Wet & Dry Scrubb

Wet & Dry Scrubb

Paul Farber Paul Farber

Sargent & Lundy, LLC Sargent & Lundy, LLC

Chicago, IL Chicago, IL
Dry FGD/DSI Topics Dry FGD/DSI Topics

DRY FGD DRY FGDTechnology Variations Technology VariationsTechnology Description Technology Description

Reagent Handling and Prepa

Reagent Handling and Prepa

Absorber System Absorber SystemBaghouse System Baghouse SystemWaste Recycle System Waste Recycle SystemFlue Gas System Flue Gas System

Dry FGD Technology Suppliers Dry FGD Technology Suppliers
Dry FGD/DSI Topics Dry FGD/DSI Topics

DRY SORBENT INJECTION (DSI) DRY SORBENT INJECTION (DSI)DSI vs. Other FGD Options DSI vs. Other FGD OptionsTypes of Types of Sorbent Sorbent

Trona vs. SBC Trona vs. SBCCurrent Industry Trends Current Industry Trends
DRY FGD DRY FGD

Technology Variations Technology Variations

Dry Scrubbers Dry Scrubbers

Spray Dryer Absorber (SD

Spray Dryer Absorber (SD

Rotary Atomizer Rotary AtomizerDual-Fluid Nozzle Fluid Nozzle

Circulating Dry Scrubber 

Circulating Dry Scrubber 

Fluidized Bed FGD Fluidized Bed FGD

NIDS

Dry Sorbent Sorbent Injection (D

Injection (D
Dry FGD Dry FGD –Rotary Atomi

Rotary Atomi
Dry FGD Dry FGD –Dual Fluid No

Dual Fluid No
Dry FGD Dry FGD –Circulating Dr

Circulating Dr

Scrubber Scrubber
Dry Sorbent Sorbent Injection (D

Injection (D
Dry FGD Dry FGD

Spray Dry Flue Gas Desulphurization (FCirculating Dry Scrubber (CDS) or CircFluidized Bed (CFB) ScrubberNIDS

A subset of CDS

Dry Alkali Injection for SO2 control
Commonality Between Dry 

Commonality Between Dry 

(SDA and CDS) (SDA and CDS)

All Systems Require a Particulate Collection D

All Systems Require a Particulate Collection D

downstream of the absorber downstream of the absorber –preferably 

preferably 

could use an ESP could use an ESP

Both use a lime derivative Both use a lime derivative –Ca(OH)2as the 

as the 

Spray Dryer uses it wet in a slurry Spray Dryer uses it wet in a slurryCDS uses semi CDS uses semi

-dry hydrate & adds water separat

dry hydrate & adds water separat

Both have limited module sizes: Both have limited module sizes:

SDA = 450 MWCDS = 400 MW operating, up to 490MW

NID = 75 MW/module, multiple modules compos

NID = 75 MW/module, multiple modules compos
Commonality Between D

Commonality Between D

Systems Systems

Because both systems stay at least 30 Because both systems stay at least 30°F abo

F abo

point, both use carbon steel as the primar

point, both use carbon steel as the primar

construction. construction.

Because both systems stay at least 30 Because both systems stay at least 30°F abo

F abo

point, the existing chimney can be re point, the existing chimney can be re

-used 

used 

Both systems recycle large amou Both systems recycle large amounts of bagh

nts of bagh

to the absorber to improve lime usage. to the absorber to improve lime usage.

Both produce a sulfite Both produce a sulfite

-sulfate mixed materia

sulfate mixed materia

landfilled landfilled.

Can be used in low grade concrete aggre

Can be used in low grade concrete aggre

mixed with fly ash. mixed with fly ash.
Dry FGD Chemistry Dry FGD Chemistry

Coal Sulfur forms gaseous SO Coal Sulfur forms gaseous SO2& SO

3

Lime is received as CaO (pebble lime) Lime is received as CaO (pebble lime)

(3/4”x 0”for Dry FGD or CDS, 1/8 for Dry FGD or CDS, 1/8”x 0”for 

for 

Lime is slaked/hydrated as follows: Lime is slaked/hydrated as follows: 

CaO + H CaO + H2O 

→ Ca(OH)2 

In the absorber, SO In the absorber, SO2is captured as: is captured as:

Ca(OH)2 

2 + SO2 

2

→ CaSO3 

3•1⁄2H2O + 1/2 H H2O + 1/2 H2O (70-75

Ca(OH)2 

2 + SO2 + H2 

2O+1/2O2 

2

→ CaSO4 

4

•2H2O (25 2H2O (25

In a CDS absorber, CO In a CDS absorber, CO2is captured as: is captured as:

Ca(OH)2+ CO2

→ CaCO3+ H2

O
Stoichiometric Stoichiometric Ratio often referred 

Ratio often referred 

ratio

Actual moles of calcium/theoretical am

Actual moles of calcium/theoretical am

required for the moles of SO required for the moles of SO2 

2 collec

collec

For wet FGD it is expressed as a ra

For wet FGD it is expressed as a ra

collected. collected. 

