Process for Producing Low-CO2 Wood Fuels With High Energy Density

Abstract

The production of low-CO2 wood fuels (for example, wood pellets or wood briquettes) with high energy density by adding coal dust, such as wood, stone, or lignite dust, during the production process.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This patent application claims priority to German Patent Application No. 102024125512.9 filed Sep. 5, 2024, the contents of which are incorporated herein by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The present invention relates to the production of low-CO2 wood fuels with high energy density by adding coal dust, such as wood, stone, or lignite dust, during the production process.BACKGROUNDWood as a Raw Material:

[0003] Humans have used wood since ancient times as a fuel and building material. For thousands of years, wood provided the energy needed to power early industries and enable survival in colder climates. This renewable raw material has proven its worth in various areas of life right up to the modern age. Wood pellets and wood briquettes, for example, have been widely used as fuel in recent decades. Wood chips and pieces are usually pressed into small sticks using a binding agent, water, and additives. Coniferous woods or other soft woods are used primarily as wood substrates because, unlike hardwoods, they can be processed with less wear and tear. Wood pellets or wood briquettes are used worldwide as a heating fuel in the private sector, but are also used by end consumers and the catering industry for smoking food.Raw Material Coal:

[0004] Coal is formed when biomass, such as dead plant parts, is exposed to both pressure and temperature over long periods of time. Depending on the stage of carbonization, coal is classified as wood, peat, lignite, hard coal, anthracite, or, in rare cases, graphite. The three most commonly used types of coal are hard coal, lignite, and charcoal.

[0005] The two types of coal, lignite and hard coal, are products of the advanced carbonization of biomass that occurs in nature. The biomass is converted into peat through biochemical processes close to the surface at low temperatures. The carbonization of biomass increases as it lies deeper in the earth. This is due to higher pressures and temperatures in deeper layers of the earth. The first product of this process is lignite. If pressures and temperatures continue to rise, the biomass is converted into hard coal. Further conversion to anthracite can only take place via geochemical processes.

[0006] Unlike hard coal and lignite, charcoal can be obtained from the renewable raw material wood. The carbonization of wood is referred to as dry distillation of wood. The carbonization process takes place in the absence of oxygen. Wood can be pyrolyzed at up to 550° C. in various forms, such as chips, pieces, or flour. The charcoal is then used for various industrial and private applications. Depending on how the carbonization process is carried out, liquid by-products such as alcohols (methanol, ethylene glycol), acids (acetic acid, formic acid, propionic acid), wood oils, and tar oils are also produced. Sustainable charring of wood involves the utilization of all main and by-products.

[0007] Wood pellets and wood briquettes differ mainly in their shape or geometry and dimensions. A wood pellet usually has a small, cylindrical geometry with diameters of around 6 mm and lengths of up to about 3 cm. A wood briquette is significantly larger in its geometry and can also have different shapes. The two most common variants are:

[0008] Cylindrical briquettes, for example, have a diameter of between 3 cm and 10 cm and can be up to 30 cm long. The shape can be round, square, or octagonal, for example. The exterior of the briquettes sometimes has a dark color, which is due to the manufacturing method.

[0009] Cuboid briquettes: The geometry can vary depending on the machine manufacturer, but common sizes are 15 cm×6 cm and 24 cm×7 cm up to approximately 10 cm.

[0010] The raw material used to produce wood pellets should be relatively clean and homogeneous, which is why wood dust and chips from sawmills are often used.

[0011] For the production of wood briquettes, on the other hand, larger pieces of wood up to, for example, 10 mm can be used, or even 20 mm in the case of softwood. Homogenization of the material can be advantageous, usually to small chips of, for example, 10 mm in size, provided that neither wood chips nor wood dust are used. A binder is not necessarily required for the production of wood briquettes, as pressure and temperature are usually sufficient to activate the binding effect of the lignin in the wood. However, a commercially available binder can, of course, be used if desired or necessary.

[0012] The following section describes the production of wood pellets as an example. This can be done in different ways. In the industry, pellets are typically produced from wood chips, water, and vegetable binders. The wood chips should be dried at temperatures between 60° C. and 90° C. before processing. To prevent the introduction of metals, stones, and unwanted foreign substances, all foreign materials are separated. The wood is then crushed using grinding techniques to a grain size of less than 6 mm. Water and plant-based starch are added to the chips to produce a processable mass. Moisture contents of 10% to 15% and binder contents of a maximum of 2% are typical for the industry. Once the water has penetrated the entire raw mass homogeneously, the pellets are produced in a suitable press. Matrix presses are typically used in industry, where friction heat reaches temperatures of approximately 110° C., and theoretical pressures of approximately 20 tons per matrix borehole are reached. This activates the biopolymer lignin in the cells of the wood as an adhesive, which acts as an independent binding agent in the presence of water. The final step is cooling. During the subsequent steps from storage to transport, fine particles are continuously sieved out to minimize the amount of dust for the end user.

