US2734853A

US2734853A - Integrated coking and calcining process

Info

Publication number: US2734853A
Authority: US
Publication date: 1956-02-14
Anticipated expiration: 1973-02-14

Description

Feb. 14, 1956 s. 1. SMITH ETAL INTEGRATED COKING AND CALCINING PROCESS Filed March 22, 1954 E tozmbc 2 $60 1 N mm v Sq \hmqmzoomm Iv onl mzo- @2233 mw 1((5EL 9 -Lmi. $.82 3 mm Emrmmm (f 9w Qmmm I' tObxZOPO t Oh mhoDQOtl tmxou Brook I. Smith I f Charles E. Jahnig By X 5 Attorney INTEGRATED COKING AND CALCINING- PROCESS Brook I. Smith, Elizabeth, and Charles E. Jahnig, Rumson,

N. 5., assignors to Esso Research and Engineering Company, a corporation of Delaware Application March 22, 1954, Serial No. 417,748

5 Claims. (Cl. 202-31) This invention relates to a novel coke calcining process.

It is an object of this invention to prepare a coke from petroleum sources which will be useful in the manufacture of carbon electrodes.

It is also an object of this invention to integrate the coke calcining process with the coking process itself.

It is also an object of this invention to provide a multistage process for calcining coke wherein maximum heat economies are affected.

In the coking of heavy hydrocarbon oils such as heavy crudes, crude residua, vacuum still residues, tars, pitches, etc., either for the production of fuel products, such as gasoline and gas oils, or for the production of chemical raw materials, such as aromatics and olefins, one of the major by-products is petroleum coke. The amount of coke formed depends on the character of the materials being processed and to some extent upon the coking conditions. In the case of high Conradson carbon stock, such as residuum from Hawkins crude, the coke yield may be 20 weight per cent or higher on the residuum. Other stocks have been found wherein the yield may be as high as 35 weight percent. Since the value of the coke as fuel alone detracts from a coking process, more attractive uses for the coke have been sought. One of the major uses to which the coke has been put has been the manufacture of electrodes therefrom. Carbon electrodes find their major use in the electrical refining of alumina to produce aluminum metal. For this purpose, petroleum coke is said to be preferable to metallurgical coke. Green (uncalcined coke) petroleum coke contains volatile matter which must be removed before the material is suitable for electrode purposes. This removal is accomplished by calcining the coke at a high temperature, e. g. 2300 F. or higher depending on the process employed. The calcining operation reduces the volatile content of coke to 0.5% or lower of the final product, raises its true density and reduces the electrical resistivity of the coke to 0.0015 ohm-inch or lower. Calcining is performed commercially at temperatures of 1800 F. to 2400 F. in rotary kilns, vertical retorts and in electrode baking pits. The petroleum coke used today is largely from delayed coking plants. In general, and perhaps universally so, the green coke is calcined elsewhere than at the site of the coking plant. This is a wasteful practice from the standpoint of unnecessary coke handling and also because of the heat wasted.

There has recently been developed a process known as the fluid coking process. The fluid coking unit consists basically of a reaction vessel or coker and a burner vessel. In a typical operation the heavy oil to be processed is injected into the reaction vessel containing a fluidized bed of inert solid particles, preferably coke particles, maintained at a temperature in the range of 850 to 1200 F. and preferably at 950 to 1050 F. for the production of fuels or at a higher temperature, e. g. 1200" to 1600 F. for the production of chemicals, i. e., aromatics and olefins. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermic nited States Patent Patented Feb. 14, 1956 conditions and efliects instant distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery ofgas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles thereof.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel. A stream of coke or coke-coated solid inert particles, if the latter are used, is transferred from the reactor to the burner vessel em ploying a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Sufiicient coke or carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature sufficient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke on the feed is burned for this purpose. This amounts to approximately 15% to 30% of the coke made in the process. The unburned portion of the coke represents the net coke formed in the process. This coke is preferably withdrawn from the burner, normally cooled and sent to storage. The coke normally contains about 86% to 94% carbon, 1.5% to 2% hydrogen, 0.5% to 7.5% sulfur, 0.6% to 1.5 volatile matter at 1100 R, up to 6% volatile matter at 950 C., and approximately 0.5% to 3.0% ash at 1100 F.

