US3264210A

US3264210A - Fluid bed process to produce coke and hydrogen

Info

Publication number: US3264210A
Application number: US333897A
Authority: US
Inventors: Waghorne Robert Harry; Molstedt Byron Victor
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: 1966-08-02
Anticipated expiration: 1983-08-02

Description

Aug. 2, 1966 R. H. WAGHORNE ETAL 3,264,210

FLUID BED PROCESS TO PRODUCE COKE AND HYDROGEN Filed Dec. 27, 1963 Inventors ROBERT HARRY WAGHORNE BYRON VICTOR MOLSTEDT M I n St Patent Attorney United States Patent 3,264,210 FLUID RED PROCESS TO PRODUCE COKE AND HYDROGEN Robert Harry Waghorne and Byron Victor Moistedt,

Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Dec. 27, 1963, Ser. No. 333,397 Claims. (Cl. 208-127) This invention relates to a high temperature process of cracking hydrocarbons to produce coke. The 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 of the hydrocarbons. The invention relates particularly to a process of producing high temperature fluid coke and a process of case hardening and calcining coke compactions. Particularly, the invention provides an improved method of thermally hardening coke compact-ions of fluid coke and a suitable binder which comprises contacting the compactions and binder cocurrently in a fluid bed of fine coke particles at case hardening and calcining temperatures. The temperatures utilized are in the range of 1500 to 2400 F.

More particularly, the invention relates to a process of case hardening and calcining coke agglomerates in a fluid bed and moving bed calciner wherein the heat for case hardening and calcining is provided by radiant heat from the combustion of product hydrogen from high temperature coking of a hydrocarbon feed and by the sensible heat of hot product coke.

It is known that hydrocarbons can be cracked at high temperatures, for example, 1800-2500 F., to form prod ucts 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 circulating coke product in an external heater. These heretofore used techniques have several disadvantages, among which were that they required twoor threevessel systems. They required means of transferring solids from the reactor to the heater vessel, such as risers and downcomers. They required means of recovering very fine coke particles that are entrained in the fluidizing gas, such as cyclone gas separators. In a system where there is a great deal of solids circulation and several transfer means, plugging and caking of coke materials in the transfer means frequently required shutting down the reactor.

Also, in the heretofore used high temperature process, ifthe 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,

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 to the endothermic cracking reaction carried out in the reaction zone. This circulation frequently ran as high as -40 times the weight of the withdrawn product. Also, an extraneous fuel was normally needed in the burner zone to provide the heat for carrying out the endothermic cracking reaction.

Heretofore, in order to prepare suitable coke formulations for the manufacture of molded coke bodies, such as coke electrodes for the aluminum industry, it was found necessary to calcine the coke, form coke compactions or agglomerates of a portion of the coke with a suitable binder, press the compactions, heat harden, and calcine the compactions before they could be used in 3,2642 10 Patented August 2, 1966 ice making suitable electrodes. These compactions, after case hardening, calcining, and cooling, were generally crushed or ground to a suitable particle size to be used in a coke formulation wherein they supplied the coarse fraction. It has been necessary in order to calcine coke agglomerates to first case harden the agglomerates in an oven at temperatures of 400-1100 F., cool them and then heat them in a moving bed in a kiln .at a temperature of 1400-2000" F. Another technique was to case harden the compressed compactions or agglomerates in a fluid bed of fine hot coke particles at a temperature of 200- 800 F., and then heat the agglomerates in .a moving bed of fine hot coke particles and agglomerates at temperatures of 1000-1800 F. In each situation it was necessary to carry out a low temperature pretreatment step to case harden the agglomerates so that they would not subsequently be broken during the calcining step due to escape of volatile materials. The case hardening also prevents sticking together and distortion of the agglomerates when subjected to subsequent calcining temperatures of 1000- 1800 F.

Another problem was to find an eflicient high temperature source of heat to carry out the case hardening and calcining step. It had been considered to use the sensible heat of the product coke from the low temperature fluid coking process by directly contacting the agglomerates with the product coke to provide the heat for case hardening and calcining of the compactions. It was found, however, that there was not suflicient heat in the hot coke product to carry out this step. This is partially because only about 1 part in 30 or 40 parts of the circulated coke is available for case hardening and compaction since in the low temperature fluid coking processes 30-40 volumes of coke are circulated to the fluid bed heater and recirculated through the reactor to provide the endothermic heat for the cracking reaction. It had been considered to contact the compactions that were to be case hardened and calcined with a stream of the recycle coke prior to feeding the coke to the fluid bed reactor. It was found, however, that taking heat from the circulating coke subjected the fluid bed burner to an unacceptable high heat load. This required burning large amounts of extraneous fuel in the fluid bed burner to provide suflicient heat as sensible heat of the circulating coke to provide the heat needed to carry out both the cracking reaction and the heat needed to carry out the calcining step. Where large amounts of extraneous fuel were burned and large volumes of coke circulated in the external heater, the product coke was found to undergo excessive gasification from the combustion products of the extraneous fuel.

In accordance with the present invention, high quality, high temperature, hard coke product of relatively large particle size is obtained with hydrogen as a byproduct, which hydrogen is burned -as fuel to provide the heat for carrying out the cracking reaction and the case hardening and calcining of the coke compactions. The high temperature fluid coking process of the present invention and the calcining step can be carried out in a single vessel. This vessel will generally have a relatively large diameter in relationship to the bed depth providing a large diameter, relatively shallow fluidized bed of coke particles. The calcining vessel is an elongated vessel located Within the reactor, preferably at one end.

