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Page 1 of 135
S. No TOPICS PAGE No.
UNIT I POWER GENER ATION
1
R eview of con vent i on al m ethods
6 2 Th erm al Pow er gen er at i on 6 3 Hyd ro Pow er gen er at i on 7 4 Nu cle ar Based Pow er gen er at i on 8
5
Non - conv ent i on al m eth od s of pow er gen er at i on fu el
cel l s
10
6 Tidal wa ves Pow er gen er at i on 15 7 Wind Pow er
gen er at i on 1
7 8 Geothe r mal Pow er gen er at i on 19 9 Solar Pow er
gen er at i on 2
5 10
Bio - Mass Pow er gen er at i on 27 1
1 Muni cipal Waste 2
9 12
Cogen er at i on 29
1
3
Ef fect of dis tribut ed gen er at i on on pow er system
oper at i on
3
2
UNIT II ECONO M IC ASPECTS OF GENE R ATI ON
1
4
Econom i c aspects of p ow er gen er at i on
3
4 15
Load and load du r at i on cu r ves 34 1
6 Numb er and si ze of u n i ts 3
5 17
Cost of ele ctric al en er gy 36 1
8 Tari f f 3
7 19
Econom i cs of po w er factor imp r ovement 38 2
0 Pow er capac i tor s 4
1 21
Pow er qu al i ty 42 2
2 Impor tan ce of el ectric al en er gy con serv ati on 4
4 23
En er gy ef fi cient equip me nts 44 2
4 Introd u cti on to en er gy au di t ing 4
4 UNIT III I LLUM IN ATION
2
5
Impor tan ce of
li ght i n g
4
6 26
Prop erties of good l i ght i ng sch eme 46 2
7 Laws of i l lu m ination
47 2
8 Photo m etr y 5
1 26
Types of l amps 55 3
0 L i ght i ng ca lcu l at i ons
59
3
1
Basic d esi gn of illum i n ati on s ch emes for r esident i a l,
com m er cial, stre et l i ght i n g, and sports
gr ound
60
32
En er gy ef fi cie n cy lamps 67
Page 2 of 135
UNIT IV IN D USTRI AL H EATING AND
WE LDI NG
33 Role ele ctric h eati ng for i ndustri a l applic at i ons 69
34 R esi stan ce h eati n g 71
35 Ind u cti on h eati n g 74
36 Di ele ctric h eati n g 78
37 Ele ctric arc fu rn aces 7 9
38 Bri ef introd u cti on to el ectric we ld i ng 80
39 Weld i ng gen er ator 82
40 Weld i ng tr ansfo r m er and the ch ar ac terist i cs 84
UNIT V ELECTRIC
TR ACTION
41 Me r i ts of ele ctr i c tr ac t i on 85
42 R equir ements of el ectric tr ac t i on system 86
43 Supp l y systems 87
44 Me ch anics of t r ain m ovement 88
45 Trac t i on mo tor s and con trol 88
46 Br aki n g 93
47 R ecent tr ends in el ectric t r act i on 100
QUE STION BANK 104
UNIVER SITY QUE STION PAPERS 121
GLOSSAR Y 132
Page 3 of 135
A IM
To ex pose students to the m ain asp ects of gen er at i on, ut i l iz at i on and
conser vati on.
OBJEC TIVES
To imp art kno w le d ge on
i. G en er at i on of ele ctr i ca l pow er b y con vent i on al and no n
conv ent i on al m ethods. i i . El ectric al en er gy con serv ati on,
en er gy audi t i n g and pow er q u al i t y.
i i i. Prin cip l e and d esi gn of i l lu m ination systems and met hods
of h eati n g an d w eld i n g. iv. El ectric t r act i on systems and th eir
per form an ce.
v. Industr i a l applic at i ons of ele ctr i c driv es.
1. POWER GENER ATION
R eview of conv ent i on al methods the r mal, h yd r o and nu cle ar based pow er gen er at i on. No n - con vent i on al
methods of pow er gen er at i on fu el cel l s - t i d al w aves wind geothe r mal
solar - bio - mass - mun i cipal w aste. Cogen er at i on.E f fect of dis tribut ed
gen er at i on on pow er system op er at i on.
2. ECONO M IC ASPECTS OF GENER ATION
Econom i c aspects of pow er gen er at i on load an d load dur at i on cu rv es numbe ra nd si ze of uni ts cost of
ele ctri cal en er gy tari f f. Econom i cs of po w er factorimp r ovement pow er
capaci tor s pow er q u al i ty . Impor tan ce of ele ctr i ca l en er gy cons erv ati on
methods en er gy ef f ic i ent equip m ents. Introd u cti on to en er gy audi t i n g.
3. I LLUM IN ATION
Impor tan ce of l i ght i n g pr operties of good l i ght i ng sch eme la w s of i l lu m ination photo m etr y - types of
lamps l i ght i n g ca lcu l at i ons basic d esi gn of i l lu m inations ch emes for
r esi d ent i a l, com m er ci a l, str eet l i ght i n g, and sports gro u nd en er gy ef f ici en cy
l amps.
4. IN D USTRI AL H EATING AND WE LDI NG
Role ele ctric h eati n g for industrial appl i ca t i ons r esi stan ce h eati ng ind u cti on h eati ng diel ectr i c h eat ing
- ele ctric arc fu r n aces.Br ief in trodu cti on to ele ctric w eld i ng w eld i n g
gen er ator, w eld i n g tr ansf or mer and the ch ar ac terist i cs.
5. E LECTRIC TR ACTION
Me r i ts of el ectric tr act i on r equi r ements of el ectric tr act i on system suppl y systems me ch anics of tr a in
Page 4 of 135
movem ent tr ac t i on mo tor s and control b r aking r ecent tr ends in ele ctric
tr ac t i on.
TOTAL: 45
PERIODS TEXT
BOOKS
1. C.L. Wadhw a, Gen er at i on, Distribution and Uti l i zat i on of Ele ctric al En er gy New Age Inte r n ati on al
Pvt. Ltd, 2003.
2. B.R. Gupt a, Gen er at i on of Ele ctri cal En er gy , Eu ra sia Publ i shing Hou se
(P) Ltd, New D el h i, 2003. RE FEREN CES
1. H. Pa r tab, A rt and Sci en ce of Uti l isation of Ele ctric al En er gy D h anp at R ai and Co, New D elh i , 2004.
2. E. Openshaw Taylor, Uti l i zat i on of Ele ctr i ca l En er gy in SI Ori ent
Lon gman Pvt. Ltd, 2 0 03.
3. J .B. Gupt a, Uti l i zat i on of Ele ctric Pow er and Ele ctric Tr ac t i Kata r ia
and Sons, 2002.
Page 5 of 135
1.1 In trodu ction
UNIT-
1
POWER
GENER ATION
In th i s unit a b r ief idea of a mode r n pow er system is ou t l ined. Emph asis
is given to cr eate a cl ear ment al pictu r e of a po w er system to a b eginn er of the
course El ectric al Technolo gy. As consum ers, we use ele ctrici ty for various
pu r poses su ch as:
1. L i ght i n g, h eati n g, cool ing and oth er dom esti c el ectric al
appl i an ces u sed in ho m e.
2. Str eet l i ght i n g, flood li ght i n g of spo r t i n g ar en a, of fi ce bui l di n g
l i ght i n g, pow eri n g PCs etc.
3. Ir r i gat i n g w ast agr icultur al l ands us i ng pumps and oper at i n g
cold stor ages for various agr icultur al prod u cts.
4. Running mo tor s, fu r n aces of v arious
kinds, i n industries.
5. Running locomot i ves (ele ctric
tr a ins) of r ai l w ays.
1.1.1 Basic i dea of
gen eration
Prior to the disco ver y of Far ad a s Laws of el ectrom agn eti c
discussi on, el ectric al pow er w as avai l able f r om batteri es with l i m i ted
vo l ta ge and cu r r ent lev els. Althou gh comp l ic ated in cons tru ct i on , D.C
gen er ators w ere d eveloped fi r st to gen er ate pow er in bulk. Howe ver, due to
l i m i tation of the D .C ma chine to gen er ate vol tage beyond few hund re d vol ts, it
w as not econom i ca l to tr ansm i t la r ge amount of pow er over a lo n g dis tan ce. For
a give n amount of pow er, the cu r r ent magnitude (I=P/V ), h en ce sect i on of the
copp er cond u ctor w i ll be la r ge. Thus gen er at i on, tr ansm i ssi on and dis tribution
of d.c pow er w ere r estrict ed to ar ea of few ki l omet er r adius with no
in ter con n ecti ons betw een gen er at i ng plants. Th er efor e, area specif i c
gen er at i n g stations alo n g with i ts distribu t ion n etwor k s had to be us ed.
1.2. R eview of con ven ti on al
Page 6 of 135
metho ds:
1.2 T h ermal , h ydel & n u clear
power statio n s
In th i s sect i on w e b r i ef l y out l ine the basics of the thr ee most
w ide l y found gen er at i ng stations the r mal, h yd el and nu cle ar pl ants i n
our count r y and els ewh er e.
1.2.1 T h ermal
pla n t
Gen er ate vol ta ge at 50 Hz we h ave to run the gen er ator at some fi x ed rpm by some ex ter n al agen cy.
A turbine is used to ro tate the gen er ator. Tu r b i ne m ay be of two types,
n ame l y steam turbine and w ater turbin e. In a th erm al pow er station coal is
burnt to pr odu ce steam whi ch in turn, d r ives the steam turbine h en ce the
gen er ator (tu r bo set) the elem enta r y featur es of a th erm al pow er plant is
shown. In a the r mal pow er pl ant coil is bu r nt to pr odu ce h i gh
tem per atu r e and h i gh p r essur e steam i n a boi le r. The steam i s p assed thro u gh
a steam tu r bine to pr odu ce rot at i on al mo tio n . The gen er ator, me ch an i ca l l y
coupl ed to the turbine, thus rot ates pr odu cing el ectrici ty . Ch em i ca l en er gy
stor ed in coal a ft er a cou ple of tr ansfo r mations p rodu ces ele ctr i ca l
en er gy at the gen er ator ter m i n als as d epic ted in the f i gu r e. Thus
pr ox i m i ty of a gen er at i ng sta tion n earer to a coal r eserve and w ater
sou rce s will be most econom i ca l as the cost of tr ansporti n g coal gets r edu ced.
In our count r y coal is avai l able in abu nd an ce and n atur al l y the r mal pow er
plants ar e most popula r . Howe ver, these plants pol l ute the atm osph ere because
of bu rning of coals.
