As part of NETL's focus on clean fossil power systems, the Coal By-products Laboratories are dedicated to resolving environmental issues associated with residues and by-products from coal combustion. These facilities provide valuable data about Coal Utilization By-products (CUB) from both conventional and advanced power plants. Data from these laboratories are able to show improvements inherent in new combustion technologies compared to conventional plants, with respect to the nature of combustion residues and CUBs.

Under current practice, power plant operators collect residues and safely dispose of them or recover them for sale and re-use. Developing more effective procedures for using and disposing of these materials requires accurate information on the potential for these materials to leach into soil after disposal, and the chemical and physical characteristics of the residues. The data NETL has collected through this research has provided important science that supports regulatory decisions related to CUB.

Key NETL resources for testing and analyzing residues include the long-term leaching columns (LTLC) and continuous, stirred-tank extractor (CSTX) . Additional specialized instruments and tools are used to trace and analyze mercury and other potentially hazardous residues.

The LTLC is suitable to analyze samples that have complex leaching chemistries. The column leaching technique provides data over extended periods of time and at different liquid-to-solid (L/S) ratios, usually over a range of pH values. The leachate is analyzed both for major and trace elements. Lab results demonstrate how the release of those elements is affected by both pH and concentration.

NETL Engineer George Kazonich monitors flow through LTLCs

The CSTX is an alternate leaching technique. It provides information similar to column leaching data, but in a different environment that avoids permeability issues associated with disposal of CUBs. The continuous stirring action avoids the clogging that is associated with the chemical and physical properties of certain residues.

NETL Chemist Karl Schroeder examines conditions in a CSTX

Because continuous leaching is a slow method not suited for routine characterization of CUBs, the By-product Team has developed a bulk characterization method to determine the total and leachable concentration of “cations” (positively charged ions), and how the release of cations is affected by pH and L/S ratio. Low L/S values indicate the release of metals in a decade or less, and higher values with release over longer periods.

In addition, NETL's database of metals that are released from CUBs can be used to compare the difference in environmental impact of residues from old versus new combustion technologies. NETL scientists have obtained gasification residues as well as slag and ash samples to estimate the potential release of coal-derived metals from Integrated Gasification Combined-Cycle (IGCC) plants compared to conventional pulverized coal (PC) plants.

Analysis of combustion leachate is performed for inorganic elements including mercury using a variety of instruments and tools, including the following:

• ICP-MS (Inductively Coupled Plasma – Mass Spectrometer)
  Used to identify and quantify metals in solution. In selected cases, High-Pressure Liquid Chromatography (HPLC) is used to separate individual metal species prior to determining their atomic composition via ICP-MS. (Perkin Elmer, ELAN DRC-II)
• ICP-OES (Inductively Coupled Plasma – Optical Emission Spectrometer)
  Used to identify and quantify metals in solution. (Perkin Elmer, Optima 3000)
• CVAFS (Cold Vapor Atmospheric Fluorescence Spectrometer)
  Used to analyze mercury in solution. (CETAC, Quick Trace M8000)
• DMA (Direct Mercury Analyzer)
  Used to determine mercury in solids. (Milestone, DMA-80)

For more information contact: Karl Schroeder