Modeling for industrial heat exchanger type steam reformer

In a heat exchanger type steam methane reformer, the temperature profiles and mole fractions along the axial distance from the top of the reformer can be predicted by using the channel model, considering radiation heat transfer. The cross-section of the reformer tube was divided into several channels as concentric circles and then heat transfer and mass transfer at the interfaces between adjacent channels were considered. Because the steam reformer is operated at high temperature, the radiation and convection were combined into one heat transfer coefficient to simplify the transfer analysis. This model predicts the industrial plant data very well; therefore, it may be used with confidence to design the industrial heat exchanger type reformer.     

Modelling of heat transfer and pyrolysis reactions in an industrial ethylene cracking furnace

The development of a relatively simple mechanistic model for an industrial ethylene cracking furnace is described, including the estimation of selected model parameters to improve model predictions. Energy balance equations are developed to account for radiative, conductive, and convective heat transfer in the radiant section, and for convection and conduction in the ultra‐selective heat exchanger (USX) and in the transfer line exchanger (TLE). Kinetic schemes by Ranjan et al. and Sundaram and Froment are used to model the cracking reactions. 1 , 2 The heat transfer model is combined with mass and momentum balances to model gas composition, pressure, and temperature changes as a function of position along the reactor tubes. Initial values and uncertainty ranges are assigned to 44 model parameters based on information in the literature and our industrial sponsor. A sensitivity‐based technique and a mean‐squared‐error (MSE) criterion are used to select the appropriate subset of 22 parameters for tuning. Parameters are estimated and model predictions are validated using industrial data. Model predictions provide a good match to data that were not used for estimation.     

Measurement of metabolic heat in a production-scale bioreactor by continuous and dynamic calorimetry

Measurement of metabolic heat has been attempted in an industrial-scale bioreactor using continuous and dynamic heat balance calorimetry. The contributions of individual heat sources influencing the temperature of the broth were evaluated and the magnitude of metabolic heat was calculated from general energy balance. Good correlations were obtained between oxygen uptake rate (OUR) and metabolic heat with heat yield under continuous and dynamic conditions with the values of Y Q/O =444 kJ/mole O 2 and Y Q/O =431 kJ/mole O 2 , respectively. There was also correlation between biomass production and heat generation. The value of heat yield, Y Q/X , was calculated to be 14546 kJ/kg; however, this was not constant and slightly decreased towards the end of fermentation. A similar value for heat yield was obtained under dynamic conditions and found to be 14667 kJ/kg. The consistency of experimental data was checked using carbon, electron, and heat balances. It was shown that reasonable accuracy could be achieved in an industrial environment. The difficult-to-measure variable biomass concentration was estimated using continuous metabolic heat flux, and good correlation was obtained between measured and estimated biomass concentrations. The results of this study suggest that heat balance around an industrial bioreactor can be simplified by accurately identifying individual heat sources as opposed to laboratory bioreactors where the contribution of each source can have significant impact. This reduces the number of measurements for accurate heat balance and makes use of heat balance feasible in a large scale.     

Study of Curing Kinetics of an Epoxy-Amine Adhesive System Using a Calorimetric Analysis Approach

Various dynamic curing experiments for an epoxy-amine adhesive system were conducted using a differential scanning calorimetry. The obtained data were corrected using a proposed baseline method, and fitted to a generalized autocatalytic model of chemical reaction to determine the model parameters. It was shown that with classical fourth-order Runge-Kutta numerical algorithm, the kinetic model as derived from the dynamic experiments could be used to reliably simulate an industrial curing process, which may include nonisothermal and quasi-isothermal curing steps. In addition, various quasi-isothermal curing experiments were performed; the heat flows of cure were measured, and numerically compared with relevant model calculations.     

MEASUREMENT OF METABOLIC HEAT IN A PRODUCTION-SCALE BIOREACTOR BY CONTINUOUS AND DYNAMIC CALORIMETRY

Measurement of metabolic heat has been attempted in an industrial-scale bioreactor using continuous and dynamic heat balance calorimetry. The contributions of individual heat sources influencing the temperature of the broth were evaluated and the magnitude of metabolic heat was calculated from general energy balance. Good correlations were obtained between oxygen uptake rate (OUR) and metabolic heat with heat yield under continuous and dynamic conditions with the values of Y Q/O =444 kJ/mole O 2 and Y Q/O =431 kJ/mole O 2 , respectively. There was also correlation between biomass production and heat generation. The value of heat yield, Y Q/X , was calculated to be 14546 kJ/kg; however, this was not constant and slightly decreased towards the end of fermentation. A similar value for heat yield was obtained under dynamic conditions and found to be 14667 kJ/kg. The consistency of experimental data was checked using carbon, electron, and heat balances. It was shown that reasonable accuracy could be achieved in an industrial environment. The difficult-to-measure variable biomass concentration was estimated using continuous metabolic heat flux, and good correlation was obtained between measured and estimated biomass concentrations. The results of this study suggest that heat balance around an industrial bioreactor can be simplified by accurately identifying individual heat sources as opposed to laboratory bioreactors where the contribution of each source can have significant impact. This reduces the number of measurements for accurate heat balance and makes use of heat balance feasible in a large scale.     