[0013] In the field of wood pellets, there are constant developments, both in terms of technology and materials science. Technical developments can be seen, for example, in EP3010693B1, in which the monitoring, sampling, and control of pellet production have been improved. Other approaches pursue optimization through the addition of additives, for example, to increase production rates. The inventions devised range from the use of mixtures of wax emulsions and lignosulfates, as in U.S. Pat. No. 4,612,017, to various fractions of tall oils in U.S. Pat. No. 1,662,387B2, to the use of waste materials from the coffee industry, as in US2020 / 0262100A1.

[0014] Many of these inventions are based on the principle that the additives act as lubricants. This increases the lubrication of the machine components on the one hand and prevents the raw pellet material from sticking to them on the other. The result is higher throughputs but also improved binding strength, which leads to fewer fine and broken fractions (U.S. Pat. No. 4,612,017). Inventions such as US2006 / 0037236A1 use wood oil in addition to lubricants to produce flavored pellets for use in smoking meat. As described in U.S. Pat. No. 5,427,804, charcoal briquettes can be added to the pellets themselves as a supplementary fuel. This creates an additional smoking effect when grilling without using a pellet smoker.

[0015] The production of wood pellets or wood briquettes with higher energy density is a relevant topic at the present time. One possibility is the addition of monolignol-based biopolymers, as used in U.S. Pat. No. 11,618,862B2. Monolignol-based biopolymers are based on extracted lignin fractions from wood. The biopolymers are impregnated onto the dried wood raw material at 149° C. or 300° F. The mixing ratios range from 30% to 70% biopolymer, and the wood raw material must have a residual moisture content of 5% to 7% before impregnation. The loaded wood is then processed into pellets in the usual manner. The inventors found that various characteristics were improved. Properties such as water and UV resistance, as well as combustion properties, were improved. Another way to enhance these characteristics is to add charcoal to the mixture. As García et al. (Renewable Energy 180 (2021), 850-859) showed, the addition of glycerol as a lubricant and eucalyptus charcoal as an additive leads to more stable pellets. Resistance to friction, grinding, and water was effectively increased. Pellets containing 20% eucalyptus charcoal and 4% glycerin had calorific values of 20.0 MJ / kg, energy densities of 13.3 GJ / m3, and particle densities of 1.24 g / cm3. According to the authors, glycerol acts as both a lubricant and a binding agent.

[0016] One of the following three processes is used in particular for the production of wood briquettes:

[0017] Press chamber process (hydraulic): The material is dried to 10-15% residual moisture and fed into the press chamber via a screw conveyor from the feed tank. There, the material is pressed into the respective mold at 60° C. with a pressure of up to 1,700 kg / cm2. If necessary, e.g., for hardwood, a pre-compressor is used and the material is compressed in two stages. Once the target pressure has been reached in the press chamber, the press device is opened and the block is ejected. The process begins again.

[0018] Extruder pressing process (mechanical): The material is dried to 10-15% residual moisture and pressed through a continuous die at high pressure using a screw conveyor. The material is pushed through the die at up to 1,050 bar and around 150° C. Optionally, the material can have a hole in the middle through which gases can escape, and the material can expand. After the die, the material is cut into the desired piece sizes. The briquettes are slightly singed on the outside by the production process, giving them a typical dark brown color and a slight smell of burnt wood.

[0019] Eccentric process (mechanical): The material is dried to 10-15% residual moisture and transported into a small chamber via a screw conveyor. Using a flywheel, a piston with a pressure of up to 1,200 bar continuously pushes / presses / compacts the wood chips forward into a round channel. The rods are ejected and cut to size in a subsequent process step. The process generates temperatures between 70° C. and 180° C., which is why these briquettes are also darker in appearance.SUMMARY

[0020] Based on this, the task of the present invention is to at least partially alleviate the problems mentioned in relation to the prior art by providing low-CO2 wood fuels such as wood pellets or wood briquettes with high energy density.

[0021] A method comprising the steps of claim 1 contributes to this. Advantageous and / or preferred embodiments of the method proposed here are the subject of the subclaims. The description explains the invention and provides further examples of embodiments. The features / steps mentioned in the claims can be combined with each other and / or with facts from the description, thereby enabling even more specific embodiments to be demonstrated.

