Adding oxygen to the air in the gas desulfurizing process results in a number of benefits, e.g. increased plant capacity, more flexibility, improved conversion of ammonia. 

In the refining of petroleum oil, oxygen is typically used to increase capacity of key units where air blower bottlenecks, particularly in summer months, limit capacities of the Claus sulfur recovery unit (SRU) or fluidized catalytic cracker unit (FCCU).

In SRUs, injection of oxygen in the combustion air to achieve up to 28% O2 by volume in low level enrichment applications can increase sulfur production by as much as 25% without burner modifications. In FCCUs, oxygen can be injected into the air main up to 28% O2 by vol of the spent catalyst regeneration unit to increase FCCU throughput and efficiency without shutting down the FCCU or the high capital and downtime associated with expanding air blower capacity. The higher oxygen levels can also lead to improvements in FCC yields, ability to handle coke forming feedstocks, and catalyst life.

In both cases, economical source of oxygen is key to achieving favorable economics. For low level enrichment of SRUs and FCCUs requiring oxygen volumes up to 20-30 TPD, oxygen is typically most economically supplied by vaporizing liquid oxygen (LOX) where pipeline oxygen is not available or oxygen usage is seasonal or variable.

PCI VSAs can offer a more economical supply down to below 5 TPD compared to LOX where utilization needs reach 50% or more. In addition, the supply of oxygen from non-cryogenic separation such as the VSA is attractive from a safety perspective in a refinery environment since the inventory of oxygen is much lower compared to the storage of LOX. Oxygen can also be used to accelerate the biochemical treatment of refinery wastewaters. In addition, nitrogen is used widely in refinery complexes for its inerting properties to blanket potentially flammable liquids during storage or product movement and to purge pipelines and reactors.