Juro Umoto

Performance of coal-fired MHD generators with large leakage current

Abstract The objective of the present paper is, through numerical analyses, to study the performance of coal-fired MHD generators which suffer from large leakage current. Three channels are examined, of which the scale varies from experimental to pilot-plant size. The MHD channel and external circuits are simultaneously analysed, where a 2-D equivalent circuit method is applied for the electrodynamics and the gasdynamical behaviour is treated with a time-dependent 1-D approximation. The following results are obtained: (1) the overall channel performance predicted with the present model shows excellent agreement with the experimental data for medium and large experimental channels; (2) the leakage current becomes about 70 A for a channel with about 500 kW output, about 150 A for a channel with about 1.5 MW output, and about 200 A for a channel with about 10 MW output; (3) the loss due to slag leakage becomes about 30% of generated power for the CDIF channel and 20% for the generator of 10 MWe.

New conceptual design method of non-equilibrium disk MHD generator

Abstract It is important to develop a conceptual design method of a high performance non-equilibrium disk MHD generator. The objective of the conceptual design is to determine the basic specifications of the generator which satisfies many restrictions, in case some fixed conditions are given. The plasma in the designed generator should be stable and the isentropic efficiency should be as high as possible. One conceptual design method has already been propose. In this conventional design method, at first, the electron temperature distribution in the generator is fixed and next, many design calculations are performed for various inlet conditions to find a generator which has high performance and satisfies all restrictions. The above procedure, however, takes much trouble because a trial and error process is contained in it. Considering the above facts, in this paper, the authors propose a new conceptual design method of a non-equilibrium disk MHD generator. The method contains no trial and error process and can design a generator with a stable plasma and high isentropic efficiency. The procedure of the proposed method is explained and then generators with 100 and 20 MW thermal input are conceptually designed to confirm the usefulness of the proposed method.

Environmentally attractive oxygen-coal-fired MHD-steam combined system with CO2 recovery

Cycle analyses of an environmentally attractive oxygen-coal-fired MHD-steam combined system are carried out and compared with conventional MHD-steam combined systems. The following results are obtained: (1) the conventional MHD-steam combined cycle can achieve 50% cycle efficiency with 1000 MW thermal input if the air heater can be operated at 1620 K, and can obtain 55% with 2000 MW thermal input and the air heater operated at 1780 K; (2) the conventional cycle with 2000 MW input can achieve 60% cycle efficiency if the air heater operated at 2100 K and the wall temperature of 2000 K can be realized; (3) an oxygen-fired MHD-steam combined cycle can achieve 41% cycle efficiency with 1000 MW thermal input even when CO2 is recovered from the exhaust gas. The high temperature air heater can be eliminated; (4) the oxygen-fired MHD-steam combined cycle can achieve 46% cycle efficiency with 2000 MW thermal input with CO2 recovery. This cycle efficiency is very high compared with conventional power systems in which CO2 is recovered.

Responses of MHD generators of about 10 mw output to temperature fluctuations

Abstract A preliminary design of four MHD generators is made, of which the thermal input and electrical output are about 110 and 10–12 MW, respectively. Then, the effects of temperature fluctuations, given at the entrance, are examined over a wide range of fluctuation frequency. It will be shown that Faraday-type generators are very stable, both with subsonic and supersonic flows. Disturbances induced in diagonal-type generators are larger than those of Faraday channels. The shock is induced in the supersonic diagonal channel when the frequency of fluctuation is 200 ± 50 Hz. A simple filter, equipped for the external electric circuit, will be examined. The filter can substantially reduce the fluctuation of electrical output. The disturbances within the MHD channel, however, remain very large.

Stability of open-cycle supersonic disk MHD generator

The present paper proposes a method of linear stability analysis for subsonic disk MHD generators taking into account their loading condition and gasdynamical boundary condition. The flow in the MHD channel is described by quasi-one-dimensional equations, whose variational equations describe the behavior of perturbations of the flow. The time growth rate of the perturbations is determined by the characteristic equation which is derived from the gasdynamical boundary condition and the loading condition. Whether the perturbations grow or decay is judged diagrammatically in a way similar to the Nyquist method. The stability is analyzed of a coal-fired inflow subsonic disk MHD generator of commercial scale. The linear stability analysis and time-dependent calculations show that both the inlet condition and the loading condition much affect the stability. The generator often becomes unstable when the inlet swirl ratio is kept constant, whereas it is stable under the constant current loading condition or under the ohmic loading condition when the inlet azimuthal velocity is held constant.

