Filtration process and equipment studies for coal liquefaction processes. Quarterly report, December 1977--February 1978

Filtration runs resumed using in situ precoating with pressure instead of suction. Detail of the new precoating technique is described. Four series of filtration runs were made with Tacoma Filter Feed, but all were considered only partially successful because of precoat failure before completion. This was attributed to a high proportion of the precoat dropping off and allowing progressive blinding or plugging. Detailed observations of the precoat failures have been reported. Apparently, the precoat failures were associated with the new procedures and conditions being used for in situ precoating. Considerable attention has been given to analyzing the cause of these failures. It has been concluded that the most likely cause was due to flashing of the solvent used for pre-coating and/or precoating. This flashing could occur during the filtration step at 600/sup 0/F. Flashing during filtering was not, however, a problem when precoating under vacuum. It is unlikely, therefore, that flashing occurs during the filtration step once the precoat solvent has been purged from the precoat, by the filtered liquefied coal. Flashing could, of course, take place during this purging period. Special precoating experiments were performed to confirm this reasoning.