Permeation Membranes Can Efficiently Replace Conventional Gas Treatment Processes

Abstract

Summary. This paper presents the implementation of permeation for a different gas treatment process involving CO2, H2S, and H2O. Performance and cost comparisons between these and conventional processes, taking into account both existing and future potential membranes, allow us to draw conclusions about what fields are best for the application of permeation. permeation. Introduction Membrane technology is rapidly emerging in the oil industry for use in the treatment of production gases. Many papers have discussed permeation principles, where a polymeric membrane is used to separate certain gaseous polymeric membrane is used to separate certain gaseous components like CO2, H2S, and water vapor from a natural or associated gas stream under a partial pressure differential. Implementation of a new permeation process, where these membranes are formed in flat sheets-spiral wound or in hollow fibers-gathered in bundles and then introduced into pressure vessels, has also been discussed. Performance and economic comparisons between Performance and economic comparisons between permeation and conventional processes have been presented permeation and conventional processes have been presented for some specific cases. Some process engineers and managers, however, still have trouble answering such questions as what permeation can do now and in the future, whether permeation should be considered for a specific case, and how permeation would be implemented in a specific process diagram. This paper is intended to help in answering the first two paper is intended to help in answering the first two questions. The third question will not be addressed because it relates more to the engineer's knowledge, experience, and skill in process engineering. Fields of Application The best way to illustrate the fields of application of permeation is to consider the selectivity scale of an permeation is to consider the selectivity scale of an average permeation membrane (see Fig. 1). This scale shows the separations with such a membrane that appear feasible for hydrocarbon processing on a production field. These separations includeCO2/hydrocarbons for natural gas sweetening and CO2 extraction and concentration from an EOR produced gas,H2S/hydrocarbons for natural gas sweetening, andH2O/hydrocarbons for dehydration of natural gas. These three fields of application (CO2, H2S, and H2O) are discussed below. Cost comparisons will be used for balancing the advantages and disadvantages of these applications. Note that the costs presented for the existing membrane-based processes and conventional processes are drawn from actual processes and conventional processes are drawn from actual production cases and thus incorporate supplier production cases and thus incorporate supplier information. For new membranes, the cost could be only roughly estimated because no real change has occurred in membrane prices. CO2. The removal of CO2 from a hydrocarbon gas by permeation has to be considered differently, depending permeation has to be considered differently, depending on whether the gas is to be sold in the liquid or gaseous phase. phase. Gas To Be Sold as Liquefied Natural Gas. The CO2 content specification is extremely low (about 100 ppm, vapor) to avoid CO2 solidification during the liquefaction of the gas. To define the technical and economic performances of permeation in this case, we used the example of Gas GN1 permeation in this case, we used the example of Gas GN1 presented in Table 1. The computer calculations were first presented in Table 1. The computer calculations were first performed with an existing membrane, called M1, and performed with an existing membrane, called M1, and are presented in Table 2 for a single-stage permeation system (see Fig. 2). The performance of such a system, presented in Table 3, is defined by the membrane area presented in Table 3, is defined by the membrane area necessary for treating 10 normal m3/d [372 × 10 scf/D] (normal indicates measured at 0C) of inlet gas and also by the percentage of gas permeated onto the low-pressure side of the membrane, considered as a gas loss. A cost comparison with conventional processes-an amine unit, for example-is then presented, considering a permeation cost investment in direct relation to the membrane area and the gas loss as an operating cost. We can see that the use of permeation for such a treatment is not at all competitive with conventional processes. Furthermore, when a new generation of membranes that could have extremely high selectivities (Membranes M2 and M3, Table 2) is projected, no real improvement is obtained for such a treatment. This example used a single-stage permeation process; however, it appears obvious that even if a multistage process can significantly reduce the gas loss, the total process can significantly reduce the gas loss, the total investments (membranes and compressors) will remain far more expensive than the conventional processes. In conclusion, permeation should not be considered when very low CO2 specifications are appraised. P. 707