Anna Nakano

Vanadium Oxidation State Determination by X‐Ray Absorption Spectroscopy

Vanadium is found in slags produced during metal refinement and fossil fuel combustion/gasification. The oxidation state of vanadium in slag has technological and environmental implications. For example, it may affect slag flow and refractory wear inside reactors, as well as leachability and toxicity of industrial by-products. Determination of vanadium’s oxidation state in crystalline phases can be achieved via the widely adopted X-ray diffraction (XRD) technique. However, this technique does not provide information on vanadium in amorphous phases. The objective of this research is to determine the oxidation state of vanadium in petroleum coke gasification samples and laboratory samples using X-ray absorption spectroscopy (XAS) with Canadian Light Source’s soft X-ray micro-characterization beamline (SXRMB). Linear combination fitting of XAS spectra with reference samples allowed quantitative determination of vanadium speciation.

Gasification Slag and the Mechanisms by Which Phosphorous Additions Reduce Slag Wear and Corrosion in High Cr2O3 Refractories

Gasification is a high-temperature/high-pressure process that converts carbonaceous materials such as coal and/or petcoke into CO and H2, feedstock materials used in power generation and chemical production. Gasification is considered an important technology because of its high process efficiency and the ability to capture environmental pollutants such as CO2, SO3 and Hg. Ash impurities in the carbon feedstock materials melt and coalesce during gasification (1325-1575 °C), becoming slag that attaches to and flows down the gasifier sidewall, corroding and eroding the high Cr2O3 refractory liner used to protect the gasification chamber. Phosphate additions to high Cr2O3 refractory have been found to alter slag/refractory interactions and dramatically reduce refractory wear by the following mechanisms: a) spinel formation, b) slag chemistry changes, c) two phase liquid formation, and d) oxidation state changes. The mechanisms and how they work together to impact material wear/corrosion will be discussed.

Synthesis of nano-manganese ferrite by an oxalate method and characterization of its magnetic properties

Abstract In this work, nano-sized manganese ferrite (MnFe2O4) was synthesized through the decomposition of the mixed oxalates. The formation of the spinel manganese ferrite was confirmed by X-ray diffraction analysis. The morphology of the ferrite products was studied by scanning electron microscopy. The particle size, which was determined using the Scherrer formula, ranged from 25 to 30 nm. Magnetic properties of the manganese ferrite were analyzed using a vibrating sample magnetometry technique; a narrow hysteresis loop indicated the MnFe2O4 obtained was a soft ferromagnet. Magnetic properties of the manganese ferrite produced were in agreement with those reported in literature for MnFe2O4 nanoparticles prepared by conventional methods, including co-precipitation and mechanochemical processes. By plotting a series of literature data determined by different authors and techniques, a correlation between saturation magnetisation and particle size has been noted regardless of the synthesis methods. In general, the oxalate method seems to be able to produce nano-manganese ferrite in a shorter time (2–3 h) as compared to other conventional techniques reported in literature (up to 54 h).

Impact of Temperature and Oxygen Partial Pressure on Aluminum Phosphate in High Chrome Oxide Refractories

Gasifiers are reaction vessels used to process carbon feedstock such as coal and/or petcoke at elevated temperature, high pressure, and in a reducing atmosphere (low oxygen partial pressure) to form CO and H2, called synthesis gas or syngas. Syngas is used as a fuel in power generation or as a feedstock material in chemical production. By-products of the gasification process include unreacted carbon, gases such as CO2 and H2S, and slag formed from mineral impurities or organic metallic compounds in the carbon feedstock that liquefy during gasification. In the gasifier, slags interact with the high chrome oxide refractory liner, causing wear and eventual failure of the refractory lining by two primary means - spalling (structural and chemical) and chemical dissolution. Failure of the refractory lining causes the gasifier to be shut down for repair, with increased service time identified by users as important for greater usage of gasification as an industrial process. Phosphate additions to high chrome oxide refractories have been found to increase service life during commercial service by reducing spalling and lowering chemical dissolution of the refractory liner. The mechanism of how they improve service life is not well understood. The microstructure and physical properties of high chrome oxide refractories with and without phosphate additions removed from a commercial gasifier after approximately eight months of exposure to a coal slag are evaluated in this report, with the emphasis on evaluating slag/refractory interaction in refractory pores. Details of the investigation are presented and possible mechanisms of how phosphate additives improve wear resistance discussed.

