WO2023098945A1

WO2023098945A1 - Wood pellets and wood briquettes with reduced co emission

Info

Publication number: WO2023098945A1
Application number: PCT/DE2022/100899
Authority: WO
Inventors: Bo JÖNSSON
Original assignee: Comasa Gmbh
Priority date: 2021-12-01
Filing date: 2022-12-01
Publication date: 2023-06-08
Also published as: DE102021131629A1

Abstract

The present invention relates to wood pellets or wood briquettes, comprising 100 parts by weight of wood compound as a starting material for wood pellets or wood briquettes; and 0.001 to 2.00 parts by weight of preservative. The present invention further relates to methods for producing wood pellets or wood briquettes and to the use thereof.

Description

"Wood pellets and wood briquettes with reduced CO emissions"

The present invention relates to wood pellets or wood briquettes comprising 100 parts by weight of wood pulp as a starting material for wood pellets or wood briquettes; and 0.001 to 2.00 parts by weight preservative. Furthermore, the present invention relates to methods for producing the wood pellets or wood briquettes and their use.

State of the art

Wood pellets and wood briquettes are mainly used as fuel, with wood pellets, wood briquettes and their combustion as fuel in e.g. pellet heating systems or fireplaces increasingly serving as an attractive source for the provision of heating energy. With the increasing use of wood pellets, the required storage capacities are growing in addition to the production in order to be able to meet the demand. The storage of wood pellets and wood briquettes has its own special requirements due to their nature.

Traditionally, wood pellets or wood briquettes are stored as bulk goods or stacked goods in silos, in big bags or in sacks. Insufficient or restricted ventilation can lead to microbial reactions. In addition to C0 ₂ (carbon dioxide), this produces CO (carbon monoxide) in further steps. CO is odorless, colorless and mixes well with normal air. Even in low concentrations, it can cause side effects such as headaches, nausea, unconsciousness and death. The formation of CO in the warehouse sometimes happens very quickly. Very high concentrations of CO can even lead to explosive mixtures with air. the lower one Explosive limit is 10.9 vol% CO and upper flammable limit is 76.0 vol% CO.

Wood pellets and wood briquettes are small pieces of wood whose internal structures are partially destroyed during pelleting or pressing. As a result, decomposition products such as carbon monoxide and hydrocarbons can escape from the pellets or briquettes and accumulate in the air, for example in a pellet silo (cf. Nicole J. Seitz, Danger from alternative energy?, 2011). In this context, deaths due to severe poisoning have already occurred after people stayed in insufficiently ventilated pellet storage rooms. If wood pellets or wood briquettes become damp, increased water contents of more than 30% in particular can lead to the multiplication of microorganisms (fungi, spores, bacteria) and even cause self-ignition (cf. Martin Kaltschmitt, Energie aus Biomasse, Springer-Verlag, 2016).

Furthermore, the binding of dust through the use of a binder, in particular starch, both during production and storage, is a decisive factor in minimizing the risk of self-ignition or dust explosion. However, the starch, if used, is again a form of nutritional supplement for the unwanted microbial growth, which promotes the formation of CO.

It is therefore the object of the present invention to provide wood pellets or wood briquettes that can be stored easily and safely, even over long periods of time. The wood pellets or wood briquettes make it possible in particular to reduce toxic or possibly combustible or explosive emissions, in particular emissions of carbon monoxide. In addition, an object of the present invention is to provide a method for producing the wood pellets or wood briquettes according to the invention, which allows easy and safe storage of wood pellets or wood briquettes, even over longer periods of time.

The object is achieved by wood pellets or wood briquettes according to the invention, comprising 100 parts by weight of wood mass from starting material for wood pellets or wood briquettes; and 0.001 to 2.00 parts by weight preservative. Furthermore, the object is achieved by the method according to the invention for the production of wood pellets, in which a) 100 parts by weight of a starting material for wood pellets (wood pulp) are mixed with 0.001 to 2.00 parts by weight of preservative, and b) the mixture of starting material for wood pellets and preservative is pelletized ; and the method according to the invention for the production of wood briquettes, in which a) 100 parts by weight of a starting material for wood briquettes (wood pulp) are mixed with 0.001 to 2.00 parts by weight of preservative, and b) the mixture of starting material for wood briquettes and preservative is pressed.

Surprisingly, it was found that wood pellets and wood briquettes produced according to the invention tend to significantly reduce the formation of moulds, yeasts or bacterial colonies. This can slow down or even stop degradation processes in the wood pellets and wood briquettes. As a result, the emissions of e.g. carbon monoxide or hydrocarbons from the wood pellets and wood briquettes are also reduced, which means that they can be stored longer and more safely.

