Download Biomass-based Fuel Cells

Biomass-based Fuel Cells
- Application to Manned Space Exploration
Prof. Aarne Halme
Dept. of Automation and Systems Technology
Helsinki University of Technology
Content:
• Fuel cells – a short introductory
- chemical fuel cells
- biocatalyzed fuel cells - what they are?
• Current status of research and practice
- chemical fuel cells
- biocatalyzed fuel cells
• Biocatalyzed electrolysis – a recent new innovation
• Application to manned space flights
• Summary
Fuel cells – a short introduction
Energy Conversion Schemes
Fuel cell technology
• Chemical fuel cell concept is already 100 years old
innovation.
• There are many different type of fuel cells, but they all
work accoding to the same main principle shown below.
• Electrode reactions need a catalyst – Pt most comonly
used, but there are also other alternatives.
Chemical fuel cells
•
Low temperature fuel cells
- PEMFC (Proton Exchange Membrane Fuel Cell)
- DMFC (Direct Methanol Fuel Cell)
- AFC (Alcaline Fuel Cell)
- PAFC (Phosforic Acid Fuel Cell)
•
High temperature fuel cells
- MCFC (Molten Carbonate Fuel Cell)
- SOFC (Solid Oxide Fuel Cell)
•
Most fuel cells operate with hydrogen gas. Exceptions are
- DMFC, which operate with liguid methanol
- high temperature cells (SOFC), which operate also with more
complex fuels, like natural gas/methane, co, or even diesel
Reactions and ion flow in different type of fuel cells
Technology trends
• AFC is the oldest technology (used already in
60’s in Apollo program)
• Today development priority
- PEM (car industry, small CHP-plants…)
- DMFC (electronics etc applications)
- high temperature fuel cells (SOFC, MCFC for
CHP and larger power station applications)
Biocatalyzed fuel cells
• Opposite to chemical fuel cells biocatalyzed fuel
cells are a quite recent innovation
• The early studies are from the beginning of 90’s
• The basic idea is similar to PEM, but reactions
take place in liguid phase and are catalyzed
biologically either by living microbes or
enzymes.
• A very recent close innovation is biocatalyzed
electrolysis to produce hydrogen
Biocatalyzed fuel cells – operating principle
•
•
•
Above a bacterial fuel cell (BFC)
Enzyme fuel cells operates in the same way, only bacteria are
replaced with an enzyme
Most biocatalyced fuel cells need a mediator (above HNQ) to
transport electrons to electrodes
Biocatalyzed fuel cells vs chemical
fuel cells
Biocatalyzed fuel cells
•
•
•
•
•
Wide fuel selection, in principle
all biodegrable substrates
Final products water +CO2 +
anode process products
Low temperature (ambient)
operation only
Low power density
~ 1 mW/cm2
High operational time
acheivable (BFC)
Chemical fuel cells
•
•
•
•
•
Restricted fuel selection:
hydrogen, methanol, methane..
Final product water if hydrogen
is used as fuel, otherwise more
complex (+C02+reforming side
products)
Low and high temperature
operation possible
Higher power density
DMFC ~ 60 mW/cm2
PEM ~ 300 mW/cm2
SOFC ~ 400 mW/cm2
High operational time still a
problem in many cases
Biocatalyzed electrolysis – a
recent new innovation
Biocatalyzed electrolysis - Operation principle
E
eOx
Fuel:
Organic
Fuel:
organic Biocata
substrate
lyst
substrate
Re
Ox
H2
Mediator
H+
Re
H+
Anode
•
•
PEM Cathode
External electrical power source E is needed to make system Gipps free
energy negative allowing hydrogen reduction going freely
E is a very low voltage ~0,2-0,3 V. Energy of released hydrogen is (much)
more than taken by the external power source.
State of the art
•
•
•
•
Biocatalytic electrolysis has been known only for a couple of years
now
Published experimental results are available using a bacterial
catalyst using organic acids and communal waste water as fuel
(2006, Prof. Logan, Pensylvanian State University, and Dr
Rozendahl, Wageningen University).
Unpublished experimental tests have been done by this author
using fructose as fuel and fructose dehydrogenase (FDH) enzyme
as catalyst (2007)
Experiments clearly show that the method is working and worth of
further development. Logan reports 92W/m3 reactor volume
hydrogen production (burning value) with 288% electrical efficiency
(Web-site information).
Application to manned space flights
• NASA and ESA have preliminary plans for
manned exploration flights to Mars around the
middle of this century.
• According to one scenario 6 astronauts make
2,5 years return mission spending 1 year in a
camp in Mars.
• Especially during the camp phase it is rational to
establish a micro ecological life supporting
system with plant cultivation, where organic
wastes are recirculated and the related energy is
recovered as electricity.
