Preliminary Considerations for Power Generation Using a Downhole Coaxial Heat Exchanger System (II)

Studies on the Downhole Coaxial Heat Exchanger (4th Report)

Abstract

The purpose of this study was to clarify the level of thermal output per DCHE at which power generation using a downhole coaxial heat exchanger (DCHE) becomes economical. Another goal was to clarify the geothermal resources favourable for this system.
The following conclusions are drawn in this paper:
(1) When heat is transferred only by conduction in the formation as in Hot Dry Rock, the power generation sytem appears to be uneconomical. On the other hand, in the case of Hot Wet Rock where the convective heat transfer mechanism is dominant, there appears to be a greater possibility of the realization of this system.
(2) In the case in which the estimated net thermal output after one year of operation was 10.4 MWt/DCHE, the adjusted mean power generation cost for 15 years of plant operation under the current subsidy system was estimated to be 16.4 Yen/kWh. In this case, the power generation system might become economical in the near future. Hence, under conditions similar to those assumed in this study, 10 MWt/DCHE of the net thermal output is though to be a good criterion for judging whether the system is practical or not.
In order to investigate the possibility of the realization of this system and to clarify the favourable characteristics of the formation in further detail, it is essential to accumulate in-situ data carrying out heat extraction experiments in high temperature and permeable formation.