High Temp Corrosion by Fuel Impurity

8/6/2019 High Temp Corrosion by Fuel Impurity

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IH I GH- TE MP E R AT U R E C ORR OSI ON I N GAS T U R B I N E S A ND S T E AM B OI L E R S B Y F U EL I M P U R I T I E S .P A R T V I I I . EVALUATION OF T H E E F F E C T S OF MANGANESE, CALCIUM, AND SEVERAL HEAVYMETALS ON CORROSION AND SLAG FORMATIONWalter R. May, Michael J . Z e t l m e i s l , Robert R. Annand, D avid F. La ure nceTRETOLITE DIVISION/PETROLITE CORPORATION, 369 H a r sh a l l Avenue, S t . Louis , NO. 63119I N T R OD U C T I ON

There are two recognized approaches to co nt ro l l i ng vanadic corros io n . Bothr e su l t i n the product ion of dry , non-adhering and th er ef or e non-corroding s l ag s .The more widely accepted approach i s th e formation of h igh er mel t ing compounds i nt h e s l a g v ia f u e l a d d i t i v e s . The o t h e r a pp ro a ch u t i l i z e s l ow e x c e s s a i r o p e r a t i n gco nd i t i ons which produce higher m el t i ng, lower vale nc e s t a t e vanadium compoundsand less SO3 which re u ce s s u l f a t e i n t h e s l a g .t h i s se r i e s of papersq, we have examined magnesium, s i l i c o n , aluminum, andcombinat i ons of t hese e l emen ts a s ad d i t i v sad d i t i ves wi th va ry ing deg rees of success5-6. The d i f f i c u l t y i n ob t a in ings u f f i c i e n t d at a t o t ho ro u gh ly e v a l u a te a n a d d i t i v e p a r t i a l l y e x p l a i n s t h e p a u c i t yof info rma tion on combinat ion systems. Our electroche mical approach t o measuringc o r r o s i o n r a t e s c o up le d w i th t h e s t e pw i se l i n e a r r e g r e s s i o n a n a l y s i s o f t h e d a t ah e l p s f i l l t h i s g ap and o f f e r s a r a p i d b u t t h o ro ug h s c r e e ni n g o f a n a d d i t i v esys tem. The t echnology i n t h i s a re a , p a r t i c u l a r l y fo r gas t u rb ines , has beentoward u se of l ower qu a l i t y fu e l s and h igher t empera tu res fo r be t t e r e f f i c i ency .The r e su l t has been a demand fo r an add i t iv e wi th be t t e r sodium and temperaturet o l e r a n c e s .aluminum-si licon system which showed co nsi de ra ble promise i n th i s area .paper , w e a r e p r e s e n t i n g d a t a o bt a in e d o n s e v e r a l o t h e r s y st em s of i n t e r e s t .

Manganese improves combust ion ef fi ci en cy which permits lower ex ces s a i roperation' '. Av ail ab le commerc ially are combinat ions with magnesium and /or s i l i c ont o permi t low exces s a i r op e ra t i on where pos s ib l e wi th t he magnesium and /o r s i l i c onp r e s e n t to in h i b i t s lag ging and corro s ion i n the convent ion al manner. The purposeof th e s tu dy on manganese was t o f in d i f it h a s an y i n h i b i t i n g e f f e c t s i n t h econvent ional manner o r in t e r f e r e s wi th magnesium and/or s i l i co n .s tu dy ing calcium, zi rconium and t h e r a re e a r t h s was t o e va l u a te t h e i r e f f e c t s on t h ec o r r o s i o n pr o c e ss and s l a g c h a r a c t e r i s t i c s .

