MHD emissions and their controls Magnetohydrodynamics, an advanced energy technology, is being supported by DOE at a funding level approaching $1 00 million
Paul Matray Gordon Huddleston Montana Energy and M H D Research and Development Institute Butte, Mont. 59701 Magnetohydrodynamics ( M H D ) is considered to be one of the more promising new energy technologies because it is energy efficient and economically competitive. Also, it is potentially less polluting than are conventional electrical power generation processes. For these reasons, rapid development is being encouraged through federal funding to various private and government organizations. The technological problems associated with the development and construction of an open-cycle, coal-fired M H D facility of commercial size are being studied through various DOE-funded programs all over the U S . (Table 1). Three major goals of the DOE program are: achieving overall coal-to-busbar efficiencies near 50% in M H D demonstration facilities (conventional coal-fired steam generating plants typically have thermal-to-electric efficiencies of 30-40%) 1208
Environmental Science & Technology
demonstrating the economic feasibility of M H D meeting environmental emission standards for sulfur dioxide (SO*), nitrogen oxides (NO,), and particulates. Figure 1 presents the general sources of emissions from an M H D facility.
What is MHD? Magnetohydrodynamics ( M H D ) is an advanced technology designed to produce electricity more efficiently than conventional steamgenerating power plants can. The concept was proposed first by Michael Faraday in 1832, when he theorized that electricity could be generated by passing an ioniied gas through a magnetic field. Practical applications of Faraday’s idea are being pursued today not only in the U.S. but also i n Japan, the U.S.S.R.. and several other countries. In the US.,the Department of Energy presently is supporting the M H D program a t an annual level approaching $100 m i I I i on.
The current DOE program assumes a three-step approach to commercialization (Figure 2 ) . The first step, Phase I , lays the engineering groundwork for Phase 11, the design of the M H D pilot plant (Engineering Test Facility or ETF). Engineering development progress in Phase I is monitored through a succession of critical 50-MWt tests in the Component Development and Integration Facility (CDIF), managed by the Montana Energy and M H D Research and Development Institute (MERDI), located in Butte, Mont. Successively improved component and subsystem designs are selected from the Coal-Fired Flow Facility’s (CFFF) 20-MWt development work, scaled up, and integrated into the C D I F tests. The CFFF is located a t the University of Tennessee Space Institute (UTSI) near Tullahoma, Tenn. Tests will commence at both facilities in late 1980, and will help determine E T F design. Presently, two Phase I1 alternatives are being considered: Retrofit an existing fossil plant by adding an M H D topping generator, (several designs are under consideration), or construct a new 500-750 MW, coal-fired plant
0013-936X/79/0913-1208$01 .OO/O @ 1979 American Chemical Society
KICOj must be regenerated. and recycled t~ the conibustor. Efficient seed
recover! and regeneration processes :ire being evaluated by DOE. I t has been 5uggested that KlSOj be used for seeding. and that conventional f'luc gas desulfurization ( F G D ) scrubbers be eniplo>,edto remwe SO?. HoLvever. p r e s e n t FGD scrubber tcchliolopj cannot achieve the removal efficient) possible M i t h pot carbonate seeding. hloreover. future \e\! Source Performnnce Standards ( N S P S ) Ict,els m i ) dictate the use of the seed regeneration process. so that hl t-10 ma!. meet emission standards. Tlie \SPS I'or large coal-fired poner plants 01' 1.7 Ib of SO?/ I O h Btu 01' h e a t input has recentl! been made iiior'c stringcnt in order to reflect more .idvanccd control technology. The new regulation$. coupled uith strict Prev e n t i o n of S i g n i f i ca n t Deterioration ( P S D ) requirements mandated by the 1977 Clcaii A i r tlct Amendments, \+auld make the dc\clopnient of an cco n o i i i i c;i 1 seed reg c :1 e r ;i t i o n s y s t e in highlj. desirable. if not mandator), for the succcjs of coal-fired M H D power generation. T h e consideration of in u I t i iiied i :I c n v i ron menta I i i i i pac t s (such a 3 \ \ a j t c disposal. land use. and t h e like) It:nds t'urther impetus t o these dct,eIo pin en t efforts Pr,cIi ni i n a rq e \pe r i n i en t al r es u 1t s performed a t the Pittsburgh Energy Technology Centcr ( P E T C ) and :\Vc'O Everett Corporation have ,