The terms wood pellet and wood briquette also include compressed wood chips and shavings. In particular, the term "wood pellet" includes wood pellets according to EN 14961-2 or particularly preferably ISO 17225-2. In particular, the term "wood briquette" includes wood briquettes according to EN 14961-3 or particularly preferably ISO 17225-3.

Wood pellets are rod-shaped pellets with a diameter of less than 25 millimeters that are made entirely or mainly from wood or sawmill by-products. They are a subgroup of fuel pellets. Other fuel pellets are straw pellets, straw pellets, peat pellets, pellets made from olive stones and pressed olive pomace, coconut shells or other biogenic residues. On the other hand, wood pellets with a diameter of 25 mm or more are called wood briquettes.

Wood briquettes are a form of wood fuel made by mechanically pressing dry wood particles, such as wood shavings, shavings, chips or sawdust. They are a subgroup of fuel briquettes. The wood briquettes have a diameter of at least 25 millimeters. Basically, wood briquettes have an even density and a uniform cross-section and often also a uniform length. The starting material for wood pellets or wood briquettes (wood mass) is preferably selected from spruce, pine, hardwood, coniferous wood, deciduous wood, round wood, industrial wood, residual forest wood, dead wood and mixtures thereof. Softwoods such as spruce and pine are particularly preferred. Spruce, pine and mixtures thereof are very particularly preferred.

Tropical wood can also be used as the starting material for wood pellets or wood briquettes. However, its use should preferably be avoided due to the difficult situation with regard to raw materials.

Suitable preservatives are preferably benzoic acid and salts thereof, sorbic acid and salts thereof, parabens, sulfites, hydrogen sulphites, ortho-phenylphenol, nitrates, nitrites and carboxylic acids having at least 3 carbon atoms and salts thereof and mixtures thereof.

Suitable preservatives are preferably selected from the group consisting of benzoic acid salts, sorbic acid salts, propionic acid salts and mixtures thereof.

Particularly preferred preservatives are Na, K and/or Ca salts of benzoic acid, sorbic acid, propionic acid and mixtures thereof.

Very particularly preferred preservatives are Na, K and/or Ca salts of benzoic acid and sorbic acid and mixtures thereof. Most preferred as preservatives are sodium benzoate and/or potassium sorbate.

The proportion of the preservative, based on 100 parts by weight of the wood mass as the starting material for wood pellets or wood briquettes, is 0.001 (10 ppm) to 2.00 (20,000 ppm) parts by weight, preferably 0.0015 (15 ppm) to 0.1 (1000 ppm) Parts by weight, preferably 0.0016 (16 ppm) to 0.44 (4400 ppm), more preferably 0.0018 (18 ppm) to 0.40 (4000 ppm), more preferably 0.002 (20 ppm) to 0.020 (200 ppm) Parts by weight, more preferably 0.0025 (25 ppm) to 0.01 (100 ppm) parts by weight, further more preferably 0.0028 ppm to 0.0090 (90 ppm) and most preferably 0.003 (30 ppm) to 0.005 (50 ppm). ) parts by weight. Any combination of the lower and upper limits mentioned herein is also preferred. The wood pellet or wood briquette preferably has a pH of 3.0 to 6.0, preferably 3.5 to 5.5, particularly preferably 4.0 to 5.0 and most preferably 4.5 to 4.9 . Any combination of the lower and upper limits mentioned herein is also preferred. It is believed that the preservatives can achieve their optimum effect in this pH range. The pH can be measured by mixing 50 g of wood pellets or wood briquettes in 300 mL of distilled water and stirring for 5 min. The pH value can then be determined, for example using a pH meter such as a konjac pH meter PH-02 (BellaCoCool GmbH) or indicator paper.

Preferably, the wood pellet or wood briquette may contain 0.1 to 5 parts by weight of one or more polysaccharide(s) as a binder based on 100 parts by weight of the wood mass of raw material for wood pellets or wood briquettes.

Preferably, the wood pulp from starting material for wood pellets or wood briquettes can contain 0.2 to 2.0 parts by weight, more preferably 0.25 to 1.0 parts by weight and more preferably 0.3 to 0.7 parts by weight and most preferably 0.4 to 0 5 parts by weight of one or more polysaccharide(s) as a binder. Any combination of the lower and upper limits mentioned here is also preferred.

