347-91232-1224-PBc

Anumaka. M.C.* et al.(IJITR) INTERNATIONAL JOURNAL OF INNOVATIVE TECHNOLOGY AND RESEARCH

Volume No.2, Issue No. 4, June July 2014, 1078 1084.

2320 5547 @ 2013 http://www.ijitr.com All rights Reserved. Page | 1078

Feasible Classification of Magnetohydrodynamic(Mhd) Generating Power Plant

ANUMAKA, M.C.Ph.D, M.Eng, MBA, B.Sc. PGD (EEE), Adv.Dip.(EEE): FIIA,COREN,MCPN, MIEEE

Department of Electrical / Electronic EngineeringFaculty of EngineeringImo State UniversityOwerri, Nigeria.

Abstract:- This paper reviews the current status and classification of MHD generating plants with theview of determining the commercial viability of different MHD generating plants. The techniques whichare vital for successful operation of the plant are discussed. This paper also attempts to investigate recentdevelopment in the field of MHD electric power plant generation and identifies the problem areas thatrequire research and development efforts in order to achieve the commercial viability of the MHDsystem.Keywords: Open cycle, hybrid, closed cycle, Lorentz force

I. INTRODUCTIONThe rapid growth of civilization and sophisticationhas triggered ever-increasing demand for energy.An energy-deficient society is weak and cannotmake tangible economic advancement. Electricalenergy has captured the highest level of energyhierarchy. Basically, the electrical energy propelsthe wheels of progress that moves at acceleratingpace [1]. More than 80% of the generated electricenergy is powered by fossil fuels. In fact, the entireworld is threatened by this ugly trend because ofrapid depletion of fossil fuels, and there ispremonition that the fossil fuel will run out if notchecked. Moreover, environmental pollutionproduced by fossil fuel-fired power plants hashazardous effects on human being, socio-economicdevelopment and increases global warming.Despite the above challenge, fossil fuel-firedgenerating plants have low energy conservationefficiency, not more than 35%- 40%. Hence, thereis need for intensive research to improve thethermal efficiency of fossil fuel-fire turbine units[2] [3].Presently, the search for a dependable alternativeenergy mix has become a global issue, which thisstudy attempted to explore. Magnetohydrodynamic(MHD) power generation is deemed the mostappropriate and unique method of powergeneration that can overcome the shortcomings ofthermal generating plants.The MHD power generation technology (MHD)entails the production of electrical power by meansof passing high temperature conducting plasmathrough intense magnetic field. The MHD powergeneration has important role in the socioeconomicdevelopment of the nation as well as providingdependable solution to the present power crisis in

many nations of the world. Efficiency is very vitalin the design and establishment of thermal enginesand power plant. The efficiency of all modernthermal power generating system lies between 35-40% as they have to reject large quantities of heatto the environment [ 4 ] [5 ]. There is need toimprove this efficiency level in all other thermalconventional power plants like gas and oil turbineplants, nuclear power plant and hydro-electricpower plant. MHD power plant have overallefficiency of 55%-60%, but efficiency of 80% ormore can be achieved through the recent researchand development programme or by utilizingsuperconducting magnets. So, MHD power plantshave high efficiency if compared with thermalplants and orther non conventional methods ofelectric power generation such as wind, solar, tidaland geothermal, which have maximum efficiencyof 35%. With the present research anddevelopment programmes, the MHD generator canbe used not only for commercial power generationbut also for so many other applications. The MHDgeneration will reduce the cost of generatingelectricity and save billions of dollars on fossil fuelprospects.

II. OBJECTIVES OF THE STUDYThis research work attempts to:1. Provide dependable alternative electric power

generating mix.2. Reduce or eliminate depletion of fossil fuels.3. Provide a solution to the unpalatable constant

scenario of atmospheric and environmentalpollution due to fossil fuel-fired generatingplants.




