Process for recovering propylene from a propane dehydrogenation process

Abstract

In a propane dehydrogenation (PDH) process, the purpose of the deethanizer and cooling train system is to separate the cracked gas into a methane-rich tail gas product, a C2 process stream, and a C3 process stream. The method described herein reduces refrigeration power requirements and provides a simple and reliable design by using staged cooling, process-to-process interchange of the propane feed to the reactor, and the use of high-efficiency heat exchangers and distributed distillation technology.

Description

Technical Field

[0001] The present invention relates to a method for recovering propylene from a propane dehydrogenation (PDH) process, and more particularly, to recovering methane-rich, C2-rich, and C3-rich products from a PDH process.

[0002] background

[0003] Propane dehydrogenation (PDH) is a process step in the production of propylene from propane. PDH is important to the petrochemical industry because propylene is the second most important starting product in the petrochemical industry after ethylene. In the PDH process, the purpose of the deethanizer and cooling train system is to separate the cracked gas into a methane-rich tail gas product, a C2 process stream, and a C3 process stream. Improvements to the PDH process, such as by reducing refrigeration power requirements, simplifying the design, and / or making the design more reliable, are always beneficial. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 is a non-limiting schematic diagram of a PDH process as described herein.

[0006] Overview

[0007] In one non-limiting embodiment, a method for recovering propylene from a propane dehydrogenation (PDH) process comprising a PDH reactor is provided, wherein the method comprises: feeding dry process gas from a process gas dryer to a first deethanizer feed cooler and cooling it with propane; sending the cooled dry process gas to a first deethanizer feed drum; feeding liquid from the first deethanizer feed drum to the deethanizer; sending overhead vapor from the first deethanizer feed drum to a process gas compressor (PGC); C); cooling the effluent from the PGC with propane in the second deethanizer feed cooler and then with propylene refrigerant in the third deethanizer feed cooler, and sending the effluent to the second deethanizer feed drum; feeding the liquid from the second deethanizer feed drum to the deethanizer; cooling and partially condensing the vapor from the second deethanizer feed drum in the cold box; separating the process effluent from the cold box into a vapor phase and a liquid phase in the first cold drum; evaporating the liquid from the first cold drum in the cold box and recycling it to the PGC First stage: reheat the vapor from the first cooling drum to become a methane-rich tail gas product; separate ethane and lighter components from C3 and heavier components in the deethanizer; reboil the deethanizer bottom liquid with quench water or propylene refrigerant vapor in the deethanizer reboiler, and partially condense the top vapor with propylene refrigerant in the deethanizer condenser; in the deethanizer reflux drum, separate the process effluent from the deethanizer condenser into vapor and liquid phases, send the vapor phase to the cold box, and return the liquid to the deethanizer; extracting a liquid stream above the upper feed stage of the deethanizer, pumping the liquid stream and then optionally cooling it with propane and then with propylene refrigerant in a first pump-circulation cooler, and returning the cooled liquid to the deethanizer at a position above the extraction tower tray; feeding the deethanizer bottom liquid to the C3 splitter; and a cold box superheating the tail gas from the first cold drum, the PGC recycle stream, the C2-rich stream and the propane feed to the PDH reactor, while also subcooling the liquid propylene refrigerant.

