Optimal conditions for CANMET coprocessing of Rheinish coal and refinery VTB

Abstract

A series of coprocessing PDU experiments was conducted using 30 wt % Rheinish brown coal and refinery vacuum tower bottoms. Runs were carried out in CANMET's hydroprocessing and process development unit (PDU) using a 10-L tubular reactor. Three key operating variables were examined: slurry space velocity, reactor temperature and superficial gas velocity. The maximum pitch (525°C+) and, coal (THF insolubles) conversions were 94.3 wt % and 98.0 wt %, respectively. Pitch, coal (THF insolubles) and asphaltene conversions were determined and properties of the products were measured. Gas holdups as a function of reactor height were measured by a narrow beam gamma-ray densitometer. Space mean holdups and effective space times, which were defined as quotients of the mean liquid holdup to the nominal weight slurry hourly space velocity, were derived. Statistical analyses of conversions and fractional yields indicated that the responses could be characterized by temperature and effective space time. For pitch conversion, the effects of these two variables were found to be nearly independent, thus the linear model was applicable. However, the effects of the interaction of these two variables were significant for coal and asphaltene conversions. Empirical response surfaces were generated for the presentation of experimental results. Predicted conversions and yields agree well with the experimental data. By superimposing pitch and coal conversions response surfaces, an operation domain was determined to achieve high pitch conversion and avoid significant regressive reaction.