Track: Operations Management

Abstract

The United Nations sustainable development goals call for responsible consumption and production. Coal is the dominate fuel used in most power stations worldwide and in South Africa where over twelve power stations are coal fired. The solid by-products associated with pulverized coal combustion at about 1200 in a power station furnace are splitted into 15% bottom ash and 85% fly ash. Bottom ash is collected at the bottom of the furnace through hoppers , while fly ash is collected from particulate matters found in flue gas leaving the combustion system, thereby being collected through utilization of electrostatic precipitators (ESP). ESP typically operates at about 99.80% fly ash collection efficiency from the flue gas stream passing the magnetic plates of the ESP, however, on average around 6 electricity generation units of a 3700MW coal fired power station, ESP efficiency of 99.83% has been achieved at a certain month.  ESP efficiency of a 3700MW coal fired power station consumed 50 000 tons of pulverized coal per day across 6 electricity generation units. The coal consumed had 42.00% ash content. Total daily and monthly fly ash production at the power station was calculated through simplified material balances. The monthly calculations on the fly ash material balance were completed over three years period. The cement industry use fly ash for reduction of clinker substitution or clinker factor in the final cement being manufactured. The industry makes use of raw fly ash and fine fly ash that is produced from a raw fly ash classification process which is associated with fly ash rejects that needs to be disposed. The available fly ash at year 1 for extraction was 4.35 million tons compared to 1.10 million that was extracted for use by the cement industry which indicated that about 74.60% were left for further management. At year 2, 4.35 million tons was available for extraction, 0.84 million tons was extracted by the cement industry leaving 80.72% to be still managed by the power station. Meanwhile, at year 3, 4.35 million tons was available for extraction, 1.07 million tons was extracted by the cement industry leaving 75.71% to be still managed. Disposal of the excess fly ash to the accredited disposal site continues to pose environmental risks such as leaching and unavailability of the land for occupation and agricultural use by the growing population of South Africa. Although the Just Energy Transition strategy poses a long-term risk of fly ash availability out of this power station. Consideration of 50-year power generation lifespan of the power station, which was commissioned fully in 1980, is expected to end life , thus decommission date is between 2035 to 2040 which is staged per generation units. The expected growth in cement demand until between year 2030 and 2050 associated with clinker production thereby contributing to the greenhouse emissions can potentially be covered by the excess fly ash available for usage from the power station studied. This will further help reduce carbon footprint from the cement industry. To create a closed loop system, the annual fly ash rejects of 0.13 million tons, 0.10 million tons and 0.13 million tons at year 1, year 2 and year 3 respectively can be further managed through using ball mill to increase their surface area so value is added. This can assist in finding potential application of the fly ash rejects other disposal at dump fly ash site which is costly. Furthermore, it was recommended that research on new application of fly ash to reduce the excess fly ash that needs to be disposed has potential to further reduce amount of fly ash that goes to disposal facility.