AU624369B2 - Pyrolysis of oil containing shale - Google Patents

Description

Jr COMMONWEALTH OF AUSTR IF FORM

COMPLETE

PATENTS ACT 1952

SPECIFICATION

FOR OFFICE USE: Class Int.Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: 9 Name of Applicant: WOLLONGONG UNIADVICE LIMITED P 9 a Address of Applicant: Northfields Avenue, Wollongong, New South Wales, 2500 Actual Inventor: HOWARD KNOX WORNER and PETER BURTON Address for Service: Complete Specification for the Invention entitled: |r g., "PYROLYSIS OF OIL CONTAINING SHALE" 22.1 u The following statement is a full description of this invention, including the best method of performing it known to me/us:- Complete of PI7623 dated 7.4.1988 1 *I I 1~

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~Lj S006615 06/04/89 This invention relates to the extraction of hydrocarbons from oil shale.

Oil shale is a sedimentary rock containing organic matter, mainly the geological remains of marine algae.

The dominant organic constituent is kerogen which may be decomposed by pyrolysis to release liquid hydrocarbons.

During pyrolysis sulphur- and nitrogen-containing compounds may also be released from the remains of biological amino acids, and in addition, other organic i constituents may release bitumens. The spent shale which remains contains char derived from kerogen as well as the original minerals and other minerals formed during heating.

In the past the philosophy of oil recovery from oil shale has been to drive off and collect the maximum obtainable organic content.

Traditionally, the economic assessment of oil shales has invariably involved the Fischer assay, a process which proceeds as follows: shale from the mine is ground i; a. a up into small pellets which may then be partially dried; j the pellets are then heated in a retort at a constant rate 'ae. 0 0 of 10 O per minute until the temperature of 500 C is i reached. All the evaporated water and vaporized organic I content are then collected as a distillate from which f 1 various organic fractions can be separated. The spent 'i shale may then be used in a second combustion step to provide process heat for the pyrolysis of more shale. The shale oil produced by a process of this kind is 2- 1 i i y 1 1 1 l l 1 1 i *y 1 1 not suitable for conventional cracking because it is polluted with sulphur- and nitrogen-containing compounds. These compounds could poison the petrochemical catalysts used in conventional cracking, and in addition would lead to pollution of the atmosphere. It has therefore been necessary to hydro-treat the shale oil with hydrogen under extremely high pressures, in the range of 15 to 18 MegaPascals, to remove the sulphur and nitrogen. The cost of this hydro-treating is the main economic barrier to the use of shale oil as an alternative transport fuel refinery feedstock.

t A further major problem with the extraction of oil ts from shale is that pyrolysis expands the shale matrix so that spent shale cannot be returned to the same volume from which the raw shale was extracted. Thus there is an environmental problem of what to do with the large amount of spent shale. Further costs arise from the requirements to clean retort waters, to revegetate mine sites and to prevent the leaching of toxic materials from spent shale.

Under the current philosophy of oil recovery from 00 shale there is no prospect of income or profit from shale deposits within the next two decades, or until the crude oil price exceeds U.S.$50.00 per b.b.l. which is unlikely prior to the year 2010.

Some 50% of the oil from shale is in the form of simple alkanes (C nH2+2) and alkenes (C H2n) in 3ii ;I £i l 1 1 i. w general formula. These compounds originate in the breakdown in the lipid double layers of the cell walls of the algae. This invention makes use of the fact that pyrolysis of the oil from shale at temperatures less than 550°C (but greater than 350°C below which essentially no oil is yielded) will lead to a chemically simpler component mixture, even more dominated by a high hydrogen to carbon ratio than the Fischer assay oil components, namely by the alkanes and alkenes. At the same time a much lower proportion of nitrogen-containing compounds will result in the pyrolysate oil. The disadvantage is that a lesser proportion of the available organic content of the shale is converted to oil.

It is an object of this invention to provide a method of extracting selected hydrocarbons from oil shale which will overcome or at least ameliorate one of the above disadvantages.

ii extracting selected hydrocarbons from oil shale comprising the steps of coarsley crushing the raw ale, irradiating the crushed shale with microwa energy whilst mechanically mixing the crus shale to exfoliate and heat the shale to a subs tially uniform temperature between 300°C and 550 and recovering released hydrocarbons a distillate.

