GB2081302A - Fuel pellets and methods of making same - Google Patents

Abstract

Fuel pellets comprise a particulate, combustible material, a binder which is activatable as a binder without the application of heat and, optionally, a waterproofing agent.

Description

SPECIFICATION Fuel pellets and methods of making same The present invention relates to fuel pellets and to methods of making such fuel pellets.

It is known to manufacture charcoal pellets from a mixture comprising charcoal powder, starch and water; the starch being used as a binder material. In order to activate the starch as a binder material it is necessary to heat the initially formed pellets, for example, to a temperature of approximately 1 500C. This need to heat the initially formed pellets in order to activate the starch is a disadvantage in view of the energy requirements. It would, therefore, be advantageous to be able to produce pellets, for example charcoal pellets, utilizing a binder which does not require a heating step in order to activate it.

According to the present invention there is provided a fuel pellet, which comprises a particulate, combustible material and a binder material, the binder material being activatable as a binder without the application of heat.

Suitable materials for use as the particulate, combustible material include carbonaceous materials such as coal dust or powdered charcoal.

The binder material may, for example, be a cement, a material which is activatable as a binder without the application of heat and which at least partially decomposes at elevated temperatures, or a mixture of such binder materials. Suitable cements for use as the binder material include hydraulic cements such as Portland cement, high alumina cements such as Ciment Fondu Lafarge, and mixtures of such cements.

High alumina cements generally contain about 36 to 42% by weight Al203, about 36 to 42% by weight CaO, 7 to 18% by weight oxides of iron, 5 to 10% by weight SiO2 and small amounts of TiO2, Moo and alkalis. For example, Ciment Fondu Lafarge contains about 40% by weight Al203.

A rapid setting cement may be produced by utilizing a mixture of a hydraulic cement, e.g.

Portland cement, and a high alumina cement, e.g.

Ciment Fondu Lafarge; the speed of setting depending on the proportions of the two constituents used.

The materials suitable for use as the binder material in the fuel pellets of the present invention and which are activatable without the application of heat and at least partially decompose at elevated temperature include materials such as gypsum and Plaster of Paris but do not include the cements which contain complex silicates and aluminates of calcium as the major constituents.

The binder material may, for example, be present in an amount of least 3% by weight, based on the weight of the particulate, combustible material. Preferably, the binder material is present in an amount of not more than 10% by weight, based on the weight of the particulate, combustible material. Most preferably, the binder material is present in an amount of not more than 6% by weight, based on the weight of the particulate, combustible material.

The fuel pellets in accordance with the present invention may optionally contain water, for example, in an amount of up to 20% by weight, based on the weight of the fuel pellets. Any such water will usually originate from water which may, for example, be added during formation of the pellets and/or water which may, for example, be present in the constituents used to form the pellets and/or from water or moisture which may, for example, be absorbed from the surrounding environment.

The presence, in the formed fuel pellets, of water in excess of 20% by weight, based on the weight of the fuel pellets, may have a deleterious effect on the properties of the pellets and may even result in their breakdown. The amount of any water present in the fuel pellets, and originating from water added during formation of the pellets and/or from water present in the constituents used to form the pellets, can be controlled, for example, by controlling the amount of water added during formation of the pellets and/or removing part or all of any water present in the constituents used to produce the pellets and/or partially or completely drying the formed pellets. However, in order to prevent, or substantia,ly reduce, the absorption of water or moisture by the formed fuel pellets from the surrounding environment, the pellets may comprise a waterproofing agent.The waterproofing agent, may for example, be present in the fuel pellets in addition to any water originating from water added during formation of the pellets and/or from water present in the constituents used to form the pellets but will function to prevent, or substantially reduce, the absorption of further water or moisture by the pellets from the surrounding environment.

The waterproofing agent may, for example, be present in an amount of at least 0.5% by weight, based on the weight of the particulate, combustible material. The waterproofing agent may, for example, be present in an amount of up to 5% by weight, based on the weight of the particulate, combustible material. Preferably, the waterproofing agent is present in an amount of about 1% by weight, based on the weight of the particulate, combustible material.

Waterproofing agents suitable for use in the fuel pellets according to the present invention include: waxes, for example, paraffin wax which may be in powder, liquid or molten form; oils, for example, waste engine oil and boiled linseed oil; and silicones. Waste engine oil has the advantage that it is a readily available, cheap waste product.

According to the present invention there is also provided a method of making fuel pellets in accordance with the present invention, which comprises homogeneously mixing the particulate, combustible material and binder material, and forming the resulting mixture into pellet form in the presence of water and before the binding action of the binder has been completed.

