CA2932517A1 - Method of and apparatus for upgrading diluted bitumen at the sagd central processing facility - Google Patents

Abstract

Diluent is separated from the Diluted Bitumen and most of it is recycled back to the Free Water Knock-out Drum. The separation of diluent from the bitumen is done by a unique and novel procedure using conventional equipment. Asphaltenes are then removed from the bitumen in a unique and novel solvent deasphalting unit designed specifically for the Steam Assisted Gravity Drainage (or SAGD) installations. The only value for the asphaltenes is their fuel value, and they require approximately 2.28 volumes of diluent per volume of asphaltenes to be transported by pipeline. Therefore, an independent power producer, or the SAGD operator could build a gasifier downstream of the solvent deasphalting unit, and recover the fuel value from the asphaltenes. The fuel value could be recovered as High Pressure Steam for the SAGD operation and/or converted into electric power to be put on the Alberta Power Grid. The flue gas from the gasification of the asphaltenes could be reinjected into the formation to provide a vapor cap above the steam to help in forcing the bitumen into the producing well.
This eliminates any greenhouse gas production from burning the asphaltenes by sequestering and storing the Flue Gas in the formation, and potentially from the entire SAGD operation. The Deasphalted Oil remaining after the asphaltenes have been removed from the bitumen is composed of catalytic cracker hytrotreater feedstock, and diesel hydrotreater feedstock, with just enough diluent added to pipeline the combined refinery feed streams to the end user. This takes Alberta Bitumen from one of the dirtiest oils produced to one of the cleanest oils produced, and removes it from the heavy diluted bitumen pool and places it in the refinery feed stream pool.

Description

Method of and apparatus for Upgrading Diluted Bitumen at the SAGD
Central Processing FacilitV
Description TECHNICAL FIELD
This invention relates to a method of and apparatus for recovering diluent from diluted bitumen, removing asphaltenes from the bitumen, gasifying the asphaltenes to recover their fuel value, sequestering and storing the flue gas from the asphaltene gasification back into the formation from where the bitumen came, and producing a deasphalted bitumen that could be used by most refineries without modification.
BACKGROUND OF THE INVENTION
Typical SAGD operations recover bitumen from the reservoir as a water-in-bitumen emulsion along with a substantial amount of free water. Chemicals and diluent are added to break the emulsion and lower the density and viscosity of the bitumen so that the diluted bitumen can be separated from the water. In cases where the diluent needed to separate the water is not enough to dilute the bitumen to pipeline specifications, additional diluent is added. As a result, the typical oil product is diluted bitumen that is worth about 85% of benchmark crude oil (West Texas Intermediate or WTI). For a typical Athabasca Bitumen in the colder months, about 70.2 m3 of diluent needs to be transported in order to transport 100 rn3 of Bitumen. This works out to 41.2 vol% Diluent and 58.8 vol% bitumen in the Diluted Bitumen.
Component m3 Volume %
Bitumen 100.0 58.8%
Diluent 70.2 41.2%
Total 170.2 100.0%
A typical Athabasca Bitumen contains about 17.0 wt% (15.0 vol%) n-05 asphaltenes and 84.1 vol% non-asphaltenes. In order to dilute these asphaltenes to pipeline specifications (350 cSt @ 7 C in winter), about 2.28 times as much diluent as asphaltenes needs to be blended. About 0.423 times as much diluent as non-asphaltenes are required to meet pipeline specifications (350 cSt @ 7 C in winter).
Component m3 Volume %
Asphaltene Stream 15.0 8.8%
Diluent for Asphaltenes 34.2 20.1%
Non-Asphaltenes 85.0 49.9%
Diluent for non-Asph. 36.0 21.1%
Total 170.2 100.0%

