compressor and hot section fouling in gas turbines - causes and effects by meher-homji (1987)

7/29/2019 Compressor and Hot Section Fouling in Gas Turbines - Causes and Effects by Meher-Homji (1987)

1/9

COMPRESSOR AND BOT SECTION FOOLING IN GAS TURBINES - CAUSES AND EPFECTSCYRUS B. MEHER-HOMJI

Manager, Advanced TechnologyBoyce Enginee r ing I n t e r n a t i o n a l , I n c .

Houston, Texas

ABSTRACT

Th e f o u l i n g o f a x i a l f low co mp resso r s an dt u r b i n e s i s a s e r i o u s o p e r a t i n g problem ingas t u r b i n e en g i n e s . These pr ime moversa re b e in g i n c r e a s i n g l y used in c o g e n e r a t i o na p p l i c a t i o n s an d with t h e l a r g e a i r massf low r a t e ( e . g . 63 3 Lbs/Sec fo r a 80 MWegas t u r b i n e ) f o u l a n t s even in t h e ppm rangecan cau se d e p o s i t s on t h e b l a d i n g r e s u l t i n gi n s e v e r e performance dec rement s . Th i s i sa common o p e r a t i n g problem expe r i enced bya lmo s t a l l o p e r a t o r s o f g as t u r b i n e s .Th e e f f e c t o f compressor f o u l i n g i s a dropin a i r f l o w an d a drop in compressori s e n t r o p i c e f f i c i e n c y . Foul ing o f t h e

a x i a l compressor r e s u l t s in a drop ino u t p u t an d t he rma l e f f i c i ency o f t h esys t em. In some c a s e s , f o u l i n g c an a l s or e s u l t i n su rge problems as i t s e f f e c t i st o move th e compressor s u rg e l i n e t o t h er i g h t i . e . to w ard s t h e o p e r a t i n g l i n e .Th is paper d i s c u s s e s th e mechanism o ffoul ing and the aerodynamic an dthermodynamic e f f e c t s . Th is pape r a l s od i s c u s s e s t y p e s o f f o u l a n t s commonlye x p e r i e n c e d , d e t e c t i o n methods an df i l t r a t i o n t e c h n i q u e s . A b r i e f d i s c u s s i o no f t u r b i n e f o u l i n g , which i s p a r t i c u l a r l yr e l e v a n t when he a vy f u e l s a r e u t i l i z e d , i sa l s o d i s c u s s e d .

INTRODUCTION

Gas t u r b i n e s being a i r b r e a t h i n g mach in es ,i n g e s t l a r g e q u a n t i t i e s o f a i r . Th e s o l i d so r condensing p a r t i c l e s in t h e a i r and int h e combus t ion 9 a s s e s c an p r e c i p i t a t e onth e r o t a t i n g an d s t a t i o n a r y b l a d i n g caus ingchanges in a e rodyna mic p r o f i l e , d ro p p in gth e compressor mass f low r a t e an d a f f e c t i n gt h e t u r b i n e f low c o e f f i c i e n t an d e f f i -c i e n c y. Th is h as an a d v e r s e e f f e c t on t h eu n i t ' s pe r fo rmance . Th e o u t p u t o f a gast u r b i n e can drop by as much as 10%.Moreover, t h e con tamina t ed a i r ca n cause ah o s t o f problems t h a t i n c l u d e e r o s i o n ,f o u l i n g , c o r r o s i o n an d i n some c a s e splugg ing o f t h e h o t s e c t i o n c o o l i n g

p a s s a g e s .CAUSES OF FOULING

Ex p er ien ce has shown t h a t a x i a l co mp resso r sw i l l f o u l in most o p e r a t i n g env i ronment s ,be t h e y i n d u s t r i a l , r u r a l o r mar ine . Therea r e a wide range o f i n d u s t r i a l p o l l u t a n t san d a wide range o f e n v i ro n men ta l c o n d it i ons ( fog r a i n , e t c . ) t h a t a l s o p l a y ap a r t in th e f o u l i n g p r o c e s s .

Compressor f o u l i n g can be cau sed by th efo l l owing f a c t o r s . Thi s i s n ot an exhaust i v e l i s t .

1 . A irb o rn e S a l t .

2 . I n d u s t r i a l P o l l u t i o n - f l y a s h , hydroc a r b o n s , smog, e t c . Thi s causes agr imey c o a t i n g on t h e e a r l y s t a g e s an dcan g e t baked on in t h e l a t t e r s t a g e s( e s p e c i a l l y wi t h high p r e s s u r e r a t i ocompresso rs ) .

3 . I n g e s t i o n o f Ga s Tu rb in e Exhaus t .

4 . Min era l D e p o s i t s .

5 . Ai rborne M a t e r i a l s - s o i l s , d u s t an ds a n d , ch emica l f e r t i l i z e r s , i n s e c t i -c i d e s , i n s e c t s , an d p l a n t m a t t e r .

6 . I n t e r n a l Ga s Turb ine O i l Leaks - a x i a lco mp resso r f r o n t b e a r i n g i s th e commonc u l p r i t . O il l e a k s combined wi th d i r ti n g e s t i o n cause heavy f o u l i n g p r o blems.

7 . Impure wate r from Evapora t ive C o o l e r s .

8 . Coa l , D u s t , an d Sp ray P a i n t t h a t i si n g e s t e d .

Th e f o u l i n g r a t e t h a t a compressor w i l le x p e r i e n c e w i l l be a f u n c t i o n o f t h e e n v i -ronment , t h e c l i m a t i c c o n d i t i o n s an d th ef i l t r a t i o n sys t em.

