Modeling of Differential Pressure Buildup during Flow through Beds of Fibrous Materials

Modeling of the pressure drop buildup across beds of fibrous materials at strainers is reported. Special attention is drawn to the compressibility of the fibrous filter cake. The influence of the penetration depth of sludge particles to the overall pressure drop in conjunction with the thin‐bed effect has been investigated. Numerical results are compared with pressure drop measurements.     

Hydrodynamic continuum model for two-phase flow structured-packing-containing columns

A two-zone two-fluid one-dimensional model was developed for the prediction of the irrigated two-phase pressure drop and the total liquid holdup in gas-liquid countercurrent columns containing structured packings and operated in the pre-loading zone. The model is based on the volume-average mass and momentum balance equations and the double slit model approximation. The model parameters, i.e., the two b2ed Ergun constants, were estimated using gas flow three-dimensional computational fluid dynamics (CFD) within representative elementary units coupled with a combined mesoscale—microscale predictive approach to apprehend the aerodynamic phenomena occurring at the macroscale in structured-packing-containing columns. The two-fluid model proved powerful in the prediction of the column hydraulics under various operational conditions such as atmospheric scrubbing or high-pressure/temperature distillation conditions for the Flexipac, Mellapak, Gempak and Montz packings. The satisfactory results obtained highlighted the breadth of applicability of the proposed approach especially for new designs or for optimal rating of existing equipments. The model can also prove powerful in the simulation and design of new geometries for structured packings.     

Transient biofilter aerodynamics and clogging for VOC degradation

Removal of volatile organic compounds like toluene from waste gases with a biofilter can result in clogging of the reactor due to the formation of an excessive amount of biomass. Excessive biomass formation changes the bed's pore structure and leads to the progressive obstruction of the bed that is accompanied with a build-up in pressure drop and flow channeling. While the existing biofilter models appear to capture adequately the transport and reaction phenomena at the biofilm scale, they poorly address, or provide little insight about the connection between the aerodynamics, biological filtration (or clogging) and biokinetics at the bioreactor length scale. An attempt has been made with this contribution to fill in this gap by developing a unidirectional dynamic flow model based on the volume-average mass, momentum and species balance equations coupled with conventional diffusion/reaction equations describing apparent kinetics in the biofilm. Toluene biodegradation by biodegrading microbes immobilized on pelletized diatomaceous earth biological support media was chosen as a case study to illustrate the consequences of formation of excessive amounts of biomass. The simulation results were rationalized in terms of biofilm thickness, bed local porosity, gas-phase substrate residual concentration, and pressure drop rise in biological fixed-bed filters.     

Hydrodynamics of power-law fluids in trickle-flow reactors: Mechanistic model, experimental verification and simulations

A fully predictive one-dimensional mechanistic model was developed for describing the hydrodynamics of power-law fluids in trickle-bed reactors. The model is a generalization of the slit approach to the case of non-Newtonian fluids obeying Ostwald-deWaele rheological behavior. Without recourse to adjustable parameters, the proposed model enabled prediction of the experimental values of (i) total two-phase total pressure drop and total liquid holdup in the trickle flow regime, (ii) frictional pressure drop in single-phase flows through packed beds, and (iii) total liquid holdup in gravity driven liquid downflow and stagnant gas through packed beds. Parametric simulations guided by knowledge of the behavior of highly viscous Newtonian liquids in trickle beds highlighted the capability of the model in the simulation and design of trickle flow operation using power-law fluids.     

Modeling pressure drop coefficient for cyclone separators: A support vector machine approach

As one of performance critics for cyclone separators, pressure drop is an important parameter to evaluate and design cyclone separators. In order to accurately predict the complexly nonlinear relationships between pressure drop coefficient (PDC) and geometrical dimensions, a support vector machine (SVM) model is developed and employed to model PDC for cyclone separators. Based on the normalization method and the random sampling technique for the experimental sample dataset, a dynamically optimized search technique with cross validation is introduced to determine optimal algorithm parameters in the model. Then the optimized SVM model is trained and tested by the simulation results. According to the predicted accuracy of PDC for cyclone separators, the SVM model performance is compared and evaluated. It is found that the SVM model provides the higher generalization performance than the conventional models including the theoretical and statistical models as well as the artificial neural network model, with the mean squared error of 3.64×10⁻⁴ and the correlation coefficient of 0.9974. The result also demonstrates that SVM can offer an alternative and powerful approach to model cyclone pressure drop.     

