Abstract

The traditional treatment of coal-gasification wastewater produces high solvent and operation cost, secondary pollution and long processing cycle. The aim of the paper was to attempt an alternative approach of wastewater treatment in coal gasification process. With wastewater being heated and sprayed into the gasifier, water participates in the water–gas shift reaction; meanwhile, organic constituents in wastewater are thermally degraded in specific conditions. In the study, thermal degradation and kinetic analysis of COD and NH₃-N from Lurgi coal-gasification wastewater were conducted experimentally. The results showed that COD degradation can be divided into three reaction regions: 200–600, 600–1000 and 1000–1200°C. Also, NH₃-N degradation can be divided as 200–400, 400–800 and 800–1200°C. The reaction temperature, oxygen concentration and reaction residence time can improve organic constituents’ degradation rate. The COD and NH₃-N degradation rate ranks in the order oxidative > inert > reductive. It is because increasing oxygen concentration indicates more free radical generation and aromatic hydrocarbon polymerization was weakened. In addition, NO conversion with NH₃ occurs within a narrow temperature window (800–1000°C). Thus, NO concentration reached the peak 230 mg/m³ at 800°C and then reduced with the increase in reaction temperature. Furthermore, a pseudo-first-order reaction model was implemented to analyse the kinetics of COD and NH₃-N degradation rate. The results of the present study indicate that the proposed wastewater treatment is feasible and can be preferable reference for further practical application.

中文翻译：

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新型处理方法对煤气化废水中有机物的热降解和动力学分析

摘要

煤气化废水的传统处理产生高溶剂和运行成本，二次污染以及较长的处理周期。本文的目的是尝试在煤气化过程中采用另一种废水处理方法。随着废水被加热并喷入气化炉，水参与了水煤气变换反应。同时，废水中的有机成分在特定条件下会热降解。在研究中，对鲁奇煤气化废水中的COD和NH ₃ -N进行了热降解和动力学分析。结果表明，COD降解可分为三个反应区域：200–600、600–1000和1000–1200°C。另外，NH ₃-N降解可分为200–400、400–800和800–1200°C。反应温度，氧气浓度和反应停留时间可以提高有机成分的降解速率。COD和NH ₃ -N的降解速率依次为氧化>惰性>还原。这是因为增加的氧浓度表明更多的自由基产生并且芳烃聚合被削弱。此外，在狭窄的温度范围内（800-1000°C），会发生NH _3的NO转化。因此，NO浓度在800℃达到峰值230mg / m ³，然后随着反应温度的升高而降低。此外，建立了伪一级反应模型以分析COD和NH ₃的动力学。-N降解率。本研究结果表明，所提出的废水处理方法是可行的，可为进一步的实际应用提供参考。