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多层流化床低阶煤分级热解提高产物品质研究
Alternative TitlePyrolysis of low-rank coal in multistage fluidized bed for improving product quality
周琦
Subtype博士
Thesis Advisor高士秋
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline应用化学
Keyword低阶煤提质   多层流化床   复合流化床   热解   气化
Abstract低阶煤一般包括褐煤和次烟煤,在我国煤炭保有储量中占比约55%,其挥发分含量高、氧含量相对高、化学反应性好,尤其是褐煤含水量高、热值低、热稳定性差,在加工和储存过程中容易风化和自燃。因此,对于褐煤提质不仅要降低低阶煤的含水量,而且要提高其热稳定性。本研究采用上部煤热解和下部半焦气化的方式,以提高半焦热稳定性和焦油轻质化为目标,提出了多层流化床低阶煤多段分级热解与气化耦合提质新工艺。针对所提工艺的技术特点,通过冷模实验确定了多层流化床可稳定操作的结构和操作参数,采用三层流化床获得了多段分级热解制备高品质半焦和焦油的热解条件,并与耦合流化床气化和输送床热解的复合流化床低阶煤提质工艺进行了对比研究。 本论文的主要研究内容和获得的重要结果如下: 1. 溢流管式多层流化床稳定操作范围。以褐煤颗粒为物料,研究不同结构和操作参数对稳定操作范围的影响,在连续进料溢流管式四层流化床冷态实验装置中,考察了分布板开孔率及孔径、溢流管内径、褐煤粒径、加料速率等对稳定操作气速范围的影响。结果表明:(1) 最小稳定操作气速(Umin)随颗粒加料速率、颗粒粒径、分布板开孔率增大而增大,随溢流管管径增大而减小,与分布板孔径大小无关。(2) 最大稳定操作气速(Umax)随颗粒粒度、分布板开孔率和孔径的增大而增大,随溢流管管径的增大而减小。(3) 平均粒径为276 μm (0.2-0.5 mm)和583 μm (0.5-1.0 mm)的煤的最小稳定操作气速分别为最小流化速度的1.34-1.75 倍和1.61-1.77倍,最大稳定操作气速分别为终端速度的0.28-0.36倍和0.16-0.19倍,表明粒径小的煤颗粒比粒径大的煤颗粒具有较大的操作弹性。平均粒径276 μm煤颗粒的Umax/Umin数值大约是583 μm煤颗粒的3.8倍。 2. 多层流化床低阶煤热解提高产物品质。以0.2-0.5 mm的褐煤为物料,在溢流管式三层流化床热态实验装置中,分别考察了不同操作模式(改变床层数)、过量空气系数、水蒸汽煤比、热解和气化温度、停留时间、反应气氛等对煤热解和气化产物分布及品质的影响。结果表明:(1) 双层和三层流化床操作模式下得到的热解气中的CO、H2和CH4的含量明显高于单层床。(2) 三层流化床热解所制备的焦油中的轻油含量比较高,轻油和酚油之和达到了99.5 wt.%,揭示出多层流化床煤热解能够抑制焦油中重质组分的形成。(3) 采用多层流化床热解所得半焦,由于其挥发分含量大幅降低,其表面的大部分官能团被脱除,使得半焦的热稳定性显著提高,表现为其燃点提高,自燃倾向性降低。 3. 复合流化床低阶煤热解制备高品质半焦。以0.2-0.5 mm和1.0-2.0 mm的不粘煤颗粒为物料,在复合流化床实验装置中,考察过量空气系数、热解和气化温度、加料口位置、停留时间等对煤热解和气化行为的影响。结果表明:(1) 输送床进料时,因停留时间过短造成从输送床获得半焦的挥发分含量比较高,而从流化床进料时得到了高固定碳含量的半焦,特别是小颗粒的半焦经过部分气化及热解后固定碳含量相对较高。(2) 从流化床进料时,在流化床内气化温度为850 ℃、颗粒停留时间90 s,输送床内热解温度为750 ℃、停留时间为2 s,过量空气系数为0.107的操作条件下,通过复合流化床热解和部分气化可以制备出固定碳含量超过82 wt.%的高品质半焦(兰炭)。 4. 多层流化床与复合流化床热解的比较。以长焰煤为原料,分别在多层流化床和复合流化床热态实验装置中,考察了过量空气系数、水蒸汽煤比、停留时间等参数对热解产物的影响。结果表明:与复合流化床相比,在相近操作条件下,多层流化床热解能够有效抑制焦油中重质组分的生成。多层流化床通过延长煤在低温下的热解停留时间,减少高温下的焦油裂解,利用低温半焦对重质焦油的捕集和原位催化作用,并在合成气气氛下发生热解,可以抑制焦油中重质组分的生成,提高焦油的品质。
Other AbstractLow-rank coal including lignite and sub-bituminous coal accounts for about 55% of China’s total coal reserve. It is characterized with high volatile content and high reactivity, with as well relatively higher oxygen content. For lignite, it has further high moisture content, low calorific value and low thermal stability, which is easy to burn spontaneously during processing and storage. Thus, upgrading of lignite not only lowers its moisture content but also suppressing its propensity of spontaneous combustion. By combining coal pyrolysis in the upper stage and char gasification in the lower stage, a multistage fluidized bed pyrolysis process was proposed in this study to produce thermally stabile char and suppress the formation of heavy tar. The major configuration and operating parameters were first investigated for stable operation in a cold-model four-stage fluidized bed, and then the coal pyrolysis was conducted in a three-stage fluidized bed for producing high quality char and tar products. This multistage fluidized bed pyrolysis process was also compared with an integrated fluidized bed pyrolysis process that consists of a gasification bottom in fluidized bed and a transport bed pyrolysis top section. The following summarizes the major research contents and results. 1. Stable operation range of multistage fluidized bed with overflow standpipes. For lignite particles the stable operating gas velocity range was investigated in a four-stage fluidized bed. The tested influential parameters included opening ratio and orifice size of gas distributor, inner diameter of overflow standpipes, particle sizes, superficial gas velocity and particle feeding rate. The following results were obtained. (1) The minimal stable operating gas velocity (Umin) increased with increases in the particle feeding rate, particle size, opening ratio of gas distributor, while it decreased with increasing the inner diameter of the overflow standpipe and was independent of the orifice size of gas distributor. (2) The maximal stable operating gas velocity (Umax) increased with increasing the particle size, opening ratio and orifice size of gas distributor,but it decreased with the increase in the inner diameter of the overflow standpipe.
Pages130
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8258
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
周琦. 多层流化床低阶煤分级热解提高产物品质研究[D]. 中国科学院研究生院,2013.
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