WO2016004502A1

WO2016004502A1 - Apparatus and method for recovering residual solvent from diluted bitumen

Info

Publication number: WO2016004502A1
Application number: PCT/CA2014/050650
Authority: WO
Inventors: Saba Moetamed-Shariati; William Nicholas Garner
Original assignee: Total E&P Canada Ltd
Current assignee: TotalEnergies E&P Canada Ltd
Priority date: 2014-07-09
Filing date: 2014-07-09
Publication date: 2016-01-14
Anticipated expiration: 2017-01-09

Abstract

A system is described for treating diluted bitumen product underflow from known solvent recovery units in the oil sands processing, the system comprising vertically spaced trays capable of providing isolated countercurrent flow of liquid bitumen for recovery as bitumen product and residual solvent vapors evaporated therefrom. Each tray comprises a pool portion for receiving the diluted bitumen in shallow liquid pools having a surface area for enhanced evaporation of the solvent therein, and a transport portion for directing the liquid along a flow path for mixing the liquid and bringing more solvent to the surface, while minimizing re- contact between the solvent vapors and the liquid bitumen.

Description

"APPARATUS AND METHOD FOR RECOVERING RESIDUAL SOLVENT

FROM DILUTED BITUMEN" FIELD

Embodiments disclosed herein relate to processes and apparatus for removing small amounts of a low boiling component from a high boiling point hydrocarbon, and more particularly to the recovery of residual solvent vapors from liquid bitumen or heavy oil product streams produced from oil sands operations. BACKGROUND

Bitumen is produced from oil sand such as is found in the Fort McMurray region of Alberta, Canada. The oil sand is mined and recovered using hot water processes to produce bitumen-rich froth. The bitumen froth is diluted with a hydrocarbon diluent, such as a naphthenic or paraffinic solvent, to reduce the viscosity and density of the bitumen, and to aid in separating the diluted bitumen from water and solids contained in the froth. As a result, such separation procedures result in an underflow component (containing water, fine solids etc.) and a diluted bitumen-rich overflow stream that also contains solvent, water and residual impurities. The overflow undergoes subsequent separation procedures in various vessels, known as solvent recovery units (SRUs), to recover and recycle the solvent, to an earlier stage of the process, and to produce a bitumen product ready for upgrading or pipelining. Supplementary processing of the diluted bitumen underflow from known SRUs is desirable to recover residual solvents (e.g. 2000 ppm solvent remaining), thereby maximizing recovery of expensive and hard-to- source solvent, and further purifying the bitumen before delivery to a refining facility.

Diffusion of solvent within liquid bitumen is slow and does not contribute to evaporation, particularly because the vapor release is significantly inhibited by upward transport, if any, through the pool of liquid bitumen. As such, only solvent at or near the surface of the liquid bitumen evaporates. Wiped film evaporators or agitated thin film evaporators can be used for difficult evaporation processes, but such evaporators require mechanical rotors and other moving parts. Large horizontal separator vessels designed to provide a shallow pool of liquid can be used to increase the interface area making it easier for solvent vapors in the liquid bitumen to escape into the vapor space. Such known horizontal "bitumen stabilizers" vessels configured to receive the diluted bitumen bottoms product from SRUs must be long and have a considerable diameter to achieve the desired results, requiring significantly more plan area and at increased capital costs compared to vertical vessels. Vertical vessels, however, are not configured to provide large shallow pools of liquid.

There is interest in providing improved processes and apparatus for maximizing recovery of residual solvent from diluted bitumen product produced in conventional SRUs. Such processes and apparatus may have the capacity to provide a large surface area and passive "mixing" of the liquid bitumen (limiting the need for moving parts), increasing the escape of solvent vapors near the surface, while minimizing re-contact and re-absorption of the vapors. It is desired that such a system enable the use of smaller vessels (vertical or horizontal) to reduce capital and energy costs and to provide recycle of hard-to-source solvents at remote oils sands processing locations. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a cross-sectional schematic representation of a vessel according to an embodiment taught herein;

Figure 2 is a perspective view of one tray according to an embodiment taught herein;

Figure 3A is a cross-sectional schematic representation of vertically spaced trays according to a first example embodiment taught herein (showing upper and lower baffles of the trays arranged and angled downward and radially outwardly);

