Method for catalytic cracking heavy oils

A riser cracking operation is described for the production of gasoline and distillate material by the combination of cracking fresh gas oil charged to the base of a riser cracking zone for admixture with freshly regenerated catalyst to form a suspension thereof at an elevated cracking temperature, a second hydrocarbon fraction of more difficult cracking characteristics is charged to the suspension rising in the riser cracking zone at a point selected from 10 to about 30 feet above the riser bottom and the riser inlet temperature is restricted to be within the range of 900.degree. to 1000.degree. F.

BACKGROUND OF THE INVENTION 
It has been known for a long time that gasoline product of desirable octane 
can be obtained from selected hydrocarbon fractions by catalytic cracking. 
However, the yield of such desired gasoline products varies considerably 
with the composition of the oil feed charged to the cracking operation as 
well as the severity of the operating conditions employed. It is further 
known that heavy oils such as residual oils have a large percentage of 
very refractory components which are more difficult to crack and, in 
general, cause excessive amounts of coke to be deposited on the catalyst. 
Furthermore, metal contaminants in a heavy oil feed poison and inactivate 
the catalyst. Therefore, in the prior art, these undesirable components in 
the oil feed have been reduced by techniques such as hydrogenation, 
thermocracking, and/or adsorption on absorbent particle material of little 
or no cracking activity for the recovery of a more suitable oil feed. In 
this connection, mild thermal cracking and visbreaking operations, with or 
without the presence of hydrogen, have been relied upon to produce a more 
desirable feed material for conversion by catalytic cracking to desired 
gasoline and/or light fuel oil products. 
Residual oil, coker gas oils and other materials high in polynuclear 
aromatics are known as distress stocks in the petroleum industry. These 
oils are, therefore, often sold in fuel oil blends or thermally processed, 
as recited above, to obtain lighter, more desirable components. Residual 
oils contain large quantities of components, having coke forming 
tendencies as well as metal contaminants which adversely affect the 
stability and activity of modern-day cracking catalysts. Coker gas oils 
high in polynuclear aromatics generally low in metal contaminants also are 
coke formers and generally considered to be poor cracking feed stocks. 
The utilization of relatively high activity catalysts comprising high 
activity crystalline zeolite cracking catalysts has been responsible for 
developing refinements in cracking technology or techniques to reduce 
catalyst inventory systems and to more effectively take advantage of the 
catalyst activity, selectivity and its operating sensitivity. Reducing the 
size of equipment and catalyst inventory contributes to an economic 
advantage readily accepted by the industry. 
The following U.S. patents have been considered in the preparation of this 
application; U.S. Pat. Nos. 3,904,548; 2,994,659; 3,158,562; 3,193,494; 
3,896,024; 3,894,936; 3,886,060; 3,856,659; and 3,847,793. 
The present invention is concerned with the use of a low catalyst 
inventory, riser cracking operation using high activity crystalline 
zeolite catalyst to effect a selective conversion of hydrocarbons varying 
considerably in chemical and physical composition characteristics. More 
particularly, the present invention is concerned with disposing of 
distress stocks such as coker gas oils by fluid cracking. 
SUMMARY OF THE INVENTION 
The present invention relates to a method and system for converting 
hydrocarbon feed materials varying considerably in crackability in the 
presence of high activity crystalline zeolite catalysts. In a more 
particular aspect, the present invention is concerned with a technique for 
converting feed materials of different cracking properties or 
characteristics in a riser cracking system to particularly optimize the 
conversion of the feed to one of gasoline and distillate or a combination 
thereof and minimize the yield of a clarified slurry oil (CSO). It is 
particularly desirable to accomplish this cracking operation without 
exceeding the coke burning limits of a regeneration operation used in 
conjunction with the riser cracking operation. 
A particular operating expedient of the processing concept of this 
invention is concerned with identifying and restricting the residence time 
of various oil fractions brought in contact with an active cracking 
catalyst and particularly a zeolite catalyst so that one can optimize the 
yield of gasoline and/or distillate product and, at the same time, 
restrict the deposition of undesired carbonaceous and nitrogenous products 
obtained by what is referred to as extended overcracking of a heavy 
hydrocarbon or residual type material charged to a riser cracking 
operation. 
