Partial Seeding Policy for Controlling the Crystal Quality in Batch Cooling Crystallization

Partial seeding, in which the nuclei originating from seed crystals grow to yield the product crystals, was simulated and optimized for controlling the batch cooling crystallization process of L-arginine. The product quality was evaluated by the coefficient of variation (CV) of the crystal size distribution. First, the optimum seed amount for partial seeding was estimated by simulation. Then, the simulated values of the optimum seed amount and the resulting local minimum CV were correlated with the seed crystal size and the cooling rate. The correlation can be utilized for estimating the seed amount in the case that the seed crystals are added in a slurry. Finally, these simulated values were compared to the measured ones. Consequently, the optimum seed amount was suggested to be reasonably predicted.     

On the use of process analytical technologies and population balance equations for the estimation of crystallization kinetics. A case study

The batch cooling solution crystallization of ammonium oxalate was performed in water at various constant cooling rates. Measurements of the solute concentration were obtained using in situ attenuated total reflectance fourier transform infrared (ATR‐FTIR) spectroscopy, and final estimates of the crystal size distribution (CSD) were computed; thanks to in situ image acquisition and off‐line image analysis. The crystallization process was then simulated using population balance equations (PBEs). Estimates of the nucleation and the growth parameters were computed through model/experiments fitting. According to the cooling rate, the PBE model allowed distinguishing between two distinct crystallization regimes, separated by an “intermediate regime.” The respective contributions and shortcomings of solute concentration measurements and granulometric data to the identification of nucleation and growth kinetic parameters are analyzed and discussed. It is shown in particular that no real separate estimation of nucleation and growth parameters can be obtained in the absence of CSD data. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

溶液自发结晶过程动力学参数研究

The batch cooling crystallization initiated from spontaneous nucleation for aqueous solution of potas- sium nitrate was studied.The concentration and transmittance data were acquired on line throughout the operation. Based on solute mass transfer in both liquid and solid phases,a kinetic model was deduced by assuming that the late period of primary nucleation resembles the initial period of the secondary nucleation.Nucleation and crystal growth stages were identified.Kinetic parameters were estimated piecewise from online experimental data and compared with those in literature.The estimated kinetic parameters for stages without apparent primary nucleation agreed well with those in literature.Further,a simulated concentration curve was also drawn from the estimated kinetic parameters and it matched well with that in experiment.     

Refractive Index Drop Observed After Precision Molding of Optical Elements: A Quantitative Understanding Based on the Tool–Narayanaswamy–Moynihan Model

The room-temperature refractive index is measured for three different prior cooling rates (approximately 10, 50, and 250 K/h) for two glasses especially developed for precision molding. The empirical logarithmic relationship between the cooling rate and the refractive index is also reproduced for the comparatively high cooling rate of ca. 250 K/h. The same relationship is found in a simulation of these cooling rates by the semiempirical Tool–Narayanaswamy–Moynihan model for structural relaxation, with the necessary parameters obtained from differential scanning calorimetry and temperature jump experiments. The measured and the simulated refractive indices coincide within the limits of experimental error. The results demonstrate that the index drop, which is observed when these glasses are first cooled at a regular optical cooling rate (e.g., 2 K/h), and then precision molded (typical cooling rate 1000 K/h), can be understood considering the concepts of structural relaxation.     

估量冷却水成垢的新模式

在大量循环冷却水模拟试验的基础上,对冷却水在换热器水侧所产生的污垢热阻进行了探讨.提出用一个可进行线性回归的、能反映诱导期的指数函数R_f=R_f~e-A/t-t.来描述污垢增长的规律.经将60轮模拟试验数据进行回归分析表明,这个指数函数能很好地与实验数据相符合.采用新的模式,就能由实验所得的R_f和相应的t值,直接回归出极限污垢热阻R_f~.     

喷雾场多参数层析算法的仿真效验与实验测量

根据层析技术原理,对喷雾雾滴粒径和浓度的空间分布开展了研究,并编制了喷雾粒径和浓度层析计算程序.对给定粒径和浓度空间分布的喷雾场,根据脉动法测量原理在计算机上仿真了雾滴粒径和浓度的线投影值,根据仿真的投影值重建了雾滴粒径和浓度的空间分布,重建结果与给定的分布结果完全吻合.在喷雾实验台上用光脉动法装置测量了喷雾雾滴粒径和浓度的线投影值,并用编制的程序对喷雾雾滴粒径和浓度的空间分布进行了层析计算.     

