Application Processes

Technology for large-scale application of chemical reduction is well developed. The reduction of residual chlorine in a chlorination or superchlorination process system is termed dechlorination, which is the most common process in municipal water and wastewater treatment. The reduction of chromium waste by sulfur dioxide is another classic process and is in use by numerous plants employing chromium compounds in operations such as electroplating. 

The chemical reduction process is also being used on a limited basis to remove mercury and lead from wastewater. Sodium borohydride is currently used in some chlor-alkali plants (inorganic chemicals manufacturing) to reduce the soluble mercury ion to metallic mercury, which is then removed from solution by granular activated carbon adsorption, or solid-water separation process. 

The major advantage of chemical reduction when used to reduce hexavalent chromium, or residual chlorine, is that it is a fully proven technology based on many years of experience. Operation at ambient conditions results in minimal energy consumption. 

One limitation of chemical reduction of hexavalent chromium, residual chlorine, and others, is that for high concentrations of chromium the cost of treatment chemicals may he prohibitive. When this situation occurs, other treatment processes are hkely to be more economical. Chemical interference by oxidizing agents is possible in the treatment of mixed wastes, and the treatment itself may introduce pollutants if not properly controlled. Storage and handling of sulfur dioxide is somewhat hazardous. 

In 1988 producers of basic industrial chemicals, plastics, and fibers in tlie United States increased tlieir sales at least 10% to about 90 billion (exclusive of foreign subsidiaries) primarily as a result of increased demand at home and abroad. Along witli die increase of chemical production safety and accident prevendon liave become more critical and essential. Such dramadc releases of toxic chemicals as diose tliat occurred in Bhopal and at Three Mile Island have lieightened publie eoneem for die integrity of process facilities dial liandle liazardous materials. 

It is virtually impossible to design a fail-safe operation of a chemical process. However, many companies have attempted to minimize liazardous conditions by developing a systematic approach to process design. Implemention of these acdons hoped to aeliieve maximmn protection to personnel, equipment, and die public. 

Toxic chemicals tliat could potentially cause a major problem if accidentally released into tlie atmosphere include clilorine, hydrogen fluoride, hydrogen chloride, ammonia, chloropicrin, gasoline lead additives, vinyl cliloridc. and benzene. Hiis chapter addresses the process application of some chemicals from the foregoing list, as well as some others that are considered to be highly toxic hydrogen cyanide, sulfuric acid, and etliylene. Process considerations, physical and chemical properties, healtli effects, and metliods of manufacture of tliese chemicals are discussed in conjunction with potential causes of release. 

FIGURE 10.5. Optimal pulse sequence for production chromatography. Successive pulses of feed are introduced at intervals (T) such that == 4o,/r, fssSfo, + o ), a, = a /2. Components A and B are just resolved both within a given sample and between adjacent samples. 

From Eq. (10.1) it is clear that the requirement to minimize H(v)/v leads to the conclusion that the fluid velocity should be as large as possible. Under these conditions 

The particle size should be as small as possible to maximize k, but the benefits of the reduction in the column volume must be balanced against the greater energy costs arising from the higher pressure drop with small adsorbent particles. 

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The 3D inspection system has a number of measuring and report utilities that enables the user to easily find, analyse and report possible indications in the test object. As an example, a moveable 2D projection view plane can be moved along e.g, the welding geometry dynamically updating the content of the 2D projection view window. Indications can be measured using any referenee co-ordinate system and the results and screen dumps can automatically be dumped in report files suited for later import into a word processing application. 

Kuhni contacters (Eig. 15e) have gained considerable commercial application. The principal features are the use of a shrouded impeller to promote radial discharge within the compartments, and a variable hole arrangement to allow flexibility of design for different process applications. Columns up to 5 m in diameter have been constmcted (176). Description and design criteria for Kuhni extraction columns have been reported (177,178). 

