Fuel Pellet and Process

The present invention relates to a fuel product and a process for making same.

Many industries and domestic homes rely heavily on carbon based or fossil fuels as a source of heat and power generation. However, with increasing awareness of climate change and global warming, renewable energy is being increasingly employed as an alternative source of fuel. Renewable energy technology such as biomass combustion is known to provide heat and power at low efficiencies and helps to reduce net emissions of carbon dioxide and nitrogen oxide (NOx) when compared with equivalent fossil fuel generation technologies.

Biomass can be defined as any biological material, derived from plant or animal matter, either living or recently living, which can be used for producing heat and/or power, fuels including transport fuels, or as a substitute for fossil fuel-based materials and products. Biomass falls into two main categories 1 ) woody biomass includes forest products, untreated wood products, energy crops and short rotation coppice (SRC), which are quick-growing trees like willow; 2) non-woody biomass includes animal waste, industrial and biodegradable municipal products from food processing and high energy crops. Examples are rape seed, hemp seed, corn and sugar cane residues.

The present demand for useable biomass solid fuels in the UK and Europe currently exceeds supply. Biomass waste technologies are based around heat and pressure pelletisation processes similar to briqueting, which requires a high energy input, with the burn characteristic therefrom being lower than the energy input. However the high capital and running costs of presently available pelletising equipment to produce such biofuel pellets is very high.

On a political level, renewable energy production targets in the EU are not currently being met, and there is considerable impetus to increase their usage with a 12% target for 2010, although currently less than 2% is provided from renewable sources.

One problem for many industries and domestic homes when converting to biofuels is the cost of interchanging burner systems or incinerators such as interchanging from a coal burner or incinerator to a wood burner or incinerator. Biomass fuels such as wood chips or pellets have different burn characteristics compared to fossil fuels so that conventional condensing burners or fossil fuel fire burners may not be suitable for use with biofuels. The cost of conversion is generally high, and the pay-back period can be long. Thus the cost of converting to biofuels is often initially overcome by the use of cofiring.

Cofiring is the combustion of two different types of materials at the same time such as a biomass material and a fossil fuel such as coal generally in a coal-fired burner. Cofiring of material does not involve the high capital costs of building a new biomass plant or buying a new domestic biomass burner, but involves significantly lower retrofitting costs of an existing plant or domestic fossil-fuel fired burner. Retrofitted burners can fire biomass

when biomass supplies are plentiful but switch back to coal when biomass supplies are low.

However, retrofitting an existing plant to handle the combustion of two or more separate materials having burn characteristics can cause problems for the control of boiler temperatures, water flow temperatures, optimum start strategies, and maintenance intervals.

This again raises costs and increases the complexity of control and the amount of management and maintenance.

It is an object of this invention to provide a more energy efficient fuel product and process for dealing with biomass materials and carbon-based materials.

Accordingly in a first aspect of the present invention, there is provided a process for producing layered rigid fuel pellets comprising:

a biomass material, a particulate carbon-based material, and a silicate-based binder,

the process comprising at least the following steps:

admixing one of the biomass material and the particulate carbon-based material with the binder; agglomerating the first so-formed mixture by tumbling at ambient temperature to form core pellets; admixing the other of the biomass material and the particulate carbon- based material with the binder; and

agglomerating the second so-formed mixture around the core pellets by tumbling at ambient temperature to form the layered rigid pellets.

Biomass materials usable with the present invention include any material generally of a biological origin, generally being carbon based and usually based on recently living biological material, as opposed to coal and other fossil fuels.

Preferably, the biomass material is one or more of the group comprising: wastewater sludge, sewerage sludge, chicken litter, bone-meal, spent mushroom compost, wood, organic plant material, products, by-products or plant residues including rape seed, hemp seed, corn and sugar cane residues.

A sludge material is preferably dewatered sludge i.e. reduced water content. This allows for easier combustion of the sludge once pelletised and less energy requirements for the incinerator to deal with any excess water. In particular, the present invention is able to use sludge material which can be derived from any definition of sludge including wastewater sludge, sewage sludge or 'biowaste'.

Woods can include any waste wood material, generally being in a dust or 'fine' form, or able to be provided in such form. Processes such as torrification are known for making wood fines, and wood fines and dust are also natural by-products in many wood shaping, forming or manufacturing processes or industries.

Chicken litter, bone meal and spent mushroom compost are biomass materials, much of which can already be in a fine or particulate mode.

