Preparation method of graphite block for graphite heat exchanger

Abstract

This invention discloses a method for preparing graphite blocks for graphite heat exchangers, comprising the following steps: Batching: Weighing 74%-78% dry material and the remainder asphalt according to weight percentage; the dry material includes 60% graphitized coke, 15% needle coke, 10% asphalt coke, 5% carbon black, and the remainder being graphitized granules according to weight percentage; Heating and kneading to obtain a paste; Drying to remove asphalt fumes; Pressing and molding using molding equipment to obtain graphite block green blanks; Firing the graphite block green blanks in a ring furnace to obtain graphite block cooked blanks; Graphitizing the graphite block cooked blanks in a graphitization furnace, then cooling and removing them from the furnace to obtain the graphite block product. Through the combination of the components, the graphite block product prepared according to this invention has good thermal conductivity and mechanical strength. The outer surface of the graphite block product is free of cracks and pores, has a uniform structure, an ash content of less than 0.5%, and a bulk density of 1.60-1.64 g / cm³. 3 Flexural strength 6.5–9.0 MPa, coefficient of thermal expansion 2.4–2.7, resistivity 14.3–17.5 μΩ·m.

Description

Technical Field

[0001] This invention relates to the field of graphite heat exchanger accessory manufacturing technology, and in particular to a method for preparing graphite blocks for graphite heat exchangers. Background Technology

[0002] In the chemical industry, heat exchangers, as crucial heat transfer devices, are widely used in various processes. With technological advancements and increasingly stringent environmental regulations, traditional metal heat exchangers can no longer meet the demands of certain special operating conditions. Graphite heat exchangers, as a new type of high-efficiency, corrosion-resistant, and high-temperature resistant heat exchanger, are gradually becoming a focus of attention in the chemical industry. Graphite heat exchangers mainly consist of graphite blocks, seals, and fasteners. The graphite blocks, as the primary heat transfer element, achieve efficient heat transfer between hot and cold fluids through their internal flow channel design. The seals and fasteners ensure a tight connection between the graphite blocks, preventing fluid leakage. Their working principle primarily involves the counter-current or parallel flow of hot and cold fluids within the internal channels of the graphite blocks, achieving heat transfer.

[0003] Currently, graphite blocks are made using graphitized coke and other dry materials, and asphalt as a binder, as raw materials. The process involves mixing, molding, calcining, and graphitizing the raw materials to obtain graphite block products that can be used in the processing of graphite heat exchangers.

[0004] However, existing graphite blocks used in graphite heat exchangers suffer from brittleness due to improper raw material ratios, making them prone to damage during transportation, installation, and use. Furthermore, their relatively low thermal conductivity can also affect heat exchange efficiency. Therefore, a graphite block product suitable for graphite heat exchanger manufacturing is needed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing graphite blocks for graphite heat exchangers, which solves the problem of poor mechanical strength and thermal conductivity of graphite blocks in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing graphite blocks for graphite heat exchangers, comprising the following steps: (1) Ingredients: Weigh 74%-78% of the dry material and the remainder asphalt according to the weight percentage; The dry material, by weight percentage, comprises 60% graphitized coke, 15% needle coke, 10% pitch coke, 5% carbon black, and the remainder being graphitized granules. (2) Heating and kneading: Dry mixing of dry materials to remove moisture, followed by wet mixing of melted asphalt to obtain a paste; (3) Drying: Stir the paste and dry it to remove asphalt fumes, then set it aside for later use; (4) Molding: The paste processed in step (3) is pressed and molded using molding equipment to obtain a graphite block blank; (5) Calcination: The graphite green blocks are calcined in a ring furnace to obtain the graphite green blocks. (6) Graphitization: After graphitizing the graphite block blanks in a graphitization furnace, the blanks are cooled and removed from the furnace to obtain graphite block products.

