Reggie Mitchell

Since coal is the cheapest and most abundant energy resource in the United States, it is quite likely that it will continue to be the primary fuel for electricity generation for the next few decades. However, when coal is used in conventional power plants, copious quantities of CO₂ are released into the atmosphere. Carbon dioxide is a greenhouse gas that is instrumental in causing global warming. Three research projects are underway in Professor Mitchell’s laboratories that have the goal of enabling the development of technologies that produce electricity using coal as the energy source that facilitate CO₂ capture, so that the CO₂ is not released into the atmosphere. One of the projects involves the development of a coal-driven fuel cell, where the oxygen for coal oxidation is separated from air using an electrolytic membrane. Coal oxidation products are rich in carbon dioxide and water vapor, and after water condensation, a nearly pure stream of carbon dioxide is ready for sequestration. Another project involves coal conversion in supercritical water (SCW), water at conditions above its critical point. When coal and oxygen are injected into SCW, the combustion products are dissolved in the water. In our novel scheme, the water is obtained from a deep saline aquifer, and the water containing the dissolved combustion products is returned to the aquifer. Deep saline aquifers have been identified as good site for CO₂ sequestration. In a third project, the possibility of applying chemical looping combustion (CLC) technology to coal is being investigated. In CLC, a metal oxide is used to provide the oxygen for coal combustion, yielding a product stream that is nearly all CO₂ and H₂O. After removing the water, a sequestration-ready stream of CO₂ is available.

Fundamental studies on coal and biomass combustion and gasification phenomena are undertaken by students in Mitchell’s group in order to gain insight into the chemical and physical processes that govern coal conversion processes. Of particular concern are the chemical reaction pathways responsible for converting the solid, carbonaceous fuel into gaseous species. Experiments are performed to not only identify the dominant reaction pathways but also to determine the rates at which the individual reactions occur. Efforts are directed towards developing the framework needed to design efficient, environmentally-friendly coal- and biomass-based electric power generation plants on the computer.