Biomass solid fuel and method of manufacture

Abstract

A method for manufacturing a biomass solid fuel comprises: shredding dried plant matter from the Juncaceae family into particles, pressing the particles under high pressure with no binder into require

Description

This invention relates to a method for manufacturing a biomass solid fuel comprising rushes, and to a solid fuel comprising rushes. Juncaceae is a family of flowering plants, commonly known as the rush family. It consists of 8 genera and about 464 known species of rhizomatous, herbaceous monocotyledonous plants that may superficially resemble grasses and sedges. They often grow on infertile soils in a wide range of moisture conditions. The best-known and largest genus is Juncus. Most of the Juncus species grow exclusively in wetland habitats. Several species of rushes, in particular Juncus effuses, grow as weeds and thrive on farm land in Ireland and Britain. Being unpalatable to most livestock, they must be removed by farmers, at great economic cost, typically using a program including topping (removing the mature rushes above ground which are not susceptible to weedkiller) and the use of weedkillers. MCPA (2-methyl-4-chlorophenoxyacetic acid) is a powerful, selective phenoxy herbicide used frequently to control rushes, resulting in documented ingress to water courses and contamination of public water. There are further concerns where the chemically treated land is used as pasture for animals for meat and milk human consumption. Present on every continent, rushes have been used by people all over the world as a material for flooring, roofing and woven products such as mats but their use as fuel is not known. Despite biomass being carbon neutral, the use of rushes as a solid fuel has been dismissed as they are high in moisture when harvested and have very low density when dry, making them uneconomical to transport. There are also several obstacles to overcome in compacting the rushes into pellets or briquettes, in particular when avoiding the use of non-biomass components. The present invention is a solid fuel made from rushes and a method of manufacturing the solid fuel in a form such as a briquette. The solid fuel is dense and robust, making it easy to transport and store, and has comparable energy output per kg to a traditional peat used to form briquettes. Rushes are particularly environmentally friendly to grow and harvest as they thrive in wet and low nutrient soil and are not a preferred food source for animals and therefore do not require the application of pesticides, herbicides or fertilisers. Unlike many crops, rushes can be cultivated in environmentally sensitive areas, for example near areas of conservation such as natural peat bogs and other delicate ecosystems such as waterways. Several methods of making biomass briquettes and pellets are known but none are applicable to rushes. Each type of plant material has its own properties such as the content of sticky substances such as lignin and pectins, which aid binding, the ease of drying, the content of volatile chemicals, the ease of drying the material and other factors which complicate the blending and binding of the components into a solid fuel. Summary of Invention Provided is a method for manufacturing a biomass solid fuel comprising: shredding dried plant matter from the Juncaceae family into particles; pressing the particles under high pressure into required shape. Optionally, the pressure is from 1000 kg / cm2 to 2500 kg / cm2, or at least 1000 kg / cm2, at least 1000 kg / cm2, at least 1100 kg / cm2, at least 1200 kg / cm2, at least 1300 kg / cm2, at least 1400 kg / cm2, at least 1500 kg / cm2, at least 1600 kg / cm2, at least 1700 kg / cm2, at least 1800 kg / cm2, at least 1900 kg / cm2, at least 2000 kg / cm2, at least 2100 kg / cm2, at least 2200 kg / cm2, at least 2300 kg / cm2, at least 2400 kg / cm2, or at least 2500 kg / cm2. The rushes contain compounds which aid binding within their structure. However, they require high pressures to release the binding compounds. Optionally, the required shape is achieved by use of a mold. Optionally the partices are placed in the mold and pressed in the mold to form solid fuel in the required shape. Optionally, the method does not include any additional extrusion step. The pressing and molding are performed in one step. Optionally, the pressure is 1700 kg / cm2 to 2500 kg / cm2. This range has been found to give satisfactory results. Optionally, the particle size is in the range 0.002-2.0 mm, 0.063-0.63 mm, 0.0063-0.63 mm, 0.63-2.0 mm, 