Flexible hydrocarbon gas separation process and apparatus

• US 20080016909A1
• Filed: 03/05/2007
• Published: 01/24/2008
• Est. Priority Date: 07/19/2006
• Status: Active Grant

• Current Assignee: Yingzhong Lu
• Original Assignee: Yingzhong Lu
• Inventors: Lu, Yingzhong
• Granted Patent: US 7,856,848 B2
• Time in Patent Office: Days
• US Class Current: 62/623
• CPC Class Codes: C10L 3/10 Working-up natural gas or synthetic natural gas

Abstract

The present invention related to a flexible hydrocarbon gas separation process that could dehydrate the water-saturated hydrocarbon gas mixture and recover thereof the required higher hydrocarbons (NGL) therein with a controllable ethane recovery rate (ranging from >95% to <2%) while keeping high recovery rate of all other heavier components. The flexible process comprises the following steps: deep-cooling and dehydrating the raw gas and get the NGL condensate; flowing the deep-dehydrated gas into the flexible absorber to get the rich oil with desirable ethane content; completely demethanizing and partially deethanizing as desired the rich oil and the NGL condensate to get purified rich oil and purified NGL condensate, respectively; separating the NGL vapor from the purified rich oil; cooling and compressing the NGL vapor; mixing the NGL vapor with the purified NGL condensate; and liquefying the mixture to get the final NGL product. The present invention also provides a flexible apparatus with highly efficient components for the flexible process.

Claims

1. A flexible hydrocarbon gas separation process that could dehydrate the water-saturated hydrocarbon gas (“

raw gas”

hereafter) and recover thereof the higher hydrocarbon liquid (“

NGL”

hereafter) with controllable ethane recovery rate ranging from >

95% to <

2% while keeping high recovery rate of all other heavier hydrocarbon components comprises the following steps;

(a) Pre-cooling and pre-dehydrating the raw gas with directly contact a counter-flowing liquid coolant comprising of an aqueous solution of a gas hydrate inhibitor to get the pre-cooled pre-dehydrated gas and the partial NGL condensate;

(b) Deep-cooling and deep-dehydrating the pre-cooled pre-dehydrated gas with the refrigerant from an external refrigerator to get the deep-cooled deep-dehydrated gas and the deep-cooled NGL condensate;

(c) Flowing the NGL condensate into a condensate pre-demethanizer and a flexible condensate deethanizer in tandem to remove all the methane content therein and simultaneously reduce the ethane contend therein to any desirable level to get the deep-cooled purified NGL condensate;

(d) Flowing the deep-cooled deep-dehydrated gas into a flexible absorber wherein contacting the gas with a counter-flowing liquid absorbent (“

lean oil”

hereafter) to get the cold residue gas and the cold rich absorbent (“

rich oil”

hereafter) with desirable level of ethane content;

(e) Flowing the cold rich oil into a rich oil pre-demethanizer and a flexible rich oil deethanizer in tandem to remove all the methane content therein and simultaneous reduce the ethane content therein to any desirable level to get the purified rich oil;

(f) Depressurizing the purified rich oil and distilling the purified rich oil in a rich oil fractionator to get the NGL vapor and the regenerated lean oil;

(g) Cooling the NGL vapor with a heat transport medium to transport the heat energy from the NGL vapor to the deep-cooled rich oil in the flexible rich oil deethanizer;

(h) Compressing the NGL vapor and mixing the compressed NGL vapor with the deep-cooled purified NGL condensate to get the low-temperature NGL vapor-liquid mixture; and

(i) Liquefying the low-temperature NGL vapor-liquid mixture to get final NGL product.

2. A flexible hydrocarbon gas separation process of claim 1 wherein in step (a) the liquid coolant comprising of an aqueous solution of a gas hydrate inhibitor is pre-cooled with the cold residue gas and the cold rich oil before being used as the coolant in step (a).

3. A flexible hydrocarbon gas separation process of claim 1 wherein in step (b) the pre-cooled pre-dehydrated gas is mixed with the partial NGL condensate before being deep-cooled with a refrigerant to get the deep-cooled deep-dehydrated gas and the NGL condensate.

4. A flexible hydrocarbon gas separation process of claim 1 wherein in step (b) the pre-cooled pre-dehydrated gas is mixed with a spray of concentrated gas hydrate inhibitor solution before being deep-cooled with a refrigerant to get the deep-cooled deep-dehydrated gas and the NGL condensate.

5. A flexible hydrocarbon gas separation process of claim 1 wherein in step (b) the pre-cooled pre-dehydrated gas is further deep-dehydrated with a solid desiccant to get the deep-dehydrated gas before further deep-cooled with a refrigerant.

6. A flexible hydrocarbon gas separation process of claim 5 wherein the solid desiccant is calcium chloride or other deliquesce solid desiccants that would be liquefied when absorbing sufficient water, and the deliquescent liquid is then used as the concentrated hydrate inhibitor solution.

7. A flexible hydrocarbon gas separation process of claim 1 wherein in step (c) and (e) the working pressure and bottom temperature of the deethanizer could be controlled to precisely reduce the ethane content of the purified condensate to desirable level.

8. A flexible hydrocarbon gas separation process of claim 1 wherein in step (c) and (e) the tandem process with a pre-demethanizer and a deethanizer is replaced with the integrated process of the integrated cascade flexible deethanizer.

