AU2008203855B2 - Process of forming a composite briquette - Google Patents

Abstract

A process of forming a composite briquette from low rank coals and aggregate material comprising: drying a low rank coal feed to produce a dried 5 coal having a moisture content of between 8 to 16% by weight; mixing the dried coal with an aggregate material; and compacting the dried coal and aggregate material mixture into briquettes.

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: PROCESS OF FORMING A COMPOSITE BRIQUETTE Applicant: Mecrus Pty Ltd The following statement is a full description of this invention, including the best method of performing it known to me: 1 6067 DG 2 PROCESS OF FORMING A COMPOSITE BRIQUETTE Field of the Invention 5 The present invention generally relates to a process of forming a composite briquette. The invention is particularly applicable for forming a briquette that includes low rank coals and an aggregate material such as mineral fines and/or industrial waste briquette and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. 10 However, it is to be appreciated that the invention is not limited to that application. Background to the Invention 15 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. 20 Low rank coals such as lignite and sub-bitumous coals are generally regarded as a low quality fuel source due to their high moisture content, low density and soft, friable material properties. Brown coal (lignite) for example has a carbon content of between 60 to 75 % on a dry basis, and a moisture 25 content of between 50 to 70 % on a weight basis. Sub-bituminous coals have a carbon content of between 75 and 80 % on a dry basis and a moisture content of between 25 to 30 % on a weight basis. The moisture content and material properties of low rank coals must therefore be addressed to industrially exploit these types of coals. 30 Briquetting has been used to convert low rank coals to a hard fuel of higher calorific value. In this process, the low rank coal is dried to a moisture content of less than 18% and then compressed into a homogeneous body using X:\ECFPaterM Spedfications\COMPLETES\Coa4rn bdquettes\Process for bdquettng lower rank oais with mineral fines - Prov- final .doc 3 an extrusion press or roll briquetting machine. Binder agents can be used to hold the briquette together. Most low rank coal of this form is burned for electric power generation close to 5 the mine sites for both economic and safety reasons. Low rank coal is generally not used in other industrial processes due to the comparably low calorific value compared to higher ranked coals such as bituminous and anthracite and comparably inferior material properties. 10 It would therefore be desirable to provide a briquette formed from a low rank coal that can be suitably formulated in certain embodiments for use in an industrial process such as iron smelting or the like. Summary of the Invention 15 According to the present invention, there is provided a process of forming a composite briquette from low rank coals and aggregate material comprising: drying a low rank coal feed to produce a dried coal having a moisture content of between 8 to 16% by weight; 20 mixing the dried coal with an aggregate material selected from mineral fines, industrial waste material or a combination thereof; and compacting the dried coal and aggregate material mixture into briquettes. The process of the present invention therefore produces a composite briquette 25 which includes a carbon content from the low rank coal feed intermixed with one or more selected aggregate materials. The aggregate material is preferably selected to improve the material property of the briquettes and/or to enrich the composition of the briquettes. For example, the 30 aggregate material can include mineral fines where it is desirable to enrich the composition of the briquettes. Additionally, or alternatively an industrial waste material such as sand, rubber, agricultural waste or the like could be used as the aggregate material where it is desirable to improve the material property of the briquettes. <filename> 4 Mineral fines are mineral particles produced from or in a mineral extraction process or a mineral processing process. Examples include iron ore fines, magnesium ore fines, nickel ore fines, copper ore fines, gold mining fines or tailings, silver mining fines or tailings, uranium mining fines, a combination 5 thereof or similar. Mineral fines from these processes can be difficult to process due to the handling difficulties associated with the small particle size of the fines. These small particles can therefore be more easily handled and transported when included within a briquette. The briquette also provides a combustion material from the low rank coal. This type of briquette can therefore 10 be used as a mineral and combustive feedstock for an industrial process. For example, a briquette formed using the process according to the present invention that includes a low rank coal content and an iron ore content, such as magnetite, can be used as a feed material of an iron smelting process. 