In a number of commercial fluid cracking operations presently employed, the 
fresh gas oil hydrocarbon feed and recycled product of cracking or other 
high boiling recycle products of cracking usually identified as the heavy 
cycle oil separated from clarified slurry oil, are introduced together for 
admixture and contact with hot catalyst at the bottom of a riser 
conversion zone. The combined oil feeds and hot catalyst admixed therewith 
flow concurrently as a suspension upwardly through the riser conversion 
zone, thereby deactivating the catalyst with a carbonaceous residue of 
cracking as the oil charge is converted to gasoline, lower and higher 
boiling products. In such an operation, it has been found that 
overcracking of some portions of the oil charged undesirably contributes 
to the deposited coke load on the catalyst and thus reduces the yield of 
available gasoline obtainable under more selective conversion conditions. 
On the other hand, the riser conversion temperature conditions may be 
restricted by downstream equipment operating conditions. In a particular 
aspect, the present invention is concerned with converting in a single 
riser reactor a combination of feed materials, such as recycled products 
of cracking, coker gas oils, shale oils, and other less desirable oils of 
varying properties and coke forming characteristics. 
It has been found in developing the concepts of the present invention that 
several factors contribute to the effectiveness of the point of injection 
of feed materials considered to be of poor cracking characteristics to a 
riser conversion zone. For example, it has been found that it is possible 
to maintain a higher inlet temperature for converting fresh feed charged 
to the riser cracking operation by practicing the processing concepts of 
this invention to maintain a desired riser top or outlet temperature than 
is possible when charging the total feed to the base of the riser. This 
limited high temperature conversion of fresh feed contributes to improving 
the octane rating of the gasoline obtained. It has also been found that 
coke deactivation of the catalyst is more desirably controlled following 
the processing concepts of this invention. In this connection, it has been 
observed that the injection point of a less desirable secondary feed to a 
downstream portion of a riser conversion zone will depend on the quantity 
of the feed charged, the composition of the feed charged, the coke burning 
restraint of an associated catalyst regenerator and the processing 
conditions relied upon. 
The catalyst employed in the combination operation of this invention is 
preferably a catalyst comprising a crystalline zeolite of relatively high 
cracking activity comprising an FAI activity of at least 46 and of a 
fluidizable particle size. The catalyst is caused to flow suspended in 
hydrocarbon reactants under elevated temperature cracking conditions 
through a riser hydrocarbon conversion zone providing a hydrocarbon 
residence time in contact with catalyst therein in the range of 0.5 up to 
about 10 seconds and more, usually not above about 8 seconds but at least 
2 seconds. Separating hydrocarbon conversion products or gasiform product 
material from the suspended and entrained catalyst is accomplished 
substantially immediately following traverse of the riser conversion zone. 
This immediate separation is most desirable if not essential to minimize 
overcracking where high temperatures exist to reduce undesired coke 
deposition. On the other hand, temperatures of at least 985.degree. F. 
improve the octane rating of the gasoline obtained. During the hydrocarbon 
conversion step, hydrocarbonaceous material deposits accumulate on the 
cracking catalyst particles and the particles tend to also entrain 
hydrocarbon liquid and vapors upon initial separation from vaporous 
conversion products. Entrained hydrocarbon is thereafter normally removed 
from the catalyst with stripping gas such as steam in a separate catalyst 
stripping operation. Hydrocarbon conversion products separated from 
catalyst particles along with gasiform stripping material are recovered 
together and passed to a product fractionation or separation step. 
Stripped catalyst containing deactivating amounts of carbonaceous material 
often referred to as coke is then passed to a catalyst regeneration zone 
for removal of deposited coke by burning with oxygen containing 
regeneration gas thereby heating the catalyst in the regeneration 
operation to a temperature within the range of 1200.degree. to 
1600.degree. F. and more usually not above 1400.degree. F. 
The riser hydrocarbon conversion system and method of operation is unique 
according to this invention for accomplishing the conversion of different 
hydrocarbon fractions within riser outlet temperature constraints 
identified below wherein the hydrocarbons vary in coke deposition 
characteristics and the hydrocarbons vary considerably in boiling range. 
For example, it is contemplated converting relatively low coke producing 
gas oils in a lower initial portion of a riser conversion zone at a 
temperature within the range of 960.degree. F. up to about 1100.degree. F. 
in the presence of suspended catalyst particles recovered at an elevated 
temperature from a catalyst regeneration zone. Thereafter, the upwardly 
flowing gas oil-catalyst suspension following a selected conversion time 
interval of contact between hydrocarbon feed and catalyst within the range 
of 0.5 seconds up to about 2, 3 or 4 seconds, depending on the conversion 
desired, is thereafter contacted with a less desirable hydrocarbon feed 
fraction such as one of higher coke producing characteristics or a higher 
aromatic index boiling range material, a heavy recycle oil product of 
cracking, or a product of thermal cracking such as coker gas oil. 
