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SPM Refinery Series
SPM-2700 Atmospheric/Vacuum Crude Units (ADU/VDU)

Click to view schematic display A Click to view schematic display B Click to view schematic display C Click to view schematic display D
       
Click to view schematic display E Click to view schematic display F Click to view schematic display G Click to view schematic display H

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.

The VDU (Vacuum Distillation Unit) takes the residuum from the ADU (Atmospheric Distillation Unit) and separates the heavier end products such as vacuum gas oil, vacuum distillate, slop wax, and residue.

Heavy crude oil is preheated by the bottoms feed exchanger, further preheated and partially vaporized in the feed furnace, and passed into the vacuum tower where it is separated into slop oil, vacuum gas oil, vacuum distillate, slop wax, and bottoms residue.

This tower contains a combination of 14 fractionation trays and beds. It is equipped with three side draws and pump around sections for vacuum gas oil, vacuum distillate, and slop wax products.

The liquid from the feed furnace enters the tower bottoms, where it is collected and sent for further processing. 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 14.

At tray 14, a draw pan is located from which slop wax product is drawn. The slop wax product and pump around are cooled, with the slop wax product going to storage, while the pump around is returned to the tower at tray 11.

The next product draw is located at tray 8, where the draw for vacuum distillate product is located. The vacuum distillate draw tray is a total draw tray, where the reflux from the tray is pumped under flow control to the tray below. The product and pump around are cooled, with the vacuum distillate product going to storage, while the pump around is returned to the tower at tray 7.

The last product draw is located at tray 4, where the draw for vacuum gas oil product is located. The vacuum gas oil draw tray is also a total draw tray, where the reflux from the tray is pumped under flow control to the tray below. The product and pump around are cooled with the vacuum gas oil product going to storage, while the pump around is returned to the tower at tray 1.

The overhead from the VDU is condensed and combined with the vacuum steam. The slop oil and water are separated by gravity in the vacuum drum. The water is drained to disposal, while the slop oil is accumulated and occasionally drained to slop collection.


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).

The VDU feed is pumped by P-114 (HS-114) controlled by LIC-114 and indicated by FI-124. It is preheated by the bottoms feed exchanger E-200 before entering the Feed Furnace (F-200). TIC-200 controls the temperature of the feed entering the VDU (T-200) by adjusting fuel gas flow to the furnace.

Bottoms liquid is collected and sent to storage through pump P-214 (HS-214), controlled by LIC-214, and indicated by FI-224. This residue's 95% point is monitored by AI-224. Stripping steam is injected into the VDU bottoms by FIC-234.

Hot slop wax is pumped from the tower by pump P-213 (HS-213). The slop wax product flow to storage (FI-223) is controlled by LIC-213, and it's 95% point is monitored by AI-123. Cooled pump around is controlled by FIC-213 and returned to the tower above the slop wax draw tray.

Hot vacuum distillate is pumped from the tower by pump P-212 (HS-212). The vacuum distillate product flow to storage (FI-222) is controlled by LIC-212, and it's 95% point is monitored by AI-122. Cooled pump around is controlled by FIC-212 and returned to the tower above the vacuum distillate draw tray. Vacuum distillate reflux is controlled by FIC-232 and returned to the tower below the vacuum distillate draw tray.

Hot vacuum gas oil is pumped from the tower by pump P-211 (HS-211). The vacuum gas oil product flow to storage (FI-221) is controlled by LIC-211, and it's 95% point is monitored by AI-121. Cooled pump around is controlled by FIC-211 and returned to the tower above the vacuum gas oil draw tray. Vacuum gas oil reflux is controlled by FIC-231 and returned to the tower below the vacuum gas oil draw tray.

The VDU overhead vapor flows through the overhead condenser E-210 (HV-212) into the Overhead Vacuum Drum D-211. The hydrocarbons are fully condensed and mixed with the vacuum condensate flow from E-211.

The water separates from the hydrocarbon liquid by gravity, where the drum's water level is maintained by LIC-210 which sends the water to treatment via P-210 (HS-210). The hydrocarbon phase overflows from the water phase, and slowly accumulates (LI-209). When a sufficient level of slop oil has accumulated, the level can be drained via P-209 (HS-209).

The VDU vacuum pressure is maintained by the steam to the vacuum ejector (HV-211), the cooling water (HV-212) to the steam condenser E-211, and the hydrocarbon condenser E-210. The pressure is regulated by PIC-210, which reduces the vacuum by circulating water to the vacuum ejector. The VDU bottoms pressure is indicated by PI-214.

The VDU tower temperature profile is indicated by TI-210 (overhead), TI-211 (gas oil), TI-212 (vacuum distillate), TI-213 (slop wax), and TI-214 (VDU residuum).