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Polyamidoamine epichlorohydrin (PAAE) is a permanent wet strength resin used in papermaking. When applied to paperboard, some amount of resin is retained in the sheet, and some is lost to the white water. The papermaker usually knows the amount of PAAE charged to the pulp but has no idea how much chemical is retained in the sheet. In addition, the influence of PAAE dosage, freeness, zeta potential, and pulp kappa number variability on PAAE retention is not well understood. Factorial design experiments using unbleached and bleached softwood (loblolly pine) kraft pulps were conducted to understand the factors that affect PAAE retention. The results revealed that PAAE retention, wet tear index, and tensile index not only depended on the PAAE charged of the pulp but also depended significantly on the pulp freeness. In lieu of freeness, zeta potential data can be used to predict PAAE retention. In addition, at similar freeness, bleached pulp has the highest retention of PAAE compared to low and high kappa unbleached kraft pulps. The results also suggest that lignin may have potential as a wet strength agent. [ABSTRACT FROM AUTHOR]

Alkenyl Succinic Anhydride (ASA) is a sizing agent used in papermaking to increase the water repellency of paper. Almost 60 years after the introduction of the chemical in papermaking, scientists still have differing views on how ASA interacts with cellulose. Several experiments were conducted to bring more clarity to the ASA sizing mechanism, especially on the contentious question of ASA-cellulose covalent bonding or the esterification reaction between ASA and cellulose during papermaking. Herein, research papers and patents, including experiments and results, from the 1960s to 2020 were reviewed. Our investigation revealed that the ester bond formation between ASA and cellulose is insignificant and is not a prerequisite for sizing effectiveness; the main ASA-related material found in sized paper is hydrolyzed ASA or both hydrolyzed ASA and ASA salt. In addition, ASA emulsion stability and ASA emulsion retention are important for sizing efficiency improvement. [ABSTRACT FROM AUTHOR]

Within the past 15 years, three North American pulp mills experienced catastrophic equipment failures while using 50 wt% hydrogen peroxide. In two cases, explosions occurred when normal pulp flow was interrupted due to other process problems. To understand the accidents, a kinetic model of alkali-catalyzed decomposition of peroxide was developed. Modeling a normal start-up condition where peroxide and sodium hydroxide flow to a mixer in a stoichiometric ratio does not show a significant pressure rise, but a scenario in which peroxide enters the pump in advance of the sodium hydroxide displays a rapid pressure rise that greatly exceeds the rated pressure for the pumps.

This paper assessed the blood pressure, heart rate, and mouth-pressure responses to indoor rock climbing (bouldering) and associated training exercises. Six well-trained male rock climbers (mean ± SD age, 27.7 ± 4.7 yr; stature, 177.7 ± 7.3 cm; mass, 69.8 ± 12.1 kg) completed two boulder problems (6b and 7a+ on the Fontainebleau Scale) and three typical training exercises [maximum voluntary contraction (MVC) isometric pull-up, 80% MVC pull-ups to fatigue, and campus board to fatigue]. Blood pressure and heart rate were measured via an indwelling femoral arterial catheter, and mouth pressure via a mouthpiece manometer. Bouldering evoked a peak systolic pressure of 200 ± 17 mmHg (44 ± 21% increase from baseline), diastolic pressure of 142 ± 26 mmHg (70 ± 32% increase), mean arterial pressure of 163 ± 18 mmHg (56 ± 25% increase), and heart rate of 176 ± 22 beats/min (76 ± 35% increase). The highest systolic pressure was observed during the campus board exercise (218 ± 33 mmHg), although individual values as high as 273/189 mmHg were recorded. Peak mouth pressure during climbing was 31 ± 46 mmHg, and this increased independently of climb difficulty. We concluded that indoor rock climbing and associated exercises evoke a substantial pressor response resulting in high blood pressures that may exceed those observed during other upper-limb resistance exercises. These findings may inform risk stratification for climbers. NEW & NOTEWORTHY This case study provides original data on the exercise pressor response to indoor rock climbing and associated training exercises through the use of an indwelling femoral arterial catheter. Our subjects exhibited systolic/diastolic blood pressures that exceeded values often reported during upper-limb resistance exercise. Our data extend the understanding of the cardiovascular stress associated with indoor rock climbing. [ABSTRACT FROM AUTHOR]

