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A Seminar on
Submitted in partial fulfilment of the requirement for
Savitribai Phule Pune University
DEPARTMENT OF MECHANICAL ENGINEERING
TSSM’S BHIVARABAI SAWANT COLLEGE OF ENGINEERING AND RESEARCH,
TSSM’S BHIVARABAI SAWANT COLLEGE OF ENGINEERING AND
C E R T I F I C A T E
This is to certify that
Mr.AKSHAY RAMDAS NAWALE,
has successfully completed the Seminar work entitled
Under the guidance of
Towards the partial fulfilment of the requirement for
TE (Mechanical Engineering)
Savitribai Phule Pune University
Prof.N.A.DOIFODE Examiner Examiner
(Seminar Guide) (External) (Internal)
(Seminar Coordinator) (Head of Department)
Sr.No Name ofTopic
List of Figures I
List of Tables II
1. Introduction 1
1.1 Micro Electro Mechanical System 1
1.2 Gas Turbine 1
1.3 Microturbine 4
1.4 Technology Discription of Microturbine 11
1.5 Design Characteristics of Microturbine 17
1.6 Microturbine and Distributed Generation 17
1.7 Advantages of Microturbine 18
1.8 Economics of Microturbine 20
1.9 Fuel Flexibility of Microturbine 20
1.10 Application of Microturbine 21
1.11 Future Scope 22
2. Literature Review 23
3. Experimental Setup 24
4. Experimental Results 26
LIST OF FIGURES
Fig No. Title Page No.
1.1 Idealized Brayton Cycle 3
1.2 Sectional View of Microturbine 7
1.3 Working Cycle of Microturbine 8
1.4 Capstone Turbine 9
Basic Part of Microturbine
Microturbine Based Combined heat & Power System
Experimental Setup for Baseline Performance Testing of
Natural Gas Fired Microturbine
Efficiency of 30 kw gas microturbine as a function of nominal
power demand with damper 3/8 closed
Effect of turbine backpressure on the performance of the unit
LIST OF TABLES
Table No. Title Page No.
1.1 Microturbine Overview 7
Performance of Microturbine
Distributed Generation Technology
Capstone 30-kw microturbine with damper fully open
Capstone 30-kw microturbine with damper 3/8 closed
Microturbine performance with approximately constant engine
speed and varying turbine backpressure
It is my privilege to undertake the seminar project “Microturbine ”. I am thankful to our principal
Dr. D.V. Jadhav principal TSSM’S BSCOER College, for encouraging me to do this seminar.
I am deeply indebted to Prof. P.R. Kale Head of the Department, whose motivation in the field
of mechanical designs made me overcome all the hardships during the course of study.
I am heartily thankful to my guide Prof. N.A. Doifode for his moral support who was always
there to comforting me at the times of queries. Our exchanges of knowledge, skills and his insightful
comments during my seminar work program helped me to enrich my experience. I thank of all of them for
their moral support.
NAWALE AKSHAY R.
A new small gas turbine technology is being developed which promises to bring the economic,
environmental and convenience benefits, advancements in the automotive sector, generation of
electricity and mechanical power needs of the commercial sector. The technology is of the
microturbines. The microturbine is an example of Micro Electro Mechanical Systems, which is
efficiently used to develop power at a small scale. Microturbines are small combustion turbines
approximately the size of a refrigerator with outputs of 25 kW to 500 kW. Microturbines are part
of the future of onsite, or distributed energy and power generation. They are actually single shaft
machines, in which turbine, compressor and generator are mounted on the single shaft. This unit
can be used for distributed power, stand-alone power, stand-by power and vehicle application
like turbocharger. The commercial customer requirement for small prime movers are that they be
very cleans (low NOx, CO and unburned hydrocarbons), of better efficiency than the
reciprocating engines, require infrequent maintenance, have a very low forced outage rate and of
course be of low installed cost so as to provide rapid payback for the owner. These conditions are
better fulfilled by the microturbines compared to the conventional Reciprocating Engines, Gas
turbines, Coal fired steam engines etc.
Keywords: Microturbine, Micro-Electro-Mechanical systems, Gas turbine, Microturbine in
Distributed generation, Experimental Setup.
1.1 Micro-Electro-Mechanical Systems [MEMS]:
Micro-Electro-Mechanical Systems (MEMS) is an integration of mechanical elements,
sensors, actuators, and electronics on a common silicon substrate through the utilization of micro
fabrication technology. MEMS are truly an enabling technology allowing the development of
smart products by augmenting the computational ability of microelectronics with the perception
and control capabilities of micro sensors and micro actuators. MEMS technology makes possible
the integration of microelectronics with active perception and control functions, thereby, greatly
expanding the design and application space. Although MEMS devices are extremely small (e.g.
MEMS has enabled electrically-driven motors smaller than the diameter of a human hair to be
realized), MEMS technology is not about size. Furthermore, MEMS is not about making things
out of silicon, even though silicon possesses excellent materials properties making it a attractive
choice for many high-performance mechanical applications. Instead, MEMS is a manufacturing
technology; a new way of making complex electromechanical systems (like power generation)
using batch fabrication techniques. Already, MEMS is used for everything ranging from in-
dwelling blood pressure monitoring to active suspension systems for automobiles. Recent
examples of the advantages of MEMS technology consider the MEMS accelerometers, which are
quickly replacing conventional accelerometers for crash air-bag deployment systems in
automobiles. Micro turbine is one of the best examples of the recently used MEMS. The
technology is to generate power for at a small level for a few houses or as a stand-by power
source. It is given hype now days and further research work is also in progress. Now let us know
what exactly the micro turbine is.