I t i s i m p o r t a n t t o note t h a t wi th h igh a i ri n g e s t i o n r a t e s o f 33 lb s /K w /H r, even p o l -l u t a n t s in t h e ppm r an g e w i l l accoun t Eo rs e v e r a l pounds o f p o l l u t a n t being i n g e s t e din 24 h o u r s . For example, a 75 MW u n i tl o c a t e d in an i n d u s t r i a l a i r l oad ing o f 10ppm w i l l r e s u l t in 59 4 l b s . o f p a r t i c u l a t e sb e in g i n g e s t e d in a day.

Some t y p i c a l a i r l oad i n g s , as repo r ted byUpton [1 ] a r e :

Country 0.01 - 0.1 ppm by w eig h tC o a s t a l 0.01 - 0 .1 ppm by w eig h tI n d u s t r i a l 0.1 - 10 ppm by w eig h tD e s e r t 0.1 - 70 0 ppm by w eig h t

Tab le 1 p r o v i d e s a t a b u l a t i o n showing e n v i -ro n men ta l f a c t o r s [ 2 ] .

Even a e r o - e n g i n e s o p e r a t i n g a t "c lean"c r u i s e a l t i t u d e s o f 40,000 f t . havei n c u r r e d f lame-ou t s as a r e s u l t o f v o l c a n i c

261

ESL-IE-87-09-43

Proceedings from the Ninth Annual Industrial Energy Technology Conference, Houston, TX, September 16-18, 1987


2/9

NVIROtIo4ENl COUNTRY SIDE LARGE: CITIES lHOUSTRIAL OESERTS MTIC MOOllE(P'OWirS'lifT'Qn,) AREAS (SanT"'S'TCi7iiis) ltlSTALLAT 10145(Chemical (St..1 iliOJ"ku


3/9

Th e power de ve lope d by a t u r b i n e i s givenby :

1(ower m 1 1 )'Y - 1( : ~ ) ~

Where,

m Mass Flow Rate Through Tu rb in e

m + ma f

C = S p e c i f i c Heatp

T = F i r i n g Temp. (Tu rb in e I n l e t Temp.)3

p3 Expans ion Rat io

p

4

C

--E...C

v

Th e p r e s s u r e P3 e n t e r i n g th e t u r b i n e i st h e compressor d i s c h a r g e p r e s s u r e l e s s th ep r e s s u r e d ro p i n t he combus t ion s y s t e m . Ast h e mass f low d r o p s an d th e d i s c h a rg ep r e s s u re f rom th e compressor d r o p s , ( i . e .P3 d ro p s as P3 P2 - 6 P ) , t h e workfrom th e t u r b i n e d r o p s . Th is d ro p in powerw i l l be masked by t h e c o n t r o l system i n -c r e a s i n g Tu rb in e I n l e t Tempera ture (T3 ) .

As much o f 60-70% o f t h e power d ev e lo p ed int h e t u r b i n e g o es i n t o d r i v i n g t h e com-p r e s s o r , l e a v i n g 40-30% fo r u s e f u l s h a f to u t p u t . As t h e c ompre s s o r e f f i c i e n c yd r o p s , i t w i l l consume even more power,t h u s f u r t h e r lo w er in g th e g a s t u r b i n e ' so u t p u t . Th e f i r i n g t e m p e r a t u r e T3 ca nbe i nc rea sed on ly upto a 1 im i t b ecau se o fh o t s e c t i o n l i f e r e d u c t i o n c o n s i d e r a t i o n s .This p r o c e s s i s s c h e m a t i c a l l y shown inFig u re 2.

An a x i a l c ompre s s o r i s a machine where th eaerodynamic p er fo rman ce o f each s t a g edepends on t h e e a r l i e r s t a g e s . Thus , whenf o u l i n g o c c u r s i n th e i n l e t guide v an es an dt h e f i r s t fe w s t a g e s , t h e r e ma y be adrama t i c d ro p i n c ompre s s o r p e r f o r m a n c e .

Th is can o f t e n o c c u r when o i l an d i n d u s -t r i a l smogs o r p o l l e n a r e p r e s e n t an d forman adhes ive we t t i ng a g e n t . Th e e a r l ys t a g e s a r e o f t e n t h e w o rs t f o u led s t a g e s .I f t h e r e a r s t a g e s f o u l , t h i s seems t ohave a s m a l l e r impact on p er fo rman ce , b u tdue t o t h e h i g h e r t e m p e r a t u r e s , th ed e p o s i t s ca n g e t baked on an d becomed i f f i c u l t t o c l e a n . Th is baking e f f e c t i smore s e v e r e on t h e high p r e s s u r e r a t i oco mp resso r, e . g . , 18 t o 30:1 p r e s s u r e r a t i oo f a e r o d e r i v a t i v e machines as opposed t ot h e t y p i c a l 10 : 1 o r 12: 1 p r e s s u r e r a t i o sfound on t h e heavy d u t y i n d u s t r i a lmach in es .

~ E S F O ~ ~

me drops

!Wturblne = Wcompr + WopWturblne = hhe+mf] CplT3 - T4JP3/P 4 91# P2/P l ' Neglecting comb. AP

Pr ROlliDrops .'. Pz Drops ,', P3 /P " Drops Ability toextract A T drops. T4 (Ie. EOT) Increases.

'\ c drops\ (

TlT[T3] Incr8DS8s till red IIne-; then Outpul [WopJ drops.

n th drops =>- fuel costs Increase.