I n e a r l i e r s t u d i e s pr es en te d i nMany elements have been t r i e d a s

I n t h e l a s t p ape r i n t h i s series', we pres en te d d a ta on t h e magnesium-I n t h i s

The purpose of

EXPERI ENTALMaterials. The me lts were prepared from reag ent gra de chemicals obta ine d fromFishe r S ci en t i f i c Company wi th t h e except ion of t h e fo l lowin g . The cer ium oxid e ,

z i rcon ium ox ide and r a r e e a r t h ox ide mix ture w e r e obta ined from th e Davison ChemicalDivis ion of W.R. Grace and Company.ma te ly 48% CeO , 23% La2O3, 5% Pr60 11, 16 %Nd2O3, 4% Sm20e a r t h o x i de s . l am p le sof t h e con st i t ue nt s and thorou ghly mixing t o in su re a homogeneous sample.w a s added i n th e form of a n oi l- so lu bl e ma te ri al , vanadium Ten-Cemtm ( 6 p e r c e n tvanadium ), ob ta in ed from Mooney Che mica ls, In c. The sodium was added as a n o i l -so l ub l e sod ium-naph thenat e p repa red i n t h i s l abo ra to ry by neu t ra l i z i ng anin d u s t r ia l grade napthenic ac id wi th sodium hydroxide .4.3 pe rc en t sodium a s deter mined by atomic ad so rp tio n. The magnesium was added asKONTOLm KI-15 co nt ai ni ng 1 0 pe rc en t met al.con t a in ing 16 pe rcen t me t a l .cont a in i ng 8 percen t of each meta l .TRETOLITE DIVISION of PETROLITE CORPORATION. The aluminum so ur ce was a s u l f o n a t eobta ined from Witco Chemicals Company co nt ai ni ng 14.4 perc en t meta l. Su lfu r wasadded as a s u b s t i t u t e d 1, 2-d i t h io , 3 - th ione (36 pe rcen t su l fu r )

The r a r e e a r th ox ide mixture conta ined approx-and 4% of o the r r a r eof 40 g s i z e were prepared by weigging approp r ia t e q ua nt i t i e s

The f ue l fo r t he bu rne r t e s t was re ag en t gr ad e hexanes and xy le ne s. Vanadkum

The f i n a l p roduct con t a inedThe s i l i c a was added a s KONTOLmKI-39d,

The magnesium-s ilicon mix tur e was KONTOLW KI-18DThese a r e oi l- so lu bl e compounds from t h e


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2pre par ed i n t h e TRETOLITE D IV I S ION ' S p i l o t p l a n t .Electrochemical Measurements. The co rro sio n r a t e measurements were made i nan e lec t rochemical c e l l cons i s t i ng o f t h r ee e l e c t r ode s immersed i n a s l a g of t h edes i red compos it ion . The cor ros i on curre n t was determined from po la r i za t io ncu rves o r by t he po l a r i za t i on admi tt ance technique . The c e l l , co r ro s ion r a t emeasur ing ap para tu s , source of ma te r i a l s , and sample p repa ra t i on t echn iques a r ed e sc r ib e d i n ou r e a r l i e r p a p e r7 .The s lag t e s t cons i s t ed o f bu rning a f u e l c o n t a in i n g t h e d e s i r edl e v e ls of contam inants and in h i b i to r s . The flame impinges upon a coupon which i sa d j u st e d t o g i v e t h e d e s i r e d t e m pe r at ur e . The s l a g c h a r a c t e r i s t i c s a r e e va lu ae edby measuring t h e amount of ma te ri a l t h a t can be brush ed from t h e coupon. The t e s ti s d e s c r ib e d i n much g r e a t e r d e t a i l i n a n e a r l i e r p u b l ic a t i on 8 .

Slag Test.

RESULTSCorro sion r a t e d a ta from Na2S04-V205-Mn02 syste ms co nt ai ni ng var io us

