Crude oil emulsion treating apparatus and method

The treating apparatus and method of the present invention improve the efficiency and reliability of flash treating crude oil by including a recycled oil pumping loop that takes crude oil from a flashing section of a vessel and feeds it to either the inlet of a treater section or through a heater into a connecting pipe between the treater section and the flashing section, thereby eliminating the need of a fired heater in the flashing section.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to apparatus for treating crude oil, and 
in particular to an improved apparatus and method to improve the 
efficiency and reliability of flash treatment of crude oil. 
2. Description of Related Art 
U.S. Pat. No. 4,995,495 to Krynski ("'495") discloses a Crude Oil Emulsion 
Treating Apparatus having a pressure vessel with two sections. The first 
section is a conventional heavy oil treater which utilizes heat addition, 
mechanical coalescence, and electrostatic coalescence to gravity separate 
most of the water and solids from the oil. The second section is an 
integral low pressure flash compartment where the remaining water is 
evaporated and separated from the crude oil. The flash section also 
contains an internal heater for vaporizing the water remaining in the oil. 
The first section or treating section of the '495 patent is typically 
operated at about 60 to 70 psig and 280.degree. to 300.degree. F. The 
exact operating conditions are a function of the crude oil properties, but 
higher temperatures are generally required to reduce the viscosity of 
heavy oil and higher pressures are required to stay above the saturation 
pressure of steam at the operating temperature. This prevents foaming in 
the vessel. 
The second or flash section of the '495 patent is typically operated at 
atmospheric pressure, or up to about 1 to 2 psig, to overcome back 
pressure in the vapor discharge system. The hot crude oil which may 
contain small quantities of water, discharges from the treating section 
and is throttled from 60 or 70 psig down to 1 psig across a control valve. 
As the pressure is reduced, the heat of the crude oil/water mixture is 
normally sufficient to vaporize all of the water. The flashing takes place 
immediately down stream of the control valve. The fluid entering the 
second section is oil with water vapor. The fired heater in the flash 
section is not required to vaporize water. 
U.S. Pat. No. 1,580,956 to Cameron of Apr. 13, 1926 ("956") teaches the use 
of recycling a portion of hot dry oil from the bottom of a flash section, 
re-heating the recycle stream with an external heater, and mixing it with 
the incoming wet oil. This is recognized as an effective method of 
maintaining the temperature of the flash section above the boiling point 
of water. Another effect of this recycle system not recognized by the '956 
patent, however, is the reduction in water concentration of the inlet 
mixture. If larger quantities of hot oil are used, this allows for more 
water vaporization as the mixture flashes across control valve, such as 
used in the '495 patent discussed above. However, no such device or method 
is known to exist, and was not previously considered. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to provide an 
improved oil treating apparatus. It is a particular object of the present 
invention to reduce the capital and operating costs of a crude oil 
emulsion treating apparatus by eliminating a fired heater in a flashing 
section of the apparatus. It is a still more particular object of the 
present invention to increase the water vaporizing capacity of a crude oil 
emulsion treating apparatus by incorporating a heated recycle loop from a 
dry oil outlet of a flashing section back to an inlet of the apparatus. It 
is a further object of the present invention to increase the operating 
reliability of a crude oil emulsion treating apparatus during upset 
conditions and to allow the apparatus to be more flexible and more 
forgiving to operate. It is still another particular object of the present 
invention to enhance the capability of a crude oil emulsion treating 
apparatus to handle foam at an inlet of a flashing section by adding a 
recycled light hydrocarbon liquid inlet at the top of the flashing 
section. And, it is yet a still further object of the present invention to 
provide an improved method of treating crude oil in an apparatus having 
two separate sections, a treating section and a flashing section. 