F i g . 2

An i m p o r t a n t e f f e c t o f f o u l i n g , e s p e c i a l l yn o t i c e d on s p l i t s h a f t (mech an ica l d r i v e )machines i s t h a t f o u l i n g can c a u s e a move-ment oE t h e co mp resso r s u rg e l i n e . Thee f f e c t o f f o u l i n g i s t o move th e s u rg e l i n et o t h e r i g h t where it ca n i n t e r f e r e witht h e o p e r a t i n g l i n e . Th is i s shown i nFigure 3 . The re have been c a s e s w iths i n g l e s h a f t t u r b i n e s i n c o n s t a n t speedo p e r a t i o n t h a t have had d i s a s t r o u s su rgeprob le ms [ 5 ] . Sev ere e r o s i o n can a l s os h o r t e n th e b l a d e t i p ch o rd which r ed u cesb l a d e t i p s o l i d i t y which e f f e c t s s t a g es t a b i l i t y .

Figure 4 shows a d iag ram d ev e lo p ed by Zaba[3 ] where th e change in ou tpu t an d s p e c i f i ch e a t consumption o f a g as t u r b i n e wa sexamined as a f u n c t i o n o f c ompre s s o r volumef low r a t e an d e f f i c i e n c y (o f c ompre s s o r an dt u r b i n e ) . Th e r e f e r e n c e i s h i g h l yrecommended Eor anyone w ish in g t o s t u d yt h i s phenomenon f u r t h e r .

EFFECTS ON BLADING INTEGRITY

Blad in g E a i l u r e s in g as t u r b i n e s r e l a t e t oa b o u t 42% o f t h e damage c a u s e s . Whilef o u l i n g canno t be s a i d t o he a major cau se

263

ESL-IE-87-09-43



4/9


5/9

w i l l d e g r a d e , c a u s i n g b l a d e damage.Cement d u s t , c o a l d u s t an d f l y ash canbe r e s p o n s i b l e fo r t h i s prob lem.Plu99 ing o f c o o l i n g h o l e s can be as low p r o c e s s an d may go u n d e t e c t e du n t i l major o v e r h a u l s .

Figure 5 shows a f o u l i n g p r o ~ e s s t h a to c c u r s i n a l a r g e g as t u r t i n e e n g i n e . This

graph shows th e changes i n compressor e f f i -c i e n c y and h e a t r a t e over t i m e .

COMPRESSOR ADIABATIC EFFICIENCY VS TIME

0.855-

0.850

0.845

0.840

0.835

0.830

0.825

0.820

0.815

HEAT RATE DROP OVER TIME

107

106

105

104

103

102

101

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38

F i g . 5 E f f e c t s o f Fou l ing on a Ga s Turb ine

ECONOMIC E F F E C ~ S OF COMPRESSOR FOULING

Fou l ing c a u s e s d l v e r s e conce rns t od i f f e r e n t o p e r a t o r s . ~ o r example , t h epr ime concern o f t h e A i r f o r c e o r Navy i st h e l o s s o f perfo rmance o f t h e gas t u r b i n eo f th e a i r c r a f t o r s h i p which would impa i rth e m i s s i o n . To some p e t r o c h e m i c a l u s e r s ,t h e l o s s o f o u t p u t i s o f conce rn as i tr e s u l t s in l e s s t h r o u g h p u t . For p i p e l i n eo p e r a t o r s an d c o g e n e r a t i o n p l a n t s , t h e r ea r e tw o economic a r e a s o f c o n c e r n :

1 Loss o f Th e rmal Ef f i e i e n c y ( i . e .h i g h e r f u e l c o s t s ) .

0.8104-. . , . - 'T'"" '"-r-r-r-r---1 , . . . , ---, . ---r- . . --r--- . ---r--r--r- . -- . . . . -. . ,

o 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38

~ T H S

2 . Loss in Throughpu t /Ou tpu t ( i . e . l e s sg as pumped o r lower MW's g e n e r a t e d ) .

Th e economic impac t can b e s t be judged byt h e f o l l o w i n g f i n d i n g s :

1 . Th e l a r g e s t c o s t d u r i n g t h e l i f e c y c l eo f a tu rbomach ine i s t h e f u e l c o s t . A80MW e gas t u r b i n e , f o r example , may

consume $2 3 m i l l i o n i n f u e l i n a y e a r.Based on 1986 e s t i m a t e s in t h e gasd i s t r i b u t i o n i n d u s t r y, on a 12 MWa e r o d e r i v a t i v e g as t u r b i n e , t h e f u e lc o s t i s $ 8 7 0 / f i r e d hour compared t o ano v e r h a u l / m a i n t e n a n c e c o s t o f $ 2 0 / f i r e dhour ( i . e . f u e l c o s t s a re app roxi ; r ~ t e l v 4 0 t m r : ~ ~ o v e r h a u l c o s t ) [ 7 ] .Because o f t h i s , and t h e f a c t t h a t t h eg a s p i p e l i n e i s a ma jor consumer o ff u e l i t s e l f , t h e i n c e n t i v e f o r maint a i n i n g h i g h t h e r m a l e f f i c i e n c y i s o fpa ramount i m p o r t a n c e .

2 . Opera t ing wi th d i r t y compresso rs cani n c r e a s e f u e l consumption by up t o 5%.A 2% l o s s in compresso r e f f i c i e n c y cani n c r e a s e f u e l consumpt ion by 3%.

3 . A f o u l e d compresso r might e a s i l yr e s u l t in an o u t p u t drop o f 10%. As t u d y conduc ted by Zaba [ 3 ] , i n d i c a t e dt h a t f o u l i n g , which r e s u l t e d in a 5%drop in a i r f l o w c a p a c i t y, w i l l a l s oy i e l d a 2.5% reduct io l1 in compressore f f i c i e n c y , a r e d u c t i o n o f 10% in gast u r b i n e power o u t p u t and a r e d u c t i o no f g a s t u r b i n e e f f i c i e n c y o f a b o u t 5%.

