Hydrochloric Acid can be emitted from many industrial processes, where it is either used in that form, or generated from the process.
HCl will usually be in fine, sub-micron mist form.
The gas comes from the process or vapours are drawn to the chimney by a suction fan.
In a PVC processes the VCM gas is condensed and the liquid is then fed to a reactor, before passing H2O seal boxes and gas tank stages, prior to compression. At some stage the gas must be neutralised in an absorbing tank of NaOH flakes.
HCl mist load typically 50 ppm
High consumption cost of NaOH in VCM process