WET FLUE GAS 

DESULFURIZATION FGD 

SYSTEMS 

ADVANCED TECHNOLOGY FOR 

MAXIMUM SO2 REMOVAL
B&W WET FGD 

SYSTEMS – FLEXIBILITY OF DESIGN AND ADVANCED 

FEATURES TO MEET CUSTOMER NEEDS

When performance counts

SINCE 1971, THE BABCOCK & WILCOX COMPANY’S (B&W) WET 

FLUE GAS DESULFURIZATION (FGD) SYSTEMS, OR SCRUBBERS, HAVE 

OPERATED EFFICIENTLY, ECONOMICALLY AND RELIABLY, HELPING 

OUR CUSTOMERS MEET PERMIT REQUIREMENTS WHETHER AS A 

NEW SOURCE OR RETROFIT APPLICATION. CURRENT DESIGNS CAN 

ACHIEVE MORE THAN 99% REMOVAL OF SO2. IMPROVEMENTS 

IN B&W’s WET SCRUBBER DESIGN AND AUXILIARY EQUIPMENT HAVE 

RESULTED IN SYSTEM AVAILABILITY GREATER THAN 99.5%.
largest network of field service 

engineers to support project 

development, project execution, 

and long-term operation and 

maintenance. We also conduct 

extensive research and development (R&D) activities to continue 

product advancement.

Experience

Original Equipment Supply

At the time of publication, B&W 

has provided wet FGD systems for 

a total scrubbed capacity of more 

than 60,000 MW. Through licensees 

in China and Germany, B&W wet 

FGD technology has been utilized 

for an additional capacity of more 

than 45,000 MW.

Upgrades

B&W has also improved the 

performance of more than 8,000 

MW of non-B&W wet FGD systems 

by replacing the original absorber 

internals with our absorption tray 

technology and through forced 

oxidation conversions. Benefits have 

included improved SO2 removal, 

reduced absorber pump power 

Scope of supply

B&W is a full-scope supplier. In 

addition to flue gas absorbers, 

we supply reagent preparation 

systems, dewatering systems 

and related system equipment. 

We also provide complete 

construction services through 

our subsidiary, Babcock & Wilcox 

Construction Co., Inc. (BWCC).

B&W employs an experienced 

staff of design engineers, project 

managers, and the industry’s 

Current B&W designs are achieving 99% SO2 removal with system availability greater than 99.5%.

3
systems with two to four smaller 

boilers feeding one absorber 

and three larger units feeding 

two absorbers.

Choice of reagents

B&W has designed FGD systems 

using a variety of reagents. While 

most of our experience is with 

limestone, designs have utilized 

lime, magnesium-enriched lime, and 

soda ash. Limestone-based systems 

using organic acid enhancement 

have also been provided.

Oxidation experience

All new wet FGD systems are 

designed and supplied with forced 

oxidation. Existing units can also be 

converted to forced oxidation. 

This beneficial process converts 

calcium sulfite to calcium sulfate 

and improves scrubber operation 

while providing a marketable 

gypsum byproduct. B&W has more 

than 16,000 MW of commercial 

units successfully operating with in 

situ forced oxidation systems. In 

addition, we have 2,800 MW of 

commercial units operating with 

specialized forced oxidation 

systems that are separate from 

the absorber reaction tank, most 

notably on magnesium-enhanced 

lime systems.

Advanced design 

benefits 

B&W continues to optimize its 

FGD systems by refining the 

technology to improve SO2 

removal efficiency, improve longterm operating reliability, and reduce 

capital and maintenance costs. As 

an indication of our constant efforts 

to improve our designs, we currently 

have more than 40 patents involving 

wet FGD technology.

 As a full-scope supplier, B&W can provide complete FGD systems including reagent preparation, 

dewatering and other system equipment as well as a wide range of multi-pollutant control technologies.

consumption and maintenance 

costs, reduced limestone 

consumption, the elimination of 

costly additives, decreased landfill 

requirements, and the opportunity 

to provide a marketable byproduct.

