I. Mechanical Strength and Influencing Factors

1. Compressive strength: The ultimate resistance of a material at the moment it is crushed under an external compressive force.

Flexural strength: The ultimate resistance of a material to bending, measured as the maximum load it can withstand before fracturing when an external force is applied perpendicular to the object’s axis.

Tensile strength: The ultimate resistance of a material at the moment it breaks under tensile stress.

2. Influencing factors:

(1) Particle Strength Coefficient

(2) Ingredients

(3) Binder

(4) Calcination.

II. What is a prebaked anode?

Prebaked anodes (code name TY) are conductive anodes used in aluminum electrolytic cells. The raw materials for producing prebaked anodes include petroleum coke, needle coke, and coal tar pitch. These materials undergo a series of processes—including calcination, crushing and blending, kneading, shaping, and roasting—to produce the final product.

III. What are the different categories of petroleum coke?

Depending on the coking process used, petroleum coke can be classified into delayed petroleum coke and kettle coke. Currently, delayed coke produced via the delayed coking process is the most widely adopted type.

4. What are the characteristics of modified asphalt when used as a binder in carbon production?

1. Coking: A high residual carbon value results in more cohesive coke formation during roasting, leading to higher mechanical strength of the finished product. 2. High softening point makes it easier to address long-distance transportation and handling issues during summer.

3. During the kneading and molding process, fewer fumes are emitted from the asphalt, which helps reduce environmental pollution.

4. When using modified asphalt, the temperatures of the asphalt conveying pipeline, the mixing and kneading temperature, and the temperature of the forming and feeding chamber must all be raised accordingly. The melting temperature of this asphalt is also higher than that of medium-temperature asphalt.

5. Modified asphalt contains a higher proportion of β-resin and secondary QI, exhibiting superior thermal stability, which helps improve the quality of carbon block products.

5. Why is petroleum coke crushed before calcination?

If the petroleum coke lumps are too large, not only will it be difficult to ensure uniform quality of the calcined coke in the calcination process, but also—limited by the calcination equipment—it will create difficulties in discharging and feeding materials and reduce the efficiency of the intermediate crushing equipment. Therefore, before calcination, carbonaceous raw materials must be pre-crushed to a medium-sized lump size of around 40 mm to ensure that both large and small lumps receive uniformly heated temperatures during calcination. However, the carbonaceous raw materials should not be crushed too finely either; otherwise, excessive fines will be produced, leading to increased burn-off losses.

Six, what is calcination?

The process of thermally treating carbonaceous raw materials at high temperatures (1200–1350ºC) under air-isolated conditions is called calcination. Calcination is the first thermal treatment step in carbon production, and it induces a series of structural, physical, and chemical changes in various carbonaceous raw materials.

7. What is the purpose of calcining petroleum coke feedstock? What are the quality indicators for calcination?

The purpose is:

1. Remove moisture and volatile components from petroleum coke;

2. Increase the density and mechanical strength of petroleum coke;

3. Improve the electrical conductivity of petroleum coke;

4. Enhance the anti-oxidation performance of petroleum coke.

The calcination quality of petroleum coke is typically controlled by two indicators: powder specific resistivity and true density. The higher the degree of calcination of petroleum coke, the lower its powder specific resistivity after calcination, and the higher its true density.

8. What precautions should be taken during the production operation of a retort kiln?

1. Temperature control;

2. Add discharge material;

3. Sealing of the calcination furnace and cooling of the calcined material;

4. Mix proportion and particle size requirements.

9. How can we prevent coking and furnace blockage when calcining high-temperature volatile petroleum coke?

1. Maintain the base material and appropriately increase the temperature of the first-layer flue gas passage, enabling the petroleum coke added into the furnace to rapidly release large amounts of volatile components shortly after entering the furnace, thereby reducing the likelihood of coking and furnace blockage.

2. Add materials frequently, but avoid adding too much at each feeding. At the same time, employ a continuous feeding and discharging mechanism to keep the material inside the tank constantly loose and prevent it from clumping into large chunks.

3. Maintain a high negative pressure and regularly clean the outlet for volatile components as well as the collection duct for volatiles.

