High pressure difference in the liquid nitrogen cooling tank
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Our company’s production process involves the production of synthetic ammonia from coal, and for the liquid nitrogen cooling tank system, Zhongtai has been chosen as the supplier. Under normal operating conditions, the pressure difference from the filter before the cooling tank (after the molecular sieve) to the nitrogen washing tower does not exceed 50 kPa. After the ammonia compressor stopped operating this time, and again after it was restarted (due to fluctuations), the pressure difference reached 100 kPa and gradually increased to 350 KPa. What could be the cause of this? How should it be handled?
First, the molecular sieve may be carried into the filter screen and clog it; second, the molecular sieve may be damaged, causing carbon dioxide to freeze inside the pipes. Is there a slight excess?
It’s likely the previous system – perhaps excessive CO2 levels resulting from methanol washing led to the adsorber being saturated. CO2 has entered the heat exchanger channels in the cold box; it’s possible to try increasing the temperature of the process gas fed into the tower, while ensuring that CO levels remain low. This can be achieved by reducing the flow rate of the fuel gas or increasing the flow rate of the washing nitrogen, with all other parameters remaining unchanged. The increase must be made gradually
The levels are within the normal range; I just opened the filters today, and neither filter is clogged. A few days ago, as the temperature rose, the pressure difference increased even more, reaching a maximum of 500 KPa
OP, how was the problem resolved later? Could you reveal it?
The raw material gas pipeline inside the cold box is blocked; it is possible to reduce the load and the outlet pressure in order to continue production. Once the opportunity arises, the cold box will be reheated, and after reheating, dew point and gas analysis will be conducted inside the cold box.
The raw material gas pipeline inside the cold box is blocked; it is possible to reduce the load and the outlet pressure in order to continue production. Once the opportunity arises, the cold box will be reheated, and after reheating, dew point and gas analysis will be conducted inside the cold box.
:If the LCO2 level is within the normal range, then it could be methanol. An increase in the pressure difference across the second heat exchanger indicates either CO2 or methanol, while an increase in the pressure difference across the third heat exchanger suggests methane.
It is unclear whether the valve connecting the NWU to the RECTISOL was closed at the time of parking; moreover, there could be a high pressure in the low-temperature methanol wash system and a low pressure in the cold box, which might allow impure hydrogen gas (containing CO2) to enter the NWU, ultimately leading to freezing in the cold box. If it has already been resolved, it would be best for the original poster to explain what caused it.
It is possible that the pressure in the system was too low at the time of exiting the vehicle, which caused carbon dioxide or methanol to penetrate the molecular sieve and led to crystallization inside the nitrogen washing tower. During production, the system temperature can be increased appropriately (as long as trace amounts remain within acceptable limits); if possible, the cold box should be thoroughly reheated