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 gas. These gases effectively fluidize the coke bed. Hydrogen gas rises in the vessel to the top of the reaction vessel. Near the top of the vessel an oxygen-containing gas is injected into the vessel in controlled amounts to burn a major portion of the evolved hydrogen. The amount of air injected into the vessel is controlled so that the combustion zone of hydrogen is maintained near the top of the vessel and is not allowed to be brought into contact with the dense phase of the fluidized coke bed. Careful control of the combustion of the hydrogen is important since if this flame closely approaches the dense phase, a substantial amount of finely divided carbon particles will be oxidized resulting in a substantial 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.

A portion of the product coke is removed from the calciner, cooled, ground and mixed with an unground portion of the product coke and added to a suitable carbonaceous binder to form coke agglomerates or compactions which are case hardened and calcined in the calcining section of the reactor vessel. These compactions are fed to the calcining section of the reactor. The product coke in the reactor overflows into the elongated calcining vessel, the upper portion of which is maintained as a fluidized bed of fine coke. The middle portion of the calcining vessel is maintained as a moving bed of agglomerates and fine coke. The lower portion is maintained as a moving bed of fine coke and agglomerates and functions as a cooling section. Agglomerates are introduced directly into the fluid bed and are case hardened in the fluidized section of the vessel and move cocurrently with the product coke down the calciner section of the vessel and are calcined.

This invention provides a method of obtaining high quality fluid coke and calcined coke agglomerates in an apparatus which has minimum investment and complexity without the need for circulation of large volumes of coke to be externally heated to provide the heat for the reaction. Also, when utilizing the process of the present invention, it was found the high temperature coke product produced in accordance with the present process could be made into compactions or agglomerates which could be fed directly to the reactor vessel, that is, to the fluid bed and calcining vessel, at temperatures of 18002400 F. that exist in the fluid bed and calcining section of the calciner without a previous separate case hardening at 2001100 F. without detrimental effect on the compactions. This eliminates the previous separate case hardening step in an oven at 400 to 1100 F. or in a separate fluid bed at 200800 F. The compactions and agglomerates formed in this manner do not crack or become distorted in shape during the calcining step. Also, by incorporating the calcining vessel within the high temperature fluid coking vessel, effective use is made of the excess heat available from the high temperature combustion of the hydrogen in the coke reactor vessel. The coke agglomerates or compactions are heated while dropping through the gas space in the vessel into the top of the calciner vessel and are heated directly by radiation while at the top of the fluid bed before proceeding through the fluid bed.

FIGURE 1 of the drawings is a side view of one embodiment of the present invention where 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. At one end of the reactor and within the reactor vessel is an elongated, cylindrically or rectangularly shaped calcining vessel which contains in the upper region a fluid bed of fine coke particles and in the middle region a moving bed of coke agglomerates and fine coke particles, and in the bottommost region, i.e., the cooling section, a moving bed of agglomerates and fine coke particles.

FIGURE 2 of the drawings is an end view of the drawing illustrated in FIGURE 1 taken through the center of the vessel.

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, hydrocarbon oil feeds that are suitable for the coking process are heavy or residua crudes, vacuum bottoms, pitch, asphalt, and other heavy hydrocarbon petroleum vacuum bottoms, pitch, asphalt and other heavy petroleum residua or mixtures thereof. Typically, such feeds can have an initial boiling point of about 700 F. or higher and an API gravity of about 20, and a Conradson carbon residue content of about 5-40 wt. percent (as to Conradson carbon residue, see ASTM test D18052).

The gas with which the hydrogen is combusted in the reactor to provide 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 hydrocarbon feed rates determines the temperature of the cracking reaction and of the combustion flame.

The fluid coke product is laminar in structure and can comprise some 30-2000 superimposed layers of coke. The real density of these coke particles as recovered from the reactor is in the range of about 1.80 to 1.95 gm./cc. and have a bulk resistivity of 2060 1O ohmsinch. This resistivity is determined at 500 p.s.i. on a sample of coke 1 sq. inch cross section area by 1 inch length comprising material of 210420 microns diameter.

The high temperature coke produced in accordance with this invention has high density, low porosity, and a relatively large size. A photograph of the cross section of the coke revealed a tightly packed, onion-skin appearance. A close examination of photomicrographs shows the absence of voids from the coke particles.

The high temperature fluid coker is operated in such a manner as to obtain a product having average particle size of 150 to 500 microns and preferably about 200 to 300 microns. About 2040 wt. percent of the withdrawn coke product is treated to remove the fine particles and the remainder ground to an average particle size of 70- 300 microns, and preferably 100200 microns, to provide seed coke for the reactor. The seed coke is continuously fed into the fluid bed to maintain the desired average particle size of the coke in the bed. The grinding of the product to obtain a seed coke is carried out in a conventional manner. Due to the relatively wide diameter, shallow bed geometry of the fluid bed of coke, relatively low superficial linear gas velocities can be utilimd to obtain fluidization of the bed. The gas velocity is controlled by the amount of feed used and the temperature and pressure at which the reaction is carried out. The superficial linear fluidizing gas velocity in the fluid bed in the coking reactor is maintained at about 0.1 to 2.0 ft./sec., preferably 0.3 to 0.6 ft./sec. The gas velocity and particle size of the coke in the reactor are 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 about 5-60 feet in diameter and generally about -30 feet in diameter. Where a rectangular shaped vessel is used, the length can be 5 to 200 feet, and generally 10 to 150 feet, and can have a width of 5 to 50 feet, and generally 10 to 30 feet. These reactors will have heights of about to 100 feet, and generally about to feet.

