Corrosion of heat exchanger materials

Transcription

1 Corrosion of heat exchanger materials M. Spiegel Aachen, den

2 Introduction HT-Materials Oxidation and Passivation 550 C C > 1200 C Low alloyed steels Ferritic, austenitic steels Ni-based alloys, IMP Ceramics 2.25 Cr-1Mo St Fe-9-12%Cr, Fe-18Cr-10Ni MCrAlY, FeAl, NiAl Oxide layers MoSi 2, SiC, Si 3 N 4 Fe 3 O 4 /Fe 2 O 3 Spinelle Cr 2 O 3 Al 2 O 3 SiO 2 2

3 Introduction Oxidation and Passivation 0.5 O 2 + 2e - = O 2- Fe 2+ + O 2- = FeO x Fe 2+, 2e - Fe = Fe e - Oxid Metall 3

4 Introduction Oxidation and Passivation X or m parab. Bereich dx dt = k ' x p x 2 = 2k' p t Übergangsbereich Linearer Bereich Parabolic growth: Diffusion control [k p ] = cm 2 /s [k p ] = g 2 /cm 4 s t 4

5 5 Introduction Oxidation and Passivation Parabolic constants of oxides

6 6 Introduction Oxidation and Passivation

7 7 Corrosion in power plants Introduction Boiler Corrosion areas Firing unit Grate

8 Corrosion in power plants Corrosive fuels Gaseous and solid combustion products Cl wt.% S wt.% Na 2 O wt.% K 2 O wt.% CaO mg/kg Pb mg/kg Zn mg/kg RA Altholz Holz <5 <35 Braunkohle Steinkohle < Chlorine > Sulfur > heavy metals > Alkali-elements Waste > Biomass > Coal 8

9 Corrosion in power plants Materials issues Combustion gas (CO, HCl, SO 2,.., solids) Fireside Corrosion Condensate-Metal-Gas Creep strength Steam oxidation Steam ~ 300 bar 9

10 10 Corrosion of heat exchangers Examples 1:1

11 Corrosion of heat exchangers 24/06/08 Corrosion penetrates along dendritic structures 11 Corrosion layer of (Fe, Cr, Ni) oxides, Metal-chlorides (Ni, Cr, Fe) 30 µm 100 µm Corrosion of heat exchanger materialsn Examples

12 Corrosion of heat exchangers Fireside Corrosion: Chlorine and chlorides Ar vppm HCl O Cr-1Mo Strong accelerated oxidation Temperature dependent 12 A.Zahs, M. Spiegel: Corr. Sci. 42 (2000)

13 Corrosion of heat exchangers Fireside Corrosion: Chlorine and chlorides Thick and porous oxide layer Formation of FeCl 2 at the Metal/oxide interface 300 µm Oxide Metal Metal-chloride 50 µm 13

14 Corrosion of heat exchangers Fireside Corrosion: Chlorine and chlorides 2HCl + 1/2O 2 = H 2 O + Cl 2 2NaCl + Fe 2 O 3 + 1/2O 2 = Na 2 Fe 2 O 4 + Cl 2 Cl 2 2FeCl 2 (g) + 3/2O 2 = Fe 2 O 3 + 2Cl 2 Fe + Cl 2 = FeCl 2 (s) = FeCl 2 (g) Oxide tube surface 14 M. Spiegel, H.J. Grabke: Mater. at High Temp. 14 (1997)

15 15 Corrosion of heat exchangers Fireside Corrosion: Chlorine and chlorides 320 C, FactSage calculation

16 Corrosion of heat exchangers 24/06/08 porous oxides in solidified melts 16 Corrosion layer of (Fe, Cr, Ni) oxides, Metal-chlorides (Ni, Cr, Fe) 100 µm 100 µm Corrosion of heat exchanger materialsn Fireside Corrosion: molten salts

17 Corrosion of heat exchangers Fireside Corrosion: molten salts composition [wt. %] Melting point [ C] ZnCl PbCl ZnCl 2-52 KCl ZnCl 2-18 KCl ZnCl 2-16 KCl ZnCl 2-27PbCl NaCl - 69PbCl KCl - 79PbCl NaCl - 83PbCl ZnCl 2-50KCl - 11PbCl ZnCl 2-48NaCl - 17PbCl NaCl - 40KCl - 44PbCl K 2 SO 4 - Na 2 SO 4 - ZnSO KCl - ZnCl 2 - K 2 SO 4 - ZnSO K 2 SO 4 - Na 2 SO 4 - CaSO

18 Corrosion of heat exchangers Fireside Corrosion: molten salts N 2-5vol.% O vppm HCl 350 C 15 Mo 3 ohne salz KCl-ZnCl 15 Mo 3 2 -PbCl Korrosionsschichtdicke [µm] 18

