(681b) Supercritical Fluid Carnot Cycle for Low Temperature Waste Heat Utilization

Supercritical
Fluid Carnot Cycle for Low
Temperature Waste Heat Utilization

Many chemical processes reject low-grade heat to
the environment. While it is difficult
to recover low temperature waste
for work production,
it would be useful to design processes
that, in principle, could do this.
In our presentation we describe computer simulations of a process
for doing this using supercritical carbon dioxide as a working fluid for the
power cycle. Given the low critical temperature of carbon dioxide and the desirability of keeping the working fluid in its one phase region, CO₂ is an ideal fluid for designing
such a process. Using a temperature close to its critical point for the rejection
leg of the Carnot cycle,
we exploit the natural flattening of the critical isotherm in this region which leads to
efficient work production
in Carnot engines
using small temperature driving forces between
the input and rejection legs of the process. The concepts
appear promising as a basis for designing experimental systems for recovering
low- grade waste heat for conversion into work using supercritical
CO2 as the power cycleÕs working fluid.