Preheating of the gas oil feed or low coke producing oil feed to a 
selected elevated temperature level up to about 800.degree. F. before 
contacting hot regenerated catalyst at a temperature within the range of 
1200.degree. to 1400.degree. F. is contemplated. This combination of feed 
preheat and regenerated catalyst temperature may be relied upon in 
substantial measure to control the extent of conversion achieved in the 
riser conversion operation. Charging the less desirable and generally 
higher coke producing hydrocarbon material to a downstream portion of the 
riser conversion zone with little or no preheat and as temperature 
recovered from a distillation or separation operation may be used to lower 
the temperature of the feed-catalyst suspension in the lower portion of 
the riser conversion zone. Generally the riser conversion zone outlet 
temperature may be restricted to within the range of 850.degree. F. to 
1050.degree. F. or as hereinafter provided. 
The riser conversion of different feeds with suspended catalyst according 
to this invention is unique in several respects. That is, in a riser 
reactor conversion operation of restricted outlet temperature as herein 
provided, the yield of selected and desired product may be varied. One or 
more of the hydrocarbon conversion reactions herein identified may be 
effected in the riser zone designed to be of constant diameter or the 
riser reactor may be designed to vary in diameter in various sections 
thereof and be of a selected length in any one section thereof to provide 
desired conditions in severity of operation. That is, conversion of the 
fresh feed such as a gas oil feed or another low coke producing material 
charged to the riser is accomplished in a lower bottom and/or a more 
restricted diameter portion of the riser providing relatively rapid 
acceleration of the highest temperature suspension initially formed 
therein and retained for a limited time period particularly providing a 
selective conversion desired to gasoline before contact in a more 
downstream portion of the riser with a higher coke producing feed under 
decreasing temperatures. The initially formed suspension may also be 
contacted with the secondary coke producing hydrocarbon charge material in 
a downstream portion of the riser of the same diameter or in a transition 
zone between the smaller and larger diameter portions of the riser and 
under temperature conversion conditions supporting riser outlet 
temperatures herein defined. The secondary feed varying in properties from 
the initial hydrocarbon charge such as by a higher coke producing 
hydrocarbon charge may be added to the riser adjacent to or in an 
elongated and generally diverging or transition section to the larger 
diameter section of the riser conversion zone. It is contemplated in yet 
another embodiment of charging additional regenerated catalyst to the 
riser at an elevated temperature to provide a higher catalyst to oil 
suspension and to effect conversion of the combined feeds to the riser 
within the riser outlet temperature constraints herein identified. 
Generally, the temperature of the suspension in the bottom portion of the 
riser will be from 50 to 150 degrees higher than the herein identified 
riser outlet temperature in the range of about 900.degree. F. to about 
1100.degree. F. The suspension temperature will be lowered primarily due 
to the endothermic heat of conversion of the hydrocarbon feeds. The lower 
suspension temperature following contact with the introduced secondary 
hydrocarbon charge material will normally require a longer residence 
contact time with catalyst for effecting a desired conversion thereof in 
the remaining downstream portion of the riser. A temperature differential 
(.DELTA.T) in the riser downstream of the secondary feed injection point 
within the range of 25 to 100 degrees is contemplated. However this 
temperature differential will normally be in the range of 50 to 55 degrees 
.DELTA.T. 
In the riser conversion arrangement of this invention, it is also 
contemplated improving naphtha boiling hydrocarbons octane in a very 
bottom portion of the riser with freshly regenerated catalyst at its 
highest activity and temperature, effecting conversion of fresh gas oil 
feed of relatively low coking characteristics downstream of said naphtha 
upgrading and effecting conversion of a residual oil, a heavy cycle oil 
product of catalytic cracking or a coker gas oil in a further downstream 
portion of the riser as herein particularly discussed. It is also 
contemplated effecting conversion of a low aromatic index gas oil fraction 
to gasoline boiling products initially in the riser under relatively high 
temperature conditions of at least 1000.degree. F. and charging a higher 
aromatic index gas oil as the secondary feed to a downstream portion of 
the riser. 
