WO2014071448A1

WO2014071448A1 - Briquetting process and system

Info

Publication number: WO2014071448A1
Application number: PCT/AU2013/001282
Authority: WO
Inventors: Jason NUNN; Carel PIETERS; Ross Lawrence Meakins; Todd ROLLASON
Original assignee: White Energy Innovations Pty Ltd
Priority date: 2012-11-06
Filing date: 2013-11-06
Publication date: 2014-05-15

Abstract

A briquetting process for briquetting a bituminous particulate coal material to form end-product briquettes is described. The process includes lowering the moisture content of the particulate coal material to at least a predetermined maximum total moisture content level and performing one or more intermediate briquetting processes including feeding the particulate coal material into an intermediate briquetting apparatus; operating the intermediate briquetting apparatus to form an intermediate agglomerate material from the particulate coal material; and crushing the intermediate agglomerate material. The process further includes a final briquetting process including feeding the particulate coal material obtained by crushing the intermediate agglomerate material into a final briquetting apparatus; and operating the final briquetting apparatus to briquette the particulate coal material at a sufficient pressure to compact the particulate coal material into formed end-product briquettes.

Description

Briquetting Process and system

Field of the invention

The present invention relates to processes and systems for briquetting materials, especially for, but not limited to particulate coal material, in particular bituminous fines, such as coking coals or fine high rank bituminous coal.

Background of the invention

Briquetting of coal has been carried out since the late 19th century. The traditional approach to coal briquetting involved mixing the coal particles with binders to bind the coal particles together into a larger mass. Binders that have been tried include organic binders such as coal-tar pitch, petroleum bitumen and asphalt, wood tar, synthetic and natural resins, starch, sulphite liquors, sugars and molasses, cellulose compounds, vegetable pulps, alginates, glue or gum, albumates, casein, peat, lignite and wood. Inorganic binders that have been used include cement, clay, lime, magnesia, gypsum, sodium or other alkali silicates. Compound binders including blends of two or more of the above have also been tried. The criteria by which binders used in briquetting of coal have been judged include: type of coal being briquetted, briquette strength and handling properties, moisture and weather resistance, combustion characteristics effect on the physical properties of the coal, physical integrity of the briquette during combustion, toxicity of the binder or its de-composition and combustion products cost of the binder, processing costs for the use of the binder, such as blending and curing.

Experience with coal briquettes that incorporate binders has shown that a generally applicable coal binder that meets all of the above criteria has not yet been found. For example, pitch, bitumen and asphalt give adequate strength and moisture resistance but result in smoking combustion, toxicity problems, change to coking properties, high cost and high processing costs. Starch provides good strength and clean burning but is expensive and has poor weathering resistance. Sulphate liquor binders burn with little smoke but produce toxic sulphur dioxide emissions and have poor weathering properties. Sugars, particular molasses, have inferior moisture and weathering resistance and may suffer mould growth during storage. Cellulose-type binders typically suffer from low strength and rapid deterioration, with the briquettes tending to disintegrate in the early stages of combustion. It has been reported that the inorganic binders all suffer relatively low strengths, poor weathering resistance and high ash levels after combustion.

The necessity to add the binder component to the briquette also unavoidably increases the complexity and cost of briquette production. In order to try and avoid some of the difficulties involved with producing briquettes using binders, various attempts have been made to produce binderless briquettes. However, briquetting processes for coal that do not require a binder typically require the coal to be hot and dry.

For example, briquetting processes by which coal particles are fed into a hot gas stream in a flash dryer are known. The coal particles are entrained and heated by the gas stream to cause water to evaporate from the coal. The coal particles are transported by the gas stream to a cyclone separator, where the hot, dried coal particles are separated from the gas stream, dropped into a hopper and passed through the rollers of a briquetting apparatus to form the briquettes. High temperatures in the range of about 300 to 700 °F (about 149 to 371 °C) are necessary during the compression stage. In another example of a binderless briquetting process, high temperature, high pressure mould forming of the coal fines material is employed in an apparatus incorporating a high pressure roll-type briquetting press. The system incorporates a positive pressure, controlled oxygen, gas re-circulation flash dryer and a direct briquette product to feed a heat exchange system for high system efficiency. ^} Binderless briquetting of higher rank coals thus generally involves the heating of the coal to near its softening point (400°C to 500°C) before its compaction. Although such known processes produce strong briquettes with good weather resistance and no contamination of the coal with binders, the heating of the coal feed to such high temperatures does require that expensive measures be taken to prevent the oxidation of the coal and the emission of toxic vapour. Such processing also destroys the coal's coking properties such that the product can only find use in the thermal coal market.

It would be desirable to provide a briquetting process and/or system which maintain the coking properties of the feed coal in the end-product briquettes. Further additionally, or alternatively, it would be desirable to provide a useful alternative to existing briquetting processes and apparatus.

Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Summary of the invention

In one aspect the present invention provides a briquetting process for briquetting a bituminous particulate coal material to form end-product briquettes, the process including: lowering the moisture content of the particulate coal material to at least a predetermined maximum total moisture content level; processing the particulate coal material in one or more intermediate briquetting processes, at least one intermediate briquetting process including: feeding the particulate coal material into an intermediate briquetting apparatus; operating the intermediate briquetting apparatus to form an intermediate agglomerate material from the particulate coal material; and crushing the intermediate agglomerate material; processing the particulate coal material obtained by crushing the intermediate agglomerate material in a final briquetting process, the final briquetting process including: feeding the particulate coal material into a final briquetting apparatus; and operating the final briquetting apparatus to briquette the particulate coal material at a sufficient pressure to compact the particulate coal material into formed end-product briquettes.

In a second aspect the present invention provides a briquetting system for forming end- product briquettes from a bituminous particulate coal material to, the system including: one or more intermediate briquetting assemblies, the or each intermediate briquetting assembly including: an intermediate briquetting apparatus for forming an intermediate agglomerate material from the particulate coal material; a crusher for crushing the intermediate agglomerate material, and a final briquetting assembly down stream of the one or more intermediate briquetting assemblies, the final briquetting assembly including: a final briquetting apparatus for briquetting the particulate coal material at a sufficient pressure to compact the particulate coal material into formed end-product briquettes.

