METHOD FOR FRACTIONATING A STREAM OF CRACKED GAS TO OBTAIN AN ETHYLENE-RICH CUT AND A STREAM OF FUEL, AND RELATED INSTALLATION

• US 20120266630A1
• Filed: 10/26/2010
• Published: 10/25/2012
• Est. Priority Date: 10/27/2009
• Status: Active Grant

• Current Assignee: Technip France (TechnipFMC, plc)
• Original Assignee: Technip France (TechnipFMC, plc)
• Inventors: Laugier, Jean-Paul, Simon, Yvon
• Granted Patent: US 10,767,924 B2
• Time in Patent Office: Days
• US Class Current: 62/613
• CPC Class Codes: C10G 2400/20 C2-C4 olefins
• CPC Class Codes: C10G 70/04 by physical processes
• CPC Class Codes: F16D 2023/141 characterised by using a fork; Details of forks
• CPC Class Codes: F16D 21/00 Systems comprising a plurality of actuated clutches for synchronisation F16D23/04
• CPC Class Codes: F16D 23/12 Mechanical clutch-actuating mechanisms arranged outside the clutch as such specific for combined clutches F16D21/00; mechanisms specific for synchronisation F16D23/02
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/04 Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/06 with multiple gas expansion loops
• 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 2290/34 Details about subcooling of liquids
• 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 3/0252 separation of hydrogen production of hydrogen containing gas in general C01B3/00, e.g. separation of hydrogen or hydrogen containing gases form gaseous mixtures at low temperatures C01B3/506
• CPC Class Codes: F25J 3/062 : Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: Y02P 30/40 : Ethylene production

Abstract

This method includes introducing a downstream stream (140) of cracked gas from a downstream heat exchanger (58) in a downstream separator (60) and recovering, at the head of the downstream separator (60), a high-pressure fuel gas stream (144).

The method includes the passage of the stream (144) of fuel through the downstream exchanger (58) and an intermediate exchanger (50, 54) to form a reheated high-pressure fuel stream (146), the expansion of the reheated high-pressure fuel stream (146) in at least a first dynamic expander (68) and the passage of the partially expanded fuel stream (148) from the intermediate exchanger (50, 54) in a second dynamic expander (70) to form an expanded fuel stream (152).

The expanded fuel stream (152) from the second dynamic expander (70) is reheated in the downstream heat exchanger (58) and in the intermediate heat exchanger (50, 54).

Claims

1. A method for fractionating a stream of cracked gas from a hydrocarbon pyrolysis installation to obtain an ethylene-rich cut and a stream of fuel having a low C₂⁺ hydrocarbon content, the method comprising the following steps:

upstream cooling and partial condensation of a stream of raw cracked gas by at least partial heat exchange with a coolant fluid circulating in a first external refrigeration cycle and separation of an upstream liquid in at least one upstream drum to form an intermediate stream of cracked gas pre-cooled to a first temperature;

intermediate cooling and partial condensation of the intermediate stream of cracked gas in at least one intermediate heat exchanger and separation of an intermediate liquid in at least one intermediate separation drum to form a downstream stream of cracked gas cooled to a second temperature lower than the first temperature;

downstream cooling and partial condensation of the downstream stream of cracked gas in at least one downstream heat exchanger to a third temperature lower than the second temperature;

introducing the partially condensed downstream stream of cracked gas obtained from the downstream heat exchanger in a downstream separator;

recovering, at the head of the downstream separator, a high-pressure gas stream of fuel, with a low C₂⁺ hydrocarbon content, and recovering, at the bottom of the downstream separator, a downstream liquid, with a high C₂⁺ hydrocarbon content;

passing the high-pressure fuel stream through the downstream exchanger and the intermediate exchanger to form a heated high-pressure fuel stream;

expansion of the reheated high-pressure fuel stream in at least a first dynamic expander to obtain a partially expanded fuel stream;

heating the partially expanded fuel stream through the downstream exchanger and the intermediate exchanger;

processing at least one liquid obtained during the upstream cooling, intermediate cooling and downstream cooling steps to form the ethylene-rich cut;

wherein the method comprises the following steps;

passage of the partially expanded flow of fuel from the intermediate exchanger into a second dynamic expander to form an expanded stream of fuel;

reheating the expanded fuel stream from the second dynamic expander in the downstream heat exchanger and in the intermediate heat exchanger;

compressing the reheated expanded fuel stream in at least one compressor coupled to at least one turbo-expander of the first dynamic expander and/or the second dynamic expander to form the stream of fuel having a low C₂⁺ hydrocarbon content.

2. The method according to claim 1, wherein the thermal power needed to cool the intermediate stream of cracked gas towards the second temperature is provided in the intermediate heat exchanger by heat exchange with the high-pressure fuel stream, by heat exchange with the partially expanded fuel stream and by heat exchange with the expanded fuel stream, without heat exchange with an external coolant fluid circulating in a refrigeration cycle.

