【作者】 周淑霞；

【导师】 董玉平；

【作者基本信息】 山东大学 ， 机械电子工程， 2012， 博士

【摘要】 由于化石能源紧缺,价格上涨及其所引起的环境污染问题使沼气能源的利用成为近年来研究热点。沼气液化能提高沼气能量密度和燃烧特性,使其可作为清洁能源替代天然气用于生产生活领域,同时也能解决沼气储存、运输困难问题,是实现沼气综合化、规模化利用的重要技术手段。液化后的沼气称为生物质LNG(Liquefied Natural Gas),然而与天然气相比,沼气存在甲烷含量低、二氧化碳含量高、净化工艺不完善、液化系统能耗高等问题,制约着沼气液化技术的发展。本文在深入分析研究国内外沼气净化与液化技术现状的基础上,研究沼气液化制取生物质LNG的关键技术问题；根据厌氧发酵理论,以黄储玉米秸秆作为原料,研究了密闭存放的预处理方法对秸秆中纤维素和半纤维素降解率的影响,以及秸秆与其他发酵原料混合发酵对沼气产量和甲烷含量的影响。基于相平衡理论,采用低温液化冷能技术,对二氧化碳的分离进行了研究；依据热力学焓熵(?)理论,研究工艺参数对沼气液化系统的(?)损失影响;在深入分析天然气液化流程的基础上,研究了沼气液化系统中的工艺参数对系统能耗的影响；将撬装化设计技术引入沼气液化系统,建立了净化与液化耦合的沼气液化系统。以厌氧发酵理论为指导,研究了黄储玉米秸秆密闭处理培育自然菌种提高纤维素降解的预处理方法。对玉米秸秆进行了CMC酶、木聚糖酶、滤纸酶及外切酶的酶活分析,发现中层秸秆酶活比底层高；对玉米秸杆分别与牛粪、污泥混合发酵进行实验研究,得到了甲烷含量较高的发酵原料的混合比例。实验表明黄储玉米秸秆合理储存既能培养微生物又可以降低预处理成本。基于液化冷能技术,构建了适用于分离沼气中二氧化碳的净化系统。模拟分析了压力和温度对二氧化碳分离的影响规律,利用气液相状态方程计算了该系统的热力学工艺参数,结果表明该系统技术适合分离二氧化碳含量在20%-50%的沼气,分离后沼气中二氧化碳摩尔分数降至9%以下；通过实验优化了低温液化分离二氧化碳的工艺条件：在压力3.7MPa、温度-78.5℃、流量0.8g/s条件下,沼气中的甲烷体积分数由58.2%提高到82.8%,二氧化碳体积分数由36.4%下降到8.8%。基于热力学焓熵(?)理论,研究了沼气液化系统的(?)变化规律。设计混合制冷剂沼气液化流程,模拟系统中设备(?)损失分布,结果表明沼气液化系统(?)损失最大的设备是压缩机,其次是换热器和冷却器；建立小型实验平台,对混合制冷剂沼气液化体系进行实验研究,提出了沼气液化后的闪蒸气体预冷液化系统内混合制冷剂的节能方法,实验结果表明：采用该节能方案后,压缩机的(?)损失减少12.2%,冷却器的(?)损失减少27.2%,实验证明了该方法的有效性。基于热力学最小能耗原理,设计氮气膨胀、混合制冷剂两种液化系统,模拟得出系统中压缩机、冷却器功耗及沼气液化率等性能参数,分析了各换热器中管路换热负荷—温度的分布情况,得到了多组元混合制冷剂在换热器中相变耦合的性能曲线；研究了制冷剂级数对液化系统的影响,研究表明带预冷混合制冷剂的流程能耗低于单级制冷流程能耗；分析了该流程中的各参数对压缩机的比功耗与比冷却水负荷影响,得到了高、低压制冷剂的压力、温度、沼气及制冷剂中组分变化等对液化系统比能耗的影响规律。在深入研究小型天然气撬装化系统基础上,将撬装化与模块化引入沼气液化系统,建立了净化与液化耦合的沼气撬装化液化系统。采用低温液化分离二氧化碳的净化系统与预冷和混合制冷耦合的冷箱,得出液化系统的全流程节点的温度、压力、摩尔焓、摩尔熵、摩尔流量和气相分数。结果表明：生物质LNG液化率为0.9242,系统的能耗为0.455kWh/Nm3更多还原

