Alternatives to Heat

Heat is typically used to bring a solution to its vapor point (boiling) so that it may be distilled, reduced, or purified. Although this procedure works in most cases, not all solutions can be safely heated. Some materials break down in heated conditions, and some do so violently. Fortunately, there are two alternative methods to 

Place a Dewar (filled with an appropriate coolant) over this container to collect the solvent from the flask on the left 

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The alternative to using a dish is to form the material into a bag and this so-called pouch or sachet method is often used for plastics films. The advantages are that a larger surface area is exposed, leaks through the wax seal are eliminated, and the conditions are more similar to packaging applications. It is less attractive for rubbers because they are not often used in that sort of packaging application and an alternative to heat sealing the pouch would be necessary. 

Oil-in-water emulsions provide a cost-effective alternative to heated pipelines or diluents for transportation of heavy crude oil or bitumen. A typical ""transport emulsion is composed of 70% crude oily 30% aqueous phase, and 500-2000 ppm of a stabilizing surfactant formulation. The resulting emulsion has a viscosity in the 50-200-cP range at pipeline operating conditions. Nonionic surfactants have the advantage of relative insensitivity to the salt content of the aqueous phase. The ethoxylated alkylphenol family of surfactants has been used successfully for the formation of stable emulsions that resist inversion. Correlations have been developed for prediction of emulsion viscosity as a function of emulsion life and process conditions. The cost of stabilizing surfactants is estimated at 0.50 to 1.00 per barrel of crude oil for a transportation distance of200 to 400 miles. 

Cheek and Linnenbom (1) found for the spectrophotometric method standard deviations of the order of 10% based on a G-value of 4.9. For the NaOH-titration method they emphasized the importance of effective removal of C02 from the irradiated solution. As an alternative to heating they proposed to remove the C02 by purging the solution with a stream of H20-saturated, C02-free air. By titration they found the G-value to be 4.4 for a 75 mM oxalic-acid solution. 

Emulsions can be used in pipeline transportation of heavy crude oils [247]. This is a cost-effective alternative to heated pipelines. O/w emulsions are composed of 30% aqueous phase and 70% crude oil and have a viscosity range from 50 to 200 cP. A mixture of ethoxylated alkylphenols was used for the emulsion stabilisation. Emulsion stability is provided in a solution containing 1.7% NaCl at total consumption of the mixture of 1500 ppm. The emulsion is prepared at 50 - 70 °C. For the subsequent demulsification, it is necessary to raise the temperature up to 100 °C and to add a demulsifier. 

Cold-seal adhesives are members of a general category sometimes termed coadhesive substances that have a great tendency to stick to themselves, but often not to much else. Cold-seal adhesives are typically based on natural rubber, which has been applied in a latex (suspension in water) form. One major application is in plastic packaging for chocolate candy. The seal between the two parts of the wrap can then be activated with pressure, as an alternative to heat-sealing, which is problematic with the low-melting temperature candy. 

The relatively low cost of coal when compared to other energy sources gives coal-water slurries a competitive alternative to heating oil and gas and a relatively environmentally friendly fuel for heat and power generation. One side effect of the coal-water slurry making process is the separation of non-carbon material (such as pyrite and other inorganic mineral matter) mixed with the coal before treatment. This results in a reduction of ash yield to as low as 2% for the treated CWSF. 

Microwave curing of epoxies is an effective alternative to heat curing because it heats through the sample and produces uniform curing as well as more rapid curing curing time is reduced by a factor of 10 or more. However, epoxy modified by addition of 25% polysulfone was found to have lowered by as much as 25 °C when compared with comparable thermally cured epoxy. 

Alternatives to heat generating fuel movements include the use of dummy assemblies, shield plugs, targets or other assemblies manipulated in a manner to simulate fuel movements. 

Example 6.5 The stream data for a heat recovery problem are given in Table 6.7. A problem table analysis for AT , = 20°C results in the heat cascade given in Table 6.8. The process also has a requirement for 7 MW of power. Two alternative combined heat and power schemes are to be compared economically. 

