SK279871B6 - Process for treating high sulphur petroleum coke particles, carbonaceous filler used in carbonaceous electrode production, and apparatus for said process - Google Patents

Abstract

There is disclosed a process for treating high sulphur petroleum coke particles prior to incorporating thereof into a carbon mixture, for obtaining a carbon article or shaped electrode, wherein said petroleum coke particles are subjected to a reaction, in absence of a binder, with a compound containing an alkali metal which is selected from the group contanining sodium and potassium at 1200 to 1400 degrees Celsius. Thereby obtained coke particles and said compound are kept at the above-mentioned temperature during at least 30 seconds. Thus treated articles are cooled down, thereafter being, if desired, mixed with the carbonaceous binder and then formed into the shape of the carbon article or shaped electrode. Carbonaceous filler used in the process for the production of carbon electrodes as well as an apparatus for processing raw petroleum coke articles is the subject of this solution.

Description

Technical field

The invention relates to a process for treating high sulfur petroleum coke particles prior to incorporation of the coke into the carbon composition to obtain a carbon product or a shaped electrode, carbon fuel for use in the manufacture of carbon electrodes, and apparatus for treating crude petroleum coke particles. The process serves to obtain carbon and graphite products, in particular electrodes for electric furnaces, the electrodes having a better quality obtained by using such a high sulfur content petroleum coke. In particular, the invention relates to a method of treating calcined petroleum coke with a swelling (or bulking) inhibitor before incorporating these coke particles into the carbon blend. An important aspect of the present invention is a carbon filler or additive comprising discrete particles of calcined petroleum coke having a high sulfur content and containing a blowing agent distributed throughout the particle mass, which inhibitor serves to reduce or eliminate coke blowing during the production and use of graphite or carbon products.

BACKGROUND OF THE INVENTION

It is common to use calcined petroleum coke (e.g. crude petroleum coke treated by heating above 1200 ° C) as a filler or additive in the manufacture of carbon or graphite electrodes for an electric furnace and to mix the filler or additive with a carbonaceous binder such as for example tar pitch. The mixture is then processed to form an electrode, which can be carried out either by compression or extrusion, followed by firing at an elevated temperature sufficient to carbonize the binder (e.g., at about 800 ° C). In the case where a graphitized electrode is to be produced, the electrode is further baked by heating to a temperature of at least about 2800 ° C.

Petroleum coke particles tend to “swell” (or increase in volume), that is, they expand and even tend to degrade when heated to temperatures above about 1500 ° C if they contain more than about 0.3% by weight of sulfur. The electrodes made of such coke lose density and strength and sometimes break up along the high temperatures when heated. As already mentioned, graphite electrodes are generally heated to at least 2800 ° C during the manufacturing process. In the case of carbon electrodes which are not graphitized in their manufacture, temperatures of approximately 2000 ° C to 2500 ° C are achieved during their use in silicon and phosphor furnaces.

The swelling is associated with releasing sulfur from its carbon bond within the coke particles. If the sulfur-containing vapors cannot escape from the particles or cannot escape from the electrodes fast enough, they create an internal pressure which then increases the volume of the particles and can cause the electrode to break.

A common anti-swelling measure is the addition of a swelling inhibitor such as iron oxide or other metal compound to the coke / tar pitch mixture prior to electrode formation. For example, it has been shown that the addition of approximately 2% by weight of iron oxide can effectively reduce coke bloating. However, some types of coke that have a higher tendency to swell or that exhibit low temperature swellings cannot be adequately treated with this iron oxide additive.

A number of efforts have been developed in the art to find and develop other improved methods of inhibiting flatulence to overcome the shortcomings of the prior art. For example, U.S. Pat. No. 2 81 4076 (JW Gartland, Nov. 26, 1957) discloses an improved process for the production of graphite products such as electrodes for using an alkali metal compound of Group I of the periodic system, in particular carbonate, as blowing inhibitors solution. According to this process, sodium carbonate can be supplied to the articles by impregnating the articles after firing with a sodium carbonate solution or by adding a blowing inhibitor directly to the coke / pitch mixture. Although the addition of sodium carbonate to the coke-pitch mixture is more common than the supply of sodium carbonate to the fired products by impregnation, the finished electrodes are of lower quality, i.e. they have a lower density and lower strength.

Another problem of adding the swelling inhibitor directly to the coke / pitch mixture is that the sodium carbonate reacts with the acidic additives used to extrude the products that are used as additions to the processed mixture. Unfortunately, in this case, however, this reaction often causes extrusion problems leading to poor electrode structure.

Another approach to solving the problem of coke bloating is the process for producing carbon and graphite electrodes as described in U.S. Pat. No. 3,506,745 (L. H. Juel et al., Issued April 14, 1970). According to the present invention, the high sulfur petroleum coke particles are treated by contacting the coke particles with a blowing inhibitor prior to incorporation into the carbon blend, followed by heating the particles in a substantially non-oxidizing atmosphere to temperatures above about 1400 ° C, optionally to temperatures above, at which temperature the coke particles begin to swell in the absence of a swelling inhibitor, preferably at temperatures above 2000 ° C. The blowing inhibitors may be incorporated into these products by spraying the fine powder of the inhibitor onto petroleum coke granules, or an aqueous suspension containing the blowing inhibitor may be prepared, then spraying the suspension onto the coke particles before heating the coke particles to the blowing temperature. The coke particles are then cooled to approximately ambient temperature and mixed with a tar pitch binder to form a conventional carbon blend. The blowing inhibitor reacts with the sulfur and is gasified when the coke is heated to or above the blowing temperature. This problem lies in the need to heat the coke particles to temperatures that are considerably higher than those commonly used in normal calcination processes. Therefore, this process can also be applied only in cases where these methods differ from conventional calcination processes, i.e., these processes are carried out with higher energy consumption, but such processes also require more expensive equipment.