combinations of magnesium and s i l i c o n a r e pres ented i n Table I - 111. Theco r re l a t i on equa t i ons genera ted by t h e t echn ique desc r i bed e a r l i e r ' a re presentedi n T a bl e V . Comparisons of c or ro si on ra tes found i n t h e s e s l a g s w i t h o t h e r a d d i t i v esystems a t 800 and 900 a r e g iven in F igure 1 and 2.CaS04-V205 system a r e give n i n Tab le IV . The c o r r e l a t i o n e q u a t i o ns f o r t h i ssys tem and those conta in ing aluminum, s i l i c o n and l ead a r e g iven i n Table V. Alsoincluded i n Table V a r e e q u a t io n s f o r t h e s ys te ms c o n t a i n in gt he r a r e e a r t h o xi de c om bin ation . The d a t a f o r t h e s e a r e n o t k k d e d $0 maintaina r easonab l e s i ze fo r t h i s paper . However, t hese da t a a re ava i l ab l e on r eques tfrom th e author s . and MgS04-Si02 systemsar e i ncluded f o r compari son wi th t h e da t a p resen t ed i n t h l s paper .L L L C ~ Ctwo a r e diso iound i n F i g u r e i and 2. i n a i i c as es , t he N a i V c o e f f i c i e n ts a r epo s i t i ve ind i cat i ng th e s t ro ng cor ros i on promoting e f f ec t o f sodium. Thec o e f f i c i e n t f o r Mn/V i s po s i t iv e i nd ic at in g tha t manganese promotes corros ion .examined se ve ra l ot he r cas esw he re the Mn/V + Pb r a t i o was held a t 2 . I n t h o s ecases , t he Mg (+S i) /V (+Pb) r a t i o s were nega t i ve i nd i ca t i n g t ha t t he ad d i t i veinh ib i t ed co r ros ion . W c h os e t h o s e c a s e s b ec au se i n a c t u a l p r a c t i c e , t h emanganese level i s more l i k e ly t o be held c ons tan t whi le th e Mg + S i l e v e l v a r i e sw i th t h e t r a c e m e ta l c o n t e n t i n t h e f u e l .when present alone, i t promoted c orr os io n i n re la t i on t o aluminum and s i l i c o n whena l l were inc luded. Although th e ra re e a r t h s had n e g a ti v e c o e f f i c i e n t s , co r ros ionc u r r e n t s p r e d i c t ed by t h e c o r r e l a t i o n e q u a t i o n s i n d i c a t e d t h a t t h e s e m a t e r i a l s w er en o t i n h i b i t o r s .t he y a r e n ot al wa ys s t a t i s t i c a l l y s i g n i f i c a n t . I n t h o s e cases i n which t he F Levelwas below appr oxima tely 2.25, th er e i s l e s s th an a 95% c ha nc e t h a t a l l t h e c o e f f i -c i e n t s a r e s i g n i f i c a n t f o r t h e c o r r e l a t i o n. However, ad di t i on of th ese doe s no tm a t e r i a l l y e f f e c t t h e s t an d ar d e r r o r a nd i t i s w o rt hw il e t o i n c l ud e t h e s e i n o ure xa mi na ti on of t h e i r e f f e c t o n t h e c o r r o s i o n r a t e .magnesium and magnesium-sil icon a r e pre sen ted i n Table V I .Na/V l e v e l s a r e summarized f o r comparison.w i t h t h e l i n e a r s t e p w is e r e g r e s s i o n a n a l y s i s t ec h ni qu e .sodium, a dd i t iv e and tempera ture a re c l e a r l y e v id e nt .compares favo rably w it h th e Mg-Si system.h ig h Na/V r a t i o s , t h e f r i a b i l i t y d e c r e a se s ve r y r a p i d l y .

Data for the Na2S04-

CeO and Reog

The co rr e la t i on e qua t ion s f o r th e MgSOThe p l o t s f o r

&L_ _ -W

Another i n t e re s t i n g o bse rva t i o n was t h a t a l t hough ca lc ium w a s a n i n h i b i t o r

A l l c o e f f i c i e n t s a r e in cl ud ed i n t h e c o r r e l a t i o n e q ua t io n s al though

Slag f r i a b i l i t y dat a f o r the calcium-aluminum-si licon system compared withThe da t a fo r va r i ou s

There were not enough data t o e valu ateHowever, th e eff ec t of

A t 820, t h e Ca-Al-Si systemHowever, a t 900' and p a r t i c u l a r l y t h e

DISCUSSIONOver t he pas t s ev e ra l yea r s , t h e t r a de l i t e ra tu r e has abounded wi th c la ims

fo r t he e f f e c t s of manganese on f i r e s id e corr os io n , s l ag problems and co ld-endcorrosion". There now appea rs l i t t l e doubt th a t manganese a s w e l l a s a few othermeta l s such as i r on and copper w i l l reduce carbonaceous ef f l u e nt s or smoke through


