Starting point and motivation:

In the context of the European Energy Efficiency Directive there is a need for improved and competitive technologies for upgrading heat at low to medium temperatures (60 to 400°C) either into electricity or into heat at higher temperature. The working fluid CO₂ offers many advantages compared to water/steam or to organic fluids. During the last 15 years there has been an increasing research effort which was driven by projects in the nuclear and solar thermal industry, mainly in the USA and mainly for high temperature applications. As a positive side effect for the energy efficiency industry, commercial turbo machinery is starting to become available on the market also for moderate temperatures as targeted in this project. Preparatory work at TU Wien has shown that CO₂ offers in the cement industry considerably higher process efficiency than conventional solutions based on water or organic fluids. In addition to the energetic advantage in trans- or subcritical Rankine cycle, CO₂ offers being  thermally stable, non-combustible, non-inflammable, non-toxic, non-reactive, having a low greenhouse effect and a strongly reduced size of machinery (hence cost reduction potential).

Objectives:

Objectives of the project are the development of the most appropriate CO₂ heat recovery cycle, based on the criteria of efficiency, cost and operational stability; developing appropriate control strategy for CO₂-cycles, the validation o heat exchanger designs valid for the use in dust loaded gas streams, the analysis of the influence of thermal/transport property variations on performance and operational stability, the development of solutions for heat transformation and heat storage and last but not least the discussion and negotiation with potential machinery suppliers for phase 2 of the project.

Innovation and targeted project results:

The innovation lies in the systematic analysis and experimental validation of the CO₂ working cycle fired by process-off-heat.