不同生物炭制备条件对重金属在秸秆生物炭中存留的影响
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摘要
项目研究了重金属修复基地水稻、玉米、油菜、高粱4种修复材料秸秆的热重反应,并首次探讨了重金属修复材料在制备生物炭过程中,不同生物炭制备条件对重金属在生物炭中留存的影响。结果表明:四种秸秆热重反应变化趋势基本一致,失重主要发生在200～400℃之间,而在400～600℃区间,基本保持恒重。水稻秸秆失重率90%明显高于其他三种秸秆失重率75%。在不同终点温度条件下(350～550℃),重金属在生物炭中浓度有增加趋势,其百分比例均随温度的升高而降低,原料利用热值则在400℃最高。在不同升温速率和保温时间下,重金属在生物炭中的含量随升温速率升高和保温时间的延长而升高,生物炭得率和秸秆综合利用热值却随之下降。因此,秸秆生物炭制备过程中为获得较低重金属含量和高热值的生物炭,建议以400℃为终点温度,升温速率不宜过快,保温时间不宜过长,分别在1℃min~(-1)和1 h左右即可。
The effect of straw biochar production on the transport of heavy metals in biochar and tar was explored. The thermos-gravimetric analysis was conducted on the straws of four major crops(rice, maize, rape and sorghum). And the heavy metals’(Cd, Cu, Mn, Pb, Zn) distribution in straw biochars at different production conditions was analyzed. The results showed that the thermos-gravimetric reaction was similar among the straws of four crops. The loss of weight was mainly found in the pyrolysis processes from 200 ℃ to 400 ℃ and then the weight kept very stable at 400-600 ℃ for all the straws. The rate of weight loss of rice straw(90%) was higher than that of the other straws(around 75%).During biochar production, the heavy metals’ distribution in biochar and tar was significantly affected by the ending temperature, heating rates and holding time. At different ending temperatures(350-550 ℃), the content of heavy metals in biochar increased with the temperature, but the calorific value of raw materials was the highest at the ending temperature of 400 ℃. The contents of heavy metals in biochar increased, but the total calorific value decreased with the increasing of holding time. Therefore, the ending temperature of 400 ℃, the increasing rate of 1 ℃ min~(-1) and the holding time of 1 h were suggested to prepare farmland straw biochar with lower contents of heavy metals in biochar and higher calorific value.
The effect of straw biochar production on the transport of heavy metals in biochar and tar was explored. The thermos-gravimetric analysis was conducted on the straws of four major crops(rice, maize, rape and sorghum). And the heavy metals’(Cd, Cu, Mn, Pb, Zn) distribution in straw biochars at different production conditions was analyzed. The results showed that the thermos-gravimetric reaction was similar among the straws of four crops. The loss of weight was mainly found in the pyrolysis processes from 200 ℃ to 400 ℃ and then the weight kept very stable at 400-600 ℃ for all the straws. The rate of weight loss of rice straw(90%) was higher than that of the other straws(around 75%).During biochar production, the heavy metals’ distribution in biochar and tar was significantly affected by the ending temperature, heating rates and holding time. At different ending temperatures(350-550 ℃), the content of heavy metals in biochar increased with the temperature, but the calorific value of raw materials was the highest at the ending temperature of 400 ℃. The contents of heavy metals in biochar increased, but the total calorific value decreased with the increasing of holding time. Therefore, the ending temperature of 400 ℃, the increasing rate of 1 ℃ min~(-1) and the holding time of 1 h were suggested to prepare farmland straw biochar with lower contents of heavy metals in biochar and higher calorific value.
引文
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[2]陈再明,陈宝梁,周丹丹.水稻秸秆生物碳的结构特征及其对有机污染物的吸附性能[J].环境科学学报,2013,33(1):9-19.
[3]田松峰,薛海亮,付小倩,王亮..玉米秸秆燃烧特性的实验分析[J].电站系统工程,2008,24(1):21-23.
[4]刘圣勇,王艳玲,白冰,等.玉米秸秆致密成型燃料燃烧动力学分析[J].农业工程学报,2011,27(9):287-292.
[5]韩彬,周美华,荣达.稻草秸秆活性炭的制备及其表征[J].农业环境科学学报,2009,28(4):828-832.
[6]常西亮,胡雪菲,蒋煜峰,等.不同温度下小麦秸秆生物炭的制备及表征[J].环境科学与技术,2017,40(4):24-29.
[7]严伟,陈智豪,盛奎川.适宜炭化温度及时间改善生物质成型炭品质[J].农业工程学报,2015,31(24):245-249.
[8]侯静文,王瑞斌,孟梁,等.秸秆类生物质热解的热重-红外联用分析[J].实验室研究与探索,2015,34(2):4-7.
[9]姬登祥,艾宁,王敏,等.热重分析法研究水稻秸秆热裂解特性[J].可再生能源,2011,29(1):41-44.
[10]廖洲,薛勇,蒋东燕,张义烽.基于热重分析的油菜秸秆热解特性研究[J].安全与环境学报,2014,14(2):195-199.