15 Industrial waste can be any processed and sized waste particle that contains an energy/calorific value, a mineral element value and/or a mechanical property that can be combined with the coal and/or mineral fines to increase the economic value of a briquette formed from that combination. Examples include waste from rubber production or tyres, wood products, fibre products, 20 agricultural waste, plant material or similar. For example, a briquette formed using the process according to the present invention that includes a low rank coal content and an agricultural waste content such as pressed sugar cane fibre can have superior material properties from the inclusion of this fibre and an altered calorific value. 25 Low rank coal such as lignite, sub-bitumous or a combination is mined as a mass of soft, friable, low density material having a high moisture content (typically between 25% and 70% by weight). This mined material is preferably pre-conditioned prior to the drying step to provide a low rank coal feed which 30 can be optimally dried and mixed with a selected aggregate material. The preconditioning steps generally include a comminution step and a sizing step to process the low rank coal to a desired particle size. The comminuting step can include any process equipment for crushing, cutting, shearing, powdering, pulverising or the like. Suitable process equipment for the crushing process X:\ECP\Patent Spedfications\COMPLETES\Coalion brquottes\Prpcess for blxMue~ttr lower rank coals with mineral fines - Prov- final .doc 5 includes hammer mills, roll crushers, beaters, ball mills, grinding equipment, rolling mills or similar. The comminuted low rank coal particles are then preferably sized through at least one screen. Screening equipment can include grizzlies, bar screens, and wire mesh screens. However, the screen equipment 5 is preferably vibratory screening equipment due to the material handling properties of the high moisture content coal material. The grate size of the screens preferably size the feed to a maximum particle size of less than 10mm and more preferable less than 6 mm. The applicant has found that comminuted low rank coal particles of this size are more easily dried to a moisture content of 10 between 8 to 16% by weight in the drying step. During the drying step, the moisture content of the low rank coal is reduced from between 25% to 70% by weight to between 8 to 16% by weight. The loss of this moisture content in the coal forms pores and/or voids in the low 15 rank coal material. While not wishing to be limited to any one theory, the applicant has found that aggregate material particles of an appropriate size, such as less than 10mm, preferably being fines particles having a particle size of less than 1mm and more preferably less than 50 mesh in size, can be trapped within the porous structure created during this drying process. During 20 the compaction step, it is thought that these pores and other inter-particle void spaces in the dried coal collapse, thereby compressing any aggregate material contained in the pores and in the inter-particle void spaces within the structure of the dried low rank coal. 25 The drying step can be conducted in any suitable drying equipment such as fluidised bed driers, rotary driers, fixed bed ovens, solar drying equipment, convection driers, radiative drying equipment alone or in combination. A rotary drier has been found to be particularly advantageous. In one form, a rotary drier having an average drying temperature of between 1200C and 1600C is 30 used to dry the low rank coal. This drying temperature can be achieved using heating element, heat transfer fluid or similar. In some instances the drying equipment can be heated using waste steam produced from another process or process stage in the industrial site in which the process of the present invention XtECP\Patent SpedficationsCOMPLETES\CoImn brkquettesPmoess for bdqueting lwer rwn mals with mineral fnes - Pmv- final .doc 6 is situated. In one embodiment, exhaust gas from a gas turbine is used to heat the drying equipment. 5 The briquettes produced by a process of the present invention to have preferably have a binderless construction. In this regard, the briquette is compressed into a solid form without the addition of binders such as cement, coal-tar pitch, petroleum bitumen and asphalt, wood tar, synthetic and natural resins, starch, sulphite liquors, sugars and molasses, cellulose compounds, 10 vegetable pulps, alginates, glue or gum, albumates, casein, peat, lignite and wood, and Inorganic binders such as cement, clay, lime, magnesia, gypsum, sodium or other alkali silicates or a combination thereof. The mixing step can be conducted in any suitable mixing equipment. For 15 low rank coal feed and a solid aggregate material, it has been found that a rotary mixer, a screw mixer and an agitated vessel can be used alone or in combination to mix the two phases together. The dried coal and aggregate material are preferably substantially blended together in the mixing step in order to produce an even distribution of dried coal and