel briquettes, the durability and functionality of the apparatus used for burning them, the burning result or incineration properties of the fuel briquettes, or the environmental safety of the fuel briquettes as well as of the apparatuses used for their production, transportation or consumption.

In the dough formation, it is also possible to use moist or wet mass that remains from black liquor after evaporation. The mash-like remaining mass of black liquor can be introduced in the same vessel with the raw materials of the biomass dough, and when this mixture is stirred, the lignin in the remaining mass of black liquor causes glueing of the raw materials into a solid mass with the remaining mass of black liquor. If the raw materials include wheat flour or another meal that contains glutein, a biomass dough is formed of the raw materials and the remaining mass of black liquor, thanks to both the gluten property of the gluten protein and the adhesive property of lignin, and the dough formation of the biomass dough involves two adhesives that bind the raw materials of the dough together to form a solid mass: lignin and gluten.

The fuel briquette is the final product made of the biomass dough made by mixing the raw materials by the baking method, and it can be burnt for the purpose of producing energy, for example in a thermal power station or in a suitable combustion furnace. The fuel briquette can also be called a dougette, when it is a fuel briquette made of a biomass dough by the baking method and intended for energy production.

A single fuel briquette is made of the biomass dough by slicing or cutting the biomass dough to pieces of a fixed size, after which the final product is dried. After drying, the fuel briquette remains solid for the time of packing, transportation and feeding into a furnace. The fuel briquette is a finished form-cut article made of a biomass dough, normally a cylindrical piece that resembles a bun or a piece of a French loaf. The appearance of the fuel briquette may resemble, for example, a rusk or a cylindrical brick that is used as sauna stove stone. To improve the cohesion of the fuel briquette, it is possible to add a chemical additive or, for example, a thickener used in the food industry, to the above-mentioned mixture.

Alternatively, it is possible to make slabs or sheets of the biomass dough by form-pressing, wherein the final product is plate-like and it comprises several fuel briquettes attached next to each other and after one another.

A sheet of fuel briquettes can be burnt as such for the purpose of energy production, if this is possible by the properties of the furnace, or it can be broken into smaller parts, for example by knocking it against the floor, breaking it or hitting it against a tangential surface that provides a resistance, such as a knee or the edge of a stool. The strength and breaking resistance properties of the fuel briquette sheet are adjusted in the preparation process to comply with the purpose of con- sumption of the final product or with the target client group, by modifying the composition of the dough. The form-pressing of the fuel briquette sheet can be done in large batches on a production line of the conveyor belt type. A typical fuel briquette sheet has a thickness of about 1 to 5 cm, and its topography repeats the conformation of the single briquettes. The pressing form determines the topography of the fuel briquette sheet and thereby also the conformation of the single briquettes that can be detached from the sheet.

In the manufacture of the fuel briquette, during its pressing, extrusion or compression, or in a separate step in the manufacturing process, an ignition wick can be embedded, for example a so-called tar wick, to be

used as the point of igniting the fuel briquette. The ignition wick for the fuel briquette is made, for example, by injecting or extruding an inflammable, relatively solid material inside the fuel briquette so that the ignition wick extends from within the fuel briquette up to its surface. Instead of tar, in the ignition wick it is possible to use a corresponding material that is runnable in a controlled manner, relatively solid, syrupy, and inflammable. This property of the fuel briquette can be utilized, for example, when the fuel briquette is consumed by burning in a camp fire. The fuel briquette having an ignition wick can also be utilized for setting fire in households.

As a raw material or as an additive in the biomass dough, it is possible to use a lubricant that facilitates the mixing of the biomass dough or the passing of the biomass dough towards the cutting step in the manu- facturing apparatus, in which the fuel briquette gets its physical shape. The lubricant can be used both on the surfaces of the manufacturing apparatus and as a raw material in the biomass dough. At the stage of baking the biomass dough, the lubricant, for example a fatty substance or a natural oil, such as castor oil or rapeseed oil, facilitates the mixing of the raw materials of the biomass dough together. At the stage of forming the final product, the lubricant lubricates the passage of the ready biomass dough towards the cutting step in the manufacturing apparatus. As the lubricant in the manufacture of the biomass dough, it is possible to use, for example, an animal fat, a vegetable fat, coconut butter, rapeseed oil, turnip rapeseed oil, beeswax or other natural waxes, discarded deep-frying fat, glycerin, or castor oil. For form- pressing of the briquette sheet, it is possible to use a lubricant that acts as an ingredient to facilitate the separation of the press mould and the biomass dough from each other. The lubricant used in the baking of the biomass dough and in the formation of the fuel briquette contributes to a trouble-free and functional production process and a uniform final product. The same lubricant can also be used as an ingredient to facilitate burning. For example an animal fat or castor oil can be added to the raw material mixture both as an additive to promote the burning of the final product and as a lubricant to facilitate the production of the biomass dough and the final product to be made of it. The fatty

substance, natural oil or lubricant having an effect to facilitate the burning of the final product can be added to the dough at the stage of baking the biomass dough, or mixed to another ingredient even before the baking step, for example by adding said ingredient to black liquor, or by impregnating a dry substance with it.