【Abstract】 Due to the shortage of fossil energy, rising prices and the resultant environmental pollution problems, the use of biogas energy has become a research hotspot in recent years. Biogas liquefaction can improve the energy density and combustion characteristics of biogas, so it can be used as clean energy to replace natural gas used in various fields of production and living. At the same time, biogas liquefaction system can solve the problem of biogas storage, transportation difficulties, and it’s also a technology means to achieve a comprehensive, large-scale use of biogas. Liquefied biogas was referred to as biomass LNG (Liquefied Natural Gas). However, in comparison with natural gas, biogas has several problems, such as low composition of methane, high content of carbon dioxide, imperfect in the purification process and liquefaction system, and high-energy consumption and so on. These problems have seriously restricted the development of liquefaction biogas technology.Based on the analysis of LNG liquefaction and purification, the key technologies of preparing biomass LNG was studied. Based on the anaerobic fermentation theory, the effect of the pretreatment method of corn straw mixing with cow dung and mud on the content of methane in biogas was researched, respectively. Based on LNG cold energy utilization technology and obvious difference in critical temperature and pressure between CH4and CO2, the separating efficiency of separating CO2from biogas was calculated by PR equation and phase equilibrium theory. According to thermodynamic law. the effect of process parameters on exergy loss of the biogas liquefaction system was analyzed. Based on the research of liquefied natural gas system, the effect of process parameters on system energy consume was analyzed. Skid-mounted package and modulization were introduced into the biogas liquefaction system, and the coupling biogas liquefaction system with purification and liquefaction was established.In this paper, the pretreatment method of storing corn straw in obturation environment was proposed to improve cellulose degradation rate, based on the anaerobic fermentation and microbial fermentation theory. CMC enzyme, xylanase, filter paper enzyme and exonuclease activity were tested for the pretreatment stalk. The results showed that the enzyme activity of middle corn stalks reached the highest level. The mixed fermentation experiment including two parts was conducted. One part was mixing corn straw with cow dung, and the other part was mixing corn straw with the sludge. The results showed that the methane content of the former was about20%above the latter. Corn straw closed cultivation of microorganisms can culture microorganisms and reduce pretreatment costs, which provides an effective pretreatment method for large-scale dry fermentation biogas industrialization.A purifying system separating CO2from biogas was constructed based on LNG cold energy utilization technology. The effects of the different temperature and pressure on separating efficiency were analyzed. The CO2separation system by liquefaction in low tempreture was constructed, and the thermodynamic parameters of this system were calculated by PR equation. The simulation results indicated that the volume fraction of CO2reduced to less than9%. The system is ideal for separating CO2in the range of20%to50%from biogas. The optimum technological conditions was obtained, with the pressure of3.7MPa, the temperature of-78.5℃and the flow rate of0.8g/s. Under this condition, the volume fraction of CH4increased from58.2%to82.8%, and the volume fraction of CO2decreased from36.4%to8.8%.According to thermodynamic law. the exergy loss of the biogas liquefaction system was analyzed. A small mixed refrigerant gas liquefaction process was designed and the exergy loss of the equipment was computed and simulated. The results showed that the compressor was subjected the most impairment from the exergy loss of the system, followed by the heat exchanger and cooler. The mixed refrigerant biogas liquefaction system was studied in a small experimental platform. The experiment conclusions indicated-that the exergy loss of the compressor was reduced by12.2%, and the cooler was reduced by27.2%, by adopting the cooling capacity of flash gas to cool the outlet gas of compressor, which proved the validity of the method.According to the thermodynamic theory of the core principle, two liquefaction systems were designed and the parameters of compressors and coolers were calculated. The key parameters of the two processes were compared. The distribution of heat load-tempreture in heat exchangers was also analyzed. And then the performance curves of multi-component mixed refrigerant existing phase changes coupling in the heat exchanger were determined. Effect of the number of stages of mixed refrigerant cycle on biogas liquefaction system was analyzed. The results showed that the energy consumption of the mixed refrigerant process with precooling was lower than that of the single-stage one. The effect of parameters on the energy of liquefaction system was simulated. The laws on effect of the change of temperature, pressure and component fraction at the same time on the energy consumption of liquefaction were obtained.Based on the research of small-scale liquefied natural gas system in skid-mounted package, skid-mounted package and modulization were introduced into the biogas liquefaction system. Temperature, pressure, enthalpy, entropy, molar flow and vapors fraction in liquid and gas phase fraction of every node in the whole process were obtained by using the coupling precooling and refrigerant purification system. The results showed that the liquefaction rate of biogas liquefaction system was0.9242and the power consumption of the equipment was0.455kWh/Nm3更多还原