Combined synthesis gas separation and LNG production method and system

• US 9,243,842 B2
• Filed: 02/15/2008
• Issued: 01/26/2016
• Est. Priority Date: 02/15/2008
• Status: Active Grant

• Current Assignee: Black & Veatch International Company (Black & Veatch Corporation)
• Original Assignee: Black & Veatch Corporation
• Inventors: Price, Brian C.
• Primary Examiner(s): Jules, Frantz
• Assistant Examiner(s): Mengesha, Webeshet
• Application Number:
  US12/069,962
• Publication Number:
  US 20090205367A1
• Time in Patent Office: 2,902 Days
• Field of Search: 626/20, 629/20, 629/31, 629/34, 62611-613, 62617-619, 626/23
• US Class Current: 1/1
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2215/04 Recovery of liquid products
• 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 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/42 Quasi-closed internal or closed external nitrogen refrigeration cycle
• CPC Class Codes: F25J 2270/66 Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 3/0223 H2/CO mixtures, i.e. synthesis gas; Water gas or shifted synthesis gas production of carbon monoxide containing gas in general C01B32/40, C10J, C10K; production of hydrogen containing gas C01B3/00
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0271 separation of H2/CO mixtures, i.e. of synthesis gas production of carbon monoxide containing gas in general C01B32/40, C10J, C10K, production of hydrogen containing gas C01B3/00

Abstract

A method and system for the separation of a synthesis gas and methane mixture which contains carbon monoxide, hydrogen and methane with the process producing synthesis gas and liquid natural gas (LNG).

Claims

1. A method for co-producing a syngas stream and a liquefied natural gas (LNG) stream from a feed gas stream containing carbon monoxide, hydrogen and methane, the method comprising:

a) cooling a feed gas stream comprising carbon monoxide, hydrogen, and methane and having a pressure less than 6 MPa via indirect heat exchange with a mixed refrigerant stream in a first closed-loop refrigeration cycle to provide a cooled mixed gas and liquid stream, wherein the cooled mixed gas and liquid stream has a temperature from −

145 to −

160°

C.;

b) separating at least a portion of the cooled mixed gas and liquid stream in a fractionator to thereby produce a carbon monoxide and hydrogen enriched overhead vapor stream and a liquefied bottoms stream enriched in methane;

c) cooling at least a portion of the overhead vapor stream via indirect heat exchange with a nitrogen refrigerant stream in an overhead heat exchanger of a second closed-loop refrigeration cycle to thereby provide a two-phase overhead stream and a warmed nitrogen refrigerant stream;

d) separating the two-phase overhead stream into a predominantly liquid portion and a predominantly vapor portion;

e) compressing at least a portion of the predominantly vapor portion to thereby provide a compressed vapor stream;

f) introducing at least a portion of the predominantly liquid portion into the fractionator as a reflux stream and using at least a portion of the compressed vapor stream to perform at least a part of the cooling of step (a);

g) producing a vapor phase syngas product stream and a liquid LNG product stream, wherein the syngas product stream comprises at least a portion of the predominantly vapor portion of the two-phase overhead stream separated in step (d), wherein the LNG product stream comprises at least a portion of the liquefied bottoms stream withdrawn from the fractionator,

h) subsequent to the cooling of step c), compressing the warmed nitrogen refrigerant stream to thereby provide a compressed nitrogen refrigerant stream;

i) cooling at least a portion of the compressed nitrogen refrigerant stream via indirect heat exchange to provide a cooled nitrogen refrigerant stream, wherein the cooling is performed with at least one of at least a portion of the mixed refrigerant stream used during the cooling of step a) and at least a portion of the compressed vapor stream;

j) expanding at least a portion of the cooled nitrogen refrigerant stream to provide a cooled, expanded nitrogen refrigerant stream, wherein the cooled, expanded nitrogen refrigerant stream is used to cool the overhead vapor stream during the cooling of step c); and

k) after heat exchange with the overhead vapor stream, passing the warmed nitrogen refrigerant stream from the outlet of the overhead heat exchanger to the compressor.

2. The method of claim 1 further comprising prior to the separating of step (b), introducing at least a portion of the cooled mixed gas and liquid stream to a cold separator to separate the stream into an overhead gas stream and a bottoms liquid stream;

expanding the overhead gas stream to form an expanded gas stream; and

introducing the expanded gas stream and the bottoms liquid stream into the fractionator to undergo the separating of step (b).

