Problems Commonly Encountered

There are several problem areas which seem to appear often in the results of hazards analyses. The most common are  

Relief valves are often seen to be undersized for the required relieving rate, due either to poor initial design or changes in the process conditions which occurred during design. The most common system problem is that the relief valve was adequately sized for blocked discharge but not sized for the flowrate that could occur as a result of a failure in the open position of an upstream control valve (i.e., gas blowby). See Chapter 13. 

Another common problem area is having open and closed drain systems tied together. Liquid which drains from pressure vessels flash at atmospheric pressures giving off gas. If this liquid flows in the same piping as open drains, the gas will seek the closest exit to atmosphere it can find, causing a potential fire hazard at any open drain in the. system. 

Many accidents have occurred where gas has migrated through the drain system to an unclassified area where welding, or other hot work, was being performed. See Chapter 15. 

Piping pressure ratings should be designed so that no matter which valve is closed, the piping is rated for any possible pressure it could be subjected to, or is protected by a relief valve. 

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This chapter is intended to provide an idea of the application of the various techniques described in the previous chapter to the problems commonly encountered by the electrochemist. Constraint on space precludes an exhaustive treatment of the various systems to be described below for such a treatment, the reader is encouraged to consult the further reading list at the end of the chapter... 

Heat and mass transfer, especially mass transfer, in multiphase systems are problems commonly encountered in processing units in the chemical, petrochemical, and many other process industries. Because transfer rates significantly affect the efficiencies and technical-economic indexes of the processes, the enhancement of transfer has been a continuing topic of interest in chemical engineering since the late 1930s. A vast number of theoretical and experimental investigations have been carried out in the search for new methods of enhancing transfer between phases. 

Preparation of Samples for Liquid Scintillation Counting. Quenching in its various forms constitutes the major concern during sample preparation for liquid scintillation counting. The following sections discuss some of the problems commonly encountered and also present some remedies to overcome these problems. 

Profile A small UK contract research organization, the company was established to address the problems commonly encountered when natural samples are used for drug screening. The three founding members have expertise in the field isolation of fungi and actinomycetes, and are developing new methods for field and laboratory cultivation of unusual microbial groups. 

The goal of this book is to present modern chemometric methods utilized in capillary electrophoresis (CE) to help alleviate the problems commonly encountered during routine analysis and method development. Its scope is to focus on current chemometric methods utilized in CE endeavors—techniques developed and routinely incorporated by research-active experts in the field. 

When the liquid flow rate, L, the gas flow rate, F, the inlet and outlet partial pressure of the reacting component A of the gas phase, ipA)in and (p Xut, respectively, and the inlet concentration of the reacting component B of the liquid phase are given, the problem is to find the outlet concentration of B, written (Cb) ui and the volume, V, of the reactor. This is the kind of problem commonly encountered in absorbers. In reactors, on the other hand, conditions are often imposed on the liquid component—in hydrodesulphurization, for example, but also in hydrogenations, oxidations or chlorinations—and L, F, (CB>i , (Cb)<, , (p )i would be given or imposed through certain constraints like flooding rates, to be discussed in later sections. The unknowns would then be pA)out and the volume V. 

This table summarizes problems commonly encountered in capillary electrophoresis (CE) experiments, and plausible solutions to these problems. 

A problem commonly encountered in the development of both gas and liquid phase chromatographic methods of analysis is that of tailing. In such cases it is difficult to characterize the retention time of a particular species because of the long tail associated with the peak. Consider the detector output indicated in Figure PI 1.7. The time dependence of the effluent concentration of this species can he represented by... 

Figure 1. Problems commonly encountered in the chemical process industries which could be solved by use of reactions or reaction paths...

To obtain satisfactory results, concrete mixes made with type M cement must be heat-cured at a temperature exceeding 70°C. At these temperatures trisulfate is thermodynamically unstable it cannot be formed in the hydration, and monosirUate is formed instead, without causing expansion. Upon subsequent cming in water at ambient temperature, the primary formed monosulfate converts to trisirlfate, and this reaction is associated with a generation of expansive stresses in the concrete body. Type M expansive cement is suitable for the production of precast reinforced concrete products to be heat-cured in the course of production, but is hardly suitable for use at ambierrt temperature. Quick setting and umeliability are problems commonly encountered in the use of this type of cement. 

A problem commonly encountered in organic chemistry is identifying a compound that has been obtained from a chemical reaction or isolated from a natural source or the environment. The spectroscopic characteristics of a sample provide important clues to the identity of the substance. Collections of spectral data of known compounds provide a source of such information that may be used either to identify known compounds or to assist in the determination of the structure of an unknown substance. 

When the apparatus is charged with the mobile phase, the sample is loaded into the injector loop and transferred to the first column. Within each loculus, the sample is partitioned between the mobile and stationary phases whose interface is constantly renewed by the rotation of the apparatus at 60 to 80 rpm. This rotation speed does not allow excessive agitation to occur this could result in the formation of emulsions, a problem commonly encountered in countercurrent distribution. 

Timmons et al. (2000) and Latour (1979) have discussed opportunities for the application of on-line optimization or supervisory control in refinery operations. Three general types of optimization problems commonly encountered in industrial process operations are discussed next. 

This chapter provided the introduction to various unit operations described in this book. Introduction to solution techniques involved in solving differential equations, optimization, and optimal control problems commonly encountered in batch processing is also presented. 

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