Also known as:
The purpose of a hydrotreater unit is primarily to remove contaminants such as sulfur from intermediate streams before blending into finished product or before being fed into another refinery process unit.
Hydrotreaters have become increasingly important as sulfur limits have been lowered in finished products. Also, for some key conversion units such as the reformer, feed must be hydrotreated to keep contaminants from poisoning the conversion catalyst.
Hydroteaters also address other contaminants such as oygen and nitrogen, and saturate aromatics and olefins, which is great for diesel quality (raises cetane) but bad for gasoline (reduces octane).
The hydrocarbon is mixed with hydrogen and heated to 500-750 degrees F. The mixture is injected into a reactor vessel filled with a solid metal catalyst (cobalt, molybdenum or tungsten). In the presence of the catalyst and heat, the hydrogen reacts with the hydrocarbon, removing sulfur (to form H2S) removing nitrogen (to form ammonia) and saturating olefins and aromatics with hydrogen. Typically there is also a small amount of hydrocarbon cracking to form methane, ethane, propane and butane.
The operating pressure of any hydrotreating unit is elevated to reduce the amount of coke laydown on the catalysts, which are normally in fixed beds. In general, the heavier the type of feedstock, the higher the operating pressure of the unit.
It is quite common for a refinery to have multiple hydrotreaters. Some of the more common are:
Naphtha hydrotreater - (NHT) hydrotreats heavy naphtha before it is fed to the reformer
Kerosene hydrotreater - (KHT) hydrotreats kerosene to remove sulfur and improve smoke point properties for jet fuel
Distillate hydrotreater - (DHT) hydrotreats diesel to remove sulfur and nitrogen and raise cetane
VGO hydrotreater - (GOHT) hydrotreats VGO before feeding into the FCC. This reduces sulfur resulting in lower sulfur products (FCC gasoline, cycle oil)
FCC gasoline hydrotreater - This hydrotreats the FCC gasoline coming out of the FCC, which is often high in sulfur
Resid hydrotreater - hydrotreats atmospheric resid (ARDS) or vacuum resid to reduce sulfur, sometimes before sending it to an RCC unit for upgrading.
HEFA - hydrotreats vegetable oil and or animal fats to elimanate oxygen and produce a renewable fuel such as renewable diesel or SAF.