3. The method of claim 1 wherein said cooling of step (a) comprises cooling the feed gas stream to a temperature in the range of from −

70 to −

100°

C. in a first heat exchange passageway of a refrigeration heat exchanger to provide a cooled feed gas stream and subsequently cooling the cooled feed gas stream to a temperature in the range of from −

145°

C. to −

160°

C. in a second heat exchange passageway of the refrigeration heat exchanger.

4. The method of claim 1 wherein the syngas product stream has a temperature of at least 30°

C. and a pressure of at least 2.4 MPa.

5. The method of claim 1 further comprising cooling at least a portion of the liquefied bottoms stream enriched in methane via indirect heat exchange with at least a portion of the carbon monoxide and hydrogen enriched overhead vapor stream withdrawn from the fractionator.

6. A method for co-producing a syngas stream and a liquefied natural gas (LNG) stream from a feed gas comprising carbon monoxide, hydrogen, and methane, the process comprising:

(a) cooling and partially condensing a feed gas stream comprising carbon monoxide, hydrogen, and methane in a first heat exchange passageway of a primary heat exchanger via indirect heat exchange with a first refrigerant stream to thereby provide a cooled two-phase feed stream;

(b) further cooling the cooled two-phase feed stream in a second heat exchange passageway of the primary heat exchanger via indirect heat exchange with the first refrigerant stream to thereby provide a further cooled feed stream;

(c) dividing the further cooled feed stream into a first fraction and a second fraction;

(d) separating the first fraction in a first vapor-liquid separator to thereby provide a first vapor stream rich in hydrogen and carbon monoxide and a first liquid stream rich in methane;

(e) simultaneously with the separating of step (d), introducing the second fraction into a fractionator;

(f) expanding the first vapor stream withdrawn from the first vapor-liquid separator to thereby provide an expanded vapor stream;

(g) introducing the expanded vapor stream and the first liquid stream in the fractionator;

(h) withdrawing a second vapor stream and a second liquid stream from the respective upper and lower portions of the fractionator;

(i) compressing at least a portion of the second vapor stream withdrawn from the fractionator to thereby provide a compressed vapor stream;

(j) using at least a portion of the compressed vapor stream to perform at least a portion of the cooling of step (a);

(k) producing a syngas product stream enriched in carbon monoxide and hydrogen, wherein the syngas product stream comprises at least a portion of the compressed vapor stream;

(l) cooling at least a portion of the second liquid stream withdrawn from the lower portion of the fractionator via indirect heat exchange with at least a portion of the second vapor stream to provide a warmed vapor stream and a cooled second liquid stream, wherein the cooling is performed prior to the compressing of step (i); and

(m) recovering an LNG product stream, wherein and the LNG product stream comprises at least a portion of the cooled second liquid stream.

7. The method of claim 6, wherein the vapor portion of the cooled two-phase feed stream comprises predominantly hydrogen and carbon monoxide and the liquid portion of the two-phase fluid stream comprises predominantly methane, wherein the temperature of the first fraction introduced into the vapor-liquid separator is in the range of from −

145°

C. to −

160°

C.

8. The method of claim 6, wherein the temperature of the second vapor stream withdrawn from the fractionator is less than −

160°

C.

9. The method of claim 6, wherein the expanded vapor stream is introduced into the fractionator at a higher vertical elevation than the first liquid stream.

10. The method of claim 6, further comprising, cooling at least a portion of the second vapor stream via indirect heat exchange with a nitrogen refrigerant stream and separating the resulting cooled vapor stream into a liquid portion and a vapor portion in a fractionator reflux drum, wherein at least a portion of the liquid portion of the cooled vapor stream is refluxed into an upper portion of the fractionator.

11. The method of claim 10, further comprising prior to the cooling of the second vapor stream, expanding at least a portion of the nitrogen refrigerant to provide an expanded nitrogen refrigerant stream, wherein at least a portion of the expanded nitrogen refrigerant stream is used to carry out the cooling of the second vapor stream, wherein the temperature of the expanded nitrogen refrigerant stream prior to the cooling is in the range of from −

175°

C. to −

198°

C.

12. The method of claim 6, wherein at least a portion of the cooling of step (a) is carried out via indirect heat exchange with mixed refrigerant stream and nitrogen refrigerant stream.