19 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic Phase diagramm: FactSage calculation 800 #: LIQUID + K 3 Zn 2 Cl 7 (s) LIQUID + ZnCl 2 (g) LIQUID LIQUID + K 2 ZnCl 4 (s) LIQUID + LIQUID + ZnCl 2 (s) KZn 2 Cl 5 (s) # 200 ZnCl 2 (s) + KZn 2 Cl 5 (s) + KZn 2 Cl 5 (s) K 3 Zn 2 Cl 7 (s) 19 T [ C] K 2 ZnCl 4 (s) + K 3 Zn 2 Cl 7 (s) LIQUID + KCl (s) KCl (s) + K 2 ZnCl 4 (s) mol KCl/(KCl+ZnCl 2 )

20 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic Oxidation of Fe in Ar - 8% O mol-% KCl - 50 mol-% ZnCl C parabol. / log linear Inkubationszeit 0 0,0 1,0 2,0 3,0 4,0 5,0 time [h] 20 mass gain [mg/cm 2 ]

21 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic Nickel, 320 C, KCl-ZnCl Ni 16 vol.% O 2 15 mg/cm 2 ZnCl 2 /KCl 2 Ni 8 vol.% O 2 30 mg/cm 2 ZnCl 2 /KCl time [h] 21 mass gain [mg/cm 2 ] Ni 8 vol.% O 2 15 mg/cm 2 ZnCl 2 /KCl 4 Ni 8 vol.% O 2 15 mg/cm 2 ZnCl 2 /KCl 5 Fe 0 vol.% O 2 30 mg/cm 2 ZnCl 2 /KCl 6 Pt 0 vol.% O 2 30 mg/cm 2 ZnCl 2 /KCl 7 Fe 0 vol.% O 2 15 mg/cm 2 ZnCl 2 /KCl

22 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic Chromium, 320 C, KCl-ZnCl time [h] 22 mass gain [mg/cm 2 ] Cr 8 vol.% O 2 30 mg/cm 2 ZnCl 2 /KCl 2 Cr 16 vol.% O 2 15 mg/cm 2 ZnCl 2 /KCl 3 Cr 8 vol.% O 2 15 mg/cm 2 ZnCl 2 /KCl 4 Fe 0 vol.% O 2 30 mg/cm 2 ZnCl 2 /KCl 5 Pt 0 vol.% O 2 30 mg/cm 2 ZnCl 2 /KCl

23 Corrosion of heat exchangers Fireside Corrosion: molten salts p(hcl,cl 2 ) 2FeCl 2 (l) + 3/2O 2 = Fe 2 O 3 + 2Cl 2 FeCl 2 (l) x Fe + Cl 2 = FeCl 2 (l) (dissolution) Fe 23

24 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic Measured solubility of chloride at 320 C and N 2-8 % O time [h] 24 Cr/Ni/Fe [mg/cm 2 ] Fe Cr Ni Cr Ni Fe

25 25 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic

26 26 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic

27 27 Corrosion of heat exchangers Fireside Corrosion: ZnCl 2 -KCl eutectic

28 28 mass change [mg/cm 2 ] Liq.+CrCl 3 +K 2 ZnCl 4 CrCl 3 +K 2 ZnCl 4 +KCl 0.27 Liq.+CrCl mole fraction 0.9 Liquid dissolved metal [mg/cm 2 ]

29 Corrosion of heat exchangers Fireside Corrosion: Summary Temperature dependent corrosion mechanisms 600 C 450 C 250 C Gas phase: HCl solid: Chlorides melts: Sulfates melts: Chlorides active Oxidation Hot Corrosion Corrosion by chloride melts 29

30 Corrosion in power plants Outlook FactSage Simulation 550 C NiCl 2 A. Ruh, M. Spiegel: unpublished NiSO 4 + NiCl 2 + NiKCl K 2 SO 4 LIQUID + NiSO 4 + K 2 SO 4 LIQUID + NiSO 4 LIQUID + NiSO 4 + NiKCl 3 LIQUID + K 2 SO 4 LIQUID LIQUID + NiKCl weight fraction LIQUID + K 2 SO 4 + KCl LIQUID + KCl KCl 30

31 Corrosion in power plants Outlook creep strength fireside corrosion K 2 SO Plus LIQUID + NiSO 4 + K 2SO LIQUID + K 2SO 4 LIQUID + K 2SO 4 + KCl LIQUID + NiSO LIQUID + NiSO4 + NiKCl3 LIQUID LIQUID + KCl NiSO4 + NiCl2 + NiKCl3 LIQUID + NiKCl3 steam oxidation NiCl weight fraction KCl 31