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褐煤低焦油两段气化基础研究
Alternative TitleFundamentals of Two-stage Gasification of Lignite with Low Tar Content
刘殊远
Subtype硕士
Thesis Advisor汪印 ; 武荣成
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword褐煤   热态半焦   冷态半焦   焦油   两段气化
Abstract两段气化工艺可以直接利用煤/生物质热解产生的具有一定催化活性的半焦催化焦油的裂解,从而获得焦油含量较低的燃气。中国科学院过程工程研究所提出了流化床热解耦合下吸式固定床气化的新型低焦油两段气化技术,适合处理低阶碎煤和高含水生物质残渣。先前的研究对冷态褐煤半焦催化裂解焦油特性进行了考察,证明了该两段气化技术在生产低焦油燃气方面的可行性。本论文重点研究热态半焦与冷态半焦的差异性(热态半焦和冷态半焦的定义见第三章引言部分),半焦活性变化与再生及半焦气化耦合焦油催化裂解等,主要研究内容与结果如下: (1)热态半焦和冷态半焦催化裂解煤焦油活性差异研究。在实验室两段气化装置上,研究了热态半焦和冷态半焦对焦油的催化裂解特性。实验结果表明,热态半焦比冷态半焦催化裂解焦油的能力更强。当焦油催化裂解温度为1100 ℃,气体停留时间为1.2s时,经热态半焦催化裂解后所得燃气中焦油含量最低可降低至100 mg/Nm3。在相同的裂解条件下,热态半焦活性高于冷态半焦,即经过热态半焦催化裂解后的燃气中焦油含量更低。一方面是因为,相同热解条件下制得的热态半焦比冷态半焦具有更大的比表面积和更发达的孔结构。另一方面,随着裂解温度的提高,加入到高温固定床反应器的冷态半焦二次热解程度加深,导致半焦中的碳微晶结构有序度明显增加,比表面积和微孔结构数量有所降低。 (2)半焦活性变化与再生研究。通过SEM分析催化裂解焦油前后的半焦发现,催化裂解焦油后的半焦表面出现了严重的积碳现象,尤其是当焦油催化裂解温度在1000℃以上时更严重。这主要是由于随着温度升高,焦油的在半焦表面的裂解反应增强,导致了半焦表面出现了大量来自焦油分解产生的积碳,进而导致半焦催化裂解焦油的活性降低。SEM-EDS联用分析则表明,使催化裂解焦油后的半焦在900℃以上与水蒸气发生部分气化反应后,半焦的表面可以得到有效更新,同时半焦表面上还观察到了碱金属和碱土金属元素的富集,这些都有助于半焦催化活性的恢复,有利于两段气化工艺的连续操作。研究结果还表明,焦油经半焦高温催化裂解产物主要是积碳和H2。 (3)两段气化条件下半焦气化耦合焦油催化裂解研究。当向固定床热态半焦床层中通入水蒸气时,半焦催化裂解焦油的同时,发生气化反应。实验结果表明,在整个两段气化操作过程中,半焦活性可以保持基本稳定,所得燃气中焦油含量最低可达50 mg/Nm3。这也证明了两段气化工艺是生产低焦油燃气的一种有效途径。在气化/裂解温度1100 ℃和S/C=1.0时,两段气化实验的碳转化率达95%,灰渣中碳含量为0.12%,干煤气产率为2.1m3/kg。 关键词:褐煤,热态半焦,冷态半焦,焦油,两段气化
Other AbstractBy directly using the char with certain catalytic activity from coal/biomass pyrolysis as a catalyst for tar cracking, two-stage gasification process can provide an effective method to get clean fuel gas with low tar content. Institute of Process Engineering, Chinese Academy of Sciences proposed a novel two-stage gasification process, which is capable of dealing with low rank coal and biomass with high moisture content. By examining tar catalytic cracking over cold lignite char, previous research verified the feasibility of two stage gasification process mentioned above in producing fuel gas with low tar content. This thesis mainly focuses on the difference between hot char and cold char in catalyzing tar cracking (See the definition of hot char and cold char in Chapter 3), the variation of char properties after catalyzing tar cracking and its regeneration. Char steam gasification coupled with tar cracking in a continuous two-stage gasification process was also studied. The following summarizes the major research contents and their results. (1) Investigation of tar catalytic cracking over both hot char and cold char. Intrinsic fundamentals of tar catalytic removal over coal char were studied in a laboratory two-stage gasification facility. The hot char from coal pyrolysis (without cooling down) exhibited higher activity for tar removal than the char experiencing its cooling in N2 down to room temperature. The tar content in the producer gas can be as low as 100 mg/Nm3 over the hot char in 1.2 s of gas residence time inside the char bed at 1100℃. BET results showed that hot char has larger specific surface area and more micro pores than cold char while XRD analysis clarified that the ordering of the carbon crystallite structure in the char increased with raising the temperature of tar removal due to the facilitated secondary pyrolysis occurring to the cold char. The secondary pyrolysis of cold char also caused the decrease of its specific surface area and amount of micro pore structures. (2) The variation of activity of spent char and its regeneration. Severe coke deposition on the surface of spent char was observed, especially at temperatures above 1000℃. With SEM-EDS analysis, it was shown that partial steam gasification of the spent char at temperatures above 900℃ could renew the surface of the spent char effectively and caused a simultaneous enrichment of the alkali and alkaline earth species on the char surface. This may contribute to the recovery of char’s catalytic activity for tar removal. The study also revealed that the main products of tar catalytic cracking over char at high temperature are soot and H2. (3) Tar catalytic cracking coupled with char gasification. When steam is introduced to hot char in the fixed bed, tar cracking is coupled with char gasification. The results showed that the activity of char can be well maintained during the entire operation process of two stage gasification and tar content in the producer gas can be further reduced to as low as 50 mg/Nm3. The carbon conversion and dry gas production reached 95% and 2.1m3/kg, respectively while carbon content in the residue ash was only 0.12% at 1100℃ and S/C=1.0. Key words: Lignite, hot char, cold char, tar, two-stage gasification
Pages80
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8353
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
刘殊远. 褐煤低焦油两段气化基础研究[D]. 中国科学院研究生院,2013.
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