The Dundee operations in KwaZulu-Natal, South Africa, consist of two coal processing plants and a rotary kiln for anthracite calcining, with the Magdalena Plant designed at 250 tonnes per hour.
The Dundee coal processing operations, located in KwaZulu-Natal, South Africa, comprise the original Coalfields Plant, the newer Magdalena Plant, and a rotary kiln designated as the Calcine Plant. The Coalfields Plant, commissioned in 1992 within a decommissioned Consol Glass factory, was originally designed to batch treat coal on a toll basis before primarily processing ore from the Dundee mining operations. The processing configuration at both the Coalfields and Magdalena plants consists of five sections: crushing, large coal washing via Heavy Media Separation (HMS) in a Teska Bath, small coal HMS cyclones, a spirals plant, and slimes handling. The Calcine Plant is used to drive off volatiles in the anthracite, thereby increasing the Fixed Carbon of the saleable product.
Site visits were undertaken in early October 2012 to update performance data from a 2011 report. The washing plants operate on a two-shift cycle of 10 hours per shift, five days a week, with occasional Saturday work and four hours of daily maintenance included. The tailings extension is designed with a 22-year life and a design capacity of 14 million tonnes, with an annual deposition rate of 640,000 tonnes per year. The railway siding is connected to the Transnet grid and has the capacity to load 160,000 tonnes per month, with 50 wagons reportedly loaded in a four-hour period.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant capacity (Magdalena) | 250 | tph | Design capacity |
| Crushing stages | 2 | stages | Roll crushers |
| Crushing product size | 50 | mm | Second stage roll crusher |
| HMS large coal feed | 25 x 50 | mm | Teska Bath feed |
| Cyclone plant feed | 1 x 25 | mm | Produces Duff and Peas |
| Spirals circuit feed | Minus 1 | mm | Produces concentrate |
| Kiln capacity | 10 to 11 | tph | Anthracite feed |
| Kiln coal firing rate | 300 | kg/h | Pea coal |
| Kiln operating tonnage | 6,000 to 7,000 | tpm | Historical operating data |
| Tailings design tonnes | 14 | Mt | Extension design |
| Tailings tonnes per year | 640,000 | t | Design specification |
| Tailings rate of rise | 4.5 | m/year | Design specification |
| Tailings life | 22 | years | Design specification |
| Large Nut product | 40 x 90 | mm | Classical product range |
| Small Nut product | 25 x 45 | mm | Classical product range |
| Peas Standard product | 6 x 28 | mm | Classical product range |
| Siding capacity | 160,000 | tpm | Loading and tramming capacity |
| Maintenance | 4 | h/day | Daily included maintenance |
| Shift length | 10 | h/shift | Two shifts per day, five days a week |
Overview
The Dundee Coal processing operations include the original Coalfields Plant and the newer Magdalena Plant. The Coalfields Plant, commissioned in 1992, was built in two parallel strings and was originally designed for toll treatment of coal from different sources. The plant is located at the site of a decommissioned Consol Glass factory. Additionally, a rotary kiln, known as the Calcine Plant, is operated to process anthracite by driving off volatiles to increase the Fixed Carbon content of the saleable product. The kiln operated from September 2010 until it was shut down in April 2011 due to market constraints, and was being re-commissioned at the time of the report.
Key Process Stages
Raw Coal Handling and Crushing
For the Coalfields Plant, raw coal is delivered by truck to a stockpile. From there, it is fed through two stages of crushing for primary sizing before delivery to the plant stockpile. At the Magdalena Plant, raw coal is broken underground by mechanical feeders to a size amenable for conveyor transport to the surface stockpile, where it is then fed through two stages of roll crushers, reducing the size down to 50 mm.
Heavy Media Separation (HMS)
The screened coal at a size of 25 mm to 50 mm is processed through a Teska Bath HMS separator at the Magdalena Plant. The discard is rejected to waste, while the product is screened to the desired size fraction. The 1 mm to 25 mm fraction is upgraded in a cyclone washing plant to produce washed Duff and Peas.
Spiral Circuit
The minus 1 mm material is treated in a spirals circuit to produce a concentrate. The tailings from the spiral circuit are discarded to the residues, although this material may be blended with certain products when necessary.
Dewatering and Slimes Handling
Slimes from the spiral plant cyclone overflow are settled in an Ultrasep high-rate thickener at the Coalfields Plant. This thickener separates solids from water, allowing clean water to be recycled to the plant while the thickener underflow is sent to settling paddocks. At the Magdalena Plant, slimes are settled in a settling dam to recover clean water for return to the plant and to reject settled solids.
Calcination
The Calcine Plant rotary kiln has a capacity of 10 to 11 tonnes per hour of anthracite feed. The kiln is fired by approximately 300 kg per hour of Pea coal to generate sufficient heat for adequate calcining.
Product Handling and Dispatch
The Magdalena Plant produces a range of products including large nuts, small nuts, and export peas, with standard size ranges of 40 x 90 mm, 25 x 45 mm, and 6 x 28 mm respectively. Saleable products are stored in dedicated areas and dispatched by road to the Coalfields siding for rail or road distribution. Final classification and preparation of material for sale is carried out at the Coalfields Plant. Processed coal is stockpiled at the Coalfields siding for export or domestic inland transport, with the railway siding connected to the Transnet grid.
Additional Interesting Data and Summary
The current tailings dam was nearing its end of life, and in April 2012 Forbes Coal appointed African Innovation Solutions and Projects CC to design additional tailings dam space. The proposed tailings extension is situated to the south of the existing discard dam and is designed to handle 640,000 tonnes per year with a 22-year life. The return water dam was designed to adhere to the Nation Water Act and SANS 10286:1998 regulations. The plants were not fully utilised because of the current mining plan. Since May 2011, sidings management has improved considerably, and Transnet Freight Rail service delivery improved from around 23% to approximately 70%. The tailings dam specifications include a design capacity of 14 million tonnes with a rate of rise of 4.5 metres per year.
Key Processes
- Crushing: Two stages of roll crushers reduce coal size to 50 mm
- Heavy Media Separation: Teska Bath for large coal, HMS cyclones for small coal
- Spiral concentration: Spirals circuit treats minus 1 mm material
- Dewatering: Ultrasep high-rate thickener and settling dam for slimes handling
- Calcination: Rotary kiln treating anthracite to increase Fixed Carbon content
- Product classification: Sizing to produce Large Nut, Small Nut, and Peas Standard products
Source: Qualified Persons’ Report on Forbes Coal’s Dundee Operations, 2012.
Project website: Qualified Persons’ Report on Forbes Coal’s Dundee Operations