As can be seen from the previous table, the diluted bitumen being pipelined is 8.8 vol%
asphaltenes, 20.1 vol% diluent to pipeline the asphaltenes, 49.9 vol% non-asphaltene bitumen, and 21.1 vol% diluent to pipeline the non-asphaltene portion of the bitumen. In order to transport 100 m3 of bitumen 170.2 rn3 of Diluted Bitumen has to enter the pipeline or the railcar.
A typical solvent deasphalting unit will produce a deasphalted oil having about 2 (1-3) wt% asphaltenes, and the asphaltenes will have about 20 wt% non-asphaltene bitumen adhering to the asphaltenes. By using a solvent deasphalting unit to remove the asphaltenes, 100 rri3 of bitumen produced results in 120.2 m3 of diluted deasphalted bitumen being shipped. The 120.2 rn3 of diluted deasphalted bitumen is made up of 82.3 m3 of deasphalted bitumen and 37.9 rn3 of diluent.
Component m3 Volume '%
Deasphalted Bitumen 82.3 68.5%
Diluent 37.9 31.5%
Total 120.2 100.0%
From a pipeline perspective, for every 100 m' of bitumen produced, 120.2 m3 of diluted deasphalted bitumen needs to be pipelined or shipped.
To store, transport, and thus dispose of heavy residual oil, it is conventional to reduce its viscosity by mixing with lower viscosity diluent such as diesel fuel produced by the refinery. The resultant residual fuel oil is usually sold as fuel to electric utilities.
Disposing of residual oil by blending with valuable diesel fuel is not always cost effective; and in many refineries, solvent deasphalting processing of the residual oil is carried out to produce charge stock for catalytic cracking, or hydrocracking units, and thus to reduce the amount of less valuable by-products. Such processing involves mixing the residual oil with a light hydrocarbon solvent, such as propane, iso-butane, normal-butane, iso-pentane, normal-pentane, or mixtures of these hydrocarbons.
When a light hydrocarbon solvent is mixed with the residual oil under conditions of high pressure and temperature in an equilibrium vessel, the residual oil separates into two distinct fractions: a Deasphalted Bitumen (DABTm 1) oil fraction essentially free of asphaltenes, and an asphaltene stream fraction containing a small portion of deasphalted oil which is soluble in this fraction. By providing additional equilibrium vessels, intermediate products can be produced which are not as "clean" as the DABTMI
oil, but are "cleaner" than the bitumen.
1 DAB is a trademark of Brighton Engineering Solutions Limited Immediately after separation, all fractions contain an appreciable amount of solvent.
U.S. Pat. No. 2,940,920 discloses a solvent recovery system for a pentane solvent deasphalting unit wherein the output of the asphaltene separator contains about 0.6 volumes of solvent per volume of asphaltene. For a ratio of solvent to residual oil from the refinery of 4:1 to only 10:1 and a deasphalted oil yield of 40 to 80%
volume, the volume of solvent to deasphalted oil ratio ranges from a low of 4.85:1 to a high of 24.1:1.
Once the solvent has been removed from the fractions, the solvent is available for re-use in deasphalting additional produced bitumen, and the resultant substantially solvent-free product can be stored or further utilized. The deasphalted bitumen can be sent to a refinery for conversion to gasoline, jet fuel, diesel fuel, and heating oil. The asphaltene fraction only has fuel value whether it is shipped or used at the central processing facility.
A typical asphaltene stream has a fuel value of approximately 40.9 MJ/kg. This is nearly 70% higher than Alberta coal and roughly 76.4% of natural gas.
Alberta Coal produces almost twice as much CO2 as natural gas. The asphaltene stream produces 46% more CO2 than natural gas, but by gasifying the asphaltenes, the entire flue gas can be sequestered and stored in the place where the bitumen came from making the asphaltene gasification at a SAGD Facility producing no greenhouse gas. If the heat generated by gasifying the asphaltenes is used to generate the steam for the bitumen production, the bitumen can be recovered without greenhouse gas production, which would make the facility cleaner than a natural gas fired facility. If the heat from gasifying the asphaltenes was also used for removing the diluent and the asphaltenes from the diluted bitumen the entire site would be producing no greenhouse gasses.
Since the 1930s, solvent recovery systems for use with solvent deasphalting units were based on evaporative techniques such as that shown in FIG. 4.13 of Lubricating Base Oil and Wax Processing by A. Sequeira, published by Marcel Decker, New York, 1994.
In such units, hot residual oil from a refinery, for example, and propane that has been heated and pressurized, are fed to a treating tower from the bottom of which issues a liquid stream of asphaltene and solvent whose rate is controlled by the setting of a flow control valve, and from the top of which issues a liquid stream of DAO and solvent at almost the temperature and pressure of the tower. Each of these streams is conveyed to separate flash drums where the solvent flashes to a vapor that is cooled and sent to a solvent drum for storage, the pressure of the vaporized solvent from the high pressure DA0 flash drum being at a much higher pressure than that of the vaporized solvent from the low pressure flash drums and the solvent drum.