Page 7 of 135
Strin gent condi t ions (su ch as use of more chi m n ey h ei ghts a lo n g
with the compu l sor y use of ele ctrostatic pr ecip i tato r ) are put by
re gulato r y auth orities to see th at the ef fects of pol l u t i on is m i ni m i zed.
A l ar ge amount of ash is pr odu ced ever y d ay in a t h erm al p l ant and ef fect i ve
h andl i ng of the ash adds to the running cost of the plan t . Non ethel ess 57% of
the gen er at i on in our count r y is f r om the r mal plants. The speed of a l tern ator
used in the r mal plants is 3000 rpm whi ch me ans 2 - pole a l tern ators are used
in such pl ants.
1.2.2 Hy del
pla n ts:
In a h yd el pow er station, w ater h ead is used to d r ive w ater turbine cou p led
to the gen er ator. Water h ead m ay be avai l able in hi l ly r egion n atur al l y in
the fo r m of w ater r eservoir (l ak es etc.) at th e hi l l tops. The potential en er gy of
w ater can be u sed to d r ive the turbo gen er ator set i nstall ed at the base of
the hi l ls throu gh pip i n g ca l l ed penstock Water h ead m ay also be cre ated
artifi cial l y b y constru ct i n g d ams on a sui table r ive r . In contr ast to a t h erm al
p l ant, h yd el pow er plants are eco- f r i end l y , n eat and cl ean as n o fu el i s to be
burnt to p rodu ce ele ctrici ty . Whi l e running cost of s u ch plants is l ow, the
Page 8 of 135
in i t i a l ins ta l l at i on cost i s r ather h i gh com par ed to th erm al plants due to
ma ssive ci v il constru ct i on n ecessar y. Also si tes to be sele cted for such p l ants
d epend u pon n atur al avai l abi l i ty of w ater r eservoi r s at hi l l tops or
avai l abi l i ty of sui table riv ers for constr u ct i ng d ams. Water turbin es gen er al l y
oper ate at low rpm, so number of pol es of the al tern ator is h i gh. For ex amp l e a
2 0 - pole a l tern ator the r pm of the turbine is on l y 300 r pm.
Page 8 of 135
Adva n tages:
On ce the d am i s buil t , t h e en er gy is v i rtu al y f r ee.
No wa ste or pol l ut i on p r odu ced.
Much mo r e re l i ab l e than wind, sol ar or w ave po w er.
Water can be stor ed abo ve the d am r ead y to cope with pe aks in d emand.
Hyd ro - el ectric pow er st at ions c an inc r ease to ful pow er v er y quick l y ,
unl i ke other pow er st at i ons.
Ele ctrici ty can be gen er ated cons tant l y .
Disa dvan tages:
The d ams a r e ver y ex pensive to build.
Howe ver, m an y d ams are a lso u sed for f lood cont r ol or ir r igation, so bui l ding costs can be sh ar ed.
Bui l ding a l a r ge d am wi l l flood a ver y la r ge area upstr eam, causi n g
p robl ems for ani m als that u sed to l ive th er e.
Find i ng a sui table si te can be di f fi cult - the i mpa ct on r esidents and the environme n t m ay be
un acceptabl e.
Water qu al i ty and q u ant i ty downst r eam can be af fected, w hich can h ave an i m pact on plant l i fe.
Page 9 of 135
1.2.3 Nucl ear
pla n ts:
As coal r eserve is not unl i m i ted, the r e is n atur a l thr eat to the r mal pow er p lants based on coal. It is
esti mat ed that with i n n ex t 30 to 40 years, coal r eserve will ex h aust if it is
consum ed at the pre sent r ate. N u cle ar pow er plants ar e thou ght to be the
sol u t i on for bulk pow er gen er at i on. At pr esent the ins ta l l ed capaci ty of nu cl ear
po w er plant is about 4300 MW and ex pected to ex pand fu r th er in our
cou nt r y . Th e .
p re sent d ay atom ic po w er plants w ork on th e pr inci ple of nu cl ear fission of U
In th e n atu r al u r aniu m , U
consti tutes on l y 0.72% and r emaining parts is con sti tu ted by 99.2 7 % of U
andon l yabout0.05%o fU.
The con centr at i on of U m ay be inc r eased to 9 0 % by gas dif fusion
p roc ess to obtain en r ic h ed U. Wh en U is bomba r d ed by n eutrons a lot of h eat
en er gy alo n g with addi t i on al n eutrons is pr odu ced. Th ese n ew n eutrons fu rth er
bomba r d pr odu ci n g more h eat and mo r e n eutrons.
Page 10 of 135
Thus a ch ain r eact i on sets up. Howe ver th i s r eact i on is a l l ow ed to take
pl ace in a con troll ed mann er ins i de a clo sed ch amber ca l l ed n u cle ar re ac tor.
To ensure sustainable ch ai n r eact i on, mode r ator an d control rods are used.
Mode ra tors such as h eavy w ater (d eute r iu m ) or ver y p u re ca rbon C are used to
r edu ce the spe ed of n eutrons. To control the number n eutrons, control rods
made of cadm i um or boron steel are inse r ted ins i de the re ac tor . The control
rods can absorb n eutrons. If w e w ant to d ecr ease the number n eutrons, the
control rods are low er ed down fu r th er and vice v ersa. The h eat gen er ated ins i de
the re ac tor is tak en out of the ch amber with the h elp of a coolant such as
l i quid sodi u m or some gaseous fluids. The coolant gives up th e h eat to w ater
in h eat ex ch an ger to con vert it to steam as shown in fi gu r e. The steam then
d r ives the turbo set and the ex h aust steam f r om the turbine is cooled and
fed back to the h eat ex ch anger with the h elp of w ater feed pump. Calcul at i on
shows that to pr odu ce 1000 MW of ele ctri cal pow er in coal based the r mal
plant, about 6 1 0K g of coal is to be bu rnt d ai l y w hile for the same amount
of pow er, on l y about 2.5 Kg of U is to be used per da y in a n u cle ar p ow er
stat i ons.
The in i t i a l investm ent r equir ed to ins ta ll a n u cle ar pow er station is
qui te hi gh but runni n g cost is low. Althou gh, nu cle ar plants pr odu ce
ele ctr i ci ty without causing a i r pol l ut i on, i t r emains a dorm ant sour ce of
Page 11 of 135
r adiation h azar ds due to le ak age in the r eactor. Also the used fuel rods are to
be ca r eful l y h andled and dispos ed of f as th ey sti ll r emain r adioa cti ve. The
r eserve of U is a lso l i m i ted and cannot last lon ger if i ts consumpt i on cont i nu es
at the pre sent r ate. Natu r al l y sear ch for a l ter n ati ve fission ab le mat eri a l
cont i nu es. For ex amp l e, plu tonium (Pu) and (U) are fission able. Althou gh th ey
are n ot dir ect l y avai l abl e. A bsorbing n eutro ns g ets conv ert ed to fission able
pluton i um Pu in the atom ic reac tor d escrib ed above.
Disa dvan tages:
Althou gh not m u ch w aste is produ ced, it is ve r y , ver y d an gerous.
It m ust be s ealed up and buri ed for ma n y thous an ds of years to a l ow t h e
r adioa ct i vi ty to d i e aw ay.
For a ll that t i me it must be k ept safe f r om earth qu ak es, floodi n g, ter r or is ts
and ever yth i n g else. This is dif f icult.
Nu cle ar pow er is r el i ab l e, but a lot of mo n ey h as to be spent on safety - if
it do es go w r on g, a n u cle ar
EE2451 EEGUC
Page 10 of 135
acc ident can be a major d isaste r .
People are inc r easi n gl y con cer n ed about th i s - in the 1990 's nu cle ar
pow er w as the fastest - gr owing sour ce of p ow er in mu ch of the w or ld. In
2005 it w as the s econd slo w est- gr owin g.
1.3 Non - con ven tional m etho ds of power
gen eration:
1.3.1 Fu el
Cel l s:
A fu el cell is a d evice that conv erts the ch em i ca l en er gy f rom a fu el in to ele ctrici ty thro u gh a
ch em i ca l r eact i on with ox ygen or anoth er
ox id i z i ng agent
Hyd r ogen pr od u ced f rom the steam meth ane r efo r m i n g of n atu r al gas i s
the most com m on fu el, but for gre ater ef f ic i en cy h yd r ocarbons can be u sed
dir ect l y su ch as n atu r al gas and alcohols l i ke m ethanol . Fu el cel l s ar e
dif fer ent f rom batteri es in that th ey r equire a cont i nuous sour ce of fu el and
ox ygen/air to sus ta in the ch em i ca l r eact i on wh er eas i n a batter y the ch em i ca ls
pre sent in the batter y r eact with each other to gen er ate an ele ctro m ot i ve (emf ).
Fu el cel l s can pr odu ce el ectrici ty cont i nuous l y for as long as these inpu ts a r e
supplied.
The fi r st fu el cel l s w ere invent ed in 1838. The fi r st com m er cial use of fu el cel l s came m ore t h an a centu r y l ater in NA SA space pr ogr ams to gen era te pow er for pr ob es, satel l i tes and space capsul es. Sin ce then, fu el cel l s h ave been used in ma n y oth er appl i ca ti ons . Fu el cel l s are u sed for pr i ma r y an d backup pow er for com m er ci a l, industrial and r esidenti a l bui l din gs and in r emo te or ina ccessi ble ar eas. Th ey are a lso used to pow er fu el - cell vehicl es, includi n g fo r kl i fts, auto m ob i l es, buses, boats, mo tor cycl es and subm arin es.
Th ere are ma n y types of fu el cel l s, but th ey a ll consist of an anod e, a cathode and an ele ctro l y te that a l l ows ch ar ges to move betw een the two sides of the fu el cel l . Ele ctrons are d r awn f r om the ano d e to the ca thode thro u gh an ex ter n al cir cui t , p rodu ci n g di r ect cu r re nt ele ctrici ty . As the main d i f fer en ce among fu el cell types is the ele ctro l y te, fu el cel l s are class i fi ed by the type of el ectro l y te th ey use follo w ed by th e dif fer en ce in star tup t i me r an gi n g f r om 1 sec for PEM FC to 10 m in for SOFC. Fu el cel l s come in a vari ety of si zes. Indiv i du al fu el cel l s pr od u ce r el a t i vel y small ele ctri cal potent i a ls, about 0.7 vol ts, so cel l s ar e "stack ed ", or p l aced in seri es, to i n cre ase th e vol ta ge and m eet an appl i ca t i on 's r equir em ents .[ 2 ] In ad d i t ion to ele ctr i ci t y , fu el cel l s pr odu ce w ater, h eat and, d epending on the fu el sou r ce, ver y small amoun ts of ni trogen dio x ide and other em i ssi ons. The
http://en.wikipedia.org/wiki/Chemical_energyhttp://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Methanolhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Fuel-cell_vehiclehttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-2http://en.wikipedia.org/wiki/Nitrogen_dioxidehttp://en.wikipedia.org/wiki/Nitrogen_dioxideEE2451 EEGUC
Page 11 of 135
en er gy ef f ici en cy of a fu el cell is gen er al l y betw een 4 0 60%, or up to 85% ef f ic i ent i n cogen erat i on if w aste h eat i s captu re d for u se.
