RO106118B1 - Coke treating process from oil with high content of sulphor, with a view to obtain electrode and producing therefor - Google Patents

Abstract

The present invention relates to a process for treating petroleum coke with high sulfur content and a device for its achievement. The process consists in treating petroleum coke, in the absence of a binder, with a alkali metal compound at a minimum temperature 750 ° C, and maintaining at this temperature, time long enough to allow its reaction continue the reaction products to penetrate the granules coke, and, finally, cooling the treated granules. The appliance consists of a calciner furnace (10), a coke supply chamber (16), o the coke outlet chamber (20), a coke chamber clinker (22) of coke granules, a device (50, 52) for introducing the mass inhibitor granules.

Description

The present invention relates to a process for treating high coke oil with high sulfur content, in order to obtain, in particular, electrodes and to an apparatus for carrying out this process. ·

More specifically, the invention relates to a process for treating calcined petroleum coke with a swelling inhibitor prior to incorporating the coke into a carbon mixture. In an important aspect, the invention relates to a carbon filler or aggregate containing separate particles of calcined petroleum coke having a high sulfur content and a coke inflation inhibiting agent distributed throughout the particle mass, serving as an inhibiting agent. when reducing or eliminating coke swelling during the manufacture and use of graphite and carbon articles.

It is a well-known fact that in the manufacture of graphite and carbon electrodes for electric furnaces, a calcined oil coke (for example, crude oil coke that has been heated to fish temperatures of 1200 ° C) as filler or material is used. which mixes with a carbon binder, such as tar. The mixture is brought to the electrode profile either by formation or by extrusion for carbonization of the binder (at about 800 ° C). In cases where a graphite electrode is required, the electrode treated as above is further heated to temperatures of at least about 28 ° C.

Petro coke particles have a tendency to swell, ie to expand or even break, heated to temperatures above about 1500 ° C, if they contain more than about 0.3% by weight sulfur. Electrodes made of these coke lose their density and strength and often crack in length when heated to these high temperatures. As indicated, graphite electrodes are normally heated to at least 2800 ° C during their manufacturing process. Carbon electrodes that are not graphite during the manufacturing process, reach temperatures between about 2000 and 2500 ° C, during their use in silicon or phosphorus cups5.

Swelling is associated with the release of sulfur from its bond with the carbon inside the coke particles. If the vapor content of the sulfur cannot be released from the particles or the electrode quickly enough, it creates internal pressure which, in turn, increases the volume of the particles and can cause the electrode to split.

A conventional means of remedying the swelling was to add an inhibitor, such as iron oxide or another metal compound to the coccyxial mixture before forming the electrode20. It has been illustrated, for example, that about 2% by weight iron oxide may be effective in reducing coke swelling. Some coke that has a high tendency to swell or start swelling at a low temperature cannot be adequately controlled with iron oxide.

Various attempts have been made to create other methods of inhibiting swelling that eliminate the above disadvantages and other disadvantages of the prior art. For example, in US patent no. 2814076 discloses an improved method of producing graphite articles, such as electrodes for electric furnaces in which an alkali metal compound in Group I of the Periodic Table, namely, sodium carbonate is used as a swelling inhibitor. Sodium carbonate may be added to article 40 by impregnating it, after baking, with a solution of sodium carbonate, or by adding the direct inhibitor to the coke-pit mixture. Although the addition of sodium carbonate to the coke-pit mixture is more convenient than the addition of the baked article, this method produces a lower quality electrode, ie having a low density and resistance.

Another problem, when the swelling inhibitor is added directly to the coke-pit mixture, is that the sodium carbonate reacts with the acidic extrusion aids that can be used in the mixture. Unfortunately, this reaction often causes extrusion problems leading to poor electrode structure.

Another attempt to solve the problem of swelling of the coke in the production of carbon and graphite electrodes is described in US Pat. 3506745. In this test, high sulfur particles are treated prior to their incorporation into a carbon mixture by contacting the coke particles with a swelling inhibitor and heating the particles in a practically non-oxidizing atmosphere, at temperatures above about 1400 ° C and also above those where the coke begins to swell in the absence of the swelling inhibitor and preferably above 2000 ° C. The swelling inhibitor may be introduced by spraying fine inhibitor particles on the granular oil coke or an aqueous mud may be prepared containing the inhibitor which is sprayed on the coke prior to heating its particles at the swelling temperatures. The coke particles are subsequently cooled to about ambient temperature and mixed with a pitch binder to form a conventional charcoal mixture. The swelling inhibitor is combined with the sulfur and volatilized when the coke heats up to swelling temperatures or higher. The problem that arises here is that the process requires heating of the coke particles at temperatures that are substantially higher than those commonly used during the usual calcination process. As a result, this treatment can only be performed in a process different from the normal calcination practices by consuming more energy and requiring one. more expensive equipment.

