Process for treating high paraffin diluted bitumen

Abstract

A paraffinic solvent recovery process for treating high paraffin diluted bitumen includes supplying the latter to flashing apparatus; separating into flashed paraffinic solvent and diluted bitumen underflow; and returning a portion of the underflow as returned diluted bitumen into the high paraffin diluted bitumen prior to introduction into the flashing apparatus, at temperature and amount to shift asphaltene precipitation equilibrium to reduce asphaltene precipitation. The process includes pre-heating the high paraffin diluted bitumen by transferring heat from hot dry bitumen, flashed paraffinic solvent and/or a portion of diluted bitumen underflow. Flashed paraffinic solvent may contain residual light end bitumen contaminants that increase asphaltenes solubility and the process may include removing contaminants to produce reusable paraffinic solvent at given solvent-to-bitumen ratio range to maintain given asphaltene precipitation. The process may also include a bitumen fractionation column producing hot dry bitumen underflow containing at most 0.5 wt % paraffinic solvent

Claims

1. A paraffinic solvent recovery process for treating a high paraffin diluted bitumen containing bitumen and residual water, fine solids and asphaltenes, the high paraffin diluted bitumen being derived from a paraffinic froth separation operation that separates a bitumen froth into a solvent diluted tailings component and the high paraffin diluted bitumen, comprising: supplying the high paraffin diluted bitumen to a paraffinic solvent flashing apparatus; separating the high paraffin diluted bitumen within the paraffinic solvent flashing apparatus into a flashed paraffinic solvent component and a diluted bitumen underflow component; returning a portion of the diluted bitumen underflow component as a returned diluted bitumen component into the high paraffin diluted bitumen prior to introduction into the paraffinic solvent flashing apparatus, at a temperature and in an amount sufficient to shift asphaltene precipitation equilibrium so as to reduce asphaltene precipitation in the paraffinic solvent flashing apparatus.

2. The paraffinic solvent recovery process of claim 1, wherein the paraffinic solvent flashing apparatus comprises: a first flash vessel for receiving the high paraffin diluted bitumen and producing a first flashed paraffinic solvent component and a first diluted bitumen underflow component; and a second flash vessel for receiving the first diluted bitumen underflow component and producing a second flashed paraffinic solvent component and a second diluted bitumen underflow component.

3. The paraffinic solvent recovery process of claim 2, wherein the returned diluted bitumen component comprises the first diluted bitumen underflow component.

4. The paraffinic solvent recovery process of claim 2, wherein the returned diluted bitumen component comprises the second diluted bitumen underflow component.

5. The paraffinic solvent recovery process of claim 2, wherein the returned diluted bitumen component is returned to feed the first flash vessel.

6. The paraffinic solvent recovery process of claim 2, wherein the returned diluted bitumen component is returned to feed the second flash vessel.

7. The paraffinic solvent recovery process of claim 1, wherein the paraffinic solvent flashing apparatus comprises inlet feed piping, outlet flash piping and outlet underflow piping.

8. The paraffinic solvent recovery process of claim 1, wherein the paraffinic solvent flashing apparatus comprises valves, pumps, monitoring devices, fittings or heat exchangers, or a combination thereof.

9. The paraffinic solvent recovery process of claim 1, comprising heating the returned diluted bitumen component prior to feeding the paraffinic solvent flashing apparatus.

10. The paraffinic solvent recovery process of claim 1, comprising imparting sufficient backpres sure on the high paraffin diluted bitumen prior to introduction into the paraffinic solvent flashing apparatus to maintain the high paraffin diluted bitumen in liquid phase.

11. The paraffinic solvent recovery process of claim 10, wherein the backpressure is imparted by a valve or flow restriction.

12. The paraffinic solvent recovery process of claim 10, wherein the backpressure is imparted by a valve arranged downstream of the returning of the returned diluted bitumen component into the high paraffin diluted bitumen.

13. The paraffinic solvent recovery process of claim 1, comprising pre-heating the high paraffin diluted bitumen prior to introduction into the paraffinic solvent flashing apparatus.

14. The paraffinic solvent recovery process of claim 13, wherein the pre-heating of the high paraffin diluted bitumen is at least partially performed by recovering heat from the flashed paraffinic solvent component.

15. The paraffinic solvent recovery process of claim 14, wherein the pre-heating is at least partially performed in at least one flashed paraffinic solvent heat exchanger and the process comprises providing a bypass line for bypassing the flashed paraffinic solvent heat exchanger.

16. The paraffinic solvent recovery process of claim 15, wherein the bypass line allows bypassing the high paraffin diluted bitumen around the flashed paraffinic solvent heat exchanger.

17. The paraffinic solvent recovery process of claim 13, comprising recovering a hot dry bitumen component from the diluted bitumen underflow component and wherein the pre-heating of the high paraffin diluted bitumen is at least partially performed by recovering heat from the hot dry bitumen component.

18. The paraffinic solvent recovery process of claim 17, wherein the pre-heating is at least partially performed in at least one hot dry bitumen heat exchanger and the process comprises providing a bypass line for bypassing the hot dry bitumen heat exchanger.

19. The paraffinic solvent recovery process of claim 18, wherein the bypass line allows bypassing the hot dry bitumen component around the hot dry bitumen heat exchanger.