Modeling and Bayesian parameter estimation for semibatch pH‐shift reactive crystallization of l‐glutamic acid

A mathematical model for semibatch pH‐shift reactive crystallization of l ‐glutamic acid is developed that takes into account the effects of protonation and deprotonation in the species balance of glutamic acid, crystal size distribution, polymorphic crystallization, and nonideal solution properties. The crystallization mechanisms of  α‐ and β‐forms of glutamic acid are addressed by considering primary and secondary nucleation, size‐dependent growth rate, and mixing effects on nucleation. The kinetic parameters are estimated by Bayesian inference from batch experimental data collected from literature. Probability distributions of the estimated parameters in addition to their point estimates are obtained by Markov Chain Monte Carlo simulation. The first‐principles model is observed in good agreement with the experimental data and can be further used for model predictions in robust control strategies. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2828–2838, 2014     

闭路浮选流程计算机模拟程序包GFSTESIM

建立了按粒度、矿物组成和可浮性划分的多组分物料的分批磨矿模型、解离模型和分批浮选模型,开发了实验室闭路浮选试验模拟程序包GFSTESIM。该程序包已用于云浮硫铁矿贫矿石含再磨作业的闭路浮选流程的模拟。根据简单的开路分批浮选试验估计出模型参数,模拟了13种结构的浮选流程,从中推选出较优的浮选流程。对建议的工艺流程进行了磨矿细度模拟研究,模拟结果令人满意,与传统试验方法相比,有明显的优点。     

Development of novel protein refolding using simulated moving bed chromatography

In vitro protein refolding is still one of the baffles in both structural biology and development of new biopharmaceuticals, especially for large-scale production of valuable proteins that are overexpressed as inclusion bodies inEscherichia coli. A new continuous refolding method using four zone simulated moving bed process based on size exclusion mechanism was developed to overcome difficulties of inclusion body refolding. Protein refolding using size exclusion SMB enables us to obtain refolded protein continuously with high productivity, low consumption of refolding buffer, and high efficiency of size exclusion medium. Thermodynamics and kinetic parameters for SMB operation were estimated from the best-fit values by comparing the simulation and experimental chromatography results. The SMB operation condition was obtained from the triangle theory, and experimental results were in good agreement with the simulation results     

三级活塞推料离心机数值模拟与操作参数优化

针对新型三级活塞推料离心机的研发,在转鼓尺寸和物料增大情况下,操作参数对分离过程中转鼓内侵蚀现象和分离效率有重要影响。采用样机实验结合CFD数值模拟,对三级活塞推料离心机进行三维建模和仿真,并利用密集离散粒子模型(DDPM)模拟侵蚀过程。基于粒度分析可知,氯化钠颗粒粒径dm为0.070~0.200 mm时,随颗粒粒径增加,固相对离心机转鼓内部的侵蚀越大。结合响应面分析法可知,响应模型各因素的交互影响明显,以更高分离率与更低侵蚀率作为评价指标,得出最优值为推料频率40次/min、转鼓转速1431 r/min、进料浓度60%。与实验数据进行对比,模拟结果的误差在可接受范围内。     

Multivariable real‐time optimal control of a cooling and antisolvent semibatch crystallization process

This article presents an experimental study of simultaneous optimization with respect to two variables (cooling rate and flow‐rate of antisolvent) in an offline and online (real‐time) manner on a semibatch crystallizer. The nucleation and growth kinetic parameters of paracetamol in an isopropanol‐water cooling, antisolvent batch crystallizer were estimated by nonlinear regression in terms of the moments of the crystal population density. Moments of crystal population were estimated from the measured chord length distribution, generated by the FBRM®, and the supersaturation was calculated from the measured concentration by attenuated total reflectance‐fourier transform infrared spectroscopy. The results of real‐time optimization showed a substantial improvement of the end of batch properties (the volume‐weighted mean size and yield). For the same objective function, the real‐time optimization method resulted in an increase in the volume‐weighted mean size by ～100 μm and 15% of theoretical yield compared with the best result obtained in an offline optimization manner. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Demand reduction in building energy systems based on economic model predictive control

This paper proposes and demonstrates the effectiveness of an economic model predictive control (MPC) technique in reducing energy and demand costs for building heating, ventilating, and air conditioning (HVAC) systems. A simulated multi-zone commercial building equipped with of variable air volume (VAV) cooling system is built in Energyplus. With the introduced Building Controls Virtual Test Bed (BCVTB) as middleware, real-time data exchange between Energyplus and a Matlab controller is realized by sending and receiving sockets. System identification is performed to obtain zone temperature and power models, which are used in the MPC framework. The economic objective function in MPC accounts for the daily electricity costs, which include time-of-use (TOU) energy charge and demand charge. In each time step, a min–max optimization is formulated and converted into a linear programming problem and solved. In a weekly simulation, a pre-cooling effect during off-peak period and a cooling discharge from the building thermal mass during on-peak period can be observed. Cost savings by MPC are estimated by comparing with the baseline and other open-loop control strategies. The effect of several experimental factors in the MPC configuration is investigated and the best scenario is selected for future practical tests.     