[0008] In one non-limiting form, there is further provided a system for recovering propylene from a propane dehydrogenation (PDH) process including a PDH reactor, wherein the system comprises: a process gas dryer configured to feed dry process gas to a first deethanizer feed cooler and cool it with propane; a first deethanizer feed drum configured to receive dry process gas from the first deethanizer feed cooler; a deethanizer configured to receive liquid from the first deethanizer feed drum; a process gas compressor (PGC) configured to receive overhead vapor from the first deethanizer feed drum; a second deethanizer feed cooler configured to cool an effluent from the PGC with propane; a third deethanizer feed cooler configured to cool the effluent from the PGC with propylene refrigerant; The system further comprises a first deethanizer feed drum configured to receive the effluent from the third deethanizer feed cooler and send the feed liquid to the deethanizer; a cold box configured to receive, cool, and partially condense the vapor from the second deethanizer feed drum; a first cold drum configured to separate the process effluent from the cold box into a vapor phase and a liquid phase, and to recycle the evaporated liquid to the first stage of the PGC; a top deethanizer condenser configured to partially condense the top vapor with propylene refrigerant; a deethanizer reflux drum configured to separate the process effluent from the top deethanizer condenser into a vapor phase and a liquid phase, and to send the vapor phase to the cold box; a line directing the liquid from the deethanizer reflux drum to the deethanizer; and a C3 splitter configured to receive the bottom liquid from the deethanizer. Optionally, the system may further include a deethanizer reboiler configured to reboil the deethanizer bottom liquid with propylene refrigerant vapor.

[0009] Details

[0010] It has been discovered that the use of staged cooling, process-to-process interchange of the propane feed to the reactor and the use of high efficiency heat exchangers and distributed distillation techniques reduces refrigeration power requirements and provides a simple and reliable design for a propane dehydrogenation (PDH) process.

[0011] For more details, refer to Figure 1 , which, when viewed together, is a complete but non-limiting schematic diagram of the process as described herein, dry process gas and liquid are fed to the deethanizer system. More specifically, from the process gas dryer (not shown - from Figure 1Dry process gas 1 (shown on the left side of the diagram) is cooled in first deethanizer feed cooler 20 with propane from propane inlet stream 15 and sent as gas 2 to first deethanizer feed drum 22. Liquid 4 from first deethanizer feed drum 22 is fed to deethanizer 24, in a non-limiting manner, by being pumped by condensate pump 52. The overhead vapor reaches third-stage process gas compressor (PGC) 26. Discharge 3 from process gas compressor 26 is cooled in second deethanizer feed cooler 28 with propane, also from propane inlet stream 15, and then cooled with propylene refrigerant in third deethanizer feed cooler 30 and sent to second deethanizer feed drum No. 2 (V-4002). Liquid 6 from second deethanizer feed drum No. 2 (V-4002) 32 is fed to deethanizer 24. The propane 14 from the second deethanizer feed cooler 28 is sent to a cold box 34 before being fed to the PDH reactor.

[0012] The vapor 5 from the second deethanizer feed drum 32 is cooled and partially condensed in a cold box 34. The process effluent from the cold box 34 is separated into a vapor phase and a liquid phase in a first cold drum 36. The liquid 12 from the first cold drum 36 is evaporated in the cold box 34 and recycled to the first stage of the PGC to recover the contained propylene. The vapor from the first cold drum 36 is reheated and becomes a methane-rich tail gas product 13.

[0013] Deethanizer 24 separates ethane and lighter components from C3 and heavier components. The deethanizer bottoms liquid is reboiled with quench water or propylene refrigerant vapor in deethanizer reboiler 38. The overhead vapor is partially condensed with propylene refrigerant in deethanizer condenser 40. The process effluent from deethanizer condenser 40 is separated into vapor and liquid phases in deethanizer reflux drum 42. Vapor phase 7 reaches cold box 34. The liquid is directed back to deethanizer 24, optionally pumped by deethanizer reflux pump 44. The deethanizer bottoms liquid serves as feed to the C3 splitter.

[0014] The pump loop 9 on the upper section of the deethanizer 24 is cooled by propane from the propane inlet stream 15 in the deethanizer first pump loop cooler 46 and by the intermediate grade propylene refrigerant in the deethanizer second pump loop cooler 48, and the cooled stream 10 is returned to the deethanizer 24 at a higher tray position to reduce the requirement for low grade refrigerant on the top deethanizer condenser 40.

[0015] The cold box 34 superheats the tail gas from the first cold drum 36, the PGC recycle stream 12, the C2-rich stream 11 and the propane to the reactor, while subcooling the liquid propylene refrigerant 16.

