The Basic And Application Study On Biomass Catalytic Pyrolysis And Gasification

In view of the severe lack of energy and increasing environmental pollution worldwide, to explore clean energy technologies has become an important and timely research topic. Biomass, as the only reproducible energy that can be stored and transported, is taking great attentions of worldwide researchers with its high effect and cleanness. Biomass pyrolysis/gasification is one of the most efficient processes for converting biomass to energy, especially for gas fuel and power production. However, tar is generally formed in the process, which inhibits the further development and commercialization of biomass gasification. The catalytic pyrolysis is considered as the most potent technique to remove tar, thus to improve gasifying effect and the quality of produced gas. Under the scheme of the research cooperation between Huazhong University of Science and Technology (HUST) and Institute of Environmental Science and Engineering (IESE), Nanyang Technological University (Singapore), the PhD candidate has spent two years of research in IESE on his project entitled"Developing novel catalysts for advanced biomass pyrolysis and gasification", aiming to develop an advanced biomass gasification technique to convert efficiently palm oil wastes and sawdust into bioenergy. The main findings of this study are summarized as follows:Sawdust and palm oil wastes are the main solid wastes coming respectively from wood process and palm oil plants in ASEAN countries. In the practical application and lab work, the wastes were dried, crashed, and sieved in order to get raw materials in different particle sizes. The physicochemical property of these materials showed that palm oil waste and sawdust both contained more volatiles and lower fixed carbon comparing to coal, and their low heat values are ~ 20 MJ/kg, which are similar with that of soft coal and lignite coal. In addition, the baneful elements N and S are of very low contents in raw materials, which are less than 5%. Therefore, palm oil wastes and sawdust are both environment-friendly biomass sources.A main task of the thesis research is to develop catalysts suitable for biomass catalytic pyrolysis and gasification. Based on the knowledge obtained on the latest development of nanotechnology, the supported Nano-NiO/γ-Al2O3 catalysts were developed in this study, involving Nano-NiO particles as an active component loaded on carriers such as commercialγ-Al2O3 and the carriers produced in this study. Meantime, the catalytic activity of the developed Nano-NiO/Al2O3 catalysts in biomass pyrolysis/gasification was evaluated systematically using several reactors.Nano-NiO particles were prepared by homogeneous precipitation method. Different approaches such as FTIR, TGA, XRD and TEM were used to characterize and analysis the NiO nanoparticles and their precursors. Meanwhile, the optimum conditions for preparing NiO nanoparticles were screened. The catalytic activity of NiO nanoparticles in pyrolyzing three main biomass components was evaluated by TGA, and the catalytic performance was compared with that of Micro-NiO. The results indicated that nano-NiO could reduce markedly the activation energy in reaction, leading to biomass pyrolysis at lower temperature. Compared with micro-NiO, nano-NiO had a better catalytic activity over micro-NiO. From the above successful work, the supported nano-NiO/γ-Al2O3 catalysts were further developed involvingγ-Al2O3 as carrier through deposition-precipitation (DP) Method. The loaded capacity of NiO was more than 12 wt%, the sizes of NiO particles were found between 12 and 18 nm, and its surface area was larger than commercial Nickel-based catalysts. Furthermore, in view of saving cost and protecting environment, industrial solid wastes, i.e. red putty and fly ash were used as raw materials of carriers in this study. The influence of calcinations conditions on preparing the carrier and the optimum proportion of raw materials were investigated. It's the performance test showed that the prepared carrier met the industrial standards. Following that, the supported catalyst, with nano-NiO coated on putty-fly ash carrier, was prepared following the same method as preparing nano-NiO/γ-Al2O3. The loading capacity of NiO in the supported catalyst was over 10 wt%, and its specific surface area showed larger than nano-NiO/γ-Al2O3.A countercurrent fixed bed reactor was used for detailed investigation of palm oil waste pyrolysis. The study focused on the influence of two important pyrolysis conditions such as temperature and gas residence time on the distribution of pyrolysis products. Meanwhile, various analytical means were utilized to characterize the obtained products. In particular, the full screening method of tar in different fractions was established. It demonstrated that temperature played an important role in biomass pyrolysis. As the pyrolysis temperature increased, the gas yield enhanced while that of tar and char reduced. Meanwhile, the amount of H2, CO, and CH4 in product gas increased with the increasing temperature; contrarily, that of CO2 in gas dropped significantly. Furthermore, the proportion of oxygenated compounds in tar declined with temperature increasing, while that of the aromatic hydrocarbons and PAHs showed a marked increase, and the changing trend of oil components versus temperature could be concluded. Gas residence time also demonstrated a big effect on pyrolysis process. When the residence time was 15 s, the yield of gas products reached the biggest. At the same time, HSC software was used to simulate thermodynamically the process and products generated in biomass pyrolysis. The simulation results were consistent with those derived from experimental investigation. Besides, anisole was utilized as a tar model component to explore the mechanism and pathway of tar pyrolysis, and a radical reaction mechanism was put forward to explain preferably the changing trend of the tar components derived from biomass pyrolysis.On a double-bed system equipped quartz reactor, the catalytic pyrolysis of palm oil wastes was conducted to evaluate the performance of various catalysts, and to test the lifetime and potential regeneration of nano-nickel catalysts. The results indicated that the char had certain catalytic activity on biomass pyrolysis, especially in upgrading CO amount in gas products, in a price of itself consumption. Dolomite could remove effectively tar in gas, and increased the yield of gas, but it had almost no impact in methane reforming and transforming. The two nano-nickel catalysts developed in this study showed a similar catalytic activity, and they both reduced sharply the yield of tar in biomass pyrolysis whilst increased markedly the gas production and improved significantly the quality of the produced gas. Both the developed nano-nickel catalysts were superior to dolomite and char in removing tar during biomass pyrolysis. In particular, nano-nickel catalysts had strong anti-deactivation and slow deactivation rate, and they could possibly be regenerated by adding H2O and CO2.A home designed double-fixed bed system equipped steel reactor with continuous feeding was used to investigate systematically the catalytic gasification of sawdust with adding stream vapor. The influence of various technical parameters on sawdust catalytic gasification was analyzed experimentally. It was found that the higher temperature and adding vapor were favorable for increasing the gas yield and upgrading H2 gas, and the optimum quantity of adding vapor is 1.33 (S/B) in biomass gasification. The developed nano-NiO/γ-Al2O3 catalyst was proven to have a better performance over dolomite and char for catalytic gasification of biomass. Compared with catalytic pyrolysis, biomass gasification with the presence of vapor was more beneficial owing to the higher gas yield and larger proportion of the valuable H2, the higher efficiency for tar removal, as well as lower residue yields.To further develop and utilize the products derived from biomass thermochemical conversion, the feasibility of using bio-gas generated from this study as the fuel of solid oxide fuel cell was explored, and the influence of gas composition on the efficiency of power production was investigated. Meanwhile, the absorption performance of residual char on Cu2+ in industrial wastes water was tested. The results revealed that the absorption efficiency of char on Cu2+ was over 86%. These explorations and preliminary studies would facilitate the further development and advances of biomass thermochemical conversion technology.