Title: Bed materials for fluidised bed reaction methods and fluidised bed reaction methods

Description of Invention

The present invention relates to bed materials for fluidised bed reaction methods. The present invention also relates to fluidised bed reaction methods. Combustion is the high-temperature exothermic reaction between a fuel and an oxidant. Gasification is a method that converts organic (for example biomass) or fossil fuel based carbonaceous materials (fuels) into carbon monoxide, hydrogen and/or carbon dioxide. Fluidised bed combustion and fluidised bed gasification are both fluidised bed reaction methods. Combustion and gasification can be considered oxidation methods in the sense that the fuel is oxidised in both cases.

Fluidised bed technology is used in the combustion and gasification of fuels. In fluidised bed combustion, particles of fuel are suspended in a bed of particulate materials (for example ash, sand and/or limestone). Jets of oxygenated gas (for example air or oxygen depleted air) are blown through the bed to provide the oxygen required for the combustion of the fuel. In some examples, fluidised bed combustion occurs at a temperature of combustion of from 750 to 850°C. Fluidised bed combustion can occur at different temperatures, depending on the reactor design and the fuel.

Similarly, in fluidised bed gasification, particles of fuel are suspended in a bed of particulate materials (for example ash, sand and/or limestone). Jets of oxygenated gas (for example air) and/or steam are blown through the bed to effect gasification of the fuel. One difference between fluidised bed

combustion and fluidised bed gasification is the amount of oxygen in the gas. Generally, less oxygen is required for fluidised bed gasification because the amount of oxidation of the fuel in gasification is less than in fluidised bed combustion. Another difference between fluidised bed combustion and fluidised bed gasification is the temperature of the fluidised bed; combustion utilises higher temperatures than gasification, for any particular fuel. In some examples, fluidised bed gasification occurs at temperature of gasification of from 650 to 749°C. Fluidised bed gasification can occur at different

temperatures, depending on the reactor design and the fuel. Fluidised bed combustion is an increasingly common source of energy because fluidised bed combustion can be used to burn fuels which prove difficult to burn using other technologies. Furthermore, SO _x emissions can be precipitated out using limestone in a fluidised bed. Fluidised bed combustion releases lower levels of NO _x emissions than other combustion methods because the temperatures of combustion are relatively low.

A fluidised bed, used in either fluidised bed combustion or fluidised bed gasification, can be formed by introducing pressurised gas (pressurised higher than atmospheric pressure) through a bed material. The bed material is formed of a plurality of solid particles. The solid particles are typically formed of ash, sand and/or limestone. A fluidised bed consists of a gas-solid mixture (the gas being the pressurised gas; the solid being the solid particles) that exhibits fluid-like properties. A fluidised bed can be considered a

heterogeneous mixture of gas and solid.

A fluidised bed can be used to promote contact between gases and solids and enhance reactions between gases and solids.

There is a need to further increase the efficiency of fluidised bed combustion and fluidised bed gasification. According to one aspect of the present invention, there is provided a particle for a fluidised bed reaction method, the particle comprising:

a bed material; and,

a catalyst.

Preferably, wherein the particle consists essentially of:

a bed material; and,

a catalyst;

wherein the bed material and the catalyst combined make up at least 98% of the particle by weight, the balance being unavoidable impurities.

Further preferably, consisting of:

a bed material; and,

a catalyst.

Advantageously, wherein the bed material is any one or more of: ash, sand (optionally quartz sand or feldspatic sand), olivine, limestone, ilmenite, feldspar, crushed ceramics, calcined bauxite, Chamotte and/or calcined clays. Preferably, wherein the bed material is Chamotte.

Further preferably, wherein the catalyst is any one or more of: nickel-chromium (optionally forms of olivine which include both nickel and chromium or compounds of the formula Ni _2- xCr _x AI ₃ where x = 0.07 or 0.1 1 ), iron (metallic Fe), iron oxides (optionally FeO, Fe ₃ O ₄ , Fe ₄ O ₅ , Fe ₅ O ₆ , Fe ₅ O ₇ or Fe ₂ O ₃ ), FeTiO3 (ilmenite), NiO, CaO, CaCO3, Na2CO3, K2CO3, nickel enriched olivine, olivine and/or CuO.

