【作者】 庞云芝；

【导师】 王奎升；

【作者基本信息】 北京化工大学 ， 化工过程机械， 2010， 博士

【摘要】 提出了通过碱预处理显著改善和提高麦秸的可生物降解性能,然后通过厌氧消化方法把麦秸转化成沼气(biogas)这一生产生物能源新的技术途径。开展了如下多方面的试验和机理研究,并对研究结果进行了工程应用。1.不同碱预处理剂对麦秸厌氧消化性能影响的试验研究。选择氢氧化钾(KOH)、氢氧化钠(NaOH)、氢氧化钙(Ca(OH)2)和尿素(CO(NH2)3)为预处理剂,采用四个不同添加量(1%,2%,4%,6%)对麦秸进行预处理,然后在四个有机负荷率(35,50,65和80 g·L-1)下对预处理麦秸进行了厌氧消化产气性能试验。发现NaOH预处理麦秸在65 g·L-1有机负荷率下取得了最好的厌氧消化产气效果,因此选择NaOH作为适宜麦秸的预处理剂。2. NaOH预处理参数试验研究及其优化参数确定。研究了不同NaOH预处理参数对麦秸厌氧消化性能的影响,这些参数包括NaOH添加量、预处理时间、预处理温度、物料含水率、物料粒度、接种物等。研究发现：①与未处理麦秸相比,在各种添加水平下,预处理麦秸的产气率、平均甲烷含量、TS和VS降解率都得到了明显提高,其中2%、4%NaOH预处理麦秸的产气率提高的最为显著,分别提高了44.0%、48.0%,两者之间无显著区别。因此,从经济效益上考虑,选用2%作为最佳NaOH预处理添加量。②经过不同温度预处理后,麦秸的产气率、平均甲烷含量、TS和VS降解率并无显著差异,但10℃的消化时间(dT80)比30℃的缩短了4天,且在大多数情况下,10℃在室温下即可达到,因此,确定10℃为适宜预处理温度。③NaOH添加到麦秸后,只需3天时间即可被基本利用完。试验结果表明,3天和6天预处理对麦秸的厌氧消化产气性能没有明显影响,更长的预处理时间没有实际意义。因此,确定3天预处理时间为宜。④与600%含水率相比,900%预处理含水率的产气率和TS/VS降解率上分别提高了6.1%、5.1%／4.9%,消化时间(dT80)缩短了2天,说明900%含水率有利于NaOH对麦秸结构的破坏和组分的降解。⑤麦秸的产气率、TS和VS降解率随着物料粒度的减小而增大,但不呈线性关系。磨碎麦秸的产气率只比粉碎的提高2.6%,但磨碎却要消耗更多的电能；揉搓的产气率稍低,但与粉碎相比,产气率相差不大,而能耗却明显降低,因此揉搓是比较实用的选择。⑥污泥消化液作为接种物,厌氧消化效果最差,猪粪消化液和麦秸消化液接种效果较好；与猪粪消化液相比,麦秸消化液的产气率、TS和VS降解率略高,且可就地取材,应是首要选择。综上所述,确定NaOH的最佳预处理参数为：添加量2%、预处理温度10℃、预处理时间3天、有机负荷率65 g·L-1、搓揉处理、以麦秸消化液为接种物。3. NaOH预处理麦秸的机理研究。采用扫描电镜(SEM)、傅立叶变换红外光谱(FTIR)、X-射线衍射(XRD)等先进的分析手段,对NaOH预处理提高麦秸厌氧消化产气性能的内在机理进行了探讨。发现：①在微观物理结构上。经预处理后,麦秸的表面物理结构变得疏松、碎裂,出现了明显的分层脱落现象。这种破坏有利于释放包裹在木质素和半纤维素中的纤维素,使之变得更容易被消化利用。经厌氧消化后,预处理麦秸完整的表面被彻底破坏,出现了明显的裂片、凹凸不平的沟槽和微孔,证实了NaOH预处理的有效性。②在化学结构上。预处理使得麦秸中纤维素中的重要连接键发生部分断裂和破坏,纤维素被降解成了小分子物质成分；木质素与碳水化合物之间的酯键发生了断裂,使得纤维素发生了部分降解,并被更多地从木质素的包裹中释放了出来。③在化学组分上。预处理后,麦秸的纤维素、半纤维素、木质素和木质纤维素含量分别由原来的30.6%、28.1%、12.4%和71.1%降低到25.6%、21.9%、10.8%和58.3%；冷水抽出物、热水抽出物和1%NaOH抽出物的百分比含量分别提高了92.3%、83.1%和20.0%；苯-醇抽出物百分比含量降低了37.8%；总糖百分比含量提高了106.7%。可以看出,预处理麦秸厌氧消化性能的提高并不是某一因素作用的结果,而是麦秸表面微观物理结构、化学结构和化学组分变化综合作用的结果。4.工程应用研究。基于课题试验研究确定的氢氧化钠预处理方法,并通过与厌氧消化、沼气净化贮存、沼气输配和沼渣沼液利用系统的集成,建成了秸秆沼气示范工程。对工程项目中的关键单元和设备进行了设计计算,对反应器内外温度、沼气产量、甲烷含量、pH值等主要性能参数进行了监测,获得了较好的实际应用效果。证明NaOH预处理方法和整个生产系统可以完全满足实际生产的要求。本研究发明的NaOH预处理方法,突破了利用纤维素材料生产沼气的核心关键技术,开辟了完全利用麦秸为原料生产清洁能源新的技术途径。对减少秸秆的环境污染、开发新能源具有重要意义,在我国具有十分广阔的推广应用前景。更多还原

