Evapostop floating discs are ellipsoidal, UFO-shaped discs with flat collars (or Saturnian rings), which remove effective evaporation surface and overlap to form a cover on surface of the liquid, thus creating an effective mass transfer barrier. The optimum geometry of the discs ensures that they seek to maximise the liquid surface coverage at all times, achieving a 99.6% coverage factor.  The discs were originally developed in Germany, in association with the University of Berlin.  They are usually constructed of 316 stainless steel and are manufactured to the highest quality, according to ISO 9000 standards.

Evapostop discs reduce Volatile Emissions from tanks by up to 90% (depending on tank turnover and product vapour pressure).

The discs can be used in place of internal floating roofs and have a number of benefits over conventional systems:

• Useful when retrofit or flexible solutions are required;
• Tank working volume is maximized.  In comparison to internal floating roof tanks, tank can be run with higher maximum and lower minimum levels;
• Can be installed in tanks with minimal effort  thus substantially reducing downtime;
• Non-corrosive and non-static (do not cause incendive sparks which may lead to internal explosions);
• Maintenance free;
• Greatly reduce the fire risk in tanks.
• Lower lifetime cost
• Flexible use - discs can be reused for different applications, or in tanks with different diameters
• No risk of unbalancing, jamming or sinking commonly associated with internal floating roofs;
• No hot work (welding work) required for installation
• No recalibrating or restrapping of tanks required

A significant advantage of Evapostop discs is that they can easily be used in combination with other end-of-pipe VOC emissions abatement equipment to increase total VOC abatement efficiencies to greater than 99%.

Evapostop applications include:

• Storage of volatile liquids, e.g. gasoline, BTX’s, naphtha, alcohols, solvents in Fixed Roof Tanks
• Storage of oxidation-sensitive base oils for the production of lube oils
• Storage of hazardous air pollutants such as Benzene, Toluene, Xylene (BTX’s)
• Prevention of heat loss
• API Separators (VOC Mass Transfer Barrier)
• Boiler Feedwater Tanks (reduces O2 ingress and heat loss)
• Tanks of variable diameter, e.g. Horizontal Cylindrical Tanks
• In conjunction with a vapour recovery system or vapour destruction system (such as thermal oxidiser), to reduce the cycle time and equipment size of the abatement system, resulting in a highly cost effective overall solution.
• To reduce the release of odourants into the atmosphere