An experimentally validated simulation model for a four-stage spray dryer

In this paper, we develop a dynamic model of an industrial type medium size four-stage spray dryer. The purpose of the model is to enable simulations of the spray dryer at different operating points, such that the model facilitates development and comparison of control strategies. The dryer is divided into four consecutive stages: a primary spray drying stage, two heated fluid bed stages, and a cooling fluid bed stage. Each of these stages in the model is assumed ideally mixed and the dynamics are described by mass- and energy balances. These balance equations are coupled with constitutive equations such as a thermodynamic model, the water evaporation rate, the heat transfer rates, and an equation for the stickiness of the powder (glass transition temperature). Laboratory data is used to model the equilibrium moisture content and the glass transition temperature of the powder. The resulting mathematical model is an index-1 differential algebraic equation (DAE) model with 12 states, 9 inputs, 8 disturbances, and 30 parameters. The parameters in the model are identified from well-excited experimental data obtained from the industrial type spray dryer. The simulated outputs of the model are validated using independent well-excited experimental data from the same spray dryer. The simulated temperatures, humidities, and residual moistures in the spray dryer compare well to the validation data. The model also provides the profit of operation, the production rate, the energy consumption, and the energy efficiency. In addition, it computes stickiness of the powder in different stages of the spray dryer. These facilities make the model well suited as a simulation model for comparison of the process economics associated to different control strategies.     

Comparison of three control strategies for optimization of spray dryer operation

Spray drying is the preferred process to reduce the water content of many chemicals, pharmaceuticals, and foodstuffs. A significant amount of energy is used in spray drying to remove water and produce a free flowing powder product. In this paper, we present and compare the performance of three controllers for operation of a four-stage spray dryer. The three controllers are a proportional-integral (PI) controller that is used in industrial practice for spray dryer operation, a linear model predictive controller with real-time optimization (MPC with RTO, MPC-RTO), and an economically optimizing nonlinear model predictive controller (E-NMPC). The MPC with RTO is based on the same linear state space model in the MPC and the RTO layer. The E-NMPC consists of a single optimization layer that uses a nonlinear system of ordinary differential equations for its predictions. The PI control strategy has a fixed target that is independent of the disturbances, while the MPC-RTO and the E-NMPC adapt the operating point to the disturbances. The goal of spray dryer operation is to optimize the profit of operation in the presence of feed composition and ambient air humidity variations; i.e. to maximize the production rate, while minimizing the energy consumption, keeping the residual moisture content of the powder below a maximum limit, and avoiding that the powder sticks to the chamber walls. We use an industrially recorded disturbance scenario in order to produce realistic simulations and conclusions. The key performance indicators such as the profit of operation, the product flow rate, the specific energy consumption, the energy efficiency, and the residual moisture content of the produced powder are computed and compared for the three controllers. In this simulation study, we find that the economic performance of the MPC with RTO as well as the E-NMPC is considerably improved compared to the PI control strategy used in industrial practice. The MPC with RTO improves the profit of operation by 8.61%, and the E-NMPC improves the profit of operation by 9.66%. The energy efficiency is improved by 6.21% and 5.51%, respectively.     

A fuzzy PID thermal control system for casting dies

In high-pressure die casting processes, proper control of die temperature is essential for producing superior quality components and yielding high production rates. However, die temperature distribution depends on various die design and process variables for which accurate models are normally very difficult to obtain. In this paper, a new intelligent control scheme is proposed for die thermal management. In this scheme, extra cooling waterlines controlled by a pump and solenoid valves are attached to the established cooling channels. A fuzzy PID controller is designed to minimize the temperature differences between channels. The experimental results obtained from a laboratory die casting process simulator indicate that the developed control system is capable of adjusting the desirable supply of cooling water into multiple cooling lines. Hence, the local temperature distribution of the die insert may become more homogeneous.     

