Steam reforming

Steam reforming or steam methane reforming is a chemical synthesis for producing syngas (hydrogen and carbon monoxide) from hydrocarbons such as natural gas. This is achieved in a reformer which reacts steam at high temperature and pressure with methane in the presence of a nickel catalyst. The steam methane reformer is widely used in industry to make hydrogen. Steam reforming or steam methane reforming is a chemical synthesis for producing syngas (hydrogen and carbon monoxide) from hydrocarbons such as natural gas. This is achieved in a reformer which reacts steam at high temperature and pressure with methane in the presence of a nickel catalyst. The steam methane reformer is widely used in industry to make hydrogen. Steam reforming of natural gas is the most common method of producing commercial bulk hydrogen at about 95% of the world production of 500 billion m3 in 1998. Hydrogen is used in the industrial synthesis of ammonia and other chemicals. 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. Catalysts with high surface-area-to-volume ratio are preferred because of diffusion limitations due to high operating temperature. Examples of catalyst shapes used are spoked wheels, gear wheels, and rings with holes. Additionally, these shapes have a low pressure drop which is advantageous for this application. Additional hydrogen can be obtained by reacting the CO with water via the water-gas shift reaction. The first reaction is strongly endothermic (consumes heat, ΔHr= 206 kJ/mol), the second reaction is mildly exothermic (produces heat, ΔHr= -41 kJ/mol). 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 144 million metric tonnes in 2014. This steam reforming 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. Steam reforming of natural gas is approximately 65–75% efficient. Production of H2 and CO from hydrocarbon gases (e.g. natural gas) is performed by two well-known “primary” and “secondary” reformers. Steam methane reforming (SMR) and autothermal reformer (ATR) are two industrial examples of the primary and secondary reformers, respectively. Each of which uses only special characteristics. On the other hand, the process of combined reforming utilizes both of primary and secondary tools for production of synthesis gas, as it is commonly practiced in ammonia manufacturing. For the case of methanol, ATR is fed with nearly pure oxygen (99.5%) rather than air since the presence of excessive N2 in the syngas would overburden compression and retard the methanol production. The ATR reformer consists of a partial oxidation (POX) chamber (usually non-catalytic medium) and a fixed bed catalytic section. The catalytic fixed bed not only adjusts the H2/CO ratio, but also destroys any probable soot and precursor (e.g. ethylene and acetylene) that may be formed in the POX chamber. Natural gas (NG) is partially oxidized in the combustion chamber by oxygen or air (as an oxidant). Steam to carbon (S/C) ratio that is usually 0.6 in the oxygen-based case has been commercialized by Haldor-Topose Company.