Lignin is a by-product of the pulp and paper industry that can be precipitated by acidification from black liquor as a potential feedstock for valuable green materials. Precipitation and quantification of lignin from softwood black liquors have been documented and commercialized with well-established methods; however, applying those methods to the precipitation of lignin from hardwood black liquors has produced low lignin yields. A need to understand the main differences between hardwood and softwood lignin precipitation prompted the current investigation. Multiple black liquor samples from sweetgum and pine pulping were obtained at different times of standard kraft cooks. Two lignin fractions were precipitated from each of these black liquors, one at pH 9.5 and one at pH 2.5. Detailed lignin and carbohydrate material balances were performed around each of the sample sets, starting with the wood and ending with precipitated lignin fractions. For all conditions tested, the amount and purity of pine lignin precipitated were superior to sweetgum lignin. The maximum recovery for sweetgum lignin was 69.7%, while for pine lignin, it was 90.9%. [ABSTRACT FROM AUTHOR]

Coffee edge-wicking testing was conducted on two groups of highly-sized paperboard manufactured at two mills with similar manufacturing processes, but with vastly different local fiber sources. Although the Hercules size test (HST) indicated similar internal size levels between the two types of board, the edge-wicking behavior was noticeably different. Analysis of fiber structure revealed that the board with more edge-wicking had fibers with thicker fiber walls, which kept the fiber lumen more open after pressing and drying on a paper machine. It was demonstrated that liquid penetration through voids between fibers in highly-sized paperboard was limited, because the fiber surface was well protected by the presence of sufficient sizing agent. Nevertheless, freshly exposed fiber walls and lumens at the cut edge of the sheet were not protected by sizing material, which facilitated edge-wicking. The correlation between fiber structure and edge-wicking behavior was highlighted in this work to inspire development of novel sizing strategies that protect the freshly cut edge of the sheet from edge-wicking. [ABSTRACT FROM AUTHOR]

Recycled fiber-based papermaking in America is experiencing a persistent reduction in the strength of the incoming fiber. To maintain paper strength properties, paper mills respond by increasing basis weight, dry strength, etc. On average, the fiber cost component in recycled paper is approximately 40% of the total manufacturing cost. Increased fiber weight results in higher operating cost and has a negative effect on production rate, especially on dryer-limited paper machines. Increased pH and use of certain enzymes can improve strength during subsequent refining. The ProLab refiner was used to generate laboratory refining curves to evaluate changes in fiber bonding. The effect of pH and enzymes pretreatment on the strength development and change in drainage of recycled fibers with refining was evaluated. [ABSTRACT FROM AUTHOR]

The present work focused on characterizing the chemical and structural properties of isolated lignin from six hardwoods and their kraft pulps in an attempt to better understand the relationship between lignin's chemical properties and resultant oxygen delignification performance. Several hardwood samples were cooked under the same conditions with varying alkali charges to obtain unbleached pulps with kappa numbers between 19 and 20. These pulps were then subjected to an oxygen delignification stage. Both processes were evaluated for pulp quality, residual lignin, and O-stage delignification efficiency. The oxygen delignification stage was carried out under fixed conditions and evaluated with regards to kappa number, which was corrected for hexenuronic acid (HexA) contributions. Results revealed that different hardwood species exhibited differing oxygen delignification efficiencies. A high correlation was found between the O-stage delignification efficiency and the content of phenolic groups in the unbleached lignin, which confirmed that free phenolic groups are the reactive site for molecular oxygen attack. When different hardwood species were compared, the HexA contents were not found to affect O-stage delignification efficiencies. [ABSTRACT FROM AUTHOR]

The current trend to further reuse water within paper mills has resulted in more accumulated salts, as reflected by increased conductivity values. Although conductivity measurement is widely used in paper mills, its fundamental principles and interpretation are not often fully understood. This keeps papermakers from reaching the full benefits of using conductivity measurements to help manage the wet end chemistry of paper or board machines. High and variable conductivity affects the intrinsic properties of pulps, the performance of chemical additives, and the interaction between them. This paper reviews principles of conductivity; its measurement; its effect on important aspects of papermaking operations, such as retention, drainage, sizing, strength development and deposit control; and the fundamentals behind the effects of conductivity on the papermaking process. Specific mill examples are also provided. Potential solutions for operating a mill under high and variable conductivity conditions are discussed. [ABSTRACT FROM AUTHOR]

