Air volume added to the two-stage furnace

It depends on whether the methane content at the outlet of the two-stage furnace is below the specified value; meanwhile, the hydrogen-to-nitrogen ratio in the synthesis tower also needs to be taken into consideration.

The last edit to this post was made by ZZJJAA70 on 2009-12-9 at 11:29. The purpose of adding air to the second-stage furnace is to supply nitrogen for ammonia synthesis and to further reduce the methane content in the gas from the first stage of conversion. However, the amount of nitrogen, and thus the amount of air, is determined by the hydrogen-to-nitrogen ratio in the synthesis system; it cannot be used simply as a means to adjust the methane content at the outlet of the second-stage furnace.

H2+CO/N2 = 2.8~3.1

There must be some approximate ratio, right, to reduce randomness in operations.

There is certainly a ratio; according to the principles of the ammonia synthesis reaction, a hydrogen-to-nitrogen ratio of 3 represents the most ideal condition. Of course, each facility has its own range of control parameters. To reduce the randomness of operations, it can be done as follows: there is generally a designed value for air flow rate, right? During normal production adjustment operations, adjustments can be made in a timely manner according to changes in load, and the basis for these adjustments is the relationship between the device’s load and the amount of air flow. Generally, there won’t be any major problems with doing this. Of course, changes in air volume also need to take temperature changes into account; when the temperature is low, the air density is higher, and the flow rate (volumetric flow rate) will be slightly lower. Of course, this effect is not very significant. The ultimate test of these control measures is the hydrogen-to-nitrogen ratio in the synthesis tower; however, there is a certain time lag between the hydrogen-to-nitrogen ratio in the synthesis tower and the air volume in the secondary furnace. Therefore, in order to improve operational accuracy and timeliness, the adjustment of the air volume in the secondary furnace should be carried out ahead of schedule. Of course, advanced control in chemical processes is also recognized as a good approach.

Calculate the hydrogen content in natural gas and that in air, then compare them; keeping the ratio between 2.8 and 3.0 should be sufficient. You should derive the results from your own experiments – it’s just my personal opinion

I’m not sure whether this is a design issue or an operational one. If it’s a design issue, then what we need to keep in mind is that the air introduced into the two-stage furnace serves two purposes: one is to provide oxygen for combustion, thereby generating heat, and the other is to balance the nitrogen content. Theoreticalally, the ratio of nitrogen to hydrogen should be 3:1; in this case, the amount of oxygen should be such that approximately 11–13% of the total combustible components in the gas entering the two-stage furnace are burned. The theoretical value can be calculated based on this. The specific details vary depending on the composition of the air entering the system; generally speaking, this is the approach used for calculations. There are some diagrams that can be found in textbooks on inorganic chemical engineering processes. As for operational aspects: factories usually do not treat this as the only parameter to be controlled. They typically monitor the methane content in the exhaust gas from the second-stage furnace, as well as the hydrogen-to-nitrogen ratio, and use feedforward control to regulate the amount of air supplied. It is also important to ensure that the furnace does not become overloaded and that the temperature remains within the range required by the catalyst

You can take a look at the study titled \"Research on Adding Excess Air to the Second Stage Furnace of Ke l l og g-Type Ammonia Plants\" (Cangzhou Fertilizer Factory, Hebei Province). Starting from actual production conditions, it analyzes from a theoretical perspective the impact of adding excess air on the system, as well as how to optimize operations.

6# Huang Xinhui: According to what you said, is it like this? For example, if the amount of air introduced when I’m operating at full load is 35,000, then 40% load would be 40%*35,000? Is that so?

This post was last edited by ZZJJAA70 on 2009-12-12 at 19:48. Ask your supervisor for a simple method: take over and check whether the fresh hydrogen and recycled hydrogen are stable. If they are stable, divide the air volume by the raw gas volume to obtain a ratio; adjust the load by using this ratio – increase the load slightly above this ratio and decrease it slightly below it. Also, monitor the fresh hydrogen-to-nitrogen ratio and make adjustments accordingly. Actually, you get used to it with more practice. This ratio cannot be used continuously, as it changes constantly with factors such as temperature and pressure.