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Membrane and Desalination Technologies - TCE Moodle Website

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Adsorption <strong>Desalination</strong>: A Novel Method 427<br />

Fig. 9.25. Regenerative heat flows from the adsorber towers (extracted from patent document of Ng<br />

et al. (3)).<br />

The range of COPAD would be comparatively better than that of the “kettle-type” boiler or<br />

desalinator when the heat regenerative index, n, varies from 0.3 to 0.55. Between these<br />

values, the regeneration index “n” would have an optima where the water production is<br />

maximum <strong>and</strong> thus, a realistic operating point for the adsorption plant. For the water<br />

temperature of evaporator (that could be utilized by the regenerative processes), it should<br />

be equal or lower than the cooling tower temperature. However, the COP of the proposed<br />

heat-driven adsorption desalination plant is comparably better than that of the conventional<br />

“kettle” boiler, <strong>and</strong> it has the added advantage of much lower fouling at the evaporator.<br />

For a heat source temperature less than 85 C <strong>and</strong> to assist the designer in sizing the largescale<br />

AD plants, Figs. 9.26 <strong>and</strong> 9.27 provide the dimensions of the silo-type tower where the<br />

rate of heat input could be estimated with respect to the amount of silica gel used. For a<br />

packing density of silica gel of 700 kg/m 3 , the required tower height is estimated at different<br />

masses of silica gel <strong>and</strong> different tower diameters, namely, 3, 4, <strong>and</strong> 5 m, respectively.<br />

Similarly, the heat input required to operate such AD plants can be calculated by using the<br />

following relation:

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