Page 223 - Materials Chemistry, Second Edition

206 Practical Design Calculations for Groundwater and Soil Remediation

The stoichiometric requirements would be inversely propor-
tional to the ratio of the “moles of electrons accepted per unit
mass of oxidant” of two oxidants listed in Table 5.3.
Stoichiometric amount of Na S O (using the mass ratio)
2 2
8
= (15.85 g O /kg soil) × (0.125/0.0084)
2
= 236 g Na S O /kg soil
2 2
8
Discussion:
1. The stoichiometric oxygen requirements for typical petroleum
hydrocarbons range from 3.0 to 3.5 g O /g COC.
2
2. The stoichiometric amounts of other oxidants can be readily
found from that of oxygen by using the molar ratio or the mass
ratio.

5.7 Thermal Destruction

5.7.1 Description of the Thermal Destruction Process
Thermal destruction, considered here, is an ex situ remediation technique
to remediate soil impacted by organics. Ex situ thermal treatment gener-
ally involves destruction or removal of organic COCs through exposure
to high temperature in treatment cells, combustion chambers, or other
means used to contain the impacted media during the treatment. There are
many different thermal treatment alternatives available, including thermal
destruction/oxidation, pyrolysis, vitrification, thermal desorption, plasma
high-temperature recovery, infrared, and wet-air oxidation. This section
focuses on thermal destruction/oxidation (or combustion).
The common combustion units used for hazardous wastes are incinera-
tors, boilers, and industrial furnaces. During combustion, organic wastes
are converted into gases. The stable gases produced from combustion of
organics are primarily carbon dioxide and water vapor. However, small
quantities of carbon monoxide, hydrogen chloride, and other gases may
form. These gases have potential adverse impacts to human health and the
environment [9].

5.7.2 Design of the Combustion Units
The key design components of combustion units are the three Ts, which are
combustion temperature, residence time (also called “dwell time”), and turbu-
lence. They affect the size of a reactor and its destruction efficiency. Other
important parameters to be considered include heating value of the influent
and the requirements of auxiliary fuel and supplementary air.