Multi-pollutant control solutions for coal based power plants By Luca Mancuso and Hans Janssen
Content SOx control Wet Scrubbers Open towers Dual Flow Tray Technology Semi-Dry SDA CFB Scrubbers Dust control Electrostatic precipitators Fabric Filters Questions and answers
Desulfurization Chemical Reaction All commercial technologies are based on a reaction between Calcium and Sulfur Wet Type Cooling down of flue gas below water dew point Sorbent is limestone based [CaCO3] Technology: Wet Scrubber Semi-Dry Type Dry Cooling down of flue gas above water dew point Sorbent is lime based [CaO] Technologies: Spray Dry Absorber or CFB Scrubber No cooling of flue gas Sorbent is hydrated lime based [Ca(OH)]
Wet Scrubbers Performance Open Spray Towers Typically applied on low sulfur fuel 95+% removal Dual Flow Tray Typically applied on high sulfur fuel 97%+ removal
Sorbent preparation Limestone is ground to powder by ball mill powder is classified and mixed to slurry Absorption Slurry is injected into the recycle tank Absorber slurry is sprayed into the gas stream to allow for the absorption. Acid Gasses are absorbed by liquid Treated flue gas passes through mist eliminator which collect excess droplets liquid returns to the recycle tank at base Gypsum treatment Air is added to the recycle tank to convert calcium sulfite to gypsum Gypsum slurry is extracted and dewatered Flue Gas Out Mist Eliminators Multiple Spray Headers Recycle Tank Agitators Flue Gas In Oxidation Air Recycle Pumps
Tower Concrete with ceramic lining Stainless / Alloy steel Carbon steel with rubber / glassflake lining Spray headers FRP Alloy PVC Spray nozzles Silicon carbide with Victaulic coupling Single or bi-directional
Dual Flow Tray Increase in removal of 5 to 10% Lower stoichiometric rate Construction Perforated plate (Alloy or PP) Located above flue gas inlet Pressure drop over tray 3-5 mbar lower emissions with same L/G ratio Additional functionality as maintenance platform Solution for rebuilds / retrofits Short overhaul / outage time Lowering emissions Without increasing L/G ratio Without adding pumps / levels Low capital expenditure No major reconstruction of existing FGD
Semi Dry Scrubbers Performance Spray Dry Absorber SO 2 emission level <60 mg/nm3 with >95% removal CFB Scrubber SO 2 emission level <20 mg/nm3 with up to 99% removal Additionally high removal and low emissions possible on: HCl HF Hg
Spray Dry Absorber Sorbent preparation Lime is slaked to a sorbent fluid Absorption Sorbent fluid is atomized as droplets into flue gas Pollutants from the flue gas dissolve into the droplets Dissolved pollutants react in the droplet with the sorbent Flue gas is cooled by evaporation of droplets to 15 C above dew point Reaction product is dry Flow Distribution Reaction Vessel Flue Gas In Sorbent Injection Nozzles Flue Gas Out Solids Discharge Hopper
Technologies Rotary Type Power Consumption Limited turn down Nozzle Type Air consumption High Turn down Construction Carbon steel reactor vessel Thermal insulation Sorbent and Product Sorbent: Slaked lime (slurry) Product: Dry
CFB Scrubber Sorbent preparation The sorbent is utilized in dry form Absorption Flue gas enters the bottom of the absorber, flowing upward through venturi to accelerate the gas flow causing turbulence flow Sorbents and water mix with the turbulent flue gas providing high efficient capture of pollutants Flue gas is cooled by evaporation of droplets to 15 C above dew point Reaction product is dry
Technologies Single or Multi Venturi Possible Cyclone between reactor and fabric filter Construction Carbon steel reactor vessel Thermal insulation Sorbent and Product Sorbent: Dry Hydrated lime Possible onsite production from Lime Product: Dry
De-Dusting Two Principles Physical barrier: Fabric Filter Induced electrostatic charge: ESP Sensitive to resistivity of the gas Fabric Filter ESP Particulate emission level <5 mg/nm3 Porous filter surface removes particulates from gas flow Product build up on filter causes pressure loss Energy for cleaning of filter Removal of 99.9% of particles Charge and gas characteristics determine removal efficiency Open gas path provides low pressure los Energy for charging flue gas
Fabric Filter Economics and Design criteria Capital Expenditure Gas flow vs filtration surface ratio Pressure loss Dust loading on filter Operation Expenditure Cleaning pressure Cleaning frequency Bag length
Electrostatic Precipitator PLATE RAPPED DISCHARGE ELECTRODE COLLECTING PLATE CORONA DISCHARGE GAS MOLECULES IONIZED PARTICULATE CHARGED PARTICULATE FREED FROM PLATE Step 1: Charging Gas ions formed by corona discharge Particulate charged by gas ions Step 2: Collection Ions transport particles to collect plate Particulate charge given to collect plate Step 3: Cleaning Collecting plate rapped for cleaning CHARGE RETURNS TO TRANSFORMER HIGH VOLTAGE TRANSFORMER
European vs American Design Hammer rapping Variable frequency Programmable sequencing Staggered hammer positions to reduce puffing Variable intensity rapping Variable intensity Variable frequency Programmable sequencing Rappers Rapping insulator HV support insulator Upper frame
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