Reforming of natural gas

The steam reforming of natural gas to manufacture hydrogen is a mature industry. In this process, methane is reacted with steam over a nickel-based catalyst at around 900 °C and at elevated pressure (several MPa)  

The resulting mixture is known as synthesis gas (or syngas ) because it may be used for the preparation of a range of commodities that include various organic chemicals such as methanol, formaldehyde, 0x0 alcohols and polycarbonates. (It should be noted that synthesis gas is in fact a generic term that is used to describe the combined products - hydrogen and carbon monoxide -from the gasification of any carbonaceous fuel.) The steam reaction is 

At present, syngas is used largely for the manufacture of organic chemicals, as mentioned above, or is converted to hydrogen by the water-gas shift (WGS) reaction , as represented by reaction (2.5) below. There is, however, a further option that has sometimes been employed in the past and is likely to prove of 

When the object of reforming natural gas is to produce hydrogen and not to prepare organic chemicals or carbonaceous fuels, it is necessary to complete the conversion by subjecting the syngas to the WGS reaction. This converts the carbon monoxide to carbon dioxide by further reaction with steam over a catalyst at a much lower temperature, i.e.. 

The process may be undertaken in two steps by which the carbon monoxide content is first reduced to 2vol.% at 400 °C and then to 0.2vol.% at 200 °C. If ultra-pure hydrogen is required for use in fuel cells, the remaining small quantity of carbon monoxide is selectively oxidized to 0.002 vol.% by admitting air at 100 °C. As in the case of reaction (2.1), the use of excess steam assists the WGS reaction and enhances the yield of hydrogen, although at the expense of a reduction in overall thermal efficiency. 

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Coal gasification technology dates to the early nineteenth century but has been largely replaced by natural gas and oil. A more hydrogen-rich synthesis gas is produced at a lower capital investment. Steam reforming of natural gas is appHed widely on an iadustrial scale (9,10) and ia particular for the production of hydrogen (qv). 

Synthesis Gas Chemicals. Hydrocarbons are used to generate synthesis gas, a mixture of carbon monoxide and hydrogen, for conversion to other chemicals. The primary chemical made from synthesis gas is methanol, though acetic acid and acetic anhydride are also made by this route. Carbon monoxide (qv) is produced by partial oxidation of hydrocarbons or by the catalytic steam reforming of natural gas. About 96% of synthesis gas is made by steam reforming, followed by the water gas shift reaction to give the desired H2 /CO ratio. 

Higher range based on a 2.8 X 10 m /d steam reformer of natural gas at 1.90/kJ. Cost varies based on volume deflvered. 

High temperature steam reforming of natural gas accounts for 97% of the hydrogen used for ammonia synthesis in the United States. Hydrogen requirement for ammonia synthesis is about 336 m /t of ammonia produced for a typical 1000 t/d ammonia plant. The near-term demand for ammonia remains stagnant. Methanol production requires 560 m of hydrogen for each ton produced, based on a 2500-t/d methanol plant. Methanol demand is expected to increase in response to an increased use of the fuel—oxygenate methyl /-butyl ether (MTBE). 

Steam Reformings of Natural Gas. This route accounts for at least 80% of the world s methanol capacity. A steam reformer is essentially a process furnace in which the endothermic heat of reaction is provided by firing across tubes filled with a nickel-based catalyst through which the reactants flow. Several mechanical variants are available (see Ammonia). 

In the catalytic steam reforming of natural gas (see Fig. 2), the hydrocarbon stream, principally methane, is desulfurized and, through the use of superheated steam (qv), contacts a nickel catalyst in the primary reformer at ca 3.04 MPa (30 atm) pressure and 800°C to convert methane to H2. 

Based on these developments, the foreseeable future sources of ammonia synthesis gas are expected to be mainly from steam reforming of natural gas, supplemented by associated gas from oil production, and hydrogen rich off-gases (especially from methanol plants). 

A major route for producing synthesis gas is the steam reforming of natural gas over a promoted nickel catalyst at about 800°C ... 

The steam reforming of natural gas process is the most economic near-term process among the conventional processes. On the other hand, the steam reforming natural gas process consists of reacting methane with steam to produce CO and H2. The CO is further reacted or shifted with steam to form additional hydrogen and CO2. The CO2 is then removed from the gas mixture to produce a clean stream of hydrogen. Normally the CO2 is vented into the atmosphere. For decarbonization, the CO2 must be sequestered[l,2]. The alternative method for hydrogen production with sequestration of carbon is the thermal decomposition of methane. 

Hydrogen, when produced from reforming of natural gas, petroleum or coal, generates C02 as a by-product. In the current processes, C02 has been released into the atmosphere. 

Nuclear energy can produce hydrogen in several ways (1) nuclear heated steam reforming of natural gas, (2) electrolysis of water using nuclear power, (3) HTE using minor heat and major electricity from nuclear reactor, and (4) thermochemical splitting of water using... 

Table 7.18. Input and output data for the production of hydrogen via onsite steam reforming of natural gas ...

Until around 2030, steam reforming of natural gas plays a role for central production (with CCS), but in the long term this option becomes less attractive owing to the assumed increase of gas prices. 

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