Over the last several decades, the Office of Fossil Energy performed RD&D activities that made significant advancements in the areas of coal conversion to liquid fuels and chemicals. Technology improvements and cost reductions that were achieved led to the construction of demonstration-scale facilities. The program is now supporting work to reduce the carbon footprint of coal derived liquids by incorporating the co-feeding of biomass and carbon capture.
In the area of direct coal liquefaction, which is the process of breaking down coal to maximize the correct size of molecules for liquid products, the U.S. DOE made significant investments and advancements in technology in the 1970s and 1980s. Research enabled direct coal liquefaction to produce greater yield, quality, and safety of the liquids and enabled the successful demonstration of continuous operation of plants such as the 200 tons of coal per day Ashland Synthetic Fuels plant in Catlettsburg, KY.
DOE had also successfully partnered with industry to develop liquid phase methanol technology. The project was successfully demonstrated at a capacity of 250 tons of methanol per day at a facility located in Tennessee. During its demonstration period, the facility produced nearly 104 million gallons of methanol from coal-derived synthesis gas with a demonstrated plant capacity in excess of 300 tons of methanol per day, more than 15 percent greater than the plant's design rate. As a result, the technology is still being utilized to provide a portion of the facility’s methanol feedstock requirements.
Based on past research, many of the technical challenges associated with conversion of coal to low-carbon fuel alternatives have been addressed. However, achieving greater reductions in carbon dioxide emissions is one of the key challenges that remain. One option being explored is the co-feeding of biomass with coal. Co-feeding allows biomass to take advantage of the economies of scale associated with coal, while helping to reduce the carbon dioxide emissions of coal by integrating it with a renewable feedstock. Studies have shown that the life cycle carbon emissions of coal derived liquids are below the petroleum baseline when implementing biomass co-feeding and/or carbon capture, utilization, and storage.
While there has been some commercial testing of co-gasification of coal and biomass, these tests have not been conducted on the range of coal and biomass types available and at varying concentrations. Specifically, the impacts of coal-biomass mixtures on gasification kinetics, operating conditions, gasifier effluent components and concentration, downstream processes, and capability to feed the mixture across a pressure gradient and into a gasifier, must be addressed.
Production of low-carbon fuels from coal and coal-biomass mixtures offers several benefits. These fuels will reduce the amount of petroleum that the United States imports because they are produced from domestic resources. These fuels are also considered "drop-in" fuel substitutes, which can be used in existing engines with little or no modification required. Coal and biomass to liquids offers an effective way to provide quality, reliable fuels while reducing the amount of CO2 produced in the transportation sector.