ALDEN

Solving Flow Problems Since 1894

The Wet vs. Dry Question for 

Scrubbers

Alden Webinar Series

December 8, 2011

For audio, 

please dial 1 (866) 809-5996, participant code 6504656 

We will begin shortly
ALDEN

Solving Flow Problems Since 1894

Housekeeping

• Questions and Audio

• Availability of slide pdf file

• Q&A period

For audio, 

please dial 1 (866) 809-5996, participant code 6504656 
ALDEN

Solving Flow Problems Since 1894

• Introduction - Martin Kozlak, Alden

• The Regulatory Environment and Short Overview of 

Scrubbing Technologies - Chris Wedig, Shaw

• Wet versus Dry FGD Case Study - Ned West, Southern 

Co.

• On the Choice of a Dry Scrubber for Dominion’s 

Brayton Point Power Plant - Thomas Penna, 

Dominion

Agenda
ALDEN

Solving Flow Problems Since 1894

Introduction

Martin Kozlak

Director, Gas Flow Systems

Engineering

Alden
ALDEN

Solving Flow Problems Since 1894

• Engineering services:

– Hydraulic Modeling & 

Consulting

– Fish protection consulting 

and laboratory work

– Field measurement 

services

– Flow meter calibration

About Alden
ALDEN

Solving Flow Problems Since 1894

– Dry and wet scrubbers

– Other air pollution control 

equipment

– Process equipment

– Gas turbine peripherals

– Ventilation (pollutant, smoke, fire)

About Alden

• Physical and computational modeling to 

ensure the proper performance of gas 

flow systems:
ALDEN

Solving Flow Problems Since 1894

Regulatory Environment and 

Short Overview of Scrubbing 

Technologies

Chris Wedig 

Senior AQCS Technology Specialist

Shaw
ALDEN

Solving Flow Problems Since 1894

Regulatory Environment

• Utility MACT 

- Particulate Matter

- Hydrogen Chloride 

- Mercury

• Cross State Air Pollution Rule (CSAPR)

- Nitrogen Oxides

- Sulfur Dioxide
ALDEN

Solving Flow Problems Since 1894

Regulatory Environment

• Regional Haze (where applicable)

- Particulate Matter

- Sulfur Dioxide 

- Nitrogen Oxides

• Consent Decree (if applicable)

- Particulate Matter

- Sulfur Dioxide

- Nitrogen Oxides

- Other
ALDEN

Solving Flow Problems Since 1894

Related Potential Future 

Regulatory Environment

• Coal Combustion Residuals (CCRs)

• GHG NSPS (potential)

• Thermal Power Plant Cooling Water Intake 

(316 b)

• Waste Water Discharge Issues

• Permit Renewal Process
ALDEN

Solving Flow Problems Since 1894

Options to Consider 

• Utilities may consider a range of options in 

addressing the regulatory environment.

• One of several options is to evaluate 

different retrofit technologies for flue gas 

cleaning.

• There are a variety of processes available 

for consideration, including “scrubbers”.
ALDEN

Solving Flow Problems Since 1894

Factors Considered in Scrubber 

Technology Selection

• Stack emission requirements. 

• Fuel type and flue gas properties. 

• Site-specific technical and economic 

(capital and annual O&M costs) 
ALDEN

Solving Flow Problems Since 1894

Factors Considered in Scrubber 

Technology Selection (con’t)

- Site-specific technical and economic (capital and annual O&M costs) 

• Financial factors and costs (e.g. economic life, interest rate, unit costs, etc.)

• Size of plant,

• Capacity factor,

• Reagent type and usage rate,

• Byproduct type and production rate,

• Electrical power usage, 

• Water type and usage rate, 

• Waste water production rate and permit issues, 

• Steam requirement (if required), 

• Cooling water usage (if required), 

• Impacts on the existing draft system, stack, plant electrical distribution and 

other systems,
ALDEN

Solving Flow Problems Since 1894

Factors Considered in Scrubber 

Technology Selection (con’t)

- Site-specific technical and economic (capital and annual O&M costs) (continue)

• Impact of the retrofit scrubber on the existing air quality control (AQC) 

equipment at the power plant (e.g. PAC or Trona impact on flyash), 

• Methods to dispose or reuse scrubber waste byproducts and/or conversion of 

scrubber by-products to useful materials,

• Real estate required for the scrubber system equipment, 

• O&M personnel (staffing), 

• Maintenance required, including parts replacement (e.g. bag/cage),

• Spare part requirements, 

• System reliability required,

• Compatibility of retrofit scrubber with any future potential systems such as 

cooling water systems, waste water systems, solid byproduct waste landfill 

projects, and carbon dioxide (CO2) capture systems,

• Permit issues, including issues related to retrofit scrubber and byproducts.
ALDEN

Solving Flow Problems Since 1894

Types of Scrubbing Technologies

• Dry Sorbent Injection (DSI with Trona, SBC, HL)

• Spray Dryer Absorber (SDA with lime, HL)

• Circulating Dry Scrubbers (CDS/NID with lime, HL)

• Wet Scrubbers (e.g. limestone, lime, etc.)

