Dry Scrubbing - True Cost Investigation

Operators of combustion equipment are tasked with removing acid gases and particulate. Traditionally, wet scrubbers were used to absorb the gases. The problem with wet scrubbers is the resultant water pollution. The exception is the limestone gypsum process which produces wall board quality gypsum. However, even this process has some water pollution due to washing of the gypsum to remove excess chlorides.


Over the last thirty years designers have utilized reaction with granular particles as an alternative method for capturing acid gases. The approaches include the spray dryer absorber (SDA). This utilizes the same principle used in manufacturing instant coffee or powdered soft drinks. A slurry is sprayed into a vessel through which the hot gas flows. The liquid evaporates. The acid gas reacts with the absorbing particles. The particles are then captured in a fabric filter.


The circulating fluid bed (CFB) scrubber functions by passing the acid gas through a fluidized bed of lime particles. Lime or sodium particles are injected into the flue gas duct with Dry Sorbent Injection (DSI) systems. The catalytic filter uses the DSI principle ahead of a ceramic filter medium with embedded catalyst for both particulate control and NOx reduction.


Dry scrubbing is being used in the power, cement, waste-to-energy, steel, nonferrous and other industries where acid gases are emitted. There are a number of materials, fibers, media configurations and element designs which are utilized.


The collection media in the fabric filter has a major impact on cost. The optimum gas velocity can vary depending on the media selected.  If the velocity can be doubled then the size of the unit can be halved. Instead of 4,000 bags for a big installation maybe only 2,000 would be needed.


On the other hand, the cost of ownership is significantly affected by the bag life.  If bags last one year rather than 4 or 5 years, then bag costs become a significant part of the total expense. The energy cost is also a factor. Energy consumption increases in direct proportion to velocity. It also increases in direct proportion to the thickness of the dust cake on the filter media.


In the case where only particulate is to be captured it is best to establish a semi-permanent cake on the bags and then pulse off the new cake. In accounting terms this is LIFO (last in first out).  However, for dry scrubbing it is best to remove the reacted gypsum and retain the fresh lime (FIFO). The industry has not formally addressed FIFO vs. LIFO and needs to do so.


The need to maximize acid gas capture and the resultant substantial increase in particulate loading affects the choice of fibers and filter media. The type of cleaning (reverse air or pulsing with compressed air) also determines the selection of the lowest true cost medium.


The fuel or product being calcined or treated also impacts the medium. If a high sulfur fuel is burned, the costs of dry scrubbing are comparatively higher than if a low sulfur fuel is burned. Various fibers react differently to various combinations of acid gases, temperature and humidity. One fiber may handle SO2 and HF in relatively humid conditions at 300°F whereas another cannot.


Temperature resistance is important for several reasons. One is that a fiber which can withstand the temperature excursions will have a longer life than one which is dependent on more perfect operation of the system.  Another consideration is the potential to recover heat.


An alternative to glass and polymeric resins is a ceramic fiber matrix.  Elements can contain embedded catalysts. Dry sorbent injection ahead of the ceramic media can be utilized to provide removal of dust and acid gases while reducing NOx. The resultant clean hot gas at 600 F or higher can then be directed to an efficient heat exchanger and most of the  potential energy recovered.


The material, fiber, media construction and filter element shape all have to be designed to address the unique requirements of the application and the technology being employed.

The two major fiber types are glass and polymers.


Type of Fiber




Woven generally but also some non-woven


·         Laminates

·         Laminate with Membrane


Performance varies both in terms of temperature, abrasion and chemical resistance.








Abrasion Resistance



















Very Good



There are differences in laminates with multiple non-woven layers being employed with varying support materials and designs. Fiber shape is also a variable.


How complex are the decisions: There are at least 1500 combinations to assess.


But there are also site-specific considerations such as cost of electricity, reagents, pollution limits, plant life, existing equipment. So, these can present another 100 variables resulting in 150,000 factors.


There are mountains of information available on all the different variables. Determining which information will help select the lowest total cost of ownership product is a daunting task. The answer is “shared responsibility and collaboration.”  Organizations focused on components such as filter media or reagents can contribute but only if there is a clear path on how to do so. The Dry Scrubber Users Group which is focused on the subject in the broadest terms can be the catalyst to help bring other organizations into what can be titled a True Cost program. The program can provide access to the needed evidence for validation of lowest total cost of ownership. Conferences and exhibitions such as Power-Gen  can provide a forum for actual validation of  supplier claims.


Shared responsibility and collaboration are best driven by suppliers who are convinced that their product has the lowest true cost and are willing to help provide all the evidence pro & con to support their position. These suppliers include members of INDA. Dry scrubbing true cost is being pursued by INDA in the International Filtration News magazine and with a tour guide and breakfast discussion at FILTXPO.