4. Survey the economic potentialities of MHDplant and the possibility of establishing MHDelectric power plant.

5. Devise feasible technology for theestablishment of MHD electric power plant.

III. PRINCIPLES OF MHD OPERATIONThe MHD generator is similar to that of rocketengine but surrounded by intense magnet thatproduces the external magnetic field. In an MHDelectric generation, the hot gas from thecombustion chamber is accelerated by a nozzle andinjected into the magnetic channel. Once the gas isheated to the range of 2750o K to 3000o K andpressurized between 7 to 15 atm pressure. Toensure good performance of the MHD generator,the hot gas is seed with ionisable alkali material. Asmall fraction of ionizable alkali metal like cesiumor potassium carbonate (or sodium) is injected inorder to increase the electrical conductivity of gasto the range of 10 to 50 siemens per meter. Thiscan be achieved by adding 1% by mass into the hotgas. Cesium has the lowest ionizing potential(3.894 electron volts), while potassium has ionisingpotential (4.341 electron volts) and less costly too.A powerful magnetic field is set up across themagnetic channel. While expanding in the presenceof powerful magnet, and electric field isestablished, which acts in a direction perpendicularto both the gas flow and the magnetic field. Thepositive and negative ions moves to the electrodesand constitute an electric current. The walls of thechannel parallel to the magnetic field serve aselectrodes and enable the generator to providedirect current electricity to an external circuit.This is basically in accordance with Faradays lawof motional electromagnetic induction. But not theusual one, in which charge flows in a conductorwhen time varying magnetic field is applied. Hereboth electrons and heavy gas particles are inthermal equilibrium due to high collisionfrequencies and energy transfer/collision. While inclosed MHD system plasmas are thermally non-equilibrium with elevated electron temperatures ininert gas plasmas to keep sufficient conductivitybut relatively low temperature with open cyclesystem. To achieve this we use the concept ofohmic heating under relatively low collisionfrequencies between electrons and ions.

Figure 1 MHD generating principleThe power output of an MHD generator for eachcubic metre of its channel volume is proportional tothe product of the gas conductivity, the square ofthe gas velocity, and the square of the strength ofthe magnetic field through which the gas passes.IV. THEORETICAL ANALYSIS OF MHD

ELECTRIC GENERATIONIn a typical MHD generation, let:J = Current dens ity = Electrical conductivityU = flow velocity of motionalelectromotive fieldB = Magnetic field densityE = Electric fielde = Electron chargeme = Mass of electronYe = Electron mean collisionfrequencye = Mean electron velocityThe Lorentz force (or retard force) is given as:

- e u x B- Ue x B ----------------- (1)- me Ye ( Ue U ) -------------- (2)

If the flow velocity u is much less than Ue thecurrent density is:J = -en ----------------- (3)

= e2 neme Ye ------------- (4)

e = eme Ye ------------- (5)

Considering the force balance and equation (1) &(4), Generalization of ohms law gives:











= e2 neme Ye ------------- (4)

e = eme Ye ------------- (5)












= e2 neme Ye ------------- (4)

e = eme Ye ------------- (5)





J = ( E + U x B ) e J x B---- (6)

In equation (6), the first term describes Faradayscurrent, while the second term gives the hallcurrent. The Faraday current is directly as a resultof the net electric force in the plasma. The hallcurrent and hall electric field are consequence ofthe electromotive force acting on the electrons asindicated in equation (1). The Lorentz force JxBacts in opposition to the gas flow and magneticfield. The Lorentz and factorial forces along thedirection of the gas flow x are balanced with theaid of the pressure gradient dp/dx. Since U must bekept constant because of the motional induction,the force balance for unit volume of plasma isgiven as:dp = ( J x B )x f -------------- (7)

dxFrom the above, power generated by Lorentz forceper unit volume is:

U (J x B) --------------- (8)The energy dissipated as ohms heat in the plasmais given as:

(J . J/) --------------- (9)The power output to the load is:

