US2743216A - Calcination of fluid coke utilizing shot - Google Patents

Description

April 1956 c. E. JAHNIG ET AL 2,743,216

CALCINATION OF FLUID COKE UTILIZING SHOT Filed Sept. 17, 1954 I2 FLUE GAS II l0 GASES TO V SULFUR 9 RECOVERY 1 v f &1 25 Qn l9 CALCINING s ZONE l'v mg n 27 8 0 a-r- \-\M\AA-A\ O .2 OFF 6 02 0 0 r- 000 /"2 l5 O AIR COOL PRODUCT COKE 7 AIR Charles E. Johnig Br k Smith Inventors Attorney United States Patent beth, N. 1., assignors to Esso Research and Engineering Company, a-corporation of Delaware Application September 117,- 1954,*Seriall1o. 456,652

8 Claims. .(c|.-202-'-14 vThis 'inventionrelates to improvements in calcining cokeand 'in heat exchanging'particulate solids requiring heat conditioning. More particularly it relates to an "efficient heat balanced operation 'which'uses shot in the calcination of fluid coke.

There hasrecently been developed an improved process known as the fluid-cokingprocess for "the production of coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions. The fluid coking unit consists basically of are'action vessel or 'coker and a 'heater'or burner vessel. In a typical opera'tionthe heavy oil to be processed is injected into the reaction vessel containing a "dense turbulent "fluidized bed of hot inert solid particles, preferably coke particles. Staged reactors can be employed. 'Uniform temperature exists in the coking bed.

"Uniform mixing in the bed results in virtually isothermal conditions and eifects' instantaneousdistribution of the feed stock. In the reacton zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from-the coking-vessel and sent to a fractionator for therecovery of gas and lightdistillates' therefrom.

Any heavy bottoms is usually returned to'the coking vessel. The coke produced in thepr'ocess remains in the bed coated' on:the solid particles. Stripping steam is [injected 'intoathe stripper .to remove oil'from the coke particles prior to the passage ofcthe coketo the'burner;

The fheatfor. carrying .out the endothermic coking. vreaction isygeneratedzin the burner vessel, usually but not .necessarily'separate. 1A. stream of coke is thus trans- :ferred from the reactor .to the burnervessel employing a .standpipe-and riser systemaair being supplied .to the riser for conveying .the solids to the burner. vSufiicient coke or added carbonaceous matter is. burned in the burning vessel to bring. the solids therein up .toa temperature suflircie'n't to maintain'the system hea'tb'alance. The burner solids are maintained: at a higher temperature than "the solids in the reactor. A'bou't"5'% of coke, based on the lfeed, is 'burned'f'or this -purpose. f "This may amount .to approximately'l5'%"to 30% 'of'flthe coke made in the process The net coke production, which representsthe coke make'less' the cdke burned, --iswithdrawn.

'H'e'avy hydrocarbonoll"feeds suitable for"the coking process include heavy crudes, atmospheric and crude vacuum bottoms, pitch; asphalt, other heavy" hydrocarbon petroleum residua-or mixtures thereof. Typically, such ife'ed-s ean ha-ve an initiahboiling point of about 700"F.

'Uonrad'son carbonuresidue' content :of about to 40 :wt. .ipercent. (As to Conradson carbonresidue see ASTM .T'est D-l80-T52.) 3

' .The method of fluidsolids circulation describedabov'e -is-well known tin the ;-prior-: art. Solids handling technique is described broadly in Packie Patent 2,589,124 issued -:Marcl1=1=1, 1952.

'lhefluid coke product particles have a particle diameter predominantly, i. e., about 60 to 90 percent in the range of to 80 mesh, a sulfur content in many cases above 6 wt. percent, and. a volatile content of '2 to 10 wt; percent. "It has; a real density of about 1.5 to 17 which is"t'oo 'lowlfor use inthe manufacture of carbon electrodes in making aluminum. "Increased density and lower/sulfur and volatile content isparticular'lynecessaw before the fluid coke is suitable for manufacture into electrodes, .one of the. major "uses of petroleum coke. 'These latter objectives are accomplished by calcining 'th'e cok'e at. a high temperature,.e. g., temperatures of 1*800"0r usually"2l' 0'()"' F. or. higher. "These temperaturesv andthe times required make the calcining. opera- 'tion relatively expensive.

