Mining offers a number of fly ash management solutions to coal ash, the solid fossil fuel combustion residue from coal burning boilers and plants, mainly power stations and petrochemicals fuel-from-coal plants.
Coal waste includes fly ash, bottom ash, flue gas desulfurisation sludge (FGDS), fluidised bed combustion waste (FBC), and some by-products like cenospheres, which are used as a lightweight filler in many products.
South Africa’s energy industry, driven by abundant coal resources, has resulted in generation large quantities of coal ash in various forms, mainly from Eskom and Sasol.
SA fourth largest fly ash generator
About 550 mega ton per year of fly ash is produced by coal power plants around the world ,and South Africa is the fourth largest producer of fly ash at 30 Mt per year, after China, USA and, India.
Generation of such large amounts of coal ash and fly ash (FA) calls for a paradigm shift in management and alternative use of coal ash, away from the traditional option where coal ash is simply disposed of in unlined dumps and stockpiles.
This calls for industry, private sector, government, academic institutions and public to work together to develop innovative and environmentally sustainable options for management and alternative use of coal ash.
Cement, bricks, paving
A number of options for alternative use of fly ash are being implemented and studied around the world and in South Africa, like cement, concrete, bricks, dry fuel, soil stabilisation, road base or embankment, ground consolidation, land reclamation, agriculture, and even a possible remediation option for acid mine drainage, which has been called South Africa’s single biggest environmental problem.
Options for hydraulic stowing of underground mines include fly ash include;
• lean slurry
• medium concentration slurry
• paste fill
• backfilling of open cast mines by overburden mixture
• stabilisation of backfilled benches and dumps
• fire stoping in approachable areas
• isolation of fires in non-approachable areas
• improvement of haul roads
• bio-remediation of mine spoils
• ventilation stoping by ash bricks, blocks, hollow blocks
• roof support props.
Fly ash types
• Coal bottom ash and fly ash are different physically and mineralogically. Bottom ash is an incombustible by-product collected from the bottom of furnaces, coarser than fly ash.
• Boiler slag is coarser than conventional fly ash and is formed in cyclone boilers that produce a molten ash, generally a black granular material with numerous engineering uses.
• Flue gas desulfurisation (FGD) gypsum, also known as scrubber gypsum, is the by product of an air pollution control system that removes sulfur from flue gas in calcium oxidation in scrubbers, composed mostly of calcium sulphate, and used for agricultural and wall board production.
Specialists meeting in September
On September 13 -14, a Fly Ash seminar at Gallagher Estate in Midrand will disicuss hydraulic stowing, safety of fly ash transportation, and relevant developments.
Conference director Kal’air Tresor Trezeguet explains that fly ash is the finest of coal ash particles, including silt sized and clay sized glassy spheres, like talcum powder.
Fly ash can be referred to as either cementitious or pozzolanic. A cementitious material hardens when mixed with water. A pozzolanic material hardens with water only after activation with an alkaline, like cementitious and pozzolanic properties that make some fly ashes useful for cement replacement in concrete and other building applications.
• Sep 13 -14 Fly Ash seminar at Gallagher Estate, Midrand; including hydraulic stowing in underground mines, by slurry, paste fill,backfilling, stabilisation of opencast benches, haul road improvement, bio-remediation, safety of fly ash transportation, bottom ash, boiler slag, ash utilisation, cement, cenospheres; 021 671 0541, 078 215 7716, 078 108 1071, firstname.lastname@example.org or www.isiqaloubomi.co.za
PHOTO; Coal fly ash has many uses, yet most of it is disposed of by landfilling, partly for lack of co-ordination among waste generators, resource users, policy, and legislation authorities.