Extraction heat transfer

Because the properties (melting point, density, viscosity) and behavior of the ILs can be adjusted to suit an individual synthesis type, extraction, heat transfer, or electrochemistry problems, they can truly be described as designer solvents. 

Major applications of solvents are found in paints/ coating and cleaning applications. However, they are also widely used in chemical processes (as solvent as well as raw material), inks, solvent extraction, heat transfer systems, and electrochemistry. Some solvents are also used as catalysts in a chemical reaction. 

The pure organic chemical produced in the greatest quantity per year is sucrose sugar. The process of converting raw sugarcane or beets into uniform-size sucrose crystals involves extraction, heat transfer, multieffect evaporation, adsorption, crystallization, filtration, and drying—not to mention mass transfer and instrumentation. 

Most of the trichloroethylene produced is used for metal degreasing. Other important uses are in the scouring of wool and as an extractive solvent, e.g. for olive and soya bean oils. Minor uses are as a heat transfer medium, anaesthetic, insecticide and fumigant, paint remover and fire extinguisher. 

Scraped-surface exchangers are particularly suitable for heat transfer with crystalhzation, heat transfer with severe folding of surfaces, heat transfer with solvent extraction, and heat transfer of high-viscosity fluids. They are extensively used in paraffin-wax plants and in petrochemical plants for ciystallization. 

Coughlin and von Berg [Chem. Eng. Sci., 21, 3 (1966)]. Continuous heat transfer and extraction of ethylbiityric acid between kerosine and water unbaffled vessel, Pump-Mix design (Fig. 15-28). Interfacial area measured. 

Cooling or heating a liquid hy direct contact with another Although liquid-hquid-contact operations have not been used widely for heat transfer alone, this technique is one of increasing interest. Applications also include cases in which chemical reaction or hquid extraction occurs simultaneously... 

Equipment suitable for reactions between hquids is represented in Fig. 23-37. Almost invariably, one of the phases is aqueous with reactants distributed between phases for instance, NaOH in water at the start and an ester in the organic phase. Such reac tions can be carried out in any kind of equipment that is suitable for physical extraction, including mixer-settlers and towers of various kinds-, empty or packed, still or agitated, either phase dispersed, provided that adequate heat transfer can be incorporated. Mechanically agitated tanks are favored because the interfacial area can be made large, as much as 100 times that of spray towers, for instance. Power requirements for L/L mixing are normally about 5 hp/1,000 gal and tip speeds of turbine-type impellers are 4.6 to 6.1 i7i/s (15 to 20 ft/s). 

Economizers Economizers improve boiler efficiency by extracting heat from the discharged flue gases and transferring it to feedwater, which enters the steam generator at a temperature appreciably lower than the saturation-steam temperature. 

This design has a number of tubes embedded inside the turbine biade to provide ehanneis for steam. In most cases these tubes are constructed from copper for good heat-transfer conditions. Steam injection is becoming the prime source of cooiing for gas turbines in a combined cycie appiication. The steam, which is extracted from the exit of the HP Turbine, is sent through the nozzie biades, where the steam is heated, and the biade metai temperature decreased. The steam is then injected into the flow stream entering the IP steam turbine. This increases the overaii efficiency of the combined cycie. 

There are two basic types of packed-bed reactors those in which the solid is a reactant and those in which the solid is a catalyst. Many e.xaniples of the first type can be found in the extractive metallurgical industries. In the chemical process industries, the designer normally meets the second type, catalytic reactors. Industrial packed-bed catalylic reactors range in size from units with small tubes (a few centimeters in diameter) to large-diameter packed beds. Packed-bed reactors are used for gas and gas-liquid reactions. Heat transfer rates in large-diameter packed beds are poor and where high heat transfer rates are required, Jluidized beds should be considered. ... 

Operations such as blending, solids-suspension, dissolving, heat transfer and liquid-liquid extraction are typical of systems requiring high flow relative to turbulence, while gas-liquid reactions and some liquid-liquid contacting require high turbulence relative to flow. The case of (1) 100% of suspension—requires head to keep particles suspended and (2) 100% uniformity of distribution of particles—requires head for suspension plus flow for dis-tiibution. 

Where the product shape is irregular, the only way to extract its heat will be by using a cold fluid surrounding it. The most common of these is air. The air temperature will be of the order of - 40°C and the air speed over the product will be high, to get good heat transfer. 

With ceiling inlet and extract systems, the opportunity is presented to remove heat from light troughs. This can reject a proportion of the cooling load, possibly as high as 20%, in the exhaust air. The recirculated air is also warmer, improving heat transfer at the cooling coil. (See also Example 26.3.)... 

Looking at the overall heat transfer surfaces available in a large boiler plant, the economizer and air heater may typically provide 50% of the total heating surfaces yet extract only 15% of the available heat energy. 

In modem, packaged horizontal FT boilers, the furnace is the most important heat-transfer component, typically providing 50 to 60% of the total heat transfer from only 30% or so of the total available heating surfaces. This level of heat transfer, coupled with the additional heat extraction obtained by the various multiple-pass designs (four passes is a practical maximum) provide efficiencies of 80 to 83% GCV. As a result, there generally is little additional benefit to be obtained from the use of economizers or air heaters, especially when using oil-fired boilers, which can operate at up to a 3% or so higher efficiency level compared to gas-fired units. 

Economizers are heat transfer tube bundles that preheat MU water or FW flowing within the tubes by extracting waste heat from the flue gas during its exit path to the stack. They typically account for approximately 10% of the total boiler heat transfer surfaces, while absorbing only 7% of the total heat generated in the boiler system. 

Liquid-gas-solids mixing 275 Liquid-liquid extraction, mass transfer 599 Liquid metals, heat transfer 523 meters 269... 

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