SUMMARY OF THE INVENTION

The present invention relates to a process for treating high sulfur petroleum coke particles prior to incorporating the coke into a carbon composition to obtain a carbon product or a shaped electrode, the process comprising:

- the petroleum coke particles react in the absence of a binder with an alkali metal compound selected from the group consisting of sodium and potassium at a temperature ranging from 1200 ° C to 1400 ° C,

said coke particles and said compound are maintained at said temperature for at least 30 seconds, and

- the coke particles thus treated are cooled,

optionally, these cooled coke particles are mixed with the carbonaceous binder to form a carbon product or shaped electrode.

In a preferred embodiment of the process, said coke particles are crude oil coke particles or calcined coke particles.

Said coke particles are preferably heated according to the process of the invention to a pretreatment temperature of at least 750 ° C prior to reacting said coke particles with said alkali metal compound at said temperature.

Said alkali metal compound may be mixed with the coke particles prior to reacting with said alkali metal compound with the coke particles at said temperature.

According to another preferred embodiment, an aqueous solution containing the alkali metal compound is sprayed onto the coke particles prior to the reaction of said alkali metal compound with the coke particles at said temperature.

The alkali metal compound is preferably in the form of a dry granular powder, the alkali metal compound preferably being sodium carbonate or potassium carbonate. According to an even more preferred embodiment, the alkali metal compound is sodium carbonate and the sodium carbonate is added to the calcined coke particles at a temperature above 1200 ° C. It is also preferred to add the sodium carbonate to the calcined coke particles in the form of a granulated powder.

This sodium carbonate powder is added to said calcined coke particles preferably at a temperature in the range above 1200 ° C to 1400 ° C.

According to a further preferred embodiment, the sodium carbonate powder is added to the calcined coke particles in an amount greater than 0.2 percent by weight based on the amount of the calcined coke particles.

According to one alternative embodiment of the process of the invention, the coke particles are preferably passed through a rotary calcining apparatus with an outlet end, the particles being heated to a calcination temperature, the calcined coke particles being treated to inhibit the bloated coke by adding sodium carbonate in dry form. granulated powder to the calcined coke particles in the hot zone connected to the outlet end of the calcining apparatus at a temperature ranging from 1200 ° C to 1400 ° C, and these calcined coke particles and sodium carbonate are then held at this temperature in the hot zone to allow carbonate to react sodium and carbon, and penetrating the reaction products into said calcined coke particles and forming sodium-containing deposits in the mass of said calcined coke particles.

According to this alternative embodiment, preferably the pulverized sodium carbonate is added to the calcined coke particles in an amount ranging from 0.2% to 2.5% by weight of the calcined coke particles, and more preferably the pulverized sodium carbonate is added to the calcined coke particles in the an amount ranging from 0.5% to 2.5% by weight of the calcined coke particles.

In carrying out this alternative process, said calcined coke particles and sodium carbonate are maintained at said temperature for at least one minute.

According to a further alternative embodiment of the process according to the invention, it is desirable to:

- the cooled coke particles are mixed with the tar binder,

this mixture is formed into a product of the desired shape, and the thus formed product is then fired to a temperature sufficient to carbonize the binder to give a carbon product.

According to this embodiment, the fired product is heated to a sufficiently high temperature to graphitize the product.

According to a further alternative embodiment, a basic embodiment is again used, preferably in the following manner:

- petroleum coke particles are calcined,

- sodium carbonate in the form of dry granular powder is added to the calcined coke particles at a temperature ranging from 1200 ° C to 1400 ° C, - the calcined coke particles and sodium carbonate are kept at that temperature for at least 30 seconds to react the sodium carbonate with carbon, and to penetrate the reaction product into the calcined coke particles and form sodium-containing deposits in the mass of the calcined coke particles,

- the calcined coke particles thus treated are cooled,

- the cooled calcined coke particles are mixed with the tar binder,

- the mixture thus obtained is formed into the desired electrode shape,

and the shaped electrode is baked to carbonize the binder. In a preferred embodiment of the process, the shaped electrode is preferably heated to 2800 ° C to graphitize the electrode.

The present invention also relates to a carbon filler for use in the manufacture of carbon electrodes comprising discrete binder-free petroleum coke particles having a blowing agent distributed throughout their mass, wherein the blowing agent comprises deposits containing sodium or potassium distributed in the mass of these particles, and the average amount of inhibitor in the petroleum coke particles is greater than 0.15 percent by weight, and said blowing agent has reacted with these petroleum coke particles at a temperature ranging from 1200 ° C to 1400 ° C.

In a preferred embodiment of the carbon filler of the invention, said inhibitory agent is sodium-containing deposits.

According to another preferred embodiment, said inhibitory agent is potassium-containing deposits.

In a preferred embodiment of the carbon filler, the sulfur content is greater than 0.7 percent by weight.

The present invention also encompasses an apparatus for treating crude petroleum coke particles according to any of the foregoing variants, the apparatus being based on a combination of:

- an elongated cylindrical calcining furnace with an inlet end and an outlet end,

- an inlet chamber and an outlet chamber, the calcining furnace having its inlet end connected rotatably within the outlet chamber,

- an elongated cylindrical condenser having an inlet end and an outlet end,

- means defining a retention chamber connected to an outlet chamber for collecting the calcined coke particles as they exit from the outlet end of the calcining furnace,

SK 279871 Β6

- means defining the hot zone which are connected to the retention chamber and the inlet end of the radiator,

- hoppers and tubular attachments for introducing the dry granular swelling inhibitor into the retention chamber in contact with the calcined coke particles, and

an outlet chamber for withdrawing coke and for collecting the cooled calcined coke particles at the outlet end of the cooler, the cooler having its inlet end connected rotatably in the retention vessel and its outlet end connected rotatably in the outlet coke discharge chamber.

In a preferred embodiment of the apparatus, a clinker box is disposed by said retention chamber, which is situated below the evacuation chamber, having an outlet and a warm zone in the space of the inlet end of the cooler.

Said warm zone is preferably formed by a refractory ring located at the inlet end of the cooler and at a predetermined distance from the outlet end of the clinker box.

According to a further preferred embodiment, the retention chamber has a warm zone located in a separate reaction vessel located below the removal chamber.

