即时局部建模在填料塔液泛气速预测的应用

填料塔在工业生产中应用广泛,准确预测填料塔的液泛气速具有重要的应用价值。实际的填料类型多种多样,获取的填料数据也存在差异,单一全局模型的预测效果受到一定的限制。首先给出了岭参数极限学习机模型及其节点增加的递推算法,以有效更新在线模型。结合即时学习方式,提出了局部递推岭参数极限学习机在线建模方法,用于填料塔液泛气速的预测。实验结果表明所提出方法能更充分挖掘数据间的相关信息,预测效果优于相应的全局模型。     

散装填料层泛点和压降的新关联

在理论分析的基础上 ,导出了散装填料层泛点气体速度和压降的新关联式 ,由实验数据计算了常用填料新关联式的液泛填料因子和压降常数。新泛点关联式对 8种填料泛点气速的计算值与实验数据的总平均计算误差为 3.5 2 % ;新压降关联式对各种填料的压降平均计算误差一般在 10 %以下。关联值与实验数据吻合很好 ,计算准确性优于文献公式 ,且比文献公式计算简便。     

General model for prediction of pressure drop and capacity of countercurrent gas/liquid packed columns

A generalized model has been developed for the prediction of pressure drop and flooding in packed columns in which gas and liquid flow countercurrently. The model has been validated for a wide variety of packings, both random and structured. A single mathematical expression is used to describe all flow regimes: dry gas, irrigated gas flow below the load point, loading region, and flooding. The approach to the model development is fundamental in character and is an improvement over models published earlier.     

Experimentelle Untersuchung von Schaum in Packungskolonnen

Foam in process engineering can cause severe problems in distillation and absorption towers. Presently, hydrodynamic models cannot consider foaming in respect of process dimensioning. In a proceeding research project, the fluid dynamic performance data (pressure loss, flooding point) of several different mass transfer packings are examined for foaming material systems. The respective origin of foam generation in the packed column is observed separately. A test cell for the qualification of potential foaming material systems adapted on the special demands of packed columns is introduced. Details on the results on the phenology of foaming, on the fluid dynamic performance data of the column operation with foaming material systems and on the experiments of the adapted test cell are given.     

局部最小二乘支持向量机回归在线建模方法及其在间歇过程的应用

当间歇生产切换于不同的工艺条件时,由于新工况下的样本一般很少,且批次间存在着不确定性（由于原材料波动或过程动态特性波动等）,基于全局学习的建模方法（如最小二乘支持向量机回归,LSSVR）建立的模型泛化性能不强。将局部学习融入LSSVR中,提出一种局部LSSVR（local LSSVR, LLSSVR）的间歇过程在线建模方法。结合前一批次离线优化后的LSSVR参数,针对待预测新样本在线选择与之相关的近邻样本集并基于此进行建模。以建立青霉素发酵过程的菌体浓度为例,验证了LLSSVR算法能够从过程的第2个生产批次开始在线建立较准确的预报模型,较LSSVR有着更好的推广能力、适应性和鲁棒性。     

Basic design of distillation columns filled with metallic structured packings

This paper reports a comparison of several available correlations to calculate flooding velocity and mass transfer efficiency by using the concept of height equivalent to a theoretical plate (HETP) for distillation columns filled with metallic structured packings. It is found that there are more correlations for pressure drop or gas velocity at flooding than correlations to predict HETP values, and that most of the correlations need empirical constants or exponents for their calculation. Nevertheless, these values are not reported for all the packings and all the sizes available. A case study is made for application of the proposed methods, and the results are presented and compared. A brief comment is made on each method and its ease of application.     

计算流体力学在填料塔中的应用

本文综述了计算流体力学在填料塔中的应用和进展情况,并根据研究方法的不同,将其分为两类,即整体平均的研究方法和单元综合的研究方法。并对各研究方法的优势和不足及其应用前景进行了评述,认为用计算流体力学来研究填料塔内流体的流动状况是今后的发展趋势。     

Determination of flooding gas velocity and liquid hold-up at flooding in packed columns for gas/liquid systems

A new model of suspended bed of droplets for describing the vaour or gas the vapour or gas velocity at the flooding point in packed of columns for rectification and absorption under vacuum and normal pressure is presented metallic, ceramic and plastic packings with diameters of 8–90 mm as well on sheet metal and gauze packings, in a wide range of liquid and vapour loads. Approximately 650 literature measurements and own data were evaluated. The mean relative error in determining the gas velocity at flooding point is less than ±5%. On the basis of the double layer model, a new equation was derived for the hold-up at flooding point, which is needed for the calculation of the flooding gas velocity. An example of calculations for sample applications is also included.     

