Kuniyasu Ogawa

Direct conversion from methane to methanol for high efficiency energy system with exergy regeneration

Abstract Direct synthesis of methanol from methane and water vapor mixtures has a high possibility to realize a highly sophisticated energy recycling system with exergy regeneration. Because, combined with a reforming process from methanol to hydrogen, exergy rate of low temperature thermal energy sources at about 100 °C can be enhanced to high quality chemical energy in hydrogen. For realizing this newly proposed energy system, direct synthesis of methanol from methane and water-vapor mixture has been successfully realized by non-equilibrium plasma chemical reactions under atmospheric pressure using a newly developed ultra-short pulsed barrier discharge in an extremely thin glass tube reactor. Various effects of reaction time, water-vapor concentration and discharge parameters on the conversion efficiency and reaction selectivity have been clarified. Methanol yield has reached the order of 1% at the water-vapor concentration of about 50%, and it has been proposed that the value can be largely enhanced by adding rare gas such as Kr or Ar to the source gas. Possible mechanisms for this effect have been also discussed.

MRI Measurement of Hydrate Growth and an Application to Advanced CO2 Sequestration Technology

Abstract: MRI measurements of hydrate thickness growth have been measured and this phenomenon applied to advanced CO2 ocean dissolution technology. CO2 droplets dissolve during the process of sinking from their release point into deep ocean, by forming fine hydrate particles inside CO2 droplets before the droplets are released from a towed pipe on a moving ship. This results in a sufficiently long sequestration period from the atmosphere and further reduces biological impact. The increasing rate of hydrate film thickness in forming hydrate particles was measured by an ultrahigh‐pressure magnetic resonance imaging (MRI) technique.

Three-dimensional velocity measurement of complex interstitial flows through water-saturated porous media by the tagging method in the MRI technique

Local velocity measurements of interstitial flow through porous media and observation of the local pore geometry, which strongly influences the flow field, are necessary in order to understand the transport mechanism in a porous system. In order to investigate the effect of pore geometry on the flow field in porous media, three-dimensional velocity measurements of interstitial flow through two porous samples with different pore geometries have been experimentally performed using magnetic resonance imaging (MRI). The porous samples were made from cylindrical tubes in one case packed with crushed glass particles and in the other spherical beads. Based on the observed images of the porous samples, the porosity and pore size distributions as pore structure parameters were determined by image analysis. The two- and three-dimensional velocity vectors of the steady-state flow in the void spaces of the crushed glass sample have been measured using a spin-echo sequence with tagging pulses. The obtained velocity maps show a strong non-uniform flow. In places, reversed flow is induced by the pore geometry. The effect of the mean flow velocity on the change in the flow pattern has been investigated in the mean flow velocity range from 3.84 to 13.2 mm s-1. The frequency distribution of the axial velocity component of the interstitial flows through the packed beads was broader than that of the crushed glass pack.

Laser-induced surface-tension-driven flows in liquids

Abstract High-intensity, short-pulse laser radiation incident on the free surface of an absorbing dielectric liquid results in heating that can alter the liquid surface tension, causing Marangoni convection. This flow can dominate the transport of thermal energy in the liquid. In this work, both a scaling analysis and a full numerical simulation of the governing equations are performed. A thermal mechanism is proposed as the driving force for these flows. The dependence on beam size and temperature increase in the liquid is investigated, with good agreement found among the scaling analysis, numerical simulations and experimental data obtained from a previous study. The importance of natural convection and thermal conduction on the fluid-thermal transport was assessed numerically, with both found to be negligible for this liquid–laser system. Velocity and temperature profiles at the liquid surface are also discussed.

High-pressure magnetic resonance imaging up to 40 MPa

A high-pressure vessel designed for use with commercial magnetic resonance imaging equipment at up to 40 MPa of pressure was used and tested. Special features of the vessel are the following: 1) 12.6 mm sample chamber i.d.; 2) only non-magnetic parts; 3) visible sample from the outside; 4) resistant to corrosive chemicals, and; 5) sample could be manually translated and rotated in situ. This apparatus was demonstrated through observation of CO(2) clathrate-hydrate growth in a water droplet injected into liquid CO(2) at 20 MPa.

Plasma chemical reactions at atmospheric pressure for high efficiency use of hydrocarbon fuels

Direct conversion of methane to methanol with minimum energy consumption could become a key technology for highly efficient utilization of fossil fuel, because low-quality or low-temperature (∼100°C) energy sources can be used and regenerated by converting methanol to hydrogen. For this purpose, a new technique for synthesizing methanol directly from a methane-oxygen mixture has been developed using a highly nonequilibrium, square-pulsed, silent discharge plasma at atmospheric pressure and temperature. Various effects of oxygen concentration, reaction time and discharge parameters on the conversion efficiency and reaction selectivity have been clarified. Reaction mechanisms for this type of plasma have been elucidated by using time-dependent optical emission measurements of CH radicals during the streamer current period just after a sharp, pulsed voltage rise. High values of 2.4 % and 32.6 % for methanol yield and selectivity, respectively, have been successfully obtained in a single-path experiment. These values may be enhanced by optimizing the reacting conditions, combining this technique with catalytic reactions, and introducing a recirculating reaction system. The formation processes for high-energy species just after the sharp, pulsed voltage rise were also analyzed theoretically. Good agreement was found between the experimental data and theoretical predictions.