A model for solids transport in flighted rotary dryers based on physical considerations

The following paper outlines the development of empirically fitted and pseudo-physically derived compartment models of a flighted rotary dryer with counter current airflow processing solid material. Underloaded, overloaded and design-loaded dryers are considered. Four key parameters are estimated to fit the empirical model to industrial residence time distribution data and common empirical mean residence time/holdup correlations. Utilising the fundamental structure of the empirical model and physical and mechanical properties such as the dryer and flight geometry as well as solids material properties, the number of estimated parameters in the pseudo-physical model was reduced to 2. The experimental data required to characterise and validate the models is discussed. Optimisations to determine the model parameters were undertaken by comparison with an experimental residence time distribution curve for an industrial dryer processing sugar. Simulation of the model using gPROMS^® illustrates model performance. The potential to integrate the solids transport model and a full heat and mass transfer model is also discussed.     

热定型过程能耗建模及PSO参数优化

热定型过程是印染工业中的主要耗能单元之一。首先,基于定型机的物理结构及工艺原理,依据换热平衡和牛顿热交换公式,推导出能耗与定型过程关键因素间的相互关联模型,即能耗模型。其次,在Matlab/Simulink软件中,对上述模型进行构建。最后,将能耗模型转化为能耗最小的优化问题,运用粒子群优化算法对其进行求解。现场工业数据的仿真研究表明：能耗模型符合现场工艺,粒子群优化结果已得到现场工程师的初步认可。     

Data reconciliation strategy with time registration for the evaporation process in alumina production

In real industrial production, many mass and heat transfer processes are influenced by high temperature, high pressure, and even strong acid or alkali conditions. In addition, some important variables cannot be measured and chemical compositions are analyzed offline with a long time delay, which leads to inaccurate measurements of the process data. In this paper, a layered data reconciliation (LDR) method based on time registration is proposed to improve the measurement accuracy and estimate unmeasured variables. Considering that the material cannot be tagged and tracked in process manufacturing, a temporal and spatial matching strategy for the process data is designed based on a time‐correlation analysis matrix which is determined to describe the correlation of each time sequence in the data matrix. Then, a layered data reconciliation model with time registration is developed by reconciling the mass balance layer and the heat balance layer separately and stepwise, and the model is solved by the state transition algorithm. Meanwhile, regular terms and engineer's knowledge are introduced into the data reconciliation model to solve the problem of insufficient redundancy. The industrial verification results from the actual industrial evaporation process indicate that the accuracy of measured values is improved by using the proposed reconciliation strategy.     

对苯二甲酸结晶热力学研究

在291.65—369.15 K下用平衡法测定了对苯二甲酸在醋酸体积分数为1.000、0.895、0.791和0.688时的醋酸水溶液中的溶解度。根据固液平衡理论建立了对苯二甲酸的溶解度模型,用溶液化学理论导出了对苯二甲酸的活度系数与溶剂化平衡常数的关系式,并建立了估算对苯二甲酸溶剂化平衡常数的关系式。应用实验得到的溶解度数据估算了对苯二甲酸的溶解热、混和热、活度系数、溶剂化平衡常数和溶剂化过程中氢键的生成焓,为对苯二甲酸的工业生产提供了热力学数据。     

A mathematical model for the dehydrogenation of methylcyclohexane in a packed bed reactor

A model for the dehydrogenation of methylcyclohexane in a tubular reactor over an industrial catalyst Pt-Sn/Al₂O₃ has been established. This model takes into account the axial dispersion at the inlet of the catalytic bed reactor as well as the heat transfer at the wall of the reactor. The heat transfer at the wall is satisfactorily represented by using a heat transfer coefficient correlation for which the parameters are obtained by fitting to the experimental data. The model provides a good representation of the radial and axial temperature profiles in the packed bed and can be also used to calculate the conversion.     