DETECTION OF FOULING

Ga s t u r b i n e m a n u f a c t u r e r s an d o p e r a t o r st y p i c a l l y d e v e l o p some g u i d e l i n e s a s t o

when d e t e r i o r a t i o n due t o f o u l i n g c a l l s fo rc o r r e c t i v e a c t i o n . T h i s i s u s u a l l y based ona combina t ion o f l o a d and e x h a u s t gas temp e r a t u r e s (EGT).

I t i s t h e o p i n i o n o f some o p e r a t o r s t h a tt h e o n l y wa y t o d e t e c t a fou led compressori s by v i s u a l i n s p e c t i o n . With ~ o s t t u r b i n ed e s i g n s , howeve r, t h i s means s h u t t i n g t h eu n i t down, removing t h e i n l e t plenum h a t c han d v i s u a l l y i n s p e c t i n g t h e compressori n l e t , be l lmouth i n l e t g u i d e vane (IGV' s )an d v i s i b l e e a r l y s t a g e b l a d i n g .

Th e r e a l prob lem i s n o t ho w to d e t e c tf o u l i n g , b u t how to d e t e c t i t a t an app ropr i a t e t ime b e f o r e a s i g n i f i c a n t power drophas o c c u r r e d an d a h i g h e r f u e l p e n a l t y c o s thas been p a i d . S e v e r a l p h i l o s o p h i e s a r e inu s e . Some o p e r a t o r s b e l i e v e in p e r i o d i cwashing o f t h e machine w h i l e o t h e r s basewashes on c o n d i t i o n s ( i . e . some 8 e t o f p e r -formance p a r a m e t e r s ) Th e p h i lo sophyu t i l i z e d i s a f u n c t i o n o f normal ly expec tedf o u l i n g l e I s an d i t s s e v e r i t y .

265

ESL-IE-87-09-43



6/9

Th e p e r i o d i c washing approach can m a i n t a i na r ea sonab le s t a t e o f c l e a n l i n e s s , b uta c t u a l o p e r a t i n g p er fo rman ce , s e a s o n a lbased f o u l i n g an d o t h e r f a c t o r s a r eobvious ly no t acco u n ted f o r .

With th e ad v en t o f o n - l i n e moni to r ings ys t e ms [ 8 ] , t h e c a p a b i l i t y now e x i s t s fo ro b t a i n i n g a good p i c t u r e o f how t u r b i n e

pe r fo rma nc e i s b e in ga f f e c t e d

by f o u l i n g .Th e fo l lo w in g f a c t o r s c an be used asi n d i c a t o r s o f f o u l i n g :

1. Drop in c ompre s s o r mass f low r a t e onf i x e d ge ome t ry e n g i n e s .

2 . Drop in c ompre s s o r e f f i c i e n c y an dp r e s s u r e r a t i o .

Th e most s e n s i t i v e pa rame te r o f t h e abovef a c t o r s i s t h e mass f low r a t e . R e f e re nc e [9 ] cove rs a t e chn ique fo r performanceco mp u ta t io n s fo r t h e a i r f l o w r a t e when i ti s n o t b e in g me a s ure d . Th is t e c h n i q u eu t i l i z e s thermodynamic h e a t ba lancemethods .

S c o t t [7] an d [10] h as co n d u c ted e x t e n s i v es t u d i e s i n t o fou l ing d e t e c t i o n me thods .His t e chn ique o f measurement o f a i r - i n t a k ed e p r e s s i o n 1 S a p r a c t i c a l an d economicalmethod. This t e chn ique invo lves l ook ing a ti n t a k e d e p r e s s i o n as an an a lo g o f a i r f l o wr a t e . In t h i s ap p ro ach , th e g as t u r b i n ei n l e t b e l lmo u th i s u t i l i z e d a s a f lowmeter.Th e l a y o u t i s shown i n F igure 6 .

EXHAUSTBE l l HOUTHPlENUH

--TURBINE

GENERATOR

fiLTER : INTA I(E DEPRESSION\ 'HANOHETER

HiCJh i1r .. . .low Ar". As . i r f loY r i l t . drops, Y . ~ o c i t.. drops

I- - - - - - 4 ) th . r. f o r. shl t i c pr.ssur. drops.

AIR VElOCITY INCREASESST ATIC PRESSURE DROPS

F i g . 6 I n t a k e D ep ress io n MeasurementMethod

By mo n i to r in g t h e i n t a k e a i r d e p r e s s i o n , agood i n d i c a t o r o f f o u l i n g ca n be a t t a i n e d .Th is t e chn ique has been a p p l i e d t o s e v e r a lAvon eng ines with good r e s u l t s . A p a r ame t r i c a n a l y s i s pe r fo rme d by S c o t t r e p o r t e dt h a t as t h e c o m p r ~ R s o r f o u l e d , t h e l a r g e s te f f e c t wa s on i n t a k e ( l ep re ss ion c e l ~ T . , ' l r l ' ~ ' : ' i t o ~ r o p in a i r f l o w an d c ha nge s in comp r e s s o r e f f i c i e n c y.

CONTROL OF FOULING

Fo u l in g i s b e s t c o n t r o l l e d by a co mb in a t io no f tw o me thods . Th e f i r s t l i n e o f d e f e n s ei s t o employ a high q u a l i t y a i r f i l t r a t i o nsys t em. I f f o u l i n g o c c u r s (and it u s u a l l yw i l l ) , t hen t h e co mp resso r ca n be c l eanedby e i t h e r a b r a s i v e m a t e r i a l s o r s o l v e n t s .

