US3347781A

US3347781A - Fluid bed process for coking hydrocarbons

Info

Publication number: US3347781A
Application number: US333853A
Authority: US
Inventors: Behrmann William Claus; Robert O Maak
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1963-12-27
Filing date: 1963-12-27
Publication date: 1967-10-17
Anticipated expiration: 1984-10-17

Description

0d- 7, 39$? w. c. BEHRMANN ETAL 3,347,781

FLUID BED PROCESS FOR COKING HYDROCARBONS Filed Dec. 27, 1963 SEED COKE

- WILLIAM CLAUS BEHRMANN I ROBERT o MAAK Pcnent Attorney United States Patent 3,347,781 FLUID BED r. ocnss Fon Cot; HYDROCARBONS ABSTRACT 9F THE DISCLQSURE High temperature fluid bed coking process wherein hydrocarbons are thermally cracked to produce coke and hydrogen and the heat for the cracking reaction is pro vided by burning the product hydrogen and radiating heat from the combustion flame to the fluid coke bed. More particularly, providing the endothermic heat of reaction by injecting an oxygen-containing gas into a reactor, near the top of the reactor, to burnthe gaseous products of the thermal cracking reaction, which combustion heats the roof and walls of the reactor whereby heat is radiated into the fluid coke bed from the combustion flame and the roof and walls of the reactor.

This invention relates to a high temperature process of cracking hydrocarbons to produce coke. This invention relates to a fluid coking process for cracking hydrocarbons to produce coke and hydrogen wherein the hydrogen is burned as fuel to provide the heat for cracking the hydrocarbons.

The invention particularly relates to a high temperature fluid bed coking process wherein hydrocarbons are thermally cracked to produce coke and hydrogen and the heat for the cracking reaction is provided by burning the product hydrogen and radiating heat from the combustion flame to the fluid coke bed. More particularly, the present invention relates to a method of providing the endothermic heat of reaction for a high temperature fluid coking process by injecting an oxygen-containing gas into a reactor, near the top of the reactor, to burn the gaseous products of the thermal cracking reaction, which combustion heats the roof and walls of the reactor whereby heat is radiated into the fluid coke bed from the combustion flame and the roof and walls of the reactor.

It is known that hydrocarbons can be cracked at high temperatures, for example, 18002500 F., to form products consisting essentially of hydrogen and carbon. Heretofore, these processes have been carried out in a fluid bed of coke whereby the heat for the endothermic cracking reaction was provided by resistance electro heating in the reactor, or the heat was provided by heating a large volume of circulated coke product in an external heater. The heretofore used techniques have several disadvantages, among which were that they required twoor three-vessel systems. They required means of transferring solids from the reactor to the heater vessels, such as risers and downcomers. They required means of recovering very fine coke particles that were entrained in the fluidizing gas, such as cyclone gas separators. In a system where there is a great deal of solids circulation and transfer means, plugging and caking of coke materials in a transfer means frequently require shutting down the reactor.

Also, in the heretofore used high high temperature process, if the process were installed where there was a ready supply of hydrocarbon feed but no use for the byproduct hydrogen, a substantial credit to the system was lost. In many circumstances where there may be a suitable feed for the process, there may not be a use for the hydrogen. 1

One of the major problems encountered in utilizing an external heater is that large volumes of coke particles had to be circulated to the heater and returned to the reaction zone to provide sufficient heat for the endothermic cracking reaction carried out in the reaction zone. This circulation frequently ran as high as 3040 times the weight of the withdrawn product. Also, an extraneous fuel was normally needed in the burner zone to provide the heat energy for carrying out the endothermic cracking reaction.

The most commonly used commercial process, particularly with low temperature fluid coking, utilizes a fluid bed reactor and a fluid bed burner scheme. With the low temperature fluid coking process, the fluid bed burner is operated at about 14001600 F. and with the high temperature fluid coking process a transfer line burner is operated at between 2400-2600" F. Under these conditions of heating the reactor by heating the circulating coke particles, 21 significant portion of coke is lost as a result of gasification of a portion of the coke in the burner. The circulating coke is gasified by reaction with water, carbon dioxide, or oxygen present in the gases in the burner which form carbon monoxide. The water and carbon dioxide are present as combustion products from burning the extraneous fuel in the heater.

