【作者】 徐军；

【导师】 王连军；

【作者基本信息】 南京理工大学 ， 环境工程， 2010， 博士

【摘要】 本文以N-甲酰吗啉(NFM)水溶液为吸收液,聚丙烯中空纤维膜接触器为吸收和再生反应器,开展了膜吸收-真空膜蒸馏组合工艺净化含甲苯废气的研究。研究内容主要包括工艺性能研究、传质理论研究及在此基础上拓展的系统能耗分析研究。工艺性能研究主要围绕甲苯-NFM水溶液体系的物性测定及工艺操作参数的优化等方面展开。传质理论研究则以双膜理论为基础,结合传质阻力方程,建立了膜吸收工艺的全微分传质模型。同时也建立了传质微分方程与传热经验关联式相结合的减压膜蒸馏传质模型,在以上两模型的基础上,又建立了系统能耗分析模型,考察了操作条件变化对系统能耗费的影响。首先,测定并计算了甲苯-NFM水溶液体系的物性参数,包括不同体积浓度NFM水溶液的密度、粘度、表面张力、亨利系数,及甲苯在气、膜、液相中的扩散系数等参数,通过线性拟合得到不同条件下物性常数的计算公式。结果表明NFM水溶液对甲苯有高的吸收容量和吸收速率,另外NFM具有较高的表面张力,难以湿润有机高分子膜表面,是膜吸收工艺良好的吸收液。在膜吸收工艺实验装置上,以NFM水溶液为吸收剂,开展了膜气体吸收净化含甲苯废气性能的实验研究,分析了气、液相流量、吸收液温度、吸收液中NFM浓度和气、液相进口浓度等操作参数对甲苯去除效率和传质通量的影响。在吸收液NFM体积浓度40%,吸收液流量20-80 mL·min-1,进口气流量50-500mL·min-1,进口气浓度16.1mg·L-1的条件下,甲苯去除率范围为54.0%-97.3%。实验结果表明采用膜吸收技术净化含甲苯废气,具有较高的去除效率和传质速率。研究还发现,在高气相流量或高气相进口浓度的条件下,气相存在较大浓度梯度的情况下,传质过程受液膜控制,在低气相流量或低气相进口浓度的情况下,传质过程受气膜控制。另外,连续运行实验表明,由聚丙烯中空纤维膜接触器-NFM水溶液组成的膜吸收工艺,具有很高的稳定性和可操作性。在双膜理论的基础上,建立了新的全微分膜吸收传质模型,对气相、膜相和液相的甲苯浓度分布进行了求解,着重考察了操作条件及膜组件形态变化对液相边界层中甲苯浓度分布的影响,进而对传质过程的影响。并将模拟结果与实验结果进行了对比,结果表明模型计算值与实验值平均误差为5.2%。模型可以较准确地描述膜吸收过程,可作为膜气体吸收技术工业放大的理论依据。在真空膜蒸馏工艺实验装置上,对膜吸收过程所产生的富甲苯NFM水溶液进行再生实验研究,以实现吸收液的循环利用。考察了减压膜蒸馏过程中,各操作参数变化对真空膜蒸馏传质过程的影响。实验结果表明料液温度是影响膜甲苯通量的决定因素,而浓度和流量是影响甲苯通量的次要因素。甲苯通量在料液入口温度为45℃,冷侧压力为2000 Pa条件下可达到3.17mol·m-2·s-1,证明减压膜蒸馏技术再生富甲苯NFM水溶液工艺具有设备体积小,再生效率高的优点。在真空膜蒸馏实验的基础上,提出一种新的经验微分相结合的动力学模型,描述真空膜蒸馏的传质传热过程,其特点是采用微分方程描述液相传质及浓度分布,用经验关联式描述传热过程。气液界面处的液温,通过传质微分方程的解与传热经验关联式的解相互迭代求得,然后反求得液相浓度的分布,该模型克服了无法从实验中获取界面温度的难点。在膜吸收及真空膜蒸馏模型的基础上,建立了系统能耗模型,建立了评价指标,考察了操作参数变化对系统能耗的影响,结果发现真空泵的能耗为整个系统能耗的关键因素,液相泵为次要因素。更多还原

