Sewage sludge chars were subjected to washing to produce a clean solid fuel of superior quality. First, sewage sludge was converted into chars at different carbonization temperatures (400–700 °C), and then the produced chars were washed with various washing techniques, i.e., water (W), hydrochloric acid (HCl), ethylenediamine tetraacetic acid (EDTA) and ultrasound-assisted water to further reduce ash and heavy metal contents. The washed chars were systematically characterized and their fuel properties were analyzed. The results indicated that all washing techniques decreased ash content of chars and improved their fuel ratio. The washed chars exhibited higher heating values, lower slagging and ash fouling indexes and higher combustion reactivity, indicating the better quality of the derived fuels. Among the washing techniques, HCl washing was the most efficient process as carbon content increased by 20%, while ash content decreased by 50%. The fuel ratio as well as slagging and ash fouling indexes were significantly improved. Furthermore, the combustion reactivity showed similar pattern to coal with high conversion rate suggesting the enhanced thermal stability of the fuel. In conclusion, pyrolysis as a single process seems inefficient to produce high quality chars; however, coupling pyrolysis with washing can yield chars with satisfactory fuel properties.

Graphic abstract

中文翻译：

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洗涤工艺对污泥炭热燃烧特性的影响

对污水污泥焦进行洗涤，以产生优质的清洁固体燃料。首先，将污水污泥在不同的碳化温度（400-700°C）下转化为焦炭，然后用各种洗涤技术洗涤生成的焦炭，例如水（W），盐酸（HCl），乙二胺四乙酸（EDTA） ）和超声辅助水以进一步减少灰分和重金属含量。对洗过的炭进行了系统表征，并分析了其燃料性能。结果表明，所有洗涤技术均降低了焦炭的灰分含量并提高了燃料比。洗涤过的炭表现出较高的热值，较低的结渣和灰分结垢指数以及较高的燃烧反应性，表明衍生燃料的质量更好。在洗涤技术中，HCl洗涤是最有效的过程，因为碳含量增加了20％，而灰分含量减少了50％。燃油比以及排渣和灰分结垢指标得到了显着改善。此外，燃烧反应性表现出与煤相似的模式，具有高转化率，表明燃料的热稳定性增强。总之，热解作为一个单一的过程似乎无法产生高质量的焦炭。然而，将热解与洗涤结合可以产生具有令人满意的燃料性能的焦炭。燃烧反应性显示出与煤相似的模式，具有高转化率，表明燃料的热稳定性增强。总之，热解作为一个单一的过程似乎无法产生高质量的焦炭。然而，将热解与洗涤结合可以产生具有令人满意的燃料性能的焦炭。燃烧反应性表现出与煤相似的模式，具有高转化率，表明燃料的热稳定性增强。总之，热解作为一个单一的过程似乎无法产生高质量的焦炭。然而，将热解与洗涤结合可以产生具有令人满意的燃料性能的焦炭。

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