Domsjö Fabriker has earlier installed a Near Infrared (NIR) spectrometer after one of their recovery boilers. The purpose is to monitor the reduction efficiency of the boiler and later do process optimization. In this work calibration models for the instrument have been created. 108 green liquor samples have been extracted. A NIR spectrum was recorded for each sample and the samples were subsequently analyzed in laboratory for total alkali, sulfide and total sulfur. Several calibration models were created with multivariate data analysis and their performance and robustness were compared. The best model was able to predict reduction efficiency with a RMSEP of 2.75 percent units. Moreover, models were created for prediction of total alkali with a RMSEP of 0.108 mol/l, sulfides with a RMSEP of 1.95 g/l, total sulfur with a RMSEP of 2.83 g/l and S/Na2 ratio with a RMSEP of 0.022. The result is good enough that the instrument could be used to optimize the process and monitor process disturbances.

Scaling in green liquor handling systems is a persistent problem in many kraft mills. Scaling is commonly believed to be the result of pirssonite (Na2Ca(CO3)2∙2H2O) deposition. In this work, scale characterization was performed by analyzing 12 scale samples obtained from 10 kraft mills. Only 4 samples were identified as pirssonite while the remaining consisted of CaCO3. The predominant presence of CaCO3 in the scale samples was found to be the result of selective dissolution of Na2CO3 from pirssonite scale, leaving CaCO3 behind. Experimental studies were also conducted to study pirssonite solubility under green liquor conditions. Results obtained from these studies were used to create and validate a database for pirssonite in the OLI Systems® software to predict its formation. This database was used to generate a family of pirssonite solubility curves that can be used by the kraft mills as operational guidelines to prevent pirssonite precipitation.

Scaling in green liquor handling systems is a persistent problem in many kraft mills. Scaling is commonly believed to be the result of pirssonite (Na2Ca(CO3)2∙2H2O) deposition. In this work, scale characterization was performed by analyzing 12 scale samples obtained from 10 kraft mills. Only 4 samples were identified as pirssonite while the remaining consisted of CaCO3. The predominant presence of CaCO3 in the scale samples was found to be the result of selective dissolution of Na2CO3 from pirssonite scale, leaving CaCO3 behind. Experimental studies were also conducted to study pirssonite solubility under green liquor conditions. Results obtained from these studies were used to create and validate a database for pirssonite in the OLI Systems® software to predict its formation. This database was used to generate a family of pirssonite solubility curves that can be used by the kraft mills as operational guidelines to prevent pirssonite precipitation.

Dry covers can be used to limit the generation of acid mine drainage from sulphidic mine waste exposed to air and water. For the covers to act efficiently a high degree of saturation should be maintained in the cover, as the diffusion of oxygen is substantially reduced in water compared to that in air. Historically, dry covers made solely from till have been applied with varying degrees of success. To improve the performance of dry covers, a multi-layer approach can be applied incorporating a sealing layer aimed at effectively preventing oxygen ingress and an overlying protective layer. Blends of till and green liquor dregs (GLD) are thought to have advantageous properties regarding the water retention capacity and hydraulic conductivity. Subsequently, the blends should have a good ability to remain highly saturated during dry periods and be able to maintain their function as oxygen diffusion barriers over time. In this study the effective oxygen diffusion coefficient (De) in blends of till and GLD was evaluated by laboratory measurements. The oxygen diffusion coefficient of till-GLD blends was evaluated through 81 diffusion tests performed at different degrees of water saturation. The blends differed in added amounts of GLD and different types of GLD. These variables were studied as they affect the blends grain size, porosity, tortuosity, and degree of saturation, which in turn affect the De. The tests were performed in two-chamber diffusion cells and interpreted using the software Vadose/W (Geoslope, 2016) to determine the De. The results provide an initial evaluation of the variation of De that can be expected for till-GLD blends. The De was found to vary greatly for the blends (10-6 > De > 10-11 m2 s-1) depending on the degree of saturation. Even though the GLD contain substantial amounts of water, a high water content of the till was still required to reach a low De. A predictive model for estimating the De based on basic geotechnical soil properties was compared to the De from the interpreted diffusion tests. The model could generally predict the De to within an acceptable range (± one order of magnitude). Additionally, diffusion tests performed on materials dried in successive steps showed how the De changed over time when exposed to drying. A sharp increase in the De was found for the blends, pure GLD and pure till when exposed to drying. Thus, no clear improvement was found for the GLD-till blends compared to the pure till. These results indicate that the till-GLD layers should not be exposed to drying as loss of cover efficiency may occur. This can have implications for the use of till-GLD blends as sealing layers in terms of the design of the protective cover and the placement of covers. To validate these results, tests on larger material quantities should be performed, preferably in field conditions, and comparison to field measurements would be of high interest.

The presence of Ca(OH)2 (or free lime) in lime mud can cause many problems in the recovery process of kraft pulp mills. Conventional free lime analyses require extensive laboratory work and give inconsistent results. A systematic study was performed to determine if zeta potential, a quickly measurable dispersion characteristic, can be used to indicate the presence of free lime in the recovery process. Measurements were made on synthetic wet lime mud to simulate samples collected after the white liquor clarifier in pulp mills. The results show that zeta potential increases from negative to positive when the free lime content in the lime mud exceeds a critical threshold. This change from negative to positive zeta potential of the lime mud slurry can be used as a basis for developing an on-line monitoring system that effectively detects free lime in the lime mud in order to avoid problems associated with overliming in the recovery process.