| Biomass pellets have been widely used in industrial boiler, agricultural greenhouse and domestic heating. At present, the measurement and control of pollutants emission from biomass pellet combustion is increasingly arousing the public attention. The parameters of biomass pellet burner affect the process state and emissions. However, the domestic biomass pellet burner on the market at present often temper during operation and burn pellet in hopper suddenly because the structure design of feeding device is unreasonable. As unsuitable parameters and conditions of combustion state, the content of CO and NOx in emmission were high and increased environment pollution. The objectives of this study are to devolpe a new feeding mechanism, investigate the relationship between parameters (feeding rate, secondary air, excess air) and content of CO, NOx, chamber temperature based on the 5G-20/85-0.23 burner and optimize these three parameters through universal rotatory experimental design method. The main research contents and results are as follow.(1) A new feeding mechanism have been designed and developed. The various feeding mechanism of biomass pellet burners and their advantages and disadvantages were presented. Based on the design principles of adjustment convenience of feeding rate, anti-tempering and structure compactness, a double screws feeder with parallel axis was developed. Thus, the feeding rate and period could be easliy adjusted. Also, the anti-buring of biomass pellet hopper could be controlled well.(2) The feeding rate is one of the most important parameters of biomass pellet burner. The effects of feeding rate on the content of CO, NOx in emission and temperature in chamber are remarkable. The results showed that the content of CO decreased with the feeding rate from 6.9 to 5.0 kg/h. The range of CO increased with feeding rate. The lowest CO concentration (66 mg/Nm3) was achieved at the feeding rate of 5.0 kg/h. The variation of NOX content was similar with CO, the lowest of NOx was 8.8 mg/Nm3 with 5.0 kg/h. The contents of CO and NOx would be lowest when the feeding mechanism was set at 2/19, however, the feeding rate effects on CO was more remarkable than that of NOx. The range of bottom temperature was wide following by the middle and the highest temperature of bottom chamber was 757? at the feeding rate of 5.0 kg/h.(3) The secondary air affects biomass pellet burning emission largely. The range of CO, NOx and temperature were observed when the secondary air varied from 0.3 to 0.7. The content of CO reached lowest 65 mg/Nm3 with fluctuation weakest but the highest was 193 mg/Nm3 when the secondary air was 0.3. The minimum and maximum emission of NOX were 9.2 and 71.8 mg/Nm3 when the secondary air were 0.4 and 0.7 respectively, however, there was not a positive correlation between the range and content of NOx. The highest bottom temperature was 758? while the secondary air was 0.4.(4) The effects of excess air on emission were explored. The results showed that the production of CO reached the lowest 107 mg/Nm3 with excess air of 2.6 and the highest 235 mg/Nm3 at excess air of 2.7. The content of CO was similar with its extent of variation, while, the NOX was not the same. The excess air did't show strong effects on variation of NOx. The highest (53 mg/Nm3) and lowest (70 mg/Nm3) NOx emission levels were presented at excess air of 2.6 and 2.5 respectively. The highest bottom temperature was 764? when the excess air was 2.6.(5) The parameters of biomass pellet burner optimization was conducted based on universal rotatory experimental design method. Through SAS 8.2 software, three-variable quadratic mathematical models were formulated by selecting the content of CO as dependent variables, choosing feeding rate, secondary air and excess air as independent variables. The lack of fit was not significant. Principal components factor analysis showed that feeding rate was the most significant impact factor, while the excess air had the least effect on the content of CO. The interaction terms between feeding rate and secondary air effected on the content of CO remarkably. The optimal parameters of biomass burner were feeding 6 kg/h, secondary air 0.4, excess air 2.6. |
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