According to the invention, the treatment of high sulfur petroleum coke with a swelling inhibitor is therefore carried out before incorporating the coke into the carbon blend. Generally, the process comprises contacting the high sulfur petroleum coke particles with an alkali metal or alkaline earth metal compound of sodium, potassium, calcium and magnesium at elevated temperatures, at a temperature of about 10 ° C. wherein the alkali metal or alkaline earth metal compound begins to react with carbon but below a level at which coke particles would begin to swell in the absence of the inhibitory compound, followed by maintaining the coke particles at this elevated temperature for sufficient time to allow the reaction to proceed; to penetrate the reaction products into the particles and to form a deposited alkali or alkaline earth metal in the particle mass and to cool the coke particles so treated.

The process of the invention is preferably carried out at a temperature of about 1200 ° C to 1400 ° C. However, it has been found according to the invention that even temperatures of 750 ° C are sufficient to induce the desired reaction between the swelling inhibitor and the coke particles and that even low temperatures can be used to pre-treat these coke particles.

Alkali metal salts are used as blowing inhibitors in the process of the invention, and alkaline earth metals may also be used, and sodium carbonate is preferably used. The inhibitor may be blended with the petroleum coke particles before or after heating during a conventional calcination process and may be incorporated with the coke particles in the form of a dry, granulated powder or a solution containing a blowing inhibitor that is sprayed onto the petroleum coke particles. The blowing inhibitor is used in an amount greater than about 0.2% by weight based on the weight of petroleum coke.

In a preferred embodiment of the process of the invention, high sulfur petroleum coke particles are calcined, sodium carbonate is added to the calcined petroleum coke particles at a temperature above 1200 ° C, but below the temperature at which petroleum coke particles begin to swell in the absence of carbonate The sodium coke particles and the calcined coke particles and sodium carbonate are maintained at elevated temperature for sufficient time to allow the reaction between the sodium carbonate and the coke and to allow the formed sodium to penetrate into the particles and store sodium in the mass of the particles.

According to another embodiment of the process of the invention, a carbon filler or admixture is prepared for use in the manufacture of carbon or graphite electrodes or articles, wherein the discrete high sulfur petroleum coke particles comprise a suspended puffing inhibitor in the particulate matter. The swelling inhibitor is a water-insoluble alkali metal compound or optionally an alkaline earth metal selected from sodium, potassium, calcium and magnesium, the average amount of metal in the particles being greater than about 0.15% by weight.

Petroleum coke is produced by coking heavy petroleum residues, a process well known in the art. Crude petroleum coke, i.e. coke which has not been calcined, generally contains 6-14% by weight of the heating components. These heating portions are generally removed by heating the crude petroleum coke in a calcining plant to a temperature in the range of about 1200 to about 1400 ° C. Alternatively, calcination temperatures of up to 1500 ° C can be used. The calorific content of the calorific material after calcination is generally less than about 1% by weight. Prior to calcination, the petroleum coke particles are generally reduced to 101.6 millimeters or even smaller.

For the purposes of the present invention, the starting coke is either crude petroleum coke or petroleum coke calcined by methods known per se. In both cases, the petroleum coke to which the process according to the invention is particularly directed is the so-called high sulfur petroleum coke, which generally contains more than about 0.7% by weight of sulfur. As a rule, these high sulfur petroleum coke types cannot be adequately treated to inhibit bloating by any of the prior art techniques known in the art. Although these types of petroleum coke are cheaper, their use in the manufacture of carbon or graphite products is either limited or requires modified, more expensive production technologies.

Sira is released from its chemical bond with carbon at the time the petroleum coke is heated to temperatures above about 1500 ° C and in most cases to at least 1600 ° C, which is higher than the commonly used calcination temperature. If this sulfur leakage is not prevented, or if the sulfur is not chemically bonded within the coke structure, the sulfur-containing vapors rapidly escape, leading to the expansion of the coke particles and sometimes to the cleavage or cleavage of the products made therefrom. This phenomenon is referred to herein as bloating.

According to the invention, it has been found that this bloating of carbon or graphite products can be substantially reduced or eliminated by treating petroleum coke particles with an alkali metal compound or an alkali metal compound, and in particular by treating with a sodium or potassium salt such as sodium or potassium carbonate. temperatures below the temperature at which the coke begins to swell before incorporating the coke particles into the carbon blend. From the literature of the prior art, see, for example, "Effect of Sodium Carbonate The Effect of Sodium Carbonate on Carbon Gasification and Gas Production", D. A. Fox et al., Industrial and Engineering Chemistry, Vol. 23, No. 3, March 7937, it follows that alkali metal compounds (e.g. sodium carbonate) can be effectively reduced by carbon in a high temperature reactor to form alkali metal and carbon monoxide vapors. According to the invention, it has surprisingly been found that when an alkali metal or alkaline earth metal compound is left in contact with petroleum coke particles for a sufficiently long time, for example, for about one or a few minutes, maintaining the temperature above the temperature at a reduction reaction, for example at about 750 ° C in the case of sodium carbonate, then the alkali metal or alkaline earth metal thus prepared penetrates into the coke particles to form an alkali metal or alkaline earth metal deposit throughout the mass of the coke particles and not only in their pores . A residence time of 30 seconds has been shown to be effective in suppressing swelling in laboratory tests. In field trials, the residence time at the reaction temperature was maintained for more than 1 minute.

It has been known for some time that sodium carbonate, used conventionally as a blowing agent and added to a mixture of petroleum coke and tar pitch, results in a product having a lower density and lower strength compared to the same product. a treated swelling inhibitor known per se, for example iron oxide. It has been found that when sodium carbonate is added as a blowing inhibitor according to the invention, there is neither a loss of density nor a loss of strength of the product, and the same product is obtained as when iron oxide is used as the blowing inhibitor.

Since the inhibitory agent is deposited inside the particle, it does not contact tar pitch during processing of the carbon blend and does not adversely affect extrusion aids such as fatty acids.

