During the start the process air injection to secondary reformer the front end load (process gas load) must be between 40 to 60% and back pressure from 20 to 25 bar according to process design, I think the back pressure value (20kg/cm2) to control the process air flow at the first introduction (ignition)and accordingly control the temperature rise at the catalyst bed.
A bit different approach, to minimize S/U gas and to ease LTS pre-heating:
25% gas rate with 10 bar backpressure
In this way LTS condensation risk is low and once air is in LTS inlet S/DG is lower at which point pressure is increased to 30 bar to go through CO2 removal
Gas rate is only increased to 70$ when the synthesis gas compressor is brought onto load which is necessary due to having added syngas driers at the third suction and the antisurge arrangement puts ammonia back to first suction.