Linear vs. nonlinear: Calculate gasoline component properties

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Author: L.E. Curcio
Date: June 2019
Publisher: Gulf Publishing Co.
Document Type: Article
Length: 1,715 words
Lexile Measure: 1310L

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The US is the largest "gasoline guzzler" in the world, producing and consuming about 9 MMbpd of gasoline--global production is approximately 45 MMbpd. Considering current gasoline prices (Regular 87 octane discounted at $2.22/gal), and a $2.5-B/yr gasoline production cashflow for an average-size US refinery, the capital involved is a staggering $250 B/yr. This means that even small production improvements have an enormous impact on the economics of the US refining industry.

However, sloppy gasoline production costs the blender money. A simple example illustrates the "sloppiness" value in terms of easily understood property giveaway; that is, the gap between a spec (e.g., 87 octane) and the actual produced gasoline property (for example, measured at 87.9 octane).

A 2013 study undertaken by Valero (1) indicates a US refining industry conservative octane giveaway of approximately 0.5 octane number (ON) and a Reid vapor pressure (RVP) giveaway of approximately 0.3 psi. This is valued at approximately $3 B/yr. Since there are 121 US refineries, $3B/121 = $25 MM per US refinery in property giveaway alone.

Several alternatives can reduce the giveaway:

* Properly optimizing a recipe using adequate tools

* Using better measurement systems--e.g., more precise analyzers

* Accounting for the nonlinearity of gasoline component properties.

This article is focused on the nonlinearity of gasoline component properties. This might appear an easy task, but more than 60% of US refineries calculate the gasoline component properties linearly. This is a mistake that can waste significant capital because it is overestimating or underestimating valuable properties (i.e., ON or RVP).

Linear vs. nonlinear. The perennial question is: What is the difference between linear and nonlinear worth? It is actually a simple blend of subjects that include physics, chemistry, engineering and math.

Since gasoline and hydrocarbon-based components don't really "like" each other when combined, chemical interactions modify the behavior of the solution or blend.

This means that 1 + 1 does not equal 2 but might be equal to 3 or 1.5. The following example illustrates the concept behind this complicated behavior.

FIG. 1 shows the blending of two components (same quantity, 1 bbl each): reformate with a research octane number (RON) of 100 and a light straight-run with a RON of 74. If the linear calculation is done [i.e., (100 + 74) / 2], the result is 87, but if a blend sample is analyzed by a lab, the result is 88.

The reason for this difference is the strong interactions between molecules in the blend that make the phenomena highly nonlinear (i.e., 1 + 1 does not equal 2).

For example, molecules differ in structure, size or...

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Gale Document Number: GALE|A602105729