Floating Roof Rim Seal Vapor Emission Loss Calculator

Estimate annual VOC evaporative emissions (kg/year and tons/year) from rim seals, deck fittings, and product withdrawal per API MPMS 19.2 / EPA AP-42.

Tank & Rim Seal Configuration

Tank Diameter D (m):

Average Ambient Wind Speed (km/h):

Rim Seal System Type:

True Vapor Pressure P (kPa): Gasoline RVP 9 at 20°C: ~32 kPa

Vapor Molecular Weight M_v (g/mol): Motor Gasoline ~ 66 | Crude ~ 50

Annual Net Throughput (m³/year):

Annual VOC Evaporative Losses

Total VOC Emissions:

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Rim Seal Losses (L_R):

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Withdrawal Losses (L_W):

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Deck Fitting Losses (L_F):

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Secondary Seal Abatement Efficiency:

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Frequently Asked Questions

What is the primary mechanism of vapor emission from floating roof tanks?

External wind flowing over the open tank rim creates negative aerodynamic suction on the leeward side. This wind-induced pressure gradient draws hydrocarbon vapors past microscopic gaps in the rim seal and out into the atmosphere.

Why are secondary rim-mounted seals mandatory under clean air regulations?

Secondary seals bridge the annular gap between the primary shoe and the tank shell, creating a stagnant secondary vapor buffer zone that reduces wind-driven emissions by 60% to 80%.

What are withdrawal losses (LW)?

As liquid is pumped out, a micro-thin clingage film remains on the descending internal shell wall. When the floating roof drops below this wet surface, the exposed film evaporates directly into the atmosphere.