Institut Teknologi Bandung

Entering the 20^th century, when several renewable energy sources such as solar energy, wind, biomass, hydro, etc. began to be utilized, environmental activists began to call for a reduction in coal use. In addition to causing greenhouse gas emissions, coal combustion also has the potential to pollute the environment with compounds such as NO_x and SO_x that cause acid rain. On the other hand, coal is still a major source of energy for industries due to its abundant reserves, lower equipment investment costs, and qualified technological support.

To answer the problems that occurred on the utilization of coal, on Saturday, March 10^th 2018, Prof. Dwiwahju Sasongko, Professor of Faculty of Industrial Technology delivered a scientific oration at the ITB Professor Forum held at the West Hall ITB, entitled "The Challenge of Development of Clean Coal Technology in Indonesia".

Prof. Sasongko, or simply Mr. Song, explained that Indonesia currently ranked at the 9^th or around 2.2% of the world's total coal reserves. Unfortunately, about 80% of Indonesia's coal reserves including the medium and low rank coal with a calorific value of less than 5000 kcal/kg. Coal with low calorific value is still little in amount and untapped. With coal production of more than 400 million tons per year, only about 20% is used for domestic purposes while 80% is exported.

To be more environmentally friendly, coal processing technology requires a breakthrough in its development. The breakthroughs that have been implemented on a commercial scale are on combustion technologies. Industries can choose three types of furnace namely fixed bed (stoker), fluidized bed (FBC = Fluidized Bed Combustion), and entrained bed (PF = Pulverized Firing). Recently, the FBC has been compelling to its user because of its relatively low operating temperature (800-900° C) which produces NO_x slightly lesser compared to 1200-1400° C in PF. The FBC uses a 15 mm scale coal particle feed that requires less energy for scouring than the PF that burns micrometer scale coal particles. Furthermore, the addition of limestone other than sand as heating medium can capture SO_x to produce gypsum. Along with the development of FBC, PF technology also developed with some modification in combustion technique so that the operating temperature is lower, hence decreasing the NO_x emission.

Aware that middle and low rank coal are still underutilized even though Indonesia has large sum of biomass waste, Mr. Song, Dr. Winny Wulandari, and Dr. Jenny Rizkiana made a breakthrough by manufacturing hybrid coal. Both of middle/low rank coal and biomass waste are converted into hybrid coal. Hybrid coal is produced by mixing coal particles and biomass (e.g. sawdust) using binders and then processing them with pyrolysis at low temperatures (200-300° C). This process often referred to as torefaction. With this process, some volatile materials are decomposed and detached from the coal/biomass matrix so that the calorific value of this solid fuel is higher than the calorific value of the feed. Biomass becomes more hydrophobic so it is not easy to decompose and the level of erodibility will be increased, hence making the reduction of the size of hybrid coal particles for FBC and PF feed is easier to do. What makes it fascinating is that the CO₂ emissions in hybrid coal combustion are lower than coal feeds because the CO₂ produced in biomass combustion is neutral CO₂.

Prof. Sasongko and team also undertake other researches to overcome the negative impact on coal processing. Besides being done physically and chemically, the sulfur content in coal can be set aside from coal biologically by utilizing Thiobacillus ferrooxidans. He also used Trichoderma sp and other biological methods to break the hydrocarbon chain in a coal matrix to generate liquid fuel through biosolubilization. By converting coal into liquid fuel, there won’t be any ashes upon combustion.

These studies are certainly the answer to the government's mandate in Article 25 paragraph (1) of Government Regulation No. 79 of 2014 on National Energy Policy, which states that the research, development and application of energy technology is directed to support the national energy industry. It is also stated explicitly stated in Article 24 paragraph (2), which is to provide greater opportunity for national companies in the management of oil, natural gas and coal. "Given some of the advantages of coal and has made many efforts to overcome its negative impacts, Indonesia has the potential to contribute to the development of environmentally friendly coal processing technology in the present and future," said Prof. Dwiwahju Sasongko.