This thesis has been devoted to the studies on selective and simultaneous production of char and light oil from biomass pyrolysis with heavy oil recycling.
Based on the results of sequential runs of a pyrolysis process with external recycling of heavy oil, a vapor-solid countercurrent moving bed biomass pyrolysis with internal recycling of heavy oil was proposed. The performance of the proposed moving bed pyrolysis was examined experimentally by employing an originally designed simulator. In addition, detailed comparative analyses of the products from biomass pyrolyses with and without heavy oil internal recycling were conducted to understand their mechanisms.
The sequential runs of the pyrolysis process with external recycling of heavy oil reached a steady state until the 7th run at a heavy-oil/cedar mass ratio around 40%
without forming agglomerates, which indicated that a continuous operation was feasible. The product distribution from the last of the 10 runs was as follows: char, 32 wt % of the total output; non-condensable gas, 19 wt % of the total output;
water, 22 wt % of the total output; and bio-oil, 27 wt % of the total output. The external heavy oil recycling increased the char mass yield by a factor of 1.33 mainly due to self-charring of the recycled heavy oil. The resulting light oil, of which the carbon number in each compound was less than 15, was nearly completely evaporated upon 250 °C and left 0.2 wt % of residue upon 450 °C.
The experimental simulator of the vapor-solid countercurrent moving bed pyrolysis with internal recycling of heavy oil achieved a steady state until the 3rd run with a maximum heavy oil sorption of 0.38 kg/kg-pine. The char, liquid, and
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gas yields in the steady state were 0.36, 0.47, and 0.17 kg/kg-pine, respectively.
The internal recycling of heavy oil increased the char yield of pine by a factor of 1.44 because of not only the self-charring of absorbed heavy oil and/or its co-carbonization with the feedstock but also chemical deposition of vaporous bio-oil onto the pyrolyzing solid. The resultant light oil was free from evaporation residue and consisted of organic compounds with carbon number no greater than 13.
Detailed products analyses showed that the heavy oil recycled into the pyrolysis zone was converted to char, water and light oil, but insignificantly to non-condensable light gases, strongly suggesting importance of dehydration reaction during the heavy oil charring. Detailed gas chromatography mass spectrometry analyses of the bio-oils showed that cellulose-derived levoglucosan, the most abundant compound in general biomass pyrolysis, was completely converted by its dehydration reaction of hydroxyl groups with char active sites. On the other hand, acetic acid, furans, and phenols became richer by 1.5–4 times with the help of re-pyrolysis of their precursors in the recycled heavy oil.
The vapor-solid countercurrent moving bed pyrolysis of biomass with internal recycling of heavy oil was successfully proposed. It was safe to say the proposed pyrolysis was promising because of the characteristics of its products, i.e., char with an elevated yield and light oil without evaporation residue. The resulting char could be used directly as fuels, reducing agent, soil enhancer, and so on. The increased char yield meant high profit regardless of its applications. On the other hand, the resulting light oil might not be suitable for direct use because of its instability, low pH, and high water content; however, it would be an attractive feedstock for catalytic steam reforming because of the minimums of catalyst deactivation and water feeding, or for recoveries of phenols and furans compounds
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employing separation due to their increased contents by heavy oil internal recycling. As the first step of gasification, the proposed pyrolysis was also suitable for low temperature gasification. The main problem of low temperature gasification was the presence of tar in the resultant gas, while the proposed pyrolysis could remove tar completely under a low temperature.
In addition to this work, several recommendations for future studies were given as follows.
The effect of particle size to heavy oil recycling was investigated by two kinds of samples with 0.5–1 and 1–4 mm, and no significant difference was found.
However, a bigger particle size of sample generally has a lower capacity of heavy oil capture. At the same time, the sample height (the reactor height) also influences the capacity of heavy oil capture. In other words, to reach the same level of heavy oil capture, a bigger particle size of sample requires a higher reactor. It makes sense to investigate the relationship between the particle size and sample height.
The increase in the char yield caused by heavy oil internal recycling was due to not only self-charring of the heavy oil and/or co-pyrolysis with biomass but also chemical interaction between volatiles and pyrolyzing solid. This study investigated the effect of the chemical interaction. To understand the self-charring of the heavy oil, it is necessary to analyze the product composition by pyrolysis of heavy oil separately. It is also worth to make clear the effect of the co-pyrolysis with biomass.
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Acknowledgements
This thesis would not be finished without the supports and contributions from many people who are gratefully acknowledged here.
Firstly, I would like to express my deepest gratitude to my dedicated supervisor, Professor Jun-ichiro Hayashi, for his invaluable supervision, encouragement, advice, and constant support throughout not only this research work but also my daily life in Japan. At the same time, sincere thanks are given to my teachers, Professors Koyo Norinaga and Shinji Kudo, for their precious guidance, patient help, and kind care in both of my study and livelihood. Also, I would like to thank my committee members, Professors Teraoka and Yoon for their advice and review of my thesis. I wish the best for all of them.
Secondly, I would like to acknowledge Global COE program, Japan. The courses of short internship, long internship, and English training are the unforgettable experiences that I have never had before, and they must be the great wealth for my future. Also, I would like to acknowledge the China Scholarship Council for financial support, which is essential for my study in Japan.
I would like to appreciate all members in Hayashi-Norinaga Laboratory, including my tutor Sueyasu-san, Kubo-san, Matsuhara-san, Sakurai-san, Soejima-san, Mori-Soejima-san, Takashima-Soejima-san, Hazeyama-Soejima-san, and so on. They gave me so much useful help and happy memories in my daily life. Special thanks are given to Mrs.
Idesh Saruul and Mr. Li-xin Zhang as my friends. The help and advice from them are genuine and beneficial. I wish a good future and health for them.
The last but not least, I would like to acknowledge and dedicate my thesis to my family and parents for their eternal love and support. It is difficult to continue my