Method for recovering solvent from froth treatment tailings with in-situ steam generation
09719023 ยท 2017-08-01
Assignee
Inventors
Cpc classification
International classification
Abstract
A method for recovering hydrocarbon diluent from froth treatment tailings comprising bitumen, solids, hydrocarbon diluent and water is provided, comprising: introducing the froth treatment tailings into a vessel chamber and allowing the coarse solids to settle to the bottom of the vessel and form a solids layer having a portion of hydrocarbon diluent and a portion of water trapped therein; and heating the water in the solids layer to generate steam bubbles in-situ and strip the hydrocarbon diluent associated with the coarse solids to produce stripped tailings.
Claims
1. A method for recovering hydrocarbon diluent from froth treatment tailings comprising bitumen, coarse solids, fine solids, hydrocarbon diluent and water, comprising: introducing the froth treatment tailings into a vessel having an upper section, a middle section and a lower section; allowing the coarse solids to settle to the lower section of the vessel to form a solids layer having a portion of hydrocarbon diluent and a portion of water trapped therein; and heating the lower section of the vessel using an indirect heat source such that the water trapped in the solids layer generates steam bubbles in-situ to strip the hydrocarbon diluent associated with the coarse solids and produce stripped tailings and hydrocarbon diluent/water vapors.
2. The method as claimed in claim 1, further comprising: allowing a portion of the fine solids and bitumen to remain suspended in the middle section of the vessel and a portion of the fine solids and bitumen to rise to the top section of the vessel to form a froth layer.
3. The method as claimed in claim 2, wherein the steam bubbles further strip the hydrocarbon diluent associated with the fine solids.
4. The method of claim 1, wherein the upper section of the vessel is operated at a temperature at or near 100 C.
5. The method of claim 1, wherein the upper section of the vessel is operated at or near atmospheric pressure.
6. The method as claimed in claim 1, wherein the hydrocarbon diluent/water vapors rise through the vessel and are removed through an outlet in the upper section of the vessel.
7. The method as claimed in claim 6, wherein the removed hydrocarbon diluent/water vapors are condensed and the condensed vapors are separated in a separator to form a hydrocarbon diluent stream and a water stream.
8. The method as claimed in claim 1, wherein heating occurs below the level of 20% of the total tailings height in the vessel.
9. The method as claimed in claim 1, wherein the indirect heat source comprises a network of steam pipes situated in the lower section of the vessel.
10. The method of claim 1, wherein the indirect heat source comprises electric coils situated in the lower section of the vessel.
11. The method of claim 1, wherein the indirect heat source comprises an external heating device.
12. The method as claimed in claim 1, wherein the froth treatment tailings are pre-heated to a temperature of about 80 C. to about 110 C. prior to being introduced into the vessel.
13. The method of claim 12, wherein the froth treatment tailings are pre-heated through heat exchanging with the stripped tailings from the vessel lower section.
14. The method of claim 1, wherein the froth treatment tailings are introduced into the vessel via an inlet situated in the middle section of the vessel.
15. The method as claimed in claim 1, wherein the stripped tailings are removed from the lower section of the vessel for disposal.
16. The method of claim 1, wherein the steam bubbles further carry bitumen and fines to form a froth layer in the upper section of the vessel.
17. The method of claim 16, wherein the froth layer is removed for disposal.
18. The method as claimed in claim 16, further comprising removing the froth layer from the vessel and treating the removed froth layer to remove bitumen and residual hydrocarbon diluent therefrom.
19. The method of claim 18, wherein the treated froth layer is removed for disposal.
20. The method of claim 16, further comprising removing the froth layer from the vessel and reprocessing it in a froth treatment plant.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings:
(2)
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(3) The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practised without these specific details.
(4) As used herein, froth treatment tailings means tailings which are produced during a bitumen froth treatment process that uses a hydrocarbon diluent such as a naphthenic diluent or a paraffinic diluent to dilute the bitumen froth prior to/during treatment. Generally, froth treatment tailings comprise water, solids, hydrocarbon diluent, and bitumen.
(5) As used herein, bitumen froth refers to primary and/or secondary froths produced during extraction of bitumen from oil sand as recognized by the industry.
(6) As used herein, hydrocarbon diluent means any substance containing one or more hydrocarbon compounds and/or substituted hydrocarbon compounds which is suitable for diluting and/or dissolving bitumen present in bitumen froth.
(7) As used herein, a naphthenic diluent means a hydrocarbon diluent including naphtha produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat and generally comprises a mixture of aromatic and non-aromatic compounds.
(8) As used herein, a paraffinic diluent means a hydrocarbon diluent including a sufficient amount of one or more relatively short-chain aliphatic compounds such as C.sub.5 to C.sub.8 aliphatic compounds.
