Thermodynamics analysis of a novel designation of LNG solid oxide fuel cells combined system with CO2 capture using LNG cold energy

Abstract

The solid oxide fuel cells (SOFC) – proton exchange membrane fuel cells (PEMFC) and waste heat recovery utilization systems employing liquefied natural gas (LNG) as fuel are designed and integrated. The cold energy from LNG supply system is harvested and supported to the CO2 capture system. The gas turbine (GT), organic Rankine cycle (ORC), steam Rankine cycle (SRC) are integrated to use LNG cold energy and waste heat of system and transfer it into useful work and power. PEMFC is constructed and coupled in an integrated system to address the disadvantage of SOFC's delay in starting and maneuvering period of vessel. To adapt regulations and standards from international and local authorities, the CO2 capture system is designed and integrated. The ORC-SOFC-GT-PEMFC-ORC-SRC-CO2 capture system is analyzed and investigated thermodynamically based on the first and second laws of thermodynamics. ASPEN HYSYS V12.1 are used to simulate and optimize the LNG SOFC integrated system combined CO2 capture utilizing LNG cold energy. Laws of thermodynamics were employed to build up the thermodynamics equations and estimate the system performance indicators. The exergy destruction of major components was established and estimated to optimizing the designation and operation of suggested system. The energy and exergy efficiencies of proposed system was calculated at 68.76% and 33.58%, respectively. The waste heat recovery combined cycles generated more 2100.42 kW which equivalent to 35.6% of the total output of system. The innovated models were validated against experiment data from literature with good agreement. Furthermore, the parametric study show that the current density varied from 930 to 1930 A/m2 influencing the main indicator which total energy efficiency varied by 33.18% from 3.29% to 5.11%. The ORC took both advantages on cold energy and high-temperature of waste heat results high efficiency of energy recovery. The use of exhaust gas boiler for waste heat recovery provides 9000 kg/h of superheated vapor at 151.5 ℃and 498 kPa for accommodating of seafarers and heating the lubricating oil on board. The combination of harvesting LNG cold energy and exhaust gas waste heat recovery to the CO2 capture system contributing to greener of exhaust gas adapting the regulations of International Maritime Organization (IMO) for emission from marine vessels.