- (J. E) --------------- (10)So, the electrical balance obtained using equation(6) is written as:

J2- U . ( J . B ) = - J . E . (11)

The power balance for the plasma is given as:

dhu = = J x E - qloss ..(12)

dxWhere:P = Gas densityqloss = Radiation heat loss

h = Rate of enthalpy drops per unitvolume

V. TYPES OF MHD GENERATINGPOWER PLANTS

The classification of MHD generating power plantdepends on the nature of processing and control ofworking fluid. Major types of MHD generatingplants are:

(a) Open cycle MHD generating plant. Hybrid open cycle MHD

generating plant.(b) Closed cycle MHD generating plants:

Inert gas closed cycle MHDgenerating plant.

Liquid metal closed cycleMHD generating plant.

5.1 OPEN CYCLE MHD GENERATINGPLANT

Open cycle MHD generating plant is illustrated infigure 2. In open-cycle system of MHD powergeneration, the working fluid after the generationof electrical energy is discharged into theatmosphere. The fossil fuel is admitted into thecombustion chamber that operates at temperatureranging from 2,0000C to 2,8000 C. The hot gasesare mixed with ionized alkali metals such ascesium and potassium to increase the electricalconductivity of the hot gas. The seeded materialpotassium is ionizeed by the hot combustion gas.The expansion nozzle causes the hot gases to passthrough the intense magnetic field at high pressure.During the movement of the gases, the positive andthe negative ions flow to the electrodes andconstitute direct current electricity, which isconverted into alternating current electricity bymeans of an inverter [9] [10] [11]. The gases fromthe MHD are channeled into the heat exchanger.The seed material is recovered for successive use atthe seed recovery apparatus. The pollutants(nitrogen and sulphur) are removed from the gasesat the purifier chamber, while the clean andunharmful gases are released to the atmospherethrough the stack.




Figure 2.Schematic diagram of open cycle MHD generating plant.5.2 HYBRID OPEN CYCLE MHD GENERATING PLANT

Figure 3. Schematic diagram of hybrid open cycle MHD generating plant.Due to shortcomings of open cycle MHD generators, there is need to improve the operation of the MHDgenerator so that it can be suitable for commercial use and ensure efficient opration. This can be achievedbyembeding a relatively complex cycle to the open cycle MHD, which is kown as hybrid or binary cycle MHDgenerator (figure 3).In this system, the exhaust gases from the MHD are channeled to steam turbine generatorunit and steam turbine compressor for generation of additional electric power and efficient perfomance of theplant.5.3 CLOSED CYCLE MHD GENERATIONIn closed cycle generation, the working fluid discharged from the MHD is continuously recycled. This studyinvestigates two basic types of closed MHD generating plants, namely:

Inert gas closed cycle MHD generating plant. Liquid metal closed cycle MHD generating plant.




5.4 INERT GAS CLOSED CYCLE MHD GENERATING PLANTIn this type of closed system, the electrical conductivity is maintained in the working fluid by ionization of theseed material. The heat from the combustion chamber is converted into working fluid, ionized gas (argon orhelium), which can be seeded with cesium and circulated in closed loop. The schematic diagram of this type ofclosed cycle MHD generator is illustrated in figure 4. This system has three distinct but interlocking loops. Thefirst loop is the external heating loop, which entails gasification of the fossil fuel. The released gases are burntin the combustion chamber and channeled into the first heat exchanger (1) where they are converted into carriergas (argon or helium). The second loop is the centre loop, which comprises the hot plasma (argon or heliumgases) seeded with cesium, passed through the MHD generator and second heat exchanger (2), recycle into thefirst heat exchanger. The third loop is the steam loop, which is used for further recovery of the heat of theworking fluid. Hot fluid from the MHD is channeled into the heat exchanger (2) and converted into steam,which is utilized for driving a turbine for generating electricity and for driving a turbine that runs the plasmacompressor [6] [7] [8].

