Nonthermal Plasma Effects on Hydrogasification of Coal

Summary form only given. A new concept for a Zero Emission Coal (ZEC) technology which captures 100% of conventional emissions in addition to providing a pure stream of CO₂ for sequestration has been proposed by Los Alamos National Laboratory in collaboration with Louisiana State University. A challenge faced by the ZEC technology is carrying out the hydrogasification reaction under a reasonable set of conditions. Although the hydrogasification reaction is exothermic and is thermodynamically favored at ambient conditions, its kinetics are far too slow. Ideally one could use catalysts to enhance the kinetics of the hydrogasification reaction, thereby reducing the required temperatures and pressures, but the hostile environment of coal gasification (abrasion, sulfur poisoning, relatively high temperatures, etc.) create a very hostile environment in which conventional costly catalysts will rapidly degrade. We have attempted to address this issue through the use of a plasma in a catalytic role, where a plasma turns a very small fraction of the coal and reactant gases into highly reactive free radicals and excited species, which are believed to promote gasification reactions. Two atmospheric pressure plasma sources, a microwave plasma and a dielectric barrier discharge (DBD), have been developed in the mixtures of hydrogen, coal powder, and argon in order to study the hydrogasification of coal. When the activated Ar/H₂ gas stream interacted with cold carbon particles downstream of the microwave cavity, CH₄ (methane) was the only stable gasification product. However, when carbon particles were injected into the plasma within the microwave cavity, both C₂H₂ (acetylene) and C₂H₄ (ethylene) were measured in addition to the CH₄. Based on UV spectroscopic measurement, the initial reaction step leading to C₂ species is thought to be a hydrogen ion reaction with a carbon particle. - For the CH₄ production, adsorption of neutral species of hydrogen onto the carbon particle is suggested. Recently, we have developed a nonthermal DBD gasifier in order to separate plasma and temperature effects on hydrogasification of coal, which will be discussed in this presentation with comparing a microwave experiment.