Polysaccharides are polymers based on carbohydrates. Preferred polysaccharides are unmodified or modified starch and unmodified or modified cellulose. The polysaccharide or polysaccharides generally serve as a binder, particularly for any fine material that is present. The polysaccharide or polysaccharides can preferably be soluble in cold water. The polysaccharide or polysaccharides can preferably be extruded, rolled or sprayed. The polysaccharide or polysaccharides can particularly preferably be soluble in cold water and extruded. Sources of polysaccharides can be, for example, potatoes, corn, corn, rice, cassava, soybeans, sugarcane, or mixtures thereof.

Starch is a natural polysaccharide made up of aD-glucose units. The starch can preferably be in the form of starch flour. The starch can preferably be obtained from potatoes, cereals, peas, corn, rice, cassava or mixtures thereof. The starch can be modified, for example by polymer-analogous reactions. The starch generally serves as a binder, particularly for any fines that are present. The starch can preferably be soluble in cold water. The starch can be particularly preferred extruded, rolled or sprayed. The starch can most preferably be cold water soluble and extruded.

In a preferred embodiment, the polysaccharide, in particular the starch, can be modified with cationic compounds, e.g. Cationically modified polysaccharides, in particular cationically modified starch, can improve the strength of the wood pellets and/or wood briquettes. It is assumed that anionic groups in the wood fibers are better bound via the cationic groups of the modified polysaccharide, especially starch. This also leads to an improvement in the yield in the production process of the wood pellets or wood briquettes. Suitable cationic compounds are, for example, glycidyl trimethyl ammonium chloride (GMAC™) or 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (REAGENS™). The cationic compound can preferably be used in a proportion by weight of from 0.0005 to 0.25, preferably from 0.001 to 0.1, more preferably from 0.003 to 0.05 and most preferably from 0.005 to 0.025 parts by weight, based on 100 parts by weight of the wood pulp as Starting material for wood pellets or wood briquettes must be available. The cationic compound is particularly preferably added to the polysaccharide, in particular to the starch, in an extrusion process

Cellulose consists of -i,4-glycosidically linked -D-glucose units in the main chain. The cellulose can be selected from microcrystalline cellulose, cellulose powder, methyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, ethylmethyl cellulose, carboxymethyl cellulose and mixtures thereof.

The wood pellets or wood briquettes can contain other additives that can be added at any processing step. Examples of preferred adjuvants are fibers, silica (silicic acid), fillers and resins. The one or more auxiliaries are preferably present in a proportion in the range from 0.1 to 3 parts by weight, more preferably 0.2 to 2 parts by weight, most preferably 0.5 to 1.0 parts by weight, based on 100 parts by weight of the wood pulp from starting material for wood pellets or wood briquettes.

Proceedings Pelleting into wood pellets or pressing into wood briquettes offers various advantages over other biogenic solid fuels, such as automated use as a fuel in special pellet heating systems. The production of wood pellets or wood briquettes usually takes place close to the source of the raw material. These are e.g. B. Sawmills and planing mills in which wood waste (wood chips, sawdust and shavings) is produced as a by-product. Around 30% of the wood pellets are also produced from round wood of lower quality. The raw materials are first crushed, for example by a hammer mill. Biomass heating plants or biomass combined heat and power plants connected to the wood pellet or wood briquette plant or wood processing can supply the heat for drying the raw materials.

In a preferred embodiment, the polysaccharide and preservative are preferably mixed mechanically, e.g., by stirring, by extrusion, by drum drying, or by spray drying. Mixing by means of extrusion is particularly preferred. The polysaccharide can be present as a solid, e.g. as a powder or flour, or in dissolved form, e.g. as an aqueous solution or in an organic solvent. The preservative may be in solid or liquid form, for example as a solution in water, an organic solvent or a mixture thereof. Suitable organic solvents preferably have a boiling point below water, e.g., methanol or ethanol, in order to keep the energy required for drying as low as possible. A cationic compound can particularly preferably be added in the extrusion process in order to cationically modify the polysaccharide.

The proportion of the preservative in the mixture of polysaccharide and preservative is in the range from 0.02 to 2000 parts by weight, based on 100 parts by weight of polysaccharide. The parts by weight of the preservative, based on 100 parts by weight of polysaccharide, can preferably be in the range from 0.05 to 100 parts by weight, preferably in the range from 0.1 to 10 parts by weight, particularly preferably in the range from 0.5 to 2 parts by weight and very particularly preferably in range from 1.0 to 1.5 parts by weight.

In a particularly preferred embodiment, starch and preservatives are preferably mixed mechanically, for example by stirring, by extrusion, by means of drum drying or by means of spray drying. Mixing by means of extrusion is particularly preferred. The starch can be used as a solid, for example Starch, or in dissolved form, for example as an aqueous solution. The preservative can be in solid or liquid form, for example as a solution in water, an organic solvent or a mixture thereof. Suitable organic solvents preferably have a boiling point below that of water, for example methanol or ethanol, in order to keep the energy required for drying as low as possible. A cationic compound can particularly preferably be added in the extrusion process in order to cationically modify the starch.

