October 18, 2007

SO₃ Removal Choice: WESP or Additives? Answers provided in the Hot Topic Hour on October 18

SO₃ converts to sulfuric acid at temperatures ranging from 200°F to 400°F depending on the concentration. The aerosols are only 0.3 microns in diameter. This means they pass through a wet spray tower. They also pass through a baghouse operating at 325°F because they are still vapors. Acid mist fouls air heaters and baghouses, creates a visible plume, and contributes to particulate emissions. Many plants are installing SCR and creating more SO₃ than existed previously. Therefore there is lots of interest in reducing this pollutant.

Yesterday 40 participants from utilities, A/Es, OEMs and materials companies asked questions of five presenters. Gary Yoder of O’Brien & Gere showed the advantages of grinding trona before injection. The comparison was made between unmilled trona: 30 - 50 microns in diameter vs. milled trona: 15 - 20 microns in diameter. The milled trona demonstrated much higher SO₃ removal efficiency leading to the following economic comparison made based on the demonstration at AES Somerset:

Trona injection rate to achieve 4 ppm SO₃: 2,600 lb/hr, unmilled (45 ppm baseline),

800 lb/hr, milled (45 ppm baseline)

Trona injection rate with inline milling and improved injection grid/nozzle design: 800 lb/hr

Annual cost savings: $600,000 to $900,000

Capital cost for milling/automated cleaning system: $600,000 to $800,000

Annual O&M: $140,000

Net Annual Savings: $460,000 to $760,000

Approximate Payback Period: 1 year

Eric Van Rens of Mississippi Lime showed graphs indicating a big difference between one lime type and another. Factors included available calcium hydroxide, surface area, porosity, particle size, and moisture content. Eric explained that injection after the ESP has advantages. The ESP performance is not affected but SO₃ capture is high. Lime is readily available, compatible with flyash and is cost effective.

Jim Jarvis of URS says that maximum benefits occur with upstream injection. By preventing problems in the air heater there are impacts on heat recovery, CO₂ reduction, SCR/SNCR flexibility, mercury capture and fuel flexibility. URS has a verbal SBS award from Duke Energy for the Cliffside 6 project.

Hardik Shah of Southern Environmental described the condensing WESP with membrane collection plates. The water used on the plates is cooled as it is recycled. This reduces the gas temperature slightly and results in water being added into the loop. He pointed out the following advantages of the membrane WESP: the washing dilutes any chlorides and allows choice of less costly materials of construction, there is no make up water requirement, and the steam plume is reduced.

Buzz Reynolds of Siemens indicated that his company is now supplying three large WESPS for new power projects including Dallman, Trimble County and Prairie State. The WESP is showing the ability to capture mercury as well as droplets and fine particulate.

The power point presentations are in the FGD Decision Tree. The links are shown below.

O’Brien & Gere – Gary Yoder

Continuing Decision Process For: Products

Case Study: Using Milling Technology to Improve Trona Utilization for SO₃ Control at AES Somerset. Hot Topic Hour October 18, 2007. Presented by Gary Yoder.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/O'Brien & Gere - Gary Yoder Air Quality VI 2007_Final Hot Topic Hour Oct. 18.pdf
 

Southern Environmental - Hardik Shah

Continuing Decision Process For: Products

New Generation Wet Electrostatic Precipitators

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Southern EnvironmentalSO3 October Hot Topic Hour_Hardik.pdf
 

URS – Jonas Klingspor

Continuing Decision Process For: Products

SBS Injection Technology: Power Industry Overview. Hot Topic Hour October 18, 2007 presented by Jonas Klingspor.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Jonas Klingspor -McIlvaine Hot Topic - URS - October 18, 2007 Final.htm
 

Mississippi Lime - Eric VanRens

Continuing Decision Process For: Products

SO₃ Mitigation with Hydrated Lime

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/Mississippi Lime Eric VanRens - SO3 Hot Topic Hour Oct. 18.pdf
 

 Wheelabrator – James “Buzz” Reynolds

Continuing Decision Process For: Products

Wet ESPs for SO₃ Control from Coal-Fired Utility Boilers including active and proposed projects. Hot Topic Hour October 18, 2007.

http://www.mcilvainecompany.com/FGD_Decision_Tree/subscriber/Tree/DescriptionTextLinks/McIlvaine -SO3 Web Presentation_092806.pdf

 

HCl Pre-scrubber Can Achieve More Than 99 Percent Mercury Removal

We have written about the advantages of the HCl pre-scrubber in past newsletters. We have reported high mercury removal but have theorized that with oxidation of the Hg ahead of the HCl scrubber even higher efficiency could be obtained. Bernhard Vosteen of Vosteen Consultants sent us the following email and two articles from VGB Kraftwerks Technik.

Email from Bernhard Vosteen:

I just did read your latest news alert. You are pointing at the multistage scrubbing systems in waste combustion.

I want to mention that some of the best papers about this problem are my late papers in VGB PowerTech, see attachments. I am sorry that the older one on mercury retainment in tail end SCR DeNOx catalysts is written in German.

A statement as "85% of mercury captured in the acidic scrubber”  as such can’t stand alone, but needs serious background information and comments, especially when comparing waste incineration and coal combustion.

The capture depends a) on the degree of mercury oxidation via chlorination and/or bromination. The rate of capture depends further b) on the operational conditions and on the design of the multistage scrubber system.  If you might look at my paper from March 2006 (see second attachment), there you can see a multistage scrubber (blue parts) with acidic quench followed by an equally acidic first scrubber and finally a neutral (so called alkaline) second scrubber. There were a great number of in-plant experiments with mercury spiking, etc. (as described) showing that the mercury capture in the acidic part (Quench + first scrubber) is as high as 100% (bringing down the mercury content from up to 20,000 µg Hgtotal/Nm³ dry in the boiler raw gas to less 3 µg Hg/Nm³ dry in the scrubbed gas). In 2000 I had already ordered TMT 15 for possible addition into the neutral scrubber to precipitate Hg++ there, i.e. in that neutral scrubber, but I did not need to add any TMT 15, because in this case there was almost no Hg++ transferred from the acidic stage to the neutral stage. This was due to strong mercury complexation in the acidic scrubber part (as often given in hazardous waste incineration systems combusting highly halogenated wastes), further this was bound to good droplet elimination after the acidic stages.

If for example the complexation is insufficient for Hg ion-complexation as well as for prevention of Hg-reduction, as often given in municipal solid waste incineration when there is a lack of chlorine total, the mercury capture in the acidic scrubber stage can be far less - 100% indeed, e.g. 85% or less, with some Hg++ being transferred into the neutral / alkaline scrubber stage. In this case scrubber additives for mercury precipitation can be useful, e.g., TMT 15 (to be added to the non acidic part) or as my PRAVO (precipitation agent of Vosteen Consulting, to be added as well to the nonacidic as to the acidic scrubber stage if necessary) and others. PRAVO has lately been demonstrated industrially and highly successful at a municipal solid waste incinerator with a two stage von Roll scrubber system.

Vosteen_VGB_April_03.pdf

Special_print_VGB March 2006 Vosteen_PT03-06-U.pdf