Multi-effect distillation with novel liquid vapor ejector utilizing the waste heat from intercoolers of a single mixed refrigerant cycle for natural gas liquefaction

Abstract

Reducing and reusing waste heat is crucial to increasing the economic benefits and energy efficiency of industrial processes. Furthermore, combating climate change relies heavily on recovering heat that would otherwise be squandered. With a growing population comes a greater need for clean drinking water. Single mixed refrigerant (SMR) cycle, one of the most practical refrigerating technologies for natural gas liquefaction, rejects a great deal of heat energy in the intercoolers between multistage compression that may be used as the primary heat source for a low-temperature multi-effect desalination plant. This research suggests combining a natural gas liquefaction system with a Liquid Vapor Ejector (LVE) and a Single Mixed Refrigerant (SMR) system, all of which use multi-effect distillation with thermal vapor compression (MED-TVC). The design code SMR-MED integrated system is developed using an in-house robust algorithm in Python. In this setting, the fact that the MED-TVC system can use waste heat from a single mixed refrigerant natural gas liquefaction facility highlights its flexibility. An energy and exergy analysis are performed to determine the feasibility of the proposed system. The design code has been validated against the existing literature. The parametric analysis has been done by changing three independent parameters: namely, refrigerant mass flow rate (10 kg/s to 30 kg/s), water mass flow rate at the intercooler (10kg/s to 40kg/s), and water inlet temperature at the intercooler (17 °C to 35 °C), as, these parameters affects both the LNG production SMR cycle as well as Distillate and Brine production in the MED-TVC system. The results suggest that increasing refrigerant flow increases the cooling effect by 299.68 %, thus producing 289.90 % more LNG; however, exponentially declines distillate by 74.22 %, thus limiting maximum refrigerant flow. Increasing the water mass flow rate improves the distillate production and Gained output ratio (GOR) by 676.07 % and 676.92 %, respectively; conversely, it reduces brine production by 72.97 %. In contrast, increasing water inlet temperature reduces distillate generation and overall system performance. The study results can be used to improve existing system performance and design more sustainable waste heat recovery systems.