In accordance with one aspect of the present invention, there is provided 
an improved oil treating apparatus having a casing means divided into a 
first treating section and a second flashing section connected together by 
a pipe having valve means therein. The second flashing section is also 
connected to an inlet pipe to the first treating section so as to recycle 
treated oil with entering crude oil at the inlet pipe to the first 
treating section. The second flashing section may alternatively be 
connected through a separate external heater to the pipe having valve 
means therein so as to recycle hot treated oil with crude oil exiting the 
first treating section, before it enters the flashing section. 
The present invention also comprises an improved method of treating crude 
oil whereby a portion of oil from the second flashing section may be fed 
to either the inlet to the first treating section or the pipe connecting 
the first and second sections to improve efficiency and eliminate the need 
for a heater in the flashing section. Furthermore, a portion of the light 
hydrocarbon liquids recovered from vapor removed from the second flashing 
section may be recycled back into the second flashing section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following description is provided to enable any person skilled in the 
art to make and use the invention and sets forth the best modes 
contemplated by the inventor of carrying out his invention. Various 
modifications, however, will remain readily apparent to those skilled in 
the art, since the generic principles of the present invention have been 
defined herein specifically to provide for an improved crude oil treating 
apparatus and method. 
Turning to FIG.1 of the drawings, the basic apparatus of the present 
invention remains unchanged except that a fire tube utilized in the 
flashing section is deleted in the present invention. The disclosure of 
U.S. Pat. No. 4,995,495 is hereby incorporated in its entirety by this 
reference thereto. 
Referring now to FIG. 2, the system of the present invention consists of a 
casing means or vessel 1 having an inlet treating section or treater 7 
that receives a raw crude oil fluid from an inlet 101 through a line 102. 
The fluid entering the treating section is a mixture of oil, water, gas, 
and solids. The treating section 7 operates at pressures from 25 psig up 
to 100 psig or more and at temperatures of 120.degree. F. up to 
310.degree. F. The treating section 7 has one or more fired U tube heaters 
17 that can heat the inlet crude oil up to these operating temperatures. 
Inside the treating section 7 the majority of the water, gas, and solids 
are removed by gravity. The separated gas is discharged from the vessel 
via outlet 32, outlet line 106, and control valve 105. The separated water 
is discharged from the vessel via outlet 52, outlet line 131, cooler 132, 
control valve 133 and line 134. Solids that settle to the bottom of the 
vessel are removed by a sand jetting and desand system. Jetting water 
enters the vessel at multiple inlets (not shown) and sand slurry is 
removed from the vessel at multiple outlets (not shown). 
The partially dehydrated crude oil leaving the treating section 7 may 
contain small amounts of water (0.5% to 4%) that is separated in the flash 
or flashing section 9. The crude exits the treating section 7 via outlet 
58, passes through control valve 107, and then via line 108 and through 
inlet 59 to the flash section 9. The flash section 9 operates at near 
atmospheric pressure. A portion of the sensible heat of the hot 
crude/water mixture is converted to latent heat of vaporization that turns 
the water into vapor as the mixture de-pressurizes across the control 
valve 107. The crude/water mixture cools as the energy is absorbed by the 
vaporizing water. The amount of temperature reduction depends on the 
amount of water evaporated. The operating temperature of the flash section 
9 is lower than the treating section 7 but is still above the boiling 
point of water. 
During this flashing process a certain amount of low boiling point 
hydrocarbons are also flashed with the water. These low boiling point 
hydrocarbons are components of the crude oil and are also vaporized by the 
pressure reduction and the sensible energy of the mixture. 
The fluid entering the flash section 9 at inlet 59 is crude oil, water 
vapor, and light hydrocarbon vapor. 
The flash section 9 is a separator where a water vapor and hydrocarbon 
vapor mixture exits from the top through an outlet 76. The vapors travel 
through a line 109 to a condenser 110 where the vapors cool. Condensed 
water, hydrocarbon, and some non-condensable gases enter a separator 
vessel 111 where the fluids separate by gravity. Non-condensable gases 
exit from the top of the separator 111 via a line 112 while the water is 
pumped from the bottom through a line 117 by a pump 118 and discharged to 
tankage via a line 119. The light hydrocarbon liquid is withdrawn from the 
separator 111 from the zone just above the water zone through a line 113 
which leads to a pump 114. A portion of the light hydrocarbon liquid can 
be routed from pump 114 via a line 115 to a line 120 and through control 
valve 116 back to the flash section 9 where it enters by an inlet 81. The 
remainder of the light hydrocarbon liquid discharge through the line 115 
to storage. 