10. What are the main factors that affect the temperature of a calcination furnace?

1. The effect of volatile matter;

2. The impact of air volume;

3. The impact of negative pressure.

11. How can we ensure normal calcination operations in the calciner?

Raw materials are stored separately in hoppers according to their different properties. To prepare for equipment maintenance, a certain quantity of pre-crushed raw materials must be kept in reserve. To meet the calcination requirements, the particle size of the pre-crushed raw materials must not exceed 40 mm. In the raw material storage area, the calcined blended coke must be thoroughly mixed and accurately proportioned. After being measured and weighed, the pre-crushed raw materials are transported via conveyor belts into feeding hoppers. From the feeding hoppers, the raw materials are intermittently or continuously fed into the calcination kiln for calcination. The feeding process should be carried out regularly, in appropriate amounts, and uniformly, matching the discharge rate.

In terms of calcination operations, the key is to properly control the temperatures of each layer of flue gas channels and the exhaust gas temperature. The flue gas channel temperatures can be regulated by adjusting the fuel consumption, flue gas negative pressure, air preheating temperature, and the rational utilization of volatile components. After calcination, the material is cooled down through a water jacket and then discharged via a discharging device. The discharged material should not contain any red-hot particles; afterward, the discharged material is conveyed to the next processing stage using the discharging equipment.

12. How to properly use a double-roll crusher?

1. Start the machine under no-load conditions; it is strictly prohibited to start the machine when there are materials inside the crushing chamber.

2. Regularly inspect the wear condition of the roller covers and promptly repair or replace them as needed.

3. Ensure that the feed material is evenly distributed; otherwise, the roller shell will wear out more quickly. Also, pay attention to the size of the feed particles. 4. Be sure to monitor the machine’s lubrication and the temperature of the bearings.

5. When shutting down, first stop feeding material and then shut down the machine only after the material has been completely discharged.

13. What factors affect ball mill production?

1. The rotational speed of the ball mill;

2. Ball loading capacity;

3. Lining plate shape;

4. Ball mill diameter;

5. Operational status.

14. How to Use a Ball Mill Correctly?

1. Before starting up, check the flexibility of each component, the position of the clutch, and tighten all fasteners.

2. Regularly inspect the lubrication system, especially the lubrication of the main bearings and the gearbox.

3. If abnormal noises occur, stop the machine and perform an inspection.

4. The clearance and contact area of meshing gears must be adjusted appropriately.

5. If the lining plates are excessively worn or have come loose, they should be replaced and repaired promptly.

6. Regularly select balls and replenish steel balls.

7. Pay special attention to ensuring the concentric alignment of the shaft ends at both ends.

15. How do we perform screening? What is screening?

The process of separating materials into several particle size levels based on their different sizes using a sieve is called sieving.

16. What factors affect screening efficiency?

1. The properties of the material;

2. Types and structural parameters of screen surfaces;

3. Operating conditions.

17. What are the types of screening machines and screen surfaces?

1. Vibrating screen;

2. Cylindrical screen;

3. Cabinet screening;

4. Shake the sieve.

18. How to properly use a vibrating screen?

1. Before starting the screen, conduct a comprehensive inspection: ensure that all fasteners are securely tightened; check whether electrical components have failed; verify that the main shaft of the vibrating (screen) unit rotates smoothly and that the bearings are well-lubricated.

2. The startup sequence for the sieve is as follows: First, start the dust-proof device; then, start the sieve itself. After it has reached normal operation, begin feeding material evenly. The shutdown sequence is the reverse of this.

3. While the sieve is in operation, pay close attention to the bearing temperature and the condition of the lubrication system.

4. During operation, pay attention to whether the screen is making any loud noises. The screen’s vibration should be balanced, and there must be no abnormal swinging or oscillation. If any swinging or oscillation occurs, check whether the elasticity of the four support springs is consistent and whether any of them are broken.

5. During operation, the vibrating screen should be regularly inspected for wear. If any parts are found to be excessively worn, they should be replaced promptly.

6. Regularly check whether the screen mesh is loose or if any material leakage occurs due to localized wear of the mesh. If any issues are found, immediately stop the machine and carry out repairs.

