CA2721732A1 - Process for extracting oil from an oil/water/solids mixture, corresponding apparatus and use of the process - Google Patents

Abstract

In the customary process for mining oil sand comprising open cast excavation, the oil sand, after being excavated and transported to the processing plant by means of trucks, is comminuted in a mill and then slurried with water for transport of the hydrated material to the extraction plant. The hydration transport already leads in each case to a reduction in surface tension of the bitumen around the individual grains. In the prior art, flotation or separation tanks are used, with use of steam. According to the invention, spontaneous emulsion breaking of the oil-water-sand mixture is forced, forming three different material phases, of which the first phase essentially comprises the oil. In the corresponding apparatus, a pressure cell is present for this purpose.

Description

Description Process for extracting oil from an oil/water/solids mixture, corresponding apparatus and use of the process The invention relates to a process for extracting oil from an oil/water/solids mixture by forced spontaneous emulsion breaking. The invention additionally also relates to the apparatus for performing the process. The invention further relates to corresponding use of this process, and to the apparatus constructed in accordance with the invention.

The invention specifically involves the treatment of specifically oil-water-sand mixtures and emulsions. These include both mixtures and emulsions with high oil contents (oil = mineral oils, bitumen, tars, etc. up to a high proportion by mass up to 99%) and emulsions with a predominant water content (proportion by mass up to about 99%, i.e. aqueous solutions).
These mixtures and emulsions may additionally comprise a high mineral solids content, i.e. sand or particles in the order of magnitude of up to a 50% proportion by mass, in which case reference is generally made to oil sands or oil shales.

As is well known, such mixtures or emulsions can be treated predominantly by mixing in an assistant, specifically propane in particular, at elevated pressure, the emulsion previously having been subjected temporarily to relatively high temperatures of up to 100 C (so-called pre-conditioning) . The result found is a spontaneous separation into an oil-containing phase, a water-containing phase and an aqueous phase with a high solids content. This phenomenon is known in the technical field and is also referred to in general terms as "spontaneous emulsion breaking".

However, the field of use at which the technique being considered in the present context is aimed is especially, but not exclusively, the mining and recovery of bitumen and/or ultraheavy oil from oil sands which occur in nature.
Alternatively, the same procedure can be used to treat oil-contaminated wastewaters as arise especially in the mining of oil sands.

In the present-day mining of oil sands, as conducted, for example, in northern Canada in the province of Alberta, an early processing stage of the mining or the subsequent processing gives rise to mixtures of oil, sand and water with high proportions of high-viscosity oil and sand. In a later stage of the treatment, these become mixtures of aqueous solutions still having a comparatively high oil content, specifically in the single-digit percent range, and also mineral and other impurities. These aqueous mixtures, some of which are in the form of emulsions, are currently, regardless of the oil raw material still present, usually being disposed of in so-called "tailing ponds". The oil present therein thus ceases to be a valued raw material and becomes a problem material.

In the latter procedure, particular problems occur as a result of the fact that the hydrocarbons are relatively sparingly soluble hydrocarbons with high surface tension. In order to be able to remove the bitumen which surrounds every sand grain, the surface tension must be overcome.

In the prior art, assistants, specifically assistant gases in particular, are used. One example of a useful assistant gas is CO2, which will not be considered any further in this context.
Relevant alternative assistant gases are volatile hydrocarbon compounds. For example, WO 2004/080567 (DE 10 31 1283 Al) describes a process for emulsion breaking of oil-water mixtures under elevated pressure and temperature by means of a breaking agent. However, what can be generally inferred therefrom is merely the use of aliphatic hydrocarbons. In addition, WO 1996/011043 Al discloses a high-pressure spray extraction to obtain materials of value.

A supercritical extraction by means of propane gas is addressed in the publication by Eisenbach (1980). In this method, a combination of extraction and distillation is proposed, a supercritical gas being used for the extraction.

