Gasoline debutanizers

Ci and lighter gas Debutanized polymer gasoline Debutanized thermal reformate Residuum Product recovery... 

In 1969,1 was working for Amoco Oil as a process design engineer. One of my earliest designs for Amoco was a gasoline debutanizer, the bottom portion of which is shown in Fig. 49.3. Note that this tower is... 

Debutanized gasoline cuts from Arabian Light crude. Specific gravity and sulfur content as a... 

The depropanizer bottoms are further processed in the debutanizer for separation of product from light pyrolysis gasoline. The debutanizer operates at a moderate pressure of 0.4 to 0.5 MPa, and is a conventional fractionator with steam heated reboders and water cooled condensers. 

Tower Internals and Equipment Modification. Tower capacity expansion can be achieved through the use of random or stmctured packing, or through the use of higher capacity trays such as the UOP multiple downcomer tray. Packing has been used in the gasoline fractionator, water quench tower, caustic and amine towers, demethanizer, the upper zone of the deethanizer, debutanizer, and condensate strippers. Packing reduces the pressure drop and increases the capacity. 

Two sources of absorption oil are normally utilized in this tower. The first is the hydrocarbon liquid from the main fractionator overhead receiver. This stream, often called wild, or unstabilized, naphtha, enters the absorber a few trays below the top tray. The second absorbent is cooled debutanized gasoline, which generally enters on the top tray. It has a lower vapor pressure and can be considered a trim absorbent. The expression lean oil generally refers to the debutanized gasoline plus the unstabilized naphtha from the overhead receiver. 

To enhance C3+ recovery, some units have installed presaturator drums that function as an additional absorption stage. In this operation, the cooled debutanized gasoline is mixed (presaturated) with the absorber overhead gas. The mixture is cooled and flashed in the presaturator drum. The liquid from this drum is then pumped to the top of the primary absorber. 

The stripper bottoms contain Cj s, C4 s, and gasoline the debutanizer separates the Cj s and C4 s from the gasoline. In some units, the hot stripper bottoms can be further preheated before entering the debutanizer. In a number of units, the stripper bottoms is sent directly to the debutanizer. The feed enters about midway in the tower. Debutanizer feed is always partially vaporized because the debutanizer operates at a lower pressure than the stripper. A control valve that regulates stripper bottoms level is the means of this pressure drop. As a result of this drop, part of the feed is vaporized across the valve. 

The debutanizer separates the feed into two products. The overhead product contains a mixture of C3 s and C4 s. The bottoms product is the stabilized gasoline. Heat for separating these products comes from an external reboiler. The heating source is usually the main fractionator heavy cycle oil or slurry. Steam can also be used. 

The debutanized gasoline is cooled, first by supplying heat to the stripper reboiler or preheating the debutanizer feed. This is followed by a set of air or water coolers. A portion of the debutanizer bottoms is pumped back to the presaturator or to the primary absorber as lean oil. The balance is treated for sulfur and blended into the refinery gasoline pool. 

A number of refiners split the debutanized gasoline into light and heavy gasoline. This optimizes the refinery gasoline pool when blending is constrained by sulfur and aromatics. In a few gasoline splitters, a third heart cut is withdrawn. This intermediate cut is low in octane and it is processed in another unit for further upgrading. 

The overhead stream from the debutanizer or stabilizer is a mix of C, s and C4 s, usually referred to as LPG (liquefied petroleum gas). It is rich in olefins, propylene, and butylene. These light olefins play an important role in the manufacture of reformulated gasoline (RFG). Depending on the refinery s configuration, the cat cracker s LPG is used in the following areas ... 

Reformulated gasoline specifications require lower vapor pressure in the blended gasoline. It also requires maximum feed to the alkylation unit. This puts more pressure on the gas plant, particularly the debutanizer. Floating the tower pressure is often the best way to meet both constraints. 

As the gasoline Reid vapor pressure (RVP) is reduced, the operation ol the debutanizer becomes more critical. The allowable vapor pressure in gasoline makes it difficult to prevent heavy ends in the alkylation feed. This can limit the production of gasoline without sacrificing alkylation. This limitation is often from insufficient overhead cooling and reboiling ... 

Table El4.1 A shows various feeds and the corresponding product distribution for a thermal cracker that produces olefins. The possible feeds include ethane, propane, debutanized natural gasoline (DNG), and gas oil, some of which may be fed simultaneously. Based on plant data, eight products are produced in varying proportions according to the following matrix. The capacity to run gas feeds through the cracker is 200,000 lb/stream hour (total flow based on an average mixture). Ethane uses the equivalent of 1.1 lb of capacity per pound of ethane propane 0.9 lb gas oil 0.9 lb/lb and DNG 1.0.

This process was fully utilized in commercial units early in 1942 and played an important part in satisfying the ever-increasing requirements of our Armed Forces. Usually, a debutanized motor gasoline was charged to the treating unit at relatively severe conditions to crack the heavier fractions and increase the yield and quality of aviation base stock. Typical results are given in Table II. 

A very high octane ceiling. Debutanized gasolines with an octane number of over 95 Research clear have been produced, with attendant carbon yields of less than 0.4%. Such octane numbers come about largely because of the ability of the process to produce... 

Figure 2. Comparison of F-2 (Motor Method) Octane Numbers of Debutanized Gasolines from Platforming and Thermal Reforming of Pennsylvania Straight-Run Gasoline...

Platforming of Pennsylvania Straight-Run Gasoline. Table IV presents the results obtained from Platforming the Pennsylvania straight-run gasoline. The product was debutanized in the unit and rather complete analyses were obtained on the debutanized product. 

Table IV. Platforming of Debutanized Pennsylvania Straight-Run Gasoline...

F-2 CLEAR OCTANE NO. OF DEBUTANIZED GASOLINE Figure 8. Lead Response (Motor Method) of Platformate and Thermal Reformate from Mid-continent Naphtha... 

Figure 11. Hydrocarbon-Type Content of Debutan-ized Pennsylvania Straight-Run Gasoline, Platformate, and Thermal Reformate...

The fractionation section of the alkylation plant consists of a deisobutanizer, a debutanizer, and a rerun tower in series, and a depropanizer. The deisobutanizer overhead, which contains about 90% isobutane, recycles to the reactor. The deisobutanizer bottoms stream passes to the debutanizer, which removes normal butane diluent as an overhead stream. The debutanizer bottoms or raw alkylate stream then goes to a rerun tower for removal of the high boiling alkylate bottoms or trimers. The rerun overhead requires no further treatment to be satisfactory as an aviation gasoline blending stock. The depropanizer removes propane diluent from a slip-stream portion of the recycle isobutane stream to prevent propane build-up in the reaction system. 

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