Q&A on Coking Technology -1

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1. How is coal used for coking classified? Answer: The so-called coking coal refers to the raw coal used to produce coke of a certain quality under the conditions of coking in chamber coke ovens. It is humic coal formed from higher plants. Coal can be classified into coking coal and non-coking coal based on its properties during the coking process. Coking coal refers to the type of coal that, when used for coking with a single coal variety, can produce coke with a certain size and mechanical strength. This type of coal has cohesiveness and is mainly used for coking. Bituminous coal, semi-bituminous coal, semi-bituminous and bituminous coal, 1/3 coking coal, coking coal, and lean coal all belong to coking coals. Non-coking coal does not soften, melt, or form lumpy coke when coked alone. This type of coal has no cohesion or only very weak cohesion, and is generally not used as coking coal. However, when there is an excess of binding components in the coal blend or when it is necessary to produce special types of coke (such as foundry coke), a small amount of non-coking coal can be added as a thinning agent. Lignite, anthracite, as well as the long-flame coal, non-caking coal, and lean coal among bituminous coals, all belong to non-coking coals. In order to expand the resources of coal used for coking, China’s coal classification standards also include several transitional coal types, such as lean coal, 1/2 medium-cohesive coal, and weakly cohesive coal. Depending on the resource characteristics of various regions and the level of development in coal blending and coking technologies, some coking plants can incorporate a certain amount of transitional coal into their blend coal. 2. What are the main characteristics of coking coal? Answer: Bituminous coal, semi-bituminous coal, semi-bituminous and bituminous coal, 1/3 coking coal, coking coal, and lean coal all belong to coking coals, with the following characteristics: (1) Lean coal (PS). It is the type of coking coal with the highest degree of metamorphism; it is characterized by low volatile matter content, but its caking property is second only to that of typical lean coals. When coking is carried out separately, a large amount of fine coke is produced ； When added in a small proportion during coal blending for coking, it can still serve to reduce the density of the coal, which in turn helps to improve the size of the coke pieces. This type of coal is also used as fuel for power generation, domestic use, and other industrial furnaces; the Xishan mining area in Shanxi Province is characterized by its typical low-quality coal. (2) Lean coal (SM). It refers to coking coal with low volatile matter and moderate caking property. A certain amount of gum is produced during the coking process, with the Y value generally ranging from 6 to 10 mm. When coked alone, it yields coke with large particle size, few cracks, and good crush resistance, but its wear resistance is poor; it is better suited for use as a blending component in coal coking. Fengfeng No. 4 Mine is a typical example of thin coal resources. Lean coals with high sulfur and high ash content are generally used only as fuel for power plants and boilers. (3) Coking coal (JM). It is a coking coal with relatively strong coking properties; its volatiles content (Vdaf) generally ranges from 16% to 28%. When heated, it can produce colloids with high thermal stability. When coking is carried out separately, coke with large particle size, few cracks, high crush resistance, and high wear resistance can be obtained. However, when coking alone, the expansion pressure is high, and it can sometimes lead to difficulties in pushing the coke out; it is generally better to use it as part of a coal blend for coking. The Fengfeng Wumine, Huaibei Houshitai, and Xishan Xiqu mines are typical representatives of coking coal in China. (4) Fat coal (FM) is a coking coal with medium to high volatility and strong cohesiveness, whose volatility ranges from about 25% to 35%. A large amount of colloids are produced during heating. When coked alone, it produces coke with good fluidity and high strength; its wear resistance is even better than that of coke produced from bituminous coal, making it a basic coal for mixed-coal coking. However, when coking is carried out alone, the coke has more transverse cracks, and bee coke often appears in the root portion of the coke. In our country, Kaiping and Zaozhuang are the main mining areas for producing fat coal. (5) 1/3 coking coal (1/3JM) is a coking coal with moderately high volatile matter and strong cohesiveness; it corresponds to Type 2 fat gas coal and some Type 2 fat coking coal in the classification of raw coal. There is also a small amount of Type 1 fat gas coal and Type 1 fat coking coal with better cohesiveness. Therefore, it is essentially a transitional coal type between coking coal and gas coal, and when used for coking alone, it can produce coke with good fluidity and high strength. The crushing strength of coke is close to that of fat coal, while its wear resistance is significantly higher than that of gas-fat coal and gas coal. Therefore, it can be coked alone for use in medium-sized blast furnaces; it also serves as an excellent base coal for blending in coke making. During coking, its addition amount can vary within a relatively wide range to produce coke with higher strength. The Huainan mining area mainly produces 1/3 coking coal. (6) Gas-fertilized coal (QF). It is a highly caking coking coal with high volatile matter content and high gel strength. Some call it liquid fertilizer coal. Its coking quality is higher than that of bituminous coal but lower than that of lignite; although it contains a large amount of gum, it is relatively thin (i.e., the viscosity of the gum is low). Coking alone can produce a large amount of gaseous and liquid chemical products. It is most suitable for high-temperature carbonization to produce city gas; its coal-rock composition contains a high proportion of chitinous components such as bark, and it mostly forms in the Lepingian Formation of the Late Permian period. The Leping coalfield in Jiangxi and the Changguang coalfield in Zhejiang are mining areas in China that produce typical gas-fertilizing coal. (7) Gas coal (QM). It is a coking coal with a relatively low degree of metamorphism and high volatile matter content. It has strong caking properties; when heated, it produces a large amount of coal gas and tar. Gelatinous substances have poor thermal stability and can also coke on their own. However, the crush strength and wear resistance of coke are generally lower than those of other coking coal grades. Coke is usually long and thin, relatively fragile, and has numerous longitudinal cracks. Generally, including more bituminous coal in coal blending for coking can increase the yield of gas and chemical products. Some gas coals can also be subjected to high-temperature dry distillation alone to produce town gas. The Laohutai, Longfeng and other mines in Fushun are typical bituminous coals. 3. What is the volatiles content of coal? Answer: The yield of volatile substances produced when coal is heated in the absence of air under specified conditions is called volatiles. In fact, the volatiles produced by coal under these conditions include the gaseous products resulting from the pyrolysis of the coal’s organic matter, as well as water vapor generated by the moisture present in the coal, and CO2 released from the decomposition of carbonate minerals. Therefore, volatile matter is not an inherent component of coal, but rather a product of the thermal decomposition of coal under specific heating conditions; hence, it is more accurate to refer to coal’s volatile matter as the volatile matter yield. 4. What are the physical properties of coke? Answer: The physical properties of coke include: (1) the true density, apparent density, and porosity of coke, as measured using Archimedes’ principle ； (2) Permeability of coke measured based on gas dynamics principles. (3) Thermal properties of coke, such as coke specific heat capacity, coke thermal conductivity, coke thermal stress, coke ignition temperature, coke coefficient of thermal expansion and thermal contraction, as well as electrical properties of coke, such as coke resistivity ； (4) Various user departments also have specific requirements regarding the size of coke particles. Therefore, the coke screening composition, which indicates the particle size distribution of coke, as well as a series of property parameters derived therefrom (such as average particle size and coke bulk density), are also important physical properties. The physical properties of coke are closely related to its mechanical strength and thermal strength at room temperature, as well as its chemical properties. The main physical properties of coke are as follows: the true density is 1.80–1.95 g/cm3 ； Apparent density is 0.88–1.08 g/cm³ ； The porosity ranges from 35% to 55% ； The bulk density is 400–500 kg/m3 ； The average specific heat is 0.80 Kj/(kg·K) at 100°C, and 1.465 Kj/(kg·K) at 1000°C ； Thermal conductivity is 3.07 W/(m·K) at room temperature, and 8.03 W/(m·K) at 900°C ； The ignition temperature (in air) is 450–650℃ ； The low calorific value of the combustible base is 30–32 Kj/g ； The specific surface area is 0.6–0.8 m2/g. 5. What is coal moisture regulation? Answer: Coal moisture adjustment is short for the \"coal moisture control process for charging into furnaces.