Why is the outlet pipe of the ammonia evaporator clogged and crystallized?
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After one year of use, the ammonia nitrate evaporator using the high-pressure method in our factory is now frequently experiencing blockages in the outlet pipes, forcing shutdowns for maintenance. There are crystals like ammonium salts. The liquid ammonia used is derived from coal, and the operating pressure of the evaporator is 1.2 Mpa. I wonder if any expert has studied this? How crystals are formed. Let’s discuss together how to handle this
This situation may be caused by ammonia and carbon dioxide forming ammonium carbonate; it is recommended to install steam purge pipes near the areas prone to blockage.
The steam purging pipeline is in use, but the effect is not significant. Where does carbon dioxide in ammonia come from?
Is it a leak in the ammonia evaporator? The water used for heating contains nitrate ions, which react with ammonia to form *ao acid an. Perform a crystal analysis to determine what substance it is.
The operating pressure of liquid ammonia in the evaporator is 1.2 Mpa, while the pressure of the heating steam is only 0.5 Mpa. In the event of a leak, ammonia will leak towards the steam side
Check carefully; there’s a high possibility of a leak somewhere.
Dude, this is easy to understand. During the separation of ammonia in synthesis, the low temperature causes certain gaseous impurities present in the recycle gas to dissolve in liquid ammonia, including methane, carbon dioxide, carbon monoxide, argon, as well as some water vapor and oils. It will be reflected in the exhaust gas recovery. Hehe.
It’s mainly oil contamination. Water cooling blockage.
It is recommended to increase the diameter of the heat exchange tubes; this will prevent blockages and also facilitate steam purging.
Every time, the blockage occurs on the ammonia gas outlet pipe after evaporation. It is not on the heat exchange tube.
What was said upstairs isn’t quite correct; it is methylamine, not carbamine, that causes crystallization at the outlet of the ammonia evaporator, thereby blocking the pipes. If this happens, it is most likely due to excessively low temperatures, which prevent the formed methylamine from melting and result in its crystallization. The poster can appropriately increase the operating temperature to prevent similar problems from occurring, and at the same time add steam purging at the pipe outlet. I think this should be able to eliminate this cleaning issue; (adding steam purging at the outlet is also intended to raise the temperature.)
It is recommended to consider analyzing whether the amount of ammonium salts in the bleaching acid discharged from the absorption tower is above the allowed limit. Do you recycle the neutralization and evaporation waste liquids from your absorption tower? If so, what is the situation regarding acidification treatment before the absorption tower? In addition, the purity of liquid ammonia, as well as the temperatures of the oxidation furnace and **evaporator, can also be taken into consideration. Nitrite content.
It was mistakenly identified as an **evaporator** above; it’s possible that the blockage in the ammonia evaporation and separation unit was caused by a neutralization reaction, with 70% of the **liquid** flowing into the ammonia evaporation and separation unit as a result of rapid startup or feeding.
You said it resembles crystals; do you mean crystals of ammonium salts? I don’t think so. Our company also has an ammonia evaporator that is heated using steam. Similar crystalline substances have also appeared inside the tube. After our analysis, it turned out to be the following: First, samples were taken for testing, and it was found that the substance inside the pipes was not ammonium salt crystals, but rather catalyst powder from the ammonia synthesis process. This substance appeared in certain areas of the pipes; upon checking the ammonia tanks, similar substances were found at the bottom of the tanks as well as at the pipe exits. Therefore, we recommend that you have the substance present in your company analyzed to determine whether it is indeed ammonium salt crystals, so that appropriate solutions can be found.