ARIADNA AO/1-4532/03/NL/MV
results
Scenario I (on Mars)
Scenario II (on Mars)
Six Astronauts
Six Astronauts
Menu:
packaged food (1500 g)
and growth food (67 g)
per day per person
Menu:
packaged food (565 g)
and growth food (1000
g) per day per person
Input and output of an astronaut
per day, all plants menu
Input and output of an astronaut per day, Extended Base, All plants menu,
limited to items applicable for fuel-cell study
INPUT
OUTPUT
O2
0.83 kg
CO2
1 kg
H20 total *
27.58 kg
Feces + toilet paper
(0.03 kg dry feces only)
0.053 kg (dry)
0.143 kg (wet)
Food (grown)
1.0 kg
Brine for urine
0.524 kg
Food
(packaged)
0.565 kg
Brine for shower/
handwash/ sweat
0.254 kg
Plant biomass (from
harvesting, cooking and
left-overs)
4.025 kg (wet)**
Wet trash (paper, wipes,
10% humidity)
0.26 kg
Dry trash (tapes, filters,
packaging , misc.)
0.60 kg
Î
Î
* 97% of water is circulated. The rest 3% goes along with brines; ** Includes 10% of left-overs and 30% processing waste
Input and output of plant field
per day (per person)
Input and output of plant field per day (per person), limited to items applicable for
fuel-cell study, Extended Base, All Plants Menu.
INPUT
OUTPUT
CO2
0.735 kg
O2
0.534 kg
H20
86.5 kg
Edible food
1.0 kg
Energy (light)*
69.7 k W
Non-edible
biomass
4.0 kg
Needed area
26.8 m2
Î
Î
*Energy (light) 2.6 k W/m2
Waste Biomass
One person
Six persons
Faeces
Rate (kg wet/day)
0.150
0.900
Ash (kg/day)
0.0075
0.045
Biodegradable waste (kg dry/day)
0.030
0.180
Energy density (MJ/kg dry biodegradable waste)
11.8
Energy (MJ/day)
0.354
2.124
Rate (kg wet/day)
4.00
24.0
Biodegradable solid waste (kg dry/day)
1.22
7.32
Vegetable residues and others
Energy density (MJ/kg dry biodegradable waste)
17.5
Energy (MJ/day)
21.35
128.1
Overall mass weight (kg wet/day)
4.150
24.90
Overall energy (MJ/day)
21.7
130.2
Overall solid biodegradable waste (kg/day)
1.25
7.50
Volume density (kg/m3)
Overall volume (liter)
300
4.17
25.0
Energy system
Solar
energy
Wind
energy
Transported
energy
from
Earth
•Heating
•Cooking
•Lighting
•Plant growth
•Motors&engines
•Electronic
devices
•…
Recycling energy
from fuel cell
Recirculation balance: SOFC and PEM fuel
cell system
Biomass
Collection
Energy Input
to the System
Net Energy
Output (Energy
Input – Output)
Digestion
Process
Byproduct as Feed for
Plant Growth
Other Byproducts
(Water and CO2)
Electricity
(Energy
Output)
Fuel Reformer
Fuel Cell
System
SOFC or PEM Fuel
Cell
Sequential batch anaerobic
composting system for space mission
Pretreatment
Post-treatment
Anaerobic Treatment
Biogas
(CH4+H2O)
Waste stream
Dewater
Biodegradables
( Excluding Urine )
Feed
Collection
5d
Particle size 2-5 cm
add wastewater to 35% TS compacted to
300 kg/m3
Compost
New
5d
Activated
5d
Mature
5d
Aerobic
5d
Organic Acid
Ambient Air
( CO2+H2 )
Inoculumm
Mass Balance
Input:
• 7.5 kg biodegradable waste
• 6 kg oxygen
Output:
• 1.5 kg methane (+4.1 kg CO2 + 1.9 kg
compost) (from AD process)
• 4.1 kg Water + 3.3 kg CO2 (from FC)
Energy Balance
Input:
130 MJ/day in biodegradable waste
Output:
26.2 MJ/day after AD process (20 %)
5.2 – 7.8 MJ/ after FC system (20-30%)
Overall energy efficiency:
4–6%
Recirculation balance: Biocatalyzed
fuel cell system
Pretreatment
(liquefaction)
Biomass Collection
Hydrogen
Production
Fermentation
Biological Fuel
Cell
Byproduct as Feed for Plant Growth
and others (water and CO2)
SOFC or PEM Fuel
Cell System
Energy Input for
Pumping and
Rotating.
Electricity
(Energy Output)
Net Energy Output (Energy
Input – Output)
Mass Balance
Input:
• 7.5 kg biodegradable waste
• 3.5 kg oxygen (100 % converted)
Output:
• 2 - 3 kg compost
• 3 – 3.5 kg Water
• 5 – 5.5 kg CO2 (from FC)
Energy Balance
Input:
130 MJ/day in biodegradable waste
Output:
39 MJ/day from the BFC system
30 MJ/day comsumed for the process
9 MJ/day or 104 W
Overall energy efficiency:
6.9 %
Summary and conclusions
• Biomass energy can be recovered in electrical form
when recycling waste in micro ecological life supporting
system during long space flights.
• Net balance of recovery is not much but positive and
seems little bit better when using biocatalyzed fuel cell
technology than classical diggestion, reforming and
chemical fuel cells.
• A new biocatalyzed electrolysis to produce hydrogen
directly from biomass seems very promising and may
bring a new dimension to this analysis.