Rare refining

We will give two examples of analysis of these components, bearing in mind that the distinction between condensable and noncondensable hydrocarbons rarely holds in actual refining streams, most of them producing both classes of hydrocarbons simultaneously. 

Pure iron is a silvery white, relatively soft metal and is rarely used commercially. Typical properties are Hsted in Table 1. Electrolytic (99.9% pure) iron is used for magnetic cores (2) (see Magnetic materials, bulk). Native metallic iron is rarely found in nature because iron which commonly exhibits valences of +2 and +3 combines readily with oxygen and sulfur. Iron oxides are the most prevalent form of iron (see Iron compounds). Generally, these iron oxides (iron ores) are reduced to iron and melted in a blast furnace. The hot metal (pig iron) from the blast furnace is refined in steelmaking furnaces to make steel... 

The end product is either cast as anodes for electrolytic refining or, rarely, as ingots for sale as fire-refined copper. A horizontal casting wheel with 12—32 horizontal molds is normally used for anode casing. Using continuous casting machines, the copper is cast as a continuous strip to be cut to the required anode shape (28). 

Materials of Construction The most common material of construction for heat exchangers is carbon steel. Stainless-steel construction throughout is sometimes used in chemical-plant service and on rare occasions in petroleum refining. Many exchangers are constructed from dissimilar metals. Such combinations are functioning satisfactorily in certain sei vices. Extreme care in their selection is required since electrolytic attack can develop. 

Biological fibers, such as can be formed by DNA and fibrous proteins, may contain crystallites of highly ordered molecules whose structure can in principle be solved to atomic resolution by x-ray crystallography. In practice, however, these crystallites are rarely as ordered as true crystals, and in order to locate individual atoms it is necessary to introduce stereochemical constraints in the x-ray analysis so that the structure can be refined by molecular modeling. 

Now you can reconsider the material balance equations by adding those additional factors identified in the previous step. If necessary, estimates of unaccountable losses will have to be calculated. Note that, in the case of a relatively simple manufacturing plant, preparation of a preliminary material-balance system and its refinement (Steps 14 and 15) can usefully be combined. For more-complex P2 assessments, however, two separate steps are likely to be more appropriate. An important rule to remember is that the inputs should ideally equal the outputs - but in practice this will rarely be the case. Some judgment will be required to determine what level of accuracy is acceptable, and we should have an idea as to what the unlikely sources of errors are (e.g., evaporative losses from outside holding ponds may be a materials loss we cannot accurately account for). In the case of high concentrations of hazardous wastes, accurate measurements are needed to develop cost-effective waste-reduction options. It is possible that the material balance for a number of unit operations will need to be repeated. Again, continue to review, refine, and, where necessary, expand your database. The compilation of accurate and comprehensive data is essential for a successful P2 audit and subsequent waste-reduction action plan. Remember - you can t reduce what you don t know is therel... 

Metal sulfides can be prepared in the laboratory or on an industrial scale by a number of reactions pure products are rarely obtained without considerable refinement and nonstoichiometric phases abound (p. 679). The more important preparative routes include ... 

The cleanliness of the surface produced by emulsifiable cleaners is rarely of a very high standard, and additional cleaning may well be necessary before further finishing operations. Success has been achieved, however, in the use of these products prior to some immersion phosphating operations, where the crystal growth can be quite refined due to the absence of the passivation effect often encountered with some heavy-duty alkali cleaners. The supplier of the phosphating solution should be asked to advise on the suitability of any particular cleaning/pretreatment combination. 

The impure copper from either process is refined electrolytically it is made into anodes and plated onto cathodes of pure copper. Other metals may be present in the impure copper and those with highly positive electrode potentials also are reduced. The rare metals—most notably, platinum, silver, and gold—obtained from the anode sludge are sold to recover much of the cost of the electricity used in the electrolysis. 

Silver, Ag, is rarely found as the metal. Most is obtained as a by-product of the refining of copper and lead, and a considerable amount is recycled through the photographic industry. Silver has a positive standard potential, and so it does not... 

A scientist s credo might be One measurement is no measurement. Thus, take a few measurements and divine the truth This is an invitation for discussions, worse yet, even disputes among scientists. Science thrives on hypotheses that are either disproven or left to stand in the natural sciences that essentially means experiments are re-mn. Any insufficiency of a model results in a refinement of the existing theory it is rare that a theory completely fails (the nineteenth-century luminiferous ether theory of electromagnetic waves was one such, and cold fusion was a more shortlived case). 

