Coke oven production and maintenance during special periods

Thread Content

Production and Maintenance of Coke Ovens during Special Periods I. Management of Coke Ovens When Reducing Their Production Load 1. Principles to be followed when reducing the production load of coke ovens: (1) When reducing the production load of coke ovens, it is necessary to adhere to the technical regulations for coke production； (2) To reduce the production load of the coking oven, it is necessary to maintain normal low-load operation of the coking system ； (3) To reduce the production load of coke ovens, corresponding plans should be formulated and implemented ； (4) To reduce the production load of the coke ovens, it is necessary to minimize damage to the oven structures. 2. The greatest possible extent to which the production load of coke ovens can be reduced: When reducing the production load of coke ovens, it should be done in an organized manner; however, the production load of these ovens cannot be reduced indefinitely. Generally speaking, when the production load of a coke oven is reduced by less than 30% (with a cycle time of around 32 hours), its operation remains relatively stable and there is less damage to the oven structure. However, once the load reduction exceeds 40%, protective measures must be taken for the oven. When the production volume drops to 70% of the designed capacity, it is only possible to keep the system running; at this point, the production load has reached its lower limit, making management more difficult. The oven structure may develop cavities or leaks, so stricter management is necessary. 3. Management of the thermal operating parameters of coke ovens: As the production load on coke ovens is reduced, meaning that their cycle time is prolonged, it becomes necessary to adjust their thermal operating parameters. However, this prolongation of the cycle time is abnormal; therefore, any adjustments to the thermal operating parameters should be based on both the properties of the materials used in constructing the coke ovens and the relevant technical regulations, with the aim of minimizing any damage to the oven structure. The most crucial aspect of extending the turnaround time is to definitely prevent high-temperature accidents. (1) To extend the turnaround time of the coke oven, the rate of extension should be controlled in order to minimize damage to the oven caused by sudden temperature drops. 　 The turnaround time of the coke oven should be less than 30 hours; if it exceeds this value, the increase in turnaround time per day and night should be kept within 2 hours. When the turnaround time is greater than 40 hours, the increase in turnaround time per day and night should be limited to 4 hours. (2) Formulation and control of the coke oven temperature regime: During the period of reduced production in coke ovens, it is advisable to maintain a high temperature during operation; the temperature should not fall below 1150°C, and under special circumstances it should not drop below 1100°C either℃ ； The temperature in the side flues of the coke oven should be maintained above 1100°C, with some areas requiring a temperature of no less than 1050°C. The overall temperature of the coke oven must be kept as stable as possible throughout the entire oven, with strict control over uniformity and stability ； The measurement and adjustment cycle for the coke oven temperature has been appropriately adjusted. (3) Formulation and control of the coke oven pressure system: Strictly control the pressure in the combustion system, maintaining the monitoring pressure in the standard flame channel at around 5–10 Pa, and keeping the а value within the range of 1.3–1.5 ； The pressure in the gas collection duct is kept 0–20 Pa higher than normal; the pressure inside the carbonization chamber must be controlled promptly, with particular attention paid to this during the final stages of coking. 4. Management of coke oven support structures At present, large-scale coke ovens are constructed using silicon bricks, which exhibit thermal expansion and contraction properties. The iron components used to support these bricks serve to hold the brick structure together, applying a compressive force that keeps the oven intact as a single unit. Therefore, when trying to extend the service life of coke ovens, it is crucial to manage these support structures properly, with a focus on the following two aspects: (1) Establishing management procedures for these support structures and increasing the frequency of measurements of key parameters. It is advisable to conduct measurements every time the temperature of the coke oven changes by 100°C. (2) Maintain the integrity of key furnace protection equipment, and ensure an appropriate tonnage level. An appropriate tonnage not only helps to preserve the condition of the furnace protection components but also ensures the tightness and stiffness of the furnace structure. The tonnage of the coke oven springs needs to be adjusted when there are large temperature changes. 5. Coke oven operation management: Due to the increased turnaround time of coke ovens and the reduced production load, the number of coke ovens from which coke is extracted will decrease significantly. To this end, we need to carry out work in four areas: First, extend the interval between coke ovens to maintain as much uniformity as possible in the coke extraction process ； Secondly, each carbonization chamber is prone to negative pressure in the later stages of coking; by adjusting the pressure to positive levels, the natural formation of coke can be reduced ； In coke ovens with dual gas collection pipes, the flap of one of the upward pipes is closed after 2/3 of the coking time, to prevent gas backflow caused by pressure differences in the gas collection pipes during the final stages of coking ； Third, the sealing of each furnace door and coal feeding port ； Fourth, appropriately reduce the amount of ammonia water sprayed, maintain the temperature of the gas collection pipe at no less than 70°C, and enhance cleaning. 6. Maintenance and management of the coke oven structure: As the turnaround time of the coke oven increases, cracks may appear in areas such as the roof of the coke oven, the brick joints in the chute area, and the sealing walls of the regenerator; close attention must be paid to these areas. Take measures to strengthen the plastering at the burner wall area in order to reduce melting and leakage. II. Management of coke ovens during “insulation with coke” and “insulation with an empty oven” – Insulating coke ovens is a very special operation in their operation. Especially in situations such as major overhauls of the coke oven structure and the raw gas exhaust system, when a long construction period is required, insulation measures for the coke oven must be employed; moreover, as the construction period extends, it becomes increasingly difficult to insulate the coke oven. The main methods for insulating coke ovens at present are \"insulation with coke\" and \"insulation with an empty oven\". In the workplace, the method to be used should depend on the circumstances on site. Generally, \"insulation with coke\" is preferred when the insulation time of the coke oven is short, while \"insulation with an empty oven\" is preferred when the insulation time is longer. 