高湿度烟气水平管降膜吸收过程的传热传质研究

发布时间：2018-06-13 19:20

本文选题：潜热回收 + 水回收　；参考：《中国科学院工程热物理研究所》2017年博士论文

【摘要】：随着经济、社会快速发展,我国天然气消费量增长迅速。天然气主要成分为甲烷,在供热装置或湿化燃气轮机循环中燃烧后,产生大量蒸汽,汽化潜热可观。对湿烟气进行潜热和水的回收利用,节能和节水效益显著。开式循环吸收式热泵是一种新型的湿烟气潜热和水回收利用方式,具有不受露点影响、水热回收量大、适用性强等优点。作为开式吸收式热泵的关键部件,吸收器的性能优劣对热泵整体性能、设备尺寸及投资造价等产生显著影响。在吸收器的诸多形式中,水平管降膜吸收器具有结构简单、阻力低及处理量大等优点,在吸收式热泵中应用广泛。但是,水平管降膜吸收过程包含复杂的气液两相流动和传热传质过程,湿烟气中不可吸收气体的存在使传质阻力增大。目前,对于高湿度烟气条件下水平管降膜吸收过程的流动、传热传质机理的认识尚不清晰,适用的吸收器设计方法缺乏。针对这两个问题,本文采用数值模拟和实验研究相结合的方法,开展了以下研究:(1)建立了适用于逆向气流存在的水平管降膜流动三维瞬态模型,能够准确反映气液两相复杂的流动行为及液体管间流型转变。开展了实验验证工作,计算所得流型转变雷诺数与实验数据的最大相对误差小于10%。利用该模型,分析了逆向气流速度对液体管间流型转变雷诺数以及三种流型液膜厚度沿管周向、轴向分布的影响。研究结果表明:随逆向气流速度增大,滴状至滴-柱状、滴-柱状至柱状以及柱-片状至片状的流型转变雷诺数均增大,而柱至柱-片状则减小;加入逆向气流后,滴状流型和柱状流型下液膜最薄点对应的周向角范围由90°～100°变为70°～80°,片状流型下无变化,出现在120°;滴状流型下,水平管上半周液膜较薄且最厚液膜约为最薄液膜的两倍,在一个流动周期内柱状流型下水平管上半周以及片状流型下管全周的液膜厚度分布呈现稳定的"稳定期-高峰-稳定期"特征。(2)基于建立的水平管降膜流动瞬态模型,针对纯蒸汽内冷型、高湿度烟气绝热型两种典型的水平管降膜吸收过程,分别建立了吸收二维瞬态模型。设计和搭建了高湿度烟气绝热型水平管降膜吸收实验台,开展了模型的验证工作。与实验结果的对比表明,该模型出口参数及溶液内部温度分布的最大相对误差不超过9.5%,可准确预测溶液和湿烟气出口参数及内部参数的局部分布特征。利用该两模型,分析了两种基本流型下溶液和湿烟气平均参数随流动时间的变化规律,及局部吸收速率沿流动方向的分布特征。研究结果表明,吸收达到相对稳定后,纯蒸汽内冷型吸收过程的管间区和降膜区溶液的吸收量随管排降低均增大,滴状流型下最低管排降膜区溶液的吸收量几乎与其他区域吸收量之和相同,柱状流型下管间区吸收量约为降膜区的1/2。湿烟气绝热型吸收过程的管间区和降膜区溶液的吸收量随管排降低均减小,滴状流型下管间区吸收量约为降膜区的1/2,片状流型下管间区吸收量约与降膜区相同。滴状流型和片状流型下,降膜区域内局部传质速率的平均值分别约为管间区域的6倍和10倍。(3)基于上述流动、吸收模型,建立了高湿度烟气内冷型水平管降膜吸收过程二维和三维瞬态模型。将二维和三维模型所得不同区域溶液和湿烟气局部参数相对比,最大相对误差不超过5%;二维模型和实验所得溶液和湿烟气出口参数相对比,最大相对误差不超过10%,两个模型精度较好。利用三维模型,分析了三种基本流型下溶液和湿烟气平均参数随流动时间的变化规律,以及局部参数和吸收速率沿管轴向和流动位置的分布特征。研究表明,滴状、柱状和片状流型下,吸收达到相对稳定状态约分别需3.0s、2.0s和2.0s,之后滴、柱状流型不同区域溶液和湿烟气平均参数等均呈周期性变化,周期分别为0.1s和0.2s,片状流型下则保持恒定。滴状流型下,沿管轴向方向,由于液滴撞击产生的轴向波动会导致溶液浓度约增大3%～9%,溶液温度约增大2%～6%,液滴形成区溶液温度约增大8%,吸收速率约增大25%～150%,湿烟气含湿量随轴向位置增大呈现"高-低-高-低-高"的变化趋势,最大值出现在第二排管两侧;柱状流型下,液柱撞击使溶液浓度约增大6%,温度约增大2%～6%,湿烟气含湿量呈现"高-低-高"的变化趋势,最大值出现在第二、三排管的两侧。(4)利用发展的高湿度烟气内冷型吸收二维瞬态模型,开展了适用于高湿度烟气潜热和水回收吸收器的性能多因子正交试验设计,提出了总传质面积的计算方法,获得了吸收性能指标与操作参数和结构参数的回归式,获得了传热、传质过程无量纲特征数方程。研究结果表明,湿烟气进口含湿量是影响界面传质系数、水回收率和湿度效率的最重要因子;溶液进口体积流量是影响界面传热系数和能量利用效率的最主要因子;管径是影响总传质面积的最主要因子。针对应用于燃气供热装置或湿化燃气轮机循环等的湿烟气潜热和水回收的吸收器,可利用获得的吸收性能指标与操作参数和结构参数的回归式,进行设计及结构优化。
[Abstract]:With the rapid development of economy and society, the consumption of natural gas in China is increasing rapidly. The main component of natural gas is methane. After the combustion in the heating device or the wet gas turbine cycle, a large amount of steam is produced and the latent heat of vaporization is considerable. The latent heat and water recovery of wet flue gas are used, the energy saving and the water saving benefit are remarkable. The open type circulating absorption heat pump is a kind of heat pump. A new type of latent heat and water recovery of wet flue gas has the advantages of not affected by dew point, high water heat recovery and strong applicability. As the key component of the open absorption heat pump, the performance of the absorber has a significant influence on the overall performance of the heat pump, the size of the equipment and the cost of investment. The falling film absorber has the advantages of simple structure, low resistance and large amount of treatment. It is widely used in the absorption heat pump. However, the process of falling film absorption in the horizontal tube includes complex gas-liquid two phase flow and heat and mass transfer process. The non absorbable gas in wet flue gas