Steam reforming

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Steam reforming is a method for producing hydrogen, carbon monoxide or other useful products from hydrocarbon fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to make hydrogen. There is also interest in the development of much smaller units based on similar technology to produce hydrogen as a feedstock for fuel cells.[1] Small-scale steam reforming units to supply fuel cells are currently the subject of research and development, typically involving the reforming of methanol, but other fuels are also being considered such as propane, gasoline, autogas, diesel fuel, and ethanol.[2][3]

Industrial reforming[edit]

Main article: Methane reformer

Steam reforming of natural gas - sometimes referred to as steam methane reforming (SMR) - is the most common method of producing commercial bulk hydrogen. Hydrogen is used in the industrial synthesis of ammonia and other chemicals.[4] At high temperatures (700 – 1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield carbon monoxide and hydrogen.

CH4 + H2OCO + 3 H2

Additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon monoxide produced. The reaction is summarized by:

CO + H2O ⇌ CO2 + H2

The first reaction is strongly endothermic (consumes heat), the second reaction is mildly exothermic (produces heat).

The United States produces nine million tons of hydrogen per year, mostly with steam reforming of natural gas. The worldwide ammonia production, using hydrogen derived from steam reforming, was 109 million metric tonnes in 2004.[5]

This SMR process is quite different from and not to be confused with catalytic reforming of naphtha, an oil refinery process that also produces significant amounts of hydrogen along with high octane gasoline.

SMR is approximately 65–75% efficient.[6]

Reforming for combustion engines[edit]

Flared gas and vented VOCs are known problems in the offshore industry and in the on-shore oil and gas industry, since both emit unnecessary greenhouse gases into the atmosphere.[7] Reforming for combustion engines utilizes steam reforming technology for converting waste gases into a source of energy.[8]

Reforming for combustion engines is based on steam reforming, where non-methane hydrocarbons (NMHCs) of low quality gases are converted to synthesis gas (H2 + CO) and finally to methane (CH4), carbon dioxide (CO2) and hydrogen (H2) - thereby improving the fuel gas quality (methane number).[9]

In contrast to conventional steam reforming, the process is operated at lower temperatures and with lower steam supply, allowing a high content of methane (CH4) in the produced fuel gas. The main reactions are:

Steam reforming:

CnHm + n H2O ↔ (n + m/2) H2 + n CO

Methanation:

CO + 3 H2 ↔ CH4 + H2O

Water-gas shift:

CO + H2O ↔ H2 + CO2

References[edit]

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