US3249528A - Countercurrent flow coking process - Google Patents

Description

May 3, 1966 v. D. ALLRED COUNTERCURRENT FLOW COKING PROCESS Filed Jan. 28, 1963 INVENTOR. VICTOR D. ALLRED ATTORN EY United States Patent Ofi ice 3,249,528 Patented May 3, 1966 3,249,523 COUNTERCURRENT FLOW (IQKING PROCESS Victor D. Allred, Littleton, Colo., assignor to Marathon Oil Company, Findlay, Ohio, a corporation of Ohio Filed Jan. 28, 1963, Ser. No. 254,291 12 Claims. (Cl. 208-46) This invention relates to the production of petroleum cokes and more particularly to a process wherein a portion of cokes formed in the cyclic process of this invention is used as a coking matrix and a process wherein the flow of oxidant and solids are cocurrent and the movement of front is countercurrent thereto.

Petroleum cokes are currently made by a variety of processes. Better grades of petroleum coke are prepared by delayed coking in a process where hydrocarbon residuum is pumped into a large container and maintained at a high temperature within the container until coking is accomplished. Fluidized coke is prepared utilizing fluidized bed techniques. In a typical fluidized bed process, a heavy residuum is injected into a reaction zone containing fluidized heated particles, usually coke. The residuum coats the particles and is coked by the heat of the particle.

I have now invented a process wherein a hydrocarbon material is used to coat coke particles which are then passed into a combustion zone in cocurrent flow with an oxidant. This process allows the practical recovery of petroleum cokes and chemical byproducts of the coking reaction.

Nearly everyone is acquainted with coal furnaces or with coal fires in a home grate. In both these devices the flow of air is generally countercurrent to the flow of coal or coke. In each device, substantially all of the combustible matter is burned, the burning rate depending on the air throughput. The same thing happens in a retort.

I have now discovered that, contrary to what would be expected, only minor amounts of the feed are consumed in a furnace or retort when the air flow is reversed, i.e., the feed and oxidant flow are cocurrent and are countercurrent to the movement of the combustion zone.

Furthermore, cokes of unique and varying properties; for example, varying but generally low density, structure, and volatile combustible matter content; can be produced readily in simple furnaces. These results probably arise from the temperature profile within the retort.

In the usual furnace the temperature rises to a peak as the combustion Zone is approached and falls rapidly below the combustion zone. In the process of the instant invention, the temperature remains low, rises abruptly within the combustion zone and remains high after the combustion zone is passed.

A study of gas flow in the two types of combustion explains this phenomenon. In the case where air flow is countercurrent to coke flow, cool air passes upwardly through the burned materials and is heated as it approaches the combustion zone. It is further heated in the combustion zone and loses its heat as it passes through the unburned matter above the combustion zone. In the case of cocurrent air flow; the air remains cool until it contacts the combustion zone, is rapidly heated and remains hot as it flows along with materials which have passed through the combustion zone.

There is no completely satisfactory explanation for the fact that all of the combustible matter burns in the usual situation and little burns in the process of this invention. It may be that, as the relatively cool coated coke particles contact the combustion zone, a portion of the volatiles on the surface of the coke escape into the gas stream and burn, thereby exhausting the available oxygen so that no further burning can take place. In such a situation, the

combustion would be substantially in the gas phase and would move ahead with relative rapidity leaving coke rather than ash.

Conversely, in the usual process where the flow of oxidant is countercurrent to the flow of combustible matter, the volatiles are distilled and exhausted by hot flue gases and only solids are left to burn. The combustion zone moves more slowly through the solid phase converting it completely to ash.

It might also be that in the usual process all of the combustible matter is burned because it is heated to combustion temperatures by the time it reaches the combustion zone, while in the process of this invention the combustible matter is relatively cool as it enters the combustion zone. This fact may also explain the unique porosity of coke made by my new process.

The materials being coked in the present invention preferably move through the apparatus in the form of a moving bed, that is, the individual particles are in contact with other particles surrounding them and are not in a fluidized state. The movement of the particles is thus caused either by gravity or by the pressure exerted by the immediately upstream particles or by both.

