【作者】 王许涛；

【导师】 张百良；

【作者基本信息】 河南农业大学 ， 农业生物环境与能源工程， 2008， 博士

【摘要】 生物质能具有资源丰富、可再生的优点,可用来转化固、液、气三种清洁燃料。二十世纪九十年代初,国内外的学者以提高转化效率为目标,开始对生物质的转化机理和影响转化因素进行研究。结果表明,如何消除或降低木质素对纤维素降解酶的阻碍作用是研究的难点和提高转化率的关键。生物质秸秆中的纤维素、半纤维素和木质素三者结构很复杂,要提高半纤维素和纤维素的转化率,就必须对生物质秸秆进行预处理,破坏其物理结构,实现三者的有效分离。预处理的目的是分离、除去生物质秸秆中的木质素,增加生物质秸秆的孔隙率和酶对纤维素的可及性,从而提高生物质秸秆中半纤维素和纤维素的转化率。生物质秸秆的预处理方法可以分为物理预处理、化学预处理、物理化学预处理和生物预处理四大类。学者们对秸秆预处理已进行了许多研究,虽取得了一定的成果,但还没有找到能够应用于生产、低成本、高效率的方法,因此,找到提高生物质转化利用率的预处理技术至今仍然是生物质高品位利用的技术关键,也是学者及企业家们苦苦追求的目标。蒸汽爆破技术是物理化学预处理方法中的一种,最初被应用于纸浆生产。到目前为止,还没有通过爆破显著提高纤维素转化率的报道。近几年来研究生物质爆破技术的逐渐多起来了,但认真分析其工艺参数和结果,其实际上为“汽喷”和“膨化”,因为真正的生物质爆破中生物质溢出时间一定要小于1秒,在这样的速度下才会出现“爆”。目前的报道,解压后生物质均在几十秒到几分钟时间内才能被完全放出来,这就不属于真正意义上的蒸汽爆破范畴了,用于秸秆预处理也无法取得好的效果。本研究采用新的蒸汽爆破技术设备对秸秆进行了爆破预处理研究,这种爆破设备采用蒸汽弹射技术,可以在0.00875s时间内完成能量的高密度突然释放,将秸秆推出高压缸并完成秸秆的爆碎。经对爆破秸秆的沼气发酵和纤维糖化等试验,所获得的相关数据均表现出了明显的预处理效果。本文较全面地反映了作者的研究工作,主要包括以下内容:⑴爆破预处理影响因素和爆破参数优化研究。通过研究汽爆后秸秆结构(半纤维素、纤维素和木质素组分含量)和还原糖得率两个指标来衡量蒸汽爆破预处理中各因素对汽爆效果的影响。在不同的压力、时间、含水率、物料填充密实度等参数组合条件下对生物质秸秆进行爆破试验,对爆破生物质进行物理、化学及结构分析,找出了经过优化的爆破预处理秸秆参数。作者首次尝试了秸秆的二次汽爆试验研究,结果表明,相对于一次汽爆来说,二次汽爆的预处理能力显著提高。⑵为了验证爆破效果和使用价值,用玉米秸秆爆破物分别在常温和中温下进行了沼气发酵试验。试验采用湿式发酵方法(总固形物浓度为5%)。结果表明,每克干物质产气量和沼气中甲烷百分比含量两个参数都较对比试验有一定提高。试验中也对汽爆后秸秆发酵醪液的pH值和COD值变化进行了观测,发现COD的去除率较高。经汽爆后玉米秸秆发酵启动和结束时间都较未经蒸汽爆破预处理的秸秆要早。⑶用蒸汽爆破后玉米秸秆进行了糖化试验。试验结果表明,糖化率较对比试验有较大程度提高。为了进一步提高汽爆的效果,进行了添加化学试剂HCl、NaOH、Na2SO4、氨水的玉米秸秆的汽爆试验。结果表明,添加HCl效果最好,但添加这些化学试剂对提高汽爆玉米秸秆糖化率作用不大。用汽爆后的玉米秸秆发酵制取燃料乙醇试验中,在3.0Mpa压力下,燃料乙醇的产率随保压时间增加呈下降的趋势,而在低压条件下,情况则相反。⑷对秸秆爆破物的显微组织进行了分析。SEM和TG分析表明汽爆后的玉米秸秆的结构破坏程度随汽爆压力和保留时间的增加而增加,虽然在高压和短的保留时间的预处理条件下酶解糖化效果较好,但汽爆后的玉米秸秆的结晶度相对于未经汽爆处理的秸秆结晶度有所增加。⑸设备改进。通过一系列的试验,验证了蒸汽爆破技术设备预处理的效果,同时也发现了设备存在的诸如密封、爆出时间、所需的蒸汽压力等方面的问题,针对发现问题对蒸汽爆破试验台进行了相应设计的改进,进一步完善了试验台的性能,为将来的工业化设备设计制造提供了依据。更多还原

