AU7935401A

AU7935401A - Process for the treatment of raw coal

Info

Publication number: AU7935401A
Application number: AU79354/01A
Authority: AU
Inventors: David Gunn; Michael Wilkes
Original assignee: TARONG ENERGY CORP Ltd
Current assignee: Aberdare Collieries Pty Ltd
Priority date: 2000-10-18
Filing date: 2001-10-10
Publication date: 2002-05-02
Anticipated expiration: 2021-10-10
Also published as: AU775653B2

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: Actual Inventors: Address for Service: Invention Title: Tarong Energy Corporation Limited David Gunn Michael Wilkes DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, Victoria 3000.

"PROCESS FOR THE TREATMENT OF RAW

COAL"

Details of Associated Provisional Application: No: PR0849/00 lodged on 18 October, 2000 The following statement is a full description of this invention, including the best method of performing it known to us: -1- Q:\OPERkAXD\2465727-NF-DC 10110/01 P:\OPERMA.d2465727-p.d-c IO/O11 -2- PROCESS FOR THE TREATMENT OF RAW COAL The present invention relates to a process for the treatment of raw coal. In particular, the invention relates to a process for the treatment of raw coal which has a high clay content.

The processing and refinement of coal is known. However, processes to date have not related to the processing of bulk mined clay rich coals, such as those found in the Walloon Coal Measures in the Surat Basin region of South East Queensland. Bulk mined coals, as distinct from selectively mined coals, include multiple coal and waste (clay) bands mined collectively. The present invention has, therefore, been developed in an attempt to provide a processing technique for such bulk mined clay rich coals which includes an initial breaking down of the raw coal and separation of clay from the raw coal.

Thus, according to one aspect of the present invention, there is provided a process for the treatment of a raw coal comprising the steps of: a) feeding the raw coal to a mixing sump, and forming a slurry of the raw coal with water in the mixing sump; "i b) pumping the formed slurry through a slurry pipeline to break down clays in the slurry associated with the raw coal; and 20 c) separating the broken down clay and removing water from the slurry to leave a too.

coal product.

ooooo **In a particularly preferred embodiment, the process includes an additional step d) of thickening and disposing of the broken down clay (tailings). Preferably, the process further comprises a preliminary treatment step whereby the raw coal, prior to mixing step is treated by sizing the raw coal to a particle size of from approximately 750mm to preferably less than about A simplified process diagram of an embodiment of the invention is provided as Figure 1, with a flowsheet representation of a preferred process provided as Figure 2.

P:\OPER\Ad i2465727capdoc- 10 10/l0 -3- Raw Coal Sizing Raw, clay rich bulk mined coal may be delivered from the mine to the optional raw coal sizing facilities. The first stage of sizing is through a feeder/breaker, which will preferably reduce the raw coal from a top size of approximately 750mm to a top size of approximately 250mm. Discharge from the feeder/breaker is collected by a raw coal conveyor for elevation to the sizing station. Raw coal transferred to the sizing station will generally undergo two subsequent stages of sizing, with secondary sizing to approximately 120mm performed by a secondary sizer. Discharge from the secondary sizer will preferably fall directly to a tertiary sizer for reduction to approximately 50mm topsize.

Discharge from the tertiary sizer reports directly to the slurry mixing sump. The feeder/breaker and sizers used to reduce the raw coal to the nominal top size of 50mm are advantageously specifically designed to cope with sticky clays which are present in the raw coal.

Raw Coal Slurry Mixing (step a) The slurry mixing sump may be any conventional mixing tank used in the art. In one embodiment the mixing tank includes a center tube-type mixing tank, preferably complete :.with an oversize protection screen and a hopper. Crushed raw coal and water are mixed in the sump to form a slurry of approximately Raw Coal Slurry Pumping (step b) The raw coal slurry is preferably pumped from the mixing sump directly into the slurry pipeline using, for example, a gravel pump. The size and power requirement for the motor of the pump will to some extent be determined based on the configuration and size of the slurry pipeline through which the slurry must be pumped.

The slurry pipeline facilitates the break down of clays, which are associated with the raw coal when bulk mined, in the slurry. In this regard, it has been found that prolonged contact with water, together with agitation from turbulent flow, is generally required to break P:\OPERAxdM465727-.d o1 /1001I -4down the coarse clay lumps into fine clay particles to facilitate removal of the clay from the coal by size separation.

