Sodium-calcium double-alkali desulfurization process

Sodium-calcium double-alkali desulfurization process

System process diagram

working principle
The flue gas from the boiler is first dedusted by the dust collector, and then the flue gas enters the desulfurization tower from the bottom of the tower through the flue. Several layers of swirl plates (according to the specific conditions) are arranged in the desulfurization tower. The swirl plate tower has good gas-liquid contact conditions. The lye sprayed from the top of the tower is atomized on the swirl plate to make the flue gas SO2 fully absorbs and reacts with the sprayed lye. The clean flue gas after desulfurization and washing is dehydrated by the demister and then enters the heat exchanger, and the heated flue gas is discharged into the atmosphere through the chimney through the induced draft fan.
During the desulfurization process, the fly ash mixed in the flue gas is wetted and captured by the circulating liquid at the same time, and the circulating slurry discharged from the absorption tower flows into the sedimentation tank. The ash and slag are regularly removed by precipitation and can be recycled, such as brick making. The supernatant overflows into the reaction tank and reacts with the added lime. The displaced sodium hydroxide is dissolved in the circulating water, and at the same time, insoluble calcium sulfite, calcium sulfate and calcium carbonate are generated, which can be removed by precipitation.
The chemical process reaction of desulfurization and regeneration is expressed as follows:
The desulfurization reaction equation is as follows:
Na2CO3+SO2→Na2SO3+CO2
2NaOH+SO2→Na2SO3+H2O
Na2SO3+SO2+H2O→2NaHSO3
The reaction product after desulfurization enters the regeneration tank and is regenerated with another alkali, generally Ca(OH)2. The regeneration reaction process is as follows:
Ca(OH)2+Na2SO3→2NaOH+CaSO3
Ca(OH)2+2NaHSO3→Na2SO3+CaSO3·1/2H2O+1/2H2O
In the presence of oxygen, the following reactions also occur:
Ca(OH)2+Na2SO3+1/2O2+2H2O→2NaOH+CaSO4·H2O
The removed sulfur is precipitated in the form of calcium sulfite and calcium sulfate, and then pumped into the gypsum dehydration treatment system or directly stacked and discarded. The regenerated NaOH can be recycled.
The dual-alkali flue gas desulfurization process mainly includes five parts: absorbent preparation and supplement system, flue gas system, SO2 absorption system, desulfurization gypsum dehydration treatment system and electrical and control system.
Process characteristics
1. The desulfurization efficiency is over 90%.
2. The desulfurizer adopts sodium alkali and lime, and the clear liquid in the tower is absorbed, which can effectively avoid scaling in the tower.
3. The ratio of liquid to gas is small. Desulfurization and dust removal can be integrated.
4. One-time investment is low, operating cost is low, and the degree of domestic production is high.
5. Wide range of adaptation.