A method for preparing high-performance coal-based needle coke by pyrolysis

Abstract

The present invention relates to a method for preparing high-performance coal-based needle coke by pyrolysis. The method uses coal tar pitch as the raw material, adds a polymerization promoter containing sulfur elements for thermal polymerization soaking, and then raises the temperature for pyrolysis. The raw material after pyrolysis is separated by flash evaporation to separate the heavy-phase asphalt and the raw material asphalt. The raw material asphalt is further separated by fractional distillation to separate the polymerization promoter and produce refined asphalt. The refined asphalt is calcined by coking to obtain a needle coke product. The present invention pre-treats the raw material by means of high-temperature soaking pyrolysis, effectively retains all beneficial components in the coal tar pitch, and the prepared needle coke has low sulfur and low CTE, and the quality is stable.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-based needle coke preparation, and particularly to a method for preparing high-performance coal-based needle coke by a thermal cracking method. Background Art

[0002] Needle coke is a high-quality carbon material, which has the advantages of low coefficient of thermal expansion (CTE), good electrical and thermal conductivity, etc. It is mainly used in the production of high-power (HP) or ultra-high-power (UHP) graphite electrodes for electric arc furnace steelmaking, anode materials for lithium-ion batteries, high-end graphite materials and other fields.

[0003] Coal tar pitch is the raw material for the production of coal-based needle coke. It is a co-soluble mixture of various organic compounds, with extremely complex composition and structure. Its composition is related to the properties of the raw coal used for coking, the coking process and the processing conditions of coal tar. The composition and properties of coal tar pitch from different sources are different, and it must be pretreated specifically before it can be used for the production of needle coke. The raw materials for needle coke require high aromatic content, low heteroatom content, low metal content, low ash content, etc. The pretreatment of raw materials is the core technology of the industrialization of coal-based needle coke. Its continuous innovation is the key to improving the quality of needle coke products and reducing production costs. While ensuring the pretreatment effect, it is crucial to improve the yield of treated pitch and eliminate the influence of raw material sources. The main purpose of raw material pretreatment is to remove harmful impurities such as quinoline insoluble matter (QI) in the raw material pitch and retain the beneficial components in the pitch to produce refined pitch with appropriate composition. The main pretreatment technologies for needle coke at home and abroad include distillation method, centrifugation method, flash evaporation and polycondensation method, solvent method. Among them, the solvent method is the only production method that has truly achieved industrialization in domestic needle coke production. However, with the development of graphite electrode and lithium-ion battery technologies, higher requirements are put forward for the performance and cost of needle coke, requiring more stable performance and lower production cost of needle coke. Although the existing solvent method for preparing needle coke is very mature, it is greatly affected by the change of coal tar pitch raw material sources. In addition, the CTE of domestic needle coke is relatively high, and the sulfur and nitrogen content of some products are relatively high. There is still a gap between domestic needle coke and imported high-end needle coke in the application of high-end anode materials for lithium-ion batteries, ultra-high-power electrode materials with a diameter of φ700 and above or joint coke. Therefore, it is of great significance to develop new technologies for the pretreatment of needle coke raw materials to prepare needle coke products with more stable performance and lower cost.

[0004] The patent document with the application number 201310289562.8 discloses a method for preparing ordered needle coke from coal tar pitch. This method removes quinoline insoluble matter from coal tar pitch, distills, extracts coal tar pitch microspheres, vacuum distills, carbonizes at high temperature, and calcines at high temperature to produce ordered needle coke from coal tar pitch. The whole process of this method is too complex, the production equipment is not easy to obtain, the production cost is high, and it is not easy to implement. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing high-performance coal-based needle coke by pyrolysis. The present invention pre-treats the raw materials by high-temperature soaking pyrolysis, effectively retaining all beneficial components in coal tar pitch. The prepared needle coke has low sulfur and low CTE, and the quality is stable.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing high-performance coal-based needle coke by pyrolysis, which uses coal tar pitch as the raw material, adds a polymerization promoter containing sulfur elements for thermal polymerization soaking, and then raises the temperature for pyrolysis. The raw materials after pyrolysis are separated by flash evaporation to separate heavy-phase asphalt and raw material asphalt. The raw material asphalt is further separated by fractional distillation to separate the polymerization promoter and produce refined asphalt. The refined asphalt is calcined by coking to obtain a needle coke product.