Advantageously, wherein the catalyst is any one or more of: elements from groups 1 or 2 of the periodic table; and/or mixtures and/or alloys from any one, two or three of groups 1 , 2 and/or 3 of the periodic table; optionally selected from: Group 1 : Ti, V, Cr, Mo, Fe

Group 2: Ni, Co, Mn, Cu

Group 3: CaO, MgO, ZnO. Preferably, wherein the catalyst is: a mixture of Ni and Cr; or, a mixture of Ni, Cr and ZnO.

Further preferably, wherein the particle has a particle size of: from 100 μιτι to 2mm; or, from 250 μιτι to 1 .5 mm; or, from 250 μιτι to 500 μιτι; or, from 0.5 mm to 1 .5 mm; or, from 0.2 mm to 0.6 mm.

Advantageously, wherein the catalyst, within the particles comprising a bed material and a catalyst, is formed of catalyst particles with a particle size of: 250 μιτι or lower; or, 100 μιτι or lower; or, 50 μιτι or lower; or, from 0.1 μιτι to 50 μηη.

Preferably, wherein the particle size is the maximum dimension of the particle.

Further preferably, wherein the particle size is measured on a Malvern™ Mastersizer 3000.

Advantageously, wherein the particle comprises, consists essentially of or consists of:

from 50% catalyst to 1 % catalyst (by weight); or from 30% catalyst to 5% catalyst (by weight); or from 20% catalyst to 5% catalyst (by weight); or from 10% catalyst to 5% catalyst (by weight); or from 30% catalyst to 8% catalyst (by weight).

Preferably, wherein the balance is the bed material and, optionally, unavoidable impurities.

Further preferably, wherein the particle is refractory. Advantageously, wherein the particle is refractory because it is stable up to at least 1 ,100°C. Preferably, wherein the particle has a Mohs hardness of at least 6.

According to one aspect of the present invention, there is provided a method of forming a particle for a fluidised bed reaction method, the particle comprising: a bed material; and, a catalyst;

the method comprising the steps of:

mixing a bed material and a catalyst; and,

calcining the mixture of a bed material and a catalyst.

Preferably, the method comprising the steps of:

mixing a bed material and a catalyst; and,

calcining the mixture of a bed material and a catalyst.

Further preferably, wherein the step of calcining occurs at: from 1 ,200°C to 1 ,675°C; or, from 1 ,550°C to 1 ,675°C; optionally, at 1 ,600°C.

Advantageously, wherein the step of calcining occurs:

for from 4 hours to 6 hours; optionally, for 5 hours; or,

as flash calcination for from 5 seconds to 10 minutes. Preferably, wherein after the step of calcining, the product is ground and/or sieved.

Further preferably, wherein the product is ground and/or sieved into particles with particle sizes of: from 100 μιτι to 2mm; or, from 250 μιτι to 1 .5 mm; or, from 250 μιτι to 500 μιτι; or, from 0.5 mm to 1 .5 mm; or, from 0.2 mm to 0.6 mm. According to one aspect of the present invention, there is provided a particle obtained by a method as described above.

According to one aspect of the present invention, there is provided a particle obtainable by the method as described above.

According to one aspect of the present invention, there is provided a plurality of particles, the plurality of particles comprising a plurality of particles according to the above particles.

Preferably, wherein the plurality of particles consists of a plurality of particles according to the above particles.

According to one aspect of the present invention, there is provided a method of oxidising fuel in a fluidised bed, the method comprising the steps of:

adding particles according to the above particles, to a fluidised bed reactor, wherein the particles are capable of forming a fluidised bed;

adding fuel to the fluidised bed reactor;

forming a fluidised bed by applying gas to the mixture of particles and fuel; and,

applying heat to oxidise the fuel.

Preferably, wherein the method of oxidising fuel is a method of fluidised bed combustion or fluidised bed gasification.

Further preferably, wherein the fuel is added over time.

