Viscosity models for New Zealand black liquor at low solids concentrations

Abstract

Availability of accurate models for prediction of the viscosity of black liquor (BL) from the chemical pulping of pine will facilitate its online monitoring and control and subsequently the optimisation of combustion in a recovery boiler. New Zealand (NZ) BL viscosity data are limited, and no predictive model is available. The viscosities of the NZ BL samples at solids concentrations (SCs) <50% were obtained at temperature of 25-85• C and shear rate up to ∼2000 s −1 . The samples showed Newtonian behaviour. Existing models from the literature and a binomial model developed in this work were used to fit the viscosity data as a function of SC and temperature. Accuracies of these models were examined for both the log-transformed and the untransformed viscosity data using coefficient of correlation (R) and maximum absolute relative error (MARE) (between the actual and predicted viscosities), respectively, as indices. Although the existing models fit NZ BL viscosity data well when they were log-transformed, they performed poorly when not transformed. Conversely, the new binomial model gave accurate predictions with both the log-transformed and untransformed viscosity data (R = 0.9997; MARE = 5.7%). It is concluded that at low SCs, the viscosity of Newtonian BL can be accurately predicted using the new binomial model. 

Solids Content of Black Liquor Measured by Online Time-Domain NMR

“…Measuring the viscosity of black liquor is one way to control the process, although it is usually conducted offline, it requires sample gathering and additional calculations based on the calibration of the viscosity with the temperature. Online viscometers have been tested in pilot mills [15,16]; however, there are no such devices that can be installed permanently in the mills [17]. Optical methods, such as refractometry and NIRS, can be used at the pulp mills for the online analysis of constituents in the kraft process.…”

“…Online viscometers have been tested in pilot mills, and an overview of their performances is provided in References [15,16]. However, there is still a need for an online viscometer that can be installed permanently in the mill [17].…”

Centrifugal Pump-Based Predictive Models for Kraft Black Liquor Viscosity: An Artificial Neural Network Approach

“…Centrifugal pumps are usually a part of an installed kraft pulp mill where the typical byproduct from the pulping unit is black liquor (BL) . The origin and the nature of BL and its subsequent processing in a pulp mill have been discussed elsewhere. , The CP-based BL viscosity models described in this paper are developed from the performance data of an Ahlstrom-made THP-10 centrifugal pump (CP) having an outer impeller diameter of 360 mm. The pumping fluid was taken as a Newtonian BL of varying viscosities.…”

Neural Network-Based Model for Joint Prediction of the Newtonian and NonNewtonian Viscosities of Black Liquor

“…Vakkilainen's [8] model is applicable over only a very narrow range of temperatures close to actual operating conditions. Ghosh's [7] model has been shown to be ineffective for predicting black liquor viscosity even at limited low-solids concentrations [9]. The recently proposed artificial neural network (ANN)-based model for predicting the viscosity of black liquor is applicable over a wide range of process conditions [10].…”