Power generation from waste heat: Ionic liquid-based absorption cycle
vs. organic Rankine cycle
Abstract
Aspen Plus® simulations using the Peng-Robinson (PR-EOS) and the
COSMO-SAC models were performed to study absorption power cycles (APCs)
using mixtures of R-134a with two ionic liquids, [C2C1im][Tf2N]
or [C6C1im][Tf2N], and compared against an R-134a organic
Rankine cycle (ORC) operating under similar conditions. The PR-EOS
results were in agreement with calculations from a PR model fitted to
the R-134a+IL experimental phase equilibrium data. The APCs have similar
efficiencies and outperform the ORC by 3-46%, with the largest
differences observed when operating with lower grade (lower TH) heating
sources, lower quality cooling (higher TL) and lower subcooling in the
pump inlet stream. The PR-EOS and the COSMO-SAC results follow similar
trends, but numerical discrepancies are observed in the cycle
efficiencies and stream flow rates and compositions due to differences
in solubilities and enthalpy changes between both models, suggesting
that improvements are needed to increase the accuracy of COSMO-SAC for
these systems.