Contamination and remediation of soil Assignment

Contamination and remediation of soil - Assignment Example Thermal desorption system The basic process of DHTD system has been illustrated in the figure 1 given below. The soil is dried through heating it directly with the help of a rotary dryer made up from a high temperature alloy. The rotary dryer comprises of a natural-gas-fired burner that has the capability to heat the feed material up to a temperature of about 550oC or 1,022oF. The rate of heating the feed soil by using the rotary dryer is primarily based upon the moisture present in the soil, the size distribution of the soil particles, and the discharge temperature of the soil. The processed-gas is conveyed to the emission control system from the discharge hood that receives the gas from the rotary dryer. The emission control system consists of the dual cyclones, evaporative cooler, thermal oxidizer, bag house, quench, draft fans with dual induction, supply system of sodium hydroxide, acid gas scrubber, stack, and continuous emissions monitoring system. The natural-gas-fired burner of the rotary dryer is basically fitted with the thermal oxidizer that functions between the temperature ranges of 930oC to 1000oC. The gas is cooled down by spraying an air atomized water stream at the top portion of the evaporative cooler. The bag house conveys the gas to a quench chamber and a packed scrubber through the induced draft fans. Then, in order to remove acid gases from the gas, a pH controlled water stream passes again through the scrubber before the stack discharges the gas to the atmosphere. A double tipping valve, steam hood, pug-mill, steam duct, stacking conveyor and shuttle conveyor are used in the construction of a cooling and handling system for the treated soil. The double tipping valve is used to discharge the soil from the rotary dryer to the pug-mill. The pug-mill also, receives the combined dust streams, through a series of screw conveyors, from the bag house and the dual cyclones. Then the soil is cooled and moisturized through spraying water in to the p ug-mill. Subsequently, the shuttle conveyor passes the cooled and moisturized soil discharged from the pug-mill to a stacking conveyor that, in turn, passes it to the stockpile of the treated soil. The steam-duct transfers the stream discharged from the pug-mill in to the evaporative cooler. The stockpiles of 500 ton each hold the treated soil until they are analyzed for complying with the treatment criteria. Figure 1: The Overview of the DHTD System (Troxler et al. 2010)2. Project Schedule The table 1 given below presents the major milestones related to the implementation and licensing of the thermal treatment plant project. Table 1: Project Schedule (Troxler et al. 2010)2. Commissioning Trials The testing sequence proposed for the selected approach at the site included a process comprising of two stages. In the first stage, the plant processes the non-contaminated soil in order to ascertain that all of the electrical, mechanical, and control equipments are working properly. Then, in the second stage, the plant processes the above-average concentration of the contaminated material which takes about 6 to 7 hours. EPA observed, in the preliminary review of the EIS, that the testing sequence should not include a one-step change from ‘0’ to above average concentration of the contaminant material. Demonstrated performance is required by EPA throughout the range of soil contamination. EPA also, suggests that the