Energy in drying

Developments in the carbonizing of fabric (77) have been aimed at reducing the volume of acid used (78,79), in order to reduce energy in drying and save neutralization costs, and at the use of generally available textile processing equipment, eg, the padmangle, for appHcation of the acid in a pad-dry-bake process (80). 

The efficiency of utilization of PAR was calculated as the quotient of chemically bound energy in dry mass (in MJ) and absorbed photosynthetically active radiation (in MJ). 

Fig. 3. Effect of feed moisture content on energy available for synfuel production. Assumes feed has a heating value of 11.63 MJ /kg (5000 Btu/lb) dry. A, 0% moisture in dried feed B, 30% moisture in dried feed. For example, reduction of an initial moisture content of 70 wt % by thermal drying to 30% moisture content requites the equivalent of 37% feed energy content and leaves 63% feed energy available for SNG production.

Infrared and Microwave Inks. These ate inks which have been formulated to absorb these radiant energies. The energy causes the inks to heat and dry through the partial evaporation of solvent. Absorption of the ink into a porous substrate can also be part of the overall drying mechanism with these inks. They have not found wide commercial success due to the variabiHty of the it absorption with ink color and the energy inefficiency of microwave systems in drying nonwater-based inks. 

Simultaneous heat and mass transfer also occurs in drying processes, chemical reaction steps, evaporation, crystallisation, and distillation. In all of these operations transfer rates are usually fixed empirically. The process can be evaluated using either the heat- or mass-transfer equations. However, if the process mechanism is to be fully understood, both the heat and mass transfer must be described. Where that has been done, improvements in the engineering of the process usually result (see Process energy conservation). 

Coke Production. Coking coals are mainly selected on the basis of the quaUty and amount of coke that they produce, although gas yield is also considered. About 65—70% of the coal charged is produced as coke. The gas quaUty depends on the coal rank and is a maximum, measured in energy in gas per mass of coal, for coals of about 89 wt % carbon on a dry, mineral matter-free basis, or 30% volatile matter. 

One further effect of the formation of bands of electron energy in solids is that the effective mass of elecuons is dependent on the shape of the E-k curve. If dris is the parabolic shape of the classical free electron tlreoty, the effective mass is the same as tire mass of the free electron in space, but as tlris departs from the parabolic shape the effective mass varies, depending on the curvature of tire E-k curve. From the dehnition of E in terms of k, it follows that the mass is related to the second derivative of E widr respect to k tlrus... 

In dry oxidation we quantified the tendency for a material to oxidise in terms of the energy needed, in kj mol of O2, to manufacture the oxide from the material and oxygen. Because wet oxidation involves electron flow in conductors, which is easier to measure, the tendency of a metal to oxidise in solution is described by using a voltage scale rather than an energy one. 

Figure 23.3 shows the voltage differences that would just stop various metals oxidising in aerated water. As we should expect, the information in the figure is similar to that in our previous bar-chart (see Chapter 21) for the energies of oxidation. There are some differences in ranking, however, due to the differences between the detailed reactions that go on in dry and wet oxidation. 

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