Advantageously, wherein the fuel is any one or more of: fossil fuels (for example coal, peat or natural gas); wood (for example untreated wood, treated wood, recycled wood or wood pellets); char; torrefied biomass; energy crops (for example Miscanthus, Switchgrass, Giant Reed, Reed Canary Grass, Cardoon, Willow, Poplar or Eucalyptus); animal manure (for example cow, horse, pig or poultry manure); organic residues/products (for example agricultural waste, horticultural waste, bagasse, black liquor, food industry products, food industry waste, grain, meal, organic domestic waste, paper, paper pulp, slaughterhouse residue, textile waste or organic residue); municipal solid waste; refuse-derived fuel; plastic; sludge (for example drainage culvert, food industry sludge, paper sludge or sewage); straw (for example stalk, cob or ear straw); a mixture of virgin wood (90% by weight) and grass (10% by weight); or any combination of any one, two, three, four, five, six, seven, eight, nine, ten or more of these fuels.

Preferably, wherein the gas is an oxidising gas; optionally, wherein the gas comprises oxygen; and/or wherein the gas is any one or more of air, steam or a mixture of air and steam; and/or, wherein the gas is at atmospheric pressure (101 ,325 Pa) or at a pressure higher than atmospheric pressure.

Further preferably, wherein the heat of the method of oxidising fuel is: from 100 to 1 ,000°C; or, from 200 to 900°C; or, from 500 to 850°C; or, from 750 to 850°C; or, from 650 to 750°C. Advantageously, wherein the fuel is a mixture of wood (90% by weight) and straw (10% by weight).

Embodiments of the invention are described below with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a fluidised bed reactor, which can be used in either fluidised bed combustion or fluidised bed gasification.

Some of the terms used to describe the present invention are set out below:

"Fluidised bed combustion" refers to the combustion of fuel, typically solid fuel, in a hot, bubbling bed, or circulating bed, of bed materials. "Fluidised bed gasification" refers to the gasification of fuel, typically solid fuel, (forming carbon monoxide, hydrogen and carbon dioxide) in a hot, bubbling bed, or circulating bed, of bed materials.

"Fluidised bed reactor" refers to a reactor that can be used in fluidised bed combustion and/or fluidised bed gasification methods. Typically, fluidised bed reactors are lined with a ceramic material. Examples of suitable ceramic materials include C71 refractories according to the ASTM standard ("non- metallic materials having those chemical and physical properties to make them applicable for structures, or as components of systems, that are exposed to environments above 538°C": see "Circulating Fluidized Bed Boilers: Design, Operation and Maintenance", Prabir Basu, Springer, 2015, the contents of which are hereby incorporated by reference). Bench scale fluidised bed reactors typically generate power of from 2kW to 10kW. Industrial fluidised bed reactors typically generate power of from 18MW to 50MW. Industrial circulating fluidised bed reactors typically generate power of from 30MW to 100MW. "Fuel" refers to a material that can react with other materials to release chemical energy as heat through oxidation of the fuel. Non-limiting examples of fuel include: fossil fuels (for example coal, peat or natural gas); wood (for example untreated wood, treated wood, recycled wood or wood pellets); char; torrefied biomass; energy crops (for example Miscanthus, Switchgrass, Giant Reed, Reed Canary Grass, Cardoon, Willow, Poplar or Eucalyptus); animal manure (for example cow, horse, pig or poultry manure); organic

residues/products (for example agricultural waste, horticultural waste, bagasse, black liquor, food industry products, food industry waste, grain, meal, organic domestic waste, paper, paper pulp, slaughterhouse residue, textile waste or organic residue); municipal solid waste; refuse-derived fuel; plastic; sludge (for example drainage culvert, food industry sludge, paper sludge or sewage); straw (for example stalk, cob or ear straw); a mixture of virgin wood (90% by weight) and grass (10% by weight); or any combination of any one, two, three, four, five, six, seven, eight, nine, ten or more of these examples of fuel. "Bed materials" refers to the materials making up the bed in a fluidised bed reactor. Bed materials are typically solid particulate materials. Examples of known bed materials include ash, sand (for example quartz sand or feldspatic sand), olivine, limestone, ilmenite, feldspar, crushed ceramics, calcined bauxite, Chamotte and calcined clays. Bed materials are typically inert but can agglomerate with fuel ash under high temperatures and/or pressures.

