The reduction of mill effluent discharge as a result of stringent environmental legislations can have a significant impact on sodium (Na) and sulfur (S) balances in the kraft pulping process. In order to maintain a proper balance of Na and S, kraft mills may need to adopt different makeup strategies. For this purpose, a dynamic model was developed to predict the Na and S balance in the kraft recovery cycle, as well as the accumulation of undesirable non-process elements such as chlorine (Cl) and potassium (K). The model was developed using the CADSIM software and was validated using data obtained from a Brazilian bleached kraft pulp mill. The calculated data from the model showed good agreement with mill data with respect to all parts of the mill simulated. Dynamic tests designed to calculate the white liquor sulfidity over specific periods of time also presented good agreement. The result indicates that the model is able to describe the balance of chlorine, potassium, sodium and sulfur in the kraft process. A study conducted to evaluate the Cl and K accumulation agrees with the expected behaviour observed in mill data. The presence of ash treatment systems allow to reduce Cl and K contents in recovery boiler precipitator ash from 4.2 mol% Cl(Na+K) to 1.25 mol % and from 2.25 mol % K/(Na+K) to 0.8 mol% for 100% ash treated. The tests performed for Na and S balances focused in the makeup requirement for two situations: ash purging and ash treatment to control Cl and K levels. The use of ash treatment systems reduced Na and S makeup requirement from 5 to 50% depending on the amount of ash treated. A simple mathematical model was then used to estimate the Cl balances around the recovery cycle. Given that the proper simplifications are applied, the CADSIM model and the CSTR model presented good agreement in estimating the Cl balances. This result provided not only another method for the CADSIM model to be validated but also a way to calculate a rough estimate for Cl balance.

L'atelier de régénération d'une usine kraft permet d'extraire des liqueurs noires les élémentschimiques nécessaires à la cuisson du bois et de les régénérer sous leur forme active, ainsi quede valoriser la fraction organique dissoute sous forme de chaleur. Les opérations unitaires enoeuvre sont nombreuses, complexes, et souvent mal décrites. Ce travail vise à permettre unemeilleure compréhension de la régénération, par la réalisation de modèles fiables décrivant lesphénomènes et processus dans chaque opération unitaire, leur implémentation algorithmiqueet leur exploitation par la simulation du procédé global.

Electrostatic precipitators (ESPs) are commonly used to control particulate emissions from recovery boilers in the kraft pulping process. The electrical resistivity of entrained particulates is known to affect the performance of ESPs. There are many factors which influence resistivity of particulate matter, such as field strength, time of exposure, particle size, particle composition, temperature, and flue gas composition. The objective of this study was to identify the ideal operating conditions and dust particle characteristics which lead to an optimum dust resistivity and maximized ESP efficiency. The effect of these factors was examined through a variety of experimental and analytical techniques on kraft recovery boiler ash samples and synthetically prepared samples. It was concluded that particle composition, gas composition, and ambient temperature had the most pronounced effects, while the other factors, such as field strength and exposure time, had a smaller impact on particle resistivity.

Electrostatic precipitators (ESPs) are commonly used to control particulate emissions from recovery boilers in the kraft pulping process. The electrical resistivity of entrained particulates is known to affect the performance of ESPs. There are many factors which influence resistivity of particulate matter, such as field strength, time of exposure, particle size, particle composition, temperature, and flue gas composition. The objective of this study was to identify the ideal operating conditions and dust particle characteristics which lead to an optimum dust resistivity and maximized ESP efficiency. The effect of these factors was examined through a variety of experimental and analytical techniques on kraft recovery boiler ash samples and synthetically prepared samples. It was concluded that particle composition, gas composition, and ambient temperature had the most pronounced effects, while the other factors, such as field strength and exposure time, had a smaller impact on particle resistivity.

