TECHNICAL PUBLICATION

Babcock Power Environmental Inc.

5 Neponset Street

Worcester, Massachusetts 01606

www.babcockpower.com

T-198

SO2 Removal Enhancement to the Vectren,

Culley Generating Station Units 2 & 3 Wet Flue Gas

Desulfurization System

by

Matthew Quitadamo

Process Engineer

Babcock Power Inc.

Clayton Erickson

Manager Process Engineer

Babcock Power Inc.

Joseph Langone

Vice President, Business Development

Babcock Power Environmental Inc.

Presented at

ICAC Forum 05’

March 7-10, 2005

Baltimore, Maryland
© Babcock Power Inc. and Babcock Power Environmental Inc. 2005

SO2 REMOVAL ENHANCEMENT TO THE VECTREN, CULLEY

GENERATING STATION UNITS 2 & 3 WET FLUE GAS

DESULFURIZATION SYSTEM

by:

Matthew Quitadamo

Babcock Power Inc.

Process Engineer

Clayton A. Erickson

Babcock Power Inc.

Manager Process Engineer

Joseph Langone

Babcock Power Environmental Inc.

Vice President

Presented at:

ICAC FORUM 05’

Baltimore, MD, March 7-10, 2005

ABSTRACT

Babcock Power Environmental Inc. (BPEI), a subsidiary of Babcock Power Inc., was

commissioned to design and implement modifications to Vectren’s Culley Generating

Station Units 2 & 3 Wet Flue Gas Desulfurization (WFGD) System to ensure that the

effluent SO2 emissions were in compliance with Environmental Protection Agency (EPA)

requirements. The objective of the modifications was to ensure that the WFGD system

achieves greater than or equal to 95.5% SO2 removal efficiency based on a 30 Day rolling

average for all fuels fired. 

Culley Generating Station Units 2 & 3 WFGD system, originally designed and

constructed by BPI, started commercial operation in 1994 and was originally designed

to handle boiler loads of 365 MWg at a maximum SO2 loading of 6.7 lb/MBtu. Today

the system is required to treat flue gas resulting from boiler loads and SO2 loadings of

up to 392 MWg and 8.0 lb/MBtu respectively.

Absorber baffles were retrofitted in the Culley WFGD System’s absorber tower during the

March 2004 outage to enhance the overall SO2 removal. The baffles serve to better

distribute the incoming flue gas over the entire absorber cross-sectional area as well as

eliminate “gas laning” along the absorber walls. Improving the absorber flow distribution

and liquid-to-gas contact increases the absorbers effectiveness to remove SO2 from the

flue gas, thus achieving higher overall SO2 removal efficiencies.

The installation of absorber baffles resulted in an average SO2 removal efficiency

enhancement of 4.1%. This paper reviews the baffle design and presents data from before

and after absorber modifications.
2

INTRODUCTION

On June 6, 2002, the U.S. Environmental Protection Agency (EPA) and the Department of Justice

announced a Clean Air Act (CAA) settlement with the Southern Indiana Gas and Electric Company,

Inc. (SIGECO), now Vectren Power Supply, for the F. B. Culley coal-fired power plant (Culley Station).

As part of the settlement, Vectren was required to improve the existing Wet Flue Gas Desulfurization

(WFGD) system serving Culley Station’s Units 2 and 3 coal-fired boilers so as to achieve and maintain

a 30 Day Rolling Average SO2 removal efficiency of greater than or equal to 95.0% by June 30, 2004.

Culley’s WFGD operation has changed several times since it started commercial operation in 1994.

Gross boiler load was increased from 365 MWg to 392 MWg and the SO2 loading was increased from

6.7 lb/mmBtu to up to 10.0 lb/mmBtu.

