Mineral oils: processes and products – Refining – Water removal
Reexamination Certificate
2000-06-27
2002-04-16
Preisch, Nadine (Department: 1764)
Mineral oils: processes and products
Refining
Water removal
Reexamination Certificate
active
06372123
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to an enhanced crude oil dehydration process and apparatus, and more particularly the present invention is directed to a crude oil dehydration process which can overcome the instability problems encountered with prior art for treating high water cut heavy oil streams, provide enhanced thermal energy input and recovery methods and remove suspended and dissolved compounds from inlet feed.
BACKGROUND OF THE INVENTION
Throughout many regions of the world, heavy oil, a hydrocarbon material having much higher viscosity or lower API gravity (less than 20° API, typically 7° to 12° API) than conventional petroleum crude, is being economically recovered for commercial sale. During the recovery process and prior to the transport to refineries for upgrading, the heavy oil receives preliminary treatment for water and solids removal to generally achieve basic sediment and water (BS & W) content less than 0.5% by volume and chloride content less than 30 ppm (wt). Water content of the treated heavy oil typically is required to be 0.3% by volume or less.
Conventional crude oil treatment methods were proven to be ineffective with respect to heavy oil until the advent of the technology set forth in U.S. Pat. Reissue No. 33,999, Clare et al., reissued Jul. 21, 1992 and Canadian Patent 1,302,937, Clare et al., reissued on Jun. 9, 1992. These patents describe a simple apparatus which can be located in remote oil producing areas for dehydrating heavy oil with low risk of foaming and unstable operating, while continuously achieving dry oil which exceeds requisite specifications. These dehydrators were found to be restricted to feed oil water content of less than 5% water cuts and susceptible to foaming and process instability during high water feed rates. Throughout the operation of several of these dehydrators known from practicing the technology in patents Re33,999 and U.S. Pat. No. 1,302,937, areas for improvement were discovered to overcome the limitations of feed oil water content and unstable operation caused by pretreatment upsets.
Further, additional problems have been experienced with the prior art in that although dehydrated heavy oil is achieved, high concentrations of suspended solids, such as clay and silica and dissolved compounds such as chlorides remain in the treated oil. These undesirable compounds continue to create many problems in pipeline transportation systems and refinery facilities to the extent that they depreciate the commercial valve of heavy oil.
Accordingly, one object of the present invention is to provide advances to overcome the limitations encountered by the previous art.
SUMMARY OF THE INVENTION
One object of the present invention is to provide for a dry crude oil recycle stream around the dehydrator to mix with the feed to reduce the ratio of residual water to oil contacting the oil surface of the dehydrator and thereby allow for higher raw crude oil water cuts, while maintaining a stable dehydration operation.
A further object of one embodiment of the present invention is to provide a method of removing water from crude oil containing water, comprising of steps of
a) providing a source of crude oil containing water;
b) providing a dehydrator for dehydrating the crude oil containing water, the dehydrator having an inlet and an outlet and a vaporizing surface of dry crude oil at temperatures sufficient to vaporize water contacting the surface;
c) exposing the source of crude oil to the dry crude;
d) vaporizing the water in the source; and
e) re-circulating at least a portion of dehydrated crude oil for contact with at least one of the dehydrator or the source of crude oil for maintaining a substantially uniform temperature at the vaporizing surface.
Conveniently, when at least a portion of the dry crude oil recycle stream around the dehydrator enters the dehydrator and is distributed below the surface of the hot crude oil in the dehydrator a consistent temperature is maintained at or above the vaporization temperature of water and at or below the surface of the oil and throughout the contained oil, thereby providing a means to mitigate the risk of process upsets and instability due to foaming.
A further object of the present invention is to provide a dry crude recycle stream around the dehydrator to mix with the feed stream, to allow an input of supplemental heat energy (external or waste heat energy) or recovery of heat energy from the dehydrator to result in an energetically efficient and balanced process.
A still further object of one embodiment of the present invention is to provide a method of removing water from crude oil containing water, comprising of steps of
a) providing a source of crude oil containing water;
b) providing a dehydrator for dehydrating the crude oil containing water, the dehydrator having an inlet and an outlet and a vaporizing surface of dry crude oil at a temperature sufficient to vaporize water contacting the surface;
c) contacting the source and the dry crude oil to flash water from the source to thereby remove the water from the source; and
d) selectively heating the surface of the dry crude to return heat energy lost from flash evaporating water from the source.
The dry crude oil surface may be selectively heated by reintroduction of dry crude oil, auxiliary heat addition, etc. The important aspect is that the heat used for vaporization is replaced so that a uniform or substantially uniform surface temperature is maintained. This is one important unit operation to maintain.
A further object of the present invention is to provide a means to remove suspended solids accumulated in the contained dry crude oil introduced with the source oil or produced during dehydration.
Suspended solids in the dry crude oil recycle stream, may be removed by a separator means on a continuous or batch basis to avoid buildup, plugging, and other complications.
A further object of the present invention is to water wash the raw crude oil source combined with the treatment in the dehydrator to remove the soluble dissolved solids or contaminants introduced the source crude oil and generate a low conductivity produced water and clean dry crude oil.
Until the advent of the present invention, prior art methods related to heavy oil dehydration had been limited by the stability of operation and risk of foaming, level of water cut or emulsion level in the heavy oil feed and the level of chloride, clay and silica compounds in the dry sales crude oil.
A still further object of one embodiment of the present invention is to provide a method of removing water from a crude oil containing water, comprising of steps of:
a) providing a source of crude oil containing water;
b) providing a dehydrator for dehydrating the crude oil containing water, the dehydrator having an inlet and an outlet and a vaporizing surface of dry crude oil at a temperature sufficient to vaporize water contacting the surface;
c) pre-washing the source of crude oil containing water to remove alkali metals and alkaline earth metals;
d) separating the alkali metals and the alkaline earth metals and oil in a preliminary separation step;
e) passing washed oil into the dehydrator to flash evaporate water from the washed oil to remove water therefrom;
f) selectively pre-heating crude oil to be treated in the dehydrator with treated dehydrated crude oil from the dehydrator to return heat energy lost from flash evaporating water; and
g) maintaining a uniform surface temperature.
Enhancements have been developed to eliminate the limits imposed by water cut of the source crude oil feed and to provide a very clean and dry heavy oil product relatively free of water, solids and chlorides.
The present invention relates to process enhancements to an apparatus used for dehydrating crude oil containing water, comprising a casing, means for admitting and distributing the liquid crude oil into the casing and onto the host surface of the dry crude oil, means for controlling the level of crude oil and a means to transfer heat energy sufficient to maintain the liquid
Kresnyak Steve
Shaw Fred
(Marks & Clerk)
Colt Engineering Corporation
Preisch Nadine
Sharpe Paul S.
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