[0007] Compared with the prior art, the present invention has the following beneficial effects: 1. The preparation method of this invention uses the most suitable raw materials. Through the combination of various components, the graphite block product prepared by this application has good thermal conductivity and mechanical strength. The outer surface of the graphite block product is free of cracks and pores, has a uniform structure, has an ash content of less than 0.5%, and a bulk density of 1.60-1.64 g / cm³. 3 Flexural strength 6.5-9.0 MPa, coefficient of thermal expansion 2.4-2.7, resistivity 14.3-17.5 μΩ·m.

[0008] 2. The graphite block prepared by this invention has a heat transfer performance 4-5 times that of stainless steel, and has high thermal stability and good chemical stability.

[0009] 3. The graphite blocks prepared using this invention can save at least 30% of raw materials compared to traditional production processes. The graphitized coke in the dry material is an auxiliary product generated during the production of graphite anode powder by our company. Graphitized coke has excellent properties such as low ash content, high conductivity, and high thermal stability. The graphitized fragments are waste products after graphitization or processing by our company, as well as cutting debris during the processing of graphite electrodes, achieving cost reduction and recycling.

[0010] Further, in step (1), the graphitized coke is composed of particles with a variety of particle size ranges. By weight percentage, the graphitized coke includes 37-41% of powder with a particle size range of 0-0.075 mm, 32-36% of powder with a particle size range of 0.075-1 mm, 16-20% of powder with a particle size range of 1-2 mm, and 7-11% of powder with a particle size range of 2-5 mm.

[0011] Furthermore, in step (1), The requirements for graphitized coke are: ash content ≤ 0.5%, sulfur content ≤ 0.3%, true density ≥ 2.18 g / cm3, and powder resistivity ≤ 150 μΩ·m; The requirements for needle coke are: expansion coefficient of 3.0x10-6 to 4.0x10-6, sulfur content ≤0.5%, and true density ≥2.10g / cm3; The required specifications for asphalt coke are: ash content ≤ 0.4%, volatile matter ≤ 0.6%, and sulfur content ≤ 0.5%. The requirements for carbon black are: ash content ≤ 0.3%, volatile matter ≤ 0.5%, resistivity ≤ 800 μΩ·m; The required specifications for graphitized granules are: ash content ≤ 0.5%, volatile matter ≤ 0.5%, and sulfur content ≤ 0.3%. The requirements for asphalt are: ash content ≤0.3%, coking value ≥56%, softening point 106℃-112℃, toluene insoluble matter (TI) 28%-32%, and quinoline insoluble matter (QI) 6%-12%.

[0012] Furthermore, in step (2): The dry materials and asphalt are mixed using a kneader. The kneading pot is preheated to 160°C. Under normal pressure, the dry materials are added to the kneading pot and heated to 130-140°C. The dry materials are dry-mixed for 30 minutes to remove the moisture from the dry materials. Then, the asphalt that has been completely melted and allowed to stand for a while and is at a temperature of 175°C is added. The mixture is wet-mixed for 45 minutes until it becomes a paste. The mixture is then discharged from the pot and placed into a hopper.

[0013] Furthermore, in step (3): Place the paste into a preheated mixing drum at a stable temperature of 80°C. After stirring and drying for 10-15 minutes to remove asphalt fumes from the paste, weigh the paste in a weighing device when the paste temperature reaches 130-140°C for later use.

[0014] Furthermore, in step (4): Using vertical molding equipment and vertical molding process, the weighed paste is pressed into a graphite block blank with a diameter of 620mm and a height of 860mm. The maximum pressure of the large cylinder of the molding equipment is 18Mpa, and the pressure holding time is not less than 20min. After pressing and demolding, it is placed in a cooling water tank for cooling for not less than 16 hours.

[0015] Furthermore, in step (5): A ring-type calcining furnace is used. Metallurgical coke particles are laid at the bottom of the ring-type calcining furnace. After the graphite green billet is loaded, the gaps around it and the top are filled with metallurgical coke particles. Under the protection of the protective medium and in the absence of air, the graphite green billet is heated according to the curve heating rate to form a graphite green billet with a diameter of 615 mm and a height of 850 mm.