Also described herein is a briquetting process for reducing the moisture content of a bituminous particulate coal material having an initial moisture content below a predetermined maximum total moisture content level, the process including: feeding the particulate coal material into a briquetting apparatus; and briquetting the particulate coal material in a briquette forming part of the briquetting apparatus at a sufficient pressure to reduce the moisture content of the particulate coal material and compact the particulate coal material into an intermediate agglomerate material.

A temperature of the particulate coal material may be kept at or below a maximum temperature to assist in maintaining coking characteristics of the particulate coal material in the end-product briquettes.

The bituminous particulate coal material may be high rank bituminous particulate coal, such as coking coal fines.

The bituminous particulate coal material may have an average particle size of less than 4 mm. The particulate coal material may have a particle size of less than 4 mm and may include material with a particle size of less than 1 mm.

The step of lowering the moisture content of the particulate coal material may include a method of thermal drying, mechanical drying or back blending of particulate coal material thereby to reach the predetermined maximum total moisture content level of the particulate coal material.

Mechanically drying the particulate coal material may include stockpile draining the particulate coal material. The maximum total moisture content level of the particulate coal material may be 20%.

Alternatively, the maximum total moisture content level may be 18%, 15%, or 14%. The maximum total moisture content level may be dependent on the average particle size and/or type of the initial particulate coal material.

The temperature of the particulate coal material, prior to first feeding the material into a briquetting apparatus, may be at an ambient temperature. The temperature of the particulate coal material may alternatively be about 10 to 20 °C above the ambient temperature. Ambient temperature may typically be in the range of 0 to 30 °C. Feeding the particulate coal material into a briquetting apparatus may include a further step of operating a pre-compactor assembly to pre-compact the particulate coal material.

The pre-compactor assembly may be operated to do the pre-compacting work at a minimum rate of approximately 10% of the rate at which a briquette forming part of the briquetting apparatus is doing briquetting work. E.g., if the pre-compactor assembly is doing work at a rate of 2 kW, the briquette forming part may be briquetting at a rate of 20 kW.

The one or more intermediate briquetting processes may result in the production of end- product briquettes with improved strength, density and/or moisture content.

The intermediate agglomerate material may include unstable lumps of coal material, partially formed briquettes, and/or fully formed briquettes.

After producing the intermediate agglomerate material, the process may include a step of crushing or partially crushing the intermediate agglomerate material.

Crushing the intermediate agglomerate material and pre-compacting the particulate coal material or agglomerate material may be performed by in the same feed hopper including one or more augers.

Moisture reduction in the particulate coal material may be achieved by evaporation caused by heat generated from friction produced between coal particles forming the particulate coal material. Evaporation may occur during both pre-compacting and the briquetting steps.

The maximum temperature may be about 110°C. Alternatively, the maximum temperature may be about 105 °C or about 100 °C.

During an intermediate briquetting process, shear forces may be applied to the material. Shear forces may be applied by operating a pair of counter-rotating rollers of a briquette forming part of the intermediate briquetting apparatus differential speeds thereby to increase the shear and therefore the friction and the drying of the intermediate agglomerate material. Corresponding pockets of the counter-rotating rollers may also be offset to introduce additional shear. Corresponding pockets of the rollers may be offset by up to 50%, such that the lip of a given pocket on a first roller of the pair of briquetting rollers approximately aligns with a midpoint of a corresponding pocket on the other of the pair of briquetting rollers. . Pocketised structures, i.e. pocket configuration, on the counter rotating rollers may be adapted to increase the moisture reduction properties of the briquetting process.

Also described herein is a process for forming end-product briquettes having a moisture content less than a predetermined end-product moisture content level and/or a true density greater than a predetermined end-product true density, the process including: processing a bituminous particulate coal material to reduce the moisture content of the particulate coal material and produce intermediate agglomerate material according to the process of the second aspect described above; crushing the intermediate agglomerate material; and briquetting the crushed intermediate agglomerate material in a final briquette forming part of a final briquetting apparatus to form end-product briquettes.

The predetermined end-product moisture content may be 10% or less. The predetermined end-product true density may be 1.2 g/cm3 or more. The end-product briquettes may also have an ash content of approximately 10% or less.

The final briquette forming part may include a pair of pocketed counter-rotating rollers. The pocketed counter-rotating rollers of the final briquette forming part may be operated at substantially synchronous speeds. The pockets of the counter-rotating rollers of the final briquette forming part may be substantially aligned. The end-product briquettes may be stable.

The final briquetting apparatus may include a final pre-compactor assembly. The final pre-compactor assembly may be operated to crush the intermediate agglomerate material. The process may further include: operating the final pre-compactor assembly to pre- compact the crushed intermediate agglomerate material, the pre-compaction process serving to reduce the moisture content of the particulate coal material; and positively feeding the pre- compacted crushed intermediate agglomerate material into the final briquette forming part of the final briquetting apparatus. The moisture reduction achieved by the processes described above may be primarily the reduction of free or surface moisture in the particulate coal material, and may be effected through the evaporation and/or the mechanical expression of moisture, i.e. forcing out of some of the free or surface moisture of the particulate coal material. Evaporation may be achieved through heat generated from friction produced between coal particles forming the particulate coal material, during both the pre-compacting and the briquetting steps of the process.

All steps of the processes described above may maintain the particulate coal material below a maximum temperature selected to maintain coking characteristics of the particulate coal material in end-product briquettes. The predetermined maximum temperature may for example be about 110 °C. Alternatively, the maximum temperature may be about 105 °C. Further alternatively, the maximum temperature may be 100 °C.

Also described herein is an end product briquette formed according to a process as described above.