In accordance with the present invention, high qualityhigh temperature, hard coke product of relatively large particle size is obtained with hydrogen as a byproduct, which hydrogen is burned as a fuel to provide the heat for carrying out the cracking reaction. The high temperature fluid coking process of the present invention can be carried out in a single vessel. This vessel will generally have a relatively large diameter in relationship to its height providing a large diameter, relatively shallow fluidized bed of coke particles. A suitable hydrocarbon feed is fed into the bottom of the coke bed which, on contact with the hot coke particles, immediately vaporizes and cracks to deposit carbon on the coke particles and to liberate hydrogen gas and, in some cases, a minor amount of methane and other light hydrocarbons. These gases effectively fluidize the coke bed. The hydrogen gas rises to in the vessel to the top of the reaction vessel. Near the top of the vessel, an oxygen-containing gas, such as air, is injected into the vessel in controlled amounts to burn a major portion of evolved hydrogen. The amount of air injected into the vessel is controlled so that the combustion zone is maintained near the top of the vessel and is not brought into contact with the dense phase of the fluid coke bed. Careful control of the combustion of the hydrogen is important since, if this flame approaches the dense phase, a substantial amount of carbon in the dense phase would be burned resulting in loss of coke to the process. Utilizing a relatively large diameter, shallow fluid bed, relatively low fluidizing gas velocities are suflicient to fluidize the bed and to obtain an adequate feed throughput. This minimizes the amount of fines entrainment in the dilute phase and loss of fines to the system. Seed coke is continuously added to the bed to maintain the average particle size in the bed as the coke is deposited from the cracking of the feed on the coke particles. As the coke particles increase in size and the bed builds up, product coke overflows, a weir and is withdrawn. Hot combustion gases are removed through a stack in the top of the reactor and can be used to indirectly preheat combustion air and/or feed. High quality, high density, hard coke product is recovered from the process.

The fluid bed of coke is heated by radiant heat energy from the combustion zone and by reflective, radiant heat energy from the walls and the roof of the reactor vessel.

The process of the present invention solves several problems encountered in the conventional either high or low temperature techniques for fluid coking. In the present invention, a single vessel is utilized operating at about atmospheric pressure in which the heating and the cracking are carried out. Because of the geometry of the reactor vessel, low fluidizing gas velocities can be utilized to provide a fluid bed. This substantially minimizes entrainment of fine particles, and eliminates the need for gas cyclone separators. By utilizing the hydrogen evolved from the cracking reaction as the fuel to provide the heat for the endothermic cracking reaction, a substantial savings in handling of fuel and preheat requirements is realized. Since the hydrogen is already at high temperatures, the addition of an oxygen-containing gas to this high temperature fuel provides a high combustion temperature for heating the coke. This invention provides a method for obtaining high quality fluid coke in an apparatus which has minimum investment and complexity, and without the need for circulation of large volumes of coke externally to be heated to provide the heat for the reaction.

The figure of the drawing illustrates one embodiment of the present invention where a high quality fluid coke is produced and the heat energy to carry out the reaction is provided by radiant heat from the combustion flame and reflected radiant heat from the walls and roof of the reactor.

The hydrocarbon feed to the high temperature fluid coking process to make coke and hydrogen can be any gaseous, liquid, or heavy residual hydrocarbon. Vacuum residuum as well as residua, which are solid at ambient temperatures, can also be used. Depending on the location and source of feed available, a naphtha or lighter hydrocarbon can be used. Also, the process can utilize mixtures of gaseous or liquid hydrocarbon feeds. Generally, however, heavy hydrocarbon oil feeds that are suitable for the coking process are heavy or residual crudes, vacuum bottoms, pitch, asphalt, and other heavy hydrocarbon petroleum residua or mixtures thereof. Typically, such feeds can have an initial boiling point of about 700 F. or higher, an API gravity of about -20, and a Conradson carbon residue content of about -40 wt. percent (as to Conradson carbon residue, see ASTM test D-180-52).

