Blog   |   Mar 16th, 2016 Managing Flue Gas Desulfurization Materials: A Brief Physio-Chemical Lesson

PRB Coal Baghouse Material Scrubbed With Pebble Lime

Following several years of increasingly restrictive emission control systems, coal-fired power plants across the country are continuing to wrestle with the recently promulgated Coal Combustion Residual (CCR) and Effluent Limitation Guidelines (ELG) regulations. Clearly, these collective regulations will significantly restrict/phase out the long-term use of surface impoundments for management of CCR, resulting in the continued shift from wet to dry handling (or closed loop) systems. In conjunction with the conversion to dry handling, many generators will need to increase beneficial reuse of by-products like fly ash, bottom ash and flue gas desulfurization (FGD) sludge, increase their landfill capacity for those materials and/or explore a combination of both. To evaluate these management options, it is critical to understand the physio-chemical characteristics of the CCR materials themselves. 

(Photo: PRB Coal Baghouse Material Scrubbed with Pebble Lime)

Use of a dry process for removal of sulfur dioxide (SO2) from coal-fired power plant emissions is becoming more common, and utilizes either lime-based or a sodium-based reagent. The FGD material from these processes is generally disposed of as waste along with bottom and fly ash materials. The materials, individually or as a mix, create varying results regarding interactions with other materials when reused or landfilled. The same is true for their leaching characteristics.

These physio-chemical properties need to be understood for the successful long-term management of environmental impacts and compatibility with other contact materials. Information on the physio-chemical characteristics of traditional bottom and fly ash byproduct streams is readily available; however, FGD material is a significantly different byproduct material that has been less studied. Performing laboratory analysis of site-specific FGD samples can be very beneficial to evaluate management options.Tests may include:

  • Calcium-to-Sodium Ratio
  • Compositional Analysis
  • Compressive Strength
  • Density
  • Hydraulic Conductivity
  • Moisture Holding Capacity
  • Particle Size
  •  pH
  • Shear Strength
  • Solids Content
  • Specific Gravity

In addition to ongoing laboratory studies and research, site specific information can often impact final disposal or reuse decisions. FGD physical and chemical test data results will enable a more detailed assessment of beneficial end-use options from a compatibility and materials management standpoint, and will provide a greater level of understanding relative to selections of landfill design components and operational considerations. The analytical data will also provide a better understanding of the leachate treatment and process considerations. More importantly, this data will allow a more detailed analysis of options to safely and economically manage the byproducts for long-term liabilities.

Stay tuned for additional posts in our ongoing series of coal ash management blogs; review our previous installments here

Related Topics

Coal Ash

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Coal Ash Management

Blog Authors

Douglas Genthe, P.E., D.GE

Douglas Genthe, P.E., D.GE

Doug Genthe has more than 29 years of project management and lead design experience in civil and environmental engineering, with particular emphasis in geotechnical engineering and solid and hazardous waste management. Doug has served as a project manager, a professional engineer of record, an office/review engineer, a technical coordinator, a lead design engineer, and a resident construction engineer. As unit leader of the Geotechnical Engineering and Solid Waste Management unit of TRC’s Environmental Business, he manages the overall delivery operations and leads the business development activities in the geo-environmental engineering service offerings. He manages several key accounts for TRC, most of which he has managed for many continuous years.

His technical responsibilities have ranged from initial field investigations through final design and construction, including the development of work plans, feasibility studies, permit applications, conceptual and final designs, operating plans, cost estimates, construction plans, bid documents, and project manuals; regulatory liaison; public relations; expert testimony; forensic engineering; and the preparation of construction quality assurance documents, closure plans, and construction observation and documentation reports for municipal, industrial, hazardous waste landfills, and containment systems.

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Curtis D. Madsen, PE

Curtis D. Madsen, PE

Curt Madsen has over 34 years of experience in the environmental field, with emphasis on solid waste management and engineering services. He has been the senior project manager for a number of long-term industrial and municipal clients, working on landfill development, including initial siting, permitting, and design; landfill expansions; plan of operation permits; gas extraction system designs and coordination for energy reuse; surface water, wetland, and leachate design and management; by-products planning, including coal combustion by-products and foundry ash; and development and management of several countywide solid waste management programs. Curt’s extensive knowledge and regulatory expertise have facilitated the fast-tracking of a number of landfill projects, resulting in increased disposal capacity, reduced construction costs, and streamlined permitting processes. He holds both a bachelor's and master's degree in civil and environmental engineering from the University of Wisconsin and is a registered professional engineer in Illinois, Indiana and Wisconsin. 

Contact Curt at