填料因子的确定方法和物理意义

本文提出了确定填料因子的简便方法，探讨了填料因子的物理意义。认为引入湿填料因子和液泛填料因子是不恰当的，推荐按Ｋｉｓｔｅｒ－Ｇｉｌｌ经验关联式计算国产填料的泛点压降。     

旋风预热器阻力损失的构成及其影响因素

从理论上对旋风预热器阻力损失的构成做了简单介绍,并在研究了国内外20多种不同形式预热器之 后,对影响旋风筒实际压降的结构参数和非结构参数进行了详细的分析研究,归纳出最佳的匹配参数。     

The effect of reliable prediction of final pressure during pressure equalization steps on the performance of PSA cycles

The present work aims at modeling the performance of isothermal PSA cycles for the production of H₂ from refinery fuel gas by introducing a more reliable calculation of the final pressure during the pressure equalization steps. The latter calculation is performed based on the law of conservation of mass in a system comprehending the depressurizing and pressurizing beds in contact. Single adsorbent (zeolite 5A) dual and six-bed PSA processes have been considered. The PSA cycle performance is compared with a conventional model considering an arithmetic mean for the final pressure during the pressure equalization steps (old model). It is shown that the new model predicts lower values for product purity and recovery when compared with the old model. The error in the estimation of the product recovery is larger than the corresponding value for product purity and may exceed 9%. It is shown that the error in the calculation of purity and recovery strongly depends on the number of beds. The error in the calculation of product recovery increases approximately two-fold increasing the number of beds from 2 to 6. Therefore, the present study shows that implementation of a more robust method for the evaluation of final pressure during the equalization steps is imperative for the development of new models of industrial PSA processes, especially for the number of beds exceeding 2.     

Application of an adsorption non-flow exergy function to an exergy analysis of a pressure swing adsorption cycle

Pressure swing adsorption (PSA) is a popular gas separation technology for the process industries and is commonly used for air separation, hydrogen purification, and isomer separation. In this study, we apply a second law analysis to this technology to identify sources of irreversibility in the process and, in particular, identify which steps in the PSA cycle are responsible for the major losses. Unlike previous exergy analyses, we derive and use expressions for the exergy of the adsorbed phase using adsorption thermodynamics. In this way, exergy loss (or entropy generation) within the adsorption cycle in each step is clearly identified. We illustrate the use of these exergy functions with the application of binary linear isotherm (BLI) theory to a four-step Skarstrom cycle. Major losses in the process are shown to be the exergy loss across the valve in the blowdown step, and feed compressor aftercooler losses. Feed repressurisation is shown to be more efficient than product repressurisation for the separation factor examined in this study since part of the feed gas is introduced at a low pressure. During the cycle, bed exergy loss during the feed step is significant, while there is no exergy loss in the adsorbent bed during the blowdown or purge steps. The exergy functions derived in this study can readily be applied to more complex PSA cycles and provide a basis for cycle design.     

催化重整装置预加氢压降分析及对策

预加氢压降高,是几乎所有催化重整装置都要面对的生产瓶颈问题.作者着重统计了中国石油大庆炼化公司炼油一厂35万t/a催化重整装置2006年至2008年预加氢部分压降变化情况,分析了该重整装置预加氢压降分布情况和压降变化情况,提出了降低重整装置预加氢压降的具体措施,以及目前该重整装置预加氢压降状况.     

勃劳特换热器的性能

勃劳特换热器的性能周绪美，陈建铭，张鹏远，冯元鼎，丁华（北京化工大学化学工程系）关键词勃劳特换热器；压降１引言在生产过程中，气体与气体之间进行热量交换的换热器，在性能评比时，应该用两项指标来衡量。其一是单位产品所需传热面积要小，其二是单位压降的传热膜...     

FLUIDIZED BED PRESSURE DROP IN PROMOTED GAS-SOLID BEDS WITH COAXIAL ROD, DISK, AND BLADE TYPE PROMOTERS

Bed pressure drop equations have been formulated for gas-solid fluidized beds with different types of promoters using Ergun's equation (Ergun, 1952) and experimental data. Four rod promoters, seven disk promoters, along with one blade promoter were used in beds supported on five different distributors with open areas of 12.9%, 8.96%, 5.74%, 3.23%, and 1.43% of the column section. The predicted values of bed pressure drop using a modified (i.e., modified numerical constant) Burke-Plummer (Burke and Plummer, 1928) equation were compared with the corresponding experimental as well as the respective values obtained with the help of Kumar et al. (submitted) and traditional gas-solid fluidized bed equations.     

THE EFFECT OF SURFACE ROUGHNESS ON PRESSURE DROP IN A PACKED BED

Particle surface roughness is shown to have a significant effect on the pressure drop in a packed bed of adsorbent particles. The packed bed friction factor is determined using three spherical adsorbents of differing degree of surface roughness in the Reynolds number range 1-62. The results were successfully correlated using a correlation of the Ergun type. It is shown that surface roughness significantly increases the friction factor.