This invention provides .an improved eflicient heat balanced operation for calciningthe coke. The method comprises in effect heating the coke outside of the calcining zone. by heat exchange with inert heat-absorbing particles which will'fbe referred .to as sho 'More specifically the shot at. elevated temperatures countercurrently contacts .heated .coke solids in. the..first heat exchange zone to raise the coke temperature to the calcination temperature. 'Thefthu-s heated coke and the resultant cooled shot are separated and'the coke sent to a soaking or calcining. zone. The cooled shot then coun'tercurrently contacts hotter coke withdrawn from the soaking .zone to cool the coke. The temperature of the shot is thus raised .again and it 'is returned tothe first'xheat exchange zone to again .heat incoming hot coke to calcination temperatures. l

Other improvements are also "incorporated I in .;the process such as subjecting the. shbtto av combustion step to raise its temperature prior to the heat exchange in'the first heat exchange zone. The product coke after an initial cooling by 'directcontact with theicool shotmay also be further cooled near itsignition temperature preferably with a combustible gas. used'for the preceding operation. .The .coke is ithen additionally cooled by contacting with combustion .air "(preferably countercurren'tly) at temperatures 'sufliciently low toavo'id substantial combustion. The air't'hus desirably'has its temperature raised 'for its use .in the combustion "step. Other advantages are obtained by treating the *co'ke in the soaking zone with a gas selected from the group:consistingofhydrogen and flower normally gaseous'hydrocarbons such as hydroformer tail 'g'as,na'tural gas, absorberresidue gas, butane, propane; etc. saturates are preferred.

As "explainedabove an inert heat 'carrieror shot is utilized for heat exchange. "This shot has "a greater free fall velocity "than the carbonaceous solids undergoing calcina'tionge. g. has'a'larger size 'and/or-is-denser than the carbon particles so that it has a' highergas settling rate than the carbonaceoussolids. 'As here used, the

4 shot may be' any-relatively hard inert refractory material such as tabular'alumina,-mullite, porcelain, quartz, sand, gravel, metal, etc. A suitable -material isthus alumina with particle diametersfin the range of :05" to 0:25". The 'shot 'mu'st not'reacrwith coke' or 'siilfur, hence siliceous materials are undesirable.

' This invention will be better understood 'by reference to the'fiow-dia'gram shown in the drawing.

' In'the drawing 1 represents a first heat exchange zone. Hot sh'otye. g.,-mullite,.at .a temperature in the range of 2400 to'3200"F., e.. g.,.'2700 F. enters the upper portion of the heat exchange zone 1 through line13. Feed fluid coke fromthe burner of-a' fluid coking unit, at a temperature in the range 0131800 to 1800 F.,.e. g., 1100" F.', enters the lower portion of zone 1 through line 27. Anelutriating and fluidizing gas such as natural gas, nitrogen, hydrogen, light hydrocarbon, or .recycle gas is injected.,through..line 16. The gas has a superficial velocity insufficient to prevent the shotfrom'falling,

e. g. 0.1 to 2 ft./sec. The latter falls through zone 1 countercurrent to the rising coke particles, resulting in the cooling of the shot and the heating of the coke. The coke is heated to a temperature in the calcination range 1800 to 3000 F., e. g. 2550 F., and the shot temperature is reduced to 1250" F. Volatile matter is cracked and removed from the coke as methane, hydrogen, acetylene, ethylene, etc. which are withdrawn through line 25 along with the fluidizing gas. The coke is maintained in the form of a fluid bed. The same variations are obtained in heat exchange zone 2 which both utilize the countereurrent contacting features.

