MechChem Africa

Tshwane-based hydrogen specialist, RTS Africa Engineering, is now introducing H2scan hydrogen analysers, which are ideally suited to optimising the performance and efficiency of oil refineries. MechChem Africa talks to the company‘s MD, Ian Fraser.

“In an oil refinery, there are between 12 and 23 key points in the process where hydrogen measurements are critical. Knowledge of the exact hydrogen percentages at these points gives a key indication of the efficiency of the reactions and using this information is key to optimising the performance of all refineries,” begins Fraser.

Hydrogen scanning for optimised refinery performanceAt the heart of the oil refining process is fractional distillation, where crude oil is heated to 350 to 400 °C in a column. Crude oil is made up many different hydrocarbon compounds – called fractions – which all have different boiling/condensing temperatures.
Insert pic: RTS H2SCAN

As the gaseous compounds rise up the column, individual fractions condense as they reach the height and temperature associated with their boiling/condensing points. Hydrocarbon gases with the lowest boiling points, therefore, rise to the top of the column; the heavier gasoline, diesel and jet fuel fractions con- dense and are taken off in the middle sections; and the very heavy fractions remain in liquid form to be tapped off from the bottom.

“All of the fractions produced, however, are processed further in other refining units, most of which require or produce hydrogen,” says Fraser.

Petrol or gasoline, which is extracted near the top of the column, is a mixture of over 500 alkanes and other hydrocarbons. Octane (C8) or Isooctane is the ‘norm’ used to achieve consistency, but petrol’s hydrocarbon chains can have between three and 12 carbon atoms, from C5 (pentane) to C12.

“A reformer converts low-octane fractions or naphthas into high octane reformates,” Fraser explains. “This is done by re-structuring the hydrocarbon molecules by separating out hydrogen. Hydrogen in a mixture with 80% hydrocarbons is recycled through the catalytic reformer from a product separator. Accurately monitoring the hydrogen released from the process is important for controlling the process and to ensure maximum process efficiency,” he tells MechChem Africa.

In addition, the isomerisation process is used to upgrade the octane rating of C5/C6 gasoline and for benzene saturation. Hydrogen is combined with the C5/C6 charge feed in an isomerisation reactor, which relies on a catalyst to promote the reaction. “Unless the composition of the recycled hydrogen is known and the partial pressure of hydrogen across the catalyst is kept above 860 kPa (125 psi), rapid coking of the catalyst will occur, which quickly stops the isomerisation reaction,” he notes.

For heavier fractions, a hydrocracker is used to break (crack) long chain molecules into more useful short chain hydrocarbons. This process starts by mixing the heavy oil ...

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