Ammonia level---in reverse gear

It is necessary to analyze the problem; perhaps you have determined that the temperatures of the two gases are different, with the temperature of the gas exiting the synthesis tower being higher. As a result, the actual volume at the same pressure reading is smaller, which leads to a lower ammonia content. Such a result will never occur under any circumstances.

I also think it’s a problem with the sampling temperature; at the same volume, gases at higher temperatures have a lower density. If the ammonia content remains unchanged at the same temperature, then the ammonia content in the same volume will definitely differ at different temperatures.

Assuming no analytical errors: Ammonia in the process gas before the inlet cooler has already partially liquefied.

This phenomenon is likely caused by the large temperature difference between the gas exiting the synthesis tower and the gas after water cooling; the temperature difference between the two should be over 240 degrees.

In my opinion, since the measured ammonia content is given as a volume percentage, the results should not be greatly affected by temperature. Is it related to the location of the sampling point?

Under normal circumstances, liquefaction does not occur before the water inlet cooler. If the analytical causes have been ruled out, it is also possible to check whether there are any changes in the circulation flow rate, with the aim of determining whether there is a leak in the circulation heater; if there is a leak, the concentration might be low.

As for whether liquefaction may occur before the water cooler, refer to the table below: Temperature, Pressure; T ºC, K, atm, Mpa: 50, 323.15, 20.4086, 2.06790; 51, 324.15, 20.9369, 2.12144; 52, 325.15, 21.4753, 2.17599; 53, 326.15, 22.0238, 2.23156; 54, 327.15, 22.5825, 2.28817; 55, 328.15, 23.1516, 2.34584; 56, 329.15, 23.7312, 2.40456; 57, 330.15, 24.3214, 2.46437; 58, 331.15, 24.9223, 2.52525; 59, 332.15, 25.5341, 2.58724; 60, 333.15, 26.1568, 2.65034; 61, 334.15, 26.7907, 2.71457; 62, 335.15, 27.4358, 2.77993; 63, 336.15, 28.0922, 2.84644; 64, 337.15, 28.7602, 2.91412; 65, 338.15, 29.4397, 2.98298; 66, 339.15, 30.1310, 3.05303; 67, 340.15, 30.8342, 3.12428; 68, 341.15, 31.5495, 3.19675; 69, 342.15, 32.2768, 3.27045; 70, 343.15, 33.0165, 3.34540; 71, 344.15, 33.7686, 3.42161; 72, 345.15, 34.5333, 3.49909; 73, 346.15, 35.3108, 3.57786; 74, 347.15, 36.1011, 3.65794; 75, 348.15, 36.9044, 3.73934; 76, 349.15, 37.7209, 3.82207; 77, 350.15, 38.5506, 3.90614; 78, 351.15, 39.3939, 3.99159; 79, 352.15, 40.2508, 4.07841

1. Sampling issues 2. Leaks in the inlet and outlet heat exchangers 3. Poor heat exchange efficiency of the heat exchanger 4. Liquid presence inside the tower

Our analysis results are exactly the opposite of yours. During the major maintenance last year, we replaced some of the synthetic catalysts; after that, we hoped that the ammonia content at the outlet of the synthesis tower would be higher than before. It was around 18.5% previously, but in reality it was lower, at around 18.2% (as measured at the outlet of the heat exchangers at the inlet and outlet of the synthesis tower). We also took samples at the inlet, where the value was around 20%. We suspect there might be a leak in the heat exchangers, but the system pressure and flow rate don’t indicate any leakage. Therefore, we suspect the problem lies with the sampling process. The analysts conducted repeated analyses, and the values ranged between 18% and 20%; they said that the accuracy of the data depends on the time of sampling. Additionally, if there were a leak in the heat exchangers, ammonia would only leak from high pressure to low pressure, so it’s impossible for the ammonia content at the outlet to be lower than that at the inlet. I still think the issue is related to the analysis. We recommend that you take more samples from different locations, rather than sticking to the usual sampling points.

I think there are several possibilities: 1. When analyzing the samples, the gas temperatures of the two samples are different. 2. The gas coming out of the ammonia synthesis tower is at a high temperature; after passing through the rear boiler and the circulating gas preheater/cooler, some liquid ammonia is formed (with a relatively high concentration). In other words: this results in high ammonia levels after the heat exchanger.

That makes sense; high-pressure processes weren’t considered initially, as liquefaction wouldn’t occur under a pressure of 15 MPa. But processes with pressures of 20–30 MPa or so should work