The process according to the invention removes the disadvantages in that the oil coke granules, in the absence of a binder, are reacted with an alkali metal compound selected from sodium and potassium, at a high temperature of at least 750 ° C, located above the temperature at which the alkali metal compound begins to react with carbon, or below the temperature at ca 10, in the absence of this compound, the coke granules would begin to swell, followed by keeping the coke granules in contact with this metal compound. Alkaline at high temperature, maintained long enough for α allows the reaction to continue and the reaction products penetrate the coke granules and form a precipitate with sodium or potassium content throughout the shell mass and then cool the granules. coke thus treated.

The apparatus according to the invention consists of a cylindrical calcining furnace, developed in the sense of length, having a feeding mouth and an outlet mouth, a coke feeding chamber and a coke evacuation chamber, at which the feeding mouth of the calcination furnace is located in the feed chamber of the coke with the possibility of rotation, and the outlet of the calcination furnace is located in the evacuation chamber of the coke with the possibility of rotation, from a rotary cylindrical chiller located in the sense of length and disposed after the calcination furnace, having a feed mouth and an outlet mouth, from a coke granulation clinker chamber, which communicates with the coke evacuation chamber for the purpose of capturing and retaining the calcined coke particles at their exit through the mouth of evacuation of the calcining furnace, from a hot zone that communicates with the clinker chamber and with the feed mouth of the rotary chiller, from a device for introducing an inhibitor into the mass of calcined coke granules in the reaction zone and from 50 a coke intake chamber for capturing the calcined and cooled coke granules disposed next to the outlet of the rotary chiller, having the feed mouth located in the parking chamber with the possibility of rotation and the outlet mouth located in the intake chamber of the coke, also with the possibility of rotation.

The present invention relates to an improved process for treating high sulfur oil coke with a swelling inhibitor prior to incorporating the coke into a carbon mixture. In the broadest sense, the improved process comprises contacting high coke oil particles with a compound containing alkali or alkaline earth metal selected from the group consisting of sodium, poia, calcium and magnesium at a high, higher temperature. the one at which the alkali or alkaline earth metal compound begins to react with carbon, but lower than that at which the coke particles would begin to swell in the absence of the compound, followed by keeping the coke particles at high temperature for a sufficient time to allow producing the reaction and penetrating by the reaction product, the particles, as well as forming a deposit with alkali or alkaline earth metal content through the mass of the particles and then cooling the coke particles thus treated.

The process according to the present invention is preferably carried out at a high temperature between about 1200 and 1400 ° C. However, it has been found that low temperatures, such as 750 ° C, are adequate to promote the required reaction between the swelling inhibitor and the coke particles and can be used.

The swelling inhibitor used in the process of the present invention may be an alkali metal or alkaline earth metal salt and is preferably sodium carbonate. The inhibitor may be mixed with the oil coke particles before or after heating during the usual calcination process and may be incorporated with the coke particles in the form of dry, granulated powders or as a solution containing the inhibitor which may be sprayed on particles. The inhibitor is used in an amount greater than about 0.2% by weight compared to coke.

In a preferred embodiment of the present invention, the process for treating high sulfur oil coke particles comprises:

- calcination of oil coke particles with high sulfur content; the addition of sodium carbonate to the calcined coke particles at a high temperature, above the level of about 1200 ° C, but below the temperature at which the coke particles would begin to swell in the absence of the sodium carbonate followed by the retention of the calcined coke particles and the carbonate of sodium at the respective high temperature, a sufficient period of time to allow the sodium carbonate to react with the coke, and the resulting sodium to penetrate the particles and deposit in the entire mass of the particles and then cool the particles thus treated.

In another aspect of the present invention, a carbon filler or a carbon mixture is used in the production of carbon or graphite articles comprising separate particles of high sulfur oil coke having a swelling inhibiting agent distributed throughout the mass of the invention. particles. The swelling inhibiting agent comprises a water insoluble compound of an alkali or alkaline earth metal selected from the group consisting of sodium, potassium, calcium and magnesium; the average metal content in the particles is greater than about 0.15% by weight.

The main advantage of this improved process is that the manufacturer of carbon and graphite articles or electrodes can now use high sulfur oil coke and produce high quality electrodes.

The following is an example of a real embodiment of the invention, in connection with FIG. 1 ... 15, which represents:

FIG. 1 is a diagram of the calcining apparatus modified to carry out the process according to the invention;

- fig. 2, section of a modified part of the apparatus illustrated in fig.

