Fundamental issues in coking: the relationship between turnaround time, coking time, and operating time

Relationship between turnaround time, operation time, coking time, and maintenance time: (1) Turnaround time: The time interval between two coke pushing operations in a carbonization chamber, including the time required for the dry distillation of coal as well as the time spent on tasks such as pushing coke and loading coal. For the entire furnace, the turnaround time is the time required to push coke out in all the carbonization chambers once. The turnaround time is determined by factors such as the material of the coke oven bricks, the width of the carbonization chamber, the condition of the furnace and its equipment, the level of operation, and the quality of the coke. The typical cycle time for silicon brick coke ovens is as follows: 350 mm chamber width – 12 hours; 407 mm – 16 hours; 450 mm – 18–20 hours; 500 mm – 22 hours. During operation, the cycle time of the coke oven should remain stable and should not change frequently. (2) Operating time: The interval between two consecutive coke pushing operations, including the time from when the door of the previous furnace is opened to the moment of coke pushing and coal leveling, up to when the door of the next furnace is ready to be opened. It is also known as the carbonization chamber incident. The operation time per batch is generally 8 to 12 minutes. Reducing operation time helps to protect the furnace and minimize environmental pollution. Operation time is related to the operator’s skill level, the condition of the vehicle, and the quality of coordination among different job roles. Generally, it takes 5–6 minutes for a coke quenching car to operate on one furnace, while a coke pushing car requires 10–11 minutes. The time needed for a coal loading car and a coke retaining car to handle one furnace is less than that of a coke pushing car. Therefore, in the case of two coke ovens commonly sharing a coke quenching vehicle, its operating time should be determined by whether the vehicle can complete the operations within the specified time. (3) Coking time: The time during which coal is dry-distilled at high temperature in the carbonization chamber. It is generally defined as the time interval from when the flat coal push rod enters the carbonization chamber to when the coke pushing rod begins to push the coke. (4) Maintenance time: the intermittent period during which none of the carbonization chambers in the entire furnace are emptied. Maintenance time is used for equipment repair and cleaning. The maintenance time is generally preferably 1.5 to 2 hours; too short a time is not conducive to proper maintenance, while too long a time can result in uneven generation of waste gas. Therefore, when the maintenance time is too long, multiple maintenance sessions can be scheduled within one cycle time. There is the following interrelationship among the four times: Turnover time = Total furnace operation time + Maintenance time = Operation time × Number of furnace chambers + Maintenance time. Production capacity = N × M × B × K × 8760 × 0.97 / Tw, where N is the number of carbonization chambers per coke oven, M is the number of coke ovens, B is the amount of dry coal loaded per chamber, K is the coking rate, 8760 represents the total number of hours in a year, and 0.97 is the reduction factor. T represents the turnover time. The above formula applies when the coke contains moisture; in that case, T × 0.94 should be used in place of T in the formula. After determining the turnaround time and coking time, the maintenance time can be calculated using the following formula: T_maint = x – (n×10/60) hours. Here, x represents the turnaround time, n is the number of chambers in the carbonization unit, and 10 represents the operating time per furnace in minutes; this value can be adjusted according to the actual conditions of the factory. For example, if the turnover time is 23 hours, the coking time is 22.5 hours, the number of holes in the carbonization chamber is 72, and the time required to remove the coke from each furnace is 10 minutes, then the maintenance time T_maint = x – (n×10/60) = 23 – (72×10/60) = 11 hours. In other words, 11 hours per day and night are available for planned maintenance work. There’s no need for such complexity. The maintenance time for each cycle = cycle time – total operation time of the furnace. Total operation time of the furnace = number of holes × operation time per furnace. As a prerequisite, when calculating the total operation time of the furnace, the number of holes must be reduced by 1, because the operation time required to service the first furnace is already included in the maintenance time. Similarly, in the case of segmented maintenance, the number of furnace holes per segment also needs to be reduced by 1. Using the figures provided by the poster, the maintenance time equals 23×60 – 71×10 = 670 minutes, which is equivalent to 11 hours and 10 minutes. If the process is divided into five segments, there are four 14-minute periods and one 15-minute period; the maintenance time for each segment is therefore 23×60 – (13×10×4 + 14×10)/5 = 144 minutes, or 2 hours and 24 minutes. For a single carbonization chamber, the turnaround time equals the coking time plus the time required to handle that chamber. For the entire furnace, the turnaround time equals the coking time plus the maintenance time. The total maintenance time for the entire furnace is equal to the turnaround time minus the total operating time for the furnace. The total turnaround time for the furnace is equal to the total operating time plus the total maintenance time. The total operating time for the furnace is equal to the operating time per chamber multiplied by the number of chambers in the furnace group. The operating time per chamber refers to the interval between the time when coke is pushed out of one chamber and the time when it is pushed out of the next chamber; the time required to handle a chamber also falls under this category. Maintenance time is related to turnaround time and the operating time per furnace; the longer the turnaround time (for example, due to production restrictions), the shorter the operating time per furnace, and thus the longer the maintenance time, and vice versa. It is not fixed.

I haven’t looked at it in detail yet, but thank you first – it seems very thorough. I will study it on my own. Thank you again for sharing!