Transformation of carbonammonium crystals
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It is said that NH3, CO2, and H2O easily lead to the formation of ammonium bicarbonate crystals. Since all three of these gases are present in the gas coming from the top of the condensate stripping tower in the conversion unit, then doesn’t it become very easy for ammonium bicarbonate crystals to form at lower temperatures? How to prevent crystallization from blocking the heat exchanger tubes?
“I’m not familiar with the equipment called “condensate stripping tower in the transformation section”; perhaps the process is different, which is why it has a different name. However, there are methods in the Lind process to prevent the crystallization of ammonium bicarbonate, and the main location for this is in the pipeline at the top of the final separation tank in the shift conversion section. The prevention methods are as follows: 1. The pipeline leading to the purification section of this tank is equipped with a heat tracing pipeline. 2. There is a spray line at the top of this tank (the spray medium is BW). In terms of process operation, it is also required that the temperature of the process gas in this tank not be too low, in order to prevent the crystallization of ammonium bicarbonate.
The upper pipelines of the condensate stripping tower in the utility conversion system are equipped with heating; you should take a close look at your company’s process – that heating pipeline is one of the streams derived from the steam used for stripping at the lower level! The main method to prevent ammonium carbonate crystallization is heat tracing!
The converted condensate stripping tower is primarily used to strip the ammonia-washing water from the ammonia-washing tower as well as the acidic water recovered from sulfur processing. No semi-heating stage is provided after the gas lift tower for the gas exiting it, mainly because the temperature of the gas leaving the tower is high, making it difficult for ammonium salts to crystallize (ammonium salts primarily form at temperatures below 75 degrees) ； It is semi-heated together with the stripping steam after exiting the pipe rack of the flash tank. A low-pressure steam line is also installed on this pipeline, mainly used for melting the crystals during the crystallization process!
So, does the process gas pipeline need to be insulated before entering the ammonia washing tower? At this point, the temperature of the pipeline is around 40 degrees
In our process, the shift gas is cooled by desalinated water and cooling water before entering the ammonia washing tower. In Tianchen’s design, the shift gas pipeline is equipped with heating elements; the main purpose of this is to prevent the formation of ammonium bicarbonate crystals, right? Is it possible to remove those heating elements?
As far as I know, in the Lindlar methanol washing unit, the pipeline carrying the process gas before it enters the ammonia washing tower is not insulated; the temperature in such pipelines drops to around 20 degrees when the outside temperature is low. The BW used for ammonia washing also has a temperature of around 20 degrees after being cooled by circulating water. Yet, no ammonium carbonate crystallization has occurred, and the ammonia content in the process gas exiting the ammonia washing tower is barely detectable
The process gas exiting the ammonia washing tower definitely contains very little ammonia. For the process gas pipeline that enters the ammonia washing tower in Phase 1, heat tracing was installed (as designed by Tianchen); in Phase 2, we handled it ourselves by removing the heat tracing. I’m not sure if this had any impact
Our company designed it with Tianchen, and heating has been added! A separate stream of washing water has also been provided! I think it’s better to add it; it won’t cost that much! If the car has to be stopped for a few days because of this crystal, all this money will be lost! Our company is in the north, so everyone is quite careful about freezing and crystallization issues!
The heat tracing cannot be removed, otherwise it can easily cause blockages in the pipes. Our company faced difficulties because cutting off the heat tracing steam led to blockages in the system pipes; it was a tricky situation!
It is best to include heat tracing pipes. Our facility was designed by the Third Research Institute, and the preliminary design documents do not mention any heat tracing pipes. It is understood that in some facilities, the lack of heat tracing pipes at the start of production led to severe contamination with ammonium carbonate, which even forced shutdowns of the equipment. Moreover, heat tracing pipes are not very expensive. The condensers in stripping towers are usually cooled by circulating water. To prevent crystallization-induced blockages in these condensers, it might be advisable to use a mixture of circulating water and condensed liquid, keeping the temperature of the condensed liquid around 70 degrees. This approach can effectively reduce the risk of blockages and ensure the stable operation of the system.
A ammonia washing tower isn’t necessary, as the levels of CO2 and NH3 inside are too low. The acidic gases coming out of the stripping tower mainly consist of H2S, CO2, NH3, as well as water vapor; at lower temperatures, these substances tend to crystallize. A heat mixer should be installed behind the cooling unit for the acidic gases in the stripping tower.
I learned it! But I wonder if the reaction in which CO2 + NH3 + H2O produce ammonium carbonate really occurs so easily Do you know the conditions for this reaction? At what temperature does crystallization occur easily?