1.2 Gas Turbine:
Gas turbines are Brayton cycle engines, which extract energy from hydrocarbon fuels
through Compression, combustion, and hot gas expansion. Air is drawn in to a compressor,
which increases the air pressure. The compressed air is mixed with fuel and ignited in a
combustor. Then, the hot gas is expanded through a turbine, which drives the compressor and
gives useful work through rotation of the compressor turbine shaft. The shaft power can be used
to drive a electrical generator, thereby providing electricity.
A gas turbine is a rotating engine that extracts energy for a flow of combustion gases that
result from the ignition of compressed air and a fuel (either a gas or liquid, most commonly
natural gas). It has an upstream compressor module coupled to a downstream turbine module,
and a combustion chamber(s) module (with igniter[s]) in between.
Energy is added to the gas stream in the combustor, where air is mixed with fuel and
ignited. Combustion increases the temperature, velocity, and volume of the gas flow. This is
directed through a nozzle over the turbine’s blades, spinning the turbine and powering the
compressor. Energy is extracted in the form of shaft power, compressed air, and thrust, in any
combination, and used to power aircraft, trains, ships, generators, and even tanks.
1.2.1 Types of Gas Turbine
There are different types of gas turbines. Some of them are named below:
Aero derivatives and jet engines
Amateur gas turbine
Industrial gas turbine for electrical generation
Radial gas turbine
Scale jet engines
1.2.2 Gas Turbine Cycle
The simplest gas turbine follows the brayton cycle (Figure 1.1) In a closed cycle (that is
the working fluid is not release the atmosphere) air is compressed isentropically, combustion
occurs at constant pressure, and expansion over the turbine isentropically back to the starting
pressure. As with all heat engine cycle, higher combustion temp. (the common industry reference
is turbine inlet temperature) means greater efficiency. The limiting factor is the ability of steel,
ceramic or other materials that make up the engine to withstand heat and pressure. Considerable
design/manufacturing engineering goes into keeping the turbine parts cool. Most turbine also try
to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchanger that
pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste
heat to steam turbine system, and combined heat and power (i.e. cogeneration) uses waste heat
for hot water production mechanically, gas turbine can be considerably less complex than
internal combustion piston engines. Simples turbine might have one moving part: the
shaft/compressor/turbine/alternator-rotor assembly not counting the fuel system. More
sophisticated turbines may have multiple shafts (spools) hundreds of turbine blades, and a waste
system of complex piping combustors, and heat exchanger.
Figure 1.1 Idealized Brayton Cycle
The largest gas turbine operate at 3000 (50 Hz European and Asian power supply),
3600(60 Hz US power supply) RPM to match Ac power grid. They require their own building
and several more to house support and auxiliary equipment, such as cooling tower. Smaller
turbines, with fever compressor/turbine stages, spin fasters. Jet engines operate around 10000
RPM and micro turbines around 100000 PRM. Thrust bearing and journal bearings are a critical
part of design traditionally, they have been hydrodynamic oil bearing or oil cooled ball bearing.
Gas turbine is used in aircraft propulsion and electric power generation.
High thermal efficiency up to 44%.
Suitable for combined cycles.(with steam power plant)
High power to weight ratio, high reliability, long life.
Fast start up time, about 2 min compared 4 hrs. for steam propulsion system.
High back work ratio (ratio of compressor work to the turbine work), up to 50%,
compared to few percent in steam power plants.
1.2.4 Advantages of Gas Turbine
Very high power to weight ratio, compared to reciprocating engine.
Smaller than most reciprocating engines of the same power rating.
Moves in one direction only, with far less vibration than a reciprocating engine.
Fewer moving parts than reciprocating engines.
Low operating pressure.
High operation speed.
Low lubricating oil cost and consumption.
Micro turbines are small gas turbines used to generate electricity. Occupying a space no
larger than a telephone box, they typically have power outputs in the range of 25 to 300kW. In
comparison, large power stations are entire buildings and have much higher power outputs of
around 600MW to 1000MW. The small size of micro turbines is a major advantage that allows
them to be situated right at the source of electricity demand. This eliminates energy losses that
usually occur when transmitting electricity from power stations. Such transmission losses are
quite significant and can easily amount to 7% of the power generated. Micro turbines are a new
class of small gas turbines used for distributed generation of electricity. Micro turbines are small
version of gas turbines emerged from four different technologies viz. small gas turbines,
auxiliary power units, automotive development gas turbine and turbochargers. Micro turbines are
new class of gas turbines used for distributed generation of electricity. Microturbine
development is based on turbines used for aircraft auxiliary power units, which have been used
in commercial airlines for decades. One way in which Microturbine can be distinguished from
larger turbines is that Micro turbines use a single shaft to drive the compressor, turbine and
generator. Whereas in large power plants, the turbines and generator are on separate shafts and
are connected by gears that slow down the high-speed rotation of the gas turbines,
simultaneously increasing the torque sufficient to turn much large electric generators. Some
micro turbines even include the ability to generate electricity from heat of exhaust gases.
In 1900 when a 2 MW steam turbine was installed at Hartford, its size was 4 times bigger
than any of the existing steam turbines. From then on economy of scale meant bigger and bigger.