A better understanding of the invention can be obtained by reference to the drawing, which is a front elevation of a retort suitable for the process of this invention together with some associated equipment. The retort is partly broken to show internal equipment and material movement.

Typically, coke particles in hopper 10 are fed through valve 11, shown as a star feeder, into retort 12. The coke exits retort 12 through valve 13 from whence it passes into separator 14, for example, a screen separator, through conduit 15. Larger particles, which constitute the product coke, exit the separator through line 16 while smaller particles are removed to hopper 10 through elevator 17a.

Coke entering retort 12 through valve 11 moves downwardly through the retort by gravity flow. Though not required, hot preheating gases can be introduced into the retort through valved preheat gas input line 17 and header 18, pass upwardly through the furnace and out valved preheat gas output line 19. Coke particles moving downwardly through retort 12 are coated with hydrocarbon introduced through hydrocarbon input line 20 and header 21. Oxidant is introduced into the retort via oxygen input line 22 and header 23.

The coated, unignited coke passes downwardly into combustion zone 24, indicated by dashed lines just below header 23, where a portion of the hydrocarbon coating on the coke particles or hydrocarbon volatiles burn to provide suflicient heat to carry out coking of the uncoked hydrocarbon material.

Substantially all the available oxygen is consumed at the face of combustion zone 24. Therefore, the combustion zone is quite limited in depth. The zone may be only three to six inches deep under some conditions. The area below the combustion zone can contain coated coke particles or a slurry of substantially solid particles and liquid hydrocarbon, depending upon the amount of hydrocarbon introduced into the retort. The material below combustion zone 24 is substantially above its spontaneous ignition temperature but, due to a lack of oxidant, does not burn. It is in this area that coking is completed. The coking time is controlled by varying the preheating temperature, the depth and temperature of the combustion zone 24, and the depth of retort 12.

Some cokes tend to expand and fuse as they flow downwardy through the retort. In such cases, breakers 25 size the coke as it leaves the retort for discharge into separator 14 through conduit 15. Weir 26 prevents the coke from blocking the exit of gases and hydrogen volatiles through valved hydrocarbon outlet 27. Vaporized hydrocarbons are separated from the noncondensables in partial condenser 28.

Where highly enriched oxygen mixtures or pure oxidant streams such as pure oxygen or chlorine are utilized, the non-condensables, such as carbon monoxide and propane, can be recycled into retort 12 through valved noncondensable return line 29 to act as a supplementary fuel.

The preheating temperature and coke and oxygen throughput should be regulated to maintain a temperature from about 400 to about 1200 C. and preferably about 750 to about 1200 C. in the portion of the retort below header 23. The pressure within the retort should be such that the combustion zone does not rise above header 23. This result can be obtained by maintaining the area between the preheat gas input header 18 and the preheat gas output header 20 at a pressure slightly higher than that below header 23. The downward flow of hydrocarbon from header 21 aids in maintaining the desired pressure conditions within the reactor.

To further aid in maintaining a desired heat balance in the reactor in combination with the lowest possible consumption of fuel, preheat gas output from line 19 can be used in conjunction with the operation of separator 14.

The oxidant used in the instant process can be oxidant gases such as fluorine, chlorine, nitrogen dioxide, and the like but is preferably oxygen or mixtures thereof with inert gases. Examples of such mixtures include air or oxygen-superheated steam mixtures. The oxidant can be preheated to any desired temperature prior to use in the process.

The amount of oxidant required in a particular process would depend on the oxidant used, the residuum to be coked, and the desired combustion zone temperature. The amount of oxidant required can be determined for a particular process through use of routine techniques. Generally, however, the oxidant introduced into a reactor will be that amount required to completely oxidize only about 2 to 15 percent, by weight, of the residuum being coked.

Any residual oil which is liquid when injected into the recycled coke can be utilized in this process. Examples of such oils or fractions thereof include number 5 and 6 fuel oils, Bunker C oil, heavy gas oil, heavy catalytic cracker residues, and cyclic fuel oils.

