| Abstract |
The author has proposed the Downhole Coaxial Heat Exchanger (DCHE) for exploitation of potential geothermal resources and has been carrying out related studies. The major features of the DCHE include the utilization of a highly insulated inner pipe, reverse circulation (i.e., cold water down the annulus and hot water up through the inner pipe) and a completely closed system. The DCHE is applicable to a wide variety of geological conditions and formation temperatures, and can be utilized for power generation, space heating and cooling, indoor swimming pools and for melting snow on roads. In 1991, the author carried out an experiment to prove the concept of the DCHE at the HGP-A well on the Island of Hawaii. Through this experiment, it was demonstrated that a highly efficient DCHE could be constructed and that the accuracy of the numerical simulation code developed by the author and others was very high. It may be possible to convert the many abandoned deep wells which exist in Poland into DCHEs to be used for space heating, swimming pools and so on. The author has carried out a preliminary study on a 3,000m deep DCHE. Numerical simulations have been carried out for the case of continuous operation of the DCHE. The greatest net thermal output at 180 days of elapsed time among the cases assumed in this study was about 450 kW at 5 ?C of injection temperature and 600 l/min of flow rate. In actual operations, the DCHE would be operated intermittently in most cases. In such cases, greater net thermal output and higher outlet temperatures than obtained in this study should be attained. The DCHE is also applicable to shallow and low temperature geothermal resources. The author has developed the Gaia Snow- Melting System, which utilizes the ground as a heat source and a heat storage body. In this system, solar heat absorbed in the pavement is recovered and stored in the ground over summertime. Hence, both geothermal heat and solar heat are used for melting snow in winter. The DCHE might be a useful tool for the utilization of potential geothermal resources in Poland. |