LabNotes - July 2013
NETL Collaborators Invent Method for Treating High Carbon Fly Ash
The U.S. Patent and Trademark Office has assigned Patent No. 8,440,015 to researchers from Waynesburg University and the National Energy Technology Laboratory (NETL) for a thermal method that retains yet passivates carbon and/or other components in fly ash. John Baltrus, a research chemist at NETL, along with Professor Robert LaCount and Douglas Kern of Waynesburg University cooperated on the invention. The research resulted from a project sponsored by the Combustion Byproducts Recycling Consortium (CBRC), which is funded by NETL.
Fly ash is the finely divided residue resulting from the combustion of ground or powdered coal and is a major by-product of coal-fired electric generating plants. Finding alternate uses for this byproduct benefits the environment by diverting it from landfills. Fly ash is most popularly used as a component of concrete. Approximately 30 percent of U.S fly ash is recycled this way, replacing a portion of the portland cement normally required. In addition to the direct environmental advantage of utilizing a potential waste stream to substitute for an ingredient that would otherwise have to be produced through an energy-intensive process, incorporation of fly ash improves concrete performance and quality.
Some fly ash is not suitable for use in concrete because its chemical composition, including high carbon content, would require excessive amounts of air entrainment agents–surfactants used to increase the workability of a concrete mixture and its durability through freeze-thaw cycles when cured.
The invention titled, “Fly Ash Carbon Passivation,” provides a means whereby a greater percentage of U.S. fly ash can be recycled by incorporation into concrete mixtures. The patent describes a thermal method for inactivating the carbon and/or other components in fly ash while retaining them in the fly ash. The process, which involves heating the fly ash to between 400°C and 800°C under an inert gas containing up to 10 percent oxygen, results in sharply decreased amounts of surfactants that need to be added to the fly ash even though most of the carbon remains in the fly ash.
The patented method has several advantages. High-carbon fly ash, typically the result of using low-NOx burners, can now be repurposed for concrete, including conductive concrete, as opposed to being sent to a landfill. To avoid landfilling, high-carbon fly ash would otherwise need treatment at temperatures greater than 800°C under an oxygen-rich atmosphere to burn the carbon out of the fly ash before it can be used in concrete. The patented method reduces that temperature requirement and the need for carbon burnout, both resulting in lower greenhouse gas emissions. The research leading to the patent has been described in several peer-reviewed journal articles and presentations.
Contact: John Baltrus, 412-386-4570
Quantum Chemistry of CO2 Interaction with Swelling Clays
Ubiquitous clay minerals can play an important role in assessing the suitability of geologic formations for secure storage of carbon dioxide (CO2). The minerals may affect the reservoir storage capacity as well as the integrity of its natural seals such as caprock formations. CO2 interaction with swelling clays such as smectites is a complex process involving physisorption in micropores and intercalation (insertion) of CO2 molecules between the layers of the clay. In montmorillonite—a swelling clay that is a member of the smectite group of clays—the width of the interlayer gap is controlled by polar water molecules hydrating the cations between layers. As the gap becomes wider the energy required for CO2 intercalation decreases.
|Dioctahedral smectites have a lamellar structure with an octahedral sheet of repeating AlO6 units between two tetrahedral SiO4 sheets. Isomorphic metal-ion substitutions (e.g., Al3+ replaced by Mg2+) result in fixed-charge imbalance that is compensated by hydrated metal cations (e.g., Ca++) residing between the negatively charged clay layers.
NETL researchers were pioneers in developing basic science involving high-pressure CO2 interaction with montmorillonite. To explain the findings of analytical techniques showing the CO2 sorption isotherm hysteresis, changes in basal distances between the clay layers detected by X-ray diffraction, and unusual infrared “fingerprints” attributed to CO2 molecular vibrations in the clay interlayer, NETL Geosciences researcher Slava Romanov and Geological and Environmental Sciences Focus Area Lead George Guthrie promoted broad collaboration across several DOE national laboratories and the NETL–Regional University Alliance (RUA).
A collaborative effort between NETL–RUA and Sandia National Laboratories resulted in a complete and consistent model of CO2 intercalation and subsequent carbonation steps within montmorillonite interlayers supported by several complementary experimental techniques and molecular dynamics simulations. Additionally, proof-of-concept experimental and theoretical work at PNNL contributed to identifying several distinct CO2 intercalation mechanisms. PNNL researchers confirmed NETL reports of bi-modal asymmetric stretch vibrations observed in the infrared spectra of the trapped CO2 and discovered that the observed vibrations are associated with in-plane and perpendicular orientations of intercalated molecules that had been previously hypothesized by NETL researchers. Such multi-laboratory collaborations accelerate advances in research. The interaction of CO2 with critical components of shale formations, such as clays, plays a significant role in carbon storage and utilization.
Contact: Slava Romanov, 412-386-5476
NETL AVESTAR® Team and Invensys Collaborate to Develop Dynamic Simulators for Supercritical Pulverized Coal and Natural Gas Combined Cycle Power Plants
|A screen shot of the new generic supercritical once-through (SCOT) dynamic simulator/OTS.
Under Cooperative Research and Development Agreements (CRADAs), NETL’s AVESTAR Center team and Invensys Operation Management (IOM) have developed prototype dynamic simulators and operator training systems (OTSs) for a generic supercritical once-through (SCOT) pulverized coal power plant and a generic natural gas combined cycle (NGCC). Based on IOM’s DYNSIM® dynamic simulation software and InTouch® human-machine interface software, both dynamic simulators are high-fidelity, real-time training systems that will provide AVESTAR users with realistic, hands-on experience with plant operations and control, including startups, shutdowns, cycling, load following, and abnormal situation handling. Both clean fossil energy simulators are also targeted for use in carbon capture and storage (CCS) research and include process- and heat-integration connections to post-combustion CO2-capture, CO2-compression, and CO2-utilization processes.
Scheduled for deployment at the AVESTAR Center by March 2014, the new SCOT dynamic simulator/OTS is based on a forced circulation, coal-fired, balanced draft once-through furnace with spiral radiant reheat bundle. The coal system includes six (6) sets of coal silos, gravimetric feeders, and pulverizers (also called mills). Coal is delivered to the furnace through six (6) elevations of four (4) corner coal burners for a total of twenty-four (24) burners. The main steam turbine is a 3600 RPM tandem compound, single reheat unit. The turbine consist of four sections: a single flow high pressure turbine, a single flow intermediate pressure and two double flow low pressure turbines. The electrical generator converts mechanical power from the steam turbine into electrical energy for supply to the grid. The nominal rating of the steam turbine/generator unit is 660 MW. The SCOT dynamic simulator will serve as the baseline power plant model for DOE’s Carbon Capture Simulation Initiative (CCSI) aimed at accelerating the commercialization and widespread use of post-combustion carbon capture technologies at the nation’s power plants.
Contact: Stephen Zitney, 304-285-1379