The coke at a temperature of 2550 F. is elutriated from zone 1 and withdrawn through line 14 to calcining or soaking zone 17. The coke is maintained in the form of a moving bed in soaker 17 for a time sufficient ,for

calcination, i. e., minutes to hours, e. g., 4 hours. The density is thus increased and the volatiles and sulfur content decreased. The coke can be maintained in the soaker in the form of a fluid bed also if desired. Hydrogen, as hydroformer tail gas, enters soaker 17 through line 18 as a flushing gas. The amount of hydrogen added is in the range of 100 to 500 standard cubic feet per ton of coke treated. If H2 is used as a treating gas to re move sulfur, the amount added would have to be 1,000 to 10,000 s.c.f./ton, and recycling may be used together with sulfur removal from the recycle gas. The pressure in the treating vessel will be about 10 p. s. i. g. However, Hz pressure is not critical here as sulfur is largely removed as CS2 rather than HzS at the elevated temperatures used. Hence, large volumes of hydrogen are not required for sulfur removal. Excess treating gas as well as carbon disulfide and hydrogen sulfide are taken overhead through line 19.

Product coke taken 05 through line at a high temperature, e. g., 2500 F., is sent into the second heat exchange zone 2. The coke is cooled by countercurrent contacting with shot particles which enter heat exchange zone 2 at 1250 F. through line 3 at an upper point. The operation of heat exchange zone 2 is similar to heat exchange zone 1. Fluidizing gas such as natural gas, hydrogen, nitrogen, etc. enters through line 4. The coke is thus cooled to about 1400 F. and the shot heated to 2350 F. The hot shot is withdrawn through line 6, mixed with an oxygen-containing gas, e. g. air, and transferred in the form of a high velocity confined stream through line 7 and through transfer line burner 9 wherein a velocity of to 100 ft./sec., e. g., 50 ft./sec., is maintained. A combustible carbonaceous material such as natural gas, absorber residue gas, coke, pitch, e. g., natural gas, is injected through line 8. The combustion of the combustible gas with air raises the shot temperature to 2700 F. and the shot is taken overhead through line 10 into cyclone separator 11. Flue gas leaves through line 12 and the shot drops into heat exchange 1 through line 13 as detailed previously.

The cooled coke at 1400 F. is elutriated from heat exchange zone 2 through line 5 and is cooled in cooler 20 to near the ignition temperature, i. e., 900 to 1200 F., e. g., 1000 F. This cooling can be performed by heat exchange with a combustible hydrocarbon entering transfer line burner 9.

The thus further cooled coke at 1000 F. is additionally cooled to below ignition temperature in cooling zone 21. The coke drops countercurrently through incoming air or other oxygen containing combustion gas which enters through line 22 at about 100 F. Vessel 21 can be conveniently partitioned or divided by baffles, perforated plates, etc., in order to obtain more etficient contacting. The coke is thus cooled to about 200 F. and therefore requires no extraneous quenching. The air which has had its temperature raised to 900 F. is withdrawn through line 7 and transports the shot to transfer line burner 9 as well as supports the combustion. The heating of the air is an important feature of this invention.

In the shot heat exchange towers, the shot settles slowly through the fluidized coke. The shot is cooled and the coke preheated by countercurrent contacting. Settling velocities of the shot may for example be in the range of 0.1 to 1.0 ft./sec.; the higher values being obtained with coarser shot, for example, 0.1 to 0.2" diameter. The total residence time of the shot in the fluid coke bed should be suflicient to give a reasonably close approach to equilibrium. This may require a shot residence time of the order to 10-60 sec., and this is related to the shot settling velocity and the height of the heat exchange zone. In many cases it will be convenient to use a somewhat larger size shot in order to facilitate separation from the finer coke. The shot may then settle too rapidly for optimum heat transfer and it will be desirable to impede the free fall. This can be done by putting battles, sheds or disc and donuts, etc., to increase the length of path through which the shot travels. It is also possible to use contacting plates with a bed of shot on them which overflows to the next lower plate.

In a typical case the coke to be processed will be largely in the size range of 20-80 mesh and may for example have 25-50% on 48 mesh and 50-75% on a 60 mesh screen. This may be fluidized at a velocity of 0.1 to 2.0 ft./sec. in the shot heat exchange zone. Shot particles of 0.05 to A diameter may be employed. The shot may be made of alumina, silicon carbide or any suitable material which does not react excessively with the sulfur and coke. The optimum shot size will depend on the density of the material and will be less for high density materials such as alumina and silicon carbide.