(9) As used herein, coarse solids mean mineral solid particles with their largest dimension larger than 44 m.
(10) As used herein, fine solids mean mineral solid particles with their largest dimension smaller than 44 m.
(11)
(12) In one embodiment, the vessel 10 is a cylindrical tank with an aspect ratio (tailings height/diameter) of about 1. In one embodiment, the vessel is essentially an empty tank. The solids layer 19 is heated by any means known in the art. In one embodiment, saturated steam 30 of any pressure heats the bottom of the unit 10 indirectly through large heat exchanging surfaces, which may be provided by a network of tubes/pipes 32. Condensed water 31 exits the heating tubes 32 and may be reused for steam generation. In another embodiment, the heating surface is provided by other means, for example, by electric heating coils. The heating section may extend upward from the bottom 36 of unit 10, but, generally, should not exceed 20% of the total tailings height (sum of layer thicknesses of 19, 34 and 39). In another embodiment, in addition to steam pipe or electric coil heating, the bottom surface 36 of the vessel 10 is heated with any external devices or means. In one embodiment, the feed stream 20 may be preheated to near boiling temperature of water, in addition to steam pipe or electric coil heating.
(13) With heating, water among the settled solids (tailings layer 19) boils sending in-situ generated steam bubbles to the top 35 of the vessel 10, thus, travelling across its entire length. These steam bubbles create turbulence among solids and slurry, and strip hydrocarbon diluent from the tailings. The steam and hydrocarbon diluent vapors rise to the top 35 of the vessel 10 and exit via outlet 33 as steam and hydrocarbon diluent vapors stream 21. Stream 21 is then condensed in a heat exchanger 11 and condensed vapors 22 are separated in a separator 12 to produce recovered diluent 23 and water 24.
(14) After coarse solids settling, the middle section 17 of the vessel 10 mainly contains a slurry layer 39 comprising water, suspended fine solids and bitumen drops. It was further observed that when steam bubbles rise through the tailings, they may also carry some bitumen, some residual solvent and fines. As a result, a froth layer 34 forms on top of the slurry layer 39 in the upper section 18 of the vessel 10. The froth layer 34 overflows and exits the vessel 10 via outlet 37 as froth stream 25. Generally, the mass flow rate of stream 25 is less than 20% of the mass flow rate of the feed stream 20.
(15) The treated/stripped tailings are removed from the bottom section 16 of the vessel 10 via outlet 38 as underflow stream 27. In one embodiment, a waste heat recovery device such as a plate exchanger is used to recover heat from stream 27 and heat the feed stream 20. In one embodiment, froth stream 25 is combined with underflow stream 27. Alternatively, the froth stream 25 may be further treated to remove its bitumen content in a unit 13 and to remove its residual solvent content in a unit 14. In one embodiment, the unit 13 includes multiple units for solvent (e.g. naphtha diluent) addition/mixing and diluted bitumen separation from water-based slurry by gravity. The treated slurry 29 is then sent to the unit 14 for solvent recovery. In one embodiment, the unit 14 is settler/stripper unit similar to the vessel 10. The cleaned-up fines and water, stream 26, is then combined with the stream 27. Thus, stream 28 is the combination of either stream 25 and stream 27 or stream 26 and stream 27. The combined waste stream 28 is disposed in a tailings pond. In another embodiment, the froth stream 25 is sent back to the froth treatment plant for reprocessing. In this case stream 27 is the sole waste stream to be disposed.
(16) In most instances, the in-situ generated steam bubbles agitate the solids layer on the bottom of the vessel 10 very vigorously. To further prevent caking in the heating section, the solids-rich slurry on the vessel bottom may be pumped around to keep solids somewhat mobile in the bottom layer. However, this pumping action should not be strong enough to homogenize the slurry in the vessel 10. Thus, besides the optional use of pumps, there are no moving parts in the vessel 10, yet adequate mixing of steam and solids/trapped hydrocarbon diluent still occurs through in-situ steam formation. Furthermore, steam bubbles are generated throughout the vessel's cross section, so no sparger is needed to distribute steam, as in the case of live steam injection into a slurry pool. Generally, the hydrocarbon diluent recovery with the present invention is above 90%. When froth treatment tailings are generated from froth treatment using naphtha, the naphtha recovery is generally above 95%. The residual naphtha content in the treated tailings is generally below 0.1 wt %.
