To make circulatively usable nitrogen without discharging it and lower the cost of concentrating heavy carbon methane by efficiently utilizing coldness of a liquefied natural gas such as a city gas necessary to be evaporated at the time of use as a fuel, liquefying nitrogen, and utilizing liquefied nitrogen as a low temperature source for a condenser.
This system is for concentrating heavy carbon methane by supplying methane which is a main component of a liquefied natural gas to a distillation tower 1 provided with a condenser 2 using liquefied nitrogen as a low temperature heat source. In this case, the evaporate nitrogen gas is circulated in a circulation route 6 by being returned to a liquefying apparatus 5 in the circulation route from the condenser and as a low temperature heat source of the liquefying apparatus 5, the liquefied natural gas is used. In such a manner, the cold of a liquefied natural gas such as a city gas necessary to be evaporated at the time of use as a fuel is efficiently utilized to liquefied nitrogen and the liquefied nitrogen is used as a low temperature heat source for the condenser. Consequently, without being discarded, nitrogen can be circulatively used to lower the cost for concentrating heavy carbon methane.
SO HIROTAKA
HAGA KENICHI
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