Method of calcining pitch coke

 

(57) Abstract:

The invention relates to a technology for coke raw material for the electrode industry, in particular for the manufacture of electrodes furnaces, as well as anodes used to produce aluminium by electrolysis of cryolite-alumina melts, and may find application in the manufacture of a wide range of products on the basis of structural graphites of different brands. The method consists in that the heat-treated coke prepared raw materials are in retort calcining furnaces were at a temperature of 1000-1400oC, while during the heat treatment and the posting of raw material in the calcining zone provide for the creation in each retort calcining furnaces were excessive gas pressure. The preferred solution to the problem of creating excess pressure in each retort calcining furnaces were, according to the invention, is creating pressure by filing in the retort furnace together with pitch coke impurities of petroleum coke, in particular admixture of petroleum coke as coke breeze. The method allows to extend the capabilities retort Prokhladny furnaces, reduce losses, coke raw materials on ash and fumes, as well as to provide processing of coke is oxboro raw material for the electrode industry, in particular for the manufacture of electrodes furnaces, as well as anodes used to produce aluminium by electrolysis of cryolite-alumina melts, and may find application in the manufacture of a wide range of products on the basis of structural graphites of different brands.

Known methods of coke calcination of raw materials - petroleum coke, pitch coke, or a mixture thereof, the vast majority focused on the process in rotary tube furnaces with high bandwidth. However, such calcining furnaces were characterized by large losses proklinaemogo raw materials because of the ash, and large thermal losses, due to implemented them in the scheme of direct heating proklinaemogo raw materials due to fed directly into the calcining zone of coolant and partial combustion proklinaemogo raw materials (mainly fine fractions). Despite the fact that the rotary tube furnace equipped with a control ratio supplied to them fluid and air, allowing you to affect the amount of smoke proklinaemogo raw materials loss on fumes may exceed 15%, and the total loss with regard to entrainment by calcining furnaces were, less bandwidth which per unit of production area can be overcome by increasing the number of retorts (cells). Compared to the rotating retort calcining furnaces were achieved by implementation of the scheme of indirect heating proklinaemogo raw materials (by washing retort is cooled from the outside), have this important advantage, as no loss of ash. However, for calcining pitch coke at temperatures exceeding 1000oC, retort furnaces are not used because of the danger of combustion of raw materials and output of the furnace out of operation. Not calcined in rotary kilns and finely divided coke (particle size less than 5 mm) due to observed hovering in narrow retorts.

There is a method of calcining pitch coke directly into the coking chamber of the coke ovens by blowing coke cake air before discharge. The air in the chamber coking served from specially established fan for 15 - 20 minutes due to combustion of residual volatiles and coke part in the amount of 1 - 1.5% of the temperature of the mass of coke is increased to 1300 - 1500oC, allowing you to get a coke with a specific gravity 2,02 g/cm3/ A. S. N 445683, C 10 L 9/08, 1977/ (1).

However, the known method prokalc the new furnace to high temperatures under conditions of oxidative environment and as a consequence, increases the cost of maintenance and repair of coke oven batteries by reducing the service life. In order to reduce the cost of coke raw material supplied to the electrode plants, in particular pitch coke is coke plants at temperatures below 1000oC. Such coke (pitch) can only be used for the production of anodes for the aluminum industry. Production of electrodes for furnaces of pitch coke is possible only after additional baking it at a high temperature to provide a higher density and low shrinkage material.

There is also known a method of calcining coke raw materials, including pitch, including the preparation of raw materials, feeds it into progulochnuju furnace and subsequent heat treatment in the process of the transaction in the calcining zone /A. S. N 173710, C 10 B 53/00, 1964 / (2). According to this method, the process is conducted in a rotary calcining furnaces were, preparing coke feedstock is produced by dividing the coke fraction, and heat treatment fractions are in different temperature zones of the rotary kiln: a large fraction - in counterflow furnaces, and small - zone furnace with a temperature of 950 - 1050oC.

There is a method of calcination is giving Pilipinas small fractions of a local-like gas flow, coke fines, supplied to the calcining zone, i.e. the reduction of the output of calcined coke per ton of downloadable materials, as well as increased fuel consumption by the heat introduced into the calcining zone trivia pitch coke with a low volatile content (1%).

The basis of the proposed method of calcining pitch coke on the task of reducing losses coke feedstock at elevated temperature calcining pitch coke and reducing costs of energy in the process.

The solution of the problem in the way calcining pitch coke, including the preparation of coke raw materials, feeds it into progulochnuju furnace and subsequent heat treatment in the process of the transaction in the calcining zone, provided that the heat treatment of the prepared raw materials are in retort calcining furnaces were at a temperature of 1000 - 1400oC, while during the heat treatment and the posting of raw materials ensure the creation of each retort furnace overpressure gases.

The solution of this problem is provided, in particular, the fact that create excess pressure in each retort calcining furnaces were in the process of heat treatment and posting of the raw materials reach by filing in the retort furnace pitch coke mixed with oil and petroleum coke in the form of pieces, coke breeze or pieces mixed with coke fines can be 20 - 80%.

It should be noted that attempts by calcining pitch coke in the retort furnaces without creating excessive pressure in each retort during heat treatment at elevated temperatures always ends up burning up to 100% proklinaemogo of raw materials due to the suction of atmospheric air. When creating the same conditions for the emergence and preservation of each retort excessive pressure in the posting process raw materials, air from the surrounding atmosphere does not penetrate into the retort, and the process of calcination is in a noncorrosive environment.

Excessive pressure in each retort can be obtained not only by the admixture of petroleum coke, but due to equipment retort calcining furnaces were external source of protective gas and connection of the source transport channels retorts calcining furnaces were. The protective gas can be any inert gas. However, creating excessive pressure in each retort during the heat treatment due to the admixture of petroleum coke is preferred as it does not require reconstruction of the furnace that eliminates the necessity of spending the special is awns retort furnaces. In fact, in retort furnaces because of the narrowness of the retort, having the form of flat tapes of a width of about 200 mm, it is impossible to make the calcining of petroleum coke fines due to the merging of small particles of coke and education codes, i.e., clogging of cassettes. Adding the same stuff petroleum coke pitch lumpy coke, this phenomenon disappears and the quantity of impurities stuff petroleum coke pitch Kuskova coke at which bridging is not observed, is from 20 to 80%. This provides additional processing capacity for detail petroleum coke, which in large quantities is formed at the coke producers, as well as in the manufacture of electrodes in the processing of petroleum coke due to the low strength of it, and, as a consequence, its crushing during transportation, crushing or any transshipments. This low strength and high electrical resistivity have been the reason that the calcination of petroleum coke in a rotary tube furnace according to the prototype [2] is performed after mixing petroleum coke pitch coke having a higher strength and a significantly lower resistivity. As a result, for aluminium electrolysis cells receive the anodes of the creation of excessive pressure in the retort calcining furnaces were the heat treatment of pitch coke through the admixture of petroleum coke is not in conflict with widely spread methods of processing coke raw materials, you can extend your retort Prokhladny furnaces, and deciding the task. The advantage of the proposed method is that the amount of impurity petroleum coke pitch can vary within a wide range (20 - 80%).

The method is implemented as follows.

Coke raw materials are cooked in a mixture of pitch and petroleum coke. This can be done as a preliminary mixing coke and alternating fed into the hopper portions pitch and petroleum coke. From the hopper coke feedstock served in the cassette (retort) calcining furnaces were brought to a temperature of 1000 - 1400oC. the Upper limit of 1400oC is determined by thermal resistance of masonry retorts. When this exercise wiring proklinaemogo raw material through the retort at a speed corresponding to the performance of one retort in the range of 12 to 21 kg/h, depending on the specific content of residual volatile substances in admixture of petroleum coke, and the speed of their allocation at the specified temperature. With this in mind, empirically pick up speed posting of raw materials.

During the heat treatment and posting coke raw material admixture of petroleum coke allocates ostatecznie. Escaping from the retort volatile mix with the coolant surrounding the retort from the outside, and burn, thereby generating additional heat. It also helps to reduce the cost of energy on the process of calcination, in addition to the main cost saving energy is provided by the implementation process of calcining pitch coke in the retort calcining furnaces were.

The described method of calcining pitch coke is illustrated by examples of the process.

Example 1.

In retort progulochnuju furnace, consisting of 12 retorts (each size 5000 x 3000 x 200 mm) were downloaded from the hopper pre-prepared mixture of pitch lump and oil lump coke in the ratio 3:2 sizes up to 55 mm, the Temperature of the coke raw material in the retort was raised at a rate of 100oC/hour up to operating temperature (1300oC). At this temperature the coke raw material is conducted through the retort at a speed corresponding to the performance of one tape 18 kg/hour. From retort coke came in the fridge and then in the hopper. In the implementation of the mode and conditions of the coke density of 2.08 g/cm3that meets the requirements for coke filler and due vydelevshimsya volatile substances (3 - 4%).

Example 2.

The calcining pre-prepared raw material was carried out according to mode, similar to example 1, with the only difference that the mixture of pitch and oil lump coke (the same size) was taken in the ratio 2:3 and through the retort furnace was carried out with a speed corresponding performance of one retort 15 kg/hour. The resulting coke with a specific density of 2.08 g/cm3. Loss of coke on the smoke and ash are missing. Weight change due to the emission of volatile amounted to 6%.

Example 3.

Pre-prepared mixture of lump pitch (to 55 mm) and stuff petroleum coke (particle size not greater than 3 mm) in the ratio of 4:1 was subjected to heat treatment in the process of wiring through the retort calcining furnaces were with a speed corresponding performance of one retort 21 kg/hour and at temperatures of example 1. The resulting coke is required density of 2.08 g/cm3. Hang coke breeze was not observed. There are no losses.

Example 4.

Pre-cooked mixture of lump pitch (sizes up to 55 mm) and stuff petroleum coke with a particle size of the grains is not more than 3 mm in a ratio of 1:4 was subjected Ter is estoya performance of one retort 12 kg/hour. In the implementation of the mode and conditions of the coke required density of 2.08 g/cm3. Hang coke breeze was not observed. There are no losses. On the flying went 9%.

Described in the examples tested the proposed method of calcining pitch coke, carried out in industrial conditions, showed its industrial applicability with empowerment retort Prokhladny furnaces, providing significant reduction of losses coke raw material and energy costs in the process.

1. Method of calcining pitch coke, including the preparation of coke raw materials, feeds it into progulochnuju furnace and subsequent heat treatment in the process of the transaction in the calcining zone, characterized in that the heat-treated coke raw materials are in retort calcining furnaces were at a temperature of 1000-1400oC, while during the heat treatment and the posting of raw materials ensure the creation of each retort furnace overpressure gases.

2. The method according to p. 1, characterized in that the excess pressure in each retort calcining furnaces were in the process of heat treatment and posting materials provide by filing in the retort furnace together with pitch coke impurities of petroleum coke.


 

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