Performance assessment of integrated solid oxide fuel cell and biomass gasification systems

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Performance assessment of integrated solid oxide fuel cell and biomass gasification systems

Hydrogen + Fuel Cells 2009

Can Ozgur Colpan

[email protected] Ibrahim Dincer [email protected] Feridun Hamdullahpur [email protected] Yeong Yoo [email protected]

PERFORMANCE ASSESSMENT OF INTEGRATED SOLID OXIDE

FUEL CELL AND BIOMASS GASIFICATION SYSTEMS

Outline

• Introduction

• SOFC

• Biomass gasification

• Integrated SOFC and biomass gasification

• Literature summary • Objectives

• Modeling

• Transient heat transfer modeling of SOFC

• System level modeling (Energy and exergy analyses)

• Results

Introduction

– SOFC

• High temperature fuel cell (500-1000°C) • Application areas:

• Stationary power and heat generation • Transportation applications

• Portable applications

• Advantages:

• No need for precious metal electrocatalysts

• Fuel flexibility (Hydrogen, carbon monoxide, methane, higher hydrocarbons, methanol, ethanol, landfill and biomass-produced gases, ammonia,

hydrogen sulfide) • Internal reforming

• Good thermal integration with other systems

• Disadvantages:

• Degradation due to carbon deposition and sulphur poisoning • Challenges with construction and durability

Introduction

– Biomass gasification

• Oxygen / Enriched oxygen

• Steam 4 Gasification Digestion Fermentation Combustion Pyrolysis Liquefaction

Introduction - Integrated SOFC and Biomass

Gasification Systems

 Researches focus on finding the optimum performance and the most economic solution for given biomass fuels and desired

outputs.

GASIFICATION GAS CLEANUP _SOFC

Biomass Product gas Cleaned gas  Reactor type  Gasification agent  Feedstock  Operating conditions Electricity Heat  Temperature level  Components  Design type  Temperature level  Reforming type  Flow configuration  Catalyst materials  Operating conditions

Literature Summary

• Omosun et al. (2004): They compared cold gas cleanup and hot gas cleanup systems to be used in biomass gasification/SOFC system.  Hot gas cleanup should be preferred.

• Panopoulos et al. (2006): They investigated the integration of a SOFC with a novel allothermal biomass steam gasification process.  the electrical efficiency of the system as 36% and exergetic efficiency as 32%.

• Cordiner et al. (2007): They studied the integration of a downdraft gasifier with a SOFC in which woody material is used as the fuel.  Electrical efficiency of the system is calculated as 45.8%.

• Athanasiou et al. (2007): They studied integrated SOFC/steam

turbine/gasifier system.  Electrical efficiency of the system is found to be 43.3%.

Objectives

• To model integrated SOFC and biomass gasification systems for predicting the performance of the system.

• Transient heat transfer model of a SOFC

• Thermodynamic models for the rest of the components

• To study the effect of gasification agent on the performance of the system. Performance assessment parameters are:

• Electrical efficiency

• Fuel utilization efficiency • Power-to-heat ratio

• Exergetic efficiency

Transient Heat Transfer Model of SOFC

• A control volume around the repeat element of a planar, co-flow SOFC • 2-D modeling in solid structure and 1-D modeling in fuel and air channels

• Input parameters: Cell voltage, Reynolds number at the fuel channel inlet, excess air coefficient. Output parameters: Current density, temperature, and molar gas composition distributions, fuel utilization, power output and electrical efficiency of the cell

• Six gas species CH₄, H₂, CO, CO₂, H₂O and N₂ at the fuel channel inlet and two gas species O₂ and N₂ at the air channel inlet

• Fully developed laminar flow conditions in channels

• Convection in the rectangular ducts and surface-to-surface radiation effects, conduction heat transfer at the section where the interconnects are in contact with PEN structure,

ohmic, activation and concentration polarizations

System Level Modeling-II

• The syngas composition (from the thermodynamic model of the gasifier) • The number of SOFC stacks that must be used in this system (using the

output of the heat transfer model of the SOFC) • The molar flow rate of dry biomass

• The enthalpy flow rate of all states • Work input to the blowers and pump • Performance assessment parameters

• Electrical efficiency

• Fuel utilization efficiency • Power-to-heat ratio









System Level Modeling-III

• The physical and chemical exergy flow rates:

• The exergy balance:

• The exergetic efficiency of the system:

D e e e i i i cv j _j j o x E ex n ex n W Q T T _     _{      }  _         1 0 ) s (s T ) h (h exPH   _o  _o  _o k k o CH k k CH x x T R x e x ex      ln process net Ex W          





(for all substances) (for ideal gas mixtures) (for C_xH_yO_z)

(for O/C<2) (Szargut, 2005)

Results-I

Syngas composition

Output of SOFC model

r Re i_c,ave[A/cm2_{] U} F Wsofc [W/cm2] nstack Case1: Air 0 10.0 0.240 0.85 0.156 13 Case2: Enriched O₂ 0 6.5 0.246 0.85 0.160 13 Case3: Steam 0 1.5 0.343 0.85 0.223 9 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0 1 2 3 4 5 6 7 8 9 10 M a x . ca rb o n a ct iv it y Distance to inlet (cm) Case 1 Case 2 Case3

Results-III

Case-2 Case-3

Results-IV

Power demand for auxiliary components, net power and heat output

Performance assessment parameters

FUE PHR

Case1: Air 18.5% 63.9% 0.409 30.9%

Case2: Enriched O₂ 19.9% 60.9% 0.487 30.7%

el



Mass flow rate of substances entering the system

Results-V

Exergy destruction ratios

• A new model for a SOFC and biomass gasification system:

• Heat transfer model for SOFC

• Thermodynamic models for the rest of the components

• Case-3 (steam):

• The highest electrical efficiency, power-to-heat ratio and exergetic efficiency • The lowest fuel utilization efficiency

• The largest portion of exergy destruction:

• Gasifier - Cases 1 (air) and 2 (enriched oxygen)

• Heat exchanger used for heating the air entering the SOFC - Case-3 (steam)

• Future study: An exergetic optimization to maximize the exergetic efficiency of the system

Acknowledgments

The financial and technical support of the following are gratefully acknowledged: • Carleton University

• University of Ontario and Institute of Technology • An Ontario Premier’s Research Excellence Award

• The Natural Sciences and Engineering Research Council of Canada • EcoEnergy Technology Initiative Program