Fuel Experience

B&W operating experience 

encompasses a complete range 

of fuels including bituminous, 

subbituminous, Powder River Basin 

(PRB), lignite and brown coals. We 

have also provided systems for 

heavy oil and Orimulsion® fuels. 

Large, Single Absorbers 

As the technology of wet FGD 

systems has improved, typical units 

have a single absorber module. 

B&W absorber modules up to 

1,300 MW are available. Absorber 

design and reliability allows many 

utilities to treat the flue gas from 

multiple boilers with one absorber. 

To reduce project costs B&W and 

our licensees have provided 

4
C

B&W’s wet FGD systems operate efficiently, economically and reliably on a variety of 

worldwide fuels to help our customers meet permitting and 

operating requirements.
Conical

Outlet

Interspatial

Spray

Levels

SO2 and

Flue Gas In

Gas

Distribution

Trays

Oxidation

Zone

Slurry

Agitators

Oxidation

Air Supply

Recirculation

Pumps

Clean

Flue Gas

Out

Moisture

Separators/

Mist Eliminators

The B&W Absorber

Babcock & Wilcox Absorber 

6

Absorption tray system

A proven design for 

high SO2 removal

B&W’s absorber design features 

provide the highest levels of SO2

removal, reduced operating costs 

and significant reductions in 

maintenance costs compared 

to other technologies. These 

benefits allow our customers to 

stay competitive with today’s 

increasingly more stringent 

environmental requirements. 

Absorber design

B&W’s absorber module is a 

counter-current flow design. Slurry 

is sprayed downward from a series 

of headers and nozzles and scrubs 

the flue gas as it moves upward 

through the absorption tray and 

spray zone. The control system 

automatically adjusts the feed of 

fresh reagent to achieve an outlet 

SO2 emission limit or the required 

SO2 removal efficiency. 

B&W’s absorber tray system serves 

the dual purpose of providing 

gas/liquid contact for SO2 

absorption and more uniform 

distribution of flue gas across the 

tower. The gas rises through the 

absorber, contacting a froth of 

slurry on the tray. This action results 

in efficient contact of gas and 

reagent throughout the absorber. 

B&W absorbers use one or two 

trays depending upon the fuel and 

specified requirements for SO2 

removal and operating parameters. 

The tray provides uniform gas 

distribution and effective gas/slurry 

contact. As an economic design 

for high efficiency, B&W offers our 

dual-tray technology for certain 

applications. Table 1 summarizes 

the benefits of the B&W tray 

absorber tower design.

The slurry and the flue gas must 

be uniformly distributed across the 

absorber tower’s cross-section for 

optimum SO2 removal. An efficient 

spray header and nozzle system is 

used to evenly distribute the liquor, 

while the tray distributes the gas 

flow. As determined by both 

physical and computer modeling, 

the gas side pressure drop induced 

by the slurry sprays is not sufficient 

by itself to adequately distribute 

the flue gas at the base of the spray 

zone. In open spray towers, uniform 

gas distribution is not achieved 

as effectively.

The B&W tray design effectively 

achieves uniform gas distribution, 

which becomes even more critical 
B&W’s absorption tray provides for 

uniform gas flow and maximizes SO2

removal. This photo shows a tray after 

two years of continuous service.

TABLE 1

EXAMPLE ABSORBER COMPARISON

Unit Size : 617 MW SO2 Inlet : 1,100 ppmdv 

Reagent : Limestone SO2 Removal : 97.6% 

 2 Trays 1 Tray Open Tower

L/G 56 82 108

 P, in. wc 10.2 8.2 7.0

Pump Flow, gpm 34,500 50,000 66,000

Fan/Pump Power, kw 6,470 6,560 7,470 

 Power Base +90 +1,000

Pump/Header Cost Base +$400k +$700k

7

High gas velocity in spray area is less effective. Uniform gas distribution through spray zone(s) 

results in more effective and efficient SO2 removal.

in larger-diameter spray absorber 

towers. Without a tray, some zones 

of the absorber have poor gas 

distribution, which results in zones 

of either inadequate or excess slurry 

and reactant. With the tray, flue gas 

is uniformly distributed for the most 

efficient SO2 removal.