[0016] The deethanizer bottoms stream 8 is fed to a heat pump C3 splitter where polymer grade propylene is separated from the propane recycle and C4+ components. In one non-limiting embodiment, most of the propane recycle is taken as a side draw from the C3 splitter that bypasses the depropanizer, while the remaining C3 recycle and C4+ materials are recycled to the depropanizer (not shown) where the C4+ is separated from the fresh feed and recycle propane.

[0017] In one non-limiting embodiment, the operating condition ranges for certain equipment of the process may be as given in Table 1.

[0018] Table I

[0019] Operating conditions for recovering propylene in the PDH process

[0020] name temperature pressure First deethanizer feed cylinder 22 10℃ to -5℃ 10–15 barg Second deethanizer feed tube 32 -25℃ to -40℃ 20–40 barg Deethanizer 24 -40℃ (top) to +40℃ bottom 10–15 barg Deethanizer reflux drum 42 -30℃ to -40℃ 10–15 barg First cooling cylinder 36 -40℃ to -100℃ 20–40 barg Cold Box 34 -120℃ to +40℃

[0021] The method for recovering propylene from a PDH process described herein has numerous advantages, including, but not limited to, reduced power requirements, high propylene recovery, simpler design, and increased reliability. In one non-limiting embodiment, liquid propane is used to feed the reactor to initially provide refrigeration to the process, resulting in power savings ranging from approximately 30% to 50% compared to designs where the propane is generated as vapor from the depropanizer overhead and fed directly to the reactor. For simplicity, this design utilizes only a propylene refrigeration system, but good propylene recovery is still achieved by recycling the liquid produced in the first cold drum, No. 1, and using it as the cooling medium in the cold box.

[0022] In the foregoing description, the present invention has been described with reference to specific embodiments thereof. However, this description should be construed in an illustrative rather than a restrictive sense. For example, equipment, processes, and operating conditions that fall within the claimed or disclosed parameters but are not specifically identified or attempted in the specific examples are intended to be within the scope of the present invention.

[0023] The present invention can be practiced in the absence of undisclosed elements. In addition, the present invention can suitably comprise, consist of, or consist essentially of the disclosed elements. For example, a method for recovering propylene from a PDH process comprising a PDH reactor can be provided, wherein the method further consists essentially of or consists of:

[0024] feeding the dried process gas from the process gas dryer to a first deethanizer feed cooler and cooling it with propane;

[0025] sending the cooled, dried process gas to the first deethanizer feed drum;

[0026] feeding the liquid from the first deethanizer feed drum to the deethanizer;

[0027] The overhead vapor from the first deethanizer feed drum is sent to the process gas compressor (PGC);

[0028] cooling the effluent from the PGC with propane in a second deethanizer feed cooler and then with propylene refrigerant in a third deethanizer feed cooler and sending the effluent to a second deethanizer feed drum;

[0029] feeding liquid from the second deethanizer feed drum to the deethanizer;

[0030] cooling and partially condensing vapor from the second deethanizer feed drum in a cold box;

[0031] separating the process effluent from the cold box into a vapor phase and a liquid phase in a first cold drum;

[0032] The liquid from the first cold drum is evaporated in the cold box and recycled to the first stage of the PGC;

[0033] Reheating the steam from the first cooling drum to become a methane-rich tail gas product;

[0034] Ethane and lighter components are separated from C3 and heavier components in a deethanizer;

[0035] reboiling the deethanizer bottoms liquid with quench water or propylene refrigerant vapor in the deethanizer reboiler and partially condensing the overhead vapor with propylene refrigerant in the deethanizer condenser;

[0036] In the deethanizer reflux drum, the process effluent from the deethanizer condenser is separated into vapor and liquid phases, with the vapor phase sent to a cold box and the liquid returned to the deethanizer, optionally through a deethanizer reflux pump;

[0037] extracting a liquid stream from above the upper feed stage of the deethanizer, pumping the liquid stream and then cooling it in a first pump-around cooler with propane and then in a second pump-around cooler with propylene refrigerant, and returning the cooled liquid to the deethanizer at a point above the extractor tray;

[0038] Feeding the deethanizer bottoms liquid to a C3 splitter; and

[0039] The cold box superheats the tail gas from the first cold drum, the PGC recycle stream, the C2-rich stream and the propane feed to the PDH reactor, while also subcooling the liquid propylene refrigerant.