For more than 40 years, conductivity has been the inline measurement of choice for inferring black liquor/soda losses from brownstock washing. If properly applied, conductivity can provide a benefit in tracking changes in black liquor filtrate concentration. The implied concentration changes in turn can be used to provide feedback for dilution factor or shower flow control on the last stage of a brownstock washing system. A further extrapolation of this application is the correlation (or lack of correlation) of conductivity to soda loss. For each type of conductivity-based application, there are fundamental principles and assumptions that must be understood and managed to achieve the expected outcomes. The fundamentals of conductivity, the application of conductivity to measure black liquor losses during brownstock washing, and laboratory considerations when attempting to correlate inline process conductivity to absolute sodium content are reviewed and investigated. Finally, the operational objectives and measurement alternatives for employing conductivity measurements are discussed. [ABSTRACT FROM AUTHOR]

Several articles have been published during the past 30 years on different methods to produce micro- to nanosize cellulose particles from pulp. Unfortunately, a general lack of information exists on the impact of differing manufacturing process methods upon the product properties obtained from these differing methods. Literature data show that wet processing of small-sized cellulosic fibers generates handsheets with approximately equal or higher density and modulus of elasticity than controls for a given amount of added microcellulose. The current work evaluated small particle generation from pulp fibers via dry processing methods and compared the physical properties of dry versus wet processed particles. Dry processing to obtain microcellulose gave considerably lower sheet density and modulus as compared with wet processed microcellulose. The lower modulus can be compensated for by refining base fibers more aggressively to obtain higher density and higher modulus sheets. Dry processing methods for making microcellulose and their impact on final board properties, including modulus and smoothness, will be discussed. Application: The impact of attritor-processed fiber on handsheet physical properties might have potential for commercial applications. [ABSTRACT FROM AUTHOR]

The use of eucalyptus as a partial replacement for mixed southern hardwoods can result in significant amounts of eucalyptus bark being incorporated into the chips going to the digester. When eucalyptus is first harvested, the bark peels off in large sheets, which will pass through chippers designed for southern hardwood. After being cut for more than about 4-6 weeks, the bark tightens onto the bole of the tree and again passes through chippers not designed for eucalyptus. As a result, significant quantities of eucalyptus bark could go to the digester. This study describes the effect of pulping eucalyptus bark in the laboratory. A series of control studies were performed on eucalyptus and mixed southern hardwood bark. The results show that incorporating bark into the cook results in increased kappa number, decreased pulp yield, and increased alkali consumption. If the percentage of applied active alkali is increased to counteract the increased alkali consumption, increased hexenuronic acid is generated. [ABSTRACT FROM AUTHOR]

The impact of commercially prepared, fully bleached pulp viscosity variation on handsheet physical properties was evaluated at different levels of pulp refining. Hardwood pulps from the same brownstock species mix, cooking parameters, and kappa numbers were processed through two different commercial bleach plants: one with a D0 (EP)D1D2 sequence and the second with an OD0 (EOP)D1 sequence. Additionally, a commercial softwood (predominately Scotts pine) brownstock pulp bleached by an OD0 (EP)D1D2 sequence was employed in this study. Pulps with viscosities ranging from 14 to 21 mPa·s were refined in a Valley beater to two freeness levels, and the associated handsheet physical properties were measured in this study. Over the pulp viscosity range of 14 to 21 mPa·s, no clear correlation was found to exist between pulp viscosity and related paper physical properties. Finally, a series of laboratory prepared bleached pulps were purposely prepared under non-ideal conditions to reduce their final viscosities to lower values. Handsheets made from these pulps were tested in their unbeaten condition for physical strength properties. Significant and rapid strength loss occurred when the measured pulp viscosity dropped below 12 mPa·s; overall strength properties showed no correlation to viscosity above the critical 12 mPa·s value. [ABSTRACT FROM AUTHOR]

