Mr.jadhav Sandip Sitara

Vol- 11, Issue- I, February- 2014 ISSN 2321 � 0397 (Online)

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International Multidisciplinary Research Journal

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MICROTURBINE

Mr.Jadhav Sandip Sitaram

M.E.IInd Year,Heat Power Engineering,

D.P.E.S.College,Wagholi,Pune University,India.

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 micro turbines. The micro turbine is an example of Micro Electro Mechanical Systems,

which is efficiently used to develop power at a small scale. Micro turbines are small combustion

turbines approximately the size of a refrigerator with outputs of 25 kW to 500 kW. Micro

turbines 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 micro turbines compared to the conventional Reciprocating Engines, Gas turbines, Coal fired steam engines etc KEYWORDS:MEMS:Micro-Electro-Mechanical Systems (MEMS), DG Distribution generation

1. INTRODUCTION:

TURBINES:�Turbo Machine� is defined as a device that extracts energy from a continuously

flowing fluid by the dynamic action of one or more rotating elements .The prefix �turbo� is a

Latin word meaning �spin� or �whirl� implying that turbo machines rotate in some way.

Types of Turbines:

1.Steam Turbines

2.GasTurbines (Combustion Turbines) 3.Water (Hydraulic) Turbines

Steam Turbines:A steam turbine is mainly used as an ideal prime mover in which heat energy

transformed into mechanical energy in the form of rotary motion. In steam turbines, the heat

energy of the steam is first converted into kinetic (velocity) energy which in turn is transformed

into mechanical energy of rotation and then drives the generator for the power generation.


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Classification of Steam Turbines

Based on action of steam or type of expansion:

1. Impulse or velocity or De Laval turbine

2. Reaction or pressure or Parson�s turbine

3. Combination turbine

Based on number of stages:

1. Single stage turbine 2. Multi-stage turbine

Based on type of steam flow:1.Axial flow turbine 2. Radial flow turbine

Impulse Turbines (De Laval Turbine): In this type of turbine, steam is initially expanded in a

nozzle from high pressure to low pressure. High velocity jet of steam coming out of the nozzle is

made to glide over a curved vane, called �Blade�.

Gas turbines:A Gas turbine uses the hot gases of combustion directly to produce the mechanical

power.Fuels used - Kerosene, coal, coal gas, bunker oil, gasoline, producer gas, etc.

Classification:

1.Open cycle gas turbine:The entire flow of the working substance comes from atmosphere

and is returned to the atmosphere back in each cycle.

2.Closed cycle gas turbine:The flow of the working substance of specified mass is

confined within the cyclic path. ( Air or Helium is the working substance)

Water (hydraulic) turbines:It is a prime mover, which converts hydro power (energy of water)

into mechanical energy and further into hydro-electric power

Classification of Water Turbines

Based on action of water:

1. Impulse turbine � pelton wheel.

2. Reaction turbine � francis and kaplan.

Based on name of originator:

1. Pelton turbine or Pelton wheel 2.Francis turbine

3.Kaplan turbine

Based on head of water:

1. Low head turbine 2.Medium head turbine

3.High head turbine

1.1MEMS:Micro-Electro-Mechanical Systems (MEMS) is an integration of mechanical

elements, sensors, actuators, and electronics on a common silicon substrate through the


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utilization of micro fabrication technology. MEM is 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. Microturbine 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 microturbine is.

1.2 Gas Turbine:

Gas turbines are Braxton 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.

1.3 Micro turbine:

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 600 MW 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


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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. Micro turbine

development is based on turbines used for aircraft auxiliary power units, which have been used

in commercial airlines for decades.One way in which micro turbines can be distinguished from

larger turbines is that micro turbines use a single shaft to drive the compressor, turbine and

generator. Where as 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.

2.0 HISTORY:

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.

3.0 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 microturbines come into the


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picture. It is one of the best options to set up a local power-generation plant, perhaps using a

micro turbine -- 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.

4.CONSTRUCTION OMICROTURBINE:

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 micro turbine is shown in Figure1. 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 micro

turbine is shown in Figure2. 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 micro turbine.

