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    Micro turbine

    Generators

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    Micro turbineGenerators

    ditedby

    M J Moore

    rofessional

    ngineering

    ublishing

    Published by Professional Engineering Publishing

    Bury StEdmundsandLondon UK.

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    FirstPublished 2002

    This publication

    is

    copyright under

    th e

    Berne Convention

    and the

    International Copyright Convention.

    A ll

    rights reserved. Apart

    from any fair

    dealing

    for the

    purpose

    of

    private stud y, research, cri ticism

    or

    review, as permitted under the Copyright, Designs and Patents Act, 1988, no part may be reproduced,

    stored in a retrieval system or transmitted in any form or by any means, electronic electrical ,

    chemical , mechanical , photocopying, recording or otherwise, without th e

    prior

    permission of the

    copyright owners. nlicensed multiple copying of the

    contents

    of this

    publication

    is

    illegal

    Inquiries

    should

    be

    addressed

    to: The

    Publishing Editor, Professional Engineering Publishing Limited,

    Northga te

    A venue , Bury St Edmunds, Suffolk, IP32 6BW , UK . Fax: +44 0) 1284 70527 1.

    2002

    TheInstitutiono fMechanical

    Engineers,

    unless

    otherw ise stated.

    ISBN 186058391 1

    A CIPcatalogu e recordfo rthis bookisavailable

    from

    theBritish Library.

    Printed by The Crom well Press, Trowbridge, W iltshire, UK

    ThePublishersare not responsible for anystatem ent m ade inthis pu blication. Data, discussion, andconclusions

    developed by authors are for information onlyand are not intended for use without independent substantiating

    investigation on the

    part

    of

    po tential users. Opinions exp ressed

    a re

    those

    of the

    Authors

    and are not

    necessarily

    those

    of the Institution of M echan ical Engineers or its Publishers.

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    ont nts

    About theEditor ix

    Foreword

    xi

    Chapter

    1 An Introduction to Micro turbine Generators

    ABullin 1

    Chapter

    2

    Micro turbine Generators

    Next Generation

    S L

    Ham ilton

    21

    Chapter 3 Analysis of Micro and Mini turbine Competitive and Supply

    Marketsin

    Europe

    T

    Shane

    27

    hapter4 Future PotentialDevelopmentsofMicro turbine Generators

    ybridCycles

    and

    Tri generation

    E

    M acchi

    andS Campanari 43

    Chapter

    5

    Design Reliability

    of

    Micro turbines

    I J

    Stares

    an d

    Q JMabbutt

    67

    Chapter

    6

    Field Experience with Micro turbines

    in

    Canada

    RBrandon

    73

    Chapter

    7

    Design Problems

    in

    Micro turbine Generators

    K RPullen R M artinez-Botas and K

    Buffard 85

    Chapter 8

    Tip leakage

    Flow: A Comparison between Axial and

    Radial Turbines

    RDambach H P Hodson

    and

    IHuntsman

    97

    Index 1 9

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    bout

    the

    Editor

    Michael Moore

    a

    former

    Editor

    of the

    IMechE Journal

    of

    Power

    and

    Energy

    was

    em ployed

    for m any years

    in the

    Research Division

    of the

    Central Electricity Generation Board.

    As

    Head

    of Engineering Science Division and Programm e Manager for Turbine Plant Research he

    gained wide experience

    o f

    power station plant.

    In

    1989

    he

    became Com m ercial Developm ent

    Manager

    in National Power before retiring to become an independent consultant. Michael

    Moore is the author of 25 papers and editor of two books on turbine and condenser plan

    design.

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    orewor

    Since

    the

    introduction

    of

    electricity supply systems

    and

    distribution

    by a

    grid network

    the

    economies

    of

    scale have been recognized. Generating plant have become

    progressively

    larger

    culminating

    in

    unit outputs

    of

    1300

    MW from

    nuclear

    and

    even some

    fossil-fuelled

    plant.

    The

    relativelyrecent availabilityofnaturalgas at economic priceshas led to thedevelopment of

    extremely large gas turbinesincombined cycle generating at thermal

    efficiencies

    of up to 60

    per cent. It is therefore surprising that a niche market has appeared for micro-turbine

    generators MTGs) with output powerof20-500kW.

    Theirappearance

    on the

    generation scene

    has

    been made possible

    by the

    development

    of

    their

    component parts. Tiny radial compressor

    and

    turbines

    are

    notoriously

    inefficient and

    prone

    to

    excessive

    tip

    leakage. Modern precision manufacturing techniques

    and

    design methods using

    computational fluid

    mechanics CFD)

    has

    substantially improved their performance. High-

    speed permanent magnet alternators

    and

    bearing systems have made

    possible

    the

    direct drive

    arrangements, which remove the cost and complexity of gearboxes. Lastly, bu t most

    importantly, modern, solid-state, power electronics

    has

    enabled

    the

    potentially unsteady

    kHz

    outputto be convertedto ahighly stable voltagea tgridfrequency.

    Disadvantages remain. Even with exhaust

    gas

    heat recuperators, these small units achieve

    onlysome30 percent thermale fficiency. Turbine entry temperatures, the key to gas turbine

    efficiency

    have limited development potential due to the difficulties of cooling such tiny

    components. With this relatively high fuel consumption

    how can

    these devicespenetrate

    the

    market?

    While

    the

    introduction

    of

    MTGs

    is in its

    early stages, their relative simplicity makes them

    suitable

    for

    mass production with correspondingly

    low first

    costs. Whereelectricity

    is in

    short

    supply,

    and

    grid strengthening

    is

    expensive

    and

    delayed,

    the

    advantage

    of

    such units

    as

    distributed

    generation

    has

    been recognized. MTGs obviously have

    a

    role

    on

    remote

    oil rigs

    where

    fuel

    is availableand nogrid connection is feasible. Combined heat andpower CHP)

    projectsarealso potential applications and, again more recently, back-up power forcomputer,

    internet,and IT installations

    benefit

    from the high quality supplyfrom the

    power

    conditioning

    units.

    Their competitors arereciprocating gas engines andgenerators and the fuel cell. The former

    it

    is

    claimed, require more maintenance,

    and the

    latter

    is

    more complex

    and may be

    less

    reliable.

    Looking ahead, the combination of MTGs an d

    fuel

    cells could raise overall

    generating

    efficiency

    to 60 percento rhigher.

    The emergence

    of MTG

    technology prompted

    the

    IMechE

    to

    hold

    a

    Seminar

    in

    London,

    December2000

    to

    introduce

    the

    concept. Since then

    the

    papers

    from the

    seminar have been

    up-dated and are reproduced in this volume. They cover the field from the general

    arrangement

    of

    components,

    the

    main design problems,

    the

    market envisaged operating

    experience to date, the fluidmechanics ofsmall turbines, and the thermodynamic cycles for

    their

    futureapplication. Ihopeyou find thevolumea useful introductionto thesubject.

    M

    oore

    itor

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    An Introduction to Micro turbine

    Generators

    Bullin

    bstr ct

    This Chapteridentifies the main elements of a micro-turbine generator and the key enabling

    technology. The elements include the micro-turbine engine, turbo alternator, recuperator,

    power conditioner,

    and gas

    boost compressor. Features, advantages,

    an d

    benefits

    of

    each

    element as preferred by Bowman Power Systems Limited are described and alternative

    solutions are discussed. T he

    features

    an dbenefits of a micro-turbine cogeneration system are

    presented and described.

    1 1

    Introduction

    The

    following

    is a brief introduction to micro-turbine technology.

    Micro-turbine generators MTGs) are based on five key areas of technology: micro-turbine

    engines running

    on

    liquid

    or gas

    fuel;

    turbo alternators

    to

    produce electrical power;

    recuperators heat exchangers) to achieve high engine

    efficiency;

    power conditioners to

    convert

    the

    power

    to

    meet customer needs;

    and gas

    boost com pressors

    to

    provide natural

    gas

    fuel at an

    appropriate pressure.

    There are various approaches to these areas of technology, but

    this

    Chapter concentrates on

    the Bowman solution to the design challenges, although alternative solutions are mentioned

    and discussed.

    Development of m icro-turbine and associated enabling technology has been m arket led; the

    driving force being the customer need fo r competitively priced distributed power solutions

    and theeaseof installation and use of the equipment.