• Multi-Pollutant (e.g. ReACT, etc.)

• Other
ALDEN

Solving Flow Problems Since 1894

Summary

• In addressing the Regulatory Environment, 

Utilities may evaluate a range of options.

• One of several options is to evaluate 

retrofit “scrubbers”.

• Selection of scrubber technology type is 

based on plant specific economic and 

technical considerations.
ALDEN

Solving Flow Problems Since 1894

Wet vs. Dry FGD Case Study

Ned West, P.E.

Southern Company Generation
ALDEN

Solving Flow Problems Since 1894

Southern Company

• 43,000 MW of generation capacity

• 73 fossil and hydro plants

• 4.3 million retail customers
ALDEN

Solving Flow Problems Since 1894

Case Study - Plants A and B

• Plant A – 2 x 250MW units, no other coal-fired 

generation on plant site

• Plant B – 375MW + 250MW units, one larger 

unit on the same site has a wet scrubber
ALDEN

Solving Flow Problems Since 1894

Traditional Factors – Wet vs. Dry

• Unit size

• Fuel Sulfur 

• Capacity Factor

• Byproduct disposal

• Req’d SO2removal 

• Draft system loss

• Power consumption

• Cost of lime versus 

limestone 

• Visible steam plume

• New vs. retrofit

• Existing stack mat’l

• Flyash disposal or 

sales
ALDEN

Solving Flow Problems Since 1894

New Factors – Wet vs. Dry FGD

• HAPS MACT Compliance 

• Mercury compliance

• Particulate emission

• Wastewater treatment

• Circulating Dry Scrubber performance 

• Modularity of new designs

• Pre-ground limestone

• Dry byproduct disposal under new CCR regs
ALDEN

Solving Flow Problems Since 1894

Reagent Cost Evaluation

• Depends on fuel sulfur content and 

reagent stoichiometric ratio

• Depends on unit capacity factor

• Relative cost of lime vs. limestone

• Ratio of lime/ LS cost per ton has 

changed from 6:1 to 2:1 in recent 

years due to our use of pre-ground 

limestone in some wet scrubbers
ALDEN

Solving Flow Problems Since 1894 1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

0.0% 0.5% 1.0% 1.5% 2.0% 2.5%

Stoichiometric Ratio

% Sulfur in Coal

Lime vs. Fuel Sulfur for Dry FGD

Derived from proposal data
ALDEN

Solving Flow Problems Since 1894

Attribute Wet FGD Dry FGD / FF Importance / Priority Notes / Comments

at Plant A

Environmental Performance

S O2 removal, 1%S Coal 98% 98% Important

S O2 removal, 2.5%S Coal 96% 96% Important Fuel Flexibility

S O3 / H2S O4 removal ~40% 98% Important Add Trona or hyd. lime for hi-S coal.

Mercury MACT Probably w. SCR Certainly w. ACI Critical Projected coal is high in mercury.

NOX Reduction 85% w. SCR 85% w. SCR Important County is now in ozone attainment.

PM 2.5 Emissions Low Very Low Important Less of an issue than ozone.

Visible Steam Plume Yes None Low Priority Not expected to be a concern.

O&M Cost / Performance

Draft Loss 7" wg 15" wg Low Priority Accounted for in O&M cost comparison

Power Consumption 4400 kW 1600 kW Low Priority Accounted for in O&M cost comparison

Bag Replacements None 3 - 5 years Low Priority Accounted for in O&M cost comparison

Trona / PAC Additive Trona for SO3 PAC for Hg Low Priority Accounted for in O&M cost comparison

Reagent and Waste Product

Wastewater Treatment Future None Important WWT system is likely, maybe by 2015

Byproduct Disposal Wet Stack Dry Landfill Low Priority Dry landfill has higher O&M cost?

Reagent Cost, Utilization Lower Cost Higher Cost Low Priority Lime is more costly than limestone

Construction Considerations

Wet Chimney Cost Re-Line Existing none Low Priority Stack re-lining not req'd for dry FGD

Draft System Mods Replace ID Fans Add Booster Fans Low Priority Existing ID fans in poor condition?