[0016] Furthermore, the temperature rise process is as follows: The furnace temperature was increased from room temperature to 360℃ at a rate of 4℃ / h over 85 hours, then increased to 360-520℃ at a rate of 1.2℃ / h over 133 hours, then increased to 520-620℃ at a rate of 1.9℃ / h over 53 hours, then increased to 620-730℃ at a rate of 1.7℃ / h over 65 hours, then increased to 730-850℃ at a rate of 2.5℃ / h over 48 hours, then increased to 850-1100℃ at a rate of 3.3℃ / h over 76 hours, then increased to 1100-1200℃ at a rate of 4℃ / h over 25 hours, and finally held at that temperature for 2 hours.

[0017] Furthermore, in step (6), the steps of loading the graphite block blank into the furnace and graphitizing it are as follows: Graphite blocks are loaded into a graphitization furnace in three layers from top to bottom. Multiple graphite blocks in each layer are arranged in a rectangular matrix. The distance between any graphite block and its horizontally adjacent graphite block is 100mm, and the distance between any graphite block and its vertically adjacent graphite block is 105mm. The distance between the first group of graphite blocks at the furnace head and the furnace head wall is 602mm. A guide coke is placed between each graphite block billet, and 8+ resistance material is filled between the graphite blocks to complete the furnace loading operation. The graphite block blank is then heated to 2300-2500℃ using resistance heating for graphitization.

[0018] Furthermore, the graphitization process is as follows: The temperature inside the graphitization furnace is raised at a constant rate to 1600-1700℃ over 56-68 hours, then at a constant rate to 2200-2300℃ over 24-28 hours, and finally to 2500℃ over 6-7 hours. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a top view of the graphite block graphite filling furnace in this invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] This invention provides a method for preparing graphite blocks for use in graphite heat exchangers, thereby improving the mechanical strength and thermal conductivity of the graphite blocks. The process flow is as follows: Figure 1 As shown, the specific steps include the following: 1. Ingredients: The graphite blocks in this invention are made from 74%-78% dry materials and the remainder as asphalt as a binder. They are mainly produced by molding, firing, graphitizing, and machining dry materials and asphalt in different proportions.

[0022] The dry material consists of 60% graphitized coke, 15% needle coke, 10% pitch coke, 5% carbon black, and the balance being graphitized crushed particles by mass percentage.

[0023] Graphitized coke possesses excellent properties such as high-temperature strength, high electrical conductivity, high thermal stability, and chemical stability, and is widely used in electrodes, graphite materials, refractory materials, and semiconductor materials. The graphitized coke in this application is composed of powder materials with various particle size ranges. Specifically, the particle size distribution principle for graphitized coke is as follows: 0-0.075mm particles account for 37-41%, 0.075-1mm particles account for 32-36%, 1-2mm particles account for 16-20%, and 2-5mm particles account for 7-11%. The graphitized coke powder particles of various particle size ranges are obtained through the following processing: The blocky graphitized coke is crushed into small pieces or particles using a crusher for subsequent grinding. The crushed graphitized coke is then fed into a grinding mill for grinding. The ground graphitized coke particles or powder are classified according to different particle sizes and masses using a classifier to obtain graphitized coke powder suitable for different applications. The graphitized coke specifications of this application are: ash content ≤ 0.5%, sulfur content ≤ 0.3%, and true density ≥ 2.18 g / cm³. 3 Powder resistivity ≤150μΩ·m.

[0024] Needle coke possesses a low coefficient of thermal expansion, meaning it does not readily expand in volume when heated, thus maintaining stable structure and properties. Its low internal porosity and dense structure contribute to improved strength and durability. Needle coke readily graphitizes, enabling it to form a stable graphite structure at high temperatures, further enhancing its high-temperature resistance. Its excellent electrical and thermal conductivity makes it suitable for a wide range of applications. Graphitized needle coke is corrosion-resistant and remains stable in harsh chemical environments. It maintains stable performance under rapid temperature changes, resisting thermal cracking or deformation. The coefficient of thermal expansion of the needle coke is 3.0 x 10⁻⁶ to 4.0 x 10⁻⁶, sulfur content ≤ 0.5%, and true density ≥ 2.10 g / cm³. 3 .

