Batch process equipment requirement

The above stagewise analyses provide only the steady state overall mass balances. The design of batch processing equipment requires solution of the dynamic equations (introduced in Chapter 4) which describe the rate of uptake of the adsorbate by the adsorbent. Important matters to consider include the shape of the isotherm, whether V may be considered to be finite or infinite, and the nature of the adsorbent and the intraparticle rate processes (Tien 1994). 

Especially for flexible batch applications, the batch logic must be properly structured in order to oe implemented and maintained in a reasonable manner. An underlying requirement is that the batch process equipment be properly structured. The following structure is appropriate for most batch production facilities. 

All but the very simplest equipment suites contain multiple process units. The minimum number of process units is one for each type of processing equipment required to make a batch of product. However, many equipment suites contain multiple process units of each type. In such equipment suites, multiple batches and multiple production runs can be in progress at a given time. 

The batch process equipment used for preparing the components is essentially a set of reactors equipped with heaters and agitators. They operate under vacuum or in an inert gas atmosphere. One of the main requirements of the chemical molding process is the production of pore- and defect-free articles. The volatile products and moisture must be thoroughly removed from the reactant mixture. Moisture imparts porosity to the final articles due to evaporation and the chemical interaction of water with the components of the reactant system, for example, with isocyanates in case of polyurethane formulations. In some cases, moisture can also inhibit the polymerization process, for example, anionic-activated polymerization of lactams. Many monomers, particularly acrylic compounds, require removal of die inhibitors to increase their shelf-life. 

Flame, hot air, electrical discharge, and plasma treatments change the surface of the polymer both physically and chemically. The plasma treating process has been found to be very successful on most low-energy surface plastics. Table 7.12 shows that plasma treatment results in improved plastic joint strength with common epoxy adhesive. Plasma treatment requires vacuum and special batch processing equipment. 

Because of the limits of industrial equipment and cost constraints, curing is done at a constant temperature for a period of time. This can be done both to cure the material initially and to postcure it. The kinetic models discussed in the next section also require data collected under isothermal conditions. It is how rubber samples are cross-linked, how initiated reactions are run, and how bulk polymerizations are performed. Industrially, continuous processes, as opposed to batch processes, often require an isothermal approach. UV Kght and other forms of nonthermal initiation also use isothermal studies for examining the cure at a constant temperature. 

Example 4.5 Given that a low rate of production is required, convert the continuous process from Example 4.4 into a batch process. Preliminary sizing of the equipment indicates that the duration of the processing steps are given in Table 4.7. ... 

In batch process optimization, one of the principal objectives is to improve equipment utilization through reduction in dead time. This requires both structural and parameter optimization, with many options available. 

On a land site where space and weight are not normally constraints, advantage can be taken of tank type separation equipment such as wash tanks and settling tanks, and batch processing methods. Such equipment is generally cheaper to maintain than continuous throughput vessels, though a combination of both may be required. 

The three principal methods of batch proportioning are accumulative, sequential, and simultaneous the best method for a given appHcation depends on the processing equipment available and the accuracy required. 

Crimp. The tow is usually relaxed at this point. Relaxation is essential because it gready reduces the tendency for fibrillation and increases the dimensional stabiUty of the fiber. Relaxation also increases fiber elongation and improves dye diffusion rates. This relaxation can be done in-line on Superba equipment or in batches in an autoclave. Generally saturated steam is used because the moisture reduces the process temperatures required. Fiber shrinkage during relaxation ranges from 10 to 40% depending on the temperature used, the polymer composition used for the fiber, and the amount of prior orientation and relaxation. The amount of relaxation is also tailored to the intended apphcation of the fiber product. 

In a batch process, all the reagents are added at the beginning of the reaction. As the reaction proceeds, the compositions change with time. The reaction is stopped and the product is withdrawn when the required conversion has been reached. Batch processes are suitable for small-scale production and for processes that use the same equipment to make a range of different products or grades. Examples include pigments, dyestuffs, pharmaceuticals, and polymers. 

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