In the use of organic plants such as rapeseed or hemp seed, corn, sugar cane, etc, from which products such as oils such as linseed oil are produced, there is commonly a significant proportion of waste material in a fine or particulate form. Rapeseed dust and hemp seed dust are known by-products of processes using rapeseed or hemp seed. Similar byproducts are formed in the use of other organic plant materials.

In the present invention, the biomass material may be one or more biomass materials as hereindescribed. Where two or more biomass materials are used, they may be pre-mixed prior to admixing with the binder, or each biomass material is brought together either simultaneously or separately with the binder.

The admixing of the biomass material and binder may occur prior to any agglomeration by tumbling, for example as a separate step, such that the so-formed mixture is then agglomerated by tumbling to form the rigid pellets.

Preferably, the biomass material and binder are admixed either by the same tumbling action which subsequently allows the mixture to agglomerate or on route thereto. For example, where the biomass material and binder are to be agglomerated in a rotary drum, the biomass material and binder could be provided to the rotary drum either simultaneously, or one after the other, such that their admixing to form a mixture occurs by the same action of the rotary drum as their subsequent agglomeration into pellets.

Where the biomass material is provided from two or more biomass materials as hereindescribed, each biomass material could be added either separately or simultaneously with one or more other biomass

materials, and/or the binder. The present invention allows for the mixing of the biomass material and the binder to be any combination of such combinations.

The admixing of the particulate carbon-based material and binder may also occur prior to any agglomeration by tumbling, for example as a separate step, such that the so-formed mixture is then agglomerated by tumbling to form the rigid pellets.

Preferably, the particulate carbon-based material and binder are admixed either by the same tumbling action which subsequently allows the mixture to agglomerate or on route thereto in a manner similar to admixing of the biomass material and binder for example in a rotary drum.

Where the particulate carbon-based material is provided from two or more particulate carbon-based materials as hereindescribed, each particulate carbon-based material could be added either separately or simultaneously with one or more other particulate carbon-based materials, and/or the binder. The present invention allows for the mixing of the particulate carbon-based material and the binder to be any combination of such combinations.

The second agglomeration of the biomass material or particulate carbon- based material around the core pellets provides a second, usually outer, layer of such material around the core pellets by providing a basis for such further material to be gathered together and provide a larger and now layered pellets which either are, or now become, rigid.

The process of the present invention is directly usable with moisture-rich biomass material, as any water content of the biomass material and/or

binder can be reduced in line with the level of moisture in the biomass material without affecting the process. Thus, the biomass material for use with the present invention may have a moisture level of up to 50, 60 or 70 total wt%, which is higher than the water content of biomass materials conventionally used.

The moisture content of the biomass material may be altered by the use of two or more biomass materials having different moisture contents. For example, use of wood dust or fines can increase the dry solid contents of the overall biomass material, and therefore reduce the moisture content of the overall biomass material. Because of the range of biomass materials that can be used by the present invention, the moisture content may even be as low as between 0-5wt%.

A reduction in moisture also provides a direct increase in the heat content value of the product which it is burned, hence increasing its efficiency and economic value. This economic benefit extends to transportation of such a product, in comparison with cost of transporting 'wet' or moisture-rich material as described hereinabove. Indeed, the present invention provides a process whereby with consideration of the type and amount of binder(s) used, and the process parameters, a fuel material can be provided which has a desired or pre-determined burn value or the like, which, in particular, could suit the local economic conditions for the fuel source.

Preferably, a majority of the dry solids content of the biomass material is 'fines' that is having a size of 1 mm or less. Preferably, at least 50, 55, 60, 65, 70, 75, or 80 wt% of the biomass material, generally 50-70 wt% or 60- 70 wt%, is of a size of 1 mm or less.

In another embodiment of the present invention, the dry solids content of the biomass material being 1 mm or less in size is at least 30 wt%, preferably at least 40, 50, 60 or 70 wt% which is sub-micron in size. More preferably, the dry solids content of the biomass material being 1mm or less in size includes at least 40% of such material being of a sub-micron size.

With respect to the particulate carbon-based material, it is generally of a maximum size or grade of about 3mm or lower.

Preferably, the particulate carbon-based material is coal dust or coal fines.

Coal 'dust' or 'fines' can often be of a sub-micron size.

The particulate carbon-based material may have a range of sizes or grades; preferably biased towards fine or finer particle sizes, e.g. approximately 40-60%, such as 50%, below 1 mm.

