“SIEVENT” FGD SCRUBBER for 100 % PET COKE — FIRED BOILER.
- PROPOSED SCHEME
The flue gases are passed through the proposed Scrubber (combination of Venturi and Sieve Tray) at the downstream of ESP and ID Fan .
The proposed Scrubber is designed to De-Sulphurize the Flue Gases in three stages, namely :
- PRIMARY TREATMENT.
- DRY SCRUBBING IN FREE BED ZONE.
- SECONDARY TREATMENT with NaOH Solution as a Solvent.
- REGENRATION SYSTEM
- PRIMARY TREATMENT : In Primary Treatment MAGO recommends using LIME STONE (CaCO3) in the furnace bed. Generally Lime addition is 2 % – 3 % of by Weight of the fuel quantity in the bed. This helps in recovering Sulphur in the combustion zone and with this SO2 is reduced to 5000 PPM – 8000 PPM in this zone.
CaCO3(solid) + SO2(gas) → CaSO3(solid) + CO2(gas)
- DRY SCRUBBING IN FREE BED ZONE : In free board zone, we spray Ca(OH)2 through specially designed Nozzles. These Nozzles are placed at strategic locations in Free Board Zone to generate Dry Scrubbing action. In this zone, the SOx level is reduced to 3500 PPM – 5000 PPM.
Ca(OH) 2 (solid) + SO2 (gas) → CaSO3(solid) + H2O (liquid)
- SECONDARY TREATMENT (with NaOH solution) : Flue gases laden with 1500 PPM – 2000 PPM SOx passes through the Boiler Bank tubes, Economiser, APH etc and finally through ESP where SPM level is brought down. Partially CLEAN Flue Gases then pass through a Sieve Tray Scrubber through which NaOH solution is sprayed to absorp balance SO In this zone, the SOx is brought down to less than 50 PPM level.
2NaOH(solid) + SO2 (gas) → Na2SO3 (sol.) + H2O (liquid)
Na2SO3 (sol.) + SO2 (gas) + H2O (liquid)→ NaHSO3 (solid)
Here onwards the Scrubbed Gases are made to pass through a set of MIST Eliminator for separation of MIST from the Clean Gases.
DISPOSAL OF LEFT OVER
REGENRATION & USUAGE OF DOUBLE ALKALI.- FULLY AUTOMATIC
The Effluent contains ‘Na2SO3 / NaHSO3 / Na2SO4“ from the Venturi & the Sieve Tray Scrubber is PUMPED to Regeneration system. Regenration system consists of Mixing tank (For CaCO3 + Effluent Solution), Thickner & Vacuum Filter for Solid Recovery ( CaSO3/ CaSO4).
REGENRATION WITH LIMESTONE
CaCO3 (solid) + NaHSO3 (sol) → Na2SO3 + CaSO3. 1/2H2O (liquid) + ½ H2O + CO2
HSO3 –+ ½ O2 → SO4+ H+
SO3 =+ ½ O2 → SO4 =
SULFATE REMOVAL AND NAOH RECOVERED
Na2SO4 + Ca(OH)2. +2 H2O → 2NaOH + CaSO4. 2H2O (sol)
Adequate amount of System AUTOMATION has been considered for periodic PURGING along with field instruments to monitor the Pressure Drop and Temperature of the gas at Different Stages.
SO2 : less than 50 Ppm on continuous basis
COST OF SOX removal Shall Be Rs 0.20 / Kg of Steam generation.
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