raw · papers · ingested 2026-09-19
Techno-Economic Assessment for the Integration into a Multi-Product Plant Based on Cascade Utilization of Geothermal Energy (Rubio-Maya et al. 2016)
Source: https://www.lehigh.edu/~inenr/research/PDF/geothermal-1.pdf
Provenance: Peer-reviewed, funded by SENER/CEMIE-GEO (Mexico) with Lehigh’s Energy Research Center. A design/optimization study, not an operating plant; absorption and ORC parameters are taken from manufacturer data. Retrieved via research agent; full text read.
Configuration
Three-level cascade on one geofluid stream, targeting Mexico’s 276 low/mid-enthalpy sites (source range 80–130 °C, average 110 °C):
- ORC power (13 commercial units surveyed: 11–280 kWe; inlet 91–135 °C; evaporator ΔT 7–26 °C; efficiency 6.1–10.6%; cost $52k–$661k).
- NH₃-H₂O absorption ice-maker, ice storage at −13 °C.
- Direct-use heat exchanger (70% effectiveness), then reinjection.
Design rules adopted (manufacturer data)
| Cycle | Activation temperature | COP | Generator ΔT |
|---|---|---|---|
| NH₃-H₂O single-effect | ≥ 90 °C | 0.6 | 10 °C |
| NH₃-H₂O half-effect | ≥ 80 °C | 0.3 | 10 °C |
Absorption capital cost correlation: I = 952.3 × Q_cool[kW] + 159,258 USD. Revenue assumptions: 0.08 USD/kWh electricity, 0.15 USD/kg ice, 0.016 USD/kWh heat.
Optimum (both NPV and efficiency)
- ORC10: 125 kWe, 10.6% efficiency. Geofluid 109.4 °C at 26.9 kg/s.
- Temperature ladder: 109.4 °C → ORC out 98.9 °C → absorption out 88.9 °C → direct-use out 78.9 °C → reinject.
- 1,179 kW to ORC; 674 kW cooling; 31,084 kg/h ice; overall energy efficiency 46.3%; NPV $10.74M; simple payback 1.7 years.
- Half-effect variant (T₂ ≥ 80 °C, COP 0.3): NPV $5.2M, 337 kW cooling, 36.4% efficiency.
Design insight
ORC units with the smallest evaporator temperature drop maximize NPV because they leave hotter fluid for the absorption and direct-use levels. “low ORC thermal efficiency is not a downside because it is compensated with more thermal energy available to feed the next level making more profit.” Also: “medium-enthalpy geothermal energy is effectively used in direct applications for heating and cooling processes, producing about three times more revenue than geothermal power applications.”
Relevance to the cooling wiki
The cleanest worked temperature ladder for power → sorption cooling → heat on one brine stream, with explicit activation temperatures and COPs by cycle. It is the design template for the “EGS brine as drive heat” question, with the caveat that it assumes a 110 °C hydrothermal resource and small ORCs, not a 195 °C EGS resource feeding a utility-scale ORC.