By the end of the 1970s and largely driven by nuclear power plants, steam turbines exceeded
1000 MW. The electric efficiency of steam turbine power plants eventually reached 34%. That
trend was broken in the 1980s. More efficient gas turbines combined with steam turbines could
produce electric power with efficiencies up to 55%. This new technology, combined cycle power
plants, was the technology of choice for independent power producers. It was now possible to
build competitive power plants down to the range of 100-200 MW. Micro turbines have been
experimented with since 1945, when Rover tried to develop one for a vehicle application. Since
that time, automobile, aerospace, aircraft and military contractors have tried to develop an
economical and functional Microturbine for different industrial and commercial applications.
1.3.2 Need of Microturbine
In today's energy economy, most electricity is produced using fossil fuel-burning
generators. These machines consist of a motor and a dense coil of copper wires that surround a
shaft containing powerful magnets. To get that power to a home or factory typically requires a
local utility to run a heavy copper cable to the residence or business site. But what if the site
requiring energy is in a remote mountain location, or it's an offshore oil rig where electricity is
scarce and hookups don't exist? Here the micro turbines come into the picture. It is one of the
best options to set up a local power-generation plant, perhaps using a Microturbine -- a small,
sometimes portable, fossil fuel-burning system that can provide enough electricity to power
anywhere from 10 to 5,000 homes. Also it has an important application as a turbocharger in
vehicles when more energy is required from the engine in less amount of fuel.
1.3.3 Construction of Microturbine
Micro turbines are typically single shaft machines with the compressor and turbine
mounted on the same shaft as the electrical generator. It therefore consists of only one rotating
part, eliminating the need for a gearbox and associated numerous moving parts. Micro turbines
are miniature versions of the huge machines used to generate power from natural gas, and
evolved from aircraft engines and automotive turbochargers. A cutaway view of a Microturbine
is shown in Figure1.2 The single stage Turbine and Compressor wheels are inertia welded to the
shaft, which supports the generator alternator rotor and provides for a cold end drive. A block
diagram showing a complete cycle of the microturbine is shown in Figure 1.3 The inner bearing
is a hydrodynamic bearing and the outer bearing utilizes a ceramic ball race. A device called
recuperator plays an important role in completing the cycle of microturbine.
Figure 1.2 Sectional view of Microturbine
1.3.4 Principle and Working of Micro Turbines
The high velocity exhaust gases coming from the combustor rotate the turbine used in the
micro turbine. The basic principle of working of the micro turbine is that the compressor as well
as the electric generator is mounted on the same power shaft as that of the turbine. Because of
this the compressor and the generator also rotate with the turbine. The generator rotates with the
same speed as that of the turbine and generates the electricity. The electricity is first given to the
power conditioning devices and then it is supplied to the required areas. The combustor is
supplied with the fuel in the gaseous form by the gas compressor. Also fresh and compressed air
is supplied to the combustor by the compressor through the recuprator. Here the recuprator plays
an important role of heat exchanger. It absorbs the heat from the hot gases coming from the
turbine. Then it gives this heat to the compressed air coming from the compressor. Thus the air
supplied to the combustor is hot and compressed. This helps to increase the overall efficiency of
Figure 1.3 Working cycle of Microturbine
1.3.5 Microturbine Overview
Table 1.1 Microturbine Overview
Commercially Available Yes (Limited)
Size Range 25 to 500 kw
fuel Natural gas, hydrogen, propane, diesel
Efficiency 20 to 30% (Recuperated)
Environmental Low (<950 ppm) NOx
Other Features Cogeneration (50 to 80°C water)
Commercial Status Small volume production,Commercial
Micro turbines are small combustion turbines with outputs of 25 kW to 500 kW. They
evolved from automotive and truck turbochargers, auxiliary power units (APUs) for airplanes,
and small jet engines. Micro turbines are a relatively new distributed generation technology
being used for stationary energy generation applications. They are a type of combustion turbine
that produces both heat and electricity on a relatively small scale.
Figure 1.4 Capstone Turbine
A micro gas turbine engine consists of a radial inflow turbine, a centrifugal compressor
and a combustor. The micro turbine is one of the critical components in a micro gas turbine
engine, since it is used for outputting power as well as for rotating the compressor. Micro
turbines are becoming widespread for distributed power and combined heat and power
applications. They are one of the most promising technologies for powering hybrid electric
vehicles. They range from hand held units producing less than a kilowatt, to commercial sized
systems that produce tens or hundreds of kilowatts.
Part of their success is due to advances in electronics, which allows unattended operation
and interfacing with the commercial power grid. Electronic power switching technology
eliminates the need for the generator to be synchronized with the power grid. This allows the
generator to be integrated with the turbine shaft, and to double as the starter motor.
They accept most commercial fuels, such as gasoline, natural gas, propane, diesel, and
kerosene as well as renewable fuels such as E85, biodiesel and biogas.
Most micro turbines are comprised of a compressor, combustor, turbine, alternator,
recuperator (a device that captures waste heat to improve the efficiency of the compressor stage),
1.3.6 Types of Micro turbine
Micro turbines are classified by the physical arrangement of the component parts: single
shaft or two-shaft, simple cycle, or recuperated, inter-cooled, and reheat. The machines generally
rotate over 40,000 revolutions per minute. The bearing selection—oil or air—is dependent on
usage. A single shaft micro turbine with high rotating speeds of 90,000 to 120,000 revolutions
per minute is the more common design, as it is simpler and less expensive to build. Conversely,
the split shaft is necessary for machine drive applications, which does not require an inverter to
change the frequency of the AC power.