Ty pes
:
Fu el cel l s come in m an y vari et i es; ho w ever, th ey all wo r k in the same gen er al mann er. Th ey ar e made
up of thr ee adja cent segments: the anod e, the el ectro l yte, and th e ca tho d e. Two
ch em i ca l r eact i ons occur at the in ter face s of the thr ee dif fer ent segments. Th e
n et r esult of the two r eac t i ons is that fu el is consum ed, w ater or ca rbon dio x ide
is cr eated, and an el ectric cu r r ent is cr eated, wh i ch can be used to pow er
ele ctric al d evic es, norm al l y r efer r ed to as the load.
At the anode a ca ta l yst ox i d i zes the fu el, usual l y h yd r ogen, turni n g the
fu el in to a po si t ive l y ch ar ged ion and a n egati vel y ch ar ged el ectron. The
ele ctr ol y te is a subs tan ce speci f ic al l y d esi gn ed so ions can pass throu gh i t , but
the ele ctrons cannot. The f reed el ectrons tr avel thro u gh a wire cre ati ng the
el ectric cu r r ent. The ions tr avel thro u gh the ele ctro l y te to the ca th od e. On ce
r eachi n g the cathode, the ions are r eun i ted wit h the ele ctrons and the two
reac t wi th a th i rd ch em ic al, usu al l y ox ygen, to cre ate wa ter or carbon dio x ide.
http://en.wikipedia.org/wiki/Cogenerationhttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/CatalystEE2451 EEGUC
Page 12 of 135
The ele ctro l y te subs tan ce usu al l y d efin es the type of fu el cel l .
The fu el th at i s used. The most com m on f ue l i s h yd r ogen.
The anode ca tal yst b r eak s down the fu el in to ele ctrons and ions. The anode
ca ta l yst is usual l y ma d e up of ver y f ine p l at i num powd er.
The ca thode ca tal yst tu r ns the ions in to the w aste ch em i ca ls l i ke w ater or
ca rbon dio x ide. The ca thode ca ta l yst i s oft en made up of nick el but it can also
be a nonmat er i a l - based ca tal yst.
A typi cal fu el cell p r od u ces a vol ta ge f rom 0.6 V to 0.7 V at full r ated load.
Volt age d ecr eases as cu r r ent inc rea ses, due to sev er al factors:
A ct i vat i on loss
Ohmic loss (vol tage d rop due to r esi stan ce of the cell components and
in ter conn ecti ons)
Mass tr ansport loss (depletion of re ac tants at cata l yst si tes un d er h i gh
l oads, causi n g r apid l oss of vol tage)
To d el i ver the d esir ed amount of en er gy, th e fu el cel l s can be
comb i n ed in seri es to y i eld hi gh er vol ta ge, and in par al l el to a l l ow a h i gh er
cu r r ent to be supplied. Su ch a d esi gn is cal l ed a fu el cell sta ck. The cell
sur fa ce ar ea can also be inc rea sed, to a l l ow h i gh er cu r r ent f r om each cel l .
Wi thin t h e stack, r eac tant gas es must be d i stribu ted unifo r m l y over each of t h e
cel l s to m ax i m i ze the po we r output.
i) P roton exch an ge membran e fu el c el l s (PEM FCs):
In the ar ch etypic al h yd r ogen ox ide p r oton ex ch an ge m embr ane fu el cell
d esi gn, a p roto n - cond u cti ng po l ymer memb ra n e (t h e ele ctro l y te) separ ates
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the anode and ca thode si d es. This w as ca l l ed a "sol i d po l ymer ele ctro l y te
fu el cel l " (S PEFC) in the early 1970s, b efo r e th e prot on ex ch an ge me ch anism
w as w el l - und erst ood.
On the anode side, h yd r ogen dif fu ses to the anode ca ta l yst wh ere it lat er dis sociat es in to pr otons an d ele ctrons. Th ese pr otons of ten r eact with ox idants causi n g them to become wh at are com m on l y refer re d to as mu l t i - faci li tat ed pr oton memb ra n es. The pr otons are condu cted thro u gh the memb ra ne to the cathode, but the el ectrons are for ced to tr avel in an ex ter n al ci r cuit (supp l y i n g pow er) because the me m bra ne is ele ctri cal l y insu l at i n g. On the cathode cata l yst, ox ygen mo l ecules r eact with the el ectrons (w h ich h ave tr aveled th r ou gh the ex ter n al cir cui t ) and p r otons to fo r m w ater .
In addi t ion to th i s pure h yd r ogen type, the r e are h yd ro car bon fu els for fu el cel l s, including dies el , meth an ol and ch em i ca l h yd rid es. The w aste pr odu cts with these types of fu el ar e ca rbon dio x ide and w ater , wh en h yd r ogen is used the CO2 is r ele ased wh en meth ane f r om n atur al gas is comb i n ed with steam in a pro cess ca l l ed steam meth an e re for m i ng to pr odu ce the h yd r ogen, th i s can ta k e pla ce in a
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dif fer ent lo cati on to the fu el cell potential l y a l l ow ing the h yd r ogen fu el cell to
be u sed indoors for ex amp l e in fo r kl i fts.
Constru ct i on of a h i gh - tempe ra tu r e PEM FC: Bi polar plate as el ectrode
w i th i n - m i l l ed gas ch ann el stru ctur e, fab ri ca ted fr om condu cti ve
composi tes (enh an ced with gra phi te, ca r bon bla ck , ca r bon fib er , and/or
carbon annotat es for more condu cti vi ty ) Por ous ca rbon paper s;
r eac t i ve l ayer, usu al l y on the po l ymer m embr an e appl i ed; po l ym er
m emb r an e.
Cond ensation of w ater pr odu ced b y a PEM FC on the air ch ann el w al l . The
gold wire aroun d the cell ensur es the col le ct i on of ele ctric cu r r ent.
The dif fer ent compon en ts of a PEM FC ar e;
1. Bipo l ar pl ates,
2. Ele ctrod es,
3. Cata l yst,
4. M embr an e, and
5. The n ecessar y h ard w ar e.
The mat eri a ls used for dif fer ent parts of the fu el cel l s dif fer by type. The
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bipo l ar plat es m ay be ma d e of dif fer ent types of mat er ials, such as,
met al, coated met al, gra phi te, fl ex ib l e gr aph i te, C C composi te,
ca rbo n po l ym er composi tes etc. The memb ra ne el ectro d e assembl y (ME A ) is
r efer red as the h eart of the PEM FC and is usual l y made of a p roton
ex ch an ge memb ra ne sandw i ch ed betw een two ca ta l yst- coated carb on paper s.
P latinum and / or si m i l ar type of noble met als ar e usual l y u sed as the
ca ta l yst for PEM FC. The ele ctro l y te could be a pol ymer mem br an e.
i i ) Ph osph or ic a cid fu el cell (PAFC):
Phosphoric ac id fu el cel l s (PA FC) w er e f irst d esi gn ed and in trod u ced in 1 961 by G. V. Elmo r e and H.
A. Tann er . In these cel l s phosphoric ac id is used as a no n - condu cti ve
el ectro l y te to pass posit i ve h yd r ogen
http://en.wikipedia.org/wiki/Graphitehttp://en.wikipedia.org/wiki/Composite_materialhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Membrane_electrode_assemblyhttp://en.wikipedia.org/wiki/Catalysthttp://en.wikipedia.org/wiki/Carbon_paperhttp://en.wikipedia.org/wiki/Noble_metalhttp://en.wikipedia.org/wiki/Artificial_membranehttp://en.wikipedia.org/w/index.php?title=G._V._Elmore&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=H._A._Tanner&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=H._A._Tanner&action=edit&redlink=1EE2451 EEGUC
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ions f r om the anode to the ca thode . Th ese cel l s com m on l y wo r k in temp er atu r es of 150 to 200 d egrees Cels i us. This hi gh tem per ature will cau se h eat an d en er gy loss if th e h eat i s not r emoved and used pr oper l y . This h eat can be u sed to pr odu ce steam for a ir condi t ion i ng systems or an y other th erm al en er gy consuming system .[3 1 ] Using th i s h eat in cogen er at i on can en h an ce the ef f ici en cy of ph osphoric acid fu el cel l s f rom 4 0 50% to about 80% .Pho sphoric acid, the ele ctro l y te used in PA FCs, is a n on -condu cti ve l i quid aci d whi ch fo rce s el ectrons to tr avel f r om anode to ca thode th r ou gh an ex ter n al el ectr ic al ci r cui t . Since the h yd r ogen ion pr odu cti on r ate on th e ano de is small, platinum is used as ca ta l yst to inc rea se th i s ion iz at i on r ate. A k ey disadv ant age of t h ese cel l s is the use of an ac id i c ele ctro l y te. This inc re ases the cor rosion or o x idation of components ex posed to phosphoric ac i d .
i i i) H i gh - temperatu re
fu el c el l s:
1) Sol i d oxi de fu el c el l s (SOFCs):
Sol i d ox ide fu el cel l s (SOFCs) use a sol i d mat eri al, most com m on l y a
cer am i c mat eri a l ca l l ed y ttri a- stabili zed zir conia (YSZ ), as the ele ctro l yte.
Because SOFCs are made en t ir el y of sol i d mat eri a ls, th ey are not l i m i ted to the
fl at pl ane conf i gu ra t i on of other types of fu el cel l s and ar e of ten d esi gn ed as
roll ed tubes. Th ey r equi r e hi gh oper at ing temp er atur es (80 0 1 000 C) and
can be run on a vari ety of fu els including n atur al gas.