Water chemistry also affects the breakdown of clays in the slurry water. It has been found that the following water chemistry is beneficial to the controlled dispersion of clays during the slurry pumping process: [Ca 2,000mg/L [Mg 100mg/L [Na 500mg/L pH 8.6 Conductivity 5,000uS/cm 2 As the clays break down, they form a "carry medium" enabling transportation of coarse raw coal particles by slurry pipeline techniques at pumping velocities of approximately 15 3.0m/s. As such, in a preferred embodiment, the slurry pipeline is of a predetermined configuration and size to promote turbulent flow of the slurry at approximately :eoeee velocity through the pipeline to facilitate the break down of the clays.

Preferably, the slurry pipeline includes small diameter tubing, such as 338mm internal diameter HDPE tubing. Required residence time to effectively break down the clays in the slurry is approximately 15 minutes, which necessitates a nominal 2.6 kilometre length e:oeo pipeline at a pumping velocity of 3.0m/s. The pipeline preferably includes long radius elbows to promote turbulent flow of the slurry through the pipeline. Sections of the pipeline, for example 6 metre sections, are advantageously coupled with bolted or victaulic couplings to facilitate turning of the sections of pipe to equilibrate wear, which will generally be concentrated at the pipe invert.

Slurry Pumped Raw Coal Processing (step c) The separation and removal process for obtaining the coal product may include any number of steps, as required for a particular instance. Generally, this process step is conducted at a coal preparation plant (CPP) directly into which the raw coal slurry is fed P:\OPER\AIWd2465727cp.do.I-101(V0I after being pumped for approximately 2.6 kilometres. The coal preparation plant will typically include two predominantly separate circuits: one for the processing of coarse particles and another for the processing of fine particles. The sizing of the circuits will be dependent on the eventual capacity of the mining operation.

A representation of typical coal processing circuits in embodiments of the invention is provided as Figure 3.

Coarse Coal Circuit In a particular embodiment, the raw coal slurry is discharged into a sampling box for presentation to a primary slurry sampler. Slurry may then discharge to the desliming screen feedbox where it may be further diluted with process water and fed directly onto the desliming screens. The desliming screens may utilise stainless steel wedgewire panels to cut at nominally 4.0mm, with two rows of high pressure sprays to assist the desliming 15 operation. The -4.0mm fine coal fraction and water may be collected in the desliming screen underpan and piped to the fine coal desliming screen feed sump for processing in the fine coal circuit.

o:o•• S.The -50 +4.0mm coarse coal fraction from the desliming screens may be handled in one of two ways, depending on the effectiveness of the clay break down in the pipeline and the presence of any non clay rock in the raw coal. If the clay break down in the pipeline has been effective and there is little or no non clay rock, the coarse coal fraction may be fed to coarse coal centrifuges to remove water before delivery to the product coal bin. If the clay removal in the pipeline has been ineffective, or there is significant presence of non clay rock, the coarse coal fraction may discharge from the desliming screens into a launder and be flushed by dense medium into a dense medium cyclone feed sump. From the dense medium cyclone feed sump, mixed dense medium and coarse coal may be pumped to Dense Medium Cyclones for further processing to remove the waste materials. Product from the Dense Medium Cyclones may be passed over drain and rinse screens, and then onto the coarse coal centrifuges for further de-watering before delivery to the product coal bin.

P:\OPER\Axdk2465727-cap.doc-1O/I IO/ -6- Coarse reject material from the Dense Medium Cyclones will generally be delivered by conveyor to a stockpile for disposal by truck in the mine waste dumps.

Fine Coal Circuit In one embodiment, the undersize of the initial desliming screens is pumped to the fine coal desliming screens, with an aperture of approximately 0.5mm Two rows of high pressure water sprays may be used to assist the desliming operation. The -0.5mm fraction and water may be collected in the screen underpan and pumped to the primary desliming cyclone feed sump. The -4.0mm +0.5mm fraction may be discharged from the fine coal desliming screen directly into fine coal centriuges. Once de-watered, this fraction may be transported by conveyor to the product bin.

