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5 <br /> L .# <br /> In the Cyclo-Purge System (CP) the air is circulated within a closed loop flow <br /> r° � path, consisting of VOC removal equipment at the surface (up to 98% removal), and <br /> well casing leading to and from the subsurface zone of contamination. The device <br /> used for contaminant removal is a heat pump, which simultaneously condenses the <br /> saturated VOC vapor mixture extracted from the ground and reheats the treated air <br /> which is returned to the subsurface zone of contamination or groundwater. -The <br /> elevated temperature of the injected air enhances the rate of VOC removal <br /> (evaporation) from the soil. <br /> Metal well-screens are installed exactly at the level where volatile contaminants <br /> are located in the vadose formation. The wells are used in two ways, each group <br /> consisting of one or more well-screens. One group is used for inigigion. of the heated <br /> air into the ground, and the other group for the extraction of the air/vapor mixture from <br /> the contaminated zone. The depth of well-screens is selected by the supervising <br /> engineer or geologist to direct the flow path, such that the air will pass through the <br /> contaminated zone. <br /> Heating the air enhances the rate of evaporation by providing the VOC latent <br /> _ heat of vaporization, while holding the temperature at or above ambient soil. The <br /> saturated vapor is collected at the surface from the group of extraction yell-screens <br /> and passed over the cold coils of the heat pump. The saturated vapors are condensed <br /> and the liquid solvent is collected in a proper receiver. The residual air is than forced <br /> through the hot coils of the heat pump by the blower (compressor). This raises the <br /> temperature, thereby decreasing the relative saturation of the VOC in the air stream. <br /> The unsaturated air stream then flows into the "injection group" of well-screens, where <br /> the cycle is repeated at a slightly higher temperature. With each cycle of air in the <br /> closed loop, the soil temperature is raised slightly until equilibrium is reached and the <br /> soil is progressively dried. <br /> An optional, auxiliary heater is available to raise the temperature of the air <br /> medium even higher than is possible with the heat pump as the only heat source. The <br /> auxiliary heat source greatly enhances the rate of evaporation of the contaminant and, <br /> indeed, makes practical the removal of semi-volatile contaminants having a higher <br /> boiling point (i.e. relatively low vapor pressure). This latter option will allow <br /> - ----- -- - --remediation of-contaminants-formerly-thoug ht-to-be-amenable only to-relative ly_hig h <br /> cost remediation techniques, e.g.: excavation, and off-site disposal. <br /> 2 <br /> YG <br />