[0008] The polymerization promoter containing sulfur elements is one or more of sulfur, mercaptan, and carbon disulfide.

[0009] After adding the polymerization promoter to the coal tar pitch, the sulfur element content in the overall solution is 30 wt%.

[0010] The thermal polymerization soaking temperature is 230 - 350 °C, and the thermal polymerization soaking time is 5 - 120 min.

[0011] The pyrolysis time is 10 - 30 min, the pyrolysis temperature is 450 - 550 °C, and the pressure is 45 - 50 kg / cm 2 g.

[0012] The flash evaporation temperature is 380 - 510 °C, the pressure is 0.1 - 2 kg / cm 2 g, and the heavy-phase asphalt components separated by flash evaporation are toluene, quinoline insoluble matter, and impurity elements.

[0013] The fractional distillation temperature is 360 - 500 °C.

[0014] The refined asphalt is preheated before coking, the preheating temperature is 400 - 500 °C, and after preheating, it enters the coking tower. The reaction pressure in the coking tower is 0 - 5 MPa; the heating rate of the coking tower is 2 - 10 °C / min, and the final reaction temperature is 500 - 550 °C.

[0015] After coking, the coke is removed by steam cutting. The obtained wet coke enters a wet coke dryer for drying, the drying time is 4 - 6 hours, and part or all of the dried coke is calcined; the reaction temperature in the calcining furnace is 800 - 1500 °C; the gas in the calcining furnace is one of nitrogen, argon, and helium.

[0016] The present invention uses coal tar pitch as a raw material, heats it by soaking in a solution, and then raises the temperature to a higher level for thermal cracking to obtain a refined pitch with high aromaticity. After coking and calcination, a needle coke product is obtained.

[0017] The present invention prepares high-performance needle coke. The coking reaction is carried out under a certain pressure value and finally the temperature is raised to the highest temperature. After maintaining at the highest temperature for 1 - 3 hours, green coke of needle coke is obtained. After the green coke is dried, a part of it can be directly used as the green coke product of needle coke, and the other part enters the calcination furnace for calcination, and the calcined product of needle coke is obtained after calcination.

[0018] The raw material of the present invention is coal-based pitch. First, thermal polymerization is carried out by adding a polymerization promoter to polymerize the unsaturated substances in the pitch to make the pitch meet the conditions for thermal cracking.

[0019] After the raw material is heat-soaked, it is fed into a thermal cracker for high-temperature thermal cracking. Under high temperature and high pressure conditions, the raw material undergoes thermal cracking and then enters a vacuum flash distillation column; in the vacuum flash distillation column, the cracked raw material is separated by flash distillation, and finally the required raw material pitch is distilled out and enters the fractionation column. The heavy-phase pitch is drawn out from the bottom of the flash distillation column and can be sold.

[0020] The raw material pitch separates the solvent (polymerization promoter) during thermal polymerization in the fractionation column, and the rest enters the refined pitch raw material tank; then it enters a preheating device to prepare for coking; the raw material is coked in a coking tower under certain conditions, and after coking, the coke is removed by the method of steam cutting; the finally obtained wet coke enters a wet coke dryer through a wet coke conveyor belt for drying and finally enters the finished green coke bin; another part of the coke is subjected to high-temperature calcination in a high-temperature calcination furnace, and then enters a dust removal blower for dust removal and finally enters the calcined product bin of the calcined coke.

[0021] The present invention can prepare high-performance coal-based needle coke through a special delayed coking device, obtain finished products with a certain output value, and can adjust the output value and product performance by adjusting parameters such as temperature and pressure.

[0022] Compared with the existing technology, the beneficial effects of the present invention are:

[0023] 1) In the prior art, the change in the source of coal tar pitch has led to differences in the composition and properties of coal tar pitch. During the solvent sedimentation process, the ease of sedimentation separation of quinoline insoluble matter in coal tar pitch raw materials from different sources varies, resulting in instability in the control of the pretreatment process and the properties of refined pitch, thereby affecting the stability of needle coke products. In the present invention, first, the raw material pitch is thermally soaked to polymerize the polymerizable part in the raw material pitch, facilitating subsequent operations. Then, the raw material is subjected to thermal cracking treatment. After flash distillation to distill out the required part and leave the non-crystalline substances, the solvent is distilled out to obtain refined pitch. The present invention can increase the yield of refined pitch by 10 - 20%, has high production efficiency, and reduces production costs by 15% - 20%.