"Catalyst" refers to a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Examples of catalysts used to catalyse oxidation of fuel in fluidised bed combustion or fluidised bed gasification include metals, metal oxides and metal carbonates. Particular examples of catalysts used to catalyse oxidation in fluidised bed combustion or fluidised bed gasification include: nickel-chromium (for example particular forms of olivine which include both nickel and chromium or compounds of the formula Ni _2- xCr _x Al3 where x = 0.07 or 0.1 1 ), iron (metallic Fe), iron oxides (for example FeO, Fe ₃ O ₄ , Fe ₄ O ₅ , Fe ₅ O ₆ , Fe ₅ O ₇ or Fe ₂ O ₃ ), FeTiO ₃ (ilmenite), NiO, CaO, CaCO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , nickel enriched olivine, olivine and CuO.

"Chamotte", sometimes referred to as grog or firesand, refers to a ceramic raw material. Chamotte has a high percentage of silica and alumina, with 95% of the total mass of Chamotte being either silica (SiO ₂ ) or alumina (AI ₂ O ₃ ), in different proportions. Chamotte can be produced by heating fire clay to high temperature (typically greater than 1500°C) before grinding and screening to different particle sizes.

"Particle size" refers to the maximum dimension of a particle. In the example of generally spherical particles, particle size refers to the diameter of the particles. Particle size is measured by whether the particles fit through a suitably sized filter, for example particles of 250 μιτι or lower fit through a filter with a mesh size of 250 μιτι. Alternatively or additionally, particle size can be measured by laser diffraction (for example using a Malvern™ Mastersizer 3000). In some examples, particles of the presently claimed invention have a particle size of: from 100 μιτι to 2mm; or, from 250 μιτι to 1 .5 mm; or, from 250 μιτι to 500 μιτι; or, from 0.5 mm to 1 .5 mm; or, from 0.2 mm to 0.6 mm.

Figure 1 is a schematic diagram of a fluidised bed reactor 1 , which can be used in either fluidised bed combustion or fluidised bed gasification. In the fluidised bed reactor 1 of Figure 1 , there is an input 2 for solid materials 7 and an input 3 for gas materials 6. The solid materials 7 sit on a porous plate 4, sometimes referred to as a distributor. The gas materials 6 enter the reactor 1 though the input 3 and then through the porous plate 4, in an upwards direction as shown schematically by arrow 5.

The solid materials 7 are illustrated schematically by the circles 7; this is a simplification, there are in fact many millions of particles of solid material in a charged fluidised bed reactor. The gas materials 6 are illustrated

schematically by the diamonds 6; this is a simplification, there are in fact many millions of particles and/or bubbles of gas material (formed of gas molecules) in an active fluidised bed reactor.

The gas materials 6 are forced into the input 3 and then through the porous plate 4. At lower gas velocities, the solid materials 7 remain in place as the gas materials 6 pass through the voids between the solid materials 7 (the fluidised bed reactor at this stage is sometimes called a packed bed reactor). As the gas velocity is increased, the reactor 1 reaches a stage where the force of the gas materials 6 on the solid materials 7 balances the weight of the solid materials 7 (this stage is sometimes called incipient fluidisation). As the gas velocity is increased further, the solid materials 7 act like a fluid, for example like water in a boiling receptacle of water (the bed in the fluidised bed reactor at this stage is now called a fluidised bed).

The above description relates to a bubbling bed reactor. Alternatively, with a circulating fluidised bed, as the gas velocity is increased, the solid materials 7 travel with the gas materials 6 to the top of reactor 1 . The solid materials 7 reach a stage where their weight is greater than the force of the gas materials 6 and the solid materials 7 fall back down into the bed of solid materials 7. With reference to Figure 1 , solid materials 7 are introduced through input 2. Typical examples of solid materials 7 added to a fluidised bed reactor for fluidised bed combustion or fluidised bed gasification include bed materials. Fuel is also introduced through input 2, either in one shot or in a number of shots over time as the fuel is depleted.

