An Oxy-MHD Topping Cycle

When developing new concepts today, it is also important to understand how the technology may evolve and become a commercial winner in the future. The path through to a genuine return on invested time and capital for stakeholders and early investors is often subject to high risk.

A good analogy is the start of the automobile industry 100 years ago where it was not immediately clear that it would be the gasoline engine and Model-T Ford that would dominate the market.  Both electric vehicles and the Diesel engine were, for a time, strong early contenders. It is only much later that also the competition managed to gain a foothold in niche market areas.

One possible technologies that we have assessed for CCS is what we term a “Topping Ready” oxyfuel cycle that integrates a magneto hydrodynamic (MHD) generator in combination with an oxy-combustor.

In the 1970´s and 80´s MHD was pursued as technology that could improve the efficiency of coal-fired power plants and be deployed for military purposes.

The oil crisis of 1973 and the Cold War justified major investments by many countries to pursue energy security and advanced weapons technology at a time when nuclear deterrent had led to a stalemate between the superpowers.

Partly for these reasons, and also because the technology looked genuinely promising at the time, research and deployment for MHD received both civil and defence funding in many of the Western and Soviet-bloc countries.

In the United States the U.S. Dept. of Energy spent over $220 million during the following decade, while the USSR built and operated (until the mid-90´s) a 25 MW MHD power plant for utility electricity production near Moscow.

At its peak there were more than a dozen countries with government funded MHD Programs.

However by the late-90´s budgets had been cut: academic research and activity at government laboratories was all that remained — coal-fired MHD was too expensive to commercialise and could not compete with the advances of gas turbines and focus on integrated coal gasification combined-cycle (IGCC) plants.

It was therefore interesting to revisit MHD almost 20 years later and to observe how oxy-combustion removed some of the original barriers to commercialisation. A summary of our initial findings from 2009 were contained in the above report that should be available if you click on it.

Although back then, over a decade ago, it was too early to say if Oxy-MHD could become commercial with CCS, it was a clear example of how known technology can be re-evaluated in the light of new challenges — this time not the Cold War, but instead climate-change.

In 2013 the project completed a Phase-2 of development work and a more detailed evaluation was also undertaken on behalf of EPRI. Now in 2020 we are also reassessing the technology given significant advances in optical seeding, nano-materials, and Machine Learning to control the plasma arcing.

For time being these web pages only present status as of 2013, but we are now actively seeking new funding to restart this project work asap.

When an electrical conductor is moved and cuts lines of magnetic induction, the charged particles in the conductor experience a force in a direction mutually perpendi-cular to the magnetic field (B) and the velocity (u) vectors.

Negative and positive charges will tend to move in opposite direction and the induced electric field pro-vides the basis for converting mechanical energy into electrical energy.

Whereas a conventional power generator rotates a solid conduc-tor between the poles of a magnet (Fig. 1 A) one can also employ a fluid conductor as the working substance through the interaction of a flowing, electrically conducting gas (or other fluid) and the magnetic field (Fig. 1 B).

The underlying principle of MHD power generation is therefore simple.

By passing very-hot ionized combustion gas through a strong magnetic field a magneto hydrodynamic (MHD) generator can convert heat to electric power, without any rotating or moving parts.

This makes it possible to reduce mechanical losses and operate at elevated temp-eratures using a “topping cycle” to increase the overall cycle thermal efficiency above what is possible for more conventional Brayton and Rankine cycles.

In the United States extensive work was conducted by the Department of Energy (DOE) in collaboration with industry during the 1980’s in a Proof-of-Concept (POC) Program that included a 50 MW (thermal) coal-fired MHD generator operating in Butte, Montana, and component tests for a coal-fired MHD bottoming (steam) cycle at University of Tennessee.

The POC Program had in principle confirmed much of the technology by the early 1990’s. However, support for full-scale demonstration projects was not forth-coming because of competition from advanced natural gas combined-cycle (NGCC) and integrated gasification combined-cycle (IGCC) technology.

In the USSR a 25 MW gas-fired MHD plant produced heat and power for residents of Moscow until the mid-90’s, and there were plans for a 500 MW (thermal) com-mercial size power plant. However, funding had disappeared after the fall of the Berlin Wall in 1989 together with ensuing demise of the Soviet Union.

Now, 15-years later and with a stronger emphasis on CCS, we have re-assessed integration of MHD with the oxy-combustor developed by Clean Energy Systems (CES), based in Sacramento, Ca.