Particulate carbon-based material suitable for the present invention can be accepted wet or dry, and could be provided by any type of maceral fuel, including peat and lignite through to sub-bituminous coals, anthracite fines, petroleum coke fines and the like, as well as other hydrocarbon materials that could be considered a fuel source. The particulate material may also be a combination of two or more such materials, not necessarily premixed, and such as those hereinbefore mentioned, so as to provide 'hybrid' fuel pellets.

The particulate carbon-based material for the present invention may be provided from two or more particulate carbon-based materials, such as those hereindescribed. Each such particulate carbon-based material

could be added either separately or simultaneously with one or more other the particulate carbon-based material, and/or the binder. The present invention allows for the mixing of the particulate carbon-based material and the binder to be any combination of such combinations.

The present invention is not affected by high ash content or sulphur content in certain carbon-based materials.

It is a further advantage that the present invention can also use any type of 'wet' or 'dry' particulate carbon-based material. Freshly mined bituminous coal can have a moisture content of up to 20%, lower ranking coal can have a moisture content of up to 30%, with lignite going up to 45%. To drive off this level of moisture (by turning it into steam) prior to conventional combustion of the actual coal requires so much energy to start with, that this coal is simply not used, as it is not efficient. Complete grinding of such coal to be more 'burnable' is also inefficient as the moisture-rich coal generally reduces the efficiency of the grinder.

Preferably, any wet particulate carbon-based material used with the present invention has a maximum water content up to 20 wt%. Such a moisture level can be achieved by subsidiary grinding, which has a drying effect. The power required therefor is a lot lower than the power required for grinding coal to a powderous form ready for immediate conventional burning as described above. Such material is generally still regarded in the art as being 'wet', especially in relation to e.g. the briquetting process, which requires its material to be absolutely dry.

In some circumstances, it is preferred to have a dry particulate carbon- based material. In other circumstances, the material may be derived from a wet fuel source, such as peat and coal tailings dams, and any reduction

in the amount of drying needed (compared with for example the briquetting process) reduces the overall energy input required to form the fuel product.

Preferably, the process does not require any pre-treatment of the particulate carbon-based material.

The present invention is particularly advantageous by avoiding the need for any pre-mixing or treatment of the constituents involved, and the requirement for any post-forming treatment. From a capital and economic perspective, the process reduces the requirements needed to set up a plant adapted to provide the process of the present invention, and lowers the costs of operation by having a process which is run at ambient temperature.

Preferably, the process reduces moisture in the particulate carbon-based material, preferably to less than 5%, compared with the weight of the moisture in particulate carbon-based material. Thus, the present invention also provides significant moisture reduction in a fuel product, converting an inefficient fuel product into an efficient fuel product.

The process of the present invention may further provide a layered rigid fuel pellet comprising one or more further layers of biomass material and/or particulate carbon-based material.

In one embodiment of the present invention, the process comprises at least the following steps:

admixing the biomass material with the binder;

agglomerating the first so-formed mixture by tumbling at ambient temperature to form core pellets; admixing the particulate carbon-based material with the binder; and agglomerating the second so-formed mixture around the core pellets by tumbling at ambient temperature to form the pellets.

Thus, the core of the final so-formed pellet of this particular process is a biomass material, such as wood fines or dust in a rigid form, and the outer layer is a particulate carbon-based material such as coal fines or dust formed into a shell.

The fuel pellets may comprise 1-99 wt% of each of the biomass material and the particulate carbon-based material.

Optionally the pellet comprises a core of biomass material comprising >50 % of the diameter of the pellet, including possibly >80% or >90 % of the diameter, and an outer layer of particulate carbon-based material comprising <50 % of the diameter of the pellet, including possibly <20% or 10% of the diameter.

Any suitable silicate-based binder can be used for the present invention, which binder may be a homogeneous or heterogeneous material, such as cements and raw silicates like calcium, sodium or potassium.

In one embodiment, the binder is partly, wholly or substantially sodium silicate or potassium silicate.

Thus, the binder of the present invention allows the fuel pellets of the present invention to be formed and to cure in a 'cold fusion' process. That

is, the pellets can be formed and cure without the need for any external heat input.

No mechanical compression force is required, (with its attendant low production rate and high cost), and the process of the present invention is carried out at ambient temperature. By being able to carry out the process at ambient temperature, no additional equipment is required for any active further stage treatment, or to provide an elevated temperature. This naturally eliminates the need for a power source, e.g. fuel to be burnt, to create the elevated temperature, which action is usually a significant economic requirement of an industrial process.