The gas with which the hydrogen is combusted in the reactor to provide the heat for the reaction can be air, oxygen, or oxygen-enriched air. Air is preferably used as the combustion gas. The air is introduced under controlled conditions to control the size of the combustion flame and to control the temperature in the reactor. The temperature to which the air is preheated and the amount of air injected into the reactor vessel at specified feed rates determines the temperature of the cracking reaction and of the combustion flame.

Hydrogen is produced as the byproduct of the cracking reaction and can be available in amounts of 87-98% purity, depending upon the temperature at which the cracking reaction is carried out. Normally, the other gases present in the evolved hydrogen will be methane and other light hydrocarbons. Also, there may be present some impurities from the hydrocarbon, such as sulfur and hydrogen sulfide. The purity of the hydrogen is no problem since most of it is burned to provide the heat for the cracking reaction. However, depending on the hydrogen to carbon ratio in the hydrocarbon feed, the reactor does not require burning all of the hydrogen to carry out the reaction and some of the hydrogen can be withdrawn out of the stack and recovered from the oxidation products of the combustion for use elsewhere.

The solid coke particles produced in accordance with this process are relatively large, homogeneous, hard particles. The coke produced has unique physical properties which permit it to be used directly in the formation of carbon electrodes without subsequent thermal treatment, such as calcining. These unique properties permit use of the new coke in novel coke formulations for the preparation of coke electrodes and other coke bodies. A particularly unique property of the coke which permits the formation of improved coke bodies is the extreme dense nature of the high temperature coke particles relative to calcined delayed coke and calcined fluid coke particles, the latter of which are produced by fluid coking at temperatures of about 900-1400 F.

The high temperature coke produced in accordance with this invention has high density, low porosity, and is relatively large in size. The coke also is generally spherical in shape and made up of laminar formation of coke deposited at the high temperatures. This presents a highly compact, hard coke particle. A photograph of a cross section of the coke reveals a tightly packed, onion skin appearance. A close examination of photomicrographs shows complete absence of voids from the coke particles.

The coke produced in accordance with this invention has a density (by hydrocarbon displacement) of 1.80- 1.90 -grn./cc., density of 48-100 mesh coke packed in 150 cc. tube of 1.25 to 1.35 gm./cc., calculated void volume of 25-35% and an electrical resistivity of 0.020 to 0.030 ohm-inch.

The high temperature fluid coker is operated in such a manner as to obtain a product having an average particle size of 150-500 microns, and generally 200-300 microns. About 20 to 40 wt. percent of the withdrawn coke product is screened to remove the fine particles and ground to an average particle size of -300 microns, and generally -200 microns, to provide seed coke for the reactor. The seed coke is continuously fed into the fluid bed to maintain the average particle size of the coke in the bed. The grinding of the product to obtain a seed coke is carried out in the conventional manner. Due to the relatively wide diameter, shallow bed geometry of the fluid bed of coke, relatively low superficial linear gas velocity can be utilized to obtain efficient fluidization of the bed. This gas velocity is controlled by the amount of feed and the temperature at which the reaction is carried out. The superficial linear fluidizing gas velocity is maintained at about 0.1-1.0 ft./sec., preferably about 0.5 ft./sec., and more generally 0.3 to 0.6 ft./sec. The gas velocity is such that there is substantially no fine coke material entrained in the stack gases.

The reactor vessel used in accordance with this invention can be generally about 5 to 60 feet in diameter, more generally 10-50 feet in diameter, and preferably about 30-50 feet in diameter. The reactor heights will be about 30-80 ft. Air, oxygen, or oxygen-enriched air is preheated to a temperature of about 100 to 2000 F., and preferably 1000 to 1500 F., is injected through inlets near the top of the reactor vessel and is used to oxidize hot hydrogen byproduct from the coking reaction to obtain an average combustion temperature of 2500 to 4500 F., and preferably about 3000-3500 F. The combustion temperature at specified feed rate is controlled by the preheat temperature of the air and the amount of air introduced into the vessel. The combustion of the hydrogen provides the heat for the cracking reaction. The heat for carrying out the reaction is conveyed to the fluid bed by radiation from the combustion flame and by reflected radiant heat from the roof and walls of the reactor vessel. The temperature in the fluid bed of coke is maintained at about 1900-2500 F., and preferably about 1950-2400 F. The hydrocarbon feed injected into the hot bed of fluidizing: coke particles is preheated to a temperature just below its cracking temperature of the feed used.