\" It is a pretreatment technique for coal used in coking, which involves heating to reduce and stabilize the moisture content of the coal intended for use in furnaces, keeping it at a level of 5% to 6%. As the moisture content of the coal fed into the furnace decreases, the bulk density of this coal increases; therefore, under the same requirements regarding coke quality, it is possible to increase the amount of weakly caking coal used. Under the same resource and coal blending ratio conditions, the quality of coke can be improved. This technology is characterized by energy savings, environmental protection, and economic benefits. 6. What impact does the heating level of the coke oven have on coke oven production? Answer: The top height of the combustion chamber is lower than that of the carbonization chamber; the difference between the two is known as the heating level of the coke oven. The heating level is an important dimension in the structure of a coke oven. The heating level is too low, resulting in excessively high temperatures in the space above the carbonization chamber; this is not conducive to improving the quality and yield of coking products, and it also increases the formation of graphite on the furnace roof ； Excessive heating levels will lower the temperature of the upper part of the coke cake, affecting its uniform maturation from top to bottom. 7. What are the hazards of loose coke oven doors? Answer: The hazards of poorly sealed coke oven doors include the following situations ； (1) In coking production, since the carbonization chamber is under positive pressure, a leaky furnace door can cause raw gas from within the chamber to escape. This affects the recovery of coke oven gas and chemical products. Moreover, the escape of raw gas deteriorates the operating environment, damages the iron components used to protect the furnace, and leads to damage to the coke oven itself, thereby reducing its service life. (2) If the coke oven doors are not airtight, air can leak into the carbonization chamber during the later stages of coking, due to factors such as fluctuations in the pressure of the gas collection pipes. This causes some of the coke to burn, increasing the ash content in the coke oven and reducing both the quality and yield of the coke. At high temperatures, local coking occurs when ash interacts with the furnace walls, leading to damage to the coke oven body. (3) Inadequate sealing of the coke oven doors can cause pressure fluctuations in the carbonization chamber, leading to severe damage to the graphite in the gaps between the oven wall bricks. This results in leakage between the oven walls, disrupts the heating system of the coke oven, and makes it difficult to control the temperature and pressure within the coke oven. 8. How to ensure the tightness of coke oven doors? Answer: The measures to ensure the tightness of coke oven doors are as follows: (1) A reasonable maintenance plan should be established to carry out regular repairs on the doors; generally, all doors should be inspected cyclically every 2 to 3 months. At the same time, it is necessary to strengthen the maintenance of furnace door repair equipment to ensure the smooth progress of furnace door repair work. (2) It is necessary to strengthen cleaning management; carefully clean the tar, coke powder, and other residues from the door knife edge, door frame, and inner surface of the door, so as to ensure proper contact between the door knife edge and the door frame. (3) Strengthen the inspection and repair of the furnace door lining bricks to keep them in good condition, thereby preventing localized overheating of the furnace door that could lead to deformation and subsequent loss of its sealing integrity. (4) Strengthen the careful operation of the coke pusher and coke stopper to prevent damage to the knife edge of the furnace door due to improper operation, which could affect the airtightness of the furnace door. (5) Strengthen technological innovation by adopting furnace doors with advanced design and good sealing performance. 9. What are the different types of coke oven protection plates, and what are their respective characteristics? Answer: The protective plates used in coke ovens are divided into three types: large protective plates, medium protective plates, and small protective plates. 10. What are the causes of fracture in the coke oven frame and protective plates? Answer: The reasons for the fracture of the coke oven frame and protective plates are as follows: (1) The material of the frame and protective plates cannot meet the requirements under high-temperature conditions, and they fracture due to thermal deformation. (2) Uneven expansion of the furnace body causes uneven stress on the protective plate and the furnace, leading to excessive local stress and subsequent fracture. (3) The tonnage control of the steel column springs is unreasonable, resulting in uneven stress distribution on the protective plate and the furnace frame, and excessive local stress that leads to fracture. (4) During heavy rainfall, the protective plate and furnace frame experience rapid heating and cooling, causing sudden increases in internal stress that lead to fracture. (5) Impact on the furnace door or the coke guide channel against the furnace frame can cause uneven stress to be generated within the protective plate and the furnace frame, leading to their fracture. 10. What are the mechanical characteristics of 6m coke ovens compared to 4.3m coke ovens? Answer: 4.3m coke ovens are generally equipped with mechanical transmission and manual operation. The coke pusher has only the functions of moving, removing the furnace door, installing the furnace door, pushing the coke, and leveling the coal ； The coke car also only has functions of moving, removing the furnace door, installing the furnace door, and guiding the coke ； The coal loading vehicle has only the functions of moving and loading coal ； The rest are all manual operations, which involve high labor intensity and low efficiency. 6m coke ovens make extensive use of hydraulic drive systems and PLC-based program control; mechanical devices for cleaning the doors, frames, and furnace beds have been added. A 5-2 sequential one-point positioning system is employed, enabling automation of most operations, which **improves work efficiency. In some cases, these 6m coke ovens can operate without human intervention.** 4.3 Coke ovens require high technical skills and involve heavy labor; moreover, 6m coke ovens are mechanically complex, demanding a high level of technical expertise from maintenance workers. 6m coke ovens are superior to 4.3m coke ovens in terms of automation, environmental protection, and safety. 11. How does coal turn into coke in the carbonization chamber? Answer: Coaling with adhesive properties is transformed into coke in the carbonization chamber of a coke oven, generally going through three stages: drying and desorption, semi-coke contraction, and coke formation. These three stages overlap with one another and cannot be distinctly separated. The first stage, from room temperature to 300°C, is the drying and degassing stage of coal. From room temperature up to 120 °C, coal mainly undergoes desorption and drying ； At 120–200°C, the coal releases gases such as CH4, CO2, CO, N2, etc., that were adsorbed, which is a desorption process ； At 200–300°C, the coal begins to decompose, producing gases such as CO2, CO, and H2, while also releasing crystalline water and trace amounts of tar. The second stage ranges from 300 to 550°C and is a stage of semi-coke formation characterized primarily by depolymerization. At temperatures between 300 and 450°C, the coal undergoes intense decomposition and depolymerization, resulting in the release of large amounts of tar and gases. These gases mainly consist of CH4 and its derivatives, as well as H2, CO2, CO, and unsaturated hydrocarbons. These gases are known as the primary pyrolysis gases. During this period, a gel-like substance is formed, comprising gas, liquid, and solid phases, causing the coal to soften, melt, flow, and expand ； In the temperature range of 450–550°C, the colloid decomposes and undergoes polycondensation to solidify into semi-coke. The third stage ranges from 550 to 1050°C and is the coke formation stage dominated by polycondensation. At 550–750°C, a large amount of gas is released from the semi-coke, mainly H2 along with small amounts of CH4; these gases are known as pyrolysis secondary gases. During this period, as the temperature rises and gas is released, cracks form in the semi-coke ； At 750–1050°C, the semi-coke undergoes further polycondensation, with a small amount of gas being released, mainly H2; the residues resulting from the decomposition also undergo further polycondensation ； The coke becomes tighter and harder, its arrangement becomes more regular, and the semi-coke transforms into coke with a certain degree of consistency and size. 12. How does raw gas flow and cool during the coking process? Answer: The waste gas discharge equipment includes risers, collectors, suction pipes, as well as a corresponding ammonia spraying system. These are used to cool and discharge the waste gas emerging from the furnace, and to maintain and control the pressure in the carbonization chamber at a positive level throughout the coking process. They also prevent excessive pressure in the carbonization chamber from causing gas leaks that could pollute the environment. The waste gas extraction system: The waste gas, with a temperature of around 700–750°C, is drawn out through the rising pipe. As it passes through the bridge tube, it is cooled by spraying it with hot recycled ammonia water at a temperature of 75–80°C. Since part of the ammonia water