Although the alkali metal or alkaline earth metal compound should be contacted with the coke particles either before or after heating the coke particles to the desired temperature to effect the reaction, it is very advantageous to add the inhibitor compound to the coke particles as dry, granulated powder after heating. % of petroleum coke to a calcination temperature ranging from about 1200 ° C to about 1400 ° C. In carrying out the process of the invention, the dry, granulated powder of the inhibitor compound is added to the calcined coke in particulate form at the outlet end of the calcining apparatus. It is also possible to add the inhibitory compound to the raw coke in the form of a dry powder or, alternatively, to spray the coke particles with a solution or suspension containing the inhibitor prior to the calcination process.

The alkali metal or alkaline earth metal compound, for example sodium carbonate, is admixed with the petroleum coke particles in an amount greater than about 0.2% by weight. Preferably, the inhibitor compound is used in an amount ranging from about 0.5% to 2.5% by weight based on the weight of the coke.

BRIEF DESCRIPTION OF THE DRAWINGS

The process for treating high sulfur petroleum coke particles according to the present invention and apparatus for carrying out the process, as well as the structure of the carbon binder and petroleum coke particles, will be explained in more detail with reference to the accompanying drawings.

Fig. 1 is a schematic front view of a calcining apparatus adapted to carry out the process of the invention.

Fig. 2 is an enlarged sectional view of a modified portion of the apparatus of FIG. First

Fig. 3 is a cross-sectional view of the device shown in FIG. 2 along line 3-3. Fig. 4 is a schematic view of a calcining device of another embodiment of the invention.

Fig. 5 is an enlarged side view of the calcining device shown in FIG. 4th

Fig. 6 is a graph depicting the rates of bloating of a petroleum coke treated with a conventional inhibitor and of the same coke treated with the process of the invention.

Fig. 7, 8, 9 are graphs illustrating the swelling rates of several different types of petroleum coke by the method of the invention.

Fig. 10a is a scanning electron microscope (SEM) photomicrograph at 200X magnification, showing an area close to an edge prepared by grinding a 12.7 millimeter coke particle treated by the process of the invention.

Fig. 10b is a photomicrograph of the same region as in FIG. 10a, but shows an X-ray elemental map of sodium, obtained by energy-dispersive X-ray analysis (EDX), which was also obtained at 200X magnification.

Fig. 10c is a photomicrograph of an EDX spectrum of the same region of FIG. 10a and 10b.

Fig. 11a is a scanning electron microscope (SEM) photomicrograph at a 45X magnification and shows another region closer to the center of the same plane as in FIG. 10a and 10b.

Fig. 11b is a photomicrograph of the same region as in FIG. 11a, but shows an X-ray elemental map of sodium, obtained by EDX analysis also at a 45-fold magnification.

Fig. 11c is an EDX image of the same region of FIG. 11 a and 11 b.

Fig. 12a is a scanning electron microscope (SEM) photomicrograph at 50X magnification, showing a third region of the same plane shown in FIG. 10a and 10b.

Fig. 12b is a photomicrograph of the same region shown in FIG. 12a, but showing the sodium elemental map obtained by EDX analysis at the same 50-fold magnification.

Fig. 12c is a photograph of an EDX spectrum of the same region shown in FIG. 12a and 12b.

Fig. 13a is a scanning electron microscope (SEM) photomicrograph at 200X magnification, showing the fourth region of the same plane shown in FIG. 10a and 10b.

Fig. 13b is a photomicrograph of the same region shown in FIG. 13a, but showing the sodium elemental map obtained by EDX analysis at the same 200-fold magnification.

Fig. 13c is an EDX spectral image of the same region as shown in FIG. 12a and 12b.

Fig. 14a is a scanning electron microscope (SEM) photomicrograph at a magnification of 15 times, showing the inner plane prepared by grinding a 6.35 millimeter particle treated by the process of the invention, as well as the original surface of the grinded pores.

Fig. 14b is a photomicrograph of the same region shown in FIG. 14a, but showing the sodium elemental map obtained by EDX analysis at the same 15-fold magnification.

Fig. 14c is an EDX image of the spectrum of the same region as shown in FIG. 14a and 14b.

Fig. 15a is a scanning electron microscope (SEM) photomicrograph at a magnification of 15 times the same surface as in FIG. 14a after soaking the particle with water.

Fig. 15b is a photomicrograph of the same region shown in FIG. 14a, but showing the sodium elementary map obtained by EDX analysis at the same 15-fold magnification.

Fig. 15c is an image of an EDX spectrum of the same region as shown in FIG. 15 a and 15 b.

Figures 1 to 3 illustrate a typical rotary-type calcining apparatus modified to carry out the process of the invention.

As can be seen, the calcining apparatus includes an elongated, cylindrical calcining furnace 10 having an inlet end 12 and an outlet end 14. The inlet end 12 of the calcination furnace 10 is mounted rotatable within a stationary coke inlet chamber 16 having a vertical flue gas chimney 18. furnaces. The outlet end 14 of the rotary calcining furnace 10 is similarly rotatable within the stationary coke outlet chamber 20, including a conventional clinker chamber 22 positioned vertically below the outlet chamber 20.

The crude petroleum coke particles 24 are fed to the calcining plant through a horizontal conveyor 26 and fed down through the coke hopper 28 to the inlet end 12 of the rotary calcining furnace 10. As can be seen from FIG. 1, the rotary calcination furnace 10 is tilted at a low angle with respect to its longitudinal axis from its inlet end 12 to its outlet end 14. The crude petroleum coke particles 24 are thus introduced into the rotary calcination furnace 10 and slowly moved along the length of the rotary calcination kiln. the furnace 10 as it rotates to the outlet end 14 from which it is discharged to the outlet chamber 20.

At the hot end of the rotary kiln 10, fuel such as natural gas and combustion gases passing through the rotary kiln 10 is combusted upstream with respect to the progress of the raw coke particles 24. The hot combustion gases heat the crude oil coke particles 24, whereby the coke heating fractions are gasified and burned.