In yet another embodiment, a light gaseous hydrocarbon fraction charged to 
the bottom of the riser comprising C.sub.5 and lower boiling hydrocarbons 
may be used to form a high temperature suspension of at least 1000.degree. 
F. which suspension is thereafter contacted with a higher boiling 
atmospheric and/or vacuum gas oil before contact with a heavy residual 
oil, coker gas oil, clarified slurry oil from the FCC main column or an 
FCC main column bottoms fraction under the riser outlet temperature 
constraints herein identified. In any of the above arrangements, dispersal 
of the light and heavy hydrocarbons to form the upflowing suspension can 
be facilitated by using a plurality of oil injection nozzle in a bottom 
cross-sectional area of the riser or about the riser circumference 
particularly at the point of secondary injection. 
DISCUSSION OF SPECIFIC EMBODIMENTS 
The charge stock properties, Table 1, used in developing the operating 
concepts of this invention were estimated from various available sources. 
Table 1 
______________________________________ 
FCC Feedstock Properties 
Coker Heavy Chemical 
Fresh Feed 
Gas Oil Reject 
______________________________________ 
API 27.2 23 13.6 
Basic Nitrogen, ppm 
161 700 24 
CCR, % wt 0.093 0.42 3.0 
650-, % wt 39.1 82.3 
Paraffins, % wt 
27.1 16.3 
Naphthenes, % wt 
43.8 9.9 
C.sub.A, % wt 
15.7 48.5 
Sulfur, % wt 
0.61 1.10 
Molecular Weight 
238 200 
650.sup.+, % wt 
60.9 100 17.7 
Paraffins, % wt 
22.7 18.7 6.5 
Naphthenes, % wt 
36.2 17.4 4.2 
C.sub.A, % wt 
17.6 30.6 61.4 
Sulfur, % wt 
0.99 1.78 1.51 
Molecular Weight 
387 330 404 
______________________________________ 
C.sub.A - aromatic carbon ring content; comprises substantial polynuclear 
aromatics 
The effect of the secondary feed injection of each feed stream was 
separately investigated so that the interactions, if any, between the 
various secondary feed streams could be uncoupled. To accomplish this, a 
base case was run for each secondary feed stream identified above in which 
the total feed to the base of the riser consisted of the fresh feed and 
the particular secondary feed stream to be injected. Each base case 
operation was then compared with the corresponding downstream secondary 
injection case, keeping the amount of the secondary hydrocarbon feed 
stream injected, the riser top outlet temperature, and the total 
hydrocarbon feed rate constant. Comparison data for these combination 
operations is presented in Table 2. It will be observed that the yield 
pattern varies significantly with the type of feed used for the secondary 
injection feed. 
Table 2 
__________________________________________________________________________ 
DETAILED YIELD COMISONS AT CONSTANT FEED RATE 
AND RISER TOP TEMPERATURE 
FF CGO MCCR Recycle 
Secondary Secondary Secondary Secondary 
Base Injection 
Base 
Injection 
Base 
Injection 
Base Injection 
__________________________________________________________________________ 
Operating Conditions 
Primary Feed, MBPSD 
89.44 FF 
86 FF 86 FF 
86 FF 86 FF 
86 FF 86 FF 
86 FF 
+3.349 +3.145 +3.0 
CGO MCCR Recycle 
Secondary Feed, MBPSD. 
3.44 FF 3.349 3.145 3.0 
(Eq. to 4% wt) CGO MCCR Recycle 
Combined Feed Ratio, wt 
1.04 1.04 1.04 
1.04 1.04 
1.04 1.08 1.08 
Riser Top Temperature, .degree.F. 
945 945 945 945 945 945 945 945 
Oil to Riser Temperature, .degree.F. 
543 543 543 543 543 543 543 543 
Regen. Temperature, .degree.F. 
1270.0 
1269.8 
1275.0 
1274.4 
1284.2 
1284.2 
1278.5 
1278.0 
Riser Mix Temperature, .degree.F. 
