Aqueous carbonaceous slurry fuel

Abstract

A direct-injection, compression ignition or diesel type engine fuel comprising: 25 to 70 wt% of a mixture of finely divided carbonaceous particles; 5 to 40 wt% ammonia; and the balance comprising an aqueous solvent, wherein the carbonaceous particles are derived from a coal based material, biomass, char, or a mixture thereof.

Description

AQUEOUS CARBONACEOUS SLURRY FUELPRIORITY CROSS-REFERENCE

[0001] The present application claim priority from Australian provisional patent application No. 2023901705 filed 31 May 2023, the contents of which should be understood to be incorporated into this specification by this reference.TECHNICAL FIELD

[0002] The present invention generally relates to aqueous carbonaceous slurry fuels for use in diesel type engines. One exemplary application is for use as a fuel for large diesel engines used for stationary power generation, marine propulsion and locomotives. However, it should be appreciated that the invention should not be limited to the application and could be applicable to a variety of engines that can use or be adapted to use aqueous carbonaceous slurry fuel.BACKGROUND TO THE INVENTION

[0003] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0004] An emerging technology is the use of alternate fuels such as carbonaceous aqueous slurry fuels or emulsion fuels to replace heavy fuel oil for diesel type engines. Carbonaceous aqueous slurry fuels typically comprise an aqueous colloidal suspension of finely ground carbonaceous particles. Emulsion or Emulsified Fuels are emulsions composed of water and a combustible liquid, either oil or a fuel, for example bitumen emulsion fuels.

[0005] The properties of these slurry and / or emulsion type fuels are therefore significantly different to conventional diesel and fuel oils, in particular having a much higher viscosity and a tendency to destabilise and settle to form sludge. The use of such alternate fuels therefore requires an understanding of thecomplex interactions between the fuel and the engine. Some of these interactions include:

[0006] Stability: The slurry and emulsion fuels are inherently unstable, with a strong propensity to destabilise and form a solid sludge in both storage tanks and piping. Stability is therefore especially important during transportation, storage and handling in fuel systems, including after preheating for use in the engine.

[0007] Specific energy: Achieving a high solids loading (and thus high specific energy of the fuel) has been the main focus of previous research, whilst producing a fuel that is readily atomised in the engine. A higher solids loading has a number of effects, including increasing fuel stability, reducing transportation and storage costs, and increasing engine efficiency via a reduction in the latent heat penalty from the water in the slurry. However, these gains are offset by the strong negative impact of higher specific energy on atomisation and combustion which may render a fuel unusable.

[0008] Atomisation characteristics: Effective atomisation is essential to ensure a short ignition delay and complete burnout of the fuel. Poor atomisation leads to large slurry droplets which are slow to ignite and give incomplete combustion. This can lead to unburnt fuel depositing on the cylinder walls causing accelerated wear and ring jamming issues, together with erosion of the exhaust turbine and exhaust system deposits from large char and ash particles after combustion. Atomisation generally worsens as the viscosity of the fuel increases (as exhibited at injection shear rates), requiring fuel preheating and / or dilution with water. However, the interplay between fuel properties and atomisation is poorly reported in prior literature.

[0009] Ignition and combustion characteristics: Diesel engines require a fuel to ignite quickly (preferably in less than 10 ms for large engines) to avoid rapid pressure rise from the spontaneous ignition of previously injected fuel. Residual fuel and coal tend to have a longer delay than lighter fuels such as marine gas oil. It is important to note that a fuel that ignites well may not result a high combustibility. For example, a coal-diesel mixture will have similar ignitioncharacteristics to diesel fuel. However, the combustibility of the coal is poor due to agglomeration of the coal when dispersed in diesel (or other non-polar hydrocarbons) which effectively creates larger coal particles which have poor combustibility. A fuel with such coal particles are highly likely to deposit unburnt carbons on the cylinder walls of an engine and result in chronic ring and liner wear.

[0010] Wear characteristics: Engine wear includes the fuel injection equipment, especially the injector nozzles, the piston rings and cylinder liner, exhaust valve seats and turbocharger turbine and inlet vanes. In the prior literature it is assumed that wear will be proportional to the total ash content of the fuel. The effects of higher ash content fuels (especially coal) are not well understood in published prior art. However, the total ash can be a poor proxy for the abrasiveness of the solid carbonaceous fuels, with some higher ash fuels forming softer abrasive particles than from lower ash fuels. For coals this erosive material originates mostly from extraneous mineral particles such as quartz, feldspars and pyrites which vary widely in both the amount present and in the mode of occurrence (mineral association and particle size). This is further complicated by the means by which the fuel is prepared to produce a carbonaceous slurry fuel - for example some cleaning methods may reduce the amount of coarse minerals, but increase the proportion of fine minerals remaining in the fuel.

[0011] Ash fouling characteristics: This involves the formation of high temperature ash deposits from the mineral and inorganic species. During combustion these form a range of oxide / sulphide / sulphate compounds which may form deposits on the piston, cylinder cover and exhaust valve and the exhaust system - including the turbo charge turbine and waste heat boiler).

[0012] Emission characteristics: CO2 and SOx emissions will be roughly proportional to the C and S content of the carbons used to produce the fuel, with only minor contributions from the dispersants used in formulation (unless low cost additives, such as lignosulphonate, which, when used at the typical 1 to 2 wt% additive (dry coal basis) can result in a significant increase in Na and S content of the fuel).

[0013] It would therefore be desirable to provide a new and / or alternate carbonaceous slurry fuel.SUMMARY OF THE INVENTION

[0014] The present invention produces an alternative aqueous carbonaceous slurry fuel for use in direct-injection, compression ignition or diesel type engines through the controlled formulation and / or blending of normally incompatible fuels. The fuel of the present invention therefore provides a range of advantageous fuel attributes not possible from a single component carbonaceous slurry fuel.

[0015] A first aspect of the present invention provides a direct-injection, compression ignition or diesel type engine fuel comprising: a. 25 to 70 wt% of a mixture of finely divided carbonaceous particles; b. 5 to 40 wt% ammonia; and c. the balance comprising an aqueous solvent, wherein the carbonaceous particles are derived from a coal based material, biomass, char, or a mixture thereof..

[0016] In embodiments, this direct-injection, compression ignition or diesel type engine fuel (an aqueous carbonaceous slurry fuel) comprises a mixture of finely divided carbonaceous particles, plus an aqueous solvent, preferably comprising water, such that the proportion of carbonaceous material is in the range 25 to 70 wt% and the proportion of ammonia is in the range 5 to 40 wt% and with the balance comprising the aqueous solvent (for example water, water-ethanol, water-methanol, water-sugar mixtures / solutions or the like) plus optional amounts of additives to control rheology, ignition, combustion and NOx formation and ash properties.

[0017] The first aspect of the present invention provides a blended fuel comprising a blended mixture of an aqueous carbonaceous slurry fuel and an ammonia fuel. This formulation can provide a range of improved properties including but not restricted to reduced CO2, NOx, SOx, ash fouling, reduced fuel system corrosion and improved fuel stability and overall combustionperformance. For example, the addition of ammonia to the water-based slurry fuel enables ammonia use without the need for pressurisation or reduced pressure storage and / or the carbonaceous fuel improves the ignition and combustion of the ammonia. The ammonia provides increased specific energy to the fuel and reduces fuel system corrosion, CO2, and SOx emissions, ash fouling and erosion due to mineral ash content of the carbonaceous fuel component(s). The ammonia also results in an increase in pH of the fuel blend which for most carbonaceous materials provides improved rheology.

