Characteristics of coke deposition onto the inner surface of a coal liquefaction preheater tube were experimentally simulated in an autoclave reactor for a range of industrial operating variables. A test piece with a tubular baffle was installed in the autoclave to generate artificial heat spots in slurry by controlling the heatflux from the piece to the slurry as well as the slurry velocity near the piece.
No coke deposition was found to occur under conditions with a bulk slurry temperature of ca. 700K, oil/coal weight ratios from 55/45 to 60/40 and slurry velocities from 0.5 to 1.0m/s. On the other hand, an appreciable coke deposition was observed at bulk slurry temperatures over approximately 720K and slurry velocities below about 0.1m/s. Surface temperature of the test piece increased with a progress of the coke deposition. Within the present experimental conditions, the deposition rate was in a range about 1.5×10-6 to 2.3×10-6g·cm-2·min-1·g-1-coal. Also, amount of coke deposited increased with S/C and O/C atomic ratios of parent coal while decreasing with the increase of H/C atomic ratio of parent coal.
