The subcritical ORC
(SCORC)
is considered
the industry standard due to its simple configuration, acceptable efficiency and low
cost
s. However
, it is known that alternative
ORC
configurations have the potential to
increase efficiency. A cycle modification
which closely resembles the SCORC
is the partial evap
orati
ng ORC
(PEORC),
where a two
-phase mixture of liquid
-vapour
enters the
expander instead of superheated vapour.
In theoretical studies
at
design conditions
, higher power outputs
are
achieved
for
the
PEORC
compared
to the SCORC.
This
work
aims to
go a step further
by investigating
the performance
of the SCORC
and PEORC under
time
-dependent
operating conditions.
A direct comparison between the SCORC and
PEORC
is made for
identically sized systems using
as input the waste
heat stream
of a waste incinerator plant
and
the changing
ambient conditions
.
Performance maps of both cycle configurations are
compiled
and the benefit of
an expander
operating at variable speed is briefly
discussed
. The results indicate that for the specific case under investigati
on, the PEORC
has
an increased
annual
ly averaged
net
power output of 9.6%
compared
to the SCORC.
Use of
annually
averaged input conditions
result
s in an overestimation of the net
power output
for both the SCORC and PEORC, and furthermore
, the relative improvement
in power output for the PEORC
is
reduced to
6.8%. As such, the use of
time
-averaged
conditions
when comparing
cycle architectures should preferably be avoided.