How to keep the acid mist from sulfuric acid exhaust below 5mg/m3

The HJ 544—2016 standard, \"Determination of sulfuric acid mist in exhaust gases from stationary sources – Ion chromatography method,\" issued by the Ministry of Environmental Protection in March 2016, involves absorbing all sulfate ions and then converting them into sulfuric acid mist; it measures the total amount of sulfates and sulfuric acid mist in the exhaust gases, rather than the actual concentration of sulfuric acid mist.

A demister (such as an electric demister) must be installed at the outlet of the tail suction tower.

This is easy to achieve; first, use ionic liquid for desulfurization and demisting

How do you handle exhaust gases these days?

The sulfur dioxide level is estimated to be below 50; electric defogging is required just to reach that level

Find a design institute; it’s generally not easy to handle this. For my acetic acid exhaust gases, I use water washing, condensation, and adsorption

The new testing method for sulfuric acid mist issued by the Ministry of Environmental Protection in March 2016: Ion Chromatography Method HJ 544-2016, which replaces the previous testing method HJ 544—2009. The biggest difference between the new testing method and the original one lies in the change in the sampling method ； The original testing method involved using filter cartridges for sampling; the exhaust gas passed through these cartridges filled with glass fiber or quartz fiber. The substances trapped by the cartridges were neutralized using NaOH solution, and then the mass concentration of SO42- was measured using an ion chromatograph. This value was subsequently converted to H2SO4, representing the sulfuric acid mist ； The sampling method for the new detection method has been changed to by connecting two NaOH absorption flasks in series after the filter cartridge; the SO42- detected in the filter cartridge and the two NaOH absorption flasks is all converted to H2SO4, which is then considered as sulfuric acid mist. The new testing method involves absorbing all sulfate ions and then converting them into sulfuric acid mist; it does not represent the actual amount of sulfuric acid mist present. Previously, the outlet of the second absorption tower was tested for the content of large-particle sulfuric acid mist in the dried exhaust gas; now, it is tested for the contents of sulfur trioxide, sulfuric acid mist, and a portion of sulfur dioxide (which is oxidized after being absorbed by NaOH) ； The original tests on the chimney at the outlet of the desulfurization tower focused on the levels of large particle sulfuric acid mist and sulfates in the wet exhaust gas; now, the tests measure the levels of sulfur trioxide, sulfuric acid mist, sulfates, and a portion of sulfur dioxide in the wet exhaust gas. The change in sampling method resulted in the measured values of sulfuric acid mist being more than 3 times higher than those obtained using the original testing method; for example, the mass concentration of sulfuric acid mist in the desulfurization exhaust gases from a sulfur-based sulfuric acid production plant increased from 20 mg/m3 (as measured by the HJ 544—2009 method) to 140 mg/m3 (as measured by the HJ 544-2016 method)

Adding a fiber mist eliminator behind the tail suction tower can help meet the standards

The key issue is that the oxidation of SO2 in the exhaust gases has a significant impact. Oxidation by 200mg of SO2 to 1% is equivalent to 3mg of sulfuric acid mist; in actual measurements, the oxidation rate is much higher than 1%, and it is therefore impossible to meet the 5mg/Nm3 standard using such measurement methods.

The Sulfuric Acid Association and **the relevant departments are coordinating and considering revisions, but no progress has been made so far