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:
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.