CO2 capture combined with H2 and CH4 purification via a membrane plant: Process design, energy integration and economic analysis

Abstract

CO₂ capture paired with H₂ and CH₄ recovery from a ternary mixture is studied in this work, with the prospect of finding new solutions able to limit the greenhouse gas emissions, meanwhile proposing a theoretical evaluation of the economic benefits and drawbacks of a membrane gas separation process adoptable for the aforementioned purpose. A simulated plant consisting of three membrane units (i.e., one Pd-based followed by two SAPO-34) allows obtaining pure streams of H₂ (about 99.999 %), CH₄ and CO₂ (about 96 %) with recovery values higher than 90 %. This solution is found to be versatile, since all the components show high purity and recovery at different feed composition.

The preliminary economic analysis, performed to evaluate whether the process can be profitable, is carried out varying the feed flow rate (from 10 to 100 kmol/h), feed material price and labour cost. The biggest plant fed with 100 kmol/h is the most profitable, showing an economic potential more than ten times greater compared to that fed with 10 kmol/h. Compression provides a significant cost (about 72 % of total equipment and utility costs), followed by heat exchange (about 17 %), whereas membranes represent only 11 % of the expenses. Considering the total costs of the simulated plant, raw material has a very high impact, whereas membrane cost can be neglected. The present investigation also reveals that this solution is convenient in a wide range of feed material price and labour cost. For a fixed feed gas price of 0.10 $/Nm³, a net profit of about 940·10³ $/y can be achieved, whereas net present value after 10 years approaches 3900·10³ $.