Cryogenic ORC to enhance the efficiency of LNG regasification terminals
Marco Astolfi, Anton Marco Fantolini, Gianluca Valenti, Salvatore De Rinaldis, Luca Davide Inglese, Ennio Macchi
Session: Session 2A: System Optimization (1)
Session starts: Wednesday 13 September, 14:20
Presentation starts: 15:40
Room: Building 27 - Lecture room 01
Marco Astolfi (Politecnico di Milano)
Anton Marco Fantolini (Saipem)
Gianluca Valenti (Politecnico di Milano)
Salvatore De Rinaldis (Saipem)
Luca Davide Inglese (Saipem)
Ennio Macchi (Politecnico di Milano)
Liquefied Natural Gas (LNG) is transported worldwide by ship in cryogenic vessels where LNG is stored at ambient pressure and temperature of -160°C. LNG is then vaporized offshore or onshore in regasification plants and pumped into gas pipelines for distribution. Several technologies for LNG regasification are available on the market; among them, the most important are the Open Rack Vaporizer (ORV), the Submerged Combustion Vaporizer (SCV) and the Intermediate Fluid Vaporizer (IFV) . In the first one, LNG flows upwards in tubes while sea water flows outside in counter flow. This technology is widely used because of its low operational costs, but it is a capital intensive solution because of the large heat transfer surfaces, the need of water treatment and, additionally, it is critical because of vibrational issues in part load. The second regasification technology consists in a pool of water heated by the flue gases obtained by the combustion of gas derived by the regasification line. This technology is compact but it entails a high consumption of primary energy. The IFV consists of a shell and tube heat exchanger in which an intermediate fluid vaporises by absorbing heat from the seawater and condenses by releasing heat to the LNG.
All these technologies require large investments and involve the consumption of electrical energy and/or fuel.
One of the most promising options to increase the regasification plants efficiency is the introduction of a power cycle working between the seawater and the vaporizing LNG. This is an interesting solution from both theoretical (LNG consists in a unique industrial-scale example of “cold exergy”) and technological points of view (because a non-conventional design of each component must be addressed to face difficulties related to cryogenic temperatures). Organic fluids are the only reliable option for this field thanks to the possibility to reach cryogenic temperatures avoiding vacuum condition in the condenser: they have been studied for this application since 1980, some pilot plants have been installed in Japan [2,3] and recently ORMAT presented a patent focused on the topic .
This paper reports the results of an extensive thermodynamic optimization of ORC for LNG regasification plants that are presented highlighting the large benefits attainable in terms of primary energy savings compared to both ORV and SCV technologies. Different cycle configurations are investigated including the option of multilevel condensation plants. The adoption of several working fluids candidate is analysed and different design constraints are included to obtain a more reliable solution. The optimal combinations of cycle configuration and working fluid are eventually presented with a preliminary design of the main components.