The concept of curing as used herein includes any drying required of the formed pellets in addition to the chemical process occurring at least the surface of the pellets as they are being formed, preferably to provide a harder or hardened shell. As such, it is not intended that the present invention provides any separate drying step or action, ("drying" being in relation to one or more liquid materials or substances, such as water, evaporating from the pellets as they are formed and cured). Any such post pellet-forming drying action is regarded as secondary or minor compared to the act of forming and curing the pellets.

Preferably, the process is carried out without requiring a separate active curing step or steps.

In one embodiment of the present invention, binder is added in the range 1-10 wt% of each of the biomass material and the particulate carbon- based material, preferably 3-7 wt%. The amount of binder required will to some extent depend on the moisture content of the biomass material or particulate carbon-based material.

Suitably, the binder includes one or more surfactants.

The use of a silicate-based binder which preferably includes one or more surfactants allows the process of the present invention to create rigid fuel pellets at ambient temperature.

The fuel pellets are 'rigid' in the sense that they are handleable, and are able to be stored, stacked, and/or transported immediately, without requiring any separate active curing step or steps. That is, the pellets cure without any assistance or further treatment, especially heat and/or pressure treatment. Prior art processes required the fuel pellets formed by agglomeration to be actively cured with heat and/or forced air pressure before such fuel pellets were rigid and handleable. Thus, the fuel pellets of the present invention could be packaged and/or transported immediately after forming.

The present invention is also advantageous in using inorganic silicate- based binders, as opposed to the generally organic materials used as binders in prior art processes. The use of such binders reduces the complexity of the process, and again reduces the need for any pre- treatment or mixing of binder materials. The use of an inorganic silicate- based binder has two further advantages. Firstly, such binders do not impact on the burn quality of the carbonaceous material (as they do not burn), in contrast with organic materials such as starches, (which do burn, and which therefore effect the burn quality and thus heat content value of the formed material). Such binders are also clear of any environmental implications (as they do not burn), again in contrast with organic binders.

In one embodiment, the binder may be sprayed onto the biomass material and/or the particulate carbon-based material. Preferably, the biomass material and/or particulate carbon-based material is moving prior to and/or during mixture with the binder.

In another embodiment, the biomass material and/or particulate carbon- based material is moving prior to and/or during mixture with the binder and/or the material(s) are in a dispersed arrangement. One particular suitable form of this is a falling curtain of material(s), such as at conveyor transfers, inside pelletising drums or pans, and from stockpile load outs, etc.

The at least one of the biomass material and the particulate carbon-based material and binder may be at least partly mixed with agitation.

Preferably, the admixing of the biomass material and/or particulate carbon-based material and each of the same or different binders may occur by the tumbling. In this way, the admixing and agglomerating steps of each material and binder are simultaneous or contemporaneous.

The tumbling action serves to agglomerate the material(s) and binder mixture to form particles of greater and greater size, generally having a spherical or ovoid shape. The size of the so-formed pellets can be adjusted based on the process conditions for tumbling, such as rotation speed, moisture content, impact force and residence time. The pellets could also be screened and/or recycled during or after pelletising to produce a desired, e.g. narrower, size distribution.

Preferably, the process is adapted to provide pellets of a variable size distribution.

One suitable apparatus for providing tumbling action is a rotary drum. Rotary drums are well known in the art. Their output can be dependent upon the length, diameter, speed of rotation and angle of mounting of the drum, and the output can vary from single figure tonnes per hour, to hundreds of tonnes per hour per drum.

The general sizes and dimensions of agglomerator drums, such as pan, rotary and conical drums, are known in the art, as are their process variations to provide variation in the products formed. See for example UK Patent No 787993.

Rotary drums have low capital and low operating costs, especially in comparison with briqueting plants. They can even be provided in mobile form, such that the process of the present invention can be provided where desired or necessary, e.g. moved and located to where the material(s) are currently stored or 'dumped', rather than requiring significant movement (and therefore cost) for transporting the material(s) to a fixed processing site.

The agglomeration action may be carried out in one or more stages, which stages could be connected, such as the tumbling conditions changing in the same drum, or the material(s) being fed directly into another agglomerator. Or, such actions could be separate. In one arrangement for multi-stage agglomeration, the tumbling conditions are variable or varied for each stage. The conditions may be altered either in a continuous manner or action, or discretely.