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3 '11more ef f i c i en t combust ion proces ses . T h i s ty p e o f a d d i t i v e i s known a s a

combustion improver.of th e engineering of th e pi ec e of equipment.tu rb in e i n sp i t e of an o v e ra l l o x yg en /fu el r a t io o f 1 5 p ass in g th rou g h th emachine. The problem i s caused by burner t i p malfu nct ions and lac k of a va i l ab leoxygen i n th e burner cans . Excess a i r i s used t o a l e s s e r e x t e n t i n o t h e r t y p e sof combustionequipment such as bo i l e r s t o preven t smoking.O f low q u a l i ty fu e l s un de r ex cess a i r co nd iti on s, pe nt av al en t vanadium compoundssuch a s V205 and NaV206 wi th low me lt in g p oi nt s occ ur.increased production of SOg which le ad s t o formatio n of Na SO i n s l a g s and2 4H2S04 downstream. A combustion improver al low s op era t io n near t h e s t o o h i o m e t r i cr a t i o of a i r t o f u e l e l i m i n a t i n g t h e p roblem d e l i n e a t e d ab ove .excess a i r o p e r a t i o n y i e l d s c o n s i de r a b le f u e l s a v i n g s du e t o more e f f i c i e n t o p e r a t i o nof th e burner .I f th e equipment does not permit good con tr ol of excess a i r , t h e a i r / f u e l r a t i o ,p r o t e c t i o n w i l l n o t b e a t t a i n e d i n t h i s manner. A combinat ion add i t ive has manyb e n e f i t s f o r equipm ent w i t h po or c o n t r o l o f a i r / f u e l r a t i o .a l l t h e ad v antages o f low ex cess a i r o p e ra t i o n wh i l e magnesium an d /o r s i l i c o ng iv es p ro tec t i o n d u r in g p e r io d s o f ex cess a i r o p e ra t io n . A qu es ti on we havet r i e d to answer h e r e i s :e ff ec ts of magnesium and si l i co n ?promote corrosion. We f e e l t h a t t h i s e f f ec t i s due t o a d d i t i o n of l i q u i d s t o t h em e l t by the manganese. The e f f e c t of manganese on t h e in hi bi t in g ef f e c t of mag-nesium and magnesium-silicon are shown i n T able I1 and I11 and Figure 1 and 2.Manganese de t r ac ts f rom th e in h i b i t i ng e f f ec t o f magnesium and s i l ic on , a l thoug hs a t i s f a c t o r y p r ot e c t io n can be a t t a i n e d a t 800 wi th t he Mg-Si combination.Comparison of t h e Mn-Mg and Mn-Mg-Si cu rv es w i th t h e Mg and Mg-Si curve s i n Fi gu res1 and 2 i l l u s t r a t e t h i s po in t.welcome exper iments o f t h i s na ture . However, th e labora t ory da ta p resen t ed her el e a d s u s t o conclude t h a t manganese i n combination wi th magnesium and magnesium-s i l i c o n c a n b e b e n e f i c i a l a t lower temperature. A t hig her temperatures, manganesea p p a r en t l y c o n t r i b u t e s t o t h e l i q u i d u s p ha se o f t h e s l a g a nd c a n be d e t r i m e n t a l t oMg and Mg-Si. I n e i t h e r cas e, th e op er at or sho uld app ly Mn-Mg and Mn-Mg-Sicombinations with a g r e a t d e a l o f ca r e and wi th f u l l knowledge o f th e p ro t ec t io nmechanism fo r t h i s ty p e of ad d i t i v e .b o i l e r s . We evalua ted ca lc ium and s ev er a l combinations wi th a luminum, s i l i c o nand lea d. The con clu sio n i s t h a t ca l c iu m i s a c o r r o s i o n i n h i b i t o r a nd i n t h e p re se nc eof aluminum and s i l i c o n ex h i b i t s a to le ranc e to sod ium a t 900' which i s s i m i l a r t ot h a t found f o r t h e Mg-Al-Si comb inati on. However, a s t ud y of t h e s l a g d a t a p r e s e n t edin Table V I i n d ica te s th a t cal c iu m p ro d uces u n accep tab le s l a g s , p a r t i cu la r l y a t t h ehigher temperatures and sodium le ve ls . The adv ers e sla ggin g behavior ca nc elsb e n e f i t s from c o r r o s i o n p r o t e c t i o n . T hes e r e s u l t s a r e c o n s i s t e n t w i t h p r i v a t ecommunications we have received from equipment manufacturers.

