There are several types of flowmeters that would work satisfactorily for this application. However, the main concern is likely corrosion resistance. For such systems we use our own MicroFLOW meter constructed from TFE and PVDF along with a differential transmitter that has Hastelloy diaphragms. The diaphragms can also be gold plated for even better resistance.
One problem with this setup can be time response (~0.1 seconds) if you are doing small quick batches. We have also used turbines meters (316ss with gold plating) which are faster.
A) The HCl is in aquous (or other disolvent) solution; in this case, you can use succesfully a magnetic inductive flow transmitter, PTFE or PFA coated, and suited with tantal electrodes. Krohne provides this type of device at our factory.
B) The HCl isn't in any liquid solution (HCl gas).
B1) If you can assure that the gas doesn't content water (dry gas), you can use a coriolis flowmeter, made by stainless steel, or Hastelloy (i.e.).
B2) If you can't assure the absence of water with the HCl gas, you have to use a PTFE orifice plate with DP transmiter, equiped with tantal membranes, or... an expensive coriollis flowmeter with PTFE coated tubes (I think Micro Motion Produces this type of flow sensor for 1 year more or less).
1 year ago, I asked several flowmeter supliers for an ultrasonic flowmeter which was able to work with HCl gas, through a GFK pipe but I didn't find any. I don't know if nowadays this product is produced by main manufacturers.
For batching, magnetic inductive devices and coriollis flowmeters are usually equipped with a configurable pulse output, ideal for that.
If you use orifice plate with DP transmitter, you must integrate the instantaneous flow to totalize the amount of HCL.