The WestRock mill in Covington, VA, USA, initiated a long term diagnostic and optimization program for all three of its bleaching lines. Benchmarking studies were used to help identify optimization opportunities. Capital expenditures for mixing improvement, filtrate changes, equipment repair, other equipment changes, and species changes were outside the scope of this work. This focus of this paper is the B line, producing southern hard-wood pulp in a D(EP)DD sequence at 88% GE brightness. The benchmarking study and optimization work identified the following opportunities for improved performance: nonoptimal addition of caustic and hydrogen peroxide to the (EP) stage, carryover of D0 filtrate to the (EP) stage, and carryover of (EP) filtrate to the D1 stage. As a result of actions the mill undertook to address these opportunities, D0 kappa factor decreased about 5%, sodium hydroxide consumption in the (EP) stage decreased about 35%, chlorine dioxide consumption in the D1 stage decreased about 25%, and overall bleaching cost decreased about 15%. Application: A long term, sustainable, bleach plant optimization and cost reduction study was performed with minimal to no capital. Mills can apply similar methodologies to their own 'bleach plants and obtain reasonable results. [ABSTRACT FROM AUTHOR]

An automated shower water control system has been implemented to reduce the volume and variability of weak black liquor being sent from the pulp mill to the evaporators. The washing controls attempt to balance the need for consistent and low soda carryover to the bleach plant with consistently high weak black liquor solids being sent to the evaporators. The washer controls were implemented on two bleachable grade hardwood lines one with oxygen delignification, one without oxygen delignification) and one pine line. Implementation of the control program resulted in an increase in black liquor solids of 0.6 percentage points for the hardwood lines. Significant foam reduction was realized on the pine line since the pine black liquor solids were able to be consistently maintained just below the soap separation point. Low black liquor solids excursions to the evaporators were eliminated. Bleach plant carryover was stabilized and no negative impact on chemical consumption was noticed when controlling weak black liquor solids to recovery. Application: This information can be used by kraft mills around the world. The authors have provided an easy approach to control brownstock washing and maximize pulp production by avoiding evaporator capacity reduction. [ABSTRACT FROM AUTHOR]

Retention of cationic dispersed rosin size was studied via turbidity measurements on stock filtrate with different alum and dispersed rosin size dosages. Stock charge characteristics were analyzed using both an analysis of charge demand determined via a streaming current detector and an evaluation of zeta potential of the fibers by streaming potential measurement. The results indicated that an optimum amount of alum existed such that good sizing retention was maintained throughout a wide range of dispersed rosin size dosages. However, when an excessive amount of alum was used and fines and colloidal particles were transitioned from anionic to cationic, the cationic size retention was reduced. Laboratory results were confirmed with a paper machine trial. All data suggested that a stock charge study was necessary to identify optimal alum dosage for a cationic dispersed rosin sizing program. [ABSTRACT FROM AUTHOR]

The MWV mill in Covington, VA, USA, experienced a long term trend of increasing episodes of paper indents that resulted in significant quantities of internal rejects and production downtime. When traditional troubleshooting techniques failed to resolve the problem, big data analysis techniques were employed to help determine root causes of this negative and increasingly frequent situation. Nearly 6000 operating variables were selected for a deep dive, multi-year analysis after reviewing mill-wide process logs and 60000+ PI tags (data points) collected from one of the major data historian systems at the MWV Covington mill. Nine billion data points were collected from November 2011 to August 2014. Strategies and methods were developed to format, clean, classify, and sort the various data sets to compensate for process lag time and to align timestamps, as well as to rank potential causes or indicators. GE Intelligent Platforms software was employed to develop decision trees for root cause analysis. Insights and possible correlations that were previously invisible or ignored were obtained across the mill, from pulping, bleaching, and chemical recovery to the papermaking process. Several findings led the mill to revise selected process targets and to reconsider a step change in the drying process. These changes have exhibited significant impacts on the mill's product quality, cost, and market performance. Mill-wide communications of the identified results helped transform the findings into executable actions. Several projects were initiated. [ABSTRACT FROM AUTHOR]