[0040] Alternatively, there may be provided a system for recovering propylene from a propane dehydrogenation (PDH) process comprising a PDH reactor, wherein the system consists essentially of or consists of:

[0041] a process gas dryer configured to feed dry process gas to the first deethanizer feed cooler and cool it with propane;

[0042] a first deethanizer feed drum configured to receive dry process gas from a first deethanizer feed cooler;

[0043] a deethanizer configured to receive liquid from a first deethanizer feed drum;

[0044] a process gas compressor (PGC) configured to receive overhead vapor from a first deethanizer feed drum;

[0045] a second deethanizer feed cooler configured to cool the effluent from the PGC with propane;

[0046] a third deethanizer feed cooler configured to cool the effluent from the PGC with propylene refrigerant;

[0047] a second deethanizer feed drum configured to receive the effluent from the third deethanizer feed cooler and deliver the feed liquid to the deethanizer;

[0048] a cold box configured to receive, cool, and partially condense vapor from the second deethanizer feed drum;

[0049] a first cold drum configured to separate the process effluent from the cold box into vapor and liquid phases and to recycle the evaporated liquid to the first stage of the PGC;

[0050] an overhead deethanizer condenser configured to partially condense overhead vapor with propylene refrigerant;

[0051] a deethanizer reflux drum configured to separate the process effluent from the overhead deethanizer condenser into vapor and liquid, sending the vapor phase to a cold box;

[0052] a line directing liquid from the deethanizer reflux drum to the deethanizer; and

[0053] A C3 splitter configured to receive the bottom liquid from the deethanizer. In another non-limiting alternative embodiment, the system may also essentially comprise or include a deethanizer reboiler configured to reboil the deethanizer bottom liquid with propylene refrigerant vapor.

[0054] As used throughout the claims, the words "comprising" and "comprises" should be interpreted to mean "including, but not limited to" and "includes, but not limited to," respectively.

[0055] As used herein, the word "substantially" shall mean "generally but not entirely as specified."

[0056] As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0057] As used herein, the term "about" in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (eg, it includes the degree of error associated with measurement of the given parameter).

[0058] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for recovering propylene from a propane dehydrogenation (PDH) process comprising a PDH reactor, the method comprising: Feeding the dried process gas (1) from the process gas dryer to the first deethanizer feed cooler (20) and cooling it with propane; The cooled dry process gas (2) is fed to the first deethanizer feed drum (22); Feeding the liquid (4) from the first deethanizer feed drum (22) to the deethanizer (24); sending overhead vapor from the first deethanizer feed drum (22) to a process gas compressor (PGC) (26); Characterized in that the effluent (3) from the PGC (26) is cooled with propane in a second deethanizer feed cooler (28) and then with propylene refrigerant in a third deethanizer feed cooler (30) and the effluent is fed to a second deethanizer feed drum (32); Feeding the liquid (6) from the second deethanizer feed drum (32) to the deethanizer (24); cooling and partially condensing vapor from the second deethanizer feed drum (32) in a cold box (34); The process effluent from the cold box (34) is separated into a gas phase (7) and a liquid phase in a first cold drum (36); The liquid from the first cold drum (36) is evaporated in the cold box (34) and recycled to the first stage of the PGC (26); Reheating the steam from the first cooling drum (36) to form a methane-rich tail gas product; Ethane and lighter components are separated from C3 and heavier components in a deethanizer (24); partially condensing the overhead vapor with propylene refrigerant in an overhead deethanizer condenser (40); In the deethanizer reflux drum (42), the process effluent from the top deethanizer condenser (40) is separated into vapor and liquid phases, with the vapor phase sent to the cold box (34) and the liquid returned to the deethanizer (24); Feeding the deethanizer bottoms liquid (8) to a C3 splitter; and The cold box (34) superheats the tail gas from the first cold drum (36), the PGC recycle stream (12), the C2-rich stream (11) and the propane feed to the PDH reactor, while also subcooling the liquid propylene refrigerant.