Typical values would be 1.03 to 1.05 Typical values would be 1.03 to 1.05

Dry system suppliers express their 

Dry system suppliers express their 

basis of the inlet SO basis of the inlet SO2not the SO not the SO2

the wet systems. the wet systems.

Typical values would be 1.1 to 1.4 for 

Typical values would be 1.1 to 1.4 for 

95% Efficiency 95% Efficiency

Stoichiometric Stoichiometric ratio
Spray Droplet Chemistry Spray Droplet Chemistry

Slurry droplet drying time is a Slurry droplet drying time is a function of the flu

function of the flu

at the SDA inlet at the SDA inlet

Higher the temperature, lower the residence 

Higher the temperature, lower the residence 

droplet droplet

Typically 1 Typically 1

-4 seconds is needed to dry the la

4 seconds is needed to dry the la

Drying time is also a function of chlorides and re

Drying time is also a function of chlorides and re

Higher the CaCl Higher the CaCl2, higher the residence time n

, higher the residence time n

slurry droplet which can increase the amou

slurry droplet which can increase the amou

The lower the amount of fly ash in the recyc

The lower the amount of fly ash in the recyc

residence time needed to dry a slurry drop

residence time needed to dry a slurry drop
Spray Dryer Absorber Spray Dryer Absorber
Dual-Fluid Nozzles Versu

Fluid Nozzles Versu

Atomization Spray Dryer

Atomization Spray Dryer

Footprint Is Smaller For Dual Footprint Is Smaller For Dual-Fluid Spray Dryer Than 

Fluid Spray Dryer Than 

Spray Dryer Spray Dryer

Removal of One Dual Removal of One Dual-Fluid Nozzle (Out of 40) For Ma

Fluid Nozzle (Out of 40) For Ma

Of An Effect On Emissions Than Of An Effect On Emissions Than One Rotary Atomi

One Rotary Atom

[B&W] or 6 [ [B&W] or 6 [Alstom])

Spare Atomizer Costs Spare Atomizer Costs –

B&W -$675,000 (1 atomizer per vessel) $675,000 (1 atomizer per vessel)

Alstom-$250,000 (3 atomizers per vessel) $250,000 (3 atomizers per vessel)Siemens Siemens -$18,000 (20 nozzles per vessel) $18,000 (20 nozzles per vessel)

Maintenance Times Maintenance Times –

Dual-fluid Nozzles fluid Nozzles -~12 –15 man-hours/week hours/week

Rotary Atomizers Rotary Atomizers -~20 –30 man-hours/week hours/week
Dual-Fluid Nozzles Versus Fluid Nozzles Versus 

Rotary Atomization Spray Dry

Rotary Atomization Spray Dry

Costs Between Dual Costs Between Dual-Fluid & Rotary At

Fluid & Rotary At

FGD Systems About Equal FGD Systems About Equal

Energy Consumption Between The Tw

Energy Consumption Between The Tw

Technologies Is About The Same Technologies Is About The Same

More Rotary Atomizer FGD Systems In 

More Rotary Atomizer FGD Systems In 

Than Dual Than Dual-Fluid Nozzles Fluid Nozzles
Rotary Atomizer Rotary Atomizer

For utility sized systems many atomizers 

are mechanical, rotary atomizers

Slurry is fed into a disc nozzle rotating at a 

high rate of speed

This spins fine droplets of slurry out into the 

gas stream – where they dry and are 

captured in the baghouse
Typical Rotary Atomizer Typical Rotary Atomizer 

(1

-3 Per Spray Dryer) 3 Per Spray Dryer)

M

Gearbox

AtomizerWheel
Dual Fluid Nozzle Dual Fluid Nozzle

Certain Manufacturers use dual fluid Certain Manufacturers use dual fluid 

nozzles as an alternative to the Rotary nozzles as an alternative to the Rotary Atomizer in SDA Atomizer in SDA 

