At oil and gas refining sites around the world, staying compliant with applicable environmental statutes is a two-front battle.
Both air and water are polluted by volatile organic compounds (VOCs) and other unwanted compounds during refining; both must be treated before they’re released into the environment.
In this article, we identified some common processes that result in water pollution. Here, we’ll walk through our ideal oil refinery wastewater treatment strategy and introduce the cutting-edge equipment we build to ensure your facility’s compliance.
Stage 1: Degasification
When VOCs and other unwanted compounds dissolve into the water used at various stages of crude oil refinement, the first step in refinery wastewater treatment is to get those compounds out of the water. That’s because the most effective elimination of those compounds occurs when they’re in the air phase.
Common degasification methods include:
• Pressure reduction, which decreases the solubility of the gases dissolved in water when the pressure of the mixture is reduced.
• Thermal reduction, which reduces solubility of gases in aqueous solutions when the temperature is increased.
• Membrane degasification, in which water with dissolved gases is pumped inside a membrane and the space outside the membrane is vacuated. This causes the gases to leave the water and escape through the membrane.
• Inert gas substitution, where inert gases like helium, argon, nitrogen or ambient air are bubbled into a vigorously-stirred solution and substitute the unwanted compounds.
BioAir Solutions’ Rainfall® degasifier is designed to efficiently eliminate compounds impacting oil refinery wastewater. The polluted water is pumped to the top of the degasifier vessel, where it falls downward through random media featuring high surface area and void fraction. This turns the water into very small droplets.
Meanwhile, ambient air is pumped upward through the media. When the air meets the small water droplets, the dissolved gas molecules move from the water phase into the air phase. The treated water drained safely away.
But refinery wastewater treatment cannot stop here. So far, we’ve traded one kind of pollution for another. The second and third stages treat the newly-polluted air.
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Stage 2: ‘Green’ biological treatment
As pressure mounts on refineries to enhance the environmental friendliness of their processes, treating polluted air using green methods is an attractive opportunity. Biological treatment of foul odors is well established. It’s not as prevalent in the treatment of oil or gas refinery emissions, but studies have shown biological methods can cost effectively eliminate many VOCs.
The newly-polluted air that results from degasification of refinery wastewater is pumped into a vessel and directed upward through porous media. Inside the media, the air is in contact with small droplets of irrigation water that trickles downward from the top of the vessel and with bacteria and other microorganisms that reside within the media.
The microorganisms are naturally selected based on their ability to metabolize organic compounds. The waste products of that consumption are drained safely away with the downward-trickling water while clean air is released from the top of the vessel.
For this stage, BioAir recommends its EcoFilter® biotrickling filter. EcoFilter units feature proprietary EcoBase® structured synthetic media which significantly enhance the conditions inside the treatment vessel. In addition, the design of the EcoFilter supports a greater diversity of biology, which translates to the consumption of a wider range of unwanted compounds.
Stage 3: Adsorptive media polishing for the cleanest possible air (optional)
Sending the air treated in Stage 2 through an adsorption filtration unit ensures it is as clean as possible. Adsorption filtration, which may include activated carbon, differs from biological treatment in that it is a physical adsorption process. During this stage, air is forced through a bed of heated or electrically-activated adsorption media. Polluting compounds stick to the adsorbent and clean air is released.
EcoCarb® adsorption media filters feature porous adsorptive beds that finely disperse air and trap offending compounds over extended service lives. Installing an adsorption media polishing stage after biological treatment creates a best-of-both-worlds scenario:
• End-stage adsorption polishing results in incredibly clean air thanks to the effectiveness of the biological system that precedes it. EcoFilter units routinely exceed 99% removal efficiency on their own.
• Due to the cleanliness of the air entering the polishing stage, adsorption media bed lifetime is extended.
The one-two punch of the EcoFilter and EcoBed treatment systems result in the cleanest possible air while also substantially reducing overall operating and maintenance costs.