1 hydrogen and fuel cells. hydrogen: the reality - hydrogen is the lightest of all gases - its...
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Hydrogen and Fuel Cells
Hydrogen: The Reality
- Hydrogen is the lightest of all gases - Its physical properties are incompatible with the requirements of the energy market (Low energy density)
CV = 13MJ/ m3 & = 0.019 kg/m3 at STP
Production, packaging, storage, transfer and delivery of the gas.
- All key components of a hydrogen economy- So energy intensive that alternatives should be
considered.
Relative Energy Consumption
• A hydrogen economy will involve transport by road• H2 or methane stored at 200 bar, delivered in a 40 ton tanker• These tanks can be emptied to only 42 bar to accommodate the 40 bar pressure systems of the receiver
(such pressure cascades are standard practice)• Thus, pressurised gas carriers deliver only 80% of their freight, while 20% of the load remains in the tanks and returned to the gas plant.
Relative Energy Consumption
• At 200 bar pressure: 3.2 tons of methane, but only 320 kg of H2 can be delivered by a 40 ton
tanker.• A direct consequence of the low density of H2 +
the weight of the 200 bar PRESSURE VESSEL and many safety installations.• Allowing for future %wt improvements in GH2
storage to provide 500kg, over 39 tons of dead weight have to be moved on the road to deliver 400kg of H2.
[ ]
0,5
9,57,0
4,8
1,4 0,4
1,21,53,7
7,4
10
6
4
20
4
2
0
8
Energy / Volume
kWhdm3
kWhkg[ ]
Gasoline
LNG-160oC
LH2
-250oCCGH2
700 bar(Composite)
CGH2
200 bar
(Steel)LNG: Liquefied Natural GasLH2: Liquefied Hydrogen
CGH2: Compressed Gaseous Hydrogen
Energy / Weight
6
8
Energy Density of Tank Systems for Passenger Cars.
© Imperial College London
What are the issues for hydrogen in fuel cells?
• Fuel cells – what, how, why and when?
• ‘Markets’ for fuel cells
• Hydrogen for stationary fuel cells
• Hydrogen for transport fuel cells
• The International Perspective
• The future?
Fuel Cells
• Fuel cell is an electrical cell, which unlike a battery can be fed with a continous supply of fuel so that electrical power production can be sustained indefinitely.
• Several different fuel cell types, all work on the same principle: converting hydrogen directly into electrical energy and heat through the electrochemical reaction of hydrogen and oxygen:
energy22 222 OHOH
energy22 222 OHOH
Fuel Cell Operation
• A fuel cell consists of an electrolyte sandwiched between two thin electrodes (a porous anode and cathode).
• Hydrogen, is fed to the anode where a catalyst separates dissociates into charged electrons, e-, and positively charged ions (protons), H+.
• Electrons at anode side of cell can’t pass through electrolyte to positively charged cathode; must travel to it via an electrical circuit (electrical current).
• Protons move through the electrolyte to the cathode and combine with oxygen and electrons, producing water and heat.
Fuel Cell Operation
H+
H+
e-
O2
load
e-
H2
depleted H2
Depleted O2 + H2O
+-anode: H2 → 2H+ + 2e- cathode: 2H+ + 2e- +1/2O2 → H2O
electrolyte
Fuel Cell Stacks
• A single fuel cell produces enough electricity for only the smallest applications [a single PEM fuel cell produces around 0.7V and 0.2A direct current (d.c.)]
• Typically combined in series into a fuel cell stack. A typical stack may consist of hundreds of fuel cells.
A fuel cell is a device that electrochemically oxidises a fuel, creating a flow of electrons
5kW stack (1993)
Evolution of Ballard Fuel Cell stacks
50kW stack (1999)
Air + WaterHydrogen ( H2 )
Air (O2)
Cell Components Single Cell Stack with End Platesand Connections
Cooling/Bipolar Element with Gas/Water Channels
Proton ExchangeMembrane (PEM)
PEM
CatalystElectrode
Proton Exchange Membrane Fuel Cell Schematic
Hydrogen Rich Fuel
• Fuel cells can also run on conventional hydrogen rich fossil fuels.
• This requires a reformer to extract the hydrogen from the fuel.
• A common fuel reformer (or fuel processor) is a steam reformer.
CO2H2O (l)
heat
hydrogen rich fuel hydrogen to fuel cell
reformer
Steam Reformer: Methanol
• As methanol comes into contact with the catalyst it splits forming carbon monoxide and hydrogen:
23 2HCOOHCH 23 2HCOOHCH
• High temperatures of reformer causes water vapour to decompose into oxygen and hydrogen, with oxygen combining with the CO to form CO2.
222 2
1OHOH 222 2
1OHOH 2222 2
1COHCOOH 2222 2
1COHCOOH
INVERTERHYDROGEN
RICH GASFUEL INPUT
HEATRECOVERY
FUEL PROCESSING PREHEATINGHEAT FOR
COGENERATION
FUELCELL
STACK
FUEL PROCESSOR
OXYGEN (AIR)
AC POWEROUTPUT
DC POWEROUTPUT
WATER
Fuel cell system components usually include a fuel processor
Though significant barriers exist, fuel cells are emerging in applications
• Other technologies already establish and perform the functions we want.
• Energy markets are frequently conservative (slow to change).
• Fuel cell costs are high, performance low
(like many new technologies)• But fuel cells are becoming available:
– PAFC systems are already installed in many areas– PEM systems are becoming available– The first FCVs are leased to customers– Hundreds of fuel cells are in test and demonstration
worldwide
The stationary fuel cell system is complex and expensive if it includes fuel processing
Powerconditioning
Fuelprocessing
Fuel cell
Thermalmanagement
Alstom/Ballard250kW system
Conventional Fuel
• A practical near future fuel source for automotive fuel cells are hydrogen-rich fuels.
• such as methanol, natural gas, petrol, or gasified coal used in combination with a reformer.
PEM fuel cell and reformer
fuel tank
2 d.c. motors
fuel
H2O + heat
H2
d.c. power
airair
As is the transport fuel cell system:Daimler NeCar 3 Methanol Fuel Cell Prototype
Methanol Tank
Gas Cleaning
Cooling
Water Tank
Fuel Cells + Air Supply
Electrical System
Reformer +Catalytic Burner
Hydrogen simplifies this:Inside Daimler’s Necar 4
LH2
Tank
FuelCells
ElectricMotor
The fuel cell ‘fleet’ is now mostly hydrogen fuelled
DaimlerChrysler
Toyota
GM/Opel
IrisBus
MAN
Ford
FC system using H2 (GM Data)
HSDI DIESEL
G-DI ENGINE
Pa
ss
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ar
Av
era
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Po
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s/T
ruc
k A
ve
rag
e
Po
we
r
0
10
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50
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0 10 20 30 40 50 60 70 80 90 100
PERCENT LOAD
PE
RC
EN
T T
HE
RM
AL
EF
FIC
IEN
CY
G-DI: Gasoline Direct InjectionHSDI: High-speed Direct Injection
FC system using MeOH
(estimate)
FC system using gasoline(estimate)
On-board system efficiency and response are other reasons for on-board hydrogen
What about the future?
• In the very long term, electricity and hydrogen are likely to become complementary energy vectors of choice.
• Hydrogen and the fuel cell are complementary, and each enables the other.
• The transition to the ‘long term’ is unclear, but the ubiquitous interest in fuel cells and hydrogen suggests it may be underway.