Figure 3B is a cross-sectional schematic representation of vertically spaced trays according to a second example embodiment taught herein (showing upper and lower baffles of the trays arranged and angled downward and radially inwardly);

Figure 4 is top down view of one tray according to an embodiment taught herein;

Figure 5 is a perspective schematic representation of a lower baffle according to one embodiment taught herein, lower baffle having liquid mixing elements or protrusions; and

Figure 6 is a perspective schematic representation of an upper baffle according to one embodiment taught herein, upper baffle comprising drain holes. SUMMARY

Paraffinic solvent is used in bitumen froth treatment operations, but economics and difficulty in accumulating sufficient amounts of the hard-to-source diluent necessitate the recovery and recycling of such solvents for stockpiling and reuse. Remote processing locations often require that solvent be piped or delivered by tanker truck to the processing locations, causing possible time delays, and cost and scheduling uncertainties. Recovery of solvent from solvent-containing bitumen predominantly occurs in solvent recovery units (SRUs), and currently results in the production of a market-ready bitumen product that is largely free of solvent, but can still contain trace amounts (e.g. as much as ~ 2000ppm).

Using embodiments herein, processes and apparatus are provided for the subsequent processing of the bitumen product and recovery of solvent from the bottoms of conventional SRUs. More specifically, a system and process for enhancing the evaporation of solvent vapors within a liquid bitumen feedstream is provided, the system and process being capable of receiving the feedstream and recovering residual solvent therefrom by passing the feedstream over a plurality of liquid surface area enhancing elements and liquid routing elements:

- the liquid surface enhancing areas for receiving the feedstream and forming shallow pools collectively having a large surface area, and

- the liquid routing elements for transporting liquid overflowing the pools and flowing downwardly through the vessel along a path for passively mixing (e.g. accomplishing a change in direction and velocity of a portion of the liquid without moving elements) the liquid and bringing solvent vapors to the surface, while preventing re-contact of the evaporated solvent vapors and the liquid bitumen. Preventing the escaped vapors from re-contacting the liquid in the present system is contradistinctive to conventional distillation columns, which aim to maximize contact of the vapor with the liquid.

In one embodiment, the present system comprises a vessel, having upper and lower ends and a sidewall, two or more trays spaced vertically along the vessel between the upper and lower ends, each tray having a pool portion and a transport portion, the pool portion receiving the feedstream and forming a pool of liquid having a surface area for evaporation of residual solvent therefrom to form an ascending vapor, the transport portion conducting overflow of the liquid from the pool portion of a first tray for descending the transport portion thereof and separated from the ascending vapor for delivery to the pool portion of a successive tray. The present system may be designed such that the two or more trays provide separate flow passageways for countercurrent flow of ascending vapors and descending liquid. The ascending vapors may be recovered from the upper end as solvent product and the liquid may be recovered from the lower end as bitumen product.

In another embodiment, the present system comprises a vessel, having upper and lower ends and a sidewall, at least one feed inlet for introducing the liquid feedstream to the vessel, at least one tray having upper and lower baffles, the upper baffle adapted to form a pool portion for collecting the liquid feedstream in liquid pools having a surface area for evaporation of residual solvent therefrom to form an ascending vapor, the upper and lower baffles being co-angled and aligned in spatial arrangement to provide a transport portion for directing the liquid feedstream overflowing the pool portion downwardly along a first flow passageway and for directing the ascending vapor upwardly along a separate second flow passageway, and at least two distinct outlets for recovering the ascending vapors and the liquid feedstream. The present system may further comprise that first and second passageways provide countercurrent flow between the ascending vapors and the liquid descending the vessel, while minimizing re-contact.

In another embodiment, the present system may comprise upper baffles being annular conical catch trays forming peripheral pool portions between the upper baffles and the sidewall, and encircling the centrally located first and second passageways. The upper and lower baffles may be spatially arranged to drain the liquid feedstream radially outwardly and to direct the ascending solvent vapors radially inwardly.

In another embodiment, the present system may comprise upper baffles being centrally located conical catch trays forming pool portions surrounded by the peripheral first and second passageways forming distinct annular openings thereabout. The upper and lower baffles may be spatially arranged to drain the liquid feedstream radially inwardly and to direct the ascending solvent vapors radially outwardly.