The CES technology enables direct combustion of either natural gas or coal-based syngas with oxygen resulting in a very-high temperature plasma.  This avoids the need to pre-heat air and the removal of significant volumes of ash from the coal combustor before the plasma can enter the MHD channel.

Both of these were identified as outstanding issues in the POC Program before commercial deploy-ment could be considered.

Our on-going work suggests that Oxy-MHD appears to be a cycle that should be assessed as a potential game-changing approach to efficient power generation using fossil fuels in a carbon constrained commercial environment. The system requirements when using the CES combustor with MHD permits simplification compared with that proposed previously for coal-fired MHD power plants.

We identify two main challenges where technology status still requires further assessment. These are;

  1. Improved enthalpy extraction within the MHD generator: Demonstrated performance is < 40% and should be higher for the MHD topping cycle to become thermodynamically more efficient than an alternative supercritical Rankine bottoming cycle. This requires improved high-temperature electrodes, more optimal channel geometry, and a fundamental understanding of plasma dynamics. 
  2. Cost-effective method for plasma seeding, regeneration and recycling: Although seed material is only in the order of 1 to 2% of plasma mass flow, the POC Program estimated that this could represent as much as 20% of operating costs for a 1,000 MW (thermal) MHD power plant.

Our recommendations and scope for future work is summarised below.

i) Technical Recommendations

A more thorough assessment regarding current technology status needs to be made. This should encompass;

  • State-of-the-art plasma physics and dynamics should be thoroughly re-assessed because major advances have been made with development of “Tokomak” fusion reactors and the use of computational plasma fluid dynamics. 
  • Detailed assessment regarding integration, size and cost of super-conducting magnets with the CES combustor needs to be evaluated. 
  • Thermodynamically the proposed cycle should offer an improvement over other CCS technology pathways, but this preliminary assessment needs to be confirmed through more detailed process and cost analysis. 
  • Seeding, ionization and recycling are issues that remain outstanding and will need to be resolved.
ii) Commercial Recommendations

We propose identifying development partners and to define a strategy for deploy-ment that includes;

  • A phased Roadmap for commercialisation to quantify annual development funding requirements. 
  • Specify performance milestones, commercial requirements and an exit strategy for early investors. 
  • Prepare proposal for international funding support to multiple agencies in order to evaluate the option of zero emission Oxy-MHD in combination with CCS. 

The phenomena of magneto hydrodynamic (MHD) electrical power generation was first recognized when Michael Faraday (1791-1867) experimented with the generation of electricity by moving a fluid electrical conductor through a stationary magnetic field.

In January 1832 he set up a rudimentary open-circuit MHD generator, or flow meter, on Waterloo Bridge in London. He immersed electrodes into the Thames River at either end of the bridge and connected the electrodes at mid-span through a galvanometer.

Faraday reasoned that the electrically conducting river water moving through the earth’s magnetic field should produce a transverse electromotive force (emf). Small irregular deflections of the galvanometer were in fact observed. However his experiment was unsuccessful owing to the electrodes being electrochemically polarized–an effect not understood at that time.

The concept had little practical use and therefore disappeared only to reappear in the patent literature from the early 1900’s and by the 1930’s with theoretical work on cosmic problems and projects for thermonuclear power generation that revived interest in MHD.

On 13th August 1940 B. Karlovitz, a Hungarian engineer proposed a gaseous MHD system and filed U.S. Patent No. 2,210,918 entitled “Process for the Conversion of Energy”. Working at the Westinghouse research laboratories, he had from 1938 conducted experiments on the products of combustion of natural gas as a working fluid using the annular Hall-type MHD generator.

By 1946 he had shown that, through seeding the working gas, small amounts of electric power could be extracted. The project however was abandoned, largely because of a lack of understanding of the conditions required to make the working gas an effective conductor.

In 1959 the American engineer Richard Rosa operated the first truly successful MHD generator producing about 10 kW of electric power. Further research by Rosa established the practicality of MHD for fossil-fuelled systems.

In 1963 the AVCO Everett Aeronautical Research Laboratory, under the direction of Arthur Kantrowitz, began a series of experiments culminating with a 35 MW MHD generator that used about 8 MW to power its magnet

For many years this remained the record power output. The assumption in the late 1960’s that nuclear power would dominate commercial power generation and the failure to find applications for space missions led to a sharp curtailment of MHD research and funding.

However the energy crisis of 1973 revived the focus on more efficient coal-based systems for power generation in the United States as summarised by Pomeroy (1978) where MHD was presented as having a major impact in the United States by year 2000!

A detailed historical and technical analysis of coal-fired MHD power generation was presented by Gruhl (1977) based on work sponsored by Exxon and the EPA.

