Design, crystallization control

Crystallization batches range from 30,000 to 60,000 Hters for each pan. Continuous centrifugals are typically used for second, third, and affination steps continuous vacuum pans are less common but are used in the U.S. for intermediate strikes. Most horizontal batch crystallizers have been replaced by continuous units, and all are designed for controlled cooling of the massecuite to maintain supersaturation. 

For effective control of crystallizers, multivariable controllers are required. In order to design such controllers, a model in state space representation is required. Therefore the population balance has to be transformed into a set of ordinary differential equations. Two transformation methods were reported in the literature. However, the first method is limited to MSNPR crystallizers with simple size dependent growth rate kinetics whereas the other method results in very high orders of the state space model which causes problems in the control system design. Therefore system identification, which can also be applied directly on experimental data without the intermediate step of calculating the kinetic parameters, is proposed. 

Proper control of the crystalline microstructure leads to products with the desired textural properties and physical characteristics. For example, tempering of chocolate prior to molding or enrobing is designed to control crystallization of the cocoa butter into a large number of very small crystals that are aU in the desired polymorphic form. When controlled properly, the cocoa butter crystals in chocolate contribute to the desired appearance (shine or gloss), snap, flavor release, meltdown rate upon consumption, and stability during shelf life (fat bloom). Similar... 

There are some problems that may be encountered when using cooling as a crystallization technique. While well-designed temperature control units ensure sufficient temperature control under many conditions, it is difficult to achieve... 

This is the heart of the microcomputer. The CPU or microprocessor examines the contents of memory and interprets them as instructions or data. The way in which the processor interprets the numbers stored in memory depends on the design of the chip, that is, on the manufacturer. This is the machine code and the microprocessor s repertoire of arithmetic and logic functions is called its instruction set. The CPU is connected to the memory by two sets of wires called the data bus and the address bus. The data bus is used to transfer data to and from the memory. The address bus is used to identify that part of memory with which the processor wishes to communicate. It is important that the processor and the memory act in a synchronized manner. All microcomputers contain a crystal-controlled oscillator which acts like a metronome to which all actions are synchronized. This oscillator is sometimes referred to as the clock. 

Virtually all industrial crystallization processes involve solutions. The development, design, and control of any of these processes involve knowledge of a number of the properties of the solution. This chapter will present and explain solutions and solution properties, and relate these properties to industrial crystallization operations. 

The control algorithm is the part of the control system that uses the available measurements and level of process understanding to determine the best means to influence the process with the available manipulated variables to achieve the designer s performance objectives. In the discussion of control algorithms in this chapter, standard control notation is used. This notation is explained below in reference to crystallizer control ... 

The remaining seven chapters deal with individual topics important to industrial practice, such as design, mixing, precipitation, crystallizer control, and batch crystallization. In addition, topics that have become important in recent years, such as melt crystallization and the crystallization of biomolecules are also included. Each chapter is self-contained but assumes that the reader has knowledge of the fundamentals discussed in the first part of the book. 

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