Microturbine generators can also be divided into two general classes:
Unrecuperated microturbines - In a simple cycle, or unrecuperated, turbine,
compressed air is mixed with fuel and burned under constant pressure conditions. The
resulting hot gas is allowed to expand through a turbine to perform work. Simple cycle
micro turbines have lower efficiencies at around 15%, but also lower capital costs, higher
reliability, and more heat available for cogeneration applications than recuperated units.
Recuperated microturbines - Recuperated units use a sheet-metal heat exchanger that
recovers some of the heat from an exhaust stream and transfers it to the incoming air
stream, boosting the temperature of the air stream supplied to the combustor. Further
exhaust heat recovery can be used in a cogeneration configuration. The figures below
illustrate a recuperated micro turbine system. The fuel-energy-to-electrical-conversion
efficiencies are in the range of 20 to 30%. In addition, recuperated units can produce 30
to 40% fuel savings from preheating.
Cogeneration is an option in many cases as a micro turbine is located at the point-of-power
utilization. The combined thermal electrical efficiency of micro turbines in such cogeneration
applications can reach as high as 85% depending on the heat process requirements.
The performance of the micro turbines is given in the tabular form as below,
Table 1.2 Performance of Microturbine
With Heat Recovery Up to 85%
Commercial micro turbines used for power generation range in size from about 25KW to
500KW. They produce both heat and electricity on a relatively small scale. The energy to
electricity conversion efficiencies are in the range of 20 to 30%. These efficiencies are attained
when using a recuperator. Cogeneration is an option in many cases as a Microturbine is located
at the point of power utilization. The combined thermal electrical efficiency is 85%.
Unrecuperated microturbines have lower efficiencies at around 15%.
Provides better power reliability and quality, especially for those in areas where
brownouts, surges, etc. are common or utility power is less dependable
Provides power to remote applications where traditional transmission and distribution
lines are not an option such as construction sites and offshore facilities
Can be an alternative to diesel generators for on-site power for mission critical functions
(e.g., communications centres )
Possesses combined heat and power capabilities
Reduces upstream overload of transmission lines
Optimizes utilization of existing grid assets—including potential to free up transmission
assets for increased wheeling capacity
Improves grid reliability
Facilitates faster permitting than transmission line upgrades
Can be located on sites with space limitations for the production of power
Provides high-quality power for sensitive applications
Responds faster to new power demands as capacity additions can be made more quickly
Facilitates less capital tied up in unproductive assets as the modular nature of micro
turbines means capacity additions and reductions can be made in small increments,
closely matched with demand, instead of constructing central power plants sized to meet
estimated future (rather than current) demand
Stand-by power decreases downtime, enabling employees to resume working
Produces less noise than reciprocating engines
1.3.10 Characteristics of Micro Turbine
Some of the primary characteristics for microturbines:
Distributed generation - stand-alone, on-site applications remote from power grids
Quality power and reliability - reduced frequency variations, voltage transients,
surges, dips, or other disruptions
Stand-by power - used in the event of an outage, as a back-up to the electric grid
Peak shaving - the use of micro turbines during times when electric use and demand
charges are high
Boost power - boost localized generation capacity and on more remote grids
Low-cost energy - the use of micro turbines as base load or primary power that is
less expensive to produce locally than it is to purchase from the electric utility
Combined heat and power - increases the efficiency of on-site power generation by
using the waste heat for existing thermal process.
1.4 TECHNOLOGY DISCRIPTION OF MICROTURBINES:
1.4.1 Basic Processes
Micro turbines are small gas turbines, most of which feature an internal heat exchanger
called a recuperator. In a micro turbine, 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, in single shaft models, turns the generator as well. Two-shaft models use the compressor
drive turbine’s exhaust to power a second turbine that drives the generator. Finally, the
recuperator uses the exhaust of the power turbine to preheat the air from the compressor. Single-
shaft models generally operate at speeds over 60,000 revolutions per minute (rpm) and generate
electrical power of high frequency, and of variable frequency (alternating current –AC). This
power is rectified to direct current (DC) and then inverted to 60 hertz (Hz) for U.S. commercial
use. In the two-shaft version, the power turbine connects via a gearbox to a generator that
produces power at 60 Hz. Some manufacturers offer units producing 50 Hz for use in countries
where 50 Hz is standard, such as in Europe and parts of Asia.
1.4.2 Thermodynamic Heat Cycle
In principle, micro turbines and larger gas turbines operate on the same thermodynamic
heat cycle, the Brayton cycle. In this cycle, atmospheric air is compressed, heated at constant
Pressure, and then expanded, with the excess power produced by the expander (also called the
turbine) consumed by the compressor used to generate electricity. The power produced by an
expansion turbine and consumed by a compressor is proportional to the absolute temperature of
the gas passing through those devices. Higher expander inlet temperature and pressure ratios
result in higher efficiency and specific power. Higher pressure ratios increase efficiency and
specific power until an optimum pressure ratio is achieved, beyond which efficiency and specific
power decrease. The optimum pressure ratio is considerably lower when a recuperator is used.
Consequently, for good power and efficiency, it is advantageous to operate the expansion turbine
at the highest practical inlet temperature consistent with economic turbine blade materials and to
operate the compressor with inlet air at the lowest temperature possible. The general trend in gas
turbine advancement has been toward a combination of higher temperatures and pressures.