aggregate material throughout 20 the briquette. Further components may be included within the dried coal - aggregate material mixture prior to forming a briquette. For example, it may be desirable to mix a fluxing agent with the dried coal, the aggregate material or a mixture 25 thereof. For example, a fluxing agent can be used to flux ash or gangue produced from a briquette in a smelting process. The fluxing agent is preferably selected from quick lime, burnt lime, limestone or a combination thereof. However, in other embodiments, dolomite or similar could also be used. Lime or limestone can also be used as a desulfurising agent when included in the 30 composition of a briquette. In one exemplary application, the briquettes can be used as a feed for iron smelting. In this application, the briquette preferably comprises on a weight basis between 40 to 80% ore, between 0 to 15% lime, and between 10 to 60% X:ECP\Patent SpedficatriSCOMPLETES\COalron brlqueUesProcess for briquettng lower rank coals with mineral fines - Pmv- nnal .doc 7 dried coal. This type of briquette can be used in iron and steel industries to utalise Fe-containing fine materials in the metallurgical furnace of the iron and steel smelting process. 5 Brief Description of the Drawings The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein: 10 Figure 1 is a process flow diagram of one embodiment of the process according to the present invention. Detailed Description 15 Figure 1 provides a process flow diagram of one embodiment of the process according to the present invention. In this process, raw low grade coal is received as a mined product. As indicated previously, a "low rank coal" is a coal having a moisture content of between 25% and 70% by weight. Brown 20 coals (lignite) and sub-bituminous coals found throughout Australia are types of coals that can be used in this process. For example Loy Yang coal has approximately 65 wt % (wet basis), but other coals, depending upon the source can have slightly different "as-mined" moisture contents. The "as mined" coal feed stock is in a roughly ground form from the mining processes used during 25 extraction. In the process shown in Figure 1, the raw low grade coal is initially fed through a crusher to reduce the size of the coal particles. The crusher includes a rough crush circuit and a fine crush circuit. The rough crush circuit includes a 30 roll crusher to reduce the size of the coal feed stock from a lump size of around 400mm to a particle size of 100mm or less. This roughly crushed feed is then fed into the fine crushing circuit including a beater and a hammer mill which reduces the size of the coal particles to a particles size of less than 10mm. The comminuted coal feed is then subjected to a sizing process, in this case a X:\ECP\Pater Spedncations\COMPLETES\Coalon lryqueteUs\Pocess for brquetng low rak oals wth mineral nnes - Pm- final doc 8 series of vibrating mesh screens, to ensure all the coal feed particles have a particle size of less than 6mm. Any oversized coal particles are re-circulated back through the hammer mill circuit. This produces a coal feed having a particle size suitable for the subsequent drying process. 5 The coal feed is transported to the drying process using belt conveyers. In the drying process, the sized coal particles are fed through several parallel rotary driers heated to 1350C to reduce the moisture content to between 8% and 16% by weight. The rotary driers are heated to 1350C using exhaust steam 10 generated from steam turbines used in another process in the industrial plant in which the present process is situated. The illustrated rotary tube drier consists of a cylindrical shell enclosing a plurality of tubes about 4 inch in diameter. The shell is set at a slight inclination 15 (less than 100) and rotates at speeds of between 5 to 8 RPM, depending on the condition of the steam entering and the characteristics of the coal feed to be dried. The coal feed is dried as it passes along the tubes, its rate of travel being regulated by the speed of rotation of the rotary drier. 20 From a given weight w of raw coal, the weight w1 of dried coal (including ash and residual moisture) obtainable is w((100-a)/(100-w)), where a is the percentage of water in the raw coal and w1 the percentage of water in the dried coal. For Loy Yang brown coal containing 65% water, dried to contain 14% water, the value of w1 is w x ((100-65)/(100-14))= w x(35/86). Accordingly, 100 25 tons of raw Loy Yang brown coal is required to produce 41 tons of briquetting coal. The dried coal particles are then fed onto a screw conveyer. The desired amounts of mineral fines and/or processed industrial waste product can also be 30 fed onto the screw conveyer from feed hoppers. The screw conveying mechanism provides a mixing medium to ensure the mixture is homogenously mixed. X:ECP\Patent Spedficatios\COMPLETESXCoa$mn bdquettes\P cess for bdqueting lower rank cals with mineral fines - Pmv- final .doc 9 As discussed previously, mineral fines can be used in the briquette formulation to enrich the mineral composition of the