The hot combustion gases are removed through a stack and, due to the removal of the gases through the stack, a slight negative pressure is maintained in the vessel. The hot product coke is removed, cooled, and a portion of it is ground to provide the seed coke, and the remainder of hot coke may be heat exchanged by suitable means to recover heat and then taken to storage. The hot combustion gases can be heat exchanged to provide preheat for the combustion air and to provide recovery of heat through suitable heat exchange means.

The particle size distribution of a coke produced in accordance with this invention and of seed coke used is shown below in Table I.

TABLE I Seed Coke Product Coke It can be seen from the above table that relatively large coke particles of a relatively large average particle size can be obtained in accordance with the present invention.

In carrying out the combustion of the hydrogen product in the reactor, normally a deficient amount of air is added to the reaction zone so that all of the oxygen mixed with the hydrogen is burned and the combustion products leaving the reaction zone contain no free oxygen. The combustion is carried out under generally reducing conditions in the reactor, i.e., with excess hydrogen. Care must be exercised so that oxygen does not leave with unburned hydrogen because they may subsequently detonate.

The reaction is carried out at atmospheric pressure as a matter of convenience. It can be carried out at superatmospheric or subatmospheric pressures, but this would require additional cost in providing suitable pressure seals and compression or evacuation equipment.

The construction of the reactor vessel is important in that the geometry of the vessel should be such that the diameter of the fluid coke is relatively large and the depth of the bed is relatively shallow. Also, the geometry of the vessel is important in that there should be suflicient height above the fluid coke bed to provide an area or zone of dilute phase of entrained fine particles which fall back into the bed, a combustion zone wherein the air is combusted with the hydrogen which is above the dilute phase, in order that significant amounts of entrained coke are not burned, and this combustion zone should be at about the proper distance from the top of the reactor and above the fluid bed so that suflicient radiant heat can go directly from the combustion flame into the fluid bed and the radiant heat which goes to the walls of the vessel and to the roof can be radiated back into the fluid bed to provide suflicient heat to carry out the endothermic cracking reaction. The reactor vessel can be spherical, square, or rectangular in shape. The shape is not critical as long as the geometry is as described above. The reactor will be operated at average temperatures, near the top of the vessel, of 2500 to 4500" F. and at temperatures near the bottom and sides of the reactor of 20002500 F., i.e., in the fluid bed. Therefore, suitable refractory material must be utilized and the construction of the reactor must be such as to withstand the temperatures at which the reaction is carried out.

The walls, roof, and bottom of the reactor are built of refractory material. The combustion of the hydrogen product gas in the reactor heats the walls and roof of the reactor and radiates heat energy to the fluid coke bed providing the heat to carry out the reaction. The roof and walls of the reactor are built of refractory brick or refractory material which is heated by the flames of combustion, which combustion flames radiate heat to the fluid bed. The radiation of heat from the flames varies with the amount and degree of preheat of the air injected into the combustion zone of the reactor, the beam length, and the emissivity of'the flame and associated particles. The

furnace consists of the furnace proper containing the fluid bed 18, ports for admitting air 45 for combustion to produce a flame 23 over the fluid coke bed. Heat exchange means 37 is used to preheat the incoming air introduced through line 36 with the outgoing combustion products 35. The furnace proper can be circular in shape, as shown in the drawing. The structure is supported on its side by steel plates 29. The roof consists of refractory bricks 30 and steel shell 31. The bottom of the furnace is supported by closely spaced steel beams 12. covered with steel plates 13. On the steel bottom plates can be placed suitable insulation material 14 and insulation concrete 15. Refractory brick 26 are laid around the corners of the fluid bed. Over this brick are laid more refractory brick 16. The refractory brick and refractory lining material are of the conventional type used in fabricating high temperature furnaces and in particular the open hearth furnaces used in the manufacture of steel. The uppermost layer 17 forming the bottom of the bed on which the fluid coke rests can be made from a suitable molded refractory material or brick. Brick for the walls 27 usually are laid above the curvature of the bottom of the bed. The walls can be lined with molded refractory material or brick 28. The Walls are tied to the furnace by steel plates 29'. The main roof 36 of the furnace arches over the fluid bed. Suitable refractory bricks can be used to construct the roof.

