SYSTEM AND METHOD FOR RECOVERING NATURAL GAS LIQUIDS WITH AUTO REFRIGERATION SYSTEM

• US 20130074542A1
• Filed: 09/25/2011
• Published: 03/28/2013
• Est. Priority Date: 09/25/2011
• Status: Abandoned Application

• Current Assignee: Ali Vatani, Mehdi Mehrpooya
• Original Assignee: Ali Vatani, Mehdi Mehrpooya
• Inventors: Vatani, Ali, Mehrpooya, Mehdi
• Application Number:
  US13/244,489
• Publication Number:
  US 20130074542A1
• Time in Patent Office: Days
• US Class Current: 62/621
• CPC Class Codes: F25J 2200/02 in a single 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 2200/50 using multiple (re-)boiler-condensers at different heights of the column
• CPC Class Codes: F25J 2200/94 Details relating to the withdrawal point
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2240/02 Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• 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 2270/60 Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• 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

Abstract

The various embodiments herein provide a method and system for a process configuration with internal refrigeration for light gas and a process configuration with external refrigeration system for rich gas. The self-refrigeration unit comprising an open-closed cycle of refrigeration provides a required refrigeration load and the external refrigeration unit provides a refrigeration load corresponding to variations in a feed composition percentage. The configuration with internal refrigeration system utilizes a slip stream from or near the bottom of the demethanizer as a mixed refrigerant.

Claims

1. An internal refrigeration method for separating a residue gas from an input gas to recover a natural liquid gas through a self-refrigeration process comprising steps of:

feeding an input gas into an internal refrigeration system;

condensing the input gas in a first multi-flow heat exchanger;

separating an output of the first multi-flow heat exchanger into a fluid stream and a gas stream using a first drum separator;

dividing the separated gas stream obtained from the first drum separator into a first gas part and a second gas part;

dividing the separated fluid stream obtained from the first drum separator into a first fluid part and a second fluid part;

passing the first fluid part obtained from the first drum separator to a middle section of a demethanizer column through a Joule-Thomson expansion valve for further fractionating;

passing the second fluid part obtained from the first drum separator to a top rectifying section in the demethanizer column through a second multi-flow heat exchanger and a first expansion valve to form a residue gas;

passing the first gas part to a work expander device;

passing a gas stream output of the work expander device to an area below a top rectifying section in the demethanizer column as an expander discharge;

passing the second gas part through the second multi-flow heat exchanger and a second expansion valve to the top rectifying section in the demethanizer column to form a reflux liquid;

passing the residue gas from the top rectifying section of the demethanizer column through the second multi-flow heat exchanger and the first multi-flow heat exchanger to a first compressor for further compression, and wherein the first compressor compresses the residue gas using a work extracted from the expander device;

passing a compressed residue gas output from the first compressor to a second compressor for further compressing the residue gas;

passing the further compressed residue gas through a first air cooler;

forwarding an output of the first cooler as a gas refrigerant;

stripping off volatile components from a liquid collected at a bottom portion of the demethanizer column by circulating liquids from four liquid draw trays provided in the bottom portion of the demethanizer column through the first multi-flow heat exchanger and the second multi-flow heat exchanger and collecting back the liquids at the demethanizer column; and

recovering the liquids from a bottom portion of the demethanizer column.

2. The method according to claim 1, wherein a step of stripping off volatile components from the liquid collected at the bottom portion of the demethanizer column comprises:

drawing a liquid from a first liquid tray and passing through the second multi-flow heat exchanger before being collected back at the demethanizer;

drawing a liquid from a second liquid tray and passing through the second multi-flow heat exchanger before being collected back at the demethanizer, wherein a direction of flow of the liquid from the first liquid tray through the second multi-flow heat exchanger and a direction of flow of the liquid from the second liquid tray through the second multi-flow heat exchanger are mutually opposite;

drawing a liquid from a third liquid tray and passing through the first multi-flow heat exchanger before being collected back at the demethanizer;

drawing a liquid from a fourth liquid tray and passing through the first multi-flow heat exchanger before being collected back at the demethanizer, wherein a direction of flow of the liquid from the third liquid tray through the first multi-flow heat exchanger and a direction of flow of the liquid from the fourth liquid tray through the first multi-flow heat exchanger are mutually opposite.

3. The method according to claim 2, wherein step of drawing liquid from the fourth liquid tray and passing through the multi-flow heat exchanger before being collected at the demethanizer column comprises:

passing a liquid drawn from the fourth tray through the first multi-flow heat exchanger;

passing an output of the first multi-flow heat exchanger to a second drum separator through a third expansion valve;

feeding a vapor output from the second drum to a first stage of a third compressor;

passing an output of the third compressor to a second air cooler through a third multi-flow heat exchanger;

forwarding an output of the second air cooler to a third drum separator for dividing the output of the second air cooler into a vapor part and a liquid part;

dividing the liquid part obtained from the second air cooler into a third liquid part and a fourth liquid part;

combining the vapor part and the third liquid part obtained from the third drum separator;

forwarding the combined the vapor part and the third liquid part obtained from the third drum separator to the demethanizer;

passing the fourth liquid part obtained from the third drum separator to the third multi-flow heat exchanger through a fourth expansion valve;

dividing an output of the third multi-flow heat exchanger into a fifth liquid part and a sixth liquid part;

passing the fifth liquid part from the output of the third multi-flow heat exchanger to the second drum separator;

feeding the sixth liquid part from the output of the third multi-flow heat exchanger to a fourth drum separator to obtain a vaporized liquid and a non vaporized liquid;

forwarding the vaporized liquid obtained from the fourth drum separator to a second stage of the third compressor;

combining and forwarding the non-vaporized liquid from the fourth drum separator and the non-vaporized liquid from the second drum separator to the demethanizer.

