According to the International Energy Agency (IEA), natural gas will have a major share in the future energy supply of the world, however, technology will be crucial in moderating supply costs. Natural gas contains significant amount of acid gases including CO_2 that must be removed to meet the pipeline specification. The concentration of CO_2 in natural gases and associated gases varies from a few percent to as high as 70-80 percent in certain reservoirs, particularly those with enhanced oil recovery (EOR). The commonly used amine absorption process is very energy intensive particularly at high CO_2 concentrations. In addition, this process is not economical for low capacities and remote areas including offshore locations. On the other hand, CO_2 capture by membranes is more economical at high CO_2 concentrations, low capacities and in remote locations, but for the sources with high acid gases, single stage membranes systems can not reduce the concentration of these gases to the required level unless they are used in multi-stages which in turn require more compression energy. Also CH_4 leakage along with CO_2 separation is another drawback of this process. To take advantage of the positive aspects of these two processes and to increase the flexibility of the process for optimum operation, hybrid systems, i.e. membrane for bulk removal of CO_2 followed by amine absorption, have been proposed and used since the early 90's. In this paper a rigorous mathematical model for simulation of membrane modules is presented which utilizes a new model for multi-component gas mixture through polymeric composite membranes. The model predicts the selectivity and the permeability of gas mixtures (CH_4, CO_2, H_2S, etc.) with good accuracy when compared with the literature data. With this new model for multi-component transport through composite polymeric membranes, the improvement in prediction of the membrane performance is significant; as high as 20%. This model is then combined with the available models (such as Hysys) for simulation of amine absorption process to predict the overall performance of the hybrid system. The model can be used to optimize the operation of hybrid systems.
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