Guo Shuai, Qi Guoliang, Zhao Deng, Gao Long, Qu Hongwei, Li Xingcan, Song Dean
School of Energy and Power Engineering, Northeast Electric Power University, Jilin, 132012, China.
College of Vehicles and Energy, Yanshan University, Qinhuangdao, 066000, China.
J Environ Manage. 2025 Sep;391:126635. doi: 10.1016/j.jenvman.2025.126635. Epub 2025 Jul 20.
Co-combustion of NH (ammonia) and hydrochar is a promising strategy to reduce fossil fuel usage and CO emissions. In this study, reactive molecular dynamics simulations (ReaxFF MD) were performed to investigate the effects of oxygen equivalence ratio (λ), ammonia co-combustion ratio, and combustion atmosphere on the combustion characteristics of the NH/hydrochar mixture. Firstly, Increasing the oxygen equivalence ratio from 0.5 to 1.5 accelerated the reaction and enhanced fuel conversion: the total molecule count rose by ∼56 % (from 2449 to 3810), and heavy coke species (C40 compounds) were completely eliminated at λ ≥ 1.0. A higher λ facilitated the conversion of H into HO and N into NO/NO, increasing HO, NO, and NO yields while suppressing H and N. At λ = 0.5, no CO or NO formed; at λ = 1.5, small amounts appeared, with CO produced being several-fold more abundant than CO. Correspondingly, the peak NH intermediate count increased from 181 to 233 as λ rose from 0.5 to 1.5, whereas NH intermediates (NH, NH, NH) declined - an oxygen-driven shift favoring NO formation over N. Secondly, increasing the ammonia co-combustion ratio from 62.5 % to 85 % led to higher final yields of CO, NO, and N, with a corresponding drop in residual unconverted carbon (UC). A greater NH proportion promoted the conversion of hydrochar into small molecules (C-C gases), thereby reducing tar and coke formation (fewer tar/coke species at 85 % NH than at 62.5 %). Mechanistic analysis showed that a hydrochar fragment (CHO) can be stepwise broken down by NH-derived radicals (e.g. NH, OH, H) into intermediate species such as CHO and CHO, ultimately producing CO. Finally, the combustion atmosphere had a notable impact on reaction heat release. Under both air (O/N) and pure O conditions, the co-combustion process began with an endothermic phase followed by exothermic heat release. The peak heat absorption at λ = 1.0 reached 69.18 Ha under pure O, much higher than the 16.78 Ha under air, indicating a more intense initial reaction in an oxygen-rich environment. By the end of 500 ps, however, the net energy released in air (20.62 Ha) slightly exceeded that in pure O (14.10 Ha). These results demonstrate that pure oxygen accelerates fuel consumption and product formation, whereas air yields a greater overall energy release - providing quantitative insight for optimizing practical NH-hydrochar co-combustion.
氨（NH₃）与水焦的共燃烧是一种减少化石燃料使用和二氧化碳排放的有前景的策略。在本研究中，进行了反应分子动力学模拟（ReaxFF MD）以研究氧当量比（λ）、氨共燃比和燃烧气氛对NH₃/水焦混合物燃烧特性的影响。首先，将氧当量比从0.5提高到1.5加速了反应并提高了燃料转化率：总分子数增加了约56%（从2449增加到3810），并且在λ≥1.0时重质焦炭物种（C₄₀化合物）被完全消除。较高的λ促进了H转化为OH和N转化为NO/NO₂，增加了OH、NO和NO₂的产率，同时抑制了H和N₂。在λ = 0.5时，没有形成CO或NO；在λ = 1.5时，出现了少量的CO和NO，生成的CO比CO₂丰富几倍。相应地，随着λ从0.5增加到1.5，NH₃中间体的峰值计数从181增加到233，而NH₃中间体（NH₃、NH₂、NH）减少——一种由氧驱动的有利于形成NO而非N₂的转变。其次，将氨共燃比从62.5%提高到85%导致CO、NO和N₂的最终产率更高，同时未转化碳（UC）相应减少。更大的NH₃比例促进了水焦转化为小分子（C-C气体），从而减少了焦油和焦炭的形成（85% NH₃时的焦油/焦炭物种比62.5%时少）。机理分析表明，水焦片段（C₁₀H₁₀O）可以被NH₃衍生的自由基（如NH₂、OH、H）逐步分解为CHO和CHO₂等中间物种，最终产生CO。最后，燃烧气氛对反应热释放有显著影响。在空气（O₂/N₂）和纯氧条件下，共燃烧过程都以吸热阶段开始，随后是放热。在纯氧条件下，λ = 1.0时的峰值吸热量达到69.18 Ha，远高于空气中的16.78 Ha，表明在富氧环境中初始反应更剧烈。然而，到500 ps结束时，空气中释放的净能量（20.62 Ha）略超过纯氧中的净能量（14.10 Ha）。这些结果表明，纯氧加速了燃料消耗和产物形成，而空气产生的总能量释放更大——为优化实际的NH₃-水焦共燃烧提供了定量见解。
