CAS OpenIR
红外快速加热与反应分级调控煤热解制油气研究
许世佩
Subtype博士
Thesis Advisor许光文
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工艺
Keyword低阶煤,快速热解,红外加热,二次反应,分级调控
Abstract

受制于我国“富煤、贫油、少气”的化石资源禀赋,导致煤炭在我国能源结构中长期占据主导位置。我国煤炭质量总体品质不高,总储量中的一半以上都是低变质煤(低阶煤)。利用热解技术将低阶煤中高附加值的富氢组分转化为我国急需的油气资源,是煤炭清洁高值利用的重要之路。快速升温是确保煤热解过程获得高焦油产率的最佳手段之一。在目前的快速热解研究方法中,克级反应器无法最大限度的抑制挥发分的二次反应,而毫克级反应器无法计算产物收率,更不能实际收集热解产物进行分析测试,因此还未揭开快速热解产物的真实特性。本论文开发了一种新型的红外快速加热反应器,能够处理大批量煤样,同时抑制热解过程中二次反应的发生,研究了低阶煤在红外反应器内在宽升温速率(1-1000 ℃/min)以及宽温度区间(500-1000 ℃)条件下的快速热解反应特性,揭示了快速热解焦油与半焦的品质特性,获得了最大化初始热解产物(焦油)的反应调控方法。针对所研究快速热解难以在实际反应器中实现的问题,提出了集成快速热解、选择性吸附和升温深度热解的反应调控方法,通过选择性吸附和重质组分裂解,避免了已生成轻质组分的再裂解;通过深度热解发生燃料颗粒高温缩聚反应,同时获得高热解气收率。主要研究成果如下:1. 低阶煤热处理与结构变迁研究。研究在低温长时间温和热处理过程中煤中有机组分逐渐脱离后煤化学组成与物理结构的变化,揭示低温长时间温和热处理导致的低阶煤化学组成与物理结构的缓慢变化以及二者间的关联。煤的芳香度和CH2/CH3比分别与超微孔(d < 1 nm)和中孔体积(2 - 50 nm)成正比。超微孔由芳香环之间的层间距构成,中孔由通过脂肪链相互连接的大分子芳香环之间的间隙构成。2. 红外快速加热速率对煤热解影响规律。低阶煤的热解过程具有复杂性、差异性和连续性。利用分布活化能模型(DAEM)描述反应整体过程,考察了热解动力学参数随转化率的变化,发现热解反应活化能分布曲线符合高斯分布,主要分布于200~240 kJ/mol的区间,且热解f(E)的最大值出现在活化能220 kJ/mol处。频率因子先随活化能的增大而升高,体现出补偿效应,且当活化能超过220 kJ/mol时,频率因子趋于稳定。利用横向红外快速加热反应器在同一温度(700 ℃)下研究升温速率(6-667 ℃/min)对3 g原煤热解的影响,发现提高加热速率的促进了共价键的集中断裂,在同一时间内生成更多挥发分产物,导致颗粒内外压差增加,提升了传质效率,降低了热解焦油前驱体在颗粒内部和床层内部的停留时间,使热解半焦和热解气的收率下降,焦油收率上升,总挥发分收率上升。但较高的加热速率促进了大分子网络中共价键的集中断裂,减少了颗粒内部的二次反应,产生了更多的重组分。高升温速率所对应的高焦油收率主要归因于重质焦油含量的上升,重组分含量从19.4 wt.%持续增加到48.5 wt.%。焦油的总收率在升温速率为18 ℃/min时超过了格金分析的油收率,在667 ℃/min时最高,达到格金分析油收率的134%。烷烃和芳香族化合物含量下降,烯烃和杂原子化合物含量上升。实验的最高升温速率产生的焦油可能最大程度地反映了一次焦油的结构和组成,具有沸点高、烷烃/烯烃比低、芳香性低、杂原子组成高等特点。随着温升速率的上升,半焦表面的光滑程度明显下降,孔隙明显增多,制得半焦的氧化反应活性略有降低。3. 红外快速加热终温对煤热解作用规律。利用本研究设计的红外加热反应器,对应热解终温500 ℃、600 ℃、700 ℃、800 ℃、900 ℃和1000 ℃的加热速率分别是300 ℃/min、314 ℃/min、667 ℃/min、978 ℃/min、1335 ℃/min和1723 ℃/min。当热解温度从500 ℃升至1000 ℃,热解气收率上升,热解半焦收率下降,焦油收率先上升后略有下降,在700 ℃时最高。整个温度区间焦油产率始终高于格金分析,在700 ℃以上时总挥发分高于格金分析收率和800 ℃以上时热解气产率高于格金分析的气产率。在1000 ℃时,焦油、热解气和总挥发分的产率分别为格金分析相应产率的125%、129%和128%。当热解温度从500 ℃升至1000 ℃,气体总产量从62.67 L/kg升到295.04 L/kg,气体产率与煤中氢元素的提取率正比例相关。随着温度的升高,轻质焦油组分含量从39.33 wt.%提高至55.00 wt.%。焦油中的烷烃含量下降,烯烃含量上升,焦油饱和度得以提高;半焦表面孔隙增多,半焦的氧化反应活性明显下降。当热解温度升至900 ℃及以上时,所得半焦的反应性测试条件下最终碳转化率骤降。 4. 热解反应分级调控产物生成。基于快速热解终温对热解产物的作用规律,提出了分级反应调控方法,包括第一步的煤中低温快速热解和第二步半焦高温深度缩聚,以最少化中低温热解挥发分在高温环境的二次反应,最大化一次焦油产率,并通过半焦二次高温缩聚,明显降低半焦的收率,提高气收率。同时,发现通过对一次挥发分的选择吸附和再升温裂解,不同吸附剂(灰分,半焦和原煤)均将快速热解产物中的重质焦油进行了选择性吸附,进而重质焦油再裂解实现提质,可获得焦油的高收率与高品质焦油。通过吸附再裂解,半焦以及热解气产量都有不同程度的上升,但焦油总产率相对降低(相对于无吸附),气体产量提升幅度与焦油产量降低幅度成正比。不同吸附剂变化幅度从大到小依次为:灰分、半焦和原煤。因此,通过分级反应调控,使第一级快速热解产物中的重质焦油选择性被吸附;通过第二步的半焦高温深度裂解与缩聚,实现重质焦油的再裂解提质和热解气收率最大化,最终获得高收率与高品质的热解焦油与热解气。这种快速热解、吸附再裂解、高温深度缩聚的分级操控所揭示的反应调控本质与内构件固定床/移动床蕴含的原理高度相似。;The characteristics of “rich in coal, poor in oil, less in gas” for China’s energy resources determines the long-term dominant position of coal in the country’s energy structure. The overall quality of coal is poor in China, and more than half of its total reserves are low metamorphic coal (low rank coal). Pyrolysis technology presents a way to utilize coal with added value and for hydrogen-rich gas as the alternative energy resources. Rapid heating ensures high tar yield for coal pyrolysis. However, literature studies using gram-scale reactors usually suffer serious secondary reactions to volatile matter, while other milligram reactors cannot calculate the yield of pyrolysis products and take product samples for analysis. The real characteristics of rapid pyrolysis products have not been revealed by far. A new type of infrared rapid heating reactor is taken in this paper to treat grams of coal as sample and suppress - minimizes secondary reactions of volatile. The pyrolysis characteristics of low-rank coal at was tested at wide-varying temperatures (500-1000 ℃) and heating rates (1-1000 ℃ / min) in the infrared heating reactor. The reaction control method for maximizing the initial pyrolysis products (tar and gas) was obtained. Considering the practical possibility of rapid heating, a staged reaction control strategy was proposed and also verified experimentally to obtain high yield of volatile through rapid pyrolysis, high gas yield via deep condensation of char at high temperature and high quality of tar via selective adsorption on low-temperature particles and in turn cracking in reheating. The main findings are as follows.1. Structure variation of low-rank coal in slow-heating treatment. The evolution of micro/meso pores and chemical composition of a kind of low-rank coal during mild thermal treatment was studied based on the observation of coal structure changes with the gradual detachment of organic matters from the coal. Aromaticity and CH2/CH3 ratio of coal organics are correlative with the volumes of super-micropores and mesopores, respectively. The super-micropores are found to consist of inter-layer distance between stacks of aromatic rings, and mesopores are the space between macromolecular aromatic rings which are inter-connected via aliphatic chains. 2. Infrared fixed-bed pyrolysis with different heating rates. The pyrolysis process of low-rank coal has the characteristics of complexity, nonuniformity and continuity. The entire process of reaction was described using the distributed activation energy model (DAEM), and the change of pyrolysis kinetic parameters with conversion was analyzed. The activation energy distribution curve was in accordance with the Gauss distribution and mainly distributed in the range of 200 ~ 240 kJ/mol. The maximum value of pyrolysis f(E) appeared at the activation energy of 220 kJ/mol. The frequency factor first increased with the increase of activation energy to show the compensation effect. When the activation energy was more than 220 kJ/mol, the frequency factor tended to become stable. The influence of heating rate (6-667 ℃/min) on pyrolysis of 3 g low-rank coal was studied at a specific temperature (700 ℃) in the infrared quick-heating reactor. It was found that the higher heating rate promoted the breakage of covalent bonds in macromolecular networks to generate more volatile components. The internal and external pressure difference of the coal particles is increased to improve the mass transfer efficiency. The residence time pyrolysis tar precursors inside particles and also in the bed is reduced. These consequently, decrease the yields of pyrolysis char and gas but increase the yield of tar and also the total volatile yield. With the increase of heating rate, more organic compounds escape from the tested coal sample, and the residence time of pyrolysis tar precursors decrease both inside coal particles and in the coal bed. The yields of tar and total volatile increase, by accompanying the decrease in pyrolysis gas and char. The higher heating rate promotes the breakage of covalent bonds in macromolecular networks and generate more heavy components to result in higher yield and heavier composition for tar. The heavy oil content in tar increases from 19.4 wt.% to 48.5 wt.