Seeking advice on the three-effect counter-current evaporation process for anhydrous sulfuric acid
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The company uses a three-effect evaporation process to remove sulfuric acid an from the water, with the resulting pure water being reused in the plant’s processes. Recently, severe foaming has occurred in the first-effect separation chamber, which has resulted in a large amount of sulfuric acid an being carried along with the pure water produced. Normally, the pressure in the first-effect separation chamber is 0.03 Mpa, but it has now risen to 0.17 Mpa, and it continues to increase. The processing volume **has declined**. No foaming occurred in the second and third effects. I hope everyone who is a sea friend can analyze the reasons and find solutions. Thank you.
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Is the demister at the secondary steam outlet blocked, or is the outlet for the condensate water from the second stage blocked? Are there any abnormalities in the second and third stages? Has there been any change in the raw materials compared to before? What are the normal operating pressures for the 1st, 2nd, and 3rd separation chambers?
From yesterday until this morning, I was working in the workshop to figure out the problems with the three-effect evaporation system, and I identified some abnormalities. First, the pressure in the first effect could be reduced by releasing steam from the secondary steam outlet, which indicates that the demister is not blocked. Secondly, connecting a pipe directly from the drain outlet of the secondary condenser to the condensate vacuum receiver tank allows the pressure in the primary stage to be maintained at 0.12 Mpa without further increase. From this perspective, I think one reason is that the condensate pipe is too thin. The amount of traffic that passes through is not enough. It causes excessive pressure. The pressure ratio of the second stage is higher than before, and there are no abnormalities in the third stage. The raw materials remain unchanged. During the initial testing, the pressure in the first stage was 0.03–0.06 Mpa. The pressure of the second effect is --0.01 --- --0.03 Mpa. The three-effect pressure is --0.08 Mpa. Let me ask a question: if the secondary steam evaporated in the first-stage separation chamber carries a large amount of sulfuric acid an into the second-stage and third-stage heating chambers, and is exposed to heat for an extended period of time, will the sulfuric acid an adhere to the tubes in those heating chambers? This could lead to a deterioration in the heat exchange efficiency of those chambers. As a result, not all of the secondary steam can be condensed into liquid after entering the heating chambers, which in turn causes the pressure in the first stage to increase.
There’s no need to think about it – foaming is caused by the material itself, especially when foaming occurs only in the first stage; in that case, it’s definitely due to the material. As for the increase in pressure in the first stage later on, it’s because too much sulfuric acid AN is present in the secondary reactor, which leads to clogging of the demister. Also, depending on the specific structure of the separation chamber, there must be some issue there, and it’s also possible that scaling has occurred in the shell side of the second stage. Poor heat transfer.