1. Process description The exhaust gas from the boiler passes through the bag filter or electrostatic precipitator and then enters the absorption tower. The flue gas flows upward in the absorption tower and is washed in a counter-current manner by the circulating slurry flowing downward. The washing slurry is sprayed into the absorption tower through the nozzle provided in the spray layer to remove SO2, SO3, HCL and HF. At the same time, the by-products reacted by the oxidation fan and oxidation spray gun are oxidized by the introduced air Gypsum (CASO42H2O), and consume limestone as an absorbent. The circulating slurry is transported upward to the spray tower layer by the slurry circulation pump, and atomized by the nozzle, so that the gas and the liquid can be fully contacted. Each pump is usually connected to its respective spray layer, that is, a unit system is usually used.
In the absorption tower, limestone reacts with sulfur dioxide to form gypsum. This part of gypsum slurry is discharged through the gypsum slurry pump and enters the gypsum dehydration system. The dehydration system mainly includes a gypsum hydrocyclone (as a first-level dehydration device) and a vacuum belt dehydrator. The cleaned flue gas stream is defogged by a two-stage demister. In addition, the mist droplets carried in the clean flue gas are removed. At the same time, the demister is rinsed with process water from time to time according to specific procedures. There are two purposes for the demister, one is to prevent the demister from clogging, and the other is to use the flushing water as supplementary water to stabilize the liquid level of the absorption tower.
At the outlet of the absorption tower, the flue gas is generally cooled to about 46-55 degrees, and is saturated with water vapor. Use GGH (optional) to heat the flue gas above 80 degrees to increase the flue gas lift and diffusion capacity. Finally, the clean flue gas enters the chimney through the flue and shoots to the atmosphere.
2. Basic process principle of lime-gypsum method
The main chemical reactions of SO2, SO3 and HCl in the flue gas during absorption in the desulfurization reaction tower are as follows:
(1) Diffusion of gas from gas phase body to gas film on liquid surface
XYm (gas phase body) → XYm (gas film) (XYm represents SO2, SO3, HCl)
(2) Diffusion and dissolution of XYm from the gas film through the gas-liquid interface
XYm (g) → XYm (aq)
(3) Hydration process of dissolved gas
SO2 (aq) + H2O → H2SO3
SO3 (aq) + H2O → H2SO4
(4) Dissociation and oxidation in solution
HCl → H + + Cl-
H2SO3 → H + + HSO3-
HSO3- → H + + SO32-
HSO3- + 1/2 O2 → HSO4-
SO32- + 1/2 O2 → SO42- (partial)
(5) In the liquid phase, CaCO3 dissolves and ionizes
CaCO3 → Ca2 + + CO32-
CO32- + H2O → HCO3- + OH-
HCO3- + H2O → H2CO3 + OH-
(6) Neutralization reaction of OH- generated
H + + OH- → H2O
(7) Salt formation
2H2O + SO42- + Ca2 + → CaSO4 · 2H2O (s)
1 / 2H2O + SO32- + Ca2 + → CaSO3 · 1 / 2H2O (s)