The -0.5mm fraction may be treated in two stages of desliming cyclones. The +0.125mm product from the cyclones may be de-watered in the coal centrifuges, then transported to the product bin. Reject material from the cyclones will generally be transported to the tailings thickener.

The clean coal from both the coarse and fine coal circuits may be transported by conveyor to the product coal bin. The product coal bin will generally be used initially to load road trucks, which will haul product coal to the power station. Larger scale operations may include product coal stacking and reclaiming equipment, with rail haulage to the power **station.

Clay Tailings Thickening and Disposal (step d) The coal preparation plant most preferably includes the process step of thickening the 0.125mm tailings from the desliming cyclones and effluent from the centrifuges. It is proposed that thickening will be conducted by using deep cone, or similar, thickeners to achieve a thickened tailings paste of nominally 50% w/w. Flocculant and lime batching and dosing plants may be included to automatically control settling rates and water pH.

P:\OPER\Axd465727- -7- Paste thickened tailings may be pumped by high pressure piston pumps to either stand alone tailings storage facilities or disposal cells in the mine waste dumps.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

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 to be understood that the invention includes all such variations and modifications which fall within its spirit and scope. The invention also includes all the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

ooooo

Claims

1. A process for the treatment of a raw coal comprising the steps of: a) feeding the raw coal to a mixing sump, and forming a slurry of the raw coal with water in the mixing sump; b) pumping the formed slurry through a slurry pipeline to break down clays in the slurry associated with the raw coal; and c) separating the broken down clay and removing water from the slurry to leave a coal product.

2. A process according to claim 1, further including a step d) of thickening and disposing of the broken down clay (tailings).

3. A process according to claim 1, further including a preliminary treatment step V 15 whereby the raw coal, prior to mixing step is treated by sizing the raw coal to a •particle size of from approximately 750mm to preferably less than about

4. A process according to claim 3, wherein said preliminary treatment step includes a first stage of sizing through a feeder/breaker reducing the raw coal from a top size of approximately 750mm to a top size of approximately 250mm, a secondary sizing using a secondary sizer to approximately 120mm and a tertiary sizing using a tertiary sizer for reduction to approximately 50mm top size.

5. A process according to claim 4, wherein at least one of the sizers used to reduce the raw coal to the nominal top size of 50mm is specifically designed to cope with sticky clays which are present in the raw coal. P:\OPER\Axd\2465727-cap.doc-10/IIV -9-

6. A process according to claim 1, wherein the mixing sump includes a centre tube- type mixing tank, preferably complete with an oversize protection screen and a hopper.

7. A process according to claim 1, wherein crushed raw coal and water are mixed in the mixing sump to form a slurry of approximately

8. A process according to claim 1, wherein the slurry is pumped from the mixing sump directly into the slurry pipeline, preferably using a gravel pump.

9. A process according to claim 1, wherein the water chemistry during the slurry pumping process includes: [Ca"] 2,000mg/L [Mg 15 [Na 500mg/L pH 8.6 Conductivity 5,000uS/cm 2 A process according to claim 1, wherein the slurry pipeline is of a predetermined configuration and size to promote turbulent flow of the slurry at approximately "3.0m/s velocity through the pipeline to facilitate the break down of the raw clay.

11. A process according to claim 1, wherein the slurry pipeline includes small diameter tubing, preferably 338mm internal diameter HDPE tubing and is of a length sufficient to facilitate a residence time of the slurry in the pipeline of at least about minutes.

12. A process according to claim 11, wherein the pipeline has a length of 2.6 kilometres and includes long radius elbows to promote turbulent flow of the slurry through the pipeline. P:\OPER\Axd2465727-cap.doc.-10/IIM

13. A process according to claim 1, wherein the separation step c) is conducted at a coal preparation plant (CPP) directly into which the raw coal slurry is fed after being pumped along the pipeline.

14. A process according to claim 13, wherein the coal preparation plant includes two predominantly separate circuits: one for the processing of coarse particles and another for the processing of fine particles. DATED this 10 th day of OCTOBER, 2001 TARONG ENERGY CORPORATION LIMITED by DAVIES COLLISON CAVE Patent Attorneys for the Applicant(s) *.2