Due to environmentally driven government programs, such as the carbon tax, it is of great commercial interest to develop a fuel briquette, which is at least partly manufactured from a renewable biomass. Such suitable biomass includes sawdust, paper mill waste, sewage sludge, straw or the like. It is important that the biomass is from a renewable source and also that it has a good calorific value when combusted.

Cellulose based products such as wood and sawdust are particularly difficult to briquette due to its elasticity and high moisture content as well as its low bulk density.

Briquetting saw dust in its raw or untreated form, even as a percentage of a briquette, is almost impossible as the briquette will spring apart as it leaves the roll press.

Hydraulic pressing is possible, but very slow and not in a suitable format for most large-scale commercial requirements. A continuous roll press will produce a product which can be used in conventional systems, such as boilers for schools as well as some coal fired power stations. However, the resilience of the cellulose material makes it particularly unsuitable for conventional briquetting.

It is therefore an aim of the present invention to alleviate at least some of the disadvantages identified above.

It is a further aim of the present invention to provide a method of producing a fuel briquette from a cellulose

material such as wood and/or saw dust.

It is a further aim of the present invention to provide a method of treating a cellulose material for use in the manufacture of a fuel briquette.

Therefore, according to a first aspect of the present invention, there is provided a method of manufacturing a fuel briquette, which method includes: a) providing a cellulose material having a moisture content of less than about 18% by weight of the cellulose material; b) extruding the cellulose material through a die plate such that at least a portion of the internal lignin in the cellulose material is forced out of the internal structure of the cellulose material; c) briquetting the mixture formed in c) so as to form a fuel briquette.

The extruded material produced in b) is typically mixed with coal or the like prior to briquetting in step c). The amount of coal added is dependent on the desired fuel product, however, it is envisaged that coal may not be added.

The cellulose material is preferably straw, sawdust, wood shavings, refuse derived fibres (RDF), trimmings from fibre board manufacture (MDF), paper mulch from sterilized clinical waste, olive cake as a by-product of the oil pressing industry, brewery waste, sewage sludge and the incorporation of waste oils.

Preferably, the cellulose material has a moisture content of less than 15% by weight of the material, further preferably less than 12% by weight of the material.

However, it is particularly preferred that the moisture

content is less than 10% by weight of the cellulose material.

The cellulose material may be treated with, for example, heat prior to the step a) such that it has the desired moisture content. It is desirable that the cellulose material has a temperature above ambient when it is extruded in step (b). Preferably, the cellulose material has a temperature above 50°C, such as above 70°C. However, it is particularly preferred that the cellulose material has a temperature at or above 100°C when extrusion is initiated in step (b).

The cellulose material may be preconditioned prior to step (b). The preconditioning may be hydraulically pressing the material to form larger briquettes which after a resting period are typically granulated prior to step b).

Advantageously, preconditioning permits use of larger material.

The die plate typically includes tapered holes. The tapered holes preferably have a diameter of less than 10 mm (such as about 5 mm in diameter).

Advantageously, the heated cellulose material is extruded through the die plate, thereby forcing a proportion of the internal lignin out from the wood's structure of the cellulose material to form a self-binding liquid bond.

The extruded cellulose material is preferably granulated or in finely divided form prior to mixing with coal or the like.

The mixing prior to step c) is typically carried out using a high sheer mixer. The mixing is typically for a dwell time of between 1 and 4 minutes, such as 2 to 3 minutes

It is envisaged that further ingredients, such as binders, may be added prior to step c).

Binders may include starch (native or pregelatinised gums such as guar, bentonite, crystalline waxes, cement as powder or slurry, molasses, slaked lime, phosphoric acid, lignosulfonate, sodium silicate or colloidal silica as well as polymers or resin systems. The binder is chosen on a cost and application basis and may be different for domestic or industrial markets.

The cellulose material may be present in the resultant briquette in an amount in the range 30% to 80% (such as 35% to 65%) of the total weight.

The coal or the like may be present in the resultant briquette in. an amount in the range 30% to 80% (such as 40% to 70%) of the total weight.

It is particularly preferred that the extruded cellulose material and the coal or the like are present in substantially equal amounts, typically between 30% to 50% by total weight of the briquette. The remaining amount being a binder and/or a filler material.

It is envisaged that an additive may be added to the mixture prior to agglomeration. The binder may include a green strength additive such as organic gum, starch, cement or a chemical component such as calgon. This is advantageous as it provides the rewly agglomerated briquette some initial strength while the resin binder system activates.

A resin is added typically after step c) and prior to step d). The resin is preferably a phenolic resin. However,

resins based on urea, and also some hybrid binder systems may be used whereby a simple molasses and lime or cement binder is used and then supplemental with a small amount (1-2%) of the resin addition to water proof the product.

The resin is typically added in an amount from about 0. 5% to 20% by weight of the mixture, preferably to 15%, further preferably 2% to 8%. It is also envisaged that water is added with the resin. The volume of water added depends upon the temperature, moisture content and also the ambient temperature and humidity. In a particularly preferred embodiment of the present invention, the resin and water are added concurrently.

