Hydrocracking in the oil & gas industry

Hydrocracking is a second catalytic cracking process applied typically to the heavy vacuum gas oil, a sidecut from the vacuum distillation column. When the oil is mixed with hydrogen and passed over a catalyst, the long chain hydrocarbon molecules are broken down into shorter ones. The rate of cracking and the end products of the hydrocracking are strongly dependent on the temperature and the catalysts present. In Hydrotreatment, a similar cracking process (already described in Section 4.3), the hydrogen is used to break the C-S and C-N bonds: in Hydrocracking the desired break is in the C-C bonds, and the major products are usually jet fuel and diesel. Hydrocracking is therefore used in areas where there is a large demand for diesel fuel. Where the major market demand is for gasoline (petrol) the fluid catalytic cracking process (FCC) is more common.

This is an extensive process, so effective control requires hydrocracking measurement solutions that can withstand the high pressures and temperatures involved. The liquid flows to be measured and controlled include the product feed and discharges from each vessel, plus the wash water input and sour water discharges. KROHNE ultrasonic flowmeters are suitable for the product feed measurements, even at the high temperatures experienced on the process vessel feeds. KROHNE electromagnetic flowmeters are typically used to measure the water-based liquid flows.

The gas instrumentation required includes hydrogen flow measurement on the feed lines to the process vessels, and in the recycle lines, plus off gas flow measurement to the various process heaters. From the final fractionator, flow measurement is needed on the lines producing the different output products, like diesel and jet fuel, light and heavy naphtha. KROHNE vortex and ultrasonic flowmeters are suitable for these measurements, even at the high temperatures experienced on the process vessel feeds.

Other hydrocracking instrumentation is needed on the separators, reactors and fractionators – these require level and interface measurement for control of the process. KROHNE radar level measurement systems, directly mounted in the vessels, or in separate bypass chambers, provide this data.