Measurements in and Modeling of a Black Liquor Recovery Boiler

Abstract

This article describes an experimental and numerical investigation of a black liquor recovery boiler from a pulp industry. Measurements are reported for major gas-phase species concentration and temperature in a representative horizontal plane across the furnace cross-section for different operating conditions. Overall, the experimental data reveal that the use of an interlaced secondary air distribution mode leads to important gradients from the back wall to the boiler nose, while the use of a rotational air distribution mode leads to more important differences between the left and right side of the furnace, in spite of the values being more uniform. A numerical model, previously available to simulate pulverized coal combustion, was adapted to simulate the combustion process of black liquor. The simulation of the droplets decomposition is based on empirical models from literature followed by the consideration of heterogeneous reactions for both the entrained droplets and the ones that fall on the smelt bed in the furnace. The numerical calculations show deviations in temperature lower than 100°C and predict the same patterns observed in the experiments, namely the temperature asymmetries. The operation of the present furnace with the use of interlaced secondary air distribution mode is favored as it leads to lower temperatures close to the superheaters and hence allow the particles to solidify earlier.

Keywords:

• Black liquor
• Combustion process
• Experimental
• Numerical
• Recovery boiler
• Secondary air distribution mode

Financial support for this work was provided by the Fundação para a Ciência e a Tecnologia through project number POCTI/EME/47900/2002 and is acknowledged with gratitude. The authors would like to thank the personnel of the Portucel pulp factory for their valuable assistance during all the stages of the experiments. The authors wish also to thank students Paulo Silva, Álvaro Santos and Cláudia Casaca and technician Manuel Pratas who assisted them in conducting the work presented here.