In order to reduce the amount of solvent that has to be evaporated, a supercritical solvent recovery process may be carried out on the lighter fraction from the asphaltene separator before the evaporative process described above is effected. U.S.
Pat. No.

2,115,003 discloses such a supercritical solvent recovery process. Solvent is recovered by bringing the solvent and deasphalted oil mixture to just below or just above the critical temperature and pressure in order to achieve a phase separation for solvents such as ethane, propane, butane, pentane and mixtures of these. The patent includes a schematic showing feed/effluent exchange from the deasphalted oil separator, and thus provides a basic, simplified process schematic for supercritical solvent recovery.
U.S. Pat. No. 2,527,404 discloses the supercritical solvent recovery of propane at 205° to 225° F. and a pressure of 580 to 650 psig. The critical properties of propane are 206.01° F. and 601.6 psig. This patent further discloses that the recovered propane will have only about 0.5% volume DAO, and the DAO will have only about 0.2 to 0.6 volumes of propane per volume of oil.
For solvents heavier than propane, U.S. Pat. No. 2,940,920 discloses that solvent ratios of 4:1 to as high as 20:1 are economically viable when the solvent is recovered by phasing out of solution when the density is decreased to less than 0.23. This patent further discloses that pentane is recovered at 420 degree F. and 525 psig, the critical properties of pentane being 386.6 degree F and 473.9 psig. From these observations, it would appear that the amount of solvent that has to be vaporized for recovery is substantially reduced by using supercritical solvent recovery as a preliminary solvent recovery step.
It is therefore an object of the present invention to provide a new and improved method of and means for upgrading produced bitumen at the SAGD site, gasifying the asphaltenes and sending the flue gas back down-hole so that there is very little or no flue gas produced from recovering the fuel value of the asphaltenes or the deasphalted bitumen.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with present invention, at an existing Steam Assisted Gravity Drainage (SAGD) Facility, the diluted bitumen has its diluent removed by two simple Flash Drums, with the bottom stream from the second flash drum being the feed to a solvent deasphalting unit. In the solvent deasphalting unit, the majority of the asphaltenes are removed from the diluent leaving a deasphalted bitumen. The asphaltene stream is sent to a gasifier operating at a sufficient pressure to allow the flue gas to exchange heat with water producing steam that is used for the bitumen production, to be mixed with the steam, and to be sent down the injection well.

BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention are described by way of the example with reference to the accompanying drawings wherein:
FIG. 1A is a block diagram of one embodiment of the present invention for economically removing the majority of the diluent from diluted bitumen so that the bitumen would be an acceptable feed for a solvent deasphalting unit;
FIG. 1B is a block diagram of one embodiment of the present invention for ensuring that no light hydrocarbons are left in the asphaltenes that will be burned in a gasifier, as light hydrocarbons are far too valuable to be burned as fuel.
FIG. 1C is a block diagram of one embodiment of the present invention for ensuring that C6+ light hydrocarbons that are left in the bitumen do not build to an unacceptable level in the solvent used in a solvent deasphalting unit;
FIG. 1D is a block diagram of one embodiment of the present invention for ensuring that 04- light hydrocarbons do not build to an unacceptable level in the solvent used in a solvent deasphalting unit;
FIG. 1D is a block diagram of one embodiment of the present invention for ensuring that light hydrocarbons are not left in the asphaltene stream, in a solvent deasphalting unit, that is destined to be burned as fuel;
FIG. 2A is a graph showing the quality of the separation that can be achieved using the two flash drum configuration shown in FIG. 1A.
DETAILED DESCRIPTION
Referring now to FIG. 1A, reference numeral 11 designates a typical Diluted Bitumen produced by a Steam Assisted Gravity Drainage (SAGD) facility for shipping by rail or pipeline to an existing refinery that has been modified to handle Diluted Bitumen. The steam for a SAGD Facility is usually generated by burning natural gas and exhausting the partially cooled flue gas into the atmosphere. In a typical refinery modified to handle the diluted bitumen, the diluted bitumen is fed to a crude distillation facility with a bottom stream temperature of 343 C-371 C. In the present invention, the intent is to use a portion of the steam that is to be sent downhole for the SAGD operation. Since this steam temperature is about 250 C, the Atmospheric Flash Drum, reference numeral 27, is designed to operate at 250 C where the effects of naphthenic acid corrosion are much less than at 343-371 C. Even so, the time spent at temperatures above 240 C
has been minimized.

