Modeling and simulation of wet-end white water system in the paper mill

A dynamic model representing the wet-end of a paper mill is developed to characterize its dynamic behavior. The model is based on the mass balance relationships written for the simplified wet-end white water network. The dynamic response of the wet-end is influenced both by the white water volume and by the level of wire retention. Effects of key manipulated variables such as the thick stock flow rate, the ash flow rate and the retention aid rate on the major controlled variables are analyzed by numerical simulations. It can be said that the consistency of the model with plant data seems to be reasonably good and can be used as a tool for plant analysis and control.     

The process dynamics of filler retention in paper using a CPAM/bentonite retention aid system

In an effort to develop robust control strategies for the wet‐end of papermaking, an experimental program was carried out to model the dynamic behaviour of the filler retention in paper using a Fourdrinier pilot paper machine and a cationic poly(acrylamide)/bentonite retention aid system. A dynamic simulation model of the pilot paper machine was developed from first‐principles. To describe the wet‐end chemistry effect, the first‐pass retention was included in the model as a new independent variable. The important factors affecting the dynamics of the wet‐end are first‐pass retention and the parameters related to the white water circulation.     

海藻酸钠TEMPO改性及其在造纸中的应用初探

钙离子对实现造纸白水封闭循环有关键性的制约作用。通过对天然海藻酸钠进行改性来制备高羧基含量的化学助剂用于造纸湿部,可以起到控制钙离子影响的效果。通过测定2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)改性海藻酸钠羧基含量和螯合值,分析研究了NaClO用量、pH值和温度对反应过程的影响。选取氧化后羧基含量为2.14%、3.61%和未氧化(1.96%)的三组海藻酸钠添加到造纸湿部中进行应用实验,结果表明在一定的添加量下海藻酸钠能提高纸料的留着、滤水性能,并同时提高纸张强度。海藻酸钠加入量0.02%时最佳,并且羧基含量为3.61%的改性海藻酸钠作用效果最好。     

The preparation and properties of acrylic and methacrylic acid grafted cellulose prepared by ceric ion initiation. II. Water retention properties

Bleached sulfite softwood pulp and the corresponding paper have been grafted with acrylic and methacrylic acids and a number of other monomers. A practical, all aqueous, ceric ion method was used as described in Part I of this series. The water and saline retention values of the grafted pulps were determined. Super water sorbency, up to 48 g/g, were obtained after suitable post treatments. A number of variables were studied including the effects of pH, counterion, crosslinking, drying, and beating. It was gratifying that drying did not affect the effeciency of water or saline water retention. Useful linear functional relationships were found between the saline water retention values and the logarithm of the percent sodium chloride in the water. The two “model” parameters of the plots also correlated well with the water retention values and with the degree of grafting expressed as the ion exchange equivalents of the pulps. The osmotic pressure approach to the water sorption as developed by Grignon and Scallan⁵ coupled with the restraining forces of the grafted polymer itself is used to interpret the process.     

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

ABSTRACT

In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10–20% of solids was dried at different inlet air temperatures (120–160°C), air flow rate of 0.19 kg dry air s^?1 and different feed rates (1.4 ? 4.2 × 10^?4 kg dry solids s^?1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.     

Prediction and quality control of the melt index during production of high-density polyethylene

In polyolefin processes the melt index (MI) is the most important control variable indicating product quality. Because of the difficulty in the on-line measurement of MI, a lot of MI estimation and correlation methods have been proposed. In this work a new dynamic MI estimation scheme is developed based on system identification techniques. The empirical MI estimation equation proposed in the present study is derived from the 1 ^st -order dynamic models. Effectiveness of the present estimation scheme was illustrated by numerical simulations based on plant operation data including grade change operations in high density polyethylene (HDPE) processes. From the comparisons with other estimation methods it was found that the proposed estimation scheme showed better performance in MI predictions. The virtual sensor model developed based on the estimation scheme was combined with the virtual on-line analyzer (VOA) to give a quality control system to be implemented in the actual HDPE plant. From the application of the present control system, significant reduction of transition time and the amount of off-spec during grade changes was achieved     

Dynamic modeling and simulation of shell gasifier in IGCC

A dynamic model of the Shell gasifier in an integrated coal gasification combined cycle (IGCC) is established based on physical principles, focusing on the time-dependent accumulation and flow on the walls. Numerical simulations are carried out to explore the system dynamic performance with respect to step changes in the inlet oxygen-to-coal ratio and steam-to-coal. The dynamic responses of key outlet variables, including the gas temperature, exiting slag mass flow rate, thicknesses of the solid and fluid slag layer, volume percentages of H₂, CO₂ and CO in syngas etc., are obtained. Three different coals are analyzed in this paper, and similar trends in their dynamic behaviors are found by using the gasifier model. The model and simulation method may be useful for providing insights to the operation and control of the IGCC process with respect to complex varying working conditions.     

