CME4002L1

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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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LHVs ± per liquid volume 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

V23

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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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Hydrogen Storage Technologies

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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

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� Slides will be put on Blackboard today

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