Application Corner: Natural gas flow measurement: Energy flow

Previous columns discussed that the composition of natural gas can and does vary over time and at different locations, and its composition may be significantly different than typical North American Energy Standards Board (NAESB) natural gas. As a result, the energy content, density and thermal properties of the flowing natural gas can also be different. Density and thermal properties can affect the performance of some flowmeters. However, energy content variations can affect all flowmeters intended to measure the flow of energy — even when the flowmeter produces measurements that accurately reflect the flow of natural gas. 

Working backwards, if one assumes that a given natural gas flowmeter accurately measures flow, the energy flow will vary directly with the energy content of the flowing natural gas because the energy content of the flowing natural gas can be significantly different than typical NAESB natural gas. 

With that said, the energy content could be more accurately determined using the actual (measured) energy content to improve measurement of the amount of energy flowing through the flowmeter. Online or laboratory composition analyzers and/or calorimeters can be used to correct for the actual natural gas composition when the measurement of energy flow is important. Laboratory analysis can be used to periodically reconfigure and/or recalibrate some flowmeters to account for the latest natural gas compositions. 

Coriolis mass, differential pressure flowmeters, positive displacement, thermal, turbine and vortex shedding flowmeter technologies are often used to measure the flow of natural gas. Next month, I will examine how each of these technologies can be affected by changes in natural gas composition.

David W. Spitzer is a principal at Spitzer and Boyes, LLC, which offers engineering, focused market research, writing/editing white papers, strategic marketing consulting, distribution consulting, seminars and expert witness services for manufacturing and automation companies. Spitzer has written more than 400 technical articles and 10 books about flow measurement, instrumentation and process control. He can be reached at 845-623-1830 or via spitzerandboyes.com.