Recognizing the difficult nature of bitumen, the present vessel 10, trays 20, dispersion unit and any other elements may be coated with a fluoropolymer, being non-reactive and useful to prevent the buildup of bitumen thereon. Periodically, diesel can be introduced to clean the present system. In another embodiment, the system comprises a process for recovering residual solvent vapors from a liquid bitumen feedstream in a vertical vessel comprising a) introducing the feedstream to a plurality of liquid surface area enhancing elements and liquid routing elements, the liquid surface area enhancing elements for receiving and pooling the feedstream in shallow pools of liquid having a surface area for evaporation of solvent forming ascending solvent vapors, b) continuously mixing the liquid by overflowing a portion of the liquid feedstream pools along the liquid routing elements bringing further vapors to the surface forming a purified descending liquid, c) directing ascending solvent vapors from the descending liquid while minimizing re-contact, and d) recovering the ascending solvent vapors as solvent product and the descending liquid as liquid bitumen product. DESCRIPTION OF THE EMBODIMENTS

As identified above, solvent diluted bitumen product produced from conventional froth treatment stages of oil sands operations is processed through a solvent recovery unit (SRU) for recovery of a majority of the solvent and producing a bitumen product stream. A system is provided herein for stripping residual solvent from the bitumen product stream and further purification of the bitumen.

A vessel for receiving the bitumen product stream is provided, the vessel incorporating a plurality of trays having surface area enhancement internals with flow routing arrangements to minimize re-engagement of released solvent and incoming bitumen. In the first aspect, solvent evaporation is enhanced by increasing the surface area within the vessel, enabling more vapors near the surface to escape. The vertical depth of pools of standing bitumen is minimized, the number of pools maximized and the pools stacked vertically for permitting a vessel having a smaller footprint and lower capital cost. Further, the bitumen in the pools is repeatedly disturbed for mixing the bitumen transferred from one tray to another bringing fresh bitumen to the surface for release of solvent therefrom. In the second aspect, in contradistinction with distillation and fractionation objectives, solvent mass transfer from vapor to liquid phase is minimized. Each tray routes the liquid and vapor flows to avoid contact. Herein, in an embodiment, each pool overflows a tray element for flow to a successive pool while minimizing contact with released vapors. Solvent rising upwardly is isolated from the bitumen feedstream flowing downwardly.

Herein, unless the context sets forth otherwise, when discussing the spacing and arrangement of the vessel and its internals described below, such as "above" or "below", the spacing and arrangement is theoretical so as to establish the evaporation and isolation of a rising vapor phase from a downwardly flowing liquid phase. Reference terms "upper", "top", "lower", and "bottom" are used for the purpose of describing the present system only. Such terms are relative and are not intended, in any way, to narrow or limit the scope of the present system.

With reference to Fig. 1 , one embodiment of the present system comprises a vertical vessel 10 having an upper and lower end and a sidewalk It is understood that such vessel 10 may be configured horizontally. Where upstanding, the cylindrical vessel 10 forms a substantially circular cross section. Vessel 10 receives a liquid bitumen feedstream 2 via at least one inlet 4 located at or near the upper end of vessel 10. Solvent vapors 6 ascending the vessel 10 (up arrows) can be recovered, via at least one first outlet 12 located adjacent the upper end, as solvent product 14. As would be understood by a person skilled in the art, first outlet 12 may be positioned anywhere along the vessel 10 as would be warranted to control vapor volumes and minimize re-contact with liquid 8. For example, outlet 12 may be positioned intermediate the vessel, or more than one outlet 12 may be provided. Example solvents may comprise propane, butane, pentane or hexane, or derivatives thereof, which can be used as recycle to earlier froth treatment processes. Liquid bitumen 8 descending through the vessel 10 (down arrows) can be recovered, via at least one second outlet 16 located near the lower end, as bitumen product 18.

