Nitrogen balances in recovery boilers, 2006 Engineering, Pulping, & Environmental Conference

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Nitrogen balances can vary a lot between different mills and recovery boilers. This presentation is based on nitrogen balance measurements for 17 boilers. They show that in modern new boilers the N conversion factor from black liquor N into nitrogen in NO_x is typically in the range of 20 – 30 %. When the boiler design has been done specially for low- NO_x emissions, the range is 15-20 %. The nitrogen split can be with low-NO_x design for instance15 % into NO_x, 10 % into smelt and 75 % into N₂ in flue gases. Low NO_x emission does not correlate with high concentration of N in out flowing smelt. On the other hand, N concentration in smelt can represent over 40 % of the incoming N in black liquor. The emission figures correlate with excess air, temperatures, staging, and in some cases with carry-over.