Minimising giveaway through online blending (TIA)
Refiners are responsible for controlling their blends of gasoline and diesel fuels to meet specifications for multiple parameters.
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Gasoline producers, for example, seek to control octane number (RON/MON), vapour pressure (RVP), distillation points, aromatics, oxygenates and more. Meeting those requirements demands the precise control of blend components to comply with specifications, while also reducing costs.
Gasoline is a high-value product. Butane, on the other hand, has relatively low value. Adding butane to a gasoline blend, therefore, can improve refinery operating margins. However, a refiner must still comply with regulations for octane number and vapour pressure. The addition of lighter butane significantly increases the vapour pressure, but maximum vapour pressure limits are strictly regulated in many areas of the world as a means for controlling emissions. At the same time, minimum octane ratings (ON) need to be strictly observed to guarantee the quality of gasoline grades, since refiners typically demand higher prices for higher gasoline grades.
Increasing the octane number adds value to the gasoline, while decreasing the vapour pressure requires adding low volatility components. Either approach is costly for refinery operations, since increasing the octane rating or decreasing the vapour pressure requires blending more expensive components into the gasoline. Thus, the closer that gasoline can be blended to the required ON and RVP ratings, the less the refiner gives away as result of blending costs.
The industry estimates that in the US the average octane giveaway is 0.7 per barrel, whereas the average vapour pressure giveaway is 0.4 psi (2.8 kPa) per barrel. A major contributor to product giveaway is the reproducibility of the ASTM or EN methods used to monitor compliance with gasoline specifications. Another contributor is the precision of the testing equipment used (see Figures 1 and 2).
Based on production data from the US and the European Union, the consolidation of octane and vapour pressure giveaways results in an annual loss of more than 4.9 billion USD in the United States and more than 4.2 billion USD in the European Union (see Table 1). Testing precision, therefore, is extremely vital to reducing giveaway costs.
To minimise RVP giveaway, an exact analysis of the vapour pressure, in combination with the exact dosing of butane, is required. The Minivap On-Line RVP tester from Ametek Grabner Instruments offers reproducibility of 0.1 psi (0.7 kPa) as well as ASTM/EN standard compliant analysis of the vapour pressure of finished gasolines or butanes in the blender.
When a Minivap analyser is installed in a Technics butane blending system, a precise blend can be achieved directly on the pipeline. The Technics blending system can achieve tight dosing, to within 0.05% of butane. A combined RVP analyser/butane blending system can achieve a positive return on investment in a matter of months, and even a medium-sized refinery can save more than $1 million/y.
To optimise octane giveaway savings, in-line near- infrared (NIR) analysis offers a distinct advantage due to its ability to measure numerous parameters simultaneously, with low system maintenance and easy operation. An NIR analyser can be installed in-line to measure directly at the blend header or in an online side-stream. The analyser can be located in an existing housing or in the field.
A multiplexed system that can analyse several points from a single unit can be configured to measure the properties of blended component streams. The optical fibre cables used to transmit NIR light to the process probes or side-stream flow cells can be placed close to the process since they are considered intrinsically safe.
The optimal choice of NIR process analyser for monitoring refinery blending is for one that ensures the accuracy of the measurement is equal to that of the calibration method (within statistical confidence). That analyser also should be flexible enough to accommodate different process integration methods, sampling systems, fuel ‘gold’ standards and facility layouts.
In an effort to provide the accurate and reliable multi-parameter analysis required in refinery blending operations, Grabner Instruments recently worked with LT Industries of Gaithersburg, Maryland, to offer a line of Parafuel NIR process analysers for octane giveaway reduction and other related refinery measurement solutions.
Payback on the investment in an NIR analysis system is rapid due to the cost reductions that can be achieved in several areas, including online monitoring of fuel blends for certification, avoiding re-blends, and integration into closed loop control. One LT Industries customer, for example, reported a payback period of less than six months. The system actually paid for itself even before it was integrated into the closed loop control.
This short case study originally appeared in PTQ's Technology In Action feature - Q1 2016 issue.
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