Nitrogen oxide formation in black liquor single droplet combustion

Nitrogen oxide formation in single droplet combustion of black liquors was measured under different combustion conditions (droplet size 5-​45 mg, temp. 800-​900 °C, O₂-​concn. 3-​21​%)​.  The NO formation in relation to the carbon conversion is presented.  The amts. of NO formed during pyrolysis (pyrolysis-​NO)​, i.e., from the burning of volatile nitrogen species, and during char burning stage (char-​NO) are reported.  Under all conditions studied, the NO formation followed the carbon conversion up to about 40-​50​%, after which the NO formation stopped, and began again only when about 90​% of the carbon had been converted.  The relative amt. of pyrolysis-​NO varied with droplet size at 900 °C and with oxygen concn. at 800°C.  Possible mechanisms for these effects are suggested.  The char-​NO originated mostly in the oxidn. of the inorg. residue left after the burnout of the char.  The amt. of char-​NO depended on temp.: more NO was formed at 800 °C than at 900 °C.  The implications of the findings for NO_x emissions in black liquor burning in recovery boilers are discussed.