Various technologies that can be used to produce hydrogen, they are:
(1) reforming of natural gas to hydrogen,
(2) conversion of coal to hydrogen,
(3) use of nuclear energy to produce hydrogen,
(4) electrolysis,
(5) use of wind energy to produce hydrogen,
(6) production of hydrogen from biomass, and
(7) production of hydrogen from solar energy.
Methods of hydrogen generation
Compared with other fossil fuels, natural gas is a cost-effective feed for making hydrogen, in part because it is widely available, is easy to handle, and has a high hydrogen-to-carbon ratio, which minimizes the formation of by-product carbon dioxide (CO2). The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (autothermal reforming).
Reaction of carbon monoxide with steam (water-gas shift) over a catalyst produces additional hydrogen and carbon dioxide, and after purification, high-purity hydrogen is recovered.
Since natural gas is a mixture containing carbon monoxide, carbon dioxide and unconverted methane bulk hydrogen is usually produced by the steam reforming of methane or natural gas. At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.
CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol
In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction, performed at about 130 °C:
CO + H2O → CO2 + H2 - 40.4 kJ/mol
Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
In most cases, carbon dioxide is vented to the atmosphere today, but there are options for capturing it in centralized plants for subsequent sequestration. For distributed generation, the cost of sequestration appears prohibitive.
Integrated steam reforming / co-generation- It is possible to combine steam reforming and co-generation of steam and power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separate hydrogen, steam and power plants.
In spite of the above facts, natural gas can not be considered as a long-range fuel for centralized plants for the hydrogen economy. Whether it will be possible to utilize partial oxidation or autothermal reforming for the distributed generation of hydrogen appears to depend on developing new ways of recovering oxygen from air or separating product hydrogen from nitrogen. This is needed because conventional, cryogenic separation of air becomes increasingly expensive as unit size is scaled down. Membrane separations, in contrast, appear amenable to this application and may provide the means for producing small, efficient hydrogen units. A mass-produced hydrogen appliance suitable for distributed generation in fueling stations is to be developed.
(1) reforming of natural gas to hydrogen,
(2) conversion of coal to hydrogen,
(3) use of nuclear energy to produce hydrogen,
(4) electrolysis,
(5) use of wind energy to produce hydrogen,
(6) production of hydrogen from biomass, and
(7) production of hydrogen from solar energy.
Methods of hydrogen generation
Compared with other fossil fuels, natural gas is a cost-effective feed for making hydrogen, in part because it is widely available, is easy to handle, and has a high hydrogen-to-carbon ratio, which minimizes the formation of by-product carbon dioxide (CO2). The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (autothermal reforming).
Reaction of carbon monoxide with steam (water-gas shift) over a catalyst produces additional hydrogen and carbon dioxide, and after purification, high-purity hydrogen is recovered.
Since natural gas is a mixture containing carbon monoxide, carbon dioxide and unconverted methane bulk hydrogen is usually produced by the steam reforming of methane or natural gas. At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.
CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol
In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction, performed at about 130 °C:
CO + H2O → CO2 + H2 - 40.4 kJ/mol
Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
In most cases, carbon dioxide is vented to the atmosphere today, but there are options for capturing it in centralized plants for subsequent sequestration. For distributed generation, the cost of sequestration appears prohibitive.
Integrated steam reforming / co-generation- It is possible to combine steam reforming and co-generation of steam and power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separate hydrogen, steam and power plants.
In spite of the above facts, natural gas can not be considered as a long-range fuel for centralized plants for the hydrogen economy. Whether it will be possible to utilize partial oxidation or autothermal reforming for the distributed generation of hydrogen appears to depend on developing new ways of recovering oxygen from air or separating product hydrogen from nitrogen. This is needed because conventional, cryogenic separation of air becomes increasingly expensive as unit size is scaled down. Membrane separations, in contrast, appear amenable to this application and may provide the means for producing small, efficient hydrogen units. A mass-produced hydrogen appliance suitable for distributed generation in fueling stations is to be developed.
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