SOFCs are uniq u e since in those, n egati vel y ch ar ged ox ygen ions tr avel f r om the cathode (posit i ve side of the fu el cel l ) to th e anode (ne gati ve side of the fu el cel l ) ins tead of posit i vel y ch ar ged h yd r ogen ions tr avel l ing f r om the ano d e to the ca thode, as is t h e case in a ll other types of fu el cel l s. Ox ygen gas is fed throu gh the ca thode, w h ere it absorbs el ectrons to cr eate ox ygen ions. The ox ygen ions then tr avel th r ou gh the el ectro l y te to r eact w i th h yd r ogen gas at the anod e. The re act i on at the anode pr odu ces el ectric i ty and w ater as b y- pr od u cts. Carbon dio x ide m ay also be a by - pr odu ct d epen ding on the fu el, but th e carbon em i ssi ons f r om an SOFC system are less than those f r om a fossil fu el combust i on plant. The ch em i ca l r eac t i ons f or the SO FC system can be ex pre ssed as follow s.
2H 2 + 2O2
2H 2 O + 4 e O2 + 4 e
2O 2H 2 + O2
2H 2 O SOFC systems can run on fu els other than pure h yd r ogen gas. Howe ver, since h yd r ogen is n ecessar y for the
r eac t i ons l i sted abov e, the fu el sele cted must contain h yd r ogen atom s. For the
fu el cell to oper ate, the fu el must be conv ert ed in to pure h yd r ogen gas. SOFCs
are capable of in ter n al l y r efo r m i n g l i ght h yd r ocarbons such as meth ane
http://en.wikipedia.org/wiki/Fuel_cell#cite_note-31http://en.wikipedia.org/wiki/Cogenerationhttp://en.wikipedia.org/wiki/Solid_oxide_fuel_cellhttp://en.wikipedia.org/wiki/Solid_oxide_fuel_cellhttp://en.wikipedia.org/wiki/Solid_oxide_fuel_cellhttp://en.wikipedia.org/wiki/Yttria-stabilized_zirconiahttp://en.wikipedia.org/wiki/Yttria-stabilized_zirconiahttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Operating_temperaturehttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Fossil_fuel_reforminghttp://en.wikipedia.org/wiki/MethaneEE2451 EEGUC
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(n atu r al gas), p r opan e and buta n e. Th ese fu el cel l s a r e at an ear l y stage of
d evelo pment.
Ch al l en ges ex ist in SOFC systems due to their h i gh oper at i n g temp er atur es.
One such ch al l en ge is the potential for carbon du st to bui l d up on the an od e,
whi ch slows d own the in tern al r eforming pr ocess. Resear ch to ad d r ess th i s
"carbon coking" is sue at the Univ ersi ty of Penn sy lvania h as shown that th e use
of copp er - based cerm et (he at- r esi stant mat eri a ls m ade of cer am i c and met al)
can r ed u ce coking and the loss of p er for ma n ce. Anoth er d i sadv ant age of SOFC
systems is slow star t - up t i me, making SOFCs less u seful for mob i le appl i ca t i ons.
D espi te these disad vant ages, a h i gh oper at i ng temp er ature p rovid es an
ad vantage b y r emov i ng the n eed for a prec ious met al ca ta l yst l i ke platinu m ,
the re by re du cing cost. Addit i on al l y , w aste h eat f r om SOFC systems m ay be
captur ed and r eused, inc r easing the th eore t i ca l over all ef f ici en cy to as hi gh
as 80% 8 5 %.
The h i gh oper at i n g tem per atu r e is la r gel y due to the ph ysi ca l pr operties of
the YSZ ele ctro l y te. A s temp er atu r e d ecre ases, so do es the ion i c cond u cti vi ty of
YSZ . Th er efor e, to obtain opt i mum per fo r man ce of the fu el cel l , a h i gh
oper at i n g temp er ature is r equir ed. A ccor di n g to their w ebsi te, Cer es Pow er , a
UK SOFC fu el cell man u factu re r, h as d eveloped a m ethod of r edu ci n g the
oper at i ng temp er atu r e of the i r SOFC system to 50 0 600 d egrees Cels i us. Th ey
r ep l aced the com m on l y u sed YSZ el ectro l yte with a CGO ( cerium
gadol i nium ox i de) el ectro l y te. The l ow er oper at i n g temp er ature a l l ows them to
use stainl ess steel ins tead of cer am i c as th e cell subs tr ate, w hich r ed u ces cost
and star t - up t i me of the system.
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2) Hy drogen - Oxygen
Fu el C el l :
The Hyd r ogen - Ox ygen Fu el Cell w as d esi gn ed by Bacon in the year 195 9 . It w as used as a pr i m ar y
sour ce of el ectric al en er gy in the Apollo space pr ogr am. The cell consists of two poro u s ca rbon el ectrod es i m pre gn ated with a sui table ca ta l yst such as Pt, A g, CoO, etc. The space betw een the two ele ctrod es is filled with a con centr ated solu t ion of KOH or NaOH whi ch serv es as an el ectro l yte. 2 H2 gas and O2 gas are bubbled in to the ele ctrol y te thro u gh th e poro u s carbon el ectrod es. Thus the over all r eact i on invo l ves the comb i n ati on of h yd r ogen gas and ox ygen gas to fo r m w ater . The cell runs cont i nuous l y unt i l the re ac tan t 's supp l y is ex h austed. This type of cell oper ates ef f ici ent l y in the tempe r ature r an ge 343 K to 413 K and p r ovides a potential of about 0.9 V.
3) M olt en carbon ate
fue l c el l s:
Molten ca rbon ate fu el cel l s (MC FCs) r equire a hi gh oper at i n g temp er atur e, 650 C (1,2 0 0 F), si m i l ar
to SOFCs. M CFCs use l i thium potassi u m ca rbon ate salt as an ele ctro l y te, and
th i s sal t l i qu efi es at hi gh temp er atu r es, allowing for the mov ement of ch ar ge
with i n the cell in this c ase, n egati ve carbon ate ions. L ike SOFCs, M CFCs are
capable of conv erting fossi l fu el to a h yd r ogen - r i ch gas in the anod e,
el i m i n ati ng the n eed to pr odu ce h yd r ogen ex ter n al l y.
Th e re for m i ng pr ocess cr eates CO
2 em i ssi ons. M CFC- comp ati ble fu els include n atu r al gas, biogas and gas pr odu ced f r om coal. The h yd r ogen in the gas r eacts with carbon ate ions f r om the el ectro l yte to pr odu ce w ater, carbon dio x ide, ele ctrons and small amoun ts of other ch em i ca ls. The el ectrons tr avel thro u gh an ex ter n al cir cuit cre ati ng el ectr i ci ty and r eturn to th e cathode. Th er e, ox ygen f r om the air and carbon dio x ide re cycled f r om th e ano d e r eact with the ele ctrons to fo r m carb on ate ions that r eplenish the ele ctro l yte, comp le t i ng the cir cui t .[4 3 ] The ch em i ca l r eac t i ons f or an M CFC system can be ex pre ssed as follows:
CO32 + H2 2 O +
CO2 + 2 e CO2 + O2 + 2 e
O3 H2 + O2
H2 O As with SOFCs, M CFC disadv ant ages include slow star t- up t i mes becau se of their h i gh oper at i n g
temp er atu r e. This mak es M CFC systems not sui table for mob i le appl i ca t i ons,
and th i s technology will mo st l i k el y be used for statio n ar y f u el cell purp oses.
The main ch al l en ge of M CFC technol ogy is the cel l s' sh or t l i fe span. The h i gh -
tem per atu r e and carbon ate el ectro l y te l ead to cor rosion of the anode and
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catho d e. Th ese factors accele r ate the d egra d ati on of M CFC com pon ents,
d ecr easi n g the d u r abi l i ty and cel l l i f e. Re sear ch ers are add r essi ng th i s pr oblem
by ex pl oring cor ros i on - r esi stant mat eri a ls for components as w ell as fu el cell
d esi gns th at m ay in cr ease cell l i fe without d ecr easing per fo r ma n ce.
M CFCs hold sever al adv ant ages over other fu el cell technol ogi es, i n clud i ng their r esi stan ce to i m puriti es. Th ey are n ot pr one to "carbon coki n g", whi ch r efers to ca r bon bui l d - up on the anode those r esul ts in r edu ced per for man ce b y slowi n g down the in tern al fu el r efo r m i n g pr ocess. Th er efo r e, ca r bon - ri ch fu els l i ke gases made f r om coal ar e com pati ble with the system. Th e D epartme n t of En er gy cl a i m s that coal, i tself, m i ght even be a fu el opt i on in th e futu re , assum ing the system can be made re si stant to i m puriti es such as sulf u r and particul ates th at r esult f r om conv erting coal in to h yd r ogen .[3 4 ]
M CFCs also h ave r el at i vel y h i gh ef f i cien cies. Th ey can re ach a fu el - to - el ectrici ty ef f i ci en cy of 50%, consid er ab l y h i gh er than the 3 7 4 2 % ef f ici en cy of a phosph oric ac id fu el cell plant. Ef fi ci en cies can be as h i gh as 6 5 % wh en the fu el cell is pair ed with a turbine and 85% if h eat is capt u r ed and used in a Comb i n ed Heat and
Pow er (CHP)
system.
Fu el Cell En er gy, a Con n ecti cu t- based fu el cell manu fac tu r er, d evelops
and sel l s M CFC fu el cel l s. The com pan y says tha t their M CFC pr odu cts ra n ge
f r om 300 kW to 2.8 MW systems that achi eve 47% ele ctri cal ef fi cie n cy and
can ut i l iz e CHP technol ogy to obtain h i gh er over all ef f i cien cies. One pr odu ct,
the D FC- ERG, is comb i n ed with a gas turbine an d, acc or di n g to the
compa n y, it achie ves an ele ctri ca l ef f ici en cy of 6 5%.
http://en.wikipedia.org/wiki/Fossil_fuel_reforminghttp://en.wikipedia.org/wiki/Fuel_cell#cite_note-Types1-34http://en.wikipedia.org/wiki/Fuel_cell#cite_note-Types1-34http://en.wikipedia.org/wiki/Cogenerationhttp://en.wikipedia.org/wiki/CogenerationEE2451 EEGUC
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1.3.2 Ti dal
Wav es:
Tidal pow er is tak en f r om the Eart h 's oceanic t i d es; t i d al fo rce s are
perio d ic vari at i ons in gra vi tat i on al attr act i on ex ert ed b y cel esti a l bodies. Th ese fo rc es cre ate cor r espondi n g mo tions or cu r r ents in the wo r l d 's oceans. Due to the stro n g attr act i on to the oceans, a bulge in the w ater lev el is cre ated, causing a tem por ar y inc rea se in sea le vel. Wh en the sea le vel is r a is ed, w ater f r om th e m i ddle of th e ocean is fo r ced to move tow ard the sho r el i n es, cr eati n g a t i d e. This occu r r en ce tak es pla ce in an unf ai l ing m ann er, d u e to the consistent pattern of the or b it around the earth .[5 ] The ma gni tude and ch ara cter of th i s mo tion r efl ects the ch an gi n g po si t ions of the Moon and Sun r elative to the Earth, the ef fects of Eart h 's rot at io n , and loc al geogr aph y of the sea f loor and coastl ine s.
