Insights into the Black Liquor Falling Film Evaporation: A Predictive Model of Heat and Mass Transfer

Abstract

A model of a black liquor falling film evaporator was developed based on the calculation of local heat transfer coefficients and the surface heat flux integration. The insight into the heat flux profile showed that the commonplace approach based on global overall heat transfer coefficients for estimating the heat flux might not always be satisfactory because it relies on the use of a specific industrial control strategy. The insight into the heat exchange process can be efficiently used to estimate the response of an existing train to small or large process variations or modifications in the control strategy. The model can easily be implemented in an evaporation train simulation along with the common industrial control strategy or a new control strategy.

Keywords:

• Black liquor
• Concentration
• Evaporation
• Heat transfer
• Mathematical modeling

ACKNOWLEDGMENTS

The authors acknowledge the Ph.D. grant offered to the first author by the French Ministry of Higher Education and Research and Pr. Patrice Nortier for valuable advice and discussion.

Notes

Heat transfer coefficients in W/m² · K.

^a Calculated from industrial data averaged over 1 h.

Data from Bhargava et al.^{[ 7 ]}

Original data from Bhargava,^{[ 43 ]} rearranged and completed in the present work.