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    An Introduction toMicro turbineGenerators

    Fig 1 1Turbog en cross section

    1 1 3 Recuperators

    Durable heat exchangers of high

    effectivity

    and low cost are needed to increase the

    efficiency

    of ga s

    turbines

    to the

    levels needed

    to

    compete with reciprocating engine-based power

    generation

    systems. The function of

    these heat exchangers

    is to

    extract heat from

    the gas

    turbine exhaust

    gases in

    order

    to

    preheat

    the air

    used

    in the

    com bustion

    process

    and

    thereby

    reduce the

    amount

    of fuel

    used

    to

    reach operating temperature.

    The Bowm an recuperator is a primary surface type manufacturedfrom

    stainless steel

    forlong

    life. With an

    effectivity

    of about 90 per cent the fuel consumption of the micro-turbine

    engine is approximately halved doubling the MTG efficiency from 15 per cent to about 30

    per cent.

    1 1 4 Power

    onditioners

    The electrical output frequency of a turbo alternator is typically 1000-3000 Hz and must in

    mostcases

    be converted to a 50 or 60 Hz useable ou tput. A microprocessor controlled power

    conditioner carries

    out the frequency

    conversion

    in

    addition

    to

    other power conditioning

    and

    utility

    connection

    functions to

    provide electrical power

    of

    appropriate quality

    and

    features.

    The power conditioner controls the output frequency independently of turbine

    speed

    and

    facilitates the

    variation

    of

    speed with load

    to

    reduce

    fuel

    consumption.

    The

    power conditioner provides

    the functionality to

    allow

    the MTG to

    operate

    in

    parallel w ith

    the

    u tility supply

    in

    various modes

    or as a

    stand-alone system. Integrated engine control

    an d

    3

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    4 Micro turbine Generators

    management capability, together with remote control

    an d

    monitoring,

    is

    either

    a

    further

    feature of this module or is provided by means of separate modules.

    1.1.5

    Gas

    boost compressors

    Natural

    gas is the fuel of

    choice

    for

    stationary power plant. Pipeline

    gas is

    usu ally supplied

    to

    small users at low

    pressure

    typically less than 1 psi. An MTG requires gas at 60-80 psi;

    therefore

    an efficient, low-cost, durable, gas boost compressor is needed.

    Su itable technology

    is

    being developed

    in

    association with experienced

    air and refrigeration

    compressor manufacturing companies and commercially acceptable units are available from

    tw o

    suppliers

    subject to

    completion

    of certification. It is

    thought that more suppliers will

    offer

    product as the M TG

    indu stry need grows.

    1.2 Bowm an Technology

    1.2.1 Micro turbine engines

    These first generation, very small, high-speed, gas turbine engines are simple radial designs,

    and as stated earlier, they are closer in concept to low-cost turbochargers than the more

    complex

    and

    costly axial designs

    of

    large industrial engines which

    are

    often derived

    from

    aero engines.

    A

    bearing system

    is

    required

    to

    support

    the

    high-speed rotating shaft;

    the

    bearing system also

    has to

    oppose

    the

    axial

    forces

    generated

    by the

    aerodynamic load.

    Any

    contacting/rolling element bearing will

    be life

    limited

    due to the

    contact

    forces

    the

    bearing

    is

    exposed

    to; for a

    system with

    an

    installed

    life of circa five

    years between

    major

    engine overhauls, contacting bearings should be avoided if possible.

    There has been experimentation with gas turbines in the power ranges of

    25-400

    kW for

    around

    50 years. The earlier developers of engines in these power ranges include Rover,

    Austin, Ford, GM, and Chrysler, all being automotive biased. These engines all used

    reduction gearboxes

    an d

    could

    n ot

    meet

    the

    ef ficiencies

    and

    man uf acturing costs achieved

    by

    reciprocating engines at the time, where a large component of the cost was the reduction

    gearbox.

    Although this type

    of

    technology

    has

    excelled

    in

    auxiliary power unit (APU) applications

    in

    the aerospace industry, the production volumes have never been high. Typically, total

    production numbers fo r

    aircraft

    AP U s will be less than 10 000 u nits over 10 years, i.e.

    circa

    1000 units

    pe r

    year. These engines

    are

    typically

    life

    limited

    to

    circa

    10 000

    hours, which

    is

    no t suitable for cogeneration an d prime power application requirements an d they are

    expensive due to the aerospace quality production systems andaccessoriesused, and their low

    productionvolumes.

    Micro-turbine

    production is benefiting from the technologies developed for automotive

    turbocharger

    applications, where the worldwide production of these devices exceeds

    50

    000 000 u nits a year (KKK, Garret, IHI, Su ltzeret al. .

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    An

    Introduction

    to

    Micro turbine Generators

    5

    The

    enab ling technologies

    fo r

    m icro-turbine systems

    h as

    matured over recent years, becoming

    more

    accessible an d cost competitive. These include the electronics fo r power conditioning,

    high-speed alternator, ana lysis and design of high-efficiency radial turbomachinery, and low-

    cost production techniques of radial turbo machinery components.

    The primary objectives of the initial MTG design are that the engine should be low

    cost,

    durable, and of reasonable efficiency. There is little difference in the materials selected and

    the manufacturing

    processes

    for the manufactured engine components used by the major

    micro-turbine engine suppliers.O ne of the main

    differences

    in the alternative design concepts

    is in the type of bearing system used in the machines.

    It

    is

    widely accepted that

    the

    Capstone Turbine Company

    ai r

    bearing technology

    has

    significant technical advantages, such as lower bearing losses than with oil lubrication and the

    elimination

    of the oil

    system components.

    It is fair to say

    that

    in

    some quarters this

    is

    considered to be current state of the art.However, there are

    successful

    alternative designs that

    make use of a variety of oil-lubricated bearings to support the rotating elem ent.

    Bowman

    experience

    is

    that

    the use of an

    inboard, oil-lubricated,

    tilting pad

    bearing provides

    long and trouble free

    life,

    while th e alternatively used oil-lubricated plain journal bearing at

    this location

    suffers

    high losses, and rolling element bearings w ill provide

    insufficient life.

    The second generation engines will possibly use active magnetic bearings, which offer

    advantages

    over ai r bearings in

    that

    th e axial clearance of the compressor can be actively

    controlled

    du ring operation to maximize the engine efficiency, and the bearing control system

    can

    be

    used

    fo r

    real-time condition mon itoring.

    A major

    benefit

    of micro-turbines is the low emissions NO

    X

    ,CO) compared with

    conventional reciprocating engines. The combustor design is critical to achieve low

    emissions.

    The

    best emission values achieved

    by any

    micro-turbine manufacturer

    to

    date

    are

    less than 10 ppm NO

    X

    ,on gaseous

    fuels.

    No company is currently claiming better than 25

    ppm NO

    X

    on

    liquid

    fuels.

    Catalytic combustion is an alternative to conventional combustion and the progress of this

    technology will be closely monitored over th e next few years to determine its suitability fo r

    use

    in MT G s. It is known that experimental machines using catalytic combustion have bee n

    developed to prototype stage in USA and Japan although there has been no commercial

    release of such machines.

    1 2 2 Turbo alternator

    1 2 2 1 Introduction

    The high-speed turbo alternator

    is a key

    element

    in MTG

    technology. Over

    a

    period

    of

    seven

    years, Bowman has worked with a number of different electrical machine companies, and

    individual consultants worldwide, and has built on that experience, aiming always to

    internalize its design capability and establish an independent expertise. These machines are

    highly stressed electromagnetically, m echanically, and therm ally, and complex in th eir detail;

    there

    is

    much that needs

    to be

    understood before they

    can be

    designed with confidence

    fo r

    long

    working life.

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    6 Micro turbineGenerators

    On the

    manufacturing

    side

    particularly

    in the

    areas

    of

    core assembly

    and

    winding, magnet

    provisionand

    bonding,

    and

    sleeve construction

    and

    pre-stressing, there

    are a

    small number

    of

    capable suppliers with

    the

    necessary capability

    and

    expertise

    to

    provide components

    and

    sub-

    assemblies

    to the

    quality required. Several

    of

    these have come

    from

    the

    aerospace industry.

    Bowman possesses

    a

    deep understanding

    of

    machine topologies alternative

    to the

    synchronous permanent-magnet PM) drum type. It has for a long time had an association

    with Southampton University, cemented by a key dual appointment, andbenefits in many

    ways: e.g. finiteelement studiesofmachine configurations, modelling of complete electrical

    system performance, development

    of

    proprietorial design software,

    a

    research programme

    in

    certain

    types

    of

    rotor power loss, micro-structure examination

    of

    material sections, etc.