[0025] Pitch coke is a high-quality coke with low ash and sulfur content. It has a dense structure and low porosity; the total porosity of pitch coke is lower than that of petroleum coke, approximately 55%-57% for the former and 64%-68% for the latter, resulting in higher mechanical strength and wear resistance. Pitch coke is also a major raw material for producing various graphitized electrodes, graphitized anodes, graphitized blocks, and other graphitized products, as well as prebaked anodes and anode pastes. The pitch coke has an ash content ≤0.4%, volatile matter ≤0.6%, and sulfur content ≤0.5%.

[0026] In carbon production, carbon black has a small particle size and a large surface area, allowing it to absorb a significant amount of binder. Carbon black possesses high strength, wear resistance, and high-temperature resistance, maintaining a stable structure at high temperatures and resisting thermal decomposition or oxidation. Compared to natural graphite, carbon black is relatively inexpensive; therefore, using a certain amount of carbon black to prepare graphite blocks can reduce production costs. The carbon black specified has an ash content ≤0.3%, volatile matter ≤0.5%, and resistivity ≤800 μΩ·m.

[0027] Graphitized fragments are waste products from various graphitized products after graphitization or processing, as well as cutting debris from the processing. The physicochemical properties of graphitized fragments are similar to those of finished graphitized products, primarily characterized by low ash content and good electrical and thermal conductivity. In carbon product manufacturing, recycled graphitized fragments are added to the ingredients of some products at a ratio of 10%-15%, mainly to reduce the resistivity of the products. For products with high ash content, this also helps reduce the ash content. The graphitized fragment particles have an ash content ≤0.5%, volatile matter ≤0.5%, and sulfur content ≤0.3%.

[0028] Pitch has a high carbon residue, so it is often used as a binder in the manufacture of graphite blocks. Adding an appropriate proportion of pitch can result in graphite blocks with advantages such as low thermal expansion, low electrical resistance, long service life, low power consumption, and increased bulk density and mechanical strength. The selected pitch specifications are: ash content ≤0.3%, coking value ≥56%, softening point 106℃-112℃, toluene-insoluble matter (TI) 28%-32%, and quinoline-insoluble matter (QI) 6%-12%.

[0029] 2. Heated mixing: Use a 3000L kneader for mixing. Preheat the kneading pot to 160℃. Under normal pressure, add dry materials of different particle sizes into the kneading pot and heat to 130-140℃. Dry mix for 30 minutes, remove the moisture from the dry materials, and then add asphalt that has been completely melted and allowed to stand for a while at a temperature of 175℃. Wet mix for 45 minutes until it becomes a paste, then remove it from the pot and discharge it into the hopper.

[0030] 3. Drying: Put the paste in the hopper into a drying mixing drum that has been preheated and stabilized at 80℃. After 10-15 minutes of stirring and drying, most of the asphalt fumes in the paste are removed. When the paste temperature reaches 130-140℃, put it into a weighing device for weighing.

[0031] 4. Molding: Using vertical molding equipment and vertical molding process, the weighed paste is pressed into a graphite block blank with a diameter of 620mm and a height of 860mm. The maximum pressure of the large cylinder is required to be 18Mpa, and the holding time is not less than 20min. After pressing and demolding, it is placed in a cooling water tank for cooling for not less than 16 hours.

[0032] 5. Calcination: A ring-type calcining furnace is used. Metallurgical coke particles are laid at the bottom of the ring-type calcining furnace. After the graphite green billet is loaded, metallurgical coke particles are laid in the gaps around it and on top. Under the protection of the protective medium and in the absence of air, the graphite green billet is heated according to the curve heating rate to form a graphite green billet with a diameter of 615mm and a height of 850mm.

