WO2008061304A1

WO2008061304A1 - Extracting hydrocarbons from oil shale

Info

Publication number: WO2008061304A1
Application number: PCT/AU2007/001789
Authority: WO
Inventors: Raymond Walter Shaw
Original assignee: Technological Resources Pty. Limited
Priority date: 2006-11-21
Filing date: 2007-11-21
Publication date: 2008-05-29

Abstract

A process for extracting hydrocarbons from solids containing hydrocarbons such as oil shale is disclosed. The process includes supplying (i) crushed hydrocarbon-containing solids, such as oil shale, (ii) a hydrocarbon solvent, and (iii) a hydrogen donor to a reactor, and digesting hydrocarbon-containing solids at an elevated temperature and pressure in the reactor and extracting kerogen from hydrocarbon-containing solids into the hydrocarbon solvent. The process also includes flashing a slurry that forms in the digestion step in a series of stages to a lower temperature and pressure and separating hydrocarbon fractions from the slurry during the course of the flashing step.

Description

EXTRACTING HYDROCARBONS FROM OIL SHALE

The present invention relates to a process for extracting hydrocarbons from solids containing substantial quantities of hydrocarbons such as oil shale.

The term "oil shale" is understood herein to mean rocks that include organic material in the form of kerogen in amounts that are sufficient to yield hydrocarbons, such as petroleum, upon treatment such as by distillation.

In addition to oil shale, other possible sources of solids containing hydrocarbons include, by way of example only, tar sands as found in Canada and low ranked coals such as are being investigated for production of liquid fuels .

Currently, there is some limited production of petroleum from oil shale using a long-established thermal retorting process . In general terms , the process includes heating oil shale to 450-500⁰C in the absence of air, whereby the kerogen is converted chemically to oil .

Potential alternatives to the retorting process are a number of in-situ processes and direct extraction processes . Research and development work to varying extents has been carried out on these processes. However, the processes are not being used commercially at this stage.

In-situ processes are based on heating oil shale underground to release gas and oil . The Shell Oil Company is one company that is developing a particular in-situ process. Chevron and ECL also have active programs.

There are difficulties with these processes in obtaining high recovery, the amount of energy and time taken, the — 5 —

need to seal the deposits to avoid leakage of fluids , and difficulties in achieving acceptable heat transfer through the rocks of the deposits . There is also limited permeability of the rocks. Moreover, the processes are only applicable to oil shale which is well below the surface.

Direct extraction processes have been attempted based on the known ability of light hydrocarbons such as toluene to extract kerogen, especially when used under supercritical conditions and with the inclusion of sources of hydrogen. One such process is that described in US patent 4108760 in the name of Williams et al. Other processes include a so-called ATS (Australian Thermal Solutions) process invented by John Rendell. The ATS process is described in a series of patent families which include Australian patents 609782 and 779333 and Australian patent application 2003255192, all in the name of John Rendell .

The above discussion of prior art processes is not to be taken as an admission of common general knowledge in Australia or elsewhere.

None of these prior art processes are being used commercially as they have not been able to be made economic whereas the present invention provides an alternative more suitable process for extracting hydrocarbons from oil shale .

In general terms , the present invention provides a process for extracting hydrocarbons from solids containing hydrocarbons such as oil shale that includes supplying (i) crushed hydrocarbon-containing solids, such as oil shale, (ii) a hydrocarbon solvent, and (iii) a hydrogen donor to a reactor, and digesting hydrocarbon- containing solids at an elevated temperature and pressure In the reactor and extracting kerogen from hydrocarbon- containing solids into the hydrocarbon solvent. The process also includes flashing a slurry that forms in the digestion step in a series of stages to a lower temperature and pressure and separating hydrocarbon fractions from the slurry during the course of the flashing step.

In more specific terms , according to the present invention there is provided a process for extracting hydrocarbons from solids containing hydrocarbons such as oil shale that includes the following steps :

(a) crushing hydrocarbon-containing solids, such as oil shale, to a predetermined particle size distribution;

(b) supplying (i) crushed hydrocarbon- containing solids from step (a) , (ii) a hydrocarbon solvent, and (iii) a hydrogen donor to a reactor, and digesting hydrocarbon-containing solids at an elevated temperature and pressure in the reactor and extracting kerogen from hydrocarbon-containing solids into the hydrocarbon solvent; and

(c) flashing a slurry that forms in digestion step (b) in a series of stages to a lower temperature and pressure and separating hydrocarbon fractions from the slurry during the course of the flashing step.

The hydrocarbon-containing solids may be oil shale .

One example of a hydrocarbon solvent for use in digestion step (b) is supercritical toluene.

The hydrogen donor facilitates direct conversion of kerogen in oil shale into a hydrocarbon that is soluble in the hydrocarbon solvent. In addition, the hydrogen donor facilitates removal of nitrogen and sulphur . This is important in terms of ultimate product quality for petroleum companies .

