Energy and chemicals group Sasol is repurposing its Twistdraai export coal plant as a destoning operation to improve the quality of coal being used in its Secunda gasifiers, in Mpumalanga, where it is also aiming to recover yearly output to a range of between 7.4-million and 7.6-million tons.

Sasol is expecting its South African energy and chemicals cluster, which includes Sasolburg, to produce between 6.8-million and 7-million tons this financial year, having last produced above the 7.4-million-ton level four years ago.

The JSE-listed group produces liquid fuels and chemicals at Secunda using both coal and gas imported from Mozambique as a feedstock.

Sasol says the gas supply plateau from Mozambique will be sustained until its 2028 financial year, after which it would no longer be supplying gas to domestic industrial customers. Supply to Sasol’s own facilities, by contrast, was due to continue until 2034.

CEO Simon Baloyi tells Engineering News & Mining Weekly that the 10-million-ton-a-year brownfield destoning project at Twistdraai is already under way at a capital cost of less than R1-billion, having been selected in preference to a greenfield plant that would have cost up to R6-billion.

The export plant is scheduled to shut in May and Sasol is planning to lease rather than sell its Richards Bay Coal Terminal entitlement, while it assesses a separate coal briquetting option that, if implemented, could raise the quality of its fines to an export grade.

The destoning project is expected to be completed before the end of the 2025 calendar year, as it does not entail any changes to the way the Twistdraai plant operates. Instead, the investment relates mostly to auxiliary systems, such as conveyors, that are needed to redirect the destoned coal to Secunda rather than for export.

All of the production from Sasol’s Thubelisha mine will be routed to the destoning facility, with the balance to be supplied from other internal operations, such as Bosjesspruit, and potentially purchased from other suppliers, such as the Isibonelo Colliery.

Once blended with other coal sources, Sasol aims to decrease the so-called “sinks” or stone content of the coal feedstock used at Secunda to less than 12%, with the material that will be processed through Twistdraai expected to have only 1% sink material.

In total, Sasol is planning to supply some 35-million tons yearly to Secunda.

Baloyi says that by recovering the quality of its coal feedstock to Secunda, Sasol expects the yield from its gasifiers to improve, while also reducing wear and tear, which has become a major problem as the stone content of the material increased above the historical level of 12%.

He tells Engineering News & Mining Weekly that this wear and tear as a result of the higher quantity of stones in the gasifiers has resulted in far longer maintenance outages of up to 150 days, rather than the 50 days such repairs took previously.

It has also decreased both the yield and the availability of Secunda’s 84 gasifiers, where Sasol requires at least 72 to be operational if it is to produce within the yearly range of between 7.4-million and 7.6-million tons.

Baloyi says the destoning project reflects the priority that is currently being given to coal quality over volume.

“For me, quality is the driving factor.

“I mean, in your own car, you're not going to supplement diesel with cooking oil from your kitchen; it just doesn't work nicely in the long term,” he mused.