Behavior of He-Cs closed-cycle disk MHD generator connected to electric power system through line-commutated inverter

The basic characteristics of He-Cs closed-cycle disk MHD generator connected to an electric power system through a line-commutated inverter are investigated in detail by carrying out time-dependent numerical simulations for the whole interconnecting system. The simulation model is assumed to consist of the closed-cycle disk MHD generator with 100 MW thermal input and 40 MW electrical output, the double-bridge line-commutated inverter, the a.c. filter, the phase modifier, the double-circuit transmission line and the infinite bus. It is made clear that the generator is stable, and its performance is excellent at the nominal operating condition. The active power can be controlled by using the firing angle as the manipulated variable. This active power control method is, however, considered to be not advisable because the ionization instability occurs when the firing angle is near 90°. The operation of the generation system should be stopped as quickly as possible in the case of a continuous inverter fault because this fault induces remarkable fluctuations of the gas dynamical quantity distributions in the generator. The continuous operation of the generation system is usually capable in the case of power line fault because the generator returns to its nominal operating condition after the fault is cleared. The operation should be stopped only in the unusual case of a continuous power line fault without clearance.

Conceptual design of coupled nonequilibrium disk MHD generator and superconducting magnet system

The authors propose a new conceptual design method for a coupled nonequilibrium disk MHD generator and superconducting magnet system. At first, a generator with constant magnetic flux density is conceptually designed by using the new generator design method recently developed by the authors, and several superconducting magnets suitable for the generator are conceptually designed. Next, considering the obtained magnetic flux density distribution of each magnet, the design calculation of the generator is performed again, and the specifications of the generator are corrected. From the obtained coupled systems, the optimum system is finally selected through synthetical consideration of various requirements. The procedure of the proposed method is very simple, and no iterative calculation is contained in the correction process. Incorporating the new generator design method makes this advantage possible because the generator size can be fixed in the correction process. In the conventional method, a change of magnetic flux density distribution leads directly to a change in the generator size, and therefore, design calculations of the generator and magnet should be iterated in the correction process until they converge to consistent sizes. The procedure of the new conceptual design method is explained in detail by taking the case of a supersonic generator with a caesium seeded helium plasma and 100 MW thermal input.

Preliminary study of the performance characteristics of a mhd generator for the compact fusion advanced rankine cycle

The feasibility of high enthalpy extraction from the in-situ radiation-catalyzed MHD generator is studied numerically as a part of the compact fusion advanced Rankine cycle for fusion reactors. The cesium seeded mercury is selected as the working medium, which is superheated by synchrotron radiation from the fusion plasma. In the MHD channel, electrons are heated by Joule dissipation, leading the electron temperature to be higher than that of the mercury vapor. A new type of disk configuration is proposed in the present paper, which is referred to as a disk type generator with separate channels. By using this type of generator, the enthalpy extraction ratio reaches about 59.44% in the case of multi-power take-offs. The obtained cycle efficiency is about 32.1% for a simple cycle. In the case of the recuperative cycle the efficiency becomes about 35.8%. If some amorphous thermoelectric conversion can be installed, the cycle efficiency reaches about 41.7%, which is similar to conventional steam-turbine cycles.

Stability of large-scale MHD channels designed for coal-fired MHD power generation

Abstract The stability of certain large-scale coal-fired MHD channels is studied by: (1) linear stability analysis and (2) time-dependent ID analysis. The channels are 15 m long with 600 electrode pairs, of which output power ranges from 220.6 to 258.7 MW. Linear stability analyses show that Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u − a ( u , a = gas and sound velocity) become unstable in the Faraday channel with a fixed loading factor. Two waves of u and u − a are unstable in the pure diagonal channel, whereas the u + a wave becomes unstable in the diagonal channel with a fixed electrode current. Time-dependent, one-dimensional analyses indicate that Faraday channels with fixed load resistance work smoothly and without growth in fluctuation. The diagonal channels with fixed electrode current are operated with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbances. being consistent with linear analysis.

Proposal for a high efficiency power generation system with CO2 recovery by oxygen-coal-fired MHD-steam combined cycle

Abstract (1) Oxygen-fired MHD-steam combined cycle can achieve 46% of cycle efficiency even when CO 2 is recovered from exhaust gas, which is very high compared with 30% of coventional power systems with CO 2 recovery. (2) Advanced MHD cycle without CO 2 recovery achieves very high efficiency more than 60%, if high temperature air heater and wall temperature can be realized.