However, micro turbine inlet temperatures are generally limited to 1750°F or below to
enable the use of relatively inexpensive materials for the turbine wheel and recuperator. For
recuperated turbines, the optimum pressure ratio for best efficiency is usually less than 4:1.
1.4.3 Basic Components
I. Turbo-Compressor Package:- The basic components of a micro turbine are the
compressor, turbine generator, and recuperator Figure 1.5 the heart of the micro
turbine is the compressor-turbine package, which is commonly mounted on a
single shaft along with the electric generator. Two bearings support the single
shaft. The single moving part of the one-shaft design has the potential for
reducing maintenance needs and enhancing overall reliability. There are also two-
shaft versions, in which the turbine on the first shaft directly drives the
compressor while a power turbine on the second shaft drives a gearbox and
conventional electrical generator producing 60 Hz power. The two shaft design
features more moving parts but does not require complicated power electronics to
convert high frequency AC power output to 60 Hz. Moderate to large-size gas
turbines use multi-stage axial flow turbines and compressors, in which the gas
flows along the axis of the shaft and is compressed and expanded in multiple
stages. However, micro turbine turbo machinery is based on single-stage radial
flow compressor and turbines. Rotary vane and scroll compression are the most
commonly used technology in the micro turbine industry. Second generation gas
compressor technologies are in development or being introduced. That may
reduce costs and target on-board application Rotary vane compression technology
offers a wide range of gaseous fuel flexibility Parasitic loads vary based on type
of gas and inlet pressures available, general rule 4 to 6% for natural gas and 10 to
15% for bio gas.
II. Generator:- The micro turbine produces electrical power either via a high-speed
generator turning on the single turbo-compressor shaft or with a separate power
turbine driving a gearbox and conventional 3,600 rpm generator. The high-speed
generator of the single-shaft design employs a permanent magnet (typically
Samarium-Cobalt) alternator, and requires that the high frequency AC output
(about 1,600 Hz for a 30 kW machine) be converted to 60 Hz for general use.
This power conditioning involves rectifying the high frequency AC to DC, and
then inverting the DC to 60 Hz AC. Power conversion comes with an efficiency
penalty (approximately five percent).To start-up a single shaft design, the
generator acts as a motor turning the turbo-compressor shaft until sufficient rpm is
reached to start the combustor. Full start-up requires several minutes. If the
system is operating independent of the grid (black starting), a power storage unit
(typically a battery UPS) is used to power the generator for start-up.
III. Recuperators:- Recuperators are heat exchangers that use the hot turbine exhaust
gas (typically around 1,200ºF) to preheat the compressed air (typically around
300ºF) going into the combustor, thereby reducing the fuel needed to heat the
compressed air to turbine inlet temperature. Depending on micro turbine
operating parameters, recuperators can more than double machine efficiency.
However, since there is increased pressure drop in both the compressed air and
turbine exhaust sides of the recuperator, power output typically declines 10 to
15% from that attainable without the recuperator. Recuperators also lower the
temperature of the micro turbine exhaust, reducing the micro turbine’s
effectiveness in CHP applications.
IV. Air bearings:- They allow the turbine to spin on a thin layer of air, so friction is
low and rpm is high. no oil or oil pump is needed. Air bearings offer simplicity of
operation without the cost, reliability concerns, maintenance requirements, or
power drain of an oil supply and filtering system. Concern does exist for the
reliability of air bearings under numerous and repeated starts due to metal on
metal friction during start up, shutdown, and load changes. Reliability depends
largely on individual manufacturers’ quality control methodology more than on
design engineering, and will only be proven after significant experience with
substantial numbers of units with long numbers of operating hours and on/off
V. Power Electronics:- The high frequency AC is rectified to DC, inverted back to
60 or 50 Hz AC, and then filtered to reduce harmonic distortion… To allow for
transients and voltage spikes, power electronics designs are generally able to
handle seven times the nominal voltage. Most micro turbine power electronics are
generating three phase electricity. Figure 1.6 show the Microturbine based
combined heat and power system.
Figure 1.5 Basic parts of Microturbine
Micro turbines are very small gas turbines that usually have an internal heat-recovery
heat exchanger (called a recuperator) to improve electric efficiency. In typical micro turbines, the
cycle is similar to that of a conventional gas turbine. It consists of the following processes:
● Inlet air is compressed in a radial (centrifugal) compressor, then
● Preheated in the recuperator using heat from the turbine exhaust.
● Heated air from the recuperator is mixed with fuel in the combustor and burned.
The hot combustion gas is then expanded in one or more turbine sections, which
produces rotating mechanical power to drive the compressor and the electric generator. The
recuperator efficiency is the key to whether a particular micro turbine is economically viable. By
comparison, in a conventional gas turbine, the gas flow path is as follows: compressed air from
the compressor (more air mass can be introduced‖ by inter cooling) is burned with fuel.
Figure 1.6 Microturbine based combined heat and power system
Figure 1.7 Microturbine Construction
1.5 DesignCharacteristics of microturbines:
Thermal output: Micro turbines produce thermal output at temperatures in the 400 to 600°F
range, suitable for supplying a variety of building thermal needs.
1. Fuel flexibility:- Micro turbines can operate using a number of different fuels:
Sour gases (high sulfur, low Btu content), and liquid fuels such As gasoline, kerosene,
natural gas and diesel fuel/heating OIL.
