Liquid ammonia unloading flow rate control

I would like to ask if there are any effective methods to prevent pump cavitation when unloading liquid ammonia

Reply to 2# MintLife: Once the installation height of the pump is fixed, cavitation occurrence is only related to operation. Temperature, pressure, exhaust gas, etc. The magnitude and fluctuations of the flow rate can affect the occurrence of cavitation; for example, when the liquid ammonia flow is not yet stable at startup, opening the outlet valve fully too quickly can easily lead to cavitation. Actually, the biggest problem here is that when starting up, if the outlet valve is opened too quickly, it causes the flow control valve at the bottom of the tank truck to close automatically. This requires thorough exhaust of air; after the pump starts, the outlet valve should be opened slowly, and in some cases multiple attempts are needed to get the pump running properly. If a compressor is used, the above two problems will not exist. But if a high flow rate is required, for example if we need 2.5 m/s, which is 18 m3/h, the valve must be adjusted slowly; adjusting it too quickly could also cause the overflow valve to close.

Regarding the flow rate of liquid ammonia, it is better to consider factors such as cavitation and corrosion prevention

Personally, I still highly recommend using nitrogen pressure or a compressor. However, pumping is still *commonly used domestically. Sure, a few days ago I got in touch with a manufacturer who recommended a side-channel pump, which seems to be capable of handling both gas and liquid phases. The gas phase can be removed through a side channel. I don’t know much about it in detail; if the original poster needs to know, they can search on Baidu

Reply to 5# MintLife: Yes, that’s indeed the case; in a narrow sense, it’s more convenient to use a shielded pump. A major advantage of using a compressor is that it allows the liquid ammonia in the tank car to be completely drained, and the remaining gaseous ammonia can be recovered, thereby improving the efficiency of transport by tank car. However, this does not seem to be very attractive, as the amount of ammonia unloaded from the liquid ammonia tankers is based on the weight upon arrival at the plant minus the weight upon departure; in other words, the remaining ammonia not entering the system has little impact on the buyer, but it does have a significant effect on the seller’s profits.

The poster uses a pump to unload and feed the material – how high is the foundation of the ammonia tank at the site?

Do your factory’s pumps use positive displacement pumps or canned motor pumps? Thank you

The basics? It’s around 500, and if we include the height of the bottom of the spherical tank, it’s about 3 meters.

It used to be a shielded pump, but now it has been changed to a compressor; the results are different. However, we encountered some problems: when submitting the purchase order, the molecular weight was specified as 17, corresponding to pure ammonia; but in actual operation, nitrogen was used, which results in a molecular weight of over 20. As a result, the compressor kept shutting down. Later, the manufacturer came and adjusted the compressor’s belt and other components, thereby reducing its speed (i.e., the load), and that stopped the compressor from shutting down, although the flow rate decreased slightly.

A higher flow rate is also related to static electricity.