Problem of water in liquid ammonia storage tanks
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My device uses ammonia as a raw material, and liquid ammonia vaporized and softened water is absorbed to produce ammonia solution. During a recent inspection of the liquid ammonia storage tank, a large amount of water was found inside the tank. Did it come from the tank truck during the filling process? Does liquid ammonia containing water (it should be ammonia water) cause severe corrosion to ordinary carbon steel liquid ammonia storage tanks?
Generally, liquid ammonia tank trucks do not carry large amounts of water. The liquid ammonia tanks in our factory have been in use for many years, and no water has been detected in them. I suspect it might be coming back from your production system; please check it carefully.
It certainly didn’t flow back, as the pressure in the liquid ammonia storage tank is around 0.5–0.8 MPa. When it was said upstairs that a large amount of water wouldn’t be introduced, it meant not a huge amount, but is that really the case? Or is it that my supplier deliberately adds water to take advantage when weighing?
In addition to doubting the supplier, please pay attention to the following two issues: 1. When the pressure in the storage tank is low (positive pressure but not high), using water to absorb ammonia can cause backflow; that is, due to the intense dissolution and absorption of ammonia by water, water is drawn back into the container； 2. When the temperature is low, the vapor pressure in a static ammonia storage tank is low; if there is a heat exchanger with circulating cooling water above the tank, a leak could very likely lead to backflow. Circulating water enters the storage tank.
It is caused by the long-term accumulation of water in the purchased liquid ammonia; when the liquid ammonia arrives at the factory, its water content needs to be analyzed. I wonder if that was done? In such a case, simply drain the water (it’s best to use a drainage container that can capture ammonia gas).
May I ask ddfmy: liquid ammonia contains water – is that water in gaseous or liquid form within the liquid ammonia? I think that when stored at room temperature, due to the high pressure, it exists in liquid form, meaning it becomes ammonia water; such repeated filling over time leads to accumulation. Additionally, I would like to ask how to conduct a content analysis of liquid ammonia upon its arrival at the plant, and what are the precautions to take? (If it’s released, it will be ammonia, with a concentration of 100%, right?) ）
May I ask the original poster: Do you purchase liquid ammonia externally? If it is purchased externally, is it possible what you mean by “delivered by a tank truck”? As for whether it was an intrusion by your own devices, it will be easier to discuss this after understanding your relevant devices. Additionally, liquid ammonia does not cause corrosion to carbon steel on its own, but corrosion will occur if water gets in, so the property owner should be aware of this.
There are many intermediaries these days who add water to the tank trucks. Our company has discovered this issue, and some suppliers now require that the tank trucks be emptied before they enter the factory and pass through the scale
How much do you mean by a large amount? The standards for liquid ammonia require an ammonia purity of ≥99.8% and a level of oil and water content of ≤0.2%. If liquid ammonia is used over a long period of time, some amount of oil and water may accumulate in it. However, over time it is usually the oil that becomes a problem. Of course, if the quality of the product supplied by your supplier is poor and does not meet these standards, then that’s a different matter. Additionally, if liquid ammonia contains too much water, it may exhibit some corrosiveness, though the degree of corrosivity is generally low.