(17) Thus, as compared to prior art diluent recovery processes, the present invention may provide the additional benefit of forming a bitumen-rich froth stream, which may be further processed to recover bitumen. Further, when heating is provided by steam circulating through a piping system (as opposed to injecting steam directly into the vessel), it allows clean water to condense (in stream 31) and be reused after steam heating so that the demand for boiler feed water is minimized. This is especially valuable in winter months when river water import is near the regulated limit.
Example 1
(18) In this example, a naphtha froth treatment tailings sample of about 520 g was placed in a cylindrical beaker of 8.3 cm diameter. The slurry height was about 9 cm. The beaker wall was insulated. The beaker was heated on a hot plate with various power settings with its top closed until boiling occurred. The sample was then boiled for a given period of time until it lost 10% of its original mass. Naphtha concentrations in the feed sample and the treated samples were analyzed and the results are shown in Table 1.
(19) TABLE-US-00001 TABLE 1 Boiling Time (min) Parameters 0 44 51 73 80 Naphtha 1.419 0.056 0.018 0.018 0.041 Concentration* (wt %) Naphtha Recovery (%) 0 96.0 98.7 98.7 97.1 *The naphtha concentration was normalized by the original sample weight. The zero boiling time value refers to the feed property.
(20) For comparison, the average naphtha concentration after live steam stripping in one commercial naphtha recovery unit (NRU) for the same sample was 0.24 wt % and the average naphtha recovery in the NRU was 83%.
Example 2
(21) Another naphtha froth treatment tailings sample of about 520 g was placed in the aforementioned beaker. The sample was either heated directly on the hot plate or heated inside a larger beaker filled with silicon oil. A Teflon dish was placed below the sample beaker to block its bottom area from being heated directly by the hot plate, thus heating was exclusively from the beaker wall through the hot oil. The boiling time was about 45 min. The sample mass loss was about 10%. Naphtha concentrations in the feed sample and the treated samples were analyzed. The values shown in Table 2 are average ones of two measurements for each heating condition and four measurements for the feed.
(22) TABLE-US-00002 TABLE 2 Parameters Feed Bottom Heating Wall Heating Naphtha Concentration* 1.591 0.37 0.138 0.01 0.657 0.02 (wt %) Naphtha Recovery (%) 0 91.3 0.6 58.7 1.4 *The naphtha concentration was normalized by the original sample weight.
(23) Note that this feed sample is not a typical one, likely generated under plant upset conditions. The normalized naphtha concentration after live steam stripping in one commercial NRU for this sample was 0.32 wt %. The average naphtha recovery in this NRU was 77%. The present method with bottom heating can still achieve a naphtha recovery above 90% on this difficult feed. Wall heating is ineffective since most of steam bubbles were generated above the settled solids layer and bypassed the naphtha containing solids.
Example 3
(24) An equilibrium simulation was run using a commercial process simulator Aspen HYSYS 7.2. The froth treatment tailings feed contains 2.6 wt % bitumen, 1.7 wt % naphtha, 27.1 wt % solids and 68.5 wt % water. The feed has been preheated to 110 C. at 220 kPa. Other stream properties are shown in Table 3.
(25) TABLE-US-00003 TABLE 3 Hydro- Abso- carbon Water Solids lute Mass mass mass mass T P flow flow.sup. flow flow Stream #.sup. ( C.) (kPa) (kg/s) (kg/s) (kg/s) (kg/s) 20 110 220 349.1 15.0 239.3 94.8 21 120 114 34.9 5.8 29.1 0 23 85 100 5.8 5.8 0 0 24 85 100 29.1 0 29.1 0 28 122 220 314.2 9.2 210.2 94.8 30 148 446 37.5 0 37.5 0 (gas) 31 148 446 37.5 0 37.5 0 (liq) Heating 79.5 MW duty @ 30, 31 Cooling 71.1 MW duty @ 11 Naphtha 99.3% rec. @ 23 Steam/Feed 0.107 .sup.Refer to FIG. 1 for stream # .sup.Sum of bitumen and naphtha flow rates
(26) The slurry density is 1080 kg/m.sup.3. In a hypothetical tank of 10 m in diameter and 10 m in tailings height, the residence time is 40 min. Assuming the heat transfer coefficient, U, for the heating section is 1000 W/m.sup.2K, the required heating area is 3118 m.sup.2. The heating area can be reduced to 1254 m.sup.2 if 1136 kPa steam is used instead of 446 kPa steam. This smaller area can be provided by a network of steam tubes at the bottom of the tank.
(27) The naphtha recovery here is the thermodynamic limit for one-stage flashing. If steam/solids contact is ideal, this value can be closely approached in operation.
(28) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and adapt it to various usages and conditions. Reference to an element in the singular, such as by use of the article a or an is not intended to mean one and only one unless specifically so stated, but rather one or more. Nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.