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Folie 1ICEPAG 2012 > Leucht > 08.02.2012

Hydrogen Rich Natural Gas as a Fuel for SOFC SystemsFlorian Leucht, Moritz Henke, Caroline Willich, Christina Westner,

Josef Kallo, K. Andreas Friedrich


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


Overview

Hydrogen production from renewable sources in Germany

System model

System reaction to hydrogen

Control approaches

System efficiency with hydrogen


Hydrogen Production from renewable sources in Germany

Rising interest in water electrolysisProduction, storage and convertion of hydrogen into electricity interesting Hydrogen content of 4 % in natural gas pipelines gives 15 TWh/a storage capacityFirst demonstration plant inaugurated in Prenzlau Oct. 2011 by EnertragMore demonstrations planned within a call financed by federal ministries of economics, environment and research

Picture courtesy of Enertrag


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


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


Control approaches

Standard approach: fuel flow control based on current via Faradays law

Extended by hydrogen equivalent

Determining fuel flow according to

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)

Fz

In

Faraday

H2

EQHFU

1

2

FaradayHrequired

NG2

nn

2624 HCOHCCH2 74EQH nnnn


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


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


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)


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


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


Thank you for

your attention

german aerospace center

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