Abstract
This study aims to explore the effects of lignite ash deposit, in particular the Ca-bearing species in ash on the tube corrosion under the oxy-firing mode. Two tubes, low-alloy steel T23 and austenite SUS347 have been coated with two ash deposits and exposed to oxy-fuel flue gas at 650 °C for a total of 50 h. The ash deposits were collected from the combustion of a lignite mixed with and without silica additive in a 30 MWth pulverised coal-fired boiler. In this study, the roles of Ca-bearing species including sulphate, free oxide/calcite have been first time revealed by using synchrotron-based X-ray fluorescence (SXRF) and μ-XANES to detail the spatial distribution of individual elements, and in particular the speciation of Cr on the cross-section of tubes. Carburisation of Cr by CO2 is inhibited remarkably upon the co-existence of flue gas and ash deposit. However, the attack from the species in ash deposit other than sodium sulphate is more influential in accelerating the tube corrosion. Calcium sulphate is corrosive against the Cr-rich protective layer formed on the tube surface, resulting in the formation of Cr sulphide even in an exposure time of 50 h. Sulfidation of Cr by calcium sulphate is thermodynamically possible under the exposure conditions tested. Moreover, the free calcium oxide and even calcite in raw coal ash deposit are detrimental, accelerating the breakdown of the two tubes upon the formation of Ca chromite (Cr3 +) and even chromate (Cr6 +). The resultant chromite penetrated underneath the protective layer that is rich in Cr-rich oxide and Fe-Cr spinel, as well as merged intimately with ash deposits. The detrimental effect of free calcium oxide/calcite is more pronounced than calcium sulphate in the 50 h tested here. The use of silica additive to coal combustion immobilised the free Ca oxide, thereby forming an extra protective layer that minimised the oxidation of Cr. Consequently, the whole tube remained intact with little being damaged.
| Original language | English |
|---|---|
| Pages (from-to) | 31-42 |
| Number of pages | 12 |
| Journal | Fuel Processing Technology |
| Volume | 167 |
| DOIs | |
| Publication status | Published - 1 Dec 2017 |
Keywords
- Calcium oxide
- Calcium sulphate
- Chromium
- Lignite ash deposit
- Synchrotron XRF
- μ-XANES
Cite this
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Spatial distribution of chromium on the corroded tube surface characterised by synchrotron X-ray fluorescence (SXRF) mapping and μ-XANES : Co-existence of Ca-rich ash deposits and oxy-firing flue gas. / Ja'baz, Iman; Zhou, Song; Zhang, Lian; Jiao, Facun; Yu, Dunxi; Etschmann, Barbara; Ninomiya, Yoshihiko; Paterson, David.
In: Fuel Processing Technology, Vol. 167, 01.12.2017, p. 31-42.Research output: Contribution to journal › Article › Research › peer-review
TY - JOUR
T1 - Spatial distribution of chromium on the corroded tube surface characterised by synchrotron X-ray fluorescence (SXRF) mapping and μ-XANES
T2 - Co-existence of Ca-rich ash deposits and oxy-firing flue gas
AU - Ja'baz, Iman
AU - Zhou, Song
AU - Zhang, Lian
AU - Jiao, Facun
AU - Yu, Dunxi
AU - Etschmann, Barbara
AU - Ninomiya, Yoshihiko
AU - Paterson, David
PY - 2017/12/1
Y1 - 2017/12/1
N2 - This study aims to explore the effects of lignite ash deposit, in particular the Ca-bearing species in ash on the tube corrosion under the oxy-firing mode. Two tubes, low-alloy steel T23 and austenite SUS347 have been coated with two ash deposits and exposed to oxy-fuel flue gas at 650 °C for a total of 50 h. The ash deposits were collected from the combustion of a lignite mixed with and without silica additive in a 30 MWth pulverised coal-fired boiler. In this study, the roles of Ca-bearing species including sulphate, free oxide/calcite have been first time revealed by using synchrotron-based X-ray fluorescence (SXRF) and μ-XANES to detail the spatial distribution of individual elements, and in particular the speciation of Cr on the cross-section of tubes. Carburisation of Cr by CO2 is inhibited remarkably upon the co-existence of flue gas and ash deposit. However, the attack from the species in ash deposit other than sodium sulphate is more influential in accelerating the tube corrosion. Calcium sulphate is corrosive against the Cr-rich protective layer formed on the tube surface, resulting in the formation of Cr sulphide even in an exposure time of 50 h. Sulfidation of Cr by calcium sulphate is thermodynamically possible under the exposure conditions tested. Moreover, the free calcium oxide and even calcite in raw coal ash deposit are detrimental, accelerating the breakdown of the two tubes upon the formation of Ca chromite (Cr3 +) and even chromate (Cr6 +). The resultant chromite penetrated underneath the protective layer that is rich in Cr-rich oxide and Fe-Cr spinel, as well as merged intimately with ash deposits. The detrimental effect of free calcium oxide/calcite is more pronounced than calcium sulphate in the 50 h tested here. The use of silica additive to coal combustion immobilised the free Ca oxide, thereby forming an extra protective layer that minimised the oxidation of Cr. Consequently, the whole tube remained intact with little being damaged.
AB - This study aims to explore the effects of lignite ash deposit, in particular the Ca-bearing species in ash on the tube corrosion under the oxy-firing mode. Two tubes, low-alloy steel T23 and austenite SUS347 have been coated with two ash deposits and exposed to oxy-fuel flue gas at 650 °C for a total of 50 h. The ash deposits were collected from the combustion of a lignite mixed with and without silica additive in a 30 MWth pulverised coal-fired boiler. In this study, the roles of Ca-bearing species including sulphate, free oxide/calcite have been first time revealed by using synchrotron-based X-ray fluorescence (SXRF) and μ-XANES to detail the spatial distribution of individual elements, and in particular the speciation of Cr on the cross-section of tubes. Carburisation of Cr by CO2 is inhibited remarkably upon the co-existence of flue gas and ash deposit. However, the attack from the species in ash deposit other than sodium sulphate is more influential in accelerating the tube corrosion. Calcium sulphate is corrosive against the Cr-rich protective layer formed on the tube surface, resulting in the formation of Cr sulphide even in an exposure time of 50 h. Sulfidation of Cr by calcium sulphate is thermodynamically possible under the exposure conditions tested. Moreover, the free calcium oxide and even calcite in raw coal ash deposit are detrimental, accelerating the breakdown of the two tubes upon the formation of Ca chromite (Cr3 +) and even chromate (Cr6 +). The resultant chromite penetrated underneath the protective layer that is rich in Cr-rich oxide and Fe-Cr spinel, as well as merged intimately with ash deposits. The detrimental effect of free calcium oxide/calcite is more pronounced than calcium sulphate in the 50 h tested here. The use of silica additive to coal combustion immobilised the free Ca oxide, thereby forming an extra protective layer that minimised the oxidation of Cr. Consequently, the whole tube remained intact with little being damaged.
KW - Calcium oxide
KW - Calcium sulphate
KW - Chromium
KW - Lignite ash deposit
KW - Synchrotron XRF
KW - μ-XANES
UR - http://www.scopus.com/inward/record.url?scp=85021358615&partnerID=8YFLogxK
U2 - 10.1016/j.fuproc.2017.06.018
DO - 10.1016/j.fuproc.2017.06.018
M3 - Article
VL - 167
SP - 31
EP - 42
JO - Fuel Processing Technology
JF - Fuel Processing Technology
SN - 0378-3820
ER -