- Fig. 3, a sectional view according to plan 3 ... 3 of a calcining apparatus from

FIG. 4 is a diagram of a calcining apparatus according to another embodiment of the present invention;

5 is a top view of the calcining apparatus, illustrated in FIG. 4;

- Fig. 6, a diagram illustrating the degree of swelling of the oil coke treated with a conventional inhibitor and the same coke treated according to the present invention;

- Figs. 7, 8 and 9, diagrams illustrating the degrees of swelling of various types of oil coke, according to the present invention;

FIG. 10a, photomicrograph performed with a scanning electron microscope (SEM) at a magnitude of 200 X, illustrating an area near the edge of an internal plane made by grinding a coke particle - 12.7 mm, treated according to the present invention;

FIG. 10b, photomicrograph of the same area, shown in figure 10a, illustrating the map made with X-rays and elemental sodium obtained by X-ray energy dispersion analysis (EDX) at a magnitude of 200 X;

FIG. 10c, photomicrograph of an EOX spectrum of the area illustrated in FIG. 10a and 10b;

FIG. 1 a, photomicrograph performed with an analysis electron microscope (SEM) at a magnitude of 45 X, illustrating another area closer to the center of the same internal plane, shown in FIG. 10a, 10b;

- Fig. lb, photomicrograph of the same area illustrated in Fig. 11 a, containing a map obtained by EOX analysis with X-rays and elemental sodium at a magnitude dc 45 X;

FIG. 11c, a photograph of the EOX spectrum of the same area shown in fig. 11a and 11b;

FIG. 12a, photomicrograph taken with SEM at a magnitude of 50 X, illustrating a third area of the same interior plane of fig. 10a and 10b;

FIG. 12b, photomicrograph of the area of fig. 12a, illustrating the map obtained by EOX analysis with X-rays and elemental sodium at the magnitude of 50 X;

FIG. 12c, a photograph of the EOX spectrum of the same area in fig. 12a and 12b;

FIG. 13 a, photomicrograph taken with SEM at a magnitude of 200 X, illustrating a fourth area of the same internal plane of fig. 10a and 10b;

FIG. 13b, photomicrograph of the area of fig. 13a, representing the map obtained by EOX analysis with X-rays and elemental sodium at the same magnitude of 200 X;

FIG. 13c, a photograph of the EOX spectrum of the area shown in fig. 12a and 12b;

FIG. 14a, photomicrograph taken with a SEM at a magnitude of 15 X, illustrating both the internal plane created by the grinding of a 6.35 mm coke particle, treated according to the invention, and an original surface of pores exposed by sanding;

FIG. 14b, photomicrograph of the area of fig. 14a, in a map obtained by EOX analysis with X-rays and elemental sodium at the same magnitude of 15 X;

FIG. 14c, photograph of the EDX spectrum with X-rays and elemental sodium at the same magnitude of 15 X;

FIG. 14c, photograph of the EDX spectrum of the same area in fig. 14a and 14b;

FIG. 15a, photomicrograph taken with an SEM at magnitude 15 X, of the same surface illustrated in fig. 14a, after the particle has been moistened with water;

FIG. 15b, photomicrograph of the same area illustrated in fig. 14a, showing a map obtained by EDX analysis with X-rays and elemental sodium at the magnitude of 15 X;

FIG. 15c, photo of the spectrum

EDX of the areas illustrated in fig.55u and 15b.

Oil coke is produced by coking heavy oil residues, as is well known in the art. Crude oil coke, ie non-calcined oil coke, usually has a volatile matter content of between 6 and 14%. Volatile matter is usually eliminated by heating the crude oil coke in a burner at temperatures of 1200 ... 1400 ° C. Occasionally, calcination temperatures can be used at 1500 ° C. The volatile content of a coke after calcination is usually less than 1% by weight. Crude oil coke is usually reduced in size to particles of 100 mm or less before calcination.

For the purposes of the present invention, the starting material for the coke may be a crude oil coke or an oil coke which has been calcined by conventional methods. In both cases, the oil coke covered by the present invention is the so-called high sulfur oil coke, which usually contains more than about 0.7% by weight sulfur. These high sulfur oil coke can usually not be adequately controlled by the currently known swelling inhibition methods. Although these cokees cost less, their use for the production of carbon or graphite articles is either limited or requires a modified, more expensive processing technology.

Sulfur is released from its chemical bond to carbon, when an oil coke is heated to temperatures higher than about 1500 ° C and in most cases to at least about 1600 ° C, which is higher than normal calcination temperatures. . If this release of sulfur is not inhibited or the sulfur is not chemically detached within the structure of the coke, then the rapid release of sulfur-containing vapors will create internal pressure in the coke particles that tends to expand the particles, in some cases even splitting Je or splitting articles made from de. This phenomenon is called swelling.