    Intermsofspecific

    output

    powerortorqueperunit volumeor perunit mass) and

    efficiency,

    thehigh-speed generator

    is far in

    advance

    of the

    conventional synchronous machine

    of

    similar

    power output. Designs arecurrently being manufacturedandsupplied inquantity, atpowers

    from 40 to 165 kW,with speeds rangingfrom 105 000r/minto 55 000r/min. Confidence in

    the

    technology

    issu fficiently

    high that machines have been designed

    at 300 kW, 500 kW , and

    atmore than

    1 MW.

    The values

    of

    power density

    and efficiency

    achieved

    in

    high-speed alternators

    are now

    both

    sufficiently

    high that there

    is

    really little pressure

    - and

    also,

    it

    must

    be

    said, little scope

    - for

    further improvement. The electro-magnetically active parts of an alternator providing

    165 kW, for

    example, corresponding very roughly

    to the

    average power demand

    of

    some

    35 domestic houses, pack into

    an

    overall length

    of

    about

    270 mm and a

    diameter

    of

    about

    120 mm, and

    produce little more waste heat

    as

    loss power) than

    a

    two-bar electric

    fire.

    Furthermore,becausethemachineis sosmall, therearetypicallynouncontrollable problems

    due to

    resonant vibrations

    of the

    complete shaft system within

    the

    rated speed range;

    centrifugal force is not so

    high

    as to

    prevent

    the

    rotor being held

    safely

    together

    by a

    containing sleeve;

    and

    bearings

    are not

    made excessively large and expensive)

    by an

    unduly

    heavysupported rotor mass.

    Figure 1.2 illustrates a 50 kW high-speed alternator rotor mounted with the gas turbine

    compressor andturbine wheelsand in the foregroundan 110 kWhigh-speed alternator rotor.

    Length

    of

    this rotor

    is

    about

    250

    mm.)

    Fig 1 2 urbo alternator

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    An

    Introduction to

    Micro turbine Generators

    1.2.2.2 echnology comparison

    1.2.2.2.1 PM drum type heteropolar

    The heteropolar drum-type machine, incorporating rare-earth permanent magnets, with

    electro-magnetic stator-rotor interaction

    acrossa

    radial gap,

    is the

    industry preferred topology

    having

    been adopted by most leading manufacturers.

    It

    is known that as power rating increases the optimum design speed for the

    turbine/compressor necessarily reduces- principal constraints being the internal mechanical

    stress

    due to centrifugal force and

    system dynamic considerations. Very similar

    effects

    apply

    in the drum-type PM m achine, and all design experience has shown that there is a good m atch

    between

    the

    optimum speed

    of

    turbomachinery

    and

    alternator, which therefore mount

    naturally together on a common shaft. This is true, in particular for the single-shaft

    arrangement, in which the po wer turbine, and therefore alternator, rotate at the full speed of

    that

    shaft. It follows that the alternator is also easily designed for the alternative, dual-shaft, o r

    free

    power turbine arrangement,

    in

    which

    the

    power turbine runs

    at an

    independent speed,

    lower

    than

    that of the m ain turbine shaft.

    1.2.2.2.2

    PM disc type

    This alternative topology has it s champions and comprises a multiplicity of interleaved

    stator-rotor discs with axial gaps. The Bowman view is that the disc approach is limited in

    speed and sub-optimal in other performance parameters. The disc-type alternator finds

    practical app lication in com bination w ith a free power turbine, as described above, rather than

    in higher speed,

    and

    cheaper, single-shaft arrangements. Interleaving discs

    are

    awkward

    for

    assembly/disassembly,

    and the

    structure

    is not

    cheap

    to

    manufacture. Magnet surfaces

    are

    necessarily exposed or thinly covered, with risk of corrosion, disintegration, and

    dispersal

    of

    this brittle material within the machine over time, whereas in the drum structure the magnets

    are

    completely

    and

    tigh tly enclosed.

    1.2.2.2.3

    Bowman

    designfeatures

    Winding

    configuration

    The preferred winding arrangement is not simple three-phase, but double three-phase with

    two sets of three-phase w indings lying in adjacent slots. The effect of this is greatly to

    reduce

    important components

    of

    internal stray power

    loss.

    Side effects that must

    be

    accepted

    are a

    doubling of the number of connection leads and a need for two (each half-rated) external

    rectifier b ridges instead of one.

    Rotor

    s tructureandre taining sleeve

    A pre-stressed retaining sleeve, to hold the magnets on to the steel hub against centrifugal

    force,

    is essential. Preferred material is carbon fibre which

    offers,

    at present the highest

    lightness-strength combination of any established technology and is electrically inert.

    Bowman conclusion, based on some six years experience, is that with proper control of sleeve

    manufacture

    and

    assembly

    and attention to simple but critical mechanical features, carbon-

    fibre technology is the best currently available.

    Alternative

    designs using inconel and titanium sleeves are available, and are used by other

    manufacturers.

    7

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    Micro turbine Generators

    Thermal design

    and ooling

    The standard cooling arrangement

    is an

    external cooling jacket

    to the

    stator core, with water

    or oil

    coolant,

    and an

    internally

    forced flow of

    cooling air, typically

    at a few

    litres

    pe r

    second

    flow

    rate. Inlet coolant temperatures

    are 70 C as

    standard, allowing ample headroom

    for

    remote heat exchange between thehottest design ambient of 45 C and the inlets. Alternative

    designs

    for

    external air-cooling

    are

    available, though

    possibly

    with some penalty

    on

    specific

    output.

    Internal hot-spot temperatures arekept below about 160 C compatible with modern

    wire enamels thatoffergood resistance

    to

    high rates

    o f

    change

    of

    voltage.

    ynamics

    To enable successful designs

    to be

    completed

    in a

    timely

    and cost-effective

    manner,

    it is

    essential that

    capabilities

    for computer-modelling

    mechanical stress

    distribution and

    dynamic vibration/resonance/unbalance effects are available. Dynamic studies of the

    complete turbine/compressor/alternator assembly,

    and

    accurate modelling

    of

    bearing

    and

    blade contributions to stiffness and damping, form an important component of necessary

    technical expertise.

    esign

    software

    Overtheyears, Bowman hasbrought togetheritsaccumulated expertisein PMalternatorand

    motor design,

    and has

    codified this

    in a

    proprietary, advanced-software design package. This

    isa

    highly supportive application, which guides

    the

    user

    in the

    process

    of

    entering

    raw

    data,

    preventing

    for

    example

    the

    insertion

    of

    incompatible groups

    of

    dimensions;

    defines the

    precise meaning

    and

    units

    of

    each displayed item; then draws

    a

    cross-section

    of the

    machine

    and

    computes

    a

    large

    field of

    electrical, mechanical,

    and

    thermal performance parameters.

    Alternative materials

    may be

    selected

    for the

    laminated core, retaining sleeve, conductor,

    coolants, etc.

    The workofdeveloping this

    software

    has been substantial, and was undertaken because no

    available

    software

    couldbe

    found

    that

    offered

    either

    sufficient

    accuracyorversatility.

    The softwarehas not

    only greatly accelerated

    the

    design process,

    but

    because

    so

    manycases

    can be

    readily studied,

    it

    enables

    far

    more detailed exploration

    of

    possibilities

    and the

    development

    of

    greater intuitive appreciation

    of

    parameter sensitivities

    in

    design.

    2 3 ecuperators

    Durable heat exchangers ofhigheffectivity and low costareneeded toincreasethe efficiency

    of

    gas

    turbines

    to the

    levels needed

    to

    compete with reciprocating engine-based power

    generation systems. Their function

    is to

    extract heat

    from the

    gas-turbine exhaust gases

    in

    ordertopreheat the airusedin thecombustion process andthereby reduce theamountof fuel

    used

    to

    reach operating temperature.

    The

    current Bowman recuperator

    is a

    primary

    surface

    recuperator (PSR), manufactured

    from

    stainless steel

    for

    long

    life.

    With

    an effectivity of

    about

    90 per

    cent,

    the fuel

    consumption

    of the

    micro-turbine engine

    is

    approximately halved, which doubles

    the MTG

    efficiency from 15 per

    cent simple cycle

    to about 30 per

    cent recuperated cycle.

    Refer to

    Fig.

    1.3.)

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    An

    IntroductiontoMicro turbine

    Generators

    Fig.