Steam is injected into a reservoir to reduce oil viscosity and make it flow more easily. This technique is used in reservoirs containing high viscosity crudes where conventional methods only yield very low recoveries. Steam can be injected in a cyclic process in which the same well is used for injection and production, and the steam is allowed to soak prior to back production (sometimes known as Huff and Puff). Alternatively steam is injected to create a steam flood, sweeping oil from injectors to producers much as in a conventional waterflood. In such cases it is still found beneficial to increase the residence (or relaxation) time of the steam to heat treat a greater volume of reservoir. 

The heat of adsorption is an important experimental quantity. The heat evolution with each of successive admissions of adsorbate vapor may be measured directly by means of a calorimeter described by Beebe and co-workers [31]. Alternatively, the heat of immersion in liquid adsorbate of adsorbent having various amounts preadsorbed on it may be determined. The difference between any two values is related to the integral heat of adsorption (see Section X-3A) between the two degrees of coverage. See Refs. 32 and 33 for experimental papers in this area. 

Direct dynamics attempts to break this bottleneck in the study of MD, retaining the accuracy of the full electronic PES without the need for an analytic fit of data. The first studies in this field used semiclassical methods with semiempirical [66,67] or simple Hartree-Fock [68] wave functions to heat the electrons. These first studies used what is called BO dynamics, evaluating the PES at each step from the elech onic wave function obtained by solution of the electronic structure problem. An alternative, the Ehrenfest dynamics method, is to propagate the electronic wave function at the same time as the nuclei. Although early direct dynamics studies using this method [69-71] restricted themselves to adiabatic problems, the method can incorporate non-adiabatic effects directly in the electionic wave function. 

Thermal Theory. The thermal approach to flame retardancy can function in two ways. Eirst, the heat input from a source may be dissipated by an endothermic change in the retardant such as by fusion or sublimation. Alternatively, the heat suppUed from the source maybe conducted away from the fibers so rapidly that the fabric never reaches combustion temperature. 

Induction furnaces utilize the phenomena of electromagnetic induction to produce an electric current in the load or workpiece. This current is a result of a varying magnetic field created by an alternating current in a cod that typically surrounds the workpiece. Power to heat the load results from the passage of the electric current through the resistance of the load. Physical contact between the electric system and the material to be heated is not essential and is usually avoided. Nonconducting materials cannot be heated directiy by induction fields. 

Air preheat temperature requirements of 2250—2300 K are anticipated for natural gas-fired systems, and about 2000 K for oil or coal-fired systems (11). Use of 32—40% oxygen enrichment lowers the preheat temperature requirement to a moderate 900—1000 K, which can be attained with conventional metal-type tubular heat exchangers. Depending on the cost of oxygen, this is a viable alternative to the use of separately fired high temperature preheaters. 

Aqueous dispersions are alternatives to solutions of Hquid and soHd resins. They are usuaUy offered in 50% soHds and may contain thickeners and cosolvents as stabilizers and to promote coalescence. Both heat-reactive (resole) and nonheat-reactive (novolak) systems exist that contain unsubstituted or substituted phenols or mixtures. A related technology produces large, stable particles that can be isolated as discrete particles (44). In aqueous dispersion, the resin stmcture is designed to produce a hydrophobic polymer, which is stabilized in water by an interfacial agent. 

Other energy considerations for cooling towers include the use of two-speed or variable-speed drives on cooling-tower fans, and proper cooling-water chemistry to prevent fouling in users (see Water, industrial water treatment). Air coolers can be a cost-effective alternative to cooling towers at 50—90°C, just below the level where heat recovery is economical. 

Styrene—maleic anhydride (SMA) copolymers are used where improved resistance to heat is required. Processes similar to those used for SAN copolymers are used. Because of the tendency of maleic anhydride to form alternating copolymers with styrene, composition drift is extremely severe unless the polymerization is carried out in CSTR reactors having high degrees of back-mixing. 

Atomic absorption spectroscopy is an alternative to the colorimetric method. Arsine is stiU generated but is purged into a heated open-end tube furnace or an argon—hydrogen flame for atomi2ation of the arsenic and measurement. Arsenic can also be measured by direct sample injection into the graphite furnace. The detection limit with the air—acetylene flame is too high to be useful for most water analysis. 

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