Organic Rankine cycle (ORC) systems are increasingly being deployed for
waste
-
heat recovery and conversion in
industrial settings. Using a case study of an exhaust flue
-
gas stream
at a te
mperature of 380 °C as the heat source
, an
ORC
system
power output in excess of 10
MW is predicted at exergy efficiencies ranging between 20% and 35%.
By
comparison with available experimental data,
the
thermodynamic properties
(including those in the supe
rcritical region)
of working fluids
are shown to be reliably predicted
by
the SAFT
-
VR Mie equation of state
; t
his verification is quite
important as this is the first time that the SAFT
-
VR Mie
equation of state
is used for
thermodynamic property prediction
of working fluids in their
supercritical
state
in
trans
-
critical ORC systems
.
Various c
ycle configurations and the use of
working
-
fluid mixtures are also investigated. ORC systems operating on
trans
-
critical cycles and those incorporating
an internal heat exchanger
(IHE)
are seen to be beneficial from a thermodynamic perspective, they are
,
however
,
more
expensive than the
simple
ORC system
considered
(subcritical cycle with no
IHE
).
Furthermore
,
ORC
systems
using
pure working fluids
are associated with
slightly
lower costs
than those with
fluid mixtures
.
It is concluded that
a
basic
ORC
system utili
zing
pur
e working fluid
s
shows
the
lowest specific investment cost
(SIC)
in the case study considered.