| 1. |
- Andersson, Niclas, et al.
(författare)
-
A new sensor and a novel control concept for optimized fiber line operation
- 2014
-
Ingår i: TAPPI Journal. - : TECH ASSOC PULP PAPER IND INC. - 0734-1415. ; 13:10, s. 39-45
-
Tidskriftsartikel (refereegranskat)abstract
- Kraft and sulfite pulp mills use several consecutive process stages for pulp production. However, usually only one key pulp parameter is used for process control and that is the lignin content in the fibers, typically expressed as the kappa number. Even so, to improve process efficiency, more variables need to be monitored. To do that, a new sensor was developed, the dissolved lignin transmitter (DLT), along with a new control concept. The DLT measures the dissolved lignin content in the pulp slurry using a unique principle based on optical measurements. The device can measure the dissolved lignin inline at low consistency and at medium consistency. The sensor has two major applications: 1) improving the efficiency in washing stages and 2) optimizing chemical charges. Results from several mill trials have shown that the contribution from dissolved lignin in the filtrate portion of the pulp is up to 30% of the total bleach load, i.e., fiber and filtrate kappa number combined into the bleach plant. Hence, chemical savings can be achieved taking this component into account compared to only measuring the washed fiber kappa number. Application: The results of this study can help mills understand how to better control the pulping stages, which might lead to significant economic savings and better pollution control.
|
|
| 2. |
- Berglin, Niklas, et al.
(författare)
-
Pilot-scale combustion studies with kraft lignin in a powder burner and a CFB boiler
- 2010
-
Ingår i: TAPPI Journal. - 0734-1415. ; 9:6, s. 24-30
-
Tidskriftsartikel (refereegranskat)abstract
- Processes have been developed to produce a solid biofuel with high energy density and low ash content from kraft lignin precipitated from black liquor. Pilot-scale tests of the lignin biofuel were carried out with a 150 kW powder burner and a 12 MW circulating fluidized bed (CFB) boiler. Lignin powder could be fired in a powder burner with good combustion performance after some trimming of the air flows to reduce swirl. Lignin dried to 10% moisture content was easy to feed smoothly and had less bridging tendencies in the feeding system than did wood/ bark powder. In the CFB boiler, lignin was easily handled and cofired together with bark. Although the filter cake was broken into smaller pieces and fines, the combustion was not disturbed. When cof ¡ring lignin with bark, the sulfur emission increased compared with bark firing only, but most of the sulfur was captured by calcium in the bark ash. Conventional sulfur capture also occurred with addition of limestone to the bed. The sulfur content in the lignin had a significantly positive effect on reducing the alkali chloride content in the deposits, thus reducing the high temperature corrosion risk. Application: This research is of interest for pulp and paper and energy and utilities companies that want to understand how kraft lignin can be used to replace fuel oil or coal in many combustion applications.
|
|
| 3. |
- Berglin, N., et al.
(författare)
-
Pilot-scale combustion studies with kraft lignin in a powder burner and a CFB boiler
- 2010
-
Ingår i: Tappi Journal. - 0734-1415. ; 9:6, s. 24-30
-
Tidskriftsartikel (refereegranskat)abstract
- Processes have been developed to produce a solid biofuel with high energy density and low ash content from kraft lignin precipitated from black liquor. Pilot-scale tests of the lignin biofuel were carried out with a 150 kW powder burner and a 12 MW circulating fluidized bed (CFB) boiler. Lignin powder could be fired in a powder burner with good combustion performance after some trimming of the air flows to reduce swirl. Lignin dried to 10% moisture content was easy to feed smoothly and had less bridging tendencies in the feeding system than did wood/bark powder. In the CFB boiler, lignin was easily handled and cofired together with bark. Although the filter cake was broken into smaller pieces and fines, the combustion was not disturbed. When cofiring lignin with bark, the sulfur emission increased compared with bark firing only, but most of the sulfur was captured by calcium in the bark ash. Conventional sulfur capture also occurred with addition of limestone to the bed. The sulfur content in the lignin had a significantly positive effect on reducing the alkali chloride content in the deposits, thus reducing the high temperature corrosion risk.
|
|
| 4. |
- Bialik, Marta, et al.
