| Abstract |
In almost all geothermal binary cycle applications, parasitic loads command a significant portion of the total produced power. In a typical geothermal system the major parasitic users include a working fluid pump on the surface, and a geothermal fluid pump located in the source well. Together, these pump loads can reduce the net produced power by more than 35% in some cases. The process described in this paper eliminates both of these pump loads by incorporating a unique thermosiphon system, referred to as the Gravity Head Energy System (GHES). The GHES process uses gravity, rather than a pump, to pressurize the working fluid by allowing it to flow down tubing in the wellbore. As the working fluid flows down the well it is heated by the geothermal fluid flowing up the well. At an optimized depth, the working fluid is expanded through a turbine before flowing back up the well to the surface. The density difference between the two working fluid streams provides the driving force for the system. The shaft power created by the working fluid turbine is used to drive the geothermal fluid pump. In addition to eliminating pump loads, the GHES process offers several other advantages. Since it is a distributed generation system (power generation equipment is located at each well site), the geothermal fluid does not have to be pumped to a central facility, thereby minimizing pressure drop and environmental impact, and accelerating the economic development of the resource. Also, the system efficiency is generally higher than a standard Organic Rankine Cycle system since the heat capacity curves of the two fluids are more closely matched, eliminating the “pinch point.” This paper presents the theory behind the Gravity Head Energy System, and compares its performance to a typical binary cycle power plant. Optimized well design parameters and expected operating conditions will also be discussed. |