BACKGROUND Raw biomass contains useful calorific materials but also many non-calorific materials such as water, carbon dioxide and nitrogen which have undesirable effects on the thermo-chemical conversion process. Consequently, it is of low energy density, low calorific value, low ignitability and low conductivity. Due to the low energy density, the use of biomass as a fuel is associated with high transport costs.

The biomass may also decompose upon storage.

In addition, large equipment is required to combust it effectively and it bums with low efficiency as a longer time is needed for reaction causing energy loss through heat transfer.

Methods of improving biomass as a fuel are known in the art. Examples of such methods are drying and compression, tolTefaction, carbonization, gasification and extraction of pyrolysis oil.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a process for making a solid fuel from biomass comprising the steps of heating the biomass to convert it to a solid phase, liquid phase and gaseous phase, separating the phases and recombining the solid phase and combustible liquid phase optionally together with the combustible gaseous phase to form a solid fuel material.

The invention also provides a solid fuel produced by the process of the invention.

The invention also provides a solid fuel material comprising an absorbent carbon substrate onto or into which is absorbed or adsorbed a combustible liquid derived fi-om heating biomass.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the reaction process of the invention DETAILED DESCRIPTION OF THE INVENTION By the invention, biomass is converted into a solid material, generally having the characteristics of activated carbon. The gaseous and liquid components of the biomass are separated fiom the residual activated carbon by heating. The liquid combustible material is then further separated from the liquid non-combustible material and similarly the gaseous products are separated into combustible and non- combustible phases. The liquid combustible material is then forced back into the activated carbon optionally along with the gaseous combustible material.

The starting material for the process of the invention is biomass which can be any carbonaceous raw material such as waste wood, bark, saw dust, wood chips, wood shavings and agricultural waste materials. Preferably the biomass is waste wood.

The biomass is first converted into particulate matter such as by grinding. The smaller the particles the more readily the liquid and gases can be removed during the process. The biomass in particulate form is then fed by a suitable feed system into the separator. In the separator the biomass is heated in the absence of oxygen. The heating is conducted at a temperate and for a time to generally produce three components, gases, liquids and the residual solid materials. The residual solids will generally also contain high molecular weight tars and that together with the residual solid materials forms a slurry which is then fed into the reactor for later processing.

The pyrolysis oil removed in the separator is ultimately designed to be added back into the solid material in the reactor to form the final product. Hence processing of the biomass in the separator is designed to maximise the production of pyrolysis oil.

The gaseous products produced in the separator will be those either trapped in the biomass or are produced by degradation of the biomass on heating. These gaseous products include steam, methane, hydrogen, carbon monoxide and carbon dioxide, nitrogen and other volatiles (VOC). The gaseous products are fed through a condensation chamber where water is condensed while the other gaseous can vented off to atmosphere, or more preferably the combustible materials are recovered either for use as energy sources or fed back into the final product.

The separator will be a chamber in which the biomass is subjected to controlled heating in the absence of oxygen. The ambient atmosphere in the chamber can hence be a non-oxygen gas such as nitrogen. Desirably the atmosphere can be created by the exhaust gases from the reactor which will be generally fully oxidised VOC, carbon dioxide, water and nitrogen. These exhaust gases are at a high temperature and thus can be used as part of the heating energy in the separator chamber, for example through a suitable heat exchanger.

The heating process in the separator is conducted in a humid environment which tends to minimise the breakdown of the desirable pyrolysis oil product. The temperature is generally below 450 C. Desirably there is a temperature gradient from the lower part of the separator to the top. A suitable system is to have an inlet temperature of about 100 C and a temperature at the upper part of the separator of about 450 C.

The biomass progresses up the separator by a suitable conveyor means such as a screw conveyor.

The biomass is heated in the separator is for a time sufficient to convert the biomass into the gaseous, liquid and solid components. The heating process time does depend on the particle size of the biomass with larger particles taking longer to separate into their component parts than smaller particles. The gases are vented out the top of the separator, the liquid bio oil separates such as through a cylindrical separator and is then forced into the final product as discussed below. The tar slurries containing the residual solid material is fed into the reactor.