996.0 
1002.4 
996.1 
1002.8 
996.5 
1003.3 
995.3 
1002.3 
Height of Sec. Injection, ft 
18 18 18 18 
Catalyst Activity (FAI) 
69 69 69 69 69 69 69 69 
Carbon on Regen., % wt 
0.16 0.16 0.16 
0.16 0.16 
0.16 0.16 0.16 
Carbon on Spent, % wt 
0.93 0.93 0.95 
0.95 0.97 
0.97 0.96 0.96 
Reactor Cat. Res. Time, sec 
15.03 
15.02 15.29 
15.16 15.35 
15.32 15.52 
15.36 
Total Coke Make, M lb/hr 
59.54 
59.36 59.48 
59.37 59.48 
59.34 59.18 
59.14 
LFO 90% Point, .degree.F. 
630 630 630 630 630 630 613 620 
Total Feed Rate, lb/hr 
1,206,923 1,206,923 1,206,923 1,206,923 
Yields, % Total Feed 
Conversion, 385 @ 90% vol 
75.32 
75.38 73.97 
74.62 73.54 
73.59 75.17 
75.74 
CSO, % vol 2.85 2.86 2.85 
2.85 2.86 
2.86 2.94 2.92 
HFO, % vol 0.38 0.38 1.05 
1.09 0.57 
0.46 0 0 
LFO, % vol 21.45 
21.37 22.14 
21.45 23.03 
23.09 21.90 
21.34 
C.sub.5.sup.+ Gasoline, % vol 
56.33 
56.00 55.49 
55.53 55.05 
54.77 56.26 
56.41 
Total C.sub.4 's, % vol 
16.44 
16.74 15.71 
16.26 15.77 
16.02 16.10 
16.49 
Total C.sub.3 's, % vol 
11.25 
11.50 10.79 
11.16 10.77 
10.96 10.97 
11.19 
C.sub.2.sup.-, % wt 
2.89 2.94 2.89 
2.95 2.90 
2.95 3.02 3.05 
Coke 5.12 5.11 5.12 
5.11 5.12 
5.11 5.30 5.29 
.increment.Gasoline, BBL/day 
-298 34 -248 123 
.increment.LFO, BBL/day 
-71 -619 57 -478 
.increment.CSO + HFO, BBL/day 
16 35 -104 -14 
.increment.C.sub.4 's, BBL/day 
272 493 228 330 
.increment.C.sub.3 's, BBL/day 
220 333 175 189 
__________________________________________________________________________ 
It will be observed from the data of Table 2 that different feed 
compositions give different results, for example, the injection of coker 
gas oil or a recycle product mixed with gas oil at the same level, are not 
necessarily optimum, results in gasoline increases of about 34 and about 
123 BBL/day respectively. Light fuel oil product obtained under this mixed 
feed injection decreases in both cases, 619 BBL/day for the charged coker 
gas oil and only 478 BBL/day for the charged recycle. Also, the light gas 
produced is significantly higher for both the coker and recycle materials 
mixed feeds due to the increased conversions. For the coker gas oil 
charge, the light gas increase is 826 BBL/day of C.sub.3 - C.sub.4 
hydrocarbons. For the recycle feed charged, the C.sub.3 - C.sub.4 
hydrocarbons increased by 519 BBL/day. 
It will be further observed that the yield pattern for the secondary 
injection of fresh feed and the chemical reject feed are both 
significantly poorer than that obtained in the above two cases for coker 
gas oil and recycle material. When injecting some fresh feed as a 
secondary feed to a downstream portion of the riser, the gasoline yield 
drops by about 298 BBL/day and the light fuel oil yield drops by 71 
BBL/day. There is however an increase of C.sub.3 - C.sub.4 hydrocarbons of 
about 492 BBL/day. For the chemical reject injection mode, the gasoline 
yield drops by 248 BBL/day, but the light fuel oil (LFO) yield increases 
by 57 BBL/day. In this operating mode, the C.sub.3 - C.sub.4 yields 
increased by about 403 BBL/day. 
The data of Table 2 above discussed clearly show for a preselected 
secondary fuel injection point and the amount thereof charged, a change in 
product selectivity is obtained by this charging of the different 
secondary hydrocarbon feeds. By secondary feed charging is meant, 
introducing a secondary hydrocarbon feed of different chemical and 
physical properties than a fresh gas oil feed to a downstream portion of 
the riser conversion zone. A fresh lower coke producing atmospheric gas 
oil feed is charged to a lower bottom portion of the riser conversion 
zone. The data obtained and discussed above clearly show the difference in 
product distribution obtained by injecting a coker gas oil and heavy 
recycle product of catalytic cracking at the same level to a riser 
downstream of the fresh gas oil feed to the bottom of the riser. This 
however is not necessarily the optimum injection point for reasons 
discussed hereinafter. The secondary feed is usually one of higher coke 
producing characteristics than the fresh gas oil feed herein identified 
and charged to the bottom portion of the riser. 