[0024] 2) During the prior solvent pretreatment process, some components that are beneficial for mesophase growth and needle coke formation are separated along with the impurity components, resulting in the loss of beneficial components, that is, the components in the raw material suitable for needle coke formation are not fully utilized, and the production economic benefits need to be further improved. In the present invention, during the thermal cracking process, only the non-crystalline substances that affect the properties of needle coke are distilled out, and all the effective components in the pitch are retained in the raw material pitch, which can increase the yield of refined pitch and significantly reduce production costs.

[0025] 3) The asphalt raw material pretreatment method provided by the present invention, the obtained refined pitch is further adjusted for process parameters during the mesophase and coke production processes in the delayed coking process to reduce the CTE and obtain high-quality needle coke products. Through the method of the present invention, the production cost of needle coke is effectively reduced, the process is simple, the product performance is excellent, and the enterprise profit is high. Description of the Drawings

[0026] Figure 1 is the process flow chart for preparing refined pitch of the present invention;

[0027] In the figure: 1 - asphalt raw material tank, 2 - solvent tank, 3 - thermal soaking tank, 4 - thermal cracker, 5 - vacuum flash distillation tower, 6 - fractionating tower, 7 - solvent condenser, 8 - refined asphalt raw material tank, 9 - preheater, 10 - coking tower, 11 - coke dryer, 12 - light component condenser of coking tower, 13 - light component storage tank of coking tower, 14 - calcining furnace, 15 - tail gas treatment device, 16 - dust removal blower, 17 - reservoir. Detailed Embodiments

[0028] The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments. The methods used in the following embodiments are all conventional methods unless otherwise specified, and the equipment used is all conventional equipment, commercially available products.

[0029] Such as Figure 1As shown in the figure, the device adopted by a method for preparing high-performance coal-based needle coke by thermal cracking includes a thermal soaking tank 3, a thermal cracker 4, a vacuum flash distillation tower 5, a fractionating tower 6, a solvent condenser 7, a refined asphalt raw material tank 8, a preheater 9, a coking tower 10, a coke dryer 11, a coking light component condenser 12, a coking tower light component storage tank 13, and a calcining furnace 14; the discharge port of the thermal soaking tank 3 is connected to the thermal cracker 4, the discharge port of the thermal cracker 4 is connected to the vacuum flash distillation tower 5, the vapor phase outlet of the vacuum flash distillation tower 5 is connected to the inlet of the fractionating tower 6, the light phase outlet of the fractionating tower 6 is connected to the solvent condenser 7, the solvent condenser 7 is connected to the thermal soaking tank 3, the heavy phase outlet of the fractionating tower 6 is connected to the refined asphalt raw material tank 8, the outlet of the refined asphalt raw material tank 8 is connected to the inlet of the preheater 9, the outlet of the preheater 6 is connected to the coking tower 10, the light phase outlet of the coking tower 10 is connected to the coking tower light component storage tank 13 through the coking light component condenser 12, and the coke produced by the coking tower 10 is sent into the coke dryer 11 through a conveying device, and the discharged material of the coke dryer 11 is sent into the calcining furnace 14.

[0030] In the method for preparing high-performance coal-based needle coke by thermal cracking according to the present invention, the coal-based asphalt preheated to a fluid state is pumped from the raw material tank into the thermal soaking tank 3 for thermal soaking treatment. After adding a sulfur-containing solution to the thermal soaking tank 3 and performing thermal soaking for 5 - 120 minutes at a temperature between 230 and 350 °C in the thermal soaking tank 3, it is pumped into the thermal cracker 4 through a pumping pump. In the thermal cracker 4, the temperature is 450 - 550 °C and the internal pressure is 45 - 50 kg / cm 3 After rapid cracking at 10 - 30, it is pumped into the vacuum flash distillation tower 5.