Figure 4. Schematic diagram of inert gas closed cycle MHD generating plant.5.5 LIQUID METAL CLOSED CYCLE MHD GENERATING PLANT.In this generator (figure 5), the conductivity is provided by the liquid metal. The carrier gas is pressurized andheated by passing through a heat exchanger and combustion chamber. The hot gas is then incorporated into theliquid metal usually hot sodium to form the working fluid. However, the system does not require hightemperature for its operation.The working fluid is introduced into the MHD generator through a supersonicnozzle. The carrier gas then provides the required high direct velocity of the electrical conductor. After passagethrough the generator, the liquid metal is separated from the carrier gas. Part of the heat is channeled into theheat exchanger to produce steam for operating a turbine generator. Finally the carrier gas is cooled, compressedand returned to the combustion chamber for reheating and mixing with the recovered liquid metal for continuousrecycle process.




Figure 5 schematic diagram of closed cycle liquid metal MHD generating plantVI. ADVANTAGES OF MHD

GENERATING POWER PLANTThe MHD generating power plants have variousadvantages over the conventional methods ofgenerating electricity as given below:

The MHD power plants have no movingparts, therefore, more reliable than otherconventional methods.

MHD plants have high temperaturerequirement and high operationalefficiency up to 60%.

Closed-cycle system of MHD powergeneration is pollution free.

It is possible to run the standby powerplant in conjunction with MHD powergeneration scheme.

The overall costs of MHD generatingplant is lower than conventional powerplant.

The MHD plants reduce the depletion offossil fuels.

MHD plants have the ability to reach thefull power level instantly.

Reduction of energy losses due to directconversion of heat into electricity.

VII. CONCLUSIONThe solution to the insufficient electric powergeneration problems ravaging many countries ofthe world can be achieved through critical researchinvestigations and harnessing different

classifications of viable MHD generating powerplants with the view of selecting suitable powerplant. It is obvious that MHD generating plants willbe the most efficient, effective and economicalrenewable and alternative energy mix for thepresent global power generation problem.

REFERENCES[1] Rohatgi,V.K,. and Venkatramani (1984)

Recent Advances in Open Cycle MHDElectrical Power Generator. Sadhana.Vol.7, Part 1. Pp.1-72.

[2] Anumaka M.C and Chidolue,G.C.Evaluation of Technical Losses in theCurrent Existing 41-Bus Nigerian 330kVTransmission Network. InternationalTransactions on Electrical, Electronics andCommunication Engineering (ITEECE).Vol. 3, No. 2. 2013.

[3] Anumaka M.C and Mbachu C.B.(2013)Modeling Nigerian 330kV Grid for PowerSystem Evacuation and Bus VoltageImprovement. International Journal ofAdvances in Science and Technology. Vol.7No.2, pp26-43.

[4] http:/seminarprojects.com[5] Vishal. d. Dhareppagol and Anaud Sauray

(2013) The Future Power Generation withMHD Generators-Magneto Hydro DynamicGeneration.IJAEEE. Volume 2. Isssue 6,2013.




[6]. Rai G.D. (2010). An Introduction to PowerPlant Technology. Khanna Publishers,New Delh.

[7]http://www.mpoweruk.com/mhd_generato

r.htm].[8] Naoyuki Kayukawa, 'open-cycle

magnetohydrodynamic electrical powergeneration: a review and futureperspectives', 30, Pg 33-60, 2004.

[9]. M.H.Saidi, A.Montazeri, 'Second lawanalysis of a magnetohydrodynamic plasmagenerator.' Journal of energy, 32, pg.1603-1616, 2007.

[10]. D.A.Gurnett and A.Bhattacharjee,'Introduction to plasma physics', CambridgeUni press, 2006.

[11]. Gupta, J.B (2008) A Course in PowerSystem S.K.Kataria & Sons. NewDelhi.ISBN 81-88458-52-X.

347-91232-1224-PBc

Documents

Transcript of 347-91232-1224-PBc