PTQ Q4 2026 Issue

From inerts to efficiency: Hybrid SRU designs

Presentation of a hybrid sulphur recovery concept that combines acid gas enrichment and high-level oxygen to redefine conventional SRU approaches

Debopam Chaudhuri, Ayan Dasgupta, and Akanksha Pandey Fluor

S ulphur recovery units (SRUs) based on the modified Claus process remain the industry standard for con- verting H₂S-rich acid gases into elemental sulphur. While the underlying process chemistry is mature and well understood, sulphur plant design continues to be strongly influenced by the presence of inert components in the feed and combustion systems. Carbon dioxide (CO 2 ) contained in acid gas streams and nitrogen introduced through combustion air increase pro- cess gas flow, reduce thermal efficiency, and drive larger equipment sizes throughout the sulphur recovery train. These effects become particularly pronounced when pro- cessing lean acid gases or when high reaction furnace tem- peratures are required for the destruction of hydrocarbon contaminants. Historically, reliability concerns have been addressed through installed redundancy, with facilities commonly employing multiple Claus trains and dedicated standby capacity. Although this approach provides operational flexibility, it also increases capital cost, plot space require - ments, and overall plant complexity. As sulphur recovery facilities become larger and more integrated, operators are increasingly seeking alternatives that maintain availability while improving asset utilisation. AGE-OE configuration Two technologies have independently demonstrated sig- nificant benefits in reducing inert loading within sulphur recovery systems. Acid gas enrichment (AGE) increases the hydrogen sulphide (H₂S) concentration of the feed gas by selectively removing CO₂, resulting in reduced process gas volumes and improved thermal performance. Oxygen enrichment (OE), meanwhile, replaces a portion or all of the combustion air with oxygen, substantially reducing nitro- gen dilution and increasing reaction furnace temperatures. While both technologies have been successfully applied for capacity enhancement and debottlenecking projects, their combined application offers an opportunity that extends beyond throughput improvement alone. Instead of relying on a dedicated standby Claus train, the proposed configuration strategically integrates AGE and high-level OE to utilise two operating trains during normal service. This retains the capability for a single train

to process the entire sulphur load under oxygen-enriched operation. This approach combines thermal and hydraulic advantages of both technologies, enabling higher sulphur throughput, reduced equipment requirements, improved operational flexibility, and lower overall capital investment. A case study from a natural gas processing facility pro - ducing 600 MTPD of sulphur is presented to demonstrate the practical implementation of this concept. The study evaluates equipment sizing, operating strategies, perfor- mance under both air-fired and oxygen-enriched modes, and the resulting economic and operational benefits. The results show that a carefully designed hybrid AGE-OE configuration can achieve high sulphur recovery efficiencies while reducing the need for conventional standby Claus capacity and minimising the sulphur block’s overall footprint. Oxygen enrichment replaces a portion or all of the combustion air with oxygen, substantially reducing nitrogen dilution and increasing reaction furnace temperatures Hybrid concept in simple terms AGE removal of CO₂ from the feed increases the H₂S con - centration entering the reaction furnace. The resulting richer stream generates higher equilibrium temperatures, reducing the need for supplemental fuel firing. As a result, total process gas flow decreases, leading to more stable furnace operation and a more efficient plant configuration. Simultaneously, replacing air with oxygen significantly reduces nitrogen dilution. This enhances heat release per unit of H₂S combusted, allowing the furnace to achieve elevated temperatures without additional preheating. The improved thermal profile ensures better destruction of hydrocarbons while lowering overall volumetric flow through the unit. Together, these effects translate into: • Reduced gas throughput. • More compact equipment design.

• Improved thermal utilisation. • Smaller overall plant footprint.

PTQ Q4 2026