[0022] The present invention is based on the surprising finding that the use of finely fractionated coal as an additive can significantly increase the energy density of wood pellets or wood briquettes.

[0023] A method for producing wood fuels (such as wood pellets or wood briquettes), in particular with high energy density, is proposed, in which:

[0024] a) raw wood material particles are mixed with up to 50% by weight, based on the raw wood material, of at least one finely fractionated coal (e.g., charcoal dust) with a particle size of 100 μm to 2000 μm, and, optionally, a binding agent to obtain a solid mixture,

[0025] b) the solid mixture is mixed with water to obtain a moist solid mixture,

[0026] c) the (optionally heated) moist solid mixture is pressed in a press to form wood fuel blanks (e.g., pellet or briquette blanks), and

[0027] d) allowing the wood fuel blanks (e.g., pellet or briquette blanks) to cure by cooling.

[0028] With regard to step a), it is preferable that the proportion of raw wood material particles is 15 to 40% by weight, based on the raw wood material.

[0029] With regard to step a), it may be specified (especially in combination with the above-mentioned preferred proportion of raw wood material particles) that finely fractionated coal (e.g., charcoal dust) with a particle size of 500 μm to 1200 μm is used.

[0030] In the case of wood pellets, step c) may optionally involve heating to, for example, 80° C., e.g., by means of steam. Compression may be carried out, for example, at die pressures of, for example, approximately 20 tons (e.g., with 6-8 mm die bores).

[0031] In the case of wood briquettes, compression can be carried out, for example, using one of the methods described above for the production of wood briquettes. The reaction parameters are, for example:

[0032] When using the press chamber process: residual moisture, e.g., 10-15%, approximately 60° C., up to 1,700 kg / cm2 pressure

[0033] When using the extruder press process: residual moisture approximately 10-15%, approximately 150° C., up to 1,050 bar pressure

[0034] When using the eccentric process: 10-15% residual moisture, approximately 70 to 180° C., up to 1,200 bar pressure

[0035] The invention is described in detail below, whereby the specific embodiments of the invention disclosed, examples, or results are intended solely for illustrative purposes and are in no way to be interpreted as limiting the scope of protection of the invention as defined in the accompanying claims.DETAILED DESCRIPTION

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as understood by a person skilled in the art of the invention. In this context, the skilled person may also refer to the introductory explanations in their entirety.

[0037] The use of definite or indefinite articles (“the,”“a,”“an”) is to be understood (especially in connection with the claims) as meaning that at least one element or component is to be included, unless otherwise specified here or unless the context clearly indicates otherwise.

[0038] The conjunction “or” is to be understood as inclusive and not exclusive, i.e. as “and / or,” unless otherwise specified here or unless the context clearly indicates otherwise.

[0039] The use of terms such as “for example,”“e.g.,”“such as,” or variations thereof is intended solely to illustrate the invention better and shall in no way be construed as limiting the scope of protection of the invention as defined in the accompanying claims.

[0040] All numerical values are to be understood as “approximate” values (at least within the usual error tolerances), regardless of whether this is expressly stated or not. The specification of value ranges is also used solely for the sake of brevity and, unless otherwise noted here, refers to each individual value that falls within the range, even if this value is not specified individually.

[0041] The raw wood material particles used in step a) of the process for producing wood fuels (e.g., wood pellets or wood briquettes) with high energy density are not subject to any special restrictions in terms of material and particle size or particle size distribution, as long as pelletizing or briquetting is possible. Examples of suitable raw wood materials are hardwoods and softwoods from the coniferous and deciduous families (such as beech, oak, ash, maple, fir, pine, spruce) or also coconut shells. Combinations of different raw wood materials can also be used.

[0042] The raw wood materials can be used, for example, in the form of individual pieces, chips, granules, grit, flour, or dust, or combinations thereof. The raw wood materials used, especially those in the above form, can have a particle size of up to 6 mm, for example. The granules used can have a particle size of up to approximately 800 μm, for example. Both fine dust with a particle size smaller than about 10 μm and coarse dust with a particle size larger than about 10 μm (e.g., up to about 300 μm) can be used as dust.

[0043] The raw wood material particles can be dried before the process is carried out. It is clear to the skilled person that the drying temperature and duration are not subject to any particular restrictions as long as the purpose is achieved. For example, depending on the moisture content of the raw wood material particles, drying can be carried out at approximately 60° C. to 90° C. (e.g., at 60° C., 70° C., 80° C., 90° C.). However, temperatures below or above this range are also possible. The drying time can be, for example, approximately 4 h to 8 h (e.g., 4 h, 5 h, 6 h, 7 h, 8 h). However, shorter or longer drying periods are also possible. It is clear to those skilled in the art that a shorter drying time may be sufficient at a higher drying temperature and, conversely, a longer drying time may be necessary at a lower drying temperature.

