Coal preparation Plants (Washeries)

Coal Preparation at Wongawilli and Port Kembla

Coal preparation plants (‘washeries’) have been used widely in the coal industry to clean as-mined coal of non-coal material (‘ash’) and hence upgrade its quality for sale and use by downstream consumers.  This was commonly the case in the Illawarra (and in NSW generally):  the list below lists some forty washery operations in NSW in the 1980s.  Coal washeries were a significant industrial operation in their own right, and the plants themselves no small operations.

While the types of separation processes used in coal washing were generally common across the industry, the details of the process (screen aperture sizes for example) and the selection and combination of the available processes reflected the nature of the coal feed, and the desired market characteristics of the coal product.  Here, the coal preparation plants at Wongawilli (built in 1917) and those later at Port Kembla Steelworks and West Cliff Colliery are used to illustrate the evolution of these plants, and the type of technology employed in them to reduce the ash content of the product.

Coal Preparation at the Wongawilli Colliery

In 1916 the Hoskins brothers opened a mine at Wongawilli (in the coal seam of the same name) to supply coal to coke ovens erected at Lithgow to supply the Hoskins Lithgow Iron making plant.  In 1917 the mine and the coke ovens were shut down to erect a coal washing plant linked to the coke ovens.  Construction of the washery was completed in 1922 and this enabled mining to resume and a more suitable coke product to be produced, by reducing the 23.3% ash of the raw coal to 17%.  This was the first coal preparation plant to be constructed on the South Coast.

The washery incorporated a picking table and a two stage Luhrig-Elmore jig plant, the latter comprising four pairs of jigs operating in parallel.  The primary or “A” jigs were fed by a scraper conveyor via a star wheel feeder.  Primary screening was conducted at ¾” (19.1mm).  Primary screen oversize (54.0% of raw coal) was fed to a picking table, where the coarse shale and stone was removed and delivered by conveyor belt to a refuse stockpile located some distance away from the washery.  Coal from the picking table was crushed in two Jeffrey roll crushers to 7/8” (22.2mm) top size, before being elevated to the washery coal bin.  Primary screen undersize was screened across two screens at 1/8” (3.2mm).  Undersize from these screens (called “First Fines”) comprised 9.3% of raw coal at 13.2% ash and 28.6% volatile matter and was directed to product  Screen oversize comprising 12.5% of raw coal was fed to the washery coal storage bin by a scraper conveyor and bucket elevator.

The combined feed to the washery coal bin comprised 90.7% of raw coal at 24.3% ash and 24.6% volatile matter.  The discharge from this bin was fed to a 1/8” screen.  The undersize from this screen (called “Second Fines”) was14.4% ash and 28.2% volatile matter.  Screen oversize was crushed in high speed rolls to ½” (12.7mm) nominal.  This comprised 73.8% of raw coal at 26.7% ash and 28.2% volatile matter.

During 1928 the Hoskins brothers relocated their ironmaking operations from Lithgow to Port Kembla.  The first coke oven battery at Port Kembla was commissioned during January 1938 (No.2 Battery) and was a recovery type facility, where gas and other byproducts were recovered rather than burnt in the ovens.  This replaced coke from the non-recovery ovens at Wongawilli.

During 1946, a road truck receival bay was erected at the Wongawilli Washery to accept Wongawilli seam coal delivered by road from the Nebo Colliery where a fully mechanised mine was opened in the outcrop of the Wongawilli seam at Mount Kembla Heights.  In 1946 a mine was opened in the outcropping Wongawilli seam in the pit top area of the Mount Keira Colliery.

The coal produced at these two mines was transported  by road to Wongawilli coal washery.  The delivery of the coal mined at the Nebo Colliery continued until 1948, when the coal handling plant and decline belt conveyor system from the plant were connected to a rail coal storage bin.  This was erected over a section of railway line linked to the original Mount Kembla Colliery railway line to Port Kembla now owned by AIS, which had purchased of the Mout Kembla Colliery in 1945. The coal from this bin was transported to the coal preparation plant in the Port Kembla steel works.  In 1950 the mining of the Wongawilli seam at the Mount Keira Colliery ceased, due to difficult mining conditions underground.

In 1938 the Wongawilli coke ovens were shut down, only to be reopened in 1941, to support the quantities of coke required by the steelworks in the making of the steel to support the needs of the second World War. The Wongawilli coke ovens were closed again in 1948, and demolished along with the washing plant.  The coal produced at the mine was delivered by rail to Port Kembla as before, to be washed in the coal preparation plant at the steelworks.

Coal Preparation at the Port Kembla Steel Works

(with thanks to Mr Keith Horrocks)

“A” Plant Washery

The 250tph “A” plant washery was commissioned at the Port Kembla steelworks during June 1948.  The “A” plant comprised two six compartment 9.3m² Coppee Baum jigs treating the 150×0 mm coal.  Jig product (9.5×0.5mm) was dewatered in vertical scraper Reineveld FKZ centrifuges whilst minus 0.5mm coal was fed to a slurry tower, flocculated, thickened and dewatered on a drum vacuum filter and later, also on two disc vacuum filters.  Coals from the Bulli seam and the Wongawilli seam were washed separately.