The light hydrocarbon that recycles back to the flash section 9 flows 
through an internal pipe with nozzles that direct the liquid downward 
counter current to the vapor flow from inlet 59. The light hydrocarbon 
mixes with the crude oil and aids in breaking down the foam inside the 
flash section 9. This assists the separation of vapor from the crude oil. 
Dry, hot crude oil is pumped from the bottom of the flash section 9 through 
an outlet 80 via a line 121. A pump 122 transfers most of the crude 
through a line 123, a cooler 125, and a line 126 to tankage. A portion of 
the hot crude oil pumped by pump 122 is recycled via a line 127. The 
recycled hot oil flows to two different places. Some of the recycled oil 
flows back into the flash section via a line 130, through a valve 129, and 
via line 128 where it enters the bottom of the vessel by an inlet 82. This 
recycled stream of oil flows through an internal pipe 85 and discharges 
through nozzles directed towards the bottom of the flash section. This 
maintains circulation in the flash section bottom to keep solids in 
suspension and prevent them from plugging the oil outlet 80. 
The second recycled stream of hot oil flows through line 127 to a valve 
135, and then through line 136 back to the inlet line 102 which flows to 
the treating section 7 inlet. The recycled, dry crude oil from the flash 
section mixes with the raw inlet crude oil. Within the treating section 7 
the recycled oil is heated by the fired U tube 17 along with the incoming 
raw crude. The recycled oil makes it way through the treating section 7, 
through the pressure reducing control valve 107, and into the flash 
section 9 again. In this way the heating means in the treating section 7 
provides all of the heat required for the flash section 9 to operate. By 
adding the mass of dry recycled oil, additional heat can be transferred to 
the oil/water mixture by the fire tube in the treating section and that 
which flashes across the control valve 107. This increases the capacity of 
the unit to vaporize additional water, which is especially important when 
short term upset conditions occur in the front treating section 7. 
Another benefit of bringing the recycled oil back to the treating section 7 
inlet is that it reduces the water concentration of the feed stream into 
the treating section. This reduces the harmful effects of sudden increases 
in water volumes entering the unit. The unit becomes less susceptible to 
upsets and more reliable in separating the water from the crude oil. 
By feeding some of the recycled oil to the bottom of the flash section 9, 
through inlet 82, oil in the flash section 9 will be kept warm during no 
inlet flow conditions. If the unit is shut down for short periods of time 
the treating section heater can be used to maintain the crude oil at 
operating temperatures by recycling a small volume of the dry crude from 
the bottom of the flash section 9 back to the treating section 7 as 
described above. 
Turning now to FIG. 3, there shown is a further embodiment of the present 
invention including all of the apparatus and connections as shown in FIG. 
2, except that line 136 is not connected to inlet line 102 for feeding the 
recycled oil into the treating section. This embodiment instead has a 
heated recycle loop with an external heater 137. That is, the recycled oil 
passes through valve 135 to heater 137, the hot dry oil from heater 137 
then travels via line 138 to line 108, where it is connected upstream of 
the control valve 107 so that the heated oil is mixed with the oil/water 
mixture exiting treating section 7. Any suitable heating 30 means or 
method, such as a heat exchanger or fired heater, of a type well known to 
those skilled in the art may be used. 
Those skilled in the art will appreciate the above described preferred 
embodiments are subject to numerous modifications and adaptations without 
departing from the scope and spirit of the invention. Therefore, it is to 
be understood that, within the scope of the appended claims, the invention 
may be practiced other than as specifically described herein.