Vessel 10 is fit with at least two annular trays 20 spaced along the vessel 10 between the upper and lower ends. Each tray 20a, 20b (20c,20d... not shown) has liquid surface area enhancing elements and liquid routing elements. More specifically, each tray 20a, 20b comprises a pool portion 22 for forming a shallow liquid pool for promoting solvent evaporation and a liquid transport portion 24 from an upper tray 20a to a successive lower tray 20b, 20c, ... .20n. The pool portion 22 supports a pool of the liquid bitumen 8 having an enhanced pool surface area for release of solvent vapor 6 therefrom to a headspace 26 above the pool portion 22. According to embodiments herein, the incoming bitumen feedstream 2 forms a shallow pool of liquid bitumen 8 in the pool portion 22 of a first upper tray 20a, then overflows the transport portion 24 of that tray 20a for transport to the pool portion 22 of a second successive tray 20b therebelow. The pool portion 22 is dynamic, receiving fresh bitumen from either the incoming feedstream 2, in the case of first tray 20a, or from the transport portion 24 of a previous tray in the case of successive tray 20b. At a bottom tray 20n, liquid 8 falls to the sump at the lower end of the vessel 10 for recovery at outlet 14.

Trays 20 are generally like-sized and are aligned with the vessel 10 so as to optimize phase separation results. The addition of successive trays can substantially enhance the liquid surface area of the pooled liquid 8 (e.g. by an order of magnitude). A skilled person understands that the placement and number of trays 20 spaced within the vessel 10 can be determined based on liquid throughput, residence time in each pool portion, relative concentrations of residual solvent, temperatures and pressures. Vessel 10 pressure and temperatures may be determined according to achieve the desired evaporation of the solvent vapors 6. It is contemplated that vessel 10 may operate as a vacuum vessel.

Each tray 20 is configured to provide separate flow passageways for countercurrent flow of ascending vapors 6 and descending liquid 8, thereby minimizing contact between the separated phases. Simply, ascending vapor 6 is guided to upward to first outlet 12 without contact with descending liquid 8. Descending liquid 8 overflows trays 20 along transport portion 24 to the pool portion 22 of successive trays 20.

With reference to Fig. 2, pool portions 22 and liquid transport portions 24 form upper and lower baffles 23, 25, respectively. Upper and lower baffles 23,25 are co-angled from horizontal and do not extend fully across the cross-section of the vessel 10 so as to form separate flow passageways for pool-to-transport portion 22,24 capture and a vapor passageway 30 to headspace 26 and outlet 12. Upper baffle 23 is angled for creating a feedstream-containing volume for forming the pool portion 22. The upper baffle 23 is spaced vertically from the lower baffle 25 for forming the transport portion 24 therebetween.

Upper baffle 23 forms a weir 28 for level control of the pool portion 22, continuously overflowing and discharging liquid 8 to the transport portion 24 as the fresh bitumen feedstream 2 enters the pool portion 22. The lower baffle 25 is angled for providing impetus to move liquid 8 to a successive tray 20b,20c while avoiding the ascending vapors 6. As shown, while separated, the vapors 6 and liquids 8 are flowing counter-current to one another.

As shown in Fig. 3A, in one embodiment, upper and lower baffles 23,25 are arranged and angled downward and radially outwardly so as to drain liquid 8 (down arrows) radially outwardly while venting escaping solvent vapors 6 (up arrows) radially inwardly to centrally located vapor openings 30. Upper baffle 23 can be sealed to the periphery of the vessel 10 for forming annular pool portion 22. The pool portion 22 is formed in the volume remaining after the frustum of a right circular cone, apex upwardly and inscribed within a right circular cylinder, is removed. The upper baffles 23 may be conical catch trays forming annular pool portions 22 containing the liquid 8 between the vessel sidewall and the weir 28 at the truncated apex.

In a converse arrangement, as shown in Fig. 3B, in another embodiment, upper and lower baffles 23,25 are arranged and angled downward and radially inwardly so as to drain liquid 8 radially inwardly (down arrows) while venting escaping solvent vapors 6 upward and radially outwardly (up arrows) to peripheral vapor passageway 30. Upper baffle 23 is a right circular cone, apex downwardly and residing generally along an axis of the right circular cylinder of the vessel 10, forming a conical pool portion 22 and annular passageways 24,30 thereabout towards the periphery of the vessel 10. The upper baffles 23 may be conical catch trays forming a central pool portion 22 for containing the liquid 8 wholly within the upper baffle 23 and the weir 28 formed about the periphery of the upward edge thereof.