briquettes. Examples of mineral fines include iron ore fines, magnesium ore fines, nickel ore fines, copper ore fines, gold mining fines or tailings, silver mining fines or tailings, 5 uranium mining fines. Processed industrial waste material such as sand, rubber, agricultural waste or the like could also be used in the briquette to improve the material property, calorific/energy value and/or mineral value of the briquettes. For example, comminuted tyre material could be used to modify the material properties of the formed briquette. Additionally or alternatively, wood 10 material could be used to decrease the carbon content of the briquette or modify the calorific value of the briquette. The mineral fines and processed industrial waste material are received as fines which are sized prior to being fed into their respective feed hoppers. 15 In some embodiments, the selected mixture of dried coal particles, mineral fines and processed industrial waste can be further blended using a blending process which included a blender such as a fluidized mixer, agitator or similar to form a blended composite mixture. 20 The composite mixture of dried coal particles, mineral fines and/or industrial waste is feed from the blending process into a briquette mould, also known as a briquetter. In the illustrated embodiment, the composite mixture is conveyed in batches to the briquetter. However, it has been found that feeding 25 could be improved by using a positive pressure feeder that includes an agitator and metering devices. This type of feeder ensures consistency in the flow of feed into the press and substantially can alleviate any compaction or bridging that may occur in the feed due to the properties of the fine dry composition of the mixed product. 30 The briquetter has a metered entry via cell wheels that allow manual adjustment of the amount of material being fed to the press so as to allow adjustment to actual size/thickness of the briquette formed. X:\ECPPatem Spedfcctns\COMPLETES\Coa-ron briqutes\Process for bdquotting lowe mnk cals ith mneral fnes - Prov- flnl .doc 10 The briquetter may comprise any of the numerous system configurations which briquettes coal particles under pressure while maintaining a confined volume. The illustrated briquetter is an extrusion type briquette press that uses a mechanically driven ram to compress and extrude each briquette through a 5 die. The mechanically driven ram forces the composite mix through a restricted orifice to compress the mixture within the extrusion die. The compaction pressure (between 8 to 10 tons per square inch) exerted by the hydraulic ram on the composite mix in the die compacts the composite mix to a desired density and strength. Each briquette is impacted by about 20 strokes of the ram 10 to be extruded through the minimum constriction point of the die. A stringer of six solid briquettes is extruded from the mould. Each individual briquette can be separated from the stringer. The formed briquettes can be readily transported and fed into a further industrial process. 15 While not wishing to be limited to any one theory, it is thought that during briquetting, the pores and inter-particle void spaces are reduced in size such that any aggregate material contained in the pores and in the inter-particle void spaces is compressed within the structure of the coal. The density and strength of the briquette is increased through the collapse of the pores and the inter 20 particle void spaces. Heat generated during compression of the composite mixture within the die seals the outer surfaces of the formed briquettes. This seal helps prevent moisture ingress and mechanical degradation during post-production storage 25 and handling. Ideally, the briquetting process produces a high density and high strength briquette without the addition of a binder. 30 The above process forms a solid briquette comprising a dried low rank coal (lignite or sub-bitumous), mineral fines and/or industrial waste. This process increases the energy value, carbon content and mineral value of dried low grade coal. The process also enables the mineral richness of mineral fines to be utilised that can otherwise be difficult to use in an industrial processes due X:\ECPLPatent SpedficaonsCOMPLETES\Coa-Imn triquettesPmcess for bquettng low"r rank mais with minml fines - Po- final .doc 11 to handling and transport issues associated with the small particle size of the fines. The briquette can be further enhanced by adding specific industrial waste streams to the composite mixture to modify specific material properties of the composite mix. 5 Examples The present invention will now be described with reference to a number of examples, which illustrate particular preferred embodiments of the present 10 invention in which various briquettes were formed using a mixture of Lignite (Latrobe Valley brown coal), Lime and Magnetite. It should be understood that these examples are in no way intended to limit the scope of the invention. Test Trial No. 1 15 The following composite feed mixture was dry mixed in a cement mixer for approximately 15 minutes: