How to deal with extended coking time in coke ovens?

1. Lower the standard temperature; as for gas pressure and suction, there’s no need to mention them. 2. Appropriate adjustments should be made to the pressure standards of the gas collection pipes, in order to prevent graphite from being burned due to negative pressure in the carbonization chamber resulting from a decrease in the amount of gas, which could cause leaks. 3. It is recommended to increase the frequency of temperature measurements. 4. It is recommended to adjust the mixing ratio appropriately to prevent difficulty in pushing the coke. 5. Close some of the upward baffles at the late stage of coking.

The treatment can be carried out by referring to the furnace holding procedures in the coking industry.

What you're referring to is the blanking of the coke oven. Generally, there are three methods. 1. Full-furnace pressure retention method. It means that the coke remains in the carbonization chamber, and coke oven gas or inert gas is forced into the space above the furnace in the carbonization chamber or into the gas collection ducts. The purpose is to ensure that the bottom of the carbonization chamber remains at positive pressure under all conditions during furnace sealing. 2. Atmospheric method with an empty furnace. It involves pushing all the coke out and isolating the raw gas outlet system from the carbonization chamber. 3. Normal-pressure full-furnace method. It involves leaving the coke in the furnace and carrying out a furnace sealing operation at atmospheric pressure. Personnel must be trained and organized in front of the sealed furnace. Also, prepare all the necessary tools, such as clay fireclay, asbestos rope, steel plates, etc. Firstly, it is necessary to ensure proper sealing of all parts of the furnace, such as the furnace top, furnace shoulder, upper part of the protective plate, furnace bed, and regenerator. Before starting the furnace, it is necessary to check the length of the furnace column as well as its curvature; the size of the springs also needs to be measured and adjusted. Inspect the walls of the carbonization chamber and other areas, and keep records. Next, a heating schedule during the furnace idling period needs to be established. It is generally advisable to extend the coking time to 25–26 hours. A standard temperature ensures that the furnace tip temperature remains at least 900 degrees; there is no need to consider the maturity of the coke cake. To eliminate the adverse effects of furnace stalling on the draw rods, the pressure at the viewing port can be maintained at -5 to -15 Pa. The suction in the regenerator should be maintained so that the pressure at the viewing port remains within the specified range; this pressure should be 10–20 Pa lower than the gas pressure at the bottom of the carbonization chamber. During the idling period, it is necessary to adjust the temperature in the straight flow direction, the temperature across the rows, and the temperature of the exhaust gas vanes in a timely manner; moreover, the pressure at the bottom of the carbonization chamber must be measured and adjusted as well. In addition, it is necessary to strengthen the measurement and adjustment of the furnace protection iron parts.

Lower the standard temperature, down to at least 1150 degrees. To increase the temperature of the furnace tip, replacing the small orifice plates on it is not very effective; instead, wires should be added in the middle along the curve of the horizontal wall – points 2 and 5 on the second floor would work. In how many days?

Maintain the burner temperature! Increase the air inlet!

It can also increase the pressure for observing the fire eye! The standard temperature cannot be too low! Control gas flow at the onset of coking

It’s actually very easy to do. After a certain period of time, turn off the addition and subtraction cocks. Then turn off the riser flap.

