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SECTIE ENERGIE EN INDUSTRIE
SECTIE ENERGIE EN INDUSTRIE
The crucial integration of
power systems;
Combining fossil and sustainable energy
using fuel cells
Kas Hemmes
Lunchlezing 21 februari 2006 ; TU Delft
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Outline
•
•
•
•
Introduction
Classification of Energy systems
MSMP Energy systems
(Energy Hubs & Modeling and optimization
methodology)
• Examples
• Conclusions
• Acknowledgements
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Introduction:
Energy System
S
Y
T
C
T
D
system
boundary
Φi,in(x,t)
C
Φj,out(x,t)
Φloss(x,t)
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Introduction: Storage often necessary
Yield & Demand
Y(x,t)
D(x,t)
S
Y
T
C
T
D
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Classification of energy system
1
Linear energy system
2
Co-generation system
3
Tri-generation system
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Linear energy system
E-net
F
1
R
2
N
3
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Input combinations of Fossil and
Renewables
F
Biomass
Co-firing
E-net
R
F
R
Bio-ethanol
Bio-diesel
mix
Transport
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Multisource-multiproduct
MSMP-systems
a
d
b
c
Etc.
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Example : simple CHP energy hub
c
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energy hub
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Power Flow Coupling
 L   c
  c
L
     
  
  
 L   c
L
c   P 
 
c  P
 
 
  
c   P 
c
c
c
C
P
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Relation between coupling matrix C and energy hub
L = C. P
T CHP ,e 0
 Le  
    0 
CHP , h  (1  ) F
 Lh  
 Pe 
 
  Pg 
H   
 Ph 
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Optimization
• How much of which input should be
consumed in order to meet the load
demand in an optimal manner ?
• (due to a certain optimality criterion, e.g.
energy cost or emissions)
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Why new energy systems?
What to optimize?
•
1.
2.
3.
4.
5.
6.
7.
8.
9.
Present systems suffer from “inefficiencies”
Conversion efficiency < 100%
Mismatch between Supply & Demand in time and space
Transport losses
Not 100% eXergy efficient (minimum entropy
production)
Not used 100% of the time
Not 100% Renewable/sustainable
Not flexible, not 100% reliable
But also mixing entropy: N2 in Natural Gas; N2 in CO2
off-gas etc.
…and Institutional, Economic…
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Integration of Fuel Cells in a
Nitrogen - Natural Gas mixing station
E - power
E - power
air
Air SEP
O2
IR-FC
FC
H2
Low T
heat
heat
NG
N2
H2
NG/N2 /(H2 )
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Example: FC replacing N2/O2 seperation unit in
N2-NG mixing station
E - power
air
IR-FC
Low-T FC
Low T
heat
NG
H2
N2
N2
The system is producing E-power instead of consuming it !!
NG/N2/(H2)
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DOE goal for the 21st century
fuel cell (higher efficiencies)
90
80
C+O2 = CO2 (DCC)
CHx pyro +DCC
70
60
Fuel-cell/turbine
hybrid technologies
50
Westinghouse
tube SOFC
40
Combined cycle
Chart source:
NETL, Nov. 1999
Conventional
Steam plants
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Concept
Direct Carbon Conversion (DCC): electric power
from electrochemical reaction of C and O2
_
+
Electric power out
Air in
Carbon
in
Reactive, nano-scale
disorder C from thermal
decomposition of CH x
••
••
••
••
Net reaction:
C+O2 = CO2
Air out
CO2 out
Total
Totalefficiency
efficiency~~80%
80%of
ofH
Hstd
std
Pure
CO
product
for
reuse/sequestration
Pure CO22 product for reuse/sequestration
Use
Usehighly
highlyreactive
reactivecarbons
carbonsfrom
fromCH
CHxxpyrolysis
pyrolysis
Inherent
Inherentsimplicity
simplicity
JFC:March 03
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Objectives
Evaluate processes for fossil conversion
to electric power at efficiencies > 70 %
Electrochemical
conversion
H-pyrolysis
• Coal, lignite
or
C & H2
• Natural gas pyrolysis
• Petroleum
• Petr. coke
• Biomass