Air oxygen or oxygen-enriched air is preheated to a temperature of about to 2000 F. and preferably 1000 to 1500 F., and is injected into the reactor 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 in the reactor of 2500 to 5000 F. and generally about 3000 to 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 combu tion of hydrogen provides the heat for the cracking re action and the calcining step by radiant heat from the combustion flame and by reflected radiant heat from the roof and Walls of the reactor vessel. Heat for the calcining step is also obtained as sensible heat of the fine product coke. The temperature in the fluid bed of coke is maintained at about 19002500 F, and preferably about 21002400 F. The hydrocarbon feed injected into the hot bed of fluidized coke particles is preheated to atemperature just below the cracking temperature of the feed used.

The coke case hardening and calcining vessel can be an elongated cylindrical shaped vessel located at one end or on one side of the high temperature coke reactor vessel. A portion of the withdrawn cool fluid coke product is ground and mixed with unground coke having a particle size distribution in the range of about 150 to 500 microns, and is mixed with about 10 to 30 wt. percent based on weight of aggregate and binder, of a suitable binder material, and pelleted, extruded or compressed into coke compactions having the size of about A to 3 inches in diameter and generally /2 to 1 /2 inch. These coke compactions are generally referred to as green agglomerates. Normal-1y, coke produced by delayed coking or low temperature fluid coking will have to be calcined prior to being made into agglomerates.

In accordance with applicants process wherein the coke is prepared at temperatures of about 19002500 F., the coke does not have to be separately calcined prior to being formulated into coke compactions. Coke agglomerates are fed directly into the hot reactor vessel and subjected to the hot radiant heat in the vessel and fall into the fluid bed of the calcining vessel. The fluid bed in the calcining vessel comprises fine coke which has overflowed from the high temperature fluid coking bed. The fluid bed comprises about /3 the height of the calcining vessel and would be in the range of 5 to 50 feet in diameter, generally l-30, and more generally about to 25 feet. The calcining vessel will have a general overall length of about to 90 feet, generally to 60 feet, and more generally about 15 to feet. The upper third of the calcining vessel is maintained as a fluid bed comprising hot overflow fine fluid coke from the fluid coking reactor. The temperature of the upper third of the calcining vessel, which is the fluid coke portion, will generally be in a range of 1900 to 2400 F. and more generally 1800 to 2200 F. Part of the fluidizing gas used to maintain this section as a fluidized bed is the cracked products from the binder of the coke aggregates. Coke aggregates fall through the radiant heat zone of the reactor into this fluid bed and are kept hot by the radiant heat from the flame, roof, and walls of the reactor. In the fluid bed zone, the coke aggregates become case hardened so that they will not stick together or be deformed in contacting other aggregates. These aggregates descend cocurrently with the fine coke into the middle third of the calcining vessel which, due to less cracked binder being present and assisted by additional fluidizing gas introduced in the base of the vessel, is maintained as a moving bed at a temperature of about 1500 to 2400 F., and generally about 1800-2000 F. In the middle zone the fine coke is still primarily a fluid bed; however, due to the large amount of coke agglomerates which are primarily a moving bed, the overall fine coke and coke agglomerate mixture is best described as a moving bed. In this bed the coke aggregates become completely calcined and cured and substantially all of the volatile materials of the aggregate binder are cracked out and volatilized.

The coke calcined aggregate and fine coke product continue downward cocurrently in the calcining vessel into the lower third of the vessel which is maintained as a cooler. In this section, cooling can be applied by a circular cooling jacket around the vessel, by indirect cooling coils immersed in the moving bed, and by cooled inert fluidizing gas introduced into the base of the bed. The temperature in this zone is maintained at about 200 to 800 F., and generally about 300 to 600 F. The fluidizing gas velocity in the fluid bed portion of the calcining vessel is at about 0.1 to 3 ft./sec., generally 0.2 to 2, and more generally 0.5 to 1 ft./sec. The gas velocity in the moving bed portion of the calcining vessel is maintained at about 0.1 to 2 ft./sec., more generally about 0.11 ft./ sec. The holdup time in the calcining vessel of the coke agglomerates, so that they can be completely cured and calcined, is about 1-3 hours, and generally about 2 hours.

The hot combustion gases from the combustion of the hydrogen byproduct and by burning of any of the cracked products of the binder of the calcined coke compactions are removed from the reactor through a stack and, due to the removal of the gases through the stack, a slight negative pressure is maintained in the reactor vessel. The

l product coke is separated from the calcined briquettes and, as heretofore stated, a portion of it is cooled and ground to provide seed coke and the remainder of the hot coke can be beat exchanged to provide preheat for the combustion air and to provide heat recovery through suitable heat exchange means, such as a waste heat boiler.

