Designing and Achieving Geothermal Power Plant Performance with Confidence
Guofu Chen, TAS Energy Inc. 6110 Cullen Blvd, Houston, TX 77021
The design and the actual performance of a geothermal air-cooled power plant utilizing a supercritical refrigerant of R134a as the working fluid are discussed. A supercritical Organic Rankine Cycle (“ORC”) in many cases outperforms a sub-critical cycle, from the net kilowatt (kW) generated point of view. Additionally, the plant configuration is simpler to design and easier to operate. An additional advantage of using non-flammable working fluid in the cycle, such as R134a, eliminates the risk of fires. During the design stage, a preliminary process flow diagram is established based on the standard process engineering practices in HYSYS, a simulation software from ASPENTECH. Based on the preliminary process requirement, the components of the cycle, including the shell and tube heat exchanger(s), expansion turbine, aircooled condenser, and working fluid feed pump are sized and selected. A true simulation model is built to analyze the off design performance of a “virtual plant”. Given the geothermal heat source information and the ambient conditions, the power output is maximized and committed to the customer (Model 1 with geometries). After the plant is successfully commissioned, by measuring the flow rate, temperature and pressure, a plant reality model is built to reflect the actual plant operating conditions (Model 2 without geometries). Normally the process conditions of Model 2 are different from Model 1. To validate Model 1, developed in the design stage, the process conditions of Model 2 are extracted and input into Model 1, thus Model 3 with actual process conditions and actual geometries is established. Model 2 is the reality, while Model 3 is used to predict the reality with actual process conditions and actual equipment selection. By comparing these two models, Model 3 accurately predicts the gross power and net power generated at various operating conditions.
