Introduction to double alkali desulfurization

   The double alkali method uses sodium-based desulfurization mechanism agent for desulfurization in the tower. Since the sodium-based desulfurizer is strong in alkali, the reaction product has high solubility after absorption of sulfur dioxide, does not cause supersaturated crystallization, and causes fouling blockage problem; on the other hand, desulfurization product It is discharged into the regeneration tank and regenerated with calcium hydroxide. The regenerated sodium-based desulfurizer is recycled to the desulfurization tower for recycling.

Double alkaline desulfurization working principle

(1) Double-alkali flue gas desulfurization technology uses sodium hydroxide or sodium carbonate solution as the starting desulfurizer, and the prepared sodium hydroxide or sodium carbonate solution is directly driven into the desulfurization tower to remove SO2 from the flue gas to reach the flue gas. For the purpose of desulfurization, the desulfurization product is then recycled to the desulfurization tower through the desulfurization regeneration tank to form sodium sulfite or sodium hydroxide.

The desulfurization process mainly consists of five parts:

     1) Preparation and supplementation of absorbents;

     2) absorbent slurry spray;

     3) The mist droplets in the tower are mixed with the flue gas;

     4) Reducing the slurry of the regeneration tank to reduce the sodium base;

     5) Gypsum dehydration treatment.

(2) Chemical reaction of double alkali desulfurization:

  1 absorption reaction

     SO2+H2O=H2SO3

     SO3+H2O=H2SO4

     Sorption of SO2 in the flue gas with a sodium-alkali solution in the main column:

     2NaOH+SO2=Na2SO3+H2O

     There is still some NaOH in the absorption liquid, so sodium sulfite is also formed during the absorption process:

     Na2SO3+SO2+H2O2NaHSO3

     Sorption of SO2 and SO3 in the flue gas with sodium carbonate solution in the main column:

     E. Na2CO3+H2SO3=Na2SO3+H2O+CO2

     F. Na2CO3+H2SO4=Na2SO4+H2O+CO2

  2 regeneration reaction

     The absorption liquid flows into the reaction tank and reacts with the added lime slurry:

     G. 2NaHSO3+Ca(OH)2=Na2SO3+CaSO3·1⁄2H2O↓+1⁄2H2O

     H. Na2SO3+Ca(OH)2+1⁄2H2O=2NaOH+CaSO3·1⁄2H2O↓

     After the regenerated slurry is precipitated by the calcium salt, the Na2SO3 supernatant is returned to the absorption tower for recycling.

  3 side reactions

     The main side reaction of the absorption process is oxidation:

     I. Na2SO3+1⁄2O2Na2SO4

     Therefore, the following reactions occur in Na2SO4 during regeneration:

     J. Na2SO4+Ca(OH)2+2H2O→2NaOH+CaSO4·2H2O↓

However, in fact, due to the presence of a considerable amount of SO or OH in the solution, the concentration of Ca is correspondingly low. Therefore, to precipitate CaSO4, OH ≤ 0.14 M during regeneration, and a sufficiently high SO concentration, for example, an OH concentration of 0.1. MSO, SO concentration of 0.5M, will produce CaSO4 precipitation.

Double alkali desulfurization process flow chart