9. A flexible hydrocarbon gas separation process of claim 1 wherein in step (d) the absorbent used in the absorber could be either heavy oils (i.e., hydrocarbon mixture with molecular weight higher than 100) or other organic compounds with hydrocarbon gas solubility higher than 20 scf/gal.

10. A flexible hydrocarbon gas separation process of claim 1 wherein in step (d) the ethane recovery rate in the flexible absorber could be precisely controlled by changing the lean oil flow rate.

11. A flexible hydrocarbon gas separation process of claim 1 wherein in step (e) the regenerated lean oil is recycled as a heating medium.

12. A flexible hydrocarbon gas separation process of claim 1 wherein in step (g) the heat transport medium is the cooled recycling lean oil.

13. A flexible hydrocarbon gas separation process that could dehydrate the water-saturated raw hydrocarbon gas under high pressure and recover thereof the NGL with controllable ethane recovery rate ranging from >

95% to <

2% while keeping high recovery rate (over 90%) of all other heavier hydrocarbon components comprises the following steps;

(a) Pre-cooling and pre-dehydrating the raw gas with directly contact a counter-flowing liquid coolant comprising of an aqueous solution of a gas hydrate inhibitor to get the pre-cooled pre-dehydrated gas and the partial NGL condensate;

(b) Deep-dehydrating the pre-cooled pre-dehydrated gas with a solid desiccant to get the pre-cooled deep-dehydrated gas;

(c) Expanding the pre-cooled deep-dehydrated gas to the lower pressure and a low temperature to get the deep-cooled deep-dehydrated gas and the NGL condensate;

(d) Flowing the NGL condensate and the partial NGL condensate into a condensate pre-demethanizer and a flexible condensate deethanizer in tandem to remove all the methane content therein and simultaneous reduce the ethane content therein to any desirable level to get the deep-cooled purified NGL condensate;

(e) Flowing the deep-cooled deep-dehydrated gas into a flexible absorber wherein contacting the gas with a counter-flowing liquid absorbent (“

lean oil”

hereafter) to get the cold residue gas and the cold rich oil with desirable level of ethane content;

(f) Flowing the cold rich oil into a rich oil pre-demethanizer and a flexible rich oil deethanizer in tandem to remove all the methane content therein and simultaneous reduce the ethane content therein to any desirable level to get the purified rich oil;

(g) Depressurizing the purified rich oil and distilling the purified rich oil in a rich oil fractionator to get the NGL vapor and the regenerated lean oil;

(h) Cooling the NGL vapor with a heat transport medium to transport the heat energy from the NGL vapor to the deep-cooled rich oil in the flexible rich oil deethanizer;

(i) Compressing the NGL vapor and mixing the compressed NGL vapor with the deep-cooled purified NGL condensate to get the low-temperature NGL vapor-liquid mixture; and

(j) Liquefying the low-temperature NGL vapor-liquid mixture to get final NGL product.

14. A flexible hydrocarbon gas separation apparatus that could dehydrate the water-saturated raw hydrocarbon gas and recover thereof the NGL with controllable ethane recovery rate ranging from >

95% to <

2% while keeping high recovery rate (over 90%) of all other heavier hydrocarbon components comprises the following components;

(a) A pre-cooler/dehydrator wherein the water-saturated raw hydrocarbon gas contact an cold aqueous solution of a gas hydrate inhibitor to get the pre-dehydrated gas and the partial NGL condensate (if any);

(b) A deep-cooler/dehydrator wherein the pre-dehydrated gas is mixed with a spray of gas hydrate inhibitor solution and cooled with cold rich oil and a refrigerant from an external refrigerator to get the deep-cooled, deep-dehydrated gas and the NGL condensate;

(c) A combination of a condensate pre-demethanizer and a flexible condensate deethanizer in tandem to completely demethanize the condensate and simultaneously reduce the ethane content herein to a desirable level to get the deep-cooled purified NGL condensate;

(d) A flexible absorber to recover NGL from the deep-dehydrated gas to get the rich oil with desirable ethane content level;

(e) A rich oil pre-demethanizer and a flexible rich oil deethanizer in tandem to completely demethanize the rich oil and simultaneously reduce the ethane content therein to desirable level to get the purified rich oil;

(f) A rich oil fractionator to get the NGL vapor and the regenerated lean oil from the purified rich oil;

(g) An energy-integration loop between the rich oil fractionator and the flexible rich oil deethanizer to transport the heat energy of the NGL vapor inside the rich oil fractionator to heat the rich oil inside the flexible rich oil deethanizer;

(h) An NGL vapor compressor to compress the cooled NGL to the required liquefaction pressure; and

(i) An NGL liquefier to liquefy the mixture of the compressed vapor and the deep-cooled purified NGL condensate into final NGL product.

15. A comprehensive hydrocarbon gas separation apparatus of claim 14 wherein in item (b) the deep-cooler/dehydrator is replaced with a solid desiccant deep-dehydrator and an integrated gas expander-compressor in tandem.

16. A comprehensive hydrocarbon gas separation apparatus of claim 14 wherein in item (c), (d) and (e) the flexible deethanizer is made of the integrated dual-functional exchanger-reactor.

17. A comprehensive hydrocarbon gas separation apparatus of claim 14 wherein in item (c) and (e) the combination of a pre-demethanizer and a flexible deethanizer in tandem is replaced with an integrated cascade flexible deethanizer.

18. A comprehensive hydrocarbon gas separation apparatus of claim 14 wherein in item (f) the rich oil fractionator is made of an integrated dual-functional exchanger-reactor.