Depropanizer overhead condenser

Depropanizer overhead condenser, top row of tubes, middle of tube bundle... 

Figure 13.2 is a sketch of a depropanizer overhead condenser. Let s make a few assumptions about this shell-and-tube condenser ... 

The overhead product is totally liquefied in the overhead condensers. A portion of the overhead liquid is pumped and returned to the tower as reflux. The remainder is sent to a treating unit to remove H2S and other sulfur compounds. The mixed Cj s and C s stream can then be fed to an ether or an alkylation unit. It can be fed to a depropanizer tower where the Cj s are separated from C4 s. The Cj s are processed for petrochemical feedstock and the C4 s are alkylated. 

The material distilled in some towers becomes super-corrosive when exposed to moisture. Some depropanizers in sulfuric-acid alkylation service are quite susceptible to moisture-initiated corrosion. One such depropanizer had a long history of corrosion failures. Most frequently, the overhead condenser tubes would start leaking. When this occurred, propane vapors rose from the cooling tower. Often, the effects of corrosion were less subtle clouds of hydrocarbons would burst forth from leaking lines. 

Specific areas where corrosion is likely to occur include the bottom of the acid rerun tower, the depropanizer tower, the overhead condensers of these towers, the reboiler of the propane stripper, and piping around the acid rerun tower. 

The overhead vapor from a depropanizer distillation column is totally condensed in a water-cooled condenser at 120°F and 227 psig. The vapor is 95 mol % propane and 5 mol % isobutane. Its design flow rate is 25,500 lb yh and average latent heat of vaporization is 125 Btu/lb . 

The cracked gas in this scheme shown on the next figure is compressed before being caustic-washed and dried. The dried cracked gas is sent to the depropanizer who e the overhead is compressed. It then goes to a fi ont-end acetylene reactor where the acetylene is hydrogenated to ethylene and ethane. After hydrogoiation, the gases are partially condensed to xovide reflux for the depropanizer. The net overhead liquid and vapor, which contain the C3 and lighter... 

Top impurity accumuiation. In some coliunns, overhead is totally condensed and then decanted to form an aqueous stream and an organic product. The organic product is then sent to a stripper to remove traces of the aqueous phase. The stripper overhead is then recycled to the column condenser inlet. A tsqiical example is a refinery HF alkylation unit depropanizer/HF stripper system. 

In the separation train, the gas stream is partially liquefied before entering the demethanizer at 320 bar. The overhead vapor, containing methane and hydrogen, is sent to a membrane separator in which these products are separated. The pressure of the bottoms product is reduced to 270 bar and fed to the deethanizer. In this column, the ethylene and ethane are removed in the distillate, whose pressure is reduced to 160 bar before the species are separated in the C-2 splitter. The bottoms product from the deethanizer, containing propylene, propane, and the heavier species, is throttled to 190 bar, mixed with the bottoms product from the condensate splitter, and fed to the depropanizer. The overhead product of the depropanizer is a mixture of propane and propylene and the bottoms product is throttled to 50 bar and sent to the debutanizer. In this column, the butylenes and butadiene are separated from the SCN. 

A different scheme is offered by C. F. Braun and Co., which takes the effluent vapor from the acid gas removal system and, after drying and cooling, feeds it to the depropanizer [15]. The overhead from this column is compressed to around 540 psia, hydrogenated to remove the dienes, and chilled to separate a hydrogen stream from the condensed hydrocarbons. Liquid condensates contain methane, plus the C-2 and C-3 hydrocarbons present in the feed to the depropanizer. These liquids are fed to the demethanizer, which strips the methane overhead. The demethanizer bottoms serve as feed to the deethanizer. The overhead from that column goes to the C-2 splitter, while the bottoms is the feed to the 03 splitter. The bottoms liquid from the original depropanizer is sent to the debutanizer for separation of the C-4 hydrocarbons from the aromatic gasoline fraction. 

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