WO 2003/008524 Al discloses a process for purifying used oils/oil-containing residual substances by means of supercritical gases. In addition, DE 100 15 049 Cl (=EP 1 272 253 B1) specifies a process for working up mill sludges which are obtained in metal processing and consist of a mixture of fine scale and water, by removing the water and oil constituents from the fine scale, wherein the mill sludge is contacted in a vessel with a destraction agent introduced into the vessel in supercritical phase.

Further information regarding the prior art involving supercritical gas extraction can be found in US 6 821 413 B1, US 2002/0011442 Al and WO 2001/072394 Al, and the secondary literature therein.

Proceeding from the above prior art, it is an object of the invention to specify an improved process for extracting oil from an oil/water/solids mixture, and to provide a corresponding apparatus. In addition, specific applications for the novel process and the corresponding apparatus should be specified.

The object is achieved in accordance with the invention by the features of claim 1. A corresponding apparatus is specified in claim 9. Specific advantageous uses are evident from claims 12 and 13. Further developments of the process, of the apparatus and of the corresponding uses are specified in the corresponding dependant claims in each case.

The invention specifically provides for the use of an assistant in subcritical conditions (pressure and temperature) for splitting oil from oil sand mixtures, where oil sand mixtures mean all mixtures of oil and/or sand and/or water. This assistant is dissolved in a particular concentration in the emulsion under pressure. In this context, it was recognized that the emulsion-breaking effect resulting from the addition of the assistant is based on action of the alkane as the solvent and extractive removal of oil from the emulsion. In addition, the viscosity of the phases is reduced on saturation with the assistant, and the interfacial tension at the phase boundary additionally decreases, which considerably accelerates the phase separation.

In this context, it is particularly advantageous when the assistant used is an alkane, for example propane, or a mixture of alkanes. Subcritical conditions can exist, for example, as a result of processing at room temperature and pressure of less than 100 bar. Appropriately, the assistant or the mixture which constitutes the assistant is gaseous under these conditions.

A distinct advantage is achieved when a second assistant is used in addition to the assistant. When the second assistant used is toluene, an increase in the oil content removed is achieved under the same temperature and pressure conditions.
Alternatively or additionally to toluene, it is also possible to use another aromatic hydrocarbon, for example an ortho- or meta-xylene. Here too, it is possible to use a mixture of aromatic hydrocarbons.

Further details and advantages of the invention are evident from the description of figures of working examples which follows, with reference to the drawing in conjunction with the claims. The figures show schematically:

figure 1 the dependence of cumulative amount of oil extracted as a function of the addition of assistants, figure 2 a flow diagram for the extraction of the oil components from oil/sand/water emulsions and figure 3 an implementation of the flow diagram according to figure 2 as an apparatus.

Possible embodiments are considered by way of example hereinafter, which comprise an addition of propane as an assistant or an addition of propane as an assistant and of toluene as a second assistant. This addition is effected in subcritical conditions, i.e. at pressures and temperature which are below critical conditions for propane. The addition of the assistants, propane alone or propane and toluene, causes spontaneous emulsion breaking of an oil/solids/water emulsion into three phases 24...26. This requires a pressure of p = 90 bar.

The first phase 24 is an oil-enriched C3H8 phase. This is yellowish but clear in experimental tests, because it is in the form of a solution. The second phase 25, in contrast, contains predominantly water, which is clear. The third phase 26 contains the proportion which has settled because it is insoluble in C3H8 and water, and includes sand, such that a sand/water mixture is present. All phases 24...26 thus lack -apart from minimal residual contents, for example in the permille range - one or two of the original constituents of the oil sand or oil shale.

The addition of a second assistant, either to the oil/water/sand emulsion or to the propane assistant, also achieves certain improvements: after the addition of small amounts of, for example, toluene as the second assistant, even at room temperature under subcritical conditions, again at a pressure of 90 bar, a significantly improved solubility or loading of the hydrocarbons present in the oil in the propane is achieved. The loading is more than twice as high as in experiments at the same pressure and the same temperature, but without toluene addition. The loading achievable and the rate of mass transfer to propane of hydrocarbons is even higher than in experiments with supercritical propane (for example at a pressure of 90 bar and a temperature of 127 C) without toluene addition.

