Product 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. 

Residual fuel oil is generally known as the bottom product from atmospheric distillation units. Fuel oils produced from cracking units are unstable. When used as fuels, they produce smoke and deposits that may block the burner orifices. 

The separate stepwise condensation of the products from Fe-LTFT and Fe-HTFT synthesis produces streams of different carbon number distributions that serve as feeds to the oil refinery (Figure 18.4).30 It is consequently not necessary to employ an atmospheric distillation unit as the first step in the refinery. The stepwise condensation products from Fe-LTFT are reactor wax (liquid at LTFT conditions), hot condensate (>100°C), cold condensate (produced by condensation with the aqueous product and then phase separated), and tail gas (typically C4 and lighter). The stepwise condensation products from Fe-HTFT are decanted oil (liquid at 145°C 1.6 MPa), light oil (produced by condensation with the aqueous product and then phase separated), and tail gas. 

The Fe-HTFT syncrude is fractionated in an atmospheric distillation unit to produce mainly naphtha and distillate, with a small amount of residue that is used as fuel oil (not shown in Figure 18.7). No vacuum distillation unit has been included in the design, since it would be superfluous with the limited residue production. The natural gas liquids are fractionated separately. 

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. 

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. 

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. 

In the 1970 s, heavy fuel came mainly from atmospheric distillation residue. Nowadays a very large proportion of this product is vacuum distilled and the distillate obtained is fed to conversion units such as catalytic cracking, visbreaking and cokers. These produce lighter products —gas and gasoline— but also very heavy components, that are viscous and have high contaminant levels, that are subsequently incorporated in the fuels. 

A combination unit is a special type of unit that was developed to reduce the investment for a small refinery. In effect, one main distillation unit serves as a crude fi-actionator as well as the cat unit primary fractionator. This same tower also serves the naphtha reformer and visbreaker. A schematic diagram of a combination unit is shown in Figure 2. Crude oil is topped (material boiling below 650°F is removed) in the atmospheric tower, and the topped crude is sent to the combination tower along with cat products and naphtha reformer products. These latter streams provide heat to distill the topped crude and also, being more volatile than topped crude, provide a lifting effect which assists in vaporizing more of the crude. 

Kerosine, a distillate fraction heavier than naphtha, is normally a product from distilling crude oils under atmospheric pressures. It may also he obtained as a product from thermal and catalytic cracking or hydrocracking units. Kerosines from cracking units are usually less stable than those produced from atmospheric distillation and hydrocracking units due to presence of variable amounts of olefinic constituents. 

In present-day refineries, the fluid catalytic cracking (FCC) unit has become the major gasoline-producing unit. The FCC s major purpose is to upgrade heavy fractions, that is, gas oil from the atmospheric and vacuum distillation columns and delayed coker, into light products. Atmospheric gas oil has a boiling range of between 650-725°F.9... 

Atmospheric distillation is least effective in converting heavier products into lighter components. A second distillation column under vacuum is needed to further separate the heavier parts of crude oil into lighter fractions. Some fractions from the vacuum units have better quality than atmospheric distillation cuts because the metal-bearing compounds and carbon-forming materials are concentrated in the vacuum residue. 

The atmospheric residuum is then fed to the vacuum distillation unit at the pressure of 10 mmHg where light vacuum gas oil, heavy vacuum gas oil, and vacuum residue are the products (Fig. 13.4). 

Atmospheric residue oil (Residue), containing compounds that boil above about 340°C (650°F). This is normally sent to a vacuum distillation unit to recover more light products, but parts of it may be blended into high sulfur fuels such as heating oil or bunker fuel (marine fuel). 

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