The secondary feed injection concept of this invention to convert 
particularly high coking feeds was investigated to also identify the 
height above the bottom of the riser at which the secondary feed should be 
charged to obtain a desired riser outlet temperature and conversion 
thereof. That is, in a riser conversion operation charging an atmospheric 
and/or vacuum fresh gas oil feed to the bottom of a riser conversion zone 
and a coker gas oil to a downstream portion of the riser conversion zone, 
the data obtained were graphically represented in FIGS. I, II and III.

Referring now to FIG. I, a hydrocarbon feed comprising gas oil and 
identified in Table 1 charged to the bottom of a riser conversion zone 
forms a rising hydrocarbon-catalyst suspension. To this suspension is 
charged different volumes of coker gas oil. The level of secondary 
injection of the coker gas oil substantially altered the yield of gasoline 
obtained as shown when restricting the riser top temperature to about 
965.degree. F. Also, the amount of secondary feed injected substantially 
influenced the product selectivity and yield. For example, when charging 
about 2000 BPSD of coker gas oil (the lower curve A) at a temperature of 
about 267.degree. F. to the suspension in the riser, the gasoline volume 
percent yield achieves a maximum of not more than about 44.25 vol. 
percent, or less, no matter at what level 25, 50 and 75 feet charged to 
the riser. When charging about 4000 BPSD of the coker gas oil curve B, the 
yield of gasoline achieves a maximum when the oil was charged at about the 
25 foot level of the riser. At higher charge levels, the gasoline yield 
was reduced. Charging 6000 BPSD of the coker gas oil (curve C) also shows 
maximizing the gasoline yield when charging the secondary feed at the 25 
foot level. On the other hand, charging 8000 BPSD of the coker gas oil 
produced maximum gasoline yield at a charge level to the riser in the 
range of about 10 to 25 feet. 
Referring now to FIG. II, the riser temperature profile obtained is 
identified when charging 8000 BPSD of a heavy coker gas oil. In a base 
case for comparison wherein all of the feed is charged to the bottom of 
the riser as represented by the solid curve of the figure, an initial 
feed-catalyst suspension temperature of about 990.degree. F. or slightly 
higher rapidly dropped off to below 970.degree. F. at the 30 foot level of 
the riser and gradually decreased in temperature above that level to the 
156 foot riser level at the top of the riser maintained at 965.degree. F. 
When charging the coker gas oil as a secondary feed (10 feet above the 
riser bottom) and downstream of the fresh feed-catalyst suspension formed 
at a temperature of 1010.degree. F., the riser temperature profile follows 
the curve ABC and adjusts to a temperature of about 970.degree. F. at 
point C. The temperature profile thereafter follows substantially the 
solid line temperature profile as shown and briefly discussed above for a 
riser outlet temperature of about 965.degree. F. Charging the coker gas 
oil at the 30 foot level of the riser, a temperature profile of ABDE is 
obtained, with point E being relatively close to the solid line 
temperature profile of the base case. Charging the coker gas oil at the 60 
foot level of the riser produces the temperature profile ABDFG and 
charging it at the 90 foot level produces the temperature profile ABDFHI. 
Thus, the graphical representation of data comprising FIGS. I and II 
clearly show the desirability of charging secondary feed such as coker gas 
oil and other less desirable coke producing oil fractions to a riser 
conversion zone between the 10 and 25 foot level above the charged fresh 
feed (gas oil) to the riser bottom. In addition, the yield of gasoline can 
be substantially improved by maintaining the temperature profile of the 
riser for a riser outlet temperature of 965.degree. F. in accordance with 
that particularly identified by FIG. I. It must also be observed from FIG. 
I that as the volume of the secondary feed is increased, the level of 
injection of the secondary feed becomes more restricted. 
It is recognized from the data and information herein presented that the 
secondary feeds boiling above about 650.degree. F. and identified above 
can be processed under selected condition with advantage in combination 
with an atmospheric gas oil feed to high yields of gasoline boiling 
product following the operating techniques herein described. On the other 
hand, some secondary hydrocarbon materials generally lower boiling than 
about 650.degree. F., such as the chemical reject material of Table 1, do 
not contribute to improved gasoline product yield as do other higher coke 
producing materials. 
