Feedstock reduced crude

The polar aromatics plus asphaltenes relationship versus coke yield was investigated for a number of reduced crudes. Table V gives the results of findings for eight RCC feedstock reduced crudes. As can be seen in a number of instances the predictions are consistent. 

The atmospheric reduced crude is the feedstock for the vacuum distillation unit. To prevent thermal decomposition (cracking) of the higher boiling point hydrocarbons in the crude oil, the pressure in the vacuum distillation fractionation column is reduced to about one-twentieth of an atmosphere absolute (one atmosphere pressure is 14.7 psia or 760 mm Fig). This effectively reduces the boiling points of the hydrocarbons several hundred degrees Fahrenheit. The components boiling below about 1050°F (565°C) are vaporized and removed as vacuum gas... 

As work began on the process, it quickly became apparent that the extraordinary catalyst properties required for the process were not then available, and even with a superior catalyst, consumption would undoubtedly be severe. Figure 3 shows how Ramsbottom Carbon and nickel plus vanadium vary in the same reduced crude oils. All levels are very high far beyond anything normally encountered in a gas oil feedstock. 

RCC process catalysts with metals contents as high as 12,300 ppm nickel plus vanadium, plus 6,000 ppm of iron, have operated in the 200 B/D demonstration unit on feedstocks containing up to 84 ppm nickel plus vanadium.(4,5) Presently in our refinery, when metals levels are at still higher levels, the reduced crude is first processed in the Ashland ART unit, where some 85-95% of the metals and 75% of the Ramsbottom Carbon are removed.(6)... 

If the reduced crude is not required as a source of lubricating oils, the lubricating and heavy gas oil fractions are combined or, more likely, removed from the residuum as one fraction and used as a catalytic cracking feedstock. 

Coking is a thermal process for the continuous conversion of heavy, low-grade oils into lighter products. The feedstock can be reduced crude, straight-run residua, or cracked residua, and the products are gases, naphtha, fuel oil, gas... 

A number of refiners have processed residue containing feedstocks in commercial FCC units. Feeds with as much as 5.1%w RCR ( 6.5%w CCR) and 85 ppm Ni + V have been processed in Phillips Borger Refinery.(4) Ashland has processed feedstocks of up to 7.1%w RCR ( 8.5%w CCR) and 85 ppm Ni + V in their RCC (Reduced Crude Conversion) process.(5,6) A commercial scale ART (Asphalt Residual Treating) unit has processed residues containing levels of contaminants as high as 13.5%w RCR and 300 ppm Ni + V (7,8). However, in typical day-to-day operation of residue cat crackers, feedstock quality is not as extreme as those illustrated above. 

In the program of feedstock quality analysis, the goal was to predict the product distribution that can be expected from the reduced crude conversion of each feedstock. In this paper the results of slurry oil and coke yield predictions will be discussed. The next section gives a brief overview of the chemistry of catalytic cracking and some of the basic concepts which were used to guide the development of the slurry oil and coke yield predictions. 

Of course, the reduced crude conversion process is not 100% efficient. By this it is meant that to date no catalyst and operating conditions have been developed which completely remove saturates, monoaromatics, diaromatics, and alkyl substituents of polynuclear aromatics from the slurry oil. Therefore, to predict slurry oil plus coke yield one must determine what proportion of each molecular type present in the reduced crude feedstock remains in the slurry oil and coke. 

Table I. Typical HPLC Analysis of Reduce Crude Feedstocks...

The coke yield from a given feedstock is affected by many variables such as reactor temperature, metals on catalyst, and catalyst type. It was also found that coke yield predictions did not agree when the RCC feedstocks were high API gravity reduced crudes. 

In order to predict slurry oil plus coke yield one must determine what proportion of each molecular type present in the reduced crude feedstock remains in the slurry oil and coke. 

Analysis of many feedstocks and slurry oils indicated that the monoaromatics followed a pattern similar to the saturates. Therefore, a monoaromatics slurry oil plus coke factor was developed. The monoaromatics slurry oil plus coke factors for 10-20 and 20-30 API gravity reduced crudes are given in Table VII,... 

The diaromatics were found to follow a different pattern. No relationship was found between the diaromatics content of a slurry oil and its API gravity. It was determined, however, that approximately one third of the diaromatics in the reduced crude feedstock remained in the slurry oil. 

From the above discussion one can propose an equation for the prediction of slurry oil and coke yields in the RCC unit from a particular reduced crude feedstock. The equation is the following ... 

Table X shows the results of calculations for two RCC tests made on the same feedstock. The predictions are consistent with actual yields. Tables XI and XII are also results of slurry oil plus coke yield predictions from various reduced crudes. All prediction made in Tables X-XII were made with reduced crudes having an API gravity of 10-20. The saturates and monoaromatics factors change as the API gravity of the reduced crude feedstock changes. Tables XIII and XIV give the results of slurry oil plus coke predictions for West Texas Intermediate and Illinois Basin reduced crudes. These two reduced crudes have API gravities of 20-30. Again consistent predictions were made.

Hydrotreating refers to a relatively mild operation whose primary purpose is to saturate olefins and/or reduce sulfur and nitrogen content without changing too much the boiling range of the feed. Hydrotreating is applied to a wide range of feedstocks from naphtha to reduced crude oil. If the process is used specifically for sulfur removal, it is usually called hydrodesulfurization or HDS. 

T]rpes of Fractionators. Some operations such as the separation of distilled catalytic feedstock from a reduced crude oil can be accomplished by substantially a single flash vaporization (see Fig. 7-27). Entrainment is removed from the vapor by a wire-mesh blanket, means of washing any accumulation of (asphaltic) entrainment from the mesh is provided, and the top of the tower contains only a means of withdrawing the overhead product. Most heavy-oil towers also function in some degree as condensers note that all overhead product except noncondensable gases is condensed in the top of the tower shown in Fig. 7-27. 

Upgrading and refinery capacity While essentially all of the mined bitumen is upgraded in Alberta, the majority of in-situ production is shipped as bitumen blend with a light diluent to refineries in the United States that are suitably equipped to handle such feedstock. This historical split needs to be overcome in the future and further upgrading capacities will have to be installed in Canada, especially to reduce the need for diluents. In addition, the proposed extension of synthetic-crude-oil supply will require new refinery capacities, either in Canada or the United States. 

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