3. The method according to claim 2, wherein the thermal power needed to cool the downstream stream of cracked gas to the third temperature is provided in the downstream heat exchanger by heat exchange with the high-pressure fuel stream, by heat exchange with the partially expanded fuel stream and by heat exchange with the expanded fuel stream, without heat exchange with an external coolant fluid circulating in a refrigeration cycle.

4. The method according to claim 1, wherein it comprises the recovery of the downstream liquid and reheating thereof through the downstream heat exchanger, and the intermediate heat exchanger,

the downstream liquid being sub-cooled in the downstream heat exchanger before it is reheated in the downstream heat exchanger, then in the intermediate heat exchanger.

5. The method according to claim 1, wherein all of the reheated high-pressure fuel stream from the intermediate exchanger is introduced into the first dynamic expander, all of the reheated partially expanded fuel current from the intermediate exchanger being introduced into the second dynamic expander.

6. The method according to claim 1, wherein at least a fraction of an intermediate liquid recovered in the intermediate cooling step is reheated in the downstream heat exchanger and in the intermediate heat exchanger.

7. The method according to claim 6, wherein the fraction of the intermediate liquid recovered in the intermediate cooling step is sub-cooled in the downstream heat exchanger before being reintroduced into the downstream heat exchanger, then in the intermediate heat exchanger.

8. The method according to claim 4, wherein at least one of the at least one fraction of the intermediate liquid and the downstream liquid evaporates during its passage in the downstream heat exchanger and in the intermediate heat exchanger to form a gas recirculation flow, the recirculation flow being mixed with the stream of raw cracked gas, before the passage of the raw cracked gas in the at least one compressor.

9. The method according to claim 1, wherein the processing step comprises the introduction of at least one stream formed from said upstream liquid, intermediate liquid and/or downstream liquid in a fractionating column and the production in the fractionating column of a stream with a high ethylene content intended to form the ethylene-rich cut.

10. The method according to claim 9, wherein in the processing step, the upstream liquid and the intermediate liquid are introduced into the fractionating column.

11. The method according to claim 1, wherein the overhead stream from the fractionating column is completely conveyed towards the upstream heat exchanger and advantageously towards an upstream reheating exchanger, before being mixed with the raw cracked gas, without a fraction of the overhead stream being condensed to be sent to the fractionating column as reflux.

12. The method according to claim 1, wherein the first dynamic expander and the second dynamic expander each comprise at least one dynamic turbo-expander, advantageously each comprise between two and three dynamic turbo-expanders.

13. The method according to claim 1, wherein the molar content of hydrogen in the high-pressure fuel stream is greater than 75%.

14. The method according to claim 1, wherein the first temperature is below −

63°

C., in that the second temperature is below −

85°

C., and in that the third temperature is below −

120°

C.

15. The method according to claim 1, wherein the first refrigeration cycle is provided without a heat level between 95°

C. and −

102°

C. between the upstream drum and the downstream drum.

16. An installation for fractionating a stream of cracked gas from a hydrocarbon pyrolysis installation to obtain an ethylene-rich cut and a stream of fuel having a low C₂⁺ hydrocarbon content, the installation comprising:

upstream means for cooling and partial condensation of a stream of raw cracked gas including at least partial heat exchange means with a first external refrigeration cycle and means for separating an upstream liquid including at least one upstream drum to form an intermediate stream of cracked gas pre-cooled to a first temperature;

intermediate means for cooling and partial condensation of the intermediate stream of cracked gas including at least one intermediate heat exchanger and means for separating an intermediate liquid including at least one intermediate separation drum to form a downstream stream of cracked gas cooled to a second temperature lower than the first temperature;

downstream means for cooling and at least partial condensation of the downstream stream of cracked gas including at least one downstream heat exchanger to cool the downstream stream of cracked gas to a third temperature lower than the second temperature;

a downstream separator and means for introducing the downstream stream of cracked gas from the downstream heat exchanger in the downstream separator;

means for recovering, at the head of the downstream separator, a high-pressure gas stream of fuel, with a low C₂⁺ hydrocarbon content, and means for recovering, at the bottom of the downstream separator, a downstream liquid with a high C₂⁺ hydrocarbon content;

means for passing the high-pressure fuel stream through the downstream exchanger and the intermediate exchanger to form a heated high-pressure fuel stream;

means for expanding the reheated high-pressure fuel stream including at least a first dynamic expander to form a partially expanded fuel stream;

means for reheating the partially expanded fuel stream through the downstream exchanger and the intermediate exchanger;

means for processing at least one liquid obtained from the upstream cooling means, intermediate cooling means and downstream cooling means to form the ethylene-rich cut;

wherein the installation comprises;

a second dynamic expander and means for passage of the partially expanded stream of fuel from the intermediate exchanger into the second dynamic expander to form an expanded stream of fuel;

means for reheating the expanded fuel stream from the second dynamic expander in the downstream heat exchanger and in the intermediate heat exchanger;

means for compressing the reheated expanded fuel stream including at least one compressor coupled to at least one turbo-expander of the first dynamic expander and/or the second dynamic expander to form the stream of fuel having a low C₂⁺ hydrocarbon content.