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

TABLE I Weight percent Product Coke Seed Coke -200 Mesh It can be seen from the above table that relatively large coke particles of 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 ofthe air mixed with the hydrogen is reacted and the combustion products leaving the reaction zone contain no free oxygen. The combustion is carried out under generally reducing conditions in the reactor, that is, with excess hydrogen. Care must be exercised so that oxygen does not leave with the unreacted hydrogen because they may subsequently detonate. I

The reaction is carried out at about atmospheric pressure as a matter of convenience. It can. be carried out at super-atmospheric pressure or sub-atmospheric pressures, but this would require additional costs for providing suitable pressure seals and compression or evacuation equipment. 1

The construction of the reactor vessel is important in that the geometry of the vessel should be such that the diameter of the fluid coking bed is relatively large and the depth of the bed is relatively shallow. The geometry of the bed is important in that there must be suflicient height above the fluid coke bed to provide a disengaging zone in which entrained fine particles fall back into the bed, and a combustion zone above the disengaging zone wherein the air is combusted with the hydrogen. The combustion zone should be a sufiicient distance from. the top of the i reactor and above the fluid bed so that radiant heat can go directly from the combustion flame and radiant heat from the walls and roof of the vessel can be radiated into the fluid bed to provide sufficient heat to carry out the endothermic cracking reaction and the case hardening and calcining steps.

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 temperatures near the top of the vessel in the gas phase of 30005000 F. with the walls and roof of the reactor at 2500 to 3400 F. and at temperatures near the bottom of the vessel of 20002500 F., i.e., in the fluid bed. Suitable high temperature refractory material must be utilized in the construction of the reactor to withstand the temperatures at which the reaction is carried out.

The reactor consists of the reactor proper containing the fluid bed 11, ports for admitting air 30 for combustion to produce a flame zone area 19 over the fluid coke bed. Heat exchange means 23 is used to preheat the incoming air introduced through line 28 with the outgoing combustion products 21. The reactor proper can be rectangular in shape as shown in the drawing. The structure is supported on its side by steel plates 47 and on its ends by plates 47A. The roof consists of refractory bricks 43 and 44 and steel shell 54. The bottom of the furnace is supported by closely spaced steel beams 49 covered with steel plates 51. On the steel bottom plates can be placed suitable insulation material and insulation concrete 52. Refractory brick 46 are laid around the corners of the fluid bed. Over this brick are laid more

refractory brick

54 and 55 filling the curvature in the ends and sides of the reactor and lining the elongated calcining vessel. 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 53 in the bot tom of the bed on which the fluid coke rests can be made from suitable molded refractory material or brick and which can also form the inner lining of the calcining vessel. The walls of the reactor are thickest at the base of the walls. Brick for the walls 46A usually are also laid around the curvature of the bottom of the bed. The walls can be lined with molded refractory material or brick 45. The walls are contained within steel side plates 47 and steel end plates 47A. The main roof of the furnace arches over the fluid bed. Suitable refractory bricks 43 and 44 can be used to construct the roof.

The roof, itself, can be hemispherical or other concave shape. It can be composed of refractory brick or blocks built up into the arch shape. Construction can he in some cases without opening but in the drawing it is described as having a central circular opening, which opening could be located at either end. 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 utpwards through stack 22 and vented to the atmosphere. This stack is refractory lined with refractory material 61 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 the differ. ences 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 is injected through air inlets 30. Seed coke is fed through inlet seed coke means 12 and coke product is withdrawn into the calcining vessel through overflow weir 62. Feed or inert fluidizing gas for startup is injected into the bed through inlet means of 4-9. Outward stress of the roof is restrained by steel beams 63.

With reference to FIGURE 1 of the drawing, at one end of the reactor vessel is located the elongated, cylindrically shaped calcining vessel. This vessel is included within the reactor zone and receives heat radiated from the combustion of the hydrogen product with air and reflected radiant heat from the walls and roof of the reactor. Coke agglomerates are introduced into the reactor through inlet means 17 or can also suitably be introduced into the reactor from the top of the reactor vessel by means, not shown, which would (penetrate the roof of the reactor and allow the green agglomerates to drop directly down into the calcining vessel. Hot product coke 13 from fluid bed 11 overflow weir 62 into the top one-third portion of the calcining vessel forming a fluidized bed of fine coke particles 14. The green agglomerates 16 fall into the fluid bed and are case hardened and move cocurrently with the fine coke downwardly. As the agglomerates are case hardened, the binder material cracks providing a substantial amount of fluidizing gas to maintain bed 14 as a fluid bed. As these agglomerates proceed downward in the vessel, there is less and less cracked binder material to fluidize the bed and, due to agglomerate holdup, the bed becomes a moving bed in the middle third portion of the calcining vessel indicated by 15. In this portion of the vessel the green coke agglomerates are calcined and substantially all the remaining volatile material is removed.

The calcined agglomerates and hot fine coke particles continue moving cocurrently downward into the bottom third of the calcining vessel wherein they are cooled by indirect cooling means such as a coil immersed in the moving bed to which is circulated a suitable cooling fluid 34. Additional cooling is provided by water jacket 36 to which is circulated cooling fluid by means 35. Additional gas is added into the bottom of the vessel at a controlled rate by line 33 and the aggregate withdrawal rate is controlled so that a moving bed is maintained in the lower section with a fluid bed at the top. The gas can be inert nitrogen or hydrogen separated from the combustion products from the reactor. The cooled, calcined agglomerates and fine coke proceed downward to conveyor means 37 through line 38 into a suitable screening device 39 wherein the fine coke is withdrawn through line 40 and the calcined coke agglomerates 42 are withdrawn through line 41 and taken to storage.

