The circulating gas in the dry quenching process has a high oxygen content and a low CO level
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In the dry quenching process at our plant, the oxygen content in the cycle gas is 1–2% higher, while the CO level is 4–6% lower; CO2 levels also increase accordingly. I can’t figure out where the extra oxygen comes from – shouldn’t CO levels rise if it enters from the negative pressure area or the furnace opening? At the moment, the furnace lid isn’t airtight and the nitrogen isn’t pure, but the shift leader told me that no nitrogen is being supplied from the outside. So where exactly is this oxygen coming from?
A possible reason is that the furnace lid is not airtight, allowing external air to enter the system. The oxygen in the external air increases the oxygen content in the circulating gas, and this oxygen participates in the oxidation reaction of CO to CO2 once it enters the system, resulting in a decrease in CO levels and an increase in CO2 levels. It is recommended to check and repair the sealing issue of the furnace lid to reduce the infiltration of external air. At the same time, other possible leak points such as pipe connections and valves should also be checked. .
I know; the issue lies in the oxygen content – the air intake is set at only 3%
If the air intake is set to only 3%, the influx of external air may mainly come from leaks in the furnace lid or other parts of the system. A loose furnace lid is a likely source of leakage, especially at high temperatures, as the seal may become inadequate due to uneven expansion or damage of the materials. In addition, check for potential leakage points in the system such as access doors, observation ports, and connection pipes, as these areas can also be pathways for oxygen to enter the system. It is recommended to conduct a thorough leak detection to ensure that all connections and sealing points are in good condition. .
Doesn’t the air that enters through the furnace lid come into direct contact with the coke? Doesn’t oxygen react directly with the coke to produce CO? Shouldn’t the level of CO be high in that case?
Indeed, if oxygen comes into direct contact with coke, it theoretically promotes the formation of CO. However, if oxygen reacts partially with the existing CO at high temperatures to form CO2, it is also possible to result in lower detected levels of CO and higher levels of CO2. This process depends on the specific conditions of contact between oxygen and coke or CO, such as temperature, contact time, and the oxygen concentration in the reaction area. Furthermore, if the amount of air that leaks in is relatively small, some of the oxygen may not be completely converted into CO, but instead be oxidized by the existing CO into CO2. In this case, although fresh oxygen is supplied, it is not completely converted into CO, which may result in a relatively low CO concentration. Further analysis can be carried out by improving leak detection, monitoring the operating parameters of the coke oven, and visually observing the reactions inside the oven using cameras or probes, in order to more accurately determine the source and impact of oxygen. At the same time, it is also possible to consider adjusting the operating conditions of the coke oven (such as temperature, pressure, and gas flow rate) in order to optimize the balance of CO and CO2 production. .