[0018] It should be appreciated that ammonia was initially added to the fuel composition of the present invention to assist in reducing the CO2 formed during combustion and to raise the pH of the fuel to assist in corrosion protection / protection of the engine. However, other advantages have been found. Whilst not wishing to be limited to any one theory, it was discovered that the addition of ammonia to the slurry improved overall combustion in terms of reducing by ignition delay and the time for combustion as was measured from accurate measurement of cylinder pressure and crankshaft rotation. The inventor postulates that this combustion improvement is due to the explosive evaporation of the ammonia within the slurry droplets formed by atomisation, which thereby improve the effective quality of atomisation for a given fuel viscosity and injection conditions. This enabled a reduction in injection pressure, with the lower injection velocity also reducing atomiser wear.

[0019] The aqueous solvent can comprise any suitable water based solvent. In some embodiments, the aqueous solvent comprises water. However, it should be appreciated that a number of other aqueous solutions are possible, for example water-ethanol, water-methanol, water-sugar mixtures / solutions.

[0020] The ammonia content of the fuel can be selected to provide a selected specific energy improvement and / or improved properties as discussed above. In embodiments, the mass fraction of ammonia in the fuel mixture is from 10 to 40 wt%, preferably from 20 to 40 wt%. In other embodiments, the mass fraction of ammonia in the fuel mixture is from 5 to 30 wt%, preferably from 5 to 25 wt%. In yet other embodiments, the mass fraction of ammonia in the fuel mixture is from10 to 30 wt%, preferably from 15 to 25 wt%. In embodiments, up to 25 to 30 wt% can be added to the aqueous / water component of the fuel depending on the temperature of the fuel, with the fuel at atmospheric pressure. It should be appreciated that the ammonia content of the fuel exists as ammonium ions in solution.

[0021] The mass fraction of the carbonaceous particles in the fuel depends on a number of factors, including the size, composition of the particles and the like. In some embodiments, the mass fraction of the carbonaceous particles in the fuel is in the range of 40 to 70 wt% of the fuel, preferably 45 to 70 wt% of the fuel. In other embodiments, the mass fraction of the carbonaceous particles in the fuel is in the range of 50 to 70 wt%, preferably 50 to 60 wt%. In yet other embodiments, the mass fraction of the carbonaceous particles in the fuel is in the range of 40 to 65 wt%, preferably 45 to 60 wt%.

[0022] The carbonaceous particles may comprise a number of carbonaceous materials. In the slurry fuel, the carbonaceous particles are derived from a coal based material, biomass, char, or a mixture thereof. In some embodiments, the carbonaceous particles are derived from at least one coal based material. In other embodiments, the carbonaceous particles comprise 2 to 70 wt% carbonaceous particles derived from biomass or char. Typically, the balance of the carbonaceous particles is derived from a coal based material. In embodiments, the balance of the carbonaceous particles (for either of the first or second aspect of the present invention) may be selected from the group selected from coal, charcoal, wood, various hydrocarbons, and organic matter whether biological in nature or organic compounds etc.

[0023] In particular aspects of the present invention, the first aspect of the present invention provides a direct-injection, compression ignition or diesel type engine fuel comprising: a. 25 to 70 wt% of a mixture of finely divided carbonaceous particles; b. 5 to 40 wt% ammonia; and c. the balance comprising an aqueous solvent,wherein the carbonaceous particles comprise 2 to 70 wt% carbonaceous particles derived from biomass, char or carbon black.

[0024] It should be understood that the carbonaceous particles in the fuel are “derived from” a coal based material, biomass, char, or a mixture thereof, and in embodiments those carbonaceous particle sources are mixed and blended to form the final blended carbonaceous particles mixture. It is to be understood that “derived from” means that the carbonaceous particles are sourced from a particular carbonaceous particle type source material. It should be appreciated that whilst the compositions of these sources may have similarities, and in some cases have a compositional overlap, the composition of the final blended mixture can still be understood to be linked back to the carbonaceous particles that make up the distinctive carbonaceous particle sources.

[0025] Any type of coal may be used, for example anthracite, bituminous coal, or a brown or lignitic coal may be used. This is particularly advantageous as coal is readily available as a carbonaceous source.

[0026] It should be understood that char covers a carbonaceous residue obtained by heating organic substances such as woody plant material in processes involving carbonisation, or incomplete pyrolysis or gasification, or obtained as a residue when carbonaceous material is partially burned or heated with limited access of air. Char is the solid residue.. Char is the solid material that remains after light gases (e.g. coal gas) and tar have been driven out or released from a carbonaceous material during the initial stage of combustion, known as carbonization, charring, devolatilization or pyrolysis. One example, is the partial combustion of wood or plant fibre.

[0027] It should be understood that carbonaceous particles derived from biomass covers carbonaceous by-products formed from incomplete biomass gasification, pyrolysis or from low temperature carbonisation and torrefaction of a biomass source. Biomass in this sense comprise any organic matter sourced from living organisms including plants, and animals, and can include waste sources from those living organisms. In embodiments, biomass comprises organic plantmatter. Biomass carbonaceous particles can be derived from a variety of sources. In embodiments, the biomass carbonaceous particles comprise carbonaceous by-products from incomplete biomass gasification, pyrolysis or from low temperature carbonisation and torrefaction.

[0028] A second aspect of the present invention provides a direct-injection, compression ignition or diesel type engine fuel comprising carbonaceous particles suspended in an aqueous solvent, wherein the fuel comprises:40 to 70 wt% carbonaceous particles comprising: 2 to 100 wt% carbonaceous particles derived from biomass, or char; the balance comprising an aqueous solvent.

[0029] This second aspect of the present invention provides an aqueous slurry fuels based on alternate carbonaceous particles source, selected from biomass, or or char. This fuel formulation can advantageously provide a range of improved properties including but not restricted to reduced CO2, NOx, SOx, ash fouling, reduced corrosion and improved fuel stability and overall combustion performance.

[0030] In some embodiments, the carbonaceous particles comprise 2 to 70 wt% carbonaceous particles derived from biomass or char. Typically, the balance of the carbonaceous particles is derived from a coal based material. In embodiments, the balance of the carbonaceous particles may be selected from the group selected from coal, charcoal, wood, various hydrocarbons, and organic matter whether biological in nature or organic compounds etc.

[0031] These formulations can also provide a range of improved properties including but not restricted to improved resistance to microbial activity (the formation of moulds etc.), increased specific energy and improved rheology including for stability and shear thinning behaviour.

[0032] In some embodiments, the fuel further comprises from 5 to 40 wt% ammonia, preferably from 10 to 30 wt% ammonia, more preferably from 20 to 40 wt% ammonia. As noted for the first aspect of the present invention, the additionof ammonia provide a range of improved properties including but not restricted to reduced CO2, NOx, SOx, ash fouling, reduced fuel system corrosion and improved fuel stability and overall combustion performance. The ammonia provides increased specific energy to the fuel and reduces fuel system corrosion, CO2, and SOx emissions, ash fouling and erosion due to mineral ash content of the carbonaceous fuel component(s). The ammonia also results in an increase in pH of the fuel blend which for most carbonaceous materials provides improved rheology. In embodiments, the mass fraction of ammonia in the fuel mixture is from 10 to 40 wt%, preferably from 20 to 40 wt%. In other embodiments, the mass fraction of ammonia in the fuel mixture is from 5 to 30 wt%, preferably from 5 to 25 wt%. In yet other embodiments, the mass fraction of ammonia in the fuel mixture is from 10 to 30 wt%, preferably from 15 to 25 wt%.

