Factors affecting product yields and oil quality during retorting of Stuart oil shale with recycled shale: a screening study

Abstract Seven process variables—retort temperature, solids recycle ratio, char content of recycle solids, recycle solids temperature, pretreatment of recycle solids with ammonia, solids residence time and steam concentration—were studied. The Plackett-Burman statistical experimental design, highly effective for detecting main effects of large number of variables with a minimum number of experiments, was used to screen these variables. Each variable was tested at low and high levels. The bench-scale integrated retorting-combustion oil shale (BIRCOS) facility at Lucas Heights was used to obtain product yields and compositions under realistic recycle shale conditions. The significance of the main effects of the variables on product yields and carbon conversions decreased in the order: retort temperature, solids residence time, steam concentration, char content, solids recycle ratio, recycle solids temperature, and ammonia treatment. Retort temperature was the only variable to affect the H C atomic and nitrogen content of the oil. The sulfur content of the oil was independent of all variables.