In wet flue gas desulfurization (FGD) technology, the FGD gypsum cyclone wet FGD system is a complete desulfurization process based on the limestone-gypsum process, with the FGD gypsum cyclone as the key dehydration equipment. It efficiently removes SO₂ from flue gas and recycles desulfurized gypsum as a resource. This system is widely used in industries such as thermal power, steel, and chemicals, and is currently one of the leading flue gas desulfurization technologies globally.

The FGD gypsum cyclone wet FGD system is designed around the four key objectives of flue gas purification, gypsum generation, dehydration recovery, and wastewater treatment. It consists of a flue gas system, an absorption tower system, a gypsum dehydration system (including the FGD gypsum cyclone), and auxiliary systems. II. Core System Workflow: The Entire Chain from Flue Gas to Gypsum

The core logic of the FGD gypsum cyclone wet process system is "flue gas desulfurization → slurry generation → cyclone pre-concentration → deep dehydration → resource recovery." The specific process can be divided into six key steps, with the FGD gypsum cyclone being the core node connecting "slurry generation" and "deep dehydration":

1. Flue Gas Pretreatment: Cooling and Dust Removal

The high-temperature flue gas (approximately 120-180°C) discharged from the boiler first enters the flue gas heat exchanger (GGH), where it exchanges heat with the desulfurized, low-temperature clean flue gas (approximately 50-60°C), reducing its temperature to 80-100°C (to prevent rapid evaporation of the slurry in the absorber). The flue gas then enters the inlet duct before the absorber. If the dust content is high, it must be pretreated by an electrostatic precipitator or bag filter (controlling the inlet dust concentration to < 50mg/Nm³) to prevent impurities from affecting the quality of the gypsum.

2. Desulfurization Reaction in the Absorber: Gypsum Slurry Production

Pretreated flue gas enters the bottom of the absorber and comes into countercurrent contact with limestone slurry (CaCO₃ concentration 15%-25%) sprayed from the top spray layer:

·Step 1: SO₂ reacts with water to produce sulfurous acid (SO₂ + H₂O → H₂SO₃);

·Step 2: Sulfurous acid reacts with limestone to produce calcium sulfite (H₂SO₃ + CaCO₃ → CaSO₃・0.5H₂O + CO₂ + 0.5H₂O);

·Step 3: An oxidation blower blows compressed air into the bottom of the absorber, oxidizing the calcium sulfite to gypsum (2CaSO₃・0.5H₂O + O₂ + 3H₂O → 2CaSO₄・2H₂O);

The final solids content is 10%-20%. The gypsum slurry is deposited in the slurry pool at the bottom of the absorption tower.

3. Primary Dehydration: FGD Gypsum Cyclone Pre-concentration

When the slurry pool level in the absorption tower reaches the set value, the gypsum discharge pump delivers the gypsum slurry tangentially to the FGD gypsum cyclone (usually multiple units are connected in parallel, with the processing capacity matching the system load):

· Underflow (concentrated gypsum): Gypsum crystals with a particle size greater than 40μm and a small amount of unreacted limestone particles are discharged downward along the wall of the cyclone under centrifugal force, increasing the solids content to 40%-60% and directly conveyed to the vacuum conveyor;

· Overflow (diluted slurry): Fly ash with a particle size less than 20μm and fine gypsum particles are discharged upward along the internal cyclone, with a solids content of only 5%-8%. The overflow is collected in the overflow tank and returned to the absorption tower (recycling water and unreacted limestone). A small amount is diverted to the wastewater treatment system to prevent the accumulation of Cl⁻ and heavy metals.

4. Secondary Dehydration: Deep Dehydration via Vacuum Belt Conveyor

The underflow from the FGD gypsum cyclone (40%-60% solids content) enters a vacuum belt conveyor, where deep dehydration is achieved through a "vacuum extraction + belt conveyor" process:

A vacuum box beneath the belt creates negative pressure, extracting moisture from the gypsum. After filtration through a filter cloth, the gypsum's solids content is increased to > 90% and its moisture content is < 10%.

The dehydrated desulfurized gypsum (purity > 90%, ash content < 3%) is conveyed by belt conveyor to a gypsum silo for storage and can be used as a building material (such as gypsum board, cement retarder) or disposed of in a landfill.

5. Clean Flue Gas Emissions

After desulfurization in the absorption tower (SO₂ concentration ≤ 35 mg/Nm³, meeting the national standard GB 13223-2011), the clean flue gas (SO₂ concentration ≤ 35 mg/Nm³, meeting the national standard GB 13223-2011) passes through a top demister to remove water mist (controlling the droplet content to < 75 mg/Nm³). The gas then enters the flue gas heat exchanger (GGH) for heat exchange with the original flue gas to increase its temperature (to prevent excessively low clean flue gas temperatures, which could lead to chimney corrosion and white smoke emissions). It is finally discharged through the chimney in compliance with standards.

6. Wastewater Treatment: Preventing Impurity Accumulation

A portion of the overflow slurry from the FGD gypsum cyclone (containing high concentrations of Cl⁻ and heavy metals) is diverted to the wastewater treatment system. After a process of "neutralization (addition of lime) → flocculation (addition of PAC/PAM) → sedimentation → filtration," the wastewater quality meets the "Water Quality Control Standards for Limestone-Gypsum Wet Desulfurization Wastewater in Thermal Power Plants" (DL/T 997-2021) and can be reused or discharged in compliance with standards.