Continuous high purity hydrogen generation from a syngas chemical looping 25 kW(th) sub-pilot unit with 100% carbon capture

The syngas chemical looping (SCL) process circulates iron-based oxygen carrier particles through three reactors, namely the reducer, the oxidizer, and the combustor, to perform reduction-oxidation reaction cycles for converting gaseous fuels to highly concentrated discrete streams of hydrogen (H-2) and carbon dioxide (CO2). The counter-current moving-bed operation of the reducer enhances the extent of oxygen carrier conversion, which facilitates the generation of hydrogen as confirmed in lab and bench scale studies. The 25 kW(th) sub-pilot SCL unit represents an integrated continuous demonstration of all 3 reactor sections. Previous studies have analyzed the design criteria, construction, and preliminary demonstration of the sub-pilot unit with promising results. In this study, the results from extended demonstrations conducted using two reactor configurations and two oxygen carrier types differing in size and iron composition are presented. In each demonstration, the solids and syngas flow rates are varied to analyze the effect on the unit performance. Steady profiles of 99.99% H-2 production and nearly 100% syngas conversion are achieved. Post-experiment solids analysis on the oxygen carrier particles revealed no deterioration in oxygen carrier performance after the extended demonstration and highlights the longevity of the oxygen carrier. Additionally, the abraded oxygen carrier fines collected during operation could be reprocessed to match the fresh particle performance, making solids make-up more economically viable. Multistage equilibrium moving bed model reducer studies are conducted to compare the experimental syngas conversions for each test condition with the theoretical thermodynamic results. The experimental results matched well with the model results. A total of over 300 h of integrated sub-pilot unit demonstration have been conducted with a longest continuous run of 3 days validating the reliable performance of the SCL process for cogenerating high-purity H-2 and electricity with 100% CO2 capture. (C) 2012 Elsevier Ltd. All rights reserved.