Problem
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.
Action
After thorough technical and supplier evaluation, the
design-builder selected Global Technologies, a division of Anguil
Environmental Systems, Inc., 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.
Solution
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.