【Abstract】 Bioenergy is rich in resource and reproducible which can be convert into clean fuels—solid、liquid and gas. Scholars began to study the mechanism and the influence factors of conversion at the aim of improving the biomass conversion efficiency at the beging of 1990s. Among these problems how to eliminate or decrease the hindrance of lignin to the cellulase is the difficulty of research.It is because the complex structure of hemicellulose, cellulose and lignose in the biomass stalk that pretreatment on biomass must be done to destory the physical sturcture of biomass and have them seprated effectively if we want to enhance the conversion rate . The aim of pretreatment is to separate or remove the lignin and increase the porosity and accessibility of cellulase to the straw stalk, thereby to improve the cellulose and hemicellulose conversion rate of the biomass straw stalk. The pretreatment methods can be classified into four kinds: physical pretreatment, chemical pretreatment, physical and chemical pretreatment and biological pretreatment. Though the scholars has made many achievements in pretreatment research, the pretreatment method with high efficiency, low cost and to the biomass straw stalk had never been found till today. So it is still the key technology of bioenergy utilizing in high grade to found the pretreatment technology if we want to increase the conversion and utilization efficiency of biomass, it is also the goal that scholars and entrepreneurs hardly pursuited.The steam explosion technic was first used into the paper pulp production, which is one kind of physical pretreatment method. Up to now, there is still no report on significantly increasing the cellulose conversion by steam explosion pretreatment technic. even more; there is no report about the study on the mechanism of anaerobic fermentation with steam explosion pretreated stalk straw. More and more scholars began the research of steam explosion technic in recent years; we can make a conclusion that they are all belong to steam spout or swollen technic in fact by analyzing their technics parameters and the pretreatment result. Because that the real biomass explosion occurred only when it was released out of high pressure vessel within 1 second. The explosion technics reported at present were not the real steam explosion technic indeed, which always cost about several ten seconds to several minutes to spout the biomass out of the boiler. So the good result could not be achieved with these kinds of pretreated technics. The steam eject technology was introduced in the steam explosion equipment in this study. The new steam explosion technique can complete the high density release of energy only in 0.00875s, so the straw stalk was break down easily. Lots of explosion experiments of straw stalk have been done and the result of the biogas anaerobic fermentation and saccharification experiments with the steam explosion pretreated straw stalk showed that the pretreatment effect was satisfied.The author’s study was perfectly reflected in this doctoral dissertation, including:(1)The study is mainly focus on impact factors of steam pretreatment and optimization of the steam explosion parameters. Through the two index: structure variety (the content of hemicellulose, cellulose and lignose) and saccharification rate of steam exploded corn stalk we can weigh the impact of factors on the pretreatment effect and found the main impact factors , the best parameters of steam explosion pretreatment technics. Accordingly, lots of experiments with the different combination of pressure, retained time, moisture content and the loaded density have been done, the physical,chemical and the structure analysis of the steam exploded straw stalk were carried through. The optimal steam explosion pretreatment parameters were found. Dual-steam explosion experiments have been done in this study; the result showed that the pretreated ability of dual-steam explosion technic was significant higher than the ordinary steam explosion.(2)To validate the effect and applicable value of the steam explosion technic, the experiments of anaerobic fermentation on steam exploded corn stalk under normal and moderate temperature have been done, which with the TS concentration of 5%. The result showed that the biogas prodution and the methane content of per gram dry steam exploded corn stalk were all increased than the contrast test, the COD removal ratio was high. The starting and closing time of anaerobic fermentation was all about 10 days earlier exploded under the condition of 3.0Mpa and 90s than the unpretreated straw stalk.(3) The saccharification experiments of steam exploded corn stalk showed that the saccharification ratio was increased than the contrast test. The steam explosion with addition of chemical have been done to look for efficiency pretreatment technic, the chemicals such as HCl, NaOH, Na2SO4 and ammonia were added into the corn stalk during the steam explosion process. Though the saccharification ratio of steam exploded corn stalk that used HCl as addition was higher than that use the other chemical as addition, the effect of chemical addition was not so useful in increasing the saccharification ratio of steam exploded corn stalk. The prodution rate decreased along with the increaseing of retained time in the experiments of fermentation for fuel ethanol under the pressure 3.0Mpa, but it increased under the condition of low pressure.(4)The analysis on microstructure of steam exploded corn stalk with SEM showed that the degree of damage to structure of the steam exploded corn stalk increased along with the increase of pressure and retained time. The better saccharification effect can be achieved with the steam explosion pretreatment condition of high pressure and short retained time. The crystallinity of steam exploded corn stalk increased to some extent than the unpretreated.(5)Equipment improvement. The effect of steam explosion was proved by a series of experiments, the problems such as the seal, retained time, the needed steam pressure, the thermal insulation etc were found. The corresponding improvement of steam explosion test-bed design have been done, which perfects the performance further. The moderate steam explosion was established according to the experiments on the test-bed. Also the study will provide basis for the design and manufacture of equipment industrialization.更多还原