The tray is rugged, made from an 

alloy steel. The tray is also used 

as a convenient inspection and 

maintenance platform when using 

appropriate planking. Costly and 

time-consuming scaffolding is 

not required.

B&W’s tray design has been proven 

through extensive laboratory testing 

and modeling and many years of 

successful operation.

B&W uses both 

advanced numerical 

modeling and 

physical modeling 

to design the most 

efficient wet flue gas 

desulfurization systems.

a) Wet FGD Without B&W Tray b) Wet FGD With B&W Tray 

Outlet Outlet

Gas Velocity

Magnitude

(ft/s)

30

28

26

24

22

20

18

16

14

10

8

6

4

2

0

Slurry Level Slurry Level

Inlet Inlet

Mist Eliminator 2

Mist Eliminator 1

Spray Header 2

Spray Header 1

Mist Eliminator 2

Mist Eliminator 1

Spray Header 2

Spray Header 1

Tray
Two levels of moisture separators 

effectively prevent slurry carryover and 

deposition in the downstream flue. 

Multiple side-entering agitators 

on B&W’s absorber tower provide 

uniform slurry mixing. 

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test the performance of moisture 

separators in our hydraulic model. 

We also work closely with our 

suppliers in the development 

of advancements to moisture 

separator technology.

Patented inlet awning

B&W’s patented inlet awning 

design prevents the buildup of 

deposits in the absorber inlet flue. 

The awning deflects the falling 

slurry away from the inlet, shifting 

the wet-dry interface out into the 

absorber away from the inlet flue. 

This design provides high reliability 

and lower maintenance costs.

Tank agitators

Slurry in the recirculation tank 

is agitated to keep the solids in 

suspension. B&W’s standard 

design allows for operation with 

one of the agitators out of service 

for high system reliability. 

Patented interspatial 

headers

Achieving overlapping spray 

coverage with an effective spray 

header design is critical for optimal 

SO2 removal performance. B&W’s 

patented interspatial header 

technology allows the location of 

two spray headers at the same 

elevation while maintaining full 

overlapping coverage with one or 

both spray headers in service. The 

use of interspatial spray headers 

results in a shorter absorber 

tower, reduced pump power, 

lower building height, less external 

recirculation piping, and easier 

nozzle inspection and maintenance. 

Moisture separator

Efficient moisture separation is 

essential to prevent slurry 

carryover and deposition in the 

flue downstream of the module. 

B&W absorbers utilize two levels of 

chevron-shaped moisture separators 

that are rugged in design and have 

a history of low replacement. We 

have performed extensive R&D 

to optimize gas flow distribution, 

develop velocity profiles, and Deposit buildups in the absorber 

inlet flue are reduced by B&W’s 

patented inlet awning. 
Materials of 

construction

B&W can supply absorber 

modules in a variety of materials 

for dependable operation and 

reliability: rubber and flake glass 

lined, stainless steel, and duplex 

stainless. Concrete and tile 

designs can also be supplied. 

Abrasion-resistant fiberglass 

reinforced piping (FRP) or alloy 

piping can be used for internal 

spray headers. Abrasion-resistant 

materials are used for the spray 

nozzles. External piping is typically 

FRP or rubber-lined carbon steel.

Multi-pollutant 

capability

B&W provides a full range of 

flue gas cleaning equipment. 

Our products include wet and dry 

precipitators, baghouses, wet 

and dry scrubbers, reagent injection 

systems for SO3 and acid mist 

control, and a variety of technologies for the control of mercury. 

