OPTIMIZATION OF PRESSURE SWING ADSORPTION EQUIPMENT PART I EFFECT OF EQUILIBRIUM CONSTANTS, AXIAL DIFFUSION AND INITIAL TO FEED CONCENTRATION RATIO ON COLUMN PRESSURIZATION AND PURGING

This paper consisting of two parts proposes a suitable method for the numerical optimization of pressure swing adsorption devices and comparison of multiple beds equipments with different piping and valves systems required to interconnect the adsorption cycle. In Part I a flexible isothermal and isobaric local equilibrium mathematico-physical model respecting axial dispersion and volumetric changes caused by adsorption has been formulated. The convergency of both the implicit form with central differences and explicit form with upwind differences is discussed. The effect of adsorption equilibrium on the oxygen concentration profile developed in the column at pressurization and the flow at constant pressure is simulated as well as the effect of axial dispersion. The creation of simple and shock concentration waves under various feeds to initial column oxygen concentration ratios is demonstrated. The proposed model is used also in Part II to compare the performance and gas purity of three types of two beds oxygen generators. On the bases of our local equilibrium model the condition for PSA equipment scale-up was proposed.     

化工装置设计压降的优化

传统的单个设备或管道的经济设计导出的“经济流速”有一定局限性。本文通过对化工装置系统压降性能的技术经济分析,得出合理的压降设计策略。     

间歇精馏塔启动过程的模型化

引　言在以往的研究中 ,间歇精馏塔的模型大部分建立在平衡模型的基础上[1] ,系统初值的选取基于伪热初始状态 ,即每层塔板上有足够的积液量 ,塔板温度在泡点温度以上的汽液平衡状态 .多数间歇精馏过程的仿真模拟软件中使用伪热状态作为初始状态[2 ] ,例如 ,ＨＹＳＹＳ Ｒ○ (Ｈｙｐｒｏｔｅｃｈ )、ＢＡＴＣＨＦＲＡＣＴＭ (Ａｓｐｅｎｔｅｃｈ )和ＣＣ -ＢＡＴＣＨ Ｒ○(ＣＨＥＭＣＡＤ) .它们都是通过稳态和平衡计算为微分代数方程组提供了满足一致性要求的初始值 .间歇精馏过程的一个特点就是精馏塔频繁地从冷状态启动 ,初始状态会因再…     

城市垃圾在回转窑内传输过程的模型和优化

基于物料在回转窑内传输过程是由其在表面层内滚落运动和固定层内回转运动组成的这一特征 ,从散体运动的机理出发继承和发展了回转窑单颗粒轨道模型 ,并首次采用统计平均分析和受力矢量分析研究了窑内颗粒的运动轨迹 ,从而得出了平均停留时间 (MRT)和体积流率 (MVF)的简化模型 ,结合试验采取修正系数ε_t 和ε_f 完善了模型对非均质物料 (如城市垃圾 )、内构件等工况的适用性 ,同时对本文模型和几种已有的计算模型进行了比较研究 ,最后提出了回转窑热解反应器的设计和运行的优化模型 .     

尿素流程高压洗涤器的模拟计算及分析

基于严格的热力学机理模型 ,对尿素工艺流程中高压洗涤器中下两段分别建立了平衡级模型 ,通过迭代求解两个模块 ,使连接两模块的中间流股收敛 ,完成了对整个洗涤器的模拟计算 ,计算结果同设计值吻合较好。针对该体系的强非理想性及数学模型的强非线性 ,提出可行的求解策略 ,算法稳定且收敛性较好。该研究为改造、优化工艺操作及单元设备结构提供了理论依据     

STABILITY OF THE LENSLIKE LIQUID THICKENING (THE DROP) ON A SOLID SUBSTRATE

The quasi equilibrium of a liquid lens or a liquid drop on a solid substrate is considered on the basis of the thermodynamics of microscopic thin liquid films. Both contact angles, corresponding to the membrane model and to the finite thickness layer convention of the film, have been derived as a function of the disjoining pressure isotherm. The analytical expressions for the line tension terms have been obtained, and the criterion for the stability of a liquid drop on a solid substrate has been proposed.     

STABILITY OF THE LENSLIKE LIQUID THICKENING (THE DROP) ON A SOLID SUBSTRATE

The quasi equilibrium of a liquid lens or a liquid drop on a solid substrate is considered on the basis of the thermodynamics of microscopic thin liquid films. Both contact angles, corresponding to the membrane model and to the finite thickness layer convention of the film, have been derived as a function of the disjoining pressure isotherm. The analytical expressions for the line tension terms have been obtained, and the criterion for the stability of a liquid drop on a solid substrate has been proposed.     

