Coal Combustion Solid Waste, pucuk dicinta ulam pun tiba.
Pile of coal combustion ash at one of the Thermal Power Plant in West Sumatra (Source: documentation of F. Anggara)
The national energy policy sets the primary energy mix target in Indonesia in 2025 with the composition of the commodities of oil (20%), gas (30%), coal (33%), as well as new and renewable energy (17%). The demand for energy is dominated by electricity consumption and is expected to increase due to economic development and the fast-growing population. In order to balance this energy demand, the Indonesian government has set targets for power generation up to 135.5 GW by 2025, set forth in Presidential Regulation (PerPres) No.22/2017. A significant increase in coal consumption in the power generation sector from 56 million tons in 2006 to 123.2 million tons in 2025 will produce 11.38 million tons of fly ash and bottom ash (FABA). This certainly provides opportunities as well as challenges for Indonesia. Then, what exactly is FABA and can we utilize FABA as a future resource?
What is FABA?
Thermal power plant coal combustion system in general is a fluidized bed system, which is a system where air is blown from below using a blower so that the solid objects above it behave like a fluid. This technique is the most efficient technique for producing energy, but it produces fly ash waste and bottom ash waste. They are often abbreviated as FABA. Fly ash is defined as fine grains resulting from coal combustion residues which are the result of decomposition of silicate minerals, sulfates, sulfides, carbonates, and oxides contained in coal (ASTM C.618). Combustion of coal in power plants takes place at temperatures between 1.100 – 1.500ºC. In this condition, chemical and physical changes will occur, so that the composition of the combustion ash will be far different from the composition of the original mineral. Meanwhile, bottom ash is the residue of the coal combustion process in power plants that have larger particle sizes and heavier than fly ash, so that it will fall on the bottom of the boiler. The chemical composition of bottom ash is mostly composed of Si, Al, Fe, Ca, and Mg, S, Na, and other chemical elements (Kinasthi et al., 2018).
FABA as Indonesia’s future unconventional resource
FABA is categorized as hazardous and toxic solid waste that can affect all creatures (plants, animals, and humans) (Bashkin and Wongyai, 2002; Dai et al., 2005, in Anggara et al., 2018). In Indonesia, Government Regulation (PP) Number 101 of 2014 states FABA as B3 waste. Facing a large amount of FABA that will be generated from the production of coal-fired power plants in the future, the disposal will certainly be a big problem because it requires extensive land that does not disturb the surrounding environmental ecosystem. On the other hand, FABA can actually be utilized again as a substitute for raw materials or as a substitute for future unconventional resources in line with the development of science and technology.
Several uses of FABA have been proposed from the results of experts’ research including utilization as raw material for cement, concrete, structural contents (Duminda et al., 2014), soil stabilization, agriculture (Yao et al., 2015), and extraction of valuable elements (Dai and Finkelman, 2018). No exception in Indonesia, research on the topic of FABA utilization has been carried out. Unconventional Geo-Resources Research Group (UGRG) at Faculty of Engineering UGM has also conducted several studies related to the use of FABA as an alternative resource in the future, including the discovery of valuable elements such as cenospheres (Hirajima et al., 2008; Hirajima et al., 2010; Petrus et al., 2011) and the potential extraction of rare earth elements and yttrium (Anggara, et al., 2018; Rosita et al., 2020, etc.) that are very promising for their potential in the future. The low radioactive element in coal also provides simple extraction process.
As the saying pucuk dicinta ulam pun tiba, coal combustion by-products (FABA) turned out to be able to provide added value to coal commodities as an alternative to unconventional resources of rare and valuable elements that have very promising economic value and future demand, while realizing the fulfillment of environmentally friendly energy.
Source:
- Anggara, F., et al. (2018). Rare Earth Element and Yttrium Content of Coal in the Banko Coalfield, South Sumatra Basin, Indonesia: Contributions from Tonstein Layers. Proceeding of International Journal of Coal Geology. vol. 196. pp. 159–172.
- Dai, S., Finkelman, R.B., 2018. Coal as a promising source of critical elements: Progress and future prospects. Int. J. Coal Geol. 186, 155–164. https://doi.org/10.1016/j.coal.2017.06.005
- Hirajima, T., Oosako, Y., Nonaka, M., Petrus, H., Sasaki, K., and Ando, T., 2008, Recovery of hollow and spherical particles from coal fly ash by wet separation process, Journal of MMIJ 124 (12), 878-884
- Hirajima, T., Petrus, H., Oosako, Y., Nonaka, M., Sasaki, K., and Ando, T., Recovery of cenospheres from coal fly ash using a dry separation process: Separation estimation and potential application, International Journal of Mineral Processing 95 (1-4), 2010, pp. 18-24.
- Petrus, H., Hirajima, T., Oosako, Y., Nonaka, M., Sasaki, K., and Ando, T., 2011, Performance of dry-separation processes in the recovery of cenospheres from fly ash and their implementation in a recovery unit, International Journal of Mineral Processing 98 (1-2), 15-23.
- Rosita, W. Bendiyasa, I., Perdana, I., Anggara, F., 2020. Recovery of rare earth elements and Yttrium from Indonesia coal fly ash using sulphuric acid leaching. AIP Conference Proceedings.
- Yao, Z.T., Ji, X.S., Sarker, P.K., Tang, J.H., Ge, L.Q., Xia, M.S., Xi, Y.Q., 2015. A comprehensive review on the applications of coal fly ash. Earth-Science Rev. 141, 105–121. https://doi.org/10.1016/j.earscirev.2014.11.016
