Patent attributes
The present invention is a heat recovery fluid to be used in a closed loop, hot dry rock system, where the fluid remains in a liquid state flowing down from the surface in an annular, downflow conduit to a terminal end heat exchanger. At the terminal end heat exchanger, the heat recover fluid partially vaporizes as a result of indirect heat transfer locally from the geological formation, resulting in a dual-phase fluid or vapor stream flowing out from the terminal end heat exchanger to an axial, return upflow conduit. In one embodiment, the upflow conduit is separated by a single wall from the downflow conduit. When the upflow conduit bears a dual-phase fluid, it has been found that the degree of vaporization of the heat transfer fluid does not result in substantial separation of the vapor and remaining liquid, i.e., which could result in plugging or slug flow in a sloping upward direction, but instead produces a stable flow regime for return of the heated heat recovery fluid to the surface. At the surface, vapor is separated from a liquid phase of the heat transfer fluid from the upflow conduit or is directed as a single vapor stream. Said vapor phase stream can be used directly in a turbine or said separated liquid and vapor phases can indirectly transfer heat to a water or light hydrocarbon liquid, vaporizing it as a working fluid for driving a turbine for electrical power production.
