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Oxy-combustion can enable efficient CO 2 capture from fossil fuel power plants in combined cycle systems; however, air separation is expensive. In order to directly utilize the high gas temperatures associated with oxycombustion and offset any oxygen separation penalties, a magnetohydrodynamic (MHD) generator has been proposed as a plant topping cycle. Accurately predicting the electrical conductivity of combustion products with the addition of potassium "seed" compound is necessary to evaluate the performance of this modern approach to MHD. In order to make these predictions, improved species collisional cross-section data (momentum transfer cross-section, MTCS) are needed at relevant conditions. A gas electrical conductivity model for use in open-cycle MHD power generation applications is presented, which makes use of updated MTCS data not represented in previous legacy publications. Based on the results of a detailed review and analysis of currently available MTCS data relevant to open-cycle MHD combustion systems, recommendations have been provided for relevant species and a gas temperature range of 1500-3500 K (~0.13-0.3 eV electron energy). Model predictions utilizing updated MTCS data are validated against limited experimental data found in literature for oxy-combustion with potassium seed compound. Model results are presented from a parametric study, which show the effect of combustion conditions and seeding on ionization processes and gas electrical conductivity, highlighting differences between modern oxy-combustion MHD systems and legacy approaches implementing air-fired combustion and high levels of preheat.

Figure 1. Cross Section of a typical industrial VAR furnace. Sketch is courtesy of ATI-Allvac, with a modification to show the video camera's location during the experiments.Abstract It is has previously been shown that arcs can constrict during Vacuum arc remelting (VAR), and this constriction can lead to undesired defects in the material. This paper describes a novel measurement system capable of locating arcs in an existing industrial VAR furnace. The system is based on non-invasive magnetic field measurements and VAR specific forms of the BiotSavart law which relate the measurements to the positions of arcs. Electromagnetic finite element modeling assists the analysis. The measurement system is applied to a commercial VAR furnace, and data are taken during production of titanium alloy. It is shown there exists arc distribution differences during this VAR operation and these differences are not apparent in the existing measurements used to control the furnace. It is also shown that there is more than one arc at an instant, and likely more arcs present at an instant than can be resolved with the number of sensors applied. Still, the described methodology can be extended to locating additional arcs by adding additional sensors.