[0033] The specific temperature rise curve is as follows: First, the furnace temperature of the roasting furnace is increased from room temperature to 360℃ at a rate of 4℃ / h, taking 85h; then, it is increased from 360-520℃ at a rate of 1.2℃ / h, taking 133h; then, it is increased from 520-620℃ at a rate of 1.9℃ / h, taking 53h; then, it is increased from 620-730℃ at a rate of 1.7℃ / h, taking 65h; then, it is increased from 730-850℃ at a rate of 2.5℃ / h, taking 48h; then, it is increased from 850-1100℃ at a rate of 3.3℃ / h, taking 76h; then, it is increased from 1100-1200℃ at a rate of 4℃ / h, taking 25h; and finally, it is held at the temperature for 2h.

[0034] 6. Graphitization: The average height of the graphite block blanks is 850mm, and the height of the graphitization furnace electrode is 2460mm. Therefore, this application sets up a graphitization furnace body that can load 3 layers of graphite block blanks.

[0035] The graphite ingots are loaded into the furnace according to their own dimensions and the furnace interior, in 3 layers and 50 sets. Figure 2 As shown, each group has 4 horizontal groups, and the graphite blocks are arranged in a rectangular array. The spacing between the horizontal groups is 100mm, and the distance from the outer edge of the graphite blocks on both sides to the furnace core plates on both sides is also 100mm. The spacing between the vertical groups is 105mm. The distance between the first group of graphite blocks at the furnace head and the furnace head wall is 602mm.

[0036] It is worth noting that those skilled in the art refer to the graphitization furnace as "front" and "rear" along its length. Therefore, the rectangular array of graphite blocks is based on their positions at the front and rear of the furnace, using coordinates as references. Figure 2 The distance markings are correct.

[0037] Sufficient guide coke is placed between each graphite block blank, and 8+ resistance material is filled between the graphite blocks. The resistance material must be packed tightly to prevent arcing caused by poor material contact during power supply. The graphite blocks are heated to 2300-2500℃ using resistance heating.

[0038] The heating method for graphitization involves first uniformly raising the temperature inside the graphitization furnace to 1600-1700℃ over 56-68 hours, then uniformly raising it to 2200-2300℃ over 24-28 hours, and finally raising it to 2500℃ over 6-7 hours. To avoid cracks and fractures, power is supplied slowly, resulting in a longer power supply curve period; the power supply curve duration is 120 hours, the power output is 18000 kW, and the total power supply is 850,000 kWh.

[0039] After graphitization, the product is cooled and removed from the furnace using conventional methods to obtain graphite blocks. The graphite blocks can then be machined (cut, drilled, or otherwise mechanically operated) according to subsequent production needs.

[0040] It is worth noting that, to further conserve energy, this application utilizes the waste heat from the calcination process for heating the asphalt. Specifically, the heat transfer system uses the waste heat generated by the tank-type calcination furnace in the calcination workshop as a heat source. This waste heat is then transferred to the heat transfer oil via a heat pipe boiler through radiation and convection. The heat transfer oil circulates within the system via a circulating pump, and the heated high-temperature heat transfer oil exchanges heat with the working medium, asphalt, in a heat exchange device, thus achieving the purpose of heating the asphalt. Therefore, the preparation method of this application also has energy-saving and environmentally friendly effects.

[0041] To verify the suitability of the various performance characteristics and proportions of the products of this application, this application will demonstrate the data through Examples 1-3 and Comparative Examples 1-4.

[0042] Examples 1-3 and Comparative Examples 1-4 were all prepared using the above-described preparation process, differing only in the proportions of the various substances in the dry material and the ratio of asphalt to the dry material, as shown in Table 1. Table 1: The basic performance parameters of each graphite block prepared based on Examples 1-3 and Comparative Examples 1-4, tested according to national standards, are shown in Table 2.

[0043] Table 2: According to the data in Tables 1 and 2, specifically Example 1 and Comparative Examples 3 and 4, it can be seen that changes in the ratio of graphitized coke and pitch coke in the dry material affect the coefficient of thermal expansion and resistivity of the product, thus reducing the product's relevance.

[0044] Based on the data from Examples 1 and 2 (Comparative Examples 2 and 4) in Tables 1 and 2, it can be seen that carbon black has a significant impact on the mechanical strength of the product, and its use is indispensable. Excessive or insufficient needle coke content in the dry material affects the mechanical properties, thermal conductivity, and electrical conductivity of the product.