increases the mass transfer resistance. At present, the horizontal pipe under the condition of high humidity flue gas is used. The understanding of the flow of the falling film absorption process, the understanding of the mechanism of heat and mass transfer is not clear, and the applicable absorber design method is short. In this paper, the following research is carried out by combining numerical simulation and experimental research. (1) the three-dimensional transient model of the horizontal tube falling film flow suitable for the existence of reverse flow is established. The experimental verification is carried out. The maximum relative error between the Reynolds number and the experimental data is less than 10%., and the Reynolds number of the flow pattern in the liquid tube and the circumferential direction of the three flow patterns are analyzed. The results show that, with the increase of the reverse flow velocity, the Reynolds number of dripper to drop column, drop column to columnar and column to sheet form is increased, but the column to column flake decreases, and the circumferential angle ranges from 90 to 10 when the reverse flow is added. The 0 degree changes from 70 to 80 degrees, and there is no change under the flake flow pattern, which appears at 120 degrees. Under the dripping pattern, the liquid film on the horizontal tube is thinner and the thickest liquid film is about two times that of the thinnest liquid film. In a flow period, the thickness distribution of the liquid film in the half cycle of the horizontal tube and the flake flow pattern under a cylindrical flow pattern is stable "stable period peak stability". "Characteristics. (2) based on the transient model of the horizontal tube falling film flow established, the two dimensional transient model was established for the absorption process of two typical horizontal tube falling film absorption process of pure steam internal cooling and high humidity flue gas adiabatic type. A high humidity flue gas adiabatic horizontal tube falling film absorption experimental platform was designed and built, and the verification of the model was carried out. The comparison with the experimental results shows that the maximum relative error of the model exit parameters and the temperature distribution in the solution is not more than 9.5%. It can accurately predict the local distribution characteristics of the outlet parameters and the internal parameters of the solution and wet flue gas. By using the two model, the changes of the average parameters of the solution and the wet flue gas under the two basic flow patterns are analyzed with the change of the flow time. The results show that the absorption of the solution in the intertubular and falling film region of the pure steam absorption process increases with the decrease of the tube discharge, and the absorption of the lowest pipe discharge zone under the dripping flow is almost the same as that of the other regions after the absorption is relatively stable. The absorption of the intertubular and falling film zone in the 1/2. wet smoke heat absorption process under the columnar flow pattern is approximately reduced with the decrease of the tube discharge. The absorption of the intertubular area under the dripping pattern is about 1/2 in the falling