NGL Recovery Methods and Configurations

• US 20100043488A1
• Filed: 07/20/2006
• Published: 02/25/2010
• Est. Priority Date: 07/25/2005
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John, Nielsen, Richard B., Graham, Curt
• Granted Patent: US 9,410,737 B2
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• 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 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/60 Methane
• CPC Class Codes: F25J 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• 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 2240/40 Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2280/02 Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• 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

Contemplated NGL plants include a feed gas bypass circuit through which a portion of the feed gas is provided downstream to a vapor portion of the feed gas to thereby increase turbo expander inlet temperature and demethanizer temperature. Contemplated configurations are especially advantageous for feed gases with relatively high carbon dioxide content as they entirely avoid carbon dioxide freezing in the demethanizer, provide additional power production by the turboexpander, and recover C2+ components to levels of at least 80% while achieving a low carbon dioxide content in the NGL product.

Claims

1. A plant comprising:

a feed gas separator that is configured to separate a feed gas into a liquid portion and a vapor portion;

a demethanizer fluidly coupled to the separator and configured to receive the vapor portion and the liquid portion;

a turboexpander configured to receive and expand at least part of the vapor portion in a location upstream of the demethanizer; and

a feed gas bypass circuit that is configured to provide part of the feed gas as a bypass gas to the vapor portion upstream of the demethanizer in an amount sufficient to prevent carbon dioxide freezing in the demethanizer and to reduce carbon dioxide content in a demethanizer bottom product.

2. The plant of claim 1 further comprising a control device that is configured to variably control flow of the bypass gas as a function of at least one of a temperature of the demethanizer and a temperature of a turboexpander inlet stream.

3. The plant of claim 1 further comprising a heat exchanger that is configured to cool another part of the feed gas using refrigeration content of a demethanizer overhead product to thereby form a demethanizer reflux stream.

4. The plant of claim 1 wherein the feed gas separator is configured to receive the bypass gas.

5. The plant of claim 1 further comprising a feed gas cooler that is configured to utilize refrigeration content of a demethanizer overhead for cooling at least a portion of the feed gas.

6. The plant of claim 1 further comprising a second bypass that is configured to use the chilling by at least a portion of a demethanizer overhead product to form the demethanizer reflux.

7. A control device, comprising:

a processing unit electronically coupled to a plurality of temperature sensors and a flow control valve;

wherein the plurality of temperature sensors are thermally coupled to at least one of a feed gas stream, a bypass gas stream, a vapor stream of a feed gas separator, and a demethanizer;

wherein the flow control valve is coupled to a feed gas bypass circuit that fluidly couples the feed gas stream with a vapor stream in or downstream from the feed gas separator; and

wherein the processing unit is configured such that, using the flow control valve, a flow rate of the feed gas through the bypass circuit is a function of a temperature in at least one of the demethanizer and the bypass gas stream.

8. The control device of claim 7 wherein the plurality of temperature sensors are thermally coupled to the bypass gas stream, the vapor stream of a feed gas separator, and the demethanizer.

9. The control device of claim 7 wherein the bypass circuit is configured to fluidly couple the feed gas stream with the vapor stream in the feed gas separator.

10. The control device of claim 7 wherein the processing unit is configured such that the flow rate of the feed gas through the bypass circuit is determined by the temperature in the demethanizer and the bypass gas stream.

11. The control device of claim 7 wherein the feed gas comprises ethane and wherein ethane recovery from a demethanizer bottom product is at least 80%.

12. The control device of claim 11 wherein the feed gas comprises carbon dioxide, and wherein the carbon dioxide content in the demethanizer bottom product is no more than 10 mol %.

13. A method of separating a feed gas, comprising:

providing a feed gas, and separating a first portion of the feed gas into a vapor portion and a liquid portion;

expanding part of the vapor portion in a turboexpander, and feeding the expanded part of the vapor portion into a demethanizer;

combining a second portion of the feed gas with the vapor portion upstream of the demethanizer in an amount sufficient to eliminate carbon dioxide freezing in the demethanizer.

14. The method of claim 13 further comprising a step of measuring a temperature of at least one of the vapor portion upstream of the demethanizer prior to combination, the vapor portion upstream of the demethanizer after combination, and a tray in the demethanizer.

15. The method of claim 14 further comprising a step of using a control device that controls the amount of the second portion of the feed gas that is combined with the vapor portion.

16. The method of claim 13 further comprising a step of cooling a third portion of the feed gas using refrigeration content from a demethanizer overhead product to thereby generate a demethanizer reflux.

17. The method of claim 13 wherein the demethanizer produces a demethanizer overhead product, and wherein the demethanizer overhead product is used to cool the feed gas.

18. The method of claim 13 wherein the demethanizer produces a demethanizer overhead product, and wherein part of the demethanizer overhead product is used to provide cooling to the feed gas that forms a lean reflux stream to the demethanizer.

19. The method of claim 13 wherein the demethanizer produces a NGL bottom product, and wherein at least 80% of ethane in the feed gas are recovered in the bottom product.

20. The method of claim 13 wherein the demethanizer produces a NGL bottom product, and wherein the carbon dioxide content in the NGL product is no more than 10 mol %.