Residual solvent to bitumen ratios can be targeted and designed at the tray 20 level and can be used to determine the size, shape and quantity of the upper and lower baffles 23,25 within the vessel 10. Countercurrent flow of liquid and gas phases within the vessel may be capable of creating vacuum vapor zone (Fig. 4).

Enroute through the transport portion 24, the liquid 8 is inherently or directly mixed for exposing residual solvent heretofore trapped in the bitumen feedstream 2. In embodiments contemplated herein, upper and lower baffles 23,25 may be further configured to mix or agitate liquid 8 as it enters the transport portion 24 and flows along the upper surface of lower baffle 25. For example, having regard to Fig. 5, the upper surface of lower baffle 24 may be adapted to provide liquid mixing elements 50. In embodiments contemplated herein, such elements may comprise annular protrusions, ridges, teeth or angled vanes capable of further mixing liquid 8 as it descends the transport portion 24. The lower surface of the lower baffle 25 separates the vapor 6 ascending therebelow from pool portion 22 of the lower tray 20b from the liquid 8 flowing in the transport portion 24 on the upper surface there above. In further embodiments herein, inlet 4 and/or vessel 10 may be configured with dispersion means (not shown) for creating and scattering droplets of feedstream 2 into the vessel 10, each droplet increasing the surface area of the liquid and enabling further solvent to escape. Such feedstream dispersion means may be any unit known to a skilled person for creating liquid droplets of sufficient size to increase the surface area of the liquid, without forming a mist of droplets so small as to be inadvertently recovered from outlet 12. For example, dispersion means may be, without limitation, a flat spray plate or a spray nozzle(s).

The upper and lower baffles 23,25 may be releasably or permanently connected to one another. Upper and lower baffles 23,25 may each alone or together be releasably or permanently affixed to vessel 10 or other structure within the vessel 10. Having regard to Fig. 6, upper baffle 23 may comprise drain holes 52, or other such elements, at the base of the pool portion 22 for enabling draining thereof during maintenance. The drain holes 52 sized to drain at a rate less than the rate of the feedstream 2 so the pool portion accumulates liquid 8 for overflow at the weir 28.

The present system further comprises a process for recovering residual solvent vapors 6 from the solvent-diluted liquid bitumen feedstream 2, the process comprising: i) introducing the feedstream 2 to a plurality of liquid surface area enhancing elements and liquid routing elements, the liquid surface area enhancing elements for receiving and pooling the feedstream in a pool of liquid having a surface area for evaporation of solvent vapors, ii) providing sufficient liquid to overflow the pool and to conduct the liquid along the liquid routing elements for continuously mixing the liquid, bringing further solvent to the surface of the liquid descending the vessel, while minimizing re-contact between the vapor and liquid, for recover of the solvent vapors from the vessel as solvent product and the recovery of liquid from the vessel as bitumen product. In embodiments contemplated herein, the present process comprising providing a plurality of trays designed to provide the liquid surface area enhancing elements comprise and liquid routing elements.

Example embodiments are described in the following Examples, which are set forth to aid in the understanding of the present vessel 10, and should not be construed to limit in any way the scope as defined in the claims which follow thereafter. EXAMPLE 1

The present Example describes vessels as contemplated herein, such vessels having a length or height of 23 meters and an internal diameter of 8 meters. Where the vessel is horizontal, the maximum liquid surface area may be 23x8 = 184 m² Where the vessel is vertical, the maximum liquid surface area may be (8/2)²Xpi= 50.26 m², the trays forming a liquid transport portion 24 of approximately 0.5 m and a vapor opening 30 of approximately 1 meter in diameter. As such, the effective surface area per tray 20 may be approximately A= (8/2)²Xpi - (1.5/2)²Xpi = 48.5 m² More specifically, a 23 meter vertical vessel having 16 trays, with a tray-to-tray distance of 1 meter therebetween, and a combined bottom (pool) end and headspace of 7 meters, may have a total liquid surface area of 16 x 48.5 + 50.26 (pool) = 826 m² A similar vessel have 22 trays with a tray-to-tray distance of 0.7 meters and a combined bottom pool and headspace of 23 - 22x0.7 = 7.6 m, may provide a total liquid surface area of 22 x 48.5 + 50.26 (pool) = 1 1 17 m².