The results of some of these experiments are reproduced in figure 1. The mass of propane in grams is plotted on the abscissa, and the mass of oil in grams on the ordinate. The pressure used in all experiments shown was 90 bar. A first graph 11 shows the result in the case of use of propane as an assistant at room temperature. A second graph 12 shows the result at 67 C, likewise with propane as an assistant. A third graph 13 shows the result at 127 C, likewise with propane as an assistant. A fourth graph 14 shows the result at room temperature, approx. 20-22 C, on addition of a small proportion of toluene as a second assistant. What is important is that -as already explained above - even a small addition of toluene noticeably improves the extraction of oil, as evident in the fourth graph 14.

Figure 2 shows a flow diagram for performance of the process, according to which individual phases 24, 25, 26 of different compositions are obtained as the result from the oil sand 27 as the starting material. The oil sand 27 is introduced into a stage 21 for slurrying, to which water 28 is added at the same time. Optionally, this slurry is heated to a preset temperature. By means of hydrotransport 29, the mixture thus pretreated is introduced into a unit for processing 23. The unit 23 has means for mixing 30 the substances and an associated unit for compression 22. There is additionally an integrated unit for removal 31. The propane 32 is added via the unit for compression 22. Optionally, toluene 33 is added. After discharge from the unit for compression 22 and decompression 34, the phases 24, 25 and 26 comprising oil, water and sand already defined above are obtained.

Essentially the same situation is shown by figure 3 for the individual streams. In this figure, 40 means the suspension/emulsion of the oil/sand/water mixture. 41 means the extracted oil fraction and 42 the water fraction. 43 is the sand fraction. 44 denotes the optional metered addition of toluene as a second assistant. What is important is that the reaction apparatus is configured as a closed pressure cell 50, the part 51 being what is known as a decanter. The decanter is advantageously integrated in the pressure cell itself.

In addition, a separating stage 52 for solid/liquid is present, which is designed as a hydrocyclone. There is also a separating stage 54 for oil/assistant, which is designed as a simple decompression stage.

In the above-described apparatus according to figure 3, there are individual zones: a zone 61 for mixing the emulsion of oil/sand/water supplied and the first assistant, a settling zone 62, i.e. calming zone for the third phase 26 composed of sand/water, a settling zone 63, i.e. calming zone for the first phase 24, i.e. water, and a settling zone 64 in the form of a calming zone for the second phase 25, i.e. the oil fraction.
There is also a zone for the assistant 65 which is recycled, and a zone for the settled sand 66 and the cleaned water 68. A
further zone for the liquid phase composed of the oil fraction is 67 in the separating stage 54.

The streams from the hydrocyclone 52 and the decanter 51 can be removed either separately or combined.

Appropriately, there are valves upstream and downstream of the pressure-tight cell 50, the different fractions from the oil-sand extraction, for example the oil sand itself or else the residues from primary separation and the so-called tailings, being introduced via the upstream three-way valve. In addition, a bitumen/water emulsion is also added here from an SAGD
(= steam-assisted gravity drainage) process. In addition, the assistant gas(es) is/are appropriately supplied by means of a pump. By means of a four-way outlet valve, for example, it is especially possible to remove the product and the waste substances, i.e. water/sludges.

In the above-described process, the prior art is simplified in that a one-stage extraction can be effected. In this case, the assistant is used under subcritical conditions. Advantageously, an additional assistant can be used. In this case, the oil-sand-water mixture can be heated up after the hydrotransport and contacted with moderate pressure of the assistant in a closed cell, such that there is spontaneous formation of the three phases 24...26. This process is favored by the fact that the propane mixed in under pressure lowers the viscosity of the suspension and hence accelerates the settling of phases of different density, for example of solids. The different phases 24...26 are advantageously drawn off by means of a decanter.
This allows the three phases 24...26 to be provided directly.
After the separation of the phases 24...26, the assistant can be recovered from the first phase 24 by simple decompression, for example in a closed vessel. Propane is already converted to the gaseous state at room temperature in the course of decompression. The oil content remains as a high-boiling liquid phase 25, and can then be sent in virtually anhydrous form to further processing. The propane assistant is advantageously recycled into the circuit.

