Coker feed

The vacuum residua or vacuum bottoms is the most complex fraction. Vacuum residua are used as asphalt and coker feed. In the bottoms, few molecules are free of heteroatoms molecular weights range from 400 to >2000, so high that characteri2ation of individual species is virtually impossible. Separations by group type become blurred by the sheer mass of substitution around a core stmcture and by the presence of multiple functionahties in a single molecules. Simultaneously, the traditional gc and ms techniques require the very volatiUty that this fraction lacks. 

Coker feed Coking Coking coal Coking coals... 

Forecast the quantity of 1,000+ material required to meet the demand for other products such as residual fuel oil and asphalt. The remaining 1,000+ material is assumed to be coker feed. 

AVAILABLE FOR COKER FEED CALCULATED BY DIFFERENCE AFTER OTHER DEMANDS ARE MET... 

Fluid coke (Table 16.2) is produced during the fluid coking process—a continuous process in which heated coker feeds are sprayed into a fluidized bed of hot coke particles that are maintained at 20 0 psi and 500°C (932°F) (Chapter 2) (Speight and Ozum, 2002). The feed vapors are cracked while... 

In the studies reported in this ehapter, the hydrocarbon (continuous) phase of the emulsion was composed of coker feed bitumen, extracted from Athabasca Oil Sand deposit (18). To attain workable viseosities, bitumen is diluted in a 1 1 mixtme, by volume, of n-heptane and toluene (both... 

The yield of precipitated asphaltenes cannot be reduced because the asphaltenes in the coker feed will produce coke regardless of coke drum operating parameters. 

The formation of free radicals in the coker feed is favored by exposure of the crude or resid to oxygen. Particulate matter in the resid also accelerates shot coke formation. The particulates can be controlled by improving the operation of the crude unit desalter. 

Reducing the virgin gas oil content ol coker feed by 10% reduces coke yield by 1.5 wt% on feed. 

The coker feed nozzle at the bottom of the coke drum can plug with shot coke. How can this be prevented ... 

The hot coke drum vapors are a valuable source of high-level heat. This energy, which is partially recovered in the combination tower heavy gas-oil pumparound section, can be used for generating steam, preheating coker feed, or reboiling a gas plant. The higher the temperature level at which this heat is made available for recovery, the greater is its potential value. This is the second law of thermodynamics in action. 

I had noticed upon first reviewing the product ASTM distillation lab data that fractionation between HCO and slurry were both quite good. As can be seen in Figure 8-5, however, the HCO and slurry products were commingled as coker feed. Evidently, packed section 5 in this tower was not serving a useful purpose. With this in mind, we proceeded with the following (see Fig. 8-5) ... 

The process conditions shown in Figure 13-7 were the design-basis operating parameters. Note that the 715°F flash-zone temperature and the 25-in. Hg flash-zone pressure (128 mm Hg) are indicative of an operation that results in excessive gas oil left in the vacuum tower bottoms. This downgrades virgin gas oil from FCCU feedstock to delayed coker feed at a penalty of 5/bbI. A properly designed and operated vacuum column that employs steam stripping of the heater coils operates at 27-in. Hg flash-zone pressure and 760°F flash-zone temperature. 

The final result on this tower was a 3,200 B/SD gain in FCCU feed at the expense of coker feed, about 200 B/SD more than the revamp was supposed to achieve. At 5/bbl, that amounted to a 16,000/day yield improvement on the tower. 

We have heard of helical baffle exchangers being used in oil refineries to preheat delayed coker feed with vacuum resid on the shell side (with the helical baffles). In this service, the helical baffles seem to work well, resulting in less fouling, slower rate of increase in... 

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