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Notes from Call with Babcock & Wilcox on January 9, 2014

On Thursday, January 9, 2014, ERG and EPA participated in a call with Babcock & Wilcox (B&W)

to discuss their research on the effects of oxidation reduction potential (ORP) changes within the wet

flue gas desulfurization (FGD) system. Participants on the call included representatives from EPA, ERG,

and B&W, as listed in Table 1.  

Table 1. List of Participants

Name Organization

Shannon Brown Babcock & Wilcox

Dan Johnson Babcock & Wilcox

Mike Klidas Babcock & Wilcox

Steve Feeney Babcock & Wilcox

Melanie Schmeida Babcock & Wilcox

Ryan Cornell Babcock & Wilcox

Ron Jordan EPA

Phillip Flanders EPA

TJ Finseth ERG (contractor to EPA)

Danielle Lewis ERG (contractor to EPA)

B&W began by providing EPA and ERG with an update on their research related to ORP and wet

FGD systems. According to B&W, the industry started focusing on ORP because it was identified as a

potential cause of corrosion issues seen in the wet FGD systems related to manganese precipitates.  

B&W’s analysis is based on field sampling data from two wet FGD systems, one which controlled the

ORP in the scrubber and the other which did not control the ORP during the test period, with data under

further internal review.  Based on B&W’s experience in this area, it is possible that ORP control in the

wet FGD system and associated waste water treatment (WWT) is likely possible with a combination of

other upstream air quality control systems (AQCS) operational modifications and controls and

downstream chemistry monitoring and trim.  One option for this trim may be the use of reducing agents

in coordination with optimizing the wet FGD system. B&W believes that the wet FGD chemistry is

usually not the source of the strong oxidants within the absorber that lead to high ORP values within the

wet FGD absorber slurry and, thus, is not a primary contributing factor to observed increases in ORP.  

The coal chemistry may be one contributing factor to increases in ORP, especially when coals burned

greatly deviate from the coal used as the AQCS design basis. Further, load swings have been implicated

in wet FGD ORP fluctuations.  B&W’s expected optimization steps for controlling the ORP in the wet FGD

system and effluent include a control system involving the AQCS equipment to allow the systems to

respond to changes in coal and load swings.  The control system should take into consideration

operational changes to upstream unit operations in the AQCS train, wet FGD system operational

optimization (including oxidation air reduction), and may also include the addition of reducing agent(s)

to the wet FGD system as a trim. B&W noted that since the ORP swings can happen rapidly, with

changes of 300 mV occurring in approximately 40 minutes, preemptive responses are desired for system

control.    
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B&W looked at ORP at two utilities, one is described in the paper “Optimization and Process

Control of Air Quality Control Systems for Improved WFGD Oxidation Chemistry and Effluent

Composition for Wastewater Treatment” (DCN SE04975). Both utilities operate similarly, but burn two

different types of coal. Due to a nondisclosure agreement, B&W is not at liberty to identify the names of

the plants or utilities.

For the one plant included in the B&W paper, two generating units were evaluated. One unit

was held as the control while operational parameters of the other unit were changed in order to analyze

effects on ORP and other parameters. B&W reports that they are unable to draw any conclusions with

respect to the industry as a whole because the dataset evaluated to date is not large enough.

When asked why they are focusing on oxidation air and electrostatic precipitator (ESP) controls

related to ORP changes, B&W reported that these have been the main focus primarily because they are

easiest to adjust and show prior evidence of affecting ORP. B&W did add that changes in oxidation air

only make a difference in ORP when the system is close to the dissolved oxygen threshold.  

B&W does not believe that particulate loading to the wet FGD is a major cause of ORP changes.  

However, fly ash chemistry could be a contributing factor.  B&W reported that ash loading was definitely

not the cause at one utility, although the ash chemistry could be part of the cause at the second utility.  

A larger dataset would be required in order to begin to draw any definite conclusions. Research has

shown that other causes for ORP changes could be SCR performance, ESP operations, excess oxygen in

the boiler, and combustion issues related to different coal types. They are still trying to determine other

potential contributing factors.

B&W identified persulfate and hypochlorous acid as the primary oxidants present in the wet

FGD wastewater as a result of high ORP. Conflicting lab reports indicate that the wastewater likely

contains a mix of various oxidants rather than just one specific compound. With these oxidants present

in the wastewater, B&W stated that plants may experience the following issues in wet FGD WWT

systems:

 Potential corrosion in the chemical precipitation equipment,

 Chemical precipitation system may require more base to control pH as solids from high ORP are

acidic, and

 Biological treatment system reactors could be temporarily disabled as a result of the strong

oxidative loading associated with high ORP conditions.