0.2-0.63 mm, 0.063-0.2 mm, 0.02-0.063 mm, 0.0063-0.02 mm, 0.002-0.0063, or <0.002 mm, as measured by sieve aperture, or a combination of ranges. While there is no international standard for particle sizes for shredded plant matter, below are the ISO 14688-1:2017, establishes the basic principles for the identification and classification of soils on the basis of those material and mass characteristics most commonly used for soils for engineering purposes. The sizes are measured by sieve aperture. These may be useful for comparative purposes. Coarse sand 0.63-2.0 mm Medium sand 0.2-0.63 Fine sand 0.063-0.2 Coarse silt 0.02-0.063 Medium silt 0.0063-0.02 Fine silt 0.002-0.0063 Clay <0.002 Wheat flour generally has a particle size of from 15 pm to 400 pm, defined by sieve apertures, depending on the type of wheat flour. The particles used in the present method resemble a fine dust. Optionally the required shape is achieved by use of a mold. Optionally, the method further comprised cooling the mold during pressing. It has been found that the heat generated during pressing reduced the binding. Optionally, wherein cooling comprises circulating water cooled to 4 to 10 QC. Optionally, circulating the cooled water around the outside of the mold. This was performed with a refrigerator unit in tests. It is not necessary to freeze the mold or use chemical coolants. Optionally, no binder is added. The rushes contain a binding agent which is released under pressure. Optionally, no other plant matter is added, or no other plant matter is deliberately added. Various mixtures of plant matter including mixing the rushes with barley straw, wheat straw, hemp and maize in various ratios was tested. It was found that binding was unsuccessful when mixtures of rushes with other plants were used. Binding was only successful for rushes when no other plant matter was deliberately added to the rushes. Optionally, the particles comprise at least 80 wt%, at least 90 wt%, at least 95 wt% or at least 99 wt% plant matter from the Juncaceae family. As the rushes used were wild plants found growing in Ireland, it was unavoidable that a small amount of other plants were present. However, since grasses were found to reduce binding the presence of grass and other plants was avoided as much as practicable. Optionally, the plant matter is a mixture of Juncaceae species, optionally Juncus and / or Luzula species. Optionally, the plant matter is a mixture of Juncus species, or wherein the plant matter is Juncus effusus or wherein over 80 wt% of the plant matter is Juncus effusus. Juncus effuses is known as the common rush or soft rush. Optionally, the plant matter comprises the stalks, flowers and seeds of Juncaceae species, or the plant matter comprises the stalks of Juncaceae species. All parts of the plant which grow above ground are suitable for the process. Optionally, the plant matter comprises less than 15 wt% moisture content, less than 14 wt%, preferably less than 13 wt%, less than 12 wt%, less than 11 wt%, less than 10 wt%, less than 9 wt% or less than 8 wt% moisture content. The inventor has found that moisture content below 13% is preferable and has obtained good results with a water content of 11 wt%. A moisture content of approximately 9 wt% can be achieved with air drying and produces good results. Optionally, the plant matter is air dried. Optionally, the method further comprises drying the plant matter, prior to the shredding, optionally wherein drying comprises air drying. Air drying can be carried out indoors or outdoors. It was found that rushes dried adequately when laid outdoors in 80% humidity. Optionally, the shredding is performed by mechanical means. Any means known to shred or grind may be used. The shredding is performed optionally a hammer mill. Optionally, pressing the particles under high pressure into required shape comprises using a compacting motion. Optionally, the mold is shaped in the form of a briquette, or optionally the solid fuel is shaped in the form of a cuboid, or optionally wherein the solid fuel is shaped such that it comprises at least two parallel planar surfaces. The size of the solid fuel affects the time it takes to burn. Since the heat output is similar to the heat output of peat weight for weight, and the solid fuel has a similar density to peat briquettes, the solid fuel can be used to replace peat briquettes. The size is preferably similar to the conventional size of peat briquettes, as many stoves and fireplaces are adapted to peat briquettes. Peat briquettes are typically cuboidal and approximately 15-25 cm