The Naphtha Hydrotreater (NHT) unit is an essential part of a refinery, particularly in the production of high-quality naphtha. The primary function of the NHT unit is to remove impurities such as sulfur, nitrogen, oxygen, and metals from the naphtha fraction of crude oil. This is important for producing cleaner and more refined products, especially to meet environmental regulations.

Naphtha Hydrotreater (NHT) Unit Process:

1. Feedstock Introduction:
   • The feedstock for the NHT unit is typically naphtha derived from the distillation of crude oil or from other refining processes (e.g., catalytic cracking).
   • This naphtha usually contains undesirable impurities like sulfur, nitrogen, oxygen, and aromatics.
2. Preheating:
   • The feedstock is preheated to a specific temperature (usually around 350–400°C) using a heat exchanger or furnace before it enters the reactor.
3. Hydrogen Supply:
   • Hydrogen gas is also supplied to the NHT unit, as it is required for the hydrogenation reactions that remove impurities.
   • Hydrogen is typically produced in a hydrogen plant and mixed with the naphtha before entering the reactor.
4. Catalytic Hydrodesulfurization (HDS) and Hydrodenitrogenation (HDN):
   • The hydrogenated feedstock enters the reactor containing a catalyst (typically made from cobalt-molybdenum or nickel-molybdenum).
   • In the reactor, the following processes occur:
     • Hydrodesulfurization (HDS): The sulfur compounds are removed by reacting with hydrogen to form hydrogen sulfide (H₂S), which is then separated and removed.
     • Hydrodenitrogenation (HDN): Nitrogen-containing compounds are also treated with hydrogen to remove nitrogen, forming ammonia (NH₃).
     • Hydrodeoxygenation (HDO): Oxygen is removed as water (H₂O).
5. Reaction and Separation:
   • After the reaction in the reactor, the product stream (treated naphtha) exits the reactor.
   • The treated naphtha contains much lower levels of impurities such as sulfur, nitrogen, and oxygen.
6. Cooling and Separation:
   • The reactor effluent is then cooled and passed through a separator where the hydrogen sulfide (H₂S) and ammonia (NH₃) are separated from the liquid phase.
   • The treated naphtha is then sent for further treatment or blending depending on its intended use.
7. Hydrogen Recovery:
   • A portion of the hydrogen used in the process is recovered and recycled back into the system to optimize the overall hydrogen consumption.
   • The remaining hydrogen (along with the sulfur compounds) is typically processed in a gas treating unit or sulfur recovery unit to convert H₂S into elemental sulfur.
8. Final Product:
   • The final product from the NHT unit is a cleaner naphtha with a lower sulfur content, making it suitable for use in the production of gasoline or as a feedstock for further refining processes, such as reforming or blending.

Main Objectives of the NHT Process:

• Sulfur removal: To produce low-sulfur naphtha that meets environmental standards, especially for gasoline production.
• Improve quality: To remove nitrogen, oxygen, and metal impurities to prevent catalyst poisoning in downstream processes (like catalytic reforming).
• Improve environmental compliance: By reducing the sulfur content, the process helps meet environmental regulations related to air quality and emissions from gasoline engines.

Summary of the NHT Process:

• Preheat and mix the naphtha feed with hydrogen.
• Hydrotreat the mixture in the reactor using a catalyst to remove sulfur, nitrogen, oxygen, and metals.
• Separate the impurities (e.g., H₂S, NH₃) and recycle hydrogen.
• Produce high-quality naphtha suitable for further refining or use in gasoline production.

This unit is essential for ensuring the refinery can produce cleaner fuels and meet regulatory standards, especially those related to sulfur content in gasoline.