Fig 1: Sectional view of a typical micro turbine .

4. PRINCIPLE AND WORKING OF MICROTURBINES:

The high velocity exhaust gases coming from the combustor rotate the turbine used in the

microturbine. The basic principle of working of the microturbine 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


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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.

Fig. 2 Working cycle of a microturbine.

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.

5.1. Microturbine System Components

A block diagram of a single shaft microturbine system is shown in Figure. 2. In a

microturbine, a radial flow (centrifugal) compressor compresses the inlet air that is then

preheated in the recuperator using heat from the turbine exhaust. Next, the heated air from the

recuperator mixes with fuel in the combustor and hot combustion gas expands through the

expansion and power turbines. The expansion turbine turns the compressor and, 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. This power is rectified to direct current

(DC) and then inverted to 50 or 60 hertz (Hz) for commercial use. The components of a single

shaft microturbine system are well defined in the this sections.

A. Turbo Compressor

The basic components of a microturbine are the compressor, turbine generator, and

recuperator (see Figure 1). The heart of the microturbine is the compressor-turbine package,

which is commonly mounted on a single shaft along with the electric generator. Two bearings


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support the single shaft. The single moving part of the one-shaft design has the potential for

reducing maintenance needs and enhancing overall reliability. In microturbines, the

turbocompressor shaft generally turns at high rotational speed, about 96,000 rpm in the case of a

30 kW machine and about 80,000 rpm in a 75 kW machine. One 45 kW model on the market

turns at 116,000 rpm There is no single rotational speedpower size rule, as the specific turbine

and compressor design characteristics strongly influence the physical size of components and

consequently rotational speed. For a specific aerodynamic design, as the power rating decreases,

the shaft speed increases, hence the high shaft speed of the small microturbines. 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 microturbine

operating parameters, recuperators can more than double machine efficiency. The controllers of

the gas turbine implements three major control loops: start up, speed and temperature. For the

purpose of these modeling tests, the speed control, recives the most attention. The reason for this

is that during start up, the unit is not on-line, and in temperature control mode, the governor will

not respond to system frequency changes. The primary valve demand control signal is selected

by a low value select gate from the outputs of these control loops [3].

B. Generator

The microturbine produces electrical power via a highspeed generator turning on the

single turbo-compressor shaft. 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 50 or 60 Hz for general use.

This power conditioning involves rectifying the high frequency AC sto DC, and then inverting

the DC to 50 or 60 Hz AC. Power conversion comes with an efficiency penalty (approximately

five percent).

C. Power Conditioning Unit-As discussed, single-shaft microturbines feature digital power

controllers to convert the high frequency AC power produced by the generator into usable

electricity.The high frequency AC is rectified to DC, inverted back to 60 or 50 Hz AC, and then

filtered to reduce harmonic distortion.This is a critical component in the single-shaft

microturbine design and represents significant design challenges, specifically in matching

turbine output to the required load. To allow for transients and voltage spikes, power electronics


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designs are generally able to handle seven times the nominal voltage. Most microturbine power

electronics are generating three phase electricity

6. PERFORMANCE:

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

Table No.1 MICROTURBINE EFFICIENCY for 25 to 500KW

CONFIGURATION EFFICIENCY

Unrecuperated

15%

Recuperated

20-30%

With Heat Recovery Up to 85%

Commercial microturbines 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%.

7.0 FEATURES:

Microturbines offer many potential advantages for distributed power generation. Selected

strengths and weaknesses of microturbine of the microturbine technology are listed below:

Advantages :-

Small number of moving parts.

Compact size.

Light weight.

Good efficiency in cogeneration.

Low emission.

Can utilize waste fuel.

Long maintenance intervals

Limitations:-

Low fuel to electricity efficiency.

