Document Type: Research Paper
Department of Chemical Engineering Norwegian University of Science and Technology
Department of Chemical Engineering, Norwegian University of Science and Technology
Electron Microscopy Laboratory at Department of Oral Biology, University of Oslo, UiO, Oslo, 0316 Norway
Natural gas produced at high pressure (50-70 bar) is the only industrial source of helium (He). A membrane separation process may offer a more efficient production system with smaller footprint and lower operational cost than conventional cryogenic system. Inorganic membranes with high mechanical strength are known to exhibit good stability at high pressure. In this work, two inorganic membranes, porous silica and carbon molecular sieve (CMS) were studied by simulation for their applicability in the He recovery process and compared against a Matrimid polymeric membrane. An in-house developed membrane simulation model (Chembrane) interfaced with Aspen HYSYS was used to simulate the membrane area and energy requirement for the He separation process. He was separated directly from a mixture containing methane (CH4) and 1-5 mole% He in the feed stream, and natural gas containing 1-5 mole% of He in a mixture of CH4 and N2. These streams were considered at 70 bar pressure and 25 °C. Single and two-stage membrane separation processes with and without recycle stream were simulated to achieve 97 mole % purity and 90% recovery of He. The simulation results showed that all three membranes can achieve required purity and recovery in a two-stage separation process. However, a recycle is required while using Matrimid membrane which adds cost and complexity to the system. The highest net present value (NPV) for silica, CMS, and Matrimid membrane was $M 2.5, 2, and 1.75 respectively when 5% He is present in feed gas and 15 years of plant life is considered.