As a result of the viscosity-reducing effect of the propane, it may be advantageous not to release the pressure until the site of further processing of the oil fraction, and hence to exploit the improved transport properties owing to the reduced viscosity. The regenerated assistant can be transported over relatively large distances in a simple manner as a gas or even in liquefied form.

Since methods in which bitumen-water emulsions are produced are usually used in "in situ" bitumen production processes, for example in the SAGD process or else in the CSS process, the sand tends to remain in the reservoir. Thus, the delivery tube can directly feed the above-described pressure cell 50.

Typically, the water-bitumen emulsion already arrives at the processing plant with temperatures of 25 to 70 C, such that the step of further heating does not appear to be absolutely necessary.

In summary, it is assumed that, in the customary process for mining oil sand comprising open cast excavation, the oil sand, after being excavated and transported to the processing plant by means of trucks, is comminuted in a mill and then slurried with water for transport of the hydrated material to the extraction plant. The hydration transport already leads in each case to a reduction in surface tension of the bitumen around the individual grains. In the prior art, flotation or separation tanks are used, with use of steam. According to the invention, spontaneous emulsion breaking of the oil-water-sand mixture is forced, forming the three different material phases described, of which the first phase essentially comprises the oil. In the corresponding apparatus, a pressure cell 50 is present for this purpose.

Claims (13)

1. A process for extracting oil from a mixture of oil, water and solids components by forced spontaneous emulsion breaking, comprising the following process steps:
- introducing at least one assistant into the mixture, - mixing the first assistant with the mixture until spontaneous emulsion breaking into three phases occurs, of which the first phase is essentially oil and the assistant, the second phase is essentially water and the third phase is essentially water and the solids, - mechanically separating the three phases and - separating the oil in the first phase from the first assistant.

2. The process as claimed in claim 1, in which the first assistant used is propane or another alkane, or a mixture of alkanes.

3. The process as claimed in claim 2, in which the propane is introduced at pressures below 100 bar and room temperature.

4. The process as claimed in any of the preceding claims, in which a second assistant is used in addition to the propane.

5. The process as claimed in claim 4, in which the second assistant used is an aromatic hydrocarbon, especially toluene or an ortho/meta-xylene.

6. The process as claimed in any of the preceding claims, in which the assistant(s) is/are recovered from the removed first phase by the action of pressure.

7. The process as claimed in claim 6, characterized in that the pressure is not released until the site of further processing of the first phase.

8. The process as claimed in any of the preceding claims, in which the second and third phase are processed by filtration or by means of a hydrocyclone.

9. An apparatus for performing the process as claimed in any of the preceding claims, comprising a unit for mixing oil sand (27) with water (28) and for supplying thermal energy, with additional presence of a unit (30, 50) for mixing the water/solids mixture with a first assistant and of separate starting units, the unit (30, 50) for mixing being used to mix in the first assistant under subcritical conditions and the first assistant bringing about a removal of individual material phases (24...26), of which the first phase (24) comprises predominantly oil, the second phase (25) predominantly water, and the third phase (26) predominantly solids, and the individual material phases (24...26) being introducible into the separate starting units.

10. The apparatus as claimed in claim 9, comprising means (33) for metered addition of the second assistant.

11. The apparatus as claimed in claim 10, characterized in that the unit for mixing is a closed pressure cell (50).

12. The use of a process as claimed in any of claims 1 to 8 or of an apparatus as claimed in claims 9 to 11 for removal of oil from naturally occurring oil sands or oil shales.

13. The use of a process as claimed in any of claims 1 to 8 or of an apparatus as claimed in claims 9 to 11 for processing of oil-contaminated water.