20. The paraffinic solvent recovery process of claim 13, comprising a heat exchanger series to serially heat the high paraffin diluted bitumen, the heat exchanger series comprising: a downstream heat exchanger for transferring heat from a hot dry bitumen component to the high paraffin diluted bitumen, producing a partially cooled dry bitumen; a middle heat exchanger for transferring heat from the flashed paraffinic solvent component to the high paraffin diluted bitumen; and providing an upstream heat exchanger for transferring heat from the partially cooled dry bitumen to the high paraffin diluted bitumen.

21. The paraffinic solvent recovery process of claim 13, wherein the pre-heating of the high paraffin diluted bitumen is at least partially performed by passing the high paraffin diluted bitumen in a heat exchange line through an upper part of the paraffinic solvent flashing apparatus.

22. The paraffinic solvent recovery process of claim 1, wherein the paraffinic solvent comprises C.sub.4 to C.sub.6 paraffins.

23. The paraffinic solvent recovery process of claim 1, wherein the paraffinic solvent has a boiling point range between varying by at most about 25 C.

24. The paraffinic solvent recovery process of claim 1, wherein the paraffinic solvent comprises pentane.

25. The paraffinic solvent recovery process of claim 1, wherein the paraffinic solvent consists essentially of pentane.

26. The paraffinic solvent recovery process of claim 1, comprising temporary downtime operation comprising: flowrate reduction of the high paraffin diluted bitumen; flowrate augmentation of the returned diluted bitumen component sufficient to maintain circulation of fluids within the paraffinic solvent flashing apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block flow plan illustrating a froth treatment separation and diluent recovery according to an embodiment of the present invention.

(2) FIG. 2 is a block flow plan illustrating a diluent recovery operation according to an embodiment of the present invention.

(3) FIG. 3 is a block flow plan illustrating part of a diluent recovery operation according to another embodiment of the present invention.

(4) FIG. 4 is a block flow plan illustrating a dilute recovery operation according to a further alternate embodiment of the present invention.

(5) FIG. 5 is a block flow plan illustrating an example of an overall PFT operation comprising a froth separation unit, a tailings solvent recovery unit and a solvent recovery unit.

(6) FIG. 6 is a block flow plan illustrating an example of a froth separation unit of a PFT operation.

(7) FIGS. 7A and 7B are a block flow plan illustrating an example of a tailings solvent recovery unit of a PFT operation.

DETAILED DESCRIPTION

(8) Referring to FIGS. 1 and 2, the following is a parts list for elements illustrated therein:

(9) Equipment/Plant:

(10) 101 Froth Separation Plant

(11) 102 Solvent Recovery Plant

(12) 103 Hot Diluent Storage

(13) 104 Feed/Bitumen Product Heat Exchanger

(14) 105 Feed/Flash Heat Exchanger

(15) 106 Feed/Bitumen Product Heat Exchanger

(16) 107 Flash Vessel

(17) 108 Flash Vessel Recycle Pump

(18) 109 Flash Vessel Feed Heater

(19) 110 Flash Vessel #2

(20) 111 Bitumen Column Feed Pump

(21) 112 Bitumen Column Feed Heater

(22) 113 Bitumen Column

(23) 114 Bitumen Product Pump

(24) 115 Water Draw Off Pump

(25) 116 Column Condenser

(26) 117 Column Separator

(27) 118 Column Solvent Pump

(28) 119 Recovered Water Pump

(29) 120 Flash Solvent Drum

(30) 121 Flash Solvent Pump

(31) 122 Flash Solvent Condenser

(32) 123 Condensed Solvent Drum

(33) 124 Condensed Solvent Pump

(34) Lines and Valves:

