Results and interpretation of rapid-pyrolysis experiments using the LLNL solid-recycle oil shale retort

Virtually all rapid pyrolysis oil shale retorting processes currently under study utilize some form of hot-solid as the heat carrying medium. The conditions under which rapid retorting is achieved call for rapid mixing of the solid heat carrier and raw shale followed by a 2 to 3 minute soak period during which pyrolysis occurs. Both chemically active and inactive solid heat carriers have been proposed along with a number of processing strategies. To assess the merits of the various processing alternatives, a thorough understanding of the chemistry and physics involved in solid-recycle retorting is required. At Lawrence Livermore National Laboratory we are studying the chemistry and physics of solid-recycle retorting in a 2 ton/day continuous-loop pilot scale facility. We have operated our continuous-loop system, over the past two years, using both a two-stage fluidized bed pyrolyzer and a cascading mixer and gravity bed pyrolyzer, with recycled shale as the heat carrying medium. The majority of runs have used an Anvil Points 24 GPT shale with dolomite and calcite concentrations typical of western oil shale. The quantity and quality of the oil produced under rapid-pyrolysis conditions is of key interest in continuous-loop systems. We have determined oil yields and have characterizedmore » the oil in a number of ways under a variety of processing conditions. The effects of product sweep, recycle ratio, retorting temperature and atmosphere have been studied in both pyrolyzers and are reported. The facility provides a unique opportunity to study sulfur and nitrogen chemistry throughout the recycle system. Oxidized shale has been shown to effectively scrub H/sub 2/S from the pyrolysis gas, and only trace quantities of SO/sub 2/ have been measured from the combustion of recycled shale. Nitric oxides in the combustor effluent have been measured and are discussed. 12 refs., 7 figs., 14 tabs.« less