According to the present invention, coke made in the coking process is transferred continuously without quenching or cooling to a calcining operation. In the calcining operation. the coke is subjected to high temperature or high temperature and soaking in order to remove volatile material therefrom to increase its true density and to lower its electrical resistivity. In the calcining step, preheated coke is heated to calcining temperatures by burning a portion of the coke or some other fuel selectively to CO, and the CO after passing through the preheat stage is employed as all or part of the fuel for the burner of the coking unit. With relatively lower temperatures (10001500 F.) in the coker burner the CO is selectively burned to CO2 or to a COz/CO ratio of about 4/1 Without difiiculty.

The accompanying figure illustrates one method for integrating the coking and calcining process. Referring to the figure, vessel 1 is a coking vessel constructed of suitable materials for operation at temperatures in the range of 850 F. to 1600 F., e. g. 1000 F. A bed of coke particles preheated to a sufficient temperature to establish the required bed temperature, is made up of suitable particles in the rangeof about 70 to 600 microns. The bed of solid particles reaches an upper level indicated by the numeral 5. The bed is fluidized by means of a gas such as steam entering the vessel at the bottom thereof via pipe 3 at a velocity e. g. of 2 ft./sec. The fluidizing gas passes upwardly through the vessel establishing the solids at the indicated level. The fluidizing gas serves also to strip the vapors and gases from the coke which flows down into the vessel via pipe 9 as will be later related.

Oil to be converted, e. g. a crude residuum, is preferably preheated to a temperature not above its cracking temperature, e. g. 600 F. It is introduced into the bed of hot coke particles via line 2, preferably at a plurality of points in the system. The oil upon contacting the hot particles undergoes decomposition and the vapors resulting therefrom assist in the iluidization of the solids in the bed and add to its general mobility and turbulent state. The product vapors pass upwardly through the bed and are removed from the coking vessel via line 4 after passing through cyclone .6 from which solids are returned to the bed via dipleg 7. A stream of solid particles is removed from the coking vessel via line 8 and transported with the assistance of air or other free oxygen from lines 38 containing gas into burner vessel 10. Secondary air is supplied via line 11 with the assistance of pump 12. In the burner CO and/or a portion of the carbonaceous materials, e. g., coke or materials deposited thereon, is burned to raise the tempera ture to a point sufficient to supply the heat to the endothermic reaction occurring in the coking vessel 1. The temperature of the burner solids is usually 100 F. to 300 F. higher than that of the solids in the coking vessel, i. e., about 1000 F. to 140.0" F. for fuel production and proportionately higher for the production of chemicals, and in this example 1200 F. The bed of coke is fluidized in vessel in much the same manner as the bed in vessel 1. The solids are fluidized by the incoming air and resulting combustion gases and are maintained at a level indicated by the numeral 13. Combustion gases leave the hot bed, pass through cyclone 14 and are vented via line 16. Any entrained solids are returned to the bed via dip-pipe 15. A greater portion of the hot solids are continually removed from burner 10 via line 9 and introduced into vessel 1 at one or more points in order to maintain heat balance in the system.

