US2219345A - Combination cracking - Google Patents

Description

' Oct. 29, 1940'. E. w. THIELE Er AL COM'BAINATIO CRACKING Filed Jan. 2e, 193s Patented Oct. `29, 1940 UNITED. STATES COMBINATION CRACKING Ernest W. Thiele and Jay H. Forrester, Chicago,

Ill., assignors to Standard Oil Company, Chicago, Ill., a, corporation of Indiana Application January v26, 193s, serial No. 187,099

- Claims'.

This invention relates to combination cracking processes and it pertains more particularly to processes for obtaining maximum yields of high octane gasoline from charging stocks which contain relatively heavy oils.

In combination cracking processes heretofore employed the gasolines produced from light and heavy gas oils have had high octane numbers, but those produced from coking operations have been w characteristically inferior in this respect. An object of our invention is to provide a method and means for increasing the antiknock rating of gasolines produced by coking.

A further object is to provide an improved combination of coking withv catalytic cracking whereby the charge to the catalyst chamber may come directly from the coking drum and will operate at about the same temperature `and pressure conditions as those of the coking drum.

t@ A further object is' to provide an improved method for conditioning a dirty charging stock for catalytic cracking. A further object is to extend the catalyst life ina catalytic cracking process by a preliminary treatment of the chargl ing stock to remove therefrom those carbonacevous materials which would otherwise tend to form deposits on the catalyst. A further object is to provide a new and improved combination of an intermittent catalyst treatment 'with intermittent coking treatments so that the catalyst may be regenerated or revivied while 'the coke is being removed from the coking drum. Other objects will be apparent as the detailed description of our invention proceeds.

Our invention is applicable to coking processes both of the delayed coker type and of the clean circulation type, but it will be described in connection with the delayed coker operation which y forms a part of a combination cracking process.

d@ In practicing the invention we operate the delayed coker at about 50 pounds pressure and 850 F., and we introduce the hot gases and vapors from the coker with or without the introduction of small amounts of steam directly into the catalyst chamber. The catalytically treated products may thenl be fractionated in any conventional manner.

The invention will be more clearly understood from the following description and from the accompanying drawing which forms a part of this specication, and which diagrammatically illustrates a preferred embodiment of the apparatus or system for carrying out our improved combination cracking process.

The 'crude charge which may be a crude or (ci. 19e-4y s) topped petroleum oil is introduced through line I0, crude oil heater II and line I2 to crude flash tower I3, fromwhich straight run gasoline and gases' are removed through line I4. Heavy naphtha or light gas oil is removed in side stream I5 and heavy gas oil is removed in side stream I6; The bottomsfrom the crude flash tower may be recycled through line Il for admixture with incoming charging stock to increase heat input to tower I3. A portion of this stream may be introduced as reflux through line Ila into the upper part of vis breaker evaporating tower 24. which will be hereinafter described.

The heavy gas oil is introduced into the socalled vis breaker bubble tower I8 operating at about 20 pounds pressure and with a top temperature of about 560 F. The overhead from this tower is withdrawn through line I9 and cooler ISA to a high pressure bubble tower which will be hereinafter described.

A side stream from bubble tower I8 is withdrawn through line 20, cooledin cooler 2I and passed by pump 22 through line 23 to the top of vis breaker evaporator tower 24 which operates at about 25 pounds pressure, with a top temperature o about 725 F.

'The bottom from the vis breaker bubble tower IB are withdrawn through line 25 and forced by pump 26 through line 21 into heavy gas oil 4heater 28, thence through line 29 to the bottom of the vis breaker evaporating tower 24. The overhead fractions from this evaporator tower are withdrawn through line 30 to the lower part of the vis breaker bubble tower I8. A side stream from the evaporator tower 24 is withdrawn through line SI and forced by pump 32 through line 33, coking furnace 34 and line 35 to one of a battery of coking drums 36. These coking drums and their method of operation are wellknown in the art and need not be described in detail. We prefer to operate these drums at a pressure of atmospheric to pounds, preferably about 50 pounds per square 'inch and a temperature of about 800 to 950 F., preferably about 850 F. We prefer to employ six coke drums in a unit, the working cycle of each drum being 96 hours. By using a 2-stream system through the coking furnace, this system is operated so that one drum will befull at the end of vevery sixteen hours. The coke, after being allowed to stand for about a day, is quenched with steam and water and is then discharged into cars by means of cables wound in the drums.

The vapors leaving the coking-drum at a temperature of about 850 F. are passed by line 3l to catalyst chamber 88. We prefer to introduce about 2 to 5% of steam into line 31 through line 31A, but the use ofsteam is not in all cases essential.