In the dual fluid nozzle lime slurry is In the dual fluid nozzle lime slurry is 

atomized by a high pressure second atomized by a high pressure second fluid –predominantly compressed air predominantly compressed air 

to produce the fine spray needed to produce the fine spray needed

Dual fluid nozzles do not have high speed Dual fluid nozzles do not have high speed 

rotating parts like the Rotary atomizer rotating parts like the Rotary atomizer

16

-20 per absorber 20 per absorber
Typical Dual Fluid Nozzle Typical Dual Fluid Nozzle

(16

-20 Per Spray Dryer) 20 Per Spray Dryer)

SLURRY FEED ATOMIZING AIR

AIR RESERVOIR INSERTS

PENTHOUSE FLOOR

PERFORATED PLATE

GAS DISTRIBUTION
SO2Absorption Continue

Absorption Continue

Baghouse Baghouse

SO3

HF

HCl

SO2

Baghouse contributes 10 to 20% of the total S

design SDA and FF as a system

Bag Fab

Dust Cake
Dry FGD Dry FGD

Subsystems Subsystems

Reagent Handling and Preparatio

Reagent Handling and Preparatio

Absorber System Absorber SystemBaghouse System Baghouse SystemWaste Recycle and Storage Syste

Waste Recycle and Storage Syste

Flue Gas System Flue Gas System
Reagent Handlin

and Preparation
Reagent Handling and Prepa

Reagent Handling and Prepa

System

Lime Handling and Storage Lime Handling and Storage

Pneumatic Conveying to long term s

Pneumatic Conveying to long term s

30 days capacity factor storage 30 days capacity factor storagePneumatic conveying to Preparation 

Pneumatic conveying to Preparation 

Lime Slurry Preparation system Lime Slurry Preparation system

24 hours day bin 24 hours day bin2 x 100% slakers 2 x 100% slakers20% slurry 20% slurry8

-16 hours slurry storage 16 hours slurry storage

slurry piping (loop to absorbers) slurry piping (loop to absorbers)
Lime Handling and Stora

Lime Handling and Stora
Lime Unloading System Lime Unloading System
Lime Slaking/Hydra

Lime Slaking/Hydra

Process Process:

Exothermic Hydration Process Exothermic Hydration ProcessOperating Temperature Operating TemperatureQuality of Lime Quality of Lime

MgO, CaCO MgO, CaCO3, 

“Grits

”

Quality of Water (SO Quality of Water (SO4 

4

=, SO3

=

)

CaO + H CaO + H

2O 

→ Ca(OH)

2
Ball Mill Slakers Ball Mill Slakers

• Conventional Ball 

Mill Slaker

• Rotating cylinder

• Steel balls create 

the grinding action

• Ball mills grind the 

grit
Ball Mill Slaker Ball Mill Slaker
VertiMill Slakers VertiMill Slakers

•Steel balls create Steel balls create 

the grinding action the grinding action

•Finer Particle Size Finer Particle Size•Less Power Than a Less Power Than a 

Ball Mill Slaker Ball Mill Slaker
Vertimill Vertimill Slaker
Detention Slakers Detention Slakers

•Violent Agitation Violent Agitation 

– No steel No steel 

balls

•Opposed Pumping Turbines Opposed Pumping Turbines•Particle to Particle Contact = Particle to Particle Contact = 

Attrition Attrition

•Grit is removed by screens Grit is removed by screens 

that follow the slakers. Also that follow the slakers. Also included in recycle trains included in recycle trains
Detention Slakers Require 

Detention Slakers Require 

Removal Removal
CDS Systems Use Hydrato

CDS Systems Use Hydrato

Instead of Slakers Instead of Slakers

•Same chemical reaction in a Same chemical reaction in a 

hydrator as a slaker hydrator as a slaker

–CaO + H CaO + H2 

2O 

→ Ca(OH)

2

•500 Btu 500 Btu’s of heat released per s of heat released per 

pound of lime slaked pound of lime slaked (278 kcal/kg) (278 kcal/kg)

