INTRODUCTION

  • Micro Turbines are new type of  combustion turbine used for stationary energy generation.
  • The concept is evolved from automotive and truck turbocharges, auxiliary power units(APU) for airplanes.
  • Approximately the size of a refrigerator with outputs of 25 kW to 500 kW.
  • They provide not only electricity, but also the thermal energy to provide for  all heating and cooling needs.

Microturbine Overview

  1. Commercially available                 -  Yes (limited)
  2. Size range                                       -  25-500 kW
  3. Fuel                                                -   Natural gas, hydrogen, propane, disel
  4. Efficiency                                       -  20 - 30 % (recuperated)
  5. Environmental                                -  Low (<9-50 ppm)NOx
  6. Other features Co-generation         -  Small volume production, Commercial                                                                                             prototypes now.                     

Components of Microturbine

  • Turbo compressor
  • Combustor
  • Generator
  • Recuperator (internal Heat Exchanger)
  • Turbine
  • Power Electronics (Rectifier & Inverter)

Working Principle

  • Microturbines are small gas turbines, most of which feature on internal heat exchanger called a  recuperator.
  • In a microturbine, a radial flow(centrifugal) compressor compresses the inlet air that is then preheated in the recuperator using heat from the turbine exhaust.
  • Next, the heated air from the recuperator mixes with  fuel in the combustor and hot combustion gas  expands through the expansion and power turbines.The expansion turbine turns the compressor and, single-shaft models, turns the generator as well.
  • Finally, the recuperator uses the exhaust of the power turbine to preheat the air from the compressor.
  • Single-shaft models generally operates at speeds over 60000 revolutions  per minute(rpm) and the permanent magnet  generator  generates electrical power of  high frequency, and of variable frequency(alternating current---AC) . This power rectified to to direct current (DC) and then inverted to 50/60 Hz for commercial use.

Types of Microturbine

  1. Unrecuperated microturbine (simple cycle)
  2. Recuperated microturbine

Comparision

       Unrecuperated                                                            

  • Compressed air is mixed with the fuel and burned under constant pressure conditions.
  • efficiency 15%

      Recuperated

  • A sheet metal heat exchanger (recuperator) recovers temperature of the air stream supplied to the combustor.
  • Efficiency 20-30%.

Distributed Energy Generation

  • Energy produced in thermal and hydro electric power plants is distributed to the users through network of  line(transmission & distribution) called the power grid.
  • Any technology of getting electric energy other than power grid, directly at the distribution level, is called Distributed energy  generation.
  • In IUT, when load-shedding occurs, IUT generator serves as  distributed energy source.
  • Example: Microturbine, diese generator (backup generator), solar panel etc.,.

Advantages of distributed  Generation

  • The loss during  power transmission are eliminated.
  • The combined heat and power(CHP) technology can be applied.
  • Low emission and operating cost.
  • High efficiency.

Advantages of Microturbine

  • Small number of moving parts
  • Compact size
  • Light weight
  • Good efficiency in co-generation
  • Low emission
  • Can utilize waste fuels
  • No vibration
  • Less noise than reciprocating engines

Economics

    Capital cost                         $ 700 - $1,100/ kW
    O&M cost                           $0.005 - $ 0.016 /kW
    Maintenance Interval           5,000 - 8,000 hrs ( 7 - 11 months approx.)