COLD ENERGY RECOVERY IN LNG PLANTS WITH ORGANIC RANKINE CYCLE

Abstract

During the production phase, natural gas (NG) is compressed and chilled to liquid state (liquified natural gas, LNG) for sake of volume reduction, hence to ease transportation. Approximately, 500 kWh of electricity or mechanical power per ton of LNG is needed for LNG compression and refrigeration during the production phase, which makes cold energy exploitation interesting from a thermodynamics point of view. An effective way to harness the cold energy contained in LNG is through an Organic Rankine Cycle system. A Cold Energy Plant (CEP) is an efficient system based on ORC technology which regasifies liquified natural gas and converts the heat absorbed from sea water into electricity by recovering the valuable exergy content of LNG. This solution allows to produce electrical power onsite without any additional external fuel consumption and no emissions at stacks. The CEP is a lowmaintenance and cost-effective solution that can be efficiently applied in the LNG industry to increase energy efficiency and sustainability of operations. The CEP system designed by Exergy achieves high efficiency thanks to the use of the proprietary Exergy Radial Outflow Turbine combined with the Multilevel Condensation Cycle, maximizing the revenue from electricity production. This paper will outline the technical features of a CEP power plant and will present a case study based on a Liquified Natural Gas regassification system engineered to produce Nominal 4 MWe (4000 kWe) net electric power while simultaneously fulfilling the regasification of 180 ton/h (~1 MTPA) of LNG.