The hydrogen donor may be in the form of a hydrogen-containing gas or compound.

The above-described multi-stage flashing step (c) is an effective and efficient means of separating hydrocarbons from the slurry with minimal carry-over of solids , particularly fines , with the separated hydrocarbon fractions. In particular, the use of the multi-stage flash train overcomes the problems commonly found with separating fine solids and liquids and avoids technically complex and costly steps such as are required in the ATS process. Specifically, the multi-stage flashing step (c) is selected in any given situation having regard to an objective of separating hydrocarbons that are in the hydrocarbon solvent in the slurry away from solids , particularly fines less than 10 microns, in the slurry.

Preferably the flashing step (c) includes injecting fluids, such as hot water/steam, into the slurry between at least one stage of the flashing step (c) to facilitate separation of hydrocarbons from the slurry.

The flashing step (c) may include the following stages:

(i) a first stage of flashing the slurry from 450° to a lower temperature, typically around 275°C, and removing a fraction of the hydrocarbons as a gas phase where this flashing stage is carried out in one or more flash vessels; (ii) injecting hot water/steam into the remaining slurry following the first stage to give a mixed aqueous-hydrocarbon slurry where the temperature is at or below the lower temperature, typically 275⁰C, at a point where the pressure from the aqueous phase sets the total pressure of the system

(iii) a second stage of flashing the slurry from at or below the lower temperature, typically 275⁰C, to a further lower temperature and removing the hydrocarbons and some of the water as a gas phase .

Preferably the final slurry remaining after step (iii) above includes solids in an aqueous phase with little or no hydrocarbons remaining in the aqueous phase.

In situations where this outcome cannot be achieved in just the two stages of flashing, preferably flashing step (c) includes repeating the second stage of injecting water/steam and thereafter flashing off vapour one or more times until the objective of having all of the solids in the aqueous phase with little or no hydrocarbons present is achieved.

Preferably the process further includes a step of recovering the hydrocarbons separated from the slurry in the flashing step (c) in a suitable form, for example by any one or more of condensation and distillation, selective fractionation, and solvent extraction.

Preferably the process includes supplying a light fraction of the hydrocarbons recovered in the recovery step to the digestion step (b) .

Preferably the crushing step (a) crushes mined oil shale to particles in a size range of 200-500 microns. The size range is suitable for forming a slurry in digestion step (b) that can be pumped.

Preferably the slurry that forms in the digestion step (b) is a pumpable slurry.

Preferably the pumpable slurry feed in the digestion step (b) has a solids density of at least 30%_f more preferably at least 35% , by weight of the slurry .

High pressure grinding rolls are one, although not the only, suitable option for crushing the mined oil shale .

Preferably the process includes a step of drying crushed oil shale produced in crushing step (a) prior to supplying the oil shale to the digestion step (b) .

Preferably the drying step includes drying crushed oil shale to remove at least 80% , more preferably at least 90%, of the water in the oil shale.

Preferably the drying step is carried out without affecting the kerogen using techniques such as (a) using an added solvent as described in US Patent 4210518 or as being developed for coal as described in US patent

56955323 or (b) more conventional direct drying techniques with hot gases .

In a situation in which the hydrocarbon- containing solids also contain valuable metals, preferably the process includes contacting the slurry from the flashing step (c) with an acid, typically a mineral acid such as nitric and/or hydrochloric, to dissolve valuable metals, such as uranium, nickel, vanadium and molybdenum, in solids that typically are present in a solid fraction in the slurry produced in the flashing step (c) and forming a metal-containing liquor. Preferably the process includes processing the liquor containing the metals to recover the metals .

The present invention is described further by way of example with reference to the accompany drawing which is a flow sheet of one embodiment of a process of extracting hydrocarbons from oil shale in accordance with the present invention .

With reference to the flow sheet, mined oil shale is crushed in a feed preparation step typically using high pressure grinding rolls to a fine particle size distribution of 200-500 microns.

The crushed oil shale is then beneficiated as required having regard to the chemical composition and physical characteristics of the oil shale .

Depending on the characteristics, the beneficiation may include sorting on the basis of particle size and flotation to remove undesirable components of the oil shale such as sulphur. The beneficiation may also include washing with aqueous liquor to remove soluble impurities that may cause corrosion or contamination problems within a downstream reactor (s) .

The beneficiated oil shale is then dewatered by being dried to remove sufficient of the water to avoid problems in the extraction step arising from water: (a) forming an immiscible phase that causes the overall system pressure to become too high, and/or (b) dissolving out inorganic contaminants in the oil shale and becomes a source of corrosion within a downstream reactors . In this context, "sufficient" means typically at least 95% of the water from the oil shale. The oil shale may be dried by any suitable direct or indirect means, including using filters for a first part of the water removal in cases where the shale has been treated in an aqueous slurry.

