High temperature operation

The main justification for diesel fuel desulfurization is related to particulate emissions which are subject to very strict rules. Part of the sulfur is transformed first into SO3, then into hydrated sulfuric acid on the filter designed to collect the particulates. Figure 5.21 gives an estimate of the variation of the particulate weights as a function of sulfur content of diesel fuel for heavy vehicles. The effect is greater when the test cycle contains more high temperature operating phases which favor the transformation of SO2 to SO3. This is particularly noticeable in the standard cycle used in Europe (ECE R49). 

Accidents. In an industry that has massive equipment, high temperature operations, and many moving objects, the potential for accidents is always present. Safety is taken seriously and is the direct responsibiUty of the plant superintendent. Accidents do occur, although in the United States the rate in the steel industry compares favorably with heavy industry as a whole. 

AI + 3O2 +2H20r 2 ALOvH.O aluminum—air 2 2 233 1.6 360 250 high temperature operation circulating electrolyte, low cost, low energy efficiency, replaceable negative electrode... 

These systems, commercially known as Tberminol VP or Dowtherm A, differ from steam in some key areas which can result in operating problems unless handled properly in design (14). The low pressure—high temperature operation means that the AT/AP ratio at saturation is quite high for example, at 315°C the ratio is 25 times that of steam. This means that a pressure drop that would be nominal in a steam system (10 kPa (0.1 atm)), can not be tolerated if precise temperature control is needed. 

Thermal oxidization devices are widely used, and generally provide a high degree of assurance that the process oxidizes the material in the exhaust gas. The high temperature operation causes other problems, however, especially compared to alternatives such as catalytic oxidation. The thermal oxidation... 

While theoretical compressor power requirements are reduced slightly by going to lower evaporating temperatures, the volume of vapor to be compressed and hence compressor size and cost increase so rapidly that low-temperature operation is more expensive than high-temperature operation. The requirement of low temperature for fruit-juice concentration has led to the development of an evaporator... 

In tunnel equipment, the solids are usually heated by direc t contact with hot gases. In high-temperature operations, radiation from walls and refractory lining may be significant also. The air in a direc t-heat unit may be heated directly or indirectly by combustion or, at temperature below 475 K, by finned steam cods. 

Direct rotary kiln. This is a metal cyhnder lined on the interior with insulating block and/or refractory brick. It is suitable for high-temperature operations. 

Gravity vessels are suitable for low-, medium-, and high-temperature operation in the last case, the housing will be lined completely with refrac tory brick. Dust-recoveiy equipment is minimized in this type of operation since the bed actually performs as a dust col-lec tor itself, and dust in the bed will not, in a successful application, exist in large quantities. 

The fluids are also used in shock absorbers, hydraulic fluids, dashpots and other damping systems designed for high-temperature operation. 

During the high-temperature operations, intermolecular hydrogen transfer reactions occur, transforming some indene to indane. The high indane concentration in the resin feedstock causes low yield and poor quality in the polymerization process. The indene loss can be reduced by decreasing the temperature and the residence time during distillation. 

Trays in multiple-tray settling chamber may warp during high-temperature operations. 

Operating problems. High-temperature operations create high maintenance requirements and can reduce equipment reliability. 

Hydraulic oils need to be of the highest oxidation stability, particularly for high-temperature operations, because... 

A type of high-temperature operation, ion-exchange plant. It can remove contaminants from condensate by both exchange and filtration mechanisms. 

Methane decomposition is the most important reaction step, especially for high-temperature operations. Thus, carbon deposition occurs commonly and is a major problem, especially with the Ni-based anode. However, carbon deposition may not deactivate the anode [10, 11]. In some cases, the anode activity increases due to carbon deposition whieh increases the electrical conductivity of the low-Ni-content anode [II]. 

It should be possible to reduce the cost of monoliths by making use of the experience of manufacturers of modern heat exchangers, which contain similar structures. It should also be noted that the high cost of monoliths is in part explained by the fact that they are mostly designed to meet demands of high-temperature operation. 

There are materials-of-construction problems associated with high-temperature operation. The main problem is creep. 

Low temperature. Low-temperature processes (below 0°C) contain large amounts of fluids kept in the liquid state by pressure and/or low temperature. If for any reason it is not possible to keep them under pressure or keep them cold, then the liquids will begin to vaporize. If this happens, impurities in the fluids are liable to precipitate from solution as solids, especially if equipment is allowed to boil dry. Deposited solids may not only be the cause of blockage but also in some cases the cause of explosions. It is necessary, therefore, to ensure that the fluids entering a low-temperature plant are purified. A severe materials-of-construction problem in low-temperature processes is low-temperature embrittlement. Also, in low temperature as in high-temperature operations, the equipment is subject to thermal stresses, especially during start-up and shutdown. 

Drilling fluids usually contain water as the primary component. However, oil-based muds may be used for high temperature operations and for drilling highly water-sensitive formations. Oil-based muds are of two types, oil-external emulsions containing as much as 50% water in the internal phase or an oil-based fluid containing little if any water. 

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