19. What factors affect the production capacity of a vibrating screen?

1. Screen mesh area;

2. Vibration frequency and amplitude;

3. Screen mesh inclination;

4. Feeding conditions.

20. What causes the screening to fail to meet the standards?

In carbon production, many factors influence the purity of the screening process, including the amount of feed material, the uniformity of the feed, the shape of the screen openings, the motion mode of the screen surface, the particle shape of the material, and its moisture content. If the feed quantity is too high, the layer of material on the screen becomes excessively thick, which can reduce the purity. Uneven feeding can lead to unstable purity levels. In carbon production, inertia vibrating screens with square-shaped screen openings are widely used. The reciprocating motion and vertical vibration of the screen surface facilitate contact between material particles and the screen openings, while the relatively large movement between the material blocks and the screen surface helps improve the screening purity.

21. What are the key aspects involved in the raw material preparation for carbon production?

1. Select the type of carbonaceous raw material;

2. Determine the proportions of different types of raw materials;

3. Determine the particle size distribution of the solid carbon raw material;

4. Determine the softening point and dosage of the binder.

22. How can the batching position ensure stable material mixing?

To ensure the stability of the particle size of product ingredients, on the one hand, samples should be regularly taken from each storage hopper for sieve analysis to check whether the purity of the ingredients is fluctuating. If excessive fluctuations are detected, corrective measures should be taken promptly.

On the one hand, it is necessary to regularly take samples of materials of various particle sizes from the storage hopper and conduct sieve analysis according to the percentage composition specified in the formulation, checking whether they meet the technical requirements. If they do not meet the requirements, the batching process should be immediately halted, the formulation adjusted or updated, or the nonconforming materials removed until the requirements are satisfied before resuming batching. The batching equipment must be inspected regularly to ensure its accuracy and prevent batching errors. Weighing must be carried out strictly according to the batching schedule and performed swiftly and accurately, without exceeding the prescribed tolerance limits.

23. What is the function of the binder?

1. It exhibits excellent wettability and binding strength toward carbonaceous materials, which ensures that the paste has good plasticity.

2. The binder should have a high carbon content and a high coking value.

3. The binder should be a thermoplastic material that is solid at room temperature, melts into a liquid upon slight heating, and hardens immediately upon cooling.

4. Wide availability and low price.

24. How do you determine the amount of binder to use?

1. Composition of the binder in the product formulation;

2. Properties of material particles;

3. Molding method.

25. What is kneading? What role does it play in carbon production?

Solid carbon raw material particles and powders are mixed with a binder and stirred at a specific temperature to form a plastic paste. This production process is known as kneading. In carbon production, kneading serves the following three purposes:

1. Ensure uniform mixing of various raw materials, while also achieving even blending and filling of particles of different sizes, thereby forming a mixture with high compactness.

2. It facilitates the uniform mixing of materials and binders, ensuring that the liquid binder is evenly coated onto the surface of the dry material particles. The binding force of the binder then holds all the particles together, imparting plasticity to the paste and enabling it to be shaped into desired forms.

3. Allow the binder to partially penetrate the pores of the dry material particles, further enhancing the binding performance and compactness of the paste.

26. Why is it necessary to control the dry-mixing temperature of dry ingredients?

If the dry-mixing temperature of the dry ingredients is too low, the moisture already adsorbed onto the surface of the solid carbonaceous raw material particles cannot be removed. This moisture forms a highly adhesive layer on the particle surfaces, significantly reducing the asphalt's wetting effect on the solid carbonaceous raw material particles.

If, during dry mixing, the temperature of the various dry-material particles is lower than the temperature of the liquid asphalt being added, when the asphalt comes into contact with the dry-material particles, the asphalt’s temperature will drop slightly, thereby increasing its viscosity and impairing the asphalt’s ability to wet and penetrate the dry materials. This results in poor plasticity of the paste and a decline in the quality of paste kneading. Therefore, it is essential to ensure that the dry-mixing temperature of the dry materials is close to the temperature of the liquid asphalt being added—typically, the dry-material temperature should be about 10ºC lower than the asphalt temperature.

27. How do you control the mixing temperature of the paste?

The optimal kneading temperature for the paste depends on the softening point of the binder. Generally, the kneading temperature should be set 50 to 80ºC higher than the softening point of the binder. When using medium-temperature asphalt, the kneading temperature is best maintained within the range of 115 to 150ºC, with around 130ºC being the most suitable. When using modified asphalt, the kneading temperature should be raised to between 160 and 180ºC.

