Specifications atmospheric distillation unit

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] ... 

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. 

As shown in Figure 1, hydrocracking often is an in-between process. The required hydrogen comes from catalytic reformers, steam/methane reformers or both. Liquid feeds can come from atmospheric and/or vacuum distillation units delayed cokers fluid cokers visbreakers or FCC units. Middle distillates from a hydrocracker usually meet or exceed finished product specifications, but the heavy naphtha from a hydrocracker usually is sent to a catalytic reformer for octane improvement. The fractionator bottoms can be recycled or sent to an FCC unit, an olefins plant, or a lube plant. 

Each of the processes shown in Figure 2.1 is quite extensive and can be surprisingly complex in an integrated refinery. In this work, we limit the scope by presenting brief summaries of the unit and how to deal with each unit in a modeling context Our specific focus is how to model the atmospheric distillation section. 

Since cracking stocks generally do not have to meet the color specifications that lube distillates do, higher flash zone temperatures (up to 8(X)°F) can be tolerated. Fuel units are normally designed to distill material boiling up to 1100°F (at atmospheric pressure) from the feed, and some units have distilled beyond 12(X)°F at low feed rates. 

The catalytic cracking unit is often referred to as the gasoline workhorse of a refining unit. As shown in Fig. 18.9, feeds to the catalytic cracking unit are gas oils from the atmospheric and vacuum distillation columns and delayed coker. These heavier fractions also carry metals such as nickel, vanadium, and iron. More important, sulfur compounds concentrate in the heavier product fractions. Table 18.8 lists a typical mass balance for sulfur.25 FCC blend-stocks comprise 36 percent of the volume of the gasoline pool. However, this stream also contributes 98 percent of the sulfur concentration to blended procucts.25 As specifications on sulfur concentrations in diesel and gasoline tighten, more efforts are focused on how feeds and product streams from the FCC are pre- and posttreated for sulfur concentrations. 

Properties. — Thallium is a white metal with blue tint, and when freshly cut it has a brilliant metallic luster. It is so soft that it may easily be marked with the thumb nail and leaves a black streak on paper. It is malleable but has little tenacity, and when an attempt is made to cut it with a file or saw it stops up the teeth of the tool. It has a crystalline structure and emits a sound similar to the tin cry. It exists in two modifications, the transition temperature bang 226°. It melts at 303°, commences to volatilize at 174°, boils under atmospheric pressure at 1515°, and may be distilled in a stream of hydrogen. The coefficient of expansion is 0.000031 and the coefficient of compressibility is 2.33 X 10- per atmosphere. The latent heat of fusion is 7.2 calories per gram, the mean specific heat is about 0.03. The electrical conductivity1 in reciprocal ohms per cubic centimeter at 20° is 5.28 and the magnetic susceptibility is—29 X 10-6C,g.s. units per unit volume. In the electromotive series thallium comes between iron and cobalt. 

To run a refinery alkylation unit isobutane and light olefins are required as feedstock. However, the composition of the olefin stream varies significantly with the local refinery situation and this requires careful adjustment of the process conditions. The most commonly used olefins are butenes and propene but sometimes the use of pentenes is also considered. New gasoline specifications and the Chan Air Act (a United States federal law) amendments make it necessary to remove pentenes from the gasoline pool, because of their potential for atmospheric pollution. The main sources of olefins are catalytic cracking and coking processes. The isobutane feed for alkylation units is mainly obtained from hydrocrackers, catalytic crackers, and catalytic reformers. Additional amounts of isobutane are directly available from crude distillation and natural gas processing. Moreover, n-butane can be... 

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