B&W is currently researching ways to mitigate the effects of ORP on the biological treatment system.

They are evaluating upstream controls to mitigate the effects of coal changes and operational variations

to lower the ORP, and the use of ORP monitors within the wet FGD system and the biological treatment

system. The ORP monitors being evaluated are real‐time monitors similar to pH probes placed in the wet

FGD scrubber and measure ORP within the scrubber. B&W noted that it took approximately 24 hours for

changes in ORP within the scrubber to begin increasing the ORP in the wet FGD wastewater. Therefore,

B&W believes that by monitoring the ORP in the wet scrubber, plants should have sufficient lead time to

anticipate the increased ORP in the wet FGD wastewater.  
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High ORP and high concentration of oxidants could also lead to corrosion in the wet FGD system

and WWT system.  B&W reports that the potential for corrosion exists for all metal components

including the scrubber, hydroclones, and wastewater treatment system components. Some plants have

installed tiles or resin coatings on components to prevent corrosion.

EPA requested a copy of any data B&W may have related to mercury and selenium at high ORP

levels. B&W reports that several sites have experienced trends in speciation of selenium with changes in

ORP. B&W representatives also reported that they have seen other data that supports the hypothesis

that high ORP results in higher concentrations of dissolved mercury but they only have specific data for

one utility. B&W cannot provide any of the data they have collected on selenium or mercury at high ORP

due to confidentiality agreements.

In general, B&W feels that a control system for mitigation of rapid ORP swings is achievable with

further development.  The number of plants monitoring for the ORP parameter is increasing. B&W

estimates that roughly 50% of the industry is monitoring the ORP in the scrubber, but industry‐wide

monitoring is still likely a few years away from occurring. Plants initially began monitoring for ORP back

in 2005 or 2006 due to an increase in corrosion.  Since that time, plants have observed spikes in ORP,

with the spikes usually taking a day to recover. The spikes could, in theory, be controlled more quickly

through upstream AQCS operational controls, wet FGD system operational changes, and, potentially,

with the addition of a reducing agent in the scrubber as a trim when needed. The specific utility in

B&W’s paper experienced 14 spikes in ORP within a 2‐month period.  Some plants have reported very

few spikes while others experience them more frequently.  In B&W’s opinion, ORP doesn’t seem to be

enough of an issue to make systems inoperable.  

After the call ERG sent a follow up email to B&W with several questions that representatives

were not able to answer while on the phone.  Below is the list of follow up questions along with B&W’s

response.

Q: Shannon Brown to provide to EPA copies of other papers regarding the ORP issues (e.g., the papers

included as references to the "Optimization and Process Control of Air Quality Control Systems for

Improved WFGD Oxidation Chemistry and Effluent Composition for Wastewater Treatment)."

A: http://www.powermag.com/orp‐as‐a‐predictor‐of‐wfgd‐chemistry‐and‐wastewater‐

treatment/?pagenum=1

http://www.reinholdenvironmental.com/public/57ccc3652e5342469c348812847d8009/Training%20Cla

ss%2009,%20WFGD%20Chemistry,%20Tuning%20and%20Optimization%20for%20Improved%20Wastew

ater%20Characteristics%20and%20Treatment,%20Brown%20&%20Johnson,%20B%20&%20W,FINAL.pdf

http://www.reinholdenvironmental.com/LibraryConferenceDetail.aspx?conf_id=57ccc365‐2e53‐4246‐

9c34‐8812847d8009
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http://wpca.info/pdf/presentations/Charlotte2013/4‐

Causes%20and%20Impact%20of%20WFGD%20ORP%20on%20Effluent%20Composition%20by%20Shann

on%20Brown,%20BandW.pdf

http://wpca.info/pdf/presentations/Charlotte2013/5‐

Optimization%20and%20Control%20of%20AQCS%20Systems%20for%20Optimal%20Bleed%20Stream%

20Chemistry%20by%20Dan%20Johnson,%20BandW.pdf

http://wpca.info/pdf/presentations/Atlanta2013/Wastewater%20Characteristics%20by%20Shannon%2

0Brown,%20B&W.pdf

  

Q: B&W to provide EPA a list of operating performance data elements (i.e., PI data) that B&W would

request from plants during time periods related to ORP issues (e.g., load, ORP, pH).

A: We are not in a position to provide any information at this time on this particular issue.