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INTERNATIONAL J OURNAL OF M ULTIDISCIPLINARY S CIENCES AND ENGINEERING, VOL . 3, NO. 7, J ULY 2012

Assessment of Economic Impact and Efficiency of a Combined Gas Turbine with a Thermoelectric Generator Onoroh Francis, Ikebudu Kingsley O., and Okafor I.O.U

Abstract– The research presents how to scavenge waste heat from a gas turbine plant using a thermoelectric generator and to assess the economic implication. On comparing the equivalent uniform annual worth of the combined GT/TEG with GT only, the annual disbursement for the GT/TEG is $2,288,231.908 and for the GT only is $2,316,738.107. Therefore, the combined GT/TEG is found to be more economical. The gas turbine whose operating condition was used for the design of the thermoelectric generator is based at Ughelli Thermal power station, Ughelli, Delta state, Nigeria. Also, the efficiency of the gas turbine was increased from 0.342 to 0.453 with the introduction of a thermoelectric generator containing lead telluride modules. Keywords– Economic Analysis, Efficiency, Gas Turbine, Thermoelectric Generator, Sankey Diagram and Equivalent Uniform Annual Worth

I.

INTRODUCTION

I

ncreased overall plant efficiency is possible by coupling a thermoelectric generator to an existing gas turbine plant. A combined GT/TEG system is more economical than a GT only. One way to improve the sustainability of electricity base is through the scavenging of waste heat with thermoelectric generators i.e. thermoelectric materials. Gas turbine exhaust, automotive exhaust, steam turbine and industrial processes all generate waste heat that could be converted to electricity using thermoelectric generator. Fig. 1 shows the Sankey diagram for most thermal engine plant. Up to 40% of the combustion energy supplied leaves in the exhaust. Furthermore, the exhaust temperature is much greater than that of the other heat rejection streams; therefore, the potential conversion efficiency of a bottoming cycle connected to this stream is expected to be the largest.

As thermoelectric generators are solid-state devices with no moving parts, they are silent, reliable and scalable, making them ideal for distributed power generation. The efficiency with which thermoelectric materials generate energy is determined by the thermoelectric figure of merit, ZT, where T is absolute temperature and Z is proportional to the electrical conductivity and the square of the Seebeck coefficient, and inversely proportional to the thermal conductivity. When ZT increases, the efficiency of energy generation ultimately approaches the Carnot limit, i.e. the maximum allowed by the laws of Thermodynamics. Historically, the ZT value of the best bulk thermoelectric materials have remained below or around one due to the difficulty of increasing the electrical conductivity or Seebeck co-efficient without increasing the thermal conductivity [1]. However, ZT values approaching three have been reported for nanostructured materials that exploit reduced dimensionality to lower the thermal conductivity of the crystal lattice in these structures. ZT values of three or more are required for competitive energy generation [1]. II. BASIC THERMOELECTRICITY A. The thermoelectric phenomena The three basic thermoelectric effects are the Seebeck effect, the Peltier effect, and the Thomson effect. These effects underlie the conversion of heat energy into electrical energy or vice versa. When a steady temperature gradient is maintained along a finite conductor, the free carriers at the hot end will have greater kinetic energy and tend to diffuse to the cold end. The accumulation of charge results in a back

Onoroh Francis is currently a research engineer with Electronics Development Institute (ELDI), National Agency for Science and Engineering Infrastructure (NASENI), Federal Ministry of Science & Technology (FMST), Nigeria. PH- +2348074648666, (Email: onofrankus@yahoo.com) Ikebudu Kingsley O. is currently an academic staff, Mechanical...
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