According to the invention, it has been found that the swelling of the formed carbon or graphite articles can be significantly reduced or eliminated by treating the oil coke particles with an alkali or alkaline earth metal compound and, in particular, with a sodium or potassium salt. , such as sodium or potassium carbonates, at temperatures well below the temperature at which the coke begins to swell before incorporating the coke particles into a charcoal mixture. From the literature (Article Effect of Sodium Carbonate upon Casification of Carbon and Production of Producer Gas by DA Fox et al., Industrial and Engineering Chemistry, vol. 23, no. 3, March, 1931) it is known that nn alkali metal compound (e.g. Sodium carbonate) can be effectively reduced with carbon in a high temperature reactor to produce alkali metal vapors and carbon oxide. According to the invention, it has been surprisingly found that if the alkali metal or alkaline earth metal compound is allowed to stay in contact with the oil coke particles for a sufficiently long period of time, for example about one minute or more, maintaining the temperature above which this reduction reaction occurs, for example, about 750 C in the case of sodium carbonate, then the alkali or alkaline earth metal thus produced will penetrate and form a deposit containing alkaline or alkaline earth metal content. through the whole mass of coke particles not even in their pores. In order to remove the swelling, a residence time of 30 s was found to be effective in the laboratory. In the experiments on production scale, the residence time at the reaction temperature was maintained for more than one minute.

It has been known for some time that the sodium carbonate used as an inhibitor in the conventional manner, by adding to the coke-pit mixture, causes the product to have a lower density and a lower resistance compared to the same product made with the inhibitor. conventional swelling, ie iron oxide. It has been found that sodium carbonate, when used as a swelling inhibitor, according to the invention, does not cause loss of density or resistance in the product and produces a product equal to that formed using iron oxide as a swelling inhibitor.

Since the inhibiting agent is deposited inside the coke particles, it has no contact with the pitcher during the processing of the carbon mixture and does not interfere with any extrusion auxiliary products, such as fatty acids.

Although the alkali metal or alkaline earth metal compound may be placed in contact with the oil coke particles either before or after heating the coke particles at the temperatures required for the reaction, it is very advantageous to add the inhibitory compound to the coke particles in the form. of dry powder, granulated, after they have been heated to the calcination temperatures between about 1200 and 1400 ° C. In current practice, the granulated dry powder of the inhibitor compound is added to the calcined coke particles at the discharge end of the calciner. It is also possible to add the inhibitory compound to the raw coke, in the form of dry powder, or to spray the coke with a solution or sludge containing the inhibitor prior to calcination.

The alkali or alkaline earth metal compound, for example sodium carbonate, is mixed with petroleum coke particles in quantities greater than 0.2% by weight. Preferably, the inhibitor is used in quantities ranging from about 0.5 to 2.5% by weight relative to the coke.

In Fig. 1 ... 3, a typical rotary calcination apparatus is illustrated, which has been modified in order to practice the improved process according to the invention. As shown, the calcining apparatus comprises an elongated cylindrical rotary kiln 10 having an inlet end 12 and an outlet end 14. The inlet end 12 of the calcination furnace 10 is mounted to rotate in a chamber 16 stationary, inlet of the coke, having a tower 18 for the exit of gases. The output end 14 of the furnace 10 is similarly mounted to rotate in a stationary coke evacuation chamber 20, including a conventional clincher chamber 22 vertically disposed below the chamber 20.

The crude oil coke particles are fed into the calcining apparatus by means of a horizontal conveyor 26, being directed downward by a dc mouth. coke 28 at the end of the inlet 12 of the rotary kiln. The furnace 10 is inclined at a small angle along its longitudinal axis from its inlet end 12 downward to the outlet end 14. Thus, as the coke particles enter the furnace 10 they are forced by gravity to move slowly along the length of the oven 10 as it rotates until it reaches the output end 14, from where they are unloaded into room 20.

A fuel, such as natural gas, is burned at the hot end of the furnace, and the combustion gas passes through the furnace 10 in counter current with the flow of coke particles a. The hot combustion gases heat the coke particles a, causing vaporization and burning of the products. volatile.

The hot coke particles have, calcined, falling from the chamber 20 into the clinker box 22, where they flow over the refractory block 30 (fig. 2). The block 30 is located at the bottom of a rectangular exit opening 32 provided in the stationary head 34 of the cooler 36.

Below the discharge chamber 20 is an elongated cylindrical rotary cooler 36. This cooler has an inlet end 38 which is mounted to rotate around the stationary head 34 of the clinker chamber 22. The output head 40 of the cooler 36 is mounted to rotate in a stationary delivery chamber of the coke 42.

