Process analytics in methanol plants – Case Study

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Courtesy of Siemens Industry, Inc. - Process Analytics

Methanol is a clear liquid usually made from natural gas. It is a clean burning fuel, containing almost no sulphur or nitrogenous materials. It is a petrochemical that is used to make countless industrial and consumer products. In the future, methanol could be used as a source of hydrogen for fuel cells. Different concepts are in use to produce methanol looking always for higher plant efficiency and product quality.

All processes require the use of extensive process analyzer systems to monitor both process chain and product quality. Siemens, a leader in process analytics, has proven over decades its capability to plan, engineer, manufacture, implement and service such analyzer systems. This Case Study provides details about the Methanol process and related analyzer tasks.

Methanol

Methanol (CH3OH) is an important multipurpose base chemical, a simple molecule which can be recovered from many resources, predominantly natural gas. By tradition, methanol is principally used to produce formaldehyde, methyl tertiary butyl ether (MTBE) and acetic acid. To a lesser extend, methanol is used as a general solvent. Today, Methanol is projected to be increasingly used as a fuel, so a comparison to LNG could be made. Like LNG, methanol is manufactured from natural gas, but with higher capital costs per unit of energy. But it is easier and cheaper to transport.

Natural Gas (NG) is one of the cleanest, safest, and most useful of all energy sources. NG is colorless, shapeless, and odorless in its pure form. It is combustible, and when burned it emits lower levels of potentially harmful by-products into the air than other fuels. NG is a mixture of hydrocarbon gases. While it is formed primarily of methane, it can also include ethane, propane, butane, pentane and certain impurities.

To produce methanol, Natural gas is heated, desulfurized, mixed with steam, heated further and fed to the synthesis gas production reactor. Synthesis gas is then cooled and compressed to a suitable pressure for methanol synthesis in a cascade of reactors. The crude methanol passes to a methanol distillation section where it is stabilized and treated for transport.

Many different Methanol production technologies exist (Lurgi, Haldor Topsoe, Davy, Uhde e.a.). Whatever technology is applied, the process steps require always to be monitored and controlled continuously. Process analyzers play an important role for that. Up to 100 and more process analyzers, most of them process gas chromatographs, are in use in a typical methanol plant.

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