FILTRATION

The re a r e s e v e r a l t y p e s o f f i l t e r s t h a t canbe broke n i n t o t h e fo l l owing g roups :

I n e r t i a l F i l t e r s . Th e o b j e c t i v e he rei s t o make th e a i r change d i r e c t i o nr a p i d l y caus ing s e p a r a t i o n o f d u s tp a r t i c l e s . These f i l t e r s a r ep erman en t ly f i x e d an d r e q u i r e minimalmain tenance . I n e r t i a l f i l t e r st y p i c a l l y o p e r a t e a t face v e l o c i t i e so f 20 f t / s e c o n d .

2. P r e f i l t e r s . These a r e medium e f f ic i e n c y f i l t e r s made o f c o t t o n f a b r i co r spun f i b e r g l a s s . They a r e r e l at i v e l y i nexpens ive and s e r v e as " p r ot e c t i o n " fo r high e f f i c i e n c y f i l t e r s .

3 . C o a l e s c e r s . These a r e c o n s t r u c t e d byt h e use o f wire mesh which a c t s as anag g lo mera te r . Th e mi s t in t h e i n l e ta i r i s ag g lo mera ted and th e m o i s t u r ei s t h u s removed.

4. Louvers an d Va ne s . These a r et y p i c a l l y used in th e f i r s t s t a g e sa lo n g w i th c o a l e s c e r f i l t e r s t oremove w ater d r o p l e t s .

5 . H ith E f f i c i e n c y F i l t e r s . Thesef i t e r s remove s ma l l e r p a r t i c l e s of.

d i r t . They a r e t y p i c a l l y b a r r i e r o rbag t ype f i l t e r s .

6 . S e l f - C l e a n i n g F i l t e r s . These c o n s i s to f a bank o f high e f f i c i e n c y mediaf i l t e r s . A ir i s drawn th ro u g h t h emedia a t a lo w v e l o c i t y . At a p r ed e te rmin ed p r e s s u r e d ro p ( abou t 2-3"Water Gauge) a r e v e r s e b l a s t o f a i r i sused t o remove d u s t b u i l d u p . Thesef i l t e r s a r e made by s e v e r a l manuf a c t u r e r s an d a r e ve ry s u c c e s s f u l .

Figure 7 shows th e e f f i c i e n c i e s o f f i l t e r son d i f f e r e n t p a r t i c l e s i z e s [ 1 1 ] .

A ve ry impor t an t p o i n t i s t h a t a i r t i g h tness i s a must fo r a ny g as t u r b i n e i n l e tsystem a s - - e - v e n th e most e f f i c i e n tf i l t r a t i o n system w i l l be u s e l e s s i fu n f i l t e r e d a i r f l o w l e a k s in an d e n t e r s t h eco mp resso r. Some common causes o f l e akagea r e :

1 . Bypass door l e a k a g e .

266

ESL-IE-87-09-43



7/9

PARTICLE SIZE'IIICROIIS

CORROSION

FOILINGEIIOSIllN

f- .v - ~ ." . . ,~ ...... . // ~ / V

/V

/ /IME~ RE- f l l ~ 1 ~ V

I'- r ~ I N E R rlAL ~ L : IEJI

V

.4.11.1 .11 1.0 2 3 4 5 III 20 30 40

1010

10

li 11015 70

!:I::10

o .2 3

Fig . 7 E f f i c i e n c i e s o f F i l t e r s [11 ]

2 . Poor g a s k e t s an d s e a l s . a t f l angedp o i n t s .

3 . Modi f ica t ions made on th e i n l e td u c t i n g . Over t h e y e a r s , personne lmay ad d s t r u c t u r e s o r d e v i c e s t o t h ei n l e t system which migh t causep ro b lems .

Corros ion in carb o n s t e e l i n l e t d u c t s hasa l s o been a source of p ro b lems . At t imest h e c o r r o s i o n can b e severe enough t o causea l o s s o f i n t e g r i t y . Because o f t h i s ,s e v e r a l users a re now using s t a i n l e s s s t e e lfo r th e f i l t e r h o u ses an d i n l e t d u c t s . Th ee f f e c t i v e n e s s o f t h e f i l t r a t i o n system i simpacted by i t s d e s i g n , i n s t a l l a t i o n an dmain ten an ce .

COMPRESSOR CLEANING

Two ap p ro ach es t o co mp resso r c l e a n i n g a r ea b r a s i o n an d s o l v e n t c l e a n i n g . Th e cho iceas t o which t echn ique sh o u ld be used i sd ep en d en t on th e n a t u r e o f t h e d e p o s i t s an dth e m a n u f a c t u r e r ' s recommendat ions .

Common a b r a s i v e s used a r e n u t s h e l l s , r i c eor spen t c a t a l y s t . Th e a b r a s i v e s shouldhave s u f f i c i e n t mass to ach ieve th emomentum requ i red t o d i s l o d g e th e d i r t . Ast h e y a re i n g e s t e d , t hey a re h i t by th elead ing edge o f t h e a i r f o i l s an d t h e r e f o r eth e t r a i l i n g ed g es a r e no t ab raded . Th ea b r a s i v e s must be s u f f i c i e n t l y d u r a b l e t o

r e s i s t breakage .