[0031] Flash cutting is carried out in the vacuum flash distillation tower 5. The aromatic part in the asphalt after thermal cracking undergoes flash vaporization at a temperature of 380 - 510 °C and a pressure of 0.1 - 2 kg / cm 2 g and enters the fractionating tower 6, and the remaining part is discharged from the bottom of the flash distillation tower and sold as a by-product.

[0032] In the fractionating tower 6, the sulfur-containing solution is distilled out and enters the solvent condenser 7 and is recycled back to the thermal soaking tank 3, and the remaining liquid is the refined asphalt for preparing needle coke and enters the refined asphalt raw material tank 8.

[0033] The refined asphalt enters the preheater 9, and the preheating temperature is about 400 - 500 °C. After preheating, it is pumped into the coking tower 10. In an environment of 0 - 5 MPa, an intermediate phase thermal reaction is carried out through a heating program of 400 - 550 °C. The light component steam during the thermal reaction process enters the coking tower light component condenser 12, and after condensation, it enters the coking tower light component storage tank 13 and is also packaged and sold.

[0034] After the coking reaction is complete, the coke is cut with water vapor and then sent to the coke dryer 11 via a conveyor belt. Part of the dried coke is sold as green coke for high-performance coal-based needle coke.

[0035] Another part enters the calcining furnace 14. The high-temperature calcining furnace conducts high-temperature calcination at a temperature of 800°C to 1500°C under the protection of one of the protective gases, nitrogen, argon, or helium. The generated gas enters the tail gas treatment device, and the obtained coke then enters the dust removal blower 16 for dust removal treatment. After dust removal, it is sold as calcined coke for high-performance coal-based needle coke.

[0036] Example 1:

[0037] The coal-based pitch preheated to a fluid state is pumped from the raw material tank into the hot soak tank 3 for hot soak treatment. A sulfur-containing solution is added to the hot soak tank 3. After hot soaking for 60 minutes at a temperature between 300°C, it is pumped into the thermal cracker 4 by an extraction pump. In the thermal cracker 4, the temperature is 500°C and the internal pressure is 48 kg / cm 3 After rapid cracking for 1 - 2 minutes, it is pumped into the vacuum flash tower 5.

[0038] Flash cutting is carried out in the vacuum flash tower 5. The aromatic part in the pitch after thermal cracking vaporizes by flash at a temperature of 400°C and a pressure of 1 kg / cm 2 g and enters the fractionating tower 6.

[0039] In the fractionating tower 6, the sulfur-containing solution is distilled out and enters the solvent condenser 7 and is recycled back to the hot soak tank 3. The remaining liquid is the refined pitch for preparing needle coke and enters the refined pitch raw material tank 8.

[0040] The treated refined pitch enters a 400°C pitch preheater and then enters the coking tower under the conditions of a pressure of 2 MPa and a temperature of 420°C in the coking tower. It is heated to 530°C at a heating rate of 5°C / h. The obtained green coke enters the calcining furnace, and the temperature of the calcining furnace is 1200°C, finally obtaining calcined anode material coke.

[0041] Example 2:

[0042] The coal-based pitch preheated to a fluid state is pumped from the raw material tank into the hot soak tank 3 for hot soak treatment. A sulfur-containing solution is added to the hot soak tank 3. After hot soaking for 80 minutes at a temperature between 280°C, it is pumped into the thermal cracker 4 by an extraction pump. In the thermal cracker 4, the temperature is 520°C and the internal pressure is 49 kg / cm 3 After rapid cracking within 10 minutes, it is pumped into the vacuum flash tower 5.

[0043] Flash distillation cutting is carried out in the vacuum flash distillation tower 5. The aromatic part in the asphalt after pyrolysis vaporizes by flash distillation at a temperature of 450 °C and a pressure of 1.5 kg / cm 2 g and enters the fractionating tower 6.

[0044] In the fractionating tower 6, the sulfur-containing solution is distilled out and enters the solvent condenser 7 and is recycled back to the hot soaking tank 3. The remaining liquid is the refined asphalt for preparing needle coke and enters the refined asphalt raw material tank 8.

