US2700017A - Method of coking residual hydrocarbons - Google Patents

Description

Jan. '18, 1955 J. w. BROWN 2,700,017

METHOD OF coxmc RESIDUAL HYDROCARBONS Filed June 5, 1951 4 05;. GAs

EwQrQEQ (94. T M Ana f Jame Inf Brown. SnvcnboY e523 actor-ne s United States Patent METHOD OF COKING RESIDUAL HYDROCARBONS James W. Brown, Elizabeth, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application June 5, 1951, SerialNo. 230,020

9 Claims. (Cl. 202-14) This invention relates to a process for treating hydrocarbons and more particularly relates to the cracking or conversion of heavy residual hydrocarbons to produce lower boiling hydrocarbons.

The petroleum oil residuum or residual oil which is to be converted or coked according to the present process is a high boiling hydrocarbon oil which cannot be v-aporized at ordinary pressures without cracking the high boiling constituents. The residual oil may be that produced by distilling crude petroleum oil at ordinary atmospheric pressure or under subatmospheric pressure such as vacuum distillation.

At present there are large amounts of residual stocks available for cracking or coking and better methods of coking the oil are being sought. Also the residual stocks are high boiling, that is, their initial boiling point is extremely high because of the treatment of crudes to obtain as much catalytic cracking stock as possible from the crude oil.

Processes are known in the prior art for cracking or coking residual oils in the presence of finely divided inert or substantially inert solids maintained as a fluidized bed. The present process is concerned with coking or cracking of residual oils.

According to the present invention, the finely divided solids are heated by directly contacting the solidswith hot flue gas in a transfer line, that is, a line in which the velocity of the gases is high and the suspension of solids in the gases is of relatively low density. The rate of heat transfer to the solids is extremely high and it is necessary to have only a relatively short time of contact after which the heated solid particles are separated from the combustion or flue gas and returned to a zone for supplying heat thereto.

For the coking of residual oils a dense fluidized bed of finely divided solids is used and preheated residual oil is sprayed or otherwise introduced into the dense fluidized bed. Vaporous products of coking are taken overhead and further treated as desired to recover lower boiling hydrocarbon fractions. During coking more coke is formed and coke to be withdrawn from the process is passed to a stripping zone associated with the coking zone where volatile hydrocarbons are stripped from the coke. Some of the stripped coke is withdrawn as product coke and some coke is withdrawn and heated by direct contact with hot combustion or flue gas and then in its heated condition the coke particles are returned to the coking zone to supply heat thereto, to the stripping zone to raise the temperature of the particles being stripped or the heated coke particles may be returned to the coking zone and the stripping zone.

To supply the heat fuel gas or the like is burned with air and the hot combustion gas is mixed with withdrawn coke particles to heat them about 150 to 300 F. above the temperature of the coking zone. The heated solid or coke particles are then removed from the combustion or flue gas and returned to the coking zone and/or the stripping. During heating of the solid particles, the combustion gas and solids are passed upwardly through a transfer line heater in which the velocity of the gas is relatively high and the solids remain in the heater for only a short time. This method of heating has many advantages over the two vessel system using a fluidized bed of solids Where burning takes place to heat the solids. In the first place using a fluidized dense bed of solids as a heating or burning vessel results in a solids hold up many times that required in a transfer line heater where the 2,700,017 Patented Jan. 18, 1955 In the drawing, the figure represents one form of ap-' paratus adapted for carrying out the process of the present invention.

Referring now to the drawing the reference character 10 designates a line for conducting residual petroleum oil such as tar, pitch, crude residuum, heavy bottoms having an API gravity between about -l0 and 20, a Conradson carbon between about 5 and 50 weight percent and an initial boiling point between about 850 F. and 1100 F. The oil is passed through coil 12 or other heating means in furnace 14 and the oil preheated to a temperature between about 700 F. and 850 F. is passed through line 16 into a coking vessel 18 containing a dense fluidized bed of inert solids 22 having a level indicated at 24 with a dilute phase 26 thereabove.