The B&W wet scrubber provides 

control of several pollutants in 

addition to SO2.

Filterable (solid) particulate is 

removed in the wet scrubber. The 

wet scrubber removes 40-90% of 

the flyash entering the scrubber, 

depending upon the ash inlet 

loading and the type of upstream 

particulate collector.

Acid mist (H2SO4) is removed in 

the wet scrubber. The removal is 

dependent upon a number of 

operating conditions such as gas 

temperature, gas humidity, inlet 

concentration, etc. H2SO4 removal in 

wet scrubbers ranges from 35-70%.

Mercury is also removed in the wet 

scrubber. Using B&W’s patented and 

proprietary additives, a minimum of 

90% removal of oxidized mercury 

can be achieved. Ongoing research 

at the time of this publication 

indicates the potential for at least 

20% removal of elemental mercury.

Extensive R&D 

activities for improved 

performance

B&W is continuously working to 

improve our wet scrubber 

product line. Our research center 

is equipped with a wet scrubber 

pilot plant. The flue gas is supplied 

by a small boiler unit capable of 

firing a variety of coals, liquid 

and gaseous fuels. B&W also has 

an advanced hydraulic model 

that is used to study tray and 

spray fluid hydraulics and mist 

eliminator carryover.

Through extensive research and 

development, B&W scientists continually 

strive for product improvements to 

help our customers reduce emissions.

9

B&W’s interspatial spray 

header design provides 

complete spray coverage 

for optimal performance 

and easier maintenance.
systems for mercury and SO3 control, 

low NOx combustion systems, and 

selective catalytic and non-catalytic 

reduction systems for NOx control. 

In addition, B&W provides a 

complete package of aftermarket 

services including engineered 

equipment upgrades, startup and 

commissioning, performance testing 

and monitoring, field engineering 

and replacement parts.

Full -Scope Integration

B&W FGD 

systems are 

backed by an 

experienced 

staff of design 

engineers, 

project 

managers and 

a network of 

field service 

engineers.

10

Modularization

B&W designs its scrubber systems 

with modularization in mind. 

Components are manufactured to 

minimize on-site labor requirements, 

particularly in locations with limited 

laydown area. This technique 

significantly reduces both the 

project schedule and construction 

costs and represents an important 

advancement in manufacturing and 

construction technology.

Project management

Many times, a project calls for new 

ways of thinking. B&W’s innovation 

goes beyond traditional project 

management and vendor/supplier 

relationships. Innovative approaches, 

such as strategic alliances, can 

allow us to collaborate with our 

customers and key suppliers on 

ideas and solutions and ultimately 

share in the cost savings that can 

result from such an arrangement. 

Effective communication and trust are 

vital to make any project a success.

Total-scope services

B&W provides total-scope 

services, such as project 

engineering and management, 

component fabrication, and 

installation of complete 

environmental emissions control 

equipment. Our environmental 

equipment capabilities include 

fabric filter baghouses, 

precipitators, sorbent injection 

B&W is the only FGD supplier with a full capability 

construction company operating as a subsidiary on 

the same campus. Complete project integration, 

from concept to commercial operation, is necessary 

to control costs and schedule and is achievable 

through the team of B&W and BWCC.
Q R S

MIDWESTERN U.S. UTILITY, UNIT 8

NOMINAL BOILER CAPACITY

NOMINAL SCRUBBER CAPACITY (ACFM)

INLET SO2 CONCENTRATION (PPM)

PERCENT SO2 REMOVAL

COMMERCIAL OPERATION

FUEL

REAGENT

OXIDATION METHOD

550 MW

2,127,000

2764

97

APRIL 2007

PULVERIZED COAL

LIMESTONE

FORCED

PROGRESS ENERGY, ROXBORO UNIT 2

NOMINAL BOILER CAPACITY

NOMINAL SCRUBBER CAPACITY (ACFM)

