Sulfur recovery is a core process in both midstream and downstream oil and gas industries. Changing the feed composition, temperature, and pressure, degrading the equipment and catalysts, suboptimal operations due to inadequate control of temperature, pressure and air flow rate are some of the obstacles which reduce the performance of the sulfur recovery units. Low performance of sulfur recovery units creates the issues of safety and environmental problems. The objective of work is improving the performance of sulfur recovery unit in a gas plant. Aspen HYSYS V10 sulsim modified Claus three stage simulation model is used to mimic the behavior of a real sulfur recovery unit and it is considered as the base case. The performance of the base case is 93.89%. Base case process is optimized by controlling the air demand percent and the adjusting the sulfur dew point margin. These changes improved the performance to 98.60%. The performance of the plant is tested for a challenging feed composition case and this change reduced the performance to 96.39%. Arranging the selective oxidation converter improved the performance to 99.14%. Adding the tail gas section with the recycle stream and replacing the alumina catalyst with titania catalyst improved the performance to 99.92%. The simulation procedure developed in this work is useful to process engineers to smoothly handle the sulfur recovery unit in challenging situations. © 2019 Petroleum and Coal.