Regenerative Thermal Oxidizer for Chlorinated Groundwater Treatment

A remedial project was implemented by a Fortune 50 company to collect and treat polluted groundwater from a site located in the Central New York area. The aim was to prevent the mitigation of impacted groundwater from flowing into local waterways.

An engineering and construction company was contracted to design and build an efficient groundwater treatment system. Polluted water would be collected via equalization tanks and air strippers which would then be sent to a facility situated along the shoreline of a water body for treatment. These collection devices emit off-gases that would contain air laden with Volatile Organic Compounds (VOCs). This would require further treatment prior to being released into the atmosphere. The anticipated VOCs comprised benzene, chlorobenzene and dichlorobenzene.

Groundwater Treatment Technology

A treatment system was required to destroy approximately 99% of the VOCs and to safely remove the ensuing inorganic acid that would be formed. Since this was a long-term project, the VOC control system had to be extremely reliable with low operational costs. Figure 1 shows the chlorinated groundwater treatment plant.

Figure 1. Chlorinated groundwater treatment plant

Upon evaluation, the design-build consultant finally selected Anguil’s remediation division, Global Technologies, to deliver the VOC treatment solution. The division is renowned for solving complex halogenated destruction problems across the globe. Engineers at Global Technologies recommended the Model 50 Regenerative Thermal Oxidizer (RTO) with an Acid Gas Scrubber. The system can process up to 5,000 SCFM of VOC-laden air, and delivers 99% by weight hydrochloric acid removal efficiency and 99% VOC destruction efficiency.

Process of Groundwater Treatment

Engineering resources and extensive experience in processing halogenated contaminants were important in this project. In the two bed RTO, the polluted air is first heated as it travels via stoneware beds integrated in an energy recovery chamber. From the recovery chamber, the process air travels toward the combustion chamber, where the VOCs are oxidized and energy is released into the second energy recovery chamber. Following this, a flow-diverter valve changes the airflow direction so that both energy recovery beds are completely used, thus reducing the need for auxiliary fuel. This system is specifically designed to recover 95% of heat. This effective and efficient energy recovery means the Global RTO could offer reduced operating costs when compared to other treatment technologies.

After leaving the RTO, the air, laden with acid gas, is exhausted to a countercurrent scrubber module that easily removes and neutralizes inorganic acids. The scrubber includes recirculation pumps, which inject considerable amounts of water into the adiabatic quench via individual spray headers. Following this, the RTO exhaust is cooled via evaporative cooling. The water that does not get evaporated flows to the recycle sump. The air then exits the quench and enters the base of a countercurrent packed tower scrubber, re-circulating solution to the top of the tower via a nozzle.

The solution absorbs the residual acid gases as the air moves up the column. The air travels via a mist eliminator to remove entrained water prior to leaving the scrubber column. A sodium hydroxide solution is added to the re-circulating water to neutralize the adsorbed acids and form a salt solution. Additional rates of sodium hydroxide is controlled by a pH analyzer with the blown-down salt water managed by a conductivity analyzer.

The vapor treatment system includes a number of design features that guarantees safe and effective operation in anticipated environments. It is comprised of an induced draft arrangement, with the fan, situated downstream of the scrubber. This arrangement is desirable for halogenated applications as it results in negative air pressure and also reduces the corrosive conditions that can occur in a forced air system.

Since the halogenated hydrocarbons are oxidized, the RTO emits corrosive hydrochloric acid vapors. In case of a forced draft arrangement, the oxidizer would remain under positive pressure and the corrosive gases could leak to atmosphere at instrumentation penetrations. Condensation of corrosive gases at this interface can possibly corrode the outer shell.

Construction Materials

Specific attention was also paid to construction materials so as to ensure excellent performance in the corrosive environment. The RTO outer reactor shell is made of carbon steel and painted with a specialty coating to eliminate corrosion. This coating is resistant to hydrochloric acids that could potentially reach the outer shell. The RTO includes diverter valves that were constructed of a high nickel alloy, and transitions from the acid gas scrubber quench and the RTO outlet plenum were made of Hastelloy. Fiberglass Reinforced Plastic was used to make the scrubber tower, sump, and stack.

To reduce equipment downtime and installation costs, the location of the equipment was carefully selected. The scrubber was set up within the treatment building to eliminate the issue of freezing during cold winter months, and the oxidizer was located outdoors next to the treatment building and close to the scrubber system to prevent lengthy ductwork runs.

Conclusion

Global Technologies has the required expertise and engineering know-how to address customers’ unique application needs. The RTO with acid gas scrubber proved effective in treating chlorinated groundwater.

About Anguil Environmental Systems

Anguil Environmental Systems is a global provider of industrial air pollution control and energy recovery systems. The thermal and catalytic oxidizers supplied by Anguil are used to destroy Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) that are by-products of various manufacturing processes. When released into the atmosphere these carcinogens are known to cause respiratory ailments, heart conditions, birth defects, nervous system damage and cancer in humans and animals.

In addition to their harmful effects on plants and trees, when left untreated VOCs and HAPs degrade in the presence of sunlight and contribute to low-lying ozone or smog. Anguil differentiates itself from the competition by offering all of the different vapor combustion technologies used for the destruction of these pollutants. This ensures an unbiased equipment selection for each application based on the destruction requirements, efficiency needs and process parameters. We not only design, manufacturer, service and install Regenerative Thermal Oxidizers (RTOs) but also direct-fired, catalytic and thermal recuperative systems. In addition, Anguil offers a wide variety of heat recovery and energy conservation technologies. Our energy recovery systems help manufacturers achieve greater energy efficiency, lower operating costs and reduce greenhouse gas emissions through the utilization of waste heat. The recovered energy is often used in process and comfort heating applications or converted into electricity.

This information has been sourced, reviewed and adapted from materials provided by Anguil Environmental Systems.

For more information on this source, please visit Anguil Environmental Systems.

Comments

  1. Enviro-Equipment Inc Enviro-Equipment Inc United States says:

    Concerning the site in central New York State, what type of the VOCs was the groundwater contaminated with?

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