Knowledge Management System Of Institute of process engineering,CAS
|关键词||生物甲烷 生物沼气 系统建模 单元模拟分析 系统综合评价|
生物质废弃物通过厌氧发酵方式生产生物沼气是生物质高效资源化利用的重要手段之一，具有经济和环境的双重效益，是可再生能源领域的研究热点。现有研究主要针对生物质的厌氧发酵及生物沼气的利用等关键单元技术，从全系统角度的研究较为缺乏，而该体系涉及多种技术、多个单元过程以及多种影响评价指标，是一个复杂拓扑网络系统评价问题。因此，需要借助系统工程的方法对该复杂系统进行深入剖析，了解各单元及变量对系统性能影响的机制，并对影响系统效率的多种技术采用多种指标进行综合评价，筛选出具有代表性的可持续发展路线为生物沼气技术的大规模应用提供指导。基于上述背景，本文对生物沼气全系统进行了能量、环境及经济综合评价，并对系统中的沼气提纯及厌氧发酵关键单元进行了建模与能耗分析。主要研究内容与成果如下：（1）针对粗沼气提纯分离单元，开展了变压吸附法（PSA）粗生物沼气提纯制备生物甲烷工艺的动态模拟与评价研究。分别以13X沸石（Zeolite 13X）、 3K碳分子筛（CMS-3K）和508b金属有机骨架材料（MOF-508b）为吸附剂，建立了两塔-六步的改进 Skarstrom 动态变压吸附模拟流程，对变压吸附过程的关键参数如吸脱附压力、进料吹扫比等进行了灵敏度分析，确定了优化工艺参数； 考察了吸附塔内的压力、CH4 及CO2 组分的浓度随塔高及循环时间的变化；对三种吸附剂装填条件下工艺过程的能耗、设备尺寸及吸附剂装填量进行了计算与比较。结果表明，采用MOF-508b和CMS-3K作为吸附剂时的工艺能耗比Zeolite 13X作为吸附剂时分别低56%和50%；MOF-508b及CMS-3K填充的吸附塔塔径比 Zeolite 13X 填充的吸附塔塔径分别小13%和27%。（2）针对生物质厌氧发酵单元，建立了容积产气率及单元的热平衡模型。对中温 35?C 和高温 55?C 厌氧发酵状态，根据实验数据拟合了三种二元共发酵体系（牛粪与秸秆、鸡粪与秸秆、人粪与秸秆）的容积产气率模型，模型预测结果与实验结果平均偏差在 7%以内。 对热平衡模型， 考察了沼液低温余热的回收对减少过程外供热量的影响。结果表明，发酵过程所需热量的约 89%用于加热进口的冷物料，而约 11%用于维持发酵罐的恒温。 因此， 对沼液的低温余热加以回收以减少过程热量供给是十分必要的。以沼气锅炉供热发酵罐方式为例，通过沼液余热回收， 在中温发酵和高温发酵状态下，每天可以分别减少42%和49%的沼气消耗。（3）针对生物甲烷生产全系统，开展了物流与能量分析研究。在单元过程模拟基础上，建立了该系统的能耗模型和能量效率评价指标。考虑了2种发酵技术、4种粗沼气提纯技术、2 种系统热量供给及是否进行沼液低温余热的利用等因素，设计了32种情景路线；考察了发酵温度、系统热量供给方式及沼液低温余热回收模式对系统能效的影响。结果显示，采用高温发酵技术， 粗沼气及生物甲烷转化率比中温发酵分别提高120%及110%，能量的转化效率提高1倍；高温发酵比中温发酵减少了约3.1 wt%沼液及沼渣的处理量及26%的能量损失； 对中温及高温发酵情景下系统的能效分析与比较，结果表明，采用高温发酵及加压水洗技术，系统所需的热量由外部热源供给且沼液与发酵原料换热回收低温余热，系统的能效在 32 种情景中最高（46.5%）；采用中温发酵及变压吸附技术，系统所需的热量由燃烧发酵过程自产沼气供给且沼液与发酵原料不进行换热回收低温余热，系统的能量效率在 32 种情景中最低（15.8%）；在系统的热量供给方式及沼液与发酵原料换热模式相同的情况下，高温条件下系统的能效约为中温条件下的2倍。在对系统能效影响的三个因素中，发酵温度是对系统能效影响最大的因素，其次是系统热量的供给方式，最后是沼液与发酵原料的换热模式。（4）针对三种不同沼气利用方式（提纯制备生物甲烷、热电联产、固体燃料电池）构成的生物沼气生产及利用系统，对其进行了概念设计，并分别对其能效、绿色度及净现值等指标进行了综合评价与比较。结果表明， 对于系统的能量效率，为沼气提纯 >沼气 SOFCs > 沼气 CHP，提纯利用方式系统能效最高，SOFCs利用方式系统的能效比 CHP 利用方式系统的能效高 2.5%；对于系统绿色度变化量，沼气SOFCs > 沼气 CHP > 沼气提纯；对于系统的投资回收期，沼气 CHP > 沼气 SOFCs >沼气提纯。
Biowaste via anaerobic digestion to produce biogas is one of the high efficiency method for utilizing the biomass, which could bring both economic and environmental benefits, thus it becomes a hot spot in the renewable energy reasearch area. Although there are a lot of merits for this process, it is difficult to study due to the fact that it is a systematic topology network problem with great complexity. There are many technologies, units in the system and assessment indexes for assessing this system are various. Moreover, the units and variables in the system are not independent but have trade-off relationship. Thus, the complex renewable energy resource system should be studied by process system engineering method in order to have an insight understanding of the trade-off relationship inside the system and the coupling mechnism between the variables and units. At last, a comprehensive assessment of the technologies and indexes that affect the system performance should be given for selecting a representative routes and providing a guidance for larger scale biogas technology utilization. Based on the backgound above, a comprehensive assessment was conducted from energetic, environmental and economic perspective for this thesis, futhermore, some key units in this system like biogas upgrading and anaerobic digestion were simulated and analyzed from energetic angle, which will be useful for larger scale biogas utilization. The main content and results for this thesis are listed below: (1) For the biogas upgrading unit, the study is focused on the energetic analysis and assessment of biogas upgrading process with pressure swing adsorption (PSA) dynamic simulation method. The dynamic simulation work was conducted by establishing a modified Skarstrom PSA process with two columns and six steps, and Zeolite 13X, CMS-3K and MOF-508b were used as adsorbents. Then, the sensitivity analysis for the key parameters like adsorption pressure, desorption pressure and purge feed ratio was conducted to obtain the optimal parameters. Meanwhile, the process pressure, CH4 and CO2 concentration variation with the column height and cycle time and were investigated. Finally, the process energy consumptions, column sizes and adsorbent usage with three adsorbents packing are calculated and compared respectively, the results indicated that the energy consumption of PSA process using MOF-508b adsorbent is 56% lower than that using Zeolite 13X, and the column packed with MOF-508b is estimated to be 13% smaller in diameter