浮选柱中液相轴向返混的研究

An experimental study on the axial dispersion of liquid was carried out in a 0.382-m-ID flotation column packed with different structured packings or free of packings. The correlations of axial Peclet numbers with the liquid and gas superficial Reynolds numbers were developed for various packings. Among the packings tested, it is found that in the column packed with 250Y or 350Y packings the axial dispersion is the lowest. The addition of frother can decrease the axial dispersion. By the simulation analysis of the one-dimension dispersion model of packed flotation column, it is found that small axial dispersion, high collection rate constant and low axial liquid velocity can increase the collection zone recovery.     

Packungskolonnen

Packed columns . Packed towers with dumped or regular packings are widely used in industry for accomplishing chemical engineering processes. Packed columns are able to work economically even under extreme process conditions (e. g. vacuum, high temperature, aggressive flow mediums), because of the available variety of packing types and the straight-forward manufacture of the individual packing elements from almost any material. The present contribution shows the different kinds of packings arranged according to their geometry and physical properties. A packed tower for gas/liquid countercurrent operation is shown as a basic construction with the necessary internals. Since packed columns are mostly used in gas/liquid countercurrent operation, the fundamentals of fluid dynamics and mass transfer are presented for this operating condition.     

Optimizing a Cooling‐Condensing Tower

Heat recovery from a flue gas stream by cooling and condensation in a packed bed column is widely used to increase plant's energy efficiency. Mass transfer equipment manufacturers have the possibility to optimize the size of such cooling towers and therefore its derived investment costs through selection of best suitable mass/heat transfer components. In this work, a real industrial design case of a cooling‐condensing tower equipped with different high capacity random and structured packings is presented. The impact of the selected packings on tower dimensions and investment costs is evaluated and discussed.     

Estimation of phase velocities at flooding point in packed columns for any gas/liquid system

A method for the estimation of gas velocity at the flooding point of various packings, based on such fundamental parameters as the porosity and specific surface of the packing itself, has been developed and introduced herein. The proposed relationships can be applied to the computation of rectification and absorption towers alike, within a wide range of physical/chemical properties of the gas and liquid phases. The method presented in this paper should be particularly useful for estimating the flooding-point gas velocity of new packing elements, mostly, because it needs no empirical constants to be determined.     

A tool for mass transfer evaluation in packed-bed columns for chemical engineering students

This paper presents a Microsoft Excel tool to calculate liquid-gas mass transfer coefficients in packed towers to support numerical design activities in the courses of Unit Operations for Industrial Process and Sustainable Process Design for the Master’s degree in Chemical Engineering of the University of Naples Federico II (Italy).The Mass Transfer Solver Tool (MT Solver Tool) uses several available models to estimate, separately, the values of liquid and gas mass-transfer coefficients and the wet surface area for 144 random and structured packings of interest for absorption/stripping and distillation processes. In addition, a separate spreadsheet can be used in a user-defined mode, to evaluate the mass transfer coefficients with new packing types or to interpret experimental data when the geometrical and physical characteristics of the packing are known. Eventually, the tool is supplied with a data library, where packing geometry and model fitting parameters can be retrieved.The software is aimed to support students and educators in the Unit Operations for Industrial Process and Sustainable Process Design courses. In particular, this is meant to be an example on how the accuracy of design algorithms adopted in unit operation processes is affected by the use of the underpinning correlations for mass transfer rate or pressure drops. Besides, this is aimed to encourage comparison of different correlations when exact field data are not available. Besides, chemical engineers and researchers interested in packed columns design and modelling data may also benefit from the utilization of the software. The MT Solver Tool was introduced to students in a dedicated tutorial lesson after lecturers on packed column design algorithms for distillation, absorption and stripping. Most of the students of the course participated to a group training aimed to simulate the design of an absorption column supported by the MT Solver Tool providing feedback on its application.After the training, an anonymous survey was proposed to the students to monitor the approval rating of the proposed activity and the use of the MT Solver Tool software to support numerical calculations.     

Online Flooding Supervision in Packed Towers: An Integrated Data‐Driven Statistical Monitoring Method

The development of simple and efficient monitoring methods for flooding supervision is an important but difficult task for the safe operation of packed towers. A data‐driven online flooding monitoring method named Bayesian integrated dynamic principal component analysis (IDPCA) is assessed. In the first step of IDPCA, using the fuzzy c‐means clustering method, the multivariate samples collected during plant operation are first classified into several groups. Then, in each subset a dynamic principal component analysis (DPCA) model is constructed to extract the process characteristics. To improve the monitoring performance, Bayesian inference is utilized to combine these DPCA models in a suitable manner. Consequently, the control limits are formulated using the probabilistic analysis. The superiority of IDPCA is illustrated using a lab‐scale packed tower by comparison with the conventional principal component analysis (PCA) and DPCA methods.     