[0033] In embodiments, the carbonaceous fuel comprises a mixture of finely ground carbonaceous particles, an aqueous solvent preferably comprising water and optional additives. The mass fraction of carbonaceous particles is in the range 45 to 70 wt% with the balance comprising water plus optional amounts of additives. In some embodiments, the carbonaceous particles comprise 2 to 70 wt% carbonaceous particles derived from biomass, or char. The biomass can include but is not restricted to carbonaceous by-products from incomplete biomass gasification and pyrolysis and from low temperature carbonisation and torrefaction. In some embodiments, the carbonaceous fraction comprises from 10 to 70 wt% biomass, or char, and preferably from 20 to 70 wt% biomass, or char. In other embodiments, the carbonaceous fraction comprises from 5 to 60 wt% biomass, or char, and preferably from 10 to 50 wt% biomass, or char.

[0034] Furthermore, the aqueous solvent can comprise any suitable water based solvent. In some embodiments, the aqueous solvent comprises water. However, it should be appreciated that a number of other aqueous solutions are possible, for example water-ethanol, water-methanol, water-sugar mixtures / solutions. In embodiments, the aqueous solvent comprises water and optional additives.

[0035] The resulting fuel is classified as carbonaceous slurry because at room temperature the main combustible components (coal, char, biomass, algal matterand residual fuel oil) are solids - i.e. will not conform to the shape of their container.

[0036] Again, the mass fraction of the carbonaceous particles in the fuel depends on a number of factors, including the size, composition of the particles and the like. The mass fraction of the carbonaceous particles in the fuel is typically in the range of 40 to 70 wt% of the fuel. However, in embodiments, the mass fraction of the carbonaceous particles in the fuel is from 45 to 70 wt% of the fuel. In other embodiments, the mass fraction of the carbonaceous particles in the fuel is in the range of 50 to 70 wt%, preferably 50 to 60 wt%. In yet other embodiments, the mass fraction of the carbonaceous particles in the fuel is in the range of 40 to 65 wt%, preferably 45 to 60 wt%.

[0037] The carbonaceous particles of the first and second aspects of the present invention may comprise a number of carbonaceous materials as required above.

[0038] Biomass carbonaceous particles can be derived from a variety of sources. In embodiments, the biomass carbonaceous particles comprise carbonaceous by-products from incomplete biomass gasification, pyrolysis or from low temperature carbonisation and torrefaction.

[0039] In some embodiments, the carbonaceous fuel comprises a mixture of carbonaceous particles preferably derived from coals, biomass, or char with the balance comprising an aqueous solvent, preferably comprising water and optional additives. In these embodiments, the carbonaceous particles comprise 2 to 70 wt% carbonaceous particles derived from biomass or char, with the balance of the carbonaceous particles being derived from at least one coal based material. Any type of coal based material may be used, for example anthracite, bituminous coal, or a brown or lignitic coal. This is particularly advantageous as coal is readily available as a carbonaceous source.

[0040] It is preferred that the carbonaceous source has low ash content, preferably less than 2 wt%, more preferably less than 1 wt%, most preferably less than 0.5 wt%.

[0041] In the case where the carbonaceous particles are coal, it is preferred that the coal has undergone some form of pre-treatment. Pre-treatment may include removal of the bulk of the mineral ash contamination and in the case of the lower rank coals some form of densification and alteration of the surface properties to render the coal more hydrophobic to enable a fuel with a higher coal loading to be achieved. For example, bituminous coal demineralisation can be achieved by selective agglomeration, flotation and cyclones.

[0042] In embodiments, the carbonaceous particles are hydrophobic. This is preferred as it improves the dispersion of the particles within the solvent.

[0043] The carbonaceous particles are preferably finely divided or finely ground particles. In terms of particle size this typically requires the carbonaceous particles preferably have an average particle size of less than about 30 pm on a mass basis, preferably equal to or less than about 20 pm on a mass basis. In some embodiments, the average particle size is between about 10 pm, and about 20 pm on a mass basis.

[0044] The upper size of the carbonaceous particles is preferably about three to about ten times larger than the mass mean size. The upper size I top size is understood to be the size occupied by the largest 5 % of population and therefore may include far larger sizes with diminishing probabilities. The upper size range is also known as the d-'OS, which is the diameter below which 95 % of the mass is distributed. Thus, the d95 is from about three to about ten times larger than the mass mean size. More preferably, the d95 of the carbonaceous particles is about four to about five times larger than the mass mean size. It will be appreciated that adopting a large size distribution ratio allows the solids loading to be raised for a given viscosity limit. There is a strong inverse correlation between fuel viscosity and particle size distribution(s) for a given solids loading. Similarly, there is reasonable correlation between viscosity and stability.

[0045] Preferably, where the carbonaceous particles have a mass average particle size of equal to or less than 20 pm, the carbonaceous particles exhibit abroad size range, for example from greater than 0 pm and up to about 100 pm. More preferably, the carbonaceous particles exhibit a size range from greater than about 1 pm and up to about 80 pm. The provision of a broad size range is advantageous as it improves the packing efficiencies of the coal particles within the fuel composition which allows fuels with a high loading of carbonaceous particles to be produced. This is because smaller particles are able to fit into the interstitial spaces between the larger particles.

[0046] Alternatively, the fuel composition may be formed using multiple populations of carbonaceous particles having different size ranges. For example, the fuel may include carbonaceous particles having a bimodal size distribution. In this case the fuel includes a first population of carbonaceous particles having a first size distribution about a first mass mean value, and a second population having a second size distribution about a second mass mean value, wherein the first mass mean value is less than the second mass mean value. In this case at least some of the particles in the first population are sized so that they fit into interstitial spaces formed between particles in the second population.

[0047] In a further example, the fuel may include particles having a tri-modal size distribution in which case the fuel is as described above, but additionally includes a third population of carbonaceous particles having a third size distribution about a third mass mean value. The third mass mean value is smaller than the first mass mean value such that these particles are sized to fit into the interstitial spaces formed by particles in the first and second populations.

[0048] As discussed previously, the d95 of the particles is about three to about ten times the mass mean size and preferably about four to about five times the mass mean size. Preferably, in this case the top size is around 200 pm - noting that the ratio of mass mean to top size is likely to be reduced by classification and re-milling (i.e. close circuit milling) to ensure that the coal can burn out within the engine combustion time. As the top size increases the particle size distribution naturally becomes sufficiently broad to achieve high solids loadings, where smaller particles in the size distribution are able to fit into interstitial spaces formed between larger particles in the size distribution.

[0049] It should be understood that unless otherwise specified, all the viscosities listed in the present specification are as measured at (a controlled) 25 °C. It should also be appreciated that the term “viscosity” is intended to refer to the apparent “dynamic viscosity” also known as “shear viscosity” rather than “kinematic viscosity”. Suitable means for determining the viscosity of the fuel are readily apparent to those skilled in the art. However, a suitable means of determining the viscosity is through the use of a rotational viscometer with cylinder and cup over a shear rate range of from 0.1 to 3000 per second. For higher shear stress measurements (greater than 3000 per second) an extrusion viscometer may be used.