GPU-based model predictive control for continuous casting spray cooling control system using particle swarm optimization

Model predictive control (MPC) for spray cooling control system requires a repeated online solution of an optimization problem that includes partial differential equations (PDEs). To simulate the future temperature behavior of steel billets, 3D dynamic heat transfer model is used. The special solution domain of PDEs has led to large computation cost, which is the main challenge in the real-time practical application of spray cooling control system. Meanwhile, the heat transfer coefficients need to be identified using the measured surface temperature. This work presents a two-level parallel solution method implemented on a Graphics processing unit (GPU) for MPC of spray cooling control systems and a weighted least squares modified conjugate gradient method (WLS–MCG) for identification of heat transfer coefficients. Two-level parallel solution method consists of parallel-based heat transfer model and stream parallel particle swarm optimization (PSO). PSO is used to solve the optimization problem. WLS–MCG consists of the weighted least squares (WLS) and modified conjugate gradient method (MCG). The experimental results show that the two-level parallel solution method has good computational performance and achieves satisfactory control performance.     

汽轮机润滑油温模糊调节系统的仿真研究

在汽轮发电机组中,润滑油温度的控制对汽轮机系统的安全运行具有很重要的意义。研究了润滑油温自动控制系统的模糊设计与仿真,为电站自动化程度的进一步提高提供了理论基础。对汽轮机润滑油的实际工作流程和作用做了具体分析,选择了不严格依赖于系统数学模型的模糊控制方案,详细地设计了汽轮机润滑油温度的模糊控制算法。根据工程实际经验,建立了润滑油温度调节系统的非线性数学模型。最后用Matlab程序进行了仿真,仿真结果证明了模糊控制的可行性与有效性。     

Modelling to determine the optimal porosity of shelterbelts for the capture of agricultural spray drift

Shelterbelts are not only useful as windbreak protection for stock and crops but can also be used to capture spray drift and reduce the spread to non-crop areas with important environmental consequences. The porosity of a shelterbelt can significantly influence the ability to capture spray drift. The aim of this work is to determine the optimal shelterbelt porosity that maximises spray drift capture. This has implications to future shelterbelt plantings and species selection. Here a model is developed for the flow through and over a shelterbelt. This model is used in conjunction with a spray capture model to determine the capture efficiency of shelterbelts with different porosities. Values of the optical porosity between 10% and 40% are found to give the best capture efficiency over a range of shelterbelt structures with the optimum generally around 25%. It is hoped that in the future experimental validation of these models will be undertaken. This will further enhance the understanding and use of shelterbelts as spray mitigation devices.     

工业加热炉燃烧过程的模糊专家控制策略

本文将模糊控制与专家控制相结合，提出了一种模糊专家控制策略，用于工业加热炉燃烧过程的温度控制、在温度偏差较小时使用模糊控制，保证较好的控制精度；在温度偏差较大时采用专家控制，保证快速的升温和降温效果，实际应用表明，本文提出的控制策略具有响应快、鲁棒性强的特点，达到了较好的控制性能。     

植保机钟摆式喷杆主动悬架自适应模糊控制

针对具有不确定性与参数时变性的钟摆式喷杆主动悬架系统的运动控制问题,设计出一种基于间接型自适应模糊控制方法的喷杆位姿主动控制器。为一种结构简单、成本低廉且应用广泛的钟摆式喷杆主动悬架系统建立了数学模型,并在此基础上,为了不失一般性,对系统模型进行了输入输出线性化变换。应用间接自适应模糊控制方法克服由于系统不确定性以及外部干扰带来的一些负面影响。此外,应用Lyapunov综合法设计控制器中调整参数的自适应律。仿真结果表明,所提出的控制方法具有快速响应性以及较强的自适应性和鲁棒性。所设计的控制器有利于提高植保机的喷雾均匀性及喷杆的稳定性。     

LPG sensing properties of ZnO films prepared by spray pyrolysis method: Effect of molarity of precursor solution

Nanocrystalline ZnO films were deposited onto glass substrates by spray pyrolysis of zinc nitrate solutions and used as a liquid petroleum gas (LPG) sensor. The dependence of the LPG sensing properties on the molar concentration of zinc nitrate solutions was investigated. The ZnO films were oriented along (0 0 2) with the hexagonal crystal structure. The grain size and grain density increased with an increase in molar concentration of zinc nitrate solutions. The gas sensing properties for LPG of the ZnO films for LPG with different grain sizes were measured at different temperatures. The maximum sensitivity of 43% at the operation temperature of 673 K was found for the ZnO film prepared by spraying a 0.1 M solution. The ZnO thin films exhibited good sensitivity and rapid response–recovery characteristics to LPG. Further, it has been shown the gas sensitivity of the ZnO gas sensor depends upon its grain size.     