Tie-in Outage Duration ~ 6 weeks ~2 weeks Low Priority Longer outage for stack and ID fans

Evaluated Cost

Capital Cost $74M $92M - $112M Important Includes direct costs only

Extended Outage Cost $5M - Low Priority for 6-week outage, both units

O&M Cost, NPV $40M $53M - $64M Important 2009 $ for 10-year economic life

Total Cost $119M $145M - $176M Important
ALDEN

Solving Flow Problems Since 1894

Has the Tipping Point Shifted?

• Should we now include the cost of wastewater 

treatment in the wet scrubber economics?

• How will anticipated regulations on disposal of 

Coal Combustion Residuals affect our plans? 

• Must we now assume that 

a baghouse will be required 

for MACT on wet FGD?
ALDEN

Solving Flow Problems Since 1894

$-

$100 

$200 

$300 

$400 

$500 

$600 

$700 

$800 

0.00% 0.20% 0.40% 0.60% 0.80% 1.00% 1.20% 1.40% 1.60% 1.80%

NPV (Capital and O&M) in Millions

Fuel Sulfur Content (%)

Wet FGD + Baghouse vs. Dry FGD w. Baghouse

NPV Calculated over 20 Year Plant Life for 500 MW Plant A

Wet FGD

Dry FGD
ALDEN

Solving Flow Problems Since 1894

Case Study - Plants A and B

• Plant A – 2 x 250MW units, no other coal-fired 

generation on plant site

• Plant A would get a dry FGD system

• Better overall economics when a baghouse 

and wastewater treatment are included in the 

analysis
ALDEN

Solving Flow Problems Since 1894

Case Study - Plants A and B

• Plant B – 375MW + 250MW units, one larger 

unit on the same site has a wet scrubber

• Plant B would get a wet FGD system

• Would replicate the existing wet scrubber to 

treat combined flue gas from both units.

• Shared reagent prep and gypsum disposal

• Shared O&M staff, parts inventory, etc.
ALDEN

Solving Flow Problems Since 1894

On the Choice of a Dry Scrubber for Dominion’s 

Brayton Point Power Plant

Presented by Thomas Penna, PE - Dominion Brayton Point Unit 3 Scrubber Project Manager 12/8/11
ALDEN

Solving Flow Problems Since 1894

• Brayton Point Station is located on Mount Hope Bay, near Fall River, MA.

• Station comprised of three coal fired units, Units 1 and 2 – 250 MW each and Unit 3 –

630 MW, Unit 4 - 450 MW gas/oil fired unit, and five diesel generators.

• Existing air quality control systems include Babcock Power Environmental (BPEI) 

selective catalytic reduction systems on Units 1 and 3, Chemco mercury reduction 

systems on Units 1, 2, and 3, and Wheelabrator/Siemens spray dryer absorber (SDA) 

semi-wet scrubbers on Units 1 and 2.

• Unit 3 is a Babcock and Wilcox, opposed-fired, supercritical, double reheat boiler, 

with air heaters, two (2) sets of cold side electrostatic precipitators in series, ID fans, 

and a concrete stack with an acid brick liner.
ALDEN

Solving Flow Problems Since 1894

SDA vs. CDS Review

• Unit 1 and 2 SDAs operational by December 2008.

• Planning for Unit 3 scrubber started in early 2009 and initially considered rotary 

atomizer SDAs and circulating dry scrubbers (CDS). 

• Wet scrubber technology could achieve high SO2removal rates, but was not 

considered cost effective based on the Unit 3 fuel sulfur content (0.5 to 2.5 lb 

SO2/MMBTU ) and treating purge stream.

• Contracted consultant to conduct a study comparing the SDA and CDS technologies.

• Dominion developed pro forma comparing CAPEX, annual variable O&M, annual fixed 

O&M, and fuel costs, and considered required duration for tie-in outage.

• Dominion held meetings with the SDA and CDS original equipment manufacturers 

(OEM) and visited U.S. installations. 

• Dominion developed a ranking matrix based on CAPEX, O&M, constructability, 

performance, schedule, experience, and commercial risk.
ALDEN

Solving Flow Problems Since 1894

Technology Decision

• SDA appeared to be the better technology for Unit 3 based on lower capital and annual 

O&M costs, performance based on fuel with a maximum of 2.5 lbs SO2/MMBTU, domestic 

and international operating experience, operating facilities that are equal to or larger than 

required for Unit 3, contractor familiarity with SDA technology (less risk with design, 

construction, and contract guarantees), qualified and reputable OEMs, Station experience 

with operating and maintaining SDA type scrubbers. SDAs could achieve 90% SO2removal 

based on Station operating experience.