The roof itself can be of hemispherical or other concave shape. It can be composed of refractory bricks or locks built up into the arch shape. The roof construction can be without an opening, but in the drawing it is illustrated as having a central circular opening. The circular ring of bricks or blocks at the center will serve as the keystone. The gaseous combustion products can be withdrawn through this circular opening, upwards through stack 33 and vented to the atmosphere. This stack is refractory lined 34 at the lower portion to prevent damage to the stack from the hot combustion gases. The stack is supported independently of the arch in the reactor, by means not shown. Due to differences in expansion of the refractory roof and the stack, provision is made for vertical movement of the stack in relation to the roof.

Air for combustion with the hydrogen product is injected through air inlets 45. Seed coke is fed through inlet seed coke means 25 and coke product is withdrawn through overflow opening 19. Feed, or inert fluidizing gas, for startup, is injected into the bed through inlet means 6, 7, 8, and 9. Outward stress of the roof is restrained by steel beams 32.

In order to start up the reactor vessel, it is necessary to bring the vessel and the refractory materials in the vessel up to operation temperatures of about 2500-4000 F. This is done by starting with a bed of coke which can be fluidized by introduction of an inert gas through line 5, valve 2, header 10, and lines 6, '7, 8, and 9. The inert gas is preferably preheated to a temperature of about 1000-2000" F. These hot gases fluidized the coke in the bed and heat it. An extraneous fuel is added through line 39, valve 40, blower 38,

lines

42 and 43, and air inlets 45. This extraneous fuel can be premixed With air. The fuel is burned is the vessel and heats refractory material in the reactor to temperatures of about 25003000 F. When the reactorvessel and coke particles are brought up to operating temperature, the inert gas introduced in line 5 is cut off by valve 2, and hydrocarbon fuel is injected into the hot fluid coke bed through lines 6, 7, 8, and 9. The fuel, on contact with the hot coke, cracks at temperatures of about 19002200 F. to form coke and hydrogen. As soon as the vessel is filled with hydrogen, the extraneous fuel introduced through line 39 is cut off and air alone is introduced through air inlets 45. The air combusts the product hydrogen and the temperature of 2500'50 00 F. is maintained in the flame area 23 in the top of the vessel. The temperature of 25005000 F. in the top of the vessel maintains the fluid coke bed at a temperature of about 19002400 F.

The gaseous atmosphere in the reactor is kept on the reducing side, i.e., contains excess hydrogen. Near the top of the vessel, air will be admitted through air inlet means. The basic principle of the process is that heat is transferred as radiant heat from the combustion of high temperature product hydrogen with high temperature air to the fluid bed of coke. Under design conditions, the flame will radiate a considerable amount of heat directly to the fluid bed. It will also radiate to the inside surface of the side walls and roof of the vessel which will, in turn, radiate to the surface of the fluid bed. Some particies of coke will be entrained in the fluidizing gas, particularly small particles varying in size down to soot. These particles rising into the flame will become luminous due to their becoming heated and due to their oxidation. The glowing particles will aid in the radiant heat transfer.

In the process of the present invention, a hydrocarbon feed having constituents boiling in the range of about 700-1400" F. is introduced through hydrocarbon inlet means 6, 7, 8, and 9. Prior to introduction to the vessel, the feed is preheated to a temperature of about 800 F. Immediately on contacting the fluidized bed of hot coke maintained at a temperature of 20002400 F. by radiant heat from the combustion gases and the walls of the vessel, the hydrocarbon is cracked to form carbon and primarily hydrogen. In order to minimize the formation of soot and entrainment and loss of soot to the system, it is important to minimize the bubble size and channelling and bypassing of vapors rising through the dense fluid bed. This is accomplished in the present invention by minimizing the average superficial gas velocity of the fluidizing gas through the bed at less than one fL/sec. The hydrogen product of the cracking reaction passes up through the fluidized bed into area 22 which contains some entrained fine coke particles. These particles fall back into the bed and the hot hydrogen proceeds up into zone 23 where it is mixed with hot, preheated air introduced through air ducts 45 and is burned at temperatures of about 25005000 F. The combustion temperature of the hydrogen and air is determined by the amount of air introduced and the temperature to which the air is preheated, which is generally about l2000 F.

