Assessment of LNG Regasification Systems With Cogeneration

Abstract

Natural gas is usually transferred to consumers through pipelines, which may cover distances of thousands of kilometers. In some cases, however, when the path of the pipelines crosses seas or countries where the politic situation does not ensure a continuous and reliable flow, other means of transportation are preferred. In these cases, the natural gas is liquefied and transported in tankers, which load the tanks at liquefaction plants and discharge them at regasification plants. This gives a considerable chance to differentiate supply sources and allows gas imports from producing countries that are otherwise inaccessible via pipeline. The aim of this paper is the study of systems, which carry out liquefied natural gas (LNG) vaporization using cogenerative solutions. The following configurations were studied in particular: • Gas-steam combined cycles; • Closed gas-gas combined cycles using three different working fluids. Two typical plant sizes and two gas pressure sendout levels (7.3 MPa for long distance pipeline networks and 2.5 MPa for terminals linked to power production plants with combined cycles) have been analyzed. The suggested solutions have been optimized, and performance calculated. The discussion is completed by a simplified economic analysis.

System Analysis of Waste Heat Applications With LNG Regasification

“…This calculation agrees with results reported in other studies [8], [31], and shows that by pumping the LNG at supercritical pressure (> 46 bar) it is possible to reduce energy losses in the heat transfer process from the bottoming cycle to the natural gas. For the delivery conditions adopted in this investigation (13 °C, 205 bar) the specific energy required to vaporize LNG is 592 kJ/kg.…”

“…• Cascaded cycle with gas turbine (topping) and closed Brayton cycle (bottoming) using nitrogen, helium or other inert gas: Desideri and Belli [31], Briesch and Feller [32], option of regasified LNG storage by Ciccarelli [33].…”

The exploitation of the physical exergy of liquid natural gas by closed power thermodynamic cycles. An overview

“…In Ref. [53] we have efficiency calculations for a combined cycle with a steam cycle, with one level of evaporation. The LNG (assuming pure methane at 76 bar is available at À155 C) recovers heat from the seawater, from the condenser in the steam cycle (condensation pressure 24 mbar, condensation temperature 20 C) and, in the case of a delivery pressure of LNG at 25 bar, from the exhaust gases of the GT.…”

A Novel Brayton Cycle With the Integration of Liquid Hydrogen Cryogenic Exergy Utilization

“…For significant volume reduction it can be stored and transported much more conveniently in the compressed (0.069 m 3 /kg at 200 bar/298 K) or liquid state (0.014 m 3 /kg at 1 bar/20 K). Liquefaction reduces the volume 5-fold more than such compression, using cryogenic vessels which are rather common in the 19 states on the cycle flow sheet source, in a system where the liquefied hydrogen (LH 2 ) (or LNG) is the heat sink [1][2][3][4][5][6][7][8][9][10][11][12][13], for recovering power during the re-evaporation process needed for making the hydrogen (or LNG) usable for power production by combustion or fuel cells. From the energy perspective, this approach is clearly superior to conventional re-evaporation systems which just use the heat of seawater or ambient air, or even burn part of the gasified LH 2 or LNG without any concomitant power production.…”

“…Other methods use the LNG coldness to improve the performance of conventional thermal power cycles. For example, LNG vaporization can be integrated with compressor inlet air cooling in gas turbine power cycles [5,11,12], or in steam turbine condenser system (by cooling the recycled water [13]). Some pilot plants have been built in Japan from the 1970s, combining closedloop Rankine cycles (with pure or multi-component organic working fluids) and direct expansion cycles [1].…”