[0050] The viscosity of the present invention (both the first and second aspect) is preferably a generally shear-thinning viscosity. A generally shear-thinning viscosity is one in which the slope of the viscosity vs shear rate curve is usually negative. It should be appreciated that fuels of the present invention can still exhibit regions where the slop becomes positive (shear thickening), and in these areas conditioning (controlled shear mixing) may be required to massage out such kinks. It should therefore be understood that “generally” shear thinning means the viscosity is lower on the right hand side of a viscosity vs shear rate curve at high shear rates, then at the left, even if the curve has an inflexion point in between.

[0051] The fuel of first or second aspect of the present invention can be formulated to give workable rheology’s within a variety of ranges. In embodiments, the fuel can have an apparent viscosity (measured using a Kinexus rheometer) of <500 mPa.s at 100 / s, and >20,000 mPa.s at 0.1 Is. The fuel is also preferably generally shear thinning up to 100,000 / s. Whilst not wishing to be limited to any one theory, the above rheology is selected as <500 mPa.s viscosity to ensure satisfactory injection and atomisation behaviour for engines operating below 1000 rpm. The >20,000 mPa.s viscosity at 0.1 / s ensures good stability, with negligible settling over 90 days in unagitated storage.

[0052] The fuel of the first or second aspect may comprise the slurry alone, or could include one or more additives including at least one of a dispersant, a stabiliser, a biocide or combination thereof.

[0053] In some embodiments, the fuel additionally includes a dispersant. The dispersant is important for maintaining the suspension of the carbonaceous particles within the aqueous solvent. Preferably, the dispersant is selected from the group consisting of: an anionic dispersant which provides a surface negative charge and steric hindrance, a non-ionic dispersant which provides steric hindrance, or an amphoteric dispersant which provides both negative and positive charges. More preferably, the anionic dispersant is selected from the group consisting of: sodium salts of: polystyrene sulphonate, polyisoprene sulphonate, carboxyl methyl cellulose, humic acid, polyacrylates, and copolymers of acrylic acid and other acrylic monomers; sodium or ammonium salts of: lingo suphonates, naphthalene sulphonate, or naphthalene sulphonate formaldehyde condensate. More preferably, the non-ionic dispersant is selected from the group consisting of cellulose ethers, such as hydroxyethyl cellulose or hydroxypropyl cellulose; polysaccharides, such as dextrin; polyoxyethylene sorbitan monooleate, or rosin or saponin based dispersants. More preferably the amphoteric dispersant is a polycarboxylate.

[0054] The fuel may also include stabilisers such as natural gums including guar, rhansam, xanthan and gellan gums, phosphate salts, or ferrous sulphate.

[0055] The fuel may also include biocides such as formaldehyde to reduce microbial activity.

[0056] The fuel may additionally or alternatively further comprise at least one additive to control at least one of rheology, ignition, combustion and NOx formation or ash properties. The at least one additive preferably include the condensate by-products from biomass pyrolysis and carbonisation including but not restricted to solutions of “wood vinegar”.

[0057] It should be appreciated that the fuel of the present invention is suitable for use in a directly injected combustion chamber of a compression ignition or diesel type engine. It should also be understood that diesel type engine encompasses any engine manufactured, constructed or modified to operate using a fuel including carbonaceous particles suspended in an aqueous medium. The particular engine may therefore by a conventional compression ignition or diesel engine, or an engine improved, modified or otherwise derived from conventional compression ignition or diesel engines to operate using a fuel including carbonaceous particles suspended in an aqueous solvent. One example is a direct injection carbon engine (DICE) - a diesel engine which has been modified to enable combustion of water-based slurry of micronised refined carbon fuel (MRC).

[0058] Other examples include diesel type engines used in power generation, ships and locomotives. In some embodiments, the fuel is used in a stationary power generation engine. In these embodiments, the engine comprises a large engine typically fixed in place within a building or other enclosure which primarily used to generate electricity. In other embodiments, the fuel is used in a transportation engine, typically to propel a vessel. Examples of transportation engines include use of an engine to power and propel locomotives, ocean going vessels such as ships, ocean liners, barges or the like. However, it should be appreciated that other vehicle engines such as trucks or the like could utilise suitable sized and powered engines using the fuel of the present invention.

[0059] In another aspect of the invention, there is provided the use of a fuel as previously described in a combustion chamber, such as the combustion chamber of an engine, such as a direct-injection, compression ignition or diesel type engine. More preferably the fuel is for use in a modified diesel engine, such as a diesel engine having a blast injector. An example of one suitable injector nozzle, forming part of a blast atomiser type injector is taught in International Patent Publications WO2013142921A1 and WO2015048843A1 by the same applicant, the contents of which should be understood to be incorporated into this specification by this reference. In some embodiments, the diesel engine comprises a power generation, ships or locomotive engine.

[0060] A third aspect of the present invention provides a method for preparing a fuel for a combustion chamber of a direct-injection, compression ignition or diesel type engine including: mixing carbonaceous particles and a water to form a fuel mixture of carbonaceous particles suspended in water, wherein the carbonaceous particles are derived from a coal based material, biomass, char, or a mixture thereof; and adding ammonia to the fuel mixture, thereby producing a fuel mixture comprising 25 to 70 wt% of a mixture of finely divided carbonaceous particles; 5 to 40 wt% ammonia; with the balance comprising water.

[0061] In the slurry fuel, the carbonaceous particles are derived from a coal based material, biomass, char, or a mixture thereof. In some embodiments, the carbonaceous particles are derived from at least one coal based material. In other embodiments, the carbonaceous particles comprise 2 to 70 wt% carbonaceous particles derived from biomass or char. Typically, the balance of the carbonaceous particles is derived from a coal based material.

[0062] In embodiments of this invention the ammonia could be added to the fuel at any point along the fuel production chain after the production of the slurry, including the water used to produce the slurry, during storage, or between the fuel storage tank and the engine’s injector valve nozzle orifices. For example, ammonia can be added to either the water used to make the slurry, or the slurry. In such embodiments, ammonia is added to the fuel mixture during at least one of: storage of the fuel mixture; or a mixing location between a fuel storage reservoir and injection of the fuel in an engine’s injector. As the pressure is much higher once the fuel is in the engines fuel system additional ammonia can be added. The amount of ammonia within the fuel follows as taught in relation to the first aspect of the present invention. Again, in embodiments, up to 25 to 30 wt% can be added to the aqueous / water component of the fuel depending on the temperature of the fuel, with the fuel at atmospheric pressure. It should be appreciated that the ammonia content of the fuel exists as ammonium ions in solution.

[0063] A fourth aspect of the present invention provides a method for preparing a fuel for a combustion chamber of a direct-injection, compression ignition or diesel type engine including: blending carbonaceous particles and a water to form a fuel mixture of carbonaceous particles suspended in water; wherein the mass fraction of carbonaceous particles in the fuel mixture comprises 40 to 70 wt% selected from:2 to 1000 wt% carbonaceous particles derived from biomass or char.

[0064] In some embodiments, the carbonaceous particles in the fuel mixture comprise at least two different carbonaceous particles blended together selected from 2 to 70 wt% carbonaceous particles derived from biomass or char, with the balance comprising coal based particles.

[0065] The blending step is preferably conducted to achieve consistent components at different points in the fuel delivery chain to the engine to avoid incompatibilities, optimise the required properties, and / or simplify the fuel production chain. The different carbonaceous particles can be preferably blended immediately prior to use in an engine.