    1.3

    Cyclearrangements

    The

    majority

    of

    micro-turbine manufacturers consider stainless steel primary surface

    recuperators and users to be the current state of the art, although there are users of an

    alternative

    recuperator design utilizing brazed plate

    and fin

    technology.

    hi the PSR

    design

    the

    plates

    forming

    the air and gas

    paths

    are not

    bonded brazed) together.

    They

    arewelded aroundtheedge,but areclamped together thus allowing movementdue to

    thermal

    expansion without the high stresses being transmitted to the

    joints

    as in the brazed

    structure.

    This

    is

    considered

    to

    give potentially higher reliability

    and

    durability

    due to the

    lower

    potential

    for

    thermal stress failure

    and

    consequential leakage.

    Refer to

    Fig. 1.4.)

    Fig 1 4

    ecuperators

    9

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    1

    Micro-turbine Generators

    further

    difference is in the use of annularor box arrangementsto integratet herecuperator

    to the gas turbine engine.

    Annular

    is a

    concentric recuperator

    that

    wraps around

    the

    engine

    and

    generally

    has all of

    the interconnection pipe work as part of the casing.

    Box is a cuboid shape that sits outside the engine envelope and requires interface

    connection pipework.

    There

    are

    pros

    and

    cons

    for

    both types

    of

    technology

    asdetailed

    below.

    Parameter

    Initial development cost

    Integration cost

    Thermal soak back to

    engine coreafter

    prolonged operation

    Package thermal

    management

    Package assembly time

    Interface issues

    ox

    Lower

    Higher

    Noissue

    Higher radiated losses requiring

    more thermal insulation

    and

    hence higher cost

    Higher

    Three more interfaces withengine

    and recuperator to consider at

    package level-engine casings

    have to be manufactured to

    reasonable tolerances to

    guarantee interchangeability

    nnular

    Higher

    Lower

    Potential issue requiring

    prolonged shut down

    phase to cool recuperator

    Lower radiated losses

    requiring

    less thermal

    insulation and lower cost

    Lower

    Allrecuperator interfaces

    are withintheengine,

    therefore only one

    interface exhaust)

    required

    to be considered

    at

    package level

    Bowmanhas considered all of the above interface issues at the recuperator design stage, and a

    cuboid recuperator, close coupled to the engine, is currently their

    preferred

    approach. An

    example of a cuboid recuperator close coupled to the engine is shown in Fig. 1.5.

    Fig 1 5 Cuboid recuperator

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    12 Micro turbine Generators

    1 2 4 4

    Utility

    mode operation

    The system is capable of operating in parallel with the utility. This mode is particularly cost

    effective

    as asite s

    base load

    can be

    efficiently supplied while planned long-

    or

    short-term

    overload requirements

    are

    supported

    by the

    utility.

    1 2 4 4 1

    Export

    mode

    The system can export power to the utility and meets current harmonic limits defined in

    specification IEEE 519

    2).

    1 2 4 4 2 Load following

    mode

    A

    load following mode allows on-site power generation

    to be

    balanced with site demand

    resulting in zero power

    flow

    to, and in some cases from, the utility. This maximizes the

    benefits of embedded generation where no agreement has been made with the utility on

    purchase terms for exported power, i.e. the optimum amount of low-cost, embedded

    generation is always produced without consuming additional fuel to export power to the

    utility.

    1 2 4 4 3

    Peak shaving mo de

    The system can be operated just during times of peak demand, which reduces the tariff paid

    by the customer to the utility as this is usually set by his max imu m site dem and.

    1 2 4 5 Dual mode switching

    Switching between island mode

    an d

    utility mode operation

    is

    available

    by

    means

    of a

    proprietary switching unit. This enables

    the MT G to

    serve dual functions

    of

    prime power

    an d

    stand-by pow er generator

    from one

    ratherthan

    tw o

    systems.

    1 2 4 6

    Power condit ioningsystem elements

    Thepower conditioning system comprizes of a solid-state power converter assembly, power

    filter,power controller, andmanagementof the utility interconnection.

    A typical systemisshown in Fig. 1.6.

    High

    efficiency

    * IGBT technology

    *

    Solid

    state

    high reliability

    Aircooled

    Programmable voltage/current/

    fr qu n y

    * Voltage

    L-L rm s.) 400-480,

    3

    phase,

    50-60Hz

    * Integratedgas

    turbine start

    facility

    Fig.

    1.6

    Power conditioning units PCUs)

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    Micro turbine

    Generators 13

    Thesolid state

    power converter consists of rectification, power boost, and inverter stages.

    Efficient

    power conversion and

    effective

    thermal management allow

    full

    power operation

    over

    a

    wide tem perature range.

    Bowman

    has developed and patented an innovative cooling technique that achieves very

    effective

    thermal

    transferat low

    cost.

    The power electronic assembly synthesises the high quality output waveform using a pulse

    width mod u lating PW M) switching technique.

    The

    power

    filter

    efficiently

    removes

    modulation frequency components from the output

    waveform.

    Advanced materials are used

    for the filter elements in order to minimize power loss and permit operation with severe

    electrical loads.

    1 2 5 Engine managem ent

    and

    control

    Bowman has over five years experience developing controllers for a variety of micro-turbine

    engines. The

    features

    of the engine controller inclu de:

    au tomated start sequence;

    batteryoru tility start;

    gas orliquidfuel algorithms;

    recuperated

    or

    simple cycle engines;

    fault detection

    and

    protection;

    advanced

    user

    interface.

    Thedesign isfully digitalso it has theflexibilityto beadaptedfor arangeo fengine typesand

    sizes. Each type of engine has its own

    fuel

    system, starting characteristics, running speed, etc.,

    and all these va riations are accom modated within the same controller.

    Digital control also gives precise and repeatable control of engine

    speed

    and load transients.

    Where appropriate the engine controller can also interact with other parts of the generator

    control system, for example, by asking for the power output to be reduced if the engine is

    running

    near its max imu m permitted temperature.

    All

    the engine systems are monitored to

    verify

    good health and correct operation. Critical

    systems oil pressu re and engine speed) also have additional,

    software

    independent, backup

    monitoring. This data may be

    accessed

    both locally and remotely, and is used extensively by

    the technical and support teams, and is also available to the customer. Special

    software

    tools

    have

    been developed in-hou se to assist with the development and proving of engines, starting

    algorithms and control algorithms.

    Advanced controls already developed include:

    constant exhau stgastemperatu re E GT) run ningforoptimu mefficiency an d emissions;

    variable speed operationtooptimize

    efficiency

    andem issionsatpart load;

    bypass valve control orvariable heat ou tput;

    gassafetymonitor.

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    1.2.6

    as

    boost compressors GBC)

    The GBCmust

    deliver

    natural gas at apressure higher than the airpressure in the MTG s

    combustion chamber.Forexample, if the micro-turbine engine s airpressure ratio is4.5, then

    the GBC

    should

    be

    capable

    of a

    pressure ratio slightly over 4.5. Therefore,

    a

    design pressure

    ratioof 5 isassignedto theGBC.

    The

    efficiency

    of the GBC impacts theMTG s overall efficiency. A n increasing GBC power

    draw lowers the turbo generator

    efficiency.

    The MTG s

    efficiency

    drops sharply when the

    GBC efficiency fails

    below

    0.20, therefore, to enableit to efficiently generate electricity at or

    about

    thetarget of 30 percent the GBCsystem efficiency must remain well above 0.20.

    From

    calculations an d test verification, it hasbeen determined that about 2.5 per cent of the

    power output of a 50 kW MTG is used to compress the

    fuel

    gas. This does not take into

    account

    themotor or coupling efficiency. The electrical-to-mechanical efficiency of a 5 hp

    motor

    is about 0.80 an d when this is taken into account, the power requirement of the

    compressor system is about 1.5 kW.

    The MTGmarketwill include power users, such as office buildings, apartment complexes,

    an d

    small businesses, where minimal involvement in the power source is aprerequisite. A

    design

    requiring minimal maintenance is consequently needed if the MTG is to be well

    received.

    Bowman has evaluated tw o types of compressor for usewith its range of MTGs. These are

    the sliding vane and the scroll types of

    compressor;

    the merits of each are discussed as

    follows. A typical sliding vane packaged unitisshown in Fig. 1.7.