The reduction of mill effluent discharge as a result of stringent environmental legislations can have a significant impact on sodium (Na) and sulfur (S) balances in the kraft pulping process. In order to maintain a proper balance of Na and S, kraft mills may need to adopt different makeup strategies. For this purpose, a dynamic model was developed to predict the Na and S balance in the kraft recovery cycle, as well as the accumulation of undesirable non-process elements such as chlorine (Cl) and potassium (K). The model was developed using the CADSIM software and was validated using data obtained from a Brazilian bleached kraft pulp mill. The calculated data from the model showed good agreement with mill data with respect to all parts of the mill simulated. Dynamic tests designed to calculate the white liquor sulfidity over specific periods of time also presented good agreement. The result indicates that the model is able to describe the balance of chlorine, potassium, sodium and sulfur in the kraft process. A study conducted to evaluate the Cl and K accumulation agrees with the expected behaviour observed in mill data. The presence of ash treatment systems allow to reduce Cl and K contents in recovery boiler precipitator ash from 4.2 mol% Cl(Na+K) to 1.25 mol % and from 2.25 mol % K/(Na+K) to 0.8 mol% for 100% ash treated. The tests performed for Na and S balances focused in the makeup requirement for two situations: ash purging and ash treatment to control Cl and K levels. The use of ash treatment systems reduced Na and S makeup requirement from 5 to 50% depending on the amount of ash treated. A simple mathematical model was then used to estimate the Cl balances around the recovery cycle. Given that the proper simplifications are applied, the CADSIM model and the CSTR model presented good agreement in estimating the Cl balances. This result provided not only another method for the CADSIM model to be validated but also a way to calculate a rough estimate for Cl balance.

The effects of UV pretreatment on alkaline bleaching (EOP) wastewater from a kraft pulp and paper mill were investigated prior to anaerobic digestion (AD) in an upflow anaerobic sludge blanket (UASB) reactor. The aim was to enhance the methane production, increase the reduction of total organic carbon (TOC) and determine the best UV exposure time. The exposure time of 2.6 minutes partially degraded the organic material in the EOP wastewater since it generated higher biogas and methane production than the reference period, while it also increased the reductions of solved chemical oxygen demand (CODsol) and TOCsol. The exposure time of 16 minutes, on the other hand, did not show any significant improvement regarding increased biogas and methane production nor did it increase the reduction of CODsol. However, it did increase the reduction of TOCsol, but not to the same extent as the exposure time of 2.6 minutes. The presence of unwanted microbial growth in the system during the experiment might have affected the effectiveness of the UV pretreatment more during the exposure time of 16 minutes as the amount of growth was more substantial during this period of time. Furthermore, no optimal exposure time could be determined due to lack of time.

One of the problems encountered in paper converting is caused by the occurrence of "baggy webs", which essentially is when the tension profile of the paper web is uneven. In an area with low tension the paper is longer, which results in bagginess. The baggy parts can not usually be stretched to even out the tension of the paper web in a converting machine, with the result that runnability problems are likely to occur. The aim of the work described in this thesis was to investigate three particular stages in papermaking, namely drying, calendering and storage, and rank them according to their propensity for inducing baggy webs. The focus was placed on investigating the effects of uneven moisture and grammage profiles on the machine-direction strain difference profile. The largest strain difference occurred when there were systematic thick streaks throughout a reel that formed ridges. Stress relaxation during storage then gave rise to a difference in strain of 0.14% when the ridge height was around 2-3 mm. Thickness variations due to variations in grammage is also a source of moisture variation. A difference in moisture of 5% in the calendering stage resulted in strain differences of about 0.05-0.08%. These strain differences resulted in creases being formed as early on as in the calender nip when differences in both grammage and moisture content were present. Most creases appeared when the moisture difference was 2-8%. The difference in grammage could be large without creases being formed when no differences in moisture content were present. A moisture difference of about 5-6% during drying resulted in a strain difference of 0.1% measured on isotropic samples. The moist area turned into a tight streak when the moisture difference appeared at moisture contents higher than 25%. At moisture contents lower than 20%, on the contrary, the moist area turned into a slack streak. The conclusion drawn is that papermakers should concentrate first and foremost on eliminating variations in grammage, especially if these are systematic. This would also eliminate some variations in moisture content, which would solve more problems.

Techn. University, Diss., 2006--Darmstadt.

Techn. Universiẗat, Diss.--Dresden, 2007.

Techn. Univ., Diss--Dresden, 2005.