1. When a coke oven is kept warm with coke in place, its management: The advantages of keeping a coke oven warm with coke include the fact that, due to the presence of coke in the carbonization chamber, the oven has a large heat storage capacity, which enables the oven temperature to remain stable and easy to control ； Secondly, less graphite is lost from the furnace wall, which contributes to a better seal of the furnace ； Third, it is not difficult to resume coke pushing operations ； Fourth, the waste gas extraction system is easy to maintain, allowing for rapid restoration of production when needed. Disadvantages of \"insulating with coke\" in coking ovens: First, the raw gas system of the coking oven must remain operational, using gas to maintain pressure ； Secondly, when initial heat retention is in effect and the coal material in the carbonization chamber is at the end of its decomposition stage, measures must be taken to isolate the raw gas exhaust system from the carbonization chamber, so that the latter remains within an independent system ； Third, there must be sufficient external gas available to heat the coke ovens. When a coke oven is in a \"coke-retained insulation\" state, the management of such an oven focuses on the following aspects: (1) Sealing of various parts of the oven. Before insulation is applied, each part of the oven must be carefully inspected; the surface of the oven roof should be blown to clear debris, and gaps should be filled with grout ； Seal the upper part of the furnace shoulder protection plate; fill any gaps between the furnace frame and the furnace walls, as well as any straight seams at the furnace tip, tightly ； The tight fit between the front of the incline and the regenerator enclosure wall, as well as the sealing of the edges of the large and small furnace doors, etc. (2) Determination of the heating regime: Before insulating the coke oven, its turnaround time is extended to over 32 hours, which facilitates the insulation process. Insulation of the coke oven with coke is employed to determine the standard temperature for the coke oven; the requirement is that the temperature at the oven front remain above 900°C, which allows the standard temperature of the coke oven to be maintained within the range of 1050–1100°C. (3) Determination of the pressure system: The pressure at the sight glass can be maintained at 0–0.15 Pa, and later it can be kept around 10 Pa ； Keep the air excess factor within 1.5. (4) Measurement and adjustment of furnace protection iron components: During the measurement and adjustment of these components, and as the temperature at the base of the furnace is increased to extend the coke oven’s cycle time, it is necessary to adjust the pressure of each spring so that it remains at the specified level. During the insulation period, attention should be paid to any changes in the load capacity. (5) When resuming production, attention should be paid to first applying a coating to the coke oven walls to secure them. 2. During the “empty furnace insulation” phase of a coking oven, it involves removing all the coke from the carbonization chambers of the oven, and then using gas supplied from the outside to heat the oven in order to maintain its temperature. Its advantages are: first, the coke oven is simple to operate and easy to manage ； Second, it can maintain heat for a long time. Its drawback is severe burnout of the furnace wall graphite. This phenomenon is particularly severe when air leaks into the carbonization chamber through gaps in the furnace door and burner, so it is necessary to improve the sealing. Like insulation with coke, insulation of an empty furnace also requires all the tasks associated with insulation using coke. However, when the furnace is kept at a constant temperature with an empty load, the temperature of the coke oven can be maintained at a lower level; 750–850°C is sufficient. During this period of maintaining a constant temperature, it is necessary to pay close attention to the temperature at the furnace tip to ensure proper combustion of gas in the flame channels there. III. Management of coke ovens during forced shutdown of production The shutdown of a coke oven means the complete cessation of operations in the entire coking system, which is a complex systematic task involving tasks such as emptying the coke oven, disconnecting the waste gas system, purging and cleaning the coal gas pipelines and related equipment, systematically cooling the coke oven, and shutting off supplies of water, electricity, steam, and air. If forced to stop coke oven production, plans should be formulated with the goal of protecting the coke ovens as much as possible. It is recommended to pay attention to the following three points: 1. Determine the cooling plan. Natural cooling is used to cool the coke ovens, so it is difficult to control the cooling rate effectively. Before starting the cooling process, a cooling plan must be devised. This plan is formulated based on the properties of the silica brick material; cooling should take place gradually, with an effort to maintain a slow decline in temperature throughout the entire cooling process. 2. Measurement and management of furnace-related iron components ⑴ Furnace operator’s measurements: Original data are measured before pushing the coke oven, with measurements taken every 100°C until normal temperature is reached ； ⑵ The measurements of furnace height and width are taken once each at 600°C, 300°C, 200°C, 100°C, and room temperature. ⑶ Measurement and management of large springs: Maintain a high pressure in the springs; adjust them every 100°C above 300°C ； Measure and adjust at every 50℃ between 100℃ and 300℃, and measure and adjust once at room temperature. Simultaneously measure the pressure of the longitudinal tension bar spring assembly. ⑷ The sliding condition of each sliding point should be observed and recorded at all times. 3. Detailed implementation plans and organizational structures should be established. IV. Some suggestions: The choice of design for the coke oven has an impact on its condition, and careful consideration should be given during this special period. For enterprises that lack the technical expertise in this area, the following recommendations are offered: (1) Professional technicians should be hired to provide guidance, in order to minimize the losses resulting from work-related issues ； (2) A reliable implementation plan should be formulated for organization and execution. (3) Under the current circumstances, the preferred approach for coke ovens is to extend their operating cycle and operate at reduced load; next is maintaining the oven at a temperature by keeping it empty; and finally, shutting down the oven to protect it.