    High reliability

    High

    efficiency

    * Self con tainedpackage

    * Compact

    *

    Low

    cost

    * Low oil

    consumption

    * Low maintenance

    * Acoustic attenuation

    * Easy

    installation

    Fig

    1 7 Gas

    boost compressor

    2 6 liding vane compressors

    Thesearepositive displacement compressors that operate in thefollowing cycle:

    gas isdrawn into the suction side andisolated within a chamber;

    the gas isthen compressed byreducing thechamber s volume;

    gasexitsthe compressor through discharge ports orvalves.

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    An Introduction to Micro turbine Generators 15

    Sliding vane compressors consist of a rotor, vanes, and a cylindrical easing. The rotor is

    mounted eccentrically in the casing. Machined slots in the rotor guide

    flat

    rectangular vanes.

    These vanesa re

    free

    to move in the slots and are held against the casing by centrifugal force.

    As the rotor turns (typically at250-1200 r/min), pockets, which increase then decrease in

    volume, are created. Gas is drawn into the expanding pocket and compresses as its volume

    decreases. The cross-section of a sliding vane compressor is shown in Fig. 1.8.

    ig 1.8 Gasboost compressor GBC)- rotary vane type

    Vane

    wear is the greatest maintenance concern in sliding vane compressors (not bad though in

    flooded types). The vanes remain in contact with the casing a s they wear, bu t eventually they

    run

    the risk of becoming too short and may break causing damage to the compressor.

    Sliding vane compressors are a favoured GBC option because they meet the flow rate and

    pressure ratio requirements. In lubricated versions, Pr = 4 may be reached in a single stage. In

    addition,

    the

    discharge

    is

    nearly pulsation

    free,

    thereby reducing

    or

    eliminating

    the

    need

    for

    an accumulator tank.

    1 2 6 2 croll

    type

    compressor

    The compression cycle

    of

    scroll compressors

    is

    less

    intuitive

    than most other compressor

    types. There

    are

    three main parts

    - a

    stationary scroll,

    an

    orbiting scroll,

    and a

    casing. Both

    scrolls are identical, with one rotated 180 degrees out of phase from the other. The orbiting

    scroll

    is

    attached

    to an

    eccentrically mounted shaft. This shaft orbits

    the

    moving scroll about

    the stationary scroll s centre. A sectional view of a scroll compressor is shown in Fig. 1.9.

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    16

    Micro turbine

    Generators

    ig 1.9 Gas

    boost compressor GBC)

    scroll type

    A

    crescent shaped cavity

    is formed at the

    outside edge

    of the

    contacting scrolls.

    Gas

    enters

    this cavity through

    the

    suction port.

    As the

    moving scroll orbits

    the

    stationary scroll

    the

    cavity s size

    is

    reduced until

    it

    reaches

    the

    discharge port

    at

    their centre.

    A

    graphic

    of

    this

    motion can be

    found

    on Copeland Corporation s web page at http://ww w.copelan d corp.

    com/airconditioning/scrollintro.html

    Scroll compressors have several advantages that enhance their potential

    as

    suitable micro-

    turbinegas

    boost compressors:

    their volumetric an d isentropic efficiencies are high in fact scroll efficiencies exceed

    reciprocating efficiencies;

    thereisonlyonemoving part;

    theyareavailableforsmall capacities;

    there

    is no

    clearance volume.

    Scroll compressors are widely used in refrigeration applications (air conditioners) an d have

    recently been converted

    to air and gas

    compressors. Pressure ratios reach

    as

    high

    as

    eight

    in a

    single stage, while capacities

    are low

    compared

    to

    most compressor types. These features

    make them suitable for MTG applications.

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    An

    Introduction

    to

    Micro turbine Generators 17

    1 3 Bowmancogeneration CHP)system

    The Bowman cogeneration system consists of an MTG integrated with a waste heat recovery

    boiler to provide a compact, high

    efficiency

    low emission, and vibration

    free

    system

    producing heat

    and

    electrical power.

    The

    system

    is

    shown diagrammatically

    in

    Fig. 1.10.

    Fig 1 10 BPS Cogen System

    Cogeneration CHP) systems burning natural

    gas

    incorporate

    two key

    areas

    of

    technology:

    waste heat recovery boilers;

    chillers/refrigeration systems.

    High-efficiency

    stainless-steel, waste heat boilers have been designed and integrated into the

    cogeneration package to enable hot water, typically at 90 C, to be produced

    from

    the exhaust

    gas

    stream.

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    Micro turbineGenerators

    It is

    possible

    to

    produce chilled water

    from the

    exhaust

    heat

    through

    the use of an

    absorption

    chiller

    driven either directly

    from the gas

    turbine exhaust stream

    or

    indirectly

    from the hot

    waterfrom the

    waste heat boiler. Several

    of the MT G

    manufacturers

    are

    evaluating alternative

    designs

    of

    chillers

    and

    alternative chiller suppliers with

    an aim of

    commercially introducing

    a

    suitable product

    in

    2002/3

    for air

    conditioning applications.

    In

    order to increase the

    efficiency

    of the hot water absorption chiller the hot water is produced

    at

    110 C forthis typeofapplication.

    1.4

    Benefits

    and

    advantages

    of the

    Bowman turbogen

    cogeneration product

    1.4.1 Recuperated or simple cycle configuration

    The micro-turbine engine can be configured in either of the above modes to enable the

    cogeneration system

    to

    best match

    the

    customers site needs.

    The

    recuperated machine provides

    a

    heat

    to

    power ratio

    of

    about

    2:1 and an

    overall system

    efficiency ofabout80 per cent. Whereasitehas aneed fo rmore heat up to aheat to power

    ratio of 4:1 then a simple cycle system can be installed. In this latter case although the

    electrical efficiency naturally falls the overall system efficiency can

    rise

    to around 90 per

    cent. The use of a simple cycle system can be particularly advantageous if it enables a site

    boiler to be decommissioned or eliminates the need for a new purchase.

    1.4.2 Environmentally friendly

    The

    Bowman cogeneration system

    is

    environmentally

    friendly in

    that

    the NOx

    emissions

    from

    the

    machine when operating on natural gas are no more than 20 ppm by volume. It is

    confidently predicted that this level will

    fall to

    single digit values within

    the

    next

    one to two

    years

    and in

    factsome machines

    are

    already achieving this value.

    The

    design target

    for

    diesel

    and

    kerosene

    fuels is to

    achieve below

    25 ppm NOx

    although this

    is

    a

    much more challenging target

    due to the

    more

    difficult

    atomization

    and

    combustion process

    of

    these

    fuels

    particularly when considering

    the low

    cost requirement

    of the fuel

    system.

    1.4.3 Fuelflexi ility

    Naturalgas is the

    primary

    fuel of

    choice although

    the

    need

    to

    burn propane

    fuel

    light

    diesel

    and

    kerosene

    is

    essential

    to

    gain penetration

    of

    certain markets.

    It is now

    possible

    to

    select

    engines

    to

    reliably achieve

    effective

    combustion

    of all

    these

    fuels.

    To expand the market for the micro-turbine product then capability to bum digester gas

    landfill gas coal seam gas flare gas and low calorific value man ufactured gas e.g. wood

    gasification

    gas

    is

    necessary.

    Progress

    is

    being made

    in the

    development

    of

    suitable

    combustors

    to

    enable

    all

    these gases

    to be

    burned economically

    and

    with

    low

    exhaust

    gas

    emissions. There

    are

    several

    pilot project

    schemes underway

    to

    address

    the

    combustion

    of all

    these gaseous

    fuels.

    1.4.4 Simplicity of design and operation

    There are few moving parts in an MTG system in some cases only the single rotating

    element. This naturally leads to a highly reliable system with limited needs fo r routine

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    AnIntroductionto Micro turbineGenerators 19

    maintenance and low

    consumption

    of

    spare parts. When evaluating through life costs

    of a

    system

    then

    these benefits

    an d

    advantages

    are

    very significant

    in

    comparison with

    reciprocating engine systems.

    A further benefit of

    this simplicity

    of

    design

    is the

    tremendous potential

    fo r

    low-cost volume

    manufacture. The parts count is dramatically reduced in comparison with alternative

    technologies.

    1 4 5 Modular design

    of

    compact size

    and low

    weight

    The

    factory

    assembled and tested packag e system is easy to install, it s compact size and

    low weight being easily handled and requiring little specialist skills to install correctly. The

    civil

    engineering

    costs

    are

    inexpensive

    due to the

    small footprint

    of the

    system

    and

    also

    due to

    the fact that the

    m achine

    is

    virtua lly vibration

    free.

