Chemical Technology March 2015

Effective gas analysis critical in biogas production

the engines that generate electricity from biogas will experience high rates of corro- sion, leading to inefficient running of the engines to produce electricity. In addition, when the wastes used to process biogas are varied, the amount of methane will change due to the behaviour of the anaerobic bacteria in the digester used to generate the biogas. A natural gas chromatograph can help address these operational and mainte- nance needs for biogas producers. Plants require a cost-effective, online gas chro- matograph (GC) that can measure the bio- gas composition within a four-minute cycle time for ongoing real-time analysis. It’s also critical that the GC is easy to use and has low maintenance requirements to reduce time personnel spend on maintenance. Unlike larger gas processing plants, petrochemical plants and refineries that are able to employ skilled personnel for maintenance of the gas chromatographs, biogas plants usually will only have techni- cians who are skilled in the operation and maintenance of the typical instrumentation required in the plant. In addition to lowmain- tenance requirements on an ongoing basis, the 370XA from Rosemount Analytical also includes maintainable module technology that allows operators to easily replace the

Biogas is a mixture of different gases pro- duced by the breakdown of organic matter and is used as a renewable energy source that exerts a very small carbon footprint. Global production of biogas is increasing all the time, however, there are some important process challenges biogas producers face, one of these being accurate gas analysis. The composition of biogas is typically 40- 60 %methane, 40-50 % carbon dioxide, the remainder being water, hydrogen sulphide, and other impurities. Biogas producers need to know what the purpose and use of the biogas is for end users and they need to know the exact composition of the biogas. It’s especially important that they know the carbon dioxide levels which are usually dif- ficult to predict. For example, biogas contains hydrogen sulphide, which is usually toxic, and it can be high in biogas that is produced from animal wastes, such as from chicken, or from certain vegetables. Biogas is also usu- ally very wet, and when carbon dioxide and hydrogen sulphide are mixed with water, it can be quite corrosive. For these reasons, it’s usually good to remove or lower the amount of hydrogen sulphide, water, carbon dioxide and other impurities to minimal levels before the biogas is processed. If this isn’t done, then

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GC module in the field in under two hours, reducing downtime and repair costs. Effectivemeasurement of biogas compo- sition is a critical step to ensure a high quality product and reduce the risk of corrosion and potentially dangerous toxic gas leaks, a cost- effective, easy-to-use gas chromatograph is a key element in biogas processing. For more information go to http://com- munity.emerson.com/process/emerson- exchange z