The dried oil shale, a suitable light hydrocarbon solvent such as toluene, and a suitable hydrogen donor such as hydrogen gas and/or compounds such as decalin or tetralin are then supplied to a reactor, preferably in the form of a tube digester (not shown) , in amounts such that the solids content is at least 35%, preferably at least 40%, of the total weight of the solids and liquids in the digester.

The contents of the digester are heated at temperatures of the order of 450⁰C under pressure in an extraction and conversion step such that the solvent phase is in the supercritical form for sufficient time to extract kerogen from the oil shale and to convert the kerogen into hydrocarbons that are soluble in the solvent. This step is described by the box marked "Extraction and Conversion" in the flow sheet.

The heating can be carried out within the digester, as is commonly done with tube digesters, or could partially be done prior to feeding the liquids and solids into the digester as is done in other designs, with the choice of method being dependent upon which system is most cost effective to meet the needs, especially residence time , for a given feed material .

During the period of the above-described digestion step there can be periodic release of gas from the digester to remove volatiles, sulphur, and residual water .

At the end of the digestion step, the slurry of solids and liquids is processed in a multi-stage flashing step to extract and thereafter separate hydrocarbons from the slurry. This step is described by the box marked ^λΛSolid/Liquid Separation" in the flow sheet.

The stages of the flashing step are selected to ensure that there is minimal carry-over of solids with the flashed hydrocarbons and to avoid the slurry having high viscosity such that it will not flow properly and/or become sticky and adhere to exposed surfaces of the reactors and/or the flash vessels used in the flashing step.

The flashing step includes the following stages :

(i) a first stage of flashing the slurry from of the order of 450° to around 275⁰C and removing hydrocarbons as a gas phase;

(ii) injecting hot water/steam into the remaining slurry following the first stage and displacing hydrocarbons from the slurry into an organic phase that is largely immiscible with the slurry;

(iii) optionally separating the organic phase containing predominantly hydrocarbons from the slurry;

(iv) injecting hot water/steam into the remaining slurry when the slurry reaches a temperature at which the steam pressure matches the pressure in the system; and

(v) a second stage of flashing the slurry from the order of 275°C to a lower temperature and removing hydrocarbons as a gas phase.

The final slurry remaining after the final step in the flash train includes solids in an aqueous phase . The process generates a large tonnage of fine solids for disposal . One option for handling the slurry is a process based on the process used to handle "red mud" in Bayer plants . This may also include additional treatments to remove or destroy any residual organics present with the solids in the residue such as using ultrasonics as described in International application PCT/AU2004/001458 in the name of Comalco Aluminium Limited or by using unproven technologies such as solar photochemical destruction by titanium dioxide or bacterial remediation.

The use of the above-described flash train for hydrocarbon removal avoids costly extra steps required in prior art processes such as the ATS process and the operation is advantageous in that it is part of the extraction process - as is the case for an alumina plant.

The hydrocarbons extracted from the above- described flash train are processed in a distillation column that splits the hydrocarbons into (a) a product fraction, (b) a light fraction for use in the digestion step, (c) a high melting point fractions as a solid residue, and (d) a fraction to use to produce the hydrogen donor for the digestion step .

The processing of the hydrocarbons extracted from the flash train will vary depending upon the composition achieved from the circuit for any given feed material . Preferably the hydrocarbons from the first stage of flashing will be fed directly to a distillation system without the need for cooling, conditioning and then reheating to achieve separation. In cases where this is not possible, and with the hydrocarbons from the second and later stages of flashing, these hydrocarbons may need cooling and some treatment to remove water and any solids carried over before treating them in a distillation process to separate out the desired components . The above-described digestion and multi-stage flashing steps result in an aqueous slurry which is well suited to further processing to recover any valuable metals that may be present in the slurry.

For example, for oil shale, such as that found in Sweden, the slurry can be contacted with a mineral acid such as nitric and/or hydrochloric to dissolve valuable metals, such as uranium, nickel, vanadium and molybdenum, that typically are present in a solid fraction in the slurry. The acidic liquor containing these metals can then be processed further to recover the metals for sale using conventional processing. This residue is more suited to metal recovery than would be the case using a pre- treatment step such as that proposed by Audeh in US patent 4,514,378.

Many modifications may be made to the embodiment of the process of the present invention without departing from the spirit and scope of the invention.

By way of example, whilst the embodiment of the process of the present invention is concerned with extracting hydrocarbons from oil shale, the present invention is not so limited and extends to extracting hydrocarbons from a range of other solid materials containing hydrocarbon materials, such as the tar sands as found in Canada and low ranked coals such as are being investigated for production of liquid fuels .

