Carbon dioxide hydrocarbons separation process

• US 4,576,615 A
• Filed: 08/20/1984
• Issued: 03/18/1986
• Est. Priority Date: 08/20/1984
• Status: Expired due to Fees

• Current Assignee: The Randall Corporation
• Original Assignee: The Randall Corporation
• Inventors: Huebel, Robert R., Netzer, David
• Primary Examiner(s): Hart, Charles
• Application Number:
  US06/642,308
• Time in Patent Office: 575 Days
• Field of Search: 55/46, 55/68, 55/73, 55/48, 55/51, 55/40, 55/41, 55/42, 55/43
• US Class Current: 95/174
• CPC Class Codes: B01D 53/1475 Removing carbon dioxide
• CPC Class Codes: C07C 7/11 by absorption, i.e. purification or separation of gaseous hydrocarbons with the aid of liquids
• CPC Class Codes: Y02C 20/40 of CO2
• CPC Class Codes: Y02P 20/151 Reduction of greenhouse gas [GHG] emissions, e.g. CO2

Abstract

Carbon dioxide is separated from light hydrocarbons such as methane and ethane by absorbing CO₂ gas with water at a pressure of at least 500 psia thus avoiding the CO₂ --C₂ H₆ azeotrope problem. The CO₂ is recovered from the absorbing water by pressure reduction and flashing and/or by heating and flashing. The process is particularly applicable to the recovery of high pressure pure carbon dioxide from the wellhead products of carbon dioxide flooding used in enhanced oil recovery. The high pressure pure carbon dioxide is liquified and reinjected to the well at the desired pressure.

Claims

1. A process for the separation and recovery of CO₂ from an enhanced oil recovery or naturally occurring gas stream containing a mixture of at least 45 mol % CO₂ and less than 0.2 mol % H₂ S with light hydrocarbons containing ethane as a primary light hydrocarbon component comprising the steps of:

(a) providing a gas stream of said mixture at a pressure of at least 500 psia,

(b) introducing said gas stream into the lower portion of an absorption system,

(c.) introducing a first liquid water phase containing at least 65 mol % water and containing less than about 1.4 weight % CO₂ into the top portion of said absorption system and a second liquid water phase containing at least 65 mol % water and containing between about 1.4 and 3.0 weight % CO₂ into the middle portion of said absorption system to form a downwardly flowing liquid water phase whereby said gas stream flows upwardly in contact with said downwardly flowing liquid water phase and said downwardly flowing liquid water phase absorbs CO₂ from said gas stream to form a CO₂ -rich liquid water phase,

(d.) withdrawing said gas stream depleted in CO₂ from the top portion of said absorption system,

(e.) withdrawing said CO₂ -rich liquid water phase from the bottom portion of said absorption system at a pressure of at least 500 psia,

(f.) separating gaseous CO₂ from said withdrawn CO₂ -rich liquid water phase to form said recovered CO₂ and said first liquid water phase containing less than 1.4 mol % CO₂ and said second liquid water phase containing between about 1.4 and 3.0 weight % CO₂, and

(g.) recycling said separated first and second liquid water phases to the top and middle portions of said absorption system respectively.

2. The process of claim 1 wherein said separating step (e) comprises reducing the pressure of said withdrawn CO₂ -rich liquid water phase and flashing said CO₂ at a pressure of at least 100 psia therefrom.

3. The process of claim 2 wherein said separating step (e) further includes the step of heating said withdrawn CO₂ -rich liquid water phase and further flashing said CO₂ therefrom.

4. The process of claim 3 wherein said heating at least partially comprises transferring heat from said separated first liquid water phase to said withdrawn CO₂ -rich liquid water phase.

5. The process of claim 1 wherein said separating step (e) further comprises additional pressure reduction and flashing steps.

6. A process as recited in claim 1 wherein said gas stream also contains less than 0.2% H₂ S, said H₂ S being withdrawn with said CO₂ -rich liquid water phase from the bottom of said absorption system and being separated with said gaseous CO₂ and further including the steps of oxidizing said H₂ S in said gaseous CO₂ stream to elemental sulfur and removing said elemental sulfur.

7. The process of claim 1 wherein said step (a) of providing a gas stream comprises the step of fractionating a feed gas stream containing said CO₂ and said ethane and further containing heavier hydrocarbons and H₂ S into an overhead product containing primarily said CO₂ and said ethane and a bottom product containing primarily said said heavier hydrocarbons and H₂ S and further including the step of transferring heat from said recovered CO₂ to said bottom product from said fractionation to liquify said recovered CO₂.