Determination of the Mechanisms and Rate of Alkali Transport in Typical Coal Gasification Processes. Final Report

摘要

The primary objectives of this project were to assess and evaluate the degree and significance of alkali vaporization and transport under temperature, pressure and atmosphere conditions similar to those occurring in various coal gasification processes. 172 runs were made under atmospheric pressure conditions and 35 runs were made at pressures from 50 psig to 1000 psig. The principal observations from the work are: (1) Alkali carbonates, hydroxides and silicates appear to have relatively low transport rates in the reducing atmospheres and test conditions. (2) Alkali sulfates appear to react with the gaseous atmosphere causing transport of alkali as well as sulfur. The sulfur-bearing species does not appear in the early stages to be the alkali-bearing species. It appears that there is some reduction of the sulfur-bearing condensed phase that is, sulfites and sulfides appear in the reaction products. (3) The transport of sulfates appears to have an induction period followed by a rapid transport for a limited time. The formation of more stable condensed phases appears to limit the transport in the later stages. (4) Under dry atmosphere conditions the alkali sulfates migrate out of the transport crucible to cooler regions. Under wet atmosphere conditions the migration is inhibited but reoccurs as the system pressure is increased. (5) It appears that as the system pressure is increased the alkali carbonates become less stable and disappear as a condensed phase below 500 psig, that is, sulfites and sulfides appear to be formed. (6) In addition to alkali transport both calcium and magnesium appear to be transported. (7) Alkalis transported from Ohio-10 coal ash were characterized by a high initial rate which decreased to a value essentially consistent with background after a few hours exposure. 10 references, 17 figures, 5 tables. (ERA citation 10:012041)