Liquid effluents naphtha

In the process (Figure 9-22), fresh vacuum residuum, microcatalyst, and hydrogen are fed to the hydroconversion reactor. Effluent is sent to a flash separation zone to recover hydrogen, gases, and liquid products, including naphtha, distillate, and gas oil. The liquid bottoms from the flash step is then fed to a vacuum distillation tower to obtain a 565°C (1050°F ) product oil and a 565°C + (1050°F+) bottoms fraction that contains unconverted feed, microcatalyst, and essentially all of the feed metals. 

A typical process flow diagram of a catalytic reformer is shown in Figure 3.17. Desulfurized naphtha is heated in feed-effluent exchangers and then passed to a fired heater, where it is heated to 850 to 1,000° F (455 to 540° C) at 500 psia (3,450 kPa) in a series of reactors and fired heaters. In the reactors, the hydrocarbon and hydrogen are passed over a catalyst (often platinum/rhenium based) to produce rearranged molecules, which are primarily aromatics with some isoparaffins. The reactor effluent is cooled by exchange and then passed to a separator vessel. The gas from the separator is recycled to the reactors. The liquid is fed to a fractionator. 

A typical steam cracker consists of several identical pyrolysis furnaces in which the feed is cracked in the presence of steam as a diluent.The cracked gases are quenched and then sent to the demethanizer to remove hydrogen and methane. The effluent is then treated to remove acetylene, and ethylene is separated in the ethylene fractionator. The bottom fraction is separated in the de-ethanizer into ethane and C3, which is sent for further treatment to recover propylene and other olefins. Typical operating conditions of ethane steam cracker are 750-800°C, 1-1.2 atm, and steam/ethane ratio of 0.5. Liquid feeds are usually cracked at lower residence time and higher steam dilution ratios compared to gaseous feeds. Typical conditions for naphtha cracking are 800° C, 1 atm, steam/hydrocarbon ratio of 0.6-0.8, and a residence time of 0.35 sec. Liquid feedstocks produce a wide spectrum of coproducts including BTX aromatics that can be used in the production of variety of chemical derivatives. 

Main fractionation column. Reactor effluent is separated into various products. The overhead includes gasoline and lighter material. The heavy liquid products, heavier naphtha, and cycle oils are separated as side cuts and slurry oil is separated as a bottom product. 

The studies were conducted in stainless steel tubular reactors approximately 3.8 cm in diameter and about 1200 cm3 in volume. The reactors were immersed in electrically heated fluidized solids baths. A naphtha fraction to be reformed was vaporized and heated to reaction temperature before contacting the catalyst. The reactor effluent was separated into liquid and gaseous fractions. A portion of the hydrogen-rich gaseous fraction was recycled through the reactor to simulate commercial reforming practice. The recycle gas was combined with the vaporized naphtha fraction prior to the reactor inlet. The mole ratio of recycle gas to naphtha at the reactor inlet was approximately 7 in all of the runs to be discussed here. 

The liquid and gaseous effluents obtained are quenched and sent to a primary fractionation column, which produces an oil at the bottom, partly used as a quenching fluid, and pitch, tars and a naphthalene-rich aromatic oil at the side withdrawals. Naphtha and tighter fractions are recovered at the top of the column. Alter compression, the different fractionation operations required on the light products are identical to those of conventional steam cracking, while the only significant difference relates to the acetylene recovery unit, which is larger. 

The distillate rate is set at 20,000 B/D. This will be adjusted later to obtain a desired ASTM 95%pointof 375 °F for the liquid distillate product, which is a fight naphtha stream. Note that there is only one degree of freedom in this rectifying column since there is no reboiler. All of the vapor coming up the column comes from the partially vaporized furnace effluent. 

Figure 1. Each sloped line represents the loci of all possible combinations of average residence times and hydrocarbon partial pressures which are consistent with a fixed pyrolysis yield pattern, i.e., constant pyrolysis selectivity lines. For liquid feedstocks, the methane-to-ethylene ratio found in the pyrolysis reactor effluent has been used as a good overall indicator of pyrolysis reactor selectivity. Low methane-to-ethylene ratios correspond to a high total yield of ethylene, propylene, butadiene and butylenes. Consequently, the yields of methane, ethane, aromatics and fuel oil are reduced. TL refore, each constant pyrolysis selectivity line shown in Figure 1 is identified with a fixed methane-to-ethylene ratio. This specific selectivity chart applies to a Kuwait heavy naphtha which is pyrolyzed to achieve a constant degree of feedstock dehydrogenation, i.e., a constant hydrogen content in the effluent liquid products, which in this case corresponds to the limiting cracking severity.

Using the back-blending concept from the previous section, develop a FCC effluent TB P curve from a reference set of product yields. These yields include all liquid products such as light and heavy naphtha, light and heavy cycle oil or diesel, slurry or decant oil. 

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