The Diluted Bitumen stream, reference numeral 11, is heated by cooling, and condensing the overhead stream from Atmospheric Flash Drum, reference numeral 13, in the shell and tube heat exchanger identified as reference numeral 12. The cooled Atmospheric Flash Drum overhead stream, reference numeral 14, is depressurized and sent to the Diluent Tank or a Recovered Diluent Tank for reuse. The bottom stream, reference numeral 28, from the Atmospheric Flash Drum is not immediately cooled.
Instead, the Atmospheric Flash Drum bottom stream, reference numeral 28, is depressurized into a Partial Vacuum Flash Drum, reference numeral 35. The Partial Vacuum Flash Drum's overhead stream, reference numeral 36 is cooled and condensed in a glycol cooler, reference numeral 37, and collected in the overhead drum, reference numeral 41. The overhead drum floats on the Vapour Recovery (VRU) Unit's Compressor and with the pressure drop in the lines and in the glycol cooler, reference numeral 37, the Partial Vacuum Flash Drum, reference numeral 35, will definitely be running below atmospheric pressure.
The bottom stream, reference numeral 48, from the Partial Vacuum Flash Drum, reference numeral 35, is cooled by further heating the Diluted Bitumen, reference numeral 15, in the Bitumen/Diluted Bitumen Heat Exchanger, reference numeral 16.
Since the Bitumen will be the feed to a Solvent Deasphalting Unit there is no need to cool the Bitumen, reference numeral 18, below the outlet temperature of the Diluted Bitumen, reference numeral 19, and thereby avoid the use of multiple shells in series from this heat exchanger, reference numeral 16, however the capacity may require multiple shells in parallel. Only the Diluted Bitumen/Recovered Diluent heat exchanger, reference numeral 12, and the Heavy Recovered Diluent/Glycol heat exchanger, reference numeral 37 will likely have multiple shells in series. FIG. 2A is a plot of the simulated distillation results of processing Christina Lake Diluted Bitumen in the apparatus shown in Figure 1A. This separation would be an acceptable feed for a solvent deasphalting unit getting relatively pure n-pentane as its make-up solvent, like the ones in the Houston, Texas area of the United States. Even though some companies are importing their n-pentane solvent from Texas, it is more economical to recover the solvent from the diluted bitumen and the diluent that is readily available at a SAGD Facility.
Referring now to FIG. 1B, reference numeral 21 designates a typical asphaltene/solvent stream from an Asphaltene Separator. Since the Asphaltene Separator operating temperature is about the same as the Ring & Ball Softening Point (1.08 x 106 cSt) of the asphaltenes the asphaltene/solvent stream is heated to at least 42 C above the temperature of the Asphaltene Separator to ensure that sticky asphaltenes are not deposited on the trays below the feed tray of the Asphaltene Stripper. The mixture of supercritical solvent and hot liquid asphaltenes, reference numeral 25, is depressurized to about 370 kPa onto the third physical tray from the top of the stripper. A
mixture of steam and hot liquid asphaltenes (300 C or higher) enters the tower on the top tray.
Additional steam is injected into the tower below the bottom tray and above the liquid level. In most of the solvent deasphalting units, the asphaltenes are blended with light diluent and cooled downstream of the spill-back line, reference numeral 31, to the reboiler, reference numeral 32, but according to the present invention, the light diluent addition and the coolers are eliminated and the hot liquid asphaltene stream is delivered to the gasification unit at whatever pressure is required. In most other solvent deasphalting units, the Asphaltene Stripper Overhead line goes directly to a cooler/condenser.
According to the present invention, the Asphaltene Stripper Overhead stream, reference numeral 28 on FIG. 1B and reference numeral 32 on FIG.
1C, is sent to the feed line, reference numeral 31 on FIG. 1C, on the Deasphalted Bitumen/solvent line after depressurization.
Referring now to FIG. 1C, in a conventional Solvent Deasphalting Unit, the deasphalted oil/solvent mixture enters a conventional stripper on the top tray. According to the present invention, the material from the Asphaltene Separator overhead when using conventional solvent recovery, or the Supercritical Separator when using supercritical solvent recovery, is depressurized and sent to the 4th theoretical tray from the bottom.
Stripping steam enters below the bottom tray. Solvent losses in the asphaltene stream and the deasphalted bitumen stream were made up by adding diluent from the diluent tank, reference numeral 34, into the feed to the Refluxed Deasphalted Bitumen Stripper, reference numeral 38.
The Deasphalted Bitumen/Solvent mixture, reference numeral 31, is depressurized across the interface level control valve, in a supercritical solvent recovery unit, or a pressure control valve in the case of evaporative solvent recovery, and mixed with the Asphaltene Separator overhead stream, reference numeral 32, and the amount of diluent, reference numeral 33, that will need to be added to maintain the liquid level in the Solvent Drum. The mixture then enters the Refluxed Deasphalted Bitumen Stripper.
A portion of the overhead material, reference numeral 52, is refluxed back to the Stripper in order to keep the CB+ material in the solvent at less than or equal to 2.0 vol%. A portion of the bottom stream, reference numeral 61, is heated and returned to the tower in order to keep the solvent contained in the bottom stream at a rate of less than 100 barrels per day.
In FIG. 1C, the Overhead Reflux Drum, reference numeral 46, is shown as a vertical separator, it could also be a horizontal vessel with a water boot or an internal weir to separate the liquid water. In our preferred configuration, the water from the Overhead Reflux Drum, is pumped to the outlet of the Solvent Cooler, reference numeral 74 on FIG. 1D, in front of the Solvent Drum, this minimizes the power requirements for the water pump, reference numeral 55, and accumulates all of the outlet water from the process into the Solvent Drum for disposal.

