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Custody Transfer, compressor and pressure reduction stations in natural gas production
High accuracy custody transfer measurement
Large volumes of natural gas are transported using high pressure transmission pipelines, delivering to power plants, LNG liquefaction plants, large industrial users and city gates. Compressor stations along the pipeline maintain the flow, and the line pressure - at around 60bar: these stations normally use gas from the pipeline to power the compressor. If the gas is to be used in a local gas grid, the pressure would be reduced to around 8 bar at the city gate in a pressure regulating station.
The gas transported in these typically long distance pipelines can be from several different suppliers, and delivered to various separate users – and the pipeline itself can be operated by a separate company. High accuracy flow measurement is extremely important: the large volumes that are transported means that any inaccuracy would represent a significant financial error, and cannot be tolerated. In the case of international transactions, for example when gas from Russia is supplied into Europe, the transmission pipelines run through several countries, across borders. Natural gas measurement systems are found at each pipeline inlet and delivery point, at international border crossings, and also at compressor stations where this is required by the set-up of the pipeline.
Pipeline measurement systems usually consist of multiple meter runs in parallel. Each meter run has at least one flowmeter - it is quite common that two meters are installed in series to cross-check each other. Additionally there can be a master-duty Z-configuration of the pipework on the gas metering skid to enable in-line verification against a master meter. Systems can be supplied as a skid or can be constructed directly on site. Besides measurements of flow, pressure and temperature, often a gas chromatograph is installed at each metering station to confirm the calorific value and compressibility of the gas. Additional equipment may include analyzers for dew point, sulphur, mercury and trace oxygen.
KROHNE has vast experience with natural gas pipeline flow measurement systems. Their ultrasonic and Coriolis flowmeters and metering systems were specifically developed to meet the high accuracy needed for natural gas custody transfer duty. Fully engineered metering skids and analyzer houses are supplied. In addition KROHNE is an established supplier of pressure reduction stations and pipeline leak detection systems for gas pipelines.