Babcock Power Environmental Inc. (BPEI) was commissioned to design and implement modifications

to the existing WFGD system to meet or exceed SO2 performance parameters as listed below:

* The primary objective was to achieve greater than or equal to 95.5% SO2 removal efficiency 

based on a 30 day rolling average for various fuels fired at the Culley Station

* Also, while fulfilling the primary objective, the system was to maintain a high degree of 

availability. A minimum of one of the six recirculation pumps was to be treated as a spare

Modifications selected/implemented for the existing Culley WFGD system were the addition of new

recirculation pump gear reducers, absorber sump suction line screens, and absorber baffles. This

paper focuses on the implementation of the absorber baffles only; no recirculation pump modifications

have been made.

BACKGROUND

Vectren’s F. B. Culley Station is located on the Ohio River near Newburgh, Indiana. Culley Units 2

and 3 are rated for 105 MWg and 287 MWg respectively. 

Unit 2 is an upgraded balanced draft furnace. It consists of one Babcock and Wilcox pulverized coalfired steam generator, two FD fans, one electrostatic precipitator (ESP) with two chambers, and two

ID Fans with variable speed drives.

Unit 3 is also an upgraded balanced draft furnace. It consists of one Babcock and Wilcox pulverized

coal-fired steam generator, two FD fans, two ESP’s, two air heaters, a Selective Catalytic Reactor

(SCR) system, and two constant speed ID Fans.

The WFGD System was designed and supplied by BPEI, formerly Riley Inc. The system is limestone

based and utilizes a counter/co-current open spray tower with in-situ forced oxidation. The flue gas

exits Unit 2 and 3 ID fans and flows through a single absorber tower to a common wet stack.
3

PROBLEM

Inherent in open spray tower absorbers utilizing spray nozzles to introduce reagent slurry to the inlet

flue gas is a region of lower spray density near the absorber walls. Nozzle arrangements are designed

to produce a given amount of spray overlap. This ensures optimal coverage of the bulk absorber vessel

cross-sectional area. However, absorber geometry and spray nozzle symmetry does not allow for the

same degree of spray overlap near the vessel wall. In order to provide uniform spray coverage across

the entire vessel cross-sectional area, designs would have to implement additional nozzles located

closer to the wall. Apart from being uneconomical, locating nozzles too close to the vessel wall can

lead to rapid wear and as a result require constant maintenance.

Lower spray densities and inadequate spray coverage can lead to the inlet flue gas bypassing the

main reagent slurry spray zone. This can be generally termed as “wall sneakage” or “gas laning.”

Typically areas where wall sneakage is present are less efficient at removing SO2 from the flue gas

and in turn have higher SO2 concentrations at the absorber outlet resulting in lower overall absorber

removal efficiencies.

BPEI designed absorber baffles for the Culley WFGD absorber vessel to reduce the presence of wall

sneakage. The baffles fill in areas of minimal reagent spray coverage forcing the flue gas to pass

through the existing effective spray zones.

Baffles were installed at the level 2 and level 4 spray header supports during the 2004 outage.

DATA EVALUATION

Digital Control System (DCS) data was provided to BPEI by Culley in Microsoft Excel format

representing the actual operating and performance parameters for the Culley WFGD system before

and after the recent modifications. Each data set represents approximately one week’s worth of data

taken directly after a scheduled outage for the respected year. Data was obtained to directly compare

the pre and post retrofit time periods. Utilizing data recorded immediately after the 2003 and 2004

outages allows for the comparison of the system's operation on an equal basis. 
4

DATA ANALYSIS

Examining the effect of the installed absorber baffles in the Culley WFGD absorber was performed in

two ways.

First, raw data from 2003 was directly compared to raw data from 2004. 

Secondly, data from both the 2003 and 2004 time periods was normalized to the design conditions as

defined below in table 1. The average of the corrected 2003 data was directly compared to the average

of the corrected 2004 data to produce an estimated percent enhancement due to the addition of

absorber baffles.

