【作者】 彭震；

【导师】 廖强； 王永忠；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2011， 硕士

【摘要】 沼气是厌氧产甲烷微生物分解有机物产生的清洁可再生生物质能源,也是我国农村利用形式最广的可再生生物质能源,它不仅具有将有机废弃物资源化利用和保护环境的双重效益,还具有生产成本低,产出效益高等优点。但在沼气发酵过程中发酵原料在附着的气泡上升力作用下上浮至沼液表面,经水分蒸发而形成结壳,由此影响了发酵原料的充分降解和产生的沼气扩散逸出分离,导致沼气池发酵速率减慢、产气率和甲烷含量降低、燃烧热值低等不足。此外,户用沼气池还存在保温性能较差,沼液发酵温度较低,常用发酵原料营养成分单一,氮、磷、钾等微生物代谢必需元素和部分维生素含量较低的问题,延长了沼气反应器的发酵启动时间,降低了发酵原料的水解率和产气率,限制沼气技术实际推广应用。针对上述问题,根据沼气反应器内沼渣结壳原理,设计了一种兼有防止沼渣上浮和集气功能的抗结壳装置,并实验研究该新型沼气反应器的抗结壳性能和产气性能,以及固体物浓度、外源添加物对沼气发酵性能的影响。此外还研究了有机玻璃钢池体材料的机械和传热特性,并中试试验了具有抗结壳装置和保温特性的玻璃钢沼气池发酵产气特性。课题研究得到以下主要研究成果和结论:1.实验室制备的有机玻璃钢沼气池池体材料具有较高的机械强度和一定保温性能,当厚度为6 mm,材料压缩强度达到140 MPa以上,弯曲强度超过120 MPa。以聚乙烯泡沫保温板为保温材料的沼气池池壁导热系数为0.099 W/(m·K ),能够有效降低沼气池壁的导热性能,保证低温下的连续产气,提高沼气利用效率。同时该有机玻璃钢材料具有较好耐酸性,但耐碱性较差。2.自行研制的抗结壳装置能有效地阻挡原料中固体物的上浮,具有显著的抗原料结壳性能,使发酵反应更充分,提高了基质利用率,增强了反应器的产气能力。同时该装置还增强了沼液中的气液分离效果,改善了沼液的酸碱平衡能力,促进了产甲烷菌群的代谢活动,从而显著提高反应器的产气能力和产甲烷能力。3.固体物浓度对抗结壳沼气反应器产气影响较大,在以马铃薯皮为发酵原料,控制沼液温度为27(±3)℃,当固体物(TS)浓度为4%时,抗结壳沼气反应器对原料的利用更充分,产甲烷菌群活性强,有利于甲烷的产生,得到的最大日产气量为11.2 L,原料产气率为600.0 L/(kg·TS),COD去除率为69.7%,产气中甲烷浓度较高,长期地稳定在62%左右,而较低或较高的TS浓度均不利于抗结壳沼气反应器的发酵和产气。4.实验研究了尿素、复合磷酸盐、复合维生素等外源添加物及添加量对抗结壳沼气反应器发酵产气特性的影响,结果表明:添加一定浓度的外源添加物能显著提高沼气反应器的发酵产气性能,加快发酵启动,增强了产甲烷菌群的活性和代谢产热,促进了甲烷的生成和日产气量的提高。实验得到尿素、复合磷酸盐、复合维生素的添加量为1.0、1.20、0.015 g/L时,其最大的池容产气率分别为0.869、0.732、0.843 m~3/(m~3·d),总产气量分别比未添加时提高了52.9%、28.9%、48.4%,产气中甲烷浓度最高达到72.4%。5.一定浓度的镁离子缩短了抗结壳沼气反应器的发酵启动时间,增强厌氧微生物对底物的利用效率,促进了甲烷合成,显著提高了反应器日产气量。其中以莴笋皮为发酵原料,镁盐最佳添加量为0.30 g/L,总产气量提高了71.4%,池容产气率为0.398 m~3/(m~3·d);以马铃薯皮为发酵原料,镁盐最佳添加量为0.10 g/L,总产气量提高了41.6%,池容产气率为0.804 m~3/(m~3·d)。6.具有保温性能的抗结壳沼气反应器(8 m~3)中试试验结果表明:在平均气温为8℃左右的冬季,反应器连续运行15天产气仍然稳定,最大日产气量为2.688 m~3/天,平均池容产气率为0.215 m~3/(m~3·d);产气气压最高达12 kPa,沼液表面无结壳现象;同时反应器保温性较好,充分利用了发酵的代谢产热,沼液温度比常规沼气池高3-4℃,有利于冬季低温条件下的沼气生产。更多还原