[0066] The blending step is preferably conducted to provide a homogeneously mixed slurry fuel. In this respect, blending can be undertaken with sufficient intensity and duration to ensure homogeneity of the slurry fuel and with an intensity / duration / temperature combination sufficiently low to avoid unwanted negative changes to the fuel properties (such as agglomeration of coal particles). The formulated fuel is handled in a way that reduces to an acceptable level the effects of fuel incompatibility. For example, by avoiding long duration at high temperature or excessive shear and mixing intensity which could partially destabilise the slurry.

[0067] Like the third aspect of the present invention, the method of this fourth aspect can also further comprise: adding 5 to 40 wt% ammonia to the fuel mixture. As noted above, the addition of ammonia provide a range of improvedproperties including but not restricted to reduced CO2, NOx, SOx, ash fouling, reduced fuel system corrosion and improved fuel stability and overall combustion performance. The ammonia provides increased specific energy to the fuel and reduces fuel system corrosion, CO2, and SOx emissions, ash fouling and erosion due to mineral ash content of the carbonaceous fuel component(s). The ammonia also results in an increase in pH of the fuel blend which for most carbonaceous materials provides improved rheology.

[0068] In the fuel mixture, 2 to 70 wt% carbonaceous particles are derived from biomass, or char.

[0069] The formulations described in the first and second aspects of the present invention can be achieved by blending the consistent components at different points in the fuel delivery chain to the engine to avoid incompatibilities, optimise the required properties, and / or simplify the fuel production chain. This includes blending immediately prior to use in the engine.

[0070] A fifth aspect of the present invention provides a method according to the third or fourth aspect of the present invention, wherein the fuel mixture comprises a fuel according to the first or second aspect of the present invention.

[0071] Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example.DETAILED DESCRIPTION

[0072] The present invention relates to the formulation of carbonaceous aqueous slurries for alternative fuel for large diesel engines for stationary power generation, ships and locomotives. The carbonaceous slurry fuel of the present invention includes carbonaceous particles suspended in an aqueous solution. Embodiments of the fuel of the present invention can be categorised as a type of micronised refined carbon fuel (MRC). Such fuels are formulated for use in an engine, such as a diesel or modified-diesel engine, for example a direct injection carbon engine (DICE).

[0073] There are many issues in using alternative fuels based on carbonaceous slurries and emulsions fuels in diesel engines, most of which are strongly interrelated and involve complex interactions between the fuel and the engine. Various strategies have been considered to overcome these issues, but all have missed the opportunity of using blended fuels to achieve optimum fuel properties to mitigate against the limitations of individual fuels. The Inventor presumes that this lack of investigation of the opportunities possible from selective formulation is the result of a lack of understanding of the complex phenomena affected fuelengine interactions for these complex alternative fuels.

[0074] Whilst not wishing to be limited to any one theory, the Inventor considers that they have challenged accepted wisdom on the formulation of slurry fuels and have discovered that a number of advantageous formulations that provide a range of improved fuel properties that can be optimised to suit the end use application. The Inventor has surprisingly found that a range of useful slurry fuels can be formed by blending widely different carbonaceous fuels that by conventional wisdom are not considered compatible, to produce a slurry fuel with optimal properties including, but not restricted to, stability in settling, resistance to microbial activity and with optimal specific energy, rheology, ignition characteristics, combustion characteristics, wear characteristics, CO2 and sulphur oxide and nitrogen oxide emission intensity, cost and availability.

[0075] The present invention provides two main blended fuel embodiments:

[0076] A first blended fuel embodiment comprising a blended mixture of an aqueous carbonaceous slurry fuel and an ammonia fuel comprising: 25 to 70 wt% of a mixture of finely divided carbonaceous particles derived from a coal based material, biomass, char, or a mixture thereof; 5 to 40 wt% ammonia; and the balance comprising an aqueous solvent. In particular embodiments, the carbonaceous particles may be made up of 2 to 70 wt% carbonaceous particles derived from biomass, or char; and

[0077] A second blended fuel embodiment comprising a blend of aqueous coal based slurry fuels and an alternate carbonaceous particles source, selected from biomass, or char comprising 40 to 70 wt% carbonaceous particles suspended in an aqueous solvent, made up of 2 to 100 wt% carbonaceous particles derived from biomass, or char. In some embodiments, the carbonaceous particles source comprises a mixture of : 2 to 70 wt% carbonaceous particles derived from biomass or char, with the balance of the carbonaceous particles are derived from at least one coal based material.

[0078] It should be appreciated that the fuel formulations of the present invention can produce a slurry with optimal properties for the required application by blending solids, slurries, emulsions and other novel fuels under controlled conditions. The resulting fuel is classified as carbonaceous slurry because at room temperature the main combustible components (coal, char, algal matter and residual fuel oil) are solids - i.e. will not conform to the shape of their container.

[0079] Whilst not wishing to limit the scope of the present invention, the Inventor considers that the following issues and accepted wisdom in the alternate fuel art prior have been overcome in the formulation of particular embodiments of the fuel of the relevant embodiments / aspects of the present invention. It should be understood that these comments relate to particular embodiments of the present invention, and may not cover all aspects of the broadest form of the present invention. The following should therefore not be interpreted as to generally apply to all embodiments of the invention covered in the appended claims:1. Previous attempts of utilising coal-oil / diesel mixtures in diesel engines (for example Sulzer / Thermoelectron 1978-82, CSIRO 1987, Performance tests of a slow-speed, two-stroke diesel engine using coal-based fuels by J. B. Dunlay, J.P. Davis, Thermo Electron Corporation and H. A. Steiger, M. K. Eberle Sulzer Brothers, Work Performed Under Contract No. EF-77-C-01-2647), these have all resulted in poor atomisation and combustion performance due to agglomeration of the coal. Therefore, all recent attempts to use carbonaceous slurries in diesel engines have been restricted to single component carbonaceous water slurries (eg coal A-water, coal B-water, char A-water).2. While it is known that black coals (hydrophobic in nature) produce higher specific energy slurries, and low rank lignitic coals and char (hydrophilic in nature) produce higher stability slurries albeit with very low specific energy (requiring for example over 3x more fuel to be injected) which renders them difficult to use, there have been no attempts to combine these different solids to improve both the overall specific energy and stability to produce a usable fuel.3. While it is known that coal produces high specific energy slurry fuel but result in high CO2 emissions than biomass-based fuels, there has been no attempt to produce blended carbonaceous slurry fuel for diesel engines.4. It is known that ammonia, and in particular anhydrous ammonia (ammonia without water) can be a substitute for petroleum as a transportation fuel in modified diesel engines to overcome severe combustibility issues. Furthermore, if produced from renewable power, ammonia modified engines have a very low CO2 intensity. However, the inventor has surprisingly discovered that for embodiments of the present invention, ammonia can be blended with aqueous coal- or char-based slurry fuel to both reduce CO2 and SOx intensity and to improve the combustibility of the ammonia. This advantageously provides other overall benefits in fuel storage of use of ammonia alone, as the use of an aqueous blended ammonia fuel eliminates or reduces the need for pressurised storage of ammonia.5. The Inventor has additionally surprisingly discovered that the addition of ammonia to the slurry improved overall combustion in terms of reducing by ignition delay and the time for combustion as was measured from accurate measurement of cylinder pressure and crankshaft rotation. In experimental runs, the inventor has found that there is a with a >25% reduction in ignition delay and being able to operate the engine with a lower air inlet temperature of 95°C compared to 150 °C for coal-only slurry. The inventor postulates that this combustion improvement is due to the explosive evaporation of the ammonia within the slurry droplets formed by atomisation, which thereby improve the effective quality of atomisation for a given fuel viscosity and injection conditions.This enabled a reduction in injection pressure, with the lower injection velocity also reducing atomiser wear. An improvement in combustion was unexpected, as the evaporation of ammonia is highly endothermic which retards ignition, and the combustion rate of ammonia in engines is much slower than other gaseous fuels (for example natural gas). It was discovered that contrary to expectations, these negative effects were substantially offset by the positive effects on atomisation. It is also surmised that the slow combustibility of ammonia was being greatly increased by the multiplicity of ignition sites in the form of burning char, which reduced the unburnt ammonia in the engine exhaust gases (measured by a mass spectrometer) by over 75% for a given overall combustion stoichiometry.

