To limit air pollution, federal, state and local emissions standards require filtration of gaseous pollutants, including VOCs, from vapor emissions.
Petrochemical plants, refineries, chemical blending facilities, tank farms and other industrial facilities are required to remove VOCs including BTEX chemicals (benzene, toluene, ethylbenzene and xylene), as well as hydrogen sulfide, from process wastewater emissions and gas exhaust streams. Vapor filtration also reduces unwanted odors.
Most facilities filter vapors via a carbon media, but there’s another approach that’s often significantly more effective: wet scrubbing.
In wet scrubbing, a vapor stream is passed through a vessel filled with a chemical scrubbing agent designed to absorb or neutralize specific contaminants. Multiple scrubbing agents can be added to handle complex vapor streams. The filtered vapor is then discharged through an outlet in the vessel. If desired, it can be directed to a carbon bed as a polish phase to capture any remaining contaminants.
Efficiency and cost advantages of wet scrubbing
Wet scrubbing: An alternative to carbon for vapor filtration
Wet scrubbing is an effective filtration method on its own. Since most facilities have committed to using carbon filtration, wet scrubbing can be used prior to carbon filtration to greatly increase filtration efficiency and boost contaminant capture.
Wet scrubbers have the potential to filter up to 98.5% of BTEX emissions and can handle much higher contaminant concentrations than carbon — up to 2000 ppm compared to 500 ppm. When wet scrubbing is utilized prior to carbon filtration, most contaminants have already been captured by the time the vapor stream encounters the carbon filter. The result is improved filtration and carbon filters that last significantly longer, reducing both costs and waste.
Wet scrubbing also eliminates or reduces the cost and time involved with solid waste disposal. Water-based amine scrubbing media is used to filter hydrogen sulfide, and spent media can often be disposed of through the normal wastewater treatment process. An oil-based scrubbing agent used to capture BTEX emissions can be drained from the tank once it’s spent and added to a slop oil tank, which decreases the consumption of virgin fuel.
Reduced risk of fire
When filtering vapor streams that contain high levels of VOCs — more than 500 ppm —wet scrubbing offers a major safety advantage over carbon filtration.
With carbon filtration, some VOC molecules stick to the carbon, creating a small amount of heat. Over time, as the heat accumulates, it can become hot enough to create a spark that turns into a flame. A flashback could result in a fire or even cause the tank to ignite.
By reducing the concentration of VOCs prior to carbon filtration, wet scrubbing significantly reduces any fire or explosion risk. Unlike carbon, it does not create heat.
The role of filtration equipment experts
Every facility faces unique challenges when cleaning vapor emissions to comply with air quality regulations. By employing wet scrubbing, managers can answer many of those challenges if the system is designed properly.
To utilize a wet scrubber effectively, it’s necessary to first identify the types of contaminants in the vapor and their concentrations, as well as the anticipated vapor volume and flow rate. Then choose the right vessel and the appropriate scrubbing agent or mix of scrubbing agents.
Partnering with a temporary equipment provider that has the knowledge and experience to design, install and maintain a vapor scrubbing solution can help managers gain peace of mind while saving time and money and reducing hazards.
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