MWV Forestry has been actively pursuing the establishment of cold- and frost-tolerant eucalyptus plantations in southeast Texas and in the higher, frost-prone regions of southern Brazil for several years. Currently, the major species being examined is Eucalyptus benthamii. Interspecific crossing efforts, cold tolerance established from field trials, and intercountry cooperation in this program are discussed. The ability of the southeastern Texas program to return value to our collaborators in southern Brazil and other locations is reviewed. Pulp and papermaking properties of the cold-tolerant species are also reviewed. Currently, E. benthamii plantations in southeast Texas are producing trees with a density range of about 460-523 kg/m3, suggesting some degree of genetic variability within the bulk seeds currently being employed. Good pulping yields of around 48% on o.d. wood have been obtained in laboratory studies. For comparison, this yield is about 3 percentage points higher than for traditional mixed southern hardwoods. In general, the physical properties of pure E. benthamii are inferior to those of mixed southern hardwoods. When used in a blend, the differences in physical properties are substantially mitigated. [ABSTRACT FROM AUTHOR]

We used two different experimental methods to study the effects of sheet temperature at a given moisture content on web densification and sheet smoothness. Commercially prepared paperboard obtained from the WestRock Mahrt mill in Cottonton, AL, USA, was used in this study. Laboratory made handsheets prepared from Mahrt high yield kraft pine pulp were also used for portions of this work. Sheets were sealed in moisture-proof bags, heated to various temperatures, and calendared at multiple nip loads. The resulting changes in sheet density were determined. Additionally, a pilot-scale calendar was modified to preheat the non-print side of the sheet before entering the nip. The modified sheet run allowed for an increase in the bulk temperature of the board with minimal changes in the moisture content of the print surface. Increasing the bulk temperature increased board density at a given print surface smoothness. We determined that increasing the board temperature by 14°C resulted in about a 1% increase in board density. The results of this study help explain the commercial results obtained with thermal gradient calendaring. [ABSTRACT FROM AUTHOR]

The effect of using acid pretreated eucalyptus wood chips in the Lo- Solids® pulping process was evaluated in the laboratory. Lo-Solids® cooking technology was chosen to evaluate the impact of acid pretreatments on the cooking performance, brown stock chemical composition, and black liquor heating value. The acid leaching stage reduced the contents of transition metals and other non-process elements in the wood chips and in the pulps produced. Benefits were detected in terms of the reduction in white liquor charge, increase in pulp yield, as well as pulp viscosity and black liquor heating value. Carbohydrate content and other wood/pulp constituents were not affected by the acid leaching pretreatments. [ABSTRACT FROM AUTHOR]

A case study is presented in which several articles and patents suggested a specific outcome. When the actual experimental work was performed, the results were found to be several orders of magnitude away from predicted values. Close re-inspection of the literature suggested that most of the authors actually extrapolated the results to conditions that were not applicable to their specific studies, resulting in the reporting errors. It is important to use literature to assist in research, but it is equally important not to blindly follow it either. [ABSTRACT FROM AUTHOR]

The kinetics of the bulk and residual delignification phases of Eucalyptus nitens, E. globulus, E. benthamii, acacia, maple, and loblolly pine were determined in an effort to improve the use of various hardwoods. Kinetic experiments were performed using a microwave digestion system for fast heating of the kraft liquor. Delignification rates were obtained for three different temperatures (150°C, 160°C, and 170°C) and correlated with the wood's syringyl-to-guaiacyl ratio. A linear correlation between the kraft delignification rate and the syringyl-toguaiacyl ratio was found to exist. [ABSTRACT FROM AUTHOR]

When evaluating the composition of black liquor using material balance techniques that estimate the organics from the wood and the inorganics from the cooking liquor, the solids content of the black liquor is determined to be roughly 1/3 inorganic matter and 2/3 organic matter. When actual laboratory testing using simplified ashing methodologies are performed, the results typically suggest that black liquor solids contain roughly 43%-49% organics and 51%-57% inorganics. We determined that the applied hydroxide and sulfide mineralize carbon and oxygen from the organic portion of the black liquor and convert it to carbonate and sulfate during the cooking and ashing process, thus increasing the apparent inorganic content of the black liquor. This becomes problematic when attempting to estimate total black liquor production using the organics removed during cooking and the inorganic content using results from the ashed black liquor sample. We used Microsoft Excel material balances to develop a conversion factor to correct the laboratory test results. Multiplying the percent ash in the laboratory test by 0.65 to 0.70 provided a more realistic estimate of the initial inorganics to be used along with organics removed in the digester to estimate black liquor production. This conversion factor was determined to be independent of pulp yield and white liquor charge in the digester. The initial white liquor composition, as reported by the ABC test, does have a slight effect on this value. Application: The results from this work may be used to reconcile laboratory testing results with actual material and energy balances. Using the new factor developed in this work will allow simplified laboratory methods to be used to obtain real world results. [ABSTRACT FROM AUTHOR]

