Gasoline blending is a refinery operation that blends different ingredient streams into different grades of gasoline. Typical grades include 83 octanes that are blended later with an oxygenated fuel like ethanol, regular 87 octanes, and premium 92 octanes.
The Reid Vapor Pressure (RVP) is always
set according to several factors like the average temperature of the location,
the gasoline will be used. It is quite evident that cold temperatures require
higher RVP than warmer climates. These two features are the most important and
they are ensured with each blend, to reduce the capability for octane giveaway.
While gasoline is obtained from
crude oil for most of the decades since the evolution and in its current
formulation it was usually a blend of oil-derived components forever. There are
many gasoline blending consultant
that are active in the industry. Blending biofuels into the gasoline pool is a contemporary
development. Today gasoline that is sold in the US market should always meet
the operational requirements of:
Modern combustion engines
Stringent environmental standards
Biofuel blending mandates
These three themes always govern
gasoline blending.
Octane: An operational requirement
With the pace in the adoption of
automobiles at the beginning of the twentieth century, the consumption of gasoline
increased at a faster pace. In initial days, gasoline-powered automobiles had
engines of low compression. Apparently, light naphtha or straight-run gasoline
was enough. But the auto manufacturers hunted ways to accommodate the increasing
demand for vehicle power quickly.
More power could be obtained if
there is an increase in the number of cylinders in an engine; another way was
to increase the compression of engines.
To diminish and eliminate
knocking, straight-run gasoline required a thing to delay or prolong combustion.
RVP (Reid Vapor Pressure) and
Seasonal Blending: Operational requirements
While the octane of a specific
grade is the same throughout the year, the RVP specification changes as winter
arrives. It is quite obvious that all gasoline produced for sale must meet all
local environmental specifications and include set standards at the national
level for blending in biofuels.
Blending advisory services suggests
that a usual summer gasoline blend must consist of approximately 40% FCC gas, nearly
25% straight run gas, about 15% alkylate, near to 18% reformate, and some 2%
butane.
The RVP of the gasoline blend
depends on how much of each ingredient is present in the blend, and what the
RVP is of each component.
Butane is a comparatively
inexpensive component in gasoline, but it has the highest vapor pressure of approximately
52 psi. In a gasoline blend, each ingredient gives some contribution of a
fraction to the overall RVP.
As evident, in the case of
butane, if there is a 10% butane present as a component in the blend, it will give
the contribution of around 5.2 psi (10% of 52 psi) to the overall blend.
This implies that in the summer,
the butane fraction should be very less in the gasoline, or the overall RVP of
the blend will be too much. That is the main difference between winter and
summer gasoline blending services.
For more info:- Diesel Blending Training
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