Preferably superheated steam is introduced into the preheated oil in line 16 through line 28 and the resulting mixture is introduced or sprayed into the dense fluidized bed 22 below or above the level 24 thereof. The fluidized coking bed 22 is maintained at a temperature between about 800 F. and 1200 F. preferably about 850 to 1050" F. Theinert solids of the fluidized bed have a particle size between about 20 and 500 microns, preferably between about 20 and.200 microns and may comprise sand, petroleum coke or other coke or coke formed in the process, spent cracking catalysts, pumice, kieselguhr, Carborundum or other refractory materials etc.

Vaporous products of coking pass overhead leaving fluidized bed 22 and contain entrained solids forming the dilute phase 26. The vaporous products are passed through gas-solids separating means 32 such as one or more cyclone separators to separate entrained solids which are returned to the dense fluidized bed 22 by means of dip pipe 34 while the vapors pass overhead through line 36 for further treatment in a recovery system.

The fluidized bed is maintained as such by the upflowing hydrocarbon gases and vapors formed by the coking of the residual oil and also by the introduction of superheated steam through line '38 below distribution grid member 42. The superficial velocity of the gases and vapors passing upwardly through the dense fluidized bed 22 is between about 1 and 4 feet per second and when using finely divided coke of about to 200 standard mesh and a superficial gas velocity of about 3 feet per second, the density of the fluidized bed will be about 30 lbs. per cu. ft. but may vary between about 10 and 60 lbs. per cubic foot depending on the gas velocity selected.

A stripping zone 44 is provided by partition 46 in coking vessel 18 with the top of the partition being below level 24 of the dense fluidized bed 22. Coke particles formed during coking are collected in stripping zone '44 and stripped by superheated steam introduced below grid member 48 by line 52 to remove volatile hydrocarbons from the coke particles. Some of the stripped coke particles are withdrawn from the lower portion of the stripping zone through withdrawal line 54 and recovered'as coke. The withdrawn coke particles are quenched or cooled in any suitable manner. In some cases it is de sirable to heat the coke particles in the stripping zone to a higher temperature than exists in the coking zone to further crack residual oil on the coke particles or to dry the coke particles and this heating is done by removing coke particles, heating them by direct contact with combustion gas in a transfer line heater and then returning them to the stripping zone as will be hereinafter described in greater detail.

Heat is supplied to the coking zone by removing coke particles from the stripping zone, heating them by contacting them with hot flue gas or combustion gas in a transfer line heater, recovering the heated coke particles from the gas and returning them to the coking zone. For supplying heat to the coking zone 22 and/or stripping zone 44 an external auxiliary burner 58 is provided. Line 62 is provided for introducing fuel such as fuel gas into the burner 58 and line 64 is provided for supplying air for the burner 58. Fuel gas rather than coke is preferred for burning in burner 58. Hot flue gas or combustion gas resulting from the combustion of the fuel gas passes through line 66 into vertical transfer line heater 68. The flue gas in line 66 is at a temperature between about 1300 F. and 3500 F.

Coke particles to be heated are withdrawn continuously from stripping zone or section 44 through line 72 having control valve 74 and introduced into the lower part of transfer line heater 68 where they are contacted with the hot flue gas and maintained in a highly turbulent condition during passage through the transfer line heater. The rate of heat transfer to solid particles around 100 microns or 20 to 200 microns is so high due to the turbulence that the holding time for substantially complete transfer of heat is generally less than one second. The coke or other solid particles being used are heated from about 850 F. up to about 1100 F. or higher in the transfer line heater 68. The superficial velocity of the gas passing upwardly through vertical transfer line heater 68 is between about 30 and 60 feet per second so that the suspension of solids is dilute having a density of about 0.01 to 1.0 pound per cu. ft. As above mentioned, the suspension passing through heater 68 is maintained in a violently agitated or turbulent condition so that high rates of heat transfer are obtained.

The heated solid particles and flue gas or combustion gas are then introduced into a solids-gas separating means 78 such as one or more cyclone separators or the like to separate heated solids from combustion gas, the separated solids passing into standpipe 82 and the hot combustion gas passing overhead through line 84. Heat may be recovered from the flue gas passing through line 84 by waste heat boilers or the like. Standpipe 82 is provided with slide valve 86 for controlling rate of flow of solids from the standpipe 82 into line 88 which introduces the heated solids into the fluidized bed of solids 22 in the coking zone 18 to supply heat to the coking zone 18. Another line 92 having slide valve 94 communicates with standpipe 82 for delivering hot solids preferably to the upper portion of the stripping zone 44 to raise the temperature therein and to facilitate removal of volatile hydrocarbons from the solid particles in the stripping section.

