Environmental Engineering Reference
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On the other hand, water electrolysis, which is an intrinsic carbon-free method
as it involves splitting water into its component parts, hydrogen (H 2 ) and oxygen
(O 2 ), is strongly limited because of the present high costs of electricity generation.
Thus, the costs will certainly represent one of the most important barriers to be
overcome for a sustainable massive production of hydrogen.
An overview of the strategies for hydrogen manufacture is reported in Fig. 2.1 ,
where all likely production technologies are related to the different resource
options.
The different methods could be classified as: (i) thermal, (ii) electrolytic or (iii)
photolytic processes, they will be all detailed in this Section.
The heart of the thermal processes consists of using the energy associated with
chemical reactions to obtain directly hydrogen (see Sect. 2.1.1 ). Hydrocarbon
reforming reactions as well as coal gasification are part of this type of processes. In
natural gas SR the fuel reacts with steam at relatively high temperature, producing
hydrogen and carbon dioxide [ 5 ]. In partial oxidation and gasification processes
the fuels react with a controlled oxidant mixture (air or/and oxygen, and steam)
producing similar product mixtures. A further method that should be considered as
'thermal' is the technology based on thermochemical cycles involving different
Thermal processes
Natural gas
Steam reforming
Partial oxidation
Oil
Coal
Gasification
Biomass
H 2
Thermochemical
cycle
Nuclear
Solar
Wind
Power plant
For electricity
production
Electrolysis
Photolysis
Fig. 2.1
Flowsheet of the main hydrogen production technologies
 
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