Cure kinetics of a flexible aromatic dicyanate with schiff base structure

Polycyclotrimerization of a flexible aromatic dicyanate with a Schiff base structure was studied by means of differential scanning calorimetry (DSC). The study on dynamic DSC evaluated an apparent activation energy (E_a) of 75.8 kJ/mol and autocatalytic first-order kinetics with rate expression Af(α) = 1.96 X 10⁵ (1 + 4.39 α) (1 - α) min^?1. The kinetic feature can be explained by a proposed mechanism consisting of hydroxyl-catalyzed and autocatalytic paths. The lower value of E_a compared with other aromatic dicyanates is due to the electron-withdrawing linkage of the inherent imine (—CH?N) structure. The kinetic feature is affected by the content of the residual impurities (e.g., phenols or absorbed water) in the corresponding sample. © 1995 John Wiley & Sons, Inc.     

An analytical model for material line kinematics in steady and unsteady buoyancy driven flows in 2-d channels

In this note, we use both developing and fully developed buoyant flow in a 2-d channel as a simple flow model useful for approximating buoyancy driven interpenetrating mixing phenomenon, such as the Rayleigh-Taylor instability. Our approach towards understanding and quantifying mixing within this flow follows the development by Ottino (The kinematics of mixing: stretching, chaos and transport, Cambridge University Press, Cambridge, 1989) that mixing is the kinematically efficient stretching and folding of material lines. Like Ottino, we use simple flows as a prototype to understand more complex problems. Here we derive the stretch length i.e. the deformation of a unit filament subjected to both the fully developed and developing buoyant channel flow. We use the simpler fully developed flow to compute the specific rate of stretching for the fully developed flow. An early time contraction-expansion effect is noted for stretching. Asymptotically, the stretching rate decays by the expected t⁻¹ behavior. This note indicates that early time buoyancy induced inter-penetrative mixing is a typical 2-d, shear driven phenomenon, exhibiting neither strong re-orientation (with attendant enhance mixing) nor negligible filament deformation (indicating minimal disruption of material surfaces).     

Dynamic behaviour and simulation of a liquid-liquid extraction column

Dynamic behaviour of a stirred liquid-liquid extraction column was studied experimentally. Various input variables of the column were varied stepwise and the resulting variations in the system and output variables were measured. In addition to experimental work, a computer model was developed on the basis of the dispersion model to simulate the dynamic behaviour of the extractor. This model forms a component program of the dynamic process simulator DIVA, developed at the TU Stuttgart. The experiments showed that the hydrodynamic parameters exhibit no significant dynamic behaviour of their own. Therefore, changes occurring in these parameters closely follow variations in input and system variables. As a result, steady-state relationships for the calculation of flow parameters could be used in the simulation program. The simulator satisfactorily reproduced the experimental results for a number of disturbances. However, this was not always the case. As shown in the following, the model did not take into account the column level controller which, under certain conditions, exerts a very strong influence on the column's dynamic behaviour. As a result, larger differences occurred between experimental and simulated data. This influence on the extractor's dynamic behaviour can, however, be eliminated by a simple modification of the level controller arrangement.     

Experimental Investigation on the Holdup Distribution of Oil‐Water Two‐Phase Flow in Horizontal Parallel Tubes

An experimental investigation was conducted to study the holdup distribution of oil and water two‐phase flow in two parallel tubes with unequal tube diameter. Tests were performed using white oil (of viscosity 52 mPa s and density 860 kg/m³) and tap water as liquid phases at room temperature and atmospheric outlet pressure. Measurements were taken of water flow rates from 0.5 to 12.5 m³/h and input oil volume fractions from 3 to 94 %. Results showed that there were different flow pattern maps between the run and bypass tubes when oil‐water two‐phase flow is found in the parallel tubes. At low input fluid flow rates, a large deviation could be found on the average oil holdup between the bypass and the run tubes. However, with increased input oil fraction at constant water flow rate, the holdup at the bypass tube became close to that at the run tube. Furthermore, experimental data showed that there was no significant variation in flow pattern and holdup between the run and main tubes. In order to calculate the holdup in the form of segregated flow, the drift flux model has been used here.     

