Overview
Isomerisation in SAF Production
Hydrodeoxygenation effluent separation and hydroisomerisation to improve SAF cold-flow properties
Hydrodeoxygenation (HDO) effluent from the hydrogenation unit consists of an oil/water/gas mixture, which is separated using a high-pressure separator followed by a low-pressure separator. In these separators, water is removed as sour water. The separated gas stream consists mainly of hydrogen, with smaller amounts of CO₂ and propane, and is routed to the amine unit. There, the acid gases are removed, and the unused hydrogen is recovered and recycled back into the process.
The gas flow can be measured using either vortex or ultrasonic flowmeters, both of which are equipped with integrated pressure and temperature (P&T) compensation. This enables accurate gas flow calculation without the need for an external flow computer. The separator level can be measured using guided radar, which is available with SIL2 certification. For additional redundancy, the guided radar can be combined with a mechanical level gauge such as the BM26-8000, providing a mechanical backup to the electronic measurement.
The purpose of the isomerisation reactor is to reduce the cloud point of the HDO feed to a level that meets aviation fuel specifications. Similar to the hydrogenation stage, hydrogen is injected and the reaction is exothermic. The reactor operates under high temperatures and pressures and utilises a similar instrumentation setup to the hydrogenation reactor.
The isomerate is routed to a flash tank or stripping column, where remaining gases and unused hydrogen are removed. The level of the flash drum can be measured using guided radar installed in a bypass chamber. For additional redundancy, the radar measurement can be combined with a mechanical level gauge, providing a reliable backup level indication.