Tidal pow er is the on l y technolo gy th at d r aws on en er gy inh er ent in th e or bi ta l ch ar acterist i cs of the E arth Moon system, and to a lesser ex tent in the Eart h Sun system. Oth er n atur a l en er gies ex p l oi ted by human technol ogy or i ginate di r ect l y or ind i r ect l y w i th the Sun, in clud i ng fu el, conv ent i on al , wind , bio fu el , w ave and solar en er gy. Nu cle ar en er gy m ak es use of Eart h 's m i n er al d eposits of fission able elem ents, while geothe r mal po w er taps the Eart h 's in ternal h eat, whi ch comes f rom a comb i n ati on of r esid u al h eat f rom plan etar y accr et i on (about 20 %) and h eat pr od u ced thro u gh r ad ioa ct i ve d ecay (8 0 %).
A t i d al gen er ator con ver ts the en er gy of t i d al flo w s in to ele ctrici ty . Gr eater t i d al vari at i on and h i gh er t i d al cu r r ent velo ci t ies can dr amatic al l y inc r ease the potential of a si te for tid al el ectrici ty gen er at i on . Because the Eart h 's t i d es are ul t i m atel y d u e to gr avi tat i on al in ter act i on with the Moon and Sun and the E art h 's rot at i on, t i d al pow er is prac t i ca l l y ine x h aust i ble and classifi ed as a r en ew able en er gy r esour ce. Movem ent of t i d es causes a loss of me ch anic al en er gy in the Earth Moon system: th i s is a r esult of pump i ng of w ater thr ou gh n atur al r estrictions around coastl ines and consequ ent viscous dis sipation at the seabed and i n turbul en ce. This loss of en er gy h as caused th e rot at i on of the Earth to slow in the 4.5 bi l l i on years sin ce i ts fo r mation.
http://en.wikipedia.org/wiki/Tideshttp://en.wikipedia.org/wiki/Tidal_forceshttp://en.wikipedia.org/wiki/Tidal_power#cite_note-5http://en.wikipedia.org/wiki/Coriolis_effecthttp://en.wikipedia.org/wiki/Bathymetryhttp://en.wikipedia.org/wiki/Bathymetryhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Wind_powerhttp://en.wikipedia.org/wiki/Biofuelhttp://en.wikipedia.org/wiki/Wave_powerhttp://en.wikipedia.org/wiki/Solar_energyhttp://en.wikipedia.org/wiki/Solar_energyhttp://en.wikipedia.org/wiki/Nuclear_powerhttp://en.wikipedia.org/wiki/Fissile#Fissile_vs_fissionablehttp://en.wikipedia.org/wiki/Fissile#Fissile_vs_fissionablehttp://en.wikipedia.org/wiki/Geothermal_powerhttp://en.wikipedia.org/wiki/Internal_heathttp://en.wikipedia.org/wiki/Gravitational_binding_energyhttp://en.wikipedia.org/wiki/Radioactive_decayhttp://en.wikipedia.org/wiki/Radioactive_decayhttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Tidal_accelerationhttp://en.wikipedia.org/wiki/Tidal_accelerationhttp://en.wikipedia.org/wiki/Viscosityhttp://en.wikipedia.org/wiki/Seabedhttp://en.wikipedia.org/wiki/TurbulenceEE2451 EEGUC
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Ti dal st ream gen erator :
Tidal str eam gen er ators (or TSGs) make use of th e kinetic en er gy of mov i ng
w ater to pow er turbin es, in a si m i l ar w ay to wind turbin es that use wind to
pow er turbin es. Some t i d al gen er ators can be bui l t in to the stru ctur es of
ex is t i n g b r i d ges, invo l ving vir tu al l y no aesthetic pr ob l ems. Land constri ct i ons
such as str a i ts or in l ets can cr eate hi gh velocit i es at speci fic si tes, whi ch can be
captur ed with the use of tu r bines. Th ese turbin es can be h or i zontal, vertic al,
open, or du cted and are typic all y pl aced n ear the bot tom of the w ater colu m n.
Ti dal barr age
Tidal bar ra ges make use of the po tent i a l en er gy i n the di f fer en ce in h ei gh t (or h yd r aul i c h ead ) betw een
hi gh and low t i d es. Wh en using t i d al bar r ages to gen er ate po w er, the pot ent i a l
en er gy f r om a t i de i s sei zed throu gh str ategic pl acem ent of speciali zed d ams.
Wh en the sea le vel ris es and the t i de begins to come in, the tempo r ar y
in cr ease i n t i d al pow er is ch ann eled in to a la r ge basin behind the d am,
hold i n g a la r ge amount of potential en er gy. Wi th the r eceding t i d e, th i s en er gy
is then con vert ed in to m ech an i ca l en er gy as the w ater is r el eased th rou gh l ar ge
turbi n es th at cr eate el ectric al po w er throu gh the use of gen er ators. Bar ra ges are
essential l y d ams across the full width of a t i d al estu ar y.
Dyna mic tidal power
http://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Wind_turbineshttp://en.wikipedia.org/wiki/Potential_energyhttp://en.wikipedia.org/wiki/Hydraulic_headhttp://en.wikipedia.org/wiki/Mechanical_energyhttp://en.wikipedia.org/wiki/DamEE2451 EEGUC
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D yn am i c t i d al pow er (or DTP) is an untri ed but pr om i sing technol ogy th at would ex plo i t an in ter act i on
betw een po tent i a l and k i n et i c en er gies in t i d al f l ows. It p r oposes that ver y
lo n g d ams (for ex amp l e: 3 0
50 km len gth) be bui l t fr om coasts str a i ght out in to the sea or ocean, with out
en clos i ng an are a. Ti d al ph ase dif fer en ces are in trodu ced across the d am,
le adi n g to a si gnifi cant w ater - l evel dif fer ent i a l i n shall ow coastal s eas
featuri n g stro n g coast- par al l el o sci l lating t i d al cu r r ents su ch as found in the
UK, Ch i n a, and Korea . Ti dal l agoon
A n ew er t i d al en er gy d esi gn opt i on is to constru ct cir cular r etaini n g w al l s embedd ed with turbin es
that can capture the pot ent i a l en er gy of t i d es. The cr eated r eservo i rs are
si m i l ar to those of t i d al bar r ages, ex cept th at the loc ati on is artifi cial and do es
not contain a pr eex is t ing ecosystem.
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1.3.3 Wi n d Power
Generatio n : Hori zon tal
axi s:
Hor i zontal - ax is wind turbin es (HA WT) h ave the main rotor sha f t and
ele ctri ca l gen er ator at the top of a tow er, and must be po i nted in to the wind.
Sma l l turbin es ar e poin ted by a si m ple wind vane , while la r ge turbin es
gen er al l y use a wind sensor coupled with a servo mo tor . Most h ave a gearbo x ,
whi ch turns the slow rot at i on of the bl ad es in to a quick er r otation th at i s more
suitable to drive an el ectric al gen er ator .
Since a tow er pr odu ces turbulen ce behind i t , the turbine is usua l l y
posi t ioned upwind of i ts supporting tow er. Tu r bine bla d es ar e made sti ff to
pre vent the blad es f r om bei n g pus h ed in to the tow er b y h i gh winds.
Addit i on al l y , the blad es are pla ced a consid er ab l e dis tan ce in f r ont of the
tow er and are sometim es t i l ted fo r w ard into the wind a small amount.
Do w nwind ma chi n es h ave b een bui l t, d espi te the p r oblem of turbu l en ce
(m ast w ak e), because th ey don 't n eed an addi t ional me ch anism for k eepi n g
http://en.wikipedia.org/wiki/Rotor_(turbine)http://en.wikipedia.org/wiki/Electrical_generatorhttp://en.wikipedia.org/wiki/Wind_vanehttp://en.wikipedia.org/wiki/Servo_motorhttp://en.wikipedia.org/wiki/TurbulenceEE2451 EEGUC
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them in l i ne w i th the wi n d, and because in hi gh winds the blad es can be
a l l ow ed to bend whi ch r edu ces their swept ar ea and thus their wind r esi stan ce.
Since cycl i ca l (th at i s r epeti t i ve) tu r bul en ce m ay l ead to fat i gue fa i l u re s, most
HA WTs are of u pwind d esi gn.
Tu r bines used in wind farms for com me r cial pr odu cti on of ele ctr ic po w er are usual l y thr ee- bla d ed and poin ted in to the wind by compu ter -control l ed mo tor s. Th ese h ave hi gh t i p speeds of over 320 km / h (200 mph), hi gh ef f ici en cy, and low torque rip p le, whi ch contribute to good r el i abi l i ty . The bl ad es are usual l y color ed w hi te for d ayt i me vis i bi l i ty b y a ir cr aft and r an ge in le n gth f r om 20 to 40 met ers (66 to 131 ft) or mo re . The tub u lar steel tow ers ra n ge f r om 60 to 90 met ers (200 to 300 ft) tall. The bla d es rot ate at
10 to 22 r evolu t ions per m i nute. At 22 ro tat i ons per m i n ute th e t i p speed
ex ceeds 90 m eter s per second (300 ft/s).A gear box is com m on l y used for
stepping up the speed of the gen er ator, a l thou gh d esi gns m ay also use dir ect
d r ive of an annular gen er ator. Some models oper ate at consta nt speed, but
more en er gy can be col l ected b y var i abl e- speed turbin es wh i ch use a
sol i d - state pow er conv ert er to in ter face to the
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tr ansm i ssi on system. A l l turbin es are equipped with pr otect i ve featu r es to
avoid d ama ge at hi gh wind spe eds, b y feathe r i n g the blad es in to the w ind
which ceases their r otat i on, suppl ement ed b y bra k es.
