Turning coal fines into briquettes a daydream
Fine coal particles and slurry ponds litter the Mpumalanga coalfields. An unwanted by-product of the industry, they present a significant disposal challenge and an environmental hazard.
Lack of investment in new mines has led to SA’s coal supply dwindling. Eskom, which buys 120Mt of coal a year, is in a tight spot as it looks to procure long-term coal supply at a reasonable price.
Adequate and affordable coal is important if Eskom is to keep the lights on. Last week, it was a snapped conveyor belt and the inability to get coal to Medupi power station that tipped the constrained power system over the edge, forcing Eskom to use emergency hydro and diesel power and ultimately to implement load-shedding.
But as Eskom’s input costs spiral and the government presses producers to cut their rates, could the briquetting of this waste coal be the answer to the utility’s coal price prayers? Experts say it is unlikely. Even if it were technically feasible, the economics probably would not add up.
The idea of making briquettes from coal fines or slurry dates back to the 1980s when SA had become a major exporter of coal, says Rosemary Falcon, a coal expert and cofounder of the Fossil Fuel Foundation.
This meant mined coal had to be crushed and washed to produce different qualities and sizes of products for export. The process caused a high proportion of fine particles to break off, which turned into slurry at the washing plants. This was then stored in slurry ponds, where it has remained ever since.
Attempts to briquette coal back then failed for a number of reasons, Falcon says.
First, it was costly to make briquettes because binder materials had to be added. Second, briquettes cracked and disintegrated during transport or broke down when exposed to rain or humidity. And when really strong binders were used, the briquettes were difficult to ignite in industrial boilers.
Back then, the coal was of better quality. Making briquettes out of the lower-quality coal produced today could be even more challenging as the properties are likely to be different, Falcon says.
Xavier Prévost, senior coal mining analyst at XMP Consulting, says if one were able to get rid of the water, rock and other inorganics from slurry, the product could potentially be good enough for Eskom.
The problem lies in commercial beneficiation, he says. To make briquettes, the fines require a very specialised plant. Once the unwanted elements are removed and the fines are briquetted, they are likely to have cost between R300 and R400 a ton, while Eskom procures coal at an average price of R400 to R440 a ton.
“If you can’t make a profit, you are wasting your time.”
Energy analyst Chris Yelland says power stations consume millions of kilograms of coal a day and briquettes have to be tested at scale. “To produce on such a massive scale you have to invest billions. It’s like investing in a coal mine — no-one is going to do it without a 20-year contract from Eskom.”
Even if a plant is built, it is not to say that Eskom, or anyone else, will buy the briquettes.
In 2015, JSE-listed Mine Restoration Investments (MRI) built a 5,000-ton-a-month briquetting plant in KwaZulu-Natal. The project has since been discontinued and impaired due to operational challenges.
Richard Tait, chair of MRI, says briquetting coal had made technical sense, but the company built the plant before it had a market. When it came to finding an off-taker, industrial users were either not interested or cited bad experiences, Tait says.
When Eskom was approached, the utility put forward “ridiculous criteria” for specifications and testing —“it was about that point that we gave up on the coal briquettes”.
Yelland says using briquettes in Eskom plants poses technical risks. “A power station is designed for a particular coal source; if you change the fuel from what it is designed for, the technical risk you are taking is enormous,” he says.
According to Falcon, there is much to consider. “Hardness, crushability, grindability and abrasion are key issues in milling, all of which can lead to intense wear in mills, feed pipes and, ultimately, on boiler walls.”
Yelland says fines and slurry exist everywhere in the world, yet no country uses briquettes in power stations.
Eskom did not respond to questions.