【Abstract】 In this paper, an experimental and theoretical study was carried out to evaluate the performance of a newly process which combined gas-liquid membrane absorption with vacuume membrane distillation in toluene/nitrogen separation process by using an aqueous N-Formylmorpholine(NFM) solution as absorbent. The reseaching work included process performance study, theoretical study of mass transfer and the expansion of the system based on the researching of energy consumption. The process performance researching mainly focused on the determination of physical properties of aqueous NFM solution-toluene system and the optimization of operating parameters. A total differential mathematical model which based on the double films theory and serially resistance was developed to simulate the absorption process in order to gain an insight into the experimental observation. The other mathematical model that combine differential mass transfer equation with experiential heat transfer equation was developed to simulate the heat and mass teansfer process in vacuume membrane distillation process. The third model was developed to simulate the effect of operation parameters on the system consumption.Firstly, the determination of determination of physical properties of aqueous NFM solution-toluene system was carried out. The physical properties parameters included the density, viscosity, surface tension and Herry number of aqueous NFM with different volume concentration. The diffusion coefficient of toluene in different volume concentration aquous NFM and N2 were also calculated. Fitting equations of experimental data were obtained. The results showed that the absorbent has absorption Capacity for toluene and has high surface tension which made it difficult to invade into the PP membrane pores. This efficiently decreased the risk of the decreasing of mass transfer efficience which caused by the wetting of membrane. The NFM aqueous was proved as a suitable absorbent for the separation and recovering of toluene from Nitrogen in gas-liquid membrane contactor.An experimental study was carried out to evaluate the performance of self-made membrane absorption device.The effects of operating parameters such as the gas and liquid flow rates, the feed gas and the initial liquid concentrations, the liquid temperature, the absorbent concentration and the long term operation on the toluene flux and removal efficiency were investigated in this study. The results showed that the removal efficiency achieves 54.0%-97.3% when following conditions were used:volume ratio of NFM,40%; flow rate of absorbent,20-80 mL·min-1; flow rate of feed gas,50-500 mL·min-1; feed gas concentration,16.1mg·L-1. It was proved that membrane absorption process has high stability and operability. It was also found in this study that the liquid mass transfer process is the key process in membrane absorption process when the feed gas concentration and gas flow rate were high enough. However, the gas mass transfer process became the key process when the feed gas concentration and gas flow rate were low enough. Additionly, The long term performance test showed that the aqueous NFM solution is a suitable absorbent to be applied to the polypropylene(PP) hollow fiber gas-liquid membrane contactor.Based on the double-film theory, a total differential mass transfer model was established to simulate the process of mass transfer process. The solution of the model could perfectly describe the concentration distribution of toluene in both gas phase and liquid phase. The researching work was foused on the way of removal efficiency and toluene mass flux effeced by operatrion paramemters and membrane contactor formation changings by observing their effect on the concentration distribution at liquid film. The prediction values were compared with those of experiment. The results showed that the average error of touluene removal efficiency was 5.2%. The mass transfer process could be accurately simulated by the differential equations, which could be used as the theory basis for the industrial enlargement of membrane absorption technology.An experimental study was carried out to evaluate the performance of self-made vacuume membrane distillation device.The effects of operating parameters such as the gas and liquid flow rates, the feed liquid concentrations, the liquid temperature, the vacuume side pressure on the toluene flux and removal efficiency were investigated in this study. The result showed that liquid temperature is the most important factor for the toluene removal efficiency and mass flux and the following two factors were feed liquid concentration and liquid flow rate. The toluene flux could achieve 3.13×10-3mol·(m2·s)-1 and toluene removal efficiency could achieves 78.1% when following conditions were used:liquid flow rate of absorbent, 20mL·min-1; Vacuume side pressure,2000Pa; feed liquid concentration,350mg·L-1. It proved Vacuume membrane distillation to be a high efficiency device for recovering the toluene from absorbent.A newly mathematical model which combined differential mass transfer equation with experiential heat transfer equation was developed to simulate the heat and mass teansfer process in vacuume membrane distillation process. This model simulated the mass transfer in the process by using differential equation and simulated the heat transfer by experiential heat transfer equation. The temperature in the liquid surface could be gained by iterating the solutions of two equations.Beased on the memnbrane absorption model and vaccume membrane disllation model, the system energy consumption model was established to evalute the effect of operation parameters on the system energy consumption. The results showed that the energy consumption of vaccume pump is the key ingredients and the following factor is liquid pump energy consumption.更多还原