Scott D. Carter

Fluidized bed steam retorting of Kentucky oil shale

Abstract A three-inch (7.6-cm) diameter fluidized bed reactor has been used at the Kentucky Center for Energy Research Laboratory (KCERL), operated by the Institute for Mining and Minerals Research (IMMR), to investigate the fluidized bed retorting characteristics of Kentucky oil shales. Because steam has been indicated to be a reactive pyrolysis gas for both Eastern and Western U.S. oil shales by many, a main objective of the fluidized bed investigation was to determine the effects of steam as a fluidizing medium. This was accomplished by comparing the yields and compositions of the products from steam and N2 retorting under otherwise equivalent fluidized bed conditions. Oil yields obtained from steam fluidization were approximately 2% greater than oil yields obtained from N2 retorting. Steam retorting released significantly more pyritic sulfur from the shale, providing evidence that reduced hydrogen scavenging from the kerogen for H2S production was a possible mechanism for the increased oil production. Steam fluidization resulted in increased oil collection efficiency, and represented the most significant difference between the steam and nitrogen systems. Liquid product quality was similar for both steam and N2 fluidization and the oils were more aromatic, more viscous, higher in density, higher in nitrogen content, and lower in volatility than Fischer Assay oil derived from the same shale.

Processing of eastern US oil shale in a multistaged fluidized bed system

Abstract A multistaged processing concept for eastern US oil shale, KENTORT II, integrates dense-phase fluidized bed pyrolysis with fluidized bed gasification and combustion steps. The fluidized bed retort produces enhanced yields for eastern US oil shale by minimizing cracking and coking reactions. Residual carbon and sulphur are converted in the gasification zone to medium-Btu, H 2 - and H 2 S-rich gas, leaving a low sulphur char for combustion. Heat is provided for gasification via recirculating solids from the combustion zone, and for pyrolysis from hot gases and recirculating solids from the gasification zone. Both experimental systems used in this study indicate that carbon and sulphur conversion are sufficiently rapid to proceed under moderate gasification conditions. Coking induced from solids recirculation was small, and particle agglomeration was not observed during combustion.

EFFECT OF PROCESS SOLIDS ON SECONDARY REACTIONS DURING OIL SHALE RETORTING

Abstract The effect of solids processing, oil vapour-solids interactions and contact time on coke formation from oils produced during Eastern US oil shale pyrolysis was investigated. Both long and short vapour contact time reactors were used to study the coking reactivity of sand, processed shales and clay minerals typically associated with Eastern US oil shales. BET nitrogen surface area and reflected light microscopy were used to correlate physical properties of the solids with carbon deposition. Combusted shales were more reactive coking substates than pyrolysed or gasified shales. Physical measurements indicated that macropores and fractures (not measured by BET) were important in coke formation. Steam treatment of oxidized shale decreased coking without changing measured physical properties. This is possible evidence for chemical alteration of the mineral matrix. Combustion temperature (773 versus 1098 K) did not affect the reactivity of oxidized shales. Therefore, high coking cannot be attributed to temperature-induced activation of the mineral matrix. Coking on clay minerals correlated to nitrogen BET surface area. Process-induced macroporosity, which allowed access to an active mineral matrix, was postulated as important in coke deposition.

Testing of an Irati oil shale in a multi-stage fluidized bed retorting process

Abstract A Permian Irati oil shale from Brazil was tested in a 7.6cm diameter prototype of the Kentort II process which is a multi-stage fluidized bed retort containing pyrolysis, gasification and combustion zones. To facilitate comparisons, test conditions were maintained similar to those from a recent study utilizing a Devonian shale (Cleveland Member of the Ohio Shale) from Kentucky. The Irati shale was processed with all three zones of the process in operation and solid recirculation was used to transfer heat throughout the reactor. Generally, the Irati shale performed well in the process, but generation of fines was more prevalent. Oil yields averaged 112% of the modified Fischer assay despite the use of recycled solids to transfer heat to the pyrolyser. Due to the more aliphatic nature of the kerogen, carbon conversion to oil was significantly greater for the Irati shale compared to the Cleveland shale. Otherwise, gasification and combustion kinetics and hydrocarbon gas production were similar for the two shales.

