August 30, 2007
FGD Calcium Sources are Limited and Could Challenge the Aggregate and Lime Industry
(Hot Topic Hour yesterday)
Joe Reilly of Martin Marietta showed some impressive statistics indicating the challenge ahead in supplying limestone and lime for FGD systems. Using projections of lime and limestone consumption from McIlvaine forecasts, Joe concludes that it will be very difficult to meet the demands with either lime or limestone. In fact it may not be a question of which to select but which is available in a particular circumstance.
Relative to limestone it will be difficult to quadruple the output of FGD limestone even though it is a small fraction of total production. The main reason is that most limestone is not high in calcium. Another aspect is the location. High calcium limestone, which is now being sold locally for another application, would only be available at a premium if it was diverted to FGD applications.
We asked Joe about this and he pointed out that if a non-FGD user is buying a locally mined high calcium limestone but could use a lower quality limestone not available locally, then transportation becomes an issue. It is an issue that would encourage the local user to pay more for the high calcium limestone. It is also an issue in that shipping this high calcium limestone long distances for FGD will be costly. So diverting high calcium limestone from an existing use to FGD will not be inexpensive.
Joe pointed out that the two million tons/yr of new lime capacity coming online still falls short of the projected increased demand from FGD, let alone other applications.
Mark Wajer of Martin Marietta compared magnesium hydroxide to DBA in terms of advantages in improving FGD efficiency. He argues that there are both cost and operational advantages to using magnesium hydroxide. In the ensuing discussion, Shiaw Tseng of Graymont brought up the odor problem with DBA and indicated good ventilation is needed.
Use Lime and fix the Sludge thereby Encapsulating the Mercury
Bill Ellison of Ellison Consultants captivated the audience with his analysis of ways that lime can be the most attractive reagent. If a utility opts to utilize magnesium lime scrubbing it can create sludge with enough moisture content that there is no need for wastewater treatment. When lime is added to this sludge a useful landfill and construction material is created. Mercury and other metals are encapsulated in the material and the leaching potential is considerably less than with gypsum.
The additional sulfite ions in the slurry will react to reduce the NO2 to N2. This can be very important where high NOx control is needed and the SO2 scrubber can be a polishing device. It can also be important where primary NOx control is effective and only a little additional reduction is needed to meet the limits.
Powerspan is reducing NOx using ammonium sulfite rather than calcium sulfite but the principle is the same. They did find, however, that considerable packing was needed in the scrubbing tower to achieve 90 percent efficiency.
When asked about SO3 removal Bill pointed out that scrubbers remove the gaseous SO3 but have a low efficiency on the acid mist. As the gas is cooled prior to entering the scrubber most of the SO3 is converted to H2SO4 mist and passes through the wet scrubber. Dry scrubbers, on the other hand, are efficient in capturing SO3. Bill mentioned that Sargent & Lundy is presently engineering a 500 MW fluidized bed scrubber for a new plant in Wyoming.
The Cliffside project at Duke Power will incorporate a dry scrubber for SO3 capture ahead of the wet scrubber. It was determined that this was a better option than a wet precipitator after the wet scrubber.
Lime or Magnesium to Make the Plant CO2 Ready
A lively discussion took place around the subject of CO2 scrubbing. A project which produces a “CO2 ready” exhaust is preferred to one which is not. In fact IGGC has been selected at several locations mostly because it was considered CO2 ready whereas pulverized coal was not. These early analyses failed to take into account the chilled ammonia processes developed by Powerspan and Alstom which would scrub CO2 out efficiently. Alstom states that pulverized coal with chilled ammonia scrubbing is more than competitive with IGCC.
There are two impacts on reagents. First to be CO2 ready the emissions from a power plant have to be lower than required by the regulators. SO2, NOx, and particulate will contaminate the scrubber solution whether it is ammonia, amines, or magnesium hydroxide. So reducing emissions is one way to make the PC plant CO2 ready. Therefore the higher efficiency of lime scrubbing could be important.
The other aspect is that the reagent for the CO2 capture should be the same or synergistic with the reagent being used for SO2 scrubbing. It would be possible to generate magnesium hydroxide using a lime system for SO2 and then use that magnesium hydroxide as the reagent in the CO2 scrubber.
The individual power points and text are displayed in the FGD Decision Tree through the links below.
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Analysis |
Continuing Decision Process For: Analysis
Analyses for lime have been divided into wet and dry.
Overview by Joe Reilly – Martin Marietta
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Wet |
Continuing Decision Process For: Wet
Advantages of Lime over Limestone for Flue Gas Scrubbing – Bill Ellison
Mercury CEMS Will Be the Focus of the McIlvaine “Hot Topic Hour” September 6
Every eight weeks we are reviewing the rapid developments in mercury continuous emission monitoring systems (CEMS). How reliable and accurate are the CEMS now being sold? What is the status of the instrumental reference method and the whole basis for determining the accuracy of the CEMS? What role do sorbent traps play? How are CEMS being used as process analyzers to control activated carbon introduction?
Here are some of the highlights from the last Mercury “Hot Topic Hour” on July 12:
John Schakenbach, USEPA was the lead speaker. John summarized the status of both the sorbent trap instrumental reference methods. They are posted and will be final in October if no adverse comments are received.
Terry Marsh of Shaw focused on the Appendix K sorbent trap alternative to CEMS. He observed that selecting a reliable analytical method for trap analysis is a key to ensure data integrity, accuracy, repeatability, and reproducibility. A problem in spiking the traps is solved by using two mass flow controllers to control the bubbling rate and, therefore, precisely spike the targeted Hg concentration into the third section of the carbon trap.
Over 100 Mercury Freedom CEMS have been shipped by ThermoFisher. Michael Corvese also reported that 30 HgCl2 generator modules have been shipped. Field operation shows greater than 70 percent oxidation.
DP&L J.M. Stuart is operating a Met Team Appendix K system on its 605 MW unit which includes SCR and ESP. Jim Wright of Clean Air Engineering reported that 1,500 hours of operation have been logged with minimal O&M problems. QA/QC targets are being met. Spike recovery issues are under control.
Joel Thompson cited features of the Sick Maihak mercury CEM and the extensive experience in Europe on municipal incinerators. Some units are operating on coal-fired boilers in Europe. Initial units are being installed in the U.S.
To learn more about this or other “Hot Topic Hours” or to register, click on: http://www.mcilvainecompany.com/brochures/FGDnetoppbroch/Default1.htm
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