(35) 201 Bitumen Froth

(36) 202 High Diluted Bitumen

(37) 203 Froth Separation Tailings

(38) 204 Hot Recycled Solvent

(39) 205 Dry Bitumen

(40) 206 Hot Dry Bitumen

(41) 207 Hot High Diluted Bitumen

(42) 208 Flashed Solvent Vapor

(43) 209 Flashed Solvent Condensate

(44) 210 Flash Solvent Drum Vapor

(45) 211 Flash Solvent Drum Condensate

(46) 212 Cooled Flash Vapor

(47) 213 Recovered Flash Solvent

(48) 214 Diluted Bitumen

(49) 215 Diluted Bitumen Recycle

(50) 216 Flash #2 Vapor

(51) 217 Flash #2 Diluted Bitumen

(52) 218 Bitumen Column Feed

(53) 219 Column Overhead Vapor

(54) 220 Cooled Overhead Vapor

(55) 221 Column Reflux

(56) 222 Column Stripping Steam! Gas

(57) 223 Recovered Column Solvent

(58) 224 Column Water

(59) 225 Recovered Water

(60) 226 Inert Purge Gas

(61) 227 Vent Gas

(62) 300 Feed backpressure valve

(63) 301a Feed/Bitumen Product Heat Exchanger bitumen bypass valve

(64) 301b Feed/Bitumen Product Heat Exchanger feed bypass valve

(65) 302a Feed/Flash Heat Exchanger feed bypass valve

(66) 302b Feed/Flash Heat Exchanger flash bypass valve

(67) 303a Feed/Bitumen Product Heat Exchanger bitumen bypass valve

(68) 303b Feed/Bitumen Product Heat Exchanger feed bypass valve

(69) 304 Hot Dry Bitumen recycle valve

(70) 306 Solvent Drum recycle valve

(71) Referring to FIG. 1, a paraffinic froth treatment plant 101 treats bitumen froth 201 with hot recycled solvent 204 to produce a high diluted bitumen 202 and rejects water, mineral and asphaltenes to froth separation tailings (not illustrated). The high diluted bitumen 202 stream is characterized by water content less than about 1500 wppm and asphaltenes on a dry bitumen basis up to about 14 wt %, optionally ranging from about 7 wt % to about 14 wt %, when treating bitumen froth by paraffinic solvent. For a specific solvent, asphaltenes in the bitumen product 205 are controlled by solvent to bitumen ratio (S/B ratio) and operating temperatures in the froth separation plant which vary the high diluted bitumen 202 feed into the diluent recovery plant 102 detailed on FIG. 2.

(72) Referring briefly to FIG. 5, the overall paraffinic froth treatment (PFT) operation preferably comprises various units including a froth separation unit (FSU), a tailings solvent recovery unit (TSRU) and a solvent recovery unit (SRU), which are interconnected and may be additionally integrated to share various product and by-product streams. FIG. 6 shows a more detailed plan of an FSU and FIG. 7 shows a more detailed plan of a TSRU, which may be used in connection with various embodiments of the SRU and solvent recovery process of the present invention, which will be further described herein below.

(73) Referring to FIG. 2, high diluted bitumen 202 is supplied from a bitumen froth separation apparatus (not shown) and is heated by exchangers 104,105,106 to recover heat from various product streams. In one optional aspect, the heat supplying streams comprise hot dry bitumen 206 which is supplied first to heat exchanger 106 and second to heat exchanger 104. In another optional aspect, the heat supplying streams comprise flashed solvent vapour 208 which is supplied to heat exchanger 105. In one aspect, the solvent vapour heat exchanger 105 is in between the two hot dry bitumen heat exchangers 104,106, and they are arranged serially as illustrated in FIG. 2. Not shown in figures is the feed pump in froth separation that pressures the high diluted bitumen stream 202.

(74) In addition, supplemental heat may be provided by other streams that are recycled from downstream units. In one aspect, the recycled stream may be fed into the high diluted bitumen 202,207 prior to feeding into the solvent recovery flash vessel 107. For instance, dilute recycled bitumen 215, which is a portion of the bottoms from the flash vessel 107, may be recycled from the flash vessel 107 and heated through a recycle heat exchanger 109.

(75) In one aspect, the hot high dilute bitumen 207 flashes sequentially in flash vessels 107 and 110. Valves or equivalent devices, schemes or means to produce backpressure, such as nozzle arrangements, limit two-phase flow upstream of the vessels as well as the pressure and vaporization in the vessels so as not to exceed the velocities for entrainment of feed to the overhead systems. In this regard, it is noted that for fluids that are susceptible to flashing when heated and contain abrasive particulate matter can cause significant damage in process lines and equipment. When such a fluid flashes in process equipment, the gas phase velocity can be so high so as cause the abrasive particulate matter to considerably and quickly damage the equipment, leading to equipment failure, vapour phase leakage of the fluid, permanent damage to equipment or significant shut-down times for process adjustments, repairs or replacement. In one preferred aspect, the incoming high diluted bitumen is kept in liquid phase along the heat exchangers 104,105,106 and corresponding lines. Providing backpressure using valves or other devices can ensure that the heat exchangers are protected from wear caused by flashing. A backpressure device such as a valve is provided to maintain a single phase through upstream heating systems and can be applied for various oil sands fluids containing abrasive particulate matter, such as clay, coke, minerals, and the like, which could cause wear such as erosion, abrasion and cavitation damage, upon flashing. Here it is noted that operations in which there are streams containing abrasive fine particulate matter, such as various froth treatment streams and fine coke particle containing streams, may also be transported and processed using placement of backpres sure valves or devices to maintain liquid phase through upstream equipment. In one preferred aspect of the present invention, backpres sure device such as valve 300 is used to provide backpressure upstream and allow flashing over the valve 300 in order to achieve greater predictably and control of the flashing-induced wear by limiting it to one point in the process. Although the flashing and wear may be more aggressive over the valve 300, it may act as a sacrificial component increasing predictability and monitoring to prevent a loss in containment, protection of more expensive equipment such as heat exchangers and overall safety of the process, are improved. Indeed, it is far easier to ensure fluid containment if the location for potential loss in containment is known and, preferably, well-understood and predictable to enable pre-determined time for valve replacement. In another preferred aspect, at least two valves such as valve 300 are provided in parallel to facilitate maintenance or replacement while minimizing or eliminating process downtime. If there are no devices or schemes to keep the liquid in single phase through the exchangers, then the vapour forms in the exchangers and high velocities result. This means that wear and loss in containment can occur between the exchangers (including within the exchangers) leading up to the flash vessel. This is logistically very hard to monitor in an actual plant environment and loss in containments and incidents are difficult to control and avoid.

(76) In another aspect, heating a higher bitumen content stream that has been stabilized by solvent removal provides the benefit that higher temperatures can be reached before fouling becomes an issue.

