Overview
Coal ash can potentially be utilized as partial replacement for cement in concrete and mortar formulations. The use of coal ash can lessen the cost and energy production, and reduce the impact on the environment. At present, the annual coal ash generation amounts to ~2.78 Mt and may reach to ~13.02 Mt by 2035 in the Philippines.
If coal ash is utilized as clinker replacement in the production of cement at a clinker-to-cement ratio of 0.7, GHG emissions can potentially be reduced to at least ~1.26 Mt CO2_eq in 2018 and could further be reduced by ~5.89 Mt CO2_eq by 2035 when surplus coal ash is utilized as partial cement replacement in concrete mixtures in concrete batching plants.
How is coal ash made?
Coal combustion is a widely adopted process to release and subsequently recover energy in coal for electricity generation and for heating. During the process, coal combustion products (CCP) such as fly ash, bottom ash and boiler slag are formed. These products are oxidized mineral matter left after combustion of coal, along with minute amounts of unburnt combustibles.
Coal ash are thrown in ash ponds and landfills, that have become inadequate for disposal because of the increasing amount of coal ash generated. This could be supported by the observed increase in coal consumption worldwide from 7,064.96 to 7,166.99 million tons (Mt) from 2017 to 2018. Improper disposal of coal ash may result to leaching of harmful metals that leads to the detriment of soil and groundwater quality, affecting health and the environment.
In other Asian countries like the Philippines, interests in coal ash utilization had increased with the accumulated coal ash due to the expanded capacity of coal-fired power plants at 8,844 megawatts (MW) in 2018 from 5,963 MW in 2015). Owing to the rising demand of energy and the lack of infrastructures and technology for advanced renewable energy systems, coal will remain as one of the main energy sources in the Philippines. Coal consumption will result to the accumulation of coal ash products that need to be collected and disposed of appropriately.
How was coal ash disposed of in the past?
Since 1980, landfilling was the most conventional method of ash disposal. Ash ponds were also used in fly ash waste management but this process would require usage of additional amount of water, energy, and space. As an alternative and possibly the best possible option for coal ash waste management is their further utilization as cement replacement in mortar and concrete formulations.
Why choose coal ash to use as a partial substitute for cement?
Several studies have been made worldwide on using coal ash as cement raw material or concrete admixture because aside from its pozzolanic properties, the use of coal ash can reduce cost, energy and environmental issues. More than 150 countries are involved in the cement industry which reached to ~ 4.2 billion tons of cement production in 2016 (World Business Council for Sustainble Development Cement Sustainability Initiative, 2016) including the Philippines with ~ 25.3 Mt or ~ 0.6% of the total cement production worldwide.
As of August 2018, the cement index in the Philippines grew by 1.5% compared to 2017. The increase in consumption may be attributed to a booming Philippine construction industry, which showed a growth of 20.7% in 2018. If this trend continues, cement demand will further increase which would result to an increase in cement production in the Philippines.
A primary ingredient in cement production is cement clinker. Manufacturing of clinker and using fossil fuels in the production of cement are main contributors of greenhouse gas (GHG) emissions, which sums up to as much as 8% of global carbon dioxide (CO2) emissions. Greenhouse gas (GHG) emissions come from direct and indirect sources in the cement industry. Direct emission sources occur during calcination of calcium carbonate (CaCO3) and combustion of fossil fuels during cement production.
How to balance cement production and reduce CO2 emissions ?
From various studies, CO2 emissions can be reduced by improving energy efficiency and using renewable energy, by producing low carbon cement, by using CFA as solid sorbent to capture CO2 and by reducing the amount of clinker in the cement mixture. Initiatives have been taken by various countries like the USA, Canada, Europe and other Asian countries on potential CO2 emission reductions by using materials other than cement.
However, practices in different countries and regions in the production of cement do vary and would best be assessed separately, accounting for a country of interest. The Philippines was reported to have clinker-to-cement ratio (CCR) of 0.9 in the year 2000, then it was reduced to as low as 0.78 in 2016 (World Business Council for Sustainble Development Cement Sustainability Initiative, 2016). The reduced clinker ratio is the result of combining other cementitious materials like limestone, pozzolana, slag and fly ash in making cement.
The other contributor to GHG emissions which is the combustion of fossil fuel had an average (2000 to 2009) coal consumption per ton of cement (Rcoal/cem) to about 153 kg having emission factor due to coal combustion (EFcoal) equal to 360 kg CO2_eq per ton of cement.
With the Philippines having continuous operations of coal-fired power plants in the past thirty years, the disposal of coal ash has become a challenge. To aid in the understanding of the potentials and benefits of using such waste resource, it would be of interest to estimate the annual coal ash available for utilization and to understand the impact of its utilization to the environment and its related cost.
Get in Touch with Dai Nam batching station
Contact Dai Nam Philippines and experience the difference our concrete batching plant solutions can make:
- Address: 5 National Road, Dampol 1st, Pulilan, Bulacan
- Regional Sales Manager: Mr. John Yap
- Phone: 0998 987 8181
- Email: [email protected]
- Website: https://dainam.ph/