By way of further example, whilst the embodiment describes a particular multi-stage flashing step to extract and thereafter separate hydrocarbons from the slurry produced in the digestion step, the present invention is not so limited and extends to any suitable form of flashing, preferably multi-stage, flashing step. In addition, whilst the embodiment describes the use of a particular hydrocarbon solvent in the form of supercritical toluene, the present invention is not so limited and extends to any suitable solvent.

Furthermore, whilst the embodiment describes the use of a hydrogen donor in the digestion step, the present invention is not so limited and is not confined to the use of a hydrogen donor.

Claims

1. A process for extracting hydrocarbons from solids containing hydrocarbons such as oil shale that includes the following steps:

(a) crushing hydrocarbon-containing solids, such as oil shale, to a predetermined particle size distribution /

(c) flashing a slurry that forms in digestion step (b) in a series of stages to a lower temperature and pressure and separating hydrocarbon fractions from the slurry during the course of the flashing step .

2. The process defined in claim 1 wherein the hydrocarbon-containing solids are oil shale.

3. The process defined in claim 1 or claim 2 wherein the hydrocarbon solvent for use in digestion step (b) is supercritical toluene.

4. The process defined in any one of the preceding claims wherein the hydrogen donor facilitates direct conversion of kerogen in oil shale into a hydrocarbon that is soluble in the hydrocarbon solvent and facilitates removal of nitrogen and sulphur.

5. The process defined in any one of the preceding claims wherein, the hydrogen donor is a hydrogen-containing gas or compound.

6. The process defined in any one of the preceding claims wherein the flashing step (c) includes injecting fluids, such as hot water/steam, into the slurry between at least one stage of the flashing step (c) to facilitate separation of hydrocarbons from the slurry.

7. The process defined in any one of the preceding claims wherein the flashing step (c) includes the following stages :

(i) a first stage of flashing the slurry from 450° to a lower temperatuew, typically around 275°C, and removing a fraction of the hydrocarbons as a gas phase where this flashing stage is carried out in one or more flash vessels ;

(ϋ) injecting hot water/steam into the remaining slurry following the first stage to give a mixed aqueous-hydrocarbon slurry where the temperature is at or below the lower temperature, typically 275°C, at a point where the pressure from the aqueous phase sets the total pressure of the system

(iii) a second stage of flashing the slurry from at or below the lower temperature, typically 275°C, to a further lower temperature and removing the hydrocarbons and some of the water as a gas phase .

8. The process defined in claim 7 wherein the final slurry remaining after step (iii) above includes solids in an aqueous phase with little or no hydrocarbons remaining in the aqueous phase.

9. The process defined in claim 7 or claim 8 includes repeating flashing step (c) and injecting water/steam and thereafter flashing off vapour one or more times until all of the solids are in the aqueous phase and there are little or no hydrocarbons present in the aqueous phase .

10. The process defined in any one of claims 7 to 9 further includes a step of recovering the hydrocarbons separated from the slurry in the flashing step (c) in a suitable form, for example by any one or more of condensation and distillation, selective fractionation, and solvent extraction.

11. The process defined in claim 10 includes supplying a light fraction of the hydrocarbons recovered in the recovery step to the digestion step (b) .

12. The process defined in any one of the preceding claims wherein the crushing step (a) crushes mined oil shale to particles in a size range of 200-500 microns.

13. The process defined in any one of the preceding claims wherein the slurry that forms in the digestion step (b) is a pumpable slurry that has a solids density of at least 30%, more preferably at least 35%, by weight of the slurry.

14. The process defined in any one of the preceding claims includes a step of drying crushed oil shale produced in crushing step (a) prior to supplying the oil shale to the digestion step (b) .

15. The process defined in claim 14 wherein the drying step includes drying crushed oil shale to remove at least 80%, more preferably at least 90%, of the water in the oil shale .

16. The process defined In any one of the preceding claims wherein, in a situation in which the hydrocarbon- containing solids also contain valuable metals, the process includes contacting the slurry from the flashing step (c) with an acid, typically a mineral acid such as nitric and/or hydrochloric, to dissolve valuable metals, such as uranium, nickel, vanadium and molybdenum, in solids that typically are present in a solid fraction in the slurry produced in the flashing step (c) and forming a metal-containing liquor.

17. The process defined in claim 16 includes processing the liquor containing the metals to recover the metals .

18. A process for extracting hydrocarbons from solids containing hydrocarbons such as oil shale that includes supplying (i) crushed hydrocarbon-containing solids, such as oil shale, (ii) a hydrocarbon solvent, and (iii) a hydrogen donor to a reactor, and digesting hydrocarbon- containing solids at an elevated temperature and pressure in the reactor and extracting kerogen from hydrocarbon- containing solids into the hydrocarbon solvent, and flashing a slurry that forms in the digestion step in a series of stages to a lower temperature and pressure and separating hydrocarbon fractions from the slurry during the course of the flashing step .