The hot calcined coke particles 24 fall from the outlet chamber 20 into the clinker box 22 where they pass through the refractory block 30 (see FIG. 2). The refractory block 30 is located at the bottom of the rectangular outlet port 32 in the stationary head 34 of the radiator 36.

The elongated, cylindrical, rotary cooler 36 is located below the outlet chamber 20. This elongated, cylindrical, rotary cooler 36 has a cooler inlet end 38 that is mounted around the stationary head 34 of the clinker chamber 22. The outlet end 40 of the cooler 36 is rotatable inside the stationary outlet. of the coke chamber 42.

The elongated, cylindrical rotary cooler 36 is also inclined downwardly by a small angle from its inlet end 38 to the outlet end 40. From FIG. 2, the hot calcined coke particles 24, collected at the bottom of the clinker chamber 22 behind the refractory block 30, eventually fall over the edge of the refractory block 30 and fall into the inlet end 38 of the elongated cylindrical rotary cooler 36. As the movement of the elongated cylindrical rotary cooler 36 slowly advances down the entire length of the rotary cooler 36 to the outlet end 40 from which they reach the stationary outlet chamber 42 and collect therein.

While some calcining devices use indirect cooling, for example by means of a steel jacket of an elongated cylindrical rotary cooler 36, most calcining devices use rapid cooling of hot calcined coke by direct dripping with water.

This direct dripping reduces the temperature of the hot coke in particulate form immediately after leaving the clinker chamber 22. As a rule, a series of spray nozzles are arranged directly below the outlet opening 32 of the clinker box 22 to achieve this goal.

As shown in FIG. 2, a conventional calcining apparatus may be modified to carry out the process of the invention by including a hot zone 44 at the inlet end 38 of the elongated cylindrical rotary cooler 36. The hot zone 44 is formed according to the invention by placing a circular refractory ring 46 at a predetermined distance from the outlet opening 32 of the clinker box 22. and by displacing the cooling water spray nozzles 56 past the refractory ring 46 in the flow direction. As can be seen from Figure 2, the refractory ring 46 is embedded in the refractory lining 45, which is lined with the inner cylindrical sidewalls of the longitudinal, cylindrical rotary cooler 36. The refractory ring 46 increases the thickness of the coke layer in the hot zone 44 thereby passing. As the coke particles 24 enter the hot zone 44, the temperature of these particles decreases somewhat as a result of the ongoing reaction, but this temperature is still above 1100 ° C.

The dry, granulated sodium carbonate powder is conveyed through the feed 48 to the hot zone 44 through a hopper 50. The hopper 50 has an elongated tube 52 extending through the side wall of the head 34 of the clinker chamber 22 and depositing powder on the surface of the hot calcined coke 24. As best shown in FIG. 3, the powder is mixed with the coke particles 24 by stirring inside a cylindrical rotary cooler 36. Powdered sodium carbonate, in contact with the hot coke particles 24, melts and reacts with the coke according to the following endothermic reaction:

Na ₂ CO ₃ (I) + 2C (s) = 2Na (g) + 3CO (g) ΔH = 812 kJ / mol at 1330 ° C, in which:

(I), (s), and (g) refer to the physical state of the reactants, wherein (I) means liquid, (s) solid, and (g) gaseous. The elemental sodium formed according to the above reaction penetrates into the coke particles and distributes in the mass of coke particles to form a modified coke containing sulfur and sodium.

After treatment with the sodium carbonate powder in the hot zone 44 for a sufficiently long time, the hot calcined coke particles 24 pass through the refractory ring 46 into the cooling section 53 of the longitudinal cylindrical rotary cooler 36.

According to this modified embodiment of the longitudinal cylindrical rotary cooler 36, a tube 54 supplying cooling water to a plurality of spray nozzles 56 formed at its outer end is mounted in a conventional manner at the bottom of the side wall of the front portion 34 of the clinker chamber 22. The water is thus sprayed from the spray nozzles directly onto the hot coke particles as they exit the hot zone 44, so that the particles are cooled rapidly and their temperature is significantly reduced.

The cooled, processed, calcined coke particles are then discharged from the outlet chamber 42 to a movable conveyor 58 that transports the coke particles to the storage space. The steam generated in the cooler from the cooling water is discharged from the cooler together with some air through the fan 62 and discharged into the ambient atmosphere. The mixture of steam and air passes through a dust separator 60 in which coke dust is trapped to prevent air pollution.

In FIG. Figures 4 and 5 illustrate a calcination plant that is specifically designed for processing petroleum coke by the process of the invention. This calcining device is provided with a retention chamber forming a separate reactor vessel 68. The reactor vessel 68 is located downstream of the calcining device and upstream of the cooler, and is designed for a long residence time. The calcined coke particles are conveyed from the discharge chamber 20 to an editorial container 68 where they are treated with dry granulated alkali metal powder or alkaline earth metal compounds, such as sodium carbonate, which is simultaneously fed inlet 70. After processing, the hot coke particles pass to 72 of the reactor vessel 68 and reach the inlet end 38 from where they advance to the cylindrical rotary cooler 36 of the elongated shape.

It will be apparent from the above description that the process of the invention may be carried out either on an existing conventional apparatus using a conventional calcining apparatus or on a new apparatus having a calcining apparatus equipped with a separate reactor according to the invention.

An important advantage of introducing a swelling inhibitor, such as sodium carbonate, into the calcined particulate petroleum coke in a separate reaction vessel located at the exit end of the calcining furnace is that no gases pass through the vessel and therefore there is no possibility for the inhibitor to be entrained by these gases. and escaped into the air

Numerous laboratory tests have been carried out to determine the amount of sodium carbonate required to carry out the process of the invention to effectively suppress coke swelling and also to determine a minimum residence time for four different petroleum coke having different sulfur contents. In these tests, 1 kg of calcined coke particles were introduced into an open graphite vessel and the vessel was placed in a muffle furnace preheated to a temperature of approximately 1200 ° C. Once the temperature of the coke (measured by the thermocouple embedded in the coke) reached 1200 ° C, the oven door and a predetermined amount of sodium carbonate, for example 0.4% by weight, 0.8% by weight, 1.2% by weight, 1.6% by weight, were opened. etc., was dropped onto the surface of the coke using a long graphite composition. The coke samples were then briefly digested. At a predetermined point in time, the graphite containers were then removed from the furnace and the coke was then quenched by dropwise addition of water and rinsed. The time required to reduce the coke temperature to 300-500 ° C was 30-90 seconds.