As the additive to facilitate the burning of the final product to be made of the biomass dough, it is possible to use, for example, an animal fat, beeswax, resin, tar, tall oil, castor oil, eucalyptus oil, or discarded deep- frying fat. The substances to facilitate the ignition can be sprayed or applied onto the surface of the fuel briquette. As an ingredient to facilitate the ignition or the burning, it is also possible to use, for example, waxy polyethylene, which is used, for example, on the inner surfaces of cardboard packages for fluid products. Using waste from such cardboard packages as a raw material for the biomass dough promotes the burning of the final product made of the biomass dough, because it contains, among other things, waxy polyethylene.

To boost or to optimate the burning or the burning result of the fuel briquette made of the biomass dough, it is possible to use, for example, granulated charcoal, charcoal dust, charcoal pieces, or another fossil fuel as a raw material for the biomass dough. As the raw material for the biomass dough, it is also possible to use ashes produced as burning waste from fuel briquettes, pellets or other biomass, and incom- pletely burnt material from these, burning waste produced from tar burning, or other burning waste. As the raw material, it is also possible to use, for example, cotton cleaning waste or paper waste that has been used in car repair work and stained with oil or liquid fuel, or, for example, absorbing peat or a powder-like absorbing substance that has been used for absorbing liquid fuel or fuel oil at service stations.

For hardening the surface of the fuel briquette, it is possible to use an adhesive or a hardening agent that is sprayed or atomized onto the surface of the finished fuel briquette or onto the dough length pressed from the biomass dough before the dough length is cut to form a fuel briquette of a fixed length.

In addition to the substances mentioned above, it is also possible to use other parts of crops and beets, and waste produced during their processing, as raw materials for the biomass dough. Suitable raw materials for the biomass dough also include vegetable waste from the manufacture of, for example, wine, juice or vegetable oil. It is also possible to use side products, waste, raw materials, or final products from paper and pulp industry as raw materials for the biomass dough.

In the following, we will describe, by way of an example, a production process and an apparatus for producing a biomass dough and a fuel briquette made of it.

The fuel briquette and the biomass dough used for its manufacture are produced, for example, by means of the production process shown in

Fig. 1. The production process shown in Fig. 1 begins already from the harvesting of the raw materials, although the actual method for preparing the biomass dough comprises the mixing and baking of the raw materials to form a solid cohesive dough. In the example process of Fig. 1 , parts of a grain crop have been used as the raw material. The drying (step 3) of the raw materials is not a mandatory step in the manufacture of the biomass dough, but a moist raw material can also be used in the preparation of the dough. The grinding (step 4) of the raw materials is not a mandatory step for all raw materials; normally, the grains of the cereal crop used as the gluten-forming adhesive are ground, and the other raw materials are left coarser.

In the production of fuel briquettes and a biomass dough, it is possible to utilize a combination of apparatuses known in agricultural and food industries, for example a grain drier and a baking machine and a baking oven known from food industry.

Figures 2 and 3 show, by way of example, a production apparatus for the production of a biomass dough and a fuel briquette made of it, according to the invention. In Fig. 2, a coarser raw material mixture 19 and a finer powdery adhesive 18 are introduced in an alternating man-

ner in a dough vessel 1. A steam drum 2 and dough mixers 6 fixed in it are rotating when the raw materials are added. When the dough vessel is almost half full of the raw materials, the introduction of warm water vapour into the dough vessel by means of the steam drum 2 is started, and the addition of the raw materials of the dough is simultaneously continued until the vessel is filled with the raw materials to about 80 percent of the height of the vessel. The introduction of steam and the mixing of the dough are continued until a dough-like mass has been formed of the raw materials. After this, a feed screw 9 at the bot- torn of the dough vessel is started, and an apparatus intended for cutting and drying the dough mass is activated. The fuel briquettes of the dough-like biomass, which have been cut to a fixed form and dried, are transferred further in a continuous flow along a line system. From the line system, the fuel briquettes are transferred to a stock of finished products, where the finished products are allowed to dry further and cool down before packaging.