In 1984, TRW, Inc. Redondo Beach, California installed the first stage of a 50 MW (thermal) two-stage combustor at the Component Development and Integration Facility (CDIF) in Butte, Montana. And in September 1986 a fully integrated topping cycle was operated successfully for 8 hours with power transmitted to the grid via an inverter supplied by the Electric Power Research Institute (EPRI).

MHD power generation was originally stimulated by the observation that the interaction of plasma with a magnetic field could occur at much higher temperatures than was possible in a rotating mechanical system.

Furthermore, if the conductor is an electrically conducting gas, it will expand and the MHD system constitutes a heat engine involving expansion similar to that of a gas turbine where the limiting performance is based on the maximum temperature.

An example of a laboratory scale Argon gas linear MHD generator is shown in the adjacent image; courtesy of Department of Pulsed MHD Power Systems & Geophysics, Moscow State Aviation University.

While a conceptual design for a large coal-fired “open cycle” MHD steam power plant is presented below.

This sytem comprises of a “topping” cycle centred about the MHD channel (with magnets) that is connected via a diffuser to a conventional steam bottoming cycle, as is shown by the two dashed rectangular areas.

In the topping cycle, it is envisaged that coal (with potassium seed material) is fed to the combustor operating at ~5 bar and is oxidised with air pre-heated to 2,800°F (1,540°C).

When seeded the products of combustion produces an ionized gas (“plasma”) with a temperature of ~4,800°F (2,650°C) that expands through a Laval nozzle and into a supersonic diffuser channel.

Conceptually this may be considered as a modified combined-cycle power plant (CCPP) comprising of the MHD generator in-lieu of a gas turbine (Brayton cycle) combined with a super-critical Rankine bottoming cycle.

Brayton cycles have limitations determined by the turbine inlet temperature (TIT) that governs maximum efficiency. Despite advances with metallurgy, ceramic coatings and blade-cooling over the past 40 years, even the most aggressive turbine development programs do not envisage TIT above 3,200°F (1,760°C).

By comparison the upper temperature in a MHD generator is governed by the plasma temperature which can be 6,000°F (3,330°C), it has no moving parts and is not constrained by turbine metallurgy.

We anticipate that within CCS there are several technologies that will not prevail despite some significant investments that are currently being made to promote them. Reasons for failure can be many, but usually come down to a fundamental understanding of thermodynamics, financial markets and risk analysis.

At the same time there are new technologies that only a few have considered and that have yet to receive mainstrean funding from government agencies and corporate R&D budgets. These often fail because they never manage to pass through the early barriers where seed financing is critical and individual champions are paramount.

In both cases it remains important to have a clear vision as to how the concept adresses genuine needs in the market, and to understand how the technology may evolve and become a commercial winner in the future.

Having a realistic Roadmap from Proof of Concept (POC) demonstration, through commercial introduction and then into market penetration, is a key pre-requisite for even the earliest stages of technology development.

Invariably the Roadmap will change with time — but this does not matter. The important point is that it will alway be a realistic indicator for the overall strategy, no matter how external market conditions vary with time.

The below Roadmap is based on our early conceptual studies and highlights how the Oxy-MHD technology may advance even while we are still focusing on the POC demonstration phase.

The red curve shows how improvements based on merging existing steam and gas turbine technology, into what we now term oxyturbines, can significantly improve efficiency of the oxyfuel cycle (Anderson et al., 2008).

This curve also benefits from the fact that oxyfuel is a closed-cycle and can therefore fully utilize the higher heating value (HHV) of the fuel in constrast to the lower heating value (LHV) that is applicable for coal and gas-fired power plants.

Furthermore the cycle efficiency is increased by (dashed green line) integrating a first generation Oxy-MHD combustor around 2015.

It is then envisaged that the MHD topping cycle could be deployed commercially by 2020 and add an estimated 6 to 10%-point on overall cycle efficiency compared with the base case technology scenario.

In chronological order:

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Sutton, G.W., (1959). “MHD Channel Flow of a Perfect Gas for Generation of Electrical Power”, General Electric Company, TIS R59SD473, Dec.

Rosa, R.J., (1961). “Physical Principles of MHD Power Generation”, Physics of Fluids, Vol. 4, No. 2, pp.182 (13 pages).