evaporates rapidly, absorbing a large amount of heat, the temperature of the waste gas drops sharply to 80–90°C; at the same time, about 60% of the tar vapor in the gas condenses and precipitates out. The cooled gas, recycled hot ammonia water, and condensed tar enter the coke gas pipe together, flowing along it toward the suction pipe in the middle of the gas collection pipe. The gas flows at the upper part of the gas collection duct cross-section, and enters the suction duct through the suction pipe, which is of type II ； Low-pressure ammonia and tar flow at the lower part of the gas collection duct cross-section, and enter the suction duct via the tar box (which maintains a certain liquid seal level to prevent raw gas from passing through). The intake elbow (type II tube) is equipped with an adjusting flap to control the pressure in the gas collection pipe, ensuring that the pressure at the bottom of the carbonization chamber below the intake pipe remains at 5 Pa before coke pushing. The raw gas in the intake pipe, along with recycled ammonia water and condensed tar, flows into the gas purification process. It first passes through a gas-liquid separator, after which the gas enters a primary cooler for further cooling. The recycled ammonia water and condensed tar go to a tar-ammonia water clarification tank, where separation of tar, ammonia water takes place. After the amount of ammonia water required is replenished, it is pumped back to the coke oven by a recycled ammonia water pump to be used for cooling the raw gas exiting the oven. 13. How to determine the maturity of the coke cake in the carbonization chamber before pushing out the coke? Answer: Under normal conditions, before removing the furnace door to push in the coke, the coke cakes in the carbonization chamber should be at a mature stage towards the end of coking. If the coke is not fully mature or has been over-coked, it indicates that there is a problem at some stage of the coking process. The maturity of the coke cake can be determined from the flame in the riser, the flame in the furnace top space, and the condition of the coke cake inside the carbonization chamber. (1) Good maturity of the coke cake. The flame in the riser is over 1 meter tall, golden in color, clear and faint, shaped like flocculent clouds, with no black smoke. The coke cake in the carbonization chamber is golden yellow, and it shrinks well, with shrinkage cracks of about 10–15 mm. The flame in the furnace top space is clear and faint, with no thick smoke, emitting a silver-white glow. (2) The condition of insufficient maturation of the coke cake. The flame in the riser is purplish-red, with black flames mixed in, and it fluctuates up and down continuously. The coke cake inside the carbonization chamber is purplish-red, but the gap between the coke cake and the furnace wall is very small, and that gap is black. The flame in the roof space is purplish-red, and it shoots straight out from the furnace mouth and the rising pipe. (3) The condition of over-matured coke cakes. The flame in the rising tube is short and sky-blue. The coke cake in the carbonization chamber is silver-white in color; it is incomplete and appears in a fragmented, gravel-like form. There is no flame in the furnace roof space, or there is a short blue flame that is extremely bright. (4) The fire drop technique is one of the effective methods for determining the maturity of coke. 14. What is the coke pushing sequence, and what are the advantages and disadvantages of the commonly used coke pushing sequences? Answer: The sequence in which coal is loaded and coke is removed from each carbonization chamber of one (or a set of two) coke ovens is called the coke pushing sequence. Currently, the pusher sequences used are 9–2, 5–2, and 2–1. Its general formula is m—n, where m represents the number of groups into which all the carbonization chambers of one or a group of two coke ovens are divided, that is, the number of oven holes between two consecutive push operations ； n is the number of carbonization chambers between the corresponding numbers in two passes. 15. What are the characteristics of operating the four major machines in 15,6m coke ovens? Answer: For 6-meter coke ovens, a 5-2 pushing sequence is employed for one-time alignment operations. That is, the pusher car aligns once; apart from removing and aligning the oven doors, operations such as coal leveling, coke pushing, and cleaning at the base of the riser pipes can all be carried out simultaneously, each spaced 5 oven intervals apart. Additionally, mechanical cleaning of the oven doors and door frames can also be performed without the need to move the pusher car again ； Similarly, with one alignment of the coke car, in addition to performing the tasks of removing and aligning the furnace doors as well as guiding the coke, it is also possible to mechanically clean the furnace doors and frame, without the need to move the coke car again. The four major units of the 6m coke oven make extensive use of PLC technology, as well as a significant amount of hydraulic drive systems. The hydraulic system features a simple structure, compact layout, and rapid response, making it suitable for achieving stepless speed control and automatic operation. Its overload protection device is well-designed, and the interlocking and control procedures for each action are simple and reliable. The organic integration of mechanics, hydraulics, and electricity has enabled a high level of automated control for coke oven pusher cars and coke stopper cars. Each of the main operating units of the four major vehicles in a coke oven is equipped with an interlock system to ensure reliable and safe operation. Under normal conditions, each operating unit must operate only when all its interlock requirements are met; however, in special situations, it is possible to send fake signals to certain interlock conditions or even disable those interlocks in order to carry out operations. In such cases, it is essential to confirm that each step of the operation has been carried out properly to avoid damaging the equipment. 16. What issues should be considered during coke pushing operations? Answer: The following points should be taken into account when performing coke pushing operations: (1) The time taken for each coke pushing session must not deviate by more than 5 minutes from the planned schedule; after removing the door, it is necessary to clean the furnace door, door frame, grinding plate, and the small door of any tar and accumulated carbon deposits. After closing the furnace door, it is strictly prohibited for the main furnace door or the smaller doors to start smoking or catching fire; if such occurrences are detected, they must be dealt with immediately. (2) There should be signaling devices between the coke pusher and the coke stopper, and interlocking should be provided between the coke pushing rod and the movement of the coke pusher. It is strictly prohibited to disengage the interlock for coke pushing; the coke pusher driver may only proceed with pushing the coke after confirming that the coke stopper car and the coke quenching car on the coke side are ready to receive it, and automatic coke pushing should be used whenever possible. The coke pusher driver must carefully record the coke pushing time, coal loading time, and the high current during coke pushing. (3) The open time of the furnace door when removing it from the carbonization chamber should not exceed 7 minutes. The furnace nozzle in the carbonization chamber suffers rapid erosion due to coal loading and coke pushing; the longer the furnace door remains open, the longer cold air can cause erosion, resulting in faster erosion of the nozzle bricks. The coke in the burner burns when exposed to air, resulting in an increase in coke ash content. The heat repair furnace should also not be used for more than 20 minutes. (4) The time for the empty furnace after the coke cake is removed and charging of reversed coal begins should not exceed 8 minutes, and the time to burn out the empty furnace should also not exceed 15 minutes. Due to the excessively long time required for emptying the furnace, not only does it cause the temperature in the carbonization chamber to rise too high, but the graphite in the gaps between the furnace walls is also prone to being burned away, which hinders the tightness of the furnace wall in the carbonization chamber. (5) Pushing coke is prohibited when the coke oven is being pushed out and when the adjacent carbonization chamber is empty. After the coke matures in the carbonization chamber, a shrinkage gap should form between the coke and the walls of the chamber to enable smooth removal of the coke. If the shrinkage of coke is small and there are no gaps between the carbonization chamber walls and the coke cake, it is difficult to push the coke out. When pushing coke, it is required that adjacent carbonization chambers be in the middle stage of coking, as the coal in these chambers is in a semi-coke state at this stage, and there is no gap between the semi-coke and the walls of the chambers. This ensures that the chambers do not get deformed or damaged due to the force exerted during coke pushing. On the contrary, if similar carbonization chambers are devoid of coke, the furnace walls are prone to deformation and damage under the force of coke pushing. Once the carbonization chamber becomes deformed, it makes it difficult to push the carbon in, which further exacerbates the deformation and damage to the walls of the carbonization chamber, creating a vicious cycle. Therefore, pushing coke is absolutely prohibited when the adjacent carbonization chamber is empty. (6) It is strictly prohibited to use a deformed pusher rod for pushing coke. Only when the coke pushing rod is straight and free from bending or deformation can smooth coke pushing be ensured. However, since the coke pushing rod is used in high temperatures throughout the year, especially during the coke pushing process, sudden power outages or mechanical failures can cause it to twist and deform under the effect of these high temperatures. When pushing coke using a deformed coke pusher, not only is the resistance high and the operation unstable, but vibrations may also occur, which can easily lead to difficulties in pushing the coke. Furthermore, the pusher rod head may scrape against the walls of the carbonization chamber during movement, resulting in damage and deformation of the furnace walls. Therefore, once any deformation of the pusher rod or its tip is detected, it must be corrected or replaced promptly. 