Rotary drying of Stuart oil shale

Short Communications Prospect for all minerals excluding coal and petroleum. Accordingly, the administrative and reporting requirements are the same as those for minerals. The ‘Authority to Prospect for Retention Purposes’, introduced in January 1986, may be applicable to some Queensland oil shale deposits. No fixed expenditure is required, but the titleholder is expected to carry out such activities as market and laboratory research, and environmental monitoring with a view to the exploitation and development of the resource when economic circumstances permit. A Green Paper released in May 1987 proposed directions for change in the Mining Act 1968-1986. Submissions on these proposals closed on 31 August 1987. The submissions are being considered by Government with a view to formulating new legislation as soon as possible. The gap between the Authority to Prospect and the mining lease is presently bridged by the ‘Retention Authority to Prospect’, but it is proposed that a mineral development licence be

introduced as the intermediate title. This licence would be granted in areas where exploration has reached a stage where there is a level of confidence sufficient to allow detailed proving, planning, costing and establishment of a marketable product, but where development is not possible due to unavailability of markets, finance or technological requirements. Rental would be half that applicable to by 50% mining leases, increasing annually. A twelve monthly report on activities would be required. This licence would be applicable to many of the shale oil projects presently awaiting economic viability. Because of the close association, general similarity in composition and similar methods used in exploration and mining, it was proposed in the Green Paper that oil shale and coal could be granted under a common ‘Authority to Prospect’. Authorities would then be granted for all minerals (excluding coal and oil shale) or for coal and oil shale. In the light of responses received, the future of this proposal is uncertain.

CONCLUSIONS Exploration activity for oil shale during 1986-87 was limited by the depressed world oil price. In established deposits, studies have concentrated on the processing and retorting of shale oil to determine the most effective technology to ensure development can take place when the opportunity arises.

REFERENCES Noon, T. A. Geological Survey of Queensland, Record 1984/56, unpublished Noon, T. A. Proceedings of the Third Australian Workshop on Oil Shale, CSIRO Division of Energy Chemistry, Lucas Heights, 1986, p. 9 Crisp, P. J., Ellis, J., Hutton, A. C., Korth, J., Martin, F. A. and Saxby, J. D. in ‘Australian Oil Shales: A Compendium of Geological and Chemical Data’, University of Wollongong, 1987, p. 109 Madre, D. A. Proceedings of the Fourth Australian Workshop on Oil Shale, CSIRO Division of Energy Chemistry, Lucas Heights, 1987, p. 17

Rotary drying of Stuart oil shale*

Bruce C. Dickson and Les A. Bakert Southern Pacific Petroleum N.L.. 143 Macquarie Street, Sydney 2000, Australia t Central Pacific Minerals N. L., GPO Box 4042, Sydney 2007, Australia (Received 7 June 1988)

Oil shale from the Kerosene Creek Member of the Stuart oil shale deposit was successfully dried from 20.1 to 3 % free moisture, as required using an existing countercurrent rotary dryer. Both the flue gas and product solids streams were monitored for hydrocarbon loss,and no loss was detected. Throughputs of 27 tonnes h- ’ were achieved and negligible size degradation was observed. This paper describes operating conditions and provides valuable scaleup information. (Keywords:hydrocarbon; moisture content; flue gas)

The aims of this drying programme were: a, to assess the feasibility of drying to 24 % free moisture without hydrocarbon loss in a commercial dryer; b, to prepare a bulk sample for retort testing; and c, to obtain process and scaleup data where applicable. There is little information on the drying of Stuart oil shales. Lane et al.’ have presented some initial data on drying kinetics for a Stuart sample. EXPERIMENTAL The equipment and plant layout is shown in Figure 1. The oil shale is moved from the feed stockpile to dryer feed hoppers

*Paper presented at the 4th Australian Workshor, on Oil Shales. 3-l December 1987. Brisbane,.

Australia

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by a front end loader. Shale is fed from 3 bin hoppers using belt feeders onto a primary feed conveyor. Shale feed enters the rotary dryer at the flue gas outlet (rate ~23-28 tonne h-l). Shale, maximum size of 8 mm and a grade of 180 1tonne-’ (at 0% retort water) is transported and falls

as

‘curtains’

from

dryer

lifters

through hot flue gases and progresses towards the burner under the influence of gravity. Coarser shale particles exit the dryer at the burner end and feed directly onto the product conveyor at temperatures between 120 and 135°C. Shale dust is carried away by the flue gas via ducting to recovery cyclones. Cyclone solids underflow, then pass downstream onto the product conveyor, and on the surface of the product outflow. Cycloned flue gas then flows into a water contact scrubber where residual fines are

suppressed and particulate matter-free flue gas can be emitted via a stack to atmosphere. Equipment