If resin is used in the briquette it is desirable to include a suitable catalyst or hardener at the same time as the resin. Advantageously, the catalysts or hardeners are applied to set off the curing process. The catalyst or hardener may include mixtures of mono-, di-, and triacetin, mixtures of ethylene glycol monoacetate and ethylene glycol diacetate, propylene glycol diacetate, alpha-butylene diacetate, propylene carbonate, propiolactone, butynolactone, valerolactone or caprolactone, or blends thereof.

The composite fuel briquette of the present invention is particularly desirable as it has a number of commercial advantageous, which includes: It can be used in existing appliances and systems (for example industrial boilers or power station burner systems).

> Has good bulk density and is well suited to mechanical handling shovel loaders and grabs that is, it does not degenerate.

> Has high energy value with much lower emissions of

Sulphur than prior art briquettes The briquette is 50% + carbon neutral > Has good handling and aesthetic qualities for the domestic user market.

> Can be manufactured cost effectively at high levels of output > Can be tailored to the users specific requirements.

The coal is typically in the form of coal fines or duff.

The coal is preferably anthracite or Steam coal, however, it is envisaged that the coal may be bituminous coal, brown coal, raw fines, reclaimed spoil heaps and duff from China, Columbia, Australia, South Africa and Russia.

The coal preferably has a moisture content of less than 15%, such as less than 10% prior to being mixed in step c).

However, it is particularly preferred that the coal has a moisture content of around 5%.

If the coal fines or duff are provided having a moisture content greater than about 15%, it is preferred that it is dried so as to achieve the desired moisture content.

Prior to mixing in step c) the coal typically has a particular size of less than 6 mm in diameter, preferably about 3 mm in diameter. The coal is typically heated prior to being passed to a grinding mill or the like for particle size reduction. The coal is typically heated to a temperature above 50°C, such as around 60°C.

According to a further embodiment of the present invention, there is provided a composite fuel briquette which includes a cellulose material which has been extruded and coal or the like The composite fuel briquette is substantially as described

hereinbefore with reference to the first aspect of the present intention.

According to yet a further aspect of the present invention, there is provided a use of an extruded cellulose material in the manufacture of a composite fuel briquette.

The composite fuel briquette is substantially as described hereinbefore with reference to the first aspect of the present invention.

The present invention will now be described by way of example only.

The process according to the present invention is achieved by preparing the coal and sawdust separately, as follows: Coal preparation:- Wet coal fines or duff (12% moisture) were delivered to the system from the washery. These were placed into a hopper and volumetrically discharged into a rotary drier. The drier was arranged to reduce the moisure content to around 5%. The hot (normally about 60°C) coal was then passed into a grinding mill for particle size reduction and control.

The coal is ground to a range of 3mm to dust. The hot coal dust was stored in a buffer hopper.

Sawdust preparation:- Wet sawdust (40% moisture) was delivered to a collection hopper. The material was screened to a range of 3mm to dust and then dried down to 15% moisture. This may be preheated with waste heat from the exhaust system of the coal drier. The hot sawdust (normally at about 100 °C) was transferred into a feed hopper where a screw feeder compressed the hot material up against a perforated die plate. The sawdust was then extruded through the die plate

where the wood is forced into continuous lengths (like spaghetti) and subsequently falls into a granulated mill.

The treated wood now resembles breadcrumbs, has much greater density and has superb agglomeration qualities.

The hot extrusion forces lignins from inside the cell structure outwards and this acts as a binder both for the crumb and also later in the briquettes themselves. The hot crumb is now transferred to a holding hopper.

Multi-fuel briquetting process: Coal and wood crumb (as prepared according to the method given above) is dosed into a continuous high shear paddle mixer. The material is controlled either by a weigh belt feeder or a volumetric discharge device, such as a dosing screw. A green strength addition will be added at approximately 0. 5% by total weight to the coal dust prior to the mixer. This green strength addition is added to give the newly manufactured briquette some initial strength while the resin binder system activates (15 minutes at 20°C). The green strength additive may be an organic gum, starch, cement or chemical component such as Calgon. Next water and phenolic resin are added; water maybe added at a rate of 1% upto 15% depending upon coal temperature, moisture content and the ambient temperature and humidity.

The resin addition is usually in the range of 4-5% by weight of product. The coal wood crumb, GSA, water and resin are mixed with high levels of shear for between 2 and 3 minutes of dwell (continuous system). The mix is then transferred to a second mixer on top of the briquetting press. At this point a catalyst is added at approximately 0. 5% by weight. The catalyst activates the resin and starts the curing process. At this point the activated mixture is fed by gravity through the feed box into the rolls of the press and briquettes are formed. The

briquettes are discharged onto a conveyer and then onto a surge or curing belt. This slow moving high volume conveyor allows the briquettes to start hardening for about 15 minutes. At the end of this belt the briquettes pass over a screen where fines a flashings are removed for reintroduction while the briquettes are transferred by conveyor into covered storage bays.