AU2005205756A1

AU2005205756A1 - Thermal treatment system and method

Info

Publication number: AU2005205756A1
Application number: AU2005205756A
Authority: AU
Inventors: Donald James Nicklin; Peter James Tait
Original assignee: Exergen Pty Ltd
Current assignee: Exergen Pty Ltd
Priority date: 2004-09-10
Filing date: 2005-08-31
Publication date: 2006-03-30

Description

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Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant(s): Exergen Pty Ltd, A.C.N. 099 189 321, of 141-143 Wilson Street, Burnie, Tasmania 7320, AUSTRALIA Actual Inventor(s): Donald James Nicklin Peter James Tait Address for Service: DAVIES COLLISON CAVE, Patent Attorneys, of 1 Nicholson Street, Melbourne, Victoria 3000, Australia Invention Title: "Thermal treatment system and method" Details of Associated Provisional Application No: 2004905240 The following statement is a full description of this invention, including the best method of performing it known to us: Q:\OPER\Axd\2005\Aug\12657120 241.doc 30/8/05 P:\OPERlAxd\12657120 spci.doc-29A8/o -1- THERMAL TREATMENT SYSTEM AND METHOD The present invention relates to a thermal treatment system and method for the thermal treatment and solar drying of a slurry of raw material. More particularly, the invention relates to a thermal treatment system for the hydrothermal dewatering of coal and methods for the hydrothermal treatment of coal.

The thermal treatment of raw or as-mined materials, such as the hydrothermal dewatering of brown coal, is known. Generally, thermal treatments are employed to alter the water content of raw materials and/or water attracting nature of such materials. In the case of the hydrothermal dewatering of brown coal, the coal is generally subjected to temperatures of between 250 0 C and 350 0 C whereby the coal is chemically altered. The primary reactions taking place during the process of hydrothermal dewatering of brown coal include decarboxylation through destruction of carboxyl groups and dehydration through the destruction of hydroxide groups. These reactions are accompanied by the ejection of gases from the coal and by shrinkage of the coal particles.

As hydrophilic groups are destroyed during the hydrothermal dewatering process, the coal takes on a hydrophobic nature. This has the effect of reducing the equilibrium moisture content of the coal below that which would otherwise exist for untreated coal.

Hydrothermal dewatering processes are generally conducted with the raw materials being present in a slurry form. That is, the raw material to processed is mixed with water to form a pumpable slurry that is pumped through heat exchanges and into an autoclave vessel where it is subjected to high temperature conditions that are required to bring about the chemical changes in the raw material. Generally, the vessel used is operated at a sufficiently high pressure to avoid evaporation of the water in the slurry. The treated slurry is typically returned through heat exchange equipment to recover thermal energy before solid liquid separation.

P:\OPER\Axd\12657120 spci.doc-29/08/05 -2- The solid liquid separation step generally employed in the hydrothermal dewatering of coal is often quite difficult. This is generally due to the fact that the treated slurry is a slurry of finely divided materials. Equipment typically used in the solid liquid separation includes solid bowl decanting centrifuges, belt filters and vacuum filters. These solid liquid separation methods generally involve high capital and operating costs. Other schemes for drying of coal, for example in vapour recompression equipment using steam fluidised beds, generally employ a high amount of shaft work thereby losing potential to export electrical power. Furthermore, such other schemes generally produce a condensate which is contaminated with organic materials, both dissolved and undissolved.

It has now been found that significant benefits can be achieved through providing a solar drying process following thermal treatments of slurries, such as the hydrothermal dewatering of coal. In particular high capital and operating costs involved in solid liquid separation can be eliminated and the treated raw material can be dried to moisture contents much lower than achievable through for example centrifugation or filtration. Furthermore, the raw material, such as coal, may undergo significant compaction during the solar drying process due to shrinkage brought about by capillary suction as the water content of the cake of treated material drops. Still further, in the case of the hydrothermal dewatering of coal, because many of the hydrophilic groups on the coal have been destroyed during the thermal treatment, the heat of wetting of the coal is reduced. This somewhat reduces the heat released during rewetting of the coal and assists in reducing the potential to achieve spontaneous ignition in stock piles. Still further, by using the thermal treatment and solar drying processes in combination for the treatment of coal, the reduction in green house gases is raised towards the maximum possibility obtained by dewatering of the coal. The electrical input and thermal input to the solar drying step is also minimal in comparison with other schemes.

It has also advantageously been found that while hydrothermal dewatering alone, or comparable thermal treatments, might reduce the moisture content of materials such as coal to half that present in the as-mined material (eg from 67% MC to 50% MC), the P:\OPERNAx,126571220 spoi.do-29/08M05 -3combination with solar drying can take the moisture content down much further (eg to With the above in mind, according to one aspect of the invention there is provided a thermal treatment system including: a thermal treatment zone for receiving a slurry of material to be treated and treating the slurry at elevated temperature and/or pressure to produce a treated slurry; and a solar drying zone for receiving and drying the treated slurry emitted from the thermal treatment zone.