“B” Plant Washery

A 230tph “B” plant washery comprising a single 13.9m² McNally Norton Baum jig, was commissioned during 1959 in conjunction with the construction of the No. 3 Simon-Carves coke ovens battery.  

From 1962 onwards the raw coals from the Bulli and Wongawilli seams were blended before washing, and this practice continued until 1983.

“C” Plant Washery

The 350tph “C” plant washery comprising an 18.5m² McNally Goodwin Baum jig was commissioned during 1966 in conjunction with the construction of the No.4 Wilputte coke battery.  The jig plants were all designed to treat 150mm-0mm coal.

During November 1965, a single stage dense medium cyclone plant treating the 9.5mmx0mm coal was added along with froth flotation treatment of the fine coal.  The nominal separation density in the jig and cyclone plants was 1.55-1.60 producing a single coking coal product only.  Dewatering of the small coal was achieved with additional Reineveld FKZ machines plus two Hurricane Reineveld V horizontal vibrating centrifuges.

The flotation plant consisted of 14 banks of four 4.1m³ Warman hog trough flotation cells – sufficient to treat the minus 0.5mm fines from “A”, “B” & “C” plants.  Three additional disc filters were installed to dewater the fine coal.  Operation of the flotation plant was difficult resulting in flotation being discontinued during 1971.

“D” Plant Washery

The 400tph “D” plant washery was built adjacent to the “A”, “B” & “C” washeries and was commissioned during August 1983, it and associated clean coal handling facilities forming part of the No.7A Coke Battery project.  Raw coal production was planned to increase from 5.3Mtpa to 7.3Mtpa.

Separate seam washing of the Bulli and Wongawilli seam coals was re-introduced with “D” plant specifically designed to treat Wongawilli seam coal, which has a characteristic high middlings component (F1.40-S1.70 RD).  Raw coal of 150x0mm is screened at 12.7mm.  Oversize is cleaned in a 160tph three product Warman dense medium drum with nominal Relative Density cutpoints of 1.40 and 1.70. Undersize is deslimed on a conventional sieve bend and vibrating screen with 0.5mm wedge wire decks.

Desliming screen oversize is fed to two 115tph primary dense medium cyclone modules comprising two 600mm x 20⁰ DSM cyclones operating at a nominal RD split of 1.40.  Cyclone overflow was added to the product conveyor after dewatering in Siebtechnik HSG1100 centrifuges.  Cyclone underflow was retreated in a single 105tph secondary module comprising two 600mm x 20⁰ DSM cyclones operating at a nominal RD split of 1.70.  Thus, a S1.40 F1.70 middlings fraction was extracted to be sold as a thermal coal product or used at a purpose-built boiler elsewhere on the steelworks site.  Both secondary module products were centrifuge dewatered.

Initially, in the absence of froth flotation treatment of the minus 0.5mm fines, the desliming screen undersize was split in two banks of five 350mm classifying cyclones separating at a nominal 100 microns.  Cyclone overflow reported to an Enviroclear 15.2m diameter high rate thickener and thence to two 4.3m diameter x 5.0m Jord belt discharge drum filters for dewatering before joining the coking coal product conveyor.  Cyclone underflow reported to one of two Broadbent 1.2m diameter x 2.5m screenbowl centrifuges with some being used to pre-coat the drum filters.

Froth flotation of the minus 0.5mm fine coal was added to “D” plant during 1986.  Two banks of 16m³ Outokumpu cells in a 2+2 configuration were installed.  Froth concentrate feeds to an 80m³ tank which is then pumped to the drum filters and screenbowl centrifuges.  Thickened tailings are fed to a 70m³ holding tank before being dewatered on four 15tph Parkson series 3500 Magnum belt presses.  During 1987 the screenbowl centrifuges were replaced by an additional belt discharge drum filter.

“B” & “C” Plant Washery

A downturn in the steel industry during 1982-83 saw coal production reduced such that the “A” plant washery was shut down during December 1983.  This presented the opportunity for further improvement in the Bulli seam coking coal product by also introducing middlings extraction on “B” & “C” plants.  The “B” & “C” plant cyclones were used as the primary modules operating at a nominal D₅₀ of 1.40.  This required an upgrade of the medium circuits due to the higher near gravity material of the Bulli seam.  The redundant cyclone circuits of “A” plant became the secondary module for “B” &”C” plants.