【Abstract】 Biogas is a clean renewable biological energy produced by anaerobic methanogenic bacteria decomposing organic matter and one of the renewable energy sources extensively used in our countryside. It does not only convert organic waste to resource and protect our natural environment, but also remain low-production cost and high yield to substrate. However, scums produced can be attached by many bubbles and float up to the liquid level,then surface crusting will be formed due to evaporation of water. It will affect the complete decomposition of substrate,gas-liquid diffusion separation of biogas produced and decrease the fermentation rate, low production rate and content of methane also combustion calorific value. Inaddition, these problems such as bad heat insulation performance, and low fermentation temperature and lack of nutrients in the household-digester can result in extended start-up time of anaerobic fermentation, low utilization rate of substrate and low gas production rate during biogas production. Therefore, the wide application of biogas technology will be affected.According to the principles of surface crusting, a device with the performance of anti-crusting and gas-collecting was designed. The performance of anti-crusting and biogas production, as well as the effect of total solids substrate concentration and exogenous supplements performance of biogas fermentation were respectively investigated. In this thesis, the characteristicses of machinery and heat transfer of glass fiber reinforced plastics were also investigated and the fermentation performance of biodigester made of glass fiber reinforced plastics with anti-scrusting and temperature-holding was tested in pilot scale. The following conclusions are obtained in the thesis:1. The research result indicates that the prepared glass fiber reinforced plastics had high mechanical strength and heat insulation. When the thickness of glass fiber reinforced plastics was 6 mm, the compression strength and bending strength were respectively achieved above 140 MPa and 120 MPa. The thermal conductivity coefficient of biodigester wall covered with polyethylene foamed insulation board was decreased to 0.099 W/(m·K ), which can be beneficial to maintain the fermentation temperature and improve the utilization rate of substrate. Moreover, the prepared digester wall made from glass fiber material could anti acid rather than alkali. 2. The designed anti-crusting device could effectively prevent scum floating up. It resulted in more completely fermentative process and high substrate utilization rate, and improved the capacity of biogas production by the degister with the anti-scrusting device. In addition, the anti-scrusting device in the degister was beneficial to maintain the netral liquid environment by the effective gas-liquid separation and the high metabolic activities of methanogenic bacteria. Therefore, the production rate of methan was significantly increased in the biodegister.3. The biogas production of the degister with the anti-scrusting device was obviously effected by total solid substrate concentration. Especially, when the total solid substrate concentration of potato peeling was set at 4%, the fermentation material was fully utilized and the more menthan was produced in the biodegister with 27(±3)℃fermentation temperature. As a result, the maximal daily gas yield of 11.2 L, biogas production rate of 600.0 L/(kg·TS) and COD remocal rate of 69.7% were achieved, respectively. And the obtained methane concentration in biogas was kept about 62%. However, too low or too high total solid substrate concentration could decrease the abilities of biogas prpduction and anaerobic fermentation.4. In the present study urea, compound phosphates and multivitamins were chosen as the supplements. The results indicate that the supplements shortened the startup time and significantly improved the daily biogas production and methane concentration of the anaerobic digester. The optimal supplement amounts of urea, compound phosphates and multivitamins were 1.0, 1.20, 0.015 g/L, respectively. Correspondingly, the highest volumetric production rate of biogas reached to 0.869, 0.659, 0.843 m~3/(m~3·d), and the methane concentration in biogas maintained at about 65%, 68%, 70% at the end of the biogas fermentation, respectively. Compared to the control, the cumulative total amounts of biogas were enhanced by 52.9%, 28.9%,48.4%.5. The effects of magnesium sulfate on biogas production performances were conducted in an anaerobic digester with anti-crusting device using asparagus lettuce peelings and potato peelings. The results reveal that the magnesium ions shortened the startup time and significantly improved the daily biogas production and methane concentration of the anaerobic digester. The optimal magnesium ions concentration for the asparagus lettuce peelings and potato peelings were 0.30, 0.10 g/L, respectively. Correspondingly, the highest volumetric production rate of biogas reached to 0.398, 0.804 m~3/(m~3·d), and the methane concentration in biogas maintained at about 70%, 68% at the end of the biogas fermentation, respectively. The cumulative total amounts of biogas were enhanced by 71.4%, 41.6%, compared to the control.6. The results of pilot test of digerter with anti-crusting device (8 m~3) indicate that the degister kept a stable biogas production after 15-day anaerobic fermentation period, and the maximal daily production rate and the average volumetric production rate of biogas in the digester reach to 2.688 m~3, 0.215 m~3/ (m~3·d) in the winter with arverage atmosphere temperature 8℃, and the highest pressure of biogas achieved 12 kPa, no scum crusting was observed on the liquid surface. Moreover, the liquid temperature in the biodegister covered with heat preservation material was higher 3-4℃than that in the traditional degister in the winter. It demonstrates that the heat insulation performance of the designed biodegister wall met the requirement of anaerobic fermentation for biogas production in low atmosphere temperature. Therefore, the metabolic heat produced by anaerobic fermentation could be utilized to maintain the relatively high fermentation temperature of liquid and improve the biogas production in the degister.更多还原