Loss of power output and efficiency with higher ambient temperature and elevation

8. FUTURE SCOPE:


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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/co regeneration

2. Fuel flexibility

3. Vehicles

4.Hybridsystems (e.g. fuel cell/microturbine, flywheel/microturbine)

9. APPLICATIONS:

While the simplest application for a microturbine prime mover is of power generation

other application exists. Microturbine prime movers can be used for cooling, refrigeration; air

compression and pump drive application whereby the inherent high speed of the power shaft can

be used to drive high efficiency and low cost centrifugal compressors.

Microturbines can be used for stand by power, power quality and reliability, peak

shaving, and cogeneration applications. In addition, because microturbines are being developed

to utilize a variety of fuels, they are being used for resource recovery and landfill gas

applications. Microturbines produce between 25kw to 500kw of power and are well suited for

small commercial building establishments such as restaurants, hotels/motels, small offices, retail

stores and many others.

The development of the microturbine technology for the transportation application is also in

progress. One of the major applications used is the turbocharger in the small vehicles.

Automotive companies are interested in microturbines to provide a light weight and efficient

fossil fuel- based energy source for hybrid electric vehicles, especially buses.

10 CASE STUDY ON DISTRIBUTED GENERATION:

10.1 Introduction:Distribution generation is a concept of installing and operating small electric

generators, typically less than 20MW, at or near electrical load. The premise of distributed

generation is to provide electricity to a customer at a reduced cost and more efficiently with

reduced losses than the traditional utility central generating plant with transmission and

distribution wires.

10.2 Microturbine in distributed generation:


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Microturbine is small scale combustion turbines ranging inside from 28 kW to 500kW, which

include a compressor, composter, turbine, alternator, recuperator and generator. Microturbines

are smaller, lighter and operate with no vibration and less noise. All of these features help to

make on - site installation possible without compromising the environmental aspects. They have

potential to be located on site having space limitations to produce power.

10.3 Working principle:The technology used for distributed generation is that of microturbine.

The three basic equipments, viz. the turbine, the generator and compressor are mounted on a

single shaft. The core of the microturbine is a high-speed compressor -turbine section, which

rotates very fast - 96000rpm in Capston model 330. On the same shaft is a high-speed generator

using permanent magnets. A key element for designs of microturbine is air bearings (or more

correctly gas bearings). Air bearings enable the high speed only air cooling a long life almost

maintenance free.The high speed generator delivers a high frequency power. To "gear it down"

to useful 50/60 Hz power, electronics is brought into application. The following table shows

the speed of microturbine for different power generation capacities.

Table No.3 Speed of Turbine For Different Power Ratings .

POWER SPEED

45 KW 90,000 TO 1,16,000

(RPM)

80 KW 70,000 (RPM)

200 KW 50,000 (RPM)

Cutaway of the Capston 330 turbine.

10.4 Advantages:

The general advantages of microturbine are that there are small number of moving parts

are compact in size, light weight and have opportunities for greater efficiencies, lower emissions,




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lower electricity costs and use renewable fuels such as land fill or sewage treatment gases.

Microturbine in general offer to be advantages

1 lower emission and 2 low maintenance.

As illustrated below (Table no.3), the Capston microturbine has one of the best emission

performances of any fossil fuel combustion.

Table no.4 COMPARISION OF EMISSIONS

Item NO (ppm) CO (ppm) THC (ppm)

Reciprocating

Engines

(500kW)

100 340 150

Gas Turbines

(4.5MW)

25 50 10

Coal Fired

Steam

(500MW)

200 N/A N/A

Microturbine 9 25 9

Source: Cambridge Energy Research Associates.

With very low emissions and maintenance, microturbines hold promise to enable small-scale

cogeneration. To exhaust heat can be use water heating, absorption cooling, dehumidification,

etc.

It is possible to reach efficiencies of 70-80%. Because of the three exhausts with no risk

of any oil fuel (due to the air bearing) it should be possible to use the exhaust gas directly in

some industrial processes.

10.5 Benefits of Distributed generation:

Thus the benefits that distributed generation could potentially provide, depending on the

technology, include reduced emissions, utilization of waste heat, improved power quality and

reliability and deferral of transmission or distribution upgrades.

