Technical Information.

Soil Remediation Process Overview

Our unit is designed to remediate soil contaminated with non-recycled light distillate petroleum hydrocarbons, including gasoline, jet fuel, diesel oil, no. 2 oil and MGP Soils by rapidly volatilizing these products from the soil, then thermally destructing them in the discharge air stream. The unit consists of a rotary drum desorber with feed, discharge and combustion control systems, a dust collector, a modular thermal oxidizer, and associated fuel and air delivery systems.

The soil remediator operates as follows. Soil in need of treatment is loaded into a feed hopper. The hopper discharges soil onto a variable speed feeder belt. The feeder belt conveys the soil to a screening device and onto a belt weigh scale. The belt scale provides soil feed rate and totalized weights to the unit's control house. The belt feeds the contaminated soil into a counter flow rotary drum desorber. Volatile compounds and moisture in the soil are evaporated by the heat supplied by a direct firing burner. Heat transfer to the soil in the rotary desorber is maximized by the veiling action of specially designed lifting flights and patented combustion volume flights.

The heated soil is discharged into an auger system connecting an integrated knock out box and baghouse. The evaporated volatiles and water, along with dust released by the desorption process, are carried over by the rotary drum exhaust gases into the knockout box, where larger particles drop out of the gas stream. These pre-cleaned gasses then flow to the baghouse. Dust collected from the knockout box and baghouse are dropped into the auger system. The collected dust is remediated in contact with the hot soil. The remediated dust and soil mix are then augured to the mixer cooler where the product is cooled from discharge from the system.

Output from the baghouse is routed through an exhaust fan into a modular thermal oxidizer/stack unit, which reduces the hydrocarbon content of the gas stream with a destructive removal efficiency (DRE) of 99%

A process flow diagram is provided below

Thermal Desorption

Thermal Desorption is an ex situ process using either direct of indirect heat exchange to heat contaminated soil, volitizing (evaporating) organic materials in the soil at temperatures ranging between 400 and 700 degrees F. Hydrocarbons then exit the chamber by way of a vacuum draft into a variety of devices designed to capture the dust in the exhaust. Following the removal of the dust, the airstream is directed into a thermal oxidizer as required. The clean air then exits the stack. As a final step, soil samples are regularly taken and processed by an independent lab with report available to the owner/generator as documentation that the soil is clean.

When compared to the alternatives, (landfills, bio remediation, and land farming) the advantages of thermal desorption are obvious. Landfilling contaminated soils entails unknown long-term liability for the generator and contractor due to regulations that leave both open to future claims. The liability remains with the generator as long as it is contaminated, meaning future cleanup costs if the landfill is later found to be leaking.

Alternatively, bio-remediation utilizes bacteria and fungus to break down the hydrocarbons. The process requires very lengthy treatment periods, and requires turning of the soil while maintaining near perfect temperature, moisture, and nutrient conditions. In periods of hot weather the moisture level is difficult to maintain, and in cold weather the process ceases. The outcome of this process is uncertain due to the above restraints. The excavation is usually left open during the months required by the process, both representing a liability and loss of the use of the land for other purposes. Finally, the soil must be spread over a large area, exposing the soil to the possibility of contaminating ground water with rain run off, and leaves the generator open to claims in later years.

Land farming does not treat the contamination but rather allows it to be released into the air. This process requires spreading the soil over large areas for extended perious on order that the hydrocarbons will evaporate. Due to the effect of releasing these contaminants into the environment, as well as the problems mentioned earlier, this process has been outlawed in several states.

Thermal Desorption remains the best available method to clean the soil and destroy the contaminants, thereby releasing the generator of future liability, providing a safer, cleaner environment and producing new materials that can be reused for the betterment of our planet.