The agglomerates are dropped into the top third of the calcining vessel which consists of a fluid bed of fine product coke. The agglomerates drop through the bed because they are larger and more dense than the emulsion of fluid coke and fluidizing gas. The fluid bed is made sufliciently deep so that the agglomerates have time to come nearly to the temperature of the fluid bed before they move into a moving bed and calcining section in the middle third of the vessel. As they are being heated in the fluid bed, they are case hardened so that the pellets or agglomerates, after their passage through the fluid bed, are strong enough to resist deformation, and sticking together in the moving bed section and in the cooling section of the vessel. The use of a fluid bed of hot fine coke heating medium around the agglomerates ensures that each agglomerate is heated uniformly throughout all of its surface and is not exposed to pressure contact until it has been completely cured or case hardened. As the agglomerates pass through the curing beds, most of the binder oil is cracked. This releases gases which rise through the bed and pass off into the upper part of the reactor chamber. Sufficient heat is radiated to the surface of this fluid bed so that the radiant heat raises the agglomerates from the feed temperature .to a temperature of about 1500-2400 F. As the agglomerates pass down into the moving bed, they maintain substantially this temperature for a considerable period of the time. The holdup time in the calciner vessel is determined by the agglomerate lfeed rate and the cross sectional area and depth of the vessel. As the agglomerates continue downward, they pass through a cooling section where the cooling is done by indirect heat exchange with a cooling medium, such as water, passing through cooling coils. A small amount of inert gas, such as nitrogen, is also used to supplement this cooling and improve heat r transfer. Because the sensible heat capacity of this gas stream is low, say the heating capacity of the moving bed, it lowers the temperature of the moving bed for only a short distance from the cooling section. This gas helps keep .the upper hot section at a uniform temperature.

Under certain operating conditions, the flame will have a low emissivity but at very high temperatures, due to the water and CO content of the flame, will radiate a considerable amount of heat to the fluid bed in the reactor. Also, under some conditions small amounts of very fine particles of coke will be entrained in the fluidizing bed, 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.

Coke pellets, briquettes, extrudates, or other compactions of coke and binder can be fed to the calcining vessel. The coke aggregate can be prepared from a high temperature coke or calcined delayed coke or calcined low temperature fluid coke. Ifthe coke is to be pelletized by tumbling it must be ground. Pellets, in general, are prepared by grinding the fluid coke to give a fines fraction, for example, minus 100 mesh, and mixing the coke with about 10% binder by tumbling. The pellets are then charged to a rotating drum for balling.

Briquettes are prepared by mixing the high temperature fluid coke as received with a portion of ground coke added with about 10% of a carbonaceous binder material at a temperature of about 200300 F. The mixture is briquetted in a hydraulic press at a pressure of about 2100-9600 p.s.i.

All coke compactions heretofore required heat hardening at temperatures above 700 F. to partially decompose the binder to a carbonaceous residue and to produce adequate strength of cohesion. In accordance with the present invention, when using high temperature fluid coke of the present process or calcined delayed coke or calcined low temperature fluid coke for the coke aggregate in the compactions, the agglomerates can be fed directly into the high temperature fluid bed region of applicants calciner vessel. Heretofore, treating uncalcined delayed or low temperature fluid coke, made into agglomerates, at these temperatures in a fluid bed of fine coke with a low temperature pretreat step to case harden caused the agglomerates to explode due to rapid volatilization of the volatile materials in the uncalcined coke. Also, where the calcined delayed coke or calcined low temperature fluid coke was used to make the agglomerates and the low temperature oven baking step was omitted, the agglomerates, when subjected to calcining temperatures of 1000 to 1800 F., deformed and stuck together.

The average particle size of the coke from which the agglomerates are prepared can be 200 to 300 microns to which are added about wt. percent binder. The mixture is formed into agglomerates having a size of about 1 inch in diameter and about 1 /2 inches in length. The cylindrically shaped calcining vessel can be about 60 feet in length and have a diameter of about 20 feet. The heat for calcining is supplied by radiation from the hot coker roof and the sensible heat of the product coke overflowing from the radiant heated fluid coke bed, which maintains the fluid bed in the calcining vessel at a temperature of 1800-2200 F. Binder oil enters the calcining vessel in admixture with agglomerated coke 16 in the form of pellets or compactions or briquettes which have been preformed as above described. The pellets are dropped into the fluidized bed section 14 through a refractory lined means 17 or through a hole or holes in the roof of the calcining vessel, not shown. Gases evolved from baking of the pellets due to cracking and volatilization of the binder rise through the fluidized bed together with other fluidizing gases as a superficial gas velocity of about 0.2

10 to 2 ft./sec. and pass up into the combustion area of the reactor.

