## 1 Introduction  
Desulfurization is very important in the petroleum refining process because oxysulfides from the petroleum refining process are one of the major sources of air pollution. The most frequently used desulfurization process is the Claus process, which converts the H\({}_{2}\)S in natural gas or crude oil into sulfur elements, which reduces the formation of oxysulfides. A sulfur recovery unit (SRU) thermal reactor is the most important equipment in a sulfur plant. It converts the NH\({}_{3}\), H\({}_{2}\)S and hydrocarbons in the reactants into sulfur. Most of the sulfur elements are recovered from the SRU thermal reactor. The first section of a SRU that uses the Claus process is composed of a burner, a thermal reactor and a waste heat exchanger. The configuration and dimensions of the first section of a SRU for a typical petroleum refinery are shown in Figure 1.  
The main chemical reactions in a SRU thermal reactor include a thermal step and a catalytic step. \[2\mathrm{H_{2}S+3O_{2}\to 2 SO_{2}+2H_{2}O}\]  
\[2\mathrm{H_{2}S+SO_{2}\to 3S+2H_{2}O}\]  
In addition to the above reactions and the combustion of hydrocarbon fuels, other chemical reactions taking place in a SRU thermal reactor are  
\[2\mathrm{NH_{3}+1.5O_{2}\to N_{2}+3H_{2}O}\]  
\[2\mathrm{NH_{3}+SO_{2}\to N_{2}+H_{2}S+2H_{2}O}\]  
The interior of a SRU thermal reactor is divided into two zones by a choke ring, in order to increase the residence time and enhance the chemical reaction. The zone ahead of the choke ring is called zone 1 and the zone behind the choke ring is called zone 2. The inner surface of a SRU thermal reactor is fabricated using a refractory to protect its walls because a SRU thermal reactor operates at very high temperatures. SRU thermal reactors are negatively affected by high temperature operations because high temperature can damage the refractory and the heat exchanger tubes. Therefore, the operating temperature range that is suggested by the manufacturers for the operation of a SRU thermal reactor must be strictly adhered to. There have been theoretical and experimental studies of SRU thermal reactors. [PERSON] et al. [1] studied the thermal decomposition of H\({}_{2}\)S into hydrogen and sulfur using a process simulator. Using  
Figure 1: The configuration and dimensions of the first section of the SRU for a typical petroleum refinery: (**a**) The overall view; (**b**) Enlarged view for the burner section. the net fraction of the acid gas feed to the cracking coils as the controlling parameter, its effect on hydrogen production, the thermal reactor's energy requirement, the stability of the burner flame, steam production, the temperature of a Claus reactor and sulfur recovery of the primary SRU was studied. [PERSON] et al. [2] presented experimental and simulation results for the addition of various amounts of toluene or carbon dioxide/toluene mixtures into the H\({}_{2}\)S gas stream. The results show that there is a decrease in the conversion efficiency when the amount of toluene or carbon dioxide/toluene added to the H\({}_{2}\)S gas stream increases. The role of the reactor's operating temperature was also studied. The addition of toluene increases the optimum reactor temperature for enhanced sulfur recovery, but the presence of CO\({}_{2}\) reduces the optimum operating temperature. [PERSON] et al. [3] examined the quality of sulfur deposits that were collected from H\({}_{2}\)S combustion. Sulfur deposits from H\({}_{2}\)S combustion under various conditions were captured and analyzed using X-ray powder diffraction and laser-induced breakdown spectroscopy diagnostics. [PERSON] et al. [4] experimentally studied the reaction between H\({}_{2}\)S and SO\({}_{2}\) using practical Claus thermal reactor temperatures between 850 and 1150 \({}^{\circ}\)C and residence times between 0.05 and 1.2 s. The kinetic data obtained were used to develop a new reaction rate expression.