17. How to handle pusher rod failures? Answer: Pusher rod failures can generally be classified into three categories, and corresponding measures should be taken based on the specific situation. (1) Interlock system failure. When the pusher rod stops inside the carbonization chamber and cannot be retracted manually or automatically, pressing the “Force Retract Pusher Rod” button allows the pusher rod to return quickly. Since all the pusher interlocks are disabled at this time, a dedicated person should be assigned to monitor the operation to prevent the pusher rod from colliding with other mechanisms. (2) Power outage. In the carbonization chamber, if there is a sudden power outage for the pusher rod, and if it is a fault in the main circuit, the power to the main circuit is restored after verification, and the pusher rod is retracted. In the event of a large-scale power outage, the backup power supply should be reactivated as soon as possible, and operations should only be resumed once it is confirmed that coke pushing can continue. In the absence of a backup power source, the power supply to the main coke-pushing circuit should be cut off, and the coke-pushing rod should be pulled back using a hand crank or a manual hoist. The power source for operating the coke pushing rod is provided by a manual device, which requires regular maintenance to ensure proper functionality. All the tools needed for manually operating the coke pushing rod must be prepared in advance, and the operating procedures need to be thoroughly studied and practiced. (3) Mechanical system failure. When faults occur in the drive systems such as the pusher rod reduction gear and gear couplings, a manual winch is used to pull the pusher rod back; any foreign objects on the pusher rod rack should be removed promptly. When the pusher rod moves too far forward and fails to engage with the pusher drive gear (commonly known as falling into the carbonization chamber), a manual winch can be used to pull it back by the excess length, after which the pusher rod can be moved back manually or electrically, with the travel controller being adjusted again. 18. What should be done if the coke pushing rod is not retracted and coal is mistakenly loaded into the coal car? Answer: Once it is discovered that the pusher rod has not been retracted and the coal car is being loaded incorrectly, the pusher car driver should promptly inform the coal loading car driver to stop loading coal. If the amount of coal loaded is not large, it is possible to use an air duct to blow away the coal accumulated on the rack of the pusher rod while retracting the pusher rod. If a large amount of coal is loaded, manual operation should be used to slowly retract the pusher rod, and personnel should be assigned to remove the accumulated coal at the furnace mouth on the machine side in order to reduce the resistance during retraction of the pusher rod. It is also important to use air pipes to clean away any accumulated coal from the rack of the pusher rod. 19. How to handle flat coal rod failures? Answer: Pingmei rod failures can generally be divided into four categories, and corresponding measures should be taken depending on the specific situation when dealing with them. (1) Interlock system failure. When the coal leveling rod stops inside the carbon treatment chamber and cannot be retracted manually or automatically, press the forced retraction button for the coal leveling rod to allow it to retract quickly; at this point, all interlocks related to the coal leveling rod are disabled. A dedicated person should be assigned to oversee safety during such operations. (2) Power outage. When there is a power outage in the carbonization chamber, if it is a trip of the main circuit, after verification, the power to the main circuit is restored and the coal leveling rod is retracted. In the event of a widespread power outage, the backup power supply should be activated as soon as possible, the coal pushing rods should be retracted promptly, and then the small furnace door should be closed. If there is no backup power supply, the power supply to the main circuit for leveling the coal should be cut off; the coal leveling rod should be pulled back using a hand-cranked device or a manual winch, and then the small furnace door should be closed manually. The hand-crank mechanism of the leveling rod must be regularly maintained to ensure its proper functioning. All tools required for operating the hand-cranked leveling rod should be prepared in advance, and the operating procedures must be thoroughly studied and practiced. (3) Mechanical system failure. When faults occur in the drive system of the coal leveling rod reducer gears, gear couplings, etc., a manual winch can be used to pull back the coal leveling rod; once the fault is resolved, coal leveling can resume. If the cable used for lowering the coal scraper breaks, it is necessary to determine whether it is the front cable or the rear cable. If the front cable breaks, the coal scraper can be retracted using a manual operating device; if the rear cable breaks, a manual winch can be used to pull the coal scraper back. (4) The coal leveling rod is stuck inside the carbonization chamber. The reason why the flat coal rod gets stuck inside the carbonization chamber is excessive graphite growth in the space at the top of the chamber, which blocks that area and causes the flat coal rod to get stuck when tried to be inserted. Due to the high temperature in the carbonization chamber, if the flat coal rod is not removed in time, it will be baked and deformed. If attempts to start the Pingmei motor have been made 2–3 times without success in pulling it out, stop trying to avoid damaging the motor or breaking the steel cable. First, carefully move the coke pusher back and forth 1–2 times to slightly shake the coal leveler, thereby moving it, and then start the motor to retract the coal leveler. Since the operation of the coke pusher is carried out while the flat coal rod is inserted into the carbonization chamber, which is strictly prohibited under normal circumstances, extreme caution must be exercised to ensure that the flat coal rod is only slightly moved. To prevent accidents that could damage the furnace or the quench car equipment, it is necessary to assign experienced quench car drivers with high skill levels to carry out this task. 21. How to handle driving faults of coke oven vehicles? Answer: When the interlock conditions for the movement of coke oven vehicles are not met, each device should be returned to its original position, the interlock should be disabled, and the vehicle should be moved to a safe location for repair. When there is a fault in the vehicle’s driving motor, or in the gears of the reducer or the gear coupling drive system, the vehicle’s main power supply should be disconnected, the main driving controller should be set to zero, the brake of the driving motor should be released, and the vehicle should be pulled to a safe location using a manual winch for repair. 22. What are the common faults and their causes of mechanical and hydraulic components in 6m coke ovens? Answer: The common faults and their causes of mechanical hydraulic components in 6m coke ovens mainly include the following aspects: (1) Common faults and causes of hydraulic cylinders: 1) Insufficient thrust or reduced movement speed. The main reasons include too small a clearance between the cylinder barrel and the piston, or misalignment between the groove in the piston’s sealing ring and the piston itself; too large a clearance between the cylinder barrel and the piston, or wear of the sealing elements on the piston, all of which lead to excessive internal leakage ； Piston rod bending ； An increase in oil temperature leads to a decrease in the viscosity of the oil, as well as a rapid increase in internal and external leaks. 2) Crawling. The main reasons include air in the hydraulic cylinder or bubbles in the oil ； Local bending or damage to the piston rod ； Local wear or corrosion on the inner wall of the cylinder and the piston surface, etc. 3) Remove from the cylinder. The main reasons include oil leakage inside the cylinder due to the aging, damage, or severe wear of the piston seal ring ； Oil leakage from the cylinder is caused by wear and breakdown of the piston rod shaft end seal ； Hydraulic lock failure ； The spool of the directional control valve is severely worn, resulting in high leakage. (2) Common faults and causes of pressure control valves: 1) Unstable pressure. The main reasons include dirt in the oil interfering with the movement of the valve spool ； The main valve core is scratched or deformed ； Spring deformation causes the valve stem to move inflexibly within the valve body ； Deformation or damage to the cone valve core results in poor sealing. 