Where the process of the present invention involves tumbling the mixture in a rotary drum, one or more rotary drums may be used for the agglomeration, preferably in series.

In an embodiment of the present invention, the process comprises the addition of water to assist the agglomeration of the components. Optionally, the water is admixed with the binder to provide a single liquid component prior to admixture with the biomaterial or particulate carbon- based material.

The amount of water needed or desired for the process of the present invention may depend upon the nature of the biomaterial or particulate carbon-based material and the binder. For example, use of a relatively high water-content biomass material reduces the amount of any additional water required to achieve agglomeration.

In a preferred embodiment of the present invention, the amount of water for the process is adjusted with the amount of binder prior to its admixing with the biomaterial and the particulate carbon-based material. The calculation of this binder to water adjustment is dependent on the moisture content of the biomaterial, and the usually separate water content of the particulate carbon-based material.

For example, where binder is added in the range 1-10 wt% of each of the biomass material and the particulate carbon-based material, water could be added thereto to provide a combined liquid component in the range 10- 40 wt%, usually in the range 15-35 wt% or 20-30 wt%, of each of the biomass material and the particulate carbon-based material added.

The process of the present invention may be carried out as a single or multi-staged process. The process may be continuous or having one or more discrete steps or stages, and may be provided in the same or different locations.

By way of example only, a first stage of the process could be the formation of the core pellets from either the biomass material or the particulate carbon-based material with a binder. The core pellets are formed by tumbling, and may be immediately useable in the next step or stage of the process, or they may be left for a time to cure naturally and at ambient temperature to provide more rigid core pellets. Curing of the core pellets may also start during or be part of the agglomeration action.

Curing of the core pellets can occur at ambient temperature, and can also occur without any active and/or separate curing step, especially a heat treatment step. The core pellets may further cure over time without any external influence. Thus, they could be allowed to stand (being stationary and/or moving) for a time, such as 1-10 days, optionally at least 3, 4, 5 or 6 days, in or at a suitable position or location, after the tumbling.

The core pellets, either directly or after any further curing, have sufficient strength to be relocatable, such as transportable, to one or more further locations for subsequent use. For example, where the source of the particulate carbon-based material is different to that of the biomass material, the core pellets could be formed in a first location and then transported or otherwise relocated to the location of the particulate carbon- based material for forming into the final pellets. In this way, the particulate carbon-based material (or one component thereof), many of which are commonly not easily transportable materials anyway, does not need to be transported to the biomass material, and vice versa.

The time required for relocating the core pellets may at least partly provide the post-agglomerating curing time required or desired prior to their subsequent use.

Once the core pellets are ready for subsequent use, the core pellets are further admixed with the other of the biomass material and the particulate carbon-based material, and binder, as part of the process of agglomerating the second so-formed mixture around the core pellets by tumbling at ambient temperature to form the layered rigid pellets. The second agglomerating preferably occurs by the tumbling of all the components together.

The final layered rigid pellets then cure naturally and at ambient temperature to provide the final form of the layered rigid pellets.

The final pellets could be allowed to stand, for example, for some time, such as 1 -10 days, optionally at least 3, 4, 5 or 6 days, at a suitable position or location, whilst curing occurs after the tumbling. Like concrete, curing may continue for some time, for example over several days, but the invention provides layered rigid fuel pellets with sufficient solidity after tumbling, that they are ready to be incinerated, stored, stacked, transported etc as they cure after forming.

In one embodiment, the layered rigid pellet may have two layers, an interior core layer comprising of a biomass material and a binder and a surrounding exterior layer comprising a particulate carbon-based material and a binder. In an alternative embodiment, the layered rigid pellet may have two layers, an inner core layer comprising of a particulate carbon-

based material and a binder and a surrounding outer layer comprising a biomass material and a binder.

The layered rigid pellet may have a plurality of layers comprising of alternative layers of biomass material or a particulate carbon-based material with a binder such as 3, 4, 5 or 6 layers. Each layer of biomass material may comprise one or more types of biomass material and each layer of particulate carbon-based material may comprise of one or more types of particulate carbon-based material.