Kantrowitz, A.R., Brogan, T.R., Rosa, R.J. and Louis, J.F., (1962). “The MHD Power Generator — Basic principles, state of the art, and areas of application”, IRE Trans. on Mil. Electr., Vol. MIL-6 Issue:1, pp. 78-83, January. (doi: 10.1109/IRET-MIL.1962.5008403)

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Brogan, T.R., Louis, J.F, Rosa, R.J. and Stekly, Z.J.J., (1962). “A Review of Recent MHD Generator Work at the AVCO-Everett Research Laboratory“, presented at Third Symposium on the Engineering Aspects of MHD, Rochester, N.Y., March 28.

Chu, T.-K. and Yeh, H., (1963). “The Optimization of MHD Generators with Arbitrary Conductivity“, NASA-CR-55183, Jan.

Swift-Hook, D.T., (1963). “Large-Scale MHD Power Generation”, Cent. Elect. Res. Lab., Leatherhead, Surrey, U.K., in Br. J. of Appl. Phys., Vol. 14, No. 2, pp. 69, Feb.

Snyder, W.T., (1965). “MHD Flow in the Entrance Region of a Parallel-Plate Channel”, Univ. of Tennessee Space Inst., AIAA Journal, Vol. 3, No. 10, Oct.

D. V. Freck, D.V., (1967). “Equilibrium and Non-Equilibrium Electrical Conductivity of Seeded Combustion Products”, Cent. Elect. Res. Lab., U.K., in Phil. Trans. of Roy. Soc. – Series A, Math. & Phys. Sci., Vol. 261, No. 1123, “A Discussion on Advanced Methods of Energy Conversion – MHD Power Generation”, pp. 471-485, July 6.

Nimmo, R.A., Shanklin, R., Buechler, L.W. and Lytle, J., (1974). “Design and Test of Selected High-Temperature Electrode Materials”, Final Technical Report (Oct. 72 – Nov. 73), Systems Research Labs. Inc., Dayton, Ohio, No. AD0786677, July.

Rudins, George, (1974). “U.S. and USSR MHD Electrode Materials Development“, Rand Corp., ARPA Order No.: 189-1 6L10 Tech. Assessment Office, Report R-1656-ARPA, pp.84, Dec.

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Kayukawa, N. and Ozawa, Y., (1980). “MHD Power Generator”, U.S. Patent 4,218,629.

Zappoli, Bernard, (1981). “Note Technique #9: La MHD – État de l’Art et Premieres Expériences Probatoires d’Application Propulsive“, Centre National d’Etudes Spatiales, Toulouse, Report No. 0273 CT/GEPAN, pp. 51, Nov. 17.

James, R.K. and Kruger, C.H., (1983). “Joule Heating Effects in MHD Generator Boundary Layers”, Stanford University, AIAA Journal Vol. 21, No. 5, May.

Okuo, Takayasu and Takano, Kiyonami, (1983). “Electrodes for MHD Power Generator”, U.S. Patent 4,404,482, Sep. 13. 

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Bauman, Leslie, E., (1993). “Potassium D-Line “Blue” Wing Absorption Coefficient under Combustion-Fired MHD Conditions”, Mississippi State University, J. of Thermophysics & Heat Transfer, Vol. 7, No.1, Jan. – March.

Bityurin, V.A., Bocharov, A.N., Krasilnikov, A.V. and Mikhailov, A.V., (2003). “Experimental Study of MHD Electrical Power Generation”, Paper AIAA 2003-357 presented at 41st Aerospace Sciences Meeting & Exhibit, Reno, Nv, January 6-9.

Okuno, Y., Okamura, T., Suekane, T., Yamasaki, H., Kabashima, S. and Shioda, S, (2003). “MHD Power Generation Experiments with the Fuji-1 Blowdown Facility”, Tokyo Inst. of Tech., J. of Propulsion and Power, Vol. 19, No. 5, Sept. – Oct. 

Kayukawa, N., (2004). “Open-Cycle MHD Electrical Power Generation: A review and future perspectives”, Progress in Energy and Combustion Sciences, Vol. 30, No. 1, pp. 33-60.

Steeves, C.A., Shneider, M.N., Macheretz, S.O., Wadley, H.N.G., Miles R.B. and Evans, A.G., (2005). “Electrode Design for MHD Power Panels on Reentering Space Vehicles”, Paper AIAA 2005-1340 presented at 43rd Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 10-13.

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Mikheev, A.V., Kayukawa, N., Okinaka, N., Kamada, Y. and Yatsu, S., (2006). “High-Temperature Coal-Syngas Plasma Characteristics for Advanced MHD Power Generation”, in IEEE Trans. on Energy Conversion, Vol. 21, No. 1, pp. 242-249, March. (doi:10.1109/TEC.2005.847994) 

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