Reduced-crude cracking

Faced with the need of obtaining more transportation fuels from a barrel of crude, Ashland developed the Reduced Crude Conversion Process (RCC ). To support this development, a residuum or reduced crude cracking catalyst was developed and over 1,000 tons were produced and employed in commercial operation. The catalyst possessed a large pore volume, dual pore structure, an Ultrastable Y zeolite with an acidic matrix equal in acidity to the acidity of the zeolite, and was partially treated with rare earth to enhance cracking activity and to resist vanadium poisoning. 

They began reduced crude cracking experimentation in a small 12,000 barrel per day (B/D) Fluid Catalytic Cracking (FCC) operating unit at Louisville, Ky. The RCC process was born from these goals, concepts and a small operating unit. The development and attributes of this process have been described in a number of articles and patents (1-6). 

Hettinger Jr, W. P. Development of a Reduced Crude Cracking Catalyst. Chapter 19 in ACS Symposium Series 375, Edited by M. L. Occelli. Washington, DC ACS, 1988. 

An old variation of the conversion type is a catalytic combination unit. Development of this scheme was necessitated by the rising cost of refinery construction after World War II and by the great demand for capital for postwar expansion. The scheme reduced the investment and operating costs for refining equipment. The basic feature of the combination unit lies in the integration of the fractionation facilities of the reduced crude distillation and catalytic cracking sections. 

The VPS overhead consists of steam, inerts, condensable and non-condensable hydrocarbons. The condensables result from low boiling material present in the reduced crude feed and from entrainment of liquid from the VPS top tray. The noncondensables result from cracking at the high temperatures employed in the VPS. Inerts result from leakage of air into the evacuated system. Steam and condensable hydrocarbons are condensed using an overhead water-cooled condenser. The distillate drum serves to separate inerts and non-condensables from condensate, as well as liquid hydrocarbons from water. Vacuum is maintained in the VPS using steam jet ejectors. 

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... 

In the development of a process to crack reduced crude, it soon became evident that the metals levels encountered in these crudes would be considerably higher. Therefore, metals would be expected to manifest themselves in very unfavorable ways. Previously, nickel was considered the worst poison by far, in terms of and coke make, and poor product distribution. 

The atmospheric bottom, also known as reduced oil, is then sent to the vacuum unit where it is further separated into vacuum gas oil and vacuum residues. Vacuum distillation improves the separation of gas oil distillates from the reduced oil at temperatures less than those at which thermal cracking would normally take place. The basic idea on which vacuum distillation operates is that, at low pressure, the boiling points of any material are reduced, allowing various hydrocarbon components in the reduced crude oil to vaporize or boil at a lower temperature. Vacuum distillation of the heavier product avoids thermal cracking and hence product loss and equipment fouling. 

Table III. Fluid Catalytic Cracking of Reduced Crude Using Activated Natural Clay...

To date, twenty-six commercial units have been installed to deasphalt residual oils for the production of lubricating oils and three units to deasphalt (decarbonize) heavy reduced crudes for preparation of catalytic cracking feed stocks. 

Nature of the feed stock to the unit. Adding 10 to 15% cracked residuum to a reduced crude feed increased the lump yield 10 to 15% at constant temperature and constant soaking time. 

Heavy Oil Cracking Kellogg Reduced Crude Conversion (Ashland) Resid Crocking (Total)... 

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... 

Houdresid catalytic cracking a continuous moving-bed process for catalyti-cally cracking reduced crude oil to produce high octane gasoline and light distillate fuels. 

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