| Abstract |
The available technologies in the market for power plants to produce electrical energy from geothermal are mainly back pressure, condensing single flash, double flash, triple flash, dry steam and binary units. The geothermal development in the feasibility stage requires the selection of the technology suitable to the geothermal field. The selection criteria considered are divided into: a) General: Available technology in the market, turbine configuration, condenser configuration, b) Process: Geothermal mass flow, productivity curve of the wells (Pressure-Flow curve), thermodynamic properties and chemical composition of the fluid, kinetics of the silica, fluid corrosion, non-condensable gases and impurities concentration, net power for each technology, altitude of site location of the power plant, thermal impact of the reinjection brine in the reservoir, c) Risk: Handling of the organic fluids, d) Economics, Investment, Operation and Maintenance cost, and lastly e) Commercial. The focus of the paper is geared towards the general, process and risk criteria, as well as a discussion on the economics and commercial criteria are presented. The approach for the analysis is to do the Heat and Mass Balance (H&MB) calculations of the power plant, utilizing a single flash and binary technology, with similar boundary conditions of the system and considering a greenfield development. The main components of the cycle of the power plant for each technology are: 1. Condensing single flash with turbine configuration of single casing, single flow and upward exhaust direction, condenser configuration of direct contact, low level, gas extraction system and wet cooling towers. 2. Binary technology with preheater, evaporator, recuperator, turbine or expander, dry cooling tower. For a base case, a geothermal field with reservoir temperature of 240 °C, wellhead pressure 7 bara, inlet turbine pressure of 6 bara, wellhead enthalpy of 1116 kJ/kg and a reinjection brine temperature of 158.8 °C, the H&MB calculations show that following findings: 1. For inlet turbine pressure above 3.5 bara single flash technology, 2. Enthalpy below 952 kJ/kg binary technology, 3. The silica kinetics can be initially controlled by a dilution of the brine with the steam condensate, so a binary technology will be preferable, 4. For non condensables gases greater than 3.4% wt binary technology, 5. For capacities less than 10 MW either single flash or binary technology, 6. An altitude greater than 2500 masl binary technology to avoid freezing in the primary cooling system , 7. To reduce the thermal impact of the reinjection brine in the reservoir a single flash and 8. Handling the organic fluids can be a risky operation then single flash. The objective of the paper is to provide a methodology for the technology selection for a geothermal power plant. With the general, process and risk criteria, the technical option for the power plant which will be complemented with the economics and commercial criteria for a particular application will be obtained. |