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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 SO2/SO3 at low temperature, increasing the risk of corrosion and fouling on low temperature heating surfaces. To solve this problem, 168-hours continuous corrosion experiments of No.20 and ND steel specimens in an oxidizing atmosphere of NH3-SO2-O2-CO2-H2O(g)-N2 at 250 ℃ and 150 ℃ were carried out. The effects of temperature, NH3 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 NH3 with volume fraction of 0.005%, and the average corrosion rate reached 0.003 6 mg/(cm2·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/(cm2·h)). At 250 ℃, CaSO3 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 NH4HSO4 and (NH4)2SO3 promoting the agglomeration effect among ash particles. In the future, when a large proportion of ammonia is mixed with coal-fired 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.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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