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

On Thursday, January 9, 2014, ERG and EPA participated in a call with Babcock and Wilcox

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

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 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 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 FGD system related to manganese precipitates.  B&W’s

analysis is based on field sampling data from two FGD systems, one which controlled the ORP in the

scrubber and the other with did not control the ORP. Based on B&W’s experience in this area, ORP can

be controlled in the FGD system by using reducing agents and optimizing the FGD system. B&W believes

that the FGD chemistry is not a contributing factor to the increases in ORP but that the type of coal

burned may be a cause of the increases in ORP. B&W expected optimization steps for controlling the

ORP in the FGD system include changing the coal source, adjusting the excess oxidation air, and adding

reducing agents to the system. B&W noted that the ORP swings can happen rapidly, with changes of 300

mV occurring in approximately 40 minutes.  To best control ORP, actions should be taken preemptively

rather than reactively.

B&W reports that swings in absorber ORP do not always happen as the result of an intentional

change to the system operation, swings can happen spontaneously.  While some natural changes can

cause swings in ORP, B&W has found that there are particular changes to the system that result in ORP

swings but they are not confident that this is the reason for all ORP changes.

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.  

Commented [D1]: Question for B&W: Could you provide us

with Steve’s last name? Those of us on the phone were not able to

catch it.
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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 effecting 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. The most

recent work by B&W shows that changes to the ESP controls do not seem to explain the ORP excursions

but rather these seem to happen naturally; but they did add that these results could be dampened by

other changes in plant operation.

B&W does not believe fly ash particulate is the cause of ORP changes.  B&W reported that this

was definitely not the cause at one utility but could be the cause at the second utility but a larger

dataset would be required in order to say more conclusively. Research has shown that other causes for

ORP changes could be SCR performance, 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 oxidants present in the 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 FGD wastewater treatment

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 shut down as a result of increasing chlorides with

shifting ORP.

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

They are evaluating adding reducing agents to lower the ORP and the use of ORP monitors within the

FGD system and the biological treatment system. B&W is still trying to determine the optimal location

for addition of a reducing agent, either in the absorber or a location downstream.  The ORP monitors

being evaluated are real‐time monitors similar to pH probes placed in the 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 FGD wastewater. Therefore, B&W believes that by

monitoring the ORP in the scrubber, plants would have sufficient lead time to anticipate the increased

ORP in the FGD wastewater.  

High ORP and high concentration of oxidants can also cause corrosion in the FGD system and

wastewater treatment system.  B&W reports that the potential for corrosion exists for all metal

components including the scrubber, hydroclones, and wastewater treatment system components. Some
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plants have installed tiles or resin coatings on components to prevent corrosion. Maintaining an ORP of

500 mV or less helps to limit corrosion within the FGD system.  B&W reports that fluoride is also a

potential cause of corrosion within the scrubber system but fluoride corrosion occurs at a much slower

rate than corrosion due to high ORP.

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.

In general, B&W feels that controlling the FGD system ORP is still one or two years out.  The

number of plants monitoring for the 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 few years 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 with the addition of a reducing agent in the scrubber.

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 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

http://wpca.info/pdf/presentations/Charlotte2013/4‐

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

on%20Brown,%20BandW.pdf

Commented [D2]: Note to B&W: Is this accurate?
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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.