Tank Degassing

Tank Degassing is the removal of organic gases (or vapors) and displacement with air or nitrogen. Degassing can be used in both aboveground storage tanks or underground storage tanks.

Typically any tank containing a fluid/liquid with a Reid Vapor Pressure (RVP) of 0.5 psi or above can be degassed. This includes: gasoline, transmix, naphtha, slop oil, butane, benzene, toluene, xylene, butadiene, sour water, crude oil, butadiene and various chemicals. Envent also has a system for degassing pressure vessels, including propane and butane spheres.

Envent can control: gasoline, fuel oil, gas oil, naphtha, sour water, butadiene, benzene, chemicals, sour (H2S) materials, materials containing mercaptan, tank sludge and any exhaust fumes from your vacuum trucks.

Typically any aboveground storage tank larger than 5,000 gallons can be degassed.

Click here a detailed discussion of Tank Degassing Methods.

The Envent Mobile Thermal Oxidization System (EMTOS) has been engineered for high flow and includes unparalleled safety systems, making it the most efficient and safest method. Chevron, ExxonMobil, Lyondell, Equistar, Valero, BP, Shell and ConocoPhillips have all performed Hazops on our EMTOS equipment. Registered customers click here to view these Hazops. For more information, click here: www.degassingsafely.com.

A typical gasoline tank of 150 ft diameter, with ONLY 1 inch of scale/product, will emit 67,000 lbs of VOCs when the tank is prepared by maintenance for safe entry with a 10,000 CFM fan blower. Even after degassing the tank to 5% LEL, your tank will emit 28,000 lbs of VOCs. Click here for Example Calculations. For the detailed calculations, see technical paper: API 2568 EVAPORATIVE LOSSES FROM THE CLEANING OF STORAGE TANKS or contact TGB Partnership (Rob Ferry) at their website.

Total compliance is ensured by contracting directly with the Tank Degassing Company. Confirm your Tank Program is in compliance (with all degassing records) - before the agency issues a Notice of Violation - contact Envent to discuss our Compliance Assurance Program (CAP). Email us at: Solutions@Envent.net.

No. Chemicals don't eat vapors. Circulation of chemicals after the tank has landed only pushes vapors out of the roof fittings, vacuum breakers, legs and from around the seals. So-called bacterial solutions, biosolve or special degassing chemicals, are surfactants and cannot "degas" tanks. Chemicals don't eat vapors - they may have the potential to suppress vaporization but only if the chemical is evenly applied to the surface of the sludge/scale. This can be logistically and financially prohibitive - do you really have the time and budget for this? Contact an Envent engineer at: Solutions@Envent.net or call us at (888) 997-9465.

The answer is a simple NO. Vapors are simply re-circulated until enough vapor has escaped the tank via the leg sleeves, the vacuum breakers and around the seals until it can be called "degassed". Regulated Tank Degassing is the displacement of vapors with fresh air or nitrogen and the capture or destruction of the vapors. If you have ever removed a tank manway cover, you know that gasoline vapors are PURGED OUT with great force - the same force pushing them out the roof fittings. This force is known as Vapor Pressure or Reid Vapor Pressure (RVP). For gasoline the RVP is typically 6-14 psi. The roof fittings typically measure 6" to 10" diameter and may number from 25 to 200. The only way to stop these vapors from escaping is to keep a positive suction on the tank, i.e., pull out more than the vapor pressure is releasing. In the case of a pressurized tank, the pressure must be bled off to the atmosphere before circulation can begin – bleading a sphere from 30 psig to ambient, or 15 psi will release the full volume of the tank. At 150 PSIG, the system will release 10 TIMES THE VOLUME OF THE TANK. In the case of a re-circulating condenser unit, you have to pull out more than the vapor pressure is releasing PLUS the volume you are pumping back in to the tank. Typically you will need to remove a minimum of 100 to 1000 CFM to eliminate the escape of vapors. Since these re-circulating refrigerator units claim to reintroduce the same volume they remove, the majority of the vapors will escape via the path of least resistance, the leg sleeves and roof fittings. Ask these questions: How does the local environmental agency view this method of "degassing"? How do you demonstrate efficiency and compliance? What do you do with the hazardous waste you have now generated (the condensed liquid)? Do you need an EPA Transportable Treatment Unit (TTU) Permit to be processing this hazardous waste? Do you really have time and money to experiment? Is this really better for the environment?

Only a system that can handle your fill rate plus the vaporization rate can be used. That is not an IC Engine at a maximum of 100 CFM and 15 lbs/hr. That is not a condenser unit that operates at ambient conditions and cannot handle a pressurized system or pull a vacuum. The only system that can do this is an Envent Mobile Thermal Oxidation System (EMTOS). For further information and a comparison of degassing systems, please visit www.degassingsafely.com.