Referring now to FIG. 1D, conventional Solvent Deasphalting Units usually get their solvent from one of their process streams, or purchase their solvent from a third party.
Therefore they have no need to have a debutanizer in their Solvent Deasphalting Unit.
The Solvent Deasphalting Units designed for use at a SAGD Facility will not have access to any internal streams suitable for solvent use and if it was purchased from a third party, the inexpensive way of removing the diluent using 2 flash drums would leave enough butane- in the bitumen that a debutanizer would still be needed.
In FIG. 1D, the solvent recovered from the Overhead Reflux Drum, reference numeral 46 in FIG. 1C, for the Refluxed Deasphalted Bitumen Stripper, reference numeral 38 in FIG. 1C, in reference line numeral 41 is preheated, reference numeral 42, by cooling the Deasphalted Bitumen, reference numeral 43 after giving up some of its heat to the Debutanizer's Reboiler, reference numeral 67.
After the Solvent from the Overhead Reflux Drum, reference numeral 41 has been preheated, reference numeral 47, the pressure is let down by the level control valve to get into the Debutanizer Tower, reference numeral 48, the liquid goes down in the tower and the vapor goes up and overhead. A portion of the bottom liquid, reference numeral 66, is split off and heated by the Deasphalted Bitumen from the Deasphalted Bitumen Pump, reference numeral 70, in the Debutanizer Reboiler, reference numeral 67, in order to make certain that the C4- in the solvent, reference numeral 73, is no more than 2 vol%. The remainder of the bottom stream is sent out through the Solvent Cooler, reference numeral 74, and cooled with glycol, reference numeral 76, so that the temperature, going to the solvent drum is 50 C.
The overhead, reference numeral 49, from the Debutanizer Tower, reference numeral 48, is cooled by glycol, reference numeral 52, in the Debutanizer Overhead Condenser, reference numeral 50, and the phases are collected and separated in the Debutanizer Overhead Reflux Drum, reference numeral 55. The vapor phase exits the top of the drum, reference numeral 56, and the pressure control valve lets the vapor out at 500KPa, more than enough to get into a fuel gas knock out drum or the fire box on a natural gas furnace. The hydrocarbon liquid phase, reference numeral 58, is pumped back to the top of the tower on level control, with no other hydrocarbon liquid outlet from the Debutanizer Overhead Reflux Drum, reference numeral 55. Since the Debutanizer Overhead Reflux Drum, reference numeral 55, is operating at 675 kPa, no pump is required for the water to get through a control valve and still be able to get into the Solvent Drum operating at 350 kPa and 50 C.
The Deasphalted Bitumen will have to be diluted with diluent to meet the pipeline viscosity specification and then cooled before it is put into tankage for shipment.