The residual oil (residuum) can be used merely to wet the coke particles or the residuum, and coke particles can be introduced in the form of a slurry. While the residuum can be introduced as a liquid, it is preferably introduced into the reactor as a vapor in amounts ranging from 8 percent to upwards of 25 percent by weight of the coke. Preferably about 12 to about 20 percent residuum is utilized.

The following example more fully illustrates my invention, but it is not intended that my invention be limited to the specific raw material, petroleum fraction, reaction condition, or process shown. Rather, it is intended that all equivalents obvious to those skilled in the art be included within the scope of my invention as claimed.

Example I Coking is carried out in a small tube furnace by filling a small furnace with 500 g. crushed coke wetted with slurry oil. Air is introduced into the top of the furnace at the rate of 6 ft. /hr. and an electric heater is utilized to ignite the wetted coke at the bottom of the furnace. As the flame front moves up through the furnace, a temperature of about 790 C. is developed in the furnace and the front moves at a velocity of about 5.5 in./hr. Coke is removed from the bottom of the tubular furnace at a rate which maintains the combustion front in a fixed position, is ground where necessary, and the fines recycled to the top of the furnace. About 15 percent of 4 the total charge is burned to maintain the desired temperature in the furnace.

While the coke in the above example is sized at 4 to +8 mesh because of the small diameter of the furnace, in large furnaces chunks larger than those having a diameter of about 5 inches could be used.

Now having described my invention, what I claim is:

1. A coking process comprising in combination the steps of contacting a moving bed of particles of coke with a fluid petroleum residuum to form a combustion zone charge; passing said charge as a moving bed cocurrently with a limited amount of oxidant into a combustion zone confined within a portion of the retort; said stoichiometrically limited amount of oxidant being insufficient to oxidize more than about one fourth of said charge; said amount of oxidant being sufficient to maintain said combustion zone at a temperature of at least about 400 C.; burning the oxidant and a portion of the charge in the combustion zone in order to coke the residuum on the coke particles; thereafter passing the product from said combustion zone through a zone containing insuflicient oxidant to support combustion; said stoichiometrically limited amount of oxidant being so controlled as to maintain said oxygen deficient zone within a substantial portion of the retort; and thereafter recovering the particles of residuum coked on coke.

2. A process for the production of coke comprising in combination the steps of introducing a moving bed of particles of coke into one end of a retort; coating said particles With petroleum in a coating zone located near the point of introduction into said retort; thereafter introducing a stoichiometrically limited quantity of an oxidantsoas to move concurrently with the moving bed of coke coated with petroleum residuum and to form a combustion zone of limited depth confined within a portion of 'the retort; said stoichiometrically limited quantity of oxidant being sufficient to oxidize from about 2 to about 15% by Weight of the residuum being coked; burning the oxidant and a portion of the coke particles coated with petroleum' residuum to coke the residuum on the coked particles; thereafter passing the product from the combustion zone through an oxygendeficient non-combustion zone of substantial size and recovering the particles of residuum coked on coke.

3. The process of claim 2 wherein the combustion zone is confined between the point of introduction of the oxidant and the non-combustion zone by control of the stoichiometrically limited amount of oxidant; and wherein both the combustion zone and the non-combustion zone are maintained at temperatures of at least about 400 C.

4. The process of claim 1 wherein the minimum temperature of the combustion zone is at least about 750 C.

5. The process of claim 1 wherein the coked particles are contacted with from about 8 to about 25% liquid petroleum residuum.

6. The process of claim 1 wherein the coked particles are contacted with from about 12 to about 25 residuum.

7. The process of claim 2 wherein the amount of oxidant passed through the combustion zone is sufficient to oxidize from 2 to about 15 by weight of the residuum charged.

8. The process of claim 2 wherein the amount of oxidant passed into the combustion zone is sufficient to oxidize from about 3 to about 10% by weight of the residuum charged.