2) The pressure cannot be increased. The main reason is that large particles of dirt clog the throttle orifice ； The main valve spool is stuck by foreign objects; the spring becomes ineffective due to severe deformation or breakage; the inlet and outlet ports are connected reversely, etc. (3) Common faults and causes of directional control valves: 1) The spool cannot be moved. The main reasons include bent spools or surface scratches ； Scratches in the inner bore of the valve cause it to get stuck ； The clearance between the valve core and the inner hole of the valve body is not appropriate, and the elasticity of the spring is not suitable. 2) The electromagnetic coil is burned out. The main reason is poor insulation of the coil ； The supply voltage is too high ； Oil supply for dry-type electromagnets ； Frequent direction changes cause the coil to overheat and get damaged, etc. 22. What interlock systems are designed for the coke pushing car, coke pulling car, and coal loading car in 6m coke ovens? Answer: The coke pusher interlock system includes interlocks for movement, coke pushing, coal leveling, furnace door operation, small furnace door operation for coal leveling, and cleaning of the small furnace door. The ladle car interlock system includes interlocks for movement, tending the ladle, and furnace door opening. The coal loading car interlock includes interlocks for movement, lifting the furnace lid, guide sleeve operation, gate plate operation, and coal removal. 23. How to handle issues with the programming of the door-opening machine on 6m coke ovens’ pusher cars or stopper cars? Answer: When the door-opening unit of the coke pusher or coke stopper is in jog mode, if the operations are not carried out according to the procedure, or if each step is not properly confirmed, it often leads to confusion in the movement sequence between the main cylinder that controls the lifting of the door-opening unit and the control cylinders responsible for lifting it upward. As a result, the door-opening unit fails to function. There are mainly two types of issues related to irregular movement of the door handling machine: (1) The door handling machine is not connected to the furnace door; the signal lights for lifting, further lifting, and lowering on the control panel are all on, yet the machine fails to move. In this case, there is a mismatch in the travel distances between the main cylinder responsible for lifting the door and the two control cylinders used for lifting and further lifting. The processing steps are as follows: 1) Switch the changeover switch of the door unit on the driver’s console to the jog position. 2) Hold down the hook button until the lifting cylinder is raised to the top. 3) Hold down the lower button; once the lowering signal light comes on, release the button. At this point, the travel master cylinder moves downward for a certain distance. 4) Hold down the lowering button; once the lowering signal light comes on, release the button. At this point, the lifting cylinder moves downward again by a certain distance. 5) Hold down the hook-lowering button until the lift master cylinder moves downward completely. 6) Set the changeover switch of the door access unit to the manual position to resume normal operation. (2) The door-taking machine has the furnace door attached to it; the indicator lights for the lifting, lowering, and hook-release signals on the control panel are all illuminated. However, the door-taking machine cannot move. At this time, the stroke sequences of the main lifting cylinder and the lifting control cylinder of the door-taking machine become disordered. The door picker cannot move; at this time, the stroke of the door lifting main cylinder and the lifting control cylinder is incorrect. The processing steps are as follows: at the hydraulic valve station, increase the pressure of the door-lifting relief valve from 2 MPa to 4–7 MPa ； Set the toggle switch of the door unit on the driver’s console to the jog position ； Hold down the front button of the trolley, and release it when the trolley is near the front limit ； Hold down the hook button to lift the main cylinder and move the furnace door upward; release the button once the horizontal bar of the furnace door is 20–30 mm above the upper surface of the furnace hook ； Press the front button of the trolley; once the front limit light comes on, release the button ； Switch the door operation unit to the manual mode to carry out the door closing action manually (if manual operation is not possible, use the jog function to close the door first, and then use the jog function to return each cylinder to its original position before switching to manual mode) ； Adjust the pressure of the relief valve back from 4–7 MPa to its original value of 2 MPa, so that the gantry crane can resume normal operation. 23. What are the reasons why the cross bar of the furnace door does not drop into place? Answer: The reasons why the cross bar of the furnace door does not descend to the proper position are as follows: (1) A malfunction in the door lifting mechanism, resulting in insufficient forward or downward movement; or leakage in the oil cylinder used for lifting the door, which causes the cylinder to retract, thereby reducing the actual movement distance of the door and leading to the cross bar not descending to the proper position. (2) The furnace door and frame are not cleaned properly, which increases the friction force experienced during the lowering of the furnace door; as a result, the actual lowering distance of the furnace door is insufficient, causing the horizontal bar attached to it to fail to descend to the proper position. (3) Tar residue or coke dust at the bottom of the furnace frame was not cleaned properly, and this blocked the furnace door as it descended, causing the horizontal bar attached to the door to fail to drop into place. 24. What should be done if the cross bar of the furnace door comes unhooked or if the furnace door falls down? Answer: When the coke pusher opens or closes the furnace door, if the operating procedure is not followed and the hook used to open the door fails to engage with the door, it can lead to accidents such as the detachment of the cross bar attached to the door or even the collapse of the door itself. Appropriate actions should be taken based on the situation that occurs. (1) The furnace door tilts outward, but the brick groove at its lower part remains on the grinding plate at the entrance to the carbonization chamber. In this case, it is stopped in time as soon as the furnace door begins to tilt; all that is needed is to operate the door-moving mechanism to push the door back to its original position using the opening mechanism, and then the hook can be used. If the furnace door collapses and the coke falls down to block it, the coke must be removed before any further action can be taken. (2) The hook is disengaged, and the area at the bottom of the furnace door where it slides out is small. First, use a steel rope to secure the furnace door to the door removal machine across it, to prevent the door from tipping over. Slightly lift the furnace door upward using the lower hook, place bricks and iron plates under the door, then lower it. Then lower the hook; after placing shims on the hook, lift it again, and then add bricks beneath the furnace door. Repeat this process several times as mentioned above, until the furnace door is lifted high enough for the hook to catch it. As the furnace door is gradually raised, care must be taken to keep the padding blocks stable, to prevent accidents such as the blocks being crushed or falling out and causing injury. The upper part of the furnace door must be secured with steel ropes. Prevent the furnace door from tipping over. During the lifting process, the furnace door will gradually rise upright; the operator should operate the door lifting mechanism to move it forward, and tighten the steel cable if necessary. When the hook can be inserted into the door lifting hook, operate the hook to lift the furnace door, then remove the steel rope and shims to resume coke production. (3) The furnace door is tilted against the furnace frame, with both the upper and lower hooks disengaged. During processing, since the hook is not far from the hook-lifting mechanism at the bottom of the furnace door, and there is a connecting spring in the middle of the hook-lifting rod, a crowbar can be used to press the lower hook down so that it can be hooked into the lifting mechanism, after which further processing can be carried out. If the hook is too far from the lower lifting hook to be used for gripping, a steel rope can be wrapped around the horizontal bar under the furnace door and hung on the hook of the door-lifting machine; the furnace door can then be raised gradually. After each lift, the rope should be tightened again and replaced. After repeating this process many times, the lower hook can be inserted into the lifting hook, allowing for the next step in the procedure. (4) The furnace door falls onto the furnace bed or drops below it; this is the most severe scenario of a furnace door falling over. The coke pusher should be driven to the door repair station to retrieve a spare furnace door; normal production of the coke oven should be resumed first, after which the fallen furnace door should be lifted using a crane and taken to the door repair station for repair. 