The proportion of the preservative in the mixture of starch and preservative is in the range from 0.02 to 2000 parts by weight, based on 100 parts by weight of starch. The parts by weight of the preservative, based on 100 parts by weight of starch, can preferably be in the range from 0.05 to 100 parts by weight, preferably in the range from 0.1 to 10 parts by weight, particularly preferably in the range from 0.5 to 2 parts by weight and very particularly preferably in range from 1.0 to 1.5 parts by weight.

The raw material for wood pellets and the mixture of polysaccharide, in particular starch, and preservative can be mechanically blended. Mixing preferably takes place in a conditioner. The pellets are formed in a pelleting system, e.g. a pellet press. The material is pressed under high pressure, e.g. 200 to 1200 bar, through a steel die, e.g. round or flat die, with holes in the desired pellet diameter, e.g. 6 to 10 mm depending on the die, and thus pelletized. The pressure causes heating and the lignin contained in the wood is liquefied, so that it partly acts as a binding agent. Upon exiting the die, a doctor blade cuts the strands into pellets of the desired length (10 to 30 mm).

The wood briquettes are formed in a compression system, e.g. a briquette press. The material is pressed under high pressure, e.g. 200 to 1200 bar. Particularly suitable pressing processes are the extrusion process, the press chamber process, eccentric pressing and extruder pressing. The pressure causes heating and the lignin contained in the wood is liquefied, so that it partly acts as a binding agent.

The pelleting to form wood pellets can preferably take place at a temperature of 60.degree. C. to 130.degree. From 60 °C, the lignin contained in the wood mass begins to liquefy. A processing temperature of more than 130 °C is considered uneconomical. The pelleting to give wood pellets can preferably take place at a temperature of 90.degree. C. to 120.degree. C., particularly preferably 100.degree. C. to 110.degree.

The pressing to form wood briquettes can preferably take place at a temperature of 60.degree. C. to 130.degree. From 60 °C, the lignin contained in the wood mass begins to liquefy. A processing temperature of more than 130 °C is considered uneconomical. The pressing to form wood briquettes can preferably take place at a temperature of 70.degree. C. to 100.degree. C., particularly preferably 80.degree. C. to 90.degree.

Suitable heat sources can be water vapor or electrical heat sources.

The wood pellets or wood briquettes according to the invention can be burned in small furnaces, in industrial furnaces or in power plants.

All combinations of preferred ranges and/or of embodiments are particularly preferred.

Further features and advantages of the invention result from the following detailed description of exemplary embodiments.

exemplary embodiments

example 1

20 kg of extruded potato starch was mixed with 200 g (1 part by weight, based on 100 parts by weight of the potato starch) of sodium benzoate using a screw conveyor, and particles smaller than 500 μm were removed by sieving.

The resulting mixture of starch and preservative was then mixed in a conditioner with 2000 kg of wood pulp consisting of sawdust and shavings from spruce (0.01 part by weight of preservative, 1 part by weight of potato starch, based on 100 parts by weight of the wood pulp). The spruce wood mass was previously dried on a belt dryer down to a residual moisture content of 10% and homogenized in a hammer mill. After conditioning, the resulting mixture of wood pulp, potato starch and preservative was pelletized in a pelletizer (“Monster” model from Graf Equipment GmbH, Germany). processed wood pellets. The wood pellets obtained were then roughly sieved and cooled to approx. 40 °C using a stream of air.

1980 kg of wood pellets with a diameter of 8 mm were obtained at an output of 1000 kg/h.

The wood pellets obtained had density, strength, moisture and length as shown in Table 1.

example 2

Example 2 was prepared as in Example 1, but 1% by weight of potassium sorbate was added as a preservative instead of sodium benzoate. The wood pellets obtained had a diameter of 8 mm and a density, strength, moisture and length as shown in Table 1.

Comparative example 1

Comparative Example 2 was prepared as Example 1, but neither starch nor preservatives were added to the wood pellet raw material. The wood pellets obtained had a diameter of 8 mm and a density, strength, moisture and length as shown in Table 1.

Comparative example 2

Comparative Example 2 was prepared as Example 1, but no preservative was added to the extruded starch. The wood pellets obtained had a diameter of 8 mm and a density, strength, moisture and length as shown in Table 1.

