What is the reason for the high oxygen content at the bottom of the ammonium sulfate storage tank?
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I encountered a problem today: the workshop plans to clean the ammonium sulfate storage tank. This is a tank that operates at normal temperature and pressure, with a radius of 1500 mm and a height of 6000 mm. It has a PTFE lining and an agitator. After the ammonium sulfate solution is removed from the tank, the gas content inside it is monitored; the oxygen level at the bottom of the tank is 26%. Source of the ammonium sulfate solution: Methane, ammonia, and air are burned in a water-cooled reactor to produce hydrocyanic acid. The reaction mixture is washed with sulfuric acid in an ammonia absorption tower to remove excess ammonia; during this washing process, ammonia reacts with sulfuric acid to form ammonium sulfate solution. After further dehydrogenation to remove hydrocyanic acid, the solution is sent to storage tanks, and from there it is transported to the storage tanks of our company. I can’t figure out where this oxygen comes from; please help analyze it.
Possible reasons are as follows: 1. **Residual air**: After the ammonium sulfate solution is removed, there may be residual air in the storage tank. Since the density of oxygen is lower than that of some other common gases, it may accumulate at the bottom of a storage tank. 2. **Incomplete sealing**: If the storage tank is not properly sealed during use or maintenance, outside air may penetrate into the bottom of the tank, especially if there are low points or other structural features that trap air. 3. **Air content before reaction**: Before the reaction between ammonia and sulfuric acid occurs, if the ammonia contains unreacted air, this air may be carried into the tank along with the chemical substances. 4. **Air intake during extraction**: During the extraction of ammonium sulfate solution, improper operation or equipment issues may cause outside air to be drawn into the storage tank, especially if a pumping system is used and there are leaks. 5. **Incomplete degassing**: Although degassing was carried out before feeding the ammonium sulfate solution into the storage tank, this process may not have been completely thorough, and a small amount of gas (including oxygen) may still remain. Checking these possible causes and ensuring the integrity of the storage tank as well as the proper operation of the pumping equipment can help reduce the risk of similar problems occurring in the future. At the same time, regular gas monitoring can help manage tank safety more effectively. .