•Only enough water used to Only enough water used to 

hydrate the lime hydrate the lime

• 

• More difficult to operate than a More difficult to operate than a 

slaker
Absorber System Absorber System

– 

– Minimum 10 Second Minimum 10 Second 

Residence time Residence time

–Carbon Steel Carbon Steel–Atomizers Atomizers– 

– Slurry mix tank Slurry mix tank
Spray Dryer Spray Dryer

•Spray Dryer introduces a lime slurry into t

Spray Dryer introduces a lime slurry into t

by means of an atomizer by means of an atomizer

–For utility sized systems atomizers are 

For utility sized systems atomizers are 

atomizers, or dual atomizers, or dual-fluid nozzles fluid nozzles

–With a Rotary Atomizer the slurry is fed 

With a Rotary Atomizer the slurry is fed 

rotating at a high rate of speed (~10,0

rotating at a high rate of speed (~10,0

–With a Dual With a Dual-fluid Nozzle compressed ai

fluid Nozzle compressed a

slurry at the nozzle tip slurry at the nozzle tip

•Droplets are dispersed into the flue gas st

Droplets are dispersed into the flue gas st

with the SO with the SO2, and are dried into fine powd

, and are dried into fine powd
Spray Dry Absorber Spray Dry Absorber

Hot flue gases are often split to aid Hot flue gases are often split to aid in drying the slurry in drying the slurrySpray dryers are generally limited Spray dryers are generally limited to low to medium sulfur fuels by to low to medium sulfur fuels by the amount of water in slurry the amount of water in slurryExit temperatures must stay above Exit temperatures must stay above the adiabatic saturation the adiabatic saturation temperature to ensure complete temperature to ensure complete drying of droplets drying of droplets Temperature above saturation Temperature above saturation defined as defined as 

“Approach to Saturation Approach to Saturation

”

B&W B&W
Rotary Atomizer Rotary Atomizer

•Rotary Atomizer shows Rotary Atomizer shows dispersion of slurry from disk dispersion of slurry from disk•Atomizers are supplied with Atomizers are supplied with quick disconnects quick disconnects – 

– as they as they are changed while the Unit is are changed while the Unit is 

on

-line

–B&W design uses one B&W design uses one atomizer in an SDA atomizer in an SDA 

vessel

– 

– Alstomdesign use design use several atomizers in a several atomizers in a 

single vessel single vessel
Dual Fluid Atomizer Dual Fluid Atomizer

•Dual Fluid Atomizer shows Dual Fluid Atomizer shows 

dispersion of slurry from nozzle dispersion of slurry from nozzle

•Atomizers are supplied with Atomizers are supplied with quick disconnects to permit on quick disconnects to permit on- 

-

line maintenance line maintenance 

•Siemens design uses 15 Siemens design uses 15 –20 dual fluid nozzles in a single dual fluid nozzles in a single vessel
Dual Fluid Atomizer Dual Fluid Atomizer

SLURRY FEED ATOMIZING AIR

AIR RESERVOIR INSERTS

PENTHOUSE FLOOR

PERFORATED PLATE

GAS DISTRIBUTION

16-20 per absorber
FABRIC FILTERS FABRIC FILTERS

Principles of Operation Principles of Operation

 Particulate Laden Gas Passes Through A W

Particulate Laden Gas Passes Through A W

Felted Fabric Felted Fabric

 Forces Of Impaction, Interception, And Dif

Forces Of Impaction, Interception, And Dif

Separate The Particles From The Gas Strea

Separate The Particles From The Gas Strea

 As The Process Proceeds Particles Will Imp

As The Process Proceeds Particles Will Imp

Previously Collected Particles Previously Collected Particles

 The Built Up Deposit May Itself Become Th

The Built Up Deposit May Itself Become Th

Medium

 Dust Is Removed From The Media Dust Is Removed From The Media With an SDA or CDS System the Fabric Filt

With an SDA or CDS System the Fabric Filt

Account for Up to 20% of the SO Account for Up to 20% of the SO2remove

remove
Waste Recycle System
Waste Recycle System Waste Recycle System

Waste Recycle System Waste Recycle System

To increase lime utilization To increase lime utilizationRecycle ash day bin (8 hours) Recycle ash day bin (8 hours) 

Distance between recycle slurry Distance between recycle slurry tanks and atomiz

tanks and atomiz

short

Current trend is to minimize retention time in rec

Current trend is to minimize retention time in rec

Waste Storage Silo Waste Storage Silo

Size based on amount of waste to disposal Size based on amount of waste to disposal
Waste Storage Silo Waste Storage Silo
Waste Recycle System Waste Recycle System To increase lime utilization To increase lime utilization

4

-8 hours storage silo 8 hours storage silo

slurry mix tank slurry mix tank2 x 4 hours slurry storage tank 2 x 4 hours slurry storage tankDeposits in the bottom of tank Deposits in the bottom of tank>35% solid >35% solid3