The catalyst chamber may be of any conventional type and the catalyst itself is preferably an activated hydrosilicate of alumina. We may use any clay type catalyst,both natural clays and synthetic clays. An acidltreated Death Valley clay has been found to be very e'ective. A still more'effective catalyst may be synthetically produced by depositing alumina on silica and limiting the amount of alumina to about 10 to 40 mol. per cent. Boron silicate has also been found to be a very good catalyst. Generally speaking, the clay type catalyst is preferred, and it may be impregnated with other metallic oxides, including nickel, copper, cobalt, thoria, manganese, etc. Also, certain promoters may be introduced along with the hydrocarbon stream entering the reaction zone. Such promoters include the hydrogen halides, organic halides, etc. The specific catalyst forms no part of the present invention and will notbe described in further detail.

We prefer to provide a separate catalyst chamber for each coking drum so' that the catalyst chamber may be regenerated while the coking drum is being cleaned. While a single coking drum and a single catalyst chamber are shown in the drawing, .it should be understood that these are only representative of a battery of chambers and drums, respectively, and that suitable means are provided for regenerating a catalyst in each lchamber by means of an oxy- 1 gen-containing gas or by any other means known to the art. v

One of the chief drawbacks of catalytic cracking systems is the fact that the catalyst becomes coated with carbon and is thus rendered ineffective in a relatively short time. By depositing carbon-forming components of the charging stock in the coking drum we obtain a much longer catalyst life than has heretofore been obtainable with this type of charging stook. Furthermore, the coking drum is operated at such a temperature and pressure that the products therefrom' may be introduced'directly `into the catalyst chamber under the optimum conditions for catalytic conversion. This conversion markedly increases the octane number or antiknock rating of the cracked gasoline, and increases the yield of cracked gasoline obtained from the gas oil. Gasolines from delayed cokers have heretofore been inferior in this respect to gasolines of other cracking processes, but by simply passing the hot gases and vapors from the coker through the catalyst chamber we can effect a remarkable increase in the knock rating of the cracked gaso line. In fact, such gasoline may even be superior to that produced from light gas oil crack- The products from catalyst chamber 38 are introduced by line 39 to vis breaker evaporating tower 24, which has been hereinabove described. Side streams from this tower are recycled to the coking furnace, coking drum and catalyst chamber. Bottoms from this tower may be withdrawn to storage as fuel oil, but are usually picked up by pump 32 and returned to the coker furnaces thru line 33.

The klighter fractions from thisl evaporator tower are introduced through line 30 to bubble tower I8. The overhead products from this bubble tower are withdrawnA through line I9, cooled and uncondensable gases are preferably -'separated therefrom in a gas separator (not shown). The gasoline and light gas oil fractions are then passed to high pressure bubble tower 40, which operates at 210 pounds per square inch, with a top temperature of about 435 F. and a bottom temperature of about '700 F. Gasoline fractions are withdrawn from the top of this tower through line 4 I, condensed and separated in high pressure gas separator 42 which operates at about 200 pounds and about F., the uncondensed gases being withdrawn through line 43. The gasoline is withdrawn through line 44 to stabilizer tower 45, which operates at about 350 pounds pressure, C3 gases, etc., being removed from the top of the tower through line 46 and stabilized gasoline from the bottom through line 41. A part of the condensate from separator 42 is returned through line 48 to bubble tower 40 as reiiux.

The bottoms from bubble tower 40 are passed by line 48 to cracking furnace 50 and thence through line 5I to high pressure evaporating tower 52, which operates at about 215 pounds and about 750 F. A side stream from bubble tower 40 may be Withdrawn through line 53 and introduced into the evaporator tower 52 along with the hot products in line 5I. 'I'he overhead from high pressure evaporator tower 52 is -introduced through line 55 to high pressure bubble tower 40. The bottoms from high pressure evaporator tower 52 are withdrawn through line 54 and introduced along with hot products in line 29 to vis breaker evaporator tower 24. The heavy naphtha or light gas oil from lin'e I5 is .introduced along with the bottoms from high pressure bubble tower 40 in line 49 to light gas oil cracking furnace 50.

From the above description it will be seen that practically all fractions of the crude oil are converted into gasoline under conditions most favorable for that conversion. The lighter products which normally yield gasolines of high knock rating are thermally cracked under optimum )conditions to yobtain maximum yields of the desired motor fuel. 'I'he products from the coking operations which have heretofore been characterized by low anti-knock ratings have been markedly improved in this respect. The amount of cracking done in the coking system is markedly increased; this markedly decreases the load on the light and heavy gas oil cracking systems, and it increases the total yield of gasoline produced, as well as vimproving the quality of the gasoline from the coking process.

The above description has been purposely slmpliiied by omitting the-details of side stream stripping, heat exchange details, and many other operating details, all of which are well-known in the art and would tend to confuse the present invention rather than to clarify it. While we have described a preferred embodiment of our invention, and have stated preferred operating teml high anti-knock gasoline from petroleum crude oils which comprises fractionating said oils intoy gas oils and heavy stocks, thermally cracking said gas oils, coking. said heavy stocks to produce va-y porized "products, wcatalytically treating the vaporized products from said coking step at a temperature of about 800 to 900 F. in the presence of a catalyst comprising alumina, returning heavy products from the gas oil cracking to said coking step, and thermally cracking the gas oil fractions of products from the catalytic treating step.

