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Ammonia Syngas Production from Coal Mine Drainage Gas with CO2 Capture via Enrichment and Sorption-Enhanced Autothermal Reforming

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journal contribution
posted on 06.01.2020, 16:57 by Junjun Yin, Shi Su, Jun-Seok Bae, Xin Xiang Yu, Michael Cunnington, Yonggang Jin
Current utilization practices have not fully appreciated the potential of coal mine drainage gas and have resulted in significant greenhouse gas emissions. This paper introduces a novel pathway of using coal mine drainage gas, regardless of its methane concentration, as a chemical feedstock for ammonia syngas production without CO2 emissions. The new pathway employs an enrichment process for concentrating drainage gas with low to medium CH4 concentrations and a sorption-enhanced autothermal reforming (SE-ATR) process for ammonia syngas production with in situ CO2 capture. Experimental results for the enrichment process showed that the CSIRO-developed single-stage adsorption process was able to concentrate drainage gas with 4.5 and 20.3% methane to 31.7 and 79.3%, respectively. Autothermal reforming (ATR) tests with a 30% CH4/air mixture using two commercial Ni-based catalysts demonstrated that, as the operating temperature decreased, the methane conversion rate decreased, while the CO2/CO molar ratio increased, leading to an almost constant H2 concentration (∼45–47% on a dry basis) in the product. With CaO as CO2 sorbents, the SE-ATR process further took the water–gas shift reaction to a complete extent at 600 °C through in situ CO2 capture and, thus, led to a completed methane conversion and a syngas product with a H2/N2 molar ratio of ∼3:2. When the CO2 sorbent became saturated, the SE-ATR test evolved to an ATR process. The experimental results for both ATR and SE-ATR tests were close to the thermodynamic equilibrium values. The H2/N2 ratio in the syngas can be further tuned to produce ammonia, which is a valuable commercial commodity with various favorable attributes and a H2 carrier for safer transportation and storage.