Air Pollution Control (APC) systems for remediation applications are becoming standard practice as more stringent air regulations are being implemented for Soil Vapor Extraction (SVE) and Pump and Treat (P&T) remediation methods. Remediation projects typically have expected clean up timeline goals and it is important to select a safe and cost‐ effective solution that will meet these life expectancy goals and stringent regulations.
Traditionally Activated Carbon is evaluated first as the Best Available Technology (BAT) but in chlorinated and halogenated application, vapor phase carbon (VPC) may not be the best long‐term solution for the following reasons. Carbon usage and cost of carbon changeouts over life of project become more expensive than alternate oxidizer technologies. There are safety concerns that in high VOC loading application there could be concerns with carbon bed fires if VOC cause exothermic reaction.
Catalytic oxidizers the VOC laden air is exhausted from the process into the system into the primary heat exchanger where it will be preheated by a heat exchanger with 50‐65% heat recovery. Should the process stream include chlorinated compounds HCL is formed during the oxidation process and will require further treatment utilizing an acid gas scrubber. In hydrocarbon application only a precious metal catalyst is used to lower the oxidation temperature to 600F. This compares to 1500 ‐ 1800F in a thermal oxidizers. Catalytic oxidizers can a cost‐effective technology but catalyst can be poisoned by process stream requiring thorough review of the contaminates entering the system before selecting this technology.
Thermal Recuperative oxidizers the VOC laden air will be exhausted from the process into the primary heat exchanger with 50‐65% heat recovery where it will be preheated. The VOC laden air will then move through the burner section and will be heated to the preset reactor inlet temperature of 1500 ‐ 1800F. The purified air will then finally be exhausted to atmosphere. Should the process stream include chlorinated compounds HCL is formed during the oxidation process and will require further treatment utilizing an acid gas scrubber.
Regenerative Thermal Oxidizers the solvent laden air (SLA) enters the oxidizer via an energy recovery chamber where the high temperature ceramic heat transfer media preheats the SLA prior to introduction into the oxidation chamber. After the chemical oxidation purification reaction occurs, the hot, clean, outgoing gas heats the exit energy recovery bed. In order to maintain optimum heat recovery efficiency at 95% of the bed, the SLA flow direction is switched at regular intervals by the automatic diverter valves on demand from the PLC control system. Typical operational cycles range from 2 to 4 minutes.
Regardless of the oxidizer selected for any given application where chlorinated compounds are present and HCL gasses are formed it is important to consider if the system will be force draft or induced draft due to safety concerns. Should induced draft be selected and there is a breach due to corrosion the system is under a negative vacuum and HCL gasses will still be safely captured and controlled via the acid gas scrubber.
Primary Author/Conference Presenter:
Ship & Shore Environmental
Signal Hill, California, USA