November 9, 2006

Spray Drier vs. Circulating Dry Scrubber Debate Continues in November 9 Hot Topic Hour

Lots of facts and figures were presented in the November 9 Hot Topic Hour on dry scrubbers. Utilities operating these systems, utilities retrofitting them, and utilities considering dry scrubbers for new plants were among the 40 participants. While much of the data was supplied in semi-formal presentations, a significant amount was volunteered.  For example, Niels Jacobsen of Niro in Denmark gave some insights on rotary atomizer performance generally and spray drier efficiency in Europe. Mike Schantz of Chemical Lime and Shiaw Tseng of Graymont addressed aspects of lime quality and performance. The cost per ton of SO₂ removed depends greatly on the slaking and other operations and on the size of the systems. Removal efficiencies of 95 percent (a day-to-day number) or higher at certain units with SDA systems were stated. Questions arose when comparing performance or lime usage between the various units using SDA systems because so many factors are involved.

In general the spray drier technology has been used longer and more widely and it is capturing a big market share for new applications, e.g. TXU 8 pack.  The circulating dry scrubbers may have a unique place for medium efficiency and medium sulfur coal and are sandwiched in between the SDA and wet limestone. There are some large CFB scrubbers being installed in China and now probably the U.S. so the experience hurdle is being crossed. In the United States, Westmoreland Coal Roanoke Valley has two units, one uses a CFB for SO₂ control (50 MW Unit 2) the other uses a SDA (182 MW Unit 1). Likewise, Black Hills operates both FGD systems. Black Hills will be using a SDA for its new 90 MW Wygen 2 unit.

This utility has become the focus of lots of a debate between the SDA and CFB suppliers. The SDA people point to the fact that the utility chose SDA for the new unit even though they are operating a CFB and an SDA. The CFB people argue that the CFB is actually doing better but that the decision on the SDA for the new unit was driven by the desire to buy a boiler/scrubber package. Thus the plant was unable to make a scrubber selection.

The following coverage of the presentations also gives the location in the FGD Decision Tree. So you can click directly to the power point presentations. This 90 minute audio/video discussion was recorded and is available through the “Hot Topic Hour recordings” link on the home page of both the Utility Environmental Upgrade Tracking System and the Power Plant Knowledge System.

Stewart Nicholson - Primex

Stewart Nicholson of Primex reported that Primex works with SDA owners and operators to optimize performance of their systems. In general the key factors in optimizing performance are the method by which the slaked lime is prepared and the spray drier absorber temperature control. Primex is bullish on dry FGD. Stuart showed the wide variation in performance among specific units. This is measured in tons of lime per ton of SO₂ removed. He provided this data for a number of dry and wet systems and showed the averages and extremes.

Stewart Nicholson is a President of Primex Process Specialists, Inc., a professional services firm offering flue gas treatment performance evaluation and optimization technologies. Mr. Nicholson has approximately twenty years of experience in design and supply of reagent preparation systems for flue gas treatment applications. More recently Mr. Nicholson has focused on research of factors affecting scrubber performance and related development of analytical test procedures, training programs and performance optimization solutions. Mr. Nicholson is a registered Professional Engineer and ASME published author

Richard Abrams – Babcock Power Environmental

Rich Abrams made a case for the Turbosorp CFB scrubber licensed by Babcock Power from ALSTOM. According to Rich CFB is suitable for units burning up to three percent sulfur coal, with sizes ranging up to 250 to 300 MW (in China), where 95 to 97 percent SO₂ removal is required. The lime is hydrated (not slaked) on site, lime usage is less than with SDA systems, power usage is less, and the water used to hydrate the lime can be poor quality water. In a CFB absorber the solids are internally recirculated and also recirculated from the baghouse. The Turbosorp system at AES 115 MW Greenidge (burning 2.9 percent S coal) will start operating soon. Even with the steel necessary to elevate the baghouse, the construction costs for the Turbosorp were less than for a SDA system.

Richard F. Abrams has been with Babcock Power Environmental for over four years in the position of Director of Business Development. In this role, he is responsible for BPE’s dry scrubber and SCR technology as well as business development for key accounts. Mr. Abrams has been involved in the design, development, and business development for environmental systems throughout his career. These systems have been used for air pollution control, hazardous waste destruction, or radioactive waste management. He has a BS in Chemical Engineering from Worcester Polytechnic Institute, holds six patents and is the listed inventor on the RSCR tail end SCR patent application

Bill Ellison of Ellison representing Wulff

Wulff is supplying 350 MW CFB systems in China. Therefore China will be the most experienced user of CFB scrubbers over the next five years. However, there are already units providing up to 99% SO₂ removal with Ca/S stoichiometry no greater than 1.5.  Efficiency of 92-95% is being achieved at ratios of 1.3-1.4.