Using 2eohte catalysts, the NO reduction takes place inside a molecular sieve ceramic body rather than on the surface of a metallic catalyst (see Molecularsieves). This difference is reported to reduce the effect of particulates, soot, SO2/SO2 conversions, heavy metals, etc, which poison, plug, and mask metal catalysts. ZeoHtes have been in use in Europe since the mid-1980s and there are approximately 100 installations on stream. Process applications range from use of natural gas to coal as fuel. Typically, nitrogen oxide levels are reduced 80 to 90% (37). 

In chemical process applications, one-dimensional gas flows through nozzles or orifices and in pipelines are the most important apphcations of compressible flow. Multidimensional external flows are of interest mainly in aerodynamic applications. 

Transfer function models are linear in nature, but chemical processes are known to exhibit nonhnear behavior. One could use the same type of optimization objective as given in Eq. (8-26) to determine parameters in nonlinear first-principle models, such as Eq. (8-3) presented earlier. Also, nonhnear empirical models, such as neural network models, have recently been proposed for process applications. The key to the use of these nonlinear empirical models is naving high-quality process data, which allows the important nonhnearities to be identified. 

Of these, the first option is the most commonly used in process applications. 

Pump shall he designed to operate satisfactorily with a reasonable service life when operated either intermittently or continuously in typical process applications. 

Process Applications The production of esters from alcohols and carboxylic acids illustrates many of the principles of reactive distillation as applied to equilibrium-limited systems. The equilibrium constants for esterification reactions are usually relatively close to unity. Large excesses of alcohols must be used to obtain acceptable yields with large recycles. In a reactive-distiUation scheme, the reac-... 

Droplet Breakup—High Turbulence This is the dominant breakup mechanism for many process applications. Breakup results from local variations in turbulent pressure that distort the droplet... 

These figures represent the usual ranges of design for water-treatment applications. For chemical-process applications, allowable flow rates are generally somewhat lower than the maximums shown, and hed depths are usually somewhat greater. 

Although intended primarily for air-conditioning applications, these units have been successfully applied to the collection of relatively nonconducting mists such as oil. However, other process applications... 

Folding is defined in Background and Definitions and is a significant problem in most process applications, and somewhat of a problem in most water applications. RO membranes may be fouled by sparingly soluble sealants which supersaturate at the membrane. 

Aromatic polyamide (aramid) membranes are a copolymer of 1-3 diaminobenzene with 1-3 and 1-4 benzenedicarboxylic acid chlorides. They are usually made into fine hollow fibers, 93 [Lm outer diameter by 43 [Lm inner diameter. Some flat sheet is made for spirals. These membranes are widely used for seawater desalination and to some extent for other process applications. The hollow fibers are capable of veiy high-pressure operation and have considerably greater hydrolytic resistance than does CA. Their packing density in hoUow-fiber form makes them veiy susceptible to colloidal fouling (a permeator 8 inches in diameter contains 3 M fibers), and they have essentially no resistance to chlorine. 

The primaiy purpose of materials selection is to provide the optimum equipment for a process application in terms of materials of construction, design, and corrosion-control measures. Optimum here means that which comprises the best combination of cost, life, safety, and reliability. 

Actually, in many cases strength and mechanical properties become of secondaiy importance in process applications, compared with resistance to the corrosive surroundings. All common heat-resistant alloys form oxides when exposed to hot oxidizing environments. Whether the alloy is resistant depends upon whether the oxide is stable and forms a protective film. Thus, mild steel is seldom used above 480°C (900°F) because of excessive scaling rates. Higher temperatures require chromium (see Fig. 28-25). Thus, type 502 steel, with 4 to 6 percent Cr, is acceptable to 620°C (I,I50°F). A 9 to 12 percent Cr steel will handle 730°C (I,350°F) 14 to 18 percent Cr extends the limit to 800°C (I,500°F) and 27 percent Cr to I,I00°C (2,000°F). 

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