Associated with an increase in cyclone feed top size from 12.7mm to 25-30mm, replacement of the six Reineveld centrifuges by two McNally Wedag A200 centrifuges was required.  Froth flotation of the Bulli seam fine coal was commissioned during April 1987, comprising two banks of five 14m³ Denver cell to cell units.  Froth concentrate is dewatered on two 100m² Delkor horizontal belt filters.  Tailings are dewatered in the Parkson belt presses described above.

Transition from steelworks to coal industry

Operational management of BHP/AIS Steel Division collieries in the Illawarra area was transferred from the Steel Division to the Brisbane-based Minerals Division coal group during July 1996.  Depletion of Wongawilli seam reserves at the 2.0Mtpa Wongawilli mine, (renamed Elouera Colliery) led to the development of the larger 5.2 million tonnes per annum (MTPA) Dendrobium mine located adjacent to the site of the abandoned Nebo Colliery.  Rationalisation of the Bulli seam operations followed with the purchase of the West Cliff Colliery and coal preparation plant from the Kembla Coal and Coke Company (KCC) during March 1997.  This purchase resulted in all Bulli seam washing operations being transferred to West Cliff.  The “B”, “C” & “D” coal preparation plants within the Port Kembla Steelworks were combined to become the coal preparation plant for the Wongawilli seam coal being mined by the Dendrobium Colliery at Mount Kembla.

The demerger of the steel operations from BHP Billiton in July 2002 ,saw the coal mining activities remaining with BHP Billiton and the coal preparation plant at the Port Kembla steelworks transferred at that time to BHP Billiton Illawarra Coal.  Illawarra Coal has since been demerged from BHP Billiton as South32 Ltd. as at May 2015.

Consolidation of plant

With the transition to dedicated processing of Wongawilli coal from the Dendrobium mine, at the now rebadged Dendrobium Coal Preparation Plant, there has been a focus on simplification of the plant to process mainly the coal from a single although highly variable source.

This has resulted in the elimination of jig washing on B&C plants, closure of B plant cyclone circuit and the integration of C Plant and D Plant into two small coal (-32mm) modules, along with a common coarse coal module with the plant feed taken from a single source comprising 3 x 1300 tonne raw coal bins that were initially dedicated solely to the above D Plant.  The fine coal flotation cells for B&C Plants are now dedicated to C module with the two Delkor horizontal belt vacuum filters now servicing both D and C modules.  A significant amount of desliming screen, cyclone product screening capacity and internal conveyors have been removed, to simplify the operation.

The plant has now been configured to process 5.2MTPA of raw coal.  To process the increased Wongawilli coal a fifth tails press (Phoenix) has been added to the plant’s tailing circuit, and the products from the fine, small and coarse coal modules have been redirected to dedicated single coking coal and energy coal bins.

The wash plant has at date of writing, been been in operation for some 72 years and continues to deliver world benchmark reliability and performance.

West Cliff Colliery Coal Preparation Plant

The development of the West Cliff Colliery by the Kembla Coal and Coke Company east of the village of Appin commenced in 1976.  The plant installed included a coal preparation plant with the capacity to treat and separate 510 tonnes of run of mine coal per hour, into three size ranges using jigs, cyclones and froth flotation processes.

The colliery was purchased by BHP Illawarra Coal in 1997, and modifications were made to the coal preparation plant in 2010/11 to increase its processing capacity.  Work was also undertaken to link the underground workings of the Appin Colliery (now named Appin East Colliery) to Westcliff colliery site to access the Westcliff bulk skip shaft winder and the coal preparation plant.

In 2010/11 major upgrade of the coal preparation plant was completed to increased the capacity of  the plant to process 10.5 million tonnes of coal per annum.  The upgrade included the installation of a rotary breaker and screen house, and the addition of coarse and fine coal storage bins.  A roll crusher circuit was installed, comprising desliming screens, cyclones and centrifuges, flotation cells, attached bed separator, coal and tailings thickeners filters, and tailings presses.  The existing Baum jig was replaced with a dense medium drum, and upgrades were made to the conveyor belt systems, piping, pumps and sumps. The existing safety and associated auxiliary systems were upgraded, along with the plant power supply and the backup features of that system.[ii]

South 32 Collieries in the Appin/Wilton Area

Tower Colliery is no longer a stand-alone operating mine, with the underground workings of that mine linked to the underground workings of the Appin Colliery (now Appin East), and the name Tower Colliery changed to Appin West Colliery. The Appin East Colliery mine workings are linked underground to deliver the coal mined by conveyor belt to the West Cliff bulk skip hoist and coal preparation plant (CPP).  This arrangement enables coal mined in the Appin East and Appin West mine complex to be hoisted to the surface by the 900 tonnes per hour capacity bulk skip hoist located adjacent to the CPP to be processed and hauled by road transport to Port Kembla.

The West Cliff Colliery itself ceased operating as a producing mine in 2016.

RAC 01102018[iii]

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[i] Mr. A.Fraser Photogaph

[ii] Cordell Projects Details Data Sheet

[iii] Mr Keith Horrocks