Eucalyptus plantations have been used as a source of short fiber for papermaking for more than 40 years. The development in genetic improvement and clonal programs has produced improved density plantations that have resulted in fast growing, increased fiber volume eucalypts becoming the most widely used source of short fibers in the world. High productivity and short rotation times, along with the uniformity and improved wood quality of clonal plantations have attracted private industry investment in eucalypt plantations. Currently, only a handful of species or hybrids are used in plantation efforts. Many more species are being evaluated to either enhance fiber properties or expand the range of eucalypt plantations. Eucalyptus plantations are frequently planted on nonforested land and may be used, in part, as a means of conserving native forests while allowing the production of high quality fiber for economic uses. Finally, eucalypt plantations can provide significant carbon sinks, which may be used to help offset the carbon released from burning fossil fuels. The development and expansion of eucalypt plantations represents a substantial revolution in pulp and paper manufacturing. Application: By understanding the breeding and clonal developments that have occurred in the past and the results of those developments, the industry may be better equipped to rapidly advance the next stage of eucalypt progress. [ABSTRACT FROM AUTHOR]

Optimization of the lime kiln requires an examination of the entire lime cycle. To increase the energy efficiency of the lime kiln, all auxiliary unit operations must function properly. It is also imperative that the lime and liquor in the system is of acceptable quality. We detail a kiln energy efficiency study performed by MWV Corp.'s Covington, VA, USA, mill. From a recausticizing standpoint, lime quality is much easier to control than liquor quality because liquor passes through many operations that are not under the lime kiln operator's control. Recausticizing is a fairly closed cyclical process where lime is concerned, so saturation of impurities to the point of operational issues must be considered. Specific cycle performance indicators (e.g., lime mud solids entering the kiln) must be viewed from a perspective that does not exclude their potential impact. To get a true picture of the cost of operating the lime cycle, all inputs must be considered. The four main inputs are power (electrical and fuel), fresh lime, caustic, and water. [ABSTRACT FROM AUTHOR]

Eucalyptus dunii has been commercially used in southern Brazil because of its relatively good frost tolerance and adequate productivity in the winter months. More recently, interest has grown in cultivating Eucalyptus benthamii Maiden & Cambage, which presents even superior frost tolerance compared to E. dunii and is highly productive as well. The quality of E. benthamii for pulp production is not yet proven. Thus, the chemical, anatomical, and technological aspects of pulp made from E. benthamii were compared with those of E. dunii for unbleached paper production. Samples of E. benthamii chips were obtained and analyzed for their basic density, chemical composition, higher heating value, trace elemental analysis, and chip size distribution. The chips were kraft cooked using conditions that produced a 74 ± 6 kappa number. The pulps were characterized for kappa number, yield, viscosity, and morphologic characteristics (e.g., length, wall thickness, and coarseness). Black liquor was analyzed for total solids, organics, inorganics, sodium sulfide, sodium hydroxide, and sodium carbonate. Brownstocks were beaten at five different energy levels in a Valley beater, and the physical strength properties of 120 g/m² handsheets were measured to develop a beater curve. The results of this study showed differences in delignification between the two woods and lower pulp yield for E. benthamii, which are related to their chemical compositions and basic densities. The E. benthamii studied in this work exhibited higher amounts of lignin and extractives, lower carbohydrate content, and lower basic density. However, cooking a blend of the two woods afforded good results in pulping and in physical pulp properties. [ABSTRACT FROM AUTHOR]