Verti cal ax i s:
Vertic al - ax is wind turbi n es (or VA WTs) h ave the main rotor sha f t ar ra n ged
vertic al l y . On e adv ant age of th i s ar ra n gem ent is that the turbine do es not n eed
to be poin ted in to the wind to be ef fect i ve, wh i ch is an adv ant age on a si te
w h er e the wind dir ect i on is hi gh l y v ari able. It is a lso an adv ant age wh en the
turbine is in tegr ated in to a bui l ding becau se it is inhe re nt l y less steer able.
Also, the gen er ator and gearb ox can be pla ced n ear th e groun d , us ing a
dir ect d rive f rom the rotor assemb l y to the gr oun d - based gearbo x ,
i m pr oving accessi bi l i ty for mainten an ce.
The k ey disad vant ages include the r elative l y low rot at i on al speed
with the consequ ent i a l hi gh er t orque and h en ce hi gh er cost of the d r i ve
tr a in, the in h er ent l y l ow er po w er coef f i cien t , the 360 d egree rot at i on of the
aero foil with i n the w ind flow during each cycle and h en ce the hi gh l y
d yn am i c loading on the blad e, the pulsating torque gen er ated by some rotor
http://en.wikipedia.org/wiki/Feathering_(propeller)http://en.wikipedia.org/wiki/Brakehttp://en.wikipedia.org/wiki/Vertical-axis_wind_turbinehttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Wind_turbine_aerodynamicsEE2451 EEGUC
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d esi gns on the d r ive tr ain, and the dif f icul ty of modeli n g t h e wind flow
accu r atel y and h en ce the ch al l en ges of an al yzi n g and d esi gni ng the rotor prior
to f ab ri ca t i n g a proto type.
Wh en a turbine is moun ted on a roo f top the bui l d ing gen er al l y r edir ects
w ind over the roof and th i s can double the wind speed at the turbin e. If the
h ei ght of a roo f top moun ted turbine tow er is appro x i m atel y
5 0% of the bui l ding h ei ght it is n ear th e op t i m um for ma x i m um w i nd
en er gy and m i ni m um wind turbulen ce. Wind speed s with i n the bui l t
envi r onment are gen er al l y m u ch low er than at ex posed ru r al si tes, noise
m ay be a con cern and an ex is t ing stru cture m ay not ad equ atel y r esi st the
addi t ional str ess.
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1.3.4 Geother mal Power Generatio n :
Flash ed steam/ dry steam cond en sin g system ; r esour ce temp er ature r an ge
f r om about 320C to some
230C.
Flash ed steam back pressu re system ; r esour ce temp er atu r e ra n ge f rom about
320C to some 200 C. Bi n ary or twi n - fl u i d system (b ased upon the Kal i an or
the Or ganic R ankin cycl e); r esour ce tem perature r an ge betw een 120C to
about 190 C.
Power h ou se equ i pmen t: Compris i ng of turbin e/ gen er ator unit comp l ete
with cond enser, gas ex h aust system.
Auto matic con trol an d commun ica tion system: Consist i ng of f r equ en cy control, servo valve con trol, compu ter system for d ata col le ct i on, r esou r ce and mainte n an ce mon i torin g, in ter n al and ex tern al com m unic at i on etc.
Cooli n g system: Cool i ng w ater pumps, con d en sate pumps, f re sh w ater (seaw ater) cool i n g, or cool i ng tow ers.
Parti cu late and /or droplet erosion : This is an erosion p robl em that is typi cal l y associ ated wi th the p arts of the system wh er e the fluid is accele r ated (e.g. in control valves, turbine no zz les, etc.) and/or abr upt l y ma d e ch an ge di r ect i on ( e.g. via pipe ben d s, T- fitt i n gs or w an es).
Heat exch an gers: Th ese are ei th er of the plate or the tube and shell type. Th ese ar e gen er al l y on l y used in b i n ar y and h ybr id type conv ersion systems, an d /or in inte gr ated systems.
Gas evacu ation systems: Hi gh temp er ature geothe r mal fluid con tains a si gnifi cant qu ant i ty of no n -
cond ensable gases (C0 2 , N2, H2S, and othe r s). Th ese h ave to be removed for
i n stan ce f r om the cond ensi n g plant for r easons of conv ersion ef f ic i en cy. Some
countri es re quire the gas to be cl ean ed of H2S or Hg to m in i m iz e atm osph eric
pol l ut i on.
R e- i n jection system: Compris i ng l i quid ef f luent col l ect i on pipelines,
in ject i on pumps, in ject i on pipelines, inj ect i on w el l s and control system.
Ch emical i n jection system: In or d er to r edu ce sca l i ng of ca lcite in pr od u cti on
w el l s sometimes a sca l e inh i bi tor is in jected throu gh capi l la r y tub i n g down
hole. Si m i l ar in ject i on is appl i ed with caust i c sod a to n eutr a l iz e ac id w el l s
to r edu ce the cor rosiv el y . A cid is used for pH mod i f ic at i on in or d er to ar re st
the s ca l i ng of sil i ca in w aste w ater goi n g to r ein ject i on, f or cases wh ere th e
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wa ter is sup ersatu r ated.
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Power Hou se equ i pmen t:
Tu rbi n e:
The pr oblems pot ent i a l l y associated w i th the tu r b i ne are sca l i n g of the flow control valve and no zz les (p r i m ari l y in the stator inl et s tage); str ess cor rosion of r otor blad es; erosion o f turbine (rotor and st ator ) blad es and turbine h ous i n g.
The ra te and s eriousness of scal i n g in the turbine are dir ect l y r elat ed to
the steam cl eanl i n ess, i .e. the qu ant i ty and ch ar acter is t i cs of s epar ator
car r y - over . Thus the o per at i on and ef f ici en cy of the separ ator are of grea t
i mport an ce to trouble f ree turbine o per at i on. Prolon ged o per at i on of the
po we r
plant o f f - d esi gn point a l so pl ays a s i gnifi cant role.
Generator :
It must be poin ted out h ere that hi gh - temp er atu r e steam contains a si gnifi cant amount of ca rbon dio x ide
CO2 and some h yd r ogen sulphi te H2S and the atm osph ere in geoth erm al ar eas is thus
perm eated b y th ese gases.
All ele ctric al equip m ent and app ar atus contains a lot of cupro u s or si lver
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components, whi ch are h i gh l y susc ept i ble to sulphi te cor rosion and thus
h ave to be k ept in an H2S f r ee environme n t. This is achiev ed by filte r ing
the ai r ent er ing the vent i lation system and maintaining sl i gh t overp re ssu re
in the control room and ele ctri ca l cont r ol c entr es.
The pow er gen er ator is e i ther cooled b y ni tr ogen gas or atm osph eric a ir th at
h as been cl ean ed of H2S
by passage thro u gh sp eci a l a ct i ve carbon filter ban ks.
Conden ser:
The steam - w ater m i x ture em i tted f r om the turbine at ou t let contains a
si gn i fi cant amount of non
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cond ensable gases comp r is i ng main l y CO2 (whi ch is u su al l y 9 5 98% of
the to ta l gas con tent), CH4 and H2S, and is thus high l y acid i c.
Since most hi gh - temp er ature geoth erm al r esou rc es are l oca ted in arid or
sem i - arid ar eas far r em oved f r om si gnifi cant f re sh w ater (r ive r s, la k es)
sou r ces, the cond enser cool i ng choic es ar e mos tl y l i m i ted to ei th er
atm osph eric cool i ng tow ers or for ced vent i lation ones.
The appl ic at i on of evapor at i ve cool i n g of the con d ensate r esul ts in the
cond ensate containing dis solved o x ygen in ad di t ion to th e no n - cond ensab l e
gases, whi ch make the cond enser fluid hi gh l y cor r osi ve and r equire the
cond en ser to be clad on the ins i de with stain l ess steel; con d ensate pump sto be
m ade of stainl ess steel, and all cond ensate pipelines ei th er of stainl ess steel or
glass r einfo r ced plasti c.
Addit i on of caust i c soda is r equir ed to adjust the pH in the cool i n g tow er cir cui t . Ma k e- up w ater an d blow - down is a lso u sed to avoid acc umu l at i on of sal ts in the w ater caused by evapor at i on. A p r oblem som eti mes en coun tere d with i n the con d enser is the d eposit i on of al m ost pure sulphur on w al l s and no zz les w i thin the cond enser. This s ca le d eposit i on must be p eriodi ca l l y cl ean ed by h i gh pr essure w ater spr ayi n g etc.
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Cooli n g tower an d associat ed equ i pmen t:
Most hi gh - temp er ature geothe r mal r esour ces a r e loc ated in arid or s em i -
ar i d ar eas far r emoved f r om si gnifi cant f r esh w ater (r i vers, l ak es) sou r ces. This
mos tl y l i m i ts cond enser cool i ng cho i ces to eith er
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a tm osph eric cool i n g tow ers or for ced vent i lation ones. Fr eshw ater cool i n g
f r om a r iv er is, how ever, used for ins tan ce in N ew Z ealand and seaw ater
cool i ng f r om w el l s on Reyk jan es, Iceland.
In old er po w er pl ants the atm osph eric versions an d/or b arom etric on es, the
la r ge par abol i c on es of con cr ete, w ere most of ten chose n . Most f r equ ent l y chosen
for mode r n pow er plants is the forc ed vent i lation type becau se of
enviro n ment al i ssues and loc al p ron en ess to earth qu ak es.
The mode r n f or ced vent i lation cooling tow ers ar e typ i cal l y of
wood en/p l asti c constru ct i on compris i n g sever al par al l el cool i ng cel l s er ected on
top of a l i n ed con cr ete con d ensate pond. The vent i lat i on f ans are norm al l y
verti cal, r eversible flow type and the cool i ng w ater pumped onto a platf orm at
the top of the tow er fitted with a la r ge numb er of no zz les, thro u gh whi ch the
hot cond en sate d rips in counte r flow to th e air f low onto and throu gh th e fill i n g
mat er i a l in the tow er and then ce in to the con d ensate pond, w h en ce th e cooled
cond ensate is su ck ed b y the cond enser va cuum b ack in to the cond enser.
To m i ni m i se sca l i ng and cor rosion ef fects th e cond en sate is
n eutr a l ised throu gh pH cont r ol, p r incip al l y via addi t ion of sodium
ca rbon ate.
Th re e types of p r oblems are found to be associated with the cool i ng tow er s, i.e.
Icing probl ems i n
cold ar eas.
Sand blown onto the tow er in s an d y
and arid are as.
ging up b y
sulphi teph yl i c bac teri a.