The hydrocarbon fuel introduced through line 1 is preheated by suitable heat exchange means 3 or by heat exchange with the hot coke product by means not shown to a temperature of 800 F. The eflluent combustion product gases 35 going into the stack in the roof of the reactor vessel will be at temperatures of about 25004500 F. and will contain a significant amount of unburned hydrogen. These hot combustion gases can be used to preheat the incoming air by suitable heat exchange means 37 located in the stack.

As the carbon is laid down on the hot coke particles, the bed height in coke bed 18 increases to a height of about 10 ft. and overflows through product withdrawal means 19. Suflicient coke is in product withdrawal means 19 to form a gas seal in the reactor. This product has an average particle size of about 200 to 300 microns and is withdrawn at about a temperature of 1800-2200" F. About to /s of the product coke is ground to make seed particles which are introduced into the reactor through seed coke inlet means 25.

The product coke at about 2200 the reactor and is sent to a cooler. The fines in the coke can be separated and returned to the reactor. The coarse coke can be cooled by generating steam in coils immersed in a dense fluid bed cooler. The cooled product is conveyed to storage.

The invention is further illustrated by the following examples.

F. is withdrawn from Example I A suitable reactor F., the walls of the reactor are usually about 3400 F. The reactor is provided with a stack for removal of combustion gases. The fluidized coke particles have an average particle size of about 250 microns and are maintained in the fluidized state by passing through the fluid bed gaseous products at a superficial gas velocity of about 0.5 ft./ sec. from a cracked hydrocarbon feed. Hydrocarbon feed boiling in the range of about '7001400 F. is preheated to a temperature of about 800 F. and introduced into the hot fluid bed at the rate of b./d. The hydrocarbon is contacted with the hot fluid coke particles maintained at a temperature of about 2400 F. by radiant heating from the combustion gases and radiation of heat from the walls and roof of the reactor. The hydrocarbon is cracked to deposit coke on the hot particles and to evolve a hot hydrogen gas which fluidizes the solids in the bed and proceeds up into the top of the reactor. Near the top of the reactor is injected 1200 s.c.f.m. of preheated air which has been preheated to a temperature of 500 F. The air, on contact with the hot hydrogen, is burned and the combustion temperatures controlled at an average temperature of about 3500 F. A deficient amount of air is added to the reactor so that all of the air is burned prior to exhausting of the combustion gases through the stack. About /3 of the coke is cooled and ground to provide a fine seed coke having an average particle size of 100 to microns which is circulated to the fluid bed. Product coke is withdrawn at a temperature of about 1800-2200 F. and in the amount of 10 tons/ day. The coke produced in the above manner has unique physical properties which permit it to be used directly in the formation of carbon electrodes without further thermal treatment. That is, this coke need not be calcined in a separate step prior to being used to make coke electrodes. The coke produced is extremely hard, spherical in shape, and has smooth surfaces, high density, and high crush resistance.

