Hydrogen Production, Storage and Fuel Cells - Springer Link

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reforming step and also reduce the amount of steam required; (3) Primary ... kJ molА1Ю whereby a fuel is reacted with oxygen to produce a mixture of carbon ... Water electrolysis is a process in which water is broken into hydrogen and ... were about 60–75% efficient, but small-scale units now achieve efficiencies closer.
Chapter 3

Hydrogen Production, Storage and Fuel Cells

3.1 Hydrogen Production Methods Hydrogen can be produced through thermal, electrolytic, or photolytic processes using fossil fuels, biomass, or water as a feedstock. Photolytic processes will not be covered here. Thermal processes used to produce hydrogen from methane include steam methane reforming (SMR), partial oxidation (POX) and autothermal reforming (ATR), which combines the SMR and POX processes. When heavy oils or coal is used, the gasification process is commonly used.

3.1.1 Steam Methane Reformation Steam reforming is a widely used method of producing syngas, a mixture of hydrogen and carbon monoxide, from methane. The typical feedstock is natural gas, which comes in several varieties including dry, wet, sweet and sour gas. These designations refer to the composition of the gas. Dry gas is mostly methane, whereas wet gas contains higher hydrocarbons. Sweet gas has little hydrogen sulfide, whereas sour gas contains higher levels of hydrogen sulfide. Steam reforming of methane typically consists of four steps: (1) Hydrogen sulfide and other sulfur compounds are removed to prevent catalyst poisoning; (2) Pre-reforming is used to protect against carbon formation during the main reforming step and also reduce the amount of steam required; (3) Primary reforming in which steam and heat are supplied to allow the reaction to proceed over a nickel catalyst at 700–830C; (4) A secondary reformer utilizes air to produce heat through combustion reactions to bring the temperature to *1300C and convert most of the remaining methane to syngas. The desulfurization process is an exothermic process that is typically carried out in a packed bed reactor. The sulfur compounds are adsorbed by the packed bed, which is usually ZnO. S. Al-Hallaj and K. Kiszynski, Hybrid Hydrogen Systems, Green Energy and Technology, DOI: 10.1007/978-1-84628-467-0_3,  Springer-Verlag London Limited 2011

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3 Hydrogen Production, Storage and Fuel Cells

Fig. 3.1 Steam reforming of natural gas process block diagram [3]

Natural Gas

Sulfur Removal Steam

ZnO Packed Bed

Desulfurized Natural Gas Pre-reforming

T=380-650 °C Ni Catalyst

Primary Reforming

T=700-830 °C Ni Catalyst

Steam

Oxidant

CO2 and H2 8-9% Methane T