Mineral oils: processes and products – Refining – Water removal
Reexamination Certificate
2002-01-21
2004-09-07
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Water removal
C423S650000, C516S194000, C516S196000
Reexamination Certificate
active
06787027
ABSTRACT:
The invention is related to a process for breaking an emulsion of bituminous oil and water into the respective bituminous oil and water phases.
In the Orinoco Basin, in Trinidad, in North America, and in other areas, deposits of heavy oil and asphalt occur which are noted for their high bitumen content. These natural substances—which resemble oil and are commonly known as bituminous oil—can only be extracted by processes reducing viscosity and not by standard refinery methods. The extraction method currently used in the Orinoco Basin comprises emulsification of the bituminous oil at bed level, extraction of the emulsion, upgrading and transport.
Emulsifying the bituminous oils with water brings about a considerable reduction in the viscosity of these oils. The original viscosity in excess of 300 Pa.s at 20° C. is reduced to the range of 12 to 35 Pa.s as a consequence of emulsification. It is only this viscosity-reducing process that permits the extraction, transport and further processing of bituminous oil. Owing to the relatively high bitumen content, the bituminous oil cannot be easily processed by traditional refinery methods.
At present, the bituminous oil emulsion is used to fire power stations. The high sulphur content in bituminous oils (from 3 to 4%) causes a correspondingly high level of environmental pollution, a level which is becoming more and more unacceptable in the industrialized countries. The alternative is to produce desulphurized fuel gas by partial oxidation, also referred to as gasification, of the bituminous oil, thus obtaining raw gas mainly consisting of CO and H
2
. The raw gas is subsequently treated to obtain desulphurized fuel gas suitable for firing combined cycle power plants. The partial oxidation of bituminous oil is also suitable for the generation of synthesis gas or hydrogen, which can be used in a Fischer-Tropsch process or in processes for preparing a wide range of chemicals such as methanol, ammonia, oxy-products, formic acid and acetic acid.
EP-A-790292 describes a process in which an emulsion of Olinoco tar and water, also containing small amounts of sulfonic acid type surface active agent, having a starting temperature of 20 to 30° C. is broken by raising the temperature of the emulsion to 150° C. in two stages by means of an indirect heat exchange.
U.S. Pat. No. 5,441,548 also describes a process in which a bituminous oil/water emulsion is broken by raising the temperature of the emulsion to a temperature of between 130 and 170° C. by means of two heat exchangers in series. The water and bituminous oil phase are subsequently separated by means of phase separation in a gravity type emulsion separator. According to the specification no additional chemicals such as for example demulsifiers are added to improve the separation of the bituminous oil phase and the water phase.
A disadvantage of the above processes is that the starting emulsion still has, a relatively high viscosity at a temperature of below 100° C. when entering the first heat exchanger. Because of this high viscosity the heat exchanger must be equipped with large diameter tubes through which the emulsion flows and/or a high pressure must be applied to overcome the pressure drop in the first part of the heat exchanger where the viscosity is still high. Large diameter tubes are less effective resulting in that the heat exchanger will become large in order to perform the desired raise in temperature or, as is the case in U.S. Pat. No. 5,441,548, more than one heat exchanger will have to be used in series. The high pressure needed is disadvantageous because special pumps must be used. Furthermore the heat exchanger and the process equipment downstream of the heat exchanger, like for example the gravity-type emulsion separator, must be designed for this higher pressure level for obvious safety reasons. The present invention provides a process, which can be operated at a lower pressure having all the obvious advantages in view of the above.
The following process achieves this object. Process for separating an emulsion of a bituminous oil and water into a liquid water phase and a liquid bituminous oil phase, wherein the following steps are performed:
(a) raising the temperature of the bituminous oil/water emulsion having a temperature of below 100° C. to a temperature of above 140° C., and
(b) performing a phase separation wherein a liquid water phase and a liquid bituminous oil phase are obtained,
wherein the heating of the emulsion in step (a) is effected by first mixing part of liquid bituminous oil phase obtained in step (b) having a temperature of above 140° C. with the bituminous oil/water emulsion and subsequently raising the temperature of the resulting mixture to a temperature of above 140° C. by making use of indirect heat exchange means.
It has been found that by mixing the emulsion feed with part of the bituminous oil phase obtained in the phase separation of the emulsion the temperature can be sufficiently raised in order to lower the viscosity of the mixture entering the heat exchanger means. This results in that a lower pressure drop in the heat exchanger has to be overcome enabling a lower inlet pressure. Accordingly smaller and more simple pumps, smaller heat exchanger means and process equipment designed for lower pressure levels can be used with the process according the invention.
Applicants have also found that the temperature at which step (b) is performed is important for an efficient process. Applicants found that for this oil-water system the water phase has a higher density than the oil phase at temperatures of below about 130° C. Above about 130° C. the oil phase has a higher density than the water phase. By increasing the temperature starting from about 130° C. the difference in density increases and thus the ease at which the phases separate in a heavy oil phase and a lighter water phase increases. At 140° C. a sufficient difference is achieved to perform a phase separation. Preferably the temperature is not higher than 200° C. because at higher temperatures the solvability of the oil in water and water in oil becomes undesirably high. A more preferred range is between 160-200° C. in which the difference in density is sufficiently high to achieve a efficient phase separation and the solvability is of water in oil and oil in water is within an acceptable range. Most preferably the temperature is between 160-180° C. The weight ratio of oil phase and emulsion which are mixed to achieve the first raise in temperature is preferably between 1 to 2 and 1 to 5.
Suitable indirect heat exchanger means to be used in the process according to the invention can be for example those means disclosed in U.S. Pat. No. 5,441,548. An example of a preferred heat exchanger means is a shell-tube heat exchanger, wherein a hot medium, like for example steam or hot oil, at the shell side exchanges its heat with the mixture comprising the emulsion present at the tube side. The temperature rise in the heat exchanger means is preferably from between 120-150° C. to a value between 160-180° C.
For some applications of the bituminous oil obtained by the process according to the invention it is advantageous to lower the level of water soluble salts in said oil. Examples of such salts are magnesium, calcium, sodium, potassium, containing salts. Such salts may cause severe fouling in for example the process equipment of a partial oxidation process. In for example the process disclosed in U.S. Pat. No. 5,441,548 the content of such water soluble salts in the bituminous oil phase will be too high for these applications. Applicants have now found that by lowering the pH of the water phase obtained in step (b) to a level of below 7 a lower content of these salts remain in the oil phase. The pH is preferably between 4 and 6. Preferably the pressure during phase separation is sufficiently high to ensure that the water phase is obtained as a liquid in step (b). Suitable pressures are between 5 and 20 bars. Obtaining the water phase as a liquid further ensures that most salts will be removed wi
Jansen Arie
Stamps Paulus Antoon
Van Den Berg Franciscus Gondulfus Antonius
Shell Oil Company
Stewart Charles
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