(77) In this regard, in another aspect, diluted bitumen 215 from the flash vessel 107 is heated by a recycle heater 109 and mixed back into the high diluted bitumen 202,207 stream. It should be understood that the recycled dilute bitumen may be derived from either one or both of the flash vessels 107,110 and may be recycled into either one or both of the flash vessel feed streams 202,207,214 at various points in the line. The illustrated embodiment shows diluted bitumen recycle and heating is performed for the first flash vessel 107. In one aspect, the bitumen in diluted bitumen 215 lowers asphaltene precipitation in the hot high diluted bitumen 207 and the risk of fouling downstream equipment. In one aspect, as illustrated in FIG. 2, the mixing point of the dilute bitumen recycle stream 215 into the high diluted bitumen is upstream the pressure let down to flash vessel 107 and downstream of the heat exchangers 104,105,106 and valves, thus into the hot high dilute bitumen 207. This recycle point has a number of advantages. First, heat input from the bitumen recycle stream 215 aids the flash across the valve 300. Second, the back pressure of the valve restricts flashing the bitumen recycle diluted bitumen in the recycle exchanger 109. Third, this configuration also facilitates process start-up. In another optional aspect, the mixing point of the dilute bitumen recycle stream 215 into the high diluted bitumen may be downstream from the pressure let down valve 300 to flash vessel 107 and still downstream of the heat exchangers 104,105,106, and thus into the hot high dilute bitumen 207. It should be noted that the mixing point of the dilute bitumen recycle stream 215 may be at other locations, such as before or in between upstream heaters 104,105,106, and in such cases appropriate trade-offs may be considered for heat exchange efficiency. There may also be a number of parallel recycle lines for recycling the dilute bitumen recycle stream as several parallel streams into any combination of addition points as mentioned above and the parallel recycle streams may be controlled or adjusted so that at least one of them is recycling dilute bitumen back into the feed stream.

(78) Referring still to FIG. 2, the flash columns 107,110 are sized and given specifications to reduce entrainment of bitumen droplets into overhead vapour systems. The partial condensation by flashed paraffinic solvent vapour 208 in the high diluted bitumen exchanger 105 facilitates returning flash condensate 211 that may contain high levels of bitumen to the bitumen column 113. The column reflux 221 minimizes bitumen in the solvent as column temperatures are preferably maintained below the initial boiling point for bitumen. This arrangement takes advantage of the gap in boiling points between the solvent and bitumen at the operating pressure for the bitumen column. S/B (solvent to bitumen) ratios are preferably controlled at the column tray level, which informs deciding which tray to enter at, to ensure contaminants do not pose a fouling risk.

(79) In another aspect, a water draw tray in the bitumen column 113 allows the column water pump 115 to transfer condensed water 224 from the column to a condensed solvent drum 117 for separation of hydrocarbon from column water. The recovered water 225 is recycled for reuse. Temperature and pressure conditions for economic column operation traps water between the overhead vapour and the dry bitumen outlets leading to unstable operation without a water draw tray.

(80) In another aspect, the heated column feed 218 flashes in the bitumen column 113. Steam or inert gas 222 is introduced below column feed 218 to strip residual solvent from dry bitumen product minimizing solvent losses in the dry bitumen product 205. The temperature and pressure operation of the column control the separation. If steam is used, its degree of super heat is controlled to ensure tray damage does not occur when encountering a hot diluted bitumen feed in the paraffinic process.

(81) In another aspect, the high diluted bitumen feed heaters 104,105,106 recover heat from the hot dry bitumen 206 and flashed vapour streams. Approach temperatures dictate economic limits to heat recovery by exchangers.

(82) In another aspect, the hot solvent 204 recovered from the PFT plant is returned directly to the froth separation vessels (not illustrated in FIG. 2). The condensing temperature for the condensed solvent drum 123 may be selected to match the temperature for solvent make up to froth separation without additional exchangers or limited number of exchangers for heating or cooling.

(83) In another aspect, the hot diluent storage 103 provides inventory management to fill or empty the froth separation vessels, the diluent recovery vessels and associated piping.

(84) Referring still to FIG. 2, the operation of embodiments and aspects of the present invention will be further described.

(85) The high diluted bitumen 202 from froth separation is heated to above the vapour pressure of the solvent at flash conditions, for example about 125 C. for some embodiments of the process, as hot high diluted bitumen 207 to feed the flash vessel 107. The preferred upper temperature limit of the hot high diluted bitumen 207 is the vapour pressure of the lighter components of the heavy oil to avoid overflashing lighter components of the bitumen. It is thus understood that the preferred temperature range is tied to the operating pressures. Here it is also noted that the preferred temperature range is determined, controlled or implemented depending on the solubility of asphaltenes contained in the fluids which may cause fouling. Here it is also noted that operations in which oil sands streams are processed to recover solvent or other components through flashing and the streams also contain fouling media, may also be managed or implemented such that the operating temperatures and pressures allow solubility of the given fouling media in the underflow stream.

(86) In one preferred aspect of the present invention, the heating of the high diluted bitumen may be done by recovering heat from hot bitumen product 206 by feed/bitumen product heat exchangers and from cooling flash vapour 208 by feed/flash vapour heat exchangers such as exchanger 105. The heat may be exchanged by heat exchanger devices, for example shell and tube heat exchangers, spiral type heat exchangers, plate and frame heat exchangers, or heat exchanger systems that are integrated or integral with the flash vessel, or a combination thereof. In one aspect, the heat exchange device comprises a plate and frame exchanger and the downstream backpres sure device ensures that no vapour phase is present in the heat exchanger, resulting in improved heating efficiency. The heat exchanger devices may be configured to recover heat from diluent recovery plant 102 product streams. As premature flashing of hot high diluted bitumen 207 can produce unstable flows in heat exchangers and fluctuating pressure on the feed pumps and add control complexity for turn-down, this may be regulated by a valve or flow restriction prior to the first flash vessel 107. In addition, each of the heat exchange devices, for example heat exchange devices 104,105,106, may be a series of multiple heat exchangers.

