Transcript DLR-Präsentation Verkehr mit Kopf

Hydrogen Rich Natural Gas as a Fuel for SOFC
Systems
Florian Leucht, Moritz Henke, Caroline Willich, Christina Westner,
Josef Kallo, K. Andreas Friedrich
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German Aerospace Center
Germany‘s national research center for
aeronautics and space
App. 7,000 people in
32 institutes at
16 national and international locations
Institute of Technical Thermodynamics
Systems analysis and technology
assessment,
Electrochemical energy
technology,
Thermal process technology
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Overview
Hydrogen production from renewable sources in Germany
System model
System reaction to hydrogen
Control approaches
System efficiency with hydrogen
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Hydrogen Production from renewable sources in
Germany
Rising interest in water
electrolysis
Production, storage and
convertion of hydrogen into
electricity interesting
Hydrogen content of 4 % in
natural gas pipelines gives
15 TWh/a storage capacity
First demonstration plant
inaugurated in Prenzlau Oct. 2011
by Enertrag
More demonstrations planned
within a call financed by federal
ministries of economics,
environment and research
Picture courtesy of Enertrag
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System Model
Based on Siemens CHP100
Tubular cells
Delivers 110 kW at
atmospheric pressure
 150 kW at 4 bar
Controls for:
Power
Air flow (temperature)
Fuel flow (current)
Humidification (low load)
Stack temperature
(electrical heating, low load)
Leucht, F. et al.: Fuel Cell System Modelling for SOFC/GT Hybrid Power Plants,
Part I: Modelling and simulation framework, Journal of Power Sources, 196 (2011) 1205-1215
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System reaction to hydrogen
System operating at full load with
pure natural gas
System does not ‘know’ about
the change in fuel composition
Constant fuel flow
Fuel utilization rises up to 100 %
System would be destroyed
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Control approaches
Standard approach: fuel flow control based on current via Faradays law
n HFaraday

2
Extended by hydrogen equivalent
Determining fuel flow according to
I
z F
H2EQ  4  n CH4  7  n C2H6  n CO  n H2
1 n H2


FU H2EQ
Faraday
n
required
NG
If no information on fuel composition is available H2EQ stays fixed
Other possibilities for control input variables could be:
Temperatures (partially long time constants)
Power, voltage and current (fast response to fuel quality)
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Combustion zone temperature
Short reaction time to changes in
offgas composition
Combustion zone temperature
stays stable
Power drops during transient
Bad indicator for fuel gas quality
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Voltage
If fuel quality drops, voltage drops
Controlling fuel flow based on
system voltage keeps power and
voltage stable
BUT: Power is controlled via cell
voltage,
If fuel control keeps voltage stable
power control is useless
Fuel flow control and power
control might have opposing
targets
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Delivered power
Fuel flow controlled based on
delivered power
System voltage controlled to
maintain safe operation point
Cell current / voltage are
influenced by fuel quality
If power cannot be maintained by
manipulation of voltage command
fuel flow is increased.
Power stays stable, deviation from
set point very small (<100 W)
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System efficiency with hydrogen
Base case efficiency drops more
than 10 %
Power set point cannot be
maintained
Major problem: missing heat sink
(reforming of methane)
All controls show large drop in
efficiency
Fuel utilization is a lot lower
than in base case
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Summary
Power to Gas and hydrogen storage has very high potential for future
power supply
SOFC systems can be operated with hydrogen rich fuels
System controls have to be able to deal with changes in fuel quality
Using system delivered power as a fuel quality indicator shows
promising results
System controls need to be enhanced in order to keep system efficiency
high
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Thank you for
your attention
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