In the low temperature fluid coking process around 850 F., it has been shown that a very large solids holdup is required in bed 22 to provide sufiicient solids holding time for completion of the coking reaction including completion of the vaporization or cracking of the heavy liquid feed so that the coke or other solid particles will be dry and the reaction will be complete.

If the coking reaction is not substantially complete, there will be loss of hydrocarbons with the solid particles entering the transfer line heater 68 via line 72. By introducing highly heated solid particles into the stripping section 44, the stripping section is maintained at a higher temperature than is maintained in coking bed 22 so that the coking reaction is accelerated and completed before the solids are withdrawn from the lower portion of the stripping section 44. With the coking zone maintained at a temperature of about 850 F., the stripping section will be maintained at a temperature of about 9001000 F., preferably about 975 F., by the addition of heated solids through line 92. With a higher coking temperature of say about 950 F., the temperature in the stripper will be maintained at about 1025 F.

The coking fluidized bed 22 is maintained at a temperature of about 800 F. to 1200 F., preferably 850 F. to 1050 F. by supplying solids heated in transfer line heater 68 through line 88 to the bed. The hot flue or combustion gas from the auxiliary burner 58 is quenched to about 1100 F. by the injection of the solid particles to be heated from line 72 so that the carbon or coke will not react with CO2 or water to consume heat. The reaction of carbon with CO2 and H20 at 1100" F. is negligible in the time of contact in the transfer line heater 68.

Instead of burning fuel gas, coke particles may be burned in auxiliary burner 58 but in this case it is preferable to add a portion of the air at the bottom of the transfer line or in the auxiliary burner through line 64 and the rest of the air to the upper portion of the transfer line heater 68 as through line 96 to burn CO to CO2: There is another advantage of contacting or quenching the hot combustion gas with coke particles having freshly deposited coke thereon. By heating the coke particles to about 1500 F. there is a substantial surface area produced in the coke particle. it has also been found out in our laboratory Work that the necessary solids hold up for fluid coking may be considerably reduced by using coke having some degree of porosity. The transfer line heater 68 is particularly adapted to produce increased surface area on the coke particles in this manner.

T further increase the surface area of the coke particles, a portion or fraction only of the withdrawn coke particles may be introduced into transfer line heater at a point below the point of injecting the bulk of the coke particles to be heated as will be presently described. In this way a part of the solids-gas mixture will be heated to a temperature of about 1500 F. and later be quenched to about 1100" F. by injecting the remainder of the coke particles at a temperature of about 850 F. For example, part of the coke particles could be withdrawn through line 72 above described and the rest of the coke particles could be withdrawn from stripping section 44 through line 98 having a slide valve 102 and picked up with air or steam introduced through line 104 and the suspension passed through line 106 for introduction at point 107 into the transfer line heater 68 a substantial distance above the point of injection of the first portion of the coke particles through line 72. In this way about 30% of circulating coke is heated to about 1500 F. (i. e. added at 72). The distance between 72 and 107 constitutes a major portion or about of the total transfer line length.

Although this invention has been described for the fluid coking process, it may also be applied to other processes where solids from a fluidized bed may be heated by combustion of fuel gas in a transfer line heater.

In a commercial design unit about 40 million B. t. u./hr. are supplied to the coke bed 22 by continuously removing about 3. tons per minute of coke from the stripping section 44 and heating the coke particles to about 1100 F. by direct contact with hot flue gas in transfer line heater 68. The coke particles at about 1100 F. are recovered in one or more stages of cyclone separators 78 and returned to the coking bed 22 through standpipe 82 and line 88. The hot flue gas is produced by burning refinery fuel gas with about excess air in auxiliary burner 58 and introduced into vertical transfer line heater 68 where the flue gas is quenched from about 3000 F. to 1100 F. by coke particles introduced into transfer line heater 68 through line 72, said coke particles being at a temperature of about 850 F. The transfer line heater 68 in this specific design is 40 feet long and has an internal diameter of 4 feet. The superficial gas velocity in the heater 68 is about 40 feet/sec. at 1100 F. and the solids holding time in heater 68 is about 2 seconds. By varying the conditions the solids holding time in heater 68 may be as high as 5 seconds.

