PTQ Q4 2026 Issue

With enriched feed gas and the implementation of high- level OE, there is no need for preheating of either the feed gas or the combustion air in the reaction furnace. As a result, the units become significantly less energy-intensive, eliminating the requirement for additional energy sources, such as fuel gas or high-pressure steam for preheating, that would otherwise be necessary in a conventional design. Avoiding fuel gas co-firing results in much lower CO₂ emissions from the unit. Adopting AGE provides potential for a further reduction in the CO₂ footprint of the unit in case further purification and carbon capture methodologies are implemented in the facility. Operational challenges and mitigation strategies For typical oxygen demands of moderate- or large-sized sul - phur plants, designing and installing dedicated VPSA- type oxygen generation packages provides the most cost-effec - tive solution while providing maximum operational flexibility. However, such hybrid sulphur plants must plan for non-availability of oxygen whenever the VPSA plant trips. Although the plant is designed for air-only operations, automatic switchover to air-only operations is to be defined in the plant shutdown logic to reduce risk. Additionally, to By adopting a smart, flexible oxygen-enrichment strategy, modern gas processing plants and refineries can drive both performance and profitability in sulphur recovery operations cover prolonged downtime of the oxygen plant, backup or even oxygen storage facilities need to be considered. High-level OE operation while processing enriched gas elevates flame temperatures, potentially imposing thermal stresses on the furnace refractory and waste heat boiler. In the case study, the calculated maximum adiabatic flame temperature is 1,390°C, which remains within the refrac - tory’s specified design limits. However, for some other operating plants, temperature excursions may occur, which would then mandate additional design features in the sul- phur plant to mitigate them Operating a hybrid SRU is more complex than a conven - tional one. Operators must manage two modes and under- stand the interactions of AGE unit adjustments with oxygen addition. There is a learning curve to managing the controls and safety systems. Comprehensive training programmes and simula - tion-based practice can be introduced so that operators can familiarise themselves with mode switchovers and emer- gency scenarios. Control systems (DCS) are configured to automate much of the transition. Clear operating guidelines and checklists are to be established for starting/stopping oxygen, switching modes, and handling upset conditions to avoid potential maloperations and subsequent plant shutdowns.

Managing high-purity oxygen introduces significant fire and explosion hazards, as any contact with hydrocarbons or incompatible materials in oxygen service can result in ignition. Additionally, oxygen leaks may create an oxy - gen-enriched atmosphere within the SRU area. These risks can be effectively mitigated through robust design and operational practices, including: • Design standards: All oxygen equipment and piping must comply with stringent oxygen service requirements: thorough cleaning for oxygen service, exclusion of organic materials, and use of suitable metals such as brass or stain- less steel. • Instrumentation: Instruments and valves should be proven oxygen-rated designs. • Layout and ventilation: Adequate ventilation around oxygen-handling equipment is essential to prevent oxygen accumulation. • Detection systems: Installation of oxygen gas detectors with alarms to alert operators if ambient oxygen levels exceed safe limits. • Maintenance protocols: Implementing strict procedures, such as nitrogen purging and leak testing before reintro - ducing oxygen following any maintenance activity. • Fire protection: Provide appropriate fire safety systems in the SRU area. By adhering to industry’s best practices for oxygen han - dling, the facility minimises the risk of fire and explosion incidents. Conclusion The hybrid SRU design, which integrates acid gas enrich - ment with high-level oxygen-enriched operation, rep - resents a major advancement in SRU configurations. It delivers an optimal balance of cost, efficiency, and reliabil - ity. The case study demonstrates that these systems can operate seamlessly while achieving energy and cost sav - ings, maintaining environmental compliance, and improv- ing plant uptime. Technical benefits such as higher thermal efficiency, elim - ination of spare trains, and reduced energy consumption, combined with operational advantages like flexibility and resilience, enable facilities to manage throughput variabil- ity and maintenance downtime without flaring or capacity loss. This approach is particularly valuable for plants with space constraints or those seeking to revamp existing units for increased capacity and performance. By adopting a smart, flexible oxygen-enrichment strat - egy, modern gas processing plants and refineries can achieve higher sulphur recovery rates, lower emissions, and enhanced operational reliability, driving both performance and profitability in sulphur recovery operations. The conclusions presented in this article are solely those of the authors and cannot be ascribed to Fluor Corp. and/or any of its subsidiaries. Debopam Chaudhuri is Principal Process Specialist and Fluor Fellow at Fluor. Email: Debopam.chaudhuri@fluor.com Ayan Dasgupta is Senior Process Specialist and Fluor Fellow at Fluor. Akanksha Pandey is Process Specialist at Fluor.

PTQ Q4 2026