Gas materials 6 are introduced through input 3. Typical examples of gas materials 6 include air (in the case of fluidised bed combustion) and steam optionally mixed with air (in the case of fluidised bed gasification). Waste gas materials are taken out of the reactor 1 through output (flue) 8. Some components of the waste gas materials can be used in refining processes, particularly in the case of waste gas materials from fluidised bed gasification. Waste solid materials are taken out of the reactor 1 through output 9, or through other outputs (not shown).

According to the present invention, the solid materials 7 include particles comprising a bed material and a catalyst. Non-limiting examples of catalysts, which can be added to a fluidised bed reactor in particles comprising a bed material and a catalyst, and some reactions they catalyse in fluidised bed reactors include:

1 . Gaseous hydrocarbons and superheated steam over a nickel- chromium catalyst (for example particular forms of olivine which include both nickel and chromium or compounds of the formula Ni _2- xCr _x AI ₃ where x = 0.07 or 0.1 1 ) react to produce carbon monoxide and hydrogen according to reaction 1 :

C _n H _m + nH ₂ O -> nCO + (2n+m)/2 H ₂ (Reaction 1 )

Without catalyst some of the hydrocarbons could not react or will only partially react in a fluidised bed reactor. Here, the nickel-chromium catalyst increases the reaction rate and prevents emission of unburned hydrocarbons.

2. The gaseous mixture containing carbon monoxide, obtained from biomass containing an excess of steam, over an iron catalyst (for example iron metal or an iron oxide), reacts according to reaction 2:

CO + H ₂ O -> CO ₂ + H ₂ (Reaction

Here the iron catalyst shifts the CO/H ₂ equilibrium in the favor of hydrogen gas. Hydrogen gas is a preferable product because it can be used as a fuel in other methods.

Reactions 1 and 2, above, do occur in combustion and gasification. In combustion, the gases will combust in the fluidised bed reactor. In

gasification, the produced gases can be removed from the reactor and used in further methods. Another catalyst, and a reaction that it catalyses in a fluidised bed reactor, is:

3. Ilmenite (FeTiOs). These reactions are shown in Reactions 3(1 ), (2), (3) and (4) below:

CO + ftiTtO-, - TiO- 2FeTiO¾ + C0 ₂

\. H . ^» 48 fc mol Oi i 2 >

H ₂ + Fe ₂ Ti0 ₅ + Ti0 ₂ <= 2FeTi0 ₃ + H ₂ 0 ^; AH

= -8 kj/mol 0) (4)

(Reactions 3(1 ), (2), (3) and (4))

In reactions 3(1 ), (2), (3) and (4), the substrate of the first reaction is FeTiOs. After undergoing reactions 3(3) and 3(4), one product is FeTiO ₃ ; therefore FeTiO ₃ is acting as a catalyst because it increases the rate of the overall chemical reaction (depleting carbon monoxide and methane and producing carbon dioxide and water) without itself undergoing any permanent chemical change. (This set of reactions was proposed in, "Using an oxygen-carrier as bed material for combustion of biomass in a 12-MW _th circulating fluidized-bed boiler", Henrik Thunman, Fredrik Lind, Claes Breitholtz, Nicolas Berguerand, Martin Seemann, Fuel, 1 13 (2013), 300-309; the disclosure of which hereby incorporated by reference).

Other examples of catalysts, and some methods they catalyse in fluidised bed reactors, include: 4. Ilmenite (FeTiOs) as a catalyst for fluidised bed combustion of agricultural waste or sludge and their mixes with wood.

5. Nickel oxide (NiO), and minerals containing nickel oxide (for example olivine), as a catalyst in fluidised bed gasification of plant based fuels.

6. Nickel oxide (NiO), and minerals containing nickel oxide (for example olivine), as a catalyst in fluidised bed combustion of agricultural waste, municipal solid waste and refuse-derived fuel.

