High temperature corrosion of candidate materials for industrial boilers in biomass combustion

1. SVÚM a.s. Research Centre Bechovice 190 11 Prague 9 CZECH REPUBLIC High temperature corrosion of candidate materials for industrial boilers in biomass combustion Jiri Krejcik and Josef Cizner 16. February 2010, Oslo

2. Corrosion test of candidate steels and alloys for biomass combustion • Laboratory test in model environment (presented in the NGBW conference in Milan) • Field test on 5 different types of biomass combustion(co-combustion) boilers

5. Test samples - cuts of tubes from candidate materialsfixed on the bar made from AISI 310 steel. Uncooled samples were installed into boilers.

6. DHD Electrofilter LUVO1 SH2 coal-mine gas natural gas SH1 ECO1 bark ECO2 air DMD LUVO2 water steam corrosion samples gas temperature 580 °C corrosion samples gas temperature 640 °C Location of the test samples in boiler Paskov (CZ) Area: pulp and paper industry Moving - grate boiler Performance: 50 t/h Produced steam: 486 °C/83 bar Fuel: bark (saw dust) + bark from deposit (with earth) + coal - mine gas Time: 580 °C - 4 224 h, 7 032 h, 9 832 h 640 °C - 4 224 h

7. Location of the test samples in boiler Štětí (CZ) samples 600 °C Area: pulp and paper industry Circumfluid – Foster Wheeler Performance: 220 t/h Produced steam: 535°C/94 bar Fuel: 50 % bark + 50 % lignite Time: 8 760 h, 17 520 h, 31 370 h Temperature: 600 °C

8. Samples (SH1-SH2) Gas temperature 540°C Samples (SH2-SH3) Gas temperature 580°C Location of the test samples in boiler Växjö (S) Area: heat and electricity generation Boiler: Sandvik II Circumfluid Performance: 90 t/h Produced steam: 535 °C/100 bar Fuel: wood chips + peat Time: 6 240 h, 15 000 h, 23 760 h Temperature: 540 °C and 580 °C

9. samples 500 °C Location of the test samples boiler Třebíč (CZ) Area: heat generation Boiler: VESKO-S Performance: 5 MW Fuel: 100% wheat straw Time: 2 000 h, 4 747 h Temperature: 500 °C

10. Location of the test samples at the instalation of Krnov (CZ) samples 450 °C Area: heat and electricity generation Ingnifluid - ČKD Dukla Prague Performance: 75 t/h Produced steam: 445°C/37,2 bar Fuel: lignite + 20% pollard - 2006 lignite + wood chips - other years Time: 1 560 h, 7 440 h, 9 456 h, 14 124 h, 21 647 h Temperature: 450 °C

11. Analysis of deposit Deposit was taken from the location of samples (scratched off from the surface of overheating tubes). Analysis of elements was carried out by EMPA analyzer, most important is the content of Cl (chlorides) and S.

12. 1.Company: BIOCEL Paskov, CZ Analysis of deposit

13. 2.Company: MONDI PACKAGING, Štětí, CZ Analysis of deposit

14. 3.Company: VÄXJÖ Energi AB, S Analysis of deposit

15. 4.Company: TTS, Třebíč, CZ Analysis of deposit

16. 5.Company: DALKIA Krnov, CZ Analysis of deposit

17. Evaluation Weight changes of test samples were evaluated during the down - time of boilers. On diagrams are corrosion curves, corrosion rate is depending on kind of biomass and temperature.

18. Martensitic and austenitic steels have the equal corrosion resistance in both temperatures, corrosion resistance of low alloy steels is unacceptable. The best corrosion resistance have Ni-base alloys

19. High alloy martensitic and austenitic steels and Ni-base alloys have very good corrosion resistance.

20. At temperature 540 °C - low alloy steels + martensitic steel T92 have very low corrosion resistance At temperature 580 °C - corrosion resistance of low alloy + both martensitic steels is very low - the effect of Cl+S The best – austenitic steels and Ni-base alloys

21. Only Ni-base alloys and austenitic steels have good corrosion resistance Good corrosion resistance of all test materials - low temperature