The fi r st menti on ed is counte re d b y r eversi n g the air f low cell b y cell
in ro tat i on whilst oper at i n g thus
melt i ng off an y ici n g and snow
col l ect i ng on t h e tow er.
The second pr oblem requir es f re qu ent cl eani n g of no zz les and
con d ensate pond. The last mentioned is
qui te bothe r some. It is m ost com m on l y a l l eviat ed by periodic appl i ca t i on of
bac teria ki l l i n g ch em ic als, and cle ani n g of cool i ng tow er no zz les by w ater
jett i n g. The sludge acc um u lation in the cond ensate pond, how ever, is r emoved
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d u r ing sch eduled mainte n an ce stop s. A second ar y p r oblem is the d eposit i on of
a l m ost pure sulphur on w al l s and other sur faces with i n the cond enser . It must
be periodi cal l y cle an ed by h i gh p re ssure w ater sp r ayi n g etc., w hich must be
car r i ed out during sch eduled tu rbine stop s.
Conden ser pu mpi n g
system:
The cond ensate pumps mus t, as r ecounted pre vious l y , be made of
hi gh l y cor rosion r esi stant mat eri a ls,and h ave h i gh su ct i on h ead capabi l i t ie s. Th ey ar e mos tl y trouble f r ee in op er at i on.
The cond en sate pipes m ust a lso be made of h i gh l y cor r osion r esi stant
ma teri a ls and all jo i nts ef f i cient l y s ealed to k eep atm osph eric a ir i n gr ess to a
m i n i mu m , beari n g in m i nd tha t such pipes are a ll in a vacuum environme n t.
A n y air le ak age in cre ases the load on the gas evacu ati on system and thus the
an ci l la r y pow er consumpt i on of the po w er pl ant.
Heat
exch an gers:
In h i gh - tempe ra tu re po w er gen er at i on appl i ca t i on s he at e x ch an ger s are
gen er al l y not us ed on the we ll fluid. Th eir use is g en er al l y confin ed to
an ci l l ar y uses su ch as h eati n g, etc. usi n g the d r y steam. In cogen er at i on
plants such as the si m ul tan eous pro d u cti on of hot w ater and ele ctrici ty , t h eir
use is
unive r s
al.
The ex h aust f r om a back pre ssure turbine or ta p - of f steam f r om a pr ocess turbine is passed as pr i m ar y fluid th r ou gh ei th er a pla te or a tube and sh ell type h eat e x ch an ger.
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The plate type h eat ex ch anger w as much in favour in cogen er at i on pla n ts
in the sevent i es to n i n et i es b ecause of th eir comp actness and h i gh ef f i cie n cy.
Th ey w er e, ho w ever, found to be r ather h eavy in mainten an ce.
The second d r aw back w as that the h i gh cor r osi on r esi stan ce plate mat eri a ls
r equir ed w er e on l y able to withstand a re lativ el y m od er ate p r essure d i f fer en ce
betw een pr i m ar y and s econd ar y h eat e x ch an ger medi a. Third l y th e plate
seals tend ed to d egen er ate fai r l y f ast and sti ck ten ac ious l y to the plat es making
removal dif f icult without d ama ging the seals. The seals that w ere n eed ed to
withs tand the r equir ed temp era ture and p re ssure w er e also pri cy and not
alw ays in stock with the supplie r s.
This has led most plant op er ators to c h an ge over to and n ew pl ant des i gn er s
to sele ct the shell and tube confi gu r at i ons, whi ch d emand less mainten an ce
and are easi l y cl ean ed th an th e plate type tho u gh r equiring more r oom.
In lo w - temp er ature bin ar y po w er pl ants sh ell and tube h eat e x ch an gers
ar e used to tr ansf er the h eat
f r om the geothe r mal pr i ma r y fluid to the second ar y (bin ar y) fluid. Th ey are a lso used as con d en sers/ and or re gen er ators in the secon d ar y system.
In sup er critic a l geoth er m al pow er gen er at i on si tu at i on it is fo re seen that
sh ell and tube h eat ex ch an gers will be used to tr ans fer the the r mal en er gy of
th e supe r critic a l fluid to the p r odu cti on of cle an steam to pow er the
envi saged po w er conv ersion system.
Gas evacu ation
system:
As p re vious l y sta ted the geoth erm al s team contains a si gnifi cant
quanti ty of no n - cond en sable gas (NCG) or some 0. 5 % to 10% by w ei ght of steam
in the ver y wo r st case. To pr ovide and maintain su f fi cient v acuum in the
cond en ser, the NCG plus an y atmosph eric air le ak age in to the cond en ser must
be fo r cib l y ex h austed. The fol l owing methods are typic al l y ad opted, vi z.:
The use of a si n gle or two stage steam ejectors, econom i ca l for NCG content less than 1.5% by w ei gh t of steam.
The use of me ch anic al gas pumps, such as l i quid ring vacuum pumps, w hich are econom ic al for hi gh con cent r at i on of NCG.
The use of h ybr id system s inco r por ati n g methods 1 and 2 in s eri es.
The adv ant ages of the ejector systems ar e the low mainten an ce, and high
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oper at i on al secu r i t y of such systems. The disadv ant age is the si gnifi cant pre ssur e steam consumpt i on, whi ch
oth er w ise would be avai l ab l e for pow er p r od u cti on.
The ad vant ages of the vacuum pumps ar e the h i gh d egree of evacu ati on
possi ble. The disadv an tage is the ele ctric an ci l l a r y po w er consumpt i on,
sensi t i vi ty to particul ate d eb ris in the cond enser, and hi gh mainten an ce
r equir em ents.
To r ed u ce th e amb i ent l evel of H2S in the p r ox i m i ty of the pow er plant, th e
ex h austed NCG is cu r r ent l y in most countri es disch ar ged below the cool i ng
tow er vent i lators to ensure a thorou gh m i x ing with the air as it is being
blown hi gh in to the air and aw ay f r om the pow er plant and i ts environs. In
the USA and Ita l y H2S abatem ent is man dator y b y l aw, and in Ital y a lso
me rc u r y (Hg) and thus r equire ch em i ca l type abatem ent m easu r es.
In some of the older Geysers fi eld pow er plants the H2S ri ch cond en ser ex h aust w as passed th r ough abed of i r on and zinc ox i de to r emove the H2S. Th ese pro ved a ver y m essy w ay of gett i n g r id of t h e
H2S and we r e mostl y abandon ed af ter a f ew year s. In a few inst an ces the Str etfo r d pr ocess and ot h er
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equival ent on es h ave been used upstr eam of the pow er plant to conv ert H2 S gas
in to sulphur for industrial use. This h as pr oved ex pensive and comp l ex and is
not in use in other geothe r mal fi elds than the Geysers fi eld i n Califo r nia.
The main H2S ab atem ent methods cu r r ent l y in use wo r ldwide ar e (on l y some are cu r r ent l y u sed for geoth erm al NCG): 1. Claus (Sele ctox ).
2. H aldor Topse WSA
pr ocess.
3. Sh el l - Paqu es Bio l ogi ca l H2S r emoval
pr ocess/ THIOPAC.
4. LO- CAT (w et sc r ubbi n g l i quid
r edox system).
5. Fe- Cl h ybr id
pr ocess.
6. Aqu eous N aOH
absor bent pro cess.
7. Polar organic
absorb ent pr ocess.
8. Photo c ata l y t i c
gen er at i on p r ocess.
9. P lasma ch em i ca l
gen er at i on pr ocess.
10. Th erm al
d ecomposi t ion pro cess.
11. Memb ra ne
technol ogy.
A stu d y in to feasib l e H2 S abatem ent methods for the Nesjav el l ir
Geothe r mal Proj ect w as ca r r ied out by Matth asdtt i r (2 0 06). Matth asdtt i r
and Gunn arsson, f r om th e Icel and Technol ogy Inst i tu te,came to the con clus i on
that of th e above l i sted methods the following four me r i ted fu r ther stu d y for
Nesjavel l ir, i.e the Ha ldor Tops e- WSA, T HIOPAQ (wit h b acter i a), LO- CAT and
the Fe- Cl h ybr id pr ocess.
Re- i n jection
system:
In most geoth erm al are as the geoth erm al fluid m ay be consid er ed to
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be b r ine because of th e
typic al l y h i gh chl oride content. It m ay also con tain some und esir ab l e tr acer
elem ents that pose d anger to humans, fa una and flo ra .
In consid eri n g the most conv en i ent w ay of disposing of th i s l i quid
ef f luent oth er than in to ef f luentponds on the sur face, the id ea of in ject i n g the
l i quid ef f luent back in to the ground h as been with the geoth erm al pow er
indust r y for a lo n g t i me (Stefnsson, 1997 ). Ini t ial l y the purp ose of r e- in ject ion
w as si m pl y to get rid of th e l i quid ef f luent in a more el egant w ay than
dump i ng it on the sur face, in to lak es or riv ers, and even to the ocean. M an y
techn i ca l an d econom i c d r awb acks w ere soon discov er ed. The more s erious of
these w ere t h e clog gi n g up of in ject ion w el l s, in ject i on pip i ng and the
fo r mations clo se to the bor ehole; the cold ef f lu ent m i gr ated in to the pr odu cti on
zone so r edu cing the enthal py of the w ell output wi th consequ ent fa l l - of f in
pow er plant out put. Inj ect i on in to sand stone and oth er poro u s al l uvial
fo r mations w as and is f rau ght wi th loss of inje ct i vi ty pro b lems that are sti ll not
ful l y und erstood.
Soon, how ever, it became gen er al l y und erstoo d and accepted that
r etu r ning the ef f l u ent l i quid b ack in to the re servoir h ad even gre ater
addi t ional ben efits, v iz .:
Grea tl y r edu ci n g the r ate of re servoir pr essu re and fluid y ield d ecl i n e.
Impro ved ex tr ac t i on of the h eat con tent cont ained with i n the re servoir
for mations.
R edu cing the fluid withdr aw al ef fect on su r face m anif estations, e .g.
hot p ools, steam vents etc. All the above i tems serve to m ain ta in r esour ce
sustainabil i ty and are thus of si gnifi cant environme n tal b en efit.
R e- in ject i on should be consi d er ed an in tegr al part of
an y m od ern, sustainable and environme n tal l y
f r iend l y geothe r mal ut i l iz at ion, both as a method of ef f luent w ater
dispos al and to counte r act pre ssur e d ra w - down b y pr ovid i n g ar t i fi cial w ater
r ech ar ge (Stef nsson, 1997 ). R e- i n ject i on is essential for sus tainable
ut i l iz ation of virtu al l y cl osed and l i m i ted rec h ar ge geothe r mal systems. Cool i ng
of p r odu cti on w el l s, which i s one of the d an gers associat ed with r e- in jecti on,
can be m i ni m ised thou gh
ca reful t esti ng and r esear ch . T r acer t esti n g, comb i n ed with comp re h ensi ve
in terp re tation, i s prob ab l y the most i m port ant tool for th i s purpo se.