[0044] In a first step of the process, the raw wood material particles (which may have been dried beforehand) are mixed with up to about 50% by weight (e.g., 5 wt. %, 10 wt. %, 15 wt. %, 20 wt. %, 25 wt. %, 30 wt. %, 35 wt. %, 40 wt. %, 45 wt. %, 50 wt. %), based on the raw wood material, of at least one finely fractionated carbon with a particle size of about 100 μm to 2000 μm [micrometer] (e.g., 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1200 μm, 1300 μm, 1400 μm, 1500 μm, 1600 μm, 1700 μm, 1800 μm, 1900 μm, 2000 μm) to obtain a solid mixture. More than 50% by weight of fine-fractionated coal and coal with particle sizes greater than 2000 μm can also be used, but this is not necessarily practical for various reasons (e.g., economic reasons).

[0045] The fine-fractionated coal is not subject to any special restrictions as such. For example, it can be charcoal from hard or soft woods of the coniferous and deciduous families (such as beech, fir, pine, spruce) or even from coconut shells. Lignite and hard coal are also suitable. Of course, combinations of different coals can also be used.

[0046] For example, in one embodiment, beech charcoal grit with a particle size of 500 μm to 2000 μm, in particular 500 μm to 1200 μm, [micrometers] is mixed with the dried raw wood material.

[0047] In a further embodiment of the invention, up to 50% by weight, in particular 15% to 40% by weight, of beech charcoal dust with a particle size of 100 μm to 500 μm, or 500 μm to 1,200 μm, is added to the dried raw wood material.

[0048] Optionally, a binding agent can be added to the resulting solid mixture of raw wood material and finely fractionated charcoal to improve pelletability. The binding agent is not subject to any particular restrictions as long as it fulfills its purpose. For ecological reasons, a vegetable starch (such as wheat starch, corn starch, pea starch, or combinations thereof) can be used, for example. The binding agent can be used in a proportion of up to approximately 5% by weight (e.g., 0.5 wt. %, 1 wt. %, 1.5 wt. %, 2 wt. %, 2.5 wt. %, 3 wt. %, 3.5 wt. %, 4 wt. %, 4.5 wt. %, 5 wt. %). More than 5% by weight of binder can also be used, but this is not necessarily advisable for various reasons (e.g., economic reasons).

[0049] Any mixer (e.g., commercially available) can be used to mix the raw wood material particles, the finely fractionated coal, and the optional binding agent, e.g., a paddle mixer.

[0050] Subsequently or later, the solid mixture of raw wood material particles, finely fractionated coal (and optional binding agent) is mixed with water in step b) of the method according to the invention to obtain a moist solid mixture. The amount of water added is not subject to any particular restrictions. Preferably, for example, the total moisture content of the solid mixture is set to between approximately 5% by weight and approximately 25% by weight (e.g., 5 wt. %, 6 wt. %, 7 wt. %, 8 wt. %, 9 wt. %, 10 wt. %, 12 wt. %, 15 wt. %, 18 wt. %, 20 wt. %, 22 wt. %, 25 wt. %).

[0051] Optionally, up to about 5% of at least one diol (e.g., 1,2-ethylene glycol, 1,2-propylene glycol) and / or at least one polyol (e.g., glycerol) can be added in step a) or step b) of the process to improve lubrication. More than 5% by weight of diol / polyol can also be used, but this is not necessarily advisable for various reasons (e.g., economic reasons).

[0052] Subsequently or later, the resulting moist solid mixture is pressed in step c) of the inventive process in a press, e.g. by means of a rotating pan mill wheel through a perforated die (approximately 20 tons of pressure per hole with, for example, 6-8 mm diameter) to form wood pellet blanks or, for example, using the press chamber process, using the extruder pressing process or using the eccentric process to form wood briquettes.

[0053] Finally, in step d) of the process, the pellet or briquette blanks are allowed to cure by cooling. It is clear to the skilled person that the curing is not subject to any special conditions with regard to cooling temperature and required cooling time. At low cooling temperatures (e.g., in a cooling device), a shorter cooling time may be sufficient. Conversely, a longer cooling time may be necessary, for example, at room temperature (e.g., 18° C. to 25° C.). According to one embodiment of the invention, cooling takes place at room temperature.

