Key Messages

A thermo-economic evaluation of a steam Rankine cycle and an ORC for similar operation conditions and power outputs suggests the promise of organic working fluids for high temperature ORCs. Key conclusions are:

1. The thermal efficiency of steam Rankine is only marginally better than that of the ORC.

2. The volumetric flow rate at the exhaust of turbine in the ORC is one-tenth of the same in steam Rankine. Hence, significant cost savings can be realized in the ORC turbine.

3. Temperature glide of the working fluid across the ORC condenser manifests into a higher LMTD and thus lesser heat transfer area facilitating a more compact and cheaper condenser. The cost savings in condenser are decisive in realizing its lower initial investment costs.

4. Although regenerator heat exchanger contributes to additional cost for the ORC, the significant difference in the $/kWe for the two cycles suggests that high temperature ORCs are viable substitutes for the steam Rankine cycle and worth investigating further in detail.

*Ankit Saini, Karthik G.M., Pardeep Garg, Pramod Kumar, and Vinod Srinivasan are other authors of this paper.

Thermo-economic analysis of a mixture of RC-318 and pentane