Polygeneration Study of Low-to-Medium Enthalpy Geothermal Reservoirs in Mexico

Abstract

This study combines the thermodynamic analysis of a polygeneration system along with the numerical modelling of the thermal behavior of geothermal reservoirs in Mexico to exploit their energy. Each reservoir was modeled as a porous medium assuming a five-spot well configuration and local thermal equilibrium. The heat conduction-convection along with the Laplace equations were solved to compute temperature distributions, the useful life and the optimum distance between injection-extraction wells. The predicted temperature and pressure of the geothermal fluid at the outlet of the reservoir were exploited in the polygeneration system consisting of: (1) a Rankine cycle, (2) an absorption refrigeration cycle, and (3) a heat exchanger. The developed approach allows calculating both the optimal distance between injection-extraction wells and the global (utilization) efficiency of six arrangements (each composed by a reservoir connected to a polygeneration system) by assuming that reservoirs have a lifespan of 30 years. Results also show that: (a) due to the low efficiency of the Rankine cycle, very little thermal energy is converted into electrical one; (b) not only the temperature and the size are important when evaluating the power production performance of reservoirs, but also the permeability plays a fundamental role; (c) the first law efficiency of the polygeneration system ranges from 41.9% to 43.7%; (d) the utilization efficiency of the six arrangements lies in the range between 25.8% and 31%.