25. How to handle the situation where the driving wheels of coke oven vehicles deviate from the track? Answer: When 1 to 2 of the vehicle’s driving wheels deviate from the track, several steel plates of various thicknesses, measuring 200–300 mm in length and 70–120 mm in width, need to be prepared. These plates should be laid in the direction opposite to that in which the wheels have deviated, starting from the bottom of the driving surface of the affected wheels and progressing from thinner to thicker plates, with them being placed closely against the track. The process continues until the elevation of the last plate is equal to or slightly above the track surface (usually at a distance of about 1 meter). Once this is done, the vehicle can be slowly moved forward in the direction opposite to the deviation of the wheels; thanks to the cushioning effect provided by these plates, the driving wheels will naturally return to the correct track position. When 2 to 4 of the vehicle’s driving wheels deviate from their track, the high amount of such wheels results in excessive driving resistance; even with steel plates laid as a transition, the vehicle may still be unable to move. In such cases, it is necessary to prepare 2 jacks of 50t or 100t each, along with several steel plates. These jacks are placed under the steel structure of the trolley on which the wheels that have deviated from the track are located, and they are used to lift the structure so that the lower edge of the driving wheel is above the track surface. After that, steel plates are laid beneath those wheels, and they are compressed firmly in the direction opposite to that in which the wheels have deviated from the track (usually at a distance of about 1m). Once the jacks are released, the same procedure is followed for the remaining wheels that have deviated from the track. After using a jack to lift the track back onto the running wheel that has fallen off its track, driving in the direction in which the wheel fell off will allow it to return to its proper position on the track. 26. What issues should be considered during coal loading? Answer: The following points should be taken into account when loading coal: (1) When loading coal into the truck, it is necessary to fill it as fully, level it as evenly as possible. Filling the carbonization chamber with coal helps increase the production of coke, gas, and chemical products. It also helps prevent excessive temperatures in the roof space, thereby improving the quality of the gas and the operating conditions in the roof area. Leveling the coal charge in the carbonization chamber reduces the resistance to pushing coke, facilitating smooth coke pushing. It also ensures unobstructed drainage of the waste gas generated during coking, which helps to reduce smoking and flaming from the coke oven doors. Even distribution of coal in each carbonization chamber helps to stabilize the heating regime of the coke oven and improve the quality of coke. (2) When loading coal into the coal car, it is necessary to do so as quickly as possible, with minimal smoke generation, and to ensure that as little residual coal as possible remains attached to the coal loading rods. It is essential to strictly follow the coal loading procedures and make proper use of the equipment and facilities designed for dust removal during coal loading. (3) When taking and loading coal into the coal cars, stacking operations must be followed strictly; when loading coal, it is necessary to align it with the correct furnace number, and loading it into the wrong carbonization chamber is strictly prohibited. It is necessary to strengthen communication with the coke pusher and coke stopper; coal loading is strictly prohibited when the coke pusher rod has not been retracted and the furnace door has not been closed. 26. What are the hazards of not pushing the coke at the right time? Answer: Pushing coke at an inappropriate time refers to doing so outside the schedule specified for coke pushing; there are two scenarios: pushing coke ahead of time or pushing it later than scheduled. When coke is pushed out in advance, the insufficient maturity of the coke affects its quality; moreover, inadequate contraction of the coke can lead to difficulties in pushing it out, thereby damaging the furnace walls and disrupting the normal operation of the coke oven. When coke pushing is delayed, excessive maturation of the coke leads to increased heating costs for coke production. Meanwhile, as the coke becomes finer and more fragmented, it may make coke pushing difficult and cause damage to the furnace walls, affecting the normal operation of the coke oven. 27. What are the principles for handling red coking on the ground? Answer: Red coke falling to the ground refers to the phenomenon where, during coke pushing, the coke does not pass properly through the guide grills of the coke car and fall into the car of the quenching car (or coke drums), but instead lands on the furnace bed or other areas. Red coke falling to the ground is caused by the tarpaulin car or quenching car not being in place, resulting in the coke pusher pushing the coke too early. It can mainly be divided into three situations ； (1) Neither the coke car nor the quenching car is in place ； Either the coke quenching vehicle is in place while the coke catching vehicle is not; in the former case, all of the red coke is pushed onto the furnace bed and the coke quenching vehicle’s roadway, whereas in the latter case, although some of the red coke falls into the carriage of the coke catching vehicle, a large amount of it spills onto the furnace bed and the coke quenching vehicle’s roadway. (2) Before the coke stopper car had completed positioning, the coke pusher car started to push the coke, resulting in a large amount of red coke falling into the body of the coke stopper car and even toppling it over. (3) The coke stopper car is in position, but the coke quenching car has not arrived yet; as a result, the red coke falls on the front of the locomotive or onto the coke quenching track. A red coke spill is a very serious operational accident. A large amount of red coke falling on the furnace bed and the quench car tracks can damage or burn out the furnace bed, the coke barrier car tracks, and the quench car tracks ； If red coke falls into the body of a coke car or the front section of a locomotive, it can render them completely unusable and cause injuries or fatalities. Therefore, it must be given utmost attention. If red coke lands in the first scenario. The solution is to quickly spray water from fire hoses on the red coke; once the coke is extinguished, the coke on the tracks of the coke quenching vehicle and the coke stopper vehicle must be removed promptly, so that these vehicles can move again as soon as possible and normal operations can be resumed. If the coke from the previous batch has not been completely pushed out, it should be removed first before pushing out that of the next batch. For coke that falls on the tracks of the coke quenching car, it can first be scooped onto the open area outside the tracks using a shovel. Once production returns to normal, arrange personnel to transport it to the cooling coke platform. The consequences of red coke falling to the ground in the latter two cases are relatively severe, and separate handling is required depending on the specific circumstances. The key is to first cut off the power supply to the grinding circuit, quickly extinguish the red coals with water, starting with the vehicle’s upper part and then the lower part, addressing the control room and fuel system first, and then the rest of the vehicle’s structure. Once it is possible to approach the vehicle, the injured should be rescued promptly, followed by an inspection of the equipment damage to restore its operation. If the quench car or coke quenching vehicle is severely damaged and cannot be repaired immediately, it can be moved to a safe parking location or lifted off the tracks using a crane, so that backup equipment can be used to resume production as soon as possible. 28. What are the main reasons for difficult coke pushing, and how should it be addressed? Answer: When the pusher current exceeds the specified maximum value during coke pushing, it is referred to as difficult coke pushing. The coke cake cannot be pushed at one attempt; when it is pushed a second time, it is generally referred to as a secondary coke accident. The main reasons for difficulties in pushing coke out are as follows: (1) The coal loaded into the carbonization chamber has poor cohesion, preventing it from forming coke properly during the coking process; or there is a lack of coal with good shrinkage properties in the blend, which results in the coke cake not shrinking sufficiently and thus makes it difficult to push the coke out. (2) The heating regime of the coke oven is unreasonable, or insufficient coking time results in poor maturation of the coke cakes; in particular, the low temperature in the vertical flue at the oven head leads to inadequate maturation of the coke in that area of the carbonization chamber, thereby causing difficulties in pushing out the coke. (3) Deformation of the coke oven’s wall or floor bricks increases frictional resistance, resulting in difficulties in pushing the coke out. (4) The coal charging and leveling in the carbonization chamber are poor; the coal material blocks the charging holes, increasing resistance during the coke pushing process and making it difficult to push the coke. (5) For various reasons, the coking time in the coke oven becomes too long, causing the coke cakes to mature excessively; as a result, the coke becomes finer and more fragmented, and it is no longer able to withstand or transmit the pushing