At industrial facilities, stormwater and process wastewater often contains hydrocarbons, types of volatile organic compounds (VOC) that can be harmful to human health and the environment if released into the air. Vapors emitted from underground oil-water separators/API sumps, industrial process sewers and process gas exhaust streams must be treated to remove these compounds. VOC filtration of vapor emissions is a federally mandated requirement aimed at reducing air pollution.

Wastewater departments at industrial facilities that deal with hydrocarbons, including petrochemical plants, refineries, chemical blending facilities and tank farms, typically perform vapor scrubbing by passing the vapors through activated carbon filters. However, there’s another, more effective approach: utilizing a wet scrubber, a type of chemical scrubber also called a wet air scrubber.

How a scrubber works

Wet scrubbers consist of a stainless-steel tank filled with a scrubbing medium designed to absorb certain contaminants. When the vapor stream is passed through the wet scrubber, the VOCs become absorbed into the liquid media. The filtered vapor is then discharged through an outlet in the vessel.

A natural oil-based media referred to as a bio scrub solution is often used to capture BTEX vapor emissions (benzene, toluene, ethylbenzene and xylene). A water-based amine solution is often used to capture hydrogen sulfide (H2S) emissions.

Compared to carbon filtration, wet scrubbers are often much more efficient at VOC filtration. Used in conjunction with carbon filtration, a wet scrubber can significantly boost VOC capture, increase safety and reduce costs.

Benefits of wet scrubbers for VOC filtration

While most industrial facilities have committed to carbon filtration as part of their standard operating procedure, introducing a wet scrubber system prior to carbon filtration can yield significant benefits. A wet scrubber is also highly effective when used on its own.

Greater VOC capture efficiency

Chemical scrubbers have the potential to filter out up to 95% to 98.5% of BTEX emissions and handle concentrations of up to 2000 parts per million (ppm). By contrast, carbon filtration systems can handle VOC concentrations of less than 500 ppm.

When plants use wet scrubbing methods prior to carbon filtration, the discharge vapor’s VOC count is greatly reduced as it exits the scrubber. The vapor is then directed to the carbon bed for a final polish. The result is not only improved VOC filtration but also carbon filters that last exponentially longer, which reduces costs.

Increased safety

Better vapor filtration increases worker protection from VOC-related health issues such as throat and eye irritation, headaches and nausea.

Wet scrubbers provide an additional safety advantage when filtering vapor streams that contain high levels of VOCs. During carbon filtration, VOC molecules bind to the carbon, which creates a small amount of heat. At VOC concentrations over 500 ppm, that heat could be sufficient to create a spark that can result in a fire. The potential exists for the ignition source to travel back to the source tank, and that could result in a fire or explosion. Wet scrubbing does not typically create excessive heat.

Recoverable BTUs

A diesel-based scrubbing agent used to capture BTEX chemicals has a hidden benefit. Once it’s been spent and can no longer absorb VOCs, it can be drained from the wet scrubber tank and added to the slop oil tank that fires the facility’s boiler.

By harnessing the BTUs recovered from the scrubbing agent, plants can reduce their consumption of virgin fuel—an environmental benefit—and lower fuel costs.

Solid waste reduction

The carbon used in carbon filtration must be sent out to be burned or landfilled. Solid waste disposal represents a significant cost for industrial facilities. Scrubbing agents are easier to dispose of than carbon. While BTEX scrubbing agents can be reused as fuel, water-based amine solutions can typically be sent through the normal wastewater treatment process.

Setting up a wet scrubber system

Engaging an experienced, knowledgeable provider of industrial vapor control scrubbers to design and install a wet scrubber system will help ensure the system functions as expected. Matching the scrubbing agent to the vapor chemistry is critical. In some cases, a custom-engineered solution may be necessary.

A company such as United Rentals will evaluate the chemicals in the vapor stream and advise on the best types of treatment vessels and scrubbing agents to accomplish the desired task. When a combination of VOCs (such as BTEX and H2S) is present, vapor filtration may be best accomplished with a combination of scrubbing liquids, including a BTEX removal solution and a water-based amine solution.

Wet scrubbing is a highly versatile, relatively compact vapor filtration solution with numerous potential applications. Capable of filtering many types of VOCs and high concentrations of VOCs, it’s a technology worth considering for the sake of the environment, regulatory compliance, worker health and the bottom line.

Contact United Rentals Fluid Solutions for more information on vapor filtration solutions.