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    Ajay S. Satpute

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Chemical and Process Engineering Resources

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Category: Refining
Question: What is the best way to measure the flow in flare stack?
Keywords: flare,stack,flow,measurement
Answer: An orifice plate is generally not suitable for this service. The reason is that the the flare line is always sized for the maximum possible flare flow, in an upset condition. The flow to the flare under normal conditions will be much smaller, by a factor of 100 to 1000, or more. The pressure drop across the orifice under normal conditions will not be high enough to permit accurate flow measurement. (Don't forget that pressure drop varies with the square of the flow).Over the years, there have been many attempts to find a suitable flowmeter for this service. I believe that the only successful type has been the utrasonic flowmeter. It also has the advantage of providing no obstruction in the line. The best-known supplier is Panametrics. They have an excellent reference list, on refineries and chemical plants. The only disadvantage is the cost - in the order of $30,000 per installation.