The article talks about the history and development of cleaner ways to use coal. It covers how coal has been turned into gas and liquid fuel over time to use it more efficiently. The main focus is on the new methods developed in the 1990s to make coal a cleaner energy source. The researchers discuss processes like coal preparation, gasification, and liquefaction, which are key steps in making coal cleaner to use. They also look at modifying how coal is burned to reduce pollution. The article provides a timeline of how coal has been used and improved to become more environmentally friendly.