Also described herein are binderless briquettes, optionally produced by the process defined above, including bituminous coal with true density of at least 1.2 g/cm³, an ash content of approximately 10% or less and a moisture content of 10% or less.

The true density of the binderless briquettes may be at least 1.23 g/cm³, 1.25 g/cm³, or may be at least 1.27 g cm³.

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 and with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 shows a schematic diagram of a process and system for forming briquettes from a bituminous particulate coal material, wherein the system includes multiple briquetting apparatus;

Figure 2 shows a more detailed schematic cross-sectional side view of a pre-compactor assembly and briquette forming part of the briquetting apparatus of Figure 1 ; Figure 3 provides a partial sectional depiction of the briquetting rollers of an intermediate briquetting apparatus used in the apparatus of Figure 1 ; Figure 4 shows a schematic cross-sectional side view of a second embodiment of a briquette forming part of a briquetting apparatus; and

Figure 5 shows a flow chart of a briquetting process for briquetting a bituminous particulate coal material. , Detailed description of the embodiments

At a general level, the process for forming end-product briquettes in accordance with one embodiment of the invention involves one or more intermediate briquetting stages in which the moisture content of a bituminous particulate coal material is reduced, and a final briquetting stage in which the end-product briquettes of a desired moisture content and density are formed. In the intermediate briquetting stages, the moisture content of intermediate agglomerate material formed from the particulate coal material is reduced by a pre-compaction and briquetting process. This process produces the intermediate agglomerate material which, as it is fed into additional downstream stages (being either further intermediate stages or the final briquetting stage) need not be stable products and may, for example be unstable lumps of coal material. The agglomerate material may also comprise fully or partially formed briquettes. In the final briquetting stage end-product briquettes are produced.

The number of intermediate briquetting stages that the particulate coal material is passed through depends on the initial moisture content of the material, the desired moisture content of the end-product briquettes (bearing in mind that the final briquetting stage will itself serve to reduce the moisture content of the particulate material). In some instances the number of intermediate briquetting stages will also depend on the desired true density of the end-product briquettes. In some instances a single intermediate briquetting stage may be suitable, while in other instances two or more intermediate briquetting stages may be necessary.

Where multiple briquetting stages are employed each briquetting stage may be performed by a dedicated briquetting apparatus, the plurality of dedicated briquetting apparatus being arranged in series such that the first intermediate briquetting apparatus receives the initial particulate coal material and each downstream briquetting apparatus receives intermediate agglomerate material from an upstream briquetting apparatus (or receives crushed intermediate agglomerate material from a crusher positioned between the upstream and downstream briquetting apparatus). W

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Alternatively, multiple briquetting stages may be achieved by passing the particulate coal and/or intermediate agglomerate material through the same one or more briquetting apparatus multiple times.

In a further alternative embodiment of the invention, the process for forming end-product briquettes may involve a single pre-compaction and briquetting stage. In this instance the briquetting apparatus used includes a pre-compactor assembly and briquette forming part which are configured/operated so as to reduce the moisture content of the original feed material sufficiently to create end-product briquettes of a desired moisture content and/or density.

In order to more fully explain the present invention, an embodiment of the invention will now be described with reference to Figure 1 , which shows a schematic flow diagram of a process for forming end-product briquettes from a bituminous particulate coal material, for example coking coal fines and high rank bituminous particulate coal.

In the diagram shown in Figure 1, a bituminous particulate coal material 10 to be processed is fed to an intermediate briquetting apparatus 16 from a coal hopper 18. The bituminous particulate coal material 10 may be high rank bituminous coal fines, such as coking coal fines. The particle size of the bituminous particulate coal material 10 is typically 4 mm or less. The particulate coal material may include material with an average particle size of approximately 1 mm or smaller, sometimes also called ultra fines.

In order for the process of the present invention successfully to compact the particulate coal material 10 into briquettes without the use of any binders or the external heating of the material during briquetting, it is necessary for the moisture content of the particulate coal material 10 to be less than or equal to a particular critical or maximum initial total moisture content prior to briquetting the material 10. This is due to the fact that moisture acts as a lubricant during the compaction of the particulate coal material 10. Thus, if the moisture content of the particulate coal material 10 has a moisture content level above the material's critical moisture content level, the moisture acts as a lubricant during compaction and the necessary interaction between particles is not provided to enable drying and/or compaction.

The critical moisture content of the particulate coal material 10 is dependent on the moisture content of the material as well as the material's particle size distribution. The coarser the particle size distribution of the material, the higher the critical moisture content will be. However, the coarser the particle size distribution, the lower the total moisture of the material tends to be.

It should be appreciated that a bituminous, and particular coking or high rank, particulate coal material does not have a high inherent moisture content, i.e., moisture within the coal itself. Rather, the moisture content is largely made up of the surface moisture of the material, which is water held on the surface of the coal particles or macerals. Due to this particular characteristic of bituminous particulate coal, the aim of the process is not to remove inherent moisture from the particulate coal or to change the equilibrium moisture in the particulate coal.

Where the moisture content of the particulate coal material exceeds the critical moisture content a number of options for reducing the moisture content are available. For example, in the illustrated embodiment the coal hopper 18 is supplied with material from a blending mill 20 in which initial feed material 21 is blended with drier particulate coal material from downstream in the process via return path 22 in order to reduce the overall moisture content. Through monitoring the moisture content level of the particulate coal material being fed into the briquetting apparatus 16, it is possible to determine to what extent feedback of drier particulate coal or intermediate agglomerate material is necessary.

In addition, and as also shown in Figure 1, the initial particulate coal material 21 may be kept in a stockpile drainage container. The hopper 18 is then fed from the upper end of the stockpile drainage container 21 where the particulate coal material is drier. Both the mentioned methods do not require any external heating of the particulate coal material. Thus, the temperature of the particulate coal material at this point in the process (i.e. prior to first feeding the material into the briquetting apparatus 16) may be at an ambient temperature. The temperature of the particulate coal material may also be about 10 to 20°C above the ambient temperature. Ambient temperature may typically be in the range of 0 to 30°C. Irrespective, it is important not to substantially increase the temperature of the particulate material as the maximum temperature that is desirable in any stage of the briquetting process is for example 1 10 °C, more preferabl 105 °C and most preferably 100 °C.

