Reasons for acid discharge at the bottom of the large chimney
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Our plant produces sulfuric acid, and recently a large amount of acid has been discharged from the bottom of the exhaust chimney, around nearly one ton per shift. I would like to ask the members in the sulfuric acid technology discussion forum to help analyze what the cause might be. I hope everyone will kindly share their insights!
Has this only happened recently, or has it been going on all along? Our facility has always had this; as long as the sulfur trioxide contained in the exhaust gases condenses, it does so within a chimney that is 105 meters high. The amount depends on the membrane separator, especially in the case of two-stage absorption towers. If your facility didn’t have this issue before but it does now, I suspect that the membrane separator in the two-stage absorption tower has corroded and become damaged.
A hole in the demister of the second absorption tower is one possible cause; uneven acid distribution in the acid separation unit, whether the gas flow rate is set appropriately, and whether the acid flow rate is normal are all potential causes – investigate them one by one!
The uneven distribution of acid, as well as the flow rate of acid supplied, can all be reflected through temperature, which can be used in combination for analysis
Are there any other exhaust pipes connected to the chimney? If not, the issue with the second absorption tower needs to be thoroughly investigated.
Our plant is new; it has just started operating, and the demister is also new (a Mengmoke demister). The exhaust chimney is 120 meters tall.
Logically, at the outlet of the absorption tower, there is almost no moisture in the flue gas; even if the absorption is incomplete, there won’t be such an amount of condensed acid, unless the concentration of the acid used in absorption is too low, there is too much acid foam, or it is raining. It is recommended to look for the cause in terms of dry absorption operations.
It might be a problem with the demister; check whether the pressure difference before and after the demister is normal Also, why is your chimney so tall? Check again to see if the pressure at the outlet of the second absorption tower is high
Regardless of the size of your system, in my opinion, focus on checking the secondary absorption tower.
The pressure drop of the demister in the second absorption tower is 1.5 KPa; the system’s production capacity is 300 Kt/year. It was converted from acid production using pyrite to acid production using sulfur, with the chimney being reused.
Condensate acid will definitely be present; if its amount is high, check the second absorption tower. Additionally, it is possible to consider adding a return pipe to lead it back to the circulation tank for reuse.
Thank you to all the members in the sulfuric acid technology discussion forum for their generous assistance. Following everyone’s suggestions, we carefully investigated the cause. Once again, I sincerely thank everyone for their help!
Check two aspects: one is the condition of the demister and whether its liquid seal device has a liquid seal in place； Secondly, the temperature of the flue gas exiting the tower must be kept above 60°C.