Studies of methyldiethanolamine process simulation and parameters optimization for high-sulfur gas sweetening K. Qiu a, * , J.F. Shang b , M. Ozturk c , T.F. Li a , S.K. Chen a , L.Y. Zhang a , X.H. Gu a a School of Chemistry and Chemical Engineering, Chongqing University of Science and Technology, Chongqing, China b Puguang Branch of Zhongyuan Oilfield Company, SINOPEC, Dazhou, Sichuan, China c School of Chemical, Biological and Materials Engineering, The University of Oklahoma, Norman, USA article info Article history: Received 4 May 2014 Received in revised form 28 August 2014 Accepted 30 August 2014 Available online Keywords: Gas sweetening Simulation Optimization Amine solution Energy abstract The energy consumption of high-sulfur gas sweetening was significantly higher than conventional gas, in order to save energy, a novel Methyldiethanolamine (MDEA) modified process is discussed in this paper. The law of operating conditions' impact on gas sweetening efficiency and economic benefits has been obtained by using process simulation and optimization. The results showed that the maximization of the treated gas yield should be selected as the optimization objective of gas sweetening rather than the minimization of the operating costs. This will enable improvement of the economic efficiency of the gas processing. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Sour gas typically contains H 2 S and CO 2 , which are toxic, cor- rosive and prone to cause environmental pollution after burning. Therefore, these acid components must be removed. When H 2 S and CO 2 exist in natural gas simultaneously, H 2 S can be selectively removed from the gas with a maximum retention of CO 2 by Methyldiethanolamine (MDEA). This feature meets the develop- ment trends of saving energy in gas processing. MDEA is not only used in general gas sweetening but also in high-sulfur gas (HSG). Although some processes have been applied in HSG sweetening such as mixed amines (Sohbi et al., 2007), DEA (Total Company, 2007), Sulfinol (Palla et al., 1998) and MDEA (Qiu et al., 2013), more and more cases (Amiri et al., 2008; Sourisseau et al., 2007) have indicated the MDEA process is rather favored in this field. The concentration of acid species in HSG is several times higher than in general gas, which leads to a dramatic increase of operating costs and energy in process (Bae et al., 2011; Banat et al., 2014). Moreover, the quantity of treated gas significantly decreases compared to feed gas. The operating conditions are obviously the main factors affecting inherent economic benefits with regard to an existing sweetening unit (Lunsford, 1996). Many authors have concluded that selective amines absorb H 2 S more than CO 2 due to the differences in solubility, rates of reaction, or a combination of the two (Huttenhuis et al., 2007; Pacheco and Rochelle, 1998). The reaction between H 2 S and MDEA is an instantaneous proton transfer reaction, but the reaction between CO 2 and MDEA is a pseudo-first-order reaction. The differences in reaction rates lead to selective absorption. Huttenhuis et al. (2009) studied the solubility of CO 2 and H 2 S in aqueous MDEA, and concluded that the H 2 S partial pressure increased significantly with increasing CO 2 liquid loading. The type of inert gas (N 2 or CH 4 ) did influence the H 2 S solubility rather than CO 2 . Calculations with the E-EOS model showed that the fugacity coefficient of H 2 S is more sensitive to an increase in CH 4 partial pressure than the fugacity coefficient of CO 2 . Denny (1994) found that additional trays may actually increase H 2 S concentration in the sweetened gas due to CO 2 absorption. Apparently, adding more trays allows more CO 2 to be absorbed which tends to displace the H 2 S. MaxwelleStefan and enhance- ment factor theories were utilized by Pacheco and Rochelle (1998) to prove that trayed columns are more selective than packed col- umns for H 2 S removal, primarily because of the greater number of liquid-film mass transfer units. By increasing the pressure, the driving forces for the H 2 S and CO 2 absorption become larger, whereas the mass transfer co- efficients and interfacial areas decrease because of the lower volumetric gas throughout. Moreover, the gas phase diffusivities * Corresponding author. Tel.: þ86 2365023762. E-mail addresses: qiucqust@163.com, 2240140082@qq.com (K. Qiu). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse http://dx.doi.org/10.1016/j.jngse.2014.08.023 1875-5100/© 2014 Elsevier B.V. All rights reserved. Journal of Natural Gas Science and Engineering 21 (2014) 379e385