During the kneading process, the kneading temperature must not be allowed to drop below the specified level; otherwise, the binder’s ability to wet the aggregate particles and the fluidity of the paste will be reduced, making kneading more difficult. Therefore, when the heating temperature is low, the kneading time should be extended until the target temperature is reached before adding the binder. The kneading temperature is also somewhat influenced by the climate: in winter, when temperatures are low, the paste cools down rapidly after being removed from the mixer. Consequently, the kneading temperature in winter should be slightly higher than in other seasons.

28. How to operate the kneading pot correctly?

1. Before starting the machine, check the oil level in the reducer and the lubrication condition of the bearings, and verify that all fasteners are securely tightened.

2. After starting the equipment, regularly check the temperature, sound, and vibration levels of the motor, reducer, and bearing housing. During operation, the rotating parts of the kneading pot should remain balanced, with no impact noises and smooth gear meshing without any unusual sounds. The temperature of each bearing should not exceed 70ºC, and the motor current should remain stable. If any abnormalities are detected, immediately stop the machine.

3. The material feeding should be uniform to prevent foreign objects from entering.

4. Before shutting down, first stop feeding material; wait until the material inside the machine is mostly emptied before turning off the machine.

29. On what basis is the kneading time determined?

1. When the kneading temperature is lower, the kneading time can be appropriately extended; when the kneading temperature is higher, the kneading time can be appropriately shortened.

2. Using a binder with a lower softening point can allow for a slight reduction in kneading time at the same kneading temperature. 3. The more fine powder particles there are in the ingredients, the longer the kneading time should be appropriately extended.

4. When adding fresh crumb, the kneading time should be appropriately extended.

5. If the machine stops unexpectedly during kneading, keep it insulated and extend the kneading time.

30. What factors affect the quality of kneading?

1. Temperature;

2. Time;

3. Properties of dry ingredients;

4. Binder.

31. Why can't dry ingredients be used to adjust the mix when there’s too much asphalt?

The amount of binder coal pitch used depends on the surface characteristics of the carbonaceous raw material particles and their adsorption capacity for the pitch. Adding a specified amount of pitch as prescribed ensures that the paste is uniformly mixed and exhibits good plasticity. During the kneading process, if too much dry material is added, pitch can be added to adjust the mixture. However, if the amount of pitch is excessive, no additional dry material should be added for adjustment. This is because the dry material particles have poorer fluidity than liquid pitch and cannot be evenly distributed throughout the paste; instead, they tend to clump together in localized areas, resulting in the phenomenon of "dry material inclusion" and leading to an uneven paste quality.

32. Why is it necessary to immediately cool the green body after pressing?

The green bodies freshly produced by the forming machine are made of a plasticizable paste containing a binder—coal tar pitch—which gives them a viscous consistency. At this stage, the green bodies still lack stability in both shape and size. Therefore, immediately after leaving the forming machine, the green bodies must be sprayed with water and then immersed in cool water for cooling, bringing their temperature down below the softening point of the pitch. As the pitch cools and solidifies again, the green bodies attain dimensional stability, preventing them from bending or deforming. The temperature of the cooling water should not exceed 30ºC. Generally, large-sized green bodies should be soaked in cool water for 3 to 5 hours, while medium- and small-sized green bodies should be soaked for 1 to 3 hours, ensuring that they cool thoroughly. In summer, green bodies extruded during hotter periods should be allowed to cool for a longer duration.

33. How does uneven green-body density arise?

1. Carbon paste is thermoplastic and exhibits certain viscoelastic properties. Its ability to transmit pressure is inferior to that of liquids, and the pressure within the paste decreases gradually, resulting in uneven green-body density.

2. Friction between the paste and the mold wall, as well as friction among paste particles, leads to pressure loss, resulting in uneven pressure distribution and consequently, uneven density.

3. The anisotropic particles in the slip exhibit different orientations at the surface and interior of the green body, which affects the uniformity of the green-body density.

34. What is roasting?

The firing of the green products after forming is an indirect heating process carried out in a firing furnace, using thermal gas as fuel and employing a protective medium under air-isolated conditions, with a specified heating rate.

35. What is the purpose of roasting?

After calcination, the binder in the carbon products is converted into coke, forming a coke-carbon network that tightly bonds the carbon powder particles together, thereby creating a monolithic structure with a fixed geometric shape, specific mechanical properties, and defined physicochemical characteristics.

