Why is the pH of flue gas desulfurization slurry less than 7?
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The pH of the circulating slurry in the flue gas desulfurization absorption tower is controlled at around 6. Based on the principles of reaction, I believe that to ensure chemical absorption, the pH should be above 7; please advise.
Your question refers to the slurry in the limestone-gypsum process; its reaction principle relies not on pH-based desulfurization but on CaCO3-based desulfurization. Under acidic conditions, calcium ions are generated and combine with SO2 to form CaSO3, which is then oxidized to CaSO4. It is absorption desulfurization rather than non-alkaline desulfurization; that is the difference. You can refer to this post: http://bbs.hcbbs.com/viewthread.php?tid=302171&highlight=%CD%D1%C1%F2%BD%AC%D2%BA Last edited by hhxxbb on 2009-3-14 16:27]
The double-alkali method for desulfurization offers better alkaline conditions; refer to the following: http://bbs.hcbbs.com/thread-414005-1-1.html. This post was last edited by hhxxbb on 2009-3-14 at 17:52.]
To ensure the dissolution of the absorbent, it is generally kept between 5.5 and 6.5!
The control of pH value is crucial in wet flue gas desulfurization; the specific pH range for control is as follows: for the limestone/lime-gypsum method, the pH should be maintained around 6. The main reason for being below 7 is that the solubility of Ca increases as pH decreases, thereby avoiding the problem of scaling.
In ammonia-based desulfurization as well, it is necessary to keep the pH of the desulfurization solution acidic, rather than alkaline.
A lower pH helps increase the dissolution rate of limestone, reduce the Ca/S ratio, and improve the utilization efficiency of limestone.