A b ras iv e c lean ing seems t o work wel l wi thha rd d ry d e p o s i t s an d may be c a r r i e d o u t a topera t ing load an d speed . I f t h e fou1an ti s o i l , s a l t , (o r a co mb in a t io n o f both )then s o l v e n t washing i s p r e f e r a b l e . Oftensome o p e r a t o r s may e l e c t t o u se both a dryan d a wet wilsh in o r d e r t o fUl ly r e s t o r ep er fo rman ce .

Water washing (w i th o r w i t h o u t d e t e r g e n t s )c l e a n s by w ater impact an d by removing t h ewate r s o l u b l e s a l t s . I t i s most impor t an tt h a t t h e m a n u f a c t u r e r ' s recommendations befol lowed wi th r e s p e c t t o water washq u a l i t y , d e t e r g e n t / w a t e r r a t i o an d o t h e ro p e r a t i n g p r o c e d u r e s . Ty p i c a l l y, wheelspace t e mp e r a t u r e s must be below 200"F t oavo id the rma l shock an d t h e wate r wash i sdone wi th t h e machine on c r a n k .

Water washing u s in g a water-soap mixture i st h e most e f f i c i e n t method o f c l e a n i n g .Thi s c l e a n i n g i s most e f f e c t i v e whenc a r r i e d ou t i n s e v e r a l s t e p s which i nvo lveth e a p p l i c a t i o n o f a so ap an d wate rs o l u t i o n , fol lowed by s e v e r a l r i n s e c y c l e s .Each r i n s e c y c l e invo lves th e a c c e l e r a t i o no f th e machine to approx ima te ly 50 p e r c e n to f th e s t a r t i n g s p e e d , a f t e r which th emachine i s a l lo w ed t o c o a s t t o a s t o p . Asoak ing per iod fo l l ows dur ing which th esoapy wate r s o l u t i o n may work on d i s s o l v i n gth e s a l t . I f th e machine i s c leaned underf u l l o p e r a t i n g c o n d i t i o n s u s in g r i c e , w alnut s h e l l s o r some o t h e r s o l i d m a t e r i a l

i n j e c t e d i n t o t h e i n l e t , t h e f o u l a n t s an dc o r r o s i v e e l ement s d e p o s i t e d w i t h i n t h eco mp resso r a re removed r a p i d l y an d f l ushedth rough th e t u r b i n e .

I f th e machine i s running a t s u b s t a n t i a ll oad an d th e g as t empera tu res a r e in th ereg ion where th e s a l t can be fu sed , it w i l lhave th e o p p o r t u n i t y o f combining wi th th esu lphu r (which i s p r e s e n t in th e f u e l ) , an dform sodium s u l p h a t e . Th e sodium s u l p h a t emay t hen f u s e , become s t i c k y an d d e p o s i ti t s e l f on th e h o t p a r t s o f th e t u r b i n ecaus ing s e v e r e an d rap id a t t a c k , which i sC h a r a c t e r i s t i c o f h o t c o r r o s i o n ( s u l p h i -d a t i o n ) .

Th e method recommended fo r de te rmin ingw h eth er or n o t t h e f o u l a n t s have a subs t a n t i a l s a l t base i s t o soap wash t h e t u r -b i n e an d c o l l e c t th e wate r from a l l d r a i n -age p o r t s a v a i l a b l e . Oisso lved s a l t s inth e wate r can then be a n a l y z e d .

wate r washing a machine under power must bec l o s e l y mo n i to r ed t o p r e v e n t t h e p o s s i -b i l i t y o f l i q u i d wate r impinging upon ho tt u r b i n e p a r t s . A c a r e f u l l y c o n t r o l l e dwate r f low using t u r b i n e o p e r a t i n g p a r amete r s a s c o n t r o l f u n c t i o n s can p ro d u cee f f i c i e n t c l e a n i n g wi th minimal o r nodamage t o th e mach i ne , an d wi t h a ve rys h o r t p e r i o d o f reduced power o u t p u t

AXIAL COMPRESSOR BLADE COATINGS

While h o t s e c t i o n c o a t i n g s have beenpopu la r fo r s e v e r a l y e a r s , an inc reas ing

~ ! 1 ~ h e r o f u s e r s ~ r e n a ~ n t i l . i ~ i ~ q c o ~p r e s s o r c o a t i n g s t o h e l p enhance d u r a b i l i t yan d pe r fo rmance . Th ere a r e s e v e r a l u s e r st h a t cove r a x i a l b lad ing w ith c o a t i n g s ino r d e r t o :

267

ESL-IE-87-09-43



8/9

1 . Reduce b l a d e f r i c t i o n , t h u s improvingaero d y n amics , t h e r e b y i n c r e a s i n g e f f i -c i ency an d p er fo rman ce .

2 . Reduce we a r.

While c o a t i n g s do n o t n e c e s s a r i l y p r e v e n tf o u l i n g , th e y enab le a more e f f i c i e n t an dd u r a b l e o p e r a t i o n o f a co mp resso r.

TURBINE SECTION FOULING

Contaminants t h a t cause t u r b i n e fou l ing cane n t e r th e g as t u r b i n e by :

1 . I n l e t A i r .

2. Fuel (may c o n t a i n Na an d V).

3 . Fuel A d d i t i v e s .

4 . NO x Cont ro l I n j e c t i o n F l u i d .

