I just finished removing 50 atm of carbon dioxide, and in another 20 years I will have finished removing the 50 atm of nitrogen, thx to my 5 Atlas class giant terraformers:
Atlas class Terraformer 2638400 tons 23075 Crew 58930.3984 BP TCS 52768 TH 21875 EM 0
414 km/s Armour 1-1700 Shields 0-0 Sensors 1/1/0/0 Damage Control 1 PPV 0
Maintenance Capacity 14 MSP
Terraformer: 100 module(s) producing 0.4 atm per annum
C- ICF Drive E0.225 (100) Power 218.75 Fuel Use 2.25% Armour 0 Exp 1%
Fuel Capacity 1 500 000 Litres Range 45.4 billion km (1269 days at full power)
This ship is classed as a commercial vessel for maintenance purposes
Yes, its ridiculously expensive, but if you want to terraform Venus you will need several hundreds modules.