[0054] In the following examples, the method according to the invention is explained in more detail using the example of wood pellet production. These examples are intended only to illustrate the invention. They should in no way be interpreted as limiting the scope of protection of the invention as defined in the accompanying claims.

[0055] The percentages given in the following examples refer to the weight of the total mixture before pressing.Example 1

[0056] The energy density of a pellet can be significantly increased by adding coal fractions. A mixture of 6720 g of dried pine chips, 750 g of beech charcoal dust, and 30.0 g of pea meal (0.4% by weight) is mixed with 2500 g of water to produce a light grayish raw material. The raw material was pressed into stable pellets, which cured by cooling at room temperature. The solid high-energy pellets have a calorific value HUB of 4.67 kWh / kg.Example 2

[0057] A mixture of 5940 g of dried pine chips, 1500 g of beech charcoal dust, and 60.0 g of pea meal (0.8% by weight) is mixed with 2500 g of water to produce a grayish raw material. The raw material was pressed into stable pellets, which cured by cooling at room temperature. The solid high-energy pellets have a calorific value HUB of 5.11 kWh / kg.Example 3

[0058] A mixture of 5160 g of dried pine chips, 1500 g of beech charcoal dust, and 90.0 g of pea meal (1.2% by weight) is mixed with 2500 g of water to produce a grey raw material. The raw material was pressed into stable pellets, which cured by cooling at room temperature. The solid high-energy pellets have a calorific value HUB of 5.89 kWh / kg.Example 4

[0059] A mixture of 4380 g of dried pine chips, 3000 g of beech charcoal dust, and 120.0 g of pea meal (1.6 wt %) is mixed with 2500 g of water to produce a dark grey raw material. The raw material was pressed into stable pellets, which cured by cooling at room temperature. The solid high-energy pellets have a calorific value HUB of 6.11 kWh / kg.Example 5

[0060] A mixture of 3600 g of dried pine chips, 3750 g of beech charcoal dust, and 150.0 g of pea meal (2.0 wt %) is mixed with 2500 g of water to produce a black raw material. The raw material was pressed into stable pellets, which cured by cooling at room temperature. The solid high-energy pellets have a calorific value (HUB) of 6.14 kWh / kg.Reference without Coal Addition:

[0061] A mixture of 7470 g of dried pine chips and 30.0 g of pea meal (0.4 wt %) is mixed with 2500 g of water to produce a wood-colored raw material. The raw material was pressed into stable pellets, which cured by cooling at room temperature. The solid high-energy pellets have a calorific value HUB of 4.61 kWh / kg.Measurement of the Performance of the Products According to the InventionPhysical Parameters:

[0062] The physical parameters were determined using standard methods and standard analysis. As expected, the carbon and ash contents of the wood pellets according to the invention increase with the addition of coal to up to 1.3 wt % and 1.4 wt % DM (dry matter), respectively. Moisture and water content vary and fluctuate between 6.6 wt % and 15.8 wt %. The volatile components decrease with the addition of coal, as the proportion of organic components in the pellets is reduced by substitution with coal.TABLE 1ExampleExampleExampleExampleExampleReference12345Carbon content (wt. %)0.010.02030.04050.0Carbon content (wt. %)16.522.13037.144.250.7Ash content (wt. %)0.40.50.80.81.01.3Ash content (wt % DM)0.60.50.80.91.11.4Moisture content (wt. %)10.610.87.08.69.76.7Water content (wt. %)12.315.87.39.010.46.6Volatile components83.277.469.462.255.048.5(wt. %)Elemental Composition:

[0063] The elemental composition of the wood pellets was determined in accordance with DIN EN ISO 16948:2015-09. The results show that the wood pellets, according to the invention, consist mainly of carbon, oxygen, and hydrogen. The proportion of oxygen and hydrogen decreases with the addition of coal, whereas the proportion of elemental carbon increases. These results are conclusive and consistent. Elemental nitrogen is contained in the wood pellets according to the invention at a proportion of 0.1 wt % to 0.3 wt %. The maximum detectable proportion of sulfur was 0.017 wt %.TABLE 2ExampleExampleExampleExampleExampleReference12345Sulfur (wt. %)0.0100.0090.0090.0150.0150.009Sulfur (wt % DM)0.0120.0100.0100.0160.0170.010Nitrogen (wt. %)0.180.10.210.220.260.25Nitrogen (wt % DM)0.210.120.220.240.290.27Carbon (wt. %)46.145.053.856.358.862.6Carbon (wt % DM)54.851.358.061.965.767.0Hydrogen (wt. %)5.05.35.24.94.44.4Hydrogen (wt %5.96.05.65.34.94.7DM)Oxygen (wt. %)32.436.932.728.725.124.8Oxygen (wt % DM)38.442.135.331.628.026.6Combustion Properties:

