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SPM Refinery Series
SPM-2500 Atmospheric Distillation Unit (ADU)

Click to view schematic display A Click to view schematic display B Click to view schematic display C Click to view schematic display D

Process Description

The ADU (Atmospheric Distillation Unit) separates most of the lighter end products such as gas, gasoline, naphtha, kerosene, and gas oil from the crude oil. The bottoms of the ADU is then sent to the VDU (Vacuum Distillation Unit).

Crude oil is preheated by the bottoms feed exchanger, further preheated and partially vaporized in the feed furnace and passed into the atmospheric tower where it is separated into off gas, gasoline, naphtha, kerosene, gas oil, and bottoms.

This tower contains 20 fractionation trays, is equipped with one top pump around, an overhead reflux system, and three side strippers (for naphtha, kerosene, and gas oil products).

The liquid from the feed furnace enters the tower bottoms, where it is collected and sent for further processing to the VDU. Steam is injected into the base of the tower to reduce the hydrocarbon partial pressure by stripping some light boiling components from the bottoms liquid. The vapors from the feed heater enter the tower below tray 20.

At tray 19, a draw pan is located from which gas oil product is drawn. The gas oil product flows by gravity to the top of the gas oil stripper. Stripping steam is used to remove the light ends, improving the flash point. The stripped gas oil product is pumped to storage.

The next product draw is located at tray 12, where the kerosene product is drawn. The kerosene product flows by gravity to the top of the kerosene stripper. Stripping steam is used to remove the light ends, improving the flash point. The stripped kerosene product is pumped to storage.

The last product side draw is located at tray 5, where the naphtha product is drawn. The naphtha product flows by gravity to the top of the naphtha stripper. Stripping steam is used to remove the light ends, improving the flash point. The stripped naphtha product is pumped to storage.

A pump around liquid stream is drawn from tray 6, cooled and returned to tray 3.

The condensed gasoline and water are separated by gravity in the reflux drum. Part of the gasoline is pumped back to the tower as reflux, with the rest going to storage. The water is drained to disposal and the vapor from the ADU overhead is passed to an untreated fuel gas system.


Instrumentation

The ADU feed is pumped by P-100 (HS-100) and controlled by FIC-100. It is preheated in the bottoms feed exchanger (E-100) before entering the Feed Furnace (F-100). TIC-100 controls the crude oil temperature entering the ADU (T-100) by adjusting fuel gas flow to the furnace.

Bottoms liquid is collected and sent to the VDU by LIC-114 through the Bottoms Pump P-114 (HS-114). This flow is indicated by FI-124. Stripping steam is injected into the ADU bottoms by FIC-134.

Hot gas oil flows by gravity to the Gas Oil Stripper (T-113) through FIC-113. The gas oil enters the stripper at the top and flows downward over six trays. Stripping steam is introduced into the bottom of the stripper through FIC-133. The gas oil product is pumped from the base of the stripper by the Gas Oil Product Pump P-113 (HS-113) to storage. The gas oil product flow is controlled by LIC-113 and the flow rate is indicated by FI-123. The gas oil product's 95% point is monitored by AI-123.

Hot kerosene flows by gravity to the Gas Oil Stripper (T-112) through FIC-112. The kerosene enters the stripper at the top and flows downward over six trays. Stripping steam is introduced into the bottom of the stripper through FIC-132. The kerosene product is pumped from the base of the stripper by the Gas Oil Product Pump P-112 (HS-112) to storage. The gas oil product flow is controlled by LIC-112 and the flow rate is indicated by FI-122. The kerosene product's 95% point is monitored by AI-122.

Hot naphtha flows by gravity to the Naphtha Stripper (T-111) through FIC-111. The naphtha enters the stripper at the top and flows downward over six trays. Stripping steam is introduced into the bottom of the stripper through FIC-131. The naphtha product is pumped from the base of the stripper by the Naphtha Product Pump P-111 (HS-111) to storage. The naphtha product flow is controlled by LIC-111 and the flow rate is indicated by FI-121. The naphtha product's 95% point is monitored by AI-121.

A naphtha pump around is drawn from tray 6, pumped through P-115 (HS-115) and controlled by FIC-115. The pump around return temperature is controlled by TIC-115 which modulates cooling water flow to E-115.

The ADU overhead vapor flows through the overhead condenser E-110 (HV-110), whose outlet temperature is indicated by TI-120, into the Overhead Reflux Drum D-111. The hydrocarbons are partially condensed and the two phases (vapor and liquid) enter the overhead reflux drum where the condensed water separates from the hydrocarbon liquid by gravity.

The reflux is returned to tray 1 of the tower from the reflux drum via pump P-110 (HS-110). The reflux flow is controlled by FIC-110 which is reset by TIC-110 to control the tower overhead temperature. The level of the overhead drum is maintained by LIC-110 which sends the gasoline product to storage, whose rate is indicated by FI-120.

Water collects in the boot of the overhead reflux drum, and is transferred to the water system for treating. LIC-120 maintains a constant sour water level. The sour water is sent to treatment through pump P-120 (HS-120).

The uncondensed gas (FI-130) is sent to fuel gas through PIC-120, which maintains the ADU back pressure. Analyzers are present to monitor the C3 composition of the off gas (AI-130) and vapor pressure (AI-120) of the gasoline.

ADU overhead pressure is indicated by PI-110 and bottoms pressure is indicated by PI-114.

The ADU tower temperature profile is indicated by TI-120 (overhead), TI-110 (gasoline), TI-111 (naphtha), TI-112 (kerosene), TI-113 (Gas Oil), and TI-114 (ADU residuum).