2-12-09

Dry Precipitator Efficiency Improvement, Hot Topic Hour February 12, 2009

As the Hot Topic this week, five highly informative speakers lead an interesting two and a half hour discussion on improving electrostatic precipitator (ESP) performance. Over the past ten or so years, improvements to power supplies, electrodes and air flow modeling, among other advances, offer the opportunity to significantly improve precipitation collection efficiency.

Thomas R. Keeler, President of TRK Engineering Services and ESPCO International , focused on how to make existing ESPs work better. He noted that problem areas often involve: 1) gas distribution, 2) material collection and/or 3) material removal. Both gas and temperature distributions within the ESP casing are important. He stated that an ESP is a simple device controlled by the weakest component and said many people see the large ESP and think there is a lot of redundancy. They don’t realize that performance can be limited if just a few wires out of the very many in the ESP are broken. The first step to improving ESP performance is to identify the weak areas.

Process improvements can often be achieved by:

1) Controlling ash resistivity

2) Improving combustion

3) Reducing gas volume or air infiltration, especially in the hopper area

4) Optimizing start up and shut down techniques to avoid acid dew point problems, and

5) Developing optimum techniques for changing load to minimize reentrainment.

Effective rapping – enough but not too much – with all the rappers operating and aligned can also improve ESP performance. A reliable ash system must be able to handle the dust collected. For if ESP collection improves, then the hopper must not be too small to handle the increased material load.

The next speaker was Gary J. Grieco, Consultant at Air Consulting Associates, LLC, who provided quite an informative presentation even though his office had a power failure in the midst of it. He discussed “ESP Performance Synergy”. Working with Southern Environmental, five units have upgraded their ESPs with customized ELEX electrodes, proper selection of collection plate spacing (16”), NWL PowerPlus energization, and physical model studies. A paper will be presented later this year, but data from two sites show stack emissions of 0.0103 lb/MMBtu at one site and 0.0038 lb/MMBtu (with 13 second treatment time) at another.

Steve Ostanek, Vice President of Sales & Marketing at Neundorfer, discussed getting the most performance from an ESP at the lowest cost. He noted that sometimes people ‘go to the toolbox’ first and decide on a solution before they understand the problem. A better way is to first define the objectives to be met, define the problems, and then evaluate possible solutions. This can be difficult to do in the ‘heat of battle’, but using this method may result in solutions that cost half as much. Questions to ask begin with “Can we use this ESP?” If so, then these steps may be helpful:

1) Don’t just focus on solving problems, but also exploit opportunities to improve performance.

2) Objectively analyze the ESP.

3) Consider ESP fundamentals.

4) Find solutions that meet expectations.

5) Measure success.

Rob Kimberl, Vice President of Operations at Clyde Bergemann EEC, talked about enhancements to existing ESPs. New power supplies today can offer a ‘quantum leap’ in improvement over older designs. Rigid discharge electrodes should be considered for high vs. low emissions, depending on their location in the ESP. Electrical field sectionalization can also be used to improve performance. Other improvements include reviewing gas distribution, optimizing rapping and minimizing sneakage. He noted that the last two procedures would most likely have the biggest effect in reducing PM_2.5.

The final speaker was well worth the wait. Ralph Altman, Project Manager at EPRI, reviewed selected options for upgrading ESPs. He grouped the options into low cost, flue gas conditioning and high cost. Under high cost, he discussed the new ElectroCore, which is a cylindrical electrostatic separator. He was ‘pretty pleased’ with the way it was working at Alabama Power Gadsden, with about a 99.9 percent separation efficiency. He next discussed a ‘peculiar’ FGC example, where hydrated lime injection still allowed enough SO₃ conditioning for the ash. Selected low cost examples included high frequency power supplies such as SIR, modified gas flow, and the Indigo Agglomerator. Ralph also discussed what the future might hold for ‘near zero emissions’, meaning 0.005 to 0.002 lb/MMBtu. For high sulfur coals, the consensus still favors dry ESPs, followed by a wet FGD that is 98-99 percent efficient, followed by a wet ESP. For low sulfur coal, he projects a spray dryer absorber, fabric filter and possibly then a wet ESP. He noted that these systems should be clean enough for CO₂ capture.

Bios, Photos and Abstracts can be accessed at

Bios, Abstracts, Photos - Hot Topic Hour February 12, 2009

The individual power points are in the Particulate Decision Tree and can be viewed as follows:

Thomas Keeler – TRK Engineering Services

Start

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Particulate Removal

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Procedural

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Maintenance & Operation

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