[0064] The combustion properties were calculated in accordance with DIN EN ISO 18125:2017-08. Compared to the reference, the addition of beech charcoal dust improves both the calorific value and the heating value. The addition of 10% by weight of charcoal dust led to a relative reduction in relation to the dry matter DM. From a proportion of 20% by weight of beech charcoal dust, both the calorific value and the heating value increase significantly. In example 4, for example, a proportion of 40% by weight of beech charcoal resulted in a relative increase in the calorific value of 22.0% and 24.4% for the heating value, based on the dry matter. An increase in the proportion of charcoal dust may require the addition of wood oils, wood tar, and larger quantities of binding agents to ensure smooth production processes.TABLE 3ExampleExampleExampleExampleExampleReference12345Calorific value (kJ / kg)180001820019700225002340023300Calorific value (kJ / kg DM)214002070021300247002610024900Heating value HuB (kJ / kg)166001680018400212002200022100Heating value HuB (kJ / kg201001940020100236002500023900DM)Calorific value (kWh / kg)5.005.065.476.256.506.47Calorific value (kWh / kg5.945.755.926.867.256.92DM)Heating value HuB4.614.675.115.896.116.14(kWh / kg)Heating value HuB5.585.395.586.566.946.64(kWh / kg DM)Change Δ compared to reference:Δ Calorific value (%)0.01.19.425.030.029.4Δ Calorific value (% DM)0.0−3.5−0.515.422.016.4Δ Heating value HuB (%)0.01.210.827.732.533.1Δ Heating value HuB (%0.0−3.50.017.424.418.9DM)

[0065] The following calculation was used to convert kJ / kg: 1 kWh=3,600 kJ.

[0066] Further investigations were carried out on wood pellets. For this purpose, pellets were produced that also included larger grit fractions of up to 2.0 mm.

[0067] In another series, pellets were produced using lignite as a fossil carbon source to highlight differences between coal types.

[0068] Table 4 below provides an overview of the proportions of different coals used for the follow-up investigation.TABLE 4Sample 1Sample 2Proportion of charcoal 0.5 mm-1.2 mm (%)20.030.0Proportion of charcoal 1.2 mm-2.0 mm (%)20.030.0Proportion of lignite 0.0 mm-0.5 mm (%)20.0—Proportion of lignite 0.5 mm-1.2 mm (%)20.0—Proportion of lignite 1.2 mm-2.0 mm (%)20.0—Procedure:

[0069] The PFROC package was used in conjunction with the FR161 preparatory test at EuroFins (www.eurofins.de, analytical laboratory) to examine wood pellets. In addition to determining water content and ash content, this test also determines various element contents and the calorific value.Observations and Results:

[0070] The following nomenclature is used for the results:

[0071] HK=charcoal;

[0072] BK=lignite;

[0073] DM=dry matter;

[0074] HuB=Operating heating value, i.e., heating value during operation.a) Results for Distinguishing Coal Size:

[0075] Table 5 below shows EuroFins' results for water and ash contentTABLE 50.5 mm-1.2 mm-0.5 mm-1.2 mm-<0.51.22.0<0.51.22.00%mmmmmmmmmmmmHK20% HK20% HK20% HK30% HK30% HK30% HKWater content12.37.311.412.39.013.45.6(%)Ash content (%)0.40.81.00.70.80.90.8Ash content (%0.60.81.10.80.91.10.9DM)Evaluation:

[0076] The ash contents are largely stable and do not vary depending on the geometry used.

[0077] Table 6 below shows EuroFins' results for the various element contents.TABLE 60.5 mm-1.2 mm-0.5 mm-1.2 mm-<0.51.22.0<0.51.22.0mmmmmmmmmmmm0% HK20% HK20% HK20% HK30% HK30% HK30% HKSulfur (m %)0.0100.0090.0120.0180.0150.0120.0Sulfur (m % DM)0.0120.0100.0140.0210.0160.0130.0Nitrogen (m %)0.180.210.120.050.220.050.1Nitrogen (m %0.210.220.130.060.240.050.1DM)Carbon (m %)46.153.852.250.956.354.558.6Carbon (m %54.858.058.958.061.962.962.1DM)Hydrogen (m %)5.05.24.64.74.94.44.8Hydrogen (m %5.95.65.25.45.35.15.1DM)Oxygen (m %)32.432.730.731.428.726.730.0Oxygen (m %38.435.334.635.831.630.931.8DM)Evaluation:

[0078] The charcoal geometry used has no significant influence on the parameters in Table 6.