force applied during coke extraction. This leads to squeezing and clamping phenomena, making coke extraction difficult. (6) Due to reasons such as excessively high temperature in the space above the furnace roof, a large amount of graphite forms on the furnace walls; this creates significant resistance during coke pushing, making the process difficult. (7) Difficulty in pushing coke occurs due to coke oven mechanical failures, such as deformation of the coke-pushing rod and deformation of the coke guiding chute on the coke pusher car. Should any difficulty in pushing coke occur, personnel should be immediately organized to determine the cause; only after rectifying the fault causing the difficulty can the coke pushing proceed. If the coke is not sufficiently matured, the furnace door should be closed to continue heating; only after the coke has matured should it be pushed out. If the coke is over-fired, the coke at the furnace head should be raked away; only after a shrinkage gap becomes visible between the coke cake and the furnace wall should coke pushing be carried out. If the problem lies with the machinery itself, a backup unit should be used, or the mechanical malfunction must be rectified before coke pushing can proceed. If the coal feed opening becomes blocked by coal, a leveling rod can be used to level out the coke blocking the opening before pushing the coke out. In cases where difficulty in coke pushing is caused by coal or graphite, a portion of the coke on the coke side should be removed to facilitate troubleshooting. It is strictly prohibited to continue pushing coke without first determining the cause. Such operations must be authorized by the duty supervisor; only in their presence may a second attempt at coke pushing be made. For any coke pushing operation performed more than three times, the workshop supervisor must be present to prevent the situation from escalating or to avoid a recurrence of difficulties in coke pushing. 27. How to control the top of a coke oven during heavy rain? Answer: During heavy rain, rainwater can flow into the carbonization chamber or combustion chamber, damaging the refractory brick lining. Additionally, the temperature of the coke in the carbonization chamber is very high; when water enters this chamber, it rapidly vaporizes and expands, potentially causing an explosion. Therefore, measures must be taken to address this issue. If water accumulates on the furnace roof, personnel should promptly be organized to remove the water from both the machine and coke sides. The gaps between the furnace cover and the fire-viewing holes must be sealed promptly; coal from the coal hopper of a coal truck can be used for temporary sealing. 28. What are the “three valves and one valve stem” in a coke oven? Answer: The “three connections” refer to the connection of the rising pipe, the coke gas pipeline, and the furnace mouth; the “one flexibility” means that the flap is flexible. The “three connections and one flexibility” requirement for coke ovens is a fundamental necessity in coke oven production; only by meeting these requirements can normal flow of raw coal gas during the coking process be ensured, thus ensuring the smooth operation of coke oven production. 29. What are the main causes of riser blockages, and how should they be addressed? Answer: At low temperatures, some tar components consisting of large molecules condense and adhere to the inner walls of the riser. When the riser is at high temperatures, this condensed tar undergoes cracking and polycondensation reactions, solidifying into a graphite-like substance. This substance, along with coal particles released from the raw coal gas, accumulates on the inner walls of the riser, gradually reducing its inner diameter. If not cleaned in time, this can lead to blockage of the riser. There are two forms of gooseneck graphite purging devices. One involves placing a compressed air nozzle near the tip of the pusher rod to purge the base of the gooseneck before the pusher rod leaves the carbonization chamber. Another approach is to install compressed air nozzles above the frame cleaning device, which are used to purge the base of the rising tube during frame cleaning. Abroad, mechanical methods are also used to remove blockages in risers from the riser openings. One method is to install a cleaning device with an electric chain on the coal car, with a prying hammer attached to the other end of the electric chain; the back-and-forth movement of this prying hammer inside the rising pipe is used to remove graphite from the inner wall of the rising pipe. Another method is to use a cleaning trolley that moves along tracks laid on the furnace top near the rising pipe. The traveling cart is equipped with a main column with a cantilever and a chain winch; a ram suspended at one end of the chain moves back and forth into the rising tube to remove graphite from the inner wall of the rising tube. 29. What are the hazards of clogged bridge pipes and gas collection pipes? Answer: During the production process in coke ovens, it is necessary to strengthen the inspection and cleaning of bridge pipes and gas collection pipes to prevent blockages from affecting production. When the bridge pipe becomes blocked, the flow of raw gas generated in the carbonization chamber during coking is hindered, which can lead to smoking and fires at the furnace door, coal loading ports, rise pipe covers, etc.; this can damage the equipment and pollute the environment. Worse still, a blockage in the bridge pipe can also cause ammonia to flow into the carbonization chamber, thereby damaging the furnace walls. A blockage in the gas collection pipe will impede the flow of raw gas in all the carbonization chambers of the furnace, affecting the normal operation of the coke oven; in severe cases, it can lead to the shutdown of the entire coke oven. 30. What are the hazards of negative operation in the carbonization chamber? Answer: When the carbonization chamber is under negative pressure, combustion exhaust gases and air enter the chamber, causing the graphite in the furnace walls and the coke inside to burn, which results in local high temperatures. This not only increases the ash content of the coke and reduces its yield, but the ash also erodes the bricks forming the walls of the carbonization chamber at high temperatures, leading to slag formation and damage to the furnace structure. Furthermore, the air entering the carbonization chamber from the combustion chamber burns part of the raw gas, thereby reducing the production of gas and chemical products. At the same time, the inert gas content in the gas increases, deteriorating its quality; the amount of free carbon in the tar rises, which can lead to blockages in the system used to convey the raw gas. The carbonization chamber being under negative pressure also allows air to enter the chamber through any gaps in the furnace door and lid, burning some of the coke and raw gas; this likewise reduces the production of coke, gas, and chemical products, and leads to an increase in coke ash content and a decline in its quality. 31. What are the various coal charging methods for top-charging coke ovens, and what are their advantages and disadvantages? Answer: A top-charging coke oven is a type of coke oven in which coal is loaded into it from the top through coal charging ports during the carbonization process. It can be loaded using coal trucks, through pipeline systems, or with buried scrapers. Most top-loading coke ovens use coal loading cars for feeding coal, while the other two coal feeding methods are mainly used for preheating coal before coking. The top-charging coal feeding method currently used in coke ovens, which involves using coal loading cars for coal feeding, includes three forms: gravity coal feeding, disk feeder coal feeding, and screw feeder coal feeding. Most coke ovens in our country use gravity coal charging, whose advantage is that it results in a high bulk density of the coal and fast charging speeds, which helps to improve the strength of the coke ； The disadvantage is that the coal loading speed and amount are difficult to control, which can lead to uneven distribution of coal under each loading hole, resulting in higher levels of dust. Disk feeder coal charging is well utilized in Japan. Its main advantages are uniform coal distribution and bulk density, which contribute to stable coke quality; at the same time, it facilitates the removal of raw gas during the coal charging process, thereby reducing environmental pollution ； The downside is that the coal loading time is greatly affected by the moisture content of the coal; when the moisture level is high, the loading time is longer. By using a briquette production line and mixing 30% briquettes into the coal fed into the furnace via a disc feeder, this problem can be effectively solved. Screw feed coal loading is widely used abroad, and it is also commonly adopted in new coal loading vehicles in China. Its advantages include good self-sealing properties of the screw feed coal loading vehicle, low dust pollution, uniform density of the coal pile, which helps to maintain stable coke quality. Moreover, the coal loading speed and quantity can be easily controlled, facilitating automated operation ； The drawback is that the bulk density of the charged coal is not high, making it prone to corner deficiencies in the charge. 