film zone, and the absorption of the intertubular area under the flake flow pattern is about the same as that in the falling film zone. The average value of local mass transfer rate in the membrane region is about 6 times and 10 times of the intertubular region. (3) based on the above flow and absorption model, a two-dimensional and three-dimensional transient model of the falling film absorption process of a high humidity flue gas internal cold type pipe is established. The error is not more than 5%, and the two dimensional model and the experimental solution and the wet flue gas exit parameters are compared, the maximum relative error is not more than 10%, and the two models are of better accuracy. Using the three-dimensional model, the variation rules of the average parameters of the solution and wet flue gas under the three basic flow patterns and the axial and absorption velocity along the tube are analyzed. The distribution characteristics of the flow position show that the absorption of the droplet, column and flake flow pattern is about 3.0s, 2.0S and 2.0S respectively, and then the droplets and the average parameters of the different region solution and the wet flue gas of the cylindrical flow pattern are all periodic, and the period is 0.1s and 0.2S respectively. In the axial direction of the tube, the axial fluctuation caused by the droplet impact will cause the solution concentration to increase by 3% to 9%, the solution temperature increases about 2% ~ 6%, the solution temperature increases by 8% and the absorption rate increases by 25% to 150%. The moisture content of the wet flue gas increases with the axial position and presents a "high to low to high to high" trend with the axial position increasing, the maximum value appears in second. At the two sides of the tube, the solution concentration increased by 6% and the temperature increased by 2% to 6% under the column flow pattern. The moisture content of the wet flue gas presented a "high to low" trend, and the maximum value appeared on both sides of the second, third rows of tubes. (4) the latent heat of high humidity flue gas was used to develop the latent heat of high humidity flue gas and the latent heat of high humidity flue gas. The performance of water recovery absorber is designed by multi factor orthogonal design. The calculation method of total mass transfer area is put forward. The regression formula of absorption performance index and operation parameters and structural parameters is obtained. Heat transfer and mass transfer process are obtained. The results show that the moisture content of the wet smoke is affected by the mass transfer coefficient of the interface and water recovery. The most important factor of rate and humidity efficiency is that the volume flow of the solution is the most important factor affecting the heat transfer coefficient and energy utilization efficiency of the interface; the pipe diameter is the most important factor affecting the total mass transfer area. The design and structural optimization of the absorption performance index and the regression formula of operation parameters and structural parameters are carried out.
【学位授予单位】：中国科学院工程热物理研究所
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK124

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