Simultaneous measurement of temperature and velocity maps by inversion recovery tagging method

A new method, called the inversion recovery (IR) tagging method, for simultaneous measurement of temperature and velocity maps of flowing fluid has been developed. The present method employs a set of tagging pulses which acts as an inversion pulse of the conventional IR method, based on the temperature dependence of the spin-lattice relaxation of water proton in a fluid, and has the advantage of being able to compensate the reduction of the NMR signal intensity due to flow motion and to reduce the total time to measure these maps. First, the accuracy of the temperature measurement of stagnant doped water in a differentially heated cell using the conventional IR method, as the basic sequence of the IR tagging method, has been evaluated. The accuracy was within 10% of the temperature difference DeltaT = 17.2 degrees C and the measurable temperature resolution was within +/-0.5 degrees C. Then temperature and velocity maps of the flowing doped-water through a cooled pipe were measured simultaneously by the IR tagging method, and the accuracy of temperature measurement was evaluated. The accuracy obtained using the present method was within 15% of the temperature difference DeltaT = 15 degrees C.

Methanol Conversion from Methane and Water Vapor by Electric Discharge (Effect of Electric Discharge Process on Methane Conversion)

The possibility of methanol conversion from a methane and water-vapor gas mixture was investigated for a new and highly efficient energy conversion system. Reforming process of methanol to hydrogen can be used for low-temperature thermal energy utilization. Direct methanol production from a methane and water-vapor mixture by spark or glowlike discharges has been achieved experimentally. A high methanol mole fraction of 0.5% has been obtained by both discharges. The effects of applied high voltage time, total pressure, and ratio of gas mixture on the conversion efficiency have been clarified experimentally. The electric energy consumption for methanol production by the spark discharge method is 1/100 that by the glow discharge method. The methanol conversion process has also been analyzed theoretically by considering the dissociation of the initial mixture gas by electrons and 104 elementary reactions. The results suggest that a very short period energy input such as a spark discharge can effectively produce methanol compared with a steady-state discharge such as a glowlike discharge.

Development of an eight-channel NMR system using RF detection coils for measuring spatial distributions of current density and water content in the PEM of a PEFC ☆

The water generation and water transport occurring in a polymer electrolyte fuel cell (PEFC) can be estimated from the current density generated in the PEFC, and the water content in the polymer electrolyte membrane (PEM). In order to measure the spatial distributions and time-dependent changes of current density generated in a PEFC and the water content in a PEM, we have developed an eight-channel nuclear magnetic resonance (NMR) system. To detect a NMR signal from water in a PEM at eight positions, eight small planar RF detection coils of 0.6 mm inside diameter were inserted between the PEM and the gas diffusion layer (GDL) in a PEFC. The local current density generated at the position of the RF detection coil in a PEFC can be calculated from the frequency shift of the obtained NMR signal due to an additional magnetic field induced by the local current density. In addition, the water content in a PEM at the position of the RF detection coil can be calculated by the amplitude of the obtained NMR signal. The time-dependent changes in the spatial distributions were measured at 4 s intervals when the PEFC was operated with supply gas under conditions of fuel gas utilization of 0.67 and relative humidity of the fuel gas of 70%RH. The experimental result showed that the spatial distributions of the local current density and the water content in the PEM within the PEFC both fluctuated with time.

NMR measurement system including two synchronized ring buffers, with 128 rf coils for in situ water monitoring in a polymer electrolyte fuel cell

A small radio-frequency (rf) coil inserted into a polymer electrolyte fuel cell (PEFC) can be used to acquire nuclear magnetic resonance (NMR) signals from the water in a membrane electrode assembly (MEA) or in oxygen gas channels in the PEFC. Measuring the spatial distribution of the water in a large PEFC requires using many rf probes, so an NMR measurement system which acquires NMR signals from 128 rf probes at intervals of 0.5 s was manufactured. The system has eight rf transceiver units with a field-programmable gate array (FPGA) for modulation of the excitation pulse and quadrature phase detection of the NMR signal, and one control unit with two ring buffers for data control. The sequence data required for the NMR measurement were written into one ring buffer. The acquired NMR signal data were then written temporarily into the other ring buffer and then were transmitted to a personal computer (PC). A total of 98 rf probes were inserted into the PEFC that had an electrical generation area of 16 cm × 14 cm, and the water generated in the PEFC was measured when the PEFC operated at 100 A. As a result, time-dependent changes in the spatial distribution of the water content in the MEA and the water in the oxygen gas channels were obtained.