CALCULATING DISTILLATION EFFICIENCIES OF MULTICOMPONENT i-BUTANE/ n-BUTANE COLUMN

This paper presents experimental data and estimated distillation efficiencies of an industrial scale distillation column separating i-butane and n-butane. The data gathered from plant instruments and laboratory analysis were reconciled and compared to distillation simulations. The simulations were performed with a number of real plates using the point and the Murphree plate efficiency calculation model. This matrix model of efficiency at first estimates the point efficiencies using the two-film and multicomponent mass transfer theory. The point efficiencies are then converted into Murphree plate efficiencies using a liquid mixing model. The whole method is implemented in a computer program to simulate an industrial distillation column with real plates. Finally the calculated product compositions are compared with reconciled measurements. The values of overall, section, point and Murphree plate efficiencies of multicomponent i-butane/n-butane system are also calculated. The results show that point efficiencies are not adequate for large industrial scale columns. The results also imply that the plate efficiency calculation method can be utilized and employed in the design and simulation of industrial scale columns.     

NEURAL NETWORK–BASED HEAT AND MASS TRANSFER COEFFICIENTS FOR THE HYBRID MODELING OF FLUIDIZED REACTORS

The complex flow patterns induced in fluidized bed catalytic reactors and the competing parameters affecting the mass and heat transfer characteristics make the design of such reactors a challenging task to accomplish. The models of such processes rely heavily on predictive empirical correlations for the mass and heat transfer coefficients. Unfortunately, published empirical-based correlations have the common shortcoming of low prediction efficiency compared with experimental data. In this work, an artificial neural network approach is used to capture the reactor characteristics in terms of heat and mass transfer based on published experimental data. The developed ANN-based heat and mass transfer coefficients relations were used in a conventional FCR model and simulated under industrial operating conditions. The hybrid model predictions of the melt-flow index and the emulsion temperature were compared to industrial measurements as well as published models. The predictive quality of the hybrid model was superior to other models. This modeling approach can be used as an alternative to conventional modeling methods.     

Mathematical modelling of an industrial furnace for high‐temperature heat treatment of wood

There are various high‐temperature treatment methods for wood. In the “Bois Perdure” process, the thermal treatment of wood is carried out in a furnace by contacting it with hot combustion gases over 200°C without the addition of any chemicals in order to improve its dimensional stability and durability. The treatment eliminates free and bound water in the wood and modifies its molecular structure. In this study, a mathematical model describing the industrial furnace has been developed. The overall model consists of a 3‐D unsteady‐state sub‐model which solves for the flow, heat, and mass transfer in the gas coupled with a 1‐D unsteady‐state sub‐model which calculates the heat and mass transfer in the wood. The 3‐D gas sub‐model was developed using the commercial CFD code CFX. The 1‐D wood sub‐model is based on the solution of simultaneous heat and mass transfer equations (Luikov equations) using the implicit finite difference formulation. The model predicts the temperature and moisture distributions in the wood as well as the flow, heat, and moisture profiles in the gas. The model results are compared with the data obtained from the industrial furnace, and a good agreement was found between them.     

Utilisation of waste heat from exhaust gases of drying process

Nowadays a lot of low-grade heat is wasted from the industry through the off- and flue-gasses with different compositions. These gases provide the sensitive heat with utilisation potential and latent heat with the components for condensation. In this paper, process integration methodology has been applied to the partly condensed streams. A hot composite curve that represents the gas mixture cooling according to equation of state for real gases was drawn to account the gas-liquid equilibrium. According to the pinch analysis methodology, the pinch point was specified and optimal minimal temperature difference was determined. The location of the point where gas and liquid phases can be split for better recuperation of heat energy within heat exchangers is estimated using the developed methodology. The industrial case study of tobacco drying process off-gasses is analysed for heat recovery. The mathematical model was developed by using MathCad software to minimise the total annualised cost using compact plate heat exchangers for waste heat utilisation. The obtained payback period for the required investments is less than six months. The presented method was validated by comparison with industrial test data.

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前置烧焦式催化裂化装置稳态模拟:再生器取热器负荷对过程的影响

应用本文作者课题组开发的前置烧焦式催化裂化装置过程模拟平台,对某工业装置进行现场条件下的稳态模拟,并完成全装置模型的校正及验证。在此基础上,模拟分析了再生器取热器负荷对该装置操作产生的影响。模拟结果显示,改变再生器取热器的负荷,能够有效调节两器热量平衡,在确保工艺范围不超限的前提下提高装置剂油比,原料油转化率提高,装置产品分布得到有效调节,但是使得密相床再生器密相区床层温度降低,从而影响再生器的再生效果,不利于提升管进口再生催化剂初始活性的提高。     

A DISTRIBUTED PARAMETER APPROACH TO THE DYNAMICS OF ROTARY DRYING PROCESSES

A nonequilibrium distributed parameter model for rotary drying and cooling processes described by a set of partial differitial equations with nonlinear algebraic constraints is developed in this work. These equations arise from the multi-phase heat and mass balances on a typical rotary dryer. A computational algorithm is devekped by employing a polynonial approximation ( orthogonal collocation) with a glotal splinc technique leading to a differential-algebraic equation ( DAE) system. The numerical solution is carried out by using a standard DAE solver.