Example II In this example a reactor vessel 60 feet in diameter and 50 feet in height is utilized to produce product coke at the rate of 360 tons/ day. The vessel is lined with refractory material suitable for withstanding temperatures of up to about 3400 F. In this reactor a fluid bed of the coke about 10 feet in height is initially fluidized by the passage of a hot, inert fluidizing gas heated to a temperature of about 1500 F. In the top of the reactor, a gaseous hydrocarbon fuel is premixed with air and introduced into the reactor and ignited. T he reactor walls and roof are gradually heated to a temperature of about 3000 F. which, by radiant heat, increases the temperature of the fluid bed of coke to about 1900 F. When the reactor and coke bed are up to temperature, inert fluidizing gas is cut oif and hydrocarbon feed having a boiling range of about 700-1400 F. is preheated to a temperature of about 800 F. and introduced into the hot bed of coke. The hydrocarbon is cracked to form coke and hydrogen. The coke deposits on the hot fluidized coke particles and the hydrogen is evolved and supplies the fluidizing gas. The evolved hydrogen has a superficial linear velocity through the coke bed of about 0.3-0.6 ft./sec. The hydrogen proceeds up in the reactor and is at a temperature of about 2400 F. Preheated air heated to a temperature of about 1500 F. is injected through a multiplicity of air injection points near the top of the reactor and is combusted with the hot hydrogen producing a combustion gas flame of about 3500 F. Sufficient amount of air is added to raise the temperature of the refractory roof and walls to about 3000" F. At this temperature the gas flame and the walls and roof of the reactor radiate sufiicient heat into the fluid coke bed to raise the temperature of the coke bed to about 20002400 F. The temperature of operation is maintained in the reactor by controlling air preheat, the volume of injected air, and the amount of hydrocarbon feed injected into the fluid coke bed.

When the reactor has reached the operating temperature, liquid hydrocarbon fuel is introduced at a rate of 3600 bbls./day and preheated air is injected at 30,000 s.c.f.m. Product coke is withdrawn. About /3 of the coke is cooled and ground as seed coke and recycled to the coke bed. The average particle size of the coke in the fluid bed is about 250 microns and the average particle size of the seed coke is 100-150 microns. Hot product coke is withdrawn at a rate of 360 tons/day.

The coke product of the present invention can be used in the formation of electrodes for the aluminum industry. The coke can be used for both Soderberg and prebake electrodes. Suitable electrode formulations can be prepared by grinding a portion of the coke product to form fine coke, mixing it with coarse coke and a suitable binder and, in the case of the prebake electrodes, baking in a conventional manner or, in the case of the Soderberg electrodes, feeding it to the Soderberg process.

While a principal use of the product coke is directed to the production of aluminum electrodes, the apparatus and process of the present invention has other utilities. For example, the hot coke product withdrawn at a temperature of 2200-2400 F. can be utilized as a heat source for carrying out other processes. The coke can be contacted with other materials to make various chemicals. For example, they can be contacted with sulfur to make carbon disulfide. They could be contacted with preheated naphtha in a short time, low partial pressure vessel under conditions so as to make a yield of about 35 wt. percent of ethylene.

The invention is not to be limited by the above description or the illustrations presented in the examples but rather only by the appended claims.

What is claimed is:

1. In a process for the production of high temperature fluid coke wherein hydrocarbon feed in injected into a fluidized bed of coke particles to crack the hydrocarbon feed to coke and hydrogen, coke depositing on the hot coke particles and the hot hydrogen gas proceeding upwardly to fiuidize the coke particles and thence ascend into a vapor space above the bed, the improvement comprising injecting an oygen-containing gas into the vapor space to admix with the hot hydrogen gas, burning the hydrogen gas, and radiating heat from the combusting gas to the fluid coke bed.

2. In a process for the production of high temperature coke wherein a fluidized bed of hot particulate coke is contained in a zone defined by the enclosing side walls of a reactor, a second zone is defined by a vapor space above the bed and below the roof of the reactor, hydrocarbon feed is injected into the fluidized bed of coke particles to crack the feed to coke and hydrogen, coke depositing on the hot coke particles while hot hydrogen gas proceeds upwardly to fluidize the coke particles and thence ascend into the vapor space above the bed, the improvement comprising injecting an oxygen-containing gas into the vapor space to admix with the hot hydrogen gas, burning the hydrogen gas, radiating heat from the walls and roof of the reactor into the fluidized bed of coke particles to maintain the bed at a temperature of from about 1900 to about 2400 F., withdrawing product coke, grinding a portion thereof to form seed coke, and returning seed coke to the fluid bed.

