Nov 16

The basic idea of thermal desorption is to heat the soil so that low-boiling contaminants evaporate, collect these contaminants, and output the repaired soil. The three main principles governing this phenomenon are: mobilization; adsorption-desorption; the heat applied by the desorber directly affects the low boiling temperature of the organic contaminant and rapidly converts it to steam or volatilizes it. Adsorption is a property of the soil; it is the ability of soil particles to aggregate contaminants on the surface of the particles. As the volatilization and temperature increase, the contaminants begin to lose from the surface of the soil particles. The energy required to adsorb organic contaminants is less than the energy required to remove them (called desorption), so energy needs to be added to the system to remove contaminants from the surface of the soil particles. Based on the characteristics of the contaminant, the desorption rate is also a function of diffusion. The entire thermal desorption process is usually carried out in three general steps. These include material handling, post-treatment and desorption.

The success of the repair process depends to a large extent on four factors: temperature, soil matrix, contaminants and moisture content. Higher temperatures have been shown to greatly reduce the final concentration of contaminants, but require more energy and result in higher costs. The complexity of the soil matrix control desorption process: sand and coarse material are easier to desorb than fine grain soil because of the smaller surface area. Some pollutants are more easily adsorbed by the soil than other pollutants. The moisture content determines the adsorption capacity of all contaminants; the moister material better adsorbs contaminants. Many of these processes vary by site, depending on the unique characteristics of the project.

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written by Decanter Centrifuge


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