It will be appreciated by a person skilled in the art that other suitable methods of drying the particulate coal material 10 prior to the briquetting process may be used, whether by thermal drying, mechanical drying or back blending with similar dry material, or a combination thereof, provided that the temperature rise in the particulate coal material is limited to the maximum temperature set out above. The reason for maintaining this maximum temperature during all stages is to ensure that there is no potential for the deterioration of coking properties in the briquettes as compared to the feed particulate coal material. Additionally, and as mentioned above, high temperatures in the particulate coal material will also present other undesirable conditions.

It will also be appreciated that if the initial particulate coal material has an acceptable moisture content it can be fed directly into hopper 18 (or, indeed, pre-compactor hopper 26) without the need for blending and/or stockpile drainage. The maximum total moisture content level of the particulate coal material may be 20%, more preferably 18%, more preferably 15% and most preferably 14%. Unless otherwise stated herein, content percentages (e.g. moisture content, ash content etc) are provided with respect to weight.

The particulate coal material 10 dried to at least its critical moisture content is collected in the hopper 18 and then fed by a feed auger 24 to an intermediate briquetting apparatus 16. Intermediate briquetting apparatus 16 includes a pre-compactor assembly 26 and briquette forming part 1 1 (being briquette rollers 12 and 14).

The particulate coal material 10 passes from the feed auger 24 into the pre-compactor assembly 26 under conditions which do not raise the temperature of the particulate coal material beyond 100°C.

As can more clearly be seen in Figure 2, the pre-compactor assembly 26 includes a pre- compactor hopper 27 fitted with an auger 28 (which is driven by an auger motor 30). The pre- compactor hopper 27 narrows into a passage 29 in which the auger 28 closely fits, thereby to compact the particulate coal material and positively feed the particulate coal material to the rollers 12 and 14 of the briquette forming part of the briquetting apparatus 16.

In pre-compacting the particulate coal material the moisture content of the material is reduced. In one embodiment, the pre-compactor assembly 26 is adapted to do approximately work at a minimum rate of approximately 10% of the rate at which the briquette forming part 1 1 is doing work. For example, if the pre-compactor assembly is doing work at a rate of 2 kW, the briquette forming part 11 is briquetting at a rate of 20 kW.

To enable the pre-compactor assembly to do this work the pre-compactor assembly may be large and ruggedized. For example, the pre-compactor assembly may have a larger pre- compaction motor, a longer screw, multiple screws and/or may be made from a better quality steel. In increasing the power of the pre-compacter, the drying features of the pre-compacter is improved.

The briquette forming part 11 of the briquetting apparatus 16 is provided with two counter rotating rollers 12 and 14. The pre-compactor assembly 26 feeds material, through the passage 29, to the nip between rollers 12 and 14, where the material is compressed into briquettes 36 (or, depending on the roller configuration, intermediate agglomerate material such as partial briquettes). The briquette formation process also serves to drive moisture out of the particulate coal material. In the present embodiment both rollers 12 and 14 are pocketed in order to increase shear forces which, in turn, increases the moisture content reduction of the material. It will be appreciated, though, that in alternative embodiments one of the rollers may be smooth. As the particulate coal material passes through the rollers, it is compressed and subjected to shear, the importance of which is described below.

Introducing shear to the particulate coal material during the production of briquettes increases the friction between the particles and, consequently, the drying/moisture reduction of the particulate coal material. In order to increase the shear, the two counter rotating rollers 12 and 14 may be operated at differential speeds and/or respective pockets of the counter rotating rollers may also be offset.

As described above, the present invention includes both intermediate and final briquetting stages. As the purpose of the intermediate briquetting stage(s) is to reduce the moisture content of the particulate coal material, the intermediate agglomerate material 36 produced by the intermediate stage need not be a physically stable product. This allows for the intermediate briquetting stage(s) to be performed using parameters that may not be appropriate for a final briquetting stage (where stability of the briquettes produced is of greater importance). For example, offsetting the pockets of rollers 12 and 14 may increase shear, but at the same time decrease the stability of the briquettes formed. In one embodiment, corresponding pockets of rollers 12 and 14 are offset by up to 50%. A partial view of rollers 12 and 14 with pockets offset by 50% is provided in Figure 3, where it can be seen that the pockets are arranged such that the midpoint 13 of a given pocket on the roller 12 aligns with a lip 15 of the corresponding pocket on the roller 14. This can be contrasted with aligned roller pockets where the lips and mid-points of corresponding pockets are substantially aligned. Offsetting the roller pockets by this amount increases the shear during the briquetting process and the amount of moisture driven out of the material. A consequence of offsetting the pockets by this amount, however, may be that the briquettes produced are not stable (i.e. are prone to falling apart), resulting in an intermediate agglomerate material. While this is not necessarily problematic in an intermediate briquetting stage of the process (and may even be advantageous as the unstable intermediate agglomerate material may be easier to crush/comminute for downstream briquetting stages), a pocket offset of this degree may not be desirable for the final briquetting stage (though this will depend on the intended use of the end-product briquettes).

It will be appreciated that a wide variety of physical and/or operational parameters of briquetting apparatus 16 may be used. By way of one non-limiting example: the two opposed rollers 12 and 14 may each have a diameter within the range of 100 mm to 600 mm, or within the range of 400 mm to 550 mm; the ratio of the briquette pocket width to roller diameter may for example be in the range of from 0.05 to 0.15, such as about 0.08; the rollers may be rotated at speeds from 20 rpm to 100 rpm, e.g., from 80 rpm to 90 rpm; the rollers may apply loadings within the range of 60 kN to 150 kN per centimetre of roller width, e.g., a loading of 115 kN to 130 kN per centimetre of roller width for a 460 mm diameter roller. Persons skilled in the art will appreciate that other diameters, pocket width to roller ratios, rotation speeds, and/or loading ranges may be suitable and preferable.