The pressure balance is adjusted so that the 1100 F. flue gas is discharged from line 84 at about atmospheric pressure. A blower (not shown) provides about 10,300 standard cubic feet per minute of air at about 1.5

' pounds/sq. in. gauge for the auxiliary burner 58. With the coke particle size in bed 22 of about to 200 microns, the density of the fluidized bed 22 in coking vessel 18 is about lbs/cu. ft. with a superficial gas velocity of about 3 feet/ sec. The total amount of steam added to manifold for lines 38 and 52 to maintain the particles fluidized in bed 22 and to strip the particles in stripping section 44 is about 22,700 lbs. per hour with the steam being at about pounds/ sq. in. gauge.

The coking vessel 18 has an internal diameter of 16 feet 5 inches and a straight vertical side of 87 feet. The temperature of the fluidized bed 22 is about 850 F. and the pressure in reactor 18 is about 9 pounds/ sq. in. gauge. The fluidized bed 22 has a height of about 72 feet and there is a hold up of about 230 tons of coke. The residual oil feed comprises 23,000 barrels per standard day of reduced crude having an API gravity of about 5, a Conradson carbon of about 21 wt. and an initial boiling point of about 1100 F. and about 6,900 barrels per standard day of recycle oil recovered as bottoms from the fractionator used for separating the products of cokinginto desired fractions. Preferably, thereare twelve of the feed lines 16 for introducing the oil feed preheated to about 850 F. into coking fluidized bed 22. About 5000 pounds/hr. of steam at 125 lbs/sq. in. gauge are mtroduced through line 28 for passage to the twelve mlet lines 16 for feeding oil to the coking zone.

The stripping section 44 is about 60 feet high and has a cross sectional area of about 9 sq. ft. About 880 tons per standard day of coke product are removed from stripper 44 through line 54, preferably cooled or quenched and used or sold as such.

For heating the fluidized coking bed and maintaining it at about 850 F. about 3.6 tons per minute of coke at about 850 F. are withdrawn from stripping section 44 through line 72 and mixed with hot flue gas in vertical transfer line heater 68 to heat the coke particles to about 1100 F. The coke particles heated to about 1100 F. are passed through line 88 to the fluidized bed 22 in coking vessel 18. t

In addition to supplying heat to the fluidized bed 22, if it is desired to heat the solids in the stripping section 44 to a temperature of about 975 F. an additional amount of about 3.5 tons per minute of coke are withdrawn through line 72 for passage to the transfer line heater 68 and about 3.5 tons per minute of coke particles heated to about 1100 F. would be passed through line 92 to the stripping section 44.

The vaporous products of coking including recycle leaving coking vessel 18 through line 36 are as follows:

6,320 B./S. D 430-650 F. 6,620 B./S. D 650950 F. 6,900 B./S. D 950 F.+.

From this table it will be seen that while there is an appreciable amount of gasoline produced, there is more higher boiling stock produced which is useful as stock for catalytic cracking operations. In this specific example there are produced about 14,940 barrels per standard day of feed stock boiling betwen about 430 and 950 F. and suitable for use as feed to catalytic cracking units.

What is claimed is:

l. A method of coking residual petroleum oils which contain constituents unvaporizable at ordinary pressures without cracking which comprises contacting residual oil with a dense fluidized highly turbulent bed of finely divided solids in a coking zone maintained at a temperature of about 800 F. to 1100 F. to produce lower boiling hydrocarbons, removing vaporous reaction products from said coking zone, passing coke particles from said coking zone to a stripping zone to remove volatile hydrocarbons from the coke particles, withdrawing coke particles from the lower portion of said stripping zone, mixing a portion of said removed coke particles with hot combustion gas produced by burning fuel gas with air to produce combustion gases at a temperature of at least 1300 and not more than 3500 F. with the resultant mixture of coke particles and gas being brought to a temperature of about 150 to 300 F. higher than the temperature in said coking zone and returning the heated coke particles directly to said coking zone to supply heat thereto.