The mixture of fine fluid coke and pellets passes downward through the calcining vessel into moving bed zone 15. The superficial gas velocity in the moving bed is maintained at about 0.1 to 1.0 ft./sec., primarily by the addition of gas that has been introduced through means 33. As the amount of gas evolved from the pellets decreases, the character of this bed changes from a fluid bed 1 4 to a moving bed 15 in the center portion of the calcining vessel. The moving bed of pellets and fine fluid coke continues to move downward. The agglomerate holdup time in the calcining vessel is about 1 to 3 hours. The temperature in moving bed 15 is maintained at about 1800 to 2000 F. The moving bed of fine coke and agglomerates moves into the cooling zone in the bottom third of the calcining vessel which is maintained at a temperature of about 300 to 600 where they are cooled indirectly by coolant circulating through cooling jackets 36 and/ or cooling coils fed by line 34. Additional cooling is supplied directly by a small volume of cool flue gas, inert gas, or natural gas which is added through line 33 to improve heat transfer in this section. This gas also serves as fluidizing gas when it reaches the top portion of the calciner vessel. The heat transfer gas added to the bottom of the cooling zone will have a small heat capacity relative to that of the coke so as not to reduce the calcining bed temperatures appreciably. The mixture of pellets and fine -fluid coke are removed from the calcining vessel via feeder 37. The mix is separated by means 39 into pellets and fine product coke. The pellets 42 are removed through line 41 and sent to storage. Product coke is removed through line 40.

The invention is further illustrated by the following examples.

Example I A suitable reactor vessel about 10 feet in diameter and about 20 feet in height lined inside with refractory material capable of sustaining temperatures up to about 3400 F. is used. The reactor is provided with a stack for the removal of combustion gases. The fluidized gas particles have an average particle size of about 300350 microns and are maintained in a fluidized state by passing through the fluid bed gaseous products from the cracked hydrocarbon feed at an average superficial gas velocity of about 0.5 to 0.6 ft./sec. Hydrocarbon feed containing constituents boiling in the range of about 700-1400 F. is preheated to a temperature of about 750 F. and is introduced into the hot fluid coke bed at a rate of bbls./ day. The hydrocarbon is contacted with the hot fluid coke particles maintained at a temperature of about 2200" 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 hydrogen gas which fluidizes the solids in the bed and which gas proceeds up into the top of the reactor. Near the top of the reactor is injected 1.5x l0 s.c.f./ day of preheated air at a temperature of about 1000" F. The air on contact with the hot hydrogen oxidizes the hydrogen in the combustion zone controlled at an average flame temperature of about 4000 F. A deficient amount of air is added to the reactor so that all of the air is burned prior to the exhausting of the combustion gases through the stack. About /3 of the product coke is ground to provide a fine seed coke having an average particle size of about 100 microns which is circulated back to the fluid bed. Product coke is withdrawn at a rate of about 10 tons/day, a portion of which is ground and admixed with a suitable binder to form coke agglomerates which are calcined in accordance with the present invention.

The combustion 7 temperature is maintained at an average temperature of about 4000 F., though the reactor wall temperature does not exceed about 3400 F. The combustion of the hydrogen supplies suflicient radiant heat from the combustion gases and heat radiated from the roof and walls of the reactor into the fluidized bed of coke and into the calcining vessel fluid bed of coke to maintain the temperature in the fluid bed of coke in the reactor at about 2000 F. and in the calcining vessel at about 1900 F.

The coke agglomerates prepared in the previously described manner are introduced at a rate of about tons/ day into the calcining vessel, and are case hardened and calcined. The calcining vessel is incorporated within the above described reactor. The fluid bed in the calciner is maintained at about a temperature of 1900 F. by the radiant heat from the reactor and from sensible heat from the overflow coke from the fluid cracking process. The temperature of the fine coke product and heated coke agglomerates in the moving bed section of the calciner is maintained at about 1800 F. The residence time of the coke agglomerates in the calcining vessel is about 2 hours. The calcining coke agglomerates are separated from the fine flu-id coke and are recovered.

Example II In this example, a reactor vessel about 150 feet in length and about 30 feet in diameter and about 80 feet in height is utilized to produce product coke and hydrogen with a net coke production of about 500 tons/ day. The vessel is lined with refractory material capable of withstanding temperatures up to about 3500 F. In the reactor, a fluid bed of coke about feet in depth is fluidized by passage of cracked hydrocarbon product consisting essentially of hydrogen. The hydrogen is mixed with air and burned in the top of the reactor to produce a combustion flame having an average temperature of about 3000 to about 4000 F. The combustion of the hydrogen provides heat to the fluid coke bed for cracking the hydrocarbon feed. The coke from the cracked hydrocarbons deposits on hot fluidized coke particles and hydrogen is evolved and supplies the fluidizing gas. The evolved hydrogen has a superficial linear gas velocity through the coke bed of the reactor about 0.10.5 ft./ sec. The hydrogen proceeds up into the reactor and is at a temperature of about l8002400 F. Preheated air at a temperature of about 1000 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 flame. Sufiicient preheated air is added to raise the temperature of the refractory roof and walls to about 3200 F. At this temperature the gas flame and the walls and roof of the reactor radiate a sufficient amount of heat into the fluid coke bed to carry out the coking reaction and the calcining reaction.

The liquid hydrocarbon feed is introduced at a rate of about 5000 bbls./day and preheated air is injected at 50-75M cu. ft./day. Product coke is withdrawn and about A of the coke is ground and recycled to the reactor as seed coke. The remainder is used to form compactions as previously described. The average particle size of the coke in the fluid bed is about 200 to 300 microns and the average particle size of the seed coke is about 100 to 200 microns. Hot product coke overflows into the elongated cylindrical calcining vessel at the rate of about 625 tons/ day. A portion of the product coke is mixed with about wt. percent of a carbonaceous binder mate rial to form agglomerates which are fed into the calcining vessel in direct contact with hot radiant heat from the combustion of the hydrogen at the rate of 250 tons/ day. The high temperature coke pellets can withstand the hot temperature present in the reactor and drop into the fluid bed in the top of the calcining vessel and are case hardened in this bed at a temperature of about 20002200 F. The fine coke and case hardened pellets or agglomerates descend cocurren-tly with the hot fine coke into a moving coke bed and are calcined in this bed and cured at a temperature of 1800-2000 F. The total holdup time in the calcining vessel is O.52 hours. Hot coke agglomerates which have been calcined and the fine fluid coke product 12 are cooledin the cooling section of the calciner and are withdrawn at a temperature of 300-500 F. About 625 tons/day of cool fine coke and 250 tons/day of calcined coke agglomerates are recovered.

