Multi-objective optimization of a multi-layer PTSA for LNG production

In this work, a novel multi-layer pressure-temperature swing adsorption (PTSA) process was designed for efficient simultaneous water and mercaptans removal from natural gas (NG) to less than 0.1 ppmv and 3 ppmv in a mini liquefied NG unit. The proposed multi-layer PTSA consists of a three-layer fixed bed including activated alumina, molecular sieves 4A and 13X. To gain in-depth insights about the process, a descriptive model considering mass, energy and momentum balances, along with the kinetic and equilibrium equations was developed. After validating the model with the experimental and operational data from the literature, the total energy requirement and long-term operational requirements (e.g. maximum water and mercaptan removal during regeneration process) were optimized. Results of the multi-objective optimization revealed that substitution of present series of dehydration and mercaptan removal columns with an integrated multi-layer PTSA for NG purification can decrease 5.1% of energy consumption, which is approximately equivalent to 137 GJ each year. The outcomes of this study can be used as an innovative design strategy for NG purification (i.e. the combination of dehydration and mercaptan removal columns in a single multi-layer PTSA bed) and can also provide process engineers with a cost-effective tool for the optimization of regeneration parameters in the present PTSA systems.