2. The process of claim 1 wherein the vaporized products from the coking step are directly introduced into said Acatalytic treating step at a temperature of about 850 F. and a pressure of atmospheric to pounds per square inch.

3. The process of claim 1 wherein the catalyst comprises both silica and alumina. and contains about 10 to 40 mol. per cent of alumina.

4. In apparatus of the class described, heating tubes for light gas oil, a high pressure evaporator tower, a high pressure bubble tower, heatingl tubes for heavy gas oil, a low pressure evaporator tower, a low pressure'bubble tower, heating tubes for heavy oil, a coking drum, a catalyst chambenmeans for passing light gas oil through said first-named heating tubes to the high pressure evaporator tower, means for passingvapors from said tower to said high pressure bubble tower, means for passing heavy gas oil to said second named heating tubes and `into said low pressure evaporator tower, means for passing vapors from said low pressure evaporator tower into lsaid low pressure bubble tower, means for passing heavy petroleum fractions through said third-named heating tubes and thence to said coking drum, means for vpassing gases and vapors directly fromsaid coking drum to said catalyst chamber, means for introducing' gases and vapors from the catalyst chamber to said low pressure evaporator tower, means for introducing heavy fractions from said high pressure evaporator tower to said low pressure evaporator tower, means for introducing gasoline and gasoil fractions from said low pressure bubble tower to said high pressure bubble tower, means for withdrawing gasoline containing vapors from the top of said high pressure bubble tower, means for returning heavy products from said high pressure bubble tower to said first-named heating tubes, means for passing heavy products from said low pressure bubble tower to said second-named heating tubes, and means for returning a heavy fraction from said low pressure evaporator tower to said third-named heating tubes.

5. The combination of claim 4 which includes means for introducing heavy gas oil into said low pressure bubble tower.

6. The combination of claim 4 which includes means for introducing steam into said system between the coking drum and the catalyst chamber.

7. 'I'he combination of claim 4 which includes means for fractionating crude oil and for introducing light gas oil to said first-named heating tubes, heavy gas oil into said second-named heating tubes, and residual products into said heavy oil heating tubes.

8. The method of converting petroleum oil into high quality motor fuel which comprises fractionating said oil into a gas oil fraction and a residual fraction, separately heating said fractions to substantially optimum temperatures for thermal conversion into motor fuel, passing the heated gas oil from the heating step to an evaporator tower, passing the heated residual fraction ,to a coking drum, passing gases and vapors from said coking drum directly to a catalytic conversion zone for the production of high knock rating motor fuel, passing gases and vapors from said catalytic conversion zone to said evaporator tower, recycling liquid from said evaporator tower for heating in admixture with said residual fraction, separating gas oil from the products leaving said evaporator tower and recycling said gas oil for heating -in admixture with said rst-named gas oil fraction and recovering gasoline from the remaining gases and vapors leaving said evaporator tower.

' heavy gas oil treating step to a low pressure evaporating zone, passing the heated residual fraction into a coking zone, passing vaporsl and gases directly from said coking zone to a catalytic conversion zone for the production of high knock rating motor fuel, passing gases and vapors from the catalytic conversion zone to said low pressure evaporation zone, passing gases and vapors from said low pressure evaporation zone to a fractionating zone for the separation of gasoline and cycle gas oil, returning said cycle gas oil for further conversion with heavy gas oil in said heavy gas oil hating step, returning liquid from said low pressure evaporation zone for treatment with said residual fraction in said residual oil heating means and said coking zone, introducing liquids from said high pressure evaporation zone into said low pressure evaporation zone, fractionatlng vapors from said high pressure evaporation zone to obtain a gasoline fraction and a. gas oil fraction, and recycling said gas oil fraction for further conversion with said light gas oil in said light gas oil heating means.

10. In a combination thermal cracking system for the conversion of heavy hydrocarbon oils into high quality ymotor fuel, which system includes a. gas oil heater, an evaporator tower, a bubble tower, a residual oil heater, a coking drum, means for passing gas oil vthrough said gas oil heater and into said evaporator tower, means for passing vapors from said evaporator tower to said bubble tower, means for passing liquids from said evaporator tower to said residual oil heating means. means for passing gas oil from said bubble tower to said gas oil heating means, and means for recovering gasoline from gases and vapors leaving said bubble tower, the method of improving a yield of high quality motor fuel which comprises interposing alcatalytic conversion chamber between said coking drum and said evaporator tower, passing gases and vapors directly from said coking drum into said catalyst conversion chamber at a temperature of at least about 850 F. and introducing gases and vapors from the catalyst chamber to said evaporator tower whereby the characteristicallylow knock rating hydrocarbons leaving said coking drum are converted into high 'knock rating motor fuels.

ERNES-T W. TH'IEL'E. JAY H. FORREBIER.

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