gas scrubbing

impossible, not enough information. Need someting with the units of time. and what you want to do, like empty the vessel of 10,000 kg in 30 minutes?

typically you use a term called "change outs per minute or hour" This means you want to remove all the air above the tank every few minutes. So the vent hood is 2 meters over the tank, the volume is 1.5 * 1.2 * 2 = 3.6 m^3. I'd change out the air 2 times per minute = 7.6 M^3/minutes of vent capacity.

In the US we have specific rules on the changeout rate, so I'm just guessing on the time.

An air scrubber exhausts to atmosphere, so the pressure is approximately 1 bar or so. For the fan capacity, your room size multiplied by the number of required air changes per hour divided by 60 will give you the required flow rate per minute.