Debutanizers

The procedure applies to stabilized, i.e., debutanized, crudes, but can be applied to any petroleum mixture with the exception of liquefied petroleum gas, very light naphtha, and those fractions having boiling points over 400°C. 

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

The butane-containing streams in petroleum refineries come from a variety of different process units consequently, varying amounts of butanes in mixtures containing other light alkanes and alkenes are obtained. The most common recovery techniques for these streams are lean oil absorption and fractionation. A typical scheme involves feeding the light hydrocarbon stream to an absorber-stripper where methane is separated from the other hydrocarbons. The heavier fraction is then debutanized, depropanized, and de-ethanized by distillation to produce C, C, and C2 streams, respectively. Most often the stream contains butylenes and other unsaturates which must be removed by additional separation techniques if pure butanes are desired. 

The overhead product from the lean-oil fractionator, consisting of propane and heavier hydrocarbons, enters the depropanizer. The depropanizer overhead product is treated to remove sulfur and water to provide specification propane. The depropanizer bottoms, containing butane and higher boiling hydrocarbons, enters the debutanizer. Natural gasoHne is produced as a bottom product from the debutanizer. The debutanizer overhead product is mixed butanes, which are treated for removal of sulfur and water, then fed iato the butane spHtter. Isobutane is produced as an overhead product from the spHtter and / -butane is produced as a bottoms product. 

Propane and light ends are rejected by touting a portion of the compressor discharge to the depropanizer column. The reactor effluent is treated prior to debutanization to remove residual esters by means of acid and alkaline water washes. The deisobutanizer is designed to provide a high purity isobutane stream for recycle to the reactor, a sidecut normal butane stream, and a low vapor pressure alkylate product. 

Whatever the fractionation scheme used, the fraction is removed as overhead from the debutanizer. References 45 and 46 give ethylene manufacturing process. 

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. 

Debutanizers or other 100-250 PSIG towers Depropanizers or other high pressure towers... 

The Hj/400°FVT streams from each system are sent to separate flash drums where the bulk of the Cj and lighter material is removed. The virgin and cat cracker streams from the flash drums go to separate debutanizers while the Powerformer stream goes to an absorber-deethanizer followed by a debutanizer. The Q and lighter overhead streams from the virgin and cat cracker debutanizers are sent to this absorber- deethanizer for final deethanization. In the flow scheme shown this tower does not have a separate lean oil. It is called an absorber-deethanizer because the Powerformer stream serves in part to absorb the Cj and C4 components in the streams from the debutanizers. A separate lean oil stream is added in cases where higher Q and Q recoveries are justified. 

Butane and heavier bottoms from the depropanizer flow to the debutanizer where the C4 stream (almost entirely olefins and diolefins) is taken overhead and sent to butadiene and isobutylene recovery facilities. 

The demand for isoprene for Butyl rubber led to the development of a recovery process for this Cj diolefin. Extractive distillation with acetone was the first process used but it has been replaced with acetonitrile (ACN ). The first step in the process is the fractionation of steam cracker debutanizer bottoms in a conventional two tower system to produce a C5 cut containing 30% isoprene. The first tower rejects C and heavier while the second rejects C4 and lighter materials. 

The minimum number of trays necessary to debutanize the effluent from an alkylation reactor will be calculated. The feed, products, and vapor-liquid equilibrium costants of the key components at conditions of temperature and pressure corresponding to the top tray and reboiler are shown in Table 8-1. 

Figure 9-4. The Octol Oligomerization process for producing Os s and Ci2 s and Cis s olefins from n-butenes (1) multitubular reactor, (2) debutanizer column, (3) fractionation tower.

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 HPS liquid consists mostly of C3 s and heavier hydrocarbons however, it also contains small fractions of Cj s, H2S, and entrained water. The stripper removes these light ends. The liquid enters the stripper on the top tray. The heat for stripping is provided by an external reboiler, using steam or debutanizer bottoms as the heat medium. The vapor from the reboiler rises through the tower and strips the lighter fractions from the descending liquid. The rich overhead vapor flows to the HPS via the condenser and is fed to the primary absorber. The stripped naphtha leaves the tower bottoms and goes to the debutanizer. Usually, at least one draw is installed in the tower to remove the entrained water. 

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 LPG stream containing a mixture of C s and C4 s must be treated to remove hydrogen sulfide and mercaptan. This produces a noncorrosive, less odorous, and less hazardous product. The C s and C4 s from the debutanizer accumulator flow to the bottom of the H S contactor. The operation of this contactor is similar to that of the fuel gas absorber, except that this is a liquid-liquid contactor. 

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 ... 

HCO is the sidecut stream from the main column that boils between LCO and decanted oil (DO). HCO is often used as a pumparound stream to transfer heat to the fresh feed and/or to the debutanizer reboiier. HCO is recycled to extinction, withdrawn as a product and processed in a hydrocracker, or blended with the decant oil. 

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. 

Increasing lean oil rate. This rate is often limited by the debutanizer hydraulic and reboiling/cooling capacity. A 50% increase in lean oil/off-gas ratio increases Cj s recovery about 2%. 

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 ... 

LPG released by operator during water draining operation of debutanizer system 25,000,000 loss... 

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.

De Broukere mean diameter, 18 135 Debt capital cost, 9 542 Debt ratio (DR), 9 541 Debt structure, 9 542-543 Deburring, surface, 9 597-598 Debutanizer, 10 614—615 Debye-Huckel theory, of electrolytes, 3 415 18... 

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