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Ma n y dif fer ent methods h ave and ar e sti ll bei n g t ri ed to over come
th ese techn i ca l pr ob l ems mentioned above such as the use of sett l i ng tan ks
that pr omo te po l ym eris at i on of the si l ica mo l ecu l es and s ett l i ng in the tanks
pr ior to i nje ct i on; i nje ct i on of the ef f luent l i quid d i r ect l y f rom the s epar ators at
temp er atu r es in the ra n ge of 1 4 5 160C, so ca l l ed hot i nje ct i on , both to
avoid cont ac t w i th
atm osph eric a ir and to h i nd er s ca l i n g in the in ject i on system; controlling
th e pH of the ef f luent com m ensur ate with r ed u cti on in the ra te of
si l ic a/ ca lcite p r ecip i tation using acids and add cond ensate f r om the plant
to d i lu te the silica in the brin e, t o n ame a few.
The d an ger of pr od u cti on w ell cool i n g can be m in i m i sed throu gh
car eful testing and r esear ch . T ra cer testin g, comb i n ed with compr eh ensive
in terp re tat i on, is pr ob ab l y the most i m port ant tool for th i s purp ose. One w ay
to d el ay t h e ef fects of cool i ng is a lso to loc ate the r e- in ject i on w el l s far eno u gh
aw ay f r om the pro d u cti on ar ea, say 2 km.
Anoth er w ay gai n ing po pula r i ty is to in ject de ep i n to the re servoi r ,
even w h ere th ere is small p erm eabi l i ty , b y pump i n g at h i gh p r essur es (6 0
1 00 b ar ).
Su r face dispos al contr aven es the environme n tal statut es of most countri es and the use of sett l i ng tanks h as ceased most l y because of associ ated cost and comp l ex i ty. T h e most com m on l y adopted i n ject i on methods are the l ast two, i.e. hot r e- in ject i on and ch em i ca l pH control on es. The main dis adv ant age of the hot re - in ject i on te chnique is the low er ed o ver all the r mal ef f ici en cy and the consequ ent gr eater fluid produ cti on (mo r e w el l s to y i eld the same pow er output) r equir ed. T h e main dis adv ant age of the pH control sch eme is the ver y la r ge ac id consumpt i on ( cost) and un cert a in t i es r egarding i ts lo ng - ter m ef fects.
Hot r e- in ject i on is pre cluded in lo w - temp er ature pow er gen er at i on an d the most com m on te chnique is to m ake use of the re verse solubi l i ty of calcite in w ater b y oper at i ng the conv ersion system at a p re ssure le vel above th e CO2 bubble point and on l y re d u ce the p r essur e on ce the f lu i d temp er ature h as atta ined a lev el l ow eno u gh to pr event c al ci te dis sipation prior to r e- in ject i on.
1.3.5 Solar Power
Generatio n :
Con centr at i n g Solar Pow er (CSP) systems use le n ses or m i r r ors and tr acking systems to fo cus a
la r ge ar ea of sunl i ght in to a small beam. The con centr ated h eat is then used as
a h eat sour ce for a conv ent i on al pow er pla n t. A wide r an ge of con centr at i n g
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technol ogies ex i sts: the most d eveloped are the p ar abol i c tro u gh th e
con centr at i n g l i n ear f r esnel r efl ector, the Sti rling d ish and the sol ar po w er
tow er. V arious techniq u es ar e used to tr ack th e sun an d fo cus l i ght. In a ll of
th ese systems a w orking fluid is h eated b y the con cent r ated sunli ght, and is
then used for pow er gen er at ion or en er gy stor age. Th erm al stor age ef fi cient l y
a l l ows up to 24 hour ele ctrici ty gen er at i on.
http://en.wikipedia.org/wiki/Working_fluidEE2451 EEGUC
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A p ar abol i c tro u gh cons i sts of a l i n ear par abol i c r efl ector that
con centr ates l i ght onto a r eceiver posit i on ed along the r ef l ector 's fo cal l i n e. The
re ceiver is a tube posit i on ed ri ght above the m i ddle of the par abol i c m i r r or
and is f i l l ed with a wo r ki n g fluid. The r efl ector is made to follow the sun
d u ri n g d ay l i ght hours b y tr acki n g a long a sin gle ax is. Par abol i c t r ou gh systems
pr ovide the best lan d - use fa ctor of an y so l ar te chnolo gy.
http://en.wikipedia.org/wiki/Parabolic_troughEE2451 EEGUC
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Compa ct L in ear Fr esnel R efl ectors are CSP- plants whi ch use ma n y
th i n m i r r or strips ins tead of p ar abol i c m i r r ors to con centr ate sunl i ght onto two
tubes with wo r king fluid. This h as the adv ant age th at fl a t m i r r or s can be used
whi ch ar e much ch eaper than par abol i c m i r r or s, and th at more refl ectors can
be pla ced in the same amount of space, a l l owing m ore of the avai l able
sunli ght to be used. Con centr at i n g l i n ear f re snel r efl ectors can be used in
eith er la r ge or m or e comp act p l ants.
The Sti rling solar dish comb i n es a par abol i c con centr at i n g dish
with a Sti rling en gine whi ch norm al l y d r ives an el ectric gen er ator. The
adv an tages of St i rling solar over photovo l taic cel l s ar e hi gh er ef f ici en cy of
conv erting sunli ght in to ele ctrici ty and lon ger l i fet i me. Par abol i c dish systems
give the hi gh est ef f ici en cy amo n g CSP technol ogies. The 50 kW Big Dish in
Canb er r a, Austr a l i a is an ex amp l e of th i s technolo gy.
A solar po w er tow er uses an ar r ay of t r acki n g r efl ectors (h el i ostat s) to
con cent r ate l i ght on a centr a l r ecei ver atop a tow er. Pow er tow ers are more
cost ef fect i ve, of fer h i gh er ef f i cien cy an d better en er gy stor age capabi l i ty
http://en.wikipedia.org/wiki/Compact_Linear_Fresnel_Reflectorhttp://en.wikipedia.org/wiki/Stirling_enginehttp://en.wikipedia.org/wiki/The_Big_Dish_(solar_thermal)http://en.wikipedia.org/wiki/Canberrahttp://en.wikipedia.org/wiki/Solar_power_towerhttp://en.wikipedia.org/wiki/HeliostatEE2451 EEGUC
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amo n g CSP technol ogi es. The PS10 Solar Pow er P lant and PS20 sola r pow er
plant are ex amp l es of th i s technolo gy.
1.3.6 Bio mass Power
Generatio n :
Bio m ass is bio l ogic al mat eri a l d eriv ed f rom l i vin g, or r ecent l y l i vi n g or ganis m s. It most of ten
r efers to plants or plan t- based mat er i a ls whi ch ar e specific al l y cal l ed
l i gn ocel l ulos i c bio m ass. As an en er gy sour ce, bio m ass can ei th er be used
di r ect l y via combust i on to pr odu ce h eat, or ind i r ectl y aft er con verting it to
various fo r ms of biofu el . Conv ersion of bio m ass to biofu el can be achiev ed by
d i f fer ent methods whi ch are br oad l y classifi ed in to: the r mal, ch em i ca l , and
bioch em i ca l methods .
http://en.wikipedia.org/wiki/PS10_Solar_Power_Planthttp://en.wikipedia.org/wiki/PS20_solar_power_planthttp://en.wikipedia.org/wiki/PS20_solar_power_planthttp://en.wikipedia.org/wiki/PS20_solar_power_planthttp://en.wikipedia.org/wiki/Biomaterialhttp://en.wikipedia.org/wiki/Lignocellulosic_biomasshttp://en.wikipedia.org/wiki/BiofuelEE2451 EEGUC
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Wood r emains the l ar gest bio m ass en er gy sour ce to d ate; ex amp l es
include fo r est r esid u es (su ch as d ead tr ees, b ra n ch es and tr ee stu m ps), yard
cl i ppin gs, wood chips and even mun i cipal sol i d w aste. In the s econd sen se,
bio m ass includ es plant or an i mal matter that can be conv ert ed in to
fib ers or other indus tri a l ch em i ca l s, including biofu el s. Industri a l bio m ass
can be gr own f r om nume r ous types of plants, including m i scanthu s,
sw i tch gr ass,h emp , cor n , popla r , wil l ow , sor ghu m , sugar can e, bamboo , and a
vari ety of tr ee species, r an ging f r om eu ca l yptus to oil palm (palm oi l ).
P lant en er gy is pr od u ced by crops specifi ca l l y gr own for use as fu el
that of fer h i gh bio m ass output per h ectare with l ow input en er gy. Some
ex amp l es of these p lants are wh eat, wh i ch typic al l y y i eld
7.5 8 tonnes of gr ain per h ecta r e, and str aw, whi ch typic al l y y ield 3. 5 5
tonn es per h ecta r e in the UK. The gr ain can be used for l i quid tr ansport at i on
fu els while the str aw can be burn ed to pr odu ce h eat or ele ctrici ty . P lant
http://en.wikipedia.org/wiki/Tree_stumphttp://en.wikipedia.org/wiki/Municipal_solid_wastehttp://en.wikipedia.org/wiki/Chemical_industryhttp://en.wikipedia.org/wiki/Biofuelhttp://en.wikipedia.org/wiki/Miscanthushttp://en.wikipedia.org/wiki/Switchgrasshttp://en.wikipedia.org/wiki/Switchgrasshttp://en.wikipedia.org/wiki/Maizehttp://en.wikipedia.org/wiki/Poplarhttp://en.wikipedia.org/wiki/Willowhttp://en.wikipedia.org/wiki/Sorghumhttp://en.wikipedia.org/wiki/Sugarcanehttp://en.wikipedia.org/wiki/Bamboohttp://en.wikipedia.org/wiki/Treehttp://en.wikipedia.org/wiki/Eucalyptushttp://en.wikipedia.org/wiki/Oil_palmhttp://en.wikipedia.org/wiki/Palm_oilhttp://en.wikipedia.org/wiki/HectareEE2451 EEGUC
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bio m ass can also be d egr ad ed f r om cel l ulose to gluco se thro u