32. What are coking time, turnover time, operating time, maintenance time, coke pushing time, and coal charging time? Answer: Coking time: This is the duration that coal remains in the carbonization chamber. Generally, it is defined as the time interval from when the coal-distributing rod enters the carbonization chamber (i.e., the coal-charging time) to the moment when the coke-pushing rod comes into contact with the coke cake upon discharging the coke from the furnace (i.e., the coke-pushing time). This interval is referred to as the coking time. Operation time: The time taken for the coke pushing and coal charging processes, that is, the interval from the moment the coke pushing rod comes into contact with the coke cake to the moment the coal loading rod enters the carbonization chamber. Turnaround time: The sum of coking time and operating time. Maintenance time: Within a given period (each small cycle, day and night, or shift), it refers to the remaining time after the coke oven carbonization chambers have completed their operations in accordance with the specified coking and operating times. This time is used for maintenance and repair of coke oven machinery; this period is known as maintenance time. 33. Why does graphite grow on the furnace wall? Answer: Graphite is formed by the gradual deposition of carbon particles resulting from the pyrolysis of raw coal gas at high temperatures. It serves to seal any gaps in the furnace walls and to consolidate the masonry. The old coke ovens with numerous cracks on the walls of their carbonization chambers can maintain long-term production. Apart from the effects of mortar joints and furnace-protecting iron components, this is mainly due to the role of graphite. However, when graphite deposits become too thick, hindering the coke pushing operation, it will make coke pushing difficult; it may even lead to deformation or collapse of the furnace walls. Therefore, graphite deposition must be controlled. The rate of graphite growth is directly related to the furnace temperature; the shorter the coking time and the higher the standard temperature, the more hydrocarbons in the gas are cracked, and the faster the graphite grows. In addition, it is also related to the following factors: (1) A narrow flue nose brick (which results in a larger angle at which air and gas meet outside the inclined opening), excessive air, and the use of coke oven gas for heating—all of these cause the flame to become shorter and slow down the growth of graphite on the furnace roof. (2) A low heating level value, a relatively low coal line at the furnace top, or a large vertical shrinkage of the coke cake all lead to an increase in the temperature in the space above the furnace top, thereby accelerating graphite growth. (3) The moisture content in the coal has a significant effect on the temperature in the furnace top space; generally, for every 1% increase in moisture content, the space temperature decreases by about 20°C, thereby slowing down the growth rate of graphite. (4) When there are leaks in the furnace wall, the combustion of raw coal gas raises the local temperature of the furnace wall, causing the raw coal gas to crack and produce graphite. (5) The furnace structure has a significant impact on the temperature in the crown space; the temperature in the crown space of overhead coke ovens is higher than that of other types of coke ovens, resulting in faster graphite growth. 34. What are the main causes of coke oven damage? Answer: During long-term use, coke ovens are subjected to high temperatures, mechanical forces, and physical and chemical reactions. The main reasons for the aging and damage of the oven body are: (1) The effects of temperature changes. During the production process, when the furnace door is repeatedly opened and closed, coal is charged, and coke is discharged, the thermal stresses caused by temperature changes on the inner and outer surfaces of the furnace wall lead to erosion or cracking of the wall. As the furnace age increases, the degree of damage continues to grow and extends inward into the furnace ； The coal-loading opening is highly susceptible to external cold air currents, making it prone to erosion and cracking ； The crown bricks at the burner section also often crack due to sudden temperature changes. (2) Action of mechanical forces. After cracks or deformations appear on the walls of the carbonization chamber, the mechanical stress generated by closing the oven door and pushing out coke causes these cracks to widen and exacerbates the wall deformation. Especially during difficult coke pushing, the impact is even more severe. (3) Physicochemical effects. At high temperatures, silicon dioxide (SiO2) in silica bricks can react with metal oxides (Na2O, FeO) present in the coal charge, forming low-melting-point silicates (NaSiO3, Fe2SiO4) on the surface of the silica bricks. Under the influence of thermal stress and mechanical forces such as coal charging and coke discharging, these low-melting-point silicates gradually peel off from the main body of the silica bricks. During long-term production, the chemical composition of the carbonization surface, intermediate layer, and combustion surface of the carbonization chamber walls undergoes redistribution. From the carbonization surface through the intermediate layer to the combustion surface, the SiO2 content is lowest at the carbonization surface. This results in different layers of the carbonization chamber walls exhibiting varying expansion rates and other properties. The thermal stresses generated by periodic and drastic temperature fluctuations cause the carbonization surface of the wall bricks to peel off. During the coking process, the dry distillation of coal produces large amounts of gases such as hydrogen and carbon monoxide. In such a reducing atmosphere, the silicon dioxide within silica bricks is reduced by carbon to silicon monoxide (SiO) at a temperature of 1300°C; this silicon monoxide then escapes in gaseous form. However, in the presence of metallic iron, this reaction also occurs at a lower temperature (1050°C). This reaction reduces the silica content on the surface of the wall tiles, making the structure porous and loose, resulting in a pitted surface. (4) Furnace length increase and graphite deposition. After the coke oven is put into operation, the volume expansion caused by the crystalline transformation of silica continues. However, this expansion will gradually diminish year by year until it eventually disappears. This expansion represents the actual expansion of the masonry itself; it is an inevitable phenomenon. Due to the temperature difference inside and outside the resistance wall, the walls of the carbonization chamber tilt towards both ends. The periodic removal of coke and loading of coal in the coke oven, along with changes in furnace temperature, cause the furnace walls to bulge gradually, the width of the furnace head opening to narrow, and accelerate the erosion of the furnace walls, the expansion of cracks, and the increase in the length of the furnace. During the long-term operation of the coke oven, methane and carbon monoxide in the carbonization chamber decompose to form carbon (i.e., graphite), which penetrates into the pores of the bricks. The graphite in the carbonization chamber is generally removed using a steel shovel; however, the graphite removed often comes along with pieces of brick, resulting in an uneven surface on the furnace walls. At the same time, graphite continuously fills and deposits in the cracks and the pores of the bricks; the cracks cannot close completely. During the heating of the graphite, high temperatures are generated, which widens the gaps between the bricks. Repeating this process over and over again causes the width of the cracks to increase (cracks turning into larger cracks, small fissures becoming bigger ones), and the number of cracks also increases, leading to damage and cracking of the furnace walls. This phenomenon is particularly severe when the coking time changes frequently or when the heating gas is changed often, as it results in frequent variations in the temperature distribution along the height of the carbonization chamber walls. The normal aging of coke ovens due to the above reasons is inevitable. But there are other reasons for coke oven damage as well, such as hidden defects remaining from the oven construction, inappropriate sizes of brick joints, failure to carry out secondary joint sealing, and inaccurate provision of expansion joints ； The quality of the refractory materials is poor; the refractory bricks and mortars do not meet the specified technical requirements ； The heating rate was not properly controlled during furnace drying ； Poor production operations lead to smoking and fires at the furnace door; accidents occur frequently. Negative pressure is used in the carbonization chamber, and the furnace door or lid is often left open for extended periods of time. Abnormalities such as coke pushing and coal leveling ； If the iron components used to protect the furnace are not managed properly, they lose their protective function ； Unstable thermal regime ； The hot repair work on coke ovens is poor. 35. How many ways are there to stop an inverter? Answer: There are mainly three ways to stop a frequency converter: (1) Deceleration stop, in which the motor gradually reduces the frequency supplied by the frequency converter to it, following a slope determined by the selected deceleration time. (2) When free coasting stops and the inverter receives a stop command, its output voltage is cut off, and the motor comes to a stop through free coasting based on the deceleration caused by the load’s inertia. (3) When the DC braking stops, after a short delay upon receiving the stop command, the inverter injects DC braking current into the motor to bring it to a stop as quickly as possible.