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
- Commercially available - Yes (limited)
- Size range - 25-500 kW
- Fuel - Natural gas, hydrogen, propane, disel
- Efficiency - 20 - 30 % (recuperated)
- Environmental - Low (<9-50 ppm)NOx
- 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
- Unrecuperated microturbine (simple cycle)
- 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.)