The influence of limestone and alumina on NO{sub x} and N{sub 2}O emissions from char combustion in a fluidized bed combustor

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20006780

Liu, H; Gibbs, B M

The effect of limestone on the conversion of coal-N, volatile-N to NO/NO{sub x} and N{sub 2}O under fluidized bed combustion conditions has been extensively investigated and well-documented by many researchers. However, so far few studies have specifically investigated the influence of limestone on the conversion of char-N under fluidized bed combustion conditions. In this study, a series of batch-type, char combustion tests was carried out on a bench-scale, electrically heated, bubbling fluidized bed reactor. Char was produced in situ within the reactor. Char combustion tests were conducted with three sets of bed materials, namely silica sand, limestone diluted by silica sand and alumina ({gt}95% {gamma}-Al{sub 2}O{sub 3}) diluted by silica sand. Comparisons of NO{sub x} and N{sub 2}O emissions from char combustion between different bed materials reveal that bed materials containing limestone always results in more NO{sub x} and less N{sub 2}O than the pure sand bed under otherwise identical char combustion conditions. Two possible explanations for this observation have been given. One is that limestone/calcium oxide catalyses the decomposition of N{sub 2}O and promotes the conversion of char-N to NO/NO{sub x}; as in the case of volatile-N. The other is that limestone reduces the SO{sub 2} level in the combustor and hence results in an increase in the pool of H, OH and/or O radicals, which in turn results in an increase in NO{sub x} and a decrease in N{sub 2}O. Experimental results also show that alumina has a similar effect on N{sub 2}O emissions as limestone. However, in contrast to limestone, alumina does not promote the conversion of char-N to NO{sub x}, which suggests that partially replacing sand with alumina may reduce the total emissions of N{sub 2}O and NO{sub x} from coal-fired fluidized bed combustors.

• Research Organization: Univ. of Leeds (GB)
• OSTI ID: 20006780
• Report Number(s): CONF-990534--
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
ALUMINIUM OXIDES
CHARS
CHEMICAL REACTION YIELD
COAL
COMBUSTION KINETICS
FLUIDIZED-BED COMBUSTION
LIMESTONE
NITROGEN OXIDES
NITROUS OXIDE
SORBENT INJECTION PROCESSES