Application of response surface methodology to optimize the operation process for regeneration of acid and base using bipolar membrane electrodialysis

BACKGROUND: Bipolar membrane electrodialysis (BMED) has been widely used for desalination, concentration, separation, and purification in many fields. The purpose of this study is to optimize the operation conditions using response surface methodology (RSM) for the regeneration of sulfuric acid and ammonia from ammonium sulfate solution by BMED coupled with ammonia in situ stripping. RESULTS: A three‐factor central composite design of RSM was used to analyze the effect of operation conditions (current density, flow rate, initial acid concentration) on average current efficiency (ACE) and establish the optimal operation conditions. The ACE was 76.7 ± 2.2% under optimal operation conditions (current density 23.8 mA cm^?2, flow rate 27.3 L h^?1, initial acid concentration 0.09 mol L^?1). CONCLUSION: A suitable regression model for predicting ACE within the ranges of variables used was developed based on experimental results. The operation conditions were optimized by RSM and the ACE obtained under the optimal operation conditions was in good agreement with the value predicted by the regression model (78%), which proved the validity of the model. Copyright © 2007 Society of Chemical Industry     

A trickling fibrous-bed bioreactor for biofiltration of benzene in air

A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C_gi) was 0·37 g m⁻³, the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1·8 m³ m⁻² h⁻¹. In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was ∽11·5 g m⁻³ h⁻¹ when the inlet benzene concentration was 1·7 g m⁻³ and the superficial air flow rate was 3·62 m³ m⁻² h⁻¹. A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K_l in this model was found to be linearly related to the inlet benzene concentration (K_l=4·64−1·38 C_gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to ∽30 g m⁻³ h⁻¹. Using this model, the maximum elimination capacity for the biofilter was estimated to be 12·3 g m⁻³ h⁻¹, and the critical loading capacity was found to be 14 g m⁻³ h⁻¹. The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m⁻¹ at a high superficial air flow rate of 7·21 m³ m⁻² h⁻¹, indicating a good potential for further scale up for industrial applications. © 1998 Society of Chemical Industry     

Flow injection analysis of iron in rain water with thiocyanate and surfactant

This paper explains a new procedure for flow injection analysis (FIA) determination of iron in rain water based on the colour reaction of Fe³⁺ with thiocyanate ions in the presence of the cationic surfactant cetylpyridinium chloride (CPC). The value of apparent molar absorptivity of the complex in terms of iron is (2.00) x 10⁴ l mole^-1 cm^-1 at an absorption maximum of 490 nm. The detection limit of the method is 8 ppb Fe. The sample throughput is 90 samples/h at a flow rate of 4.0 ml/min. The reaction mechanism, optimization of FIA variables, and effect of various types of surfactant are described. None of the tested anions and cations interfered with the determination of iron. The method was used for the quantification and flux determination of iron in rain water.     

Experimental and analytical procedures for flow dynamics of sheet molding compound (SMC) in compression molding

A package of procedures have been developed to collect and analyze the response of dynamic variables such as pressure, temperature, and mold separation during the compression molding of Sheet Molding Compound (SMC). From the dynamic responses, the molding process was found to consist of two regions: the flow and the subsequent curing reaction region. With an R-25 formulation and a mold closing rate of 30 mm/s, these two regions are well separated and the average flow time is not significantly affected by the maturation time for the material up to 30 days. Several mechanical parameters were estimated based on relatively simple flow models. The relationship between the press force, mold separation, and mold closing rate is found to be sensitive to the restrictions of the flow.     

Structure and permeability of porous films of poly(hydroxy ethyl methacrylate)

Porous films of poly(hydroxy ethyl methacrylate) have been made by photo-polymerisation of solutions of the monomer. The permeability of homogeneous films depends on the cross-link density and the concentration and composition of the polymerisation solvent. A membrane of minimum water permeability, in which the transport mechanism is principally diffusion, results from a cross-link concentration of ～9.4 mol-% and a monomer concentration of ～75% in an aqueous ethylene glycol solvent (20% ethylene glycol). More porous (macroporous) films were prepared by first cooling the solution such that the solvent freezes and the monomer occupies the interstices between the solvent crystals. After polymerisation and removal of the solvent, a porous structure results. The rate of freezing, the profile of the thermal gradient, and the solvent and crosslinker concentrations control the permeability of this film. Slow cooling gives random pores (K ?6 × 10^?15 cm²), but rapid, directional cooling from one face gives oriented pores with K ?10^?12 cm². A 6-order change in K results from varying the monomer concentration from 40 to 85% in a 4:1 water: ethylene glycol solvent, and a 3-order change from increasing the ethylene glycol content of the solvent from 0 to 40% at a fixed monomer concentration.     

