Fluidized Bed Retorting of Oil Shale

Abstract

Atmospheric pressure fluidized bed technology offers many processing advantages for retorting oil shale. The one advantage which has been most studied and emphasized is that oil yield, as compared to Fischer assay, is increased. While the nature of the shale greatly influences the degree of oil yield enhancement that is realized, there is little doubt that fluidized bed technology increases the yield of oil, at least marginally, for all oil shales. Concomitant with an increase in oil yield and decrease in gas yield by the fluidized bed technique is that the oil, compared to Fischer assay oil, has higher aromaticity, density, heteroatom content, viscosity, and Conradson carbon content. With improved heavy oil upgrading catalysts and promising non-fuel, added-value applications for the heavy fraction, however, the generation of more, but heavier, oil can be a distinct advantage for a fluidized bed process. While increased oil yield is the most renowned benefit of fluidized bed retorting, there are several other aspects of this technology which should be considered just as highly such as: precise temperature control, utilization of fine particles, rapid pyrolysis kinetics, and processing flexibility without mechanical complexity and moving parts. The Center for Applied Energy Research (CAER) is developing a multi-stage fluid-bed process called KENTORT II which incorporates pyrolysis, gasification, and combustion zones. The main features of the process are that the heat of the process is provided by the combustion of char from pyrolysis and this heat is transferred to the pyrolysis zone with recirculating shale without diluting the overhead pyrolysis products with combustion flue gases. The KENTORT II process will be used as the primary example of a fluidized bed retorting process because it includes all of the major gas/solid reactions which are relevant for thermal processing of oil shale at atmospheric pressure. While the KENTORT II process has been initially developed to process the Devonian shales of the eastern U.S., the CAER has also investigated the fluidized bed characteristics of Brazilian (Irati), Moroccan (Timahdit and Tarfaya), and Turkish (Goynuk) oil shales. These results will be compared to fluidized bed pyrolysis results from other laboratories including those for the Green River shales of the western U.S. and the oil shales from various Australian deposits.