Magnetite: 45% by weight =19kg 20 Dried lignite coal: 45% by weight =19kg Lime: 10% by weight =4.5 kg The resulting blended mixture had a similar appearance to an oil coal mix having a light and fluffy appearance and being light grey in colour. The mixture 25 was then introduced into a briquette press to briquette the material. The press was initially fed graphite for a short period and then 100% lignite coal (Loy Yang brown coal) for 5 minutes for comparison purposes. The blended composite feed mixture was then fed into the press using buckets. Approximately one meter of briquettes was produced in a slab form. A dry coal was then introduced 30 into the press to push out the remaining composite mixture from the press. The resulting briquette slab had a compression of 160 kg/cm 2 and a moisture content of 8.89 wt%. X-ECP\Patent Spcficatns\COMPLETES\Coal1on briquetesProcess for bdquetting owe rank mals wlth mineral fines- Pruv- fOnal doe 12 Test Trial No. 2 The following composite feed mixture was dry mixed in a cement mixer for approximately 15 minutes: 5 Magnetite: 45% by weight = 20.25kg at 7.04wt% moisture Dried Lignite Coal: 45% by weight = 20.25 kg at 11.36wt% moisture Lime: 10% by weight = 4.5 kg 10 The resulting blended mixture had a moisture content of 9.15% at 30*C. The mixture was then introduced into a briquette press to briquette the material. The geometry of the form of the press was changed relative to the first test trial by winding down the tongue of the form by 9 mm to increase the pinch point to obtain better separation of stringer briquettes. Each stringer of 15 extruded briquettes had better separation than the slabs produced in test trial No. 1. However, the skin/outer layer of each briquette had a rough appearance. The resulting briquette stringer had a compression of 100 kg/cm 2 and a moisture content of 5.93 wt%. 20 Test Trial No. 3 The following composite feed mixture was dry mixed in a cement mixer for approximately 15 minutes: 25 Magnetite: 45% by weight = 20.25kg at 7.04wt% moisture Dried Lignite Coal: 45% by weight = 20.25kg at 11.36wt% moisture Lime: 10% by weight = 4.5 kg 30 The resulting blended mixture had a moisture content of 9.15% at 300C. The mixture was then introduced into a briquette press to briquette the material. The geometry of the form of the press was the same as test trial No. 2 but with the press forms adjusted to a parallel position. The feed of mixture to X:\ECP\Patent SpedrcatiosCOMPLETES\Coaron bqutles\Process for bdquetting low rank col with nineral fines - Prov- final .doc 13 the press was also improved by using two operators to feed the mixture into the press to provide a more consistent and even flow. The resulting briquettes stringer had better skins and a more consistent briquette size due to the improved method of feeding the mixture into press during this trial. 5 The resulting briquette stringer had a compression of 190 kg/cm 2 and a moisture content of 7.95 wt%. Test Trial No. 4 10 The following composite feed mixture was dry mixed in a cement mixer for approximately 15 minutes: Magnetite: 55% by weight = 24.75kg at 7.04% moisture 15 Dried Lignite Coal: 35% by weight = 15.75kg at 11.36% moisture Lime: 10% by weight = 4.5kg The resulting blended mixture had a moisture content of 9.15% at 30*C. 20 The mixture was then introduced into a briquette press to briquette the material. The geometry of the form of the press was the same as test trial No. 3 using a similar two person feed system. However, in this trial amount of iron ore in mixture was greater than test trial 3. The resulting briquettes were an improvement over the briquettes formed in test trial No. 3, with the formed 25 briquettes having better separation between the individual briquettes in the formed stringer. Furthermore, each stringer had an improved skin surface, having a hard and shiny appearance. The resulting briquette stringer had a compression of 180 kg/cm 2 and a 30 moisture content of 5.66 wt%. The above coal-iron ore briquettes were found to have a high density, low moisture content, low ash content and all low sulfur content. This compares well to Anthracite based combustion products which are predominantly used in X:ECMPatent SpedfIcatonsCOMPLETES\Coaroni brIquefttsProces for bdquetting lowr rank coals wih rnW fines - Pro- final .doc 14 iron and steel smelting furnaces. In this respect, Anthracite based combustion products generally have a high ash content and high sulfur content which produce significant secondary emissions and waste disposal issues. The briquetting process also raises the calorific value of the mined brown coal from 5 9 MJ/kg to 24 MJ/kg. The above briquettes are therefore a cost effective, low sulfur, low ash composite feedstock for iron and steel making smelting processes. 10 Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention. 15 Throughout the description and claims of the specification the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps. 20 X:\ECP\Patent Spedflcatons\COMPLETES\CoaWlmn adquettes\Pmcess for biquetting lower tank coals wlth mineral lines - Prov- final .da