4. The method according to claim 1, wherein the input gas is a light gas containing a low amount of hydrocarbons that are converted into a natural gas liquid.

5. The method according to claim 1, wherein the natural gas liquid has a lower volatility degree as compared to that of the residue gas.

6. A method of external refrigeration for separating a residue gas from an input gas to recover a natural liquid gas through a propane-refrigeration process comprising steps of:

feeding an input gas into an internal refrigeration system;

condensing the input gas in a first multi-flow heat exchanger;

separating an output of the first multi-flow heat exchanger into a fluid stream and a gas stream using a first drum separator;

dividing the separated gas stream obtained from the first drum separator into a first gas part and a second gas part;

dividing the separated fluid stream obtained from the first drum separator into a first fluid part and a second fluid part;

passing the first fluid part obtained from the first drum separator to a middle section of a demethanizer column through a Joule-Thomson expansion valve for further fractionating;

passing the second fluid part obtained from the first drum separator to a top rectifying section in the demethanizer column through a second multi-flow heat exchanger and a first expansion valve to form a residue gas;

passing the first gas part to a work expander device;

passing a gas stream output of the work expander device to an area below a top rectifying section in the demethanizer column as an expander discharge;

passing the second gas part through the second multi-flow heat exchanger and a second expansion valve to the top rectifying section in the demethanizer column to form a reflux liquid;

passing the residue gas from the top rectifying section of the demethanizer column through the second multi-flow heat exchanger and the first multi-flow heat exchanger to a first compressor for further compression, and wherein the first compressor compresses the residue gas using a work extracted from the expander device;

passing a compressed residue gas output from the first compressor to a second compressor for further compressing the residue gas;

passing the further compressed residue gas through a first air cooler;

forwarding an output of the first cooler as a gas refrigerant;

stripping off volatile components from a liquid collected at a bottom portion of the demethanizer column by circulating liquids from four liquid draw trays provided in the bottom portion of the demethanizer column through the first multi-flow heat exchanger and the second multi-flow heat exchanger and collecting back the liquids at the demethanizer column;

recovering the liquids from a bottom portion of the demethanizer column; and

providing an external refrigeration process using liquid propane.

7. The method according to claim 6, wherein a step of stripping off volatile components from the liquid collected at the bottom portion of the demethanizer column comprises:

drawing a liquid from a first liquid tray and passing through the second multi-flow heat exchanger before being collected back at the demethanizer;

drawing a liquid from a second liquid tray and passing through the second multi-flow heat exchanger before being collected back at the demethanizer, wherein a direction of flow of the liquid from the first liquid tray through the second multi-flow heat exchanger and a direction of flow of the liquid from the second liquid tray through the second multi-flow heat exchanger are mutually opposite;

drawing a liquid from a third liquid tray and passing through the first multi-flow heat exchanger before being collected back at the demethanizer;

drawing a liquid from a fourth liquid tray and passing through the first multi-flow heat exchanger before being collected back at the demethanizer, wherein a direction of flow of the liquid from the third liquid tray through the first multi-flow heat exchanger and a direction of flow of the liquid from the fourth liquid tray through the first multi-flow heat exchanger are mutually opposite.

8. The method according to claim 6, wherein a step of providing external refrigeration using propane comprising steps of:

feeding a compressed liquid propane from a third compressor into a second air cooler;

forwarding an output of the second air cooler to a second drum separator through a third expansion valve;

passing a liquid propane output from the second drum separator through a fourth expansion valve;

forwarding a vapor gas output of liquid propane from the second drum separator to the third stage of a third compressor passing an output liquid propane passed from the second drum separator through the fourth expansion valve;

dividing an output liquid propane passed through the fourth expansion valve into a first liquid propane part and a liquid propane part;

feeding the first liquid propane part output from the fourth expansion valve to a first multi-flow heat exchanger for providing a required refrigeration for cooling the feed gas;

forwarding the first liquid propane part output from the first multi-flow heat exchanger to a third drum separator;

feeding the second liquid propane part output from the fourth expansion valve to the third drum separator directly through a sixth expansion valve;

forwarding a vapor gas output of the third drum separator to a second stage of the third compressor;

feeding a non vaporized liquid output from the third drum separator to a fourth drum separator after passing the non vaporized liquid output from the third drum separator through a seventh expansion valve, the second multi-flow heat exchanger and the first multi-flow heat exchanger;

passing a vaporized output from the fourth drum separator to a first stage of the third compressor; and

forwarding a liquid propane output from the fourth drum separator as an external refrigerant.

9. A system for separating a residue gas from an input gas to recover a natural liquid gas comprising:

a self refrigeration unit comprising an open-closed cycle of refrigeration; and

an external refrigeration unit;

wherein the self-refrigeration unit comprising an open-closed cycle of refrigeration provides a required refrigeration load and wherein the external refrigeration unit provides a refrigeration load corresponding to variations in a feed composition percentage.