Method and system for producing a liquefied natural gas product

1 . A method for producing a liquefied natural gas (LNG) product, comprising:

providing a feed natural gas (NG) containing methane and at least ethane, propane, butane and pentane as higher hydrocarbons,

cooling the feed natural gas (NG) to a first temperature level in a first cooling step using a first mixed refrigerant (WMR),

after the first cooling step, subjecting the feed natural gas (NG) at least in part to counter-current absorption in an absorber using an absorption liquid, in which a gas fraction depleted in the higher hydrocarbons is formed, and

cooling at least a part of the gas fraction formed in the counter-current absorption to a second temperature level in a second cooling step and liquifying the at least a part of the gas fraction formed in the counter-current absorption using a second mixed refrigerant (CMR) to form the liquefied natural gas (LNG) product,

wherein

the absorption liquid is formed from another part of the gas fraction formed in the counter-current absorption, which is condensed and returned to the counter-current absorption,

a sump product containing at least ethane, propane, butane and pentane is formed in the counter-current absorption,

the sump product formed in the counter-current absorption is directly fed to a first separation column and subjected, at least in part, to a first fractionation in which a sump product low in propane and containing butane and pentane, along with an overhead product, are formed,

the sump product formed in the first fractionation is subjected, at least in part, to a second fractionation in a second separation column in which an overhead product low in propane and containing butane, along with a sump product, are formed, and

the overhead product formed in the second fractionation is at least partially added to the first mixed refrigerant (WMR).

2 . The method according to claim 1 , wherein the overhead product formed in the first fractionation contains ethane and propane, wherein at least a part of the overhead product formed in the first fractionation is partially condensed to obtain a condensate, and wherein the condensate is partially or completely used as a return flow in the counter-current absorption.

3 . The method according to claim 2 , wherein the partial condensation of the at least a part of the overhead product formed in the first fractionation comprises cooling using the first mixed refrigerant (WMR).

4 . The method according to claim 2 , wherein a first fraction of the condensate obtained from the partial condensation of the at least part of the overhead product obtained in the first fractionation is used, in a first operating mode, as a return flow in the counter-current absorption, and a second fraction of the at least part of the overhead product obtained in the first fractionation is subjected to a third fractionation in a third separation column in which an overhead product low in propane and containing ethane and a sump product low in ethane and containing propane are formed.

5 . The method according to claim 4 , wherein a partial flow of the first mixed refrigerant is used for overhead cooling in the third fractionation.

6 . The method according to claim 4 , wherein the overhead product formed in the third fractionation is used at least partially liquefied as refrigerant.

7 . The method according to claim 1 , wherein the first (WMR) and second (CMR) mixed refrigerants are compressed using a common drive or separate drives.

8 . The method according to claim 1 , wherein the first cooling step comprises the use of a first heat exchanger, and the second cooling step comprises the use of a second heat exchanger.

9 . The method according to claim 1 , wherein the feed natural gas (NG) has 75 to 98 mole percent methane, 2 to 20 mole percent ethane, 0.5 to 5 mole percent propane, 0.3 to 3 mole percent butane, and 0.1 to 2 mole percent pentane and higher hydrocarbons.

10 . The method according to claim 1 , wherein the counter-current absorption is carried out at a pressure level of 40 to 70 bar.

11 . A system for producing a liquefied natural gas (LNG) product comprising:

means to provide a feed natural gas (NG) containing methane and at least ethane, propane, butane and pentane as higher hydrocarbons,

means to cool the feed natural gas (NG) to a first temperature level in a first cooling step using a first mixed refrigerant (WMR),

after the first cooling step, means to subject the feed natural gas (NG), at least in part, to counter-current absorption using an absorption liquid, in which counter-current absorption a gas fraction depleted in the higher hydrocarbons is formed,

means to cool a part of the gas fraction formed in the counter-current absorption to a second temperature level in a second cooling step using a second mixed refrigerant (CMR) and liquefying the part of the gas fraction formed in the counter-current absorption to form the liquefied natural gas (LNG),

means for condensing another part of the gas fraction formed in the counter-current absorption to form the absorption liquid and means to return the formed absorption liquid to the counter-current absorption,

means for removing a sump product containing at least ethane, propane butane and pentane from the counter-current absorption,

means to directly feed at least part of the sump product formed in the counter-current absorption to a means for a first fractionation wherein a sump product low in propane and containing butane and pentane, along with an overhead product, are formed from the at least part of the sump product formed in the counter-current absorption,

means to subject the sump product formed in the first fractionation, at least in part, to a second fractionation, in which an overhead product low in propane and containing butane, along with a sump product, are formed, and

means to add the overhead product formed in the second fractionation at least partially to the first mixed refrigerant and/or to the second mixed refrigerant (WMR, CMR).

12 . A system for producing a liquefied natural gas (LNG) product according to the method of claim 1 comprising:

means to provide a feed natural gas (NG) containing methane and at least ethane, propane, butane and pentane as higher hydrocarbons,

means to cool the feed natural gas (NG) to a first temperature level in a first cooling step using a first mixed refrigerant (WMR),

after the first cooling step, means to subject the feed natural gas (NG), at least in part, to counter-current absorption using an absorption liquid, in which counter-current absorption a gas fraction depleted in the higher hydrocarbons is formed, and

means to cool a part of the gas fraction formed in the counter-current absorption to a second temperature level in a second cooling step using a second mixed refrigerant (CMR) and liquefying the part of the gas fraction formed in the counter-current absorption to form the liquefied natural gas (LNG),

means for condensing another part of the gas fraction formed in the counter-current absorption to form the absorption liquid and means to return the formed absorption liquid to the counter-current absorption,

means for removing a sump product containing at least ethane, propane butane and pentane from the counter-current absorption,

means to directly feed at least part of the sump product formed in the counter-current absorption to a means for a first fractionation wherein a sump product low in propane and containing butane and pentane, along with an overhead product, are formed from the at least part of the sump product formed in the counter-current absorption,

means to subject the sump product formed in the first fractionation, at least in part, to a second fractionation, in which an overhead product low in propane and containing butane, along with a sump product, are formed, and

to add the overhead product formed in the second fractionation at least partially to the first mixed refrigerant and/or to the second mixed refrigerant (WMR, CMR).

13 . The method according to claim 1 , wherein the counter-current absorption is carried out at a temperature level of −30 to −60° C. at a head of the absorber.

14 . The method according to claim 1 , wherein the first fractionation is carried out at a pressure level of 10 to 25 bar.

15 . The method according to claim 1 , wherein the first fractionation is carried out at a temperature level of 20 to 60° C. at a head of the first separation column.

16 . The method according to claim 1 , wherein the second fractionation is carried out at a pressure level of 3 to 7 bar.

17 . The method according to claim 1 , wherein the second fractionation is carried out at a temperature level of 20 to 60° C. at a head in the second separation column.

18 . The method according to claim 4 , wherein the third fractionation is carried out at a pressure level of 20 to 30 bar.

19 . The method according to claim 4 , wherein the third fractionation is carried out at a temperature level of −20 to −50° C. at a head in the third separation column.

20 . The method according to claim 1 , wherein, in the first cooling step, at least a part of the overhead product formed in the first fractionation and the second mixed refrigerant (CMR) are cooled using the first mixed refrigerant (WMR).

21 . The method according to claim 20 , wherein, after the first cooling step, a portion of the part of the overhead product formed in the first fractionation is cooled in the second cooling step using the second mixed refrigerant (CMR).

22 . The method according to claim 1 , wherein the method does not include a separation column for separating a methane-rich flow from the feed natural gas (NG).