生物质双床气化气氛下床料聚团机理研究

发布时间：2018-08-15 13:12

【摘要】：生物质双流化床气化工艺能够产生高热值煤气,同时达到较高的碳转化率。但在生物质流化床气化和燃烧过程中,床料颗粒易发生聚团失流化。床料聚团问题严重阻碍流化床的稳定运行。聚团物的形成与生物质灰熔特性密切相关。双流化床系统中气化器和燃烧器内的气氛完全不同,但生物质灰在不同气氛下引起床料聚团的机理尚不清楚。国内生物质双流化床气化中试规模研究相对较少。本论文主要从生物质灰熔特性、生物质灰和钾盐引起的床料聚团机理以及双流化床气化中试三个方面展开研究,主要研究内容和结果如下:首先,以热机械分析仪为工具,提出一种生物质灰的灰熔温度测量方法,并分别以特征温度Ts、Tm和T90表示灰样的烧结温度、剧烈熔化温度和完全熔化温度。与角锥法相比,该方法的重复性更好,且能够更灵敏地测量到灰样的烧结和初始熔化。灰样在剧烈熔化阶段的收缩是由硅酸钾熔化引起的,硅酸钾是引起床料颗粒粘结的主要物质,Tm可用于衡量不同生物质灰熔化引起的床料聚团失流化的倾向。其次,研究生物质灰和石英砂床料在不同气氛下的聚团失流化机理。实验结果表明,与空气和二氧化碳气氛相比,氢气气氛和水蒸气气氛下的床料聚团失流化温度更低。在空气气氛和氢气气氛下,床料颗粒的聚团主要是由生物质灰熔化引起;而在水蒸气气氛下,床料颗粒表面先形成硅酸钾包裹层,硅酸钾的熔化引起床料颗粒间的粘结。在气化和燃烧气氛下,床料聚团均是由生物质灰熔化引起的,但气化气氛下的聚团失流化温度更低。FactSage模拟计算结果表明,与燃烧气氛相比,更多的K在气化气氛下转化进入熔渣相,生物质灰和床层中的熔渣相比例均明显增加。气氛主要是通过改变钾盐的转化来影响床料聚团失流化温度和聚团机理。研究不同钾盐与石英砂床料的聚团失流化机理,并研究气氛对聚团机理和钾盐转化的影响。KCl和K_2SO_4分别在水蒸气气氛和氢气气氛下与石英砂中SiO_2反应生成硅酸钾,硅酸钾的熔化引起床料颗粒的聚团失流化;在任何气氛下,K_2CO_3均能够与石英砂中SiO_2发生反应生成硅酸钾,但与空气气氛相比,K_2CO_3和石英砂在水蒸气气氛和氢气气氛下的聚团失流化温度更低。FactSage计算结果表明,在氢气气氛和水蒸气气氛下,K_2CO_3容易转化生成KOH,后者的熔化引起床料在更低温度下发生聚团失流化。在流化床燃烧和气化实验中,小麦秸秆和玉米秸秆均会引起床料颗粒的聚团失流化,而松木木屑燃烧和气化过程中无失流化现象发生。与其他两种生物质相比,松木木屑中的K含量和K/Ca均最低。在双流化床气化过程中,通过控制流化床中K与床料的比例和选取合理的燃烧温度及气化温度,能够有效避免聚团失流化的发生。在水蒸气气化条件下,煤气热值最高可达13 MJ/Nm3。空气气化和水蒸气气化条件下的循环倍率分别为11.4和14。
[Abstract]:Biomass double fluidized bed gasification process can produce high calorific value gas and achieve high carbon conversion. However, in the process of biomass fluidized bed gasification and combustion, fluidization of pellets is easy to occur. The agglomeration problem of bed material seriously hinders the stable operation of fluidized bed. The formation of aggregates is closely related to the melting characteristics of biomass ash. The atmosphere in the gasifier and burner is completely different in the double fluidized bed system, but the mechanism of the agglomeration caused by biomass ash in different atmosphere is not clear. The pilot scale study of biomass double fluidized bed gasification in China is relatively few. In this paper, the characteristics of biomass ash melting, the agglomeration mechanism caused by biomass ash and potassium salt and the pilot-scale gasification of double fluidized bed gasification are studied. The main research contents and results are as follows: firstly, the thermal mechanical analyzer is used as a tool. A method for measuring the ash melting temperature of biomass ash is proposed. The sintering temperature, the violent melting temperature and the complete melting temperature of the ash sample are indicated by the characteristic temperature TsTm and T90, respectively. Compared with the angular cone method, this method is more reproducible and can be used to measure the sintering and initial melting of ash samples more sensitively. The shrinkage of ash samples in the violent melting stage is caused by the melting of potassium silicate, which is the main material that causes the agglomeration of the bed materials to be bonded, and TM can be used to measure the tendency of the fluidization of the agglomeration of the bed materials caused by the melting of different biomass ash. Secondly, the agglomeration and fluidization mechanism of ash and quartz sand bed materials in different atmospheres are studied. The experimental results show that the loss of fluidization temperature of bed material in hydrogen and steam atmosphere is lower than that in air and carbon dioxide atmosphere. In the atmosphere of air and hydrogen, the agglomeration of bed particles is mainly caused by the melting of biomass ash, while in the atmosphere of water vapor, the surface of bed material particles first forms a layer of potassium silicate, and the melting of potassium silicate leads to the bonding between the particles of bed materials. In gasification and combustion atmosphere, the agglomeration of the bed material is caused by biomass ash melting, but the fluidization temperature of the agglomeration in gasification atmosphere is lower. FactSage simulation results show that, compared with the combustion atmosphere, the fluidization temperature of the bed material is lower than that of the combustion atmosphere. More K was transformed into slag phase in gasification atmosphere, and the proportion of biomass ash and slag phase in the bed increased obviously. The atmosphere mainly influences the fluidization temperature and agglomeration mechanism of bed material by changing the transformation of potassium salt. The agglomeration and fluidization mechanism of different potassium salts and quartz sand bed materials were studied. The effects of atmosphere on agglomeration mechanism and potassium salt conversion were studied. KCl and K_2SO_4 reacted with SiO_2 in water vapor atmosphere and hydrogen atmosphere to form potassium silicate, respectively. The melting of potassium silicate leads to the agglomeration loss of fluidization of the bed material particles. In any atmosphere, K2COS3 can react with SiO_2 in quartz sand to form potassium silicate. However, compared with the air atmosphere, the fluidization temperature of K _ 2COC _ 3 and quartz sand in water vapor atmosphere and hydrogen atmosphere is lower. FactSage calculation results show that, K2CO3 is easily converted to KOH in hydrogen and steam atmosphere, and the melting of K2CO3 leads to agglomeration loss of fluidization at lower temperature. In fluidized bed combustion and gasification experiments, both wheat straw and corn straw can cause agglomeration and fluidization of bed particles, while no loss of fluidization occurs in the combustion and gasification of pine wood chips. Compared with the other two kinds of biomass, the K content and K/Ca in pine wood sawdust were the lowest. In the process of double fluidized bed gasification, by controlling the ratio of K to bed material and selecting reasonable combustion temperature and gasification temperature, the agglomeration loss of fluidization can be avoided effectively. Under the condition of steam gasification, the maximum calorific value of gas is 13 MJ / Nm ~ (3). The cycling rates of air gasification and steam gasification are 11.4 and 14.4 respectively.
【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ541

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