Exergetic Analysis of Systems Generating Electricity Through Expansion of Natural Gas

This paper discusses the thermodynamic performance of three different system configurations used to expand natural gas: (1) A system in which all natural gas passes through a throttling valve, (2) a system that uses only an expander as the expansion device, and (3) a system using in parallel both an expander and a throttling valve as expansion devices. The overall energetic efficiencies for the second system are between 89.2 and 89.4% while for the third system they are between 89.4 and 89.9% depending on mass throughput. The corresponding exergetic efficiencies are between 25% and 32% for the second system and 10% and 25% for the third one. The sensitivity analysis demonstrated that the mass flow rate of natural gas affects the thermodynamic efficiency of the systems generating electricity through expansion of natural gas. The differences in efficiencies between the second and third system, particularly at higher mass flow rates could justify the higher investment costs required for the second system and make it the most attractive system also from the cost viewpoint among the three systems studied here.