7. Calcium oxide (CaO) as a catalyst in fluidised bed gasification of rice husk, wood or straw.

8. Calcium oxide (CaO), calcium carbonate (CaCOs), sodium carbonate (Na ₂ CO ₃ ) and/or potassium carbonate (K ₂ CO ₃ ) as catalysts in catalytic fluidised bed hydrogasification of coal char.

9. Nickel enriched olivine as a catalyst in catalytic tar reduction in fluidised bed biomass steam gasification.

10. Copper oxide (CuO) as a catalyst in fluidised bed combustion of coal.

1 1 . Calcium oxide (CaO) as a catalyst in cracking tar formed by rice husk fluidised bed gasification.

12. Olivine ((Mg, Fe) ₂ SiO ₄ ) as a catalyst in fluidised bed gasification of biomass.

13. Nickel-chromium compounds of the formula: Ni _2- xCr _x AI ₃ where x = 0.07 or 0.1 1 as a catalyst for fluidised bed gasification or fluidised bed combustion.

Beneficial combinations of catalysts include, but are not limited to elements from groups 1 and 2 of the periodic table, as well as mixtures and/or alloys from any one, two or three of groups 1 , 2 and/or 3 of the periodic table, including:

Group 1 : Ti, V, Cr, Mo, Fe

Group 2: Ni, Co, Mn, Cu

Group 3: CaO, MgO, ZnO In some examples, the size of the catalyst particles within the particles comprising a bed material and a catalyst are 250 μιτι or lower. Optionally, the size of the catalyst particles within the particles comprising a bed material and a catalyst are from 0.1 to 50 μιτι. The particle sizes are measured by whether the particles fit through a suitably sized filter, for example catalyst particles of 250 μιτι or lower fit through a filter with a mesh size of 250 μιτι. Alternatively or additionally, the particle sizes can be measured by laser diffraction (for example using a Malvern™ Mastersizer 3000).

In some examples, the particles comprising a bed material and a catalyst according to the present invention have particle sizes from 0.3 mm to 2 mm, or from 0.5 mm to 1 .2 mm. The particle sizes are measured by whether the particles fit through a suitably sized filter, for example particles of 1 .2 mm or lower fit through a filter with a mesh size of 1 .2 mm. Alternatively or

additionally, the particle sizes can be measured by laser diffraction (for example using a Malvern™ Mastersizer 3000).

In some examples, the particles comprising a bed material and a catalyst are added to a fluidised bed reactor in the form of powders, pellets, granules or slurry.

By adding particles comprising a bed material and a catalyst to a fluidised bed reactor, it is possible to increase the efficiency of fluidised bed reaction methods (for example fluidised bed combustion or fluidised bed gasification) because the catalyst is combined with the bed material. In other words, the particles act as a bed material and also provide catalyst at their surfaces such that the fluidised bed reaction method is catalysed.

The particles comprising a bed material and a catalyst are also controllable. In other words, the particles can be designed to include particular bed material and catalyst combinations to increase the efficiency of combustion or gasification of any particular fuel.

In some examples, for 1 ,000 grams of the particles comprising bed materials and catalyst, the fuel consumption is 1 .2 kg per hour (plus or minus 10 percent). These values can be scaled up to fluidised bed reaction methods where around 20,000 kg of fuel is consumed per hour. Fuel consumption can reach 100,000 kg per hour in large fluidised bed reactors. The amount of catalyst in a particle comprising bed materials and catalyst added to fluidised bed reactors ranges from: 50% catalyst to 1 % catalyst (by weight); or 30% catalyst to 5% catalyst (by weight); or 20% catalyst to 5% catalyst (by weight); or 10% catalyst to 5% catalyst (by weight); or 30% catalyst to 8% catalyst (by weight). With too little catalyst (for example less than 8% by weight) the particles comprising bed materials and catalyst do not provide high levels of catalyst at their surfaces and do not provide a strong catalytic effect. With too much catalyst (for example more than 50%, or 30%, by weight) the particles comprising bed materials and catalyst become heavier and more energy is needed to form a fluidised bed using the particles.