2. A method of coking residual petroleum oils which contain constituents unvaporizable at ordinary pressures without cracking which comprises contacting residual oil with a dense fluidized highly turbulent bed of finely divided solids in a coking zone maintained at a temperature of about 900 F. to 1200 F. to produce lower boiling hydrocarbons, removing vaporous reaction products from said coking zone, passing coke particles from said coking zone to a stripping zone to remove volatile hydrocarbons from the coke particles, withdrawing coke particles from the lower portion of said stripping zone, mixing a portion of said removed coke particles for a period not exceeding about 5 seconds with hot combustion gas produced by burning fuel gas with air to produce flue gas at a temperature between about 1300 F. and 3500 F. with the resultant mixture of coke particles and gas being at an elevated temperature 150 to 300 F. above the coking zone temperature and returning at least part of the heated coke particles directly to said stripping zone to maintain it at 6 'a temperature of about 50 to 200 F. higher than the temperature in said coking zone. 3. A method of coking residual hydrocarbon oil to produce lower boiling hydrocarbons which comprises feeding residual oil to a dense fluidized highly turbulent bed of finely divided coke particles maintained at a temperatureof about 950 F., removing vaporous reaction products overhead, passing finely divided coke particles to a stripping zone to remove volatile hydrocarbons from the coke particles, recovering solid coke particles from said stripping zone, continuously removing another portion of coke particles from the lower portion of said stripping section and mixing it with freshly produced hot combustion gas at a temperature above about 1300 F. to produce a mixture having a temperature to 300 F. above that of the coking zone, the mixing of the removed coke particles and hot combustion gas being made in a high velocity upflow transfer line heater where the time of mixing is about 2 seconds, recovering heated coke particles from the combustion gas and returning at least a part of the recovered heated coke particles directly to said fluidized bed in said coking zone to supply heat thereto.

4. A method of coking residual hydrocarbon oil to produce lower boiling hydrocarbons which comprises feeding residual oil to a dense fluidized highly turbulent bed of finely divided coke particles maintained at a temperature of about 950 F., removing vaporous reaction products overhead, passing finely divided coke particles to a stripping zone to remove volatile hydrocarbons from the coke particles, recovering solid coke particles from said stripping zone, continuously removing another portion of coke particles from the lower portion of said stripping section and mixing it with freshly produced hot combustion gas, said combustion gas being at a temperature above about 1500 F. to produce a mixture having a temperature 150 to 300 F. above that of the coking zone, the mixing of the removed coke particles and hot combustion gas being made in a high velocity upflow transfer line heater where the time of mixing is less than about 5 seconds, recovering heated coke particles from the combustion gas and returning at least part of the recovered heated coke particles directly to said stripping zone to raise the temperature of said stripping zone to about 1025 F.

5. A method according to claim 2 wherein an additional amount of coke particles at about 950 F. is introduced into a high velocity upflow transfer line heater wherein the removed coke is mixed with the hot combustion gas at a level above that at which the previously added coke particles were introduced into said transfer line llreatg 0 reduce the temperature of the mixture to about 6. A method according to claim 2 wherein the coke particles by admixture with the hot combustion gas have i a temperature of at least 1500 F. for an extended period of time in a transfer line heater wherein the removed coke is mixed with the hot combustion gases to increase the surface area of the coke particles and then an additional amount of coke particles at about 950 F. is introduced into a region adjacent the outlet of the transfer line heater to reduce the temperature of the coke particles to about 1100 F.

7. A method of coking heavy hydrocarbon oil to produce lower boiling hydrocarbons which comprises feeding heavy hydrocarbon oil to a dense fluidized highly turbulent bed of finely divided coke particles maintained at coking conditions, removing vaporous reaction products overhead, removing coke particles from said coking zone, heating the withdrawn coke particles to a temperature higher than that in said coking zone by passing them through a relatively high velocity transfer line heater, recovermg heated coke particles and returning at least a portion thereof to the inlet of said transfer line heater and returning at least another portion of said heated coke particles to said coking zone to supply heat thereto.