The dryer consists of a 7 x 1.8 m diameter drum inclined towards the burner end rotating at a fixed speed. The burner uses automotive diesel oil (ADO) as a fuel and a forced draft fan to supply primary/atomizing air and secondary air. Control of the firing rate is by means of a proportioning arm, which alters the fuel flow in proportion of primary to secondary air. The control is very coarse, due to the hysteresis in the burner head mechanisms, and control of the correct air-fuel ratio via this method was inprecise. The burner management includes a flame eye for automatic shutdown when required, as well as an

Short Communications

automatic ignition system. The burner is located directly in the discharge end of the dryer without a separate combustion chamber. Tertiary air and dryer draft are controlled by an induced draft fan with louvre dampers on the fan discharge. Dust suppression from the flue gas is by four primary cyclones (Z 3 m high and 1 m diameter) for the large fines, and a 4 x 3 m diameter water contact scrubber, for small fines recovery. The outlet from the scrubber feeds into a 20 x 1 m diameter stack. Control of the burner combustion, as well as detection of combustion was via a portable gas detector that sampled the flue gas immediately downstream of the kiln. The analyser contained various filters to prevent blockages and a thermocouple to monitor flue gas temperature. The analyser could detect combustibles (methane, ethylene and acetylene), carbon monoxide, carbon dioxide and oxygen. A combustion efficiency output could also be obtained using the oxygen and temperature variables as measured. The efficiency is calculated by an internal computer program. The drying operation was controlled to achieve the desired free moisture for the shale using the following parameters;

firing rate, throughput, and flue gas damper control. These parameters were altered based on: hourly samples of the product, for moisture content; shale temperature in the dryer discharge chute; and stack temperature and flue gas analysis (especially of oxygen and combustibles). As well as the hourly samples for moisture content (using a calibrated microwave oven other technique), samples were taken to test: 1. Feed/product LTOM (litres of shale oil/tonne of oil shale at 0 y0 retort total moisture) and free moisture analysis based on composite twice daily samples. 2. Product free moisture contents using standard laboratory analysis to verify hourly site analyses. 3. Size analysis of product. These gave a more complete analysis of the drying operation and were performed on a daily basis. Operation

Preliminary work had been performed by the CSIRO Division of Energy Chemistry concentrating on the conditions for the onset of oil shale combustion when exposed to high temperatures (up to 800°C) and naked

flames (up to 2000°C). Laboratory testing determined that combustion of oil shale at the particle size distribution of the sample was detected at temperatures as low as 200°C. Hence in the early stages of the drying operation, both material and stack temperatures were maintained between 105 and llO”C, to avoid potentially adverse temperature levels (i.e. 200°C). Simultaneously, burner adjustments were made to ensure minimal flame impingement on the shale. Product moisture contents varied from 15 % at a temperature of 70°C to 8.5 % at 95”C, and finally 5.5 % at 105°C with no evidence of oil shale organic matter loss or oil shale combustion. Gas analysis throughout this period yielded high oxygen levels between 19 and 2Ooj,, and combustibles at 1 x-1.5 y0 (probably due to inefficient burner combustion). Subsequent to the trial period, product shale temperatures were raised to 130°C to maximize moisture removal, with constant monitoring of gas analysis, product quality and dried product moisture. Free moistures between 3.2% and 3.5% were achieved, while flue gas contained more than 2.5 y0 combustibles (analyser range O%-2.5 %) and oxygen contents down to 16%. Blue smoke appeared at the stack outlet from time to time. There was still no observable

Stack

Feed

Variable

speed

stockpile

bin discharge Product stockpile

Figure 1

Pioneer asphalt dryer plant of Stuart box cut

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Short Communications deterioration in the grade of the oil shale. At this throughputs of point ~20 tonne h-i were being achieved. Reconstruction of the burner control and fuel control valve was undertaken in an attempt to achieve a greater range of control and improved air-fuel ratios, for more efficient combustion and hence reduce fuel consumption. Adjustments were made without shale feed to achieve stable flame operation from minimum to maximum firing, while optimizing primary air above secondary air. The modifications were tested the following day with the result that drier throughputs of between 25 and 27 tonne h-’ were being achieved with moistures between 2.45 and 3.00% (temperature 133-138°C) and overall improved fuel efficiency of 17.21 tonne- ‘, a 15 y0 improvement. (Average fuel consumption 20.21 tonne- ’ dried shale). Gas analyses revealed oxygen levels of 17 % with < 2 % combustibles.