The coke products of the present invention can be used in the formulation of electrodes for the aluminum industry. The coke can be used both for Soderberg and prebake electrodes. Suitable electrode formulations can be prepared by grinding a portion of the coke product to form fine coke, and mixing it with coarse coke, for example, made from crushed agglomerates, and a suitable binder, in the case of p-rebake electrodes baking in a conventional manner or, in the case of Soderberg electrodes, preparing a paste and feeding it to the Soderberg process.

In accordance with the present invention, the excess heat available by the combustion of hydrogen at elevated temperatures is utilized to provide the heat for carrying out the case hardening and calcining steps of the present invention. The present process and apparatus provides a simplified method for high temperature fluid coking of hydrocarbon feeds and case hardening and calcining of product coke in coke compaction formulations.

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

What is claimed is:

1. A process of heating and calcining coke agglomerates which comprises introducing a hydrocarbon feed into a fluid bed of coke at elevated temperatures to crack the feed to coke and hydrogen, said hydrogen providing the fiuidizing gas for said fluid coke bed, building up the bed level of said coke bed, allowing the coke to overflow into an elongated vessel, wherein the upper portion of said vessel contains a fluidized bed of fine coke particles, an intermediate portion of said vessel contains a moving bed of fine coke particles, and the lower portion of said vessel contains a moving bed of coke particles and comprises a cooling section, both said fluid bed in which hydrocarbon feed is cracked and said elongated vessel being housed in a refractory lined chamber, introducing an oxygen-containing gas into an upper level of said chamber, burning said hydrogen to produce a combustion flame in the upper portion of said vessel above and out of contact with both said fluid beds, heating said fluid coking bed by radiant heat from said combustion flame, and from the walls and roof of said refractory lined chamber, introducing coke agglomerates into the fluid bed in said elongated vessel, heating said agglomerates by radiant heat from said combustion flame, and from the walls and roof of said chamber, further heating said agglomerates by direct contact with the hot coke product which flows into said fluid bed of said elongated vessel by direct contact of the fluid coke with said agglomerates in said fluid bed, said fluid coke surrounding and cushioning said agglomerates, said agglomerates descending through said fluid bed into a moving bed of coke agglomerates and fine coke, calcining and cooling said agglomerates, and product coke in a cooling zone and separating calcined, cooled agglomerates and fine product coke.

2. A process of case hardening and calcining coke agglomerates containing a carbonaceous binder material which comprises introducing said agglomerates into an elongated vessel containing in the upper portion of said vessel a fluid bed of fine coke, an intermediate portion of said vessel containing a moving bed of fine coke, and a lower portion containing a cooling section, said heat to said vessel being supplied by introducing hot fine coke to said bed, introducing coke agglomerates into the fluid bed of fine coke, heating the agglomerates by direct contact with said fine coke, passing said agglomerates and fine coke into the moving bed section of said vessel, cracking the binder to provide fluidizing gas, passing said agglomerates into a cooling section and cooling said agglomerates, said fine coke and said coke agglomerates moving cocurrently in said vessel, withdrawing fine coke and agglomerates and separating them.

3. The process of claim 2 wherein heat to carry out the case hardening and calcining step is provided by heat radiated from the combustion of hydrogen with an oxygen-containing gas.

4. A process of heating and calcining coke agglomerates made from high temperature fluid coke and a carbonaceous binder which comprises introducing a hydrocarbon feed into a fluid bed of coke at elevated temperatures of 1900 to 2500 F. to crack the feed to coke and a gas containing hydrogen, said gas providing the fluidizing gas for said fluid coke bed, building up the bed level of said coke bed, allowing the coke to over flow into an elongated vessel, wherein the upper portion of said vessel contains a fluidized bed of coke, an intermediate portion of said vessel contains a moving bed of coke, and the lower portion of said vessel a cooling section, both said fluid bed in which hydrocarbon feed is cracked and said elongated vessel being housed in a refractory lined chamber, introducing an oxygen-conitaining gas into an upper level of said chamber, burning said hydrogen to produce a combustion flame having an average temperature of 2500 to 5000 F. in the upper portion of said vessel above and out of contact with both said fluid beds, heating said fluid coke beds by radiant heat from said combustion flame, and from the walls and roof of said refractory lined chamber, introducing coke agglomerates into the fluid bed in said elongated vessel, heating said agglomerates by radiant heat from said combustion flame, and from the walls and roof of said chamber, further heating said agglomerates by the sensible heat of the hot coke product in said fluid bed by direct contact of the fluid coke and said agglomerates in said fluid bed, said fluid bed and agglomerates having a temperature of 1700 to 2400 F., said agglomerates descending through said fluid bed into a moving bed of coke agglomerates and fine coke having a temperature of 1500 to 2400 F., calcining said agglomerates, cooling said agglomerates and product coke in a cooling zone at a temperature of 200 to 800 F. and separating cooled agglomerates and fine product coke.