Although a few embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope as claimed herein. The terms and expressions used have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope is defined and limited only by the claims that follow.

Claims

THE EMBODIMENTS FOR WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS: 1 . A system for recovering solvent from a liquid bitumen feedstream containing bitumen and residual solvent comprising:

a vessel, having upper and lower ends and a sidewall,

two or more trays spaced along the vessel between the upper and lower ends,

each tray having a pool portion and a transport portion, the pool portion receiving the feedstream and forming a pool of liquid having a surface area for evaporation of residual solvent therefrom to form an ascending vapor,

the transport portion conducting overflow of the liquid from the pool portion of a first tray for descending the transport portion thereof and separated from the ascending vapor for delivery to the pool portion of a successive tray.

2. The system of claim 1 wherein the two or more trays provide separate flow passageways for countercurrent flow of ascending vapors and descending liquid.

3. The system of claim 1 or 2 wherein the ascending vapors are recovered from the upper end as solvent product and the liquid is recovered from the lower end as bitumen product.

4. The system of claim 1 , 2 or 3, wherein the vessel may be vertical or horizontal.

5. A system for recovering solvent from a solvent-diluted liquid bitumen feedstream containing at least bitumen and solvent comprising:

a vessel, having upper and lower ends and a sidewall,

at least one feed inlet for introducing the liquid feedstream to the vessel,

at least one tray having upper and lower baffles, the upper baffle forming a pool portion for collecting the liquid feedstream in pools having a surface area for evaporation of residual solvent as an ascending vapor, and

the upper and lower baffles being co-angled and aligned in spatial arrangement to provide a transport portion for directing the liquid feedstream overflowing the pool portion downwardly along a first flow passageway and for directing the ascending vapor upwardly along a separate second flow passageway, and

at least two distinct outlets for recovering the ascending vapors and the liquid feedstream.

6. The system of claim 5 wherein the first and second passageways provide countercurrent flow between the solvent vapors and the liquid feedstream while minimizing re-contact.

7. The system of claim 6 wherein the upper baffles comprise conical catch trays forming peripheral pool portions between the upper baffles and the sidewall and encircling the first and second passageways.

8. The system of claim 7 wherein the upper and lower baffles are spatially arranged to drain the liquid feedstream radially outwardly and to direct the ascending solvent vapors radially inwardly.

9. The system of claim 5 wherein the upper baffles comprise central conical catch trays having the second passageway form an annular opening thereabout at the sidewall.

10. The system of claim 9 wherein the upper and lower baffles are spatially arranged to drain the liquid feedstream radially inwardly and to direct the ascending solvent vapors radially outwardly.

1 1 . The system of any one of claims 5 to 10, wherein the vessel is vertical or horizontal.

12. The system of claim 5 wherein the lower baffles further comprise liquid mixing elements.

13. The system of claim 12 wherein the liquid mixing elements may be annular protrusions, ridges, teeth or angled vanes.

14. The system of any one of claims 5 to 13, wherein the vessel further comprises a feedstream dispersion unit.

15. The system of any one of claims 5 to 14 wherein upper and lower baffles are releasably or permanently affixed to the vessel.

16. The system of any one of claims 5 to 14 wherein the upper and lower baffles are releasably or permanently affixed to one another.

17. The system of any one of claims 5 to 16, wherein the system is coated with a fluoropolymer.

18. A process for recovering residual solvent vapors from a liquid bitumen feedstream in a vertical vessel comprising:

introducing the feedstream to a plurality of liquid surface area enhancing elements and liquid routing elements, the liquid surface area enhancing elements for receiving and pooling the feedstream in pools of liquid having a surface for evaporation of solvent forming ascending solvent vapors, continuously mixing the liquid by overflowing a portion of the liquid feedstream along the liquid routing elements bringing further vapors to the surface forming a purified descending liquid,

directing ascending solvent vapors from the descending liquid while minimizing re-contact, and

recovering the ascending solvent vapors as solvent product and the descending liquid as liquid bitumen product.