If the fusel pellets contain a waterproofing agent, they may, for example, be formed by a method which comprises homogeneously mixing the particulate, combustible material, binder material and waterproofing agent, and forming the resulting mixture into pellets in the presence of water and before the binding action of the binder has been completed. Alternatively, the fuel pellets may, for example, be formed by a method which comprises homogeneously mixing the particulate, combustible material and the binder material, forming the resulting mixture into pellet form in the presence of water and before the binding action of the binder has been completed, and applying the waterproofing agent to the outer surface of the formed pellets.

Optionally, the method of the present invention comprises the additional step of drying the formed pellets to reduce the water content of the pellets.

The drying may be achieved by any suitable means, for example, by air drying or drying at elevated temperatures.

In the embodiment of the present invention in which a waterproofing agent is applied to the outer surface of the formed pellets, the optional drying step may be carried out before and/or after application of the waterproofing agent to the pellets.

If a waterproofing agent is applied to the outer surface of the formed pellets it may be applied by any suitable means, for example, by spraying, dipping or brushing.

The waterproofing agent, may if desired, be dissolved in a suitable solvent in order to aid in its incorporation into the fuel pellets or its application to the outer surface of the fuel pellets. Suitable solvents include those which reduce the viscosity of the waterproofing agent, i.e. the viscosity of the solvent is less than that of the waterproofing agent, and which are readily removed from the fuel pellets, for example, by evaporation. Examples of suitable solvents are white spirit and spirits of turpentine.

If a waterproofing agent is applied to the outer surface of the fuel pellets by spraying, it may be necessary to reduce its viscosity in order that it can be sprayed onto the formed pellets without blocking the spraying machine used. However, if the viscosity of the waterproofing agent is sufficiently low to enable it to be sprayed without blocking the spraying machine, the use of a solvent is generally not necessary.

If a silicone is used as the waterproofing agent, it may, for example, be used in the form of a solution, e.g. in white spirit containing about 30% or about 60% silicone. A solution containing about 30% silicone is commercially available and has a pH of about 1 3. A solution containing about 60% silicone in white spirit has, however, been found to be a better water-repellant and to have a longer life than the solutions containing only about 30% silicone.

The fuel pellets may, for example, be formed by a compression or by an agglomeration process.

When forming the fuel pellets by an agglomeration process, water, e.g. in droplet form, is introduced into a mixture comprising the particulate, combustible material and the binder material or a mixture comprising the particulate combustible material, the binder material and the waterproofing agent.

The pellets may, for example, be formed using a pelleting apparatus comprising a hollow, cylindrical tube having radial holes extending through the wall thereof, and one or more rollers, e.g. two, three or four rollers. The or each roller has its axis of rotation parallel to the longitudinal axis of the hollow, cylindrical tube and touches the interior wall of the hollow, cylindrical tube. The material to be pelleted is fed into the hollow, cylindrical tube which is positively rotated, for example, by an electric motor, and is forced through the radial holes in the hollow, cylindrical tube by the action of the freely-rotating roller(s).

The compressed material exiting from the radial holes in the hollow, cylindrical tube is then formed into pellets of the desired length, for example, by cutting, shearing or simply allowing the compressed material to break under its own weight as the hollow tube rotates.

Pelleting machines which may be used in forming the fuel pellets of the present invention include those used in pelleting animal feedstuffs.

Suitable pelleting machines are manufactured by Richard Sizer Limited under the name Orbit.

The fuel pellets according to the present invention have the advantages that the dust problem associated with the use of carbonaceous material powders is eliminated or substantially reduced and that, whereas carbonaceous material powders are not free-flowing when moisture is present, the fuel pellets according to the present invention are free-flowing.

An advantage of using gypsum or Plaster of Paris as the binder material in the fuel pellets of the present invention is that on burning the pellets, the gypsum or Plaster of Paris decomposes and leaves a residue having only approximately 1/3 of the weight of the original gypsum or Plaster of Paris used. A further advantage in using Plaster of Paris as the binder material is that it is a considerably cheaper material than starch which, as discussed above, has been previously used as a binder material.

The present invention will now be further illustrated by way of the following Examples: EXAMPLE 1 6.5 Kg coal dust, having a particle diameter of less than 1/8 inch (0.32 cm), was intimately mixed with 0.385 Kg of Plaster of Paris. 1.5 litres of water was then added and the resulting mixture was pelleted using an Orbit pelleting machine manufactured by Richard Sizer Limited. The resulting pellets were then air dried to produce fuel pellets in accordance with the present invention.

EXAMPLE 2 6.5 Kg of coal dust, having a particle diameter of less than 1/8 inch (0.32 cm), was intimately mixed with 0.385 Kg of Plaster of Paris and 65 gm of paraffin wax. 1.5 litres of water was then added and the resulting mixture was pelleted using an Orbit pelleting machine manufactured by Richard Sizer Limited. The resulting pellets were then air dried to produce fuel pellets in accordance with the present invention.

