In this study the simultaneous-modular and sequential modular methods are used to predict performance of desorption and absorption columns in the loop of an industrial sweetening plant. Mathematical model of absorption and desorption cycle for acid gases in methyldiethanolamine has been developed. This model is based on mass and energy balance and takes into account the chemical interactions between solvent and gases. Application of the simultaneous-modular method to model of the plant provides 31 equations with 31 unknowns. Simultaneous solution of these equations presents details of operating conditions on each section of the process. In the sequential modular method, the calculations have been carried out for each unit as a single module in the loop. This way, the output of each module supplies the input data to the next unit. Data of a commercial gas refinery has been used to validate the models and compare the two methods. After validating, the model effects of some parameters on the performance of the loop have been investigated.

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