[0080] In view of the above, the fuel of the present invention provides a number of advantageous formulations that provide a range of improved fuel properties that can be optimised to suit the end use application.

[0081] It should be appreciated that the present invention is suitable for use in a directly injected combustion chamber of a compression ignition or diesel type engine. The particular engine may therefore comprise a conventional compression ignition or diesel type engine, or an engine improved, modified or otherwise derived from conventional compression ignition or diesel engines to operate using a fuel including carbonaceous particles suspended in an aqueous medium. In particular embodiments, carbonaceous aqueous slurry fuels according to the present invention can be used to replace heavy fuel oil for diesel type engines, for example for stationary electricity generation at greater than the 5 MW scale, and for large shipping.

[0082] For ocean going vessels, the use of carbonaceous slurry fuels can advantageously address sulfur emissions limits for ocean vessels which in many jurisdictions have been restricted to use fuel oil on board with a sulphur content of no more than 0.5 %, and in some cases of now more than 0.10%. The sulfur content of carbonaceous slurry fuels can be tailored to meet this specific sulfur content restriction.

[0083] In the case of an ammonia:coal blended fuel embodiment of the present invention: this fuel formulation has mutual benefits for these difficult to ignite fuels, and CO2 benefits. For example:• If the ammonia is produced using renewable energy, the resulting slurry fuel has a lower CO2 intensity. In comparison, for a fuel comprising only a coal slurry, the CO2 emission intensity is approximately 94 kg CO2 / GJ (higher heating value). If 30 wt % green ammonia is added and 30 wt% coal displaced, then the slurry CO2 intensity will be reduced by around 25 % to 70 kg CO2 / GJ, depending on the calorific value of the coal in the slurry.• The other benefit of ammonia is the effect on ignition delay of the coal. Coal water slurries of the rheology described above typically have an ignition delay of 7 to 12 ms. A slurry comprising 50 wt% coal, 15 wt% ammonia, 35 wt% water under the same injection conditions typically has an ignition delay of 3 to 5 ms. This shorter ignition delay allows engine operation at higher engine speeds and with a heavier fuelling rate without mechanically stressing the engine. The shorter ignition delay is due to enhancement of atomisation due to the much higher vapour pressure of ammonia compared to water, resulting flashing of ammonia from the atomised slurry droplets during heating once inside the engines hot combustion charge in the engine.• With the latter formulation, the fuel can also be stored at atmospheric pressure at 20 °C. At higher ammonia ratios, pressurised fuel storage will be required according to the vapour pressure of the slurry.• Overall adding ammonia in the fuel formulation of the present invention displacing the use of coal (on an energy basis) in that fuel will reduce the CO2 intensity of the fuel and improve ignition of the coal component via improved atomisation.• The use of coal with ammonia allows the direct injection of ammonia with conventional injection strategy and without measures to improve ignition, as ignition of the coal will ensure ignition and faster combustion of the ammonia. In comparison, using similar injection equipment for 100% ammonia, poor ignition and very slow combustion of the ammonia would make the engine inoperable due to unburnt ammonia in the exhaust.

[0084] In the case of a charcoal blended fuel embodiment (slurry) of the present invention:• This blending provides CO2 intensity that is reduced approximately in proportion to the amount of coal displaced, providing the char is produced from purpose grown woody biomass; for example a 50:50 charcoal ratio will have a CO2 intensity of around 55 kg / GJ (HHV basis) compared to 94 kg / GJ (HHV basis) for coal only slurry. Where the char is produced from waste that would normally be consumed by incineration or wild fire, the overall CO2 benefits will be larger. Specific values (for example kg 002 / MWh electricity) require a detailed life cycle analysis for a specific energy system, as this needs to also account for what the char-coal slurry fuel is being used to displace (for example coal fired power station, natural gas fired power station, diesel backup generation etc).• This blending provides reduced CO2 and reduced cylinder wear benefits approximately proportional to the amount of coal displaced, because wear tests have shown that char combustion residues (ash) do not increase cylinder wear - i.e. produce the same wear as for clean lubricant. Coal on the other hand increases cylinder wear by 100 to 1000 over clean oil, depending on the proportion of mineral derived ash.

[0085] In view of the above, the fuel of the present invention provides a number of advantageous formulations that provide a range of improved fuel properties that can be optimised to suit the end use application.EXAMPLESExample 1 - Fuel Blending Properties

[0086] A number of advantageous formulations have been discovered that provide a range of improved fuel properties that can be optimised to suit the end use application.

[0087] Table 1 below gives a nominal ranking of key attributes (with 5=best, and 1=worst) for different carbonaceous fuels. This ranking indicates how blending could produce an optimal quality fuel for a particular application providing the mixture is compatible, noting none of the fuels below have been used in combination, nor has their use been proposed due to widely varying propertiesand reported poor results from coal-oil, coal-diesel, coal ethanol and coalmethanol mixtures.

[0088] Table 1 : Nominal ranking of key attributes (with 5=best, and 1=worst) for different carbonaceous fuels.Example 2 - Fuel Formulation ExamplesExample 2.1 -Char- Water Mixture

[0089] A slurry fuel was formed comprising 50 wt% char produced from woody material (wood sourced material, not bark, leaf or twig) carbonised at 350 °C, ground to -90pm that was blended with water using a small amount of dispersant (0.1 wt% sodium polystyrene sulphonate). The viscosity of the slurry was measured using a using a Kinexus rheometer. The resulting slurry was found to have excellent rheological properties with viscosities of 24000 mPa.s at 0.1 / s and300 mPa.s at 3000 / s. However, the fuel was found to be biologically unstable, with dense white colonies forming on the surface of the fuel within 48 hours at 21 °C. These dense white colonies were unidentified moulds, for which are normally formed within days of processing of biomass products such as torrefied wood and low temperature chars. It was discovered that the addition a small amount of condensable pyrolysis product (3 wt% of the total slurry) collected during carbonisation completely prevented microbial activity, with the fuel, remaining stable for over 200 days at 21 °C. The condensable pyrolysis product contained wood vinegar and a cocktail of liquid hydrocarbons at room temperature (for example creosote, phenols, tars - all with significant value as a fuel). These may comprise up to 50% of the energy content of the original biomass when carbonised at 350 °C.Example 2.2 - Char-Ammonia-Water Mixture

[0090] In this case, a slurry fuel was formulated using 50 wt% char produced at 350 °C blended with an aqueous-ammonia solution comprising 20 wt% ammonia - 80 wt% water. The viscosity of the slurry was measured using a using a Ki nexus rheometer.