基于模糊控制与预测控制切换的翼伞系统航迹跟踪控制

以翼伞系统的六自由度模型为基础,针对翼伞系统的平面航迹跟踪问题,对已有的预测控制器进行改进,提出模糊控制和广义预测控制相互切换的控制模式．利用横向轨迹误差法,在翼伞偏航角误差较大的情况下,采用模糊控制,直至偏航角误差达到设定的较小范围内,切换为广义预测控制,对翼伞航迹进行精确的制导,在一定程度上减少了处理器的运算量．采用真实的翼伞参数建立仿真模型,结果验证了这一控制方法的有效性．     

质子交换膜燃料电池温度模型与模糊控制

为保证质子交换膜燃料电池（PEMFC）安全高效运行,必须对其进行有效的温度控制,本文阐述了一种带积分环节的二维增量模糊控制器用于PEMFC的温度控制．首先从物料平衡和能量平衡角度对PEMFC的电能和热能的动态特性进行分析,建立了基于控制的PEMFC的温度机理动态模型;其次根据所建立的温度模型和控制经验规则设计带积分环节的PEMFC温度二维增量模糊控制器;最后对所建立温度模型及其模糊控制器进行仿真分析,结果不仅表明该模型能模拟PEMFC的动态特性,而且验证该控制器能将PEMFC温度控制在理想工作范围内,并具有较强的鲁棒性,可用于对PEMFC进行温度实时控制．     

改性塔温度模糊专家控制系统的设计与实现

本文通过采用模糊专家控制技术来处理粉状炸药连续生产工艺中改性塔温度的控制问题。在温度偏差较大时采用专家控制,使温度迅速接近工艺要求;在温度偏差较小时采用模糊控制,保证较好地控制精度。实际应用表明,该文提出的控制策略具有反应速度快、稳定性强和控制精度高等特点,达到了较好的控制性能。     

遗传算法优化模糊PID的喷雾干燥温度控制应用

针对洗衣粉喷雾的干燥过程,首先分析了产生进塔风温的燃油热风炉稳定性对洗衣粉基粉湿含量的重要意义,从而提出了一种基于遗传优化模糊PID参数的喷雾干燥温度控制方法。这种控制方法采用遗传算法优化的模糊控制中的比例因子和量化因子,从而使控制规则和隶属函数的优化更加合理,最后通过MATLAB对优化后的模糊控制器进行仿真。结果显示,经过优化后的模糊控制器的控制品质有较大的改善和提高。     

喷雾干燥过程分析及其PID控制仿真

本文研究背景源自实际喷雾干燥过程控制的工程项目。从对喷雾干燥过程的工艺流程、干燥机理的研究分析入手,讨论了喷雾干燥过程的控制思想、控制指标和要求,利用飞升曲线法拟合被控对象的数学模型,阐述了喷雾干燥过程PID控制算法的应用及系统仿真,通过ITSE最优整定法进行了参数整定。从实验仿真和实际运行的结果证明,所设计的控制系统能够满足干燥工艺和控制指标的要求,所采用的PID控制算法实现方便、控制效果较好,具有一定的稳定性和鲁棒稳定性。     

Structure and stability analysis of a Takagi–Sugeno fuzzy PI controller with application to tissue hyperthermia therapy

 In this paper, we first reveal the analytical structure of a simple Takagi–Sugeno (TS) fuzzy PI controller relative to the linear PI controller. The fuzzy controller consists of two linear input fuzzy sets, four TS fuzzy rules with linear consequent, Zadeh fuzzy logic AND and the centroid defuzzifier. We prove that the fuzzy controller is actually a nonlinear PI controller with the gains changing with process output. Utilizing the well-known small Gain Theorem in control theory, we then derive sufficient conditions for global stability of the fuzzy control systems involving the TS fuzzy PI controller. Finally, as an application demonstration, we apply the fuzzy PI controller to control issue temperature, in computer simulation, during hyperthermia therapy. The relationship between heat energy and tissue temperature is represented by a linear time-varying model with a time delay. The sufficient conditions for global stability are used to design a stable fuzzy control system. Our simulation results show that the fuzzy PI control system achieves satisfactory temperature control performance. The control system is robust and stable even when the model parameters are changed suddenly and significantly.     