Claims (19)

1. A process of forming a composite briquette from low rank coals and aggregate material comprising: 5 drying a low rank coal feed to produce a dried coal having a moisture content of between 8 to 16% by weight; mixing the dried coal with an aggregate material selected from mineral fines, industrial waste material or a combination thereof; and compacting the dried coal and aggregate material mixture into briquettes. 10

2. A process of forming a composite briquette according to claim 1, wherein the mineral fines comprise mineral ore fines from a mineral extraction process or a mineral processing process. 15

3. A process of forming a composite briquette according to claim 2, wherein the mineral ore fines include iron ore fines, magnesium ore fines, nickel ore fines, copper ore fines, gold mining fines or tailings, silver mining fines or tailings, uranium mining fines or a combination thereof. 20

4. A process of forming a composite briquette according to any one of claims 1 to 3, wherein the industrial waste material includes tyre material, wooden material, plant material or a combination.

5. A process of forming a composite briquette according to any one of claims 1 to 25 4, further including the step of: comminuting the low rank coal prior to the drying step, to produce comminuted low rank coal particles.

6. A process of forming a composite briquette according to claim 5, wherein the 30 comminuting step includes a crushing process.

7. A process of forming a composite briquette according to claim 6, wherein the crushing process includes feeding the low rank coal through a hammer mill, a roll crusher or combination thereof. <filename> 16

8. A process of forming a composite briquette according to any one of claims 5 to 7, further including the step of: sizing the comminuted low rank coal particles to provide a low rank coal feed having a desired size range. 5

9. A process of forming a composite briquette according to claim 8, wherein the sizing step includes passing comminuted low rank coal particles through at least one screen.

10 10. A process of forming a composite briquette according to any one of claims 1 to 9, wherein the low rank coal feed has a maximum particle size of less than 6 mm.

11. A process of forming a composite briquette according to any one of claims 1 to 10, wherein the drying step is conducted in at least one of a fluidised bed, rotary drier, 15 fixed bed oven, solar drying equipment, convection drying, radiative drying equipment or a combination thereof.

12. A process of forming a composite briquette according to any one of claims 1 to 11, wherein the mixing step is conducted in a rotary mixer, a screw mixer or agitated 20 vessel.

13. A process of forming a composite briquette according to any one of claims 1 to 12, further including the step of: mixing a fluxing agent with the dried coal, the aggregate material or a mixture 25 thereof.

14. A process of forming a composite briquette according to claim 13, wherein fluxing agent is selected from quick lime, burnt lime, limestone or a combination thereof. 30

15. A process of forming a composite briquette according to any one of claims 1 to 14, wherein the briquette comprises on a weight basis between 40 to 80% ore, between 0 to 15% lime, and between 10 to 60% dried coal. <filename> 17

16. A process of forming a composite briquette according to any one of claims 1 to 15, wherein the low rank coal has a water content of between 25% and 70% by weight. 5

17. A process of forming a composite briquette according to any one of claims 1 to 16, wherein the low rank coal is a lignite, sub-bitumous or a combination thereof.

18. A composite coal briquette formed from a process according to any one of claims 1 to 17. 10

19. A process of forming a composite briquette substantially as herein described in accordance with the accompanying drawings. <filename>