Here is Information on Dry Scrubber Exhibitors at Power-Gen.


Hamon is an exhibitor at Power-Gen. They were also a presenter at the 2018 SOx-NOx conference in India. They offer five types of SO2 removal systems: seawater-wet, limestone-wet, circulating dry-dry sorbent injection, and activated carbon (REACT). In their presentation the following CDS advantages were cited.


 In 2012/2013 the design changes for the venturi section and the water injection system were installed at the CDS plant at Plzeňská teplarenská /Czech Republic. Based on the successful executed improvements Hamon´s semidry BLUESORP® technology is offering a much more reliable operation at all boiler load cases. Following the optimized process, the lime consumption (molar ratio) can be significantly reduced. Details are shown at


The presentation did address ways to upgrade or use lower quality reagents. The fact that improvements continue to be made shows that continuous true cost analysis is important  to helping decision makers with their selections. 

We would ask the Hamon people to review the cost analyses for Indian FGD made by SHI-FW and provide their insights about the applicability of their system to the conditions  and cost factor incorporated into the analysis.

Sumitomo SHI FW has made a detailed analysis comparing CFB scrubbers to wet limestone scrubbers without wallboard quality gypsum production. The lower quality of limestone available, the expected 15-year life for the older plants to which the system may be applied, and the much lower capital cost of the CFB design are key aspects in the determination. Here are the factors and calculations for a 300-MWe pulverized boiler contained in the linked paper.




CECO: This exhibitor has thousands of fabric filter installations provided by the FlexKleen division. It also has dampers and other components for dry systems.

SEI has been supplying dry sorbent injection systems in the industrial markets for 20 years. SEI’s experience has installations on solid fuel boilers, waste incinerators, brick kilns and other combustion related processes. It has more than 50 installations globally.

Wood (Wheelabrator) has supplied many spray dryer absorbers. The following benefits are stated

Overall design is simple, reliable and robust

  • No special tools required
  • No high-speed rotary atomizers\


Operational Flexibility


  • Online system maintainability without decreasing boiler load
  • Continuous acid gas emissions performance even when multiple nozzles are taken out of service
  • High turndown capability (25% MCR) without recirculation
  • Fast load response
  • Wide range of acid gas control


The advantages of the two-fluid nozzle design were analyzed in a Power Engineering article.


Doosan:  One of the key advantages stated about the Circoclean® FGD/FGC system is its compact design. The  semi-dry Circoclean® technology benefits from not using rotating or wearing parts, which not only reduces investment costs, but also maintenance expenditure. More importantly, the simplicity of the system design provides high levels of availability.

·         Proven technology with excellent references

·         Removal of air pollutants in one step (dust, SO2 , SO3 , HCI, HF, dioxins, furans, polychlorinated biphenyls (PCBs), heavy metals)

·         Relatively low investment cost

·         Compact design, easy to retrofit

·         Simple aggregates, operation above dewpoint

·         No corrosion, low maintenance

·         High availability

·         Low sorbent consumption due to product recirculation

·         High desulfurization efficiency and low emissions

·         Wastewater-free

R&R Beth supplies both precipitators and fabric filters, which are used in dry scrubbing systems.


Background Data in the Fabric Filter Knowledge Network 

Over 970 articles have been posted on dry scrubbers since 1999.  Here  are examples

Dry Scrubber Market will Grow at 9 Percent per Year

... FABRIC FILTER NEWSLETTER March, 2015 No. 473 Dry Scrubber Market will Grow at 9 Percent per Year Dry scrubbers account for less than 8 percent of scrubber sales ...

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

... FABRIC FILTER NEWSLETTER December 2007 No. 375 Spray Drier vs. Circulating Dry Scrubber Debate Continues in November 9 Hot Topic Hour Lots of facts and figures were presented ...

3. Dry Scrubber Industrial Market to Exceed 500 Million Dollars This Year

... FABRIC FILTER NEWSLETTER December, 2013 No. 458 Dry Scrubber Industrial Market to Exceed 500 Million Dollars This Year The market for dry scrubbers applied to industrial processes is ...

4. Hitachi Power Systems America, Ltd. Signs Enhanced All Dry Scrubber Technology License Agreement

... 2012 No. 438 Hitachi Power Systems America, Ltd. Signs Enhanced All Dry Scrubber Technology License Agreement Hitachi Power Systems America, Ltd., a wholly-owned subsidiary of ...


... FABRIC FILTER NEWSLETTER September, 2017 No. 503 DRY SCRUBBER UPDATE Installations : A dry scrubber system with 2 modules was commissioned by Otter Tail Power in 2015. ...