Examination of eastern US oil shale by-products and their markets

Established and potential oil shale product and by-product markets are examined in an effort to identify components or process configurations that might improve process economics and to evaluate promising directions for future research. These include trace elements, sulfur, cement, asphalt, bricks, fixed gases, specialty carbon fibres, adsorbent carbons, chemicals and chemical feedstocks. Market evaluations for the most part are based on the yields of by-products expected from an eastern US oil shale using Kentort fluidized-bed technology in a 6800 t day -1 plant. For certain value-added products such as specialty fibres and adsorbent carbons, the discussion is more general.

Method for determining the kinetics of cracking and coking of shale oil vapours in fluidized beds

Abstract The secondary cracking and coking of oil vapours produced from oil shale retorting have been previously shown to depend upon the nature and temperature of the substrate over which these reactions occur. To realistically examine the kinetics of these reactions during fluidized bed retorting, an apparatus has been developed which permits shale oil vapours generated in one fluidized bed to pass over selected substrates in a second fluidized bed. Substrates can be fed as a batch or continuously. In the batch mode, the substrate is heated to reaction temperature and is then exposed to shale oil vapours for a chosen period of time. Carbon deposition onto the solid is monitored in real-time by combusting the pyrolysis products and measuring the oxides of combustion with an on-line mass spectrometer. The extent of carbon uptake is also determined by elemental analysis of the substrate following reaction. These two methods of analysis were shown to correspond well under all the conditions investigated. In the continuous mode, substantial amounts of product oil can be collected so the effects of cracking may be evaluated. The rates of carbon deposition onto processed shales and pure minerals have been measured.

The relative coke-inducing tendencies of pyrolysed, gasified and combusted Devonian oil shales☆

Abstract A dual fluidized-bed reactor system was used to examine the isothermal kinetics of carbon deposition when nascent shale oil vapours were passed through beds of pyrolysed, gasified and combusted Devonian shale. Naturally occurring samples of the principal silicate minerals found in Devonian shale (kaolinite, illite and quartz) were also tested. The rate of carbon uptake declined with increasing carbon deposition on the solids. The coke-inducing activities of the processed shales were ranked as: combusted shale gasified shale pyrolysed shale. The effect of coking temperature on carbon deposition was relatively small, which has important implications for solids-recycle oil shale retorts.

Fluidized bed gasification characteristics of Devonian oil shale char

A Kentucky oil shale char was gasified in a fluid bed reactor. The effects of mean solid residence time (MSRT), bed temperature, and steam and CO2 partial pressure were studied. Carbon reactions during gasification were found to be dependent on all three parameters. The steam/char reaction was the dominant primary gasification reaction. The CO2/char reaction did not proceed significantly under the conditions studied and COCO2 ratio was dependent on the steam partial pressure. Sulphur removal was less dependent on temperature and steam partial pressure and was essentially complete by 1800 s MSRT. Nearly complete sulphur conversion was the result of both thermal decomposition and steam reaction with pyrrhotite. Conversions of 80–85% sulphur and 70–75% carbon (raw shale basis) were obtained for combined pyrolysis/gasification. The implications of the results for the development of a retorting process for Devonian shales are discussed.

Fluidized Bed Retorting of Oil Shale

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.

Characteristics of processed shales affecting oil yield loss to coke

Abstract The objective of this research was to further examine coking during hot-solid recycle retorting. Specifically the relationship between process-induced macroporosity and the reactivity of the shale mineral matrix was investigated. Photomicrographs support a direct relation between coking and the development of macroporosity in oxidized substrates. As access to the mineral matrix increases, the effect of processing on its reactivity becomes more important. The coking activity of illite, the major mineral component of the shale used, increased slightly when heat-treated to 973 K, but further heat treatment to 1323 K decreased its reactivity. Coke deposited on combusted shale and illite either blocked access to and/or deactivated coking sites, significantly reducing substrate reactivity. Carbon removal from the illite by oxidation at 773 K increased reactivity threefold over untreated illite. Combusted shale had fewer active coking sites, as measured by temperature-programmed desorption analysis, than gasified shale. This was consistent with deactivation of the mineral matrix with increased temperature treatment. Results also indicated that deactivation of the mineral matrix was possible by heat and steam treatments. The data provided further evidence that the amount of oil yield loss to coke was primarily controlled by process-induced macroporosity, allowing access to a reactive mineral matrix.