Atmospheric crude unit

The atmospheric crude unit separates crude oil into several fractions including LPG, naphtha, kerosene, gas oil and residues. The heavy residues are then sent to the vacuum unit where they are further separated into vacuum gas oil and vacuum... 

FIG. 13-87 Crude unit with atmospheric and vacuum towers. [Kleinsch7 odt and Hammer, Exchange Networks for Cixide Units . Chem. Eng. Prog., 79(7),. 3.3 (1983).]... 

FIG. 13-94 Configuration and conditions for the simulation of the atmospheric tower of crude unit. 

Gas plants are integrated tower systems intended to recover LPG range material and separate it from naphtha products. This stabilizes the naphtha and reduces its vapor pressure. The LPG material may either be saturate gases going to LPG or unsaturates going to further processing. Gas plants on preflash and atmospheric crude processing units are saturate gas plants. Gas plants on FCC units are unsaturate gas plants. Coker and visbreaker gas plants are somewhere between the two. 

Atmospheric distillation separates the crude oil complex mixture into different fractions with relatively narrow boiling ranges. In general, separation of a mixture into fractions is based primarily on the difference in the boiling points of the components. In atmospheric distillation units, one or more fractionating columns are used. 

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... 

Crude unit with both atmospheric and vacuum distillation, 200,000 BSD 96... 

The fractions obtained by vacuum distillation of the reduced crude (atmospheric residuum) from an atmospheric distillation unit depend on whether or not the unit is designed to produce lubricating or vacuum gas oils. In the former case, the fractions include (1) heavy gas oil, which is an overhead product and is used as catalytic cracking stock or, after suitable treatment, a light lubricating oil (2) lubricating oil (usually three fractions—light, intermediate, and heavy), which is obtained as a side-stream product and (3) asphalt (or residuum), which is the nonvolatile product and may be used directly as, or to produce, asphalt, and which may also be blended with gas oils to produce a heavy fuel oil. 

A problem may occur here in that the separation of oil and water may not be complete by the time the oil exits the desalter on its way to an atmospheric fractionation unit. Any water that remains with the crude oil will have to be heated to atmospheric fractionator inlet temperature, typically 290-370 C. 

Case study crude oil atmospheric distillation unit... 

The current oil sands bitumen upgrading processes for the production of synthetic crude oil (Table 4) begin with diluted bitumen being processed through the diluent recovery units. The diluent recovery units are atmospheric distillation units that serve three purposes 1) distill off diluent naphtha and return it to the froth treatment process 2) distill off light gas oil and send it directly to a light gas oil hydrotreater and 3) produce hot atmospheric topped bitumen as feedstock for vacuum distillation unit and downstream bitumen conversion processes. 

If a crude unit contains only a two-column atmospheric unit, then in the main column a moderate vacuum has to be kept ( 0,8 atm) with the help of vacuum-creating equipment joined with c reflux drum. 

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. 

---