生物质成型燃料热解半焦产率及理化特性

Yield and physicochemical properties of pyrolysis char of biomass briquetting pellets

生物质成型燃料热解特性是其热化学转换利用的理论基础。该文以杨木屑、松木屑、松针叶、杨木锯末与花生壳混合物4种原料经模压成型后分别在不同升温速率和不同终温条件下热解制得的半焦为研究对象,对其成分及表面形貌变化情况进行试验研究及分析。研究结果表明随着升温速率的提高,半焦的固定碳含量逐渐降低,灰分含量逐渐增加;生物质原料的种类对热解半焦固定碳含量也有较大影响,试验结果发现几种原料中杨木屑成型燃料热解半焦的固定碳质量分数最高为70.94%。通过SEM图像分析可以看出,随着热解反应的进行,半焦表面结构越发复杂,孔隙开始变化主要发生在573~673K,半焦表面形成较多孔隙结构,比表面积快速增大;不同种类生物质成型燃料的热解半焦表面形貌有较大差异,杨木锯末+花生壳混合物以及松木屑在热解时都出现排列更为规则的孔隙结构;松针叶成型燃料在热解过程中一直存在更为紧密的特殊半焦表面形貌,微孔容积相对较小。

Biomass energy is considered as a new energy which can be applied in many fields by the energy utilization technological means. The characteristics of pyrolysis char obtained through pyrolysis of 4 kinds of biomass briquette(Poplar sawdust, pine sawdust, pine needles, mixture of poplar sawdust and peanut shell) were analyzed by industrial analysis and scanning electron microscopy(SEM) to investigate the composition variation of char and the evolution of pore structure with different heating rates and different temperatures. Before the experiment, the universal test machine was used to push the pressure bar to compress the materials to a certain molding pressure for a period of time, and the cylinder molding fuel was obtained after the mold was released. The pyrolysis test of the biomass forming fuel was carried out in a fixed bed reactor, and the test apparatus included an electric heating furnace, a quartz tube reactor, a condensing device and a flow meter. The biomass molding fuel was previously placed in the reactor and N2 was passed through before it was warmed. The solid product of the biomass forming fuel during the pyrolysis process was the remainder after the pyrolysis reaction, ie, the pyrolysis char. Proximate analysis(ash, volatile matter and fixed carbon content) of pyrolysis char of biomass molding fuel prepared under different pyrolysis conditions was carried out. SEM was a direct observation method for microscopic morphology research. Direct microscopic imaging was peformed by the material morphology of the surface material of the samples. The results of proximate analysis showed that the fixed carbon content of the char decreased and the ash content of the char gradually increased when the heating rate increased. The higher the ash content of biomass raw material, the higher the carbon content of char produced by pyrolysis was. The types of biomass briquette also had a great influence on the pyrolysis fixed carbon content. The results showed that the fixed carbon content of the pyrolysis char of poplar sawdust was 70.94%. The study found that the pyrolysis char surface morphology of different types of biomass forming fuels was quite different. The SEM images showed that the surface structure of char was more complex with the increase of the temperature. In addition, it was observed that the pore structure of char began to form and enrich during 573-673 ℃, meanwhile, the surface area of char increased rapidly. There was a wide range of molten structures on the surface pores at the later stage of the reaction. The SEM images also showed that the higher heating rate led to a stronger pyrolysis reaction and a more obvious pore structure evolution. Mixture of poplar sawdust and peanut shell and pine needles had more regular pore structure during pyrolysis;pine needle shaped fuel was always in a tighter special char surface morphology during the pyrolysis process, and the micropore volume was relatively small.