1. Remove volatile components;

2. Reduce resistivity to improve the conductivity of the product;

3. Further reduce the volume and alter its physicochemical properties;

4. Create conditions for the graphite processing procedure;

5. Carbonize the binder coal pitch.

36. What is the essence of roasting?

During the pyrolysis and coking processes of binder coal pitch, the primary changes with increasing temperature are decomposition and polymerization reactions.

37. What are the basic requirements for the roasting process?

The calcined product must ensure that the coal pitch produces the maximum amount of coke formation. At the same time as maximizing coke formation, the entire green body must be heated uniformly, have a correct geometric shape, and be free from internal and external defects (i.e., free from internal and external cracks, uniform carbon distribution across the product’s cross-section, and free from bubbles, etc.).

38. What are the different temperature-raising stages for fired products?

The roasting process is divided into:

1. Preheating stage;

2. The mid-temperature stage with intensifying changes;

3. High-temperature calcination stage;

4. Cooling stage.

39. What are the warning signs of a chimney fire?

1. The temperature of the main flue gas duct is rising sharply,

The current of the two smoke exhaust fans is fluctuating significantly, and the negative pressure in the main flue is decreasing and also fluctuating considerably.

3. Exhaust gases cannot be discharged, the furnace chamber is emitting black smoke, and the chimney is emitting black smoke.

40. What to do if the flue catches fire?

1. Stop the smoke exhaust fan and shut down the butterfly valves at the inlet and outlet of the fan.

2. Locate the source of the fire and extinguish it using steam injection or water.

3. After confirming that the fire has been extinguished, conduct a test run and resume production.

4. Report to the dispatcher and leaders.

41. How to handle a sudden power outage?

(1) Power outage in the entire workshop

1. Immediately turn off the gas valve;

2. Adjust the furnace negative pressure;

3. Inquire about the cause of the power outage and its duration;

(2) The smoke exhaust fan suddenly loses power.

1. Close the gas valve;

2. Ask the electrician to activate the backup smoke exhaust fan.

3. If the standby smoke exhaust fan fails to start, have the relevant personnel address the fault and promptly report to the appropriate supervisors.

42. How does the particle size of the filler material affect the firing process of the product?

If the filler particle size is too large, it can easily lead to ignition of the filler and the finished product, as well as deformation of the carbon blocks. If the particle size is too small, it hinders the escape of volatile components from the product, results in poor thermal conductivity, causes the filler to clump easily, and requires a longer time to reach the same temperature.

43. What is the function of the filling material used in roasting?

1. Prevent product oxidation;

2. Conduct heat to ensure uniform heating of the product;

3. Fix the shape of the product to prevent deformation;

4. It hinders the smooth removal of volatiles while simultaneously facilitating their extraction.

44. What are the influencing factors in the roasting process?

Temperature and pressure, filler material, furnace condition, loading quality, and the properties of the green body.

45. What are the criteria for selecting fillers?

1. Does not melt at the highest firing temperature;

2. It does not readily undergo chemical reactions with products and refractory materials;

3. Should have good thermal conductivity;

4. The volume of the particles should not undergo significant changes when heated.

5. Has a certain particle size;

6. Abundant resources, inexpensive, non-polluting, and easy to produce.

46. What are the bases for developing a roasting curve?

1. Develop a curve based on the different chemical changes that occur at various temperature stages during the heating process of the product.

2. Develop curves based on the product type and specifications.

3. Develop a curve based on the furnace’s structural design.

4. Develop curves based on the type of fuel and the type of filler material.

5. Different curves shall be established based on the number of furnace chambers in operation in the annular chamber roasting furnace.

6. Different curves are formed according to the different shaping methods used for the green body.

7. Develop a curve based on the desired product output quantity.

47. Furnace loading process?

1. Before loading the furnace, first clean the furnace bottom thoroughly and spread a layer of sawdust measuring 10–15 mm thick. Then place at least 250 mm of filler material on top of the sawdust.

2. Arrange the green bodies neatly in the furnace, ensuring that the distance between the furnace walls and the products is no less than 60 mm. After completing one layer of green bodies, cover them with a filling material at least 60 mm thick before proceeding to the second layer. Repeat this process until the final layer is loaded. The covering layer of filling material should be at least 400 mm thick, and after adding another 250 mm of powder on top, the furnace loading is complete.

48. The temperature adjustment process of the roasting furnace?

1. Check the difference between the shift handover temperature and the physicochemical temperature, and develop this shift’s heating curve.