    These

    features

    no t

    only eliminate

    the

    need

    for a

    costly foundation block

    bu t

    also eliminate

    the

    need

    fo r

    expensive isolation devices

    to

    prevent

    the transmission of structure borne noise and vibration.

    The

    standard modular approach

    to the

    package design allows

    the

    addition

    (o r

    removal)

    of

    further

    systems

    as an

    initial site load grows

    or

    reduces. Therefore

    the

    standard range

    of

    packaged systems allows loads of 30 kW to 1000 kW to be

    effectively

    addressed both

    technically

    and comm ercially an d also in a timely convenient m anner.

    1 4 6 Modern electrical design

    The

    use of advanced insulated gate bi-polar technology (IGBT), together with modern

    flexible

    software

    algorithms, allow

    the

    electrical output

    from the

    system

    to be

    selectable

    between 380 and 480 volts AC, 3 phase, 50 or 60 Hz frequency to match most of the worlds

    low voltage systems.

    The standard system has built-in protection fo r under an d over voltage, under and over

    frequency,and reverse

    power

    which a re norm ally required by the utility to allow permission

    for parallel operation.

    The

    widespread dispersal

    and

    need

    for

    cost

    effective

    despatch

    and

    maintenance necessitates

    the supply of a remote control and mon itoring system. A ll Bowman cogeneration systems are

    capable of being so monitored and the Customer Support Department uses this tool as a key

    elementin the

    provision

    of a range of support programmes tailored to suit the specific needs

    of

    it s wide range of customers.

    1 5

    onclusions

    The

    micro-turbine industry is rapidly becoming established although the projected high

    volume m anufac turing levels are yet to be realized.

    There are in 2002,

    four

    or five companies making commercial shipment of systems

    worldwide.

    Systems

    are

    available

    from

    approximately

    30 kW to 150 kW

    electrical output,

    suitable

    for operation on a variety of gaseous and liquid

    fuels.

    The

    distributed power generation market (DG) is being addressed in several key high added

    value sectors such as cogeneration and trigeneration, W aste gas utilization, secure pow er, and

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    20 Micro-turbine

    Generators

    mobile power.

    As sales

    volumes increase then

    the MTG

    cost will reduce enabling

    further

    more cost conscious sectors of the DG m arket to be addressed.

    The

    technology

    is

    largely proven

    and

    this C hapter sought

    toidentify and

    describesome

    of the

    generic

    and

    alternative technologies

    in

    use

    There remain several significant regulatory market barriers to be crossed to facilitate

    extensive market penetration by small DG systems. For example,accessand connection to the

    utility

    networks requires new standards and regulations, which recognize the new technology

    and

    the different way of

    doing things. Similarly, there

    is

    currently little commercial

    recognition

    of the low

    emission

    features and

    environmental benef its resulting

    from the use of

    these systems. However, these obstacles

    are

    being addressed through trade associations

    and

    by

    m anufacturers,

    and

    will

    be

    overcome

    in due

    course.

    cknowledgements

    ToBowm an Power Systems Limited,

    for

    giving permission

    for

    this Chapter

    to be

    published

    eferences

    1) EN 50081-1 Electromagnetic Com patibility. General Emission Standard. Residential,

    Commercial and

    Light industry.

    2)

    IEEE

    519

    Recommended practical requirements

    fo r

    Harmonic Control

    in

    Electrical

    Power Systems.

    Bullin

    Bowman Power SystemsLimited

    Southampton UK

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    Micro turbine Generators

    Next

    Generation

    S

    L

    Hamilton

    bstract

    Micro turbinegenerators (MTGs) have been

    identified

    by the US Department ofEnergyas

    one of the 27critical technologies for the United States. It hasonly been in the past three

    years that MTGs have become commercially available for sale to end users, utilities, and

    energy service providers.

    Southern California Edison (SCE) has established an MTG testing programme for

    manufacturers andothers toevaluatethecertainperformancecapabilitiesof theturbines.The

    purpose

    of

    this programme

    is to

    provide

    an

    independent, third-party, testing

    assessment

    This

    projectpurchased, installed, operated,

    and

    tested micro-turbines

    toassess their

    performance.

    Data

    was

    collected electronically

    and

    manually.

    This Chapter will discuss

    the

    next generation

    of

    MTGs.

    2.1

    MT S nextgeneration

    Recently,

    the US

    Department

    of

    Energy (DOE)

    has

    identifiedturbines

    as one of the 27

    critical

    technologies for the USsecurityandprosperity.Assuchthe DOE

    offers funding

    for research,

    development, anddemonstration (RD D) for MTG and MTGcomponent development, such

    as

    ceramic materials.

    The DOEuses three important criteriatoaward

    funding:

    1. reduction

    of

    energy consumption;

    2. improvementinenvironmental conditions, suchasemissions; and

    3

    improvement

    in the

    overall economics

    of the

    technology.

    2

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    22

    Micro turbine

    Generators

    SCE

    conducts a unique micro-turbine testing programme for DOE, the California Energy

    Commission,

    and

    EPRI.

    The

    testing

    is at

    SCE s

    host site. This site

    is at the

    Combustion

    Laboratory at the University of California (UC I) in Irvine, C alifornia. UC I was chosen

    because of its robust advanced power programme featuring both an educational and research

    facility

    built around energy technologies. The programme relies on the National Fuel Cell

    Research

    Center,

    the

    world-renowned Combustion Laboratory,

    and UCFs

    Distributed/Dispersed Energy Technologies programme and demonstration facilities,

    including the developm ent of an inverter laboratory, all housed at UC I.

    SC E s testing programm e began

    in

    1996.

    It has

    tested MTGs

    from

    Capstone Turbine

    Corporation

    and

    Bowman Power Systems. Until recently,

    no

    other turbines have been

    available for purchase and testing under the programme, although a Honeywell MTG has

    arrived for installation and testing. The programme is attempting to purchase and test MTGs

    from E lliott E nergy and new models from Capstone.

    Our programm e tests the MTGs for machine performance. It tests MTG s performance against

    its m anufacturer s performance claims for efficiency, emissions, and noise. MTGs are also

    tested against applicable industry standards, such as power quality and/or local requirements,

    such

    as the

    South Coast

    Air

    Quality Management District s

    air

    q uality standards.

    In

    addition,

    qualitatively assessed

    are the

    ease

    of MTG

    installation

    and

    startup, maintenance

    and

    operation,

    an d

    overall machine performance.

    A

    daily

    log is

    m aintained

    by the

    testing crew

    to

    ensure the integrity of the testing results and to record events to explain the data captured.

    Testing

    results include:

    Starts stops

    Ideally number of planned starts and stops are equal. A variation in the

    number of attempted starts without a planned stop indicates that the machine is

    experiencing problems.

    Overa ll unit efficiency and netpower

    output

    Based on actual conditions the machine

    should provide - a level of

    efficiency,

    within a small tolerance, as

    predicted

    by, and

    consistent with,

    the

    derating curves provided

    by

    m anufacturer.

    Operability

    Subjective assessment of the mach ine s ease of operation, performance

    reliability,

    and

    consistency,

    and its

    ease

    of

    return

    to

    operations after experiencing

    operational problems.

    Emission

    level

    monitoring

    Within

    a

    small tolerance, emissions

    are

    expected

    to be

    within

    manufacturer s claims for NOx and CO.

    Powerquality monitoring

    M easures distortion individually for current and voltage. Both

    voltage and current distortion should be below the IEEE 519 standards under actual

    consistent conditions as described in the standard.

    Enduranc e testing- Is a

    measure

    of

    longevity

    of the

    MTG. Most have

    an

    advertised

    life of

    40

    000

    hours. NREC advertises

    80 000

    hours.

    As a part of the testing programme, SCE has established facilities a t UCI that provide a level

    testing field for all MT Gs. MTG s are equipped with data acquisition equipment to ensure

    that

    data

    is

    captured

    on a

    real-time

    basis.

    A

    veteran, on-site, three-person, testing crew also

    reviews

    the electronic data capture with manual measurements to ensure that electronic

    capture is consistent with physical experience.

    The

    testing crew activity interacts with technical staff

    from the

    manufacturers.

    An

    essential

    part

    of the testing programme is to provide written feedback to each manufacturer, on an

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    Micro turbine

    Generators

    Next

    Generation 23

    individual basis, about the results of the testing programme. The testing crew offers

    suggestions

    fo r

    con sideration

    by the

    manufacturer

    forfuture

    product enhancements.