变压吸附数学模型30年进展

The pressure swing adsorption (PSA) models discussed here are divided into three categories:partial differential equation model,electrical analogue model and neural network model.The partial differential equation model,including equilibrium and kinetic models,has provided an elementary viewpoint for PSA processes.Using the simplest equilibrium modes,some influential factors, such as pressurization with product,incomplete purge, beds with dead volume and heat effects,are discussed respectively.With several approximate assumptions i.e., concentration profile in adsorbent,“frozen” column,symmetry and heat effects of bed wall,the more complex kinetic models can be simplified to a certain degree at the expense of a limited application.It has also been found that the electrical analogue model has great fxexibility to handle more realistic PSA processes without any additional hypothesis.     

外旋流管式微滤膜器压力场分布规律的实验研究

外旋流膜器是一种新型微滤装置,采用高精度动态压力测量仪,以清水和5种浓度的SiO2悬浮液为介质流体,选用PA膜管,首次对其中的压力场进行了测试研究,得到了环隙剖面压力沿径、轴向的分布规律,以及操作压力和颗粒浓度对流场压力的影响规律,分析实验结果后提出膜器最大有效长度(Lmax)的概念,并得出实验条件下的最佳操作压力范围。研究结果可用于外旋流膜器结构设计和选择操作参数。     

A COMPARISON OF GAS SEPARATION PERFORMANCE BY DIFFERENT PRESSURE SWING ADSORPTION CYCLES

By simulations using an equilibrium model, a quantative comparison is made for different pressure swing adsorption (PSA) processes for gas separation. The comparison is based on the performance curve, which is defined as the relationship between product purity and product recovery at a fixed feed throughput.

For bed repressurization in the PSA cycle, the use of the light product yields superior separations compared to that using the feed mixture. For the pressure reduction step, it is found that the separation results are better when the heavy-product purge step is used, as compared to that using cocurrent depressurization. For an ultrahigh-purity light product, however, the PSA process using cocurrent depressurization is superior.

A new PSA process is suggested in which the heavy-product purge step is accomplished by using (or pressure-equalizing with) the effluent from another bed which undergoes the countercurrent blowdown step.     

SIMULATION AND OPTIMIZATION OF THE ELECTRO-REDUCTION PULSED COLUMN FOR THE SEPARATION OF URANIUM AND PLUTONIUM

ABSTRACT

A computational model for separation of uranium and plutonium in an electro-reduction pulsed column was developed based on the diffusion model. The model contained steady state simulation, dynamic simulation, and optimum calculation. A numerical calculation method for this model has been proposed. With this model, a calculation for an electro-reduction experiment of uranyl nitrate in a pulsed column was carried out. The calculated results were consistent with the experimental results in the literature. A comparison of the dynamic and the steady state simulations at equilibrium and an optimum calculation were also conducted. This model provides a guide for further experimental study of this process.     

The effect of number of pressure equalization steps on the performance of pressure swing adsorption process

Cycle sequence has an important effect on the performance of pressure swing adsorption (PSA) processes. Pressure equalization steps influence significantly the purity and recovery of product, and therefore, may be properly designed to improve the performance of PSA processes. Open literature lacks of a systematic study on the effect of cycle sequence design on the performance of a specific PSA process as a controlling parameter. In this work, the results of recent studies on different cycle schedule design strategies have been used as a basis for comparing various cycle schedules (proposed by the authors of this work) on the performance of a six-bed PSA process for hydrogen purification. Three different cycle sequences have been designed, the pressure equalization and idle steps consisting the main controlling parameters. Simulation results showed that designs with more pressure equalization steps result in higher product recovery and those with less pressure equalization steps result in higher product purity. The proper performance of a PSA process is a tradeoff between product recovery and product purity. In this view, a target function has been developed that enables us to lump the latter performance parameters into one function for comparing the performance of the different cycles employed.     

吸收装置的优化设计

本文探讨了化工过程中吸收装置设计的优化途径,提出对板式或填料吸收装置施行优化设计的工艺方法。为使吸收装置的操作处于高效工况,实行强化之目的,对吸收装置有关的参数优化组合进行了计算分析,可供工程实践借鉴。     

Optimization design for removal of radioactive Kr from Xe using pressure swing adsorption

The goal of this paper is to remove radioactive Kr from Xe based on the development of a viable PSA (pressure swing adsorption) process, because it normally requires a few years for ⁸⁵Kr to achieve a significant decay level of this isotope. A general purpose model is built to remove ⁸⁵Kr in the cyclic PSA process with partial differential equations. Because there are no steady state and constant operating variables in the operation of the PSA process, the design of PSA at each step is critical for satisfactory performance. Thus, an optimization technique based on a genetic algorithm is used. The optimization leads to significant improvement for PSA. Moreover, for the physical model based design, changes in the operation of the process mean the original design condition may no longer be a true reflection of the desired quality. An iterative learning design is also proposed. This work aims to find out the optimal design condition for PSA.     