2. Adjust the fire passages, smoke flues, negative pressure of the exhaust fan, and gas pressure according to the temperature rise.

3. Strictly adhere to the firing curve. If the temperature exceeds the allowable fluctuation range, it must be adjusted back to normal within 20 minutes.

4. Strictly control the negative pressure: The negative pressure at the inlet of the smoke exhaust fan should exceed 2500 Pa, the negative pressure in the smoke duct should exceed 1000 Pa, and the negative pressure in the flue should be maintained within a range of 5 to 25 Pa, with the target being the temperature-adjusting furnace chamber.

5. During the heating process, if the temperature drops due to oil shutdown or other reasons, it is permissible to return to normal conditions at three times the speed of the current temperature range.

6. During the heating process, ensure a gradual temperature increase and strictly prohibit sudden rises or drops in temperature.

7. The smoke coming from the chimney should be white, and the flue gas temperature should be maintained between 120 and 150ºC.

49. Why is it necessary to hold the temperature at its highest value for a period of time after it has been raised to the maximum?

The goal is to minimize the temperature difference between horizontal and vertical directions, ensure uniform heating both inside and outside, and achieve consistent quality throughout all parts of the baked product.

50. What four aspects are covered by the roasting temperature curve?

1. Duration of the roasting process.

2. The rate of temperature increase;

3. The highest temperature;

4. Holding time at the maximum temperature.

51. What causes oxidation?

1. The filling material at the top of the product is too thin;

2. Material leakage occurs in certain parts of the furnace during high-temperature firing. (Main cause)

3. The temperature was too high when the product came out of the furnace, and the products were packed too closely together, failing to disperse in time.

4. The filling material loaded is damp; after being heated at high temperature, its volume shrinks, resulting in less material at the top of the product and exposing the filling material at the bottom.

52. The antioxidant properties of the anode?

The oxidizability is influenced by factors such as the heat treatment temperature, impurity content, degree of lattice structure integrity, porosity level, and gas pressure.

53. What are the operational precautions for temperature adjustment operators in a roasting furnace?

1. When moving the pipe, make your movements quick.

2. The furnace chamber must maintain a certain negative pressure.

3. When the gas pressure falls below the required level, effective measures must be taken.

54. What are the advantages of a rotary kiln?

The product has high mechanical strength, excellent quality, convenient temperature adjustment and control, high thermal efficiency, and high output.

55. What are the effects of excessively rapid heating and cooling rates in a roasting furnace on product quality?

Rapid heating causes a significant number of hydrocarbons to evaporate before they have sufficient time to decompose and polymerize, resulting in the loss of many carbon atoms that could otherwise be converted into coke, thus lowering the coke yield. On the other hand, rapid heating also widens the temperature gradient within the furnace chamber, causing the product to undergo decomposition and polymerization reactions at different stages. This leads to inconsistent expansion and contraction between the inner and outer layers of the product, resulting in cracks and negatively affecting product quality. By contrast, slow heating allows hydrocarbon molecules ample time to fully decompose and polymerize. Consequently, the amount of coke formed in the product increases, thereby enhancing the overall product quality.

As required, the temperature must be reduced by 50ºC per hour until it reaches 80ºC. If the temperature is lowered too rapidly, the product may crack, develop fissures, and become scrap.

56. What is the normal ignition sequence for a roasting furnace?

To start the furnace, the procedure is the reverse of shutting it down: First, close the main flue damper, then start the draft fan. Next, install the burner rack and ensure that all equipment is properly positioned (including the temperature-measuring rack). Afterward, notify the gas station to supply gas, check the gas pressure and gas venting, and once everything is normal, adjust the negative pressure in each flue to begin the heating process.

57. What is the purpose of a pipe?

It is a medium that connects the flue and the fire chamber. At the point where the pipe connects to the fire chamber, there is a flap that helps regulate negative pressure.

58. What are the functions of exhaust fans and cooling fans?

The exhaust fan draws heat out of the cooling furnace chamber, while the supply fan blows air into the furnace chamber. These two fans serve different purposes: the exhaust fan removes heat from the cooling furnace chamber to cool the product, whereas the supply fan delivers air into the cooling furnace chamber, providing a certain cooling effect and also acting as secondary air to help cool the high-temperature furnace chamber. The supply fan is also known as a cooling fan or secondary fan; it’s installed inside the cooling furnace chamber to blow cold air.

a. Lower the furnace chamber temperature after the roasting furnace has been completed;

b. Supply hot air generated after fuel combustion. The induced-draft fan is mounted behind the forced-draft fan.

