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CME4002
Hydrogen EconomyProfessor K M Thomas
Lecture 1
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Hydrogen
� Fossil fuels are a pre-existing sourceof energy.
�
Hydrogen does not come as a pre-existing source of energy
� It is a carrier. Hydrogen can be
made from both renewable and non-renewable energy sources.
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Why are we considering the possibilityof the hydrogen economy?
� We are close to, or at, peak oilproduction
�
Future decline in petroleum reserves� Future high cost of petroleum
� Security of supply
�
Climate change� Environmental benefits
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Drivers
The use of hydrogen energy fortransport applications will lead tolower«�
use of fossil fuels� CO2 emissions� Climate change� Pollution
and improved� Energy security / diversity / flexibility� New industries
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Future Sustainable Hydrogen Energy ChainJ W Gosselink (2002). Int. J. Hydrogen Energy 27 1125-1129
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Current Hydrogen Use
� Hydrogen is widely used in industrywhere safety issues and use can be
controlled. It is distributed inpipelines over a limited area todifferent chemical processes.
� The problems arise in the use ofhydrogen for transport applications
� Storage of hydrogen with a 300 milerefuelling range is an unsolved problem
� Why?
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FuelMJ / kg
FuelCO2 / kg
FuelH2O / kg
FuelCO2 /
MJH2O /
MJ
(HHV) (kg) (kg) (kg) (kg)
Carbon (s) 8.94 3.67 0 0.4 0.00
Hydrogen (g) 42.92 0 9.00 0.00 0.06
Methane (g) 55.64 2.75 2.25 0.05 0.04
Octane (l) 48.35 3.09 .42 0.06 0.03
Cetane (l) 47.56 3. 2 .35 0.07 0.03
Methanol (l) 22.70 .38 . 3 0.06 0.05
Ethanol (l) 29.70 .9 . 7 0.06 0.04
fuel + [ O2(g) ] p [ CO2(g) ] + [ H2O(l) ] + energy
32.79
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Calculation of Parameters in
Table
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Thermodynamic data (298 K)
(HfH2O(l) = -285.8 kJ mol-1
(HfH2O(g) = -241.8 kJ mol-1
(HfCO2(g) = -393.5 kJ mol-1(HfCH4(g) = -74.6 kJ mol-1
(
HfO2(g) =(
HfH2(g) =(
HfC(s) = 0 kJ mol-1
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Enthalpy calculationH2(g) + ½ O2(g) H2O(l)
(HrH2O(l) !
R(Hf
(products) ² R·(Hf
(reactants)
(HrH2O(l) = -285.8 ² (0 + ½*0) kJ mol-1
(HrH2O(l) = -285.8 kJ mol-1
Enthalpy for Reaction is negative(exothermic)
Similarly C + O2 CO2
(
HrCO2(g) = -393.5 kJ mol
-1
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Calculation for Hydrogen
Combustion� Hydrogen
� 1 mole H2 = 2g gives 1 mole of H2O
�
1kg H2 = 500 moles� Heat released = 500 x 285.8 x 103 J
= 142.9 x 106 J
= 142.9MJ/kg Fuel
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Methane� Reaction CH4 + 2O2 CO2 + 2H2O� Enthalpy of reaction(Hf -393.5 -2 x 285.8 ²(-74.6) = -890.5kJ exothermic ² heat given out
1 mol CH4 = 12 + 4 = 16 g� 1 kg = 1000/16 moles = 62.5 moles� Heat released from 1 kg = 62.5 x 890.5
kJ = 55656 kJ�
= 55.656 MJ/kg� 1 kg CH4 contains 750 g of carbon and 250
g of hydrogenCO2 = 0.75 x (44/12) = 2.75 kg/kg Fuel
H20 = 0.25 x (18/2) = 2.25 kg/kg Fuel
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Thermodynamic Calculations
� Use (HfH2O (g) = -241.8 kJ mol-1
instead of(H
f
H2
O (l) = -285.8 kJ mol-1
� H2(g) + ½ O2(g) H2O(l)(HrH2O(l) = -241.8 kJ mol-1
� 1kg H2 = 500 moles� Heat released = 500 x 241.8 x 103 J
= 120.9 x 106 J= 120.9 MJ/kg Fuel
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Lower heating values (LHVs) - per mass basis
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Calculations
� H2(g) + ½ O2(g) H2O(l)� Heat released = 142.9 MJ/kg Fuel� D
ensity H2(liquid) = 0.0708 kg L-3
� Heat released = 142.9 x 0.0708 =� =10.12 MJL-1
� H2(g) + ½ O
2(g) H
2O(l)
� Heat released = 120.9 x 0.0708=8.56 MJL-1
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The Problems for Vehicles
� The low energy density of hydrogenon a volume basis.
