Grey relational analysis of an integrated cascade utilization system of geothermal water

ABSTRACT

With the drastic decrease in fossil resources and rapid deterioration of the global environment, the utilization of geothermal resources has been strongly advocated. The combination of heat, power, and cold utility generation is commonly used to increase the utilization efficiency of geothermal resources. In this study, an integrated cascade utilization system of waste geothermal water (ICUWGW) from a flash geothermal power plant in China is established to increase the utilization efficiency of geothermal water. The waste geothermal water leaving the power plant is proposed for further use in cascade for two-stage LiBr/H₂O absorption cooling, agricultural product drying, and residential bathing. Twelve candidate temperature schemes showing different inlet and outlet temperatures of every subsystem are proposed for the ICUWGW. Several criteria are selected for the evaluation and screening of the candidate schemes. Grey relational analysis incorporating analytic hierarchy process is conducted to screen the optimal temperature scheme for the ICUWGW to meet the comprehensive criteria of thermodynamics and economics. Results show that the optimal scheme features significant improvement in energy efficiency, exergy efficiency, and equivalent electricity generation efficiency compared with those of the current geothermal power plant. The investment payback time of the additional subsystems for cooling, drying, and bathing is 1.85 years. Exergy analysis is also conducted to determine the further optimization potential of the optimal ICUWGW. Sensitivity analysis of electricity price on the performance of the optimal ICUWGW is also performed.

KEYWORDS:

• Cascade utilization
• exergy analysis
• geothermal resource
• grey relational analysis
• multi criteria

Additional information

Funding

The authors gratefully acknowledge the support from the National Natural Science Foundation of China (Grant No. 51006025) and the financial support from the Key Technologies R&D Program of China (Grant No. 2012BAB12B01) and the Open Foundation of Key Laboratory of Efficient Utilization of Low and Medium Grade Energy (Tianjin University) (No. 2014-4203).