Why can’t liquid ammonia be completely unloaded using a pump?
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When transferring liquid ammonia from a tank truck, pumps are used; why is there always some liquid ammonia remaining inside the tank truck? It seems that the vapor phase lines of the tank truck and the storage tank are connected, so the liquid ammonia in the tank truck should be able to be completely transferred out, right? Please, experts, share your thoughts on this
Would it be better to use compression and increase the gas pressure?
My analysis is: the tank truck and the storage tank form a closed system; when the pump is in operation, the liquid ammonia level inside the tank fluctuates, resulting in an increased rate of vaporization； At this time, the interior of the tank truck is under negative pressure, so a large amount of liquid ammonia vapor enters the tank truck and re-liquefies. When it is almost gone, close the gas connection line between the tank truck and the storage tank, and at the same time vent the tank truck, so that it can be cleaned thoroughly.
Technically speaking, the gas connection line between the storage tank and the tank truck is always open, so the pressure in both is equal. What seems different is that the liquid level in the storage tank rises while the liquid level in the tank truck drops. Could it be that this affects the net positive suction head of the pump?
I mainly want to explore why it can’t be emptied completely using a pump
Since the gas phases are in communication, what is the gas phase pressure? It can’t be pressed out directly; can’t it be done without a pump?
I’m also wondering why nitrogen pressure isn’t used; as for why the pump can’t finish pumping, I’m not sure
This might be related to the installation height of the pump; once the liquid level reaches a certain point, and at a certain temperature, the pump reaches its cavitation point, causing the liquid ammonia to turn into gas inside the pump, which is why it can no longer be pumped up. As for not using nitrogen, I think it’s too troublesome to replace it with a tank truck.
Is it not necessary to use a discharge compressor? Generally, a portion flows by gravity first, after which the compressor is started to pressurize the tank truck via the gas phase, with the liquid phase entering the storage tank.
I mainly want to discuss why it can’t be cleaned completely; of course, the compressor can be cleaned thoroughly. I’m curious about the disadvantages of using a pump
This post was last edited by iamduyuming on 2016-9-5 23:16 :L