In the separator, the pressure can be controlled by a valve controlling the release of the gaseous materials from the upper part of the separator. It will usually be between 1 bar and 300 bar. Higher pressures speed up the process.

In the reactor the tar sluiri. es undergo carbonisation in the presence of steam to create an activated carbon material which has a highly porous structure. The process is designed to produce activated carbon of a highly absorbent character. The heating is designed to avoid loss of the solid materials other than the carbon materials. The combustible gases which are generated can be recovered and burnt to be used as a heat source in the overall process or fed into the final product. The non-combustible gases can be fed back to the separator as described above.

The steam fed into the reactor can be derived from that generated in the separator through a suitable pressure control valve as shown. Supplemental steam can be added if necessary.

An air blower is present to provide sufficient air to combine with the fuel for heating the reactor.

The activated carbon from the reactor after cooling (if necessary through a suitable heat exchanger) is then the base material for absorption of the bio oil.

The separator can for example be at least two metres high and be constructed of a suitable non-corrosive material such as stainless stain suitably insulated against heat loss.

The bio oil recovered from the separator will be a mixture of organic substances the components of which will be dependent on the biomass source. The bio oil can for example include carboxylic acids, alcohols, aldehydes, ketones, sugars, eugenols, guaiacols, hydroxyacetaldehyde, leveoglucasan, syringols, furans mixed oxygenates, phenols and their derivates.

In the final step of the process, the activated carbon from the reactor is contacted with the pyrolysis oil from the separator. The degree of absorption of the pyrolysis oil by the activated carbon can be enhanced by pressure. Moreover volatile gas recovered from the process either in the gaseous state or in a condensed form will also be absorbed readily by the activated carbon and retained in the pores of that product. Again the degree of absorption of the gases can be enhanced by pressure.

The final product has then a higher calorific value per kilogram than. the starting biomass with a density greater than the activated carbon because the density of the pyrolysis oil is usually about 1200 kg per cubic metre. Activated carbon density is usually about 600 to 1100 kg per cubic metre. The pyrolysis oil will have a significantly higher combustion rate than the activated carbon and as well contributes to its ignitability and better thermal conductivity.

The process of the invention may be a continuous process or batch process. The separation process can take place at any pressure from 1 bar to 300 bar with higher pressures speeding up the process. In a continuous process lower pressures are required. A batch process does permit higher pressures to be used.

Hence by the invention a solid fuel product is produced by biomass which has improved use as a fuel in both industrial and domestic situations.

The following Example illustrates the process of the invention.

Example 10 kg of wood chips is first ground into a particle size of about 3 by lcm. They are then fed into a 2 meter high separator chamber at a temperature progressing from 100 degrees celsius at the inlet to 450 degree celsius at the outlet in an atmosphere of primarily nitrogen, steam and carbon dioxide (and with the exclusion of oxygen) at a pressure of 1 bar. The residence time is approximately 30 minutes. The higher the pressure applied, the shorter the time is needed for the Bio oil to be separated.

Bio oil is separated through the holes on the screw and wall. About 1.5 kg of Bio oil are extracted. The yield can be higher by increasing the pressure and the residence time but more energy is then needed for the separation. So the operating pressure and residence time is selected to achieve the best balance between yield and energy consumption. 6 kg of hot char slurries remain. The loss of 2.5 kg in weight are the transformation to steam and gases (nitrogen, carbon dioxide and small amount of VOC). At this separation process, gasefication are preferred to be minimised. The char slurries are fed into the reactor by a screw conveyor and is heated at a temperature of 800 degrees celcius for 10 minutes with steam and oxygen channeled from the blower. Oxygen is present to assist in the reaction with the VOC (CH4, H2 and CO) from the char. 2 kg of activated carbon is then recovered and transferred to the final stage. The final product yield 1. 5kg of bio oil absorbed by 2 kg of activated carbon.

While the invention has been described with reference to preferred embodiments, it is not to be construed as being limited thereto. Moreover where specific steps or materials have been referred to, and equivalents are known to exist thereto, such equivalents are incorporated herein as if specifically set forth.