(103f) Effect of Flue Gas Oxygen and Water Vapor Content on High Temperature Capture of Mercury by MinPlus Sorbent

An experimental study was undertaken to determine whether MinPlus, an inorganic sorbent that has been shown to capture mercury at high temperatures, might be useful for warm and hot cleanup of gasification off gases. Disperse phase experiments were conducted, using an externally heated quartz tube reactor, with sorbent feeding rates ranging from 1g/h to 6g/h. Experimental techniques, from the feeding of the sorbent to the measurement of ~μg/m3 levels of Hg++, and Hg in the exhaust, are described in detail. Changes of mercury concentration in the reactor off gas were passed to a Tekran mercury analyzer with a wet bubbler system (modified by thiosulfate addition). The entire Hg sampling, conditioning and analysis system were thoroughly validated in this and other preceding and contemporaneous mercury research programs.

A most important result was that both capture mechanisms (short time and long time) failed to occur in the complete absence of oxygen. It appears that previous results described in the original proposal were clouded by the (probable) presence of a small oxygen leak in the original packed bed apparatus. The current work has discovered that although some oxygen is required to allow the process to occur, the minimum amount of oxygen required might be as low as, and most probably much lower than, 4000 ppm. These results have important implications for the use of this sorbent in gasification processes, and these have been addressed in a companion volume to this Final Report. Experiments were also conducted to explore the effects of added water vapor, and although results here were somewhat ambiguous, the sorbent was still effective in the presence of water.