Feed stock coking

A formula for feed-stock coke factor (124), developed from correlated experimental data, indicates that at constant cracking conditions the concentration of carbon on spent catalyst increases with higher values... 

The feed stock, usually topped or reduced crude oil, is heated in pipe coils (Figure 1) from about 900° to 950° F. The oil is then fed to one of two or more vertical, insulated coke drums. The coke drums are connected by valves so that they can be switched onstream for filling, then switched off-stream for coke removal. The temperature in the drum will ordinarily be 775° to 850° F. and the pressure 4 to 60 pounds per square inch gage. Hot, coke-still vapors from the coke drum pass to a fractionator where gas and gasoline, intermediate gas oil, and heavy gas oil are separated. More or less of the heavy gas oil is recycled. The ratio of recycled heavy gas oil to fresh feed is usually less than 1 but may go up to about 1.6 (5,15,28, 40). 

The yields and product distribution obtained in delayed coking are functions of the character of the feed stock and the operating conditions. Gas oil yields of 60 to 85 volume % with coke yields of 10 to 30 weight % of the feed are reasonably representative 5). 

In the gas black process (Fig. 55), the feed stock is partially vaporized. The residual oil is continuously withdrawn. The oil vapor is transported to the production apparatus by a combustible carrier gas (e.g., hydrogen, coke oven gas, or methane). Air may be added to the oil-gas mixture for the manufacture of very small particle size carbon black. Although this process is not as flexible as the furnace black process, various types of gas black can be made by varying the relative amounts of carrier gas, oil, and air. The carbon black properties are also dependent on the type of burners used. 

Yields of liquid products from flexicoking are the same as from fluid coking, because the coking reactor is unaltered. As with fluid coking, the extent of desulfurization depends on the sulfur content of the feedstock as well as on the chemical nature of the sulfur in the feed stock. 

Table 7 also shows these hydrogen requirements as 0.21 Quad/year in 1980 and 0.46 Quad/year in the year 2000 (coking option) or 1.41 Quad/year (hydroprocessing option). Assuming these quantities of hydrogen are produced by steam reforming, the reformer feed stock requirements would increase from 149 thousand B/D crude oil equivalent in 1980 to 326 thousand B/D in the year 2000 option) or 1001 thousand B/D for the year... 

The inferiority of catalytically cracked gas oils, compared to virgin gas oils, as feed stocks (51) is attributable to higher concentrations of condensed-ring aromatics (95). The more-readily cracked hydrocarbons have already been converted, leaving behind the more-refractory hydrocarbons originally present in the fresh feed. In addition, some polycyclic hydrocarbons have been formed by the cracking operation. The polycyclic condensed-ring aromatics are not only difficult to crack but are also characterized by production of excessive yields of coke (79,345). 

In the moving bed, gradients exist from top to bottom of the reactor with respect to both temperature and concentration of coke on the catalyst. The activity and coke concentration vary from particle to particle at a given level in the reactor because of the intermittent addition of fresh catalyst to replace losses due to attrition or intentional discard. However, a steady state exists with regard to time, so that all increments of the feed stock are exposed to the same cracking conditions and a uniform conversion is maintained. 

Study of reaction rates is simplified by the fact that, with a given feed stock and catalyst, the concentration of coke on the catalyst is essentially independent of space velocity. With other conditions fixed, the concentration of carbon on catalyst is an exponential function of time (290,346). 

The type of unit described here can, if desired, be used to convert vacuum residues to lighter materials or to prepare feed stock for low sulfur coke production. These applications of the process have been discussed in several previous papers. A good commercial example of this flexibility is shown in Table II. These data show operations of the Lake Charles H-Oil unit when processing for conversion and for desulfurization. 

A wide range of organic products is suitable as feed.stocks for the manufacture of activated carbon. Wood, sawdust, peat, coconut shells and even olive stones are the preferred uncarbonized feedstocks. Of the (already) carbonized feedstocks coal, low temperature lignite coke, charcoal and coke from acid sludges (e.g. from the manufacture of lubricants) are utilized. The properties of activated carbon are very much influenced by the type of feedstock utilized. 

Heat transfer can also be activated by the periodic contact of the material to be heated vith an externally heated vail. This method is extensively used in Europe by tumbling the feed material in an externally heated metallic rotary kiln. Another method of activating the vall-to-feedstock heat exchange is to suspend the feed-stock in a fluidized bed of sand, coke or ash. External heating of fluidized bed reactors is often used at bench scale, tvo-bed systems being preferred at an industrial scale. 

A process is described for minimizing coke buildup in porous catalysts used in the processing of hydrocarbon feed stocks by pretreatment of the feed to reduce organic peroxides and dissolved oxygen. 

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