Solids heating

Cobali [[) oxide, CoO. Olive green solid (heat on Co(OH)2 or cobalt(Il) oxyacid salt in absence of air) with NaCl structure. 

Catalytic cracking is a key refining process along with catalytic reforming and alkylation for the production of gasoline. Operating at low pressure and in the gas phase, it uses the catalyst as a solid heat transfer medium. The reaction temperature is 500-540°C and residence time is on the order of one second. 

The chlorine and ethane are brought together in a fluid bed of finely divided, inert, solid heat-transfer medium, eg, sand, at 380—440°C the linear velocity of the gas is sufficient to maintain the finely divided solid in suspension within the reactor (26). 

Example 15 Estimate Solid Heat Capacity of Dinenzothiophene.. . ... 

Solid Heat Capacity Solid heat edacity increases with increasing temperature, with steep rises near the triple point for many compounds. When experimental data are available, a simple polynomial equation in temperature is often used to correlate the data. It should be noted that step changes in heat capacity occur if the compound undergoes crystalline state changes at mfferent temperatures. 

There are no reliable prediction methods for solid heat capacity as a function of temperature. However, the atomic element contribution method of Hurst and Harrison,which is a modification of Kopp s Rule, provides estimations at 298.15 K and is easy to use ... 

Cps = solid heat capacity at 298.15 K, J/mol K n = number of different atomic elements in the compound N, = number of atomic elements i in the compound Agi = numeric value of the contribution of atomic element i found in Table 2-393... 

Example 15 Estimate solid heat capacity of dibenzothiophene, Ci2HsS. The required atomic element contributions from Table 2-393 are C = 10.89, H = 7.56, and S = 12.36. Substituting in Eq. (2-63) ... 

TABLE 2-393 Atomic Element Contributions to Estimate Solid Heat Capacity at 298.15 K... 

Horizontal-Tank Type This type (Fig. ll-56a) is used to transfer heat for melting or cooking diy powdered solids, rendering lard from meat-scrap solids, and drying divided solids. Heat-transfer coefficients are 17 to 85 W/(m °C) [3 to 15 Btu/(h fF °F)] for drying and 28 to 140 W/(m °C) [5 to 25 Btu/(h fF °F)] for vacuum and/or solvent recovery. 

Direct contacting of hot gases with the solids is employed for solids heating and vapor removal. 

When a gas reacts with a solid, heat will be transfened from the solid to the gas when the reaction is exothermic, and from gas to solid during an endothermic reaction. The energy which is generated will be distributed between the gas and solid phases according to the temperature difference between the two phases, and their respective thermal conductivities. If the surface temperature of the solid is T2 at any given instant, and that of the bulk of the gas phase is Ti, the rate of convective heat transfer from the solid to the gas may be represented by the equation... 

Heat transfer between gas and sohds is exceedingly hard to measure because it is so rapid. Although the coefficient is low, the available surface area and the relative specific heat of solid to gas are so large that temperature equilibration occurs almost instantaneously. Experiments on injection of argon plasmas into fluidized beds have shown quenching rates of up to fifty million degrees Kelvin per second. Thus, in a properly designed bed, gas to solids heat transfer is not normally a matter of concern. 

The value of the coefficient will depend on the mechanism by which heat is transferred, on the fluid dynamics of both the heated and the cooled fluids, on the properties of the materials through which the heat must pass, and on the geometry of the fluid paths. In solids, heat is normally transferred by conduction some materials such as metals have a high thermal conductivity, whilst others such as ceramics have a low conductivity. Transparent solids like glass also transmit radiant energy particularly in the visible part of the spectrum. 

In practice, the process regime will often be less transparent than suggested by Table 1.4. As an example, a process may neither be diffusion nor reaction-rate limited, rather some intermediate regime may prevail. In addition, solid heat transfer, entrance flow or axial dispersion effects, which were neglected in the present study, may be superposed. In the analysis presented here only the leading-order effects were taken into account. As a result, the dependence of the characteristic quantities listed in Table 1.5 on the channel diameter will be more complex. For a detailed study of such more complex scenarios, computational fluid dynamics, to be discussed in Section 2.3, offers powerful tools and methods. However, the present analysis serves the purpose to differentiate the potential inherent in decreasing the characteristic dimensions of process equipment and to identify some cornerstones to be considered when attempting process intensification via size reduction. 

The share of solid wall material is typically much higher than in macroscopic equipment. Hence solid heat transfer plays an important role and has to be ac-coimted for when designing micro reactors. 

T TSJ, °F Crud thickness, mil Crud solidity Heat flux, Btu/hr ft2 ... 

One method of improving G/S contacting consists of showering solids in dilute suspension from the top into an upflowing gas stream. Experiments verified that gas/solid heat transfer coefficient for such a system is essentially the same as for the discrete particles, and that pressure drop for gas flow is extremely low. 

Fig. 1 Melting curve for a solid heated at a constant rate, with continual monitoring of the temperature being conducted during the process.

A double-effect forward-feed evaporator is required to give a product consisting of 30 per cent crystals and a mother liquor containing 40 per cent by mass of dissolved solids. Heat transfer coefficients are 2.8 and 1.7 kW/m2 K in the first and second effects respectively. Dry saturated steam is supplied at 375 kN/m2 and the condenser operates at 13.5 kN/m2. 

The right panel of Figure 1.3 displays the radial function obtained by Fourier transformation of the -weighed background-subtracted EXAFS data from the solid heated to 420°C [31], This spectrum shows two major peaks, one at about 1.5 A associated with backscattering from O neighbors, and a second at 3 A related to the Nb-Mo pairs. The measured distances are consistent with a combination of niobium oxo species and heteropolymolybdate fragments, presumably the catalytically active phase. 

Dry beans (Phaseolus vulgaris), represented by the commercial classes of navy, pinto and black were used to produce flour fractions at the Food Protein Research and Development Center, Texas A M University. Beans were dry-roasted under selected process conditions in a gas fired solid-to-solid heat exchanger, dehulled by air aspiration, pin-milled and air-classified to obtain four flour fractions. These fractions included whole, hulls, high protein, and high starch flours. 

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