基于啤酒发酵过程的时变轨迹输出反馈鲁棒模糊预测控制

考虑到实际生产中状态不易测量和设定值变化的情况以及系统本身的非线性特性,针对啤酒发酵过程温度控制系统提出了一种时变轨迹下输出反馈鲁棒模糊预测控制方法。在啤酒发酵罐温度系统的机理模型的基础上,建立包括不确定性和未知干扰的状态空间模型;通过设计模糊集,建立为具有加权系数的T-S模糊状态空间模型;并在状态变量的中引入输出跟踪误差,建立新型多自由度状态空间模型;并运用鲁棒模型预测控制方法优化参数不确定性问题,结合李雅普诺夫稳定性理论推导出线性矩阵不等式形式的稳定性条件,通过求解线性矩阵不等式中参数来计算对应子模型控制律,并对所设计的输出反馈控制器给定权值。通过仿真结果验证了提出方法的有效性和可行性。     

基于小波消噪的PEMFC先进PID控制

讨论了在功率需求快速变化下质子交换膜燃料电池的动态响应性能。从系统电气输出控制的角度考虑,根据PEMFC的系统组成构建了简化的电气模型。由于实际运行过程中的信号噪声和系统自身的非线性影响,文中采用小波消噪算法和自适应模糊PID控制相结合,应用于PEMFC的输出控制。最后使用MATLAB对系统控制方案进行仿真。仿真结果表明,采用小波消噪能够有效降低系统噪声的影响,采用模糊自适应PID控制可以有效降低超调量和响应时间。系统的整体控制方案达到了预期的效果。     

Modelling the influence of the gas to melt ratio on the solid fraction of the surface in spray formed billets

In this paper, the relationship between the Gas to Melt Ratio (GMR) and the solid fraction of an evolving billet surface is investigated numerically. The basis for the analysis is a recently developed integrated procedure for modelling the entire spray forming process. This model includes the atomisation stage taking thermal coupling into consideration and the deposition of the droplets at the surface of the billet taking geometrical aspects such as shading into account. The coupling between these two models is accomplished by ensuring that the total droplet size distribution of the spray is the summation of “local” droplet size distributions along the r-axis of the spray cone. The criterion for a successful process has been a predefined process window characterised by a desired solid fraction range at a certain distance from the atomizer. Inside this process window, the gas and melt flows have been varied and their influence on the solid fraction at the surface of the billet has been analysed.     

Musculoskeletal exposure of manual spray painting in the woodworking industry – an ergonomic study on painters

In the present study the ergonomic conditions of manual spray painting in the woodworking industry have been studied. Manual spray painting is, despite rationalisations, quite common in the Swedish woodworking industry. Interviews with spray painters showed that they had higher prevalence of musculoskeletal symptoms in their right shoulder compared with other workers with manual work. A majority of the spray painters painted work-pieces lying on a work-table. A majority of these painters abduct the right upper-arm so much when painting the horizontal surface of the work-piece that they risk supraspinatus tendinitis. The upper-arm abduction when painting horizontal surfaces could be decreased without introducing new ergonomic disadvantages by installing work-tables with powered height control or possibly also by changing the geometry of the spray gun. Gripping the spray gun trigger was for some of the painters identified as causing a high risk for WMSD in the wrist. Lower spray gun trigger force would improve the situation. This could be done by the users in several ways, such as greasing the trigger mechanism and/or decreasing the spring pressure on the fluid needle.

Relevance to industry

The study highlights some major ergonomic problems for a fairly large group of workers in the woodworking industry.