The thermal treatment zone may include any suitable arrangement, for example as used in the hydrothermal dewatering of coal or the like. Preferrably, the thermal treatment zone includes at least one autoclave vessel. The vessel is preferably provided with some form of agitation. The thermal treatment zone also advantageously includes at least one heat exchanger. For example, the thermal treatment zone may include a heat exchanger located upstream of an inlet to an autoclave vessel, and a heat exchanger located down stream of an outlet to the autoclave vessel. Preferably, the heat exchanger located down stream of the outlet to the autoclave vessel is used to recover thermal energy from the treated slurry before the slurry is processed further.

A particularly preferred thermal treatment zone arrangement is described in the applicant's International Publication No. W002/098553 which is explicitly incorporated herein by reference in its entirety. This document discloses an arrangement for the treatment of materials where at least one vessel is located beneath a surface of the ground and is adapted to receive the materials to be treated. At least one of the vessels extends to a depth below the surface sufficient to generate pressure from a hydrostatic head in an inlet to or outlet from the vessel, the inlet including at least two tubes.

It will be appreciated from the disclosure of W002/098553 that the thermal treatment zone may include a number of treatment vessels, such as autoclave vessels or reaction chambers, having any suitable configuration. Preferably, these vessels are located beneath the surface P:\OPERAxd\12657120 spei.doc-29i08I05 -4of the ground. Furthermore, each vessel may include as its inlet an array of tubes, for example seven or more, twenty or more, between fifty and two hundred or more than two hundred tubes may form the inlet to each of the vessels. The inlet tubes will generally have a diameter in the range of from 25 to 100mm, preferably around If one or more of the vessels is located beneath the surface of the ground, it is preferred that the vessel or vessels extends at least 100m below the surface of the ground, more preferably at least 500m below the surface.

Further embodiments of the thermal treatment zone of the system of the present invention may be appreciated from the disclosure of W002/098553 which is, as previously noted, incorporated herein by reference.

The thermal treatment zone is advantageously in communication with a solar drying zone.

Generally, the thermal treatment zone will be in fluid communication with solar drying zone so that treated slurry can be easily transported to the solar drying zone. Generally, the solar drying zone includes one or more solar drying pads.

In a preferred embodiment, the thermal treatment system includes a settler that is interposed between the thermal treatment zone and the solar drying zone for separating excess water from the treated slurry thereby providing a thickened treated slurry. In that case, the system preferably also includes reticulation of excess water separated from the treated slurry in the settler to a process water reservoir that supplies water to raw or asmined material thereby forming the slurry of material to be treated.

In order to further economise usage of water by the system, there is further advantageously provided reticulation of excess water from the solar drying zone to a process water reservoir that supplies water to raw materials to form the slurry of material to be treated.

This may be achieved by decanting water off treated slurry deposited on solar drying pads that form the solar drying zone. This may also advantageously assist in the drying of the treated slurry.

P:\OPER\Axd\12657120 spmi.doc-2908105 On drying in the solar drying zone, the treated material, such as coal, generally cracks.

Rain water hitting the mass of treated material therefore quickly runs into the cracks that have formed and can be drained away through a suitable drainage system. This limits the detrimental effect of rain and results in the solar drying effect being more aligned with the total evaporation achieved rather than the net evaporation (taking rain precipitation into account).

It will be appreciated from the above discussion that the system, although useful in a number of treatments for a number of different raw materials, is particularly related to the hydrothermal dewatering of coal. As such, according to a particular aspect of the invention there is provided a thermal treatment system for the hydrothermal dewatering of coal including: a hydrothermal treatment zone for dewatering a slurry of as-mined coal at elevated temperature and pressure to produce a slurry of dewatered coal; a settler for receiving the slurry of dewatered coal from the hydrothermal treatment zone, enabling removal of excess water from the slurry of dewatered coal to produce a thickened slurry; a solar drying zone for receiving and drying the thickened slurry to produce a coal product.

It will be appreciated that the hydrothermal treatment zone and solar drying zone may be in accordance with those previously described. Likewise, reticulation of excess water from the settler or solar drying zone may be provided for.

According to another aspect of the invention there is provided a method for the thermal treatment of a material including: providing a slurry of raw material to be treated; passing the slurry of material to be treated through a treatment zone at elevated temperature and/or pressure to produce a treated slurry; feeding the treated slurry to a solar drying zone; and P:\OPERkAxd\12657120 spmi.doc-29/08/05 -6drying the treated slurry in the solar drying zone.