SIMULATION AND OPTIMIZATION OF CROSS FLOW GRAIN DRYERS

In this paper simulation and optimization study on Beidahuang 5HT-15 cross flow grain dryer is presented. The p. d. e. model is employed to establish the simulation program, and the backward difference method and the predictor-corrector integration are used in the thin layer drying process estimation. The optimal analysis is conducted in a 9-dimensional domain and the specific energy consumption is taken as the main target as a weighted sum of heat and mechanical energy according to the factor of cost while the less-important features of performance are put into the target function as penalty factors. The complex polygon method is used in the optimization program. By running the optimization program, a group of optimal policies about the operation of 5HT- 15 dryer have been proposed. Possible improvement and renovation of the cross flow dryers, both in structure and in performance, have also been approached in the simulation and optimization study.     

SIMULATION AND OPTIMIZATION OF CROSS FLOW GRAIN DRYERS

Abstract

In this paper simulation and optimization study on Beidahuang 5HT-15 cross flow grain dryer is presented. The p. d. e. model is employed to establish the simulation program, and the backward difference method and the predictor-corrector integration are used in the thin layer drying process estimation. The optimal analysis is conducted in a 9-dimensional domain and the specific energy consumption is taken as the main target as a weighted sum of heat and mechanical energy according to the factor of cost while the less-important features of performance are put into the target function as penalty factors. The complex polygon method is used in the optimization program. By running the optimization program, a group of optimal policies about the operation of 5HT- 15 dryer have been proposed. Possible improvement and renovation of the cross flow dryers, both in structure and in performance, have also been approached in the simulation and optimization study.     

Simulation and experiment of six-bed PSA process for air separation with rotating distribution valve

In this work, a six-bed pressure swing adsorption (PSA) process was investigated to produce medical oxygen from air, which uses the combination of six-way rotating distribution valve and PSA and has the main advantage of effectively saving space compared to the traditional two-bed or four-bed PSA process and can obtain greater productivity. The mathematical model of adsorption beds was developed based on the separation mechanism and the interaction among different equipment. Moreover, a pilot-scale device has been constructed to verify the accuracy of mathematical model by experiment. The oxygen product conformed to the medical standard (>93% (vol)) with a recovery of over 57%. Some related parameters were also discussed in detail, such as step time, ratio of length to the diameter, flow rate of product.     

考虑动力学的反应路径多目标优化方法

提出了一种考虑动力学影响和环境约束的反应路径综合方法. 引入平衡温距的概念来估计反应的动力学属性.可从多种备选物质之中找到生产某种指定产品的较好的反应路径和相应的原料.根据原子平衡方程综合反应路径,建立模糊规则来评价反应的平衡温距,并求解带有模糊参数的多目标机会约束规划模型,得到一系列经济、环境上均优化可行的反应路径.用合成氨联产尿素的实例对该方法进行了说明.     

PSA装置的设备和管道布置探讨

随着变压吸附法(PSA法)的应用逐渐大型化,如何做好设备和管道布置值得探讨。本文阐述了PSA的工艺,介绍了PSA的设备和管道布置方案,并对厂房和设备安全方面的影响进行了分析。     

OPTIMIZATION AND NEURAL MODELLING OF PULSE COMBUSTORS FOR DRYING APPLICATIONS

Results of investigations of a valved pulse combustor to choose optimal geometry, which covered measurements of the flow rates of air and fuel, pressure oscillations, including pressure amplitude and frequency and flue gas composition are presented in the paper. Experimental studies compsiring the operation of the pulse combustor coupled with a drying chamber and working separately are described. It was found that coupling of the pulse combustor with a drying chamber had no significant effect on the pulse combustion process. Smoother runs of pressure oscillations in the combustion chamber, lower noise level and slightly higher NO_x emission were observed. The velocity flow field inside the drying chamber was measured by LDA technique. Results confirmed a complex character of pulsating flow in the chamber. A large experimental data set obtained from measurements enabled developing a neural model of pulse combustion process. Artificial neural networks were trained to predict amplitudes and frequencies of pressure oscillations, temperatures in the combustion chamber and emission of toxic substances. An excellent mapping performance of the developed neural models was obtained. Due to complex character of the pulse combustion process, the application of artificial neural networks seems to be the best way to predict inlet parameters of a drying agent produced by the pulse combustor