[0045] According to the data in Tables 1 and 2, specifically Example 1 and Comparative Example 1, it can be seen that a low content of graphitized fragments affects the mechanical strength of the product.

[0046] The graphite blocks prepared in this application possess high thermal conductivity, especially in the planar direction, where their thermal conductivity can reach several times that of metals. This enables graphite heat exchangers to efficiently transfer heat during heat exchange, achieving high-efficiency heat exchange. Therefore, graphite heat exchangers are widely used in applications requiring efficient heat conduction, such as heating, cooling, and waste heat recovery processes in chemical, power, and metallurgical industries. The graphite blocks can withstand high temperatures and possess good compressive strength. This allows graphite heat exchangers to maintain stable heat exchange performance even under high-temperature and high-pressure environments. Graphite heat exchangers are widely used in applications requiring high-temperature and high-pressure heat exchange, such as waste heat recovery from blast furnace gas and waste heat recovery from power plant boilers.

[0047] Chemical plant production processes involve large amounts of corrosive acids and alkalis. Traditional metal heat exchangers suffer from insufficient corrosion resistance and frequent maintenance. Graphite heat exchangers, however, offer superior corrosion resistance and lower maintenance costs. After installation, they effectively improve heat exchange efficiency, reduce energy waste, and, due to the self-lubricating properties and low expansion coefficient of graphite, significantly extend the equipment's lifespan, avoiding the cost burden of frequent replacements and maintenance.

[0048] The graphite blocks produced in this application exhibit lower ash content and a cleaner appearance compared to previous methods. Through practical application by downstream manufacturers, these graphite blocks have shown significantly improved antioxidant and corrosion-resistant properties.

[0049] In summary: 1. The preparation method of this invention uses the most suitable raw materials. Through the combination of various components, the graphite block product prepared by this application has good thermal conductivity and mechanical strength. The outer surface of the graphite block product is free of cracks and pores, has a uniform structure, has an ash content of less than 0.5%, and a bulk density of 1.60-1.64 g / cm³. 3 Flexural strength 6.5-9.0 MPa, coefficient of thermal expansion 2.4-2.7, resistivity 14.3-17.5 μΩ·m.

[0050] 2. The graphite block prepared by this invention has a heat transfer performance 4-5 times that of stainless steel, and has high thermal stability and good chemical stability.

[0051] 3. The graphite blocks prepared using this invention can save at least 30% of raw materials compared to traditional production processes. The graphitized coke in the dry material is an auxiliary product generated during the production of graphite anode powder by our company. Graphitized coke has excellent properties such as low ash content, high conductivity, and high thermal stability. The graphitized fragments are waste products after graphitization or processing by our company, as well as cutting debris during the processing of graphite electrodes, achieving cost reduction and recycling. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing graphite blocks for a graphite heat exchanger, characterized in that: Includes the following steps: (1) Ingredients: Weigh 74%-78% of the dry material and the remainder asphalt according to weight percentage; The dry material, by weight percentage, comprises 60% graphitized coke, 15% needle coke, 10% pitch coke, 5% carbon black, and the remainder being graphitized granules. (2) Heating and kneading: Dry mixing of dry materials to remove moisture, followed by wet mixing of melted asphalt to obtain a paste; (3) Drying: Stir the paste and dry it to remove asphalt fumes, then set it aside for later use; (4) Molding: The paste processed in step (3) is pressed and molded using molding equipment to obtain a graphite block blank; (5) Calcination: The graphite green blocks are calcined in a ring furnace to obtain the graphite green blocks. (6) Graphitization: After graphitizing the graphite block blanks in a graphitization furnace, the blanks are cooled and removed from the furnace to obtain graphite block products.

2. The method for preparing graphite blocks for a graphite heat exchanger according to claim 1, characterized in that: In step (1), the graphitized coke is composed of particles with a variety of particle size ranges. By weight percentage, the graphitized coke includes 37-41% of powder with a particle size range of 0-0.075 mm, 32-36% of powder with a particle size range of 0.075-1 mm, 16-20% of powder with a particle size range of 1-2 mm, and 7-11% of powder with a particle size range of 2-5 mm.

