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Evaporation Loss

The document discusses evaporation losses of gasoline, noting that gasoline evaporates much faster than other hydrocarbons due to its light distillates between C5 to C10. An equation is provided to calculate evaporation loss based on factors like wind velocity, vapor pressure, temperature, and exposed area. Studies showed gasoline can evaporate up to 85-94% of its original volume within 12 hours when exposed to open areas, while evaporation losses are much lower, around 0.171 kg, for gasoline transported in sealed tank trucks.

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551 views2 pages

Evaporation Loss

The document discusses evaporation losses of gasoline, noting that gasoline evaporates much faster than other hydrocarbons due to its light distillates between C5 to C10. An equation is provided to calculate evaporation loss based on factors like wind velocity, vapor pressure, temperature, and exposed area. Studies showed gasoline can evaporate up to 85-94% of its original volume within 12 hours when exposed to open areas, while evaporation losses are much lower, around 0.171 kg, for gasoline transported in sealed tank trucks.

Uploaded by

pvar06
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14/10/2010

EVAPORATION LOSSES OF GASOLINE / MOTOR SPIRIT / PETROL

The Gasoline is combination of many light distillates. The gasoline contains carbon
between C5 to C10. Due to various light distillates the evaporation of gasoline is much
faster then any other hydrocarbon. The evaporation loss depends on various associate
parameters like wind velocity, vapor pressure, temperature, exposed area, distillation
temperature, boiling point etc.

In an open oil spool the evaporation loss can be calculated using following formula:

QR = 0.284 x U^0.78 x MW^(2/3) x A x VP / (82.05 x T)

(Source Ornan.com)

Where

QR Evaporation loss in pounds / min


U - Wind velocity in meter / sec
MW Molecular weight of gasoline
A - Area in square feet
VP Vapor pressure in mm HG
T - Temp in Deg Kelvin

The evaporation of gasoline is very fast in open area and it largely depends on the wind
velocity and exposed surface area. As per the study conducted by Bureau of Energy
Management and Enforcement, USA, the gasoline can evaporate upto 85% of original
volume in just 12 hours at temperature of 15 Deg C from 151 Sqaure cm exposed area
and at a negligible wind velocity. Under the same condition, if the temperature rises to 35
Deg C then around 94% of original volume can evaporate within 12 hours. This indicates
that the evaporation rate of gasoline is very fast from an area exposed to atmosphere.

But when it comes to tight sealed container then there are many other parameters comes
in to play, which restrict the evaporation of gasoline to drastic extent. As per the study
conducted by Environment Protection Agency, USA, the evaporation in sealed container
(in our case tank lorry) depends on pressure relief valve setting, vapor tightness of the
tank, pressure in the tank at start of trip, vapor pressure of fuel being transported and
degree of vapor space. However the evaporation losses are not directly proportional to the
time spent in transit. If the container is have vapor leakage, then initially the evaporation
are at faster pace to a certain point and then the evaporation rate changes as the other
factors like surface temperature, heat transfer rate etc comes into play.

As per the reports published by EPA (AP-42), the evaporation losses from a tank lorry in
transit would be:
Typical value - 0 to 1.0 mg / liter transported
Extreme value - 0 9 mg / liter transported

Considering above value, following is the calculation for in-transit evaporation losses of
gasoline:

Capacity of tank lorry - 19000 liters


Time in Transit - NA
Evaporation loss (Extreme) - 9 mg / liter transported
Density of gasoline - 0.740

In-transit evaporation loss - 9 x 19000 mg


- 171000 mg
- 0.171 kg
- 0.231 liters

So in-transit losses of gasoline in transit would be very minimal and can not contribute to
in-transit losses even if we use the multiplication factor of 5 or 10 in above value.

Praveen varma
+91 93242 89504

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