[0091] The resulting slurry was found to have excellent rheological properties with viscosities of 20,000 to 40,000 mPa.s at 0.1 / s and 200 to 350 mPa.s at 3000 Is. Importantly, a similar result in terms of the absence of microbial activity was achieved as the comparative example.Example 2.3 - Char- Aqueous Ammonia Mixture

[0092] A slurry fuel was formulated using 5 wt% char produced at 350 °C blended with an aqueous-ammonia solution comprising 20 wt% ammonia - 80 wt% water. This char-ammonia-water slurry fuel was used as fuel in a four litre single cylinder diesel laboratory engine (adapted from a single cylinder engine, Satyjeet SL22). The char-ammonia-water slurry fuel was injected into the engine using a modified stock jerk pump and a standard fuel injection pump (not illustrated).

[0093] The engine test runs found that this small addition of char (5 wt%) gave greatly improved the combustion characteristics of (anhydrous) ammonia. Liquidammonia when directly injected into a diesel engine has very poor or no ignition without pilot injection of diesel to provide an ignition source. It was discovered that a small addition of char (5wt%) eliminated the need for a separate pilot injection of diesel fuel, and provide a reduction in CO2 emissions equal to the amount of diesel not used (approximately 78kg CO2 / GJ of diesel equivalent).Example 2.4 - Biomass char and Bituminous coal Mixture

[0094] A slurry fuel was formulated using 25 wt% biomass char produced at 350 °C blended with 25 wt% bituminous coal in water. The viscosity of the slurry was measured using a using a Kinexus rheometer. A typical analysis (on a dry ash free basis) of char produced from pinus radiata used in this experiment is as follows:Carbon: 72 wt%Hydrogen: 5.4 wt%Nitrogen: 0.08 wt%Sulphur (total): 0.05 wt%Oxygen (by difference): 22.5 wt%

[0095] The resulting slurry was found to have excellent rheological properties with viscosities of 20,000 to 40,000 mPa.s at 0.1 / s and 250 to 350 mPa.s at 3000 Is.

[0096] This slurry fuel was used as fuel in a fully instrumented 3.9 litre single cylinder diesel laboratory engine (adapted from a single cylinder engine, Satyjeet SL22). The slurry fuel was injected into the engine using a modified stock jerk pump equipped with a media separating diaphragm at up to 250 bar, or with an electronically controlled hydraulically actuated fuel pump at pressures between 350 and 500 bar (not illustrated). The experiments involved preheating the engine coolant with an external gas fired heater to 95°C, and then starting with the slurry fuel. The engine was equipped with a roots blower and an electric heated to enable a wide range of operating conditions to be simulated. To enable reasonable comparison with diesel operation, the inlet air pressure was adjusted to maintain a constant overall combustion stoichiometry (7 vol% O2 at full load). Performance in terms of torque and unburnt fuel components were investigated at engine speeds of 200 to 800 rpm - the full operating range for the engine.

[0097] The engine test runs found that the blending of biomass char and bituminous coal gave a number of advantages including a reduction in abrasive wear which was slightly higher than the proportion of bituminous coal displaced due to anti-scuff properties of the ash produced from the char and increased spheriodisation of the siliceous ash from the coal due to alkali-ash, alkaline-ash reactions (the ash from the char being high in Na, Ca and Mg, the oxides of which react with the siliceous coal ash to form low melting point phases for example mixed xNa2O.yCaO.SiO2. The use of char also reduced the CO2 emission approximately in proportion to the amount of coal displaced (around 94kg CO2 / GJ coal equivalent).Example 2.5 - Ammonia and coal / char mixture

[0098] Successful formulation of an ammonia:coal slurry blend was achieved by producing adding water containing to a coal filter cake comprising 35 wt% water in a low shear mixing tank to form a basic slurry with around 50 wt% coal. This coal had a volatiles content of 33 wt% dry basis, and an ash content of 2.1 wt% dry basis. The mass mean size was 12pm, and the D95 was 90pm. Around 0.1 wt% poly(sodium 4-styrenesulfonate) surfactant was added to ensure shear thinning rheology. The composition of the mixture was then, adjusted to give the required proportions of ammonia:water:coal by individual additions directly to the slurry in the blender. In the case of ammonia, this was by sparging directly into the slurry during agitation. However, in other cases requiring a lower proportion of ammonia, the ammonia was as an ammonia:water solution, prepared by sparging anhydrous ammonia gas directly into the water. Sparging causes rapid incorporation of the ammonia into the solution as ammonium ions. The aim was normally to add as much ammonia or coal as possible whilst maintaining a shear thinning rheology, with an apparent viscosity of 100-300 mPa.s to allow injection. The ammonia:coal slurry was then fuelled into a 3.9 litre single cylinder low- medium speed (200-800 rpm) laboratory engine (adapted from a single cylinder engine, Satyjeet SL22) or a high pressure spray combustion chamber for combustion tests. The spray chamber was CSIRO designed for these experiments, with 9 litre internal volume, and with optical access for high speedphotography via sapphire windows. The maximum working pressure is limited to 200 bar.

[0099] Overall, it was found than ammonia concentrations as low as 5 wt% in the slurry produced smoother and more complete combustion. In particular, the heat release rate in the engine was progressive and without any premix combustion spikes. CO and NOx levels were also reduced by at least 25 % over that for diesel fuel at the same engine rpm and load, and the engine was able to produce its maximum rated torque at all speeds, from 200 to 800 rpm. Engine performance was also better than with coal only slurry, with the ammonia blended fuel requiring an air inlet temperature of only 90°C to achieve combustion comparable to an air inlet temperature of 150 °C with coal slurries. Engine performance was infinitely better with the blend than for ammonia only injection (as liquid anhydrous ammonia), where direct injection of ammonia only was incapable of achieving ignition. It is noted that combustion stoichiometry was maintained constant with the different preheats by varying the inlet boost to maintain a constant 7 vol% O2 in the exhaust.

[0100] In an experiment with the high pressure spray chamber, the ignition delay with 5 wt% ammonia was around 3 to 5 ms shorter than for coakslurry and with a 2 to 3 °C wider jet angle - both showing the expansive benefits of ammonia in slurry. Conditions at the start of injection being 80 bar and 575 °C, and injection was at constant pressure at around 400 bar via a 0.4 mm single orifice injector. Higher proportions of ammonia (equivalent to 30 wt% ammonia:70 % water solution) resulted in lower viscosity fuel, allowing lower injection pressure to achieve the same injection rate. The mutual benefits of ammonia:coal slurry blends was clearly demonstrated.

[0101] The benefit of ammonia in improving carbonaceous slurry combustion through explosive atomisation due to the higher vapour pressure of ammonia compared to water, will be higher for lower calorific value carbonaceous materials such as biomass char and thermally treated brown coals / lignites which generally produce lower quality slurries in terms of calorific value for a given viscosity. The addition of ammonia improves atomisation such that a higher solids contentslurry, hence one with a higher viscosity, can be atomised sufficiently well to allow a short ignition delay and efficient combustion.EXAMPLE 3 - Ammonia and coal slurry fuel

[0102] A slurry comprising 55 wt% Hunter Valley bituminous coal (having less than 3% ash content) and 45 wt% ammonia-water solution was successfully fired into a 3.9 litre single cylinder test engine. As described in previous examples, this test engine was a fully instrumented single cylinder diesel laboratory engine adapted from a single cylinder engine, Satyjeet SL22. The slurry fuel was injected into the engine using a modified stock jerk pump equipped with a media separating diaphragm at up to 250 bar, or with an electronically controlled hydraulically actuated fuel pump at pressures between 350 and 500 bar (not illustrated). The ammonia-water solution comprised 25 wt% ammonia-75 wt% water, and was prepared by slowly bubbling anhydrous ammonia into a coalwater slurry at 22°C.

