Thermoeconomic assessment of a natural gas expansion system integrated with a co-generation unit

The paper presents a thermoeconomic assessment of an expansion system applied in the natural gas transportation process. The system consists of two turboexpander stages reducing the natural gas pressure and providing mechanical energy to drive electric generators. Gas pre-heating, required to prevent hydrate formation, is performed upstream of each expansion stage using waste heat recovered from a gas engine, which contributes to the total system electricity production. The system constitutes a hybrid energy generation unit as the generated electricity derives partially from the physical exergy of pressurized natural gas, and partially from the primary energy of fuel. The presented thermoeconomic description of the system comprises definitions of system quality indicators, as well as an identification of irreversibility bound to the operation of the system's components.