(87) Referring now to FIG. 3, there may also be bypass lines and corresponding valves in order to regulate the temperature of the hot diluted bitumen 207 and accommodate S/B ratio variations, by bypassing the heat exchangers. The preferred valve arrangements are illustrated as valves 301a, 302a and 303a, which bypass certain streams. More particularly, preferably valves 301a and 303a are provided to allow bypassing a part of the hot bitumen stream 206, instead of bypassing the high diluted bitumen feed. Nevertheless, the bypass may alternatively be achieved using valves 301b and 303b to bypass the high diluted bitumen feed. In terms of bypassing heat exchanger 105, the preferred configuration uses valve 302a to bypass a part of the high diluted bitumen feed, rather than bypassing the flash solvent vapour 208. The preferred valve arrangements 301a, 302a and 303a, allow bypassing the liquid fluid, whereas the bypass valves on the other side of the exchanger 301b, 302b and 303b are more likely to involve multiphase flow which is preferably avoided. It should nevertheless be noted that various combinations of valves 301a, 301b, 302a, 302b, 303a and 303b may be used to regulate bypassing and the temperature of the various streams as desired.

(88) High diluted bitumen 202 feed to the diluent recovery plant is preferably at equilibrium solubility between asphaltenes and the paraffinic solvent, reflecting the specific solvent to bitumen ratio and temperature in the froth separation. As high diluted bitumen is heated, the solubility equilibrium shifts causing asphaltenes to precipitate and foul equipment. By injecting the diluted bitumen recycle 215 from flash vessel 107 into high diluted bitumen, for instance pumped by flash vessel recycle pump 108 through flash vessel feed heater 109 and into the hot high diluted bitumen 207, stabilization of the hot high diluted bitumen 207 feed to the flash vessel 107 can be achieved. While steam or other heating media can provide heat for the flash vessel feed heater 109, as indicated in FIG. 2, other configurations such as recovering heat from hot bitumen 206 into the diluted bitumen recycle 215 may be used, with attention to efficiency trade-offs, to minimize diluent recovery plant 102 heat exchanger costs and utility requirements. In addition, dilute bitumen from the second flash vessel 110 or any other dilute bitumen stream may be recycled to stabilize diluted bitumen 202,207,214 prior to feeding into its corresponding flash vessel 107,110.

(89) It should be noted that FIG. 2 illustrates a two-stage flash system in which hot high diluted bitumen 207 in the first flash vessel 107 produces flash solvent vapour 208 and diluted bitumen 214, the latter of which is fed into the second flash vessel 110 that produces second flash vapour 216 and second diluted bitumen 217 stream. In one aspect, the pressures at which the flash vessels are preferably controlled permit (i) recovery of heat back into high diluted bitumen 202 feed by heat exchangers and (ii) maintaining consistent bitumen column feed 218 to the bitumen column 113 by directing the second flash vapour 216 into bitumen column 113 as a separate vapour stream.

(90) Conventional flash vessels employ gravity separation for disengagement of small droplets entrained in the vapour followed by mist eliminators as mesh pads in the top of the vessel and are specified design guidelines. However, in paraffinic froth treatment, asphaltenes in bitumen droplets precipitate at solvent concentrations in flash vessel vapour streams and to avoid premature outages due to fouling mist eliminators are preferably avoided. Without mist eliminators, the primary means to limit entrainment of bitumen droplets depends on vessel cross-sectional area to ensure vapour velocities permit droplets to settle by gravity. For a single stage flash vessel, the cross section area preferably reflects the full range of high diluted bitumen feed 202 variations to the diluent recovery plant 102, with the flash pressure limiting subsequent processing. With two or more flash stages, high diluted bitumen feed 202 variations can be distributed over the stages to optimize the cross-sectional area of each stage to minimize entrainment while minimizing adverse affects on downstream operations.

(91) It should be noted, however, that practicality can limit droplet sizes that can be achieved in a flash vessel by gravity separation alone. While precipitation of asphaltenes in paraffinic solvents from bitumen mists entrained in flash vapour can foul equipment, maltenes fraction of bitumen modifies asphaltenes solubility in the froth separation plant and adversely affects production of high diluted bitumen.

