Low-temperature system

The design of low-temperature systems, whether mechanical expansion turbine or throtding valve, is a special technology and cannot be adequately covered in this chapter. References on the subject include 20, 21, 23, 60. 

Where high temperatures are required (e.g. for process work) and lower temperatures for space heating, it is desirable to use flash steam recovery from the high-temperature condensate to feed into the low-temperature system, augmented as required by reduced pressure live steam. 

Distillation sequencing. The separation of homogeneous nonazeotropic mixtures using distillation usually offers the degree of freedom to choose the distillation sequence. The choice between different sequences can be made on the basis of total vapor load, energy consumption, refrigeration shaft power for low-temperature systems, or total cost. However, there is often little to choose between the best few sequences in terms of such measures of system performance if simple distillation columns are used. 

Woods T.L. (1988) Calculated solution solid relations in the low temperature system Ca0-Mg0-Fe0-C02-H20. Ph.D. dissertation, Univ. South Florida. 

For the chromatographic process, we discuss Fermi-Dirac s distribution function for characterizing the energetics of a solid surface, because it is known that this distribution is very powerful, especially, for the conditions such as weakly van der Waals attraction and relatively low temperature systems, as compared with B.E and/or M.B distributions [215]. 

Generally, high-temperature systems operate at temperatures above 1000°F (500-600°C), whereas low-temperature systems operate below 1000°F. High-temperature processes include (1) incineration, (2) electric pyrolysis, and (3) in situ vitrification. Low-temperature treatment systems include (1) soil roasting, (2) low-temperature incineration, (3) low-temperature thermal aeration, (4) infrared furnace treatment, and (5) low-temperature thermal stripping. 

High-temperature treatment systems involve destruction of contaminant(s) through complete oxidation, whereas low-temperature systems increase the rate of phase transfer (e.g., liquid phase to gaseous phase), and thus encourage contaminant partitioning from soil. Some of the disadvantages of heat treatment include its high cost and its ineffectiveness with some contaminants (e.g., low volatilization potential or incineration actually produces more toxic substances). 

Are the C.C. the expression of an ordering tendency, related to the movement towards minimum potential energy of complex low temperature systems, which can account both for the genesis... 

Many recent reports on the radiolysis of organic halogen compounds have involved studies of solid state or very low temperature systems (refs. 745, 781, 787, 858, 867, 906, and the use of pulsed techniques - - - - - - . Studies on species adsorbed on silica gel have also been made. The nature of intermediate species and the mechanism of scavenger action have been discussed by a number of investigators (see, for example, references 749, 906, 974, 981). 

Woods, T. L., and R. M. Carrels, 1992, Calculated aqueous-solution-solid-solution relations in the low-temperature system CaO-MgO-FeO-C02-H20. Geochim. Cosmochim. Acta 56 3031-43. 

Refrigeration systems are extensively used in the chemical industries in low temperature processes such as liquefaction of natural gas, ethylene purification and cryogenic air separation. In these kinds of low temperature systems, heat is rejected from the process by refrigeration to heat sinks being other process streams or refrigeration systems at the expense of mechanical work. The refrigeration systems employed are complex, and energy and capital intensive, and therefore, play a critical role in the overall plant economics. 

The need to convert chemical energy to electricity, efficiently and at low temperature, has increased the development of materials with electrocatalytic activity toward multi-electron charge transfer. Reactions of technical relevance are, for example, cathodic processes, such as the oxygen reduction reaction (ORR),3 13 and anodic processes, such as small organics (R-OH, where R = CH3-3-12 or CH3CH-13-17) and sugars.18-20 These complex electrochemical processes are useful in low-temperature systems such as the direct methanol FC (DMFC) or biofuel cell systems. 

The low-temperature systems heat the contaminated material to increase the rate of contaminant volatilization and cause the organics to partition to the vapor phase. The general sequence of steps for low-temperature thermal treatment is shown in Figure 11.1. For explosives contaminants, the removal mechanism will be a combination of decomposition and volatilization. The organic-laden off-gas stream is collected and processed. Low-temperature systems have been demonstrated for remediation of soil contaminated with a variety of volatile and semivolatile organic compounds. 

High-temperature thermal treatment will mineralize the explosives contaminants to form mainly C02 and H20. The fate of the explosives contaminants is not as clear in the lower temperature thermal desorption case. Low-temperature thermal treatment involves some decomposition, but volatilization is the main removal mechanism. All of the low-temperature systems provide for methods to capture the volatilized organics from the off-gas. Residuals from the off-gas treatment may be organic liquid and/or spent carbon sorbents. These residuals will require further treatment or disposal. The low-temperature techniques provide good protection of human health and the environment by either destroying the contaminants or concentrating them in a controlled manner for further processing. 

Chemical kinetic considerations are another criterion. For example, a model can be eliminated if it requires the precipitation of a mineral that is known not to precipitate readily in low temperature systems. 

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