Liquid nitrogen inlet to new storage tank
Thread Content
We have a newly installed 100 Nm3 liquid nitrogen storage tank ready to be filled with liquid nitrogen. Could you all please advise on how to proceed and share any important considerations? Thank you very much
First, use the inlet valve to fill the tank with nitrogen, which is then blown out from the bottom of the tank for displacement; once the displacement is satisfactory, close the bottom blowout valve and fill the tube with liquid.
Is it better to use a gas for displacement or to use a liquid directly? Is it necessary to pre-cool the new tank before filling it? Thank you
Before operation, pre-cooling by displacement is carried out, with the temperature being reduced step by step as required; feeding begins once the designed temperature is reached. Personally, I hope the experts here can give me some feedback. :)
For example, if a liquid is being received, it can be directly pre-cooled by replacing it with a low-temperature gas.
Is it a vertical storage tank? It is recommended to first introduce nitrogen at low temperature from the bottom, increase the pressure from atmospheric to around 0.3 MPa, then manually reduce the pressure to around 50 kPa. Repeat this process of increasing and decreasing pressure several times, and observe the gas being discharged through the overflow port; the pipeline will frost over rapidly, or the temperature of the discharged gas will be below -60°C. Then liquid can be introduced from the bottom, and any excess gas pressure is released. Make sure the pre-cooling is thorough, and the liquid flow should be steady to prevent a sudden rise in pressure.
Generally, new tanks are equipped with pressure protection; when being filled for the first time, it is necessary to purge the storage tank, pipelines, and related control components； Cooling storage tank ； Quality assurance (mainly focusing on purity and dew point requirements) ； It is also necessary to install boosters, economizers for the storage tanks, as well as pipeline pressure regulators. If a gas company is commissioned to deliver liquid nitrogen, such companies generally have standard filling procedures and will be responsible for or recommend the filling steps.
It generally involves three steps: the first step is gas-phase nitrogen displacement, typically by applying a pressure of 0.3 to 0.5 MPaG, with the pressure being increased and the displacement process repeated three to five times； Second step: pre-cooling, first in the gas phase and then in the liquid phase ； In the third step, after the storage tank has been properly pre-cooled, liquid nitrogen is unloaded.
The general instruction manual provides operating guidelines. Newly manufactured tanks are sealed with nitrogen upon leaving the factory, so there is no need for gas replacement; after that, liquid is introduced for pre-cooling, and once cooling is complete, liquid is added for filling
Under normal circumstances, new tanks leaving the factory are sealed with nitrogen at a pressure of around 0.03 Mpa, so no replacement is necessary. Check the pressure gauge in advance or open the valve to see if gas is coming out. After that, carry out pre-cooling by feeding liquid in; typically, a spray system for feeding liquid is used, which allows for rapid cooling. Once cooled, fill the tank by feeding liquid from both the top and bottom