【Abstract】 This study developed a new method using alkali to pretreat wheat straw to obviously improve the biodegradability of wheat straw, then use the pretreated wheat straw to produce biogas. Both experimental and mechanism studies were conducted and a demonstration project was also built.1. Effects of different alkali pretreatment agents on the performances of anaerobic digestion of wheat straw. Four alkalis, which were Potassium hydroxide (KOH), Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)2), and Urea (CO(NH2)3) in four addition amounts of 1%,2%,4%,6%, respectively, were used as chemical agents for pretreatment. Four organic loading rates (OLR) of 35,50,65 and 80 g·L-1 were used for anaerobic digestion tests for the pretreated wheat straw. Based on their effects on the performances of anaerobic digestion of wheat straw, NaOH was finally selected as optimal agent at the OLR of 65 g-L-1.2. Pretreatment parameters investigation and optimization. Pretreatment parameters for NaOH agent were further investigated. The parameters included NaOH addition amount, temperature, time, moisture content, straw size, and inocula. The results showed that:(1) Compared to untreated wheat straw, all pretreated ones obtained better performances.2% and 4% NaOH amounts achieved the highest biogas yields, increased to 44.0%, 48.0%, respectively, but the differences were not significant. Hence,2% addition amount was recommended. (2) There was no obvious difference in biogas yields, TS/VS reductions and average methane content at the temperatures of 10℃and 30℃, but the digestion time (dT80) of 10℃were 4 days shorter than 30℃, and 10℃is more easily achieved in practical conditions and therefore is chosed. (3) pH values were observed after NaOH were added to wheat straw when pretreated, it was found that pH values were decreased to almost neutural in three days. The wheat straws pretreated by 3 days and 6 days were anaerobically digested. The results showed that there was no obvious difference in the performances of anaerobic digestion. Therefore,3-day pretreatment time was determined. (4) Compared to 600% moisture content, the moisture content of 900% could increase biogas yield and TS/VS reductions by 6.1%,5.1%/4.9%; shorten digestion time by 2 days; implying that this moisture content was favorable to the destruction and degradation of wheat straw. (5) The biogas yield and TS and VS reductions were increased as particle size reduced, but the relationship was not linear. The milled straw got the highest biogas yield, but needed to consume more electric energy than grinding and kneading. Although the biogas yield of the kneaded straw was lower than milled and ground ones, the difference was acceptable, thus, kneading was considered to be more cost effective and more practical. (6) Compared to the digestates from swine manure and municipal actived sludge, the inoculum from stalk digester achieved the best anaerobic digestion performance. Another adavantage is the easier availability and lower cost. Hence, the digestate from stalk digester is recommended for the inoculation of wheat straw digestion.Base on the results and findings in this section, the optimal pretreatment parameters were determined as follows:2% NaOH addition amount,10℃pretreatment temperature,3-day pretreatment time,65g·L-1 organic loading rate, kneading, and use the digestate from stalk digester as inoculum.3. Investigation on the mechanisms of NaOH pretreatment of wheat straw. FTIR, SEM, and XRD were used to explore the mechanisms of NaOH pretreatment. It was found after pretreatment that:(1) The micro-physical structures were changed greatly, The surface of wheat straw was damaged, and the fiber structure was loosened remarkedly. The striping phenonium was also observed. (2) Some bondings inside cellulose were broken or damaged. It was also observed that ester bond between lignin and carbonhydrate was broken, making more cellulose exposed and become available to micro-organisms. (3) The contents of cellulose, hemicellulose, lignin, and lignicellulose were decresed from 30.6%,28.1%,12.4%, and 71.1% to 25.6%,21.9%,10.8%, and 58.3%, respectively; The percentages of cold-water, hot-water, and 1%NaOH extractives were increased by 92.3%,83.1%, and 20.0%; respectively, while the percentage of beneze-ethanol extractive decreased by 37.8%; The total sugar content was increased by 106.7%. It can be seen that the improvement on biodegradability and biogas yield of wheat straw after pretreatment were not resulted in by one reason but should be contributed to the comprehensive roles of the changes of micro-physical structure, chemical structure, and chemical compositions.4. Engineering application. The pretreatment method developed in laboratory was applied in a practical project in Dezhou city of Shandong province. The project was built through incorperating NaOH pretreatment method with new type of anaerobic digester with green house heating system. The biogas yield, temperature, methane content ect. were monitered and tested. The results showed that the technology was applicable and reliable in large-scale biogas plant of wheat straw.The NaOH pretreatment technology developed in this study solves the key technic problem with the anaerobic digestion of wheat straw, providing one practical way for the clean bioenergy production from wheat straw. It is a new model for clean energy production and pollution mitigation with wheat straw.更多还原