2. Life:- Design life is estimated to be in the 40,000 to 80,000 hour range.
3. Size range:- Micro turbines available and under development are sized
From 25 to 350 KW
4. Emissions:- Low inlet temperatures and high fuel-to-air ratios result in Nox Emissions
of less than 10 parts per million (ppm) when Running on natural gas.
5. Modularity:- Units may be connected in parallel to serve larger loads and Provide power
6. Dimensions:- About 12 cubic feet.
1.6 Microturbine and Distributed Generation:
Distributed generation, a concept first promoted by Thomas Edison in the 19th century, is
rewiring the way facility. Operators and environmental mangers think about how electric power
can be produced and distributed. For decades, energy users have waited for the promise of fuel
cells, solar panels, and wind turbines to translate into reliable and economically viable sources of
power. The table shown below compares the microturbines with other D.G. resources.
Microturbines are quietly delivering on those promises and proving to be a supplement to
traditional forms of power generation. Moving away from 100% dependence on the utility
power grid to having an onsite 25icroturbine power supplement is, admittedly, a Para diagram
shift. But for progressive environment mangers worldwide, microturbines are quickly becoming
an energy management solution that saves money, resources, and the environment in one
compact and scalable package- is it stationary or mobile, remote or interconnected with the
Table 1.3 Distributed Generation Technology
1.7 Advantages of Microturbine
Micro turbine systems have many advantages over reciprocating engine generators, such
as higher power density (with respect to footprint and weight), extremely low emissions and few,
or just one, moving part. Those designed with foil bearings and air-cooling operates without oil,
coolants or other hazardous materials. Micro turbines also have the advantage of having the
majority of their waste heat contained in their relatively high temperature exhaust, whereas the
waste heat of reciprocating engines is split between its exhaust and cooling system. However,
reciprocating engine generators are quicker to respond to changes in output power requirement
and are usually slightly more efficient, although the efficiency of micro turbines is increasing.
Micro turbines also lose more efficiency at low power levels than reciprocating engines.
Micro turbines offer several potential advantages compared to other technologies for
small-scale power generation, including: a small number of moving parts, compact size,
lightweight, greater efficiency, lower emissions, lower electricity costs, and opportunities to
utilize waste fuels.
Waste heat recovery can also be used with these systems to achieve efficiencies greater
than 80%. Because of their small size, relatively low capital costs, expected low operations and
Maintenance costs, and automatic electronic control, micro turbines are expected to capture a
significant share of the distributed generation market. In addition, micro turbines offer an
efficient and clean solution to direct mechanical drive markets such as compression and air
Micro turbines offer many potential advantages for distributed power generation.
Selected strengths and weaknesses of micro turbine technology are listed in the following table
from the California Distributed Energy Resources Guide on Micro turbines.
Small number of moving parts, Low fuel to electricity efficiencies
Compact size Loss of power output and efficiency with higher ambient
temperatures and elevation
Good efficiencies in cogeneration
Can utilize waste fuels
Long maintenance intervals
Less noise than reciprocating engines
Strengthens energy security
1.8 Economics of Microturbines
Micro turbine capital costs range from $700-$1,100/kW. These costs include all
hardware, associated manuals, software, and initial training. Adding heat recovery increases the
cost by $75-$350/kW. Installation costs vary significantly by location but generally add 30-50%
to the total installed cost.
Micro turbine manufacturers are targeting a future cost below $650/kW. This appears to
be feasible if the market expands and sales volumes increase. With fewer moving parts, micro
turbine vendors hope the units can provide higher reliability than conventional reciprocating
generating technologies. Manufacturers expect that initial units will require more unexpected
visits, but as the products mature, a once-a-year maintenance schedule should suffice. Most
manufacturers are targeting maintenance intervals of 5,000-8,000 hours.
Maintenance costs for micro turbine units are still based on forecasts with minimal real-
life situations. Estimates range from $0.005-$0.016 per kWh, which would be comparable to that
for small reciprocating engine systems.
Table 1.4 Microturbine Cost
Capital Cost $700-1,100/kw
O&M Cost $0.005-0.016/kw
Maintenance Interval 5,000-8,000 hrs
1.9 Fuel Flexibility of Microturbines
Microturbines are small power plants operate on natural gas, diesel, gasoline or other
similar high-energy, fossil fuel. However, research is progressing on using lower grade; lower
energy fuels such as gas produced from biomass to power the microturbine. This gas, called
biogas, is a combustible gas derived from decomposing biological wastes that have undergone
conversion by biological decomposition called anaerobic digestion or by thermal decomposition
in a gasifier which is called pyrolysis.
In a forest, a gasifier could be used to convert wood chips and pine needles to a biogas on
site. By making modifications, the turbine will be able to utilize low pressure fuels with lower
energy content than traditional fuels. Natural gas-fired turbines have fuel with a heating value of
1,000 British thermal units per cubic foot. Biogases typically have between 10 and 20 percent of
the heating value of fossil fuels. The thrust of current research is concentrated on fuel flexibility.
The goal is to modify microturbines so they can utilize low energy, low pressure biogases. In
order to do this, a key change is to add a catalytic combustor. An added benefit of the catalytic
combustor is that it will eliminate the formation of nitrogen oxides, a technology breakthrough.
These modified microturbines have been nicknamed "Flex-microturbines".
1.10 Applications of Micro Turbines
Micro turbines can be used for stand-by power, power quality and reliability, peak
shaving, and cogeneration applications. In addition, because micro turbines are being developed
to utilize a variety of fuels, they are being used for resource recovery and landfill gas
applications. Micro turbines are well suited for small commercial building establishments such
as: restaurants, hotels/motels, small offices, retail stores, and many others.
