A Seminar on

MICROTURBINEBY

Mr.AKSHAY NAWALE

Guided by

Prof.N.A.Doifode

Submitted in partial fulfilment of the requirement for

TE-MECHANICAL ENGINEERING

(2015-2016)

Savitribai Phule Pune University

DEPARTMENT OF MECHANICAL ENGINEERING

TSSM’S BHIVARABAI SAWANT COLLEGE OF ENGINEERING AND RESEARCH,

NARHE, PUNE-411041.

1

TSSM’S BHIVARABAI SAWANT COLLEGE OF ENGINEERING AND

RESEARCH,NARHE,PUNE-411041

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

“MICROTURBINE”

Under the guidance of

Prof.N.A.DOIFODE

Towards the partial fulfilment of the requirement for

TE (Mechanical Engineering)

Savitribai Phule Pune University

(2015-2016)

Prof.N.A.DOIFODE Examiner Examiner

(Seminar Guide) (External) (Internal)

Prof.R.N.POTE Prof.P.R.KALE

(Seminar Coordinator) (Head of Department)

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CONTENTS

Sr.No Name of TopicPage Number

List of Figures I

List of Tables II

Acknowledgement III

Abstract IV

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

3

4.1 Constant Power Output Demand 26

4.2 Constant Engine Speed 26

5. Conclusion 30

References

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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

1.5

1.6

1.7

3.1

4.1

4.2

Basic Part of Microturbine

Microturbine Based Combined heat & Power System

Microturbine Construction

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

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19

19

24

28

29

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LIST OF TABLES

Table No. Title Page No.

1.1 Microturbine Overview 7

1.2

1.3

Performance of Microturbine

Distributed Generation Technology

10

18

1.4

4.1

4.2

4.3

Microturbine Cost

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

20

27

27

28

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ACKNOWLEDGEMENT

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.

T120800968

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ABSTRACT

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.

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1. INTRODUCTION1.1 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.

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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

Micro turbines

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

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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.

1.2.3 Features

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

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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.

1.3 Microturbine:

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.

1.3.1 History

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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

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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

the cycle.

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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

prototypes now

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.

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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.

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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),

and generator.

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.

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1.3.7 Performance

The performance of the micro turbines is given in the tabular form as below,

Table 1.2 Performance of Microturbine

Configuration EfficiencyUnrecuperated 15%

Recuperated 20-30%

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%.

1.3.8 Functional

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

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1.3.9 Productive

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

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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.

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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

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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

cycles.

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.

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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.

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Figure 1.6 Microturbine based combined heat and power system

Figure 1.7 Microturbine Construction

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1.5 Design Characteristics 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

reliability.

6. Dimensions:- About 12 cubic feet.

1.6 Microturbine and Distributed Generation:

Distributed generation, a concept first promoted by Thomas Edison in the 19 th 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 icroturbine 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 utility.

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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

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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

conditioning.

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.

Micro turbines:-

Strengths Weaknesses

Small number of moving parts, Low fuel to electricity efficiencies

Compact size Loss of power output and efficiency with higher ambient

temperatures and elevation

Lightweight

Good efficiencies in cogeneration

Low emissions

Can utilize waste fuels

Long maintenance intervals

No vibrations

Less noise than reciprocating engines

Strengthens energy security

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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

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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,

flywheel/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

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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

3. Vehicles

4. Hybrid systems (e.g. fuel cell/Microturbine, flywheel/Microturbine)

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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-

conditioning.

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3. EXPERIMENTAL SETUP

Figure 3.1 Experimental setup for baseline performance testing of natural gas fired Microturbine

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.

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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.

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4. EXPERIMENTAL RESULTS

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

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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.

Table 4.1

Capstone 30-kW microturbine with damper fully open

Table 4.2

Capstone 30-kW microturbine with damper 3/8 closed

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Figure 4.1 Efficiency of 30 kW gas microturbine as a function of nominal power demand with damper 3/8 closed

Table 4.3Microturbine performance with approximately constant engine speed

(30-kW nominal output demand setting) and varying turbine backpressure

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Figure 4.2 Effect of turbine backpressure on the performance of the unit

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5. CONCLUSION

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.

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