59. Why do smoke exhaust fans and flue ducts sometimes experience fire accidents? How can we prevent and reduce the occurrence of such fire accidents?

Reason:

1. Because the smoke exhaust fan and flue have accumulated too many flammable materials, they will catch fire when exposed to an open flame.

2. During normal operation, sometimes the gas flow is set too high, causing the gas to fail to burn completely in the fire channel and instead being drawn into the flue by the flame, leading to ignition.

3. When adjusting the negative pressure, if the adjustment is too large at once, volatile substances released may ignite and enter the flue, causing a fire accident.

4. If the flue gas temperature is too high and exceeds the specified range, it can also lead to fire accidents.

Measures:

1. Regularly clean out any accumulated debris from the flue and the exhaust fan.

2. During operation, do not pull the fire; instead, ensure that the volatile components burn completely within the fire channel, causing the chimney to emit white or pale yellow smoke.

3. The smoke exhaust fan’s temperature should be controlled below 150ºC.

4. When adjusting the negative pressure, avoid increasing it too much at once, and enhance your sense of responsibility.

60. How should you handle a fire incident involving the smoke exhaust fan or flue?

In the event of a fire, immediately shut down the smoke exhaust fan and the cooling fan. Rush to the furnace, close the gas valve tightly to cut off the ignition source, then open the cover of the connecting flue duct to locate the fire’s origin. Once the fire’s location is identified, use a crane to lift the smoke hood and extinguish the fire using steam or water. After the fire is completely out, report to your supervisor or dispatcher, call in maintenance personnel for repairs, and resume production as soon as possible.

61. How does the particle size of the filler material affect the firing process of the product?

1. If the filler particle size is too large, it can easily cause the filled product to ignite and oxidize, leading to deformation of the carbon blocks.

2. If the particle size is too small, it will hinder the release of volatile components in the product, result in poor thermal conductivity, and cause the filler material to easily clump together. Consequently, it will take longer to reach the same temperature.

62. What are the effects of the cooling rate of the roasting furnace on product quality?

During the initial cooling phase, the product’s temperature actually continues to rise. If the cooling rate is too rapid, it can lead to cracking and an increase in defective products. Conversely, if the cooling rate is too slow, it can also cause inconsistent shrinkage between the inner and outer parts of the product, resulting in cracks and adversely affecting the furnace body itself. Therefore, the cooling rate must be controlled within 40–50ºC per hour, and once the temperature drops below 800ºC, the product should be allowed to cool naturally. Additionally, the cooling schedule should be adjusted according to daily production requirements and furnace chamber cycles.

63. How do you determine the oil content of the paste?

The paste is grayish-white, with many small particles and few large ones. A diffuse appearance of the paste indicates a low binder dosage. If the paste is dark and glossy, with abundant large particles and few small ones, it suggests a high binder dosage. When the paste contains roughly equal amounts of large and small particles, and the large particles range from 50 to 70 mm in size, this indicates a moderate binder dosage.

64. What are the early causes of damage to can-type furnaces? How can their service life be extended?

The furnace body of a tank-type furnace typically lasts about 8 years. The primary early signs of damage to the tank body are the formation of air pores on the brick surface, which gradually expand into cavities and can even lead to burn-through of the tank wall. Another common issue is the development of cracks in the brickwork of the tank wall, with consequences similar to those caused by cavity formation and tank-wall burn-through. In addition, it is also frequent for burner bricks inside the flue passages to fall off and for slag to clog the flue passages.

The following four factors contribute to the early damage of tank furnaces:

1. Masonry quality: Poor masonry quality is characterized by excessively large brick joints, uneven joint widths, and insufficient mortar filling. Moreover, if shaped silica bricks are not pre-laid or if the pre-laying is done carelessly, the dimensions of the furnace after construction may deviate from the design specifications. Additionally, uneven expansion joints, uncleaned mud and debris falling into the flue passages, and the furnace body being exposed to moisture, rain, or freezing during construction can all significantly shorten the furnace’s service life.

