A parametric study of process design and cycle configurations for pre-combustion PSA applied to NGCC power plants

Abstract

Natural gas combined cycle (NGCC) power plants show favourable conditions for the implementation of pressure swing adsorption (PSA) for the capture of carbon dioxide. These plants also show the advantage of a hydrogen co-production system. The challenge when implementing PSA in these plants is to achieve reference configurations that can obtain both products (hydrogen and carbon dioxide) at high purity levels, maximizing the recovery of hydrogen as a valuable product. This study presents the scale-up of a previously reported laboratory-based, four-bed, seven-step PSA model and a parametric study of the scaled-up PSA variables to maximize the product performance parameters. The capacity of the PSA model is based on the flow rate requirements of a GE-10 gas turbine, which can operate with up to 95% hydrogen purity. A parametric study using global system analysis (GSA) showed the effect of the bed diameter, length-to-diameter ratio and purge-to-feed flow rate ratio upon the product performance parameters. A purity of carbon dioxide of 95.37% and a hydrogen recovery of 92.27% was obtained with a purge-to-feed flow rate ratio of 0.22. The purity of hydrogen stayed close to 99.99%, with maximum deviations around 0.0001% for all case studies. The purity of the carbon dioxide and the recovery of hydrogen were further improved by considering additional PSA configurations. The addition of an assisted purge step and three pressure equalization steps improved these performance parameters by two percentage points. Overall, the model with one pressure equalization step, assisted purge step and rinse step after the feed step showed promising results with a purity of carbon dioxide of 98.28% and hydrogen recovery of 95.48%. Lower capitals costs are expected for this configuration, compared to adding pressure equalization steps using more than four fixed-bed units.