Kinetic Dregs Copper-catalyzed Gasification Of Biomass

As a kind of renewable energy resource, biomass has attracted vast attention over the recent years. Biomass gasification is an effective way of energy utilization. It can transform hydrocarbons which contain in biomass into very useful gases. However, high tar content in dry gas and low hydrogen yield from syngas are still both obstacles required to resolve for the development of gasification technology.The addition of catalyst and steam favor tar reduction and hydrogen production. Olivine is one of the commonly used, cheap, wear resistance catalysts during biomass gasification process. Copper slag belonging to industrial waste which is produced during copper smelting is similar to olivine in the chemical composition, and its main mineral is2FeO·SiO2, Fe3O4and Ca(Fe, Mg)(SiO3)2.In this thesis, a method of catalytic gasification of biomass with catalytic performance of hot copper slag is proposed. Mechanism analysis of copper slag in biomass catalytic gasification is also carried on. For developing this process, investigations were conducted in this thesis as follows:Firstly, using copper slag precalcined at1000℃for5hours as catalyst, the study of catalytic gasification reaction of biomass was carried on in a thermogravimetric analyzer at a fixed rate of30k/min with O2serving as the gasifying agent. The catalytic activity of precalcined copper slag was investigated in the mass ratio of precalcined copper slag to biomass ranging from0.5to2.5. The experimental results show that the values of the DTG peaks for pyrolysis and gasification of biomass first increase and then decrease for the studied range of the mass ratio, and reach the maximum in the ratio2. The homogeneous model (HM) and shrinking core model (SCM) were used to correlate the relationships between conversion (a) and temperature (T). The reaction activation energies (E) and pre-exponential factors (A) of biomass with copper slag catalysts in various proportions were obtained in the pyrolysis (low temperature) and gasification (high temperature). By looking at two correlation coefficients (R), shrinking core model is better in the pyrolysis, but the homogeneous model is better in the gasification. Also, there existes a kinetic compensation effect during the process of biomass catalytic gasification. The kinetic equations of composite samples were presented at last. Secondly, using a precalcined copper slag to biomass mass ratio of2g/g as the object, the study of catalytic gasification reaction of biomass was carried on in a thermogravimetric analyzer at different heating rates (20k/mi、30k/min、40k/min) with O2serving as the gasifying agent. The experimental results show that the heating rate is an important factor for the catalytic gasification of biomass. The catalytic gasification reaction kinetics of biomass at different heating rates were studied by Popescu method. The Jander Equation for Three Diffusion Model is the most probable mechanism function, and the differential expression of the mechanism function is f(a)=(2/3)(1-α)2/3/[1-(1-α)1/3], the integral expression is g(a)=[1-(1-a)1/3]2. At last,the calculated activation energy of the pyrolysis and gasification are51.38kJ/mol and16.45kJ/mol respectively. The activation energy of biomass calculated by Popescu method is lower than that calculated by the homogeneous model or shrinking core model, but Popescu method is more credible.Thirdly, effects of condition parameters and precalcined copper salg on gasification characterization were investigated in a self-build two-stage experimental apparatus used with steam serving as the gasifying agent for biomass gasification tests, and catalytic mechanism of copper salg was explored. The experimental results indicate that the increase of gasification temperature, steam/biomass mass ratio, copper slag/biomass mass ratio and precalcination temperature are all favorable for raising gasification efficiency and enhancing the H2production. The H2content in the product gas increased linearly with precalcination temperature of copper slag under the experimental conditions examined; in the case of copper slag calcined at1000℃for5h the H2content, the hydrogen yield, the gas yield and the gasification efficiency reach the maximum of59.16%,0.72Nm3/kg,1.22Nm3/kg and77.56%, respectively. Based on the results of these experiments, the catalytic activity of precalcined copper slag is increased because of hot precalcined temperature. The formation of Fe3O4and a-Fe2O3on the surface of copper slag particles is due to the extrusion of iron from the fayalite in copper slag during precalcination, and then iron oxides are reduced into metal iron by H2or CO in gas production during biomass gasification, which plays a key role as catalytic center. Combination of characterization and XRD analysis of precalcined copper slag before and after gasification, it can be inferred that iron acts as catalyst in the biomass steam gasification experiment. Finally, based on the results of the experiments from biomass catalytic gasification in the two-stage experimental apparatus, kinetic analysis of gases was made in the work. The results show that kinetic parameters of gases from biomass gasification under copper slag catalyst are more than that under none catalyst. So, copper slag has obvious catalytic effect on biomass gasification and reduces the activation energy in biomass gasification. The kinetic parameters of different gases which reported under different experimental conditions and with different materials in relative references were presented at last. It is difficult to compare kinetic parameters from the experiments and their parameters. But the activation energy calculated over experimental data is in forefathers research scope.It has been showed that steam gasification of biomass over precalcined copper slag catalysts could not only produce hydrogen-rich gas, but also improve gasification efficiency and carbon conversion efficiency. All the results are very useful to design and develop a new biomass gasification device.