Three‐dimensional simulation of the time‐dependent fluid flow and fouling behavior in an industrial hollow fiber membrane module

A novel three‐dimensional CFD model has been developed on the basis of fluid flow in the shell and lumen sides, and permeation and fouling behavior in the porous membrane zone. The simulated 25‐min dead‐end outside‐in filtration process showed that the energy consumed by the inlet manifold decreases during the constant pressure filtration. The velocity and pressure distributions in the module change with time. Flux distribution both in the axial and radial directions becomes increasingly more uniform, so does the cake distribution. Flux distribution and cake distribution inter‐adjust each other in different modes. A correlation equation has been developed to describe the relationship between the volumetric flow rate and accumulated water production. The correlation equation with simple experiment enables the dynamic evolution of energy consumed by shell inlet manifold to be presented, which can be the criterion of how well the shell inlet manifold or module has been designed. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2655–2669, 2018     

Comparison of experimental pressure gradient and experimental relationships for the low density spherical capsule train with slurry flow relationships

In the experimental part of this study, pressure drops that occur in the flow of a low density spherical capsule train conveyed by water in a horizontal pipe were found to be 5-30% of the capsule transport concentrations. The developed experimental relations were compared with well-known relations used for slurry flow. Experimental variables (i.e. bulk velocity, diameter of particle or capsule, diameter of pipe, concentration of particle, density of particle, etc.) were applied to the pressure gradient expressions developed for the slurry flow (asymmetric suspension flow), so that the pressure gradients calculated for a concentration by 5% and 10% were compared with the experimental findings and with the developed mathematical model. It was observed that the pressure gradient expressions of the slurry flow did not simulate the experimental results of the capsule flow. However, a comparison of the empirical expression developed for the pressure drops of the spherical capsule train flow in region (2.5 × 10⁴ < Re < 1.5 × 10⁵) with the experimental findings revealed an average deviation of 3.37%.     

Modelling of solid formation by heterogeneous reactions through a multicomponent transport model of diluted ionic species: Simulation of barite fouling in a geothermal heat exchanger

A general model is proposed in order to describe the growth of a deposit by heterogeneous reactions. The hydrodynamics in the fluid is described by a multicomponent transport model for ionic species diluted in a solvent and heat transfer is taken into account in both liquid and solid domains. The boundary condition at the interface where the reaction takes place is described thoroughly. It involves the reaction kinetics and gives access to the velocity of the interface, ie, the mass rate of the solid deposit. The model is then applied to the case of barite crystallization in a heat exchanger. The liquid phase is therefore composed of two ionic species Ba²⁺ and SO₄²⁻ diluted in water. The solid phase is modelled as a homogeneous barite deposit. The fully dynamic CFD simulation of the model is made using Comsol Multiphysics, in a cylindrical pipe. The solid growth is analyzed over time and space in terms of the relevant variables of the model.     

Experimental and neural model analysis of styrene removal from polluted air in a biofilter

BACKGROUND: Biofilters are efficient systems for treating malodorous emissions. The mechanism involved during pollutant transfer and subsequent biotransformation within a biofilm is a complex process. The use of artificial neural networks to model the performance of biofilters using easily measurable state variables appears to be an effective alternative to conventional phenomenological modelling. RESULTS: An artificial neural network model was used to predict the extent of styrene removal in a perlite‐biofilter inoculated with a mixed microbial culture. After a 43 day biofilter acclimation period, styrene removal experiments were carried out by subjecting the bioreactor to different flow rates (0.15–0.9 m³ h^?1) and concentrations (0.5–17.2 g m^?3), that correspond to inlet loading rates up to 1390 g m^?3 h^?1. During the different phases of continuous biofilter operation, greater than 92% styrene removal was achievable for loading rates up to 250 g m^?3 h^?1. A back propagation neural network algorithm was applied to model and predict the removal efficiency (%) of this process using inlet concentration (g m^?3) and unit flow (h^?1) as input variables. The data points were divided into training (115 × 3) and testing set (42 × 3). The most reliable condition for the network was selected by a trial and error approach and by estimating the determination coefficient (R²) value (0.98) achieved during prediction of the testing set. CONCLUSION: The results showed that a simple neural network based model with a topology of 2–4–1 was able to efficiently predict the styrene removal performance in the biofilter. Through sensitivity analysis, the most influential input parameter affecting styrene removal was ascertained to be the flow rate. Copyright © 2009 Society of Chemical Industry