AIR & WATER

MONITORING NEWSLETTER  

March 2013
No. 401

ON Line, Composite or Grab Samples for Natural Gas

A representative sample of a hydrocarbon project is necessary to ensure proper accounting for transactions and efficient product processing. The amount of hydrocarbon product that is transported between producers, processor, distributor and end-user is significant.

David Fish of Welker, writing in the July and August issues of Pipeline and Gas Journal, weighs the advantages of grab, composite and continuous monitoring. In the realm of gas sampling there are the continuous online analytical units — the calorimeter and the chromatograph. These units have their place in the past, present and will continue to have an important place in the future of gas sampling. It is their cost, power requirements and typical upkeep that precludes their use in thousands of locations. Online analysis is convenient though it is dependent on the accuracy of the analyzer, its correct calibration and the quality of the sample reaching it. It tends to be expensive to install and maintain. Economics, remote location and downtime for service dictate the use of spot or composite sampling techniques at a majority of sample points and installations. It is also important to point out that with online units there is no second or third chance at analysis, and no second opinion option, as is the case with a sample in a sample cylinder.

On the immediate horizon, a new technology is emerging. Energy meters are soon to be introduced as an online, instant Btu meter. They will not provide analysis in the manner of the existing GCs, but will provide immediate Btu values. This new technology will fill a current void in real-time billing and plant operations. Their value is in reduced costs compared to online GCs, reduced maintenance and calibration costs, and in providing real-time information for operations.

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