基于PSO-LSSVR的环状流截面含气率软测量方法

由于测量条件高,环状流的截面含气率直接测量往往比较困难。软测量技术的关键在于建立优良的数学模型,在分析了微粒群优化算法(PSO)和最小支持向量回归机(LS-SVR)原理的基础上,利用粒子群算法优化最小二乘支持向量回归机参数的算法,建立了软测量模型,实现了环状流的截面含气率的软测量。实验表明:该模型泛化能力强,测试精度比较高,为环状流截面含气率的测量提供了一种新的测量途径。     

填料式氧合器填料传质与溶血特性的研究

本文在直径5.2 cm的有机玻璃填料式氧合器中,分别填充几种自制小填料(6mm不锈钢O网环,6 mm PVC拉西环,以及7 mm PTFE拉西环等填料),进行血液-O_2的物理吸收实验。以体积传质系数k_Lα和溶血程度作为填料的性能指标,对所用填料进行综合评价与筛选。实验结果表明:在所选填料中,以7 mm PTFE拉西环的性能为最佳。     

CALCULATION PROCEDURE FOR FLOODING IN PACKED COLUMNS USING A CHANNEL MODEL

The combined effect of a channel-based approach for dry pressure drop and the Buchanan equation for wet pressure drop in packed beds has been numerically evaluated within the flooding region. The flooding point is an important design parameter since it establishes the maximum hydrodynamic capacity at which a packed column can operate. Upon analyzing the aforementioned approach, it was found that the usual practice of fixing a “reasonable” wet pressure drop at the flooding point (e.g., 1025 Pa/m) may not yield the correct flooding velocity of the gas, particularly at higher liquid loads. In fact, numerical evaluations of the aforementioned model showed a rather “retrograde” non-monotonic behavior of pressure drop with respect to the f factor of the gas near flooding at different liquid loads. A calculation procedure was therefore devised in this work to correctly compute the flooding point for a given liquid load when using the aforementioned modeling approach. Interestingly, it was found that the correct flooding velocity can be directly computed from liquid holdup below the gas loading point. To illustrate the use of the procedure, maximum capacity calculations were performed for a well-known random packing, a conventional structured packing, and a novel catalytic structured packing.     

Loading Capacity in Packing Towers – Database,Correlations and Analysis

Experimental results published in the literature between 1935 and 2000 were used to generate a working database of 558 loading capacity data for randomly dumped packed beds. The reported measurements were first used to review the accuracy of the few available predicting loading capacity correlations. The Billet and Schultes semiempirical correlation (Trans IChemE 77 (1999) p. 498) emerged as the best prediction method and is recommended for loading transition estimation, only when the constant C_SO of a given packing element is available. When such a model‐dependent parameter is unavailable, an alternative and generalized neural network correlation is proposed to improve the broadness and accuracy in predicting the loading capacity for packed towers. A combination of five dimensionless groups, namely the liquid Reynolds (Re_L), Galileo (Ga_L) and Stokes (St_L) numbers as well as the packing sphericity (φ) and one bed number (S_B) outlining the tower dimensions were used as inputs of the neural network correlation for the prediction of the loading capacity via the Lockhart‐Martinelli parameter (χ). The correlation yielded an absolute average relative error of 21 % and a standard deviation of 19.9 %. Through a sensitivity analysis, the Stokes number in the liquid phase exhibits the strongest influence on the prediction while the liquid velocity, gas density and packing surface area are the leading physical properties defining the loading level.     

Dehumidification of Moist Air with Simultaneous Removal of Selected Indoor Pollutants by Triethylene Glycol Solutions in a Packed-Bed Absorber

Abstract

A packed bed absorber-stripper system was used to remove selected indoor pollutants during the dehumidification of air by triethylene glycol solutions. Triethylene glycol concentrations of 90% and 95% by weight in water were used. Both random and structured packings were employed to provide the contact surface between the liquid and gas phases. A six-inch I. D. absorption column was operated between 50% and 80% of flooding conditions. The heights of a transfer unit for mass transfer for randomly packed 5/8-inch polypropylene Flexi rings and 1/2-inch ceramic Intalox saddles varied from 0.12 m to 0.17 m when dehumidifying air only. However, the height of a transfer unit was in the range of 0.31 m to 0.40 m for the cross corrugated cellulose and PVC structured packings. Heat and mass transfer coefficients were also calculated from the experimental data and were correlated with various process variables. The values predicted by these correlations were within ±10% of the experimental data.

Pollutants used in the study included formaldehyde, toluene, 1,1,1-trichloroethane and carbon dioxide, and their concentrations in the air were controlled to 0.02 ± 0.005 ppm, 3 ± 0.02 ppm, 24 ± 0.1 ppm, and 1000 ± 5 ppm, respectively. Although nearly 100% of the toluene and 1,1,1-trichloroethane were removed by the 95% triethylene glycol solution, only 56% of the carbon dioxide and 30% of the formaldehyde could be removed from the air stream under similar conditions. As expected, the removal of these pollutants by the triethylene glycol solution was not affected by varying the relative humidity of the air.