“Combustion of the coal is instant”, explains Elsabe Coetzee, of Sasol Synfuels, outlining the chain of events. Elsabe used to edit the site’s newsletter and is familiar with every activity in the plant. “The gas is very hot, 1300°C”, she says. “You’ll find here that everything works with cooling down and heating up. They cool it down to 500°C and the first stream emanates – that’s a tar oil stream. It goes to tar distillation and from that they produce tar and pitch and creosote.

“The gas, still very hot, goes to coolers – they look like enormous radiators – where they cool the gas down to 35°C, and then a second stream emanates. That’s a gas water stream, – it goes to enormous tanks. From that, they strip out ammonia, phenols and cresols.”

After that, there are scrubbing towers to remove sulphur and other contaminants (not wanted in fuel products which are intended to burn cleanly) before the ‘syngas’ goes off to be converted by a catalytic process (designed in-house by Sasol) into a broad range of hydrocarbon compounds – from C2 to C46.

A main output from this is the oil stream, which is piped away to be distilled into petrol, diesel fuel, paraffin, jet fuel and lubricants. The on-site refinery has a capacity of 450 000 barrels per day. Then there’s a watery stream, which goes off for alcohols, ketones and acids to be recovered. And thirdly there’s a gas stream which contains ethylene and propylene for the manufacture of plastics.

Chemical chain

“Notice that every step is dependent on the next one”, Elsabe says. “One before and one below. For every single step in the process, you have a control room from where they control their part of the process – but they can only see ‘their’ part of the process. So we have a central control room where they monitor the whole system, and then they will be able to notify people if there are any hiccups in the process.”

John Rush points out that this complex chain of dependencies has a significant impact on the communications requirement. “Each plant has an upstream client and a downstream client”, he says. “So if there is a problem at gasification, that affects everybody. They’ll start closing down, and then they are not giving the feedstock to the next one – and they start closing down. So you can imagine what happens on the radio: the traffic just shoots up! Yet that’s the most critical time, when you don’t want to queue. That’s our challenge.”