The particles comprising bed materials and catalyst according to the present invention are refractory, i.e. they are stable up to at least 1 ,100°C. The particles comprising bed materials and catalyst according to the present invention are also hard, i.e. they have a Mohs hardness of at least 6. These properties are the result of at least the calcining method at from 1 ,550°C to 1 ,675°C for from 4 hours to 6 hours. If the particles comprising bed materials and catalyst according to the present invention were not refractory and/or hard, they would disintegrate during fluidised bed reaction methods. Examples

In one non-limiting example, Chamotte, either on its own or mixed with catalyst, was heated so that it was calcined at 1 ,600°C in a rotary kiln, with rotation, for five hours.

In other examples, the Chamotte or the mixture can be heated, so that the mixture is calcined, at: from 1 ,200°C to 1 ,675°C for from 4 hours to 6 hours; or, from 1 ,550°C to 1 ,675°C for from 4 hours to 6 hours.

After calcining, the calcined Chamotte or the calcined mixture of Chamotte and catalyst was cooled in air at 20°C, then ground and sieved. When the starting material was a mixture of Chamotte and catalyst, the resulting material was a plurality of particles, each particle formed of Chamotte and catalyst.

In this example, the particles were ground and sieved to have particle sizes of from 250μηη to 500μηη. The particle sizes were measured by a Malvern™ Mastersizer 3000. Particle sizes of from 250μηη to 500μηη were suitable for a bench scale fluidised bed reactor as used in the present examples.

Table 1 shows the chemical composition of some example particles

comprising bed material (F1 ), or bed material and catalyst (F2 and F3), formed by the method described above. The particles had sizes from 250μηη to

500μηη.

Table 1 : amounts given in % (mass/mass)

The resulting particles (of F1 , F2 and F3) comprising bed material, or bed material and catalyst, were tested in a fluidised bed reactor. The bench scale fluidised bed reactor used in the present examples generated power of 5kW.

The fluidised bed reactor was loaded with 1 ,000 grams of the particles (of F1 , F2 and F3) comprising bed material and catalyst. The temperature of the fluidised bed reactor was 850°C with an oxygen concentration of 6%. The fuel was a mixture of straw and wood in a weight ratio of wood 90% to straw 10%. The fuel was added over 4 hours to the fluidised bed reactor and combusted. The rate of fuel consumption was 1 .2 kg per hour (plus or minus 10%).

The resulting gas emissions (flue gases) for each of the particles (of F1 , F2 and F3) comprising bed material and catalyst is shown in Table 2.

Table 2: concentrations of gas emissions given in mg/m ³

Bed material-cal talyst

Emissions F1 F2 F3

CO 210 1 12 150

NOx 291 31 1 295

THC 58 32 26 In Table 2, THC refers to total hydrocarbons. The lower the THC level, the more efficient the fluidised bed combustion method is because more hydrocarbons have been combusted and do not exit in the flue gases. The CO and NOx levels were measured by an infrared detector on the flue. The infrared detector was the same, and was set up in the same way, for each CO measurement and for each NOx measurement, respectively. The THC level was measured by a flame ionization detector. The flame ionization detector was the same, and was set up in the same way, for each THC measurement.

In another example, F1 was mixed with the loose catalyst mixtures from F2 and F3 (i.e. bed material F1 loosely mixed with catalyst mixtures). On using these mixtures as the bed materials in the fluidised bed combustion shown with reference to Table 2, the loose catalyst rapidly left the fluidised bed reactor through the flue and did not participate in the fluidised bed combustion reaction. Put another way, the loose catalyst was too light on its own to catalyse the fluidised bed combustion reaction. In other examples, the particles were ground and sieved to have different particle sizes. The particles for use in industrial fluidised bed reactors, generating power of from 18MW to 50MW, had a particle size of from 0.5mm to 1 .5mm. The particles for use in industrial circulating fluidised bed reactors, generating power of from 30MW to 100MW, had a particle size of from 0.2mm to 0.6mm. Similar results are expected in these larger scale fluidised bed reaction methods.

When used in this specification and claims, the terms "comprises" and

"comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.