Micro Geothermal Generation Device

Abstract

There are many places in the world where one has access to very high temperature water effluents and at the same time access to very cold water. This happens in many SPA thermal resources in the high mountains. The usual solution to generate electricity for those cases, if one doesn’t want to drill wells, is using the hot source and the cold sink to install an Organic Rankine Cycle (ORC) power plant. This might be a very good solution but usually expensive and complicated to maintain and operate. In this paper a very practical, simple, novel design is presented where the water from the hot spring is connected to a tube where vacuum is produced by a Torricelli pipe. The incoming hot water under vacuum will split in low pressure steam and hot water at the corresponding saturated temperature. The steam flows upward and passes through a simple design axial turbine connected to a generator. The exhaust steam is sent laterally to another vertical pipe that acts as a direct contact barometric condenser, cooled with cold water from a flowing stream. Since the system itself has a small enthalpy jump, running between low and very low steam pressures, special care is made in the design to avoid as much as possible heat and pressure losses. The design of the axial vertical steam turbine involves several interesting features; the rotor and the diaphragm are printed in 3D using a special plastic. The turbine parts (fixed and rotating) are inserted in a steal pipe. The trust bearings are made of sintered metal in oil, allowing constant lubrication. The main characteristics of a 5 kW generation plant is presented and the benefits for distributed generation are highlighted.