Why is the pH of the liquid at the bottom of the exhaust gas scrubber tower in the low-temperature methanol wash unit between 4 and 6?
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Why is the pH of the liquid at the bottom of the exhaust gas scrubber tower in the low-temperature methanol wash unit between 4 and 6?
The flue gas scrubber uses deionized water to wash CO2-containing gases as well as acidic gases such as CO2 and H2S, along with the flue gas itself; therefore, the liquid at the bottom of the flue gas scrubber is definitely acidic, with a pH of 4–6 being normal.
I asked the person on the 2nd floor: is it necessary to add an alkali to adjust the pH under acidic conditions? Some contain NaOH, while most do not; is it mainly determined by the material used in the equipment design?
If the equipment is made of stainless steel or has been treated to resist corrosion, it is not necessary to add alkali; however, if it is made of carbon steel and has not been treated for corrosion protection, alkali must be added, otherwise corrosion will occur rapidly.
Thank you all for your responses. Regarding the issue of non-condensable gases in the methanol synthesis pre-distillation tower affecting the tail gas washing tower, the main components of these non-condensable gases are dimethyl ether, along with some light compounds such as low-boiling-point organic acids. The presence of these gases in the tail gas washing tower leads to a decrease in the pH of the liquid at the bottom of the tower, as well as increased corrosion of equipment such as the methanol-water tower. Which is the primary cause: the dissolution of CO2 in water to form carbonic acid, thereby lowering the pH of the liquid in the tail gas washing tower and causing corrosion?