CO_(2)强化水洗对生物炭脱灰影响及作用机理研究

Removal of ash in biochar from carbonization by CO_(2)-enhanced water leaching and its mechanism

本实验提出一种先炭化后CO_(2)强化水洗的脱灰方法,选用甘蔗渣考察了生物炭的制备温度、CO_(2)强化水洗温度及时间对脱灰效果的影响。结果表明,炭化温度升高,脱灰率呈先增加后降低的趋势,而水洗温度升高和时间的延长则趋势相反,对于300℃甘蔗渣炭,经40℃水洗4 h脱灰率可达57%。与炭化前水洗脱灰相比,先炭化后脱灰使甘蔗渣热解炭的固定碳含量和炭收率分别提高7%和3%。分析认为,在脱灰过程中,CO_(2)通入水中扩散溶解形成碳酸,与部分盐反应形成溶于水的盐类,K、Na和Ca脱除率超过50%,部分方解石、白云石被脱除。该过程较单独水洗显示出较高的脱灰率和普适性,但是脱灰率与生物炭的灰分组成和类型相关,对花生壳、杨木热解炭脱灰率均超过30%。

Ash content is an important factor affecting the quality and combustion performance of biochar.In this paper,a method of ash removal from biomass is proposed by carbonization followed by CO_(2)-enhanced water leaching.The effects of the carbonization temperature of bagasse,the temperature and time of CO_(2)-enhanced water leaching on the deashing were investigated.The results show that the deashing rate firstly increases and then decreases with the carbonization temperature,while the opposite trend is obtained with increasing the water leaching temperature and time.For bagasse biochar carbonized at 300℃,the deashing rate reaches 57%at the water leaching temperature of 40℃for 4 h.Compared with water leaching without carbonization,the proposed method can increase the content of fixed carbon and the char yield by 7%and 3%,respectively.It is because in the process of deashing,CO_(2)diffuses and dissolves into water to form carbonic acid which reacts with part of metal salts to form water-soluble salts,resulting in the removal rate of K,Na and Ca up to above 50%,and part removal of calcite and dolomite.Also,the proposed process shows higher deashing efficiency and universality,but the deashing degree is closely related to the ash composition and kinds in biochar.As to peanut shell and poplar,the deashing rate exceeds 30%by carbonization at 300℃and CO_(2)-enhanced water leaching at 40℃for 4 h.