10.6 HYDROPOWER GENERATION:

A typical use of microturbine is the hydropower generation. Microturbine technology

equipments harness the best possible energy source that is the discharge flow of even minor




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streams, in that sense; they constitute cleaner, superior environmental alternatives to the less

acceptable fossil fuel powered generators.

The technology is very simple as shown in figure .A turbine with a generator on its shaft

is fitted in the way of water flowing in a river or a stream.

In most cases, microturbine views only a small portion of a stream's flow that is channeled

through a penstock. As it is clear from the figure, we can say that reliable and renewable hydro-

energy generation (with the help of microturbines of course) does not require a reservoir or the

flooding of low-lying areas. Microturbine technology turbines may be installed low discharge

flow streams and rivers. They are efficient even in cases of low drop river fall, as microturbine

technology turbines generate electricity from as little as one meter of hydraulic head.

10.7 TURBOCHARGER:

Turbocharger is one of the applications of microturbine. It uses the principle of mounting

the compressor on same shaft as that of turbine. Here also the exhaust gases drive the turbine.

Today with precise control offered by the computers, turbochargers are making small engines

more efficient and capable of producing more power.

Microturbines are evolved from automotive and truck turbochargers, auxiliary power

units for airplanes, and small jet engines and are comprised of a compressor, combustor, turbine,

alternator, recuperator, and generator.

10.8 Turbocharging principle:

A turbocharger is a device that uses exhaust gases, rather than the engine power to run an air

pump or compressor. The air pump then forces an increased amount of air into the cylinders.

Both the diesel and gasoline engines in the market use turbochargers. Figure 3 shows a typical

schematic of air and exhausting a turbocharged engine. High velocity exhaust gases pass out of

the exhaust ports. From there they pass through a turbine driven pump. Here the exhaust gases

cause the exhaust turbine to turn very rapidly.

The exhaust turbine causes the intake compressor to run very rapidly. As the compressor

turbine runs it draws in a large amount of fresh air. The intake air is pressurized and forced into

the intake port. The increase in the pressure in the intake manifold is called as boost. Boost may

produce pressure in the intake manifold of about 6 to 10 psi or more depending on the

manufacturer.

Figure shows a chart that compares a turbocharged and a normally aspirated engine. Note

that both the torque and the horse power are increased at all rpm. For example at 5000 rpm the




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normally aspirated engine produces about 80hp. at this rpm, the turbocharged engine can

produce about 140hp.

11. CONCLUSION:

As a breakthrough technology, allowing unparalleled synergy between hitherto unrelated

fields of endeavor such as biology and microelectronics, many new MEMS applications will

emerge, expanding beyond that which is currently identified or known. In the industrial sector,

MEMS devices are emerging as product performance differentiators in numerous markets with a

projected market growth of over 50% per year.

REFRENCES

1.Jan Peirs, Dominiek Reynaerts, Filip Verplaetsen, Michael Poesen, Pieterjan Renier, A

Microturbine for Electric Power Generation Sinaia , RomaniaSAE Paper 2002 , October 6-8,

2002

2.R. H. Staunton B. Ozpineci, Microturbine Power Conversion Technology Review, ORNL/TM-

2003/74

3. E.Schwaller, Turbocharger, Automotive Technology, Delmar publications.

4. S. E. Abdollahi and A. Vahedi, Dynamic Modeling of Micro-Turbine Generation Systems

Using Matlab/Simulink, Department of Electrical Engineering Iran University of Science and

Technology Narmak, Tehran (Iran)

5.21211 Nordhoff Street � Chatsworth � CA � 91311 � 877.716.2929 � 818 407.3770 � ⓒ2008

Capstone Turbine Corporation. 10/08 Capstone P/N 331032B

6.Environmental TechnologyVerification Report Combined Heat and Power at a Commercial

Supermarket - Capstone 60 kW Microturbine CHP System Under a Cooperative Agreement

With U.S. Environmental Protection Agency and Under Agreement With New York State

Energy Research and Development Authority SRI/USEPA-GHG-VR-27 September 2003

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Mr.jadhav Sandip Sitara