The cooler 36 is also inclined downward at a small angle from the inlet end 38 to the outlet end 40. According to FIG. 2, the hot particles of calcined coke a, are collected in a body ulα the bottom of the clincher box 22 behind the refractory block 30 and possibly leaking over the edge of the block 30 and falling into the inlet end 38 of the rotary cooler 36. The coke particles are approximately forced by gravity and the rotation of the cooler to move slightly down along the cooler 36, until they reach the end of exit 40 from where they enter and collect in the basket feed room 42.

Although some calcines can use indirect cooling, for example steel casings of the cooler 36, most calcines cool the hot coke directly calcined by spraying water thereon. Direct spraying reduces the temperature of hot coke particles as soon as they exit the clinker box 22.

Typically, for this purpose a nozzle writing is provided just below the exit opening 32 of the clincher box 22.

According to FIG. 2, a conventional calcining apparatus may be modified for carrying out the process according to the present invention by incorporating a hot zone 44 inside the inlet end 38 of the cooler 36. The hot zone is formed, according to the present invention, by placing a circular ring. refractory 46, at a predetermined distance downstream from the exit of the clinker box 32 and by moving the spray nozzles of cooling water 56 down the refractory ring 46. As illustrated, the ring 46 is mounted in front of the refractory lining 45 which is placed. adjacent to the inside of the cylindrical side walls of the cooler 36. The refractory retaining ring 46 increases the depth of the coke layer in the hot zone 44 and thus increases the residence time of the coke. The temperature of the coke particles a, as they enter the hot zone 44, is slightly reduced by the reaction process, but remains above the 1100 ° C level.

The dry, granulated powder b of sodium carbonate is introduced into the hot zone 44 through a funnel 50. This funnel has an elongated tubular body 52, which extends through the side wall 34 of the clinker box 22 and deposits the powder on the top layer of particles. of calcined coke at the bottom of the hot zone 44. As can best be seen in Fig. 3, the powder is mixed with the coke particles of the rolling action that takes place in the rotary cooler 36. The sprayed sodium carbonate melts at contact with the hot coke particles a and reacts with the coke, according to the following endothermic reaction:

Na 2 CO 3 (l) + 21 (s) = 2 Na (g) + CO (g);

H = 213 Kcal / mol ... at 133 ° C;

(1), (s) and (g) refer to the physical state of the reactants, ie liquid, solid or gaseous respectively. The elemental sodium produced by the above reaction penetrates the coke particles and is distributed throughout the mass of coke particles creating a modified coke containing sulfur or sodium.

After treatment with the sodium carbonate powders in the hot zone 44 for a sufficient period of time, the calcined hot coke particles possibly flow over the refractory ring 46 and in the cooling section 53 of the cooler 36.

In this modified embodiment of the cooler 36, a pipe 54 that carries cooling water to a series of nozzles 56, at its outer end, is mounted, in a manner known per se, in the lower portion of the side wall 34 of the nozzle. clinchcrysis 22, but in this case, the pipe 54 becomes longer so that it extends completely through the hot zone 44 and into the cooling section 53. Thus, the water is sprayed from the nozzles 56 directly onto the hot coke particles, as they leave the hot zone 44 to cool the particles and reduce their temperature substantially.

The cooled and treated calcined coke particles are then discharged from the chamber 42 onto a movable conveyor 58, which transports the coke particles to a storage area. The steam produced in the chiller from the cooling water is removed from the chiller together with a small amount of air through a fan 62 and expelled into the atmosphere. The steam / air mixture passes through a dust collector dc 60, where the coke dust is trapped to avoid air pollution.

Figs. 4 and 5 illustrate a calcining apparatus that is specifically constructed for use in treating petroleum coke according to the present invention. This calcination apparatus is equipped with a retention chamber comprising a separate reactor vessel 68. This reactor vessel is placed downstream of the calciner and upstream of the chiller and can be designed for a long resistance time. The calcined coke particles are fed from the discharge chamber 20 into the reactor vessel 68, where they are treated with dry granular powders of alkali or alkaline earth metal compound, such as sodium carbonate, which is supplied simultaneously through inlet 70. After treatment, hot coke passes through outlet 72 into the reactor vessel 68 and enters through the inlet end 38 of the rotary cooler 36.

From the foregoing, it follows that the process according to the present invention can be practiced either in an existing installation using a conventional calcination apparatus or in a new installation, using a calcination apparatus provided with a separate reactor according to the present invention.

An important advantage that is obtained by adding the inhibitor, ie, sodium carbonate to the coke particles of calcined oil in a separate reaction vessel, located at the discharge end of the calcination furnace, is that no gas is flowing through this vessel; therefore, theoretically it is not the case that the inhibitor is directed out and released into the atmosphere.