22. Evaluation of corrosion rate Corrosion rate of low alloy steels has the linear character and the weight changes of samples are much higher as compared to other test materials (except of DalkiaKrnov) . Austenitic steels and Ni-base alloys have the best corrosion resistance and the weight changes are very low in all cases. The behaviour of martensitic steels is different and depends on the combustion atmosphere in boiler (deposit): * In atmosphere with higher content of S (no Cl) -martensitic steels have very good corrosion resistance - similar to austenitic steels and Ni-base alloys (BiocelPaskov, Mondi Štětí). * Different situation is in atmosphere with Cl (Třebíč) and Växjö(Cl + S), the corrosion resistance of martensitic steels is low and issimilar to low alloy steels (except X20CrMoV12 1 at lowertemperature540 °C Växjö).

23. Mechanism of corrosion EPMA microanalysis and metallography were used for the study of corrosion mechanism.

24. Lowalloysteels EPMA microanalysisofcorrosionlayers Outer corrosion layer [wt %] Inner corrosion layer [wt %]

25. Mechanism of initiation and growth of inner • oxidic layer • Initiation - attack of carbide particles distributed on grain boundaries and equally distributed in matrix - transformation to oxides (with S, Cl) . • Documentation of this mechanism is shown on steel 10CrMo9 10 • boiler Paskov (mainly sulphidation) • boiler Växjö (combination of S and Cl corrosion).

26. Steel 10CrMo9 10 - Paskov

27. Steel 10CrMo9 10 - Växjö

28. 100 1 point - 10 µm 10CrMo9 10 - 540 °C - Växjö 80 basic material (BM) corrosion layer 60 [%] 40 20 0

29. 5 1 point - 2 µm 10CrMo9 10 - 540 °C - Växjö 4 BM corrosion layer corrosion layer penetration 3 [%] 2 1 0 5

30. Martensitic steels T 92, X20CrMoV12 1 Outer corrosion layer [wt %] Inner corrosion layer [wt %]

31. Mechanism of growth ofinner corrosion layer Penetration of O, S and Cl into basic material, prefentially carbide particles are attacked

32. Corrosion layer - thickness Penetration to BM Växjö

33. X20CrMoV12 1 - Paskov

34. 100 100 1 point - 10 µm 1 point - 10 µm T92 - Mondi 80 80 outer corrosion layer inner corrosion layer BM 60 60 [%] [%] 40 40 20 20 0

35. Austenitic steels Outer corrosion layer [wt %] Inner corrosion layer [wt %]

36. Mechanism of initiation and growth of inner corrosion layer • Initiation - attack of carbide particles and transformation to oxides. • Oxidationalongausteniticgrainboundaries. • Paskov 347H - 580 °C sulphidation • Växjö E1250 - 540 °C S and Cl corrosion

37. Paskov - 347H

38. Växjö

39. 100 Växjö - E1250 - 540 °C 1 point - 2 µm 80 corrosion layer penetration BM 60 [%] 40 20 0

40. 2 E1250- 540 °C - Växjö 1 point - 2 µm corrosion layer penetration BM % 1 0

41. Ni-base alloys SAN 28, 625 Alloys 625 - application for the atmosphere with Cl in waste incineration plants. Corrosion layers are very thin, much more thinner as compared to other test materials. Mechanism of corrosion Observed only one very thin layer - up to 6 µm.

42. Inner corrosion layer [wt %] Penetration of O, S and Cl into basic material - attack of carbide particles and transformation into oxides (with S, Cl).

44. Växjö

45. C O N C L U S I O N • Tests of candidate materials with uncooled samples from low alloy, martensitic and A-steels and two Ni-base alloys show the effect of: • corrosion atmosphere (content of sulphates, chlorides in deposit) • temperature (temperature of combustion gases) • Metallographic analysis demonstratestheinitiationofcorrosion on carbideparticlesand selective corrosionof thesurface with corrosion along grain boundaries in all test materials at higher temperatures (over 500°C). In corrosion products O, Cl and S werefound, andpenetrationofCr, W, Mo, Ni from basic materialwasanalysed (depending on chemicalcompositionofmaterial) • Austenitic steels and Ni-base alloys have very good corrosionresistance with thin corrosion layer. In low alloy steels and martensitic steels (except of lower temperatures on DalkiaKrnov boiler) high corrosion rate with thick corrosion layer was observed.

46. Thank you for your attention!