The Use of Liquid Natural Gas as Heat Sink for Power Cycles

Abstract

The thermodynamics of power cycles employing liquid natural gas (LNG) as heat sink is discussed. Condensation cycles in simple or in elaborate versions, employing nontoxic, nonflammable, inert organic fluids (CF4 , C2 F6 , CHF3 , C3 F8 ), yield the best overall performance for LNG vaporization at subcritical pressure. For supercriticial vaporization, heat rejection from Brayton cycles naturally fits heat sink thermal characteristics, which results in a particularly high efficiency for closed gas cycles. If only a fraction of the cooling capability of LNG is devoted to power uses, condensation cycles are superior to gas cycles even at supercritical LNG pressures. Under the most favorable circumstances gas cycles achieve efficiencies of around 60 percent, while some elaborate condensation cycles attain the 70 percent level.