    Another im portant value of the testing programme is that it provides independent, third-party

    information

    for the public on the perform ance of the MTGs o n a consistent

    basis

    under actual

    operating conditions. 'Lessons learned' offers expert advice on operating experience and

    observations that can be used by the public to consider how best to use MTGs under actual

    operating conditions.

    2.2 The micro turbine technology summit

    Toadvance MT G development, the DOE sponsored the micro-turbine technology summit in

    December 1998. This summit was intended to

    surface

    issues so that a

    thoughtful

    roadmap

    would emerge for

    focused

    an d results-oriented research, development, and demonstration

    (RD D). The DOE successfully got valuable ideas and comm ents to help in its efforts to

    develop a RD D programme for micro-turbines. Both policy and market-related issues were

    necessarily a

    major

    part of the discussions.

    Thesummitidentified thatthemarketfo rMTGsispo tentially quite large but thealternatives

    that

    are competing to serve industrial power need s will be hard to beat w ith toda y's existing

    MTG

    technologies. Likewise

    the

    favorable attributes

    of

    fuel cells, also

    an

    emerging

    technology, put lots of pressure o n M TGs.

    Themajor findingso f the DOEm icro-turbine summ it wereas follows.

    Achievingthegoalofincreasingtheoverall efficiency ofmicro-turbinesto 4 percentor

    greater could boost the appeal of micro-turbines substantially compared with competing

    technolo gies, such

    as

    diesel gensets.

    A number of barriers are

    affecting

    th e development of marketers fo r small-scale power

    plants, including micro-turbines,

    not the

    least

    of

    which

    is

    uncertainty about

    the

    future

    of

    thestructure

    of

    electric power m arkets.

    Aparticular issueis theinterconnection of distributed generation technologies, including

    micro-turbines, with the utility grid. Interconnection specifications are not standardized

    and

    vary byutilitysystems across the wo rld.

    A

    focused RD D programme

    can be a

    great help

    in

    improving

    th e

    prospects

    fo r

    micro-

    turbines.

    Low er-cost, moreefficient micro-turbines with known performanceandproven reliability

    are

    needed.

    RD D

    to

    lower cost

    and

    increase

    the

    reliability

    of

    equipment

    fo r fuel

    processing,

    gas

    compression, recuperation, an dpower electronics isalso important.

    Development of advanced materials that are less costly, more durable, and capableof

    operating

    efficiently at

    higher temperatures could

    be one o f the

    keys

    to

    making substantial

    improvements in the thermal

    efficiency

    and environmental performance of m icro-turbines.

    As a result of the summit referenced above, DOE and others have developed funding

    solicitationstoprovidefor

    future

    RD D

    funding focused

    on thefindings above.

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    24

    Micro turbine Generators

    Based on the findings of the summit, MTGs can be expected to increase

    efficiency

    through

    improved materials.This includes technologies such as ceramics and components like more

    efficient

    recuperators

    and

    advanced pow er electronics.

    2 3

    The next three years

    The

    next three years will expand existing niches by adding product applications.

    MTG manufacturers during the n ext three years will ad d fea tures targeted for expanding their

    entry niche markets

    and

    developing.

    This period w ill

    focus on

    enhancing

    the

    M TG s capability

    in k ey

    areas that m ake

    it a

    broader

    based product. These capabilities

    are as

    follows.

    Plug

    and

    play enhancements will

    add to the

    user-friendliness

    and the MTG

    capabilities.

    Such ease

    of use and

    expanded capabilities will

    be

    advantageous

    for

    small customers

    who

    do no t

    employ

    or

    expect

    to

    employ, highly technical

    staff.

    These customers will require

    that the MTG be

    installed simply

    and

    operated unattended.

    The MTG

    must

    be

    smart

    enough

    to trouble-shoot problems and call home w ith problems. The MTG m ust be able to

    configure

    itself given the custom er s phy sical requiremen ts and constraints. It should be

    ableto

    advise

    of future

    maintenance, such

    as

    cleaning

    filters,

    replacement parts,

    at

    routine

    intervals.

    Fuel

    flexibility

    with dual

    fuel

    capability. MTG s will need

    to

    operate

    efficiently on a

    variety

    of

    fuels,

    including natural gas, diesel, propane, digester gas, etc. Most of the m anufactu rers

    have

    realized

    the

    value

    of

    multiple

    fuel

    operations

    and

    have designed,

    or are

    designing,

    future

    models which

    can

    operate

    on a

    variety

    of fuels.

    Additionally

    the M TG

    will need

    to

    have

    the

    capability

    to

    switch between

    fuel

    types

    so as to

    provide back-up

    fueling

    capability.

    Ideally, these capabilities will be provided transparently to the customer

    requiring

    only sim ple modifications,

    if

    any.

    Tight, seamless integration to the grid will be important to micro-turbines customer

    economics. M TG manu facturers are working with software/firmw are providers to provide

    communications and controls that easily provide the ability to aggregate and centrally

    dispatch many dispersed MTGs,

    if

    used

    as

    standby,

    and

    other standby distributed

    generation

    technologies. Small generators located in constrained parts of the grid can be

    dispatched and bring needed capacity during peak demand periods when spot prices can

    soar.

    Environm ental issues related to MTG s surround emission and noise. MTGs areexpected to

    be low in NO x but even so, large central plants are catching up so M TGs w ill continue to

    push down

    the

    level

    of

    NOx. Meanwhile,

    low efficiency of

    MTGs relative

    to

    large,

    combined-cycle,central plants make reducing M TG green house emissions by increasing

    efficiency

    a

    required

    goal.

    Most

    MTG

    m anufacturers claim noise levels

    in the 6 570 dB A

    at 10 m. In

    certain locations, such

    as

    city

    and

    urban areas, this level will need

    to decline to

    55-60

    dBA. Also, the high-frequency pitch from the high-speed turbine will require

    sattenuation in

    some locations

    and

    some applications.

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    Micro turbine Ge nerators

    Next Generation

    25

    2 4 The

    next five

    to

    seven years

    For the next five to seven years, MTG manufac turers will add features that expand niches and

    attack similar niche opportunities.

    Initial niches

    for

    MTGs

    are

    commercial customers

    who

    value increased reliability

    due to

    significant costs related

    to

    spoilage

    or

    lost business.

    M TG

    manufacturers should look

    for the

    same type of customer in the industrial sector. To get this larger-size customer, MTGs will

    need to be ganged up into multiple-unit packages.

    Another attractive niche for M TG s is the customer who uses lots of energy in their p roduction

    process and wants to benefit from managing energy price volatility. As electric industry

    deregulation continues, rates will mov e toward time-of-use . Under time-of-use pricing,

    electricity is priced and sold in discrete blocks of time. During peak periods of the day,

    prices

    can

    escalate. In this instance, the MT G can provide a physical hedg e ag ainst rising prices.

    To survive into the next decade, there must be

    major

    improvement in overall product

    robustness and performance so as to grow into broad applications and secure market

    acceptance.

    2 5 Improvements in the next decade

    The most challenging and important aspect of

    future

    MT Gs will be to

    increase

    the

    efficiency

    of the MTG to 40+ per cent without raising the capital

    price,

    cost of maintenance, or

    complicating the operation of the machine. Without this

    efficiency

    improvement, MTGs will

    not be able to compete with emerging

    fuel

    cells, especially given the added environmental

    benefits of

    fuel

    cells with no emissions and no

    noise.

    Bibliography

    Building

    Operating

    Management March, 2000, page 12, Outlook, Minipower Plants:

    Microturbines Draw Interest

    Distributed Generation: U nderstanding the Econom ies , An Arthur D. Little

    White

    Paper

    1999.

    Advanced M icroturbines, DOE s Office

    of

    Industrial Technologies, Energy

    Efficiency and

    Renewable Energy,

    Project

    Fact Sheet.

    Watts

    J. H.

    Microturbines: A New Class of Gas Turbine Engine, Global

    Gas

    Turbine

    News Vol . 39: 1999, No 1.

    deRouffignac A. Back ing Up the Grid with Microturbines, RDI E nergy Insight December

    3, 1999.

    Wheat

    D. Distributed gen enhances the grid, but can t beat central

    power,

    P O W E R

    November/December 1999.

    Swanekamp R . Distributed generation seeks market niches, P O W E R

    November/December

    1999.

    Hamilton S. L. The Buzz is from the Micro Turbine Generators, Deregulation Watch

    7.31.99,Vol.

    2, No 14.