The following diagram, given as 6.8.5. on the next page, illustrates further phenomena regarding zone refining. The same situation seen in 6.8.4. occurs for the case at the bottom right of 6.8.5. except that the distribution coefficient is such that the impurity buildup is slower. Nevertheless, simple solid-solution for impurity systems is rarely the norm. The most prevalent case is that of Case III of 6.8.5. Limited solid solution occurs, and we get a two-phase system. 

Finally, it may be pointed out that none of the rare metals can be smelted directly from the ore. The concentrate must first be converted to a pure chemical compound which is utilized as the raw material for the production of the metal. The refractory rare metals are often obtained in the form of a powder or sponge. They are consolidated and refined by powder metallurgy techniques or by arc melting or by electron beam melting. In fact, the current refractory rare metals technology has been crucially dependent on the development of vacuum metallurgical techniques and processes. 

In this computer age, one may question why nobody would write a program that can solve for the roots with dead time accurately Someone did. There are even refined hand sketching techniques to account for the lag due to dead time. However, these tools are not as easy to apply and are rarely used. Few people use them because frequency response analysis in Chapter 8 can handle dead time accurately and extremely easily. 

From the conventional view of oil refining, a sulfur removal processes that yields H2S is preferred, as it is supposed to retain the maximum heating value of the desulfurized product. Notwithstanding, the application of anaerobic bacteria has rarely found opportunities in refining operations and only for the treatment of exhaust gas streams, containing sulfur species in the form of H2S, and usually by a biological combination with chemical treatments. Some of these examples will be discussed in Section 2.4 where bioprocesses for gas streams treatment are considered. 

Rarely will it be possible to draw conclusions directly from the raw data of analytical measurements and it is usual for some refinement of the data to be carried out. In its simplest form this could merely comprise background corrections, but it is often much more complex, requiring corrections for a number of factors as in mass spectrometry, X-ray fluorescence and electron probe microanalysis. More complex routines made available by computers include spectrum smoothing, stripping one component from a spectrum or making peak area measurements from chromatograms. 

Most of the kinetic models predict that the sulfite ion radical is easily oxidized by 02 and/or the oxidized form of the catalyst, but this species was rarely considered as a potential oxidant. In a recent pulse radiolysis study, the oxidation of Ni(II and I) and Cu(II and I) macrocyclic complexes by SO was studied under anaerobic conditions (117). In the reactions with Ni(I) and Cu(I) complexes intermediates could not be detected, and the electron transfer was interpreted in terms of a simple outer-sphere mechanism. In contrast, time resolved spectra confirmed the formation of intermediates with a ligand-radical nature in the reactions of the M(II) ions. The formation of a product with a sulfonated macrocycle and another with an additional double bond in the macrocycle were isolated in the reaction with [NiCR]2+. These results may require the refinement of the kinetic model proposed by Lepentsiotis for the [NiCR]2+ SO/ 02 system (116). 

The Hydrocarbon Processing Industry (HPI), has traditionally been reluctant to invest capital where an immediate direct return on the investment to the company is not obvious, as would any business enterprise. Additionally financial fire losses in the petroleum and related industries were relatively small up to about the 1950 s. This was due to the small size of facilities and the relatively low value of oil and gas to the volume of production. Until 1950, a fire or explosion loss of more than 5 million U. S. Dollars had not occurred in the refining industry in the USA. Also in this period, the capital intensive offshore oil exploration and production industry were only just beginning. The use of gas was also limited early in the century. Consequentially its value was also very low. Typically production gas was immediately flared or the well was capped and considered as an uneconomical reservoir. Since gas development was limited, large vapor explosions were relatively rare and catastrophic destruction from petroleum incidents was essentially unheard of. The outlays for petroleum industry safety features were traditionally the absolute minimum required by governmental regulations. The development of loss prevention philosophies and practices were therefore not effectively developed within the industry. 

In safety-critical systems, it is possible to document refinements precisely enough to perform automatic consistency checks on them. However, achieving this level of precision is rarely cost-effective, and we do not deal with that topic in this book. 

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