A Fortune 50 company implemented a remediation system to collect and treat polluted groundwater from a site in Central New York and prevent impacted groundwater from flowing into local waterways. An engineering and construction firm (EPC) was hired to design and build an effective, efficient groundwater treatment system. Primary treatment of the polluted water was to be accomplished using air strippers and the effluent then sent to a separate offsite facility for final treatment. The VOCs liberated from the groundwater by the air strippers, including benzene, chlorobenzene and dichlorobenzene, require treatment before being released to the atmosphere.
The design-builder required an air pollution control system which could destroy 99% of the VOCs and safely remove any of the resultant inorganic acid gasses 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 Anguil to provide the VOC treatment solution. Anguil’s extensive engineering support, industry-leading reliability, and history of solving difficult halogenated destruction problems around the world made them the obvious choice. Anguil engineers recommended a Model 50 Regenerative Thermal Oxidizer (RTO) with an Acid Gas Scrubber. The system is capable of processing up to 5,000 SCFM (8,025 Nm3/hr) of VOC-laden air while providing 99% VOC destruction efficiency and 99% removal by weight of Hydrochloric Acid.
Anguil’s engineering resources and experience processing halogenated contaminants were crucial to this project. In the Anguil two chamber RTO, polluted air is preheated as it passes over ceramic media beds located in the energy recovery chamber. From there, the process air moves into the combustion chamber where the Volatile Organic Compounds (VOC) are oxidized. Heat from the hot air stream is then recovered by the second ceramic media bed before being exhausted to the acid gas scrubber. A flow diverter poppet valve switches the airflow direction so both energy recovery beds are fully utilized, thereby reducing the auxiliary fuel requirement as much as possible. Anguil’s two chamber RTO is designed to achieve a heat recovery of 95% TER and results in significantly lower operating costs than other thermal oxidation technologies.
After exiting the RTO, the acid gas laden air is processed through a countercurrent wet scrubber that removes and neutralizes inorganic acids. In the scrubber, a quench system first brings the air temperature down via evaporative cooling by spraying water into the air stream. The cooled air then leaves the quench and enters the bottom of a countercurrent packed tower scrubber. In the tower, a recirculating solution of caustic water is sprayed into the top of the tower and cascades down over the packing material. Any acid gasses remaining in the air stream are absorbed into the water and neutralized by the caustic solution into a salt (brine) solution. To replenish the neutralizing agent, sodium hydroxide solution is added to the recirculating water through pH controls. Similarly, as the brine solution concentrates, ORP/conductivity controls allows saltwater blowdown to leave the system and adds fresh make-up water as necessary.
The specified vapor treatment system included several design features that ensure safe and effective operation in the expected environment. First, an induced draft arrangement was utilized where the process fan is located downstream of the scrubber. An induced draft arrangement is preferred for halogenated applications because it creates a negative air pressure through the entire system where acid gasses are present, minimizing the potential leaking of corrosive gasses which can be forced out of a system under positive pressure. Leakage of s corrosive acid vapors produced by the RTO from the oxidation of halogenated hydrocarbons from equipment connections and penetrations y can corrode the outer shell of the equipment and surrounding environment, as well as posing human health and safety concerns.
Special consideration was given to the materials of construction to ensure performance and reliability in the corrosive environment. Upgraded materials of construction selected for key areas of the RTO are field-proven from Anguil’s many halogenated installations. For example, RTO outer reactor shells were constructed of carbon steel but internally coated with a specialty coating to resist hydrochloric acid corrosion from the inside out. Poppet valves were fabricated from 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.
Anguil’s understanding of the customer’s unique requirements and engineering knowledge of the detailed process conditions resulted in an efficient and reliable system and ultimately another satisfied Anguil customer.