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    26

    Micro-turbine Generators

    'Distributed

    and

    Dispersed Energy Resources,

    A

    Paradigm Shift,' NFCRC Journal,

    July/August/September1998, Vol.1,Issue3.

    ahl

    K. P. and

    Hamilton S.

    L.

    'Microturbines Under

    the

    Microscope,' Power

    Gen

    International Conference New

    Orleans,

    LA

    November

    30December2

    1999.

    immer

    M. J.

    'Distributed generation offers

    T D

    cost management,' Electric Light

    Power,February

    2000,

    Vol.78, No 2.

    S

    L

    amilton

    Southern California Edison USA

    StephanieL.Hamilton 2002

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    Analysis ofMicro and Mini turbine

    Competitive

    and

    Supply Markets

    in

    Europe

    TShane

    bstract

    This Chapter provides a summary of research and analysis of the micro- and mini-turbine

    market

    in Europe, the Middle East, and

    Africa

    (EMEA). The methodological approach

    including

    extensive interviewing process is described. The analysis of the results from the

    study shows that

    the

    market

    was

    origin llyover-hyped

    by the

    suppliers,

    and

    that unit sales

    have no t reached those early expectations. While market potential exists, some changes in

    national provisions (such as in NET

    A

    or Germany's new CHP Law) are needed to facilitate

    market

    growth. Market competitors are focused on overcoming key challenges, such as high

    kW prices to help drive the market. However, the ratio between electricity and gas prices,

    demand for cooling, and the regulatory position of the energy markets will significantly affect

    installation potential.

    This Ch apter com prises excerpts

    from

    Frost

    &

    Sullivan's most recently published analysis

    of

    the micro- and m ini-turbine market.

    3 1 Methodology

    The methodological approach applied to the research into the European, Middle Eastern, and

    African market

    for

    micro-

    and

    mini-turbines (Report

    3966-14) followed Frost

    &

    Sullivan's

    twelve-step market engineering research methodology.

    The

    primary research, analyses,

    surveys, comparisons, and forecasts are based on over 100 specific interviews carried out by

    experienced analysts plus the results from research undertaken for other related market

    analyses.

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    28 Micro turbine

    Generators

    These

    100

    interviews were conducted with four groups

    of

    companies, each playing

    an

    important

    part

    in

    future market development.

    1.

    Manufacturers

    and

    developers

    of

    micro-

    and

    mini-turbines

    and

    components (multiple

    interviews w ith nine companies).

    2.

    Packagers/distributors/component suppliers (around 60 interviews).

    3. End-users (interviews with nine respondents representing a range of operators).

    4.

    Electricity

    and gas

    utilities (around

    30

    interviews with

    Europe s

    most important

    gas and

    electricityutility companies).

    The results also draw

    on

    several years

    of

    on-going discussions with companies involved

    in

    supplying

    generating sets

    and

    components

    in

    Europe

    and

    North America

    as

    well

    as a

    large

    number of utility and energy service companies.

    The research strategy

    was

    constructed with

    the aim of

    providing detailed information

    concerning the key

    issues

    affecting the

    market, strategic analysis,

    and

    specific issue-related

    recommendations.

    Interviews with manufacturers and developers of micro- and mini-turbines, packagers, and

    component suppliers were aimed

    at

    gaining access

    to

    information

    on

    existing

    and

    planned

    products,

    company insights,

    and

    strategies

    fo r

    growth

    and

    sales

    and

    expectations

    for

    future

    markets.

    Targeted end-user feedback allowed

    an

    analysis

    of the

    market

    from

    the

    bottom

    up

    providing

    key information

    such

    as

    customer attitudes, expectations,

    and

    experience.

    Utility

    survey

    information

    was

    conducted aimed

    at

    providing

    a

    highly important insight into

    the

    attitudes

    of

    utilities towards their utilization

    of

    micro-

    and

    mini-turbines

    in future

    Distributed Generation (DG ) strategies.

    3.2

    European micro andmini turbine market

    The micro-

    and

    mini-turbine market

    in

    Europe

    is now

    developing. Throughout

    the

    last five

    years or so the

    mainly

    US

    manufacturers have been talking

    up the

    market prospects world-

    wide,m aking promises for early delivery o f efficient prime-mover technologies, designed to

    revolutionize the Distributed Generation (DG) market. Initial forecasts for thousands of unit

    shipments in the

    short-term have

    no t

    been

    fulfilled,

    although market growth

    has

    been highly

    significant.

    Capstoneand E lliott were the first to comm ercialize m icro-turbine units in the U nited States

    during

    1997. However,

    it was not

    until 2000 that commercialization

    of

    micro-turbines took

    place

    in

    Europe, although Kawasaki s

    600 kW

    mini-turbine

    was

    launched during 1995 (this

    has not

    been marketed

    for

    several years

    in

    Europe however).

    Six

    m arket participants

    are now

    active

    in the European sector, offering products that range in output from 30 kW to 600 kW,

    although three

    new

    entrants

    are

    expected

    in the

    short-

    and

    medium-term.

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    Analysis of

    Micro

    andMini turbine

    Competitive

    and

    upplyMarkets

    in

    Europe

    29

    During contacts with European energy service companies, and distributed energy studies

    undertaken

    in the

    United States,

    it

    became evident that many companies anticipate making

    multiple

    micro-

    and

    mini-turbine purchases

    in the

    short-

    to

    medium-term

    as

    units become

    available,

    and

    maintenance strategies

    and

    distribution networks

    are

    developed. Also,

    by

    assessingthe market for those primary competing technologies, Frost Sullivan hasbeen

    provided with

    a

    positive view

    of the

    market

    and

    expects

    it to

    develop rapidly during

    its

    first

    years.

    Views

    regarding

    the

    primary countries

    in

    which this technology will

    be

    significantly adopted

    vary.However, the foremost European industrialized nations of Germany, France, Italy, and

    the United Kingdom will account for the

    majority

    of units. However, the ratio between

    electricity

    and gas

    prices, demand

    for CHP or

    air-conditioning,

    and the

    regulatory position

    of

    the energy market in each country, will significantly effect installation potential in all

    European countries.

    3 2 1 1 Market

    efinitions

    3 2 1 1

    Micro turbines

    Most micro-turbines are based on technologies that were originally developed for use in

    auxiliary power systems,

    aircraft or

    automotive turbochargers. Most

    are

    small, recuperated,

    or

    regenerated high-speed combustion turbines that range from 20 kW to 500 kW intotal power

    output

    and

    have

    one

    moving part. This comprises

    a

    high-speed rotating

    shaft

    that includes

    the

    compressor, turbine wheel, and generator. In some cases, the shaft is mounted on air bearings

    rather than lubricated bearings, which

    are

    commonly used

    in

    conventional turbines.

    3 2 1 2

    Mini turbines

    Mini-turbines are generally based on traditional axial gas-turbine technology and are

    essentially

    a

    scaled-down version

    of

    such.

    For the

    purposes

    of

    this study

    Frost

    Sullivan

    has

    excluded units with

    an

    output above

    600 kW

    based

    on the

    idea that they

    are not

    competing

    within

    the

    same output range bracket

    and the

    market

    for

    larger units inhabits

    a

    relatively older

    product life-cycle stage. However, mini-turbinesaregenerallyanon-viable proposition below

    around 400 kW because of performance compromises for lower output configurations.

    Several original equipment manufacturer (OEM) companies have this typeof turbineon the

    market

    or in the

    latter stages

    of

    development, including Volvo Aero Turbines, Kawasaki

    Gas

    Turbine and

    OPRA (using radial-flow technology).

    3 2 1 3 roduct features

    The

    adoption

    of a

    high-speed generator

    and a

    minimal number

    of

    moving parts provides

    a

    number of beneficial features. For example, the set-up eliminates the need for a gearbox.

    Some players, however, such

    as

    Ingersoll-Rand s PowerWorks

    andOPRA's

    Trial Units, adopt

    gearbox systems.Inaddition, micro-andmini-turbinesarehighlyreliableandrequireamuch

    reduced maintenance schedule that

    is

    understood

    to

    vary from between 8000 hours (for air-

    filter replacement),

    to 16 000

    hours (thermocouple replacement),

    to 30 000

    hours (for turbine

    hardware replacement).

    The

    systems

    run on a

    range

    of fuels

    consisting

    of

    natural

    and

    othergases,such

    as landfill and

    sour gas, diesel, and

    liquefied

    petroleumgas (LPG). Emissions have provedto be relatively

    low, co