Process evaluation high-pressure equipment

As discussed in Chapter 2, The Toller Selection Process, evaluating the site s safe work practice procedures should have been a part of the review during the toller selection process. Still, new materials may indicate a need to revise or develop special procedures to address unique chemical and physical hazards. New hazards such as vacuum, ciyogenics, ultra-high pressure, or new rotating equipment could be introduced. Medical monitoring requirements or special handling and spill response procedures for the toll s raw materials and products may indicate a need to write or revise safe work practices. 

Many times companies focus agreat deal of effort on the successful execution of the process to manufacture an acceptable product but leave out employee safety precautions. Protecting equipment and facility structures from harsh chemicals is very important, but protection of your most critical asset—the employee—should be paramount. If specific personnel protection equipment is needed for particular steps, indicate those requirements in the batch record. Also, evaluate the potential of high-pressure air lines or explosion hazards. 

High temperature and high pressure processing of materials often involves the use of supercritical fluids. Corrosion studies are quite essential for evaluation of the equipment in supercritical fluid operations. Previous electrochemical measurements for alloys in supercritical fluids are rare (1-1). The reported measurements (3) show that passivation of iron alloys is different at supercritical conditions compared to ambient conditions. The study of the electrochemistry of iron alloys can lead to control of corrosion of equipment utilizing the alloys. Thermodynamic analysis provides the information about stable species, i.e. corrosion products under given temperatures and pressures. 

The value of the monomer partition coefBcient between the CO2 and the water phase indirectly determines the ratio between the effect of enhanced polymerization and the effect of extraction on the reduction of residual monomer. Depending on the process conditions, i.e. temperature, pressure, and the phase behavior of the system involved, this ratio between enhanced polymerization and extraction may vary for different latex systems. With respect to the PMMA latex, the high partition coefBcient m2 as shown in Section 14.4, causes extraction to be the predominant effect as compared to conversion of the monomer. Therefore, a preliminary process design has been developed based on C02-extraction. For this purpose, a mass transfer model has been set up to determine the rate-limiting step in the extraction process. In addition, a process flow diagram, including equipment sizing has been developed. Finally, an economic evaluation has been performed to study the viability of this technique for the removal of residual monomer from latex-products. 

Although the direct measurement of equilibrium data for mixtures at high pressures requires detailed experimental experience and expensive equipment, it is still an es sential and reliable way in order to obtain the data needed for the evaluation of high-pressure processes. Recently, Dohrn et al. (10] presented a classification of experimental methods for high-pressure phase equilibria. Figure 2.4 illustrates the two main groups analytical methods and synthetic methods. In case of analytical... 

Chemical processing under "extreme conditions" of high temperatures and pressures requires more tliorough analysis and extra safeguards. As discussed in Chapter 7, e.xplosions at liigher initial temperatures and pressures are much more severe. Therefore, chemical processes under extreme conditions require specialized equipment design and fabrication. Otlier factors tlrat should be considered when evaluating a chemical process are rate and order of the reaction, stability of the reaction, and tlie healtli hazards of the raw materials used. 

A chemical reactor is a vessel manufactured from metal, often stainless steel or high resistant alloys. A minimum wall thickness is required to resist to different toads, and mainly to internal pressure. Accurate mechanical calculation of process equipment is a matter of mechanical engineering, and out of the scope of this book. Here we present only simple relations that permit the evaluation of weight and cost of vessels in a preliminary economic analysis. More information about mechanical design can be found in Coulson Richardson (1993). 

Ammonia converter is the key equipment of the ammonia plant. In the process, the synthesis reaction must be carried out, as much as possible, close to the optimum reaction temperature of catalyst to achieve bigger productivity and higher synthesis rate. It should also strive to reduce the pressure drop of the converter, so as to reduce the power consumption of the recycle gas. In the structure, it should strive to be simple and reliable to meet the demand of high-temperature and high-pressm e. These are the basic principles for designing ammonia converter and one of the symbols for evaluating reactor quality. 

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