The experimental reaction time is calculated from the moment when the coke blowing inhibitor is instilled until the water cooling begins. The water-cooled coke was then allowed to cool to room temperature without further dropping with water. The cooled coke samples were then tested for flatulence, i.e., the irreversible expansion of the sulfur-containing coke was detected by heating to a temperature of about 1600 to 2200 ° C.

The bloating was detected on a sample prepared from coke and placed in a dilatometric device made of low expansion graphite. The entire assembly containing the sample was then placed in a tubular furnace and heated gradually to 2400 ° C at a heating rate of 450 ° C per hour. Upon reaching 1000 ° C, differential expansion of the sample compared to the graphite vessel was recorded at 15 minute intervals.

Some values of different types can be obtained from these measurements:

(1) total expansion over the entire temperature range; (2) the swelling rate per unit time as a function of temperature; and (3) the temperature value at which the swelling rate reaches a maximum.

Figures 6 to 9 show graphically the relationship between the highest swelling rate and the amount of swelling inhibitor used. The unit of blowing in these figures is 10 ^-4 m / m in 15 minutes at a heating rate of 450 ° C per hour. The highest bloating is achieved by the test coke particles at a temperature of approximately 1750 ° C.

Figure 6 is a graph showing the relationship between the maximum swelling determined by the described assay and the percentage of inhibitor used. Curve A (lower curve) shows the graphical dependence of puffing rate of needle coke, coke D ¹ (designation D-G is used herein for identification purposes and is not related to the usual designation of coke used in industry) containing 1.05 mass sulfur , from the percentage of sodium carbonate used as well as the swelling inhibitor. The degree of blowing speed 10 is the desired limit for the processing of coke into graphite electrodes by modern graphitizing methods. It can be seen from curve A that acceptable swelling is achieved using sodium carbonate as an inhibitor in an amount of only about 1% by weight.

For comparison, the test described above was repeated with the same type of coke having the same sulfur content, but using the conventional blowing inhibitor of the prior art, namely iron oxide. Curve B (upper curve) in FIG. 6 graphically shows the results of this test. It can be seen from the graph that the swelling suppression of the conventional swelling inhibitor of the prior art is much worse than that achieved with the same sodium carbonate treated coke by the process of the invention. Iron oxide, also used at twice the concentration (4% by weight instead of 2% by weight), does not result in a comparable reduction in the swelling of the coke particles.

Furthermore, the same type of test was carried out with a conventional type of petroleum coke, coke E ¹ , containing 1.3% by weight of sulfur. In this test, the coke was treated according to the invention using sodium carbonate as a blowing agent and a residence time of approximately 1 minute. The results of this test are shown by the curve of Figure 7. It is apparent from the graphical illustration that an adequate reduction in swelling is achieved even when sodium carbonate is used as the swelling inhibitor in an amount of about 0.6% by weight.

A similar test was performed using another calcined petroleum coke, coke F ¹ , containing approximately 1.3% by weight of sulfur using sodium carbonate as a blowing agent and a residence time of approximately 1 minute. The results of this test are shown in FIG. 8. It is apparent from this graphical representation that these needle coke particles require approximately 1.3% by weight of sodium carbonate as a swelling agent to suppress swelling to an acceptable extent.

Further tests were performed with needle coke G ¹ containing 1.1 weight percent sulfur using sodium carbonate as a blowing agent and a residence time of approximately 1 minute. The results of this test are shown in FIG.

9. It is apparent from this graphical representation that in this case about 1.2% by weight of sodium carbonate is needed as a swelling agent to suppress swelling to an acceptable extent. The same type of coke G ¹ requires the use of 1.6% by weight of sodium carbonate as an inhibitor if its sulfur content increases to about 1.25% by weight.

Many test experiments were also carried out on a pilot plant modified calcination apparatus of substantially the same type as shown in Figures 1 to 3, wherein the calcination and processing was carried out by the process of the invention, and the processing process was carried out with several hundreds of three different regular needles of coke containing from about 1 to several percent by weight of sulfur. In these pilot tests, approximately 1% by weight of powdered sodium carbonate with a particle size of less than 800 microns was added to the calcined coke in the hot zone built into the inlet end of the cooling drum at a temperature ranging from 1200 ° C to 1350 ° C for at least one minute. The calcined and treated coke was then cooled, and the samples were analyzed as described above to determine the bloating rate. In carrying out these experiments, it was found that the blowing of this particulate coke was sufficiently suppressed to allow rapid graphitization to be carried out. Surprisingly, it has also been found that, in carrying out the process of the invention, it is possible to reduce the amount of chemicals, such as chlorides and sulfates, which are normally released into the air in the cooler during the calcination. In addition, the corrosion of the device is substantially reduced, since the acidity of the gases in the cooler is also eliminated.

The invention further produced graphite electrodes for an electric furnace having a diameter of 508 millimeters and a length of 2638 millimeters, using high sulfur petroleum acicular coke, calcined and treated according to the methods described. The calcined coke treated according to the invention was then used as filler additive, mixed with tar pitch as a binder and conventional extruders to form a carbon blend. The mixture was extruded, baked at about 800 ° C and then graphitized at about 3000 ° C. This procedure did not cause any problems with extrusion and firing, nor did any swelling problems occur. The electrodes were then experimentally tested in an electric arc steel furnace and found to behave in a manner comparable to electrodes made from the more expensive low-swelling needle coke.

