Paying a (say) USD $500 premium for a more accurate flowmeter is attractive because its simple payback is under 1.5 years. Shorter potential paybacks can occur when operating at higher flow rates or when flowing more expensive chemicals.

Importantly, potential chemical savings can be multiples of the values presented in the previous two tables, such as when flow control loops are installed in unmeasured chemical injection systems or in lieu of self-contained chemical injection control valves (CICV).

Excerpted from Measuring Difficult Flow Streams and More Accurate Flow Control Can Improve Oil and Gas Well Profitability in Processing magazine.

Various interface level measurement technologies were considered to implement the new control strategy of measuring and controlling the interface level above the “clean” water outlet. The existing displacer level controller had worked for decades so a differential pressure interface measurement was possible but its small range could pose calibration issues, especially outdoors in the northeastern US. A capacitance level transmitter was an option, but it required new nozzles that had to be carefully placed to avoid obstructions and the inlet/outlet ports in the separation zone. A guided-wave level transmitter could be installed but it too required a new nozzle and was relatively expensive at the time.

The good news was that there were multiple interface level technologies from which to choose. The bad news is that none stood out as being ideal. In the end, a new nozzle were carefully located and installed on the extractor for a capacitance interface level probe and transmitter. Capacitance technology was selected because the large conductivity difference between the “clean” water and the solvent made the interface easy to detect. The extractor was filled with solvent to calibrate zero and then filled with water to calibrate span.

This work was done some years ago. If done today, it is likely that a guided-wave level transmitter would be selected due to its lower cost. It would still require carefully locating a new nozzle, but its metal probe would not be as susceptible to damage as a similar-length coated capacitance probe.

This article originally appeared in Flow Control magazine.

Estimating the internal pipe diameters to be 14 and 18 inches, the fluid velocity will be approximately 40 percent (1-(142/182)) lower in the larger 18-inch pipe as compared to the 14-inch pipe. Therefore, the insertion flowmeter will tend to measure lower in the 18-inch pipe as compared to the 14-inch pipe, so Answers A, B and C are not correct.

The type of insertion flowmeter is not known. It could be a linear flowmeter using vortex shedding, magnetic or thermal technology that is directly affected by fluid velocity. If so, Answer E is approximately correct. Inferential flowmeters such as a Pitot tube are nonlinearly affected by fluid velocity and would exhibit an effect approximated by Answer D. 

Additional Complicating Factors

For estimating purposes, the internal pipe diameters were assumed to be 14 and 18 inches. This is not correct because the inside diameter of these pipes is based not only on the pipe sizes but is also on the pipe schedules. A detailed calculation would entail using the inside diameter used for calibration purposes and the actual inside diameter of the pipe where the flowmeter is installed before applying the above relationship.

This article originally appeared in Flow Control magazine.