9. The process of manufacturing petroleum coke comprising contacting a moving bed of coke particles with from about 8 to about 25 by weight of the coke particles of liquid petroleum residuum; passing cocurrently the moving bed charge of fluid petroleum residuum and coke together with from 2 to about 15% by weight of the charge of an oxidant into a combustion zone confined within a portion of a retort; said combustion zone having a temperature of from 400 to about 1,200 C.; burn.-

ing the oxidant and a portion of the charge to coke the residuum on the coke particles; and thereafter passing said particles of residuum coked on coke through a non-oxidizing zone maintained Within a substantial portion of the retort; maintaining the temperature in said non-combustion zone between about 400 and l,200 C. and thereafter permanently withdrawing the particles of petroleum residuum coked on coke from the retort as product after they have passed through the non-oxidizing zone.

10. The process of preparing petroleum cokes comprising contacting a moving bed of coke particles with fluid petroleum residuum in amounts of from 12 to about by Weight of the coke; passing cocurrently into a combustion zone confined within a portion of a retort the moving bed charge of petroleum residuum and coke particles together with an amount of oxygen suflicient to oxidize from about 3 to about 10% by weight of the charge; maintaining the combustion zone temperature within the range of about 750 to about 1,200 C.; burning the oxygen and a portion of the charge within the combustion zone to coke the residuum on the coke particles; and thereafter passing the resulting product through a non-oxidizing zone confined within a substantial portion of the retort; said non-oxidizing zone having a temperature Within the range of about 750 toabout 1,200 C. but being sufiiciently deficient in oxygen as not to permit combustion of the product.

11. A process comprising contacting a moving bed of coke particles with from 8 to about by weight of the coke of a fluid petroleum residuum to form a com bustion zone charge; passing cocurrently the combustion zone charge as a moving bed together with from about 2 to about 15% by weight of oxygen based on the weight of the charge into a combustion zone of substantial size confined within a portion of a retort, said combustion zone having a temperature of from about 400 to about 1,200 C.; burning the oxidant and a portion of the charge in the combustion zone to form a coked product; moving said coked product through the non-combustion zone maintained within a portion of said retort by control of the oxygen fed into the retort; said non-oxidizing zone having a temperature in excess of 400 C. but containing insufficient oxygen to support combustion; and thereafter withdrawing a portion of the resulting residuum coked on coke as product and returning another portion of said residuum coked on coke to the retort to form a combustion zone charge as a continuous process.

12. The process of claim 11 wherein the charge moves into the combustion zone by gravity at a rate of less than about feet per hour.

References Cited by the Examiner UNITED STATES PATENTS 2,456,796 12/1948 Schutte 2087 2,561,334 7/1951 Bowes et al 208l26 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, DANIEL E. WYMAN,

Examiners.

A. RIMENS, Asistant Examiner.

Claims (1)

1. A COKING PROCESS COMPRISING IN COMBINATION THE STEPS OF CONTACTING A MOVING BED OF PARTICLES OF COKE WITH A FLUID PETROLEUM RESIDUUM TO FORM A COMBUSTION ZONE CHARGE; PASSING SAID CHARGE AS A MOVING BED COCURRENTLY WITH A LIMITED AMOUNT OF OXIDANT INTO A COMBUSTION ZONE CONFINED WITHIN A PORTION OF THE RETORT; SAID STOICHIOMETRICALLY LIMITED AMOUNT OF OXIDANT BEING INSUFFICIENT TO OXIDIZE MORE THAN ABOUT ONE FOURTH OF SAID CHARGE; SAID AMOUNT OF OXIDANT BEING SUFFICIENT TO MAINTAIN SAID COMBUSTION ZONE AT A TEMPERATURE OF AT LEAST ABOUT 400*C.; BURNING THE OXIDANT AND A PORTION OF THE CHARGE IN THE COMBUSTION ZONE IN ORDER TO COKE THE RESIDUUM ON THE COKE PARTICLES; THEREAFTER PASSING THE PRODUCT FROM SAID COMBUSTION ZONE THROUGH A ZONE CONTAINING INSUFFICIENT OXIDANT TO SUPPORT COMBUSTION; SAID STOICHIOMETRICALLY LIMITED AMOUNT OF OXIDANT BEING SO CONTROLLED AS TO MAINTAIN SAID OXYGEN DEFICIENT ZONE WITHIN A SUBSTANTIAL PORTION OF THE RETORT; AND THEREAFTER RECOVERING THE PARTICLES OF RESIDUUM COKED ON COKE.

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