Reasons for excessive moisture in the drying tower
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This post was last edited by Danzhi on May 24, 2010, at 17:19. Danzhi noticed that the moisture content indicators for drying towers in many sulfuric acid plants were not satisfactory. In the plant where Danzhi used to work, the moisture level in the drying tower also failed to meet the required standards at the time. The analysis at that time pointed to the following reasons: 1. The foam trap in the drying tower was leaking, as it had to be opened frequently for cleaning, which resulted in inadequate sealing ； 2. Air leakage at the fan shaft seal; some fans use labyrinth seals, and sometimes the pressure of the sealing air is insufficient ； 3. The amount of acid circulating in the drying tower is low, especially when the moisture content in the flue gas at the inlet of the drying tower exceeds the design value by a large margin ； 4. Acid distributor: A cast-iron tubular acid distributor is used, but the acid distribution effect cannot be guaranteed. It is worth noting that there is a new system equipped with imported alloy tube trough acid separators, but the moisture level still does not meet the standards. The analysis at that time indicated that the moisture content of the flue gas entering the system was above the design value; due to a high amount of acid crossover, this affected the amount of acid reaching the tower. In recent years, I have visited quite a number of factories; some of them manage their moisture levels quite well. I hope everyone will share their experiences as well.
As a supplementary note, the magnetic ring filler in the drying tower presents too low a resistance to gas flow, resulting in poor moisture removal efficiency
Generally speaking, the level of moisture is directly related to the process parameters and the analysis methods used. In our company, we have observed a situation where the moisture level was high at noon but lower in the afternoon; this is also related to the moisture content in the sampling samples.
Our factory started operations in November last year and has been operating stably with good moisture levels. However, by March this year, the analysis results were very poor, with values as high as 0.35. Various aspects were checked, but no problems were found. Later, we shortened the sampling tube to the sampling port for sampling and analysis, and all results were satisfactory. Now that the temperature is higher, we have increased the production load; the temperature at the inlet of the drying tower has reached 44 degrees, yet the moisture level at the outlet of the fan remains good. I can’t figure out what the reason for this is. I’d like to ask an expert.
In addition to checking the acid separation device, it is also necessary to examine relevant parameters such as acid concentration, temperature, and spray density, as well as changes in the resistance of the drying tower and variations in the air volume of the fan. In short, there are too many influencing factors, so they need to be checked one by one.
Reply to 4# laoda: This kind of situation can indeed occur. Since the main pipeline after drying is the same as the sampling and analysis pipeline, the dried air still contains a certain amount of moisture; if the temperature of the sampling pipeline is lower than that of the main pipeline, moisture will condense inside the sampling tube.
It was quickly discovered that the moisture measurement at the fan outlet was inflated because the alkali washing bottle removed SO2 from the flue gas, thereby causing an overestimate of the moisture level. The connection diagram of the moisture measurement instrument is as follows: sampling – double-ball container (filled with desiccant) – alkali washing bottle – wet flow meter
Reply to 7# PopFinger: The SO2 absorbed by the wet flow meter has already been taken into account in the calculations
Our sampling tube also collects water, and we have to blow it out before each sampling.
Reply to 1# PopFinger: 1. Pay attention to the design of the filler height to prevent uneven acid distribution and poor absorption efficiency due to insufficient height. 2. An insufficient amount of circulating acid results in uneven distribution of acid within the trough-type acid distributor, leading to poor absorption efficiency.
Are raw materials, such as sulfur, also a factor?