2. The method of claim 1 further comprising reboiling the deethanizer bottoms liquid with propylene refrigerant vapor in a deethanizer reboiler (38).

3. The method of claim 1 further comprising reboiling the deethanizer bottoms liquid with quench water in a deethanizer reboiler (38).

4. The method of claim 1, 2 or 3, further comprising a pump circuit on the upper section of the deethanizer, wherein the pump circuit uses propane in a first pump circuit cooler (46) of the deethanizer and uses a medium-grade propylene refrigerant in a second pump circuit cooler (48) of the deethanizer, thereby reducing the requirement for low-grade refrigerant on the top deethanizer condenser (40).

5. The method of claim 1, 2 or 3, further comprising feeding the deethanizer bottom liquid (8) to a heat pump type C3 splitter and separating polymer grade propylene from the propane recycle and C4+ components.

6. The process of claim 5, further comprising recycling propane back to the depropanizer and separating C4+ from the fresh feed and the propane recycle.

7. The process of claim 6, wherein a portion of the propane recycle is taken as a side draw from a C3 splitter bypassing the depropanizer.

8. A system for recovering propylene from a propane dehydrogenation (PDH) process including a PDH reactor, the system comprising: a process gas dryer configured to feed dry process gas (1) to a first deethanizer feed cooler (20) and cool it with propane; a first deethanizer feed drum (22) configured to receive the dry process gas (2) from the first deethanizer feed cooler (20); a deethanizer (24) configured to receive the liquid (4) from the first deethanizer feed drum (22); a process gas compressor (PGC) (26) configured to receive overhead vapor from the first deethanizer feed drum (22); characterized by a second deethanizer feed cooler (28) configured to cool the effluent (3) from the PGC (26) with propane; a third deethanizer feed cooler (30) configured to cool the effluent from the PGC (26) with propylene refrigerant; a second deethanizer feed drum (32) configured to receive the effluent from the third deethanizer feed cooler (30) and to deliver the feed liquid (6) to the deethanizer (24); a cold box (34) configured to receive, cool, and partially condense vapor from the second deethanizer feed drum (32); a first cold drum (36) configured to separate the process effluent from the cold box (34) into vapor and liquid phases and to recycle the evaporated liquid to the first stage of the PGC (26); an overhead deethanizer condenser (40) configured to partially condense overhead vapor with propylene refrigerant; a deethanizer reflux drum (42) configured to separate the process effluent from the top deethanizer condenser (40) into a vapor phase (7) and a liquid, with the vapor phase being sent to a cold box (34); a line (50) directing liquid from the deethanizer reflux drum (42) to the deethanizer (24); and A C3 splitter is configured to receive the bottom liquid (8) from the deethanizer (24).

9. The system of claim 8, further comprising a deethanizer reboiler (38) configured to reboil the deethanizer bottoms liquid with propylene refrigerant vapor.

10. The system of claim 8, further comprising a deethanizer reboiler (38) configured to reboil the deethanizer bottoms liquid with quench water.

11. The system of claim 8, 9 or 10, further comprising a pump cycle on the upper section of the deethanizer, the pump cycle using propane in a first pump cycle cooler (46) of the deethanizer and using a mid-grade propylene refrigerant in a second pump cycle cooler (48) of the deethanizer.

12. The system of claim 8, 9 or 10, further comprising a depropanizer to which the propane recycle is returned.

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