中部電力

Ammonia-coal co-firing for thermal power generation has recently attracted considerable attention as a game-changer for decarbonization. However, its combustion with a 20 % or higher ammonia (NH3) ratio emits higher amounts of nitrogen oxides (NOx) than coal-fired combustion, surpassing the denitration capabilities of existing selective catalytic reduction (SCR) systems, resulting in excessing the regulation value determined by agreements on environmental conservation. To eliminate the NOx remaining after SCR, we propose a plasma-chemical hybrid process (PCHP) as a NOx treatment technology that can be easily retrofitted into existing exhaust gas treatment equipment. PCHP consists of NO oxidation using plasma ozonizers and NO2 reduction by existing desulfurization equipment. Assuming the ozone injection in the flue gas duct between the SCR and desulfurization equipment, we conducted NO oxidation and the simultaneous removal of NOx and sulfur oxides (SOx) for a simulated flue gas comprising low-concentration NO and high-concentration sulfur dioxide (SO2). This was achieved using an ozone injection tower that simulated the flue gas duct and a calcium carbonate-slurry based SO2 absorption tower that simulated the desulfurization equipment. The results show that even under conditions containing SO2 at a concentration 46-fold higher than that of NO, the NO oxidation by O3 was achieved without the effect of SO2. When the SO2 removal efficiency reached 99 %, which is equivalent to that of an actual facility, an NOx removal efficiency of 45 % was attained. Therefore, an NOx removal efficiency of 45 % can be also expected for an actual facility, contributing to further reductions in NOx.

The Aso-3 tephra is one of the most significant widespread marker layers from the Middle to Late Pleistocene, generated by a large caldera-forming eruption at the Aso volcano in Kyushu, southwestern Japan. Despite its importance, a distal co-ignimbrite ash correlative has yet to be clearly identified, primarily because although volcanic glass shows a broad chemical composition range, available refractive index and major-element glass data remain limited. This issue has made it difficult to identify the distribution area of the widespread Aso-3 tephra and utilize it as a marker layer. Consequently, the ability to synchronize terrestrial and marine records from Japan and the northwestern Pacific during the Marine Isotope Stage (MIS) 6/5 transition is limited. This study reports the identification of a previously unrecognized tephra layer (SKR tephra) within the basal part of the Furuya Formation in the Omaezaki area of central Japan as Aso-3 tephra. Petrological and geochemical analyses reveal that the SKR tephra consists of two compositionally distinct glass groups, whose major element composition closely corresponds to that of the Aso-3B unit within the Aso-3 pyroclastic flow deposits. Furthermore, the glass composition of SKR tephra matched that of cryptotephra (MD26.70 tephra) contained within a sample taken from marine core MD012422 off the coast of Shikoku at a depth of approximately 26.7 mbsf. The MD26.70 tephra was deposited during the MIS 6/5 transition, demonstrating that the SKR tephra represents a valuable stratigraphic marker synchronizing terrestrial and marine records for this period. Consequently, the SKR tephra contributes to refining the regional tephra chronology of central Japan. It serves as an indicator layer enhancing the potential for high-resolution paleoenvironmental reconstruction of the Japanese archipelago and the northwestern Pacific during the MIS 6/5 transition.

In recent years, microgrids powered by Grid-Forming (GFM) inverters have attracted increasing attention as a means of maintaining power supply during disasters when existing transmission networks are disrupted. Generally, the rated capacity of GFM inverters is limited, and when an overload causes the current limiter to activate, the resulting voltage drop makes it difficult to continue operation. This study proposes a Hybrid Demand Response (DR) scheme for Variable Refrigerant Flow (VRF) air conditioners, which performs both active power DR and reactive power DR simultaneously to reduce GFM inverter current and maintain the microgrid. Simulations were conducted for a 1 MW class microgrid model. The results show that Hybrid DR reduces inverter peak current by about 5%, limits the rise in indoor temperature to approximately 0.3 degrees C. In addition, Hybrid DR suppresses the post-DR active-power rebound by roughly 10% compared with conventional active-power DR.

Changes in the characteristics of the insulating materials that compose the Capacitor Voltage Transformers (CVT) or insulation abnormalities in the oil-impregnated paper capacitors in the CVT are manifested as changes in the CVT transformation ratio. In this paper, a diagnostic method based on the measurement of CVT secondary voltage was investigated. The change in the CVT secondary voltage (calculated value) in the event of a single element breakdown of oil-impregnated paper capacitors is sufficiently large compared to the dispersion in the secondary voltage (measured value) of actual CVTs used in the substation. It was shown that CVT diagnosis is possible by comparing the secondary voltages of CVTs connected to the same bus bar in the substation with each other. A concrete example of the CVT diagnosis flow when applied to an actual substation is also presented.

Attachment processes of a lightning flash are important for the evaluation of the lightning shielding of electrical power transmission lines. We have observed cloud-to-ground lightning flashes striking the transmission lines and the ground since 2010 using high-speed video cameras. The purpose of this study is an improvement of the calculation method for the lightning shielding failure rate of the transmission line. From 2012 to 2023, we observed 17 negative lightning flashes striking 500 kV transmission lines and 14 negative lightning flashes striking the ground. The striking distances of the transmission lines and the ground were estimated by observation results.