C
Air
CO2
H2
Electric
power
Sequester or reuse
Fuel cells, turbines, refinery, etc.
Target: 70 – 80 % efficiency
•
The pyrolysis of CHx => C + (x/2)H2 consumes 3-8% of fuel value; no ash
JFC:March 03
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Precombustion solid-gas
separation of Carbon in a
MSMP system
F (CxHy)
R (Solar)
or
Nuclear
Thermal
decomposition
C
H2
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Thermodynamic advantages of
Direct Carbon Conversion
Fuel
fc
Nernst loss
irr
tot
C
1.0
1.0
0.8
0.8
H2
0.7
0.8
0.8
0.45
CH4
0.89
0.8
0.8
0.57
Table 3 Order of magnitude comparison between the electrochemical conversion
efficiencies of C, H2 and CH4 at 700 oC (Cooper, J. F. et al 2000)
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Electrochemical gasification in
a Direct Carbon Fuel Cell
2C + O2 ==> 2CO S>0
H<0
TS
 fc  1 
 100%
H
Power
C
DCFC
Q
Syngas
• (Solar) Heat can be converted into power
with an efficiency higher than the Carnot
efficiency!
• Self regulating process
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DOE goal for the 21st century
fuel cell (higher efficiencies)
C+½ O2=CO
90
80
C+O2 = CO2 (DCC)
CHx pyro +DCC
70
60
Fuel-cell/turbine
hybrid technologies
50
Westinghouse
tube SOFC
40
Combined cycle
Chart source:
NETL, Nov. 1999
Conventional
Steam plants
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A Fuel Cell that produces
hydrogen and converts heat
into power ?
C+½O2 = CO
Power
C
DCFC
Q (solar)
Syngas
CO + H2O ==> H2 + CO2
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Looking for ways to use the full
exergetic quality of solid fuel !!
• Solid fuels become increasingly
more important (security of supply).
• Coal because it is cheap and
abundant.
• Biomass because it is CO2 neutral.
• Waste.
• Also liquids are ‘closer’ to solids
than to gases in terms of their
exergy value.
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Countries with large potential for Solar
and Biomass can become the energy
producing countries of the future.
Fuel cell
technology
Solar
Biomass
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Example of trigeneration:
H2 and power co-production using an internal
reforming fuel cell.
E - power
IR-FC
CO / H2
NG
heat
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MCFC - Hot Module
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MCFC Hot Module
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Co-production
• Co-production of hydrogen and power from
NG in an Internally reforming fuel cell (IR
FC) is worked out by flow sheet
calculations on an Internal Reforming Solid
Oxide Fuel Cell (IR-SOFC) system. It is
shown that the system can operate in a
wide range of fuel utilization values from
95% i.e. ‘normal’ fuel cell operation mode
up to 60% and lower corresponding to
hydrogen production mode.
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Internal Reforming - SOFC system flowsheet
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Mode 1 – High efficiency mode
First we kept the input flow rate of NG constant. The fuel utilization
is now decreased by decreasing the current density.
1 input
(natural gas input is kept
constant at 2000 kW)
4000
3500
3000
KW
3 outputs vs Fuel Utilization
•Electric Power
•H2 & CO
•(Waste) heat
Efficiency (%)
KW-input
2500
CO-KW
2000
H2-KW
1500
Power-KW
1000
500
0
60
65
70
75
80
85
90
95
Fuel Utilization (%)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Electric-Efficiency
Gas Efficiency
Total Efficiency
60
65
70
75
80
85
Fuel Utilization (%)
90
95
Efficiency vs Fuel Utilization
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Efficiency (%)
Mode 1 – High efficiency mode
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Electric-Efficiency
Gas Efficiency
Total Efficiency
60
65
70
75
80
85
Fuel Utilization (%)
90
95
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Fuel cell theory and modeling
Vcell
1
 OCV   .u f  i .r
2
OCV = Open Cell Voltage
 = 100 – 220 mV
uf = fuel utilisation
i = current density
r = specific resistance
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Conventional Solution for dealing with fluctuating
renewable energy sources essentially is a complex
storage device in a linear energy system.
E - power
E - power
Storage
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Conventional Solution for dealing with fluctuating
renewable energy sources
E - power
Storage
H2O
E - power
O2
FC
Electrolyser
H2
H2O
heat
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Example: Integration of a H2 - power co-production
FC with fluctuating renewable energy sources.
E - power
air
IR-FC
NG
H2
N2
H2
Optional
(NG/N2 )
heat
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Energy hub model of previous example
E - power
E - power
IR-FC
CO / H2
NG
heat
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Remarks on ‘Gasgestookte
windenergie’
• No storage of H2 needed.
• Instead the storage capacity of NG is used
• North sea provides NG and Wind !!
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Conclusions
• System thinking!!
• Identify "inefficiencies"
• An integration between Fossil and
Renewable is possible and may be crucial
in meeting our needs without sacrificing
those of future generations.
• New definitions of efficiency and green
energy in MSMP systems needed
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Acknowledgments
•
TU Delft : Anish Patil, Theo + Nico Woudstra (Cycle
Tempo flowsheet calculations)
ETH : Martin Geidle (MSMP concept & calculations)