The regular coke particles E ¹ , containing an average of 1.28% by weight of sulfur, were treated according to the invention using varying amounts of sodium carbonate ranging from 0.25% to 1.00% by weight. The treated coke particles were then analyzed using conventional analytical methods for sulfur, sodium and ash content and further tested for swelling. The results are shown in Table I. The values show the following:

(1) the addition of 0.55% by weight of sodium carbonate reduces coke bloating to an acceptable level, while the addition of 0.25% by weight is not sufficient for this purpose; (2) the sodium content of the coke is proportional to the amount of sodium carbonate added during processing in experimental (3) a sodium content of 0.18% by weight, corresponding to the addition of 0.55% by weight of sodium carbonate, reduces the bloating of coke particles to an acceptable level, while the sodium content of 0.12% by weight in coke is insufficient.

Table I

Sample number Sodium carbonate (wt.%) Bloating rate Coke ash content Sodium content in coke (% by weight) inspection 0 62.0 1 1.00 0.0 1.88 0.36 2 0.85 2.3 1.22 0.26 3 0.70 8.7 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 mass of particles treated by the process of the invention was analyzed by means of a scanning electron microscope using energy dispersive X-ray analysis (SEM - EDX). The particles were cast into an epoxy resin and ground to half length to expose the inner plane as well as to expose the surface of the natural pores.

Figures 10a to 13a show a plurality of micrographs at various magnifications (e.g., 200x, 45x, 50x, and 200x) provided by a scanning electron microscope in the region of the inner plane obtained by grinding a 6.35 millimeter particle. The area shown in Figure 10a is near the edge of the inner plane, the area of Figure 11 is near the center of the plane, and the area shown in Figure 12a is from the center of the ground plane. The fourth region shown in Figure 13a is also close to the center of the plane, similar to the region in Figure 11a.

The location and distribution of sodium at the inner plane is shown in the micrographs of Figures 10b to 13b. The micrographs were taken at the same magnification as indicated by EDX analysis of sodium using a scanning electron microscope.

As can be seen from the fairly even distribution of the bright points on the micrographs, each representing a different region in the same inner plane of the coke particle, the sodium has actually penetrated deep into each treated particle treated by the process of the invention, distributing sodium throughout the mass of each individual coke particle. is essentially uniform. The sodium concentration in the different particles may vary, but within the individual particles the sodium concentration is substantially uniform. In this context, it should be noted that the sodium formed by the reaction between sodium carbonate and coke forms, after diffusion into the mass of coke particles, a water-insoluble compound and likewise it does not react with water, and that sodium is present in the in the form of a sodium compound rather than in the form of elemental sodium. The exact composition of this compound is not yet understood.

The plurality of energy spectra images of the abraded inner surfaces of each coke zone zone analyzed in these tests is shown in Figures 10c to 13c. It is evident from these images that two peaks predominate in the energy spectrum and that the two peaks are located in the same positions corresponding to both sodium and sulfur, confirming the presence of the two elements in the coke particles. In addition, since the sodium peak occurs in each pattern representing a different coke particle zone, it can be concluded that sodium is indeed stored substantially evenly in the mass or body of coke particles treated by the process of the invention.

A sodium permeation and solubility study after reaction with coke for coke particles F 'having a size of 3 to 6.35 millimeters was carried out and treated with 20% by weight sodium carbonate at a temperature of approximately 1200 ° C. according to the invention. One of the treated particles was cast into the resin and ground to expose both the inner plane and the surface of the original pores. This particle was then analyzed by the same SEM - EDX methods as the particles in Figures 10a to 13a. After analysis, the particle was soaked with water to remove any water-soluble fractions and then analyzed again using the same methods. Figures 14a, 14b and 14c illustrate the results of the pre-soaking tests, while Figures 15a, 15b and 15c illustrate the same samples after soaking with water. In Figure 14b it is shown that sodium was distributed substantially evenly in the ground plane and is also distributed substantially evenly, but at a significantly greater concentration, on the exposed original pore surface. Figure 15b shows a situation where the distribution and penetration of sodium on the inner plane remained substantially unchanged after wetting, but the sodium concentration on the surface of the original pore was reduced to approximately the same level as in the inner plane and its distribution was substantially uniform.

It is believed that the insoluble sodium observed in the above tests is the result of the interaction between sodium and coke, while the water-soluble sodium found only on the original surface but not inside the particle body is unreacted sodium carbonate.

Aqueous extract analyzes carried out by standard analytical methods confirm the presence of sodium carbonate. The presence of unreacted sodium carbonate on the surface of the treated particles demonstrates that under certain reaction conditions the reaction between sodium carbonate and coke will not proceed perfectly.

Accordingly, the present invention provides an improved method of treating calcined petroleum coke to reduce or eliminate bloating thereof, wherein the coke particles are heated in the presence of an alkali metal or alkaline earth metal compound, preferably in the presence of sodium carbonate, to a temperature above about 750 ° C and preferably to 1200 to 1400 ° C. The inhibitor should be kept in contact with the coke particles for a sufficiently long time, for example for one minute or longer, to allow the blowing inhibitor to react with the carbon and to allow the reaction products to penetrate the depth of the coke particle mass. Although it is possible to add the swelling inhibitor directly to the raw coke before heating or calcination, it is preferable to add it immediately after draining the coke particles from the calcining apparatus. This will avoid possible problems with air pollution and will also reduce the acidity of the evolving gases as mentioned.

The invention also encompasses a process for producing carbon and graphite products, such as electrodes for electric furnaces, wherein the treated coke together with the tar pitch binder in the form of a carbon blend is shaped or extruded, fired to carbonize the binder and optionally graphitized. The main advantage of the process according to the invention is that it is now possible to use cheaper high-sulfur petroleum coke for the production of carbon or graphite products or electrodes for the production of high-quality electrodes.

