In situ analysis of ash deposits from black liquor combustion

Abstract

Aerosols formed during combustion of black liquor cause a significant fire-side fouling problem in pulp mill recovery boilers. The ash deposits reduce heat transfer effectiveness, plug gas passages, and contribute to corrosion. Both. vapors and condensation aerosols lead to the formation of such deposits. The high ash content of the fuel and the low dew point of the condensate salts lead to a high aerosol and vapor concentration in most boilers. In situ measurements of the chemical composition of these deposits is an important step in gaining a fundamental understanding of the deposition process. Mared emission spectroscopy is used to characterize the composition of thin film deposits resulting fkom the combustion of black liquor and the deposition of submicron aerosols and vapors. New reference spectra of Na2S04, K2SO4, Na2C03 and KZC03 pure component films were recorded and compared with the spectra of the black liquor deposit. All of the black liquor emission bands were-identified using a combination of literature data and ab initio calculations. Ab initio calculations also predict the locations and intensities of bands for the alkali vapors of interest.This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately'owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. , .-'. AbstractAerosols formed during combustion of black liquor cause a significant fire-side fouling problem in pulp mill recovery boilers. The ash deposits reduce heat transfer effectiveness, plug gas passages, and contribute to corrosion. Both vapors and condensation aerosols lead to the formation of such deposits. The high ash content of the fuel and the low dew point of the condensate salts lead to a high aerosol and vapor concentration in most boilers. In situ measurements of the chemical composition of these deposits is an important step in gaining a fundamental understanding of the deposition process. Infrared emission spectroscopy is used to characterize the composition of thin film deposits resulting from the combustion of black liquor and the deposition of submicron aerosols and vapors. New reference spectra of Na2SO4, K2S04, Na2C03 and K2CO3 pure component films were recorded and compared with the spectra of the black liquor deposit. All of the black liquor emission bands were iden...

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“…time from the qm(t+d)' g$%m(o (54) The rate of inertial impaction is the product of the total mass flux of particles in the flow and the fraction of these particles -which we call the impaction efficiency -that actually strike the surface. That is, (55) where qm is the local particle flux, Stk is the Stokes number, and qm is the impaction efficiency.…”

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