in their longest dimension. However, for other applications, such as boilers or industrial furnaces that use fuel pellets, smaller pellets of the solid fuel may be preferable. In that case smaller molds may be used. Larger molds may also be used. Optionally, the method further comprises harvesting the plant matter year round or, optionally, in May, June, July, August or September. Rushes are available year-round. Rushes harvested in July or later may produce solid fuel with lower ash content. However, many farmers prefer to clear the rushes from their fields before they go to seed to prevent the spread of rushes. In those cases, the rushes may be harvested early. Also provided is a solid fuel comprising plant matter from the Juncaceae family. This family are commonly known as rushes. Solid fuel made form rushes has been found to have a similar energy content to peat briquettes. Therefore, this environmentally friendly fuel can be used to replace peat briquettes in many applications, predominantly domestic use. Furthermore, peat briquettes are often used close to where they were harvested. The use of rushes allows the use of another locally produced fuel source, so that solid fuel does not need to be transported far. This is another environmental benefit of this solid fuel made from rushes. The mold could be up to 1.2 m by 1.2 m Optionally, the solid fuel comprises at least 80 wt%, at least 90 wt%, at least 95 wt% or at least 99 wt% plant matter from the Juncaceae family. Optionally, the solid fuel comprises plant matter from the Juncaceae family, with no other additives. Several binders and oils were tested in the formation of briquettes and it was found that the best result was achieved when pure rushes were used. The rushes contain sufficient binder within their natural structure. Optionally, the plant matter comprises the stalks, flowers and seeds of Juncaceae species, or wherein the plant matter comprises the stalks of Juncaceae species. Optionally, the solid fuel is shaped in the form of a briquette, optionally wherein the solid fuel is shaped in the form of a cuboid, or optionally wherein the solid fuel is shaped such that it comprises at least two parallel planar surfaces. Optionally, the solid fuel has a density of 0.5 to 5 g / mL, optionally 0.8 to 1.2 g / mL, optionally approximately 1 g / mL. This density is similar to compressed peat briquettes and allows the fuel to replace peat briquettes for many applications. Optionally, the solid fuel has a carbon content on a dry basis of 40 to 60 wt%, optionally 45 to 55 wt%, optionally 47 to 52 wt%, optionally approximately 48 wt%, or approximately 50 wt%. Optionally, the solid fuel has a sulphur content of less than 0.1 wt%, optionally less than 0.09 wt%, optionally less than 0.08 wt%, optionally less than 0.07 wt%, optionally less than 0.06 wt%, optionally approximately 0.05 wt%. Optionally, the solid fuel has a moisture content of less than 13 wt%, optionally less than 12 wt%, optionally less than 11 wt%, optionally less than 10 wt%, optionally approximately 9 wt%. Example 1 50 wt% straw and 50 wt% fibre from the hemp plant, with a combined 11 wt% moisture, was ground to a fine dust and pressed at a pressure of 1700 kg / cm2. Briquette formation failed because the blending of material was not uniform and binding was inadequate. Example 2 Rapeseed straw, fibre from the hemp plant, and rushes were blended to a ratio of 1:1:1 by weight, with a combined 11 wt% moisture, to create a fine dust and then compressed to 1700 kg / cm2. Briquette formation failed as the constituents did not blend together uniformly or bind. Example 3 Soft rushes, 9.1 wt% moisture, were blended to create a fine dust and then compressed to 1700 kg / cm2. Briquette formation was successful. The composition of the briquettes was tested according to ISO17225: 2021 series for Solid Biofuel classification and analysis. (Incorporating ISO 14780, Solid biofuels — Sample preparation). The results of the testing is set out in Table 1: Table 1 Test                                 Result Moisture Content (As received basis) 9.1 % (w / w) Carbon Content (Dry Basis) 48.6% (w / w) Sulphur Content (Dry Basis) 0.05% (w / w) Ash Content (Dry Basis) 14.9% (w / w) Calorific Value (Dry Basis) 17.6 MJ / kg Ash Fusion Temperature >1100°C** Briquette Density 1.00 g / mL** *Standard test method(s) included for reference. **Non-standard test method used. All samples tested in accordance with ISO Standards where applicable. Example 4 5 Example 3 was repeated with a pressure of 2500 kg / cm2. A briquette was formed.