(92) In some aspects, there is an additional potential problem related to contaminants that may be entrained in the flashed solvent vapour. Lighter end components of the bitumen, such as aromatics and other hydrocarbon components, may flash or be entrained with the solvent vapour as contaminants. In some cases, such aromatic or higher molecular weight hydrocarbon act as contaminants in which asphaltenes are soluble or affect asphaltene solubility and can be carried with the fraction of solvent recovered and will build-up in an optimised closed solvent loop. In some cases, the contaminants are carried with the solvent vapour and accumulate in the overall system. For instance, since the solvent is recovered and reused in the froth separation unit, the contaminants may build up in the recovered and reused solvent which reduces the effectiveness of the solvent added to the bitumen froth and, accordingly, necessitates higher S/B ratios required for the froth separation unit (FSU). If the S/B ratio is not increased, the contaminants may act as a poison to the paraffinic process and prevent the required asphaltene separation in the FSU at the designed S/B ratio. However, compensating for contaminants by increasing the S/B ratio in the FSU may lead to a detrimental loop that prevents operating the system as intended or at optimum efficiencies. For example, upfront equipment design and sizing may have inherent limits on the maximum S/B ratio that may be used. These contaminants and their corresponding drawbacks may be dealt with in a number of ways. In one aspect, the contaminants may be fractionated in the flash drum with trays or packing and an amount of reflux. In another aspect, the contaminants may be fractionated in the flash vessel by adding a tray and an amount of reflux. In another aspect, at least a part of the flashed solvent vapour of one or both of the flash vessels is integrated into the bitumen column where the contaminants may be fractionated and removed from the recovered solvent. In another aspect, aromatic and hydrocarbon contaminants may tend to have a heavier molecular weight than the solvent and, as such, can be influenced to precipitate out preferentially with the condensate. In another aspect, the contaminants may be measured, determined, modelled or estimated in a given stream, such as the recovered solvent or another stream, to determine the means of contaminant removal. In some cases, solubility data or measurements may be collected for a given contaminant, e.g. aromatics or hydrocarbons such as cycloparaffins, in order to predict the increase in asphaltene solubility brought about by the presence of the given contaminant. The data may be collected based on existing solubility studies or be gathered in the lab for a given set of variables. For example, previously obtained data on asphaltene solubilities in various solvents and compounds exist, such as Mitchell & Speight's article The solubility of asphaltenes in hydrocarbon solvents Fuel, 1973, Vol. 52, and may be used to inform system design and control. It should be noted that various calculations may be made to determine the method by which the contaminants may be most efficiently removed for given operating conditions and design constraints. For instance, while the bitumen column may be used to clean and reduce contaminants in the recovered solvent, it may be desirable and more efficient to reduce the load on the bitumen column by adding one or more trays to other separation drums or providing increased reflux in the flash vessel to knock out additional light end bitumen contaminants. It is also noted that Mitchell & Speight's article presents data for relatively low temperatures. At higher temperatures, the solubility parameters for the listed compounds will likely change; however, high temperature systems will continue to benefit from contaminant management and removal. The specific effects of various contaminants at higher temperatures may be measured or identified by various techniques in order to tailor the removal and processing for high temperature conditions, such as between 70 C. and 90 C. It should also be noted that the solubility parameter (.delta.=.gamma V sup.1/3 where .gamma is the surface tension and V is the molar volume) which is discussed in the article, may be identified for individual contaminants and also for mixtures, as described in Mitchell & Speight, wherein for mixtures two different compounds were additive on a mole-fraction basis.

(93) In another aspect, to reduce contamination of recovered flash solvent 124such contamination coming from bitumen mist entrained from the flash vessel 107the flashed solvent 208 is cooled by the feed and flash heat exchanger 105 to produce flash vapour solvent condensate 209 that is then separated in the flash solvent drum 120 into flash solvent drum condensate 211 and flash solvent drum vapour 210. The flash solvent drum 120 provides a secondary flash vessel in which bitumen mist droplets can coalesce with liquid droplets that produce the flash drum condensate 211 which is transferred by flash solvent drum 121 for fractionation in the bitumen column 113. A portion of the flash condensate 211 may be recycled as a wash on trays in flash solvent drum 120 as illustrated in FIG. 3, or alternately sprayed into the flash vapour condensate 209 and/or the feed/flash heat exchanger 105. A solvent drum recycle valve 306 can regulate the recycling. This option may be used to compensate for aromatic and other hydrocarbon contaminants depending on components that build-up over the run-time of the plant, to maintain circulation sufficiently constant so as to minimize or reduce the deposit of asphaltenes in the system. The blending of different solvent compounds can change asphaltene solubility and, as such, the contamination components and concentrations affect the solubility levels. For example, depending on the specific contaminants contained in the system and the asphaltenes'solubility parameter therein, the above-described methods may be utilized, controlled or tailored to control asphaltene solubility for given stream compositions. Some contaminants may be present in amounts of 5000 to 10,000 ppm, depending on type of contaminant. Contaminants may be present in amounts of 5000 wppm toluene equivalent or 800 wppm toluene equivalent, wherein toluene equivalent is based on the case of toluene as sole contaminant. Particularly prevalent are aromatic compounds with higher molecular weight than the paraffinic solvent which may be captured by using embodiments of the invention described herein. Known data and techniques for determining asphaltene solubilities in various solvents, such as Mitchell & Speight's article The solubility of asphaltenes in hydrocarbon solvents Fuel, 1973, Vol. 52, may be used to inform system design and control.

(94) Referring to FIG. 4, in another aspect, the first flash apparatus may include a flash vessel section 107a and an integrated flash solvent drum 120a there-above, with a feed/flash heat exchanger 105A cooling the flashed vapours internal to the combined flash apparatus resulting in a reduced footprint, reduced capital costs, and potential safety increase in the case of 105A tube leakage. In this aspect, the first stage flash, mid exchanger and flash solvent drum are combined into a single vessel.