2. The furnace heating rate was inappropriate; the furnace was heated too quickly, and during the drying process, expansion of the furnace body was poorly managed, resulting in uneven stress distribution across different parts of the furnace. After drying, the furnace body developed...

Deformation or large cracks may occur.

3. Quality defects such as loose microstructure, high porosity, low mechanical strength, insufficient refractoriness, and deviations in brick shape and dimensions—characteristic of silica bricks—can all lead to premature damage of the tank body.

4. Production Operations: Failure to follow prescribed procedures during calcination—particularly when calcining petroleum coke with high volatile content—can lead to excessively high local temperatures, causing partial melting of the silica brick masonry. Additionally, abnormal discharge operations, fluctuating material levels, improper handling of coking buildup inside the furnace, and even “blasting” incidents can all damage the furnace shell.

Therefore, extending the service life of a retort furnace requires strict control over various aspects, including furnace design, material preparation, infrastructure construction, furnace drying, and production operations. During the calcination process, feeding and discharging must be carried out according to established procedures, and furnace temperature must be carefully regulated to prevent localized overheating. If any local damage to the furnace shell is detected, corrective measures should be taken promptly; only in this way can the furnace’s service life be effectively extended.

65. How can the ingredient preparation department ensure stable ingredient ratios?

To ensure the stability of the particle size of product ingredients, on the one hand, samples should be regularly taken from each storage hopper for sieve analysis to check whether the ingredient particle size is fluctuating. If excessive fluctuations are detected, corrective measures should be taken promptly.

On the other hand, it is also necessary to periodically—according to the prescribed procedure, after every few batches of materials have been prepared—take samples of materials of various particle sizes from the storage hopper. Conduct sieve analysis based on the percentage composition specified in the formulation to verify whether the materials meet the technical requirements. If they do not meet the requirements, immediately stop the batching process, readjust the formulation, or remove the nonconforming materials until the requirements are satisfied before resuming batching. Regularly inspect the batching equipment to ensure its accuracy and avoid batching errors. Weighing must be carried out strictly according to the batching schedule, and the weighing process must be swift and precise, with no deviation exceeding the specified tolerance.

66. What are the possible causes of an explosion in a roasting furnace?

1. Shut down the smoke exhaust fan, causing gas to accumulate and form an explosive atmosphere.

2. Low-temperature extinguishing: If the temperature is too low, the flame won't be extinguished, and gas will accumulate, forming an explosive atmosphere.

3. If the low-temperature ignition procedure is performed incorrectly, and there is sufficient air present, you should ignite first and then introduce the gas; otherwise, there is a risk of explosion.

67. What types of waste products are generated during the roasting process?

Defective products may include longitudinal cracks, permanent cracks, internal cracks, delamination, impurities, voids, deformation, bending, oxidation, damage, and high resistivity.

68. What are the causes of cracked defects generated during the roasting process?

Generally speaking, defects such as transverse cracks and internal cracks in the product are often caused by factors from the preceding process. On the other hand, defects like longitudinal cracks are more commonly attributed to factors arising in this particular process. The causes of various types of cracks are as follows:

1. During pressing, the material temperature is too low, the pre-pressure is insufficient, and the pressing pressure is inadequate.

2. During the pressing and returning process, the paste material is torn apart. Although the surface appears smooth after pressing, the internal structure is poor.

3. The raw materials were not sufficiently calcined, or raw material lumps were mixed into the batch, leading to secondary shrinkage during firing.

4. Excessive oil applied to the plunger head of the press results in poor adhesion at the joint between two batches of material, leading to cracks after firing.

5. The product has too little binder content and too much powder content.

6. The paste material is not mixed evenly, or there is water present in the paste material.

7. The heating rate is too fast.

8. The products were placed too close to the furnace wall when loaded into the furnace.

9. Local leakage of material in the furnace wall, causing it to heat up too quickly.

10. Install large-sized (over ¢400mm) low-ash products in the upper layer.

69. What are the causes of oxide defects in the roasting furnace?

1. The insulation layer on the product’s upper surface is too thin.

2. Material leakage from the furnace chamber; ventilation through the motor housing.

3. The filler material has too much moisture, resulting in insufficient compaction. During firing, shrinkage and settling cause the product to expose oxidized areas.

4. The temperature was too high when the product came out of the furnace, and it wasn't promptly spread out at the cleanup site.