The two- phase-flow heat transfer coelficient is computed by introducing a correction factor to the commonly accepted correlations. Since interaction between the falling particles are considered in the correction factor,the results are more reliable than those computed by assuming that heat transfer between a single falling particle and the drying air is unaffected by other particles. The heat transfer computations can be further justified via a study on the analogies between heat and mass transfer.

The general model devloped in this work is mathematically more ritorous yet more flexible that the lumped parameter models established by one of the authors (Douglas et al., (1993)). The three major assumptions of an equilibrium operation, perfect mixing and constant drying raic, are removed in the distributed parameter model.

The simulation results are compared with the operational data from an industrial sugar dryer and predictions from earlier models. The model and algorithm successfully predict the steady state behaviour of rotary dryers and collers. The generalized model can be applied to fertilizer drying processes in which the assumption of constant drying rate is no longer valid and the existing dynamic models are not applicable.     

Heat transfer coefficient in a high pressure tubular reactor for ethylene polymerization

Heat transfer in tubular reactors for the high pressure polymerization of ethylene is very complex, since these tubular reactors are usually divided into several zones that exhibit different flow patterns and critical fouling behavior. The correct estimation of the overall heat transfer coefficient along the reactor axial distance is a major issue when assessing the predictive capabilities of a mathematical model for the process. In general, previous models employed either constant heat transfer coefficients or the usual correlations for the Nusselt number. Neither of these two approaches is accurate enough to allow a correct prediction of the reactor behavior with respect to temperature profiles and product molecular properties. The present work performs a more comprehensive estimation of the heat transfer coefficient in these reactors. At a first stage the overall heat transfer coefficients were estimated by using approapriate energy balances and a good set of experimental data. Then, a predictive model was proposed for the overall heat transfer coefficient. All flow regimes, as well as fouling effects, were taken into account, and the parameter estimation was based on temperature profiles obtained from an industrial reactor. The temperature profiles, conversions, pressures and molecular properties calculated by means of the experimentally fitted heat transfer coefficients or with the predictive model showed good agreement with plant data.     

SIMULATION OF UREA PRILLING PROCESS: AN INDUSTRIAL CASE STUDY

A local industrial urea prilling tower with a rectangular cross-sectional area under the operating conditions of free convection was mathematically modeled. In this model the prilling process has been simulated by simultaneous solution of the continuity, hydrodynamic, and thermal equations. Temperature distributions of the particles and the cooling air along the height of the tower were calculated from the model. The air temperature profile predicted by the model was compared with the measured air temperature along the tower. The data predicted by the model were almost in agreement with the plant data, indicating the validity of the model. The result of this study suggests that an increase in heat transfer from the particles using installation of induced fans can reduce the temperature of produced prills and hence reduce caking tendency of the prilled urea.     

Heat and Mass Transfer Coefficients in Computer Simulation of Paper Drying

The development of a mathematical model and a computer program to facilitate the study of thc multi-cylinder paper drying process is presented. Experimentally determined values for different heat and mass transfer coefficients are used to ensure the physical validity of the model. A unique feature of the model is its inclusion of a mass transfer coefficient for the dryer fabric. Thus far. the mass transfer mechanisms in the web have not been included. Two heat transfer coefficients are used to tune the model to actual mill data. They areassigned values that are consistent with experimental data. The agreement between predicted and experimental data, obtained hom nine industrial paper dryers, is generally very good. The investigated basis weights range from 48 to 240 g/m2.

Calculations indicate that the condensate and contact heat transfer coefficients have a major influence on the drying process. The thermal conductivity of the paper and cylinder shell, respectively, are relatively important. whereas the influence of the fabric mass transfer coefficient and the cylinder-fabric-paper heat transfer coefficient are less pronounced. Some guidelines on how to obtain corect values are discussed.     

SL-Ⅱ型工业乙烯裂解炉内燃烧传热与裂解反应的耦合模拟

采用计算流体力学(CFD)方法对SL-Ⅱ型工业乙烯裂解炉辐射段炉膛内的燃烧传热及管内石脑油裂解反应过程进行耦合模拟,建模及耦合求解在CFX中完成.计算时采用标准k-ε双方程湍流模型、旋涡耗散/有限化学速率(EDM/FRC)燃烧模型和离散传播(DT)辐射模型,其中介质辐射特性采用多灰气加权模型;石脑油裂解反应采用Kuma...