More preferably, the interior of each layer of the layered rigid fuel pellet, that is, the layer(s) comprising biomass material and the layer(s) comprising particulate carbon-based material is dry and wholly or substantially has a small, preferably micro, aerated or porous form. That is, the action of the surfactant(s) serves to draw the silicate-based binder towards the surface of the forming pellets, creating air pockets and bubbles in the interior and as they are created and start to cure, the pellets will form and then continue to have a harder outer portion, skin, shell or surface, compared to their interior. Thus, the 'shell' or outer portion of each layer will generally have a high density in comparison with the lower density of the 'interior' of each layer.

Preferably the process is adapted to provide pellets of a variable size distribution. The layered rigid pellets formed by the present invention can be of any suitable size or dimension, including below 1 mm and above 10cm. Preferably, they are generally in the range of greater than 5mm, optionally up to 2 -5cm.

The present invention is particularly advantageous because of the use of two or more different materials such as wood and coal having different

burn characteristics in a layered form. For example, it is known that the rate of burning of wood is higher than that of coal, such that the design of a wood burner is different to that of a coal burner. However, the present invention allows the combination of biomass material and particulate carbon-based material having different burn characteristics to be combined to provide layered rigid fuel pellets having a bespoke burn characteristic, which can be then be used in existing or conventional coal burners. This removes the conventional requirement and cost of having to interchange or install a new burner for a biomass-including fuel.

In particular, the present invention provides a method of balancing the relatively different, often very different, volatiles and carbon contents of biomass materials and particulate carbon-based materials. For example, biomass materials such as spent mushroom compost or wood fines have a relatively high volatiles content, which provides fast but short heat, and a relatively low carbon content. Particulate carbon-based materials such as coal dust generally have a low volatiles content, but a high carbon content for slow burning, which provides very different burn characteristics than biomass materials.

It is a particular advantage of the present invention that the burn characteristics the volatiles and carbon contents of such different materials can be combined to provide a better match and/or customised balance, which can be adjusted according to the types and amounts of biomass material and particulate carbon-based material to be used or which are available. For example, it is possible by the present invention to increase the burn temperature of the volatiles in the biomass material above their normal temperature, and to a temperature better matched to the burn temperature of the carbon content of the particulate carbon-based material.

The man skilled in the art will be aware of the different burn characteristics of various biomass materials and particulate carbon-based materials, and so their combined burn characteristic, based on different ratios.

The present invention therefore also provides a layered fuel pellet having a calculated or customised burn characteristic, which can help to overcome the problems of control of boiler temperatures, flashovers, water flow temperatures, optimum start strategies, and maintenance intervals, which can arise when co-firing two materials having different burn characteristics.

The process may include the addition of one or more further components. Preferably, the or each further component is selected from the group comprising: lime, inorganic binders and waterproofing additives.

The process may include the addition of one or more further components into the mixture, either separately or integrally with the binder. A cementitious material can assist in the green-strength of the pellets, and possibly in forming the hardened outer surface or shell for the pellets as described hereinafter.

Lime helps to inhibit sulphur emission upon burning of the so-formed pellets. It is a particular advantage of the present invention that the use of lime or other types of calcium hydroxide (which are known to be sulphur- absorbing agents) are admixed with the particulate carbon-based material. The increased mixing of such sulphur-absorbing agents with sulphur- containing carbon-based materials reduces the need for current sulphur- absorbing apparatus such as scrubbers and the like at the end of fuel- burning process. Indeed, it is considered that the present invention can

achieve a reduction of sulphur emission (usually in the form of sulphur dioxide) by 70-90%, or possibly more. Again, this is a significant reduction in current power station requirements, and therefore costs.

One or more other mineral additives such as zeolites could also be used as a further ingredient to help bind any metallic contaminants to the resultant ash of the pellets, and so prevent any soluble metals being released during combustion.

The process of the present invention may include one or more sizing steps. That is, to grade the size of the so-formed layered rigid fuel pellets to that desired or necessary. This could include extracting those pellets which are damaged or undersized, which pellet material could be recycled back into the process of the present invention.

The process of the present invention can further include the step of grinding, crushing or otherwise particularising the pellets, preferably in a form ready to use in a fuel-burning power plant.

A further advantage of present invention is that by using fuel pellets comprising a combination of biomaterial and a particulate carbon-based material, there is a direct reduction in CO ₂ emissions compared with using only carbon-based material as long as it is carbon neutral. Biomass material also contains less nitrogen thus the layered fuel pellet of the present invention also leads to lower NOx emissions.