A number of laboratory experiments were performed to determine the sodium carbonate content required in the present process for the effective suppression of swelling and also the minimum residence time for four different petroleum coke having different sulfur contents. In these experiments, one kilogram of calcined coke particles was placed in an open graphite container at the top, which in turn was placed in a preheated oven at about 1200 ° C. When the temperature of the coke (measured by a thermocouple placed in the coke) reached 1200 ° C, the oven door opened and a predetermined amount of sodium carbonate, for example 0.4%, 0.8%, 1.2% 1 , 6% etc. drip on the surface of the coke using a long graphite tool. Subsequently, the coke sample was slightly refined. At a preset time, the graphite container was removed from the oven, and the coke was cooled by spraying with water at the same time as its refining. The time required to reduce the coke temperature to 300 ... 500 ° C was from about 30 to 90 s.

The experimental reaction time reported, was counted from the dripping of the inhibitor on the coke to the time of water cooling. The cooled coconut is allowed to reach the ambient temperature without any further water spray. The cooled coke samples were then subjected to the swelling test, that is, the irreversible expansion occurred in the sulfur-containing coke when heated to a temperature between about 1600 and 2200 ° C.

The degree of swelling was measured on a mixture prepared from coke and placed in a diatom made of weak expandable graphite. The assembly containing the mixture was placed in a tubular furnace and heated at a rate of 450 ° C / h to 2400 ° C. After the temperature reached 1000 ° C, the differential expansion of the mixture over that of the graphite container was measured at intervals of 15 min.

From these measurements some different values of parameters can be derived, such as: 1) the total expansion in the temperature range; 2) the degree of swelling on the unit of time as a function of temperature; 3) the temperature at which the degree of swelling reaches a maximum.

Fig. 6 ... 9 shows the ratio between the maximum degree of swelling and the amount of inhibitor used. The unit of measurement of the degree of swelling in these figures is 10 ' ⁴ mm at 15 minutes, at a heating degree of 450 ° C / h. The temperature at which the degree of swelling of these coke particles reached its maximum value was about 1750 ° C.

Fig. 6 is a graph illustrating the relationship between the maximum degree of swelling, determined as in the experiment above, and the amount of inhibitor used. Curve A represents this relationship in the case of an acicular coke - coke D, containing 1.05%, by weight sulfur, using different amounts of sodium carbonate as an inhibitor. An inflation rate of about 10 is the desired limit for coke processing in graphite electrodes by modern hard graph methods. From the curve It will be seen that this permissible inflation rate is reached by using 1% by weight sodium carbonate inhibitor.

For comparison 'the same experiment described above, was used with needles 18 acicular coke, having the same sulfur content, but using the conventional inhibitor, iron oxide. Curve B, in Fig. 6, illustrates the results of this experiment. It can be seen that the suppression of swelling in the case of the conventional inhibitor was much lower than that obtained with the same coke treated with sodium carbonate, according to the invention. The iron oxide even used at the double concentration compared to the conventional one (4% by weight compared to 2%) did not achieve a comparable reduction of the swelling of this specific type of coke.

The same type of experience was carried out on a coke of ordinary composition oil, coke E, containing 1.3% by weight sulfur. In this test, the coke was treated according to the process of the present invention, using sodium carbonate as an inhibitor and a residence time of about one minute. The results of this test are represented by the curve in fig.7. It can be seen that an adequate degree of swelling reduction is achieved when only about 0.6% by weight of sodium carbonate inhibitor is used.

A similar test was performed on another acicular coke from calcined oil, coke F ¹ ) containing about 1.3% by weight sulfur, using sodium carbonate as an inhibitor and a residence time of about one minute. The results of this test are represented by the curve in fig.8.

It is noted that this specific coke deceased about 1.3% by weight of sodium carbonate inhibitor to suppress swelling below the allowable level.

Another experimental test was performed on another acicular coke, the G ¹ ^ coke containing 1.1%, by weight sulfur, using as a sodium carbonate inhibitor and a residence time of about one minute. The results of this test are represented by the curve in fig. 9. It can be seen that in this case 1.2% by weight of sodium carbonate is required to reduce the swelling below the permissible degree. The same type of coke, coke G 'requires 1.6% in

- g

1) The designations of coke by the D-G marks are used only for the present case identification and are not related to the standard types of coke used in the industry.

$ 10611 by weight sodium carbonate when its sulfur content is about 1.25% by weight.

A number of large-scale tests using a modified horse apparatus were also illustrated in FIG. 1 ... 3, in which several hundred tons of three ordinary, different and acicular coke containing about 1% by weight or more sulfur were calcined and treated, according to the process of the present invention. In these experiments, about 1% by weight of sodium carbonate powder with dimensions smaller than 800yU- was added to the calcined coke in a hot zone made inside the inlet end of the cooling drum at temperatures between 1200 and 135 °. C, for at least one minute. The calcined and treated coconut was then cooled, taking samples that were subsequently subjected to the same type of experiments described above for determining the degree of swelling. It has been found that the swelling of these specific cokes has been reduced sufficiently for rapid graphite length. It was also unexpectedly found that the present process substantially reduced the amount of chemicals, ie, chlorides, sulphates, etc., which are normally released into the atmosphere in the gas-free cooler during calcination. In addition, since the process also eliminates the acidity of the gas-free cooler, the possibility of corrosion of the equipment is substantially reduced.