Process correlations

RESULTS From the averages of the entire operation, the conditions and results of analyses, the achieved average moisture of 4.5% was an acceptable level of moisture removal from feed especially considering the limitations of control and the fact that it was a once-off operation. Oil yield measurements on dried product revealed that there was no loss of organic matter. Fuel consumption for the operation totalled 47320 I of dieseline. The total weight of ‘bagged’ dried shale was 2342 tonnes, which resulted in a consumption rate of 20.2 tonne- ‘. On a daily basis, consumption rates were difficult to assess due to inaccuracies in fuel tank dipping and the erratic nature of fuel deliveries. However, as more experience was gained with the operation, improvements in drying efficiency were achieved by manipulating the available parameters as previously mentioned. These improvements resulted

for Stuart

and Condor

in increased moisture removal (consistently ~3%) at higher throughputs (>26 tonnes h-l). Feed and product size distribution measurements showed that size degradation was very low and corresponded to a reduction in average size of between 0 and 5 %. CONCLUSIONS Using a small commercial countercurrent rotary dryer, Stuart oil shale has been successfully dried from 20.1% free moisture to < 3 ‘A, with measured solids discharge temperatures of 138°C without any measureable or observable hydrocarbon loss. At feed rates of 27 tonnes h-l, fuel consumption was 17.2 1tonne-‘. Size degradation of the shale was negligible. This gave valuable scale up data for future process design. REFERENCES 1

Lane, D., Ramjas, S. and Haynes, B. S. Proc. Fourth Australian Workshop on Oil Shale, Brisbane, Dec. 1987, p. 147

oil shales*

A. John Gannon and Arthur W. Lindnert Central Pacific Minerals NL. GPO Box 4024, Sydney 2001, Australia t Arthur Lindner and Associates P/L. 10 Bungowen Avenue, Thornleigh 2 120, Australia (Received I June 1988)

Fifty four oil shale samples from the Stuart and Condor deposits have been pyrolysed by material balance modified Fischer assay to extend existing, and develop new correlations between shale oil yield and organic carbon. The study has confirmed that organic carbon levels on fresh and spent shales are linearly related to oil shale grade and that organic carbon conversion to products is non linear and appears to approach an asymptotic limit. The Stuart and Condor correlations developed are remarkably similar given the differences between the deposits. (Keywords:oil shale; pyrolysis; carbon)

The Stuart oil shale deposit is centred about 15 km northwest of Gladstone, within The Narrows Graben on the Central Queensland coast. To the northwest within the graben, the Stuart deposit is contiguous with the Rundle oil shale deposit. In all, the graben trends north westerly for about 30 km, is up to 6 km wide and contains a thick sequence of mid to late Eocene sediments’. Samples from the five oil shale units contained within the Rundle Formation in the Stuart deposit (Tengingie Creek, Ramsay Crossing, Brick Kiln, Munduran Creek and Kerosene Creek) were selected and form a sample set stratified by grade ranging from ~30 to over 200 LTOW *Paper presented at the 4th Australian Workshop on Oil Shales, 3-4 December 1987, Brisbane, Australia 00162361/88/101402-03$3.00 0 1988 Butterworth & Co. (Publishers)

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(litres of shale oil/tonne of oil shale at 0 % retort water). Oil shale beds within the Rundle Formation in The Narrows Graben’ contain in excess of 5 billion barrels of shale oil based on modified Fischer assay (MFA), about half of which is contained in the Stuart deposit. The Condor deposit is part of a thick Tertiary sedimentary sequence located further north along the central Queensland coast3. Most of the resource occurs in the Condor unit, comprising tough, brown oil shale up to 400 m thick. In situ resources located onshore within the Condor unit are in excess of 9 billion barrels to a depth of 1000 m (Ref. 4). The inorganic components of the Stuart samples from the Rundle Formation are dominantly clay minerals, but with which quartz and opaline silica on occasion reach codominant pro-

portions. The clay minerals are dominantly interstratified montmorillonite and illite with lesser kaolinite and mica/illite. Calcite reaches subdominant proportions and feldspar and siderite are present in accessory amounts5. Quartz is codominant with clays and kaolinite in the brown oil shale subunit of the Condor samples, which also contain significant quantities of siderite and buddingtonite6. Hutton’ has shown that exinite is the dominant organic constituent of Australian Tertiary oil shales. The exinite can be subdivided into six macerals: sporinite, spores and pollen; cutinite, cuticles or waxy outer layers from leaves and stems; resinite, resins, fats, waxes and oils; lamalginite, small, thin walled algae and other phytoplankton; telalginite, large, colonial or thick walled unicellular algae; and liptodetrinite, fragments from