• Air permit negotiations with MADEP during 3Q 2009 indicated that future SO2 emission rate 

could be based on Best Available Retrofit Technology (BART) level - 0.15 lb SO2/MMBTU at 

stack or 95% removal, on a 30 day rolling average.

• Based on the high probability that a more stringent SO2 emission rate would be enacted in 

the future, Dominion determined it would be prudent to pursue the dry scrubber 

technology with the highest SO2removal efficiency.

• The SDA scrubber technology was eliminated from consideration due to the removal 

efficiency (approximately 94% maximum based on OEM guarantees) which would limit the 

fuel sulfur content to 1.5 lb SO2/MMBTU maximum.
ALDEN

Solving Flow Problems Since 1894

CDS Performance

• Pre-bid discussions with the CDS OEMS indicated the following emission guarantees 

could be achieved:

• SO2 Emissions: Continuously reduce SO2 emissions to meet the least stringent of 

the following: maintain an emission rate of less than or equal to 0.05 lb/MMBTU 

SO2 or 98% removal (rolling 30 day average) based on minimum, normal, and MCR 

operating conditions.

• SO3/Sulfuric Acid Removal: Continuously reduce SO3/sulfuric acid emissions to less 

than or equal to 0.75 ppmdv @ 3% O2(0.00166 lb SO3/MMBTU), based on 

minimum, normal, and MCR operating conditions.

• Mercury Emissions (Unit 3 Air Permit Requirement): Continuously reduce mercury 

emissions to less than or equal to 0.0025 pound/gigawatt-hour net (1 hour average 

basis), based on an inlet concentration less than or equal to 0.0150 lb Hg/GW-hr 

net and on minimum, normal, and MCR operating conditions.

• Particulate Emissions (Unit 3 Air Permit Requirement) : The maximum Filterable 

PM/PM10/PM2.5 rate shall not exceed 0.010 lb/MMBTU (1 hour block average) and 

the maximum Total PM/PM10/PM2.5 rate shall not exceed 0.025 lb/MMBTU (1 hour 

block average), based on minimum, normal, and MCR operating conditions. 
ALDEN

Solving Flow Problems Since 1894

CDS Technology OEMs as of 2009

– BPEI – Licensee for Turbosorp technology (Austrian Energy & Environment)

• Four (4) operating units in US and thirty eight (38) internationally.

• Largest operating installation: 570,000 ACFM (China) – single train*.

– Allied Environmental – Licensee for Lurgi Lentjes Bischoff technology

• Five (5) operating units in US and forty-two (42) internationally.

• Largest operating installation: 1,120,000 ACFM – single train*.

– Nooter/Eriksen – Licensee for Graf-Wulff GmbH technology

• Thirty five (35) operating units internationally – largest capacity is 2,400,000 ACFM 

(China) – two trains*.

– Alstom – novel integrated desulfurization (NID) technology (“J” duct design with 

mixer/hydrator)

• Four (4) operating units in US and forty-one (41) internationally.

• Largest operating installation: 840,000 ACFM – four reactors*.

* BPS U3 would be the largest domestic CDS installation – 2,400,000 ACFM.
ALDEN

Solving Flow Problems Since 1894

Typical CDS Process
ALDEN

Solving Flow Problems Since 1894

Alstom NID Process
ALDEN

Solving Flow Problems Since 1894

• Considering the SDA and CDS technology project costs to be comparable, the CDS 

technology offered fuel flexibility, allowed recovery from upset conditions as it 

pertains to the 30 day SO2 emission rolling average (could operate at a higher removal 

rate), and minimized maintenance issues (no “atomizer change-out” or slurry issues).

• Dominion toured installations in the U.S. and Europe to verify advertised operation, 

identify potential maintenance or design issues, and confirm reliability.

• Dominion further reviewed equipment space requirements, and lime usage and 

byproduct production based on operating data provided by OEMs.

• Dominion determined that the four CDS OEMS would meet project specification 

requirements and equipment could be located within site footprint. Dominion issued 

the Engineering, Procurement, and Construction (EPC) RFP in September 2009.

• The EPC RFP allowed bidders to receive pricing from all four technology suppliers – no 

exclusive teaming. The EPC bidders performed due diligence and detailed cost 

analysis to determine the most cost effective technology.

• EPC contract was awarded in April 2010.

• The successful EPC Contractor selected the Alstom NID technology for the Unit 3 

scrubber project.
ALDEN

Solving Flow Problems Since 1894

Questions

Please use the Q&A tab in

LiveMeeting

Martin Kozlak: mkozlak@aldenlab.com

Chris Wedig: christopher.wedig@shawgrp.com

Ned West: NWest@southernco.com

Thomas Penna: thomas.g.penna@dom.com