Graphite electrodes were made for electric ovens, measuring 505 mm in diameter and 2439 mm in length, using one of the high sulfur oil-containing coke coke calcined and treated in the experiments described above. The calcined and treated coconut was used as a mixture or as a filler and mixed with a pitch binder and with the usual extrusion additive to form a carbon mixture. The mixture was subsequently extruded, baked at about 800 ° C and then graphite at temperatures of about 3000 ° C. During extrusion and baking, there were no technological problems or signs of swelling. The electrodes were subsequently tested in an electric arc steel furnace and used in comparison with the electrodes made of more expensive premium aciculars with low swelling.

According to the invention, ordinary coke particles are treated, coke E, containing on average 1.28% sulfur, as well as various proportions of sodium carbonate, between 0.25% and 1%. The treated particles were then tested using routine analytical methods for sulfur, sodium and ash content, as well as for swelling. The results are recorded in the following table. The results show that: 1) the addition of 0.55% sodium carbonate reduced the swelling of this coke to an acceptable level, while 0.25% did not produce this fact; 2) the sodium content in the coke was proportional to the content of. sodium carbonate added during treatment in the experimental error field and 3) 0.18% sodium content corresponding to 0.55% sodium carbonate reduced the swelling of this type of coke to an acceptable level, while 0.12% sodium in the coke was not enough.

Sample no. % Na ₂ CO ₃ added Degree of swelling % ash in the coke % sodium in coke Control 0 62.0 1 I 0 1.88 0.36 2 0.85 2.3 1.22 0.26 3 0.7 0.7 1.0 0.24 4 0.55 11.3 0.76 0.18 5 0.25 41.0 0.68 0.12

The penetration of sodium into the body of the treated particles, according to the invention, is examined with an electron microscope for scanning, using the X-ray energy dispersion method (SEM-EDX). The particles were mounted in epoxy resin and polished to medium level, to expose an interior plan to release a surface with natural pores.

In fig. 10a ... 13a are illustrated a series of photomicrographs taken at different magnitudes (ie 200 X, 45 X-, 50 X-, and 200 X- respectively), comprising SEM images of three zones aJe of an interior plane made by sanding a 5.6 nun coke particle. The area illustrated in fig.lOa is located near the edge of the interior plane, the area of fig. 11a is close to the center of the plan, and the area of Fig. 12a is in the center of the planed plane. The fourth area shown in fig. 13a is also located near the center of the plane in a similar manner to the area illustrated in fig. 11 a.

The location and distribution of sodium in the interior plane are illustrated in the photomicrographs of fig. 10b ... 13b. Photomicrographs were performed at the same magnitudes indicated above by EDX analysis for sodium, using a scanning electron microscope.

It can be seen from the almost uniform distribution of the bright spots throughout the photomicrograph, each representing a different area from the same interior plane of the dc coke particle, that the sodium actually penetrates deeply into each treated particle, according to the process of the invention and that the distribution of the sodium throughout mass of each individual coke particle is almost uniform. Sodium concentration may vary from one particle to another, but within a particular particle the concentration is essentially uniform. It is understood that the sodium produced by the reaction between the sodium carbonates and the coke, after the diffusion through the mass of the coke particles, forms a compound that is not soluble in water and does not react with water and that the sodium is present as a dc sodium compound and not by elemental sodium. The exact composition of the sodium-containing compound is not clearly understood at this time.

in FIG. 10c ... 13c illustrate a series of diagrams of the energy spectrum taking on the polished internal surfaces of each area of the coke particles examined in these tests. From these diagrams it is seen that the intensity of two peaks predominates in the energy spectrum and that these peaks are located at the same two positions corresponding to both sodium and sulfur, thus confirming the presence of these two elements in the coke particles. In addition, since a sodium peak is made in each diagram representing a different area of the coke particle, it has been concluded that sodium is actually deposited approximately uniformly by the mass or body of the coke particles, treated according to the present invention.

