Hydrotreating Unit Available
  • Category :  Featured Plants
  • Manufacturer :  Shell Oil Company
  • Plant Type :  Hydrotreater
  • Capacity :  29,545 bbls/day
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Capacity: 29,545 bbls/day
Operating Pressure: 74 bar
Technology Provider: Shell
Year Built: 2005

Process Description
HDS3 is a Shell designed gasoil hydrotreating unit that takes a blend of straight run gas oils and desulphurises the gas oils to produce ULSD (specification of 10 ppmwt max sulphur in finished product) . The desulphurised product must also meet a polycyclic aromatics (PAH) specification of maximum 11wt% and total aromatics of min 15wt%. The design gasoil feedstock to HDS3 is a blend of straight run gas oil from Crude Distillers and High Vacuum units. The gasoil is typically derived from a mixture of Far East low sulphur crude and condensates and medium/high sulphur crudes from the Middle East.
The HDS3 unit consists of 2 main sections:
1.    High pressure (HP reactor) section
2.     Low pressure (LP work up) section
The purpose of the HP section is to remove the sulphur from the gas oil and reduce the aromatics content by contact with hydrogen rich gas in the presence of a catalyst at relatively high pressure and temperature.
In the LP section, H2S and light hydrocarbons produced in the HP section are removed via a stripper and the water and light hydrocarbons are separated in a drier to meet the water and flash point specifications. The LP section also contains a LP Amine Absorber to treat the sour off gas and supply it to the refinery gas network.
The design of the unit is based on high purity fresh gas (98%) from the HSU Unit 5700.
Fresh Gas /Recycle Compressor
The Fresh Gas Compressor and the Recycle Gas Compressor are mounted in one frame with a shared motor. H2 rich gas is sent to the Fresh Gas Compressor Suction at 22 Barg (from HSU1) and is compressed up to 85 barg. The fresh gas is compressed by means of Fresh Gas Compressor K5801A (fully spared by K5801B). This compressor is a 2 stage electric drive reciprocating machine with Hydrocom capacity control.
The gas from the discharge of K5801A/B is combined with the discharge of the Recycle Gas Compressor K5802A/B at 85 Barg, (K5802A is fully spared by K5802B). K5802A/B is a motor driven single stage reciprocating machine with pneumatic loaders. The combined gas at 85 Barg and 220 t/d enters the HP loop downstream of the P5801 Feed Charge Pump.
Feed Preheat / Heater / Reactor
The feed is boosted up to reactor pressure by the Feed Charge Pump P5801. The gas oil feed is mixed with the combined fresh and recycle gas and enters the Feed / Effluent Exchangers E5805A/E where the feed temperature is raised by exchanging heat with the reactor effluent to 330°C.
The Reactor Charge Heater F5801 is a single burner, fuel gas fired heater with air preheat and convection section, increasing the temperature to the temperature required for the reactions to commence in the first catalyst bed of Reactor R5801 (typically >340°C).  
The Reactor R5801 consists of 3 catalyst beds with a liquid quench located in between the two top beds. The quench is provided to control the temperature rise over the second bed. The reactor is fitted with HD distribution tray and internals above each bed. The reactor metallurgy is 2 ¼ Cr-1Mo with 3mm corrosion allowance and internal SS 321 cladding.  
High Pressure Separators – HHPS V5804, CHPS V5805
The cooled reactor effluent from E5805 A/E is fed into the Hot High Pressure Separator (HHPS) V5804. Part of the liquid from V5804 is sent back to R5801 as quench oil and the remainder is sent to the Product Stripper C5801 for H2S and light hydrocarbon removal.
Vapours from V5804 are mixed with a fixed amount of wash water from the Cold Low Pressure Separator (CLPS) V5806. The water is pumped by the wash water pumps P5803AB, Rotojet type pumps, and a target water injection rate of 2-3wt% is maintained. The wash water injection is necessary to prevent corrosion by NH4HS in the air cooler tubes of E5806.
The mixture is then combined with a wash oil flow from CLPS V5806, pumped by P5807 in order to improve the H2 partial pressure in the unit by absorbing the heavy ends of the recycle gas and some H2S. The mixture is cooled in HHPS Vapour Condenser E5806.
The three phase mixture enters the Cold High Pressure Separator CHPS V5805 where it separates into three streams. The H2 rich gas enters the Recycle Gas Compressor KO Vessel V5809. This gas is then boosted up to reactor pressure by K5802A/B and combines with the fresh gas.
Low Pressure separator V5806 and Product Stripper C5801 and Overheads
The combined hydrocarbons from the HHPS V5804 together with the recycle hydrocarbons from CLPS V5806 are stripped, at a steam rate of 3wt% on feed with MP steam in C5801.
The C5801 Bottoms is sent by level control via the Feed/Stripper Bottoms Exchanger E5804 to the Vacuum Drier C5802. The temperature of the feed to C5802 is controlled by adjusting the cold gas oil feed bypass around E5804.
Overheads from C5801 are condensed in E5807 and sent to the CLPS V5806.The majority of the condensed liquid hydrocarbons from V5806 are routed as wash oil to E5806 via Wash Oil Pump P5807.  P5807 is the spared Feed Charge Pump and used to recycle excess condensed liquid hydrocarbons to C5801.  The water from the boot of CLPS V5806, consisting of condensed stripping steam is used as wash water in the reactor section to M5801. Offgas from CLPS V5806 is sent to the LP Amine Absorber Column C5901 via KO Vessel V5901 for treatment before going to the refinery fuel gas system. The HP bleed from V5805 combines with this flow to Unit 5900.
Vacuum Systems – C5802
The overheads from C5802 containing the removed water and some flashed off light hydrocarbons are cooled in the Drier Overhead Condenser E5809 which condenses the bulk of the water and hydrocarbons. The resulting two phase mix goes to the Drier Overhead Separator V5807 where the water and liquid hydrocarbons are separated. The vapour from E5809 is directed to a two stage ejector system (LP steam motive fluid), which helps to maintain the C5802 vacuum at a normal operating pressure of 180mbar.
The Drier Bottoms C5802 (finished gas oil) is pumped by Gas Oil Product Pumps P5804A/B, and then cooled and directed to finished storage tanks.

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