Normal-phase dynamic imaging of supercritical-water salt precipitation using neutron radiography

Abstract

Although neutron radiography has been effectively used to dynamically image the separation of salts from supercritical water, earlier approaches have relied on an artificial model system that was limited to boron-containing salts in heavy water, D 2O. In this work we demonstrate that similar information may be obtained with the contrasts reversed: boron-free salt buildup can be seen in supercritical H 2O. This new technique enables in situ imaging as illustrated by results obtained for systems of interest for biomass gasification, where solid plugging and flow pattern changes were clearly imaged within the vessel. As compared to the D 2O method, the H 2O method does not explicitly distinguish between regions of low water density and buildup of salt; however, the H 2O method can provide information on fluid density changes that the D 2O method does not. This method was applied to determine the behavior of Na 2SO 4 in H 1 2 O , which led to plugging and erratic behavior, and to K 3PO 4 in H 1 2 O , which led to smooth operation. Plugging behavior of Na 2SO 4 was drastically reduced by the addition of K 3PO 4 to the feed, which suggests the formation of a liquid brine.