RU2487919C1 - Method for production of mesophase semi-coke - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: new coke represents replacement of oil coke of KNPS brand taken out of production. Mesophase semi-coke is produced of coal-tar pitch with softening temperature from 65°C up to 145°C by starting softening of coal-tar pitch up to thinly fluid status and by subsequent carbonisation of the melt; at that temperature of the melt is increased preliminary up to the onset temperature of distillation of 300°C with rate of 120-180°C/h, then within the range of distillation and formation of mesophase grains from 360°C up to 420°C with rate of 20-30°C/h and within the range of growth of mesophase grains not less than 30 mcm at temperature of 420-450°C with rate of 6°C/h at least.

EFFECT: invention allows production of semi-coke with different size of mesophase grain with the lease power costs.

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Description

The present invention relates to a technology for the production of coke raw materials for the production of carbon-containing materials and may find further application in the production of structural graphite materials and products operating in conditions of high temperatures, neutron irradiation, erosion, aggressive environments and regime friction, in particular in the technology for producing reactor and crucible graphite. The new coke feed is a replacement for previously discontinued petroleum coke of the KNPS brand.

Traditionally, structural graphites in the USSR were made on the basis of petroleum pyrolysis coke grades KNPS (special petroleum pyrolysis coke) and KNPE (petroleum pyrolysis electrode coke). KNPS coke possessed unique properties for the production of carbon structural materials (UKM) - low ash content and low sulfur content, had a quasi-isotropic structure, had high structural strength and shrinkage during graphitization, in contrast to all other types of cokes undergoing expansion during graphitization.

However, in the period 1992-94 the production of this coke was discontinued, and work was carried out to research and introduce into the industry as a carbon filler pitch coke, vat resin shale coke and petroleum coke of the KNG brand. These cokes differ in properties, both among themselves and from coke of the KNPS brand.

Most cokes currently used in the production of graphitized products are non-isotropic in nature, have a sufficiently high true density, low press-merit due to high elastic expansion coefficients and low relaxation, expansion during heat treatment in the field of graphitization, and have low structural strength.

The closest, in terms of physicochemical properties, to KNPS coke was shown to be coke from coal tar pitch, which, with a certain range of temperature-time regimes for its production, can acquire structural characteristics similar to KNPS coke. The predominant type of structural components is spherulitic, which provides high structural strength and low actual density of coke.

A known method of processing coal tar pitch (1), the so-called delayed coking method: temperature rise at a speed of not more than 3 degrees per minute to 740 ° C with exposure at a final temperature of 1 hour.

As a feedstock in this method, coal-tar non-mesophase high-temperature pitch with a softening temperature of 135-145 ° C is used.

Using this method, coke was obtained with structural characteristics close to those of KNPS coke, except structural strength: microstructure - 2.2 and 2.0 points, actual density 2.07 and 2.06 g / cm ^3, structural strength 165 and 182 kg / m ^2, respectively. However, it is known that the structure and composition of the pitch depends on the quality of coal coming into coking and, as a result, vary greatly. To regulate the structure of the pitch, including the content of spheroidal mesophase particles, in production conditions is extremely difficult and expensive. Therefore, it is necessary to develop a method for producing pitch coke with a quasi-isotropic structure from almost any coal tar pitch.

The closest in technical essence is the method (2) (prototype).

The method includes starting heating the high-temperature pitch to a liquid state and subsequent carbonization of the pitch melt by raising the temperature to 550 ° C. the temperature of the molten pitch is raised at a speed of not more than 20 ° C per hour from the temperature of the fluid state at 300 ° C to the temperature of the onset of carbonization and formation of mesophase grains in an isotropic carbonized mass of the pitch at 400 ° C. Upon reaching this temperature, conditions are maintained that stimulate the growth of the number and size of mesophase grains by slowly increasing the temperature at a rate of not more than 8 degrees per hour to a temperature of 480 ° C, at which the formation of the mesophase matrix is completed. By raising the temperature to 550 ° C, which is conducted at a speed of at least 50 degrees per hour, the formed mesophase matrix is fixed by transferring it to the solid state of semicoke. After fixing the mesophase matrix, accompanied by the formation of a semi-coke cake, its structure is normalized by a subsequent increase in temperature to 570-575 ° C at a speed of no more than 2 degrees per hour.

Coal tar pitch with a softening temperature of 180 ° C of an ordinary supply of Severstal OJSC (Cherepovets) was taken as an object of research on the prototype.

This method requires a longer baking time, and hence greater energy consumption. And also in this method there is no clearly defined temperature-time regime with exposure at each stage.

The basis of the proposed invention is the task of carrying out a semi-coking process of coal tar pitch with a softening temperature of 65 ° C to 145 ° C, achieving an advantageous grain size of less than 30 microns, by controlling the temperature-time regime of semi-coking, reducing the process time and, as a result, reducing consumption electricity.