In a second aspect of the invention, there is provided a process for producing rigid fuel pellets comprising:

a biomass material

a particulate carbon-based material, and a silicate-based binder,

the process comprising at least the following steps:

admixing the biomass material and the particulate carbon-based material with the binder; and agglomerating the so-formed mixture by tumbling at ambient temperature to form the pellets.

In a third aspect of the present invention, there is provided a fuel pellet having a core formed of an agglomerated material comprising one of a biomass material and a particulate carbon-based material admixed with a silicate-based binder, and an outer layer formed of an agglomerated material comprising the other of a biomass material and a particulate carbon-based material admixed with a silicate-based binder.

In a further aspect of the present invention, there is provided a fuel pellet whenever formed by a process as described within. In this way, there can be provided layered rigid fuel pellets formable at ambient temperature by agglomeration using a silicate-based binder, optionally including one or more surfactants.

Preferably, the fuel pellet is ready for combustion.

In one embodiment, the pellet includes one or more sulphur-absorbing agents.

Preferably, the fuel pellet has a hardened shell.

In one preferred embodiment, the fuel pellet at least comprises a core with a first density and an outer layer with a second different density core.

Suitably the fuel pellet has a dry interior.

The fuel pellet has sufficient rigidity after tumbling to allow handling, stacking and/or transportation without any significant breakage.

The fuel pellet may be wholly or substantially combustible, so as to leave little or no combustible fuel in the ash.

Once the rigid fuel pellets have been formed, their hardened shell wholly or substantially stops or significantly reduces water ingress, especially if waterproofing additives are used. Once fully cured, the pellets can have a moisture content of at least half that of the particulate starting material, and possibly less than 5%, and thus be sufficiently dry for immediate and easy grinding to form a suitable fuel product for a power station or incinerator.

Thus, in one embodiment, the moisture in the pellet is substantially less than the moisture in the particulate carbon-based material. More preferably, the pellet has a moisture content of < 5%.

The fuel pellet of the present invention is a material which is easily storable. It is also easily transportable due to its variable diameter distribution. This enhances stacking concentration, which also reduces abrasion and consequential breakage of the pellets.

The pellet preferably allows a very high percentage of combustion (possibly 100% combustion), so as to leave little or no combustible fuel in the ash.

Preferred features of each aspect of the invention are as for each of the other aspects mutatis mutandis.

Embodiments of the present invention will now be described by way of example only, and with reference to the accompanying drawings in which:

Figure 1 is a flow diagram of a process according to one embodiment of the present invention in the context of the material handling and production stages in an industrial plant;

Figure 2 is a front view of tumbling action of agglomerating pellets according to the present invention;

Figure 3 is a view of a number of pellets according to another embodiment of the present invention;

Referring to the drawings, Figure 1 shows a flow chart based on the use of a 'first solid feed' being one of the biomass material and the particulate carbon-based, and a second solid feed being the other of the biomass material and the particulate carbon-based. Figure 1 also shows the use of a 'first liquid feed' being a binder as hereindescribed, and a second liquid feed being the same or a different binder to the first liquid feed.

The 1 ^st agglomeration provides the core pellets for use in the 2 ^nd agglomeration, optionally in the same or different locations, and with variable time periods thereinbetween.

The present invention is usable with all types of biomass and particulate carbon-based materials, which will have a varying amount of moisture and sulphur content. Generally, pellets ranging from 5-50 mm diameter are formed, which sized pellets are easily handable, storable, transportable and then burnable, and, if required, in an optimal form and size for grinding prior to burning.

The present invention provides a simple but efficient process for combining renewable energy sources such as biomass material and waste organic carbon-based materials such as coal fines, and forming a useable fuel product, which is easily transportable and efficiently combustible. The process creates a "hybrid" product when burnt, has a direct reduction in CO2 and NOx emissions and compared with using only carbon-based material only. In addition, the present invention is particularly advantageous because the use of two or more different materials having different burn characteristics provided in a layered form provides customised fuel pellets having a pre-determined rate and/or heat of burning. Rotating drum or pan agglomerators are relatively low cost to build, and are capable of very high tonnage throughputs.

Low technology applications in countries where there is little investment for efficient biomass process plants can also easily utilise the present invention, therefore allowing the provision of high efficiency, environmentally friendly and cost effective process plants to be manufactured and operated. In such places, any materials not immediately useable such as animal by products, biomass or coal fines are currently treated as waste and simply stockpiled in bigger and bigger piles, increasing the environmental hazard thereof.