(95) In another aspect, preferably the flash solvent drum vapour 210 is condensed by flash solvent condenser 122 and the cooled flash vapour 212 is collected in the condensed solvent drum 123 for transfer as recovered flash solvent 213 by the condensed solvent pump 124 to the hot recycled solvent 202 system. The cooling media for the flash solvent condenser can be cooling water or air. For either cooling option, condensing at high pressure maximizes the temperature of the flash solvent condensate 211 to heat hot recycled solvent 202.

(96) In another aspect, the second flash vessel 110 is preferably operated at a pressure to maintain a consistent bitumen column feed 218, by flashing solvent vapour as second flash vapour 216 directly to the bitumen column 113 where fractionation minimizes entrained bitumen mist from contaminating recovered column solvent 118. The second flash diluted bitumen 217 from second flash vessel 110 may be heated by bitumen column heater 112 under pressure to prevent two phase flow in bitumen column feed 218 before introduction to the bitumen column 113. The heating media used in bitumen column heater 112 is steam or hot oil media in shell and tube or spiral heat exchangers, alternatively fuels such as natural gas in a fired heater.

(97) In one aspect, the bitumen column 113 fractionate bitumen column feed 218 to a hot dry bitumen 206 product with less than about 0.5 wt % solvent and a recovered column solvent 223 with less than about 5000 ppm bitumen, preferably less than about 800 ppm. The bitumen contained in the recovered solvent is of course the lighter end components and contaminants including light aromatics and other hydrocarbons. These values may of course change depending on the given contaminant and solvent being used. The column may also reduce the solvent loss below 1000 ppm to recover more of the solvent which is a valuable commodity, or the column may be operated for solvent loss to be able to meet particular pipeline specifications which may be a higher solvent content, possibly over 0.5 wt %. The pressure at which fractionation in the bitumen column 113 occurs is preferably selected for effective heat recovery from hot bitumen stream 206 for reintroduction into the high diluted bitumen 202, for effective utility of cooling media used by column condenser 116 for heating other processes, and for minimization of heating the hot recycled solvent 204 to the froth separation plant 101.

(98) In one aspect, the bitumen column 113 may have two distinct sections relative to the point at which bitumen column feed 218 enters the column: the lower section focuses on stripping solvent from the dry bitumen product 206 while the upper section focuses on fractionation of bitumen from the recovered column solvent 223. Column stripping steam/gas 222 may be injected below the bottom tray to strip residual solvent from bitumen. Steam stripping is a common industry practice with details provided in many texts such as Refining Processes Handbook, S Parkash, 4.sup.th edition published by Elsevier 2003, which provides guidance on a number of trays for stripping and the steam rates, which can be used and adapted for the purposes of the present invention.

(99) In one aspect, a portion of the recovered column solvent 223 is preferably returned to the top tray of the bitumen as column reflux 221. As the liquid passes through fractionation trays, entrained bitumen in flash solvent drum condensate 211, second flash vapour 215 and vapours from the stripping section of the bitumen column, residual bitumen is separated and transferred as the hot dry bitumen 206.

(100) The configuration of the upper fractionation trays preferably minimizes dead zones that promote asphaltene fouling and can adversely affect the separation.

(101) In another aspect, the column overhead vapour 219 is preferably cooled by column condenser 116 using water, where other process operations such as hot water extraction process can reuse the heat, or alternately air. Methodologies such as set out in Pinch analysis and process integration, a user guide on process integration for the efficient use of energy I. Kemp 2.sup.nd edition published by Elsevier 2007, may be applied to diluent recovery plants to improve and optimize energy use.

(102) In another aspect, the cooled overhead vapour 220 from the column condenser 116 preferably separates in a column separator 117 following design guidelines such a set out in Successfully Specify Three-Phase Separators W. Svrcek, et al Chemical Engineering Progress September 1994, into three streams: non-condensable vapours/gases, recovered column solvent 223 and column water 225. Non-condensable vapours and gases are vented as vent gas 227 with inert gas 226 maintaining pressure on the column separator 117 and the condensed solvent drum 123. Recovered column solvent 223 is transferred by the column solvent pump 118 back to the bitumen column 113 as column reflux 221 or blended with recovered flash solvent 213 as hot recycled diluent 202.

(103) In another aspect, residual water in high diluted bitumen 202 and steam introduces water into bitumen column 113. However, the temperature profile in the column between the column overhead vapour 219 and hot dry bitumen 206 is controlled or operated so as to permit water to condense within the column. To help prevent unstable operation, column water 224 may be withdrawn by a water draw tray in bitumen column 113 by water draw off pump 115 and transferred to a column separator 117 to permit separating of entrained solvent from the stream. The recovered water pump 119 transfers water separated in column separator 117 as column water 224 for reuse as process utility water for example.

(104) In another aspect, as shown in FIG. 1, the hot recycled paraffinic solvent 204 is returned directly to the froth treatment plant 101. Hot diluent storage 103 allows surge capacity for inventorying the froth treatment plant and solvent recovery plant on start-ups or de-inventory during outages. In addition, as shown in FIG. 3, valve 304 permits the recycle of dry bitumen 205 into high diluted bitumen 202 to facilitate warming up the plant during start-up or maintaining plant circulation in stand-by operational mode in event of limitations in feed supply.