The development of micro turbine technology for transportation applications is also in
progress. Automotive companies are interested in micro turbines as a lightweight and efficient
fossil-fuel-based energy source for hybrid electric vehicles, especially buses.
Other ongoing developments to improve micro turbine design, lower costs, and increase
performance in order to produce a competitive distributed generation product include heat
recovery/cogeneration, fuel flexibility, and hybrid systems (e.g., fuel cell/micro turbine,
I. Combined heat and power:
Waste heat from the microturbine can be transferred via a heat exchanger to produce
steam or provide hot water for local area. The hot water can be used in a greenhouse
to grow plants; water can be ducted to provide central heating in buildings in winter.
Thermal hosts can be found easier because the heat produced by each microturbine
unit is so much smaller than that by a large power station.
II. Distributed power generation:
Hospitals, hotels, factories and holiday resorts can install distributed power systems
on site to supplement power supplied by grid. Also, electricity can be generated at
sites without grid access. Distributed generation provides a wide range of services to
consumers and utilities, including standby generation, peak shaving capability,
baseload generation and co-generation.
III. Hybrid (microturbine connected to high speed alternator):
In hybrid vehicle applications, the power produced by a microturbine is converted
into electricity by a high-speed alternator. The power is used to drive electric
motors connected to the wheels. Any excess energy is directed to an energy
storage system such as batteries or flywheels.
IV. Hybrid vehicle (microturbine and fuel):
Hybrid systems take advantage of an increase in fuel cell efficiency with an increase
in operating pressure. The microturbine compressor stage is used to provide this
pressure. The fuel cell produces heat along with power, and this heat energy is used to
drive the microturbine’s turbine stage. If the fuel cell produces enough heat, the
microturbine can generate additional wer. For the hybrid combination, efficiency is
expected to be as much as 60% and emissions less than 1.0 ppm NOx, with negligible
Sox and other pollutants. Remote.
1.11 Future Scope
Extensive field test data collected from units currently in use at commercial and industrial
facilities will provide the manufacturers with the ability to improve the Microturbine design,
lowering the cost and increasing performance, in order to produce a competitive distributed
generation product. Utilities, government agencies, and other Organizations are involved in
collaborative research and field-testing.
Development is ongoing in a variety of areas:
1. Heat recovery/coregeneration
2. Fuel flexibility
4. Hybrid systems (e.g. fuel cell/Microturbine, flywheel/Microturbine)
2. LITERATURE REVIEW
Microturbine is one of the important components in a micro gas turbine engine. Micro
gas Turbine engine is a promising solution to provide high-density power source for micro
systems. A micro gas turbine engine consists of a radial inflow turbine, a centrifugal compressor
and a combustor. This thesis mainly deals with the design aspects of a micro turbine. Various
journals have been published on designing of various types of micro turbines Exhaustive study
has been done on these papers and the major points have been highlighted here.
Microturbines are a relatively new distributed generation technology being used for
stationary energy generation applications. They are a type of combustion turbine that produces
both heat and electricity on a relatively small scale. Microturbines offer several potential
advantages compared to other technologies for small-scale power generation, including: a small
number of moving parts, compact size, lightweight, greater efficiency, lower emissions, lower
electricity costs, and opportunities to utilize waste fuels. Waste heat recovery can also be used
with these systems to achieve efficiencies greater than 80%.
Because of their small size, relatively low capital costs, expected low operations and
maintenance costs, and automatic electronic control, micro turbines are expected to capture a
significant share of the distributed generation market. In addition, micro turbines offer an
efficient and clean solution to direct mechanical drive markets such as compression and air-
Figure 3.1 Experimental setup for baseline performance testing of natural gas fired
The experimental setup used to collect baseline performance data on the impact of
backpressure on the microturbine’s exhaust is shown in Figure 3.1 The setup includes a 3-phase
480-V/30-kW natural-gas fired commercially available microturbine system connected to
ORNL’s distribution network, which is connected to the TV A grid through a 480- V/75-kVA
isolation transformer. The natural gas flow rate of the microturbine was monitored by a natural
gas test meter equipped with a 0 to 200 in. WC (0 to 0.49 atm) pressure gauge. The Microturbine
exhaust temperature is measured by a resistance temperature detector (KID), and the inlet air
temperature to the microturbine is the average Tom nine thermocouples mounted on the face of
the microturbine unit. The backpressure on the unit is adjusted by a slide damper on the exhaust
duct and is monitored by a pressure transducer (0 to 7.5 in. WC or 0 to 0.018 atm). A flue gas
analyzer is used to monitor the oxygen, carbon monoxide (CO), carbon dioxide (CO& nitrogen
oxides (NO, NO,, NO& and excess air from the microturbine. The other parameters- monitored
via the manufacturer’s monitoring hardware and software built into the microturbine- include the
microturbine’s power output; engine speed; and voltage, current, and power in each phase.
The total power output demand of the microturbine was varied in increments of 5 kW
from 10 kW to 30 kW (0.33 to 1.0 of the microturbine’s nominal power output), and the
backpressure ranged from 0.3 to 7 in. WC (0.0007 to 0.017 atm). Series of tests on the
microturbine were conducted while constant output power demand was maintained, and then
while constant engine speed was maintained at various back pressures should be noted that
because the Microturbine was located outdoors, the microturbines air inlet temperature was
dictated by outdoor conditions.