%. The total yield of tar is above that of the Gray-King (G-K) assay at the heating rates above 18 ℃/min, and reaches its peak at 667 ℃/min (134% of the G-K tar yield). The contents of alkanes and aromatic compounds decrease, while the contents of alkenes and heteroatomic compounds increase. The tar produced at the tested highest heating rate may well reflect the structure and composition of the primary tar. It has the characteristics of high boiling point, low alkane/alkene ratio, low aromaticity and high heteroatom composition. With the increase in heating rate, the smoothness of char surface decreases, and the oxidation activity of char slightly decreases.3. Infrared fixed-bed pyrolysis at different pyrolysis temperatures. For the adopted infrared-heating reactor, the maximal heating rates corresponding to the finally reached temperatures of 500, 600, 700, 800, 900 and 1000 ℃ are 300, 314, 667, 978, 1335 and 1723 ℃/min, respectively. With increasing the pyrolysis temperature from 500 ℃ to 1000 ℃, the pyrolysis gas yield increases, pyrolysis char yield decreases, tar yield first increases and then decreases to have its peak at 700 ℃. The tar yield is always higher than that of the G-K assay, while the total volatile matter is higher than that of the G-K assay at temperatures above 700 ℃ and the gas yield becomes higher than that of the G-K assay above 800 ℃. At 1000 ℃, the yields of tar, pyrolysis gas and total volatile matter reach 125%, 129% and 128% of the corresponding yields of the G-K assay respectively. The total gas production increases from 62.67 L/kg to 295.04 L/kg to proportionally correlate with the extraction rate of hydrogen from coal. With the increase of temperature, the content of light tar increases from 39.33 wt.% to 55 wt.%. The alkane content in tar decreases, while alkene content and tar saturation both increases. The surface porosity of char increases, and the oxidation activity of char obviously decreases. When the pyrolysis temperature is above 900 ℃, the final carbon conversion of char in its reactivity test sharply decreases. 4. Staged reaction control for pyrolysis. Based on the proceeding tests an idea of staged reaction control was proposed and further experimentally validated It is a first step of low-temperature but rapid pyrolysis and a second step of high-temperature char polycondensation incorporating with the selective adsorption and cracking of heavy components. For the first stage at medium temperatures it can suppress the secondary reactions to the produced volatile matters that may be maximized via quick heating of particles. The heavy tar obtained in the rapid-heating pyrolysis is in turn internationally adsorbed onto ash, char or/and raw coal. Reheating the tar-adsorbed particles leads to upgrading of heavy tar, while high yield of gases ensured by polycondensation of char at rather increased temperatures. Testing different adsorbents found that the realized upgrading effect from large to small follows an order of ash, char and raw coal. Via such a staged reaction control strategy, it well ensures the production of high-yield tar with high content of light components and high-yield gas rich in hydrogen. This reaction control mechanism rightly reflects the principle of reaction control for the pyrolysis in the so-called fixed/moving bed with internals. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40674
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
许世佩. 红外快速加热与反应分级调控煤热解制油气研究[D]. 中国科学院大学,2019.
Files in This Item:
File Name/Size DocType Version Access License
红外快速加热与反应分级调控煤热解制油气研(7727KB)学位论文 限制开放CC BY-NC-SAApplication Full Text
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Google Scholar
Similar articles in Google Scholar
[许世佩]'s Articles
Baidu academic
Similar articles in Baidu academic
[许世佩]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[许世佩]'s Articles
Terms of Use
No data!
Social Bookmark/Share
All comments (0)
No comment.
 

Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.