The graphic arrangement of FIG. III dramatically shows an improvement in 
gasoline yield and conversion obtainable by following the processing 
concepts of this invention when restricting the riser outlet temperature 
to 985.degree. F. That is, in the arrangement of FIG. III, data points for 
two different catalyst to oil ratios identified and connected by a dotted 
line for one and a solid line for the other particularly show the 
conversion differences for the charged feed arrangements identified on the 
graph. The data points identified on the graph for different feed charged 
arrangement and connected by the dotted line to the left of the graph were 
obtained with a catalyst to oil ratio of 7.11 and the data points 
connected by a solid line to the right of the graph are for a catalyst to 
oil ratio of 9.20. The data (+) point (a) on the upper curve charging 60 
MBPSD of fresh gas oil feed only to the base of the riser identifies the 
volume percent of gasoline obtained as about 46.8, at a conversion of 
about 64.8 when using a catalyst to oil ratio of 7.11 to crack the fresh 
gas oil feed and maintain a riser discharge temperature restricted to 
985.degree. F. Data point (b) represents the results obtainable when 
charging fresh gas oil mixed with 4 M BBL of coker oil identified in Table 
1 to the bottom of a riser conversion zone under conditions to limit the 
riser outlet temperature to 985.degree. F. Data point (b) for the 7.11 
catalyst to oil ratio operation shows a loss in gasoline yield to about 
45.0 vol. percent at about 62.5 vol. percent conversion. Data point (c) 
for the 7.11 catalyst to oil ratio operation charging 4 MBPSD coker gas 
oil 10 feet up the riser provided improvement in gasoline yield of about 
45.8 at 64.25 conversion. Data point (d) shows gasoline yield of about 46 
at 64.8 conversion. Data point (e) provides slightly less gasoline 45.9 at 
65.25 conversion, data point (f) shows 45.85 gasoline at 65.35 conversion 
and data point (g) shows gasoline yield of 45.75 at 65.45 conversion 
level. Thus when operating with a catalyst to oil ratio of about 7 and 
maintaining a riser outlet temperature restricted to 985.degree. F., 
charging the secondary feed to the riser at the 30.75 foot level appears 
optimum. 
More significant, however, is the change occurring in gasoline yield and 
conversion when processing under the conditions represented by data points 
h, j, k, l, m, n and o of the solid line curve. For example, for the 
higher catalyst to oil ratio of 9.2, a significant advantage in gasoline 
yield for any given level of conversion is shown between the data points 
connected by h, j, k, l, m, n and o and the data points connected by a, b, 
c, d, e, f and g. For example data point (h) shows gasoline yield of 48.8 
for 69.25 conversion level; data point (j) shows gasoline yield of 47.35 
for 67.1 conversion; data point (k) shows gasoline yield of 47.7 for 68.6 
conversion; data point (h) shows 47.7 gasoline at about 69 conversion; 
data point (m) shows gasoline of about 47.4 at 69.2 conversion. Data 
points (n) and (o) show gasoline yields of 47.3 and 47.0 respectively for 
a conversion level of about 69.2. Thus data point (k) for a 9.2 
catalyst/oil ratio shows substantially improved result when charging the 
coker gas oil at the 10 foot level above the fresh feed inlet at the riser 
bottom. In the 7.11 catalyst to oil operation the gasoline yield jumped 
from about 45.0 to about 46.0 vol. percent between data points (b) and (d) 
and for the 9.2 catalyst to oil operation, the gasoline yield went from 
about 47.35 data point (j) to about 47.75 vol. percent for data points (k) 
and (l). However, charging the coker oil farther up the riser, as 
represented by data points e, f and g, provided a reversed trend in 
gasoline yield as shown by the dotted line curve. A similar trend is noted 
for data points m, n and o. Thus, it is undeniably clear from the graphic 
representation of FIG. III that significant variations in gasoline yield 
and conversion can be had depending on the catalyst to oil ratio employed 
and the level at which the secondary feed is injected when restricting the 
riser outlet temperature to 985.degree. F. More importantly, however, is 
the finding that the combination operation of this invention permits 
processing hydrocarbon oils known as distress stocks or stocks of high 
coking characteristics with a more desirable cracking stock such as a 
fresh gas oil feed to advantage and without undesirably influencing the 
yield of desired gasoline boiling range product. Furthermore depending 
upon the riser outlet temperature selected as herein provided, significant 
improvement in light fuel oil product known as distillate and a reduction 
in gaseous product yield can also be realized. 
