Hydrogen Economy

Sustainable Energy Systems

Lower Heating Vale LHV

theoretical energy released to burn fuel and release water vapor

Higher Heating Value HHV

LHV plus energy to condense water to liquid

Hydrogen Embrittlement

formation of stress concentrations as H ions diffuse through the metal and accumulate at grain boundaries

Steam Reforming Equation

CH₄ + H₂O = CO + 3H₂

Water Shift Reaction Equation (Steam Methane Reforming)

CO + H₂O = CO₂ + H₂

Steam Methane Reforming Overall Equation

CH₄ + 2H₂O = CO₂ + 4H₂

Steam Reforming - Details

800-1000 ^oC, 14-20 bar, Ni/Al₂O_3, endothermic

Water Shift - Details

High temp shift at 350 ^oC with Fe-Cr; Low temp shift at 250 ^oC with Cu-Zn/Al₂O₃

Stages of Steam Methane Reforming

Desulphurization, Steam Reforming, Water Shift (high temp, low temp), CO₂ removal, high purity H₂

Coal Gasification

Initial exothermic oxidation of C, CO and H₂ to provide heat for gasification of H₂O, CO₂ and 2H₂. Occurs in oxygen poor environment (20-30% O₂)

Moving Bed Reactor

Solid coal loaded from top and forced down by gravity, combustion at base with gasification and pyrolysis above

Fluidized Bed Reactor

flow of sand and coal flushed with air, reaction rate limited by mass transfer

Entrained Air Reactor

Sand and air mixed producing gas and slag

Methane Pyrolysis

Decomposition of methane under high pressure at 1100-1200 ^oC, endothermic

Methane Pyrolysis Equation

CH₄ = C + 2H₂

Thermochemical Cycles

Water heated to dissociate into hydrogen and oxygen, chemical feedstocks recycled

Water Electrolysis

Decomposition of water into hydrogen and oxygen via exchange of protons through membrane with electrons collected as current

Type 1 - Compressed Hydrogen Cylinder

seamless metallic container @ 25 MPa

Type 2 - Compressed Hydrogen Cylinder

seamless metallic container hoop wrapped with fiber resin composite @ 45-80 MPa

Type 3 - Compressed Hydrogen Cylinder

Thin metallic liner fully wrapped with fiber resin composite @ 35 MPa

Type 4 - Compressed Hydrogen Cylinder

Polymer liner fully wrapped with fiber resin composite and metal foil to prevent permeation @ 70 MPa

Pressure Release Device (PRD)

spring loaded valve released above threshold to relieve pressure

Hydrogen Boiling Point

20 K, liquid below this point

Hydrogen Liquifacture

Hydrogen precooled by liquid nitrogen bath, JT value used to liquify hydrogen. Must be kept below 73K to cool during throttling.

Metal Hydride

Hydrogen reacts with a metal to form a hydride. Absorption at low temperature, released at high temperature.

Physisorption

bonding of molecular hydrogen to surface which induces dipoles on molecular hydrogen

Langmuir Isotherm of Adsorption equation

a = a_sk_adsp_H2/1+k_adsp_H2

Combustion of Methane Equation

CH₄ + 2O₂ = CO₂ + 2H₂O

Steam methane reforming enthalpy of formation

165 kJ/mol

combustion of methane enthalpy of formation

-890 kJ/mol

Methane pyrolysis enthalpy of formation

75 kJ/mol

Hydrogen combustion enthalpy of formation

-285 kJ/mol

PEM Electrolysis Anode Equation

2H₂O = 4H⁺ + 4e_^- + O₂

PEM Electrolysis Cathode Equation

2H⁺ + 2e^- = H₂

Alkaline Electrolysis Cathode Equation

2H₂O + 2e^- = 2OH^- + H₂

Alkaline Electrolysis Anode Equation

2OH^- = ½O₂ + H₂O + 2e^-

Water Electrolysis Overall Equation

H₂O = H₂ + ½O₂

PEM Electrolysis Catalyst

anode RuIrO₂/Ti and cathode Pt/C

Alkaline Electrolysis Catalyst

Anode Ni based, cathode Ni-mesh

HHVg

ΔH/M_R

HHVv

ΔH*p/RT