Optimising profits by blending butane (TIA)
Many countries legally mandate the observation of the maximum gasoline vapour pressure to prevent air pollution and ensure the safe transport and storage of petroleum.
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In addition, gasoline vapour pressure is an important factor in preventing fuel vapour lock and in providing easy motor starting in cold weather or at high altitudes.
The regulation of maximum vapour pressure limits requires that refiners carefully blend gasoline. That blending affords refiners opportunity for incremental profits, especially when low-cost butane is available to blend into the more expensive gasoline. Butane has good anti-engine knock qualities but is a major overall contributor to gasoline vapour pressure, such that the maximum amount of butane blended into gasoline is limited by the maximum allowed vapour pressure of the fuel.
The spread between the price of gasoline and butane is a key factor in blending profitability. For example, if the market price for gasoline is $3 per gallon and the price for butane $1.5 per gallon, every gallon of butane used to replace a gallon of gasoline in a blend yields $1.5 per gallon in extra profits.
Typically, between 2% and 3% butane by volume can be blended into gasoline, depending on the vapour pressure of gasoline before blending. The most profitable time for blending butane into gasoline is during the transition between the summer and winter driving seasons, when sometimes up to 10% of butane by volume can be blended into gasoline. During colder seasons, higher vapour pressure is acceptable.
Two examples highlight how much profit can be achieved. During a six-month period, (October 2012 – March 2013) one American refinery in Milwaukee, Wisconsin, was able to blend an average of 4.8% butane, or 2.6 million gallons, into its gasoline. With an average price spread between butane and gasoline of $1.5 per gallon, the refinery was able to achieve an extra $4 million in profit (see Figure 1).
Similarly, a refinery located in Green Bay, Wisconsin, blended 4.3 million gallons of butane into gasoline between April 2012 to March 2013, with most blending occurring between September and March. At a gasoline-butane spread of $1.5 per gallon, the result is an extra $6.5 million of profit (see Figure 2).
Given the potential level of profit, it is easy to understand that a 10 000 b/d refinery that installs a blending facility worth $1 million can expect a return on its investment within a matter of weeks rather than years.
Both the Milwaukee and Green Bay refineries have installed a Technics blending facility that employs two Grabner Minivap On-Line vapour pressure process analysers and duplex sampling loops. The blending system is designed to deliver product on-spec, on-time and homogenised to a precise blend that is within 0.2 psi (1.3 kPa) directly on the pipeline. Extremely tight dosing to within 0.05% of butane is achievable.
Apart from exact butane dosing, high-accuracy vapour pressure testing contributes significantly to profitability by allowing refiners to use a narrower margin of safety and still guarantee that the gasoline vapour pressure is within limits. As a result, more butane can be added and greater profits generated.
Grabner analysers are known for high accuracy in standard compliant vapour pressure testing. The Minivap On-Line RVP tester used in the Technic system features the triple expansion method with a reproducibility of 0.1 psi (0.7 kPa), compared to the ASTM D5191 standards reproducibility of 0.4 psi â€¨(2.75 kPa).
Better precision leads directly to significantly more blending profit, even at very low butane blending ratio. If the vapour pressure of gasoline increases by â€¨1 psi (7 kPa) through blending, the Grabner analyser allows up to 0.5% more butane to be blended into gasoline, compared with the ASTM D5191 standard method.
As a consequence, a medium-sized refinery may save more than a million dollars per year and recoup the analyser’s costs almost immediately.
This short case study originally appeared in PTQ's Technology In Action feature - Q3 2015 issue.
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