Once again, in a preferred embodiment the slurry of raw material is a slurry of coal, the treatment in the treatment zone including hydrothermal dewatering of the coal. Preferably the slurry of coal is passed through at least one heat exchanger and then through an autoclave vessel to effect the hydrothermal dewatering of the coal. Still further, the treated slurry emitted from the vessel is preferably passed through at least one of the heat exchangers to provide heat to the slurry of raw material entering the vessel. Once again, it will be appreciated that the hydrothermal treatment arrangements described in International Publication No. WO02/098553 are particularly preferred for use in the thermal treatment zone according to this aspect of the invention. The disclosure of WO02/098553 is again incorporated by reference in that regard.

Prior to feeding to the solar drying zone, the treated slurry is preferably fed to a settler where excess water is separated to produce a thickened treated slurry. The excess water separated from the treated slurry in the settler is preferably reticulated to a process water reservoir that supplies water to raw material thereby forming the slurry of material to be treated.

Similarly, it is preferred that excess water is decanted off the treated slurry after it is fed to the solar drying zone. Preferably the excess water decanted off the treated slurry in the solar drying zone is reticulated to a process water reservoir as described above.

Once again it will be appreciated that the method is particularly suitable for the hydrothermal treatment of coal. Therefore, according to a particular aspect of the invention there is provided a method for the hydrothermal treatment of coal including: providing a slurry of as-mined coal to be treated; passing the slurry of as-mined coal through a treatment zone at elevated temperature and pressure to produce a slurry of dewatered coal; feeding the slurry of dewatered coal to a settler to separate excess water from the slurry and produce a thickened slurry of dewatered coal;

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P:\OPER\Axd\l 2657 20 spcsi.doc-2908i05 -7feeding the thickened slurry ofdewatered coal to a solar drying zone; and drying the thickened slurry of dewatered coal to produce a coal product.

A preferred embodiment of the invention will now be described in detail with reference to Figure 1 which illustrates such an embodiment as a simplified flow diagram. For convenience, this will be described with reference to the preferred treatment of brown coal in a hydrothermal dewatering treatment. It will be appreciated that the system depicted would be equally applicable to a variety of other applications that are considered to be within the scope of the present invention.

As a first stage of the system 10, as-mined coal X is introduced to a vessel 11 and mixed with process water 12 to form a slurry 13. The process water 12 is pumped from a reservoir by means of a pump 14 into the vessel 11.

Once a suitable slurry 13 has been formed with the process water 12 and as-mined coal X, the slurry 13 is pumped via pump 15 through a heat exchanger 16 and a further heater 17 to provide adequate heat to the slurry before treatment.

The hydrothermal dewatering process is then carried out in an autoclave 18 under agitation to provide a dewatered coal slurry that exits the autoclave 18 at outlet 19. The dewatered coal slurry is then passed back through heat exchanger 16 to facilitate heat transfer from the dewatered coal slurry to the untreated coal slurry 13 that is being introduced to the autoclave 18.

Following heat exchange through heat exchanger 16, the dewatered coal slurry is passed via a valve 20 to a settler 21 to remove excess water from the dewatered coal slurry. The excess water is then reticulated back to the process water 12 via conduit 22.

The dewatered coal slurry having been settled in the settler 21 produces a thickened treated slurry that is pumped as under X flow from the settler 21 via pump 22. The thickened treated slurry 23 is then left to dry on solar drying pads 24. During the drying process on P:\OPER\Axd\12657120 spcci.doc-29108/05 -8the solar drying pads 24, cracks 25 form in the thickened treated slurry 23. As such, in addition to decantation of excess water 26 from the thickened treated slurry 23 in order to assist drying, further water 27, for example as precipitated as rain, is easily drained from the thickened treated slurry 23.

A pump 28 is provided to pump excess water, including decanted and drainage water 26 and 27, back to the process water 12.

As previously noted above, the treatment zone, depicted within dashed lines in Figure 1 for convenience, is preferably an arrangement or assembly as described in International Publication No. W002/098553.

As described above, although the present system and method is particularly useful for the hydrothermal dewatering of coal, as noted in International Publication No. W002/098553 the system and method may also be appropriate for other processes. Some examples of such processes, but not intending to be limiting on the present invention, include: US Patent 5,312,462 Moist Caustic Leaching of Coal. Coal is slurried in a mixture of NAOH and KOH and heated under pressure to cause a reduction in the levels of ash and sulfur.

US 5,214,015. Synthesis of Iron Based Hydrocracking Catalyst. Iron oxide and sulfur are reacted with a liquid hydrogen donor in the range 180 to 240 0

C.