Comparative example 3

Comparative Example 3 was prepared as Example 1, but spray dried cold water soluble (CWA) starch was used and no preservative was added to the CWA starch. The wood pellets obtained had a diameter of 8 mm and a density, strength, moisture and length as shown in Table 1.

Determination of CO Entivickhmg Samples of all (comparative) examples were stored in the dark for 3 months in each case in separately closed, airtight containers at room temperature (20° C.) and 50% RH (relative atmospheric humidity). The CO concentration was then determined using a CO measuring device (MRU Measuring Devices for Smoke Gases and Environmental Protection GmbH, Germany).

The results are summarized in Table i below. Density, strength and moisture were determined according to ISO 17225. The length of the wood pellets was determined by randomly selecting 10 wood pellets and measuring their length.

The results show that in Comparative Examples 1 and 2 the CO value is in a range that can lead to complaints such as headaches, dizziness and nausea within about 20 minutes (see Table 2).

[Table 2]

Inventive Example 1 shows a decrease in CO concentration of almost 50% as compared to Comparative Examples 1 and 2. Example 2 according to the invention shows a decrease in the CO concentration of approx. 86% compared to comparative examples 1 and 2.

In Comparative Example 3, the spray dried cold water soluble starch has a much higher solubility compared to the extruded starch. As a result, bacteria have significantly better access to the carbohydrates as food. Consequently, the example shows an enormously high CO concentration of over 4000 ppm, which can lead to symptoms, if not even unconsciousness and/or life-threatening in a very short time. Furthermore, it is ensured in the examples according to the invention that the CO concentration does not approach the lower explosion limit (10.9% by volume CO) during prolonged storage.

Claims

Claims Wood pellet or wood briquette comprising

- too parts by weight wood mass from starting material for wood pellets or wood briquettes; and

- 0.001 to 2.00 parts by weight of preservative. A wood pellet or wood briquette according to claim i, which further contains 0.1 to 5 parts by weight of one or more polysaccharides as binder. Wood pellet or wood briquette according to claim 1 or 2, wherein the preservative is selected from the group consisting of benzoic acid and salts thereof, sorbic acid and salts thereof, parabens, sulfite, hydrogen sulfite, ortho-phenylphenol, nitrate, nitrite and carboxylic acids having at least 3 carbon atoms and salts thereof and mixtures thereof. A wood pellet or briquette according to any one of the preceding claims wherein the preservative is selected from the group consisting of benzoic acid salts, sorbic acid salts, propionic acid salts and mixtures thereof. Wood pellet or wood briquette according to one of the preceding claims, in which the preservative is selected from the group consisting of sodium benzoate and/or potassium sorbate. Wood pellet or wood briquette according to one of the preceding claims, comprising 0.0016 to 0.44 parts by weight of preservative, based on 100 parts by weight of wood pulp from starting material for wood pellets or wood briquettes. Wood pellet or wood briquette according to one of the preceding claims, comprising 0.0028 to 0.0090 parts by weight of preservative, based on 100 parts by weight of wood pulp from starting material for wood pellets or wood briquettes. Wood pellet or wood briquette according to one of the preceding claims, comprising 0.3 to 0.7 parts by weight of one or more polysaccharide(s) as binder, based on 100 parts by weight of wood pulp from starting material for wood pellets or wood briquettes. Wood pellet or wood briquette according to one of the preceding claims, in which the starting material is selected from the group consisting of spruce, pine, hardwood, softwood, deciduous wood, round wood, industrial wood, forest residues, deadwood, tropical wood and mixtures thereof. A wood pellet or briquette according to any one of the preceding claims wherein the polysaccharide is cold water soluble starch. A wood pellet or briquette according to any one of the preceding claims wherein the polysaccharide is cold water soluble starch which is cationically modified and/or extruded. A method for producing wood pellets according to any one of the preceding claims, wherein a) 100 parts by weight of a wood pellet raw material (wood pulp) is mixed with 0.001 to 2.0 parts by weight of preservative, and b) the mixture of wood pellet raw material and preservative is pelletized. Process for the production of wood briquettes according to one of claims 1 to 11, in which a) 100 parts by weight of a starting material for wood briquettes (wood pulp) are mixed with 0.001 to 2.0 parts by weight of preservative, and b) the mixture of starting material for wood briquettes and preservative is compressed . A method according to claim 12 or 13, wherein the preservative is mixed with 0.1 to 5 parts by weight of polysaccharide prior to mixing with the starting material for wood pellets or wood briquettes. Use of the wood pellets or wood briquettes according to one of Claims 1 to 14 for firing in small furnaces, in industrial furnaces or in power stations.

17