two-step optimization approach for increaseof enginge-orc efficiency
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
Two-step optimization approach for increase of
engine-ORC efficiency
Daniela Gewald, Sotirios Karellas, Andreas Schuster
ORC 2011, Delft
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
Outline
state of the art in engine-ORC technology and motivation
methods: thermodynamic and performance optimization
1. step: thermodynamic calculation:
assumptions
results
definition of reference design
2. step: performance evaluation:
variation of system design parameters
results
comparison of results conclusion and outlook
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
State of the art and motivation
Internal combustion engines:
independent power producers with high
electrical efficiency (up to 47 %)
fuel flexibility (natural gas, biogeneous
fuels, Diesel and heavy fuel oil) fast respond to load changes, good part
load behaviour
up to 45 % of fuel input as waste heat:
temperature levels:
exhaust gas: 300C to 400C engine cooling water: ~ 90C
9/23/2011 ORC 2011, Delft, Daniela Gewald 3
Heat flux diagram of state of
the art internal combustion
engine
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
State of the art and motivation
Waste heat recovery systems:
water/steam cycle: heat source temperature 350C to 600C
Organic-Rankine-Cycle: heat source temperature 90C to 400C
ORC technology especially for state-of-the-art engines with low exhaust
gas temperatures
Engine-ORC technology:
use of exhaust gas or cooling water as heat source
no integration of both
use of recuperator
standardised engine and ORC technology no combined system
optimization
fluids: pentane, R245fa, MDM
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Technische Universitt Mnchen
Methods for engine-ORC evaluation
1. step: Thermodynamic optimization:
evaluation of different system configurations
evaluation of different fluids
variation of fluid evaporation pressure
definition of thermodynamic optimum:
thermodynamic optimum = reference configuration
2. step: Fast performance evaluation:
rough calculation of heat exchanger areas:
variation of design parameters:
evaporation pressure
recuperator performance (pinch point)
engine cooling water temperature
performance optimum:
with software Ebsilon
Professional
9/23/2011 ORC 2011, Delft, Daniela Gewald 5
max, pumpturbinenetORCPPP
condrecevaporatorexhaustgastot AAAAA
max
2
,
m
kW
A
P
tot
netORC
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
Thermodynamic calculation - assumptions
turbine = 82 %
pump = 70 %
recuperator:
pinch point = 5 K
pressure loss:
MDM: 2 kPa
pentane: 50 kPa
R245fa: 100 kPa
mech, gen = 98 %
evaporator pinch
point = 5 K
condenser:
Tcond = 55C
Tcond = 7 K
thermal oil heat
exchanger:Tto/ex = 5 K
Tmin,ex = 65C
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
Thermodynamic calculation results
maximum power output:
MDM: 4 bar 555 kW
pentane: 30 bar 610 kW
R245fa: 30 bar 455 kW
300
350
400
450
500
550
600
650
0 10 20 30 40
netORCpoweroutp
ut(kW)
evaporation pressure (bar)
MDM Pentan R 245 fa
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Technische Universitt Mnchen
Definition of reference design
ORC systems pentane MDM
ORC with recuperator
pfluid = 30 bar
Tfluid = 189 C
thermal oil: 225 / 95 CTexhaust = 100 C
Pel,net = 610 kW
pfluid = 4 bar
Tfluid = 214 C
thermal oil: 270 / 158 CTexhaust = 163 C
Pel,net = 555 kW
ORC with engine cooling
water heat exchanger pfluid = 30 bar
Tfluid = 189 Cthermal oil: 225 / 92 C
Texhaust = 97 C
Tcw = 90 C
Pel,net = 607 kW
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
System design and variation parameters
evaporation pressure: 10 bar to 33 bar (critical pressure for pentane:
33,7 bar)
recuperator pinch point: 1 K to 20 K
engine cooling water temperature: 85C to 120C (within technical
feasibility of engine construction)Evaluation of:
net ORC power output
heat exchanger areas
exhaust gas temperature
power/area coefficient
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Technische Universitt Mnchen
Variation of design parameters evaporation pressure
Influence of evaporation pressure on
ORC cycle performance:
maximum net power output of
ORC system at 30 bar
minimum overall heat exchangerarea at 10 bar
great influence of decreasing
power with decreasing pressure
best power/area coefficient at 33
