Researchers Haonan Chen, Xin Tong, Linchao Yang, and Yangxue Zhang from the China University of Petroleum have conducted a study aimed at improving the efficiency of medium-deep geothermal energy systems. Their work, published in the journal Applied Energy, focuses on optimizing the thermal performance of coaxial downhole heat exchanger (DHE) systems, which are crucial components in geothermal energy extraction.
Medium-deep geothermal energy is a renewable resource that holds significant potential for heating and electricity generation. However, current DHE systems often face challenges such as low efficiency and temperature decay over time. To address these issues, the researchers analyzed field data from two geothermal wells—Well A, which is 3200 meters deep with a temperature of 130.5°C, and Well B, which is 2500 meters deep with a temperature of 103.3°C. The study evaluated the impacts of various factors, including circulating flow rate, inlet temperature, and operation mode, on the performance of these DHE systems.
The researchers found that under optimal conditions—specifically, a circulating flow rate of 50 cubic meters per hour and an inlet temperature of 30°C—Well A’s heat extraction rate improved from 35% to 42%, with its outlet temperature rising from 15°C to 20°C. In contrast, Well B experienced a decrease in its heat extraction rate from 15% to 5% under the same conditions. Over a week of continuous operation, the outlet temperature of Well A dropped from 55.7°C to 16.5°C, and Well B’s outlet temperature decreased from 68°C to 17°C. The study also revealed that adopting an intermittent operation mode—16 hours of operation followed by an 8-hour shutdown daily—reduced the temperature decay rate by approximately 10%.
Based on these findings, the researchers propose several optimization strategies for enhancing the performance of DHE systems. These include controlling the circulating flow rate to 35 cubic meters per hour, maintaining an inlet temperature between 6°C and 10°C, and implementing an intermittent operation schedule. These strategies are designed to improve the efficiency and sustainability of medium-deep geothermal energy systems, making them more viable for widespread use in the energy sector.
The practical applications of this research are significant for the energy industry. By optimizing the performance of DHE systems, geothermal energy can become a more reliable and efficient source of renewable power. This, in turn, can contribute to the reduction of greenhouse gas emissions and the transition to a more sustainable energy future. The findings of this study provide valuable guidance for the design and operation of geothermal energy systems, helping to unlock the full potential of this renewable resource.
Source: Chen, H., Tong, X., Yang, L., & Zhang, Y. (2023). A Study on Optimizing the Thermal Performance of Coaxial Heat Exchanger Systems in Medium-Deep Geothermal Wells. Applied Energy, 335, 120808.
This article is based on research available at arXiv.