DRA Mineral Projects has a renowned reputation for its processing expertise, across multiple commodities. Perhaps less commonly known is the foundation upon which its success has grown – the coal sector, writes Laura Cornish.A significant coal footprint DRA’s project portfolio is growing annually, with numerous successes across most mineral sectors. The company has experienced phenomenal growth since its inception in 1984 and has a number of large-scale prestigious projects under its belt. “Our success is based upon humble beginnings, designing small and simple wash plants for the coal sector, with feed capacities of no more than 500 tph,” says Mark Cresswell, consulting minerals processing engineer at DRA. Although the company took on its first large coal project in 1996 (the 1 400 tph Twistdraai plant for Sasol Coal), this proved to be a once off. It was only 10 years later in mid 2000s that its growth in coal really started to escalate with the awarding of the Western Coal study for the Anglo Coal/BECSA JV that eventually became the 2 400 tph Phola coal processing plant, and the rest, ‘as they say, is history’. “As the sector currently stands, DRA is singly responsible for about 50% of South Africa’s total coal washing capacity, and is furthermore accountable for establishing three of the four last major coal projects in the country – Mafube, Phola and Douglas-Middleburg Optimisation (DMO),” Cresswell explains. Considering the company is currently working on another two major coal execution projects, together with a number of studies aimed at moving into execution in the short to mid-term future, its EPCM stronghold in the sector looks set to continue. “Our strategic intention is to move and evolve with the industry, which has already started undergoing changes as more and more players look to acquire new resources and produce new products such as coking coal from coalfields other that the traditional Witbank and Highveld resource, namely the Waterberg and Soutpansberg coalfields in South Africa, Moatise in Mozambique’s Tête Province, as well as in Madagascar and Botswana,” Cresswell continues. DRA is currently developing a 4 000 tph plant design for Vale’s Moatize Phase 2 project which will double the project’s output from 11 Mtpa to 22 Mtpa of saleable product. Also in Mozambique, the company is building a 400 tph modular plant for India’s Jindal Corp, alongside a study for Rio Tinto’s Riversdale resource. The company’s largest current project is the establishment of a 2 000 tph plant for Xstrata Coal South Africa’s Tweefontein project. The design builds on the success of their Australian coal plants such as Mt Owen and Mangoola, with which is shares many conceptual features. For countries like Botswana and Madagascar, one over-riding challenge remains the sole prohibiting factor for potential coal industry booms – the lack of infrastructure such as rail and ports. Once these problems have been resolved, DRA will form an essential part of the coal fields’ development. New technologies and trends DRA prides itself on keeping abreast of the latest processing technologies applicable to the various minerals it is involved with, and this definitely includes coal.
While Cresswell points out that the coal sector is calling the contractor industry to supply larger dense media equipment, and technologies that will reduce the volume of water required for coal washing, he speaks extensively of the growing necessity to find solutions for treating coal fines.It has been discovered that in the newer coal fields like Moatise, 70% of the coking coal product can be in the -1 mm coal sizes. This contrasts with an average Witbank thermal coal where typically only 5 to 15% of product comes from this size range. Technologies best suited to such fine grade resources, according to Cresswell, who has spent the majority of his working career in the coal industry, includes spirals, teeter bed separators, reflux classifiers, derrick screens and fine dense media separation plants. DRA is in fact the only engineering house who built two 50 tph fine coal DMS plants for Exarro’s Leeuwpan mine to the successful design developed by the Coaltech 2020 programme – a collaborative research programme established to address the specific needs of the coal mining industry in South Africa using local and international knowledge and skills to ensure it remains competitive into the 21st century. And while fine coal products are normally dewatered in centrifuges, de-watering of the slimes is becoming increasingly important as new mines strive to reduce their raw water requirements. For this task, there are numerous filter press technologies emerging from Spain, China and Japan, along with older technologies that have been upgraded and refined, such as the Bokela vacuum disk filter (Roymec Technologies), the Phoenix belt press (Malvern Engineering) and paste thickening, Cresswell adds. Extending the life of power stations Some of the most exciting coal work DRA is currently involved in is the development of processing strategies for Eskom-tied collieries, whose sole purpose is to supply coal exclusively to an adjacent power station. The collieries include Khutala, which supplies the Kendal power station; New Denmark, which supplies Tutuka power station and Kriel Colliery, which supplies Kriel power station. All three mines currently supply all their mined raw coal to their respective power stations which maximises the strategic resource. “However because these mines’ reserves of Eskom quality coal are starting to reach the end of their life, more resources must be found. The short-term solution has been to supplement the supply with trucked in coal, but besides the extra expense, this has led to a severe deterioration in the local provincial roads. We have been appointed to design partial washing plants that are able to upgrade poorer quality reserves within the tied colliery mineral boundaries. The main effect on the mine will be that it has to increase its mining rate by around 15%, stockpiles and a washing plant will be required, there will also be a coarse discard to dispose of, but the great bonus will be the delivery of a consistent coal quality to the power stations. It should also be noted that there will be a reduction in the sulphur in the washed product of 10 to 15%, ” Cresswell explains. Consistency of supply to the Eskom spec is far more important than a fluctuating quality. Cresswell explains that the model being copied is Eskom’s Letaba power station which receives the lowest quality coal in the country from its tied New Vaal Colliery. The Letabo station is considered by Eskom to be one of its crown jewels because the New Vaal plant de-stones the raw coal feed and delivers a consistent quality to the boiler specification. “Our intention is to deliver New Vaal equivalent plants.” Cresswell notes that all the plants will be large, no smaller than 1000 tph, and could be approved to move into construction between 2014 and 2020. The DRA success formula The key to DRA’s processing success, across all of its commodities can be attributed to highly skilled experts in their respective fields. In addition to himself and Herman Oosthuizen (Principal process engineer) as coal preparation specialists in the Johannesburg office, DRA can also call on board director Clive Hart and Mike Salter based in their Perth and Brisbane offices respectively to offer the industry specialised skills based on long-term, in-depth industry experience. This is proving to be particularly valuable for Australian based coal mining groups who are moving into Southern Africa such as Resource Generation and Rio Tinto Coal. DRA has also recently recruited a number of young graduate process engineers both in South Africa and Australia in order to train them up for future projects.“DRA has gradually built up its processing capabilities by building on its corporate memory, establishing a ‘library’ of sound plants to base new designs on. We have home-grown engineers, base our success on repeat business and are proud of our Tier One supplier status with the Anglo Group.”