Energy Fuels 2010, 24, 446–450 Published on Web 12/07/2009
: DOI:10.1021/ef900913p
NO Reduction over Biomass Char in the Combustion Process Li Dong, Shiqiu Gao,* and Guangwen Xu State Key Laboratory of Multi-Phase Complex System, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China Received August 22, 2009. Revised Manuscript Received November 18, 2009
In the biomass combustion process, fuel N in biomass can be oxidized into NOx, causing acid rain and photochemical smog. Some measures should be taken to control NOx emissions from biomass combustion. In this paper, NO reduction over rice husk char in the combustion process was studied in a fixed-bed reactor to optimize the biomass combustion process. The results showed that biomass char was more active in the presence of oxygen to reduce NO than it was in the inert atmosphere. With the increase of oxygen, more NO can be reduced by biomass char. From 973 to 1173 K, NO reduction over rice husk char increased with increasing temperature, whereas the difference between NO reduction with and without oxygen decreased with increasing temperature. Moreover, the presence of CO and SO2 in the combustion process was shown to enhance NO reduction over biomass char to different degrees. Therefore, it is an effective way to reduce NO from biomass combustion by emphasizing NO reduction over biomass char.
reported that NO emission can be restrained by the heterogeneous reaction over char and the homogeneous reaction of NH3, HCN, CO, and other species in volatiles.11-13 Some combustion technologies that reduce NOx, such as air staging, fuel staging, and decoupling combustion, have been developed accordingly.14-16 The NO-char reaction is an important reaction to decrease the conversion of fuel N to NO in coal combustion. Many researchers had reported that NO can be reduced effectively over coal char and that the NO-coal char reaction was of first order or fractional order.17-20 Char particles with larger specific surface areas were reported to reduce more NO.21 The reaction temperature and the heating rate to produce char had important influences on char reactivity.22-24 However, the studies on NO reduction over biomass char were scarce. Sørensen et al.25 and Dong et al.26 had reported that biomass
1. Introduction NOx is a well-known pollutant produced from fuel combustion. It can injure the respiratory organs and form acid rain and photochemical smog.1-4 In comparison to N2O and NO2, NO makes 90-95% of the total NOx emitted by combusting fossil fuels and biomass. Many countries have made strict policies to limit NOx emissions from fuel combustion. Biomass is the fourth energy resource following coal, petroleum, and natural gas. As a renewable energy source and CO2-neutral fuel, biomass combustion attracts increasing interest. However, most biomass can produce NO in the combustion process because of its nitrogen content.5-9 In comparison to coal, the organic structure and morphological characteristics in biomass are different and the volatiles content in biomass is often more than 50%.10 The biomass combustion behavior and NO formation paths are different from those in coal combustion. Therefore, it is necessary to investigate NO formation and reduction during biomass combustion and to develop effective ways to control NO emissions from biomass use. In previous works, NO formation and reduction in coal combustion had been studied prevalently. It had been
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*To whom correspondence should be addressed. Telephone: þ86-1062656066. Fax: þ86-10-62550075. E-mail:
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Energy Fuels 2010, 24, 446–450
: DOI:10.1021/ef900913p
Dong et al. Table 1. Proximate and Ultimate Analyses of Fuels rice husk Proximate Analysis (wt %) 7.5 64.2 13.9 14.5 Ultimate Analysis (wt %, daf) 46.96 6.74 0.65
