Operating atmospheric distillation unit

The graph gives the yields that the refiner would obtain at the outlet of the atmospheric distillation unit allowing him to set the unit s operating conditions in accordance with the desired production objectives. 

By approaching the refinery design from a crude oil perspective, the advantage of preseparation by stepwise condensation after HTFT synthesis was reduced. The refinery design included primary separation steps typically found in crude oil refineries, namely, an atmospheric distillation unit (ADU) that is followed by a vacuum distillation unit (VDU). Despite the design intent, the operation of these units, out of necessity, had to be different. The reboiler temperature of the ADU was... 

The process specifications on raw material speed through furnaces coils imposed the use of two or four parallel passes, e.g. the fumaees from the atmospherie distillation unit, vacuum distillation unit, catalytic reforming unit, coker unit, catalytic cracking unit. The conventional control structure of radiant section for a typical tubular furnace from the atmospheric distillation unit (output capacity 3.5 Mt/year) is presented in figure 1 [1]. Because the conventional temperature control system only controls one outlet temperature or in the best case the temperature of the mixing point, in current operations there are several situations [1, 2, 3] ... 

Modern refineries operate within strong economic, regulatory and process constraints. Many times, the preferable operating mode for the atmospheric distillation unit may not be operating mode that matdmizes the yield of the most valuable product from the distillation unit alone. The atmospheric column operates in concert with many other units in the refinery. Therefore, it is important to understand how the product yield slate changes with different draws of a given cut... 

The distillated products of atmospheric distillation unit (ADU) are limited to the boiling fractions under 350 C such as gasoline and diesel because pietroleum fractions tend to thermally degrade in high tempieratures. To recover additional distillates and gas oils, the refinery uses vaaium distillation unit (VDU) following the ADU. The reduced operating pressure ofVDU allows recovery of heavy boiling fraction above 560 C from the atmospheric residue. 

Aromatic alkylation is illustrated in this paper for both individual a-olefin cuts (e.g. 1-decene and 1-dodecene) as well as typical samples of Ci0-Ci4 paraffin dehydrogenate that contain ca. 8.5% Go-Cm olefins, primarily internal olefins. Syntheses have, for the most part, been conducted in a continuous reactive distillation unit of the type illustrated in Figure 1, operated slightly above atmospheric pressure. Operational details for this unit may be found in the previous section. 

During the past several years such stills have been largely replaced by tube or pipe stills because of their lower initial cost, greater throughput, and economy of operation. A common type of operation utilizes a two-stage atmospheric and vacuum distillation unit (13). This type of operation has an important advantage—the asphaltic residue remains at the extreme temperature for only a fraction of a minute in the pipe stills as contrasted to several hours in shell-type stills. 

A continuous distillation unit, consisting of a perforated-tray column together with a partial reboiler and a total condenser, is to be designed to operate at atmospheric pressure to separate ethanol and water. The feed, which is introduced into the column as liquid at its boiling point, contains 20 mole% alcohol. The distfllate is to contain 85% alcohol, and the alcohol recovery is to be 97%. 

Obtain a sample of FCCU feed produced at the crude unit. Run an ASTM atmospheric distillation. Ask the lab technician to stop the distillation at 680°F this avoids thermal cracking. If more than a few percent is distilled off below 500°F, examine the operation of the FCCU feed stripper. 

The degree of dehydration that can be attained with a glycol solution is primarily dependent on the extent to which water is removed from the solution in the reconcentrator. The operation of atmospheric pressure distillation units for water removal is limited by the maximum temperature that can be tolerated without excessive decomposition of the glycol (about 400°F for TEG). Concentration of TEG to 98.5 to 99.0% is attainable in a simple atmospheric pressure still. When significantly higher concentrations are needed to meet stringent gas dehydration requirements, the use of an enhanced stripping technique is necessary. 

This chapter serves as a guide to model atmospheric distillation section of the crude distillation unit. We provide relevant process, operational and modeling details to model the atmospheric column. We also discuss methods to estimate missing data for model development We provide step-by-step instructions to model a particular column in Aspen HYSYS. We discuss how to validate the model predictions with plant data and how to use the model to perform industrially useful case studies. 

Cracking imposes an additional penalty in a vacuum unit in that it forms gas which cannot be condensed at the low pressures employed. This gas must be vented by compressing it to atmospheric pressure. This is accomplished by means of steam jet ejectors. Ideally, it would be possible to operate a vacuum pipe still without ejectors, with the overhead vapors composed only of steam. In practice, however, leakage of air into the system and the minor cracking which occurs make it necessary to provide a means of removing non-condensibles from the system. In addition to the distillation of atmospheric residuum, the lube vacuum pipe still is also used for rerunning of off specification lube distillates. 

The vertical thermosiphon reboiler is a popular unit for heating distillation column bottoms. However, it is indeed surprising how so many units have been installed with so little data available. This indicates that a lot of guessing, usually on the very conservative side, has created many uneconomical units. No well-defined understanding of the performance of these units exists. Kern s recommended procedure has been found to be quite conservative on plant scale units yet it has undoubtedly been the basis for more designs than any other single approach. For some systems at and below atmospheric pressure operation, Kern s procedure gives inconsistent results. The problem is in the evaluation of the two-phase gas-liquid pressure drop under these conditions. 

The teed to the cat cracker in a typical refinery is a blend of gas oils from such operating units as the crude, vacuum, solvent deasphalting, and coker. Some refiners purchase outside FCC feedstocks to keep the FCC feed rate maximized. Other refiners process atmospheric or vacuum residue in their cat crackers. In recent years, the trend has been toward heavier gas oils and residue. Residue is most commonly defined as the fraction of feed that boils above 1,050°F (565 C). Each FCC feed stream has different distillation characteristics. 

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