Deformation of the ammonia tank roof and issues with the breather valve
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Hello everyone, we have a 50-cubic-meter ammonia tank in the factory building. The top of the tank is equipped with only one vent valve and one level gauge; there are no access holes on the tank walls or anywhere else on its surface. Moreover, the exhaust pipe connected to the vent valve leads directly outside the building. This tank has been in use for over 4 years without any cleaning or inspection. When loading/unloading, it appeared that the top of the tank was deformed. Is it still possible to inspect the vent valve, replace it, and take corrective actions? Since ammonia is toxic, one does not dare to handle it without proper experience. I would like to ask if anyone has any suggestions for a solution; if corrective actions are needed, how should they be carried out? Thank you!
It’s very likely that the negative pressure caused it to collapse; it’s a fortune that no serious accident occurred! It is recommended to engage a professional firm to ensure that the safety facilities are properly implemented. During tank maintenance, the tank must be thoroughly cleaned, and all pipes need to be isolated. Since there are no manholes, it is recommended to fill the tank with nitrogen to protect it from fire during maintenance work ； Similar to car body work, the tank roof is cut off, shaped back to its original form, and then welded back in place ； Check the breather valve on the tank top and the pipelines for any blockages; wear a positive-pressure air respirator or an ammonia-resistant gas mask when removing them.
Some breather valves come with a flame arrestor function, and the mesh layer used for flame arrestation can get clogged easily; this needs to be checked. Also, make sure the air intake volume is matched to the pump
The ammonia tank uses a water seal as its venting system. It absorbs excess exhaust gases and also has a flame arrestor function. The water seal device is like a small beaker placed upside down on top of a larger beaker. Positive pressure is used to exhaust the exhaust gases, while negative pressure is used to draw back some of the ammonia water. The equipment is not subject to pressure, so it is very safe.
A breather valve is used to maintain pressure balance in the storage tank, preventing it from experiencing excessive positive or negative pressure. Both can cause tank accidents. Excessive positive pressure can cause the circumferential seams of the tank lid and wall panels to crack or burst, while negative pressure can lead to deflation or deformation. If the deflation or deformation returns to normal after equilibrium is achieved inside the tank, there is generally no problem. Therefore, the breathing valve needs to be inspected regularly, and the pipe leading outside the valve must not have any upward bends, to prevent excessive back pressure.
The tank collapses due to insufficient air supply when it is under negative pressure; from the picture, it can be seen that this vent valve only has the function of releasing air under positive pressure.
The pipeline in front of the breather valve should have a certain degree of curvature; when the pressure inside the tank is negative, air needs to be introduced to equalize the pressure
Water can be filled in to push up the deformed area.
As can be seen from the drawings, the 50-breather valve has a relatively low air replenishment volume. Based on empirical analysis, with a transfer pump of 25 units and a flow rate of 250 L/min, the air supply volume per minute is 250 L; therefore, it is advisable to use a DN100 breathing valve.