PENETRATION GRADE BITUMEN
The distillation process starts in the refinery where the crude oil is heated and delivered to an atmospheric distillation column (ADC) where the lighter fractions are vaporized and drawn off, leaving a residue of heavy oils and bitumen.
The crude oil is pumped into the ADC at temperatures between 300-350 °C (575-660°F) at the bottom of the tower. At these temperatures, the crude oil is already a mixture of liquid and vapor. The vapors rise up the ADC through holes in trays which are constructed throughout the distillation column. The temperature decreases with the height of the ADC, allowing the vapors to condense according to different boiling ranges.
In this way the lighter, lower boiling fractions rise to the top, while heavier fractions are taken out from trays as side streams part way up. The heaviest fraction, the so-called long residue, leaves from the bottom. The top fraction is LPG (liquefied petroleum gas) followed by naphtha, paraffin, gas-oil, and heavy distillates.
The long residue is then further distilled under vacuum in the vacuum distillation column (VDC). In the VDC, the long residue is separated into heavy gas-oil, heavy distillates, and a soft residue. This residue is termed short residue and can be used as bitumen feedstock. The penetration of the short residue is variable and depends on the nature of the crude oil and the vacuum distillation conditions. The penetration typically runs from 10 to 500. Different penetration (pen) levels can be obtained by blending different short residues in the right proportion or by direct distilling. Bitumen products produced this way are referred to as straight-run bitumen.
CUTBACK BITUMEN
Cutback bitumen has been blended with a volatile oil so that when the volatiles have evaporated with time the bitumen will eventually revert to its original viscosity.
Time being the critical factor, it may take many months or even years before the cutback mixture regains the viscosity of the original bitumen.
The solvents used for dilution are distillates of varying volatiles. After bitumen cutback has been applied, the diluents evaporate and leave the residual bitumen in contact with the aggregate. In this process the diluents do not play any part in the function of the binder. However, the type and amount of diluents used decide the rate of solvent evaporation and the curing rate of bitumen cutback.
The tables below show the specifications of the specific grades of bitumen that we provide.