Optimisation of off-design internal combustion-organic Rankine engine combined cycles
File(s)
Accepted version
Author(s)
Chatzopoulou, Maria Anna
Sapin, Paul
Markides, Christos
Type
Conference Paper
Abstract
Organic Rankine cycle (ORC)
engines
are an efficient means of
converting
low
-
to
-
medium
renewable or
waste heat
to useful power
. In
practical
applications, ORC
systems
experience varying
thermal
input
profile
,
due to the dynamic nature of
real
heat source
s
.
M
aximis
ing
the
uptake of this technology requires
optim
ised
ORC design
s
and sizing
to
maintain high efficiency
and power output,
not only at full
-
load operation, but also
under off
-
design conditions. Key for maintaining the efficient operation
of the
sys
tem
is the maximisation of
heat extraction from the heat source,
in
the
ORC
evaporator. In this paper, the off
-
design operation of an
ICE
-
ORC combined heat and power (CHP) system is investigated, to optimise the ORC performance under
varying ICE load condi
tions. First, the ORC
engine
thermodynamic design is optimised for the 100%
load
operation of the ICE. Alternative working fluids are inv
estigated, including low ODP/
GWP refrigerants and
hydrocarbons. The ORC system is then sized using two different heat e
xchanger (HEX) architectures; tube
-
in
-
tube
(DPHEX)
and plate
(PHEX)
design
s
, at
design
conditions.
The
sizing results reveal that the PHEX
area requirements are almost 50% lower than the respective ones
for
DPHEX, while recovering equivalent
quantities
of heat. Next, the ORC
engine
operation is
optimised
at
part
-
load
ICE
condition
s
,
and the HEX
heat transfer coefficients (HTCs) are predicted.
R
esults indicate that
:
i) PHEX HTCs are up to 50% higher
than DPHEX
equivalents
;
ii)
HTCs
decrease
at
part load f
or both HEXs, but because the
average
temperature
difference
increases, the overall HEX effectiveness improves; and iii) the ORC
system
with
a
PHEX
evaporator
has slightly higher power output tha
n
the DPHEX
equivalent
at off
-
design operation.
Overall, t
he
modelling
tool
developed here
can predict ORC performance over an operating
envelope
and
allows
the
selecti
on of
optimal design
s
and size
s
of ORC HEXs.
engines
are an efficient means of
converting
low
-
to
-
medium
renewable or
waste heat
to useful power
. In
practical
applications, ORC
systems
experience varying
thermal
input
profile
,
due to the dynamic nature of
real
heat source
s
.
M
aximis
ing
the
uptake of this technology requires
optim
ised
ORC design
s
and sizing
to
maintain high efficiency
and power output,
not only at full
-
load operation, but also
under off
-
design conditions. Key for maintaining the efficient operation
of the
sys
tem
is the maximisation of
heat extraction from the heat source,
in
the
ORC
evaporator. In this paper, the off
-
design operation of an
ICE
-
ORC combined heat and power (CHP) system is investigated, to optimise the ORC performance under
varying ICE load condi
tions. First, the ORC
engine
thermodynamic design is optimised for the 100%
load
operation of the ICE. Alternative working fluids are inv
estigated, including low ODP/
GWP refrigerants and
hydrocarbons. The ORC system is then sized using two different heat e
xchanger (HEX) architectures; tube
-
in
-
tube
(DPHEX)
and plate
(PHEX)
design
s
, at
design
conditions.
The
sizing results reveal that the PHEX
area requirements are almost 50% lower than the respective ones
for
DPHEX, while recovering equivalent
quantities
of heat. Next, the ORC
engine
operation is
optimised
at
part
-
load
ICE
condition
s
,
and the HEX
heat transfer coefficients (HTCs) are predicted.
R
esults indicate that
:
i) PHEX HTCs are up to 50% higher
than DPHEX
equivalents
;
ii)
HTCs
decrease
at
part load f
or both HEXs, but because the
average
temperature
difference
increases, the overall HEX effectiveness improves; and iii) the ORC
system
with
a
PHEX
evaporator
has slightly higher power output tha
n
the DPHEX
equivalent
at off
-
design operation.
Overall, t
he
modelling
tool
developed here
can predict ORC performance over an operating
envelope
and
allows
the
selecti
on of
optimal design
s
and size
s
of ORC HEXs.
Date Issued
2018-06-17
Date Acceptance
2018-05-07
Citation
Proceedings of ECOS 2018, 2018
Publisher
ECOS
Journal / Book Title
Proceedings of ECOS 2018
Copyright Statement
© 2018 The Author(s)
Sponsor
Climate-KIC EIT PhD added value Programme
President's PhD Scholarships
UK Engineering and Physical Sciences Research Council
Grant Number
Climate-KIC EIT PhD added value Programme
Award number: 1855813
Source
ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
Publication Status
Published
Start Date
2018-06-17
Finish Date
2018-06-21
Coverage Spatial
Guimarães, Portugal