IN-SITU ANALYSIS OF ASH DEPOSITS FROM BLACK LIQUOR COMBUSTION

Aerosols formed during combustion of black liquor cause a significant fire-side fouling problem in pulp mill recovery boilers. (Black liquor is a recycled by-product formed during the pulping of wood in the pap er-making industry). The ash deposits reduce heat transfer effectivene ss, plug gas passages, and contribute to corrosion. Both vapors and co ndensation aerosols lead to the formation of such deposits. The high a sh content of the fuel and the low dew point of the condensate salts l ead to a high aerosol and vapor concentration in most boilers. In situ measurements of the chemical composition of these deposits is an impo rtant step in gaining a fundamental understanding of the deposition pr ocess. Infrared emission spectroscopy is used to characterize the comp osition of thin film deposits resulting from the combustion of black L iquor and the deposition of submicron aerosols and vapors. New referen ce spectra of Na2SO4, K2SO4, Na2CO3 and K2CO3 pure component films wer e recorded and compared with the spectra of the black liquor deposit. All of the black liquor emission bands were identified using our new r eference spectra as well as literature data and ab initio calculations . The ab initio calculations predict the locations and intensities of infrared bands for the alkali-containing vapors of interest. (C) 1998 Elsevier Science B.V. All rights reserved.