-4 day waste storage 4 day waste storage
Flue Gas System Flue Gas System

Inlet/outlet ductwork Inlet/outlet ductwork

Carbon Steel Carbon SteelKeep Distance short between Absorber O

Keep Distance short between Absorber O

Baghouse Inlet Baghouse Inlet

Minimize turns and direction changes Minimize turns and direction changes

Chimney Chimney

Top 20’wall papered with stainless steel 

wall papered with stainless steel 

coating is the lower cost option) requir

coating is the lower cost option) requir

maintenance maintenance

Typically low load velocities/pos Typically low load velocities/possibility of cold 

sibility of cold 
Circulating Dry Scrubbers (C

Circulating Fluidized Bed (
Circulating Dry Scrubber 

Circulating Dry Scrubber 

The separate addition of water allows 

The separate addition of water allows 

system to operate on somewhat hig

system to operate on somewhat hig

fuels than the spray dryer technolo

fuels than the spray dryer technolo

CDS system is simpler in components 

CDS system is simpler in components 

than the Spray Dryer than the Spray Dryer

Both technologies recycle large amou

Both technologies recycle large amou

to help control lime consumption to help control lime consumption

High efficiencies similar to a wet FGD 

High efficiencies similar to a wet FGD 

Low levels of emissions have been gu

Low levels of emissions have been gu

the past the past

Lowest guaranteed emission Lowest guaranteed emission –0.040 

0.040 
Circulating Dry Scrubber Circulating Dry Scrubber

Very High RecirculBaghouse Solids RHigh Utilization of L

Internal Solids Recirculation Enhances Reactions
Circulating Dry Scrubber 

Circulating Dry Scrubber 

The absorber is a fluidized bed of solids 

The absorber is a fluidized bed of solids 

flue gas flue gas

At low loads clean gas is At low loads clean gas is recirculated recirculate

solids suspension solids suspension

As opposed to the spray tower design C

As opposed to the spray tower design C

hydrate to the absorber hydrate to the absorber

Water is sprayed in separately in the flu

Water is sprayed in separately in the fl

aid in collection aid in collection
Dry FGD Technology Sup

Dry FGD Technology Sup

Semi

-dry FGD dry FGD

AlstomBabcock & Wilcox Babcock & WilcoxSiemens Environmental Siemens Environmental

Circulating Dry Scrubber Circulating Dry Scrubber

AlstomBabcock & Wilcox Babcock & WilcoxFoster Wheeler (Graff Foster Wheeler (Graff Wulff)

Allied Technology Allied Technology Babcock Power Babcock PowerHitachi HitachiMarsulex Marsulex
DSI Technology Suppliers DSI Technology Suppliers

ADA

-ES

Babcock & Wilcox Babcock & WilcoxClyde Bergemann Bergemann

F L Smidth

FuelTech FuelTechNalco

-Mobotec Mobotec

Nol

-Tech

SchickUCC
When Compared to other FGD Technologies When Compared to other FGD Technologies

Lower Capital Costs Lower Capital CostsHigher Operating Costs for Reagent Higher Operating Costs for ReagentSmaller Footprint Smaller FootprintEase of Installation (Installed in Existi

Ease of Installation (Installed in Existi

Only Moderate SO Only Moderate SO2Reduction (50% to 

Reduction (50% to 

Removal) Removal)

SO2 Control – DSI
Calcium vs. Sodium Calcium vs. Sodium

Calcium Calcium(Limestone or Lime) (Limestone or Lime)

Sodium(Trona or So

(Trona or So

Bicarbonate 

Bicarbonate 

1800°F to 2200 F to 2200°F Optimum F Optimum 

for Furnace Injection for Furnace Injection

600°F to 800 F to 800°

for Trona for Trona250°F to 350 F to 350°

for SBC for SBC

Lime Could also be Injected Lime Could also be Injected After Economizer After Economizer

Dry Injection Dry Injection

Some Reduced ESP Some Reduced ESP Performance Performance

Improved ESP 

Improved ESP 

Limited to ~50% SO Limited to ~50% SO2

Removal Removal

Up to ~80% R

Up to ~80% R

SO2 Control – DSI
Sorbent Sorbent Trona S

Capture Device ESP BGH ESP 

NSR 2.6 1.15 1.2 

Sorbent Sorbent Increase by wt. Increase by wt. 3.1 1.4 1.6 

Trona SBC

Example NSR at 60% Removal (Refer to Graphs Ab

SO2 Control – DSI
Questions? Questions?