[0103] The engine was able to produce its rated torque over its operating speed range of 300 to 750 rpm. Engine performance was monitored using accurate measurement of cylinder pressure and crank position, together with exhaust gas analysis. The cylinder heat release rate was smooth and without pressure spikes from premix combustion. Exhaust gas analysis showed complete combustion, with a significant reduction in CO and NOx compared to either diesel, or coalwater slurry fuelling.

[0104] Experiments in a high-pressure spray combustion chamber (85 bar, 570 °C at the start of injection, 400 pm single orifice nozzle) showed that the fuel jet angle was around 5° wider than for coal-water slurry and combustion occurred significantly closer to the injector nozzle.

[0105] Overall, the addition of ammonia to the water liquid phase improved the rheology of the fuel as evidenced by a reduction in injection time (using a constant pressure hydraulic intensifier-type injector).

[0106] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specificallydescribed. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0107] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.

Claims

CLAIMS1. A direct-injection, compression ignition or diesel type engine fuel comprising:25 to 70 wt% of a mixture of finely divided carbonaceous particles;5 to 40 wt% ammonia; and the balance comprising an aqueous solvent, wherein the carbonaceous particles are derived from a coal based material, biomass, char, or a mixture thereof.

2. A fuel according to claim 1 , wherein the aqueous solvent comprises water.

3. A fuel according to any preceding claim, wherein the mass fraction of the carbonaceous particles in the fuel is in the range of 40 to 70 wt% of the fuel, preferably 45 to 70 wt% of the fuel.

4. A fuel according to any preceding claim, wherein the carbonaceous particles derived from biomass comprises carbonaceous by-products from incomplete biomass gasification, pyrolysis or from low temperature carbonisation and torrefaction.

5. A fuel according to any preceding claim, wherein the carbonaceous particles are derived from at least one coal based material.

6. A fuel according to any one of claims 1 to 4, wherein the carbonaceous particles comprise a mixture comprising:2 to 70 wt% carbonaceous particles derived from biomass or char, the balance comprising carbonaceous particles derived from at least one coal based material.

7. A fuel according to any preceding claim, wherein the carbonaceous particles derived from at least one coal based material are selected from anthracite, bituminous, or a brown or lignitic coal.

8. A direct-injection, compression ignition or diesel type engine fuel comprising carbonaceous particles suspended in an aqueous solvent, wherein the fuel comprises:40 to 70 wt% carbonaceous particles comprising: 2 to 100 wt% carbonaceous particles derived from biomass or char; the balance comprising an aqueous solvent,.

9. A fuel according to claim 6 , further comprising from 5 to 40 wt% ammonia, preferably from 10 to 30 wt% ammonia, more preferably from 20 to 40 wt% ammonia.

10. A fuel according to claim 8 or 9, wherein the mass fraction of carbonaceous particles in the fuel is from 45 to 70 wt%.

11. A fuel according to any one of claims 8, 9 or 10, wherein the carbonaceous particles derived from biomass comprises carbonaceous by-products from incomplete biomass gasification, pyrolysis or from low temperature carbonisation and torrefaction.

12. A fuel according to any one of claims 8 to 11 , wherein the balance of the carbonaceous particles are derived from at least one coal based material, preferably selected from anthracite, bituminous, or a brown or lignitic coal.

13. A fuel according to any one of claims 8 to 12, wherein the aqueous solvent comprises water.

14. A fuel according to any preceding claim, wherein the carbonaceous particles have a mass average particle size of less than 20 pm, preferably about 10 pm to about 20 pm.

15. A fuel according to any preceding claim, wherein the carbonaceous particles have a d95 from about three to about ten times larger than the mass average size.

16. A fuel according to any preceding claim, wherein the d95 is from about four to about five times larger than the mass average size.

17. A fuel according to any preceding claim, further comprising at least one additive to control at least one of rheology, ignition, combustion and NOx formation or ash properties.

18. A fuel according to claim 17, wherein the at least one additive comprise the condensate by-products from biomass pyrolysis and carbonisation, preferably solutions of wood vinegar.

19. A fuel according to any preceding claim, further comprising a dispersant preferably selected from the group consisting of: sodium salts of: polystyrene sulphonate, polyisoprene sulphonate, carboxyl methyl cellulose, humic acid, polyacrylates, and copolymers of acrylic acid and other acrylic monomers; sodium or ammonium salts of: lingo suphonates, naphthalene sulphonate, or naphthalene sulphonate formaldehyde condensate; cellulose ethers including hydroxyethyl cellulose or hydroxypropyl cellulose; polysaccharides including dextrin; polyoxyethylene sorbitan monooleate; rosin or saponin based dispersants; or polycarboxylates.

20. A fuel according to any preceding claim, wherein the viscosity of the fuel is generally shear thinning.21 . A fuel according to any preceding claim, wherein the fuel has an apparent viscosity (measured using a Kinexus rheometer) of <500 mPa.s at 100 / s, and > 20000 mPa.s at 0.1 Is.

22. A fuel according to claim 21 , wherein the fuel is generally shear thinning up to 100000 Is.

23. Use of a fuel of any one of the preceding claims in a combustion chamber of a compression ignition or diesel engine.

24. The use of claim 23, wherein the diesel engine comprises a power generation, ships or locomotive engine.

25. A method for preparing a fuel for a combustion chamber of a direct- injection, compression ignition or diesel type engine including: mixing carbonaceous particles and a water to form a fuel mixture of carbonaceous particles suspended in water, wherein the carbonaceous particles are derived from a coal based material, biomass char or a mixture thereof; and adding ammonia to the fuel mixture, thereby producing a fuel mixture comprising 25 to 70 wt% of a mixture of finely divided carbonaceous particles; 5 to 40 wt% ammonia; with the balance comprising water.

26. A method according to claim 25, wherein ammonia is added to the fuel mixture during at least one of: storage of the fuel mixture; or a mixing location between a fuel storage reservoir and injection of the fuel in an engine’s injector.

27. A method according to claim 25 or 26, wherein the carbonaceous particles comprise a mixture comprising 2 to 70 wt% carbonaceous particles derived from biomass or char, the balance comprising carbonaceous particles being derived from at least one coal based material.

28. A method for preparing a fuel for a combustion chamber of a direct- injection, compression ignition or diesel type engine including: blending carbonaceous particles and a water to form a fuel mixture of carbonaceous particles suspended in water; wherein the mass fraction of carbonaceous particles in the fuel mixture comprises 40 to 70 wt% selected from:2 to 1000 wt% carbonaceous particles derived from biomass or char.

29. A method according to claim 28, wherein the carbonaceous particles in the fuel mixture comprise at least two different carbonaceous particles blendedtogether selected from 2 to 70 wt% carbonaceous particles derived from biomass or char, with the balance comprising coal based particles.

30. A method according to claim 29, wherein the different carbonaceous particles are blended immediately prior to use in an engine.

31. A method according to claim 29 or 30, wherein the blending step is conducted to provide a homogeneously mixed slurry fuel.

32. A method according to any one of claims 28 to 31 , further comprising: adding 5 to 40 wt% ammonia to the fuel mixture.

33. A method according to any one of claims 26 to 32, wherein the fuel mixture comprises a fuel according to any one of claims 1 to 22.

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