(författare)
-
New challenges regarding nonprocess elements in the liquor and lime cycle
- 2015
-
Ingår i: TAPPI Journal. - : TAPPI. - 0734-1415. ; 14:7, s. 421-429
-
Tidskriftsartikel (refereegranskat)abstract
- Optimal performance of the green liquor plant, recausticizing plant, and lime cycle is vital for adequate white liquor availability and quality as well as for a mill's energy efficiency. Recently, various problems in the liquor and lime cycle have been frequently reported by our industrial partners, including poor performance of green liquor filters or sludge filters, decreased filterability of lime mud, increased lime kiln dead load, and poorquality white liquor. Those problems are most likely caused by an accumulation of nonprocess elements in the liquor and lime cycle due to increased mill closure, increased use of biofuels, or both. Data from the literature and earlier studies have been analyzed with regard to the occurrence and concentration of nonprocess elements in various process streams, including filtered green liquor, green liquor sludge, lime mud, and white liquor. The mineral forms in which nonprocess elements often precipitate were also studied, together with the common knowledge and rules of thumb used by mills for dealing with the problems. The literature data are compared with the newest analytical results from a sampling campaign involving several mills with varying process solutions with respect to nonprocess elements. The consequences and possible recommendations for the mills are presented. Application: Kraft pulp mills can use this information to diagnose and possibly solve problems related to nonprocess elements in day-to-day mill operation.
|
|
| 5. |
- Bjorklund, Robert, et al.
(författare)
-
Online monitoring of inorganic cooking chemicals in white liquor by pulse voltammetry
- 2010
-
Ingår i: TAPPI JOURNAL. - : Tappi Press. - 0734-1415. ; 9:8, s. 49-53
-
Tidskriftsartikel (refereegranskat)abstract
- White liquor parameters in the recovery area of a kraft pulp mill were monitored for a 1-year period using rhodium as an electrode material in a sensor system based on pulse voltammetry. Shift personnel performed offline titration analysis of the liquor every 4 hours. The results for effective alkali, sulfidity, and total titratable alkali were used to train and validate the sensor for online monitoring. Partial least square regression models developed from 150 reference titration results for each parameter from the first month of the study predicted concentrations for the following 11 months. Validation of the models using titration results indicated that overall relative root mean squared errors for prediction of the parameters were 3.7% for effective alkali, 3.4% for sulfidity, and 5.1% for total titratable alkali. Process stops that exposed the sensor to temperature excursions or acid washings resulted in temporary periods of poor prediction.
|
|
| 6. |
|
|
| 7. |
- Carlsson, Per, et al.
(författare)
-
Experiments and mathematical models of black liquor gasification – influence of minor gas components on temperature, gas composition, and fixed carbon conversion
- 2010
-
Ingår i: TAPPI Journal. - 0734-1415. ; 9:9, s. 15-24
-
Forskningsöversikt (refereegranskat)abstract
- In this work, predictions from a reacting Computational Fluid Dynamics (CFD) model of a gasification reactor are compared to experimentally obtained data from an industrial pressurized black liquor gasification plant. The data consists of gas samples taken from the hot part of the gasification reactor using a water cooled sampling probe. During the considered experimental campaign, the oxygen-to-black liquor equivalence ratio (λ) was varied in three increments, which resulted in a change in reactor temperature and gas composition. The presented numerical study consists of CFD and thermodynamic equilibrium calculations in the considered λ-range using boundary conditions obtained from the experimental campaign. Specifically, the influence of methane concentration on the gas composition is evaluated using both CFD and thermodynamic equilibrium. The results show that the main gas components (H2, CO, CO2) can be predicted within a relative error of 5% using CFD if the modeled release of H2S and CH4 are specified a priori. In addition, the calculations also show that the methane concentration has large influence on the reactor outlet temperature and final carbon conversion.
|
|
| 8. |
- Dogaris, Ioannis, et al.
(författare)
-
Critical parameters for tall oil separation I : The importance of the ratio of fatty acids to rosin acids
- 2019
-
Ingår i: TAPPI Journal. - : TECH ASSOC PULP PAPER IND INC. - 0734-1415. ; 18:9, s. 547-555
-
Tidskriftsartikel (refereegranskat)abstract
- Tall oil is a valuable byproduct in chemical pulping of wood, and its fractions have a large spectrum of applications as chemical precursors, detergents, and fuel. High recovery of tall oil is important for the economic and environmental profile of chemical pulp mills. The purpose of this study was to investigate critical parameters of tall oil separation from black liquor. To investigate this in a controlled way, we developed a model test system using a "synthetic" black liquor (active cooking chemicals OH- and HS- ions), a complete process for soap skimming, and determination of recovered tall oil based on solvent extraction and colorimetric analysis, with good reproducibility. We used the developed system to study the effect of the ratio of fatty acids to rosin acids on tall oil separation. When high amounts of rosin acids were present, tall oil recovery was low, while high content of fatty acids above 60% significantly promoted tall oil separation. Therefore, manipulating the content of fatty acids in black liquor before the soap skimming step can significantly affect the tall oil solubility, and hence its separation. The findings open up chemical ways to improve the tall oil yield. Application: Controlling the ratio of fatty acids to rosin acids in kraft pulping can significantly affect the tall oil separation and improve its yield and quality.