The not make coke, in Whole or in part, is removed from the burner via line 17 and introduced into the top stage of a multi-stage calcining vessel 20 while primary air or other free oxygen-containing gas is simultaneously introduced into the bottom of the vessel via line 21 through grid 24. The calcining vessel 20 consists of a tower containing gas pervious plates 28 and downcomers 29 such as will provide countercurrent contact between downflowing solids and upflowing gases. The vessel contains in descending order, one or more heating stages and 26, and one or more calcining stages 27. Uncalcined or green coke enters the top preheat stage which is maintained at a temperature of approximately 1100 F. to 1600" F., preferably 1500 F. This stage serves to preheat the incoming coke by direct contact with hot efiiuent gases, the carbon containing gas which consists essentially of CO and which ascend through the vessel and emerge via uppermost plate 28 through the bottom of bed 25. The effluent gases containing CO essentially free of CO2 after passing through the uppermost preheat stage leave the calcining vessel via line 22 and are subsequently introduced into the burner 10 entering at the bottom thereof. The coke is maintained in the preheat section 25 for a residence time of a few minutes to as 1 much as l to 2 hours, e. g. 1 hour. Preferably the time is about 1 hour in order to accomplish the desired heat transfer and to remove volatile matter from the coke. In the preheat stages and in the calcining stages in the calcining vessel the coke is maintained in the form of a dense turbulent bed on each of the bubble plates 28. The plates permit build up of coke to a level 31 controlled by the height of the weir of the downcomers 29, which permit passage of coke from one stage to the next lowermost stage. The preheated coke passes to the next preheat stage 26 wherein it is heated to a temperature in the range of l6002000 F., e. g. 1900 F. by direct contact with hot upflowing gas the carbon containing component consisting essentially of CO emerging from the calcining section 27. The residence time in this preheat section is substantially the same as that in the upper preheat section 25.

From the last preheat stage the hot coke is passed to a hotter calcining stage or soaking stage to providethe necessary heat and residence time for calcination. For proper calcination the coke usually requires a residence time of 5 minutes to 8 hours, preferably 30 minutes to 2 hours, e. g. 1 hour, depending on the temperature employed and the character of the coke undergoing calcination. In the calcining stage primary air is introduced to burn the necessary amount of coke or any other suitable extraneous fuel to essentially C0 in order to heat the coke from the preheat temperature existing in zone 26 to the desired calcining temperature, approximately 2000 F. to 3000 F., e. g. 2500 F. The calcined coke is withdrawn from the calcining stage by well 30 through pipe 23. The withdrawn coke is water-quenched or otherwise cooled externally. After cooling below the ignition temperature of the coke, it may be further cooled by contact with incoming primary air or other colder inert gas used as a heat carrier.

Depending upon the relative heat requirements of the coker and the calciner it may be desirable to have little or no coke preheat or to have a maximum amount of preheat in the calciner. With more preheat stages the flue gas will be cooled to a lower temperature upon leaving the calciner, thus less heat will be available for the coker. On the other hand lower calciner preheat will provide more heat for the coker. Thus the process has considerable flexibility in distribution of the available heat.

Although the invention has been described and'illustrated as applied to a system comprising separate burner and calciner vessels, the burning operation and calcining operation can be carried out in the same vessel in which the burning zone is situated, directly on top of the calcining zone. The invention is not limited to the calcination of coke in a fluid bed system but also includes the use of a dispersed phase or transfer line burner calciner from which the CO gas is sent to the first coke burner. Also, a similar burner can be used between preheat zone 26 and soaker 27., in which case only a small amount of aeration gas is added to soaker 27. The invention may also be employed to advantage in a moving bed system.

Extraneous fuels such as natural gas, fuel oil or various low cost fuels can be used to supplant part or all of the coke used as fuel in the calcining step.

The novelty of the invention lies in an integrated coking and calcination process wherein the coke is heated to calcining temperature by burning the coke or other fuel in the calcining zone substantially to CO, and the effluent CO then employed in the burner of the coking unit wherein it is burned to CO2 to supply all or a substantial part of the heat requirements of the fluid coking unit. In this manner the overall fuel efiiciency of the coker and calciner is maintained the same as with the coker alone or at about a level of 70%. Although not shown in the drawing, the coke removed via line 23 may be cooled to approximately 1000" F. by passing it through a waste heat boiler wherein the heat is employed to manufacture high pressure steam. From the waste heat boiler the coke is water quenched to about 250 F. and discharged into a receiving hopper.

