| Abstract |
This paper deals with two aspects of ìsizingî geothermal projects; the selection of turbine inlet pressure and attendant economic benefits, and the selection of project size to maximise economies of scale. A previous paper outlined a method to quantify, before detailed design and price estimation, the capital cost implications of alternative steam supply pressures for a steam dominated system (Kamojang in Indonesia). The method considers the size or rating of a plant item or subsystem and determines the change in size or rating for a change in steam supply pressure. Cost changes are assessed from the estimated cost of the plant item or subsystem using normal rules for the cost of size changes. Separate savings or additional costs are evaluated for the steamfield and power plant parts of the project. This method is now extended to liquid dominated systems, for which a low enthalpy case is considered as well as a medium enthalpy case. For the medium enthalpy case (1600 appreciable cost savings are predicted for bara turbine inlet pressure compared to a value of 6.5 bara. For the lowenthalpy case, the lower turbine inlet pressurewill provide lower overall costs. A strong drive for economies of scale meansthat the customary approach of matching the power plant to the geothermal field is not the only approach for project development. This paper examines the economies of scale which can be achieved with larger unit and plant sizes, and establishes some guiding principles for maximising such economies. Wherever possible, the approach should be to ìmatch the field to the plantî. In small geothermal fields, the standard approach of matchingthe plant to the field is still justified on the grounds of minimisingtechnical and commercial risk. In very large fields economies of scale will be limited by the power density of the field and other physical limitations which will require replicationof plant and equipment without economies of scale. |