基于逾渗理论的多孔过滤介质孔径分布估计方法

结合逾渗理论和网格模型,建立了过滤系数与过滤介质孔径分布的联系方程。利用此方程结合过滤实验数据获得过滤介质孔径分布的统计参数,同时与其他方法获得孔径分布参数以及其他文献中的数据进行比较,并利用计算机模拟过滤过程验证了获得的孔径分布参数,结果表明基于逾渗理论的过滤模型用于孔径分布参数的估计是比较准确和有效的。     

Quantitative design of seed load for solution cooling crystallization based on kinetic analysis

Seed load of crystallization has a direct effect on the product qualities. To further reveal the effects of seed load on crystallization kinetics and improve the product size distribution, the aqueous solution of potassium nitrate (KNO₃–H₂O) is employed as a model system and the relevant kinetic experiments are conducted in a batch cooling crystallizer. The crystal nucleation and growth rate parameters are firstly estimated with the concentration and transmittance data using a mathematical model reported in our lab, and then the backward calculations with the help of the model parameters are successfully performed. It is found that the nucleation capacity decreases and growth capacity increases with increasing seed load, and the size distribution of crystal products tends to be more uniform. However, with the increasing of seed load, the linear growth rate of single crystal and the mean size of products both reduce accordingly. Based on the calculational and experimental results, a quantitative design scheme concerning seed load is proposed by further kinetic analyses, and the corresponding verification experiments are carried out. The results show that under the guidance of the proposed scheme, the size distribution of crystal products is more concentrated and the mean size of final particles can also escape from reducing obviously.     

间歇冷却结晶过程的模拟

The general mathematical model for batch cooling crystallization was established based on the population balance equation considering the change of slurry volume, and simulated with crystallization thermodynamics,kinetics and mass balance employing bed voidage. In the system of vitamin C-water-ethanol, reliability of this model was verified by comparison between simulation results and experimental data. The effects of operation parameters on product quality can be systematically investigated by modeling simulation.     

Development and use of positron emitting particle tracking (PEPT) for velocity measurements in viscous fluids in pilot scale equipment

Positron emitting particle tracking (PEPT) can be used to trace the path of a radioactive particle within opaque fluids in pilot scale equipment. Isokinetic tracers can be used to characterize flow fields inside such equipment. A pilot scale heat exchanger was designed and used with PEPT to evaluate the accuracy and applicability of the technique; measurements were performed over a range of flows found in food processing plant, including extruder flows. Velocity distributions were estimated from the measured tracer locations for a range of barrel speeds, flow rates and rheological properties. The flow field is 3D; barrel speed and flow rate had a more pronounced effect on the velocity distributions than the rheological properties of the fluids. The flow field was simulated using a simple 2D approach and a full 3D simulation. The simulated velocity distributions compared favourably to the experimentally determined profiles: trends were correctly predicted by the 2D model whilst statistical agreement was found between data and the 3D simulation. The agreement between PEPT and CFD reinforces the validity of both methods.     

液相氧化反应失控过程的动态流程模拟

随着化工工业现代化、绿色化概念的普及,氧化工艺特别是新型氧化工艺在当前工艺中所占比重日益增加,但氧化反应多为强放热反应,反应所涉及的物料往往也具有不稳定性. 为防止反应安全事故的发生,有必要进行系统的反应安全性研究. 针对液相氧化反应,本工作利用流程模拟手段,建立了带控制条件的半间歇动态反应器模型. 介绍了反应器模型的结构、传热设置和工艺控制设置方案. 选择丙烯环氧化反应开展了模拟研究,设置了相关的动力学参数和反应器参数. 通过模拟正常反应过程对设计的反应器参数进行核算,证明在正常工艺条件下可保证反应平稳进行. 利用所建立的模型模拟了密闭绝热、冷却失效和冷却水调节阀故障条件下的多场景反应危险性,得到了各场景下反应器温度、压力和反应器内物料组成的变化曲线,为后续工作中制定合理的安全控制措施提供数据支持.     

由纤维素制取单细胞蛋白的反应机理模型

对灰黄链霉菌№.107利用纤维素制取单细胞蛋白的生化过程,提出了一个简化的机理模型、并建立了一个含4个状态变量的状态方程组的数学模型,其中包含9个待优化的参数.根据现有的实验数据,借助VAX-ll/780计算机的STYR/OPT库的优化程序,确定了这9个参数,并对模型内多组分不同的动力学表达式进行了比较.对实验模拟的结果是令人满意的.     

Ozawa方程处理PET非等温结晶动力学过程研究

采用Monte Carlo法计算机模拟在预先成核条件和不同降温速率下PET非等温结晶曲线,将模拟的结果用Ozawa方程及改进的Ozawa方程进行处理。结果表明,用Ozawa方程解析的Avrami指数与理论值相近,用改进的Ozawa方程可直接得到结晶速率常数,求出的线生长速率与理论值基本吻合。