Presentation on theme: "High temperature corrosion of candidate materials for industrial boilers in biomass combustion Jiri Krejcik and Josef Cizner 16. February 2010, Oslo SVÚM."— Presentation transcript:
High temperature corrosion of candidate materials for industrial boilers in biomass combustion Jiri Krejcik and Josef Cizner 16. February 2010, Oslo SVÚM a.s. Research Centre Bechovice Prague 9 CZECH REPUBLIC
Corrosion test of candidate steels and alloys for biomass combustion a)Laboratory test in model environment (presented in the NGBW conference in Milan) b) Field test on 5 different types of biomass combustion (co-combustion) boilers
Test samples - cuts of tubes from candidate materials fixed on the bar made from AISI 310 steel. Uncooled samples were installed into boilers.
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 Location of the test samples in boiler Paskov (CZ) Time:580 °C h, h, h 640 °C h coal-mine gas natural gas SH1 SH2 LUVO1 LUVO2 ECO1 ECO2 DHD bark DMD Electrofilter air water steam corrosion samples gas temperature 580 °C corrosion samples gas temperature 640 °C
samples 600 °C Location of the test samples in boiler Štětí (CZ) 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, h, h Temperature: 600 °C
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, h, h Temperature: 540 °C and 580 °C
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, h Temperature: 500 °C
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 lignite + wood chips - other years Time:1 560 h, h, h, h, h Temperature: 450 °C
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.
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.
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
High alloy martensitic and austenitic steels and Ni-base alloys have very good corrosion resistance.
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
Only Ni-base alloys and austenitic steels have good corrosion resistance Good corrosion resistance of all test materials - low temperature
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 Dalkia Krnov). 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 (Biocel Paskov, Mondi Štětí). * Different situation is in atmosphere with Cl (Třebíč) and Växjö (Cl + S), the corrosion resistance of martensitic steels is low and is similar to low alloy steels (except X20CrMoV12 1 at lower temperature 540 °C Växjö).
Mechanism of corrosion EPMA microanalysis and metallography were used for the study of corrosion mechanism.
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).
Steel 10CrMo Paskov
Steel 10CrMo Växjö
[%] corrosion layer basic material (BM) 1 point - 10 µm 10CrMo °C - Växjö
corrosion layerpenetration BM 1 point - 2 µm 10CrMo °C - Växjö [%] corrosion layer
Mechanism of initiation and growth of inner corrosion layer Initiation - attack of carbide particles and transformation to oxides. Oxidation along austenitic grain boundaries. Paskov 347H °Csulphidation Växjö E °C S and Cl corrosion
Paskov - 347H
Växjö - E °C 1 point - 2 µm [%] penetration BM corrosion layer
2 0 penetration BM 1 point - 2 µm E °C - Växjö % corrosion layer 1
Ni-base alloys SAN 28, 625 Alloys 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.
Inner corrosion layer [wt %] NiCrOMoClS 2, ,8-111,24,5 Penetration of O, S and Cl into basic material - attack of carbide particles and transformation into oxides (with S, Cl).
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 demonstrates the initiation of corrosion on carbide particles and selective corrosion of the surface with corrosion along grain boundaries in all test materials at higher temperatures (over 500°C). In corrosion products O, Cl and S were found, and penetration of Cr, W, Mo, Ni from basic material was analysed (depending on chemical composition of material) Austenitic steels and Ni-base alloys have very good corrosion resistance with thin corrosion layer. In low alloy steels and martensitic steels (except of lower temperatures on Dalkia Krnov boiler) high corrosion rate with thick corrosion layer was observed.