Lesme A. Corredor Martínez, Diego J. Guillen Pérez, Luz A. Castellón Pineda, David A. González Fernández, and Alberto M. Palacio Bastos
Natural gas, Distribution network, Pressure reduction, turboexpander, Columbia
LNG production used in passenger transport systems obtained trough natural gas expansion in city networks is a novel process and it has been demonstrated its small energy consumption. This process has made in two stages: first one consist of a pressure reduction and the second one in a cryogenic liquefaction. This paper is focused in the first stage and in a second paper the author will present the simulation result of LNG production optimization for urban transportation systems. This research has been supported by Colombian Science and Technology National Agency (Colciencias, in Spanish) and the company Terpel. As before mention, in natural gas distribution networks, this fuel is transported at high pressures through long length pipelines between the source and final consumers. In every place of consumption or at passing into a lower pressure pipeline the gas pressure must be reduced. Commonly, high pressure is achieved by using a number of compressors, each one attached to a natural gas combustion turbine, consuming energy, and gas pressure reduction is accomplished in mechanical letdown-valves, where an isenthalpic expansion takes place without any energy production. A few amount of the energy consumed could be recovered taking advantage of the enthalpy drop in delivery sites or in pressure reduction stations by the introduction of expander–generator units for power generation. However, this energy that could be recovered is limited to the pressure ratio and the gas mass flow magnitudes at each site, being both variable parameters depending on seasonal, daily and hourly demand fluctuations. For that reason, the optimization model proposed helps in the selection and location of the expander-generator units to recover the potential energy available and produce clean electricity, minimizing the investment payback period, based on the historical demand and operational restrictions of the Colombian natural gas distribution network.
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