Chlorinated Groundwater Treatment
A Fortune 50 company implemented a remedial project to collect and treat polluted groundwater from a site in Central New York, preventing the mitigation of impacted groundwater from flowing into local waterways. An engineering and construction firm was hired to design and build an effective, efficient groundwater treatment system. Collection of the polluted water would be done with air strippers and equalization tanks then sent to a facility located along the shoreline of a nearby body of water for treatment. The off-gases from these collection devices would contain Volatile Organic Compound (VOC) laden air that would require further treatment before being released to the atmosphere. The expected VOCs included benzene, chlorobenzene and dichlorobenzene.
The design-builder required a treatment system that could destroy 99% of the VOCs and safely remove any of the resultant inorganic acid that would be formed. As this was a long-term project, the VOC control system needed to be highly reliable and provide low operational costs.
After a thorough evaluation, the design-build consultant selected Global Technologies - the remediation division of Anguil - to provide the VOC treatment solution. Global's extensive engineering support, industry-leading reliability, and history of solving difficult halogenated destruction problems around the world, made them the obvious choice. Global engineers recommended the Model 50 Regenerative Thermal Oxidizer (RTO) with an Acid Gas Scrubber. The system processes up to 5,000 SCFM of VOC-laden air, provides 99% VOC destruction efficiency and 99% by weight Hydrochloric Acid removal efficiency.
Global Technologies' engineering resources and experience processing halogenated contaminants were crucial to this project. In the Global two bed RTO, the polluted air is heated as it passes through stoneware beds located in an energy recovery chamber. The process air moves from the recovery chamber toward the combustion chamber, where the Volatile Organic Compounds (VOC) are oxidized, releasing energy into the second energy recovery chamber. A flow-diverter valve switches the airflow direction so both energy recovery beds are fully utilized, thereby reducing any auxiliary fuel requirement. This system is designed for heat recovery of 95%. This efficient energy recovery means the Global RTO could offer the customer significantly lower operating costs than other treatment technologies.
After exiting the RTO, the acid gas laden air is then exhausted to a countercurrent scrubber module that removes and neutralizes inorganic acids. In the scrubber, recirculation pumps inject large amounts of water into the adiabatic quench through separate spray headers. The RTO exhaust is cooled through evaporative cooling. The water that is not evaporated flows to the recycle sump. The air leaves the quench and enters the bottom of a countercurrent packed tower scrubber, re-circulating solution to the top of the tower through a nozzle. The remaining acid gases are absorbed by the solution as the air passes up the column. The air then passes through a mist eliminator to remove entrained water before exiting the scrubber column. Sodium hydroxide solution is added to the re-circulating water to neutralize the adsorbed acids and form a salt solution. The sodium hydroxide addition rate is controlled by a pH analyzer and the salt water blow-down by a conductivity analyzer.
The specified vapor treatment system consists of several design features that ensure safe and effective operation in the expected environment. It included an induced draft arrangement with the fan located downstream of the scrubber. This arrangement is preferred for halogenated applications because it results in negative air pressure and minimizes the corrosive conditions that can develop in a forced air system. The RTO produces corrosive hydrochloric acid vapors as the halogenated hydrocarbons are oxidized. With a forced draft arrangement, the oxidizer would have been under a positive pressure and the corrosive gases would tend to leak to atmosphere at instrumentation (thermocouple) penetrations. The corrosive gases could have condensed at this interface potentially corroding the outer shell.
Special consideration was also paid to the materials of construction to ensure performance in the corrosive environment. These selections have been field-proven in Global and Anguil's many halogenated installations. The RTO outer reactor shell is constructed of carbon steel and covered with a specialty coating to prevent corrosion. This coating resists any hydrochloric acid (vapors or condensed acid) that could potentially reach the outer skin. Diverter valves on the RTO were fabricated out of a high nickel alloy while transitions from the RTO outlet plenum and the acid gas scrubber quench were constructed of Hastelloy. The scrubber tower, sump and stack were all fabricated out of FRP (Fiberglass Reinforced Plastic).
Equipment location at the facility was carefully selected to reduce installation costs and minimize equipment downtime. The scrubber was installed inside the treatment building eliminating the concern of freezing during cold months and costs associated with winterization. The oxidizer was placed outdoors adjacent to the treatment building and near the scrubber system to eliminate extensive ductwork runs.
Global Technologies' understanding of the customer's unique needs, coupled with the engineering know-how necessary to fulfill these needs, resulted in another satisfied Global customer.
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