RESEARCH ARTICLE An investigation of reaction furnace temperatures and sulfur recovery S. ASADI (✉), M. PAKIZEH, M. POURAFSHARI CHENAR Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad P.O. Box 91775-1111, Iran © Higher Education Press and Springer-Verlag Berlin Heidelberg 2011 Abstract In a modern day sulfur recovery unit (SRU), hydrogen sulfide (H 2 S) is converted to elemental sulfur using a modified Claus unit. A process simulator called TSWEET has been used to consider the Claus process. The effect of the H 2 S concentration, the H 2 S/CO 2 ratio, the input air flow rate, the acid gas flow of the acid gas (AG) splitter and the temperature of the acid gas feed at three different oxygen concentrations (in the air input) on the main burner temperature have been studied. Also the effects of the tail gas ratio and the catalytic bed type on the sulfur recovery were studied. The bed temperatures were optimized in order to enhance the sulfur recovery for a given acid gas feed and air input. Initially when the fraction of AG splitter flow to the main burner was increased, the temperature of the main burner increased to a maximum but then decreased sharply when the flow fraction was further increased; this was true for all three concentrations of oxygen. However, if three other parameters (the concentration of H 2 S, the ratio H 2 S/CO 2 and the flow rate of air) were increased, the temperature of the main burner increased monotonically. This increase had differ- ent slopes depending on the oxygen concentration in the input air. But, by increasing the temperature of the acid gas feed, the temperature of the main burner decreased. In general, the concentration of oxygen in the input air into the Claus unit had little effect on the temperature of the main burner (This is true for all parameters). The optimal catalytic bed temperature, tail gas ratio and type of catalytic bed were also determined and these conditions are a minimum temperature of 300°C, a ratio of 2.0 and a hydrolysing Claus bed. Keywords Claus unit, concentration of H 2 S, tail gas ratio, sulfur recovery, catalytic bed 1 Introduction A sulfur recovery unit (SRU) is an important tool in refineries, since it removes H 2 S from acidic gas streams before they are released into the atmosphere [1]. Hydrogen sulfide is present in the industrial world chiefly as an undesirable by-product of gas processing [2]. Different processes are used for recovery of sulfur from H 2 S but the most widely used is the Claus process 1) [1]. Recently, a number of studies have been performed on the main burner and sulfur recovery in this process. Wen et al. [3] studied empirical predictions for CO, COS, CS 2 and H 2 using free energy minimum equilibrium calculations. In 1990, Dowling et al. [4] conducted a study on the conversion of H 2 S into hydrogen and sulfur. This reaction is one of reactions occurring in the main burner and the kinetics indicated that the reaction rate is very fast. Low temperature is favorable for the forward reaction and the reverse reaction is enhanced at high temperature. Both forward and reverse reactions are first order reactions. Reaction kinetics for the formation of carbonyl sulfide have been determined for the reaction between carbon monoxide and hydrogen sulfide [5]. Zarenezhad and Hosseinpour [6] compared experimental values of reaction furnace temperature with calculated values from Gibbs free minimization method and concluded that the calculated values from this method are in good agreement with the experimental values. The Claus process was developed by Carl Friedrich in 1883 [7] and an overall sulfur recovery of 94%–97% was achieved for this process. Several modifications of the original process have been proposed to increase the overall sulfur recovery and to produce a tail gas which satisfies Received January 20, 2011; accepted May 22, 2011 E-mail: samerasadi@yahoo.com 1) Polasek J, Bullin, J. Effect of sulphur recovery requirements on optimization of integrated sweetening, sulphur recovery, and tail gas clean up units. Proceedings of the Seventy-Second GPA Annual Convention, Tulsa, Gas Processors Association. 1993, 170–174 Front. Chem. Sci. Eng. 2011, 5(3): 362–371 DOI 10.1007/s11705-011-1106-z