Claims (27)

PATENT CLAIMS A process for treating high sulfur petroleum coke particles prior to incorporating the coke into a carbonaceous mixture to obtain a carbon product or a shaped electrode, characterized in that: - the petroleum coke particles react in the absence of a binder with an alkali metal compound selected from the group consisting of sodium and potassium at a temperature ranging from 1200 ° C to 1400 ° C, said coke particles and said compound are maintained at said temperature for at least 30 seconds, and - the coke particles thus treated are cooled, optionally, the cooled coke particles are mixed with a carbonaceous binder to form a carbon product or shaped electrode. The method of claim 1, wherein said coke particles are crude oil coke particles or calcined coke particles. The method of claim 1 or 2, wherein said coke particles are heated to a pre-treatment temperature of at least 750 ° C prior to reacting said coke particles with said alkali metal compound at said temperature. The method of any one of claims 1 to 3, wherein the alkali metal compound is mixed with the coke particles prior to reacting with said alkali metal compound with the coke particles at said temperature. The process according to any one of claims 1 to 3, characterized in that an aqueous solution containing the alkali metal compound is sprayed onto the coke particles before the reaction of said alkali metal compound with the coke particles at said temperature. The process according to any one of claims 1 to 4, wherein said alkali metal compound is in the form of a dry granular powder. The process according to any one of claims 1 to 6, wherein said alkali metal compound is sodium carbonate or potassium carbonate. Process according to any one of claims 2 to 5, characterized in that said alkali metal compound is sodium carbonate and the sodium carbonate is added to the calcined coke particles at a temperature above 1200 ° C. The process of claim 8, wherein the sodium carbonate is added to the calcined coke particles in the form of a dry granular powder. The process according to claim 8 or 9, characterized in that the sodium carbonate powder is added to said calcined coke particles at a temperature in the range above 1200 ° C to 1400 ° C. The process according to any one of claims 8 to 10, wherein the sodium carbonate powder is added to the calcined coke particles in an amount greater than 0.2 percent by weight based on the amount of the calcined coke particles. The method of claim 2, wherein the coke particles are passed through a rotary calcining apparatus with an outlet end, wherein the particles are heated to a calcination temperature, the calcined coke particles being treated to inhibit the bloated coke by adding sodium carbonate as a dry granulated powder. to the calcined coke particles in the hot zone connected to the outlet end of the calcining apparatus at a temperature ranging from 1200 ° C to 1400 ° C, and the calcined coke particles and potassium carbonate are then maintained at this temperature in the hot zone to allow sodium carbonate to react with and penetrating the reaction products into said calcined coke particles and forming sodium-containing deposits in the mass of said calcined coke particles. The process of claim 12, wherein the pulverized sodium carbonate is added to the calcined coke particles in an amount ranging from 0.2% to 2.5% by weight of the calcined coke particles. The process of claim 13, wherein the pulverized sodium carbonate is added to the calcined coke particles in an amount ranging from 0.5% to 2.5% by weight of the calcined coke particles. The method of any one of claims 12 to 14, wherein said calcined coke particles and sodium carbonate are maintained at said temperature for at least one minute. 16. The method of claim 1, wherein: - the cooled coke particles are mixed with the tar binder, this mixture is formed into a product of the desired shape, and the thus formed product is then fired to a temperature sufficient to carbonize the binder to give a carbon product. 17. The process of claim 16 wherein the fired product is heated to a sufficiently high temperature to graphitize the product. The method of claim 2, wherein the petroleum coke particles are calcined, - sodium carbonate in the form of a dry granular powder is added to the calcined coke particles at a temperature in the range of 1200 to 1400 ° C, - the calcined coke particles and sodium carbonate are maintained at said temperature for at least 30 seconds to react the sodium carbonate with carbon and to penetrate the reaction product into the calcined coke particles and form sodium-containing deposits in the mass of these calcined coke particles, - the calcined coke particles thus treated are cooled, - the cooled calcined coke particles are mixed with the tar binder, - the mixture thus obtained is formed into the desired electrode shape, and the shaped electrode is baked to carbonize the binder. The method of claim 18, wherein the electrode so formed is then heated to 2800 ° C to graphitize the electrode. 20. A carbonaceous filler for use in the manufacture of carbon electrodes, comprising discrete binder-free petroleum coke particles, wherein said particles have a blowing agent distributed in their mass, said blowing agent comprising sodium or potassium-containing deposits distributed in the mass. and the average amount of inhibitor in the petroleum coke particles is greater than 0.15 percent by weight and said blowing agent reacted with the petroleum coke particles at a temperature in the range of 1200 ° C to 1400 ° C. 21. The carbonaceous filler of claim 20 wherein said inhibitory agent is sodium-containing deposits. 22. The carbon filler of claim 20 wherein said inhibitory agent is potassium containing deposits. Carbon filler according to any one of claims 20 to 22, characterized in that the sulfur content is greater than 0.7 percent by weight. Apparatus for treating crude petroleum coke particles according to any one of the preceding claims, characterized in that it comprises a combination of: - an elongated cylindrical calcining furnace (10) with an inlet end (12) and an outlet end (14), - an inlet chamber (16) and an outlet chamber (20), the calcining furnace having its inlet end (12) pivotally connected within the outlet chamber (20), - an elongated cylindrical cooler (36) having an inlet end (38) and an outlet end 40, - means defining a retention chamber (22) connected to an outlet chamber (20) for collecting the calcined coke (24) particles as they exit from the outlet end (14) of the calcining furnace (10), - means defining a hot zone (44) connected to the retention chamber (22) and the inlet end (38) of the radiator (36), - a hopper and tubular attachment (50, 52) for introducing the dry granular puff inhibitor (48) into the retention chamber (22) in contact with the calcined coke particles (24), and - an outlet chamber (42) for discharging coke and collecting the cooled calcined coke particles at the outlet end of the cooler (36), the cooler (36) having its inlet end (38) rotatably connected in the retention vessel (22) and its outlet end (40) is connected rotatably in the coke discharge chamber (42), Apparatus according to claim 24, characterized in that said retention chamber (22) is a clinker box located below the evacuation chamber (20), having an outlet opening and a hot zone (44) located in the space of the inlet end of the cooler (36). Device according to claim 25, characterized in that the hot zone (44) is formed by a refractory ring located in the space of the inlet end of the cooler (36) and at a predetermined distance from the outlet end (32) of the clinker box. Apparatus according to any one of claims 24 to 26, characterized in that the retention chamber (22) has a hot zone (44) located in a separate reaction vessel (68) located below the removal chamber (20).