(73a) Modeling Pyrite Behavior in Gasification Environments

The behavior of pyrite and other sulfide minerals in gasification processes are of fundamental importance to coal utilization technologies. Previous work has established that the physical and chemical transformations of impurities depend on mineralogy, the mineral distribution in the coal particles, and the presence of organically associated inorganic species. Further, the studies found that reducing the rate of oxidization of minerals, for instant pyrite, prolong the existence of sticky reduced forms iron phases and could increase the presence of hydrogen sulfide. The properties of the iron rich phases impact the release of other elements and their ability to interact with other particles.

This paper is mainly concerned with pyrite conversion during combustion-gasification processes. The objective of the study is to develop a more quantitative understanding of the impact of particle fragmentation and coalescence on the release of volatile species and on the physical properties such as surface tension and viscosity of the particles. Modeling studies are being conducted to determine the impact of residence time, temperature on particle formation and the release of volatile elements.

The detailed particle model provides an accurate characterization of particle temperature, sulfur released, and reaction and burning rates over wide ranges of gas temperatures, pressures, and compositions, and hence, will permit the accurate prediction of mass loss rates, pollutant and slag physical properties.

Preliminary results show that elemental sulfur release is greatest early in the oxidation process as a result of the formation and decomposition of pyrrhotite. In addition, the process of fragmentation was found to enhance the release of sulfur during the devolatilization process and to increase particle temperature as a result of sulfur oxidization. However, when the amount of oxygen in the bulk environment reduces, enhancing the formation of hydrogen sulfide occurs and fragmentation was decreased.