It will be recognized by those skilled in the art that numerous variations 
may be made on the processing concepts of this invention without departing 
from the spirit of the invention. 
The processing concepts of this invention are concerned with restricting a 
riser outlet cracking temperature within the range of about 900.degree. F. 
to about 1000.degree. F. and more particularly within the range of about 
950.degree. to about 985.degree. F. The operating constraints identified 
herein appear somewhat arbitrary at first blush but are important to the 
operating world of today for modifying existing refineries wherein 
temperature restriction limits are associated with downstream equipment 
such as coolers, the main column fractionating tower downstream of the 
cracking unit or a constraint based on an associated regeneration zone for 
removing deposited coke of cracking by burning. 
The data of the figures presented permit one to draw significant 
conclusions with respect to the operation described and related 
operations. For example, referring to FIG. I wherein a riser top 
temperature constraint of 965.degree. F. is identified, it is found that 
the processing combination involving secondary injection obtains best 
results with respect to gasoline yield-conversion relationship by charging 
the second feed to the riser about the 10 foot level. This is believed to 
be unusual and also unpredictable. Also, when the riser outlet temperature 
is raised to 985.degree. F., the level of secondary injection (coker gas 
oil injection) for gasoline yield-conversion relationship is preferably 
about the 10 foot level for the higher catalyst to oil ratio operation. In 
the operation of FIG. III, however, the higher catalyst to oil ratio at 
the riser outlet temperature of 985.degree. F. permits achieving a much 
higher gasoline yield than obtained at a lower catalyst to oil ratio or at 
a riser outlet temperature of 965.degree. F., FIG. I, while disposing of 
undesirable charge materials such as coker gas oil. On the other hand, 
when operating according to FIG. 1 it is observed that charging 6 MBPSD of 
secondary feed or less provides best results at the 25 foot level. Thus, 
depending upon downstream processing equipment temperature constraints to 
handle a given volume of product passed therethrough, the riser cracking 
operation comprising secondary injection can be varied over a considerable 
catalyst to oil ratio, volume of secondary charge and riser outlet 
temperature constraint to produce high yields of gasoline during disposal 
of difficult charge stocks such as coker gas oil and other difficult 
materials to crack because of coking tendencies. 
It is significant to note that, as the catalyst to oil ratio is increased 
according to FIG. III that a coker gas oil charge of 4 MBPSD can be 
charged to the riser between the 10 and 30.75 foot level for the same 
gasoline yield for slightly different conversions. However it is clear 
from these data that charging the coker gas oil with the fresh feed to the 
base of the riser produced inferior results. Therefore applicants 
concluded that the charging of residual oils, coker gas oils and heavy 
recycle products of cracking as secondary charge materials to a riser 
cracking operation restricted to an outlet temperature in the range of 
950.degree. F. to about 1000.degree. F. can be accomplished with advantage 
with respect to gasoline yield distillate product and light gaseous 
products by charging the secondary feed preferably about the 10 foot level 
and up to about the 25 foot level of the riser reactor above the fresh 
feed inlet without exceeding undesired levels of conversion or catalyst to 
oil ratios. More particularly, it is preferred that the riser outlet 
temperature be at least about 965.degree. F. but not above 1000.degree. F. 
for producing high yields of gasoline. Restricting the riser outlet 
temperature to about 965.degree. F. is more desirable when optimizing the 
yield of distillate at the expense of gasoline production. The operating 
conditions of FIG. III, at least with respect to the catalyst to oil 
ratios employed, represent a normal type of operation at about 7 catalyst 
to oil ratio and slightly higher than normal with the 9.2 catalyst to oil 
ratio operation. 
Effecting the operation herein identified at the higher catalyst to oil 
ratio is beneficial to the extent that the deposition of carbonaceous 
material is over a larger volume of catalyst to be regenerated, more 
catalyst is available to absorb the heat of regeneration and recycle of 
the larger volume of regenerated catalyst for conversion of fresh feed can 
operate to reduce fresh feed preheat to maintain a given or desired riser 
outlet temperature as herein preferred. 
Having thus generally described the method and concepts of the invention 
and discussed specific embodiments going to the essence thereof, it is to 
be understood that no undue restrictions are to be imposed by reasons 
thereof except as defined by the following claims.