Liquefaction of a hydrocarbon-rich fraction
A process for liquefying and subcooling a hydrocarbon-rich fraction, particularly natural gas, is described wherein, once cooled down, the fraction is subjected to a partial condensation to remove heavy hydrocarbons, particularly benzene, by the steps of: a) the liquefied hydrocarbon-rich fraction is subcooled in a separate heat exchanger (normal mode), b) the supply of the liquefied hydrocarbon-rich fraction to the heat exchanger is interrupted at the latest when a defined solid deposition value in the heat exchanger is reached (cleaning mode), c) the solid in the heat exchanger is melted with a defrost gas and drawn off from the heat exchanger and d) the liquefied hydrocarbon-rich fraction is subsequently returned to the heat exchanger.
1. A process for liquefying and subcooling a hydrocarbon-rich fraction comprising:
a) providing a flow of a hydrogen-rich fraction;
b) cooling the hydrogen-rich fraction in a first heat exchanger to form a partially condensed fraction;
c) separating the partially condensed fraction to form a heavy hydrocarbons-containing liquid fraction and a hydrocarbon-rich gas fraction;
d) liquefying the hydrocarbon-rich gas fraction in a further heat exchanger to form a liquefied hydrocarbon-rich fraction;
wherein the method further comprises operating a separate heat exchanger comprising:
e) operating in a normal mode comprising
e1) the liquefied hydrocarbon-rich fraction in the separate heat exchanger to produce a subcooled hydrocarbon-rich fraction;
e2) monitoring an amount of solid deposition formed in the separate heat exchanger;
f) when the amount of solid deposition reaches a defined value, operating in a cleaning mode which comprises;
f1) interrupting the supply of the liquefied hydrocarbon-rich fraction to the separate heat exchanger at the latest when the amount of solid deposition value in the separate heat exchanger reaches a defined value, such that the separate heat exchanger switches to the cleaning mode;
f2) feeding a defrost gas into the the separate heat exchanger so that the solid deposition is melted to form a melted deposition;
f3) drawing off the melted deposition from the separate heat exchanger and
g) subsequently returning to operating the separate heat exchanger in the normal mode in which the liquefied hydrocarbon-rich fraction is returned to the separate heat exchanger to be subcooled.
2. The process according to claim 1 , wherein the hydrocarbon-rich fraction is natural gas.
3. The process according to claim 1 , wherein the heavy hydrocarbon is benzene.
4. The process according to claim 1 , wherein in step e) in the normal mode, the liquefied hydrocarbon-rich fraction is subcooled in the heat exchanger against at least one refrigerant stream and/or at least one mixed refrigerant stream, and in step f) in the cleaning mode said refrigerant stream and/or mixed refrigerant stream are also used to cool the hydrocarbon-rich fraction in the first and/or second heat exchangers.
5. The process according to claim 1 , wherein in steps b) and d) the hydrocarbon-rich fraction is liquefied and subcooled against at least one refrigeration cycle having a refrigerant, wherein a substream of the refrigerant is the defrost gas.
6. The process according to claim 1 wherein the cleaning mode of step e) further includes after the solid deposition in the heat exchanger has been melted purging passages of the heat exchanger in which the solid deposition occurs.
7. The process according to claim 4 , wherein the liquefied and subcooled hydrocarbon-rich fraction is sent to an intermediate storage; and the passages of the heat exchanger are purged by a supply of dry nitrogen and/or a boil-off gas fraction generated during the intermediate storage of the liquefied and subcooled hydrocarbon-rich fraction.
8. The process according to claim 1 , wherein cooling-down, liquefaction and subcooling of the hydrocarbon-rich fraction is carried out in helically coiled heat exchangers and/or welded plate exchangers.