|
|
| 9. |
- Engström, Gunnar
(författare)
-
Causes of back-trap mottle in lithographic offset prints on coated papers
- 2016
-
Ingår i: TAPPI Journal. - 0734-1415. ; 15:2, s. 91-101
-
Tidskriftsartikel (refereegranskat)abstract
- Back-trap mottle is a common and serious print quality problem in lithographic offset printing of coated papers. It is caused by nonuniform ink retransfer from an already printed surface when it passes through a subsequent printing nip with the print in contact with the rubber blanket in that nip. A nonuniform surface porosity gives rise to mottle. A key parameter in mottling contexts is the coating mass distribution, which must be uniform. Good relationships between mottle and mass distribution have also been reported; the mottle pattern coincides with that of the coating mass distribution. High blade pressures, compressible base papers, and high water pick-up between application and metering, which plasticizes the paper, yield uniform mass distributions, but these parameters might have a detrimental effect on the runnability in blade coating in terms of web breaks. The general opinion has been that nonuniform surface porosity is caused by binder migration and enrichment of binder in the coating surface, more in the high coat weight areas and less in the low coat weight areas. Recent research has suggested that a more probable mechanism is depletion of binder in the coating surface. Nonuniform shrinkage of the pigment matrix (filter cake) formed during the consolidation between the first critical concentration (FCC) and the second critical concentration (SCC) is another possible mechanism. Relevant relaxation times for latex and the time scales for consolidation show that the high coat weight areas shrink more than the low coat weight areas in the coating layer. A recent pilot-scale experiment has shown that the drying strategy did not affect the differences in shrinkage between high and low coat weight areas. The drying strategy has a pronounced impact on mottle. A high evaporation rate at the beginning of the evaporation results in less mottle than a low evaporation rate. The least mottle is obtained if the drying is performed with a gap in the course of evaporation between the FCC and the SCC.
|
|
| 10. |
- Fernando, Dinesh, et al.
(författare)
-
Characterization of spruce thermomechanical pulps at the fiber cell wall level: a method for quantitatively assessing pulp fiber development using Simons’ stain
- 2010
-
Ingår i: Tappi Journal. - 0734-1415. ; 9, s. 47-55
-
Tidskriftsartikel (refereegranskat)abstract
- Fiber development of mechanical pulps is normally assessed by a combination of conventional numerical analyses of fiber features using FiberMaster, PulpEye, and Kajaani instruments. When observed, changes in fiber morphology are normally subjective with use of light- and electron microscopy observations of representative fibers. Thus, visualization and quantification of changes in the fiber cell wall, like delaminaton/internal fibrillation (D/IF) induced during processing, would offer a great advantage. Here, we developed a method using Simons’ stain (SS) that allows quantification of pulp fiber development in terms of fiber wall D/IF during different process conditions, as well as statistical analysis of whole pulp fiber populations of different thermomechanical pulp (TMP) types for the degree of D/IF developed in pulp fibers. The attributes of SS for producing different colored reactions (blue, green, orange, etc.) in pulp fibers through cell wall modification during processing were used in correlation with light microscopy. The method readily measured the degree of cell wall D/IF of pulp fibers from different double-disc refined TMPs produced using varying levels of specific energy and refining pressures. The SS method revealed the presence of five sub-fiber populations in a whole pulp of a given TMP type representing different categories of fibers that possessed varying degrees of cell wall D/IF as a result of process conditions/treatments. Results of statistical analysis indicated that, while D/IF was significantly induced by both the applied refining pressure and specific energy, the effect of energy had the greatest influence. Based on statistical analysis for Bauer McNett fractions of 10, 30, and 50 mesh, we suggest that fraction 30 is the most suitable fiber fraction for the analysis of TMPs using fiber characterization procedures, as this fraction possesses the most treated fibers. The method provided useful information regarding pulp fiber development at the cell wall level that has the potential to explain pulp and paper properties developed in furnishes. The present SS method represents a valuable tool for assessing fiber development at the cell wall level in mechanical pulping. Application: The present SS method can be used as a simple yet effective tool in mechanical pulp fiber characterization at the fiber level. The method provides useful information relating to fiber treatment in terms of morphological variations in the pulp fiber structure that determine most pulp and paper properties developed during processing
|
|