In one embodiment of the invention, the intermediate agglomerate material 36 formed by the intermediate briquetting apparatus 16 are directed to a downstream briquetting stage.

If the moisture content of the intermediate agglomerate material 36 is above the desired moisture content of the end product (and processing the material in the final briquetting apparatus 42 will not lower the moisture content to an acceptable level), the downstream briquetting stage will be a further intermediate briquetting stage (e.g. the material will be transferred to and processed by a briquetting apparatus similar, to apparatus 16).

As discussed further below, and by way of non-limiting example, the target properties of the end-product briquette may be a moisture content of less than 10%, and an apparent relative density of at least 1.2 g/cm³.

Alternatively, if the moisture content of the intermediate agglomerate material 36 is at or below the desired moisture content of the end product (or processing the material in the final briquetting apparatus 42 will lower the moisture content to an acceptable level), the downstream briquetting stage will be a final briquetting stage (e.g. the material will be transferred to and processed by a final briquetting apparatus such as 42 described below).

In the illustrated embodiment of the process, before being fed to the downstream briquetting stage intermediate agglomerate material 36 from the intermediate briquetting stage are collected and crushed in a briquette hopper 38. As discussed above, if the moisture content of the initial feed material is above the critical moisture content, material from hopper 38 (i.e. crushed intermediate agglomerate material 36 which have a reduced moisture content due to being processed by the intermediate briquetting apparatus 16) may be recycled into hopper 20 and blended with the initial feed material to lower its average moisture content.

In alternative embodiments, however, intermediate agglomerate material 36 from the intermediate briquetting stage may be fed directly from the intermediate briquetting apparatus 16 to a pre-compactor assembly of a downstream briquetting apparatus. In this case crushing of the intermediate agglomerate material from the upstream briquetting apparatus (e.g. 16) is achieved by the downstream pre-compactor assembly itself (such as pre-compactor assembly 26 of an intermediate processing stage or pre-compactor assembly 44 of a final processing stage), and an additional/dedicated crushing unit such as unit 38 need not be used. Once the desired moisture content has been reached (or the desired moisture content will be reached once the material has been processed by the final briquetting apparatus 42), the material is directed to the final briquetting apparatus 42 to form end-product briquettes. In this embodiment briquetting apparatus 42 is similar to briquetting apparatus 16, and includes a pre-compactor assembly 44 which pre-compacts and feeds the material into the nip between rollers 50 and 52 of a briquette forming part 49.

Given the moisture reduction that will have occurred in upstream, intermediate briquetting stage(s), the final briquetting apparatus 42 is arranged/operated to produce well- formed end-product briquettes. As such the pre-compactor assembly 44 of the final briquetting apparatus 42 (including the feed hopper 45 and auger 48) need not necessarily be ruggedized or have a power rating substantially more than that of the briquette forming part 49 of briquetting apparatus 42. Similarly, the rollers 50 and 52 of the briquette forming part 49 need not be configured operated to introduce as much shear (e.g. by offsetting pockets and/or having different rotation speeds) as was described in respect of the intermediate briquetting stage(s) (though it will be appreciated that introducing some shear may be desirable as part of the process of forming stable end-product briquettes).

As with the intermediate briquetting apparatus 16, it will be appreciated that a wide variety of physical and/or operational parameters of briquetting apparatus 42 may be used. By way of non-limiting example: the two opposed rollers 50 and 52 may each have a diameter within the range of 100 mm to 600 mm, or within the range of 400 mm to 550 mm; the ratio of the briquette pocket width to roller diameter may be in the range of from 0.05 to 0.15, e.g., with a ratio of about 0.08; the rollers may be rotated at speeds from 20 rpm to 100 rpm, e.g., from 80 rpm to 90 rpm; the rollers may e.g., apply loadings within the range of 60 kN to 150 kN per centimetre of roller width, such as a loading of 115 kN to 130 kN per centimetre of roller width for a 460 mm diameter roller. Persons skilled in the art will appreciate that other diameters, pocket width to roller ratios, rotation speeds, and/or loading ranges may be suitable or preferable.

The final briquetting apparatus 42 produces end-product briquettes 46 having a moisture content of equal to or below a desired final moisture content (e.g. less than approximately 10%), and a true density of above a desired final true density (e.g. greater than approximately 1.2 g/m ). In addition, the ash content of the end-product briquettes may be less than a desired final ash content, preferably less than approximately 10%.

Although the process and briquetting apparatus of Figures 1, 2, and 3 show material being fed to briquetting apparatus 16 and 42 moving in an essentially downwardly vertical direction, it will be appreciated that other suitable briquetting apparatus may be used. For example, Figure 4 provides a briquetting apparatus 60 where the particulate coal material moves in an essentially horizontal direction as it is fed to the briquetting rollers. In Figure 4, a feed hopper 26 A is fitted with a horizontally oriented auger 28 A driven by auger motor 3 OA. The auger 30A feeds the particulate coal material from the base of the hopper 26A through a horizontal auger pipe 62 to the nip between the rollers 64 and 66. Because the pipe 62 forms a relatively close fit with the auger, this serves to assist in building up the back pressure and reducing blowback owing to the tortuous path defined by the auger and the resultant pre- compaction of particulate matter within the auger. In this example, the pipe 62 with the auger 28 A therefore forms the pre-compactor assembly of the process. This arrangement may also be used for the vertically feeding pre-compactor assembly described above.

During the steps of pre-compaction and compaction performed by each briquetting apparatus, drying of the particulate coal material takes place via a combination of mechanical expression, i.e., forcing out of some of the free or surface moisture of the particulate coal material, and evaporation. No external heat is added to the process during the pre-compaction and compaction steps and the temperature of the particulate coal material throughout the process is kept below a maximum temperature, in one example embodiment about 100 °C. As the particles are pre-compacted and briquetted, evaporation is achieved through the heat generated from friction between the coal particles forming the particulate coal material. To achieve this friction, the critical moisture content must be achieved before the material is fed to the first briquetting apparatus in the process.