When coke ovens are unable to maintain normal production for a certain period due to natural disasters or other objective reasons, the coking time is extended to sustain low-load operation. I. Extending the coking time: In general, large coke ovens operate at reduced load when the coking time is 22 hours or more; this is referred to as operation under conditions of extended coking time. The furnace temperature is maintained at around 1200ºC to ensure that the temperature of the furnace head bricks after coal loading does not drop below the crystal transformation point of silica bricks, thereby preventing damage to those bricks. The main feature of the production process with an extended coking time is that, after the coke is matured, it remains in the carbonization chamber for a certain period before being removed; the longer the coking time, the longer the time during which the furnace remains at that temperature after maturation. Within a cycle time, the period from 20 to 22 hours is the maturation phase, while the period after 20 to 22 hours is the holding phase. 1. Maximum coking time: The so-called maximum coking time refers to the longest period of coking that can be achieved in the absence of an external heat supply. If an additional gas source is supplied, the extent to which the coking time is prolonged can be unlimited. Under conditions of extended coking time, in order to maintain the minimum temperature threshold of the coke oven itself, this limits the minimum amount of heating gas required; any lower amount would prevent the maintenance of that minimum temperature threshold. At this point, the coking time represents the maximum allowable coking time. Calculations show that when the production capacity of a large coke oven drops to 10% of its designed capacity, the amount of gas generated by the oven is sufficient to meet the heating requirements during periods of low temperature. However, since the graphite on the walls of the carbonization chamber has been burned away, the amount of waste gas leaking increases. For safety reasons, it is advisable that large coke ovens operate at no less than 15% of their designed production capacity, medium-sized coke ovens at no less than 20%, and small coke ovens at no less than 25%. Therefore, the maximum coking time for large coke ovens is approximately 100 hours, for medium-sized coke ovens it is about 80 hours, and for small coke ovens it is around 50 hours. In reality in China, individual large-scale coke ovens have reached 15% of their designed capacity when operating at low load; generally, this figure is above 25%, meaning that the coking time is below 70 hours. 2. Furnace temperature management: As the coking time increases, for every additional hour within the range of 22–25 hours, the standard temperature decreases by 10–15ºC. When the coking time exceeds 25 hours, the furnace temperature remains relatively constant; at this point, the standard temperature is maintained around 1200ºC, with it generally not falling below 1150ºC. When the standard temperature drops, the fluctuation range of the straight-line temperature increases due to reduced heat stored in the silicon bricks in the carbonization chamber, decreased heating intensity, and the effect of holding the furnace at a constant temperature during the later stages of coking. This makes it difficult to control the furnace temperature; it is necessary to analyze the temperature variation patterns throughout the carbonization cycle, rather than adjusting the gas supply arbitrarily. An extended coking time has a significant impact on the temperature distribution across the row. The coking time is between 22 and 24 hours, during which the shape of the temperature curve across the width gradually changes. When the coking time reaches around 30 hours, the temperature in the side channels drops sharply, and the cross-sectional curve takes on a \"steamed bun\" shape. This situation arises due to the following reasons. The amount of heat dissipation from the furnace surface is determined by the average temperature inside the furnace. Since the final maturation temperature of the coke cake is not dependent on the coking time, increasing the coking time results in a slight difference in the average temperature inside the furnace compared to normal coking times, but this change is not proportional. This factor leads to an increase in the heat dissipation ratio of the furnace surface. The heat dissipation from the furnace surface relies primarily on the supply of gas and air to the side flues. Since the amount of gas and air supplied to these side flues (usually 30%–40% more than necessary) is designed based on normal coking times, factors such as cracks in the upper and lower burners as well as heat loss in the regenerator area pose challenges to the heating process in these side flues. Therefore, as the coking time increases, the temperature in the side channels continues to drop, thereby disrupting the normal distribution of temperatures across the row; the degree of distortion in these temperatures depends on the extent to which the temperatures in the side channels decrease. When adjusting the temperature of the horizontal row, it is primarily necessary to increase the air supply to the side flues to compensate for the heat loss. Under normal circumstances, the temperature of the side flue should be maintained at no less than 1050ºC. Therefore, appropriate measures must be taken to ensure the temperature in the side flues, so as to achieve basically uniform curing of the coke cake. 