than that with Zeolite 13X. (2) For the anaerobic digestion unit, the study is focused on the biogas production rate fitting model and heat balance of the anaerobic digestion unit. The heat balance was conducted and the heat cosumption model was established for both mesophilic digestion 35?C and thermophilic digestion 55?C processes. The volumetric biogas production rate models for three kinds of co-digestion feedstock such as cattle manure and corn straw, chicken manure and corn straw, human feces and corn straw were established by fitting the experimental data, which showed a good prediction. Meanwhile the recovering of the low temperature waste heat from the bio-slurry to the effect of decreasing process heat consumption was investigated, the results showed that, the heat demand for heating the feedstock accounts for 89% of the total heat demand of the digester, while the other 11% was used for maitaining the temperature of the digester. Thus, the recovering the waste heat of the bio-slurry is imperative. Taking the heat demand of the digester supplied by combusting the biogas produced inside the digester for example, the biogas usage for the anaerobic digestion unit can decrease 42% and 49% for mesophilic and thermophilic case respectively via bio-slurry low temperature waste heat recoverying. (3) For the whole biomethane production system, the study is focused on the material flow and energetic analysis of the system. The energy consumption models of biomethane production system were established with the energy effciency assessment index were proposed also. Meanwhile 32 scenarios for the biomethane system were designed to investigate the factors such as digestion temperature, heating mode of the system and waste heat recoverying mode to the effect of the system energy efficiency. Finally, the systematic material and energy flows of the base case were analyzed and compared. The results indicated that the conversion rate of biomass to the biogas and biomenthane increases 120% and 110% for thermophilic digestion compared with mesophilic digestion, and the energy conversion rate increases by one time. Furthermore, the amount of bio-slurry and digestate generated and the heat loss due to bio-slurry discharge for thermophilic digestion are 3.1 wt% and 26% lower than the mesophilic digestion, respectively. Compared with the energy efficiency of the 32 scenarios in the system, the scenario employing thermophilic digestion and high pressure water scrubbing technology, with heat exchange between feedstock and slurry to utilize the waste heat, and heat demand of digester supplied by the energy source outside the system has the highest energy efficiency (46.5%), while scenario employing mesophilic digestion and pressure swing adsorption technology, without waste heat recovery and heat demand of system supplied by combusting the biogas produced inside the system has the lowest energy efficiency (15.8%). The energy efficiency of the TD scenario is twice as the MD scenario while using the same biogas upgrading technologies, heating mode of system and waste heat recovery mode between feedstock and slurry. the digestion temperature is the most sensitive factor that affects the energy efficiency, then is the heating mode of system and the last is the waste heat recovery mode between feedstock and slurry. (4) For the biogas production and utilization system, the study is focused on the comprehensive assessment of the energetic, environmental and economic performance of the system. The system conceptual design was conducted for three biogas utilization pathways such as biogas upgrading to produce biomethane, biogas combined heat and power and biogas solid fuel cells. A comprehensive assessment of the biogas utilization system with energy efficiency, green degree and net present value indexes was performed, which indicated that in terms of energy efficiency (plant efficiency) of the biogas utilization system, the order is biogas upgrading > biogas SOFCs > biogas CHP, the total plant efficiency of the system with SOFCs pathway is 2.5% higher than the system with CHP pathway. As for the systematic green degree production, the order is biogas SOFCs > biogas CHP > biogas SOFCs. Finally, for the economic results like payback period, the order is biogas upgrading < biogas CHP < biogas SOFCs.
|武斌. 生物沼气生产利用系统建模分析及可持续性评价[D]. 北京. 中国科学院研究生院,2016.|
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