3. The process of claim 2 wherein the hydrocarbon feed fed to the reactor vessel is heated to a temperature just below the cracking temperature of the feed and the oxygencontaining gas is preheated to from about 100 to about 2000 F.

comprises introducing a hydrocarbon feed, preheated to a temperature just below its cracking temperature, into the fluidized bed of coke particles maintained at a temperature of from about 1900 to about 2500" F., cracking the hydrocarbon feed to coke and a gas consisting essentially of hydrogen, the coke depositing on the hot coke particles, the evolved hydrogen fluidizing the coke particles and thence ascending into the vapor space of the reactor, injecting a preheated oxygen-containing gas at a temperature of from about to about 2000 F. into the vapor space for admixing with the hot hydrogen gas, burning the hydrogen gas at a temperature of from about 2500 to about 5000 F., radiating the heat of the combustion flame from the walls and roof of the vessel to the fluid coke bed, withdrawing product coke, grinding a portion of the product coke to form seed coke and returning the seed coke to the fluid bed.

5. The process of claim 4 wherein the coke in the fluid bed has an average particle size ranging from about to about 500 microns, and the seed coke is ground to an average particle size-ranging from about 70 to about 300 microns.

6. A process for the production of high temperature fluid coke which comprises introducing a hydrocarbon feed preheated to a temperature just below its cracking temperature, which feed is fed into a fluidized bed of coke particles having a bed diameter of about 10-50 feet, a bed depth of about 10-20 feet, the overall height of the reactor being about 30-80 feet, maintained the fluidized bed of coke at a temperature of about 2000-2400 F. to crack the hydrocarbon feed to coke and hydrogen, evolved hydrogen fluidizing the coke particles, the coke depositing on the hot coke particles to form dense, hard, laminar layers of the coke, hot hydrogen gas proceeding upwardly into the reactor and entraining fine coke particles in the reactor vessel to a height of about 10-20 feet, injecting a preheated oxygen-containing gas which has been preheated to a temperature of about l00-2000 F. at a point near the top of the reactor vessel into the hydrogen gas, burning the hydrogen gas at a temperature of about 2500-5 000 F., controlling the flow of the oxygen-containing gas into the top of the reactor vessel so as to produce a combustion flame 10-20 feet in height, and occupying the entire top area of the reactor vessel, the amount of oxygen-containing gas introduced into the vessel being such that the bottom portion of the combustion flame does not extend into the dense phase, the entrained carbon particles falling back into the fluidized bed, the temperature of the combustion being controlled by the amount of oxygen-containing gas introduced into the reactor and the temperature of said gas, radiating heat from the combustion flame, of the hydrogen and oxygen-containing gas, to the fluid coke bed, the walls and the roof of the vessel, radiating heat from the walls and roof of the vessel to the fluid coke bed, maintaining the average particle size of the coke in the fluidized coke bed at about 150 to 500 microns by withdrawing coke and separating a portion of the withdrawn coke and grinding it to form seed particles having an average particle size of 70-300 microns and returning the seed particles to the fluid bed reaction zone.

References Cited UNITED STATES PATENTS 3,013,951 12/1961 Mansfield 201-37 X 3,260,664 7/1966 Metrailer 208127 3,264,210 8/1966 Waghorne et a1 208127 3,280,021 10/ 1966 Metrailer et al 208l27 X JOSEPH SCOVRONEK, Primary Examiner.

Claims

1. IN A PROCESS FOR THE PRODUCTION OF HIGH TEMPERATURE FLUID COKE WHEREIN HYDROCARBON FEED IN INJECTED INTO A FLUIDIZED BED OF COKE PARTICLES TO CRACK THE HYDROCARBON FEED TO COKE AND HYDROGEN, COKE DEPOSITING ON THE HOT COKE PARTICLES AND THE HOT HYDROGEN GAS PROCEEDING UPWARDLY TO FLUIDIZE THE COKE PARTICLES AND THENCE ASCEND INTO A VAPOR SPACE ABOVE THE BED, THE IMPROVEMENT COMPRISING INJECTING AN OYGEN-CONTAINING GAS INTO THE VAPOR SPACE TO ADMIX WITH THE HOT HYDROGEN GAS, BURNING THE HYDROGEN GAS, AND REDIATING HEAT FROM THE COMBUSTING GAS TO THE FLUID COKE BED.