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

• Published in: Energy & fuels Vol. 34; no. 1; pp. 655 - 664
• Main Authors: Yin, Junjun, Su, Shi, Bae, Jun-Seok, Yu, Xin Xiang, Cunnington, Michael, Jin, Yonggang
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16-01-2020
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.9b03076

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.