A further study of the penetration of sodium and its solubility after reaction with the coke was carried out with coke particles with dimensions of 3 mm to 6 mm, which were treated with 20% sodium carbonate, at about 1200 ° C, according to the invention. One of these particles is fixed and polished to expose both an internal plane and an original surface with pores. This particle was examined by the same SEM - EDX methods as the particle illustrated in FIG. 10th to 13th. After examination, the particle was moistened with water to remove any water-soluble compounds, after which a further examination was performed using the same techniques. Fig. 1A, 14b and 14c illustrate the examinations before dampening, while FIG. 15a, 15b and 15c illustrate the examinations after wetting. Fig. 14b shows that the sodium was distributed almost uniformly in the polished internal plane, and also almost uniformly, but at a much higher concentration at the original exposed surface of the flowers. Fig. 15b illustrates that after wetting, the penetration and distribution of sodium in the interior plane remained essentially unchanged, but the concentration of sodium on the surface with original pores was reduced to about the same level as in the interior plane, and its distribution was essentially uniform.

It is believed that the insoluble sodium, observed in the present study is the product of interaction between sodium and coke, whereas soluble sodium, found only on the original surface, but not in the body of the particle, is unreacted sodium carbonate.

Analyzes of water extract, using standard analytical methods, confirmed the presence of sodium carbonate. The presence of unreacted sodium carbonate on the surface of the treated particles indicates that, under certain reaction conditions, the reaction between sodium carbonate and coke does not take place completely.

Thus, the present invention provides an improved method for treating calcined petroleum coke to reduce or eliminate swelling, wherein the coke particles are heated in the presence of an alkaline or alkaline-earth metal compound, preferably, sodium carbonate, at temperatures above about 750 ° C and preferably between about 1200 ° C and 1400 ° Cz The inhibitor should be kept in contact with the coke particles for a sufficiently long time, ie one minute or more, to allow the inhibitor to react with carbon and ensure its penetration deep into the mass of the coke particles. Although it is possible to add the inhibitor directly to the raw coke before heating or calcining, it is preferable to add it immediately after the coke particles have been discharged from the calciner. This avoids possible problems of pollution and also has the advantage of reducing the acidity of the exhaust gases, as explained above.

The invention also provides an improved method of producing carbonate and graphite articles, such as electrode furnaces, in which the treated coke is incorporated with a conventional pitch binder to form a carbonaceous mixture which is then profiled or extruded, baked to carbonize the binder and, if desired, graphite.

Claims (5)

claims 1. Process for the removal of high sulfur oil coke, in order to obtain electrodes, characterized in that, in order to prevent the phenomenon of swelling in carbon and graphite products, the oil coke granules, in the absence of a binder, are brought in reaction with an alkali metal compound selected from sodium and potassium, at a high temperature of at least 750 ° C, above the temperature at which the alkali metal compound begins to react with carbon, but below the temperature at which, in the absence of this compound, the coke granules would begin to swell, followed by keeping the coke granules in contact with this alkali metal compound at said high temperature for a sufficiently long time to allow the reaction to continue and the reaction products to penetrate the granules. coke and form a precipitate with sodium or potassium content throughout the coke mass and then cooling granulelo r coke thus treated. Apparatus for treating high sulfur oil coke according to claim 1, characterized in that it consists of a cylindrical calcining furnace (10), developed in the sense of length, having a feed mouth (12) and a outlet mouth (14), a coke feed chamber (16) and a coke escape chamber (20), in which the feed mouth (12) of the kiln furnace (10) is located in the coke feed chamber (16) with the possibility of rotation, and the outlet (14) of the calcination furnace (10) is located in the evacuation chamber of the coke (20) with the possibility of rotation, from a rotary cylindrical cooler (36) located in the direction length and disposed after the calcination furnace (10), having a feed mouth (38) and an outlet mouth (40), from a clinker chamber (22) of the coke granules, which communicates with the coke evacuation chamber (20) in order to capture and retain the coke particles calcined (a), at their outlet through the outlet (14) of the calcining furnace (10), from a hot zone (44) which communicates with the clinker chamber and with the supply mouth (38) of the rotary cooler (36) ), from a device (50 and 52) for introducing a mass 5 inhibitor of calcined coke granules (a) into the reaction zone and from a coke inlet chamber (42) for capturing calcined coke granules and cooled (a) disposed next to the outlet (40) of the rotary cooler (36), having the feed mouth (38) located in the rotating station and the outlet (40) located in the intake chamber of the coke (42), also with the possibility of rotation. Apparatus according to claim 2, characterized in that said clinker chamber (22) is located downstream of the coke evacuation chamber (20) and has an outlet (32) and the hot zone (44) is located in The rotary chiller feed mouth (38) (36). Apparatus according to claim 2, characterized in that the hot zone (44) is delimited by a refractory ring (46), located in the feed mouth (38) of the rotary cooler (36), 10 at a given distance from the outlet (32) of the clinker space (22). Apparatus according to claim 2, characterized in that the said 15 Clinker chamber comprises the hot zone inside a special reaction vessel (68), located downstream of the coke evacuation chamber (20) of the calcining furnace (10).