bar
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86
88
90
92
94
96
98
100
102
-35
-30
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-5
0
5
10 15 20 25 30
exhaustgastem
perature(C)
chang
einP_
ORC,net,A_
ORC
andpower/area
coefficient(%
)
evaporation pressure (bar)
%P
%A
%power/area coefficient
T_ex_out
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Technische Universitt Mnchen
Variation of design parameters recuperator pinch
point
Influence of increasing pinch point on
ORC cycle performance:
almost no influence on power:
+/- 2 %
decreasing exhaust gastemperature: 103C to 89C
optimal power/area coefficient at
a pinch pint of 10 K
highest possible cooling of
exhaust gas does not lead to the
economically best performance
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88
90
92
94
96
98
100
102
104
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-5
0
5
10
15
1 6 11 16
exhaustgastem
perature(C)
chang
einP_
ORC,net,A_
ORC
andpower/area
coefficient(%
)
recuperator pinch point (K)
%P
%A
%power/area coefficient
T_ex_out
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7/29/2019 Two-Step Optimization Approach for Increaseof Enginge-OrC Efficiency
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Technische Universitt Mnchen
Variation of design parameters cooling water heat
exchanger
Influence of increasing cooling water
temperature on ORC cycle
performance:
increasing power output (+ 5 %)
higher vapour mass flow decreasing over all heat
exchanger area
increasing power/area coefficient
up to 20 %
highest possible cooling of
exhaust gas does not lead to the
economically best performance
system optimization also has to
take into account the engine not only
the bottoming cycle
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0
20
40
60
80
100
120
140
-20
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-5
0
5
10
15
20
25
85 90 95 100 105 110 115 120
exhaustgastem
perature(C)
chang
einP_
ORC,net,A_
ORC
andarea/power
coefficient(%
)
engine cooling water temperature (C)
%P
%A
%power/area coefficient
T_ex_out
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Technische Universitt Mnchen
Discussion of optimal systems compared to basic
configuration
best economic performance for
ORC with engine cooling water
heat exchanger (120C):
+ 5 % net power output
+ 35 % power/area coefficient optimization of evaporator
pressure and recuperator pinch
point around thermodynamic
optimum does not have a great
impact:
evaporation pressure: + 2 %power/area coefficient (but higher
cost and safety efforts due to
higher power !)
recuperator pinch: + 0.5 %
power/area coefficient
9/23/2011 ORC 2011, Delft, Daniela Gewald 17
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30
35
evaporationpressure 33 bar
Rekuperatorpinch 10K
cooling waterheat exchanger
120 C
chnagein
ORCperformancepara
meters
%P %A %power/area coefficient
recuperator
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Technische Universitt Mnchen
Conclusion
two-step approach:
thermodynamic optimization: ORC net power output
performance optimization: power/area coefficient as indicator for cost efficiency
variation of important design parameters: evaporation pressure,
recuperator pinch point, engine cooling water temperature engine cooling water temperature has major influence on power/area
coefficient
not only ORC internal optimization parameters, but overall system
parameters, such as engine design parameters, have to be taken into
account for an optimization approach
9/23/2011 ORC 2011, Delft, Daniela Gewald 18
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Technische Universitt Mnchen
Outlook
further research topics:
only qualitative results: optimization for specific case of application is
necessary
specific advantages of other fluids besides pentane (e.g. MDM high
exhaust gas temperatures benefit for CHP applications) investigation of system performance during transient operation: specific
requirements due to coupling of engine and ORC system at exhaust gas
and cooling water side (e.g. engine cooling has to be ensured even when
ORC is not running, different load change rates of engine and ORC)
calculations are highly depending on the determination of heat transfer
coefficients easy and fast calculation procedures
9/23/2011 ORC 2011, Delft, Daniela Gewald 19
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