Hydrogen from fossil sources
Von The biggest part of todays 500 billion cubic metres world-wide is generated from fossil sources (natural gas, oil) or is obtained as by-product-hydrogen in chemical processes. A lot of hydrogen is obtained by chlor-alkali electrolysis and crude-oil-refinery-processes.
Altogether the hydrogen generation as by-product amounts to around 190 billion cubic metres world-wide.
There are the following processes to generate hydrogen from fossil fuels:
Small Reformer
To be able to use hydrogen in fuel cell applications in the near future small reformers (steam reforming, partial oxidation) are being developed. These systems are intended particularly for mobile use in vehicles and in small stationary applications.
For mobile applications one is hoping that the higher energy density and the easier handling of a conventional liquid fuel could be used to supply fuel cells. For this purpose the partial oxidation or reforming of methanol or gasoline is particularly important.
Steam Reforming
Steam reforming is the endothermic catalytic conversion of light hydrocarbons (methane,..., gasoline) in the presence of steam. This large-scale process normally takes place at a temperature of 850°C and a pressure of 0.25 MPa (2.5 bar). Hydrogen and carbon dioxide as well as methane and carbon monoxide are produced in the conversion process. In the so called "shift reaction" carbon monoxide reacts with steam to generate carbon dioxide and hydrogen. The carbon dioxide and other unwelcome constituents are removed from the gas mixture by adsorption or membrane-separation later on.
The separated residual gas which contains about 60% of combustible components (H2, CH4, CO) is used as a fuel in the reformer, together with a part of the input gas.
The large-scale generation of hydrogen is done in steam reformers with production capacities of usually 100.000 cubic metres of hydrogen per hour. These plants are built by companies like Linde, KTI or Uhde .
Partial Oxidation
Partial oxidation is the thermal conversion of heavy hydrocarbons (e.g. residues from oil refining or diesel oil) with oxygen and sometimes with additional water vapour. The amounts of oxygen and hydrogen are allocated in such a way that gasification without external energy supply is possible.
This hydrogen generation process works with coal as well. The coal is ground very fine and mixed with water into a pumpable suspension with 50-70% of solid matters. This process is profitable only in typical coal mining countries like China or South Africa. In Germany there are only pilot plants.
In case hydrogen is to play an important role in the energy economy in the medium or long-term it is not recommendable to base its generation on conventional steam reforming or partial oxidation from natural gas, oil or coal in view of the environmental requirements (CO2 reduction).
Modern Processes
Modern processes make it possible to generate hydrogen potentially without CO2 from natural gas and using electric power:
Since the beginning of the 80's KVAERNER ENGINEERING S.A. from Norway is developing the plasma-arc-process which at 1600°C splits hydrocarbons into hydrogen and clean coal. For this process which causes no considerable emissions electric power and cooling water are needed in addition to the primary energy sources (petroleum, natural gas).
A pilot plant in operation since April 1992 generates 500 kg/h clean-coal (activated carbon) and 2000 Nm³/h hydrogen from 1000 Nm³/h natural gas and 2100 kWe. As an additional by-product superheated steam with a power of 1000 kW is generated. Considering all potentially usable products the plant works with an efficiency of almost 100%. Of this output about 48% are contained in hydrogen, 10% in super heated steam and the remaining 40% in activated carbon.
The process is in the pilot phase. As a next step there are plans to build a plant with a capacity of 100.00 Nm³/h hydrogen under industrial conditions.
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