Dry processing – a viable option for Waterberg coal?

Limpopo Minerals Conference and Trade Show10 - 12 November 2015

Johan de Korte

Slide 2

Overview

• Geology of Waterberg coal

• Processing of Waterberg coal

• Dry beneficiation

• Conclusion

• Two distinct coal formations within Ecca Group

• Upper Ecca (Volksrust Formation) – 7 zones of intercalated shale and bright coal

• Middle Ecca (Vryheid Formation) – Sandstone and shale with 4 coal zones (mainly dull coal)

Geology

Slide 4

Geological profile

• Different beneficiation approaches for VolksrustFormation and Vryheid Formation

• Volksrust Formation: Semi-soft coking coal and thermal coal

• Vryheid formation: Mainly thermal coal

Processing

• Non-selective mining – high level of contamination

• Relatively low yields : 10 -15% semi-soft coking coal + 30 - 40% thermal coal

• Requires a primary high-density de-stoning step to remove bulk of contamination

• A second low density processing divides the coal into a semi-soft coking coal and a thermal coal

Upper Ecca

• Coal contains high amounts of near-dense material

• Requires very efficient separation process

• Coal has to be crushed to small top-size (~15 mm) to liberate semi-soft coking coal

• Coal is friable – fines generated during handling / crushing

• Effective fine coal processing techniques required

Upper Ecca

• Some of the coal (Zones 3 and 4) can be used raw as thermal coal

• Requires crushing and screening only

• Coal from Zone 4 requires high-density beneficiation to lower ash content

• Some coal from Zones 2 and 3 can be processed to yield metallurgical coal

Middle Ecca

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Processing options

• Conventional dense medium processing

• Dry processing

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Dry processing

• FGX

• X-ray sorting

• Dry dense medium

• At present, 3 dry processing technologies available

FGX separator

Source : Rick Honaker

Distribution of coal / shale on FGX

Source : Rick Honaker

Raw coal

Clean coal

MiddlingDiscard

Feed bin

Feeder

Draft Fan

Bag filter

Separator

Dust cyclone

Dust

Centrifugal blower

Vent

FGX dry processing system

FGX plant in Mpumalanga

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X-ray sorting

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1 Material feed

2 Vibratory feeder

3 Free fall acceleration

4 Line scan camera(s)

5 Data processing

6 Air pressure valves

7 Accept streamReject stream

8 Network interface for central control

X-ray sorter in operation

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Discards from X-ray Sorter

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Dry dense medium processing

• Only one plant in operation in China

• Process has much better efficiency than FGX

• Coaltech is investigating the process for application in South Africa

• Not fully proven process

Dry dense medium separation

Dry dense medium plant in China

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Advantages offered by dry beneficiation

• No water required – important consideration in SA

• No slurry produced – limited pollution potential

• Coal remains dry – heat value maintained

• Capex and Opex lower than conventional plants

• Construction time is shorter than for dense medium plants

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Disadvantages of dry beneficiation

• High relative density cut only (> 1.80)

• Efficiency of separation poor (EPM ~ 0.2)

• Dust

• Difficult to control quality of product

• Can not upgrade fine coal

0

10

20

30

40

50

60

70

80

90

100

1.300 1.500 1.700 1.900 2.100 2.300 2.500

Part

ition

num

ber

Relative density

Dense Medium (EPM = 0.02) Dry Process (EPM = 0.20)

DM vs. dry processing partition curves

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• Plant may not be able to produce required quality of coal

• Not a good choice when required to produce coal to a consistent quality specification

Potential pitfalls of dry processing

• Not the best option for long-term projects

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• Dry processing vs. dense medium for long-term thermal coal supply (target ash content 30%)

• Dense medium plant – capital cost R 120 million

Example case study

• FGX plant – capital cost R 40 million

• Dense medium operating cost R 20.00 / feed ton

• FGX operating cost R 5.00 / feed ton

Parameter FGX Dense MediumFeed % Ash 48.3 48.3Product % Ash 34.0 30.0Discard % Ash 63.1 74.2Product Yield % 51.0 58.7D50 cut-point density 1.834 1.957EPM 0.261 0.023Organic Efficiency % 74.6 99.6Sink in float % 11.8 1.4Float in sink % 11.3 1.0Total misplaced % 23.0 2.4

DM vs. dry processing (Upper Ecca coal)

Net Present Value

Years NPV - FGXNPV - Dense

medium

1 R12 654 720 (R1 727 991)

2 R59 221 435 R103 872 017

5 R171 066 827 R357 505 418

10 R290 548 099 R628 454 816

15 R358 344 982 R782 198 780

20 R396 814 754 R869 437 235

Net Present Value

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• De-stoning of ROM coal

• To improve coal quality for power generation use

Application of dry processing

• Recovery of coal from discard dumps

• Pre-beneficiation of ROM (in pit / at shaft head)

Slide 30

• Coal from the Waterberg Coalfield more complex than Witbank coals

• Dry processing can be used in some specificapplications to produce thermal coal

Conclusions

• Water availability and environment need to be considered

• Dense medium the only viable process for production of semi-soft coking coal

• Economic evaluation is required in each case

Slide 31

Thank you