Table 1

WFGD Engineering Study Design Basis

Description Units Value

Maximum Outlet Flue Gas Flow* [afcm] 1,301,571

Maximum Outlet Flue Gas Temperature* [oF] 132

Maximum Outlet Flue Gas Pressure* [iwg] 0

Maximum Inlet SO2 Concentration [lb/mmBtu] 8.0

Recirculation Pump Flow [gpm] 36,102

No. of Recirculation Pumps in Operation [# of # ] 5 of 6

ID of Recirculation Pumps in Operation [--] D, F, A, E, B

SO2 Removal Efficiency [%] 95.5

*Predicted value based on actual data.
5

RESULTS AND DISCUSSION

Figures 1 and 2 display raw data taken directly from the Culley WFGD system DCS for the time

period immediately following the March 2003 outage. 

The figures represent a wide range of operating parameters such as unit load, inlet SO2

concentration, number of operating recirculation pumps, and SO2 removal efficiency. The information

contained in the Figures 1 and 2 is summarized below:

* Data was available for four and five pumps in operation 

* In general the inlet SO2 exceeded the original design value of 6.7 lb/mmBtu

* Unit 2 and Unit 3 combined full load data is available

* SO2 removal efficiency was always greater than or equal to 95.0% over the entire range of 

conditions listed above, even when operating only four recirculation pumps

* Removal efficiencies of 98.0% and greater are obtained for five pump operation with inlet 

sulfur loading of up to 8.0 lb SO2/mmBtu

The installation of absorber baffles at the 2nd and 4th spray levels of the Culley WFGD absorber

improved the overall system SO2 removal efficiency well beyond the target value of 95.5% with five

pumps in operation.

Both raw and normalized data was used to quantify the magnitude of enhancement that can be

attributed to the addition of the absorber baffles. A summary of the raw data points, both before and

after the installation of the absorber baffles shows that the absorber baffles enhanced the overall SO2

removal efficiency of the Culley WFGD system by an average of 4.11% when four of the six pumps

were in operation.

Figure 1. Total Station Generation and SO2

Inlet Loading versus Time

Figure 2. Total Station Generation and SO2 Removal

Efficiency versus Time

Total Generation (MWg)

Inlet SO

Total Generation (MWg)

2 (lb/mmBtu)

SO2 Removal Efficiency, (%)

Date and Time, (mm/dd/yyyy) Date and Time, (mm/dd/yyyy)
CONCLUSIONS

As indicated by the results highlighted throughout this document the absorber baffles proved to be a

very successful and economical solution to the problem of “gas laning” in open spray tower absorbers

utilizing spray nozzles. 

The absorber baffles installed at the Vectren, F.B Culley Generating Station accomplished the

following:

* Allowed for the successful treatment of increased flue gas flows and inlet SO2 loading

* Eliminated the need to purchase or modify process equipment

* Experienced negligible added pressure drop

The Culley Station WFGD system is currently exceeding the guarantee value of 95.5% SO2 removal

efficiency for the maximum unit 2 and 3 load with five pumps in operation for a SO2 loading of 

8.0 lb/mmBtu and four pumps in operation for a SO2 loading of 6.7 lb/mmBtu. Further, the

modifications at the Culley Station WFGD system demonstrate the ability for greater than 98.0%

removal with high sulfur coal.

© Babcock Power Inc. and Babcock Power Environmental Inc. 2005

Figure 3. SO2 Removal Efficiency (Before and After System Modifications)

Normalizing the raw data to reflect the design conditions previously defined in Table 1 allowed for

the evaluation of the overall SO2 removal enhancement for a wider range of operating parameters,

such as the number of operating recirculation pumps. As shown below in Figure 3, for normalized

data with four pumps in operation, the WFGD system increased from an average SO2 removal

efficiency of 87.80% to 93.80%. This represents an average enhancement of 6.83%. For the same

design conditions with five pumps in operation the WFGD system experienced an average SO2

removal efficiency increase from 92.69% to 96.41%. This represents an average enhancement of

4.01%.

No. of Pumps in Operation, (#)

Average SO2 Removal Efficiency, (%)