8. A method of coking heavy hydrocarbon oil to produce lower boiling hydrocarbons which comprises feeding heavy hydrocarbon oil to a dense fluidized highly turbulent bed of finely divided coke particles maintained at coking conditions in a coking zone, removing vaporous reaction products overhead, removing coke particles from said coking zone, heating the withdrawn coke particles to a temperature substantially higher than that in said coking zone by passing them through a relatively high velocity transfer line heater, recovering heated coke partransfer line heater at aregion"adjacent-the"outlet-there- 9;.A rnethod"of= o'kingr esidtial petroleum oils which contain-co'1'1stit1ierits unvaporizable' at"ordinary pressures without cracking" whi'ch'cornpri'se's contacting a residual Oil W'ith aidense "fiuid i'z'ed' highly turbulent b'ed'bf finely *divided-solidsin a coking Zone'maintaincd at a tempera- '"ture of 211;011:900" F. to 1200? F. to produce lowerboil- "jug-hydrocarbons, removing "vaporous reaction products fro'rri fsaid coking zone,- passing coke particles from="'said coking-zone to a'stripping 'zone'to remove volatile hydrocarbons from the coke] particles; withdrawing coke 'particles" from the lower portion'of said stripping Zone; heat- "ing' aport ion'of 'said'remdv'ed coke particlcsfor aperiod not exceeding abom 5 seconds with an oxygen containing gas to a temperature from 150 F. to 300 R'abo've'the" coking 'zone' temperature; and returning at least part of the'heated coke particles directly to said stripping zone f-=to maintaiiiit at a temperatureof about'50 F: 'to"200- F. hig'her than-the temperature 'in said coking zone.

* Rfereiies Gited in th file of' this patent 1 UNITED STATES PATENTS 1,551,956 Hubmann Sept. 1, 1925 1,805,109 'Runge'et a1.- May12, 1931 1,905,055 Pu'ening Apr. 25, 1933 -2,'105,1'56 -"Morgan '-Jan. '11,- 1938 2,131,702 Berry Sept. 27, 1938 2,440,623 Voorhees Apr. 27,- 1948 2,480,670 7 v i '-1949 2,485,315 1949 2,512,076 1950 .2;5'43,884 1951 2,582,712 Howard- -5 Jan; '15, 1952 2,595,338 Greelman May 6,1952 2,600,078 Schhtt'e et al 'June-10, 1952 2,606,861 Eastwood Aug. 12,1952 2,608,526 Rcx Aug. 26, 1952

Claims (1)

1. A METHOD OF COKING RESIDUAL PETROLEUM OILS WHICH CONTAIN CONSTITUENTS UNVAPORIZABLE AT ORDINARY PRESSURE WITHOUT CRACKING WHICH COMPRISES CONTACTING RESIDUAL OIL WITH A DENSE FLUIDIZED HIGHLY TURBULENT BED OF FINELY DI VIDED SOLIDE IN A COKING ZONE MAINTAINED AT A TEMPERATURE OF ABOUT 800* F. TO 1100* F. TO PRODUCE LOWER BOILING HYDROCARBONS, REMOVING VAPOROUS REACTION PRODUCTS FROM SAID COKING ZONE, PASSING COKE PARTICLES FROM SAID COKING ZONE TO A STRIPPING ZONE TO REMOVE VOLATILE HYDROCARBONS FROM THE COKE PARTICLES, WITHDRAWING COKE PARTICLES FROM THE LOWER PORTION OF SAID STRIPPING ZONE, MIXING A PORTION OF SAID REMOVED COKE PARTICLES WITH HOT COMBUSTION GAS PRODUCED BY BURNING FUEL GAS WITH AIR TO PRODUCE COMBUSTION GASES AT A TEMPERATURE OF AT LEAST 1300 AND NOT MORE THAN 3500* F. WITH THE RESULTANT MIXTURE OF COKE PARTICLES AND GAS BEING BROUGHT TO A TEMPERATURE OF ABOUT 150* TO 300* F. HIGHER THEN THE TEMPERATURE IN SAID COKING

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