5. A process of case hardening and calcining coke agglomerates which comprises introducing said agglomerates made from coke aggregate and a carbonaceous binder into an elongated vessel, containing in the upper portion of said vessel a fluid bed of fine coke particles, an intermediate portion of said vessel containing a moving bed of fine coke, and a lower portion containing a cooling section, said heat to said vessel being supplied by introducing hot fine coke to said bed, introducing coke agglomerates into the fluid bed of fine coke heating the agglomerates, passing said agglomerates into the moving bed section of said vessel, cracking the binder to provide fluidizing gas, passing said agglomerates into a cooling section and cooling said agglomerates, said fine coke and said coke agglomerates moving cocurrently in said vessel, withdrawing fine coke and agglomerates and separating them.

6. The process of claim 5 wherein an inert cooling gas is added to the cooling section to improve heat exchange and to improve the moving bed flow of solids.

7. The process of claim 5 wherein the cracked carbonaceous binder material comprises the fluidizing gas in the fluid bed zone.

8. The process of claim 5 velocity is 0.1 to 3 ft./sec.

9. A process of heating and calcining coke agglomerates made from high temperature fluid coke and a carbonaceous binder which comprises introducing a hydrocarbon feed into a fluid bed of coke at elevated temperatures of 1900 to 2500" F. to crack the feed to coke and a gas containing hydrogen, said gas providing the fluidizing gas for said fluid coke bed, said fluid coke having an average particle size of to 500 microns, building up the bed level of said coke bed, allowing the coke to overflow into an elongated vessel, wherein the upper portion of said vessel contains a fluidized bed of coke, an intermediate portion of said vessel contains a moving bed of coke, and the lower portion of said vessel a cooling section, both said fluid bed in which hydrocarbon feed is cracked and said elongated vessel being housed in a refractory lined chamber, introducing an oxygen-containing gas into an upper level of said chamber, burning said hydrogen to produce a combustion flame having an average temperature of 2500 to 5000 F. in the upper portion of said vessel above and out of cont-act with both said fluid beds, heating said fluid coke beds by radiant heat from said combustion flame, and from the walls and roof of said refractory lined chamber, introducing coke agglomerates containing coke partides and 10-30 wt. percent of a carbonaceous binder into the fluid bed in said elongated vessel, heating said agglomerates by radiant heat from said combustion and from the walls and roof of said chamber, further heating said agglomerates by the sensible heat of the hot coke product in said fluid bed by direct contact of the fluid coke and said agglomerates in said fluid bed, said heat cracking and volatilizing said carbonaceous binder which cracked products provide the fluidizing gas in the fluid bed ata supenficial linear gas velocity of 0.1 to 3 ft./sec., said fluid bed and agglomerates having a temperature of 1700 to 2400 F., said agglomerates descending through said fluid bed into a moving bed of coke agglomerates and fine coke having a temperature of 1500 to 2400 F., calcining said agglomerates, cooling said agglomerates and product coke in a cooling zone at a temperature of 200 to 800 F. and separating cooled agglomerates and fine product coke.

10. The process of claim 9 wherein the coke agglomerates are A to 3 inches in diameter.

wherein the fluidizing gas References Cited by the Examiner UNITED STATES PATENTS 2,723,949 11/1955 McOausland 208l76 2,797,908 7/1957 Zubrzyoki 263-21 2, 890,998 6/1959 Williamson 208127 2,982,622 5/ 1961 J ahnig et a1. 23-212 DELBERT E. GA-NTZ, Primary Examiner. A. RIMENS, Assistant Examiner.

Claims

1. A PROCESS OF HEATING AND CALCINING COKE AGGLOMERATES WHICH COMPRISES INTRODUCING A HYDROCARBON FEED INTO A FLUID BED OF COKE AT ELEVATED TEMPERATURES TO CRACK THE FEED TO COKE AND HYDROGEN, SAID HYDROGEN PROVIDING THE FLUIDIZING GAS FOR SAID FLUID COKE BED, BUILDING UP THE BED LEVEL OF SAID COKE BED, ALLOWING THE COKE TO OVERFLOW INTO AN ELONGATED VESSEL, WHEREIN THE UPPER PORTION OF SAID VESSEL CONTAINS A FLUIDIZED BED OF FINE COKE PARTICLES, AN INTERMEDIATE PORTION OF SAID VESSEL CONTAINS A MOVING BED OF FINE COKE PARTICLES, AND THE LOWER PORTION OF SAID VESSEL CONTAINS A MOVING BED OF COKE PARTICLES AND COMPRISES A COOLING SECTION, BOTH SAID FLUID BED IN WHICH HYDROCARBON FEED IS CRACKED AND SAID ELONGATED VESSEL BEING HOUSED IN A REFRACTORY LINED CHAMBER, INTRODUCING A OXYGEN-CONTAINING GAS INTO AN UPPER LEVEL OF SAID CHAMBER, BURNING SAID HYDROGEN TO PRODUCE A COMBUSTION FLAME IN THE UPPER PORTION OF SAID VESSEL ABOVE AND OUT OF CONTACT WITH BOTH SAID FLUID BEDS, HEATING SAID FLUID COKING BED BY RADIANT HEAT FROM SAID COMBUSTIN FLAME, AND FROM