Method for enhanced recovery of ethane, olefins, and heavier hydrocarbons from low pressure gas

• US 8,528,361 B2
• Filed: 10/07/2010
• Issued: 09/10/2013
• Est. Priority Date: 10/07/2010
• Status: Active Grant

• Current Assignee: Technip USA Corporation (Technip)
• Original Assignee: Technip
• Inventors: Nanda, Rajeev, Singh, Rahul
• Primary Examiner(s): Lewin, Allana
• Assistant Examiner(s): SCHIERLOH, MICHAEL A
• Application Number:
  US12/899,741
• Publication Number:
  US 20120085127A1
• Time in Patent Office: 1,069 Days
• Field of Search: 626/17, 626/18, 626/19, 626/20, 626/23, 626/32
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/40 Features relating to the provision of boil-up in the bottom of a column
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2220/68 Separating water or hydrates
• CPC Class Codes: F25J 2230/30 Compression of the feed stream
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/14 External refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/66 Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 3/0219 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

A method for recovering C₂ and higher weight hydrocarbons, or alternatively C₃ and higher weight hydrocarbons, from low pressure gas, wherein the method avoids the need to significantly compress contaminated low pressure gas in most cases, and is robust in response to pressure and temperature variations in the low pressure gas feed.

Claims

1. A method for processing a low pressure gas inlet stream to recover C2 and higher weight hydrocarbons, comprising the steps of

dehydrating said low pressure gas inlet stream,

cooling said low pressure gas inlet stream to form a partially condensed hydrocarbon feed,

separating a first liquid stream and a first vapor stream from said partially condensed hydrocarbon feed,

compressing said first vapor stream,

separating said first liquid stream into a first part and a second part,

using said first part of said first liquid stream in an absorber to absorb C₂ and higher weight hydrocarbons from said compressed first vapor stream,

partially condensing a top product from said absorber,

separating said partially condensed absorber top product into a second liquid stream and a second vapor stream,

separating a bottom product from said absorber into a first part and a second part,

heating said first part of said bottom product,

distilling said heated first part of said bottom product in a distillation column,

utilizing said second part of said first liquid stream, said second liquid stream, and said second part of said bottom product as a top feed to said distillation column, and

recovering C₂ and higher weight hydrocarbons as bottom product from said distillation column.

2. The method of claim 1, additionally comprising the step of pre-chilling said low pressure gas inlet stream prior to the step of dehydrating said low pressure gas inlet stream.

3. The method of claim 1, additionally comprising the steps of

recovering top vapor from said distillation column,

mixing said top vapor from said distillation column with said second vapor stream, to form a lean gas stream, and

heating said lean gas stream to provide a lean gas output.

4. The method of claim 1, additionally comprising the steps of

recovering top vapor from said distillation column,

mixing said top vapor from said distillation column with the top product from said absorber before the step of partially condensing a top product from said absorber, and

heating said second vapor stream to provide a lean gas output.

5. The method of claim 1, additionally comprising the step of providing a closed loop refrigeration system to provide refrigeration for the process.

6. The method of claim 1, additionally comprising the step of providing a closed loop turbo expander refrigeration system to provide refrigeration for the process.

7. The method of claim 1, wherein the step of cooling said low pressure gas inlet stream to form a partially condensed hydrocarbon feed comprises the step of cooling said low pressure gas inlet stream to about −

40 to −

85°

F.

8. The method of claim 1, wherein the step of compressing said first vapor stream comprises the step of compressing said first vapor stream to about 145 to 360 psia.

9. The method of claim 1, additionally comprising the step of warming said first vapor stream to about 20 to 85°

F. prior to the step of compressing said first vapor stream.

10. The method of claim 1, additionally comprising the step of cooling said first compressed vapor stream to about −

90 to −

119°

F. prior to the step of using said first part of said first liquid stream in an absorber to absorb C₂ and higher weight hydrocarbons from said compressed first vapor stream.

11. The method of claim 1, additionally comprising the step of operating said absorber at about 140 to 350 psia.

12. The method of claim 1, wherein the step of separating said first liquid stream into a first part and a second part comprises the step of using about 20 to 60% of said first liquid stream to compose said second part of said first liquid stream.

13. The method of claim 1, wherein the step of separating a bottom product from said absorber into a first part and a second part comprises the step of using about 20 to 60% of said absorber bottom product to compose said second part of said absorber bottom product.

14. The method of claim 1, wherein the step of heating said first part of said bottom product comprises the step of heating said first part to about 10 to 85°

F.

15. The method of claim 1, additionally comprising the step of operating said distillation column at about 255 to 365 psia at the bottom.

16. The method of claim 1, additionally comprising the step of operating said distillation column at about 245 to 360 psia at the top.

17. The method of claim 1, additionally comprising the step of maintaining said distillation column bottom temperature at about 85 to 105°

F.

18. The method of claim 1, additionally comprising the step of flashing part of said bottom product for use as a refrigerant.