Sasol has officially opened its new R4,5 billion Shondoni colliery near Secunda in Mpumalanga as part of its R14 billion mine replacement programme. The event was attended by a number of VIPs, including the Minister of Mineral Resources, Gwede Mantashe. Meaning ‘a place of wealth’, Shondoni replaces Sasol Mining’s Middelbult colliery, which has reached the end of its lifespan. The other two mines forming part of the mine replacement programme are Thubelisha and Impumelelo.
Sasol Mining is South Africa’s third largest coal producer and runs one of the world’s largest underground coal-mining complexes. It produces over 40 million tons of coal annually of which more than 90 % is used as critical feedstock for the production of Sasol’s high quality synthetic fuels and a wide range of chemicals.
Sasol’s Joint President and CEO, Bongani Nqwababa, said the mine replacement programme supports Sasol’s strategy to operate its Southern African facilities until 2050. The programme commenced in 2009. “It is also part of our capital expenditure in South Africa which, over the last five years, has amounted to more than R94 billion,” said Nqwababa.
Distinguishing Shondoni from Sasol’s other collieries is the use of renewable energy, which includes the use of solar geysers and heat pumps and the maximum utilisation of natural light. In addition, movement sensors in buildings switch lights automatically off when there is no movement.
The mine also holds the record of having the longest single flight conveyor without an intermediate booster drive in Africa, at 21 km. The conveyor, consisting of five horizontal curves in a ‘C’ shape, is designed for 2 400 t/h and an operating capacity of 2 000 t/h. The installed drive capacity is 5 MW with four drives at the head and a single drive at the tail. Low rolling resistance conveyor belting has been installed with HDPE rollers to reduce conveyor noise and power consumption.
Interestingly, a 1,4 km noise barrier wall has been constructed along a section of the overland conveyor to minimise noise to the local community.
In an innovative departure from conventional practice, the winder house was constructed on surface and lifted with one lift into position which resulted in a more cost effective and safer methodology. Weighing 291 tonnes, the winder house was moved horizontally over a distance of 58 m and lifted 30 m high.
Large steel structures for the material handling system were assembled in modules on surface and were then lifted into position, reducing the exposure of people working at heights.
The mine is served by a 150-m deep, 11,7-m diameter man/material shaft with a 65-ton payload capacity (and the ability to accommodate 200 people); a 120-m deep, 9-m diameter ventilation shaft (which can extract 1 050 m3/s using three 750‑kW fans); and a 6 m x 3 m x 980 m long incline shaft which houses a 3,5 m/s incline conveyor which can extract 3 200 tons of coal per hour. Early development work on the incline shaft was complicated by weathered dolerite near surface and a high water table, requiring extensive cementation of the porous areas.
During construction of the mine more than 2,9 million cubic metres of earth were moved, 2 000 tons of steelwork fabricated and erected, over 50 000 cubic metres of concrete placed and over 70 km of electrical cabling purchased. The workforce on site numbered 2 409 at the height of construction and the project was completed with a Lost Work Day Case Rate of zero and a Recordable Case Rate of 0,53.
The capacity of Shondoni is 9,2 Mt/a expandable to 10,5 Mt/a. It will have six production sections (with maintenance facilities for ten sections) and two stonework sections (with maintenance facilities for four stonework sections).
Coal will be mined from the 4-m thick Number 4 seam at between 140 m and 160 m below surface by normal bord-and-pillar methods as employed at Middelbult. Continuous miners break the coal and load into shuttle cars, which deliver into feeder breakers; an underground crusher sizes the coal to -150 mm lump size. Section conveyers take product onto trunk conveyors, which in turn deposit it into underground bunkers; coal reports to the incline conveyor from the main underground bunker on Number 4 seam.
The 15 000-ton capacity surface bunker also adopted an interesting approach by using precast ‘planks’ up to 20 tons in weight to facilitate a safe and efficient construction process. Cast in a dedicated precast yard nearby, the components were placed sequentially by gantry crane and stitched by concreting.
The design went on to be commended at the Concrete Society of South Africa’s Fulton Awards 2015, where it was described as an excellent example of hybrid or composite reinforced concrete structures – demonstrating the benefits of precast combined with in-situ concrete.
Over the next 30 years, Shondoni is expected to deliver between 8 and 9 million tons of coal per annum and currently employs about 1 200 people.