Abstract
This work explores the use of carbon dioxide, water, and their mixtures as solvent for the precombustion beneficiation of raw coal without using any toxic mineral acids in the temperature range of 200–400 °C. The fluid polarity, ionic constant, and supercritical point can be adjusted by H2O/CO2 ratio and temperature. Adding carbon dioxide to hydrothermal fluid also increases the ionization by forming carbonic acid. Extractions with supercritical fluids have several benefits including enhanced mass transport, ease of separation and recycle, wide range of extractive capability and tunability, better inherent safety, and in the case of carbon dioxide and water–low cost. A semi-continuous extraction system was designed and built in which pressure, temperature and the relative flow rates of CO2 and H2O can be controlled. Coal powder is kept in a packed bed and the extraction is carried out at 143 bar pressure. Using sulfur as a model heteroatom, extractive efficiency is examined as a function of the temperature, fluid composition, fluid flow, and extraction time. The results indicate that carbon dioxide, water, and supercritical water-carbon dioxide (ScWC) all can effectively extract about 50% of total sulfur from bituminous coal in 1 h. Extraction above 350 °C decreased effectiveness, and extraction above the supercritical point of pure water caused hydrothermal carbonization. ScWC extraction may provide necessary control to prevent organic dissolution while removing sulfur.
Highlights
Despite recent emergence of natural gas, nuclear, solar, and wind power, coal remains an important energy source to the United States and the world
Supercritical water-CO2 (ScWC) and supercritical CO2 extractions are proposed for cleaning of coal before combustion
The coal beneficiation is demonstrated in 200–400 °C range at 143 bar using a semi-continuous process without needing any mineral acid or organic solvents by studying the sulfur removal
Summary
Despite recent emergence of natural gas, nuclear, solar, and wind power, coal remains an important energy source to the United States and the world. The United States owns 28% of the world’s coal reserves compared to only 2.3% of the world’s oil reserves Despite this reserve of coal, the production of coal has been decreasing since 2013 due to the rise of natural gas combined cycle generators, fracking, and concerns over atmospheric and local air pollution. Some commercial ash-free coal methods requiring heated oil as solvent may exist, but the process is not economically feasible Most of these extraction schemes are inspired from high-value materials; coal is a low-value commodity and these methods which call for even dilute acids and microwave radiation cannot be performed economically on an industrial scale. Power plants would be able to use carbon dioxide generated from combustion, otherwise emitted, and use waste heat to perform economical and environmentally protective extractions on raw coal. Because sulfur comprises the majority of hazardous aerosolized pollutants by mass, sulfur is studied as a model heteroatom before and after extraction in this work
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: International Journal of Coal Science & Technology
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