[0045] The treated refined asphalt is fed into the asphalt preheater at 350 °C and enters the coking tower under the conditions that the parameters of the coking tower are a pressure of 3 MPa and a temperature of 420 °C, and is heated to 540 °C at a heating rate of 4 °C / h. The resulting green coke enters the calcining furnace, and the temperature of the calcining furnace is 1200 °C, and finally the calcined negative electrode material coke is obtained.

[0046] Example 3:

[0047] The coal-based asphalt preheated to the fluid state is pumped from the raw material tank into the hot soaking tank 3 for hot soaking treatment. After adding the sulfur-containing solution in the hot soaking tank 3 and hot soaking for 100 minutes at a temperature between 320 °C, it is pumped into the pyrolyzer 4 by the extraction pump. The temperature of the pyrolyzer 4 is 490 °C and the internal pressure is 46 kg / cm 3 After rapid cracking for 1 - 2 minutes under this condition, it is pumped into the vacuum flash distillation tower 5.

[0048] Flash distillation cutting is carried out in the vacuum flash distillation tower 5. The aromatic part in the asphalt after pyrolysis vaporizes by flash distillation at a temperature of 490 °C and a pressure of 0.5 kg / cm 2 g and enters the fractionating tower 6.

[0049] In the fractionating tower 6, the sulfur-containing solution is distilled out and enters the solvent condenser 7 and is recycled back to the hot soaking tank 3. The remaining liquid is the refined asphalt for preparing needle coke and enters the refined asphalt raw material tank 8.

[0050] The treated refined asphalt is fed into the asphalt preheater at 400 °C and enters the coking tower under the conditions that the parameters of the coking tower are a pressure of 2 MPa and a temperature of 420 °C, and is heated to 550 °C at a heating rate of 10 °C / h. The resulting green coke enters the calcining furnace, and the temperature of the calcining furnace is 1200 °C, and finally the calcined negative electrode material coke is obtained.

[0051] Example 4:

[0052] The coal-based asphalt preheated to the fluid state is pumped from the raw material tank into the hot soaking tank 3 for hot soaking treatment. After adding the sulfur-containing solution in the hot soaking tank 3 and hot soaking for 90 minutes at a temperature between 250 °C, it is pumped into the pyrolyzer 4 by the extraction pump. The temperature of the pyrolyzer 4 is 530 °C and the internal pressure is 46 kg / cm 3After being rapidly cracked within the next 15 minutes, it is pumped into the vacuum flash tower 5.

[0053] Flash cutting is carried out in the vacuum flash tower 5. The aromatic part in the asphalt after thermal cracking undergoes flash vaporization at a temperature of 430 °C and a pressure of 0.9 kg / cm 2 g and enters the fractionating tower 6.

[0054] The sulfur-containing solution is distilled out in the fractionating tower 6, enters the solvent condenser 7, and is recycled back to the thermal soaking tank 3. The remaining liquid, which is the refined asphalt for preparing needle coke, enters the refined asphalt raw material tank 8.

[0055] The treated refined asphalt is fed into an asphalt preheater at 400 °C and enters the coking tower under the conditions of a pressure of 2 MPa and a temperature of 420 °C in the coking tower. It is heated to 520 °C at a heating rate of 5 °C / h. The resulting green coke enters the calcining furnace, and the temperature of the calcining furnace is 1200 °C, finally obtaining the calcined anode material coke.

[0056] Example 5:

[0057] The coal-based asphalt preheated to the fluid state is pumped from the raw material tank into the thermal soaking tank 3 for thermal soaking treatment. A sulfur-containing solution is added to the thermal soaking tank 3, and after thermal soaking at a temperature between 290 °C for 80 minutes, it is pumped into the thermal cracker 4 through a extraction pump. The temperature of the thermal cracker 4 is 460 °C and the internal pressure is 46 kg / cm 3 After being rapidly cracked within 1 - 2 minutes, it is pumped into the vacuum flash tower 5.

[0058] Flash cutting is carried out in the vacuum flash tower 5. The aromatic part in the asphalt after thermal cracking undergoes flash vaporization at a temperature of 410 °C and a pressure of 1.6 kg / cm 2 g and enters the fractionating tower 6.

[0059] The sulfur-containing solution is distilled out in the fractionating tower 6, enters the solvent condenser 7, and is recycled back to the thermal soaking tank 3. The remaining liquid, which is the refined asphalt for preparing needle coke, enters the refined asphalt raw material tank 8.