Claims

1. A method for manufacturing a biomass solid fuel comprising:shredding dried plant matter comprising at least 95 wt% plant matter from the5 Juncaceae family into particles;pressing the particles under pressure of at least 1000 kg / cm2 in a mold;wherein no binder is added; andwherein the plant matter comprises less than 15 wt% moisture content.10 2. The method of claim 1 wherein the pressure is from 1000 kg / cm2 to 2500 kg / cm2, or at least 1100 kg / cm2, at least 1200 kg / cm2, at least 1300 kg / cm2, at least 1400 kg / cm2, at least 1500 kg / cm2, at least 1600 kg / cm2, at least 1700 kg / cm2, at least 1800 kg / cm2, at least 1900 kg / cm2, at least 2000 kg / cm2, at least 2100 kg / cm2, at least 2200 kg / cm2, at least 2300 kg / cm2, at least 2400 kg / cm2, or at least 250015 kg / cm2.

3. The method of claim 1 or 2 wherein the pressure is 1700 kg / cm2 to 2500 kg / cm2.

4. The method of any one of claims 1 to 3 wherein the particle size is in the range20 0.002-2.0 mm, 0.063-0.63 mm, 0.0063-0.63 mm, 0.63-2.0 mm, 0.2-0.63 mm, 0.063-0.2 mm, 0.02-0.063 mm, 0.0063-0.02 mm, 0.002-0.0063, or <0.002 mm, as measured by sieve aperture, or a combination of ranges.

5. The method of any one of claims 1 to 4 further comprising cooling the particles25 during pressing, optionally wherein cooling comprises circulating water cooled to 4 to 10 QC around the outside of the mold.

6. The method of any one of claims 1 to 5 wherein no other plant matter is added, or wherein no other plant matter is deliberately added.

307. The method of any one of claims 1 to 6 wherein the particles comprise at least 99 wt% plant matter from the Juncaceae family.02 05 248. The method of any one of claims 1 to 7 wherein the plant matter is a mixture of Juncaceae species, optionally Juncus and / or Luzula species, optionally wherein the plant matter is a mixture of Juncus species, or wherein the plant matter is Juncus effusus or wherein over 80 wt% of the plant matter is Juncus effusus.

9. The method of any one of claims 1 to 8 wherein the plant matter comprises the stalks, flowers and seeds of Juncaceae species, or wherein the plant matter comprises the stalks of Juncaceae species.

10. The method of any one of claims 1 to 9 less than 14 wt%, preferably less than13 wt%, less than 12 wt%, less than 11 wt%, less than 10 wt%, less than 9 wt% or less than 8 wt% moisture content.

11. The method of any one of claims 1 to 10 further comprising drying the plant matter, prior to the shredding, optionally wherein drying comprises air drying.

12. The method of any one of claims 1 to 11 wherein the shredding is performed by mechanical means, optionally a hammer mill.

13. The method of any one of claims 1 to 12 wherein pressing the particles comprises using a compacting motion.

14. The method of any one of claims 1 to 13 further comprising harvesting the plant matter year round or, optionally, in May, June, July, August or September.

15. A solid fuel comprising at least 95 wt% compressed particles of plant matter from the Juncaceae family and no additional binder;wherein the solid fuel has a density of 0.8 to 1.2 g / mL;wherein the solid fuel has a moisture content of less than 13 wt%.

16. The solid fuel of claim 15 comprising at least 99 wt% plant matter from the Juncaceae family, optionally with no other additives.02 05 2417. The solid fuel of claim 15 or 16 wherein the plant matter comprises the stalks, flowers and seeds of Juncaceae species, or wherein the plant matter comprises the stalks of Juncaceae species.

18. The solid fuel of any one of claims 15 to 17 wherein the solid fuel is shaped in the form of a briquette or pellets, optionally wherein the solid fuel is shaped in the form of a cuboid, or optionally wherein the solid fuel is shaped such that it comprises at least two parallel planar surfaces.

19. The solid fuel of any one of claims 15 to 18 wherein the solid fuel has a density of approximately 1 g / mL.

20. The solid fuel of any one of claims 15 to 19 wherein the solid fuel has a carbon content on a dry basis of 40 to 60 wt%, optionally 45 to 55 wt%, optionally 47 to 52 wt%, optionally approximately 48 wt%, or approximately 50 wt%.

21. The solid fuel of any one of claims 15 to 20 wherein the solid fuel has a sulphur content of less than 0.1 wt%, optionally less than 0.09 wt%, optionally less than 0.08 wt%, optionally less than 0.07 wt%, optionally less than 0.06 wt%, optionally approximately 0.05 wt%.

22. The solid fuel of any one of claims 15 to 21 wherein the solid fuel has a moisture content of less than 12 wt%, optionally less than 11 wt%, optionally less than 10 wt%, optionally approximately 9 wt%.