GB2240341A

GB2240341A - Preparation of solid fuels

Info

Publication number: GB2240341A
Application number: GB9002052A
Authority: GB
Inventors: Eric Dennis Barford; Andrew Marc Edwards; Michael John Hardy
Original assignee: FIBA COMPACTA Ltd
Current assignee: FIBA COMPACTA Ltd
Priority date: 1990-01-30
Filing date: 1990-01-30
Publication date: 1991-07-31
Anticipated expiration: 2010-01-30
Also published as: GB9002052D0; GB2240341B

Abstract

A process for the preparation of a solid fuel comprises compacting, under pressure, a mixture comprising: (a) at least 50% by weight of a particulate carbonaceous material having a carbon content of at least 50% by weight; (b) at least 5% by weight of a wax; and (c) at least 2.5% by weight of a carbonisable binder; whereby to produce discrete pieces of compacted material.

Description

FUELS This invention is concerned with improvements in and relating to solid fuels and to the manufacture thereof.

Many proposals have been made for "synthetic8 solid fuels and their manufacture. However, only a limited number of such "synthetic" solid fuels have been made commercially available, generally the so-called "smokeless" fuels obtained by briquetting particulate carbonaceous material.

It is an object of the present invention to provide a process for the production of improved "synthetic" solid fuels.

More particularly, it is an objective of the present invention to provide a process for the manufacture of a "synthetic" solid fuel, which fuel has the following characteristics, taken alone or together; (i) the fuel is a readily ignitable, that is pieces of the fuel of an appropriate size (as discussed in more detail below) can be ignited by the simple application of the flame of a match: (ii) an array of pieces of the fuel in a conventional domestic fire-grate can, after ignition as discussed in (i) above, give a flaming fire a few minutes after ignition; and (iii) after an initial flame period an ignited array of fuel, as discussed in (ii) above, can give a lasting incandescent fire, the fire lasting for a period of hours e.g. up to about 4 hours; which incandescent fire can further serve as a basis for a fire of conventional solid fuels (common bituminous household coal or so-called "smokeless" fuels).

Basically, the process in accordance with the inventions comprises compacting, under pressure, a mixture comprising: (a) at least 50% by weight of a particulate carbonaceous material having a carbon content, on a dry basis, of at least 50% by weight, preferably at least 75% by weight; (b) at least 5% by weight of a wax; and (c) at least 2.5% by weight of a carbonisable binder; whereby to produce discrete pieces of compacted material.

The process of the invention may be carried out by tableting or briquetting individual lots of the mixture but is more preferably carried out by extruding the mixture of the three basic components, as noted above, to form a rod-like extrusion and subsequently cutting this extruded rod into pieces of the desired size. For convenience, in the following description, reference will be made only to such an extrusion process but. as will be appreciated, where appropriate reference is intended to be taken to a tableting or briquetting process.In any event, in order to achieve some or all of the preferred objectives (i)-(iii) noted above it is preferred that the pieces of fuel produced in accordance with the invention have a weight of from 50 to 1000 gms, preferably 250 to 750 gms. further. in order to achieve some or all of the above preferred objectives, it is preferred that the pieces of fuel produced in accordance with the invention have a surface area/volume ratio of from 0.5 to 0.8 cm /cm , preferably 0.6 to 0.7 cm/cm .

The starting mixture used in the process of the invention comprises three basic ingredients namely carbonaceous material, wax and carbonisable material.

The carbonaceous material forms the principal fuel source of the fuel of the invention and is present in an amount of at least 50% by weight of the starting mixture. Preferably the carbonaceous material forms from 55 to 85% by weight of the starting mixture, more preferably from 65 to 80% by weight of the mixture. The carbonaceous material should have a carbon content of at least 50% by weight preferably at least 75% by weight, and specific examples of such carbonaceous material include coke, coke breeze (i.e. partially pyrolysed bituminous coal) anthracite, wood, charcoal, and bituminous coal. The carbonaceous material must be in particulate form but we have found that the particle size of the carbonaceous material does not appear to be critical, provided that it may be formed, with the other basic components of the mixture, into an extrudable or otherwise compactable mixture.

However, for convenience in processing and handling, we have found that the particulate carbonaceous materials suitably have a particle size of such that it all passes through a screen of 4mm mesh, preferably through a screen of 2mm mesh.

The second basic component at the starting mixture is a wax component. This component must form at least 5% by weight of the starting mixture and preferably forms from 10 to 40% by weight thereof, more especially 15 to 20% by weight thereof. The wax may be a relatively low or a relatively high melting point wax.

However for convenience in storage and handling of the final product, a relatively high melting wax is preferred. e.g. a wax melting in the range of 50 to 650C, preferably 50 to 600C. The wax may be of mineral, animal or vegetable origin and examples of suitable waxes include beeswax, paraffin waxes and polyethylene waxes. From the stand points of ready availability and cost, petroleum derived waxes are generally preferred.

The third basic component of the starting mixture is a carbonisable material, present in an amount of at least 2.5% by weight of the mixture and more preferably present in an amount of from 4 to 15% by weight.

especially 5 to 10% by weight of the starting mixture.