4.1 Constant Power Output Demand
Tests were conducted at various power output demands and microturbine back pressures
(damper at three different positions of fully open, 1/4 closed, and 3/8 closed). Comparing results
for the same power demand in Tables 4.1 and 4.2, these tests showed that the microturbine’s
controller adjusts the engine speed to match its power demand setting as closely as possible, thus
keeping the power output constant either with or without the backpressure present. The engine
speed increased with the increase in backpressure. Additionally, Table 4.1 shows the
reproducibility of the measured data at 20 kW, relative power output and efficiency percentage
differences are less than 0.3%.
Figure 4.1 shows the microturbines’s efficiency to be approximately 23% when it is set to
the 30-kW power demand setting (full output). However, when a lower power demand setting is
used -for example, one- third output (10 kW) the efficiency of the unit drops significantly from
approximately 23% to approximately 18%. It should be noted that the efficiency is based on the
higher heating value (HHV) of natural gas. The HHVs were obtained daily from the East
Tennessee Natural Gas-Customer Information Access System. The efficiency based on the lower
heating value (LHV) of natural gas would be approximately 10% higher than the one based on
HHY or approximately 25% at full output (30 kW). It should be noted that the efficiencies
quoted by Microturbine manufacturers usually are based on the LHV.
The microturbine’s exhaust temperature was found to be around 500°F (533 K) at the
unit’s maximum power demand setting (30 kW). As expected, the exhaust temperature increased
with increasing turbineair inlet temperature. The flue gas results showed the NO, to be very low
at all power output demands (25 ppm or less) with 18.5% to 19.1% oxygen content. The CO,
concentrations were found to be between 1.5% at full power setting (30 kW), and 1.1% at one-
third setting (10 kW). The CO concentration consistently peaked at 127 and 134 ppm when the
microturbine was set to the 20-kW power output setting (Tables 4.1 and 4.2).
4.2 Constant Engine Speed
Another series of tests was conducted while the microturbine was maintained at constant
engine speed and varying backpressure for each nominal power output. Due to the space
limitations within this article, Table 4.3 shows only the results at full power of 30 kW. Figure 4.2
shows the effect of turbine backpressure on the Microturbine unit. Tables 4.1 and 4.2 showed
that the engine speed increased with the backpressure to maintain a constant power output with
identical efficiencies. However, at a constant engine speed, the average turbine efficiency
dropped by less than 2% and the average turbine power output decreased by less than 6% of the
values with damper fully open.
Capstone 30-kW microturbine with damper fully open
Capstone 30-kW microturbine with damper 3/8 closed
Figure 4.1 Efficiency of 30 kW gas microturbine as a function of nominal power demand
with damper 3/8 closed
Microturbine performance with approximately constant engine speed
(30-kW nominal output demand setting) and varying turbine backpressure
Figure 4.2 Effect of turbine backpressure on the performance of the unit
The drawbacks of centralized power generation and shortage of power leading to concept
of distributed generation. DG tends to several advantages and concept of DG is more feasible.
Microturbine is the application of DG .The history of IC engine . Shows several year research
works for today’s better result. Therefore microturbine is tomorrow’s world. Microturbine can
use low grade of fuel very effectively like waste gases, sour gases etc.
Thus microturbine gives chance of low fuel cost and less emission. The dimensions of
microturbine comparatively small by which it can be installed at field where power is consumed.
It has few efficiency problems. Due to chemical recuperation the thermal efficiency increases
sharply. Microturbine is also effective in CHP operation .It is having problem of Starting time
and that’s why it fails as standby power generator compared to IC engines. In India the
microturbine is quite useful. The power shortage effect can be solved using microturbine, using
fuels like biogas, etc .But in India the technology is still underdevelopment so the present
seminar is an honest attempt to introduce microturbine technology in India for solving the
problem of power generation in future.
Experimental results showed that the average turbine efficiency dropped by less than 2%
and the average turbine power output decreased by less than 6% of the values with damper fully
open, at a constant engine speed. It was found that the corrected experimental and calculated data
agree quite well. Further, the data show that the output power losses (decrease in power output)
due to backpressure range from 3.5% for 30 kW to 5.5% for 10 kW, while the efficiency losses
(decrease in efficiency) range from 2.5 to 4.0%, correspondingly.
 K.C.Goli, S.V.Kondi, V.B.Timmanpalli, “Principles and Working of Micro Turbine”,
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 V.A.Bhoyar, K.S.Kalwal, “Various Aspects of Micro Turbine Generation System”,
International Journal For Engineering Applications And Technology, ISSN:2321-8134.
 X.C.Shan, Q.Zhang, Y.F.Sun, R.Maeda, “A Micro Turbine Devices With Enhanced Micro
Air-Bearing”, DTIP 2006, Apr 2006, Lago Maggiore, Italy.
 S.Nakona, T.Kishibe, T.Inoue, H.Shiraiwa, “An Advanced Microturbine System with
Water-Lubricated Bearing”, Hindwai Publishing Corporation, International Journal of
Rotating Machinery, Volume 2009, Article ID 718107, doi:10.1155/2009/718107.
 P.D.Fairchild, S.D.Labinov, A.Zaltash, B.D.T. Rizy, “Experimental And Theoretical Study
of Microturbine Based BCHP System”, Buildings Technology Center Energy Division Oak
Ridge National Laboratory Oak Ridge, Tennessee 37831-6070, 2001 ASME International
Congress and Exposition, November 11-16,2001, New York.