Assessment of CO2 capture options from various points in steam methane reforming for hydrogen production

Steam methane reforming (SMR) is currently the main hydrogen production process in industry, but it has high emissions of CO2, at almost 7 kg CO2/kg H2 on average, and is responsible for about 3% of global industrial sector CO2 emissions. Here, the results are reported of an investigation of the effect of steam-to-carbon ratio (S/C) on CO2 capture criteria from various locations in the process, i.e. synthesis gas stream (location 1), pressure swing adsorber (PSA) tail gas (location 2), and furnace flue gases (location 3). The CO2 capture criteria considered in this study are CO2 partial pressure, CO2 concentration, and CO2 mass ratio compared to the final exhaust stream, which is furnace flue gases. The CO2 capture number (Ncc) is proposed as measure of capture favourability, defined as the product of the three above capture criteria. A weighting of unity is used for each criterion. The best S/C ratio, in terms of providing better capture option, is determined. CO2 removal from synthesis gas after the shift unit is found to be the best location for CO2 capture due to its high partial pressure of CO2. However, furnace flue gases, containing almost 50% of the CO2 in produced in the process, are of great significance environmentally. Consequently, the effects of oxygen enrichment of the furnace feed are investigated, and it is found that this measure improves the CO2 capture conditions for lower S/C ratios. Consequently, for an S/C ratio of 2.5, CO2 capture from a flue gas stream is competitive with two other locations provided higher weighting factors are considered for the full presence of CO2 in the flue gases stream. Considering carbon removal from flue gases, the ratio of hydrogen production rate and Ncc increases with rising reformer temperature.