A wide variety of carbonisable materials may be used in accordance with the invention. Generally, the carbonisable material is one having a carbon content of from 40 to 50% by weight, preferably 40 to 45% by weight (i.e. generally less than the carbon content of the primary carbonaceous material forming component (a)).

The carbonisable material should be one such that it is carbonised by the heat engendered by the burning of the wax component of a solid fuel produced in accordance with the invention, thereby to form a carbonised matrix holding the solid fuel together after combustion of the wax component but before any marked combustion of the primary carbonaceous material (a). In this connection, it should be noted that when the primary carbonaceous material (a) is a bituminous coal. this latter will contain some carbonisable material (bituminous components) to afford at least a part of the carbonisable component (c). Typical examples of other materials which may be used as carbonisable materials in accordance with the invention include natural materials such as starches, e.g. maize starch; other carbohydrates (e.g. sugars); lignins and tars.The carbonisable material (c) will also generally be present in the starting mixture in particulate form and, here again, there appears to be no critical limitation on the particle size of this component.

As noted above, the pieces of solid fuel produced in accordance with the invention suitably have a weight of from 250 to 750 gms and a surface area to volume ratio of 0.6 to 0.7 cm cm . In order that the solid pieces may have further improved burning and ignition characteristics, their physical shape also desirably meets further criteria. Thus, a typical piece of fuel produced in accordance with the invention will comprise a generally elongate block having a pair of generally parallel end-faces (produced by severing or cutting an extruded rod of material to give pieces of the desired size). The cross-sectional shape of the block may be arranged to provide more desirable characteristics and, to this end, it is preferred that, in cross-section, the block has a plurality of re-entrant or concave sections, forming more or less shallow grooves extending along the length of the block. Similarly, the block should, desirably, not be smoothly curved in cross-section but should have discontinuities, forming edges extending along the length of the block.

In operation, an array of fuel pieces produced in accordance with the invention is laid in the grate of a conventional domestic fireplace and one or two of the blocks are then lit; by the simple application of the flame of a match. Within a few minutes (two or three minutes in general experience) the whole array will be ablaze and this blaze will generally last for 45 to 90 minutes, after which the fire will continue to burn, that is primary carbonaceous material (a) will continue to burn to give an incandescent fire for a period of some hours. Such a fire may be further replenished with solid fuel pieces in accordance with the invention or with pieces of conventional fuels.

In order that the invention may be well understood, the following Examples are given by way of illustration only.

Fuel blocks in accordance with the invention were produced by extending a mixture of components as listed in Table 1 below into a solid rod about 7cm in diameter (the rod having four equispaced shallow grooves extending its outer surface) and cutting the rod into pieces having a weight of about 500 gm and a surface area:volume ratio of about 0.65 cm2/cm . In the table all percentages are by weight.

Table 1 Example Component 1 2 3 4 5 6 Coke breeze 70% 78% - - 75% - Bituminous coal - - 80% 80% - Paraffin Wax 20% - 15% 15% 15% 20% Polyethylene wax - 15% - - - - Maize starch 10% 7% 5% - - 108 Lignin - - - 5% - Sucrose - - - - 10% Charcoal - - - - - 70%

Claims

CLAIMS: 1. A process for the preparation of a solid fuel which comprises compacting, under pressure, a mixture comprising: (a) at least 50% by weight of a particulate carbonaceous material having a carbon content of at least 50% by weight; (b) at least 5% by weight of a wax; and (c) at least 2.5% by weight of a carbonisable binder; whereby to produce discrete pieces of compacted material.
2. A process as claimed in claim 1 which comprises extruding the mixture of the three components (a), (b) and (c) to form a rod-like extrusion and subsequently cutting the extruded rod into pieces of the desired size.
3. A process as claimed in claim 1 or claim 2 in which the descrete pieces of compacted material have a weight of from 250 to 750 gms.
4. A process as claimed in any one of the preceeding claims in which the descrete pieces of compacted material have a surface area/volume ratio of from 0.6 to 0.7 cm2/cm3.
5. A process as claimed in any one of the preceeding claims in which the carbonaceous material (a) formed from 55 to 85% by weight of the starting mixture.
6. A process as claimed in any one of the preceding claims in which the wax component (b) formed from 10 to 40% by weight of the starting mixture.
7. A process as claimed in any one of the preceding claims in which the wax component (b) melts within the range 50 to 650C.
8. A process as claimed in any one of the preceding claims in which the carbonisable binder formed from 2.5 to 15% by weight of the starting mixture.
9. A process as claimed in any one of the preceding claims in which the carbonaceous material (a) is a bituminous coal and a part, at least, of the carbonisable material (c) is afforded by the bituminous components of that coal.
10. A process as claimed in any one of the preceding claims in which the discrete pieces of compacted material comprise generally elongate blocks having a pair of generally parallel end-faces, the cross-section of the block having a plurality of re-entrant or concave sections to form grooves extending along the length of the block.
11. A process as claimed in claim 10 in which the block has discontinuities in cross-section forming edges extending along the length of the block.
12. A process as claimed in claim 1 substantially as hereinbefore described with reference to the Examples.