6. CFB Scrubber Meeting Emission Requirements at Dry Fork Station

... FABRIC FILTER NEWSLETTER January, 2012 No. 435 CFB Scrubber Meeting Emission Requirements at Dry Fork Station The installation of CFB scrubber at Basin Electric Power Cooperative's Dry Fork ...

7. Circulating Dry Scrubber Installed at Cooper Unit 2

... FABRIC FILTER NEWSLETTER September, 2012 No. 443 Circulating Dry Scrubber Installed at Cooper Unit 2 J. S. Cooper Unit 2 (Cooper Unit 2), ...


9. Handling Dry Scrubber PRB Ash

... FABRIC FILTER NEWSLETTER March 2002 No. 317 Handling Dry Scrubber PRB Ash The majority of plants switching to sub-bituminous coal source the sub-bituminous coal from the Powder River Basin ...

Dry Scrubber Systems and TVA Gallatin are Meeting the Emission Standards

... FABRIC FILTER NEWSLETTER May, 2018 No. 511 Dry Scrubber Systems and TVA Gallatin are Meeting the Emission Standards The AQCS at TVA Gallatin includes SCRs to reduce NOx ...

14.  Possible Erosion Leads to Dry Scrubber Failure at Gainesville, FL

... FABRIC FILTER NEWSLETTER November, 2017 No. 505 Possible Erosion Leads to Dry Scrubber Failure at Gainesville, FL Gainesville Regional Utilities is set to pursue a lawsuit against ...

31. Otter Tail Power Big Stone Dry Scrubber Project Under Budget and Performing to Guarantees

... FABRIC FILTER NEWSLETTER November, 2017 No. 505 Otter Tail Power Big Stone Dry Scrubber Project Under Budget and Performing to Guarantees Andritz's project scope included supplying the 34-foot-diameter CFB ...

32. Dry Scrubber Users 2012 Conference Addresses Survival Strategies for a Challenging Regulatory and Economic Environment


34. FABRIC FILTER NEWSLETTER August, 2012 No. 442 Dry Scrubber Users 2012 Conference Addresses Survival Strategies for a Challenging Regulatory and Economic Environment The Dry Scrubber Users Association

 The Catalytic Filter Will Have a Major Impact on the Fabric Filter, Scrubber, Precipitator, NOx and FGD Markets

36 .  The Catalytic Filter Will Have a Major Impact on the Fabric Filter, Scrubber, Precipitator, NOx and FGD Markets The catalytic filter has the potential to change ...

Terms matched: 1  -  Score: 99  -  10 Oct 2016  -  URL:,%20Scrubber,%20Precipitator,%20NOx%20%C2%A0and%20FGD%20Markets.htm

37. Jacksonville Repowers Northside with CFB

... project. To optimize overall plant performance, the JEA project incorporates a polishing SO2 scrubber. The CFB boiler provides approximately 90 percent SO2 capture via limestone injection, with ...

Terms matched: 1  -  Score: 98  -  3 Sep 2007  -  URL:

38. Dry Scrubbers a Part of Deal between MPCA and U.S. Steel

... FABRIC FILTER NEWSLETTER September, 2011 No. 431 Dry Scrubbers a Part of Deal between MPCA and U.S. Steel The state of Minnesota and U.S. Steel have ...


39. Dry Scrubber Design-Construct-Guide-Maintain Market to Reach 9.6 Billion Dollars in 2020

... FABRIC FILTER NEWSLETTER February, 2019 No. 520 Dry Scrubber Design-Construct-


Background data in the FGD  Knowledge Network

There are over 1000 articles of which here are a few

21. temp

... FGD and DeNOx NEWSLETTER March 2019 No. 491 Dry Scrubbing Discussions at the Cement Conference in St. Louis The 61st Annual IEEE-IAS/PCA Cement Industry Technical Conference ...

22. temp

... DSUA will be expanding its program for the fall meeting to include the use of dry scrubbing in waste to energy plants. One of the most versatile suppliers of dry ...

26. temp

... Power Corp. (NTPC) 's Dadri Power Plant is opting for a Dry Sorbent Injection (DSI) system for controlling sulfur dioxide (SO2) emissions and ...

20. temp

... FGD and DeNOx NEWSLETTER March 2019 No. 491 Dry Scrubbing at Powtech Powtech will be held from April 9-11 in Nuremberg. It is the largest display of powder




Background data in the Scrubber Adsorber  Knowledge Network 

There are over 1000  dry scrubber articles in the Scrubber/Adsorber Newsletter which covers all applications except power plants

73. Smelter Uses Combined System

... largest fume treatment center in North America was installed. It also combines wet and dry scrubbing. The dry process uses Pleno IV technology from Danieli Corus, where a ...