As already mentioned, part of the intermediate agglomerate material or crushed agglomerate material may also be fed back to the blending mill 20 in order to reduce the overall moisture content of the particulate coal material feed 10. For example, use may be made of a screen, if necessary, to screen out a pre-determined size fraction of the crushed intermediate agglomerate material to be fed to the blending mill.

Depending on the characteristics of the initial particulate coal material and the product requirements of the final briquettes, the briquetting process extends to re-crushing and/or re- compacting and re-briquetting the crushed briquettes a number of times. Each briquetting stage may, but need not, include a pre-compacting step. Also, the step of re-crushing of the briquettes may be omitted, depending on the specific application or process requirements. Re-crushing and pre-compacting may also be achieved in one and the same hopper, making use of one or more augers.

In the embodiment described above, the particulate coal material is agglomerated and dried via a series of briquetting apparatus with or without pre-compactor assemblies, depending on the desired briquette strength and moisture content.

The particular application of the briquetting process may determine the characteristics of the briquetting apparatus to be used. Some examples of configurations have been mentioned above. Alternatively to the mentioned configurations, the first and/or intermediate briquetting apparatus in a series may include one flat roller and employ either simultaneous or differential roller speed. As mentioned, differential roller speed is employed to produce additional shear, which in turn produces greater friction between the coal particles and generate greater compaction, agglomeration and drying.

An example of a method of a briquetting process for briquetting a^bituminous particulate coal material is now described with reference to a flow chart 68 in Figure 5. The method may, but need not, be performed by the briquetting system of Figure 1.

For ease of reference, optional steps are indicated in the flow chart by broken lines.

The process starts at block 70, where the moisture content of a bituminous particulate coal material is measured. As mentioned above, the moisture content has to be below a predetermined maximum total moisture content level. If the moisture content of the particulate coal material is above this level, steps are taken to lower the moisture content level (see block 72). In particular, the moisture content of the particulate coal material may be lowered by thermal drying of the particulate coal material (block 74), by mechanical drying of the particulate coal material as indicated by block 76 (e.g., through the use of stockpile drainage) or through back blending material from further down the process into the feed (block 78). The particulate coal material will be dried until it reaches the predetermined maximum total moisture content level. At that point, the particulate coal material is fed on to the pre- compacting and/or compacting stages of the process.

During an initial pre-compacting stage, shown by block 80, a pre-compactor assembly such as pre-compactor assembly 26, pre-compacts the particulate coal material, typically at a power rating of double that of the associated briquette forming part 11 of the briquetting apparatus 16. Once pre-compacted, the particulate coal material is passed through two counter rotating rollers, preferably having differential speeds and/or off-set briquetter pockets, thereby to introduce maximum shear during the briquetting process (see block 82). As already mentioned, both during the pre-compaction stage (block 80) and compacting or briquetting stage (block 84) the friction on the particles of the particulate coal material is increased, thereby ensuring drying of the material.

The pre-compacting step and compacting step may be repeated as intermediate pre- compacting and compacting steps in the event that a better quality briquette is required as final product. For example, if it is found that the density and moisture content of the compacted material (i.e. intermediate agglomerate material) does not meet the final product criteria (at step 84), the material may optionally be crushed (at block 86), some of the product being fed back to the moisture lowering stage 72, while the remainder of the product is either immediately re- compacted (block 82), or first pre-compacted (block 80) prior to being re-compacted (block 82). These intermediate steps may be repeated as many times as required, bearing in mind that it will decrease the production rate and increase the overall cost of production of the briquettes.

Once the intermediate agglomerate material is of sufficient quality, it may be passed through a final pre-compaction stage (see block 88) and then through counter rotating rollers of a final briquetter. The rollers preferably have synchronised speeds and aligned briquetter pockets, thereby to produce well-formed end-product briquettes. During this final stage of pre- compaction and compaction, the power ratings of the pre-compactor assembly and rollers of the compactor may be similar.

The end-product formed by the briquetting process are binderless briquettes including bituminous coal with an apparent relative density of at least 1.2 g cm³, an ash content of approximately 10% and a moisture content of approximately 10%. The apparent relative density of the binderless briquettes may preferably be 1.23 g/cm³, 1.25 g/cm³ and most preferably 1.27 g/cm³. The moisture content of the briquettes may also preferably be less than 10%. As mentioned, the bituminous particulate coal may be high rank coal such as coking coal.

A specific example of the method of the present application for manufacturing briquettes from a bituminous particulate coal material will now be described. In this example of the method, a particulate coking coal material at different initial moisture contents was introduced to the briquetting process of the invention including four briquetting stages, i.e. four passes through a briquetting apparatus. The results after each stage are given in Table 1 below.

Table 1

Initial feed moistures of the coking materials in this instance range from 6.5% to 13.2%. The apparent density of the particulate coal material feed started at approximately 700 kilograms per cubic metre (bulk) and increased to greater than 1,200 kilograms per cubic metre (apparent). The moisture content of the coal material is also reduced by an average of approximately 1.5% per pass through the briquetting apparatus. The critical moisture content of the particular feed is approximately 15%, above which point the process cannot generate the inter-particle shear to bond the particles or to generate sufficient friction to drive off any free moisture.