[0079] Table 7 below shows EuroFins' results for calorific value and heating value. The following calculation was used to convert kJ / kg: 1 kWh=3,600 kJ.TABLE 71.2 mm-0.5 mm-1.2 mm-<0.50.5 mm-2.0<0.51.22.0mm1.2 mmmmmmmmmm0% HK20% HK20% HK20% HK30% HK30% HK30% HKCalorific value18000197002020020000225002160022800.0(kJ / kg)Calorific value21400213002280022800247002490024200.0(kJ / kg DM)Heating value16600184001890018700212002030021700.0HuB (kJ / kg)Heating value20100201002170021600236002380023100.0HuB (kJ / kgDM)Calorific value5.005.475.615.566.256.006.33(kWh / kg)Calorific value5.945.926.336.336.866.926.72(kWh / kg DM)Heating value4.615.115.255.195.895.646.03HuB (kWh / kg)Heating value5.585.586.036.006.566.616.42HuB (kWh / kgDM)Change Δ compared to the sample without charcoal:Δ Calorific value0.09.412.211.125.020.026.7(%)Δ Calorific value0.0−0.56.56.515.416.413.1(% DM)Δ Heating value0.010.813.912.727.722.330.7HuB (%)Δ heating value0.00.08.07.517.418.414.9HuB (% DM)Evaluation:

[0080] The influence of charcoal geometry is clearly evident here: 0.5 mm-1.2 mm have the highest change in calorific value compared to the charcoal-free reference for both charcoal proportions.b) Results for Distinguishing the Coal Source as a Calorific Value Booster:

[0081] The table below shows EuroFins' results for the water and ash content of pellets made from char coal and lignite.TABLE 80.5 mm-1.2 mm-0.5 mm-1.2 mm-<0.51.22.0<0.51.22.00%mmmmmmmmmmmmHK20% HK20% HK20% HK20% BK20% BK20% BKWater content12.37.311.412.314.07.48.7(%)Ash content (%)0.40.81.00.70.71.11.2Ash content (%0.60.81.10.80.81.21.2DM)Evaluation:

[0082] Pellets made from lignite have a higher ash content and therefore offer an advantage over charcoal.

[0083] Table 9 below shows EuroFins' results for the various element contents of pellets made from char coal and lignite.TABLE 90.5 mm-1.2 mm-0.5 mm-1.2 mm-<0.51.22.0<0.51.22.0mmmmmmmmmmmm0% HK20% HK20% HK20% HK20% BK20% BK20% BKSulfur (m %)0.0100.0090.0120.0180.0460.0500.044Sulfur (m % DM)0.0120.0100.0140.0210.0530.0540.048Nitrogen (m %)0.180.210.120.050.210.150.14Nitrogen (m %0.210.220.130.060.250.160.15DM)Carbon (m %)46.153.852.250.945.749.948.8Carbon (m %54.858.058.958.053.153.953.4DM)Hydrogen (m %)5.05.24.64.75.05.25.3Hydrogen (m %5.95.65.25.45.85.65.9DM)Oxygen (m %)32.432.730.731.434.336.235.8Oxygen (m %38.435.334.635.840.039.139.2DM)Evaluation:

[0084] Wood pellets containing lignite have a higher sulfur content than pellets containing charcoal, so charcoal is preferable. Wood pellets containing lignite have a lower carbon content than pellets containing charcoal, so charcoal is preferable.

[0085] Consequently, in connection with the invention, it has been found that charcoal has various significant advantages over lignite.

[0086] Table 10 below shows EuroFins' results for the calorific and heating values of pellets made from char coal and lignite. The following calculation was used to convert kJ / kg: 1 kWh=3,600 kJTABLE 100.5 mm-1.2 mm-0.5 mm-1.2 mm-<0.51.22.0<0.51.22.00%mmmmmmmmmmmmHK20% HK20% HK20% HK20% BK20% BK20% BKCalorific value18000197002020020000183001990019500(kJ / kg)Calorific value21400213002280022800213002150021300(kJ / kg DM)Heating value16600184001890018700169001860018100HuB (kJ / kg)Heating value20100201002170021600200002020020100HuB (kJ / kg DM)Calorific value5.005.475.615.565.085.535.42(kWh / kg)Calorific value5.945.926.336.335.925.975.92(kWh / kg DM)Heating value4.615.115.255.194.695.175.03HuB (kWh / kg)Heating value5.585.586.036.005.565.615.58HuB (kWh / kgDM)Change Δ compared to the sample without charcoal:Δ Calorific value0.09.4%12.2%11.1%1.7%10.6%8.3%(%)Δ Calorific value0.0−0.5%6.5%6.5%−0.5%0.5%−0.5%(% DM)Δ Heating value0.010.8%13.9%12.7%1.8%12.0%9.0%HuB (%)Δ Heating value0.00.0%8.0%7.5%−0.5%0.5%0.0%HuB (% DM)Evaluation:

[0087] Wood pellets mixed with lignite have higher calorific and heating values than the coal-free reference, but this increase is not apparent in terms of dry matter.

