Exergy Analysis of Solar-Geothermal based Power Plant Integrated with Boiling and Reverse Osmosis Water Purification

Abstract

The emphasis on renewable energy sources is increasing due to the exhaustive ness of fossil fuels and their effect on the environment. Non- conventional energies are naturally available but exclusively cannot provide consistent power output. Or ganic Reheat Rankine cycle is applicable to combine it with diverse energy source types for multi-purpose and better efficiency that works at a low temperature with specifically selected suitable working fluid. In this work, solar and geothermal re newable energies have been integrated with the Organic Reheat Rankine cycle hav ing a medium of the thermocline energy storage. The objectives of the designed plant are power generation, boiling, and advanced water treatment through differ ent stages of filtration. Aspen plus V11 software has been used for the design of the system configuration. Parameters that have more impact on the system has been optimized like the dead state temperature, geothermal high pressure turbine outlet and inlet pressure, ambient temperature, geothermal injection well fluid flow rate, production well pressure, production well temperature, and geothermal low pressure turbine outlet pressure. Exergy analysis of each component has been car ried out on EES and the components of higher exergy destruction associated with energy conversion have been identified. For the Organic Reheat Rankine cycle, an appropriate working fluid biphenyl/diphenyl oxide has been selected and character ized based on the criteria of stability, environment, temperature, and toxicity has been considered. The RO water treatment process has been analyzed on GPS-X hydromantis software. The RO system is efficient and effective method of water treatment, by considering permeate pump and energy recovery unit in the design, the energy consumption has reduced. The running cost of the filtration and RO wa ter treatment system is 6149.11 $/yr and 3.35KW/m3 power is required to run the booster pump that pressurize the untreated water through semipermeable membrane. The geothermal well operating condition parameters have been estimated from the existing well source data and the newly under construction Aluto Langano power plant. In the end, the power output which can serve the case study area households and industry, at high exergetic efficiency of 51.64 % for the night time system and 49.25% for the daytime operating system with the 100 m3/day of treated water as a supplement to the municipal filtered water. As a conclusion the designed system can perfectly achieves the objectives and the thermal disinfection process consumes 13.36% of the total exergy that sterilize the water from contaminants by boiling water exposing to waste heat beyond the boiling point temperature which is esti mated 1350C. To increase the life span of RO system, the water has filtered in the clarifiers that removes large size industry and household wastes thrown in the lake