Minor effects in synthetic production

　　Trace amounts of CO2 and CO originate from substandard fresh syngas, as the levels of these gases at the outlet of the methanation reactor exceed the allowed limits, remaining above 10×10-6 on a continuous basis. The main reasons for the slight excess at the outlet of the methanation furnace are: ① Failure in the upstream decarboxylation system, resulting in an excessively high level of CO2 at the inlet; ② Failure in the upstream low-temperature shift reactor system, leading to an excessively high level of CO at the inlet; ③ Poisoning and deactivation of the catalyst in the alcohol-to-hydrocarbon conversion furnace; ④ Flow deviation and penetration incidents within the catalyst bed of the alcohol-to-hydrocarbon conversion furnace; ⑤ Improper operation, with the gas from the outlet of the alcohol-to-hydrocarbon conversion furnace being fed into the syngas compressor and synthesis tower systems without proper analysis. All of the above factors can lead to poisoning of the ammonia synthesis catalyst, resulting in a decrease in its activity, changes in tower temperature, and a shortened service life of the catalyst. During the normal operation of the equipment, it is necessary to strictly follow the operating procedures to prevent unqualified methaneation reactor outlet gas from entering the syngas compressor and synthesis tower systems. Once signs of a slight excess are detected, it is necessary to investigate as per the points outlined above as soon as possible and arrange for analysis promptly. The most important thing is to take decisive action in a timely manner.

It can be clearly seen from the catalyst hotspot temperature that when the trace amount is high, the hotspot temperature first rises and then drops, which is different from any other abnormal situation.

If there is a slight excess, the most obvious effect will likely be a significant and rapid increase in the temperature of the methanation catalyst bed. The function of methanation is to react with the remaining carbon monoxide in the decarburization system. The reason for the high trace level may be poor low-temperature conversion, which leads to an excessive carbon monoxide content at the low-temperature outlet. At the same time, if the decarbonization system fluctuates, even minor fluctuations will occur. Also, if the reaction in the conversion section does not proceed well, the concentration of carbon monoxide produced will be relatively high.

If the amount of fresh gas in the synthesis stream is high, the temperature at zero meters will increase first, and the temperature at the hot spots will drop; it is necessary to reduce the circulation rate. In cases where the excess is severe, the temperature may even fall. At this point, contact the previous section first; depending on the situation, carry out gas replenishment and venting, or quickly identify the cause and take appropriate action to resolve it.

If there is a slight increase in the amount of syngas, the temperature in the synthesis tower will respond significantly: the temperature in the initial stage will drop while the temperatures in the other stages will rise. If this is not addressed promptly, when the temperatures in all other stages also drop, the synthesis pressure will surge sharply, causing poisoning of the catalysts used in synthesis, which makes it difficult to carry out further repairs.

Principle of catalyst poisoning: When CO and CO2 enter the synthesis tower, they react with hydrogen in the presence of the catalyst as follows: CO + 3H2 = CH4 + H2O; CO2 + 4H2 = CH4 + 2H2O. The water vapor generated then reacts with the active component a-Fe in the catalyst as follows: H2O + Fe = FeO + H2; 3H2O + 2Fe = Fe2O3 + 3H2. In this way, the active a-Fe in the catalyst is oxidized to ferrous oxide and ferric oxide. The catalyst is repeatedly oxidized, causing the iron grains to grow and resulting in a decrease in its activity. phenomenon ； 1. The temperature of the synthesis tower is maintained by the heat released from the exothermic reaction 3H2 + N2 = NH3; as the catalyst’s activity declines, the amount of heat generated decreases, and consequently the temperature of the synthesis tower drops. 2. The synthesis process is a loop: the gas supplied is discharged after ammonia is produced. As the catalyst’s activity declines, the rate of ammonia synthesis decreases, causing the supplied gas to accumulate in large quantities within the loop, which in turn raises the synthesis pressure. 3. The poisoning reaction is also an exothermic reaction; therefore, during synthesis poisoning, there is a brief temperature rise at zero meters. As the catalyst’s activity decreases, the temperature throughout the synthesis tower drops sharply. In other words, the temperature rises in the first two points, while it drops in the latter ones. We commonly call it crossing. Of course, the temperature rise time for the previous points will not be long; if the poisoning is severe, the temperature of the entire synthesis tower will drop. External handling ； For Stage 1, shut off the gas supply valve to stop feeding in unqualified gas until the synthesis temperature is normal and the gas meets the requirements. (When replenishing with qualified gas, the supply pipeline must be purged.) 2. Shut off the cold bypass line to reduce the circulation volume and prevent further temperature drops. 3. Open the vent valve on the tower and control the synthesis pressure to prevent overpressure. 4 If necessary, turn on the electric furnace to raise the temperature using the heat it provides. 5 If the poisoning is severe, all the defective gases in the system must be vented, and the system should be replaced with proper gases following the standard process. The toxic reaction resulting from synthesis is also a reversible one; as long as the poisoning is not severe, it is detected in time and treated promptly and appropriately. The synthesis temperature can be completely maintained. It is only poisoning that shortens the service life of the catalyst; therefore, it is essential to prevent substandard gases from entering the synthesis tower. Please have the original poster take a look at these two links: 1. Catalyst poisoning in ammonia synthesis towers 2. Treatment of catalyst poisoning. This post was last edited by snowdfr on 2009-3-12 at 19:18.]