Ammonia-coal co-firing mode for power generation can significantly reduce the carbon emission level of the unit. But when the ammonia blending ratio is too high
the ammonia blending/pure ammonia burner is not properly arranged
and the ammonia-coal co-combustion effect is not good
the escaped ammonia will react with SO
2
/SO
3
at low temperature
increasing the risk of corrosion and fouling on low temperature heating surfaces. To solve this problem
168
-hour continuous corrosion experiments of No.20 and ND steel specimens in an oxidizing atmosphere of NH
3
-SO
2
-O
2
-CO
2
-H_2O_((g))-N
2
at 250 ℃ and 150 ℃ were carried out. The effects of temperature
NH
3
volume fraction and fly ash coating on the corrosion rate of metal specimens were mainly investigated
and the corroded metal specimens and ash samples were analyzed in terms of micro-morphology and mineral phase. The experimental results showed that the average corrosion rate of ND steel specimens decreased by 58% when the volume fraction of ammonia was increased from 0.002 5% to 0.005 0%. The corrosion rate of No.20 steel coated with fly ash was significantly accelerated in the atmosphere of NH
3
with volume fraction of 0.005%
and the average corrosion rate reached 0.003 6 mg/(cm
2
·h). Elevating temperature significantly accelerated the corrosion rate. ND steel coated with fly ash showed the fastest average corrosion rate at 250 ℃(0.011 2 mg/(cm
2
·h)). At 250 ℃
CaSO
3
was newly generated and it was detected in the ND steel-coated ash samples
which may have promoted adhesion among ash particles. After the corrosion of No.20 steel coated with fly ash at 150 ℃
the ash sample had a serious agglomeration effect
which is mainly due to the newly generated NH
4
HSO
4
and(NH
4
)_2SO
3
promoting the agglomeration effect among ash particles. In the future
when a large proportion of ammonia is mixed with coalfired units
especially when medium and high sulfur coal is used
special attention should be paid to the change of fly ash characteristics and the risk of fouling and corrosion on low temperature heating surfaces.
关键词
Keywords
references
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