I n o u r sea r ch fo r b e t t e r v anad ic co r ro s io n in h i b i to r s , we have ev alu a ted sev e ra lheavy elements. Data on zirconium, cer ium and th e r a r e ea r t h mixture descr ibed abovea r e pr e sen ted i n Tab le V. A l l of these systems e x h i b i t c o r ro s i o n r a t e s s imi la r t otho se fo r manganese and do not in h ib it corr osi on.

The minimum le v e l of ex ce s s a i r requ i red to e l i min ate smoke i s a f u n c t i o nSmoking can occu r even i n a g as

During combustionMoreover, there i s an

Furthermore, lower

Use of a combu st io n improv er d o es r eq u i r e ca r e f u l ap p l i ca t io n b y th e o p e ra to r .

The manganese yields

Does manganese in t e r f e r e wi th t h e co r ro s io n in h i b i t i n gThe data i n Table I revea ls tha t manganese i s n o t an in h i b i to r and ap p ea r s to

We know of no publis hed work t o co rrob orat e the se f in din gs and would

Ca c ium has been c i te d a s a prob lem contaminant i n fu e l s f o r gas tu rb in es and3

CONCLUSIONS1.2 . Manganese i n t e r f e r e s wi th th e co r ro s io n in h ib i t in g e f f ec t s of magnesium

Manganese c on tr ib ut es t o co rr os io n i n NazS04-V205 m el ts and w i l l n o t i n h i b i tcorrosion by forming higher melting compounds.and s i l icon .


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3. Combinations of manganese, mangnesium and si l i c o n ar e probably s a f e a t8OO 0C (1473OF) or lowe r b u t no t a t higher temperatures such as 850' o r 9500.The Mn-Mg-Si system i s p r e f e r a b l e t o th e Mn-Mg system.combination has good sodium tol era nc e.i n h i b i t i n g e f f e c t i v e n e s s .d i d n ot i n d i c a t e a ny c o r ro s i o n i n h i b i t i n g p r o p e r t i e s f o r t h e s e s ys te ms .

4.5. Calcium systems form tenac io us s la gs th a t de t ra c t f rom th e i r cor r os i onMeasurements on t h e r a r e e ar th oxide mixt ure, on zirconium, and on cerium

Calcium i n h i b i t s Na2S04-V205 co rro si on and t h e calcium-aluminum-silicon

REFERENCES1.2.3.4.5.6.7 .8.9 .0.

1.

May, W.R . , Z e t l m e i s l , M . J . , Annand, R .R . , ASME Paper No. 75IWAlCD-6 ande a r l i e r p ap er si n t h i s s e r i e s c i t ed t h e re i n .Buchanan, B.O. , Gardiner , C.R. , Sanders, G.G. , ASME Paper No. A-52-161.Lee, S . Y . , Young, W.E., Vermes, G l . , ASME Paper No. 73-GT-1.Lee, G . K . , M i t c h e l l , E .R . , Grimsey, R.G. , Hopkins, S.E., Proce edings of th eAmerican Power Co nfe ren ce, 26, 531, 1964.Lee, G.K. , F u e l S o c i e t y J o u r n a l , 2, , (1969).Lee, S.Y. , Young, W.E. , ASME Paper No. 75-WAICD-1.May, W.R. , Z e t l m e i s l , M . J . , Bsharah, L . , Annand, R.R.I & EC Product Re sea rch and Development, 11, 438 (1972).May, W.R . , Z e t l m e i s l , M . J . , Bsharah, L . , J . Eng. Power, Trans.,ASME, S e r i e s A . , 96- 24, (1974).May, W.R., Z e t l m e i s l , M . J . , Annand, R.R . , ASME Paper No. 75-WAICD-5.Plonsker , L. , k i f k e n , E .B . , Geuckstein , M.E. , B ai le , S .D . , Presen ted a t t h eCentra l S t a t es Se c t io n , The Combust ion I n s t i t u t e , Madison, Wisconsin ,Manual 26-27, 1974.Sa lo o ja , K.C. , J. I n s t . Fu e l , 1972, 37.


