What is the unknown substance appearing in the cold exchangers of the ammonia synthesis system?
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In my workshop’s ammonia synthesis system, there have been repeated instances of increased pressure differential in the cold exchangers, rising resistance, and a decrease in the system’s circulation volume. The problem could be resolved by using steam to treat the cold exchangers during shutdown periods, but similar issues reappeared after production resumed for a while. During the maintenance process, after removing the internal components of the circulator, many unknown substances were found on them; they were white crystalline substances. At the same time, the internal separation section of our cold exchanger features baffling and a filter screen, with the inlet temperature of the cold exchanger being -5 to 0°C. Are there any cases similar to ours? What is this substance? How can it be solved? Our analysis did not reveal what the substance is; could it be ammonium carbonate crystals, urea crystals, or organic compound crystals? Those who know please give some guidance! ! !
It is generally ammonium carbonate crystals. The trace levels of the synthetic make-up gases CO and CO2 should be above 15PPM; controlling these trace amounts properly is necessary to resolve the aforementioned issues.
It’s ammonium carbonate crystals; our factory has encountered this too! Control the amount in the upper section to a minimum! Raise the ammonia level to allow liquid ammonia to absorb trace amounts.
It should be ammonium carbonate crystals; it is recommended to analyze the levels of CO and CO2 to ensure they are within acceptable limits before introducing gas into the synthesis system! ~!
Reply to 4# qinyu790727: Then the synthetic catalyst will be affected
It is ammonium bicarbonate crystals; it is recommended to strengthen the management of process parameters and strictly control the levels of CO + CO2 after refining, especially the CO2 level. Additionally, I would like to know where in your company the fresh gas is supplied. If the supply gas is introduced before the water-cooling outlet and before it reaches the heat exchanger, the results should be better.
It is due to an excess of carbon dioxide in trace amounts, which causes ammonium carbonate crystals to form in the exchanger. Moreover, the filter screens in the exchanger prevent these crystalline deposits from being carried away, resulting in their accumulation over time. In such cases, one approach is to control the trace amounts carefully, and the other is to wait until the major repair is done to modify the internal components.
Install a descaler to prevent scaling; use ultrasonic descaling devices, silicon-phosphorus crystals – QQ1640246222, AC learning*
Ammonium carbonate crystals. It’s not clear what the upstream gas purification process is; if it involves alcohol alkylation, then ammonia washing can be added. If that’s not the case, molecular sieves can be used to address the issue. Based on the experience of Yueyang Petrochemical, the use of molecular sieves together with ammonia synthesis catalysts allows for operation for over 10 years, which is cost-effective from an economic perspective.
Our company has encountered this phenomenon before as well; reducing the ammonia cooling temperature by controlling it at a low level also works well
This is likely due to high levels of trace substances, which cause crystallization within the cold exchanger. Our company also experiences high levels of trace substances and faces the same issue. The solution we employ is to inject water into the sampling and analysis points located on the pipes leading into the cold exchanger; this approach proves effective, as both the pressure difference and the condensation temperature decrease significantly. You can give it a try.