In this issue we have an article on Carbon International Trading, a company that operates a vertical shaft kiln calcination plant in Sasolburg in the Free State province. The plant produces a variety of high-quality calcined petroleum and pitch cokes. The vertical shaft calciner or kiln, often referred to as a “VSK”, has a calcined coke capacity of approximately fifteen thousand metric ton per annum and was commissioned in 2019.
Carbon International has the ability to produce customised raw material blends to meet chemical and physical calcined coke properties required by a diverse spectrum of industries. Green coke material is received on site and it is then transferred to the VSK. The process of calcination involves the coke being crushed and being exposed to an indirect heat at calcining temperatures. It is then goes via the screening and bagging facility before being transferred to a storage area.
In other words it is the liquification or crushing of hard coal that is processed into a product that is very desirable to high-grade steel, ductile and grey iron foundries as a result of its low sulphur and nitrogen content, its excellent solubility and high carbon yield. Recarburisers serve the purpose to adjust the required carbon content in liquid metal before casting.
In reality the plant should look as though a good old steam locomotive has powered around the facility day and night leaving its soot from the coal-fired engine all over the place. For those of us that have had the exhilarating opportunity to travel on a train powered by a steam locomotive you will remember how when you put your head out of the coach window, instead of getting some fresh air you were pummelled by the small bits of coal grain coming from the steam locomotive. You looked as though you had bad personal hygiene habits with black pimples (blackheads) prominent on your face.
Coal is a messy raw material. The processing and the use of end product are also messy. Or so we think. Take a look at the overhead picture that we have published of the plant. It is certainly impressive in terms of its housekeeping and great care has been taken to minimise its impact on the environment.
The company has created a sustainable operation, through making a positive impact on the surrounding community, being more energy efficient, producing less waste, as well as reducing the company’s carbon footprint. The operation currently produces no process waste and a large portion of the electricity consumed by the facility is produced from its own PV Solar Plant. All this while manufacturing granular carbonaceous materials.
The company needs to be congratulated and it is an example to all our foundries in South Africa. While it might not be pouring liquid metal into moulds, it is operating a furnace and prior to being cooled down and discharged from the VSK into a common hopper, the material will have undergone a fifty-two-hour indirect heat soak.
Once the green coke enters the material channels it is exposed to an indirect heat at calcining temperatures and begins to release its inherent moisture and volatile matter. The volatile matter is captured and introduced into an air rich environment, where it spontaneously combusts. The flow of air, volatile matter and flue gas is carefully controlled and the combustion channels of the VSK are constantly kept under a slight negative pressure.
The process and plant were subjected to a vigorous environmental authorisation in terms of the National Environmental Management Act (NEMA) (Act No. 107 of 1998) prior to construction. The company did not just leave it at that though. It has continued to make the environment and working conditions safe for its staff and the surrounding area. Well done!