By "best costly" I assume you mean least expensive; there is none.
Corrosive gas flows require expensive flow meters. The wetted materials of construction must withstand the corrosive effects of the gas (like chlorine, in your example) and those materials are expensive materials such as Hastelloy and Tantalloy and Silver for metal surfaces, CPVC, Kynar (PVDF) and PTFE (Teflon) are often used. Note that PTFE is molecularly porous to most of these gases and it will "weep."
I have used differential pressure transmitters, with corrosion resistant diaphragms, vortex shedding meters with the correct wetted parts, thermal dispersion meters with the correct wetted parts, and a strange meter that was manufactured by the old Ramapo Meter Company (now part of Venture Measurement) called a target meter (also with the correct wetted parts). They have all worked to at least a limited extent. NONE OF THEM IS CHEAP.
Good luck,
Walt
Walt Boyes, FInstMC, Chartered Measurement and Control Technologist
Life Fellow, International Society of Automation
Editor in Chief, Control and ControlGlobal.com [email protected]