[0060] The treated refined asphalt is fed into an asphalt preheater at 380 °C and enters the coking tower under the conditions of a pressure of 3 MPa and a temperature of 420 °C in the coking tower. It is heated to 530 °C at a heating rate of 8 °C / h. The resulting green coke enters the calcining furnace, and the temperature of the calcining furnace is 1200 °C, finally obtaining the calcined anode material coke.

[0061] Table 1 shows the values of the coefficient of thermal expansion (CTE) of the coke obtained in each example; Table 2 is a comparison of the properties of the needle coke prepared in the examples of the present invention with those of ordinary needle coke.

[0062] Table 1 Comparison of CTE content of needle coke in examples

[0063] Example CTE of needle coke 1 <![CDATA[0.95*10 -6 > 2 <![CDATA[0.92*10 -6 > 3 <![CDATA[0.91*10 -6 > 4 <![CDATA[0.97*10 -6 > 5 <![CDATA[0.94*10 -6 >

[0064] Table 2 Comparison of CTE Contents of Two Kinds of Needle Coke

[0065] Project Common needle coke Needle coke of the present invention CTE <![CDATA[1.3*10 -6 > <![CDATA[0.9*10 -6 > 。

Claims

1. A method for preparing high-performance coal-based needle coke by pyrolysis, characterized in that, This method uses coal tar pitch as the raw material, adds a polymerization accelerator containing sulfur elements for thermal polymerization soaking, then raises the temperature for thermal cracking. The raw material after thermal cracking is separated by flash evaporation to separate the heavy-phase asphalt and the raw material asphalt. The raw material asphalt is further fractionated to separate the polymerization accelerator and produce refined asphalt. The refined asphalt is calcined through coking to obtain a needle coke product; After adding the polymerization accelerator to the coal tar pitch, the sulfur element content in the overall solution is 30 wt%; The fractionation temperature is 360 - 500 °C; The coal tar pitch preheated to the fluid state is pumped from the raw material tank into the thermal soaking tank for thermal soaking treatment, and a sulfur-containing solution is added to the thermal soaking tank; The sulfur-containing solution is distilled out in the fractionation tower, enters the solvent condenser and is recycled back to the thermal soaking tank. The remaining liquid is the refined asphalt for preparing needle coke and enters the refined asphalt raw material tank.

2. The method for preparing high-performance coal-based needle coke by a thermal cracking method according to claim 1, wherein The polymerization accelerator containing sulfur elements is one or several of sulfur, mercaptan, and carbon disulfide.

3. The method for preparing high-performance coal-based needle coke by a thermal cracking method according to claim 1, characterized in that, The thermal polymerization soaking temperature is 230 - 350 °C, and the thermal polymerization soaking time is 5 - 120 min.

4. A method for preparing high-performance coal-based needle coke by a thermal cracking method according to claim 1, characterized in that, The pyrolysis time is 10 to 30 minutes, the pyrolysis temperature is 450 to 550 °C, and the pressure is 45 to 50 kg / cm 2 G.

5. The method for preparing high-performance coal-based needle coke by a thermal cracking method according to claim 1, characterized in that, The flash evaporation temperature is 380~510°C, and the pressure is 0.1~2 kg / cm 2 G. The heavy-phase asphalt components separated by flash evaporation are toluene, quinoline insoluble matter, and impurity elements.

6. The method for preparing high-performance coal-based needle coke by a thermal cracking method according to claim 1, wherein The refined asphalt is preheated before coking. The preheating temperature is 400 - 500 °C. After preheating, it enters the coking tower. The reaction pressure in the coking tower is 0 - 5 MPa; the heating rate of the coking tower is 2 - 10 °C / min, and the final reaction temperature is 400 - 550 °C.

7. The method for preparing high-performance coal-based needle coke by a thermal cracking method according to claim 1 or 6, characterized in that, After coking, the coke is removed by the method of steam cutting. The obtained wet coke enters the wet coke dryer for drying. The drying time is 4 - 6 hours. Part or all of the dried coke is calcined; the reaction temperature in the calcining furnace is 800 - 1500 °C; the gas in the calcining furnace is one of nitrogen, argon, and helium.

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