INLET SO2 CONCENTRATION (PPM)

PERCENT SO2 REMOVAL

COMMERCIAL OPERATION

FUEL

REAGENT

OXIDATION METHOD

670 MW

2,079,000

1977

97

APRIL 2007

PULVERIZED COAL

LIMESTONE

FORCED

AMERICAN ELECTRIC POWER, MITCHELL UNITS 1 AND 2

NOMINAL BOILER CAPACITY (combined)

NOMINAL SCRUBBER CAPACITY (ACFM, per unit)

INLET SO2 CONCENTRATION (PPM)

PERCENT SO2 REMOVAL

COMMERCIAL OPERATION

FUEL

REAGENT

OXIDATION METHOD

1600 MW

3,238,700

1990

98

JAN 2007 (Unit 2)

APRIL 2007 (Unit 1)

PULVERIZED COAL

LIMESTONE

FORCED

PROGRESS ENERGY, ASHEVILLE UNITS 1 AND 2

NOMINAL BOILER CAPACITY (combined)

NOMINAL SCRUBBER CAPACITY (ACFM, per unit)

INLET SO2 CONCENTRATION (PPM)

PERCENT SO2 REMOVAL

COMMERCIAL OPERATION

FUEL

REAGENT

OXIDATION METHOD

400 MW

715,429

1990

97

NOV 2005 (Unit 1)

MAY 2006 (Unit 2)

PULVERIZED COAL

LIMESTONE

FORCED

NEW BRUNSWICK POWER, DALHOUSIE UNITS 1 AND 2

NOMINAL BOILER CAPACITY (combined)

NOMINAL SCRUBBER CAPACITY (ACFM, per unit)

INLET SO2 CONCENTRATION (PPM)

PERCENT SO2 REMOVAL

COMMERCIAL OPERATION

FUEL

REAGENT

OXIDATION METHOD

315 MW

1,078,400

2300

90

DEC 1994

ORIMULSION

LIMESTONE

FORCED

MIDWESTERN U.S. UTILITY, UNITS 2 AND 3

NOMINAL BOILER CAPACITY (combined)

NOMINAL SCRUBBER CAPACITY (ACFM, per unit)

INLET SO2 CONCENTRATION (PPM)

PERCENT SO2 REMOVAL

COMMERCIAL OPERATION

FUEL

REAGENT

OXIDATION METHOD

661 MW

2,698,000

2550

97

DEC 2006 (Unit 3)

MAY 2007 (Unit 2)

PULVERIZED COAL

LIMESTONE

FORCED

®

Recent B&W Wet FGD Projects
Babcock & Wilcox Power Generaon Group, Inc.

20 S. Van Buren Avenue

Barberton, Ohio 44203 USA

Phone: 330.753.4511

Fax: 330.860.1886

The informaon contained herein is provided for general 

informaon purposes only and is not intended nor to be 

construed as a warranty, an offer, or any representaon 

of contractual or other legal responsibility.

Orimulsion is a trademark of Bitumenes Orinoco, S.A.

© 2007 Babcock & Wilcox Power Generation Group, Inc. 

All rights reserved.

E101-3167A 2KA0G

Babcock & Wilcox Power Generaon Group, Inc. is a 

subsidiary of The Babcock & Wilcox Company (B&W). 

Established in 1867, B&W is a world leader in providing 

steam generang and emissions control equipment, 

nuclear operaons and components, and defense 

program management services.

For more informaon, or a complete lisng of our sales 

and service offices, call 1-800-BABCOCK (222-2625), 

send an e-mail to info@babcock.com, or access 

our Web site.

www.babcock.com

HELPING OUR CUSTOMERS 

PROVIDE CLEAN POWER

Working with our customers, B&W provides worldwide 

leadership in environmental products and services 

by applying the best technology through innovation, 

responsiveness and employee commitment.