| Fossil fuels are at the vergy of getting extinct, meanwhile, energy extraction from these conventional fuels causes environmental pollution. Presently, there is utmost need of alternative energy resources which are cheap, renewable and do not cause pollution. Of all the renewable sources of energy, biomass energy is unique in that it is effectively stored solar energy, providing about 15% of the world's primary energy consumption. In the conversion technologies for utilizing biomass, gasification and pyrolysis represents certainly more than 95% of the energetic valorisation of biomass, and pyrolysis is the first phrase in the conversion of biomass (gasification, liquefaction, carbonization and combustion), gasification is the best choice. Regardless of use, the primary roadblock preventing biomass gasification commercialization is formation of tars. In addition, it has been estimated that approximately 24.6 million ton of slag is generated from world copper production. Fe2SiO4, Fe3O4 and Ca(Fe, Mg)(SiO3)2 as the main phases present in the copper slag. And olivine catalysts are the common mineral catalysts since they are inexpensive and attrition resistant.In this thesis, a noval process of catalytic gasification of biomass with catalytic performance and waste heat of hot copper slag is proposed. For developing this process, the experimental study on catalytic pyrolysis and gasification of biomass over hot copper slag was carried out, investigations were conducted in this thesis as follows:Firstly, the mechanism of pyrolysis and gasification were studied. Considering the advantage of online gas analysis, the technology of thermogravimetric analyzer coupled with fourier transform infrared spectrometer (TGA-FTIR) was adopted for pyrolysis behavior of biomass, and the formation mechanism of gas products was explored. Experimental results showed that the main pyrolysis process is separated into three stages for calculation, the weight loss in the initial stage is mainly caused by the evaporation of water, in the second major pyrolysis stage the release of large molecular volatiles is caused by Cross-linking polymerization cellulose to form oligomeric heterozygosity active fibers, and in the thermal decomposition stage of residues the weight loss is caused by fracture and aromatization of C-H bond and C-O band of residual carbon to form graphite. Based on air gasification mechanism analysis of biomass, theoretical analysis shows that the gasification of biomass can be divided into drying stage, pyrolysis stage, reduction stage and the oxidation stage.Secondly, techniques such as TG, XRD, SEM/EDX and H2-TPR analysis are used to understand effects of pre-calcination on copper salg. The analysis results indicate that the calcination of copper slag is suitable in the range of 850～1050℃. The formation of Fe3O4 and a-Fe2O3 is due to the extrusion of iron from the fayalite in copper slag during pre-calcination, but severe segregation of iron is found to be uniform. With increasing calcination temperature, the characteristic peaks of fayalite is gradually weakened and then disappeared, the characteristic peaks of hematite increased, while the characteristic peaks of magnetite is present a trend of first increased and then decreased, and the free iron oxides formed on the surface of copper salg is increased. With the extension of calcination time, the characteristic peak of fayalite is disappeared, the characteristic peaks of SiO2 and a-Fe2O3 increased, and the characteristic peaks of magnetite weakened.Thirdly, effects of pre-calcined copper slag on kinetics of biomass catalytic pyrolysis were investigated in thermogravimetric analyzer. The thermogravimetric analysis indicates that the pyrolysis trend of biomass is consistent with and without copper salg catalysis. Catalytic activity of catalysts increases first in the range of 850～1000℃and then decreases at 1050℃with the increase of calcination temperature, and activation energy of pyrolysis is minimum when the copper slag was calcined at 1000℃for 5h, and it is 33.03 kJ/mol. Catalytic activity of copper slag calcined at 1000℃decreases with the prolongation of time, this trend is consistent with magnetite. So, the increase of catalytic of pre-calcined copper slag is due to the formation of Fe3O4.Finally, effects of condition parameters and pre-calcined copper salg on gasification characterization were investigated in self-build experimental apparatus used for biomass gasification tests, and catalytic mechanism of copper salg was explored. The results indicate that, the grade of gas production is decreased with the increase of F, and the grade of gas production is increased with the increase of temperature in the air gasification experiment of biomass. The grade of gas production is mainly proved with the copper slag catalysis in the catalytic gasification experiment of biomass, and the grade of gas production is gradually improved with the increase of calcined temperature and prolongation of calcined time. Based on the results of these experiments, the catalytic activity of pre-calcined copper slag is increased because of hot calcined temperature. The formation of Fe3O4 and a-Fe2O3 on the surface of copper slag particles is due to the extrusion of iron from the fayalite in copper slag during pre-calcination, and then a-Fe2O3 was reduced into metal iron and ferrous oxide by H2 or CO in gas production during biomass gasification, which plays a key role as catalytic center. Combination of pre-calcined copper slag characterization and XRD analysis of copper slag before and after gasification, it can be inferred that a-Fe2O3 acts as catalyst in the air gasification experiment of biomass.It has been showed that gas production with high CO, H2 and CH4 content and high heating value could be obtained in this process. The investigations favor further modification and optimization of orientation gasification of biomass with hot copper slag for syngas preparation, and it is benefical to broaden syngas research field with catalytic gasification of biomass. |
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