Integrated theory and technology for carbon sequestration and resource utilization via flue gas injection into coal mine goafs

Abstract Coal is crucial to China’s economic and social development. The two primary factors hindering the high-quality development of China’s coal industry are safety and emissions. Methane and coal spontaneous combustion have long posed major safety risks. Competitive adsorption experiments with coal and rock samples exposed to single-component and multi-component flue gases revealed that a mixture of N 2 , CO 2 , SO 2 , and NO X is optimal for oxygen isolation, fire prevention, and gas displacement. Thermodynamic studies further identified the ideal fire prevention formula as 79% N 2 , 8%–20% CO 2 , 0.0006%–0.001% SO 2 , and 0.001%–0.0018% NO X . Molecular simulations and quantum chemical analyses showed that coal and rock exhibit stronger interactions with CO 2 than with N 2 , CH₄, or O 2 , enabling CO 2 to preferentially occupy adsorption sites and displace O 2 and CH₄. These findings explain the mechanisms behind oxygen isolation, fire prevention, and gas displacement and highlight the strong affinity of coal’s functional groups for CO 2 , which contributes to carbon sequestration. Adsorption experiments on over 280 coal and 130 rock samples from 11 provinces found that each ton of coal can sequester 7–11 kg of CO 2 , while each ton of mudstone adsorbs 6–8 kg. Coal-rock in goaf areas exhibits even greater sequestration capacity. Three key technological breakthroughs were made: (1) flue gas injection technology for fire prevention and gas displacement, (2) high-reliability multi-phase flue gas transport technology, and (3) a safety assurance and intelligent control system for gas injection. In 2023, these technologies were successfully applied in a National Energy Group project, reducing CO 2 concentration from 10% to 18% to below 0.01% in return air, achieving an annual sequestration capacity of 12,800 tons of CO 2 per unit.