Figure 3 is a more detailed view of the apparatus for producing the biomass dough and the fuel briquettes. The biomass dough used as the raw material for the fuel briquettes is made in a dough vessel 1. In the middle of the dough vessel, a circular steam drum 2 is provided, which extends from the bottom of the vessel and whose purpose is to introduce warm water vapour into the dough vessel 1. The steam is heated in an evaporator 3 and is led to the steam drum 2 by an air blower 5. The warm steam is introduced into the dough vessel by means of dough mixers 6 having the shape of a feed screw and intended for kneading the biomass dough, for example through holes 7 in their frame part. The frame part of the dough mixer 6 is a hollow cylindrical tube, through which the hot water vapour is introduced into the dough vessel. The dough mixer 6 is rotated around its axis, wherein the stirring blades 8 mounted on it are also rotated, stirring the dry substances to make a dough of them.

A feeding gap 9 extends from the bottom of the dough vessel 1 , along which gap the finished dough-like biomass is conveyed by means of a feed screw 10 towards compressing into a briquette. The feeding gap 9

is cylindrical and accommodates a rotating feed screw having the shape of a corkscrew, which is a feeding bit rotating around its axis, or a feeding press acting in the way of a piston in a feeder cylinder. The feed screw 10 feeds the biomass forward in the apparatus when its axis is rotated. The feeding gap 9 tapers towards the end so that the calculated area of the narrower end 11 of the cylinder is 20 to 40 cm ² in the last two metres of the path, depending on the production size selected for the briquette. The ready biomass is compressed to this tapered part of the feeding gap, wherein it is compacted. At the end of the feeding gap, there is a closing lid 12, against which the baked biomass is tightly compressed when the feeding bit rotates. The closing lid is opened when the pressure on the lid reaches a set limit value. The pressure set on the closing lid can be measured by using, for example, a pressure sensor. A simplified apparatus can also be implemented without a pressure sensor for the closing lid, wherein the movement of the closing lid is designed to be mechanical and is determined, for example, by a gear mechanism according to the rotations of the feed screw.

At the stage of cutting the fuel briquette, the feed screw 10 stops just before the closing lid 12 is suddenly opened, and the rotation of the feed screw is continued, until a desired quantity of finished fuel briquette length has protruded from the feeding gap, after which the closing lid 12 is closed again. When the closing lid is closed, the feed screw 10 continues its rotation without interruptions. Downstream of the closing lid in the production apparatus, there is a cutter part 15 which cuts the biomass dough protruding from the feeding gap to a fixed length.

To achieve production of uniform quality and to facilitate the packing, the weight of the fuel briquette is standardized. The apparatus is adjusted to produce fuel briquettes having a given quality and weight. The standardization is done, for example, according to the weight of the final product. The cutter 15 cuts the fuel briquette to a fixed length and thus standardizes the final product. The degree of compacting and the cutting properties of the biomass dough, as well as, for example,

the speed of the moving parts 9 and 12 of the production apparatus according to Fig. 3, are important variables when adjusting the apparatus. Also, the composition of the biomass dough affects the compacting, cutting and coherence of the fuel briquette, as does the mutual cooperation of the parts 9, 10, 11 and 12 of the production apparatus of Fig. 3.

Downstream of the cutter, the production apparatus comprises a drying section where the fuel briquette cut to a fixed length is dried by means of an air flow generated by a drier 13 or in a baking oven 14. The operation of the drier 13 is based on the movement of air as well as on thermal energy. Thermal energy is led to the drier, for example, from a baking oven, from outside air, or from the dough preparation step of the production process by means of air blowers 16 and a heat transfer pipe system 4. The thermal energy once used and released from the production process is recovered by means of a heat collection funnel 17 at the stage of drying the fuel briquette, and is transferred further into the steam drum 2 by means of a heat transfer pipe system 4 and air blowers 16 to heat the steam to be used in the dough preparation.

After this active drying step, the fuel briquettes are transferred to a cooling section, a ventilated storage space for the passive drying step of the fuel briquettes, that is, their cooling and hardening. At the final stage of the cooling, a hardening agent or an agent to facilitate ignition can be sprayed or applied onto the finished fuel briquettes. The hardening agent can also be sprayed onto the fuel briquette or the length made of the biomass dough earlier in the production process.

The invention is not intended to be limited to the production appara- tuses or embodiments presented as examples above, but the invention is intended to be applied widely within the scope of the inventive idea defined in the appended claims.