Pr rably, the crushed shale is heated to a perature between 350°C and 5500C. The microwave -4- 4a Accordingly, the present invention provides a method of extracting selected hydrocarbons from oil shale comprising: coarsely crushing the raw shale, heating the crushed shale to a temperature of between 3000°C 350°C whilst mechanically mixing the shale, using microwave energy to heat the shale from 3000C 3500°C to 500°C 550°C, and recovering released hydrocarbons as a distillate.

1 0 Microwave energy may be used to heat the shale from ambient temperature to the desired temperature range of 500°C 5500C.

In a preferred aspect, heat from previously processed shale may be used for the heating step to 3000°C 3500°C and/or to complement heating of the shale with microwave energy.

Preferably, the crushed shale is heated to a temperature of between 350°C and 500°C. The microwave energy preferably has a frequency of between 300 and 3000

C.

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'id i 1 4 *4 0 4 rr t 4 0 4 4 o *r 44 MHz and more preferably has a frequency of approximately 2450 MHz or 915 MHz which are frequencies presently allocated for commercial microwave heating devices.

Preferably, the process takes place in a continuous line feed plant. Advantageously further heating may be applied by conventional means, and a controlled atmosphere environment may be applied during the pyrolysis process.

During the microwave treatment of the lumps of shale, water held within the shale is heated rapidly to the point where steam is generated, and the steam is then superheated causing exfoliation of the lattice and 4r heating of the resulting slivers in excess of 100 0

C.

The alkane and alkene fractions are driven off between 300 and 500 C and further heating is supplied by oS microwaves tuned to 2,450MHz and/or other frequencies or by conventional means, in order to precisely control the .o pyrolysis kinetics in the shale matrix. In this manner S pollutants and bitumens, which are not driven off until 20 temperatures in excess of 400 C are reached, are prevented from evaporating in excessive quantities.

Preferably, heat from previously processed shale is used to complement heating of the shale by irradiation with microwave energy.

The use of microwaves to pyrolyse the shale results in several further advantages. Firstly, the shale does not have to be crushed into such small pieces since microwave heating causes exfoliation of the shale. Some *0@ 9 0 04 4.

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4 *0 crushing is still required in order to limit the force with which the lumps of shale explode, so that mciage of the microwave chamber is not incurred. A further advantage is that no pre-drying is required since microwaves heat the water molecule and thus a small degree of wetness assists the process. This can be of increased effect if the microwave energy is tuned to approximately 2450 MHz at which frequency the water molecule is very efficiently heated.

The advantage of controlling the pyrolysis within the strict temperature and time parameters is that a less chemically complex shale oil is produced which contains e* reduced or even acceptable levels of nitrogen, thus 0 saving costs associated with hydro-treating the distillate. Preferably only the alkane and alkene fractions are distilled from the shale. The partial pyrolysis of the shale results in a spent shale exhibiting several advantageous properties. Firstly the organic content of the shale implies that many of the elements necessary to support plant growth must be present in the shale, and the partial pyrolysis according to the present invention leaves most of the humic acid content of the kerogen in the char. At the same time the partial pyrolysis reduces the hydrophobic nature of the I shale and increases its wettability and percolation properties significantly. This allows a more environmentally acceptable waste product to be produced. i In fact this waste product may even be saleable as a i 6 K/ by-product. The spent shale could not be thought of as a fertilizer but the partially pyrolysed product can serve as an excellent plant growth medium, especially if combined with other fertilizers. Alternatively the spent shale could serve as a soil beneficiation agent in poor soil. The shale's resistance to erosion is also a valuable property which can be used to prevent the loss of topsoil, to stabilize topsoil on sloping sites and to rehabilitate eroded land. The partially pyrolysed spent shale when returned to the mine site also serves to assist revegetation.

A further by-product of some shales is that recovery of precious metals from the residue is improved since the increased wettability and percolation properties can increase the yield of precious metals such as gold and platinum by processes such as cyanide leaching.

One experimental example of this invention will now be described, by way of illustration only with reference 0* i 0 to the accompanying drawings in which: Figure 1 is a schematic drawing of an apparatus for use in the method of this invention; Figure 2 is a graphical representation of the results of a gas chromatographic analysis of shale oil produced according to the method of this invention; and Figure 3 is a graphical representation of the results of a gas chromatographic analysis of oil produced by Fischer assay processing.

i '1 2 As shown in Figure 1 an experimental scale apparatus 1 for use in this invention comprises a spherical heating chamber 2 which contains a spherical vessel 3 of pyrex glass or other substantially microwave transparent material. The vessel 3 is encased by a layer of thermally insulating microwave transparent material 4 such as that known as "Fibrefrax" or "Kaowool'.

