A study on geothermal electricity systems for Tibet geothermal fields considering thermal performance, economic analysis, and CaCO3 scaling

Abstract

In this article, thermodynamic performance, economic analysis, and calcite scaling assessment have been completed for each of the investigated geothermal electricity systems for Tibetan geothermal fields. The seven investigated electricity production systems include the organic Rankine cycle (ORC), dual-stage ORC (DSORC), triple-stage ORC (TSORC), single-flash (SF), double-stage flash (DSF), single-flash ORC (SFORC), and double-stage-flash ORC (DSFORC). A selection map for suitable geothermal electricity production systems has been generated. The DSORC and TSORC can generate 20% more net power output than the SF system under low dryness and medium-low temperature conditions. When the geofluid temperature and dryness increase, flash systems (SF, DSF, SFORC, and DSFORC) have better applicability. In the Yambajan geothermal field, the SF system has the highest electricity production cost (EPCSF = 0.056 USD/kWh), while the DSORC system has the lowest cost (EPCDSORC = 0.047 USD/kWh). In the Gulu geothermal field, the DSORC is still the most economical system (EPCDSORC = 0.022 USD/kWh), but the DSFORC becomes the least cost-effective system (EPCDSFORC = 0.027 USD/kWh). The scaling associated with using the ORCs (ORC, DSORC, and TSORC) only occurs at the wellhead with a scaling rate of about 2.30 kg/day. In the case of using the flash systems, CaCO3 also precipitates in the system's components; it is found that the scaling rate associated with using the DSF system has a maximum value, which is around 3.864 kg/day. The results obtained in this study are considered useful for the design and operation of geothermal power industries.