shown that seeding can reduce SO2 emissions significantly in bench-scale systems. The collection and separation of spent seed have received considerable study by the UTSI, PETC, and Argonne National Laboratory, arid the results appear promising. Moreover, seed recovery studies at the Massachusetts Institute of Technology (MIT) predict efficiencies in the range ot'95-.91%. Exxon. in its Encironmentar' A s sessment of Adcanced Energy C'onrersion Technologies (work performed for the EPA). has evaluated several SO2 control methods. such as flue gas desulfurimtion, which might be used i f K:SOj is recycled, instead of being reconverted to K2CO3. Also, Babcock & Wilcox, Burns and Roc. and Mississippi State L'niversity were recently awarded a DOE contract for a demonstration MHD heat/seed system to be tested a t the CFFF. But further h1HD test facility data. are needed on SO, removal and seed regeneration, in order to validate predictions. and to assess the effect of various M H D operating parameters on SO?. Nitrogen oxide emissions High combustion temperatures encourage the formation of nitrogen oside ( h O , ) compounds. Limited prototj'pe testing and UO, sampling h a x been done by AVCO. PIETC, Stanford University, and UTSI. The majority of UO, predictions have been
TABLE 1
MHD facilitiesa Air Force Aero Propulsion Laboratory, Wright Patterson Air Force Base, Ohio Argonne National Laboratory, Argonne, 111. Arnold Engineering Development Center, Arnold Air Force Station, Tenn. AVCO Everett Research Laboratory, Everett, Mass. Battelle Pacific Northwest Laboratory, Richland, Wash. DOE Component Development and Integration Facility (CDIF), Butte, Mont. Fluidyne Engineering Corporation, Minneapolis, Minn. Francis Bitter National Magnet Laboratory, Cambridge, Mass. General Electric Company-Space Science Laboratory, Philadelphia, Pa. Massachusetts Institute of Technology, Cambridge, Mass. Mississippi State University, Mississippi State, Miss. Montana Energy and MHD Research and Development Institute, Butte, Mont. NASA Lewis Research Center, Cleveland, Ohio National Bureau of Standards, Washington, D.C. Pittsburgh Energy Technology Center, Pittsburgh, Pa. Reynolds Metal Company, Sheffield, Ala. Rocketdyne Division Rockwell International, Canoga Park, Calif. Stanford University, Stanford, Calif. STD Research Corporation, Arcadia, Calif. TRW, Incorporated, Redondo Beach, Calif. University of Tennessee Space Institute (CFFF), Tullahoma, Tenn. Westinghouse Electric Corporation, Pittsburgh, Pa. a
includes support, development, and major facilities in the US.
Volume 13, Number IO, October 1979
1209
FIGURE 1
Coal-fired MHD emission and effluent streams
recycle Seed
A,
Particulate and gaseous emissions
I
Combustor
AC power
Stack
Ash and seed residue
1
extractor
effluent
FIGURE 2
MHD program development alternativesa Phase I
component subsystem development
Phase It Retrofit or new utility plant expansion
Phase 111 Federal incentives or cost sharing
w Combustor
Definitions: AEDC U-25 = Arnold Engineering Development Center U S S R Facility CDlF = Component Development and Integration Facility CFFF = Coal-Fired Flow Facility ETF = Engineering Test Facility adoes not inc ude ETF retrof t cpt o m
..-.
1210
Environmental Science & Technology
.
.
. . ..
. . . . ... _ I
accomplished by analytical models. A NASA-coordinated Energy Conuersion Alternative Study (ECAS) predicted NO, emissions of 250 ppm, but an EPA study that used the ECAS conceptual design shows a calculated figure of 417 ppm. Allowable emissions are about 400-500 ppm, depending on coal characteristics. M H D could generate 10 times the NO, produced by conventional coal combustion if uncontrolled, but a satisfactory technique for control has been identified. Presently, it appears that NO, emissions will be controlled through several combustion modification techniques, including initial fuel-rich combustion, downstream adjustment of the fuel-air mixture to make it air-rich, and regulation of exhaust gas cooling rates in downstream components, to enhance the decomposition of NO,. The N S P S for large coal-fired plants of 0.7 Ib of N0,/106 Btu of heat input were recently reduced by about 20%. NO, emission levels from M H D may approach or exceed present standards, according to some models. As the NSPS for NO, may be further reduced by the EPA in the future, M H D research must continue to assess NO, emissions, and to develop a means of controlling their production, based on sound test data. A sampling program at experimental units is necessary to ascertain the effects of operating parameters on NO, emissions.
Particulates and trace elements Particulate matter existing in the exhaust gases will consist mainly of fly ash and unrecovered seed material. The fly ash produced in the M H D process is expected to differ in size and structure, as compared to that of conventional coal-fired power plants, because of the very high combustion temperatures, and possibly because of the superconducting magnet and NO, control methods. The fly ash probably will contain a large fraction of fine particles (and M U D Research and DrL~elopmentInstitute ( M E R D I ) . He has been incolced in MHD-related enuironm m t a l work f o r the past two years and currenrly is Project Manager f o r the M H D Et?iission and Effluent Eoaluation Program, Prior rojoining M E R D I he was an encironmental engineer in the Industrial C’hrmical Dicision of F M C Corporation. Huddleston has a degree in Chemical Engineering f r o m Montana State L’nicersity. Volume 13,Number IO, October 1979
1213
