Factors affecting the pH value of the three types of water in MTO
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This post was last edited by liaifeng on 2018-9-6 at 19:39. The pH of the quench water in our system is the lowest, followed by that of the wash water, with the purified water having the highest pH. If the pH of the purified water is adjusted to neutral, the quench water tends to be acidic. Please share your experiences so I can learn from them
The pH of the three waters is adjusted according to the amount of quench water and alkali solution injected
It would be better for you to have a separate alkali injection pump for rapid cooling and for water washing, as this facilitates pH adjustment. The pH of the purified water is basically the same as that of the washed water; once the pH of the washed water is adjusted properly, there are no issues with the purified water. By adjusting the amount of alkali added to the quench water wash in real time based on the offline measurements of the water sample, it can be kept within the desired range.
Our system is equipped with a 20% alkali solution injection pump for each stage of quenching and washing; generally, the dosage is highest during quenching, next highest during washing, and lowest during purification. The pH value during purification changes according to the pH value during washing
Could you specify which location’s water this refers to? Different companies may use different terms for it. Rapid cooling: I understand it refers to the water coming out of the rapid cooling tower. Is the washing water the water that comes out of the waste gas stripping tower? Where is the purified water? I’ve never heard of it
This post was last edited by twinkler on 2017-4-5 11:04. I really wanted to talk about this issue. The MTO product gas contains trace amounts of organic acids. The discharge volume of quench water is low, and most of the purified water is drawn from the washing water. Both quench water and washing water are recycled; organic acids gradually accumulate to a certain concentration after operation, reaching equilibrium with the wastewater discharged for purification. The organic acids in the wash water make the water acidic (reducing the pH value); after adding alkali, organic alkali metal salts are formed (raising the pH value after adjustment). When the wash water enters the wastewater stripping tower, the high-temperature gas causes partial decomposition of the organic alkali metal salts, and the organic acids evaporate, resulting in an increase in the pH value once again. It’s based on this principle; the design should take material selection into account. If it hasn’t been considered, add more acid to the purified water. Carbon steel experiences a lower corrosion rate in a weakly alkaline environment, but not in an acidic one.