Energy Generation from Waste Slags: Beyond Heat Recovery

In this study, metallurgical and gasification slags mixed at a specific composition were heated to a slag discharge temperature range (i.e., tap out temperatures in iron & steelmaking) in the presence of CO2, resulting in a reaction generating energy — enough to convert CO2 to CO which can be used in other processes such as ore reduction, gas turbine power generation, and synthetic liquid/gaseous fuel production. Computational simulations suggested that the generation of H2 from H2O would also be possible using the same mixed slag approach at no additional heat supply. Energy generated from the reaction remains largely in excess after conversion (CO2 to CO), which can be utilized independently for or support other processes. Furthermore, a final slag volume is expected to decrease to about 30%, dramatically decreasing landfill burden.

Gaseous Fuel Production Using Waste Slags ‐ Going Beyond Heat Recovery

Large quantities of carbon dioxide gas and slag are generated as waste byproducts through iron & steelmaking and slagging gasification processes, using carbon feedstock to produce metal, electric power, and/or chemicals. The increasing use of petroleum coke in the modern gasification industry has changed slag chemistry — causing it to become rich in vanadium (III) oxide. When the vanadium rich gasification slag is interacted with metallurgical slag targeting a specific slag chemistry and temperature; calcium orthovanadate forms, changing vanadium valence from 3+ to 5+. This valence change involves oxygen removal from the surrounding environment. The reaction is highly exothermic, which is more than enough to break bonding in carbon dioxide and water molecules and to still have excess thermal energy. In this work, generation of carbon monoxide from carbon dioxide was investigated using synthetic slag mixtures containing vanadium. Results indicated rapid CO2→CO conversion occurred at temperatures below those at which metallurgical slag is typically tapped out of furnaces in industries.

Understanding Phase Equilibria in Slags Containing Vanadium

In modern high temperature entrained flow gasifiers, the extensive use of petroleum coke (petcoke) as a replacement for or an addition to coal as a carbon feedstock introduces an appreciable amount of vanadium in the molten slag, resulting in unknown chemical and physical slag properties. A long-term research effort to understand phase equilibria of Al2O3-CaO-FeO-SiO2-V2O3 slag system representative of that commonly found in coal/petcoke carbon feedstock mixtures was initiated by the U.S.-DOE NETL. In collaboration with CanmetENERGY and McGill University, synthetic vanadium bearing slag was investigated for phases formed under controlled temperature, partial pressure of oxygen, and composition. The slag compositions representing U.S. and Canadian coal and petcoke ashes are considered in this work. Equilibrium phase diagrams of the vanadium slag systems are reported.

An Effect of Phosphorous Gas Generated in Slagging Gasifiers on Pt‐Rh Sensor Degradation

Entrained flow slagging gasifiers are used to covert coal, petcoke and other carbon feedstock to syngas (CO and H2), which is used as a fuel in power generation or is converted into chemical products. During the gasification process, gasifier components such as refractory liners, syngas coolers, and thermocouples are aggressively attacked by corrosive slags and gases originating from the carbon feedstock, materials that contain arsenic, sulfur, phosphorous and other impurities; –all of which are in a mixed equilibrium condition during gasification. This research evaluated the effect of phosphorous gas generated during gasification on the corrosion degradation of Pt-Rh thermocouple sensor materials. Phosphorous interactions with Pt-Rhx (x = 0 – 30 wt.%) alloys have been analyzed isothermally at 1012 °C. Phosphorous diffusion into the alloy is discussed.

A Thermodynamic Study of Mixed Carbon Feedstock Gasification Slags

Integrated Gasification Combined Cycle used in power and chemical production is considered a clean technology, with the ability to capture almost all CO2, NOx, and SOx emissions. In entrained bed slagging gasifiers, molten slags formed from feedstock’s non-volatile impurities contribute to gasifier liner degradation and can cause gasifier clogging, affecting system efficiency and operation. Increased petcoke use as a key feedstock in addition to or as a replacement for coal has drastically modified slag chemistry, leading to unknown chemical/physical slag properties and behavior in the gasifier. In this work, thermodynamic phase equilibria in synthetic slags (Al2O3-CaO-FeO-SiO2-V2O3) were evaluated under simulated gasifier conditions to establish an understanding of the phase equilibrium in these slag systems. The effects of V2O3 content, slag chemistry, and additives on amorphous and crystalline phases were studied. In this study, increasing calcium oxide and iron oxide additive agents was found to lower the slag melting temperature and caused the karelianite (V2O3) crystal size to increase. Equilibrium phase diagrams showing the additive effect on the mixed coal-petcoke slag systems studied were constructed.