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A 660 MW opposed firing boiler is designed with staggered lower over fire air (OFA) burner arrangement, in response to the problems of high NOx emission and low burn-out efficiency at the furnace outlet caused by the use of upper burners on the front wall, numerical simulation is performed to study the effects of the coal mill combinations, as well as the lower OFA ratios, injection angles, heights of the burners on front wall on the combustion and NOx emission characteristics under full load conditions. The results show that, the NOx emission mass concentration decreased by 29.49 mg/m3 and the carbon content in fly ash decreased by 0.16% after the upper burner of the front wall was deactivated. The combined operation mode of BCDEF burners should be selected in actual operation. When keeping the lower OFA ratio unchanged, the NOx emission mass concentration increased after the lower OFA ratio on the front wall was increased from 10.2% to 14.2%. When the air rate exceeded 13.2%, insufficient overfire air at the lower part of the back wall led to a decrease in burnout efficiency. The lower OFA rate on the front wall should be controlled within 12.2%~13.2% during actual operation. The NOx emission mass concentration reduced by 18.13 mg/m3 and the carbon content in fly ash increased by 0.38 percentage point after the lower OFA was changed from 15° injection to horizontal injection. When the lower OFA burners on the front wall were moved up to the height of the lower OFA burners on the rear wall, the NOx emission mass concentration decreased by 41.78 mg/m3, and the carbon content in fly ash increased by 0.68 percentage point. Compared to the opposed firing boilers with conventional lower OFA burners, the one with staggered layout of lower OFA burners has relatively weak deep air staged combustion effect, but with high burnout rate and better adjustability.
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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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