EXAMPLE 3 100 Kg (by dry weight) of coal fines containing water and 4Kg of Portland cement were intimately mixed together. 2Kg of Ciment Fondu Lafarge was then added and the resulting mixture was thoroughly admixed until thickening began to occur. 1 Kg of boiled linseed oil was then added and thoroughly mixed therewith. The resulting mixture was then pelletized using an Orbit pelleting machine manufactured by Richard Sizer Limited to produce pellets in accordance with the present invention.

EXAMPLE 4 Example 3 was repeated, except that a mixture of 1/2 Kg boiled linseed oil mixed with paraffin wax powder was used in place of the 1 Kg of boiled linseed oil. Fuel pellets in accordance with the present invention were produced.

EXAMPLE 5 Example 3 was repeated except that 1 Kg of paraffin wax powder was used in place of the 1 Kg of boiled linseed oil. Fuel pellets in accordance with the present invention were produced.

Claims (26)

1. A fuel pellet, which comprises a particulate, combustible material and a binder material, the binder material being activatable without the application of heat.

2. A fuel pellet as claimed in claim 1, in which the particulate, combustible material is a carbonaceous material.

3. A fuel pellet as claimed in claim 2, in which the carbonaceous material is coal dust or powdered charcoal.

4. A fuel pellet as claimed in any of claims 1 to 3, which also comprises water.

5. A fuel pellet as claimed in claim 4, in which the water is present in an amount of up to 20% by weight based on the weight of the fuel pellets.

6. A fuel pellet as claimed in any of claims 1 to 5, in which the binder material is present in an amount of at least 3% by weight, based on the weight of the particulate, combustible material.

7. A fuel pellet as claimed in any of claims 1 to 6, in which the binder material is present in an amount of not more than 10% by weight, based on the weight of the particulate, combustible material.

8. A fuel pellet as claimed in claim 7, in which the binder material is present in an amount of not more than 6% by weight, based on the weight of the particulate, combustible material.

9. A fuel pellet as claimed in any of claims 1 to 8, in which the binder material is a material which is activatable as a binder without the application of heat and which at least partially decomposes at elevated temperatures.

10. A fuel pellet as claimed in claim 9, in which the binder material is gypsum or Plaster of Paris.

11. A fuel pellet as claimed in any of claims 1 to 8, in which the binder material is a cement or a mixture of cements.

12. A fuel pellet as claimed in claim 11, in which the binder material is a hydraulic cement, a high alumina cement or a mixture of such cements.

13. A fuel pellet as claimed in any of claims 1 to 12, which also comprises a waterproofing agent.

14. A fuel pellet as claimed in claim 13, in which the waterproofing agent is a wax, an oil or a.

silicone.

1 5. A fuel pellet as claimed in claim 14, in which the wax is paraffin wax.

1 6. A fuel pellet as claimed in claim 14, in which the oil is waste engine oil or boiled linseed oil.

1 7. A fuel pellet as claimed in any of claims 13 to 16, in which the waterproofing agent is present in an amount of at least 0.5% by weight, based on the weight of the particulate, combustible material.

18. A fuel pellet as claimed in any of claims 13 to 17, in which the waterproofing agent is present in an amount of up to 5% by weight, based on the weight of the particulate, combustible material.

1 9. A fuel pellet as claimed in any of claims 13 to 18, in which the waterproofing agent is present in an amount of about 1% by weight based on the weight of the particulate, combustible material.

20. A method of making fuel pellets as claimed in any of claims 1 to 12, which comprises homogeneously mixing the particulate, combustible material and binder material, and forming the resulting mixture into pellet form in the presence of water and before the binding action of the binder material has been completed.

21. A method of making fuel pellets as claimed in any of claims 13 to 19, which comprises homogeneously mixing the particulate, combustible material, the binder material and the waterproofing agent, and forming the resulting mixture into pellet form in the presence of water and before the binding action of the binder material has been completed.

22. A method of making fuel pellets as claimed in any of claims 13 to 1 9, which comprises homogeneously mixing the particulate, combustible material and the binder material, forming the resulting mixture into pellet form in the presence of water and before the binding action of the binder material has been completed, and applying the waterproofing agent to the outer surface of the formed pellets.

23. A method as claimed in any of claims 20 to 22, in which the formed fuel pellets are subjected to a drying step.

24. A method as claimed in any of claims 20 to 23, in which the fuel pellets are formed by a compression or agglomeration process.

25. Fuel pellets substantially as hereinbefore described and with reference to any of the Examples.

26. A method of making fuel pellets substantially as hereinbefore described and with reference to any of the Examples.