Claims (9)

Method of and apparatus for Upgrading Diluted Bitumen at the SAGD
Central Processing Facility Claims We claim:

1. A method for removing diluent from diluted bitumen at the SAGD Central Production Facility so that the diluent can be recovered and sent back to the Free Water Knock-Out Drum, said method comprising:
a) preheating the Diluted Bitumen, with the same HP Steam that is used in the SAGD production, or hot oil, and flashing at a pressure high enough for the flashed vapors to be condensed and collected as a liquid, and a flashed bitumen stream;
b) re-flashing the flashed bitumen at a pressure high enough for the non-condensable vapors to be recompressed by the Vapor Recovery Unit's compressor, and sent to a fuel gas pool, and the condensed liquid from the second flash can be pumped and mixed with the condensed liquid from the first flash so that all of the recovered diluent can be pumped back to the Free Water Knock-Out Drum and a bitumen stream that is a suitable feedstock for the solvent deasphalting unit described herein, even though it is still an unacceptable feedstock for most other solvent deasphalting units.

2. A method according to claim 1 wherein flashing the diluted bitumen at either pressure includes:
a) trays added to the flash drum, below the feed point, and using stripping steam, added below the trays, to change the flash drum to a steam stripper, or b) higher temperatures and a fractionation tower to remove diluent from the diluted bitumen at the SAGD facility.

3. A method according to claim 1 including:
a) feeding the bitumen recovered to a solvent deasphalting unit for removing the asphaltenes, collected as a hot liquid, from the bitumen, or b) feeding the bitumen recovered to a solvent deasphalting unit for removing the asphaltenes, collected as a solid, from the bitumen.

4. A method according to claim 1 where the facility is not located at the SAGD

Facility, but located where a diluted bitumen is available.

5. A method according to claim 3, wherein the solvent deasphalting unit's solvent is cleaned by removing the C4- hydrocarbon fraction as a vapor from the solvent, said method comprising:
a) feeding the mixture of Deasphalted Oil and solvent and the overhead stream from a conventional asphaltene stripper to a combination tower wherein the undesirable light ends are removed as an overhead vapor, the solvent is recovered as an intermediate liquid stream and the Deasphalted Oil is recovered as a bottoms liquid stream, or b) feeding the mixture of Deasphalted Oil and solvent to a conventional Deasphalted Oil Stripper and the asphaltenes and solvent to a conventional Asphaltene Stripper, and sending either or both of the overhead streams, from the strippers, to a Debutanizer that removes the undesirable 04- fraction as a vapor overhead stream and recovers the solvent as the bottom liquid stream, or c) feeding the mixture of asphaltenes and solvent to a conventional Asphaltene Stripper and sending the overhead from the Asphaltene Stripper, and the mixture of Deasphalted Oil and solvent to a Refluxed Deasphalted Oil Stripper to separate the heavier materials from the solvent and then sending the overhead liquid from the Refluxed Deasphalted Oil Stripper to a Debutanizer in order to remove the lighter materials from the solvent.

6. A method according to claim 5 wherein the initial solvent is created by feeding diluent to either:
a) The combination tower in part a or b) the Refluxed Deasphalted Oil Stripper in part c.

7. A method according to claim 5 wherein the make-up solvent is created by feeding diluent to either:
a) The combination tower in part a or b) the Refluxed Deasphalted Oil Stripper in part c.

8. A method according to claim 3, wherein a) the asphaltenes, either as a solid or as a hot liquid, from the SAGD
produced bitumen are gasified to recover their fuel value, as HP Steam and/or as electricity.

9. A method according to claim 8, wherein a) the flue gas from the asphaltene gasification is sent downhole into the reservoir for sequestration and storage, or b) the flue gas from the asphaltene gasification is cleaned up and used for other carbon dioxide reclamation.