In an alternative embodiment of the invention a single briquetting apparatus (such as apparatus 16) may be used. This will be appropriate where sufficient moisture can be driven from the original feed material in a single pre-compaction/briquetting process (i.e. by passing the material through pre-compactor assembly 26 and briquette forming part 11 of the briquetting apparatus 16). In this case further downstream processing by additional briquetting apparatus is not required, with the briquettes 36 produced by apparatus 16 being the end-product. If a single briquetting apparatus is to be used, and stable end-product briquettes are desired, the amount of shear introduced in the briquetting process (consequent on the pocket configuration and roller speed of rollers 12 and 14) will be controlled to produce stable briquettes. Without wishing to be bound by theory, the mechanism underlying the briquetting process of the present invention is best explained according to the internal coal structure model of high rank bituminous coals. It is the view that the Hirsch model, as presented by Van revelen (1993), provides the best explanation of the probable phenomena involved. This model describes three differing types of coal structure: 1. An 'Open Structure'. The 'Open Structure' is characteristic of low-rank coals which contain up to about 85% carbon (d.a.f, basis). The lamellae (molecular clusters) are connected by cross-links, and are more or less randomly oriented in all directions. The crosslinks are predominantly made up of strong covalent bonds, consisting of carbon-carbon, carbon- oxygen and carbon-sulphur bonds. The coal at this carbon content range is at its strongest and least deformable and constitutes a highly porous system. This structure is, however, quite elastic, and is analogous in terms of behaviour in response to compression to that of strong chicken wire which has been rolled into a ball.

2. The 'Liquid Structure'. This structure is typical of bituminous coals with carbon contents in the range of 85-91% (d.a.f. basis). In the 'Liquid Structure', the lamellae show some orientation, which accounts for the formation of crystallite, including two or more lamellae. The number of strong covalent bonding cross-links noted in conjunction with the 'Open' structure has considerably decreased - being replaced by weaker electrostatic forces such as Van der Waals interactions. Again compared to the 'Open' structure, intra-molecular distances are greatly reduced and pore spaces are practically absent or as low as 1%. Elastic behaviour is practically nil, and it is in the 'Liquid Structure' phase of the coalification process that the coal is at its softest and most deformable (or plastic) condition.

3. The 'Anthracitic Structure'. This type of structure is seen especially in high-rank coals with carbon content > 91%. The bridge structures have disappeared altogether, and the degree of orientation of the lamellae relative to each other has greatly increased. In addition, the lamellae, or carbon clusters, at this rank are sheets including 30 to 40 rings rather than the 3 to 5 rings as was the case in the Open' and 'Liquid' structures. Due to the size and orientation of these lamellae, electrostatic forces and Van der Waals interactions between these sheets are very significant, resulting in these coals once again becoming hard and difficult to deform. Macropores tend to also develop between sheets during this stage, with the. orientation of these macropores more or less corresponding to the alignment of the intervening sheets.

Coals exhibiting a 'Liquid Structure', e.g. coking coals, tend to exhibit plastic, as opposed to elastic, behaviour during compression and because of this, careful control over the size distribution and moisture content of the material feed to the briquetting machine ceases to become a major process requirement so long as significant amounts of free moisture are avoided. Microscopic examination of briquettes produced from 'Liquid Structure' coals, such as briquettes produced in accordance with the present invention, indicate that the actual bonding mechanism in this case is the result of deformation of the vitrinite macerals under the combined influences of pressure and shear to the extent that the original grain structure is completely lost and the vitrinite forms an almost continuous matrix which binds the balance of the maceral and mineral components into a coherent mass.

It requires very little force to overcome the weak Van der Waals type bonds between the lamellae, hence deformation of the grains requires little force. It is through the very large contact area between the distorted coal grains that this weak bond is able to develop over large areas and result in considerable briquette strength. A key feature to the binderless agglomeration of the present invention is that if the lamellae are maintained in close alignment after deformation, as could occur under the high pressures of briquetting, the electrostatic interactions can re-establish and maintain the integrity of the deformed structure, without the need for additional heat. Neighbouring particles may also become integral to the structure as, through deformation, they are brought into extremely close contact with each other. This very close contact between the coal particles, coupled with the fact that higher rank coal particles do contain very little void space (if any), make them very resistant to moisture, i.e. they do not adsorb or absorb moisture readily.

The introduction of shear during the briquetting process, through various counter roller speeds, is advantageous and necessary during the present briquetting process to provide optimum strength and compaction within the briquettes formed according to the present process. However, shear also imposes limitations upon the ability to utilise roll-type presses to briquette coal without the aid of binders. When a briquette leaves the pockets of the rollers of a briquetting apparatus, much of the stress which was applied during its formation remains locked within the agglomerate. The actual amount of this residual stress is dependent upon a number of factors which include:

• geometry and size of the briquette,

• diameter and rotation speed of the rollers,

• the amount of compressive forces applied during the briquetting process, and,

• the shear strength that is developed within the briquette during the compacting process.

Provided that the lamellae are maintained in close alignment following their initial deformation, i.e., as a result of the shear forces imposed as the material is introduced into the roller 'nip', this initial shear force is proportional to some combination of the roller compressive force, roller speed and pocket geometry. The electrostatic interactions which provided initial structural integrity to the material prior to this deformation is re-established during the period of compression between the rollers. However, as the roller faces separate prior to the briquette being discharged from the roller pockets, an additional shear stress (which is also proportional to some combination of roller compressive force, roller speed and pocket geometry) is imposed on the briquette. In instances where the magnitude of this secondary shear force exceeds the shear strength that is developed within the briquette during the compression stage, the briquette breaks apart as it is discharged from the press, typically along the centreline of the briquette where the shear stress is greatest, resulting in a phenomenon known as 'clam-shelling'. In the first stage of briquetting, and indeed subsequent intermediate stages if required, this is preferable as it generates extra friction and resultant heat and drying. It also serves to reduce the particle size of the briquettes to facilitate easier feeding to the next stage of briquetting, without necessarily providing specific crushing of the briquettes.

The present invention thus provides a method of producing high quality briquettes from particulate coal material such as coking fines or high rank bituminous coal fines without the use of any binder, ensuring that the briquettes meet general requirements of coal briquettes, including briquette strength and handling properties, moisture and weather resistance, physical integrity of the briquette during combustion, lack of toxicity of the binder. Processing costs are also reduced as no blending or curing is necessary. Additionally, as no heat is added during the briquetting process or with the coal material being kept at a temperature below a maximum temperature, e.g., 100 °C, the coking properties of the particulate coal material are not deteriorated during the process.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Those skilled in the art will appreciate that the present invention may be susceptible to variations and modifications other than those specifically described. It is to be understood that the present invention encompasses all such variations and modifications that fall within its spirit and scope.