(105) In one aspect, the operating temperatures and pressures are implemented or controlled to maximize integrated operation and heat recovery, including water integration and heat recovery if used to condense overhead vapour streams.

(106) In a further aspect, the condensed solvent drum 123 and associated condensed solvent pump 124 are helpful for independent operation of the flash section of the diluent recovery plant. These elements could with increased operational complexity be integrated into the column separator operation.

(107) Various embodiments of the present invention provide advantages, in particular with regard to the production of a dry bitumen stream, such as the following:

(108) Improving level of heat recovery from product streams into the feed to minimize requirements for external heat input and cooling.

(109) Reducing size of flash vessels while maintaining acceptable levels of entrainment into overhead systems.

(110) Recovering a high quality solvent to minimize asphaltene fouling in downstream piping and equipment or adversely affecting precipitation of asphaltenes in froth treatment.

(111) Recycling a hot solvent stream to minimize heat addition in the froth separation process.

(112) Recycling diluted bitumen streams to limit asphaltene fouling.

(113) Withdrawing water in the bitumen column for increased operation stability.

(114) Minimizing solvent losses to the dry bitumen product to minimize operating expense while permitting flexibility for specialty bitumen markets.

(115) Improving heating and solvent recovery control for narrow boiling point liquids.

(116) Improving turndown and control for heating and for solvent recovery.

(117) Some embodiments of the process and system according to the present invention may be summarized as including at least one of the following enhancements:

(118) The high diluted bitumen is heated under pressure prior to two or more flash stages with each flash vessel sized to minimize overhead entrainment of liquids with or without demisting devices to increase efficiency and minimize the overall cost of the plant, preferably both capital and operating costs. Smaller vessels also increase opportunities for offsite modular fabrication.

(119) Flashed diluted bitumen is heated and recycled into high diluted bitumen streams to shift the asphaltene precipitation equilibrium away from asphaltene precipitating and fouling equipment. The recycle also minimizes a retention time which also assists reducing asphaltene depositions.

(120) Flashed vapour is partially condensed and the flashed solvent condensate is cleaned by fractionation in the bitumen column. The bitumen column overhead vapours are cleaned by the column reflux to minimize entrained bitumen in the recovered column solvent.

(121) The solvent may be partially removed in a flash drum prior to entering a column to reduce column size and vapour traffic. The flash drums may contain trays or packing with reflux to improve the quality of the solvent recovered.

(122) A water draw is incorporated in the bitumen column to permit removing water that may condense in column leading to unstable operation. Water that may contain solvent from the column may be separated in the overhead condensed solvent drum to minimize capital expense.

(123) The diluent recovery plant is closely coupled and integrated to the froth treatment plant. This permits maximizing heat recovery from the diluent product streams into the high diluent feed stream. Hot solvent storage allows for routine plant inventory changes from start-up to full operation without additional heat exchangers for heating/cooling streams.

(124) The production of dry bitumen product by stripping residual solvent minimizes the solvent make up requirements for process losses and associated operating costs. The dry bitumen also advantageously allows potential for segregation of upstream operations from downstream marketing. Varying froth treatment operating conditions using a specific solvent can target bitumen product for specific markets, such as high or low asphaltene refineries or upgraders.

(125) Furthermore, the solvent recovery plant may consist of a single dedicated plant or multiple plants in parallel processing high diluted bitumen from one or more froth treatment plants. The embodiments described and illustrated herein reflect a single train of equipment; however, at large scales multiple parallel trains of exchangers are optional and may be preferred. For instance, there may be advantages to arranging parallel trains including flash vessels to facilitate operational flexibility and partial unit outages. Exchangers and pumps in the diluent recovery plant may also consist of multiple units in parallel to provide operational flexibility and reliability. To facilitate plant start-up or shut-down or holding standby modes, pumps can re-circulate fluids back to feed systems such as returning dry bitumen back to the high diluted bitumen feed in FIG. 1.

(126) In addition, the inclusion of recycling product and by-product streams either within the unit or to upstream and downstream operations may facilitate unit start-up and standby operating modes frequently encountered in oil sand operations due range of oil sands being mined and processed (e.g. oil sands ore containing about 6 wt % to about 13 wt % bitumen) and equipment reliability in such an abrasive operating environment.

(127) Heat recovery from paraffinic diluent product streams back into the feed stream to a diluent recovery plant may be particularly advantageous. In addition, the relative volume of high diluted bitumen and temperature requirements of paraffinic froth treatment lead to advantages in integrating froth treatment and diluent recovery operations to increase efficiencies and reduce costs.

(128) It is noted that while the overall solvent recovery process described and illustrated herein is not suitable for naphthenic solvent recovery applications, there are a number of techniques and methodologies described herein that would be applicable and beneficial to a naphthenic solvent recovery process or other types of solvent recovery processes that could be employed in the oil sands industry. It is also noted that the paraffinic solvent recovery unit 102 as described herein and illustrated in detail in FIG. 2, is preferably part of an overall PFT operation as illustrated in FIG. 5 and is integrated with a FSU such as in FIG. 6 and a TSRU such as in FIG. 7. Fluid and heat integration between the FSU, SRU and TSRU as well as within each one of these units, may include mixing of similar streams together, recycling streams to increase or decrease certain concentrations or ratios (e.g. S/B ratio) of certain streams, directly or indirectly heat or cool certain streams to improve performance and efficiency of the overall PFT operation.