大型合成氨装置先进控制系统技术研究与应用

介绍先进控制系统在布朗工艺合成氨装置上的应用。先进控制与实时优化系统以常规PID控制为基础，通过与DCS的无缝链接，实施软测量系统、鲁棒多变量模型预测控制器。实践证明，APC的应用实现了改善控制性能、提高产品氨收率、减轻操作员工作强度等目标，并取得了显著的经济效益。     

A MODEL OF ISOTHERMAL ADSORPTION IN A CASCADE OF CONTINUOUS FLOW STIRRED-TANK REACTORS

An infinite-series solution is derived for a mathematical model of the cascade of steady-state continuous flow stirred-tank reactors where a solute is being adsorbed into porous spherical particles suspended in a fluid. The rate of adsorption is controlled simultaneously by the intraparticle and fluid-particle transfer resistances and by the rate of adsorption process on the pore walls. Both the counter -current and co-current flow of dispersed and continuous phase are considered.     

A MODEL OF ISOTHERMAL ADSORPTION IN A CASCADE OF CONTINUOUS FLOW STIRRED-TANK REACTORS

An infinite-series solution is derived for a mathematical model of the cascade of steady-state continuous flow stirred-tank reactors where a solute is being adsorbed into porous spherical particles suspended in a fluid. The rate of adsorption is controlled simultaneously by the intraparticle and fluid-particle transfer resistances and by the rate of adsorption process on the pore walls. Both the counter -current and co-current flow of dispersed and continuous phase are considered.     

LMI-based robust model predictive control for a continuous MMA polymerization reactor

A linear matrix inequality (LMI)-based robust model predictive control (MPC) is applied to a continuous stirred-tank reactor for the polymerization of methyl methacrylate (MMA). The polytopic model is constructed to predict the responses to various control input sequences by using Jacobians of uncertain nonlinear model at several operating points and the controller design is characterized as the problem of minimizing an upper bound on the ‘worst-case’ infinite horizon objective function subject to constraints on the control input and plant output. Simulation studies under different conditions are conducted to validate the feasibility of the optimization problem and evaluate the applicability of such a control scheme. Simulation results show that, despite the model uncertainty, the LMI-based robust model predictive controller performs quite satisfactorily for the property control of the continuous polymerization reactor and guarantees the robust stability.     

DYNAMIC ANALYSIS OF CONTINUOUS WELL-MIXED FLUIDIZED/SPOUTED BED DRYERS

A diffusion-based mathematical model is presented for the prediction of the dynamics of drying in continuous well-mixed fluidized/spouted beds. Numerical techniques are used to solve the model equations. The outlet solids moisture content, the outlet air humidity and solids temperature are predicted as a function of time for the falling rate drying period. The model is helpful in describing the drying process during the startup periods and in studying open loop behavior of drying process. The model is also useful in designing control system for fluidized/spouted bed dryers.     

EFFECT OF INTERMITTENT HEATING ON DRYING-INDUCED STRAIN-STRESS OF MOLDED CLAY

Parametric analyses of the strain-stress in the drying process are performed to study the influence of the intermittent drying on the behaviors of drying-induced strain-stress and deformation as well as the drying characteristic. The transient three-dimensional problem of strain-stress and heat and moisture transfer in a slab is solved simultaneously by the finite element method. The dimensionless parameters are introduced to generalize the problem in the conservation equations of heat and moisture transfer. The intermittent drying is modeled by applying periodically smaller and larger Biot numbers to the boundary conditions. The maximum tensile and compressive stresses fluctuate, and fall remarkably during the smaller Biot number period when a slab is heated intermittently. The peak stress of the fluctuation exceeds beyond the case in the continuous healing where the overall drying rate is almost equivalent to that in the intermittent beating, but the reduction of the stresses takes place rapidly in the low heating period.     

EFFECT OF INTERMITTENT HEATING ON DRYING-INDUCED STRAIN-STRESS OF MOLDED CLAY

ABSTRACT

Parametric analyses of the strain-stress in the drying process are performed to study the influence of the intermittent drying on the behaviors of drying-induced strain-stress and deformation as well as the drying characteristic. The transient three-dimensional problem of strain-stress and heat and moisture transfer in a slab is solved simultaneously by the finite element method. The dimensionless parameters are introduced to generalize the problem in the conservation equations of heat and moisture transfer. The intermittent drying is modeled by applying periodically smaller and larger Biot numbers to the boundary conditions. The maximum tensile and compressive stresses fluctuate, and fall remarkably during the smaller Biot number period when a slab is heated intermittently. The peak stress of the fluctuation exceeds beyond the case in the continuous healing where the overall drying rate is almost equivalent to that in the intermittent beating, but the reduction of the stresses takes place rapidly in the low heating period.     

A MATHEMATICAL MODEL FOR THE CONTINUOUS VACUUM DRYING OF HIGHLY VISCOUS FOODSTUFFS

An improved mathematical model for the continuous vacuum drying of highly viscous and heat-sensitive food-stuffs was proposed. The process of continuous vacuum drying was presented as a moving boundary problem of moisture evaporation in cylindrical coordinates. Boundary condition of the first kind for the known functional dependence of the drying body surface temperature on time was considered. Finally, the appropriate system of differential equations was solved numerically and the values of drying rate, integral moisture content of the material, moving boundary position as well as temperature in any point of the material and at any moment of time were obtained. This procedure was applied to continuous vacuum drying of foods such as natural cheese and fresh fish meat paste.     