� The very low critical temperature ofhydrogen (33 K).
� Large tanks required and possiblypressure control, cooling, insulation
etc� Hydrogen has 3 x the energy ofpetrol on a mass basis but only ¼ xthe energy on a volume basis
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How can we overcome these
Problems?� Develop new storage methods. Theissues are size, weight, resistance toimpacts, safety, durability, materialsstrength (high pressure cylinders),insulation (for cryogenic temperatures)etc
� Use of the more efficient fuel celltechnology. The issues are purity ofgas, efficiency, reliability, etc.
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Liquid H2 Storage volume
� Amount to be stored = 5-13 kg H2
Density = 0.0708 kg L-1
�
Volume storage =5/0.0708 = 64 L
13/0.0708 = 183.6 L
� If smaller cars are used for greaterefficiency these values are large evenwith liquid hydrogen
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The grand H2 storage challengesustainable produ tion of H2 store / transport energy
5 kg H2 gas (ambient)
~ 5 m diameter vessel
5 kg H2 liquid (triple point)
~ 0.5 m diameter vessel
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Co bu on 2H2(g) + O2(g) p 2H2O(l)
1H
0298
2kgMJ142
!(H
Fu Cell (proton exchange membrane)
2H2(g) p 4H+ + 4e- anode
4H+ + 4e- + O2(g) p 2H2O(l) cathode
2H2(g) + O2(g) p 2H2O(l) cell
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Fundamentals
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Hydrogen Properties
� Hydrogen is a diatomic molecule (H2)
� Molecular weight = 2 g mol-1
�
Critical temperature = 33 K (-240oC)� Liquid density
0.0708 g cm-3 at 20 K
0.0708 kg L-1
70.8 kg m-3
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Physical storageMolecular hydrogen (H2)
Chemical storage
Atomic / ionic / covalent hydrogen
Storage at low
temperatures and/or
high pressures
Fast and reversiblecharging and
delivery
Storage in close to
ambient conditions
Slow and
irreversible charging
and delivery
o ptimum ?
Different materials storage types
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Hydrogen Storage Problems� Cylinders: Materials problems are an issue above
500 bar, can the cylinder be filled easily, quicklyand safely
�
Liquid hydrogen: very low (< 240 K) temperature,fuel evaporation, safety, can the tank be filledsafely by a member of the public ² rocket fuel
� Materials Storage
Adsorption: Only works at cryogenic temperaturesHydrides: High desorption temperaturesChemical methods: regeneration of materials
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Hydrogen storage where volume
is not an issue
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The Ross Barlow Hydrogen Hybrid Canal BoatLaunched 21 September 2007
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� Most people accept the argument for reducing CO2
emissions; but few think that their owncontribution can make a difference; they holdgovernment, business and even other end-
consumers primarily responsible� Regular motorists - especially those with families
² are reluctant to change behaviour than thosealready ¶converted· (to public transport, cycling,
etc)� Most people accept that hydrogen energy may
have a part in the sustainable energy future.
� Volume sustainable production and distribution ofhydrogen would enable current car use to continueif shift to public transport unachievable.
Public Perception of Hydrogen