The effect of wood chip acid leaching pretreatment on non-process elements removal and its impact on wood chemical components has been examined. Acid leaching treatments were carried out using two different acid pretreatment approaches: (1) acidified water and (2) filtrate from an acidic bleaching stage. Optimization experiments to identify the most suitable leaching conditions with regard to non-process elements removal and chemical oxygen demand generation were performed. The incorporation of an acid leaching stage significantly reduced the non-process elements content in the wood chips. Carbohydrate content and other wood constituents were not negatively affected by the applied pretreatment. Application: Mills can apply acid leaching pretreatment to the pulping process without degrading carbohydrates and with no major yield loss. [ABSTRACT FROM AUTHOR]

The application of anthraquinone (AQ) as a pulping catalyst has been well documented in scientific studies and mill applications. AQ is known to increase the rate of delignification, enabling a reduction in pulping time, temperature, or chemical charge and an increase in pulp yield. This review does not focus extensively on specific details of AQ use but rather on critical milestones in the AQ process lifecycle, including its initial introduction, investigation of the reaction mechanism, and evaluation of best use by the pulping industry. The importance and difficulty of an economic justification for use of AQ are discussed, including their complication by modest improvement in yield obtained using AQ and low cost of the displaced chemicals. In many mills, documenting increased net mill revenue resulting from the use of AQ has been impossible. Recent health and safety studies and regulatory decisions have put the continuing use of AQ by industry in jeopardy. Given the unknown health risks, international regulatory environment, modest improvements available using AQ, and difficulty in economically accounting for the benefits, this likely represents the final chapter in the AQ life cycle. [ABSTRACT FROM AUTHOR]

A thorough analysis of the kraft pulping process makes it obvious why it has dominated for over a century as an industrial process with no replacement in sight. It uses low-cost raw materials; collects and regenerates over 90% of the chemicals needed in the process; and is indifferent to wood raw material and good at preserving the cellulose portion of the wood, the part that provides strong fibers. Although the process is odiferous, extremely capital intensive, and very poor at preserving hemicellulose yield, no alternatives have been able to replace it for process cost and product quality. There is a misconception that no new pulping processes have been discovered since the discovery of kraft pulping. Besides the minor adjustments--such as anthraquinone or polysulfide-- chlorine, chlorite, and peracetic acid holopulping were discovered and evaluated decades ago. Various solvent pulping methods were discovered and evaluated in the 1980s and 1990s. This work continues with ionic solvents, deep eutectic solvents, and most recently protic ionic liquids. Where all these alternative processes fail is process cost. The chemicals are too expensive and too difficult to recover for use in a commercial process to produce wood pulp. The premise of this review is that the only way to achieve better performance and lower cost than the existing kraft pulping process will be a process using a catalyst to control and direct the reactions. With a high enough reaction rate and a sufficiently high number of turnovers, even an expensive catalyst can still be low cost. We reviewed the literature of existing pulping and delignification catalysts and propose research areas of interest for more intensive experimental efforts. [ABSTRACT FROM AUTHOR]

A softwood continuous digester has experienced severe erosion-corrosion of the shell wall inside the internal flow channel headers of the extraction and modified continuous cooking (MCC) zones. Although erosioncorrosion is a common form, it is not typically looked for inside digester flow channels. The worst damage was located where high velocity liquor exits the screen orifices and enters the collection headers. With erosion-corrosion rates as high as 200 m/year, the damage has effectively reduced the wall thickness almost by half in the worst areas. Also affected were the horizontal backing rings that form the bottom of the flow channels. An API-579/ASME FFS-1 Part 5, Level 2 analysis was performed to allow the mill to continue operating the digester until the next scheduled outage. Owner-users are encouraged to inspect these locations in their digesters to ensure that erosion-corrosion has not caused accelerated and/or unexpected shell thinning. The internal flow channels represent locations that are not readily accessible for internal visual inspection without removal of the flow channel header cover plates and removal of the residual black liquor typically retained in these flow channels. External, on-stream ultrasonic thickness testing (UT) at the proper collection header elevations has been determined to be an effective way to detect the presence of this erosion-corrosion phenomena. Also discussed are considerations to make on-stream UT as accurate as possible. Corrosion rates determined via electrochemical corrosion probe monitoring have correlated very well with the corrosion rates determined by on-stream UT data. [ABSTRACT FROM AUTHOR]

Partial substitution of green liquor for white liquor in kraft pulping reduces