Claims

1. A briquetting process for briquetting a bituminous particulate coal material to form end-product briquettes, the process including:

lowering the moisture content of the particulate coal material to at least a predetermined maximum total moisture content level;

processing the particulate coal material in one or more intermediate briquetting processes, at least one intermediate briquetting process including:

feeding the particulate coal material into an intermediate briquetting apparatus;

operating the intermediate briquetting apparatus to form an intermediate agglomerate material from the particulate coal material; and

crushing the intermediate agglomerate material;

processing the particulate coal material obtained by crushing the intermediate agglomerate material in a final briquetting process, the final briquetting process including:

feeding the particulate coal material into a final briquetting apparatus; and operating the final briquetting apparatus to briquette the particulate coal material at a sufficient pressure to compact the particulate coal material into formed end-product briquettes.

2. A briquetting process according to claim 1 , wherein lowering the moisture content of the particulate coal material includes drying the particulate coal material by one or more drying methods selected from a group including: thermal drying, mechanical drying, and back blending of particulate coal material.

3. A briquetting process according to claim 1 or claim 2, wherein the predetermined maximum total moisture content level of the particulate coal material is 14%.

4. A briquetting process according to any one of claims 1 to 3, wherein the intermediate briquetting apparatus operated in at least one of the intermediate briquetting processes and the final briquetting apparatus are the same briquetting apparatus.

5. A briquetting process according to any one of claims 1 to 4, wherein in at least one intermediate briquetting process the step of feeding the particulate coal material into the intermediate briquetting apparatus includes operating an intermediate pre-compactor assembly to pre-compact the particulate coal material, and wherein pre-compacting the particulate coal material reduces moisture content of the particulate coal material.

6. A briquetting process according to claim 5, wherein the intermediate pre- compactor assembly is adapted to work at a minimum rate of approximately 10% of the rate at which a briquette forming part of the intermediate briquetting apparatus is doing briquetting work.

7. A briquetting process according to any one of claims 1 to 6, wherein in the final briquetting process, feeding the particulate coal material into the final briquetting apparatus includes operating a final pre-compactor assembly to pre-compact the particulate coal material, and wherein pre-compacting the particulate coal material reduces moisture content of the particulate coal material.

8. A briquetting process according to claim 7, wherein the final pre-compactor assembly is adapted to work at a minimum rate of approximately 10% of the rate at which a briquette forming part of the final briquetting apparatus is doing briquetting work.

9. A briquetting process according to claims 7 or 8 when dependent on claims 5 or 6, wherein the intermediate pre-compactor assembly and the final pre-compactor assembly are the same pre-compactor assembly.

10. A briquetting process according to any one of claims 1 to 9, wherein in at least one intermediate briquetting process the step of operating the intermediate briquetting apparatus to form the intermediate agglomerate material includes operating the intermediate briquetting apparatus to apply shear forces to the particulate coal material to reduce moisture content of the particulate coal material.

11. A briquetting process according to claim 10, wherein shear forces are applied by one or more of: operating counter rotating rollers of the briquetting apparatus at differential speeds; and offsetting corresponding pockets of the counter rotating rollers.

12. A briquetting process according to any one of claims 1 to 11, wherein the intermediate agglomerate material produced by a given intermediate briquetting process has an increased apparent relative density compared to the intermediate agglomerate material of an upstream briquetting processes.

13. A briquetting process according to any one of claims 1 to 12, wherein moisture content of the particulate coal material is reduced through the evaporation of moisture and/or the mechanical expression of surface moisture from the particulate coal material.

14. A briquetting process according to any one of claims 1 to 13, wherein during the briquetting process a temperature of the particulate coal material is kept at or below a maximum temperature to assist in maintaining coking characteristics of the particulate coal material in the end-product briquettes.

15. A briquetting process according to any one of claims 1 to 14, wherein the maximum temperature is selected from a group including 110 °C, 105 °C, and 100 °C. ¹

16. A briquetting process according to any one of claims 1 to 15, wherein the end- product briquettes have a predetermined end-product moisture content of 10% or less.

17. A briquetting process according to any one of claims 1 to 16, wherein the end- product briquettes have a predetermined end-product true density of 1.2 g/cm³ or more.

18. A briquetting process according to any one of claims 1 to 17, wherein the end- product briquettes have an ash content of approximately 10% or less.

19. An end product briquette formed according to a process as claimed in any one of claims 1 to 18.

20. A briquetting system for forming end-product briquettes from a bituminous particulate coal material to, the system including:

one or more intermediate briquetting assemblies, the or each intermediate briquetting assembly including:

an intermediate briquetting apparatus for forming an intermediate agglomerate material from the particulate coal material;

a crusher for crushing the intermediate agglomerate material, and

a final' briquetting assembly down stream of the one or more intermediate briquetting assemblies, the final briquetting assembly including:

a final briquetting apparatus for briquetting the particulate coal material at a sufficient pressure to compact the particulate coal material into formed end-product briquettes.

21. A briquetting system according to claim 20, wherein at least one of the one or more intermediate briquetting assemblies further includes an intermediate pre-compactor assembly for pre-compacting the particulate coal material and feeding the pre-compacted particulate coal material into the intermediate briquetting apparatus.

22. A briquetting system according to claim 20 or claim 21, wherein the final briquetting assembly further includes a final pre-compactor assembly for pre-compacting the particulate coal material and feeding the pre-compacted particulate coal material into the final briquetting apparatus.

23. A briquetting system according to any one of claims 20 to 22, further including a drying apparatus upstream of a first intermediate briquetting assembly, the drying apparatus operable to lower the moisture content of the particulate coal material to at least a predetermined maximum total moisture content level.