[0088] In the case of charcoal, the calorific and heating values also increase in relation to the dry matter, making charcoal the preferred option.Summary / Conclusion:1. Differentiation of coal size:

[0090] Charcoal grit in the range of <0.5 mm forms an inhomogeneous mixture with wood chips, which is more difficult to process.

[0091] Charcoal grit in the range of 1.2 mm to 2.0 mm forms an inhomogeneous mixture with wood chips, which is more difficult to process.

[0092] With charcoal grit in the range of 0.5 mm to 1.2 mm, the average particle sizes of wood chips are very similar and form a mixture that is easy to process. This has the most decisive influence on the calorific and heating values. This may be because at this size, the pieces of charcoal can be compressed well, creating a more homogeneous ratio between wood chips and charcoal in the finished pellet.

[0093] 2. Distinction of the coal source as a calorific value booster:

[0094] Charcoal contains less sulfur than lignite. When burning sulfur-containing fuels in the presence of water, the substance sulfuric acid can be produced, which can lead to increased wear on the furnace, e.g., through the formation of rust.

[0095] Charcoal as an additive increases the calorific and heating values in relation to the dry matter of the finished pellet. This is due to the higher proportion of carbon that is introduced into the pellet by the charcoal. Lignite only minimally changes the carbon content and therefore does not regularly lead to an increase in the burning performance of the pellet in relation to the dry matter.

[0096] 3. Distinction / advantages of the invention compared to known methods:

[0097] Softwood chips, such as spruce / pine / fir, are proposed as the basis for wood pellets.

[0098] Hardwood charcoal, such as beech / oak / ash / maple, is proposed as a calorific value booster (see results above).

[0099] Hardwood charcoal is proposed as a sustainable and low-sulfur coal source compared to fossil fuels such as lignite and hard coal.

[0100] A defined range of charcoal sizes is proposed, e.g., 0.5 mm to 1.2 mm; possibly also up to 1.5 mm.

[0101] A defined range of charcoal content, e.g., 15% to 40% by weight, is suggested.

[0102] Those skilled in the technical field of the invention will understand that the representative embodiments and details of the invention described above are intended only to illustrate the present invention, and that various changes and modifications may be made without departing from the scope of the invention as defined in the accompanying claims.

Claims

1. A method for producing wood fuels, the method comprising at least the following steps:a) mixing raw wood material particles with up to 50 wt. %, based on the raw wood material, of at least one finely fractionated coal with a particle size of 100 μm to 2000 μm, and, optionally, a binding agent to obtain a solid mixture,b) mixing the solid mixture with water to obtain a moist solid mixture,c) pressing the moist solid mixture in a press to form wood fuel blanks,d) curing the wood fuel blanks by cooling.

2. The method according to claim 1, in which in step a) 15 to 40 wt. %, based on the raw wood material, of the at least one finely fractionated coal is used.

3. The method according to claim 1, wherein in step a) at least one finely fractionated coal with a particle size of 500 μm to 1200 μm is used.

4. The method according to claim 1, wherein the raw wood material is dried at 50° C. to a maximum of 120° C. before step a).

5. The method according to claim 1, wherein the raw wood material is selected from hardwoods, softwoods, and combinations thereof.

6. The method according to claim 1, wherein up to 5.0 wt. % of at least one vegetable starch is added to the raw wood material as an optional binding agent.

7. The method according to claim 6, wherein the vegetable starch is selected from wheat starch, corn starch, pea starch, and combinations thereof.

8. The method according to claim 1, wherein the finely fractionated carbon is selected from charcoal dust, coconut shell dust, lignite dust, hard coal dust, and combinations thereof.

9. The method according to claim 1, wherein up to 5% of at least one diol and / or at least one polyol is added to improve lubrication.

10. The method according to claim 9, wherein the diol and / or the polyol is selected from ethylene glycol and propylene glycol.

11. The method according to claim 1, wherein in step b) a total moisture content of the solid mixture of 5 wt % to 25 wt % is set.

12. The method according to claim 1, wherein the wood fuels produced are formed as wood pellets or wood briquettes.