13. A system for co-producing a syngas stream and a liquefied natural gas (LNG) stream, the system comprising:

a main heat exchanger comprising a first cooling pass for cooling an incoming feed gas stream, the first cooling pass comprising a feed gas inlet and a cool fluid outlet, and a second cooling pass for further cooling the feed gas stream, the second cooling pass comprising a cool fluid inlet and a further cooled fluid outlet, the cool fluid inlet of the second heat exchange pass in fluid flow communication with the cool fluid outlet of the first cooling pass;

a vapor-liquid separator for separating the cooled feed gas into a vapor stream and a liquid stream, the vapor-liquid separator comprising a cool fluid inlet, a first vapor outlet, and a first liquid outlet, the cool fluid inlet in fluid communication with the cool fluid outlet of the first cooling pass;

a first expansion device for expanding at least a portion of the vapor stream exiting the vapor-liquid separator, the first expansion device comprising a high pressure fluid inlet and a low pressure fluid outlet, the high pressure fluid inlet in fluid communication with the first vapor outlet of the vapor-liquid separator;

a fractionator for separating at least a portion of the vapor and liquid streams withdrawn from the vapor-liquid separator, the fractionator comprising an upper fluid inlet, a lower fluid inlet, a cooled fluid inlet, a second vapor outlet, and a second liquid outlet, the upper fluid inlet in fluid communication with the low pressure fluid outlet of the first expansion device and the lower fluid inlet in fluid communication with the first liquid outlet of the vapor-liquid separator, and the cooled fluid inlet in fluid communication with the further cooled fluid outlet of the second cooling pass;

a compressor for compressing at least a portion of the vapor stream withdrawn from the fractionator, the compressor comprising a high pressure outlet and a low pressure inlet in fluid communication with the second vapor outlet of the fractionator; and

a multi-loop refrigeration system comprising—

a closed-loop mixed refrigerant cycle comprising a mixed refrigerant cooling pass having a warm mixed refrigerant inlet and a cooled mixed refrigerant outlet;

a mixed refrigerant warming pass having a cool mixed refrigerant inlet and a warmed mixed refrigerant outlet; and

a mixed refrigerant expansion valve having a high pressure mixed refrigerant inlet and a low pressure mixed refrigerant outlet, the high pressure mixed refrigerant inlet in fluid communication with the cooled mixed refrigerant outlet of the mixed refrigerant cooling pass and the low pressure mixed refrigerant outlet in fluid communication with the cool mixed refrigerant inlet of the mixed refrigerant warming pass; and

a closed-loop nitrogen refrigerant cycle comprising—

a condenser having a warm vapor inlet and a cool fluid outlet and a cool nitrogen inlet and a warm nitrogen outlet, the warm vapor inlet in fluid communication with the second vapor outlet of the fractionator;

a nitrogen compressor for compressing the warmed nitrogen refrigerant, the nitrogen compressor having a low pressure nitrogen inlet and a high pressure nitrogen outlet, the low pressure nitrogen inlet in fluid communication with the warm nitrogen outlet of the condenser;

a nitrogen cooling pass disposed within the main heat exchanger for cooling the compressed nitrogen refrigerant, the nitrogen cooling pass comprising a warm nitrogen inlet and a cooled nitrogen outlet, the warm nitrogen inlet of the nitrogen cooling pass in fluid communication with the high pressure nitrogen outlet of the nitrogen compressor; and

a nitrogen expansion device for expanding the cooled nitrogen from the nitrogen cooling pass, the nitrogen expansion device having a high pressure nitrogen inlet and a low pressure nitrogen outlet, the high pressure nitrogen inlet in fluid communication with the cooled nitrogen outlet of the nitrogen cooling pass and the low pressure nitrogen outlet in fluid communication with the cool nitrogen inlet of the condenser.

14. The system of claim 13, wherein the fractionator further comprises a reflux inlet, wherein the cool fluid outlet of the condenser is in fluid communication with the reflux inlet of the fractionator.

15. The system of claim 13, further comprising a second heat exchanger for cooling the liquid stream withdrawn from the liquid outlet of the fractionator, the heat exchanger comprising a warm liquid inlet, a cool liquid outlet, a cool fluid inlet, and a warm fluid outlet, the warm liquid inlet in fluid communication with the lower liquid outlet of the fractionator, the cool fluid inlet in fluid communication with the cool vapor outlet of the condenser, the cool liquid outlet configured to discharge an LNG product stream.

16. The system of claim 15, further comprising a syngas warming pass having a cool syngas inlet and a warm syngas outlet, the syngas warming pass disposed within the main heat exchanger, the cool syngas inlet in fluid communication with the high pressure outlet of the compressor and the low pressure outlet of the compressor being in fluid communication with the warm fluid outlet of the second heat exchanger, the warm syngas outlet of the syngas warming pass being configured to discharge a syngas product stream.