Abstract: In an ammonia manufacturing process, control of the hydrogen to nitrogen ratio for the feed to the ammonia synthesis reactor is accomplished by controlling the hydrogen to nitrogen ratio based on the ratio of hydrogen and carbon monoxide to nitrogen in the effluent withdrawn from the secondary reformer. Also, in an ammonia manufacturing process where parallel reformer trains are utilized, shifting of loading between the parallel reformer trains is accomplished using valve position control to override the control based on the ratio of hydrogen and carbon monoxide to nitrogen in the effluent withdrawn from the secondary reformer.