A side arm 5 extends horizontally from vessel 2 and is connected via a ball joint coupling 6 to a cold trap I and condensor 8 of substantially conventional type.

The heating chamber 2 is disposed within the cavity of a microwave oven schematically shown at 9 and means (not shown) are provided to rotate the chamber about a 4 horizontal axis co-incident with the longitudinal axis of side arm 5. These drive means can be of any suitable 44 known type.

4.

In use, finely crushed oil shale 9 sieved to a size range of 1-3mm is placed in vessel 3. The heating chamber is rotated at a speed of approximately 8rpm and irradiated with microwave energy having a frequency of 2450MHz. The microwave energy is applied at a power level of from 0.5 to 2.0 kW per kilogram of shale for periods of up to one hour. Rotation of the chamber mixes the crushed shale to provide substantially uniform heating by the microwave energy.

The irradiation described above drives off shale oil and water which are collected in the cold trap 7. The quantities of shale oil and water produced are -8substantially the same as that produced by standard Fischer assay of a similar sample.

Gas chromatographic analyses of the shale oil produced by microwave processing, and Fischer assay processing are compared in figures 2 and 3 respectively.

The chromatographic peaks indicate, by their heights, the quantities of each hydrocarbon present.

Hydrocarbon peaks representing alkanes of ten carbon atoms (C 10 and seventeen carbon atoms (C 17 are labelled in figures 2 and 3. It will be seen that the microwave oil (figure 2) has significantly more light hydrocarbons than the Fischer produced oil (figure 3).

The microwave oil also has relatively greater amounts of unsaturated hydrocarbons (alkenes) indicated by the heights of the secondary peaks, adjacent to each (alkane) peak of the major hydrocarbons. A further advantage of the microwave product is the presence of beneficial aromatic compounds, indicated by some of the minor peaks in the region of C 10 in figure 2 which includes a peak for methyl benzene, not found in the Fischer oil.

It will be apparent that the uniformity of heating of the shale, achieved by tumbling the shale in a "rotary kiln" in the above example, is important to maintain the desired uniform and controlled temperature range of the shale. Other methods of achieving uniform heating such as fluid bed processing are equally appropriate to this invention.

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The above described experimental example relates to shale crushed to have a particle size of from 1 to 3 mm for convenient comparison with a standard Fischer assay.

However, at microwave frequencies of 2450 MHz the particle size can be from 10cm to 6.4.

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Claims (14)

1. A method of extracting selected hydrocarbons from oil shale comprising: coarsely crushing the raw shale, -pheating the crushed shale to a temperature of between 300°C 350°C whilst mechanically mixing the shale, using microwave energy to heat the shale from 3000C 350°C to 5000 550°C, and recovering released hydrocarbons as a distillate. 00

2. A method as claimed in claim 1 wherein the crushed shale is heated to a Stemperature between 3500C and 5000C.

3. A method as claimed in claim 1 or claim 2 wherein the microwave energy has a frequency between 300 MHz and 3000 MHz.

4. A method as claimed in claim 3 wherein the microwave energy has a frequency of Sapproximately 2450 MHz.

5. A method as claimed in claim 3 wherein the microwave energy has a frequency of approximately 915 MHz.

6. A method as claimed in any one of claims 1 to 5 wherein heat from previously processed shale is used for said peoheating.

7. A method as claimed in any one of the preceding claims, wherein heat from 1 previously processed shale is used to sRmplipentheating of the shale with microwave energy.

8. A method as claimed in any one of claims 1 to 7 wherein the raw shale is crushed to an average particle size of between 10cm and

9. A method as claimed in any one of claims 1 to 8 wherein the microwave energy is Kilofro.m applied at a power of from 0.5 to 2.0 kW per program of shale.

J O iC L~ i. i: i _1 S12 A method as claimed in any one of claims 1 to 9 wherein the crushed shale is mixed in a rotating heating chamber.

11. A method as claimed in any one of the preceding claims, wherein the released hydrocarbons comprise alkane and alkene fractions.

12. A method as claimed in any one of the preceding claims, wherein said method takes place in a continuous line feed plant.

13. Spent shale resulting from the method of any one of the preceding claims.

14. A method of extracting selected hydrocarbons from oil shale, substantially as j hereinbefore described with reference to the accompanying drawings. DATED this 23rd day of September 1991. WOLLONGONG UNIADVICE LIMITED S I WATERMARK PATENT TRADEMARK ATTORNEYS S' THEATRIUM S' 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 i AUSTRALIA AGB/CH 'i i i i- IJ^