连续泡沫分离蛋白质

本文以空气-明胶水溶液体系为研究对象，较为详细地考察了通气量、进料流量、进料浓度、进料位置、泡沫高度、溶液pH值等因素对连续泡沫分离明胶过程中明胶富集度变化的影响．     

MULTIVARIABLE CONTROL OF CATALYTIC CRACKING PROCESSES

Simple, explicit and physically intuitive Feedforward and Feedback control policies are designed for Fluidized Catalytic Cracking Processes. The Feedforward (FF) control algorithm compensates for changes in the feed rate and feed coking tendency by the use of the air flow and catalyst circulation rates as control variables to maintain the conversion and the reactor temperature at fixed levels. Through steady state and dynamic simulations the FF controller is shown to be very effective. To improve the dynamic response of the process and to account for the process/model mismatch a feedback (FB) controller is also designed to complement the FF action. The FB action is designed by use of the transformation related to the physical modes which correspond to the extensive variables of the process. It is shown that the required control structure consists of two loops. One uses the air flow rate to control the total sensible heat content of the reactor and regenerator solid phases. The other loop controls the regenerator enthalpy by changes in the catalyst circulation rate. The air flow rate controller includes an integral action to avoid reactor temperature offsets, while the catalyst circulation rate controller requires a nonlinear static observer to predict the coke concentration on the regenerated catalyst from dense bed and flue gas regenerator temperatures. The performance of the controller for changes on the oil feed rate, caking tendency of the feed, as well as for reactor temperature set point changes is faster and smoother than Kurihara's scheme.     

CONTROL OF A CONTINUOUS POLYMERIZATION REACTOR BY WIENER INPUT/OUTPUT DATA-BASED PREDICTIVE CONTROLLER WITH DIRECT INVERSE IDENTIFICATION

This article reports an experimental study for the identification and predictive control of a continuous methyl methacrylate (MMA) solution polymerization reactor. The Wiener model was introduced to identify the polymerization reactor in a more efficient manner than the conventional methods of Wiener model identification. In particular, the method of subspace identification was employed and the inverse of the nonlinear part was directly identified. The input variables in this work were the jacket inlet temperature and the feed flow rate, while the monomer conversion and the weight average molecular weight were selected as the output variables. On the basis of the identified model a Wiener-type input/output data-based predictive controller was designed and applied to the property control of polymer product in the continuous MMA polymerization reactor by conducting an on-line digital control experiment with online densitometer and viscometer. Despite the complex and nonlinear characteristics of the polymerization reactor, the proposed controller was found to perform satisfactorily for property control in the multiple-input multiple-output system with input constraints for both set-point tracking and disturbance rejection. This was also confirmed by simulation results.     

CONTROL OF A CONTINUOUS POLYMERIZATION REACTOR BY WIENER INPUT/OUTPUT DATA-BASED PREDICTIVE CONTROLLER WITH DIRECT INVERSE IDENTIFICATION

This article reports an experimental study for the identification and predictive control of a continuous methyl methacrylate (MMA) solution polymerization reactor. The Wiener model was introduced to identify the polymerization reactor in a more efficient manner than the conventional methods of Wiener model identification. In particular, the method of subspace identification was employed and the inverse of the nonlinear part was directly identified. The input variables in this work were the jacket inlet temperature and the feed flow rate, while the monomer conversion and the weight average molecular weight were selected as the output variables. On the basis of the identified model a Wiener-type input/output data-based predictive controller was designed and applied to the property control of polymer product in the continuous MMA polymerization reactor by conducting an on-line digital control experiment with online densitometer and viscometer. Despite the complex and nonlinear characteristics of the polymerization reactor, the proposed controller was found to perform satisfactorily for property control in the multiple-input multiple-output system with input constraints for both set-point tracking and disturbance rejection. This was also confirmed by simulation results.     

Numerical modeling of continuous detonation in non-stoichiometric hydrogen-oxygen mixtures

A two-dimensional unsteady gas-dynamic mathematical model of continuous spin detonation in a non-stoichiometric hydrogen-oxygen mixture in an annular combustor of a rocket-type engine is formulated. An analysis of the governing parameters shows that this model is an eigenvalue problem, where the eigenvalue is the problem period, which cannot be arbitrarily prescribed, but which has to be sought in the course of solving the problem. Numerical modeling of the dynamics of transverse detonation waves is used to elucidate the influence of the fuel-to-oxidizer equivalence ratio on the wave structure and specific impulse, and the eigenvalue (minimum period of the problem) is determined as a function of the specific flow rate of the mixture. These eigenvalues are demonstrated to agree with experimental data. In the case of continuous spin detonation, addition of an expanding nozzle to a constant-section channel is shown to increase the specific impulse.     

