Hernández Ana Belén, Okonta Felix, Freeman Ntuli
University of Johannesburg, Chemical Engineering Department, Doorfontein Campus, PO Box 17011, Doorfontein, 2028, Johannesburg, South Africa; University of Johannesburg, Department of Civil Engineering Science, Kingsway Campus, PO Box 524, Auckland Park, 2006, Johannesburg, South Africa.
University of Johannesburg, Department of Civil Engineering Science, Kingsway Campus, PO Box 524, Auckland Park, 2006, Johannesburg, South Africa.
J Environ Manage. 2017 Jul 1;196:560-568. doi: 10.1016/j.jenvman.2017.03.036. Epub 2017 Mar 25.
Thermochemical valorisation processes that allow energy to be recovered from sewage sludge, such as pyrolysis and gasification, have demonstrated great potential as convenient alternatives to conventional sewage sludge disposal technologies. Moreover, these processes may benefit from CO recycling. Today, the scaling up of these technologies requires an advanced knowledge of the reactivity of sewage sludge and the characteristics of the products, specific to the thermochemical process. In this study the behaviour of sewage sludge during thermochemical conversion, under different atmospheres (N, CO and air), was studied, using TGA-FTIR, in order to understand the effects of different atmospheric gases on the kinetics of degradation and on the gaseous products. The different steps observed during the solid degradation were related with the production of different gaseous compounds. A higher oxidative degree of the atmosphere surrounding the sample resulted in higher reaction rates and a shift of the degradation mechanisms to lower temperatures, especially for the mechanisms taking place at temperatures above 400 °C. Finally, a multiple first-order reaction model was proposed to compare the kinetic parameters obtained under different atmospheres. Overall, the highest activation energies were obtained for combustion. This work proves that CO, an intermediate oxidative atmosphere between N and air, results in an intermediate behaviour (intermediate peaks in the derivative thermogravimetric curves and intermediate activation energies) during the thermochemical decomposition of sewage sludge. Overall, it can be concluded that the kinetics of these different processes require a different approach for their scaling up and specific consideration of their characteristic reaction temperatures and rates should be evaluated.
热化学转化过程能够从污水污泥中回收能量，例如热解和气化，作为传统污水污泥处理技术的便捷替代方案，已展现出巨大潜力。此外，这些过程可能受益于一氧化碳回收利用。如今，扩大这些技术的规模需要深入了解污水污泥的反应活性以及热化学过程特有的产物特性。在本研究中，使用热重-傅里叶变换红外光谱联用仪（TGA-FTIR）研究了污水污泥在不同气氛（氮气、一氧化碳和空气）下热化学转化过程中的行为，以了解不同气氛气体对降解动力学和气态产物的影响。在固体降解过程中观察到的不同步骤与不同气态化合物的产生有关。样品周围气氛的氧化程度越高，反应速率越高，降解机制向低温方向转变，特别是对于发生在400℃以上温度的机制。最后，提出了一个多重一级反应模型来比较在不同气氛下获得的动力学参数。总体而言，燃烧获得的活化能最高。这项工作证明，一氧化碳作为氮气和空气之间的中间氧化气氛，在污水污泥的热化学分解过程中导致中间行为（微商热重曲线中的中间峰和中间活化能）。总体而言，可以得出结论，这些不同过程的动力学在扩大规模时需要采用不同的方法，并且应评估其特征反应温度和速率的具体情况。
