Selecting a flow meter for a dirty application

Hi all learned people,
I need to select and install a flow meter to meaure infrequent flow of the
following gas mixture (in-feed to a thermal incinerator)

Nitrogen
Carbon Monoxide
Carbon dioxide
Carbonyl Sulphide
Water (H2O)

The gas stream also contains micronised Titanium Oxide (pigment) which is
capable of passing through a flame arrestor.  The TiO2 makes the gas stream
very sticky and gluey so that any in-line moving parts in contact with the
gas stream (such as turbine meter) needs to be able to withstand this
coating.

The pipe is a 400mm glass reinforced polyyester and the operating pressure
is -1 to +6 kPag, operating temperature is ~ 45 deg C and the mass flow rate
is ~18,000 kg/hr.

As mentioned before the flow is infrequent and the thermal incinerator is
kept on hot-standby using natural gas.  I have considered a V-cone flow
meter (McCrometer), a thermal mass flow meter (FCI / Kurz) and an ultrasonic
flow meter (Controlotron).  Manufacturers have been contacted and I am
awaiting their response.

In the mean time I would like to know if there are any other suitable flow
meters that I have not considered.  If so, can you please let me know?
Thanks in advance for your replies.
Regards,
Raj