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5TABLE 1

CORROSION R A T E S OF Na,SO, - MnO, - VO SLAGSWEIGHT RATIOS CO RR OS ION CURRENTS ( M o / Cm a , )

Na/V1

1

1

1

1

.1

.1

.1

.1

.1

.01

.01

.01

.01

.Ol

MnA J1

23451

23451

2345

7000.0832

6.8310.629.2010.657.631.33.578

10.693.216.21.742

13.651-.211.26

7500 8000- -.1830 .3171

10.25 12.3013.31 15.8711.96 14.7314.20 32.678.51 10.391.74 2.22.650 .795

10.36 10.164.49 6.8918.63 27.941.15 1.3517.07 20.481.60 1.46.762 .949

858 908--842313.2117.9219.1035.5113.262.541.0412.0311.5427.941.64

23.551.751.40

1.14812.5219.9720.1341.1917.912.781.5615.3714.4327.942 .1827.313.541.79

95w1.231-13.4325.3423.0142.6123.873.331.9916.0412.8331.042.5235.164.52.26


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8TABLE IV

CORROSION RATES OF NaSO. - CaSO, - V-0. SLAGSWEIGHT RATIO '-*

1

1

1

1

1

- 1

.1* l

.1

.1

.01

.01

.01

.01

.01

.001

.OOl

.001

. 01

.001

ca/v1

23451

23451

23451

2345

C O R RO S ION C U R R E NT S (Ma/Cma)

3.311.18.888.994

19.9

-m0 8500 900017.1 34.1 47.8

18.7 33.4 28.0

65 108 81.2

3.73 635 9.696.59 7.33 14.67.54 11.9 13.7

4.721.541.371.49a. 1

3.12 3.12 3.452.43 3.21 4.86,044 .072 ,092.143 .42a .M

6.04 9.06 9.662.01 2.29 2.73.290 .347 .463.0966 .c%5 ,104.214 .268 ,322

4.261.381.051.194.4

950"-4.254.5

32.711.232.313.05.671,a1.691.49

23.73.456.61

.loo

.4579.663.01.578.112.375


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a4

9

9 9 9 9 9 9 9 9999 9 9 9 9 99 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9- Q v ) VI v) v) v) v ) v ) v )Q m v ) v) v) v)

--... - - - - -n - - - - -

5f


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10TABLE V I

Comparison of dad Test Data From the Calcium-Aluminum SystemWith D ata From the Magnesium-S ilicon System

System

N a / V = 0M g / V = 3M g / V = 6Mg,D = S i / V = 3C a b = .75, A I /V =2 . 25 , S i/ V =3N a / V = .01M g / V = 3M g / V = 6Mg/V = S i /V = 3C a / V = .75, A I /V = 2 .2 5 , S i b s 3N a / V = .1M g / V = 3Mg/V = 6Mg/V = S i p = 3

Ca/V = .75, AI/V = 2.25, S i / V = 3Na/V= 1M & = 3M g / V = 6Mg/V = S i p = 3C a D = .75, AI/V = 2.25, S i / V = 3

A v e r a g e Yo L o s s o n B r u s h i n g8200 9 0 8

1 911.75863

2.7355359

2.1223561

1.5411.21.3

102 0592 6

8.33146.38.41

013.2187.703.315.31.4


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0.

0.0

Addit ive/V = 3800" C

Mn

,001 .oI 0. I 10 100Na/V Ra l l o

FIGURE 1 - Corrosion Rates v s . Na/V Ratiosfor 'Several Additives a t 800'C


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High Temp Corrosion by Fuel Impurity

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