US 5,369,214 Method of Selective Dehalogenation of Halogenated Polyaromatic Compounds. Halogenated polaromatic compounds are mixed with a hydrogen donor solvent and a carbon catalyst and pressurised and heated leading to the dehalogenation of the compounds.

P:\OPER\Axd\12657120 spcci.doc-2908/05 -9- US 4,695,372 Conditioning of Carbonaceous Material Prior to Physical Benefication.

Coal is conditioned by contact with a supercritical fluid (ie typically high temperature and pressure). A minor solute fraction is extracted leading to enhanced beneficiation.

Other examples exist in the fields of achieving phase transformations in solids, leaching, extraction, reaction, polymerisation, liquefaction, oxidation, reduction, processes involving hydrogen donor solvent reactions, dissolution, precipitation.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. Those of skill in the art will therefore appreciate that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention. All such modifications and changes are intended to be included within the scope of the disclosure.

Claims

1. A thermal treatment system including: a thermal treatment zone for receiving a slurry of material to be treated and treating the slurry at elevated temperature and/or pressure to produce a treated slurry; and a solar drying zone for receiving and drying the treated slurry emitted from the thermal treatment zone.

2. A thermal treatment system according to claim 1, wherein the thermal treatment zone includes at least one autoclave vessel.

3. A thermal treatment system according to claim 2, wherein the vessel is provided with agitation.

4. A thermal treatment system according to claim 1, wherein thermal treatment zone includes at least one heat exchanger.

A thermal treatment system according to claim 1, wherein the thermal treatment zone includes a heat exchanger located upstream of an inlet to an autoclave vessel, and a heat exchanger located downstream of an outlet to the autoclave vessel.

6. A thermal treatment system according to claim 1, wherein the solar drying zone includes one or more solar drying pads.

7. A thermal treatment system according to claim 1, including a settler interposed between the thermal treatment zone and the solar drying zone for separating excess water from the treated slurry thereby providing a thickened treated slurry.

8. A thermal treatment system according to claim 7, including reticulation of excess water separated from the treated slurry in the settler to a process water reservoir r P:\OPERAxd\12657120 spci.doc-29i08/05 11 that supplies water to raw material thereby forming the slurry of material to be treated.

9. A thermal treatment system according to claim 1, including reticulation of excess water from the solar drying zone to a process water reservoir that supplies water to raw material thereby forming the slurry of material to be treated.

A thermal treatment system for the hydrothermal dewatering of coal including: a hydrothermal treatment zone for dewatering a slurry of as-mined coal at elevated temperature and pressure to produce a slurry of dewatered coal; a settler for receiving the slurry of dewatered coal from the hydrothermal treatment zone, enabling removal of excess water from the slurry of dewatered coal to produce a thickened slurry; a solar drying zone for receiving and drying the thickened slurry to produce a coal product.

11. A method for the thermal treatment of a material including: providing a slurry of raw material to be treated; passing the slurry of material to be treated through a treatment zone at elevated temperature and/or pressure to produce a treated slurry; feeding the treated slurry to a solar drying zone; and drying the treated slurry in the solar drying zone.

12. A method according to claim 11, wherein the slurry of raw material is a slurry of coal, and wherein the treatment in the treatment zone includes hydrothermal dewatering of the coal.

13. A method according to claim 12, wherein the slurry of raw material is passed through at least one heat exchanger and then through an autoclave vessel to effect the hydrothermal dewatering of the coal. P:\OPERAxd\12657120 spci.do-2908/05 -12-

14. A method according to claim 13, wherein treated slurry emitted from the vessel is passed through one of the at least one heat exchangers to provide heat to the slurry of raw material entering the vessel.

15. A method according to claim 11, wherein prior to feeding to the solar drying zone the treated slurry is fed to a settler where excess water is separated to produce a thickened treated slurry.

16. A method according to claim 15, wherein excess water separated from the treated slurry in the settler is reticulated to a process water reservoir that supplies water to raw material thereby fonrming the slurry of material to be treated.

17. A method according to claim 11, wherein excess water is decanted off the treated slurry after it is fed to the solar drying zone.

18. A method according to claim 17, wherein the excess water decanted off the treated slurry in the solar drying zone is reticulated to a process water reservoir that supplies water to raw material thereby forming the slurry of material to be treated.

19. A method for the hydrothermal treatment of coal including: providing a slurry of as-mined coal to be treated; passing the slurry of as-mined coal through a treatment zone at elevated temperature and pressure to produce a slurry of dewatered coal; feeding the slurry of dewatered coal to a settler to separate excess water from the slurry and produce a thickened slurry of dewatered coal; feeding the thickened slurry of dewatered coal to a solar drying zone; and drying the thickened slurry of dewatered coal. DATED: 29 August, 2005 Exergen Pty Limited by DAVIES COLLISON CAVE Patent Attorneys for the Applicant(s)