In th e h o t t u r b i n e s e c t i o n , an d in t h epresence o f h o t g a s e s , lo w mel t ing p o i n ta s h e s , meta l s an d unburned h y d ro carb o n s ca nbe depos i t ed in t h e form o f s c a l e . As h o tcombus t ion produc t s pass th ro u g h t h e f i r s ts t a g e n o z z l e , t h e y e x p e r i e n c e a d ro p ins t a t i c t empera tu re an d some ashes may bed e p o s i t e d on th e nozz l e b l a d e s . As t h et h r o a t a r e a o f t h e n o zz le c o n t r o l s t h ec o m p r e s s o r - t u r b i n e match in g , a reduc t ion int h r o a t a r e a causes a movement away from th edes ign match p o i n t . This t hen causes al o s s in p e r fo rman ce . Depos i t s w i l l a l s oform on th e r o t a t i n g blades caus ing af u r t h e r l o s s in p er fo rman ce . B la de an dd i s c c o o l i n g can a l s o be impaired byf o u l a n t s caus ing a r e d u c t i o n in componentl i f e o r even f a i l u r e .

Th e prob lem o f h o t c o r r o s i o n o r s u l f i d a t i o ncan o ccu r wi th t h e N ick e l an d Co b al t baseds u p e r a l l o y s used i n ga s t u t " b ines . SIJ l f id a t i o n i s th e r ap id an d d e s t r u c t i v e r e -a c t i o n t h a t occurs when e x t e n s i v e q u ant i t i e s o f a l k a l i s a l t s (Na, to and Vanadiumat"e p r e s e n t in the combus t ion produc t salong with SUlphur. These may be found inf u e l , w ater o r s team (L1sed fo r NO x co nt r o l ) o r more impor tan t ly in i n l e t ait" .As t h e f u e l f low t"ate i s t y p i c a l l y a b o u t 2%o f t h e a i r mass f low r a t e , 1 ppm Na e nt e r i n g from th e f u e l would have t h e samee f f e c t as j u s t 20 pp b a i r b o r n e s a l t e nt e r i n g t h e a i r f l o w. Th is i s a s i g n l f l c a n tr eq u i r emen t cons ider ing t h a t most manuf a c t u r e r s c a l l fo r n ot more t han 1 ppm o fNa .

Normal ly w ith l i q u i d f u e l s ( e s p e c i a l l yheavy f u e l s ) , f u e l t r e a t me n t c a l l s fo r theremoval o f sodium by w ater washing. I fVanadium (V) i s p r e s e n t in th e f u e l , t heni t s e f f e c t i s i n h i b i t e d by th e a d d i t i o n o fEpsom S a l t s (MgS04). Th is a d d i t i v e causessevet"e t u r b i n e s e c t i o n f o u l i n g . As t h emagnesium i s added in a 3 :1 w eig h t t"a t io to

268

t h e Vanadium, f u e l s high in Vanadium c a u s ef requen t fou l ing o f t h e t u r b i n e . Th ef r eq u en cy of t u r b i n e washes requ i reddepends on t h e ash c o n t e n t , t u r b i n e i n l e tt e m p e r a t u r e an d o p e r a t i n g c y c l e ( i . e . BaseLoad Vs. Cyc l i c O p e r a t i o n ) . Peaking u n i t sopet"ated on heavy f u e l s (h igh Vanadium) don ot r e q u i r e washing s i n c e t h e t h e r m a lc y c l i n g removes t h e d e p o s i t s .

Modern g as t u r b i n e s o p e r a t e a t a tu t"binei n l e t tempet"a ture o f between laOO'F and2 2 0 0 'F which makes them h i g h l y s e n s i t i v e t oc o r r o s i o n pt"oblems. Th is c a l l s fo r cat"e t obe t aken wi th r e s p e c t t o a i r f i l t t " a t i o n an dcompressor washing . Even wi th good f i l t r a -t i o n , s a l t can c o l l e c t i n t h e compressot"s e c t i o n . OUt"ing t h e c o l l e c t i o n p r o c e s s ofbo th s a l t an d othet" f o u l a n t s , an e q u i -l i b r i u m c o n d i t i o n i s q u i c k l y t"eached, a f t e rwhich t "e in g es t io n o f lat"ge pa t" t i c l eso c c u r s . Th is r e i n g e s t i o n h as t o be pt"ev en ted by t h e removal o f s a l t ft"om t h ecompressot" priot" to s a t u r a t i o n . Th e r a t ea t which s a t u r a t i o n occut"s i s h i g h l yd ep en d en t on f i l t e t " q u a l i t y . In g e n e r a l ,s a l t s can s a f e l y pass th ro u g h th e t u r b i n ewhen gas an d m e t a l tempera tut"es a re l e s st han lOOOF. A g g ress iv e a t t a c k s w i l l o c c u ri f t h e t empera tu res a re much h i g h e r .Out"ing c l e a n i n g , t h e a c t u a l i n s t a n t a n e o u st"ates o f s a l t passage a re ve ry h i g h ,t o g e t h e r w ith g t"ea t ly inc reased p a r t i c l es i z e .

Even w ith good a i r f i l t r a t i o n , s a l td e p o s i t s w i l l o c c u r i n t h e c o m p r e s s o r. Ast h e a i r moves tht"ough th e compressot" towat"dt h e combus t ion s e c t i o n , it i s hea t ed an dco mp ressed , caus ing removal o f th eremain ing moistut"e from t h e a i rbot"ne s a l tp a t " t i c l e s . These p a r t i c l e s at"e t i epos i t ed