TRANSIENT ANALYSIS OF CRYSTALLIZATION: EFFECT OF THE SIZE DEPENDENT GROWTH RATE

The dynamics of the crystal size distribution in a continuous mixed suspension, mixed product removal crystallizer is modeled stochastically. The model is fairly general in that it involves a size-dependent growth rate function: this size-dependent growth rate as a possible cause of deviation on the behavior of the crystallizer from that of an idealized or simplified counterpart has been investigated based upon the model.     

ADAPTIVE CONTROL OF A BATCH REACTOR

A globally stable adaptive predictive control system (APCS) is evaluated by application to a simulated PVC batch reactor. The reactor is run under APCS control with the objective of either temperature setpoint tracking or constant reaction rate. The batch nature of this system makes it possible to learn about the physical problem from successive runs. This knowledge is incorporated into the control strategy to improve the performance of the reactor. The problem of excessive manipulation of the control variable has been recognized and resolved by using control weighting. Performance of the adaptive technique is compared with previous results using self-tuning and PID control of the same reactor. APCS provides good, robust control despite the nonlinear dynamics of the system.     

Optimal control and operation of drum granulation processes

Process optimisation and optimal control of batch and continuous drum granulation processes are studied in this paper. The main focus of the current research has been: (i) construction of optimisation and control relevant, population balance models through the incorporation of moisture content, drum rotation rate and bed depth into the coalescence kernels; (ii) investigation of optimal operational conditions using constrained optimisation techniques; (iii) development of optimal control algorithms based on discretized population balance equations; and (iv) comprehensive simulation studies on optimal control of both batch and continuous granulation processes. The objective of steady state optimisation is to minimise the recycle rate with minimum cost for continuous processes. It has been identified that the drum rotation-rate, bed depth (material charge), and moisture content of solids are practical decision (design) parameters for system optimisation. The objective for the optimal control of batch granulation processes is to maximize the mass of product-sized particles with minimum time and binder consumption. The objective for the optimal control of the continuous process is to drive the process from one steady state to another in a minimum time with minimum binder consumption, which is also known as the state-driving problem. It has been known for some time that the binder spray-rate is the most effective control (manipulative) variable. Although other possible manipulative variables, such as feed flow-rate and additional powder flow-rate have been investigated in the complete research project, only the single input problem with the binder spray rate as the manipulative variable is addressed in the paper to demonstrate the methodology. It can be shown from simulation results that the proposed models are suitable for control and optimisation studies, and the optimisation algorithms connected with either steady state or dynamic models are successful for the determination of optimal operational conditions and dynamic trajectories with good convergence properties.     

TURBULENCE CLOSURE MODELING OF TWO-PHASE FLOWS

A second order turbulence closure model is developed for the numerical prediction of isothermal non-reacting, two-phase turbulent shear flows. This model is based on the two-equation (k - ?) model but treats the continuous (gas) phase and (solid) particulate phase as separate interacting continua. The presence of the particles will increase the dissipation rate in the gas phase and additional terms based on the particle size and loading are added to the traditional k and ? equations. The model is tested by making predictions of the spreading rate and velocity decay in the developing region of the two-phase axisymmetric jet. The predictions agree favorably with available experimental data in this region.     

改进的模糊预测控制算法及其在CSTR过程中的应用

A finite horizon predictive control algorithm,which applies a saturated feedback control law as its local control law,is presented for nonlinear systems with time-delay subject to input constraints.In the algorithm,N free control moves,a saturated local control law and the terminal weighting matrices are solved by a minimization problem based on linear matrix inequality(LMI) constraints online.Compared with the algorithm with a nonsaturated local law,the presented algorithm improves the performances of the closed-loop systems such as feasibility and optimality.This model predictive control(MPC) algorithm is applied to an industrial continuous stirred tank reactor(CSTR) with explicit input constraint.The simulation results demonstrate that the presented algorithm is effective.     

阴离子聚合等温反应器控制的设计

根据阴离子聚合的动力学分析,得到引发剂、单体、活性基团、聚合物浓度之间的动态关系,并以这四个量为状态参量,以加入引发剂的浓度、加入单体浓度、流量为输出量,以数均分子量和聚合物的生产速率为输出量,导出控制模型。该模型经线性化、去耦后,置于闭环负反馈控制之下,得到一个比例－积分控制     

THE MINIMUM OF TOTAL AVAILABLE ENERGY (ENERGY) DISSIPATION IN THE MULTISTAGE FLUIDIZED WET BEDS

This article represents a second half of the work in optimization of the fluidized drying and moistening processes by the method of dynamic programming. The problem considered in Part I concerns the case of fluidized drying and moistening in the continuous processes for the variable inlet gas temperature. In this work, the generalized aspect of the continuous and multistage adiabatic processes for the case when the decision variables on the stage are gas enthalpy, gas humidity and dry gas flow rate, is considered. The continuous processes are considered here only as a limiting case of the multistage ones.

The two types of the thermodynamic performance indexes based on the idea of energy as a thermodynamic measure of the substance value are considered. The first type is related to the economic costs of production and the second to the overall economic costs. The equivalency of the optimization results for either of the two types of energy costs is discussed- Also, the nature of the optimal trajectories and decisions is considered.