1. Method to increase the amount of gas and air in the side flues: When using coke oven gas for heating, the coking time for bottom-firing coke ovens is less than 24 hours; in this case, increasing the diameter of the nozzles in the side flues can be used to raise the gas supply. However, when the coking time increases further, this approach becomes less effective, and it is then necessary to reduce the diameter of the nozzles in the middle section in order to increase the gas flow in the side flues. When the coking time fluctuates frequently but can return to normal levels quite quickly, it is common to use iron wires in the middle burner nozzles to increase the temperature of the side burners. After increasing the gas flow in the side flues, to ensure normal combustion, the air coefficient can be increased appropriately; in this case, it is preferable to keep the air coefficient in the central flues on the higher side. This also helps to prevent a drop in the temperature of the small flue. A method to increase the temperature of the side channels in a side-entry coke oven is to install brick orifice plates in the horizontal brick gas channels; for example, such orifice plates can be placed between channels 2–3 and 26–27, with the diameter of these orifice plates being about 30% of the diameter of the brick gas channels. When heating with blast furnace gas, to increase the temperature of the side flues, a method of inserting bricks as barriers in the small flues can be employed. However, the disadvantage of this method is that it is difficult to install and has a negative effect on downward airflow. It is also possible to reduce the suction force generated by the upward airflow; this can lower the suction force by 5–10 Pa. As a result, the air volume in the side burners increases, thereby raising the temperature of those burners. Consequently, the pressure at the observation holes also increases by 5–10 Pa. When using blast furnace gas for heating, the method of supplementing coke oven gas to the side flue yields a more significant effect in raising the temperature of the side flue. The control of the air coefficient can be increased to ensure complete combustion in each flame channel. 2. Spraying repair of burner cracks and sealing of the regenerator area. As the coking time increases, the temperature drops and the amount of graphite decreases on the furnace wall, leading to increased leakage of raw gas. This deteriorates the combustion condition of the gas in the side flues; therefore, shot blasting is used to seal the furnace wall, reduce raw gas leakage, improve the combustion conditions in those side flues, and raise their temperature. Due to leaks in areas such as the regenerator section, the front of the chute, and the fitting parts of the small flue ducts, the heating in the side flues is also compromised. Sealing these areas is essential for improving the heating in the side flues, especially when using blast furnace gas for heating. 3. Control of coal gas pressure. Due to the increased coking time, the amount of heating gas decreases, which inevitably leads to a drop in gas pressure. To maintain normal gas pressure, it is necessary to replace it with a throttle orifice plate with a smaller aperture. The orifice size of the orifice plate should be determined through calculation, depending on the extent to which the coking time is extended. When the coking time is long and the amount of gas is low, a sign-based management method can be employed: sufficient gas is supplied to the furnaces in the coking stage, while less gas is supplied to those in the holding stage. However, this method is quite complex to manage; it is necessary to establish proper identification markers and operation records, keep track of dynamic changes, etc., in order to avoid high and low temperatures. 4. Monitoring of collector gas pressure and temperature. After the coking time increases, the gas collection pressure decreases and experiences significant fluctuations due to the reduced amount of gas produced and the longer intervals between product removals. To reduce fluctuations in the pressure of the gas collection pipe and maintain it effectively, it is possible to adjust the gas circulation volume in the large circulation pipe of the blast condensation system, as well as to strengthen the operational coordination between the gas collection pipe and the blower. The temperature of the gas collection pipe should be maintained at 80–100ºC, and the pressure of the ammonia solution is controlled to keep this temperature stable. To maintain a sufficiently high ammonia pressure to ensure the spraying of ammonia in the bridge tube, the spraying at the gas collection pipe can be partially or fully shut off when the temperature of the gas collection pipe is low. 5. Formulation of the coke pushing plan. When the coking time is extended, the number of times of taking the coke out decreases. If coke pushing is carried out according to the original maintenance schedule, it will inevitably result in prolonged maintenance times and uneven gas production. Therefore, it is necessary to rearrange the frequency of maintenance and formulate a coke pushing plan that suits the conditions of extended coking time. The arrangement principles are as follows: ① The operation time per batch should not be too long, to avoid damage to the furnace body due to the door remaining open for an extended period ； ②Remove from the furnace evenly to ensure a consistent gas generation rate and stabilize the pressure in the gas collection pipe.