h e a v i l y in t h e f i r s t fe w s t a g e s , sometimesgoing back a s f a r as h a l f way t h rough thecompt"essot". In g e n e r a l , t h e condensa t ionn u c l e i t h a t pass t h rough t h e co mp resso rw i t h o u t b e in g en t rapped can a l s o passtht"ough th e t u r b i n e wi thou t d e p o s i t i n gth emse lv es or adhe r ing t o the h o t pa t " t s . Ad i f f i c u l t y a r i s e s , howevet", when t h e s a l tt h a t h as been c o l l e c t e d with in t h e compt"essor s t a g e s becomes so t h i c k t h a t l a r g ef l a k e s a re t"eingested i n t o t h e e n g i n e .When t h i s occut"s, the l o c a l concen t t " a t i ono f s a l t in th e ait" immed ia te ly surt"oundingt h e s e l a r g e f la k e s i s ex t t"emely h i g h .These s a l t f l a k e s a c t u a l l y have s u f f i c i e n tmass t o s t i c k f i r ml y t o t h e t u r b i n e h o tp a r t s an d a r e t"esponsib le fo r many gastu t"bines s u f f e r i n g from h o t c o r r o s i o ndamage. S a t u r a t i o n o f th e c01npt"essor wi ths a l t s s t i l l remains a problem and must bed e a l t w i t h .

CONCLUSIONS

Th e f o u l i n g o f a x i a l f lo w co mp resso r s an dt u r b i n e s in g as t u r b i n e e n g i n e s i s a common

ESL-IE-87-09-43



9/9

o p e r a t i n g p ro b lem. U n d er s tan d in g t h ecauses an d e f f e c t s h e l p s o p e r a t o r s combatt h i s problem. Refe rences [12] t h rough [19]prov ide a d d i t i o n a l s o u r c e s o f i n f o r ma t i o non gas t u r b i n e f o u l i n g . Th e i n f l u e n c e s o ff o u l i n g can be d e t e c t e d by performancemoni to r ing a l l owing c o r r e c t i v e a c t i o n t o bet a k e n . Th e f i r s t l i n e o f d e f e n s e , however,i s a good a i r f i l t r a t i o n system an da p p r o p r i a t e f u e l p r e p a r a t i o n an d t r e a t m e n ti n o r d e r t o minimize th e e f f e c t s o f comp r e s s o r an d t u r b i n e f o u l i n g .

REFERENCES

1. Upton, A.W.J., ~ A x i a l Flow Compressor andTurbine Blade Fouling, Some Causes, Effects andCleaning Methods", Proceedings of th e 1st GasTurbine Operations and Maintenance Symposium, Nat ional Research Council, Canada, October, 1974.

2. Allen, H.L., "Bas Turbine Operation inth e Real World" ASME Paper No. 84-GT-l.

3. Zaba, T., "Losses in Gas Turbines Due toDeposits on the Blading", Brown Boveri Review 12-8.

4. Zaba, T. and Lombardi, P., "Experience inth e Operation of Air Fi l te r s in Gas Turbine Ins tal l a t ions " , AS ME Paper No. 84-GT-39.

5. Dundas, R.E., "A Study of th e Effec t ofDeteriorat ion on Compressor Surge Margin in Cons t a n t Speed, Single Shaft Gas Turbine Engines",1986 ASME Gas Turbine Conference.

6. "History of a Gas Turbine in th e RollsRoyce Avon", Turbomachinery In ternat ional , March,1985.

7. Scot t , J .H. , "Reduced Turbomachinery Operating Costs with Regular Performance Testing",ASME Paper No. 86-GT-173.

8. Boyce M.P., Meher-Homji, C.B. , and Mani,G. , "The Development and Implementation of AdvancedOn-line Monitoring and Diagnostic Systems fo r GasTurbines", Toyko In ternat ional Gas Trubine Confer~ , October, 1983, Paper No. 83-Toyko-IGTC-94.

9. Meher-Homji, C.B. , "Aerothermodynamic GasPath Analysis fo r Health Diagnostics of CombustionGas Turbines", Proceedings of the 36th Meeting ofth e Mechanical Failures Prevention Group. CambridgeUniversity Press, 1983.

10. Scot t , J .H. , "Axial Compressor Monitoringby Measuring Intake Ai r Depression", National Research Council of Canada Symposium, 1979.

11. Lages, F. P ., "Air F i l t r a t ion and SoundControl Systems fo r Gas Turbines-The State of theArt", Proceedings of th e 8t h Turbomachinery Symposium, Texas A&M University.

269

12. Lakshminarasimha, A.N., and Saravanamutto, H.I.H., "Predict ion of Fouled CompressorPerformance Using Stage Stacking Techniques", 4t hASME Fluid Mechanics Conference, TurbomachineryPerformance Deter iora t ion , May 12-15, 1986.

13. Saravanamutto, H.I.H., and Laksminarasimha,A.N., "A Preliminary Assessment of CompressorFouling", ASME Paper NO. 85-GT-153.

14 . Matthews, T., "Field Performance Testingto Improve compressor Rel iab i l i ty" ,Proceed ingsof the 10th Turbomachinery Symposium, Texas A&MUniversity.

15. Tatge, R.B. , "Gas Turbine In le t Ai rTreatment", G.E. Publicat ion GER-3419.

16. Pulimoo d, M.K., "Field Experience withGAs Turbine In le t Ai r Fi l t r a t io n " , ASME Paper No.81-GT-193.

17. Becker, B. , and Bohn, D., "OperatingExperience with Compressors of Large Heavy DutyGas Turbines", ASME Paper No. 84-GT-133.

18 . "Causes and Cures fo r Sulf icat ion Corros ion , Erosion and Fouling", Gas Turbine World,March, 1975.

19. Bagshaw, K.W., "Maintaining Cleanlinessin Axial Flow Compressors", 1s t Gas Turbine Operat ions and Maintenance Symposium, National ResearchCouncil Canada, October, 1974.

ESL-IE-87-09-43


compressor and hot section fouling in gas turbines - causes and effects by meher-homji (1987)

Documents