What is claimed is:

1. An integrated coking and calcining process which comprises coking a heavy hydrocarbon oil by contacting the same. with hot coke particles in a coking zone wherein the oil is converted to product vapors and carbonaceous solids deposited on the coke particles, removing product vapors from the coking zone, burning a portion of coke particles removed from the coking zone with a combustible gas in a separateburning zone to increase the temperature of said particles, returning a portion of the heated coke particles from the burning zone to the coking zone, introducing a separate stream of coke particles Without substantial cooling from the burning zone to a separate calcining zone contained in an auxiliary heating zone, heating the coke in the calcining zone to a temperature in the range of 2000 to 3000 F. by burning a portion of the coke therein to essentially CO with a free oxygencontaining gas introduced thereto, maintaining the coke particles in the fluidized state in the calcining zone for a soaking period time interval in the range of 5 minutes to 8 hours, removing calcined coke from the calcining zone, removing a gas containing ()0 free of C02 from the calcining zone and introducing said gas with auxiliary free oxygen-containing gas as fuel to the burning zone.

2. A process according to claim 1 wherein the coke removed from the burning zone is preheated in the auxiliary heating zone to a temperature of 1600 F. to 2000 F. while in the fluidized state superposed above the fluidized coke in the calcining zone by contacting it with hot CO emerging from the calcining zone.

3. A process according to claim 1 in which the coke particles are maintained in a fluidized state throughout the coking, burning and calcining zones.

4. A process according to claim 1 in which the heavy hydrocarbon oil is a crude petroleum residuum, in which the coking zone is maintained at a temperature in the range of 850 F. to 1200 F., and the burning zone at a temperature of 1000 F. to 1400 F.

5. A process according to claim 1 wherein the coke is maintained in the calcining zone for a period of 30 minutes to 2 hours at said calcining temperatures.

References Cited in the file of this patent UNITED STATES PATENTS Hemminger Feb. 29, Boynton et al. Apr. 18, Schutte et al. Nov. 27, Hufl? July 17, Bowles et a1. July 24, Riblett June 17, Bowles etal. Sept. 2, Schutte Dec. 23, Barr Jan. 20, Welinsky May 4, Berg July 27,

FOREIGN PATENTS Great Britain Apr. 29,

Claims

1. AN INTEGRATED COKING AND CALCINING PROCESS WHICH COMPRISES COKING A HEAVY HYDROCARBON OIL BY CONTACTING THE SAME WITH HOT COKE PARTICLES IN A COKING ZONE WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS SOLIDS DEPOSITED ON THE COKE PARTICLES, REMOVING PRODUCT VAPORS FROM THE COKING ZONE, BURNING A PORTION OF COKE PARTICLES REMOVED FROM THE COKING ZONE WITH A COMBUSTIBLE GAS IN A SEPARATE BURNING ZONE TO INCREASE THE TEMPERATURE OF SAID PARTICLES, RETURNING A PORTION OF THE HEATED COKE PARTICLES FROM THE BURNING ZONE TO THE COKING ZONE, INTRODUCING A SEPARATE STREAM OF COKE PARTICLES WITHOUT SUBSTANTIAL COOLING FROM THE BURNING ZONE TO A SEPARATE CALCINING ZONE CONTAINED IN A AUXILLIARY HEATING ZONE, HEATING THE COKE IN THE CALCINING ZONE TO A TEMPERATURE IN THE RANGE F 2000* F. TO 3000* F. BY BURNING A PORTION OF THE COKE THEREIN TO ESSENTIALLY CO WITH A FREE OXYGENCONTAINING GAS INTRODUCED THERETO, MAINTAINING THE COKE PARTICLES IN THE FLUIDIZED STATE IN THE CALCINING ZONE FOR A SOAKING PERIOD TIME INTERVAL IN THE RANGE OF 5 MINUTES TO 8 HOURS, REMOVING CALCINED COKE FROM THE CALCINING ZONE, REMOVING A GAS CONTAINING CO FREE OF CO2 FROM THE CALCINING ZONE AND INTRODUCING SAID GAS WITH AUXILIARY FREE OXYGEN-CONTAINING GAS AS FUEL TO THE BURNING ZONE.