Sufficient shot should be circulated to give the optimum temperature differentials through the shot heat exchangers. In general, the shot circulation will be such that temperature change of the shot in a given zone will be approximately equal to the temperature change for the coke passing therethrough. This will give the most efficient utilization of the heat and allow high preheat temperatures on the coke. The shot to coke ratio will then depend upon the relative heat capacities; with alumina or silicon carbide shot the coke to shot ratio may be of the order of 0.5 to 2.0.

In the shot exchange tower fiuidizing gas will be withdrawn at the top of the zone, preferably well above the level of fluidized coke so that entrainment is minimized. The fine coke can be withdrawn oflf preferentially near the top of the bed. It may be desirable to provide a baffle to prevent shot particles from being withdrawn with the coke. For example, a segregated zone can be provided wherein the fine coke flows upwardly at low velocity to allow the shot to settle out. At the bottom of the shot heat exchange zone the shot will accumulate at high concentration. Preferably a moderate amount of stripping gas is added to strip the fine coke particles out of the bed of shot. A pure shot stream can then be withdrawn. As shown, shot is returned to the upper zone by means of an air lift (pneumatic transport), or other means may be used such as a bucket elevator, etc.

It is possible to integrate the two shot contacting zones into the calcining vessel to form a single column wherein the shot falls through the calciner zone. Thus cooled shot quenches the product coke upwardly through an upper heat exchange zone. The resultant hot shot falls through the calcining zone and then through a lower heat exchange zone where it preheats the feed coke to about calcining temperature. Additional heat is added to the calcining zone by circulating part of the shot through a heater and returning it directly to the calcining zone. Countercurrent contacting is utilized. The shot circulation can also be used in the burning zone to cool the flue gas and preheat the combustion air.

The conditions usually encountered in a fluid coker for fuels are also listed below so as to further illustrate how the coke was prepared.

Conditions in fluid coker reactor Broad Preferred Range Range Temperature, F 850-1, 200 9004, 000 Pressure, Atmospheres. 1-10 1. 5-2 Superficial Velocity of Fluidlzing Gas, Ft./sec 0. 2-10 0. 5-4 Coke Circulation (Solids/Oil Ratio) 2-30 7-15 The advantages of this invention will be apparent to the skilled in the art. Maximum realization of the coke is attained since none is burned in the calciner. Since the coke is heated outside of the calcination zone the latter can be controlled for optimum calcination rather than to secure the requisite heat exchange or combustion temperatures. The heat exchange features are of distinct value in achieving an economical process. The gases evolved from the calciner soaker are mostly in the form of hydrogen sulfide or carbon disulfide both of which are recoverable. The latter is a valuable byproduct. This should be distinguished from a process which results in the production of carbonyl sulfide which is difficult to remove and is an atmospheric contaminant; or from a process in which the sulfur is burned to S02 which also is an atmospheric contaminant. Such processes do not usually provide for recovery of sulfur.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

l. A process for the calcination of coke particles which comprises the steps of countercurrently contacting heated separate inert, heat absorbing particles having a higher gas settling rate than the coke particles with fluidized hot coke particles at a lower temperature in a first zone so as to heat the coke particles to a calcination temperature in the range of 1800" to 3000 F. and lower the temperature of the inert heated particles, separating by elutriation the thus heated coke particles from the inert particles; passing the elutriated coke particles at the calcination temperature to a calcination zone; calcining the coke particles; countercurrently contacting the inert particles separated from the first zone in a second zone with fluidized calcined coke particles withdrawn at a higher temperature from the calcining zone so as to cool the coke and raise the temperature of the inert particles, additionally heating the inert particles by combustion of an extraneous fuel with an oxygen-containing gas and returning the thus heated inert particles to the first zone to heat the coke to the calcining temperature.

2. The process of claim 1 including the additional steps of further cooling the coke from the second zone to near the ignition temperature and then additionally cooling the coke to below the ignition temperature by direct contact with the oxygen-containing gas to raise the temperature of the gas and utilizing the heated oxygen-containing gas in the heating of the inert particles by combustion of the extraneous fuel.

3. The process of claim 2 in which the coke is cooled to near its ignition temperature by heat exchange with a combustible hydrocarbon utilized in the combustion step.

4. The process of claim 1 in which the calcination is conducted at a temperature in the range of 1800 to 3000" F. for a periodof time from 5 minutes to 10 hours.

5. The process of claim 4 in which the hot coke entering the first zone is in the temperature range of 800 to 1800 F.

6. The process or" claim 5 in which the calcination is conducted in the presence of a treating gas selected from a. group consisting of hydrogen and normally gaseous hydrocarbons.

7. A process for heat exchanging a first particulate solid system, which requires a heat conditioning treatment, with inert, heat absorbing particles having a highor gas settling rate which comprises the steps of countercurrently contacting the inert particles at an elevated temperature with a dense, turbulent, fluidized bed of the first particulate solids at a lower temperature in a first heat exchange zone so as to heat the first particulate solids to heat conditioning temperature and lower the temperature of the heated, inert particles; separating by elutriation the thus heated first particulate solids from the inert particles; passing the elutriated first particulate solids at the heat conditioning treatment temperature to a heat conditioning zone; countercurrently contacting the inert particles separated from the first heat exchange zone in a second heat exchange zone with a dense, turbulent, fluidized bed of withdrawn heat conditioned first particulate solids at a higher temperature from the heat conditioning zone so as to cool them and raise the temperature of the inert particles, additionally heating the inert particles by combustion of an extraneous fuel with an oxygencontaining gas and returning the thus heated inert particles to the first heat exchange zone to heat the first particulate solids to the heat conditioning temperature.

8. The process of claim 1 including the additional step of recovering evolved carbon disulfide from the calcination zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,320,318 Simpson et al May 25, 1943 2,627,497 Robinson Feb. 3, 1953 2,690,990 Adams et al Oct. 5, 1954 2,700,642 Mattox Ian. 25, 1955 OTHER REFERENCES Chemical and Metallurgical Engineering, July 1946, pages 116-119. Pebble Heater, by C. L. Norton, Jr.

Claims (1)

1. A PROCESS FOR THE CALCINATION OF COKE PARTICLES WHICH COMPRISES THE STEPS OF COUNTERCURRENTLY CONTACTING HEATED SEPARATE INERT, HEAT ABSORBING PARTICLES HAVING A HIGHER GAS SETTLING RATE THAN THE COKE PARTICLES WITH FLUIDIZED HOT COKE PARTICLES AT A LOWER TEMPERATURE IN A FIRST ZONE SO AS TO HEAT THE COKE PARTICLES TO A CALCINATION TEMPERATURE IN THE RANGE OF 1800* TO 3000* F. AND LOWER THE TEMPERATURE OF THE INERT HEATED PARTICLES, SEPARATING BY ELUTRIATION THE THUS HEATED COKE PARTICLES FROM THE INERT PARTICLES; PASSING THE ELUTRIATED COKE PARTICLES AT THE CALCINATION TEMPERATURE TO A CALCINATION ZONE; CALCINING THE COKE PARTICLES; COUNTERCURRENTLY CONTACTING THE INERT PARTICLES SEPARATED FROM THE FIRST ZONE IN A SECOND ZONE WITH FLUIDIZED CALCINED COKE PARTICLES WITHDRAWN AT A HIGHER TEMPERATURE FROM THE CALCINING ZONE SO AS TO COOL THE COKE AND RAISE THE TEMPERATURE OF THE INERT PARTICLES, ADDITIONALLY HEATING THE INERT PARTICLES BY COMBUSTION OF AN EXTRANEOUS FUEL WITH AN OXYGEN-CONTAINING GAS AND RETURNING THE THUS HEATED INERT PARTICLES TO THE FIRST ZONE TO HEAT THE COKE TO THE CALCINING TEMPERATURE.

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