3. The method for preparing graphite blocks for a graphite heat exchanger according to claim 1 or 2, characterized in that: In step (1), The required specifications for graphitized coke are: ash content ≤ 0.5%, sulfur content ≤ 0.3%, and true density ≥ 2.18 g / cm³. 3 Powder resistivity ≤150μΩ·m; The required specifications for needle coke are: an expansion coefficient of 3.0 x 10⁻⁶. -6 -4.0x10 -6 Sulfur content ≤0.5%, true density ≥2.10 g / cm³ 3 ; The required specifications for asphalt coke are: ash content ≤ 0.4%, volatile matter ≤ 0.6%, and sulfur content ≤ 0.5%. The requirements for carbon black are: ash content ≤ 0.3%, volatile matter ≤ 0.5%, resistivity ≤ 800 μΩ·m; The required specifications for graphitized granules are: ash content ≤ 0.5%, volatile matter ≤ 0.5%, and sulfur content ≤ 0.3%. The requirements for asphalt are: ash content ≤0.3%, coking value ≥56%, softening point 106℃-112℃, toluene insoluble matter (TI) 28%-32%, and quinoline insoluble matter (QI) 6%-12%.

4. The method for preparing graphite blocks for a graphite heat exchanger according to claim 1, characterized in that: In step (2): The dry materials and asphalt are mixed using a kneader. The kneading pot is preheated to 160°C. Under normal pressure, the dry materials are added to the kneading pot and heated to 130-140°C. The dry materials are dry-mixed for 30 minutes to remove the moisture from the dry materials. Then, the asphalt that has been completely melted and allowed to stand for a while and is at a temperature of 175°C is added. The mixture is wet-mixed for 45 minutes until it becomes a paste. The mixture is then discharged from the pot and placed into a hopper.

5. The method for preparing graphite blocks for a graphite heat exchanger according to claim 1, characterized in that: In step (3): Place the paste into a preheated mixing drum at a stable temperature of 80°C. After stirring and drying for 10-15 minutes to remove asphalt fumes from the paste, weigh the paste in a weighing device when the paste temperature reaches 130-140°C for later use.

6. The method for preparing graphite blocks for a graphite heat exchanger according to claim 1, characterized in that: In step (4): Using vertical molding equipment and vertical molding process, the weighed paste is pressed into a graphite block blank with a diameter of 620mm and a height of 860mm. The maximum pressure of the large cylinder of the molding equipment is 18Mpa, and the pressure holding time is not less than 20min. After pressing and demolding, it is placed in a cooling water tank for cooling for not less than 16 hours.

7. The method for preparing graphite blocks for a graphite heat exchanger according to claim 1, characterized in that: In step (5): A ring-type calcining furnace is used. Metallurgical coke particles are laid at the bottom of the ring-type calcining furnace. After the graphite green billet is loaded, the gaps around it and the top are filled with metallurgical coke particles. Under the protection of the protective medium and in the absence of air, the graphite green billet is heated according to the curve heating rate to form a graphite green billet with a diameter of 615 mm and a height of 850 mm.

8. The method for preparing graphite blocks for a graphite heat exchanger according to claim 7, characterized in that: The temperature rise process is as follows: The furnace temperature was increased from room temperature to 360℃ at a rate of 4℃ / h over 85 hours, then increased to 360-520℃ at a rate of 1.2℃ / h over 133 hours, then increased to 520-620℃ at a rate of 1.9℃ / h over 53 hours, then increased to 620-730℃ at a rate of 1.7℃ / h over 65 hours, then increased to 730-850℃ at a rate of 2.5℃ / h over 48 hours, then increased to 850-1100℃ at a rate of 3.3℃ / h over 76 hours, then increased to 1100-1200℃ at a rate of 4℃ / h over 25 hours, and finally held at that temperature for 2 hours.

Images