The solution of this problem in a method for producing a mesophase semicoke, including starting heating of coal tar pitch to a liquid state and subsequent carbonization of the tar melt according to the temperature-time parameters in several stages of mesophase formation, is ensured by first raising the pitch temperature to 300 ° C at a speed of 120-180 degrees per hour, then up to 400 ° C at a speed of 20-30 ° C per hour and until the end of the process 420-450 ° C at a speed of at least 6 degrees per hour.

In the initial stage of thermal decomposition, to a temperature of 300 ° C, the raw material is melted and converted into a thermoplastic mass. The melting stage is considered preparatory, because at the initial stage (after softening the pitch) there is no redistribution of the component composition of the pitch. Above 300 ° C, there is an increase in the content of β-fraction due to partial distillation (distillation) to 360 ° C from the pitch of a portion of the γ-fraction and, accordingly, its decrease. With a further increase in temperature above 360 ° C, the γ fraction transfers to the β fraction, and the β fraction to the α fraction and the latter increases. Thermal condensation processes developing in pitch at the stage of 360-400 ° C lead to the formation of future mesophase embryos.

It has been experimentally established that at the stage up to 300 ° С before the start of distillation, the temperature range of the heating rate of 120-180 ° С / h is optimal, because Allows temperature to be evenly distributed over the entire mass of the pitch. After 300-360 ° C it is necessary to carry out a complete distillation of light fractions and smoothly approach the second stage.

The higher the heating rate, the greater the temperature gradient from the walls of the furnace to its middle, which leads to uneven formation of semicoke, which forms faster at the heated wall. A low heating rate leads to a slowdown in the distillation of light fractions that are not involved in coke formation, an increase in the time of the first stage and an increase in power consumption during the same processes.

The second stage of carbonization is characterized by a decrease in the content of γ and β fractions and an increase in the growth of the α fraction. The process in the temperature range 360-400 ° C is carried out with a heating rate of 30 ° C per hour, which creates supporting conditions that stimulate the growth of the number and size of mesophase grains. It has been experimentally established that at high heating rates, the resulting mesophase spheres are highly isotropic and practically not capable of deformation. With delayed heating, the mesophase grains reach relatively large sizes. And this in turn leads to coalescence and the appearance of pores of semicoke. The number of mesophase grains at low speeds does not increase.

Before the end of the process, namely 420-450 ° C, the temperature rate is set at least 6 ° C per hour, so that the structure of the material does not deform, and the size of the mesophase grain is less than 30 microns. It is at this rate of temperature rise that all conditions are created for the increase in the number of mesophase grains, but their size does not exceed 30 microns.

The temperature-time regimes at each stage of pitch carbonization are controlled by means of an automated control system for regulating the number and sizes of formed liquid crystals in which high-molecular aromatic substances are oriented in the form of layers (mesophase). In the temperature range up to 360 ° С, distillation of liquid volatile products occurs, as well as partial release of CO ₂ ; above this temperature, thermal decomposition begins with the release of a large amount of gas products, mainly methane. Some of them are involved in the pitch mass to form mesophase grains, and some of the light hydrocarbons fly away and form a light distillate. Coal tar pitch, up to a temperature of 300 ° C, is aged for 2-2.5 hours. From 300 ° C until the end of the process takes 2-3 hours. As a result, the total baking time of semi-coke is 4.5-6 hours, which is much less than when baking mesophase coke, according to the prototype, as a result of which the energy consumption is minimal.

At temperatures from 400 ° C and higher, structural transformation processes increase (thermal polycondensation), spherical mesophase grains are formed, which at the initial stage are liquid crystals the size of hundreds-tenths of a micron. With a further increase in temperature to 450 ° C, due to a decrease in the mobility of the pitch mass (in which low molecular weight γ and β fractions turn into the α fraction insoluble in toluene) and gas evolution ends, at a speed of 6-8 ° C per hour, conditions are created for growth in the number and size of mesophase particles due to their coalescence. Next, the process stops to prevent an increase in the size of mesophase grains.

The essence of the invention is illustrated by examples No. 1-5. In all examples, the use of non-standard (experienced) equipment developed specifically for the implementation of the proposed method.

Examples of specific performance:

EXAMPLE 1. Figure 1 - A thin section of a sample of semi-coke with a coalesced mesophase

Coal tar pitch according to GOST 10200 with a softening temperature of 67-75 ° C was heated in a glass oven with the help of half-ring electric heaters to 451 ° C with 7 temperature levels. The tumbler is non-standard equipment. The control of the heat treatment process of the pitch is carried out with the help of industrial control system. First, heating was carried out to 300 ° C at a rate of 200 ° C per hour, after which the melt temperature was raised to 400 ° C at a rate of 74 ° C per hour; From 400 ° C to 451 ° C, heating was carried out at a rate of 6 ° C per hour.

A semi-coke with a coalesced mesophase was obtained (Fig. 1).

The consumed amount of electricity is 1.56 kW per 1 kg of pitch.

The predominant size of mesophase grains reaches 30 and more microns.

EXAMPLE 2. Figure 2 - A thin section of a semi-coke sample with a mesophase grain size of 10-30 μm

Coal tar pitch with a softening temperature of 67-75 ° C was heated in a beaker with half-ring electric heaters to a temperature of 430 ° C with 9 steps. First, heating was carried out to 300 ° C at a rate of 180 ° C per hour, after which the melt temperature was raised to 400 ° C at a rate of 18 ° C per hour. From 400 ° C to 430 ° C, heating was carried out at a rate of 20 ° C per hour.

A semi-coke with a mesophase grain size of 10-30 μm was obtained (Fig. 2).

The predominant size of the mesophase grain reaches less than 10 microns.

The consumed amount of electricity is 1.72 kW per 1 kg of pitch.

EXAMPLE 3. Figure 3 - A thin section of a semi-coke sample with a mesophase grain size of 10-25 μm

Coal tar pitch with a softening temperature of 135-145 ° C was heated in a beaker with half-ring electric heaters to a temperature of 440 ° C with 8 steps. First, heating was carried out to 300 ° C at a rate of 170 ° C per hour, after which the melt temperature was raised to 400 ° C at a rate of 28 ° C per hour. From 400 ° C to 440 ° C, heating was carried out at a rate of 42 ° C per hour.

A semi-coke with a mesophase grain size of 10–25 μm was obtained (Fig. 3).

The predominant size of the mesophase grain reaches 20 microns.

The consumed amount of electricity is 1.75 kW per 1 kg of pitch.

EXAMPLE 4. Figure 4 - Sample thin section with coke structure

Coal tar pitch with a softening temperature of 67-75 ° C was heated in a beaker with half-ring electric heaters to a temperature of 460 ° C including 13 steps. First, heating was carried out to 300 ° C at a rate of 110 ° C per hour, after which the melt temperature was raised to 400 ° C at a rate of 40 ° C per hour. From 400 ° C to 460 ° C, heating was carried out at a rate of 1 ° C per hour.

A material with a coke structure was obtained (Fig. 4). The consumed amount of electricity is 3.09 kW per 1 kg of pitch.

EXAMPLE 5. Figure 5 - A thin section of a semi-coke sample with a mesophase grain size of 10-23 microns

Coal tar pitch with a softening temperature of 67-75 ° C was heated in a beaker with half-ring electric heaters to a temperature of 450 ° C with 11 stages of technological mode. First, heating was carried out to 300 ° C at a rate of 120 ° C per hour, after which the melt temperature was raised to 400 ° C at a rate of 24 ° C per hour. From 400 ° C to 450 ° C, heating was carried out at a rate of 24 ° C per hour.

A semi-coke with a mesophase grain size of 10-23 μm was obtained (Fig. 5).

The consumed amount of electricity is 1.7 kW per 1 kg of pitch.

The above examples show that the proposed method allows to obtain semi-coke with different sizes of mesophase grains from coal tar pitch with a softening temperature of 67-145 ° C for the manufacture of structural materials with the lowest energy costs.

Table 1 Comparative characteristics of technological indicators, controlling the process of carbonization using process control systems. Example No. 1st stage of carbonization 2nd stage of carbonization 3rd stage of carbonization The grain size in the product, microns Amount of consumed electricity, kW / 1 kg pitch up to 300 ° C Rise rate, ° С / hour 300-400 ° C Rise speed, ° C / hour The final temperature, ° C Rise rate, ° С / hour one 200 74 451 6 Over 30 1,56 2 180 eighteen 430 twenty 10-30 1.72 3 170 28 440 42 10-25 1.75 four 110 40 460 one coke 3.09 5 120 24 450 24 10-23 1.7

Information sources

1. RF patent No. 2230770 class. C10C 3/10 dated 06/20/2004; 3 No. 2002127437 dated 10/14/2002.

2. V.E. Privalov, M.A. Stepanenko Coal tar pitch. M., "Metallurgy" 1981

3. EF Chalykh Technology of carbon-graphite materials. M., "Metallurgizdat" 1963

4. GOST 10200-83 “Coal tar pitch”.

Claims (1)

A method of producing a mesophase semicoke from coal tar pitch with a softening temperature of 65 ° C to 145 ° C, including starting heating the pitch to a liquid state and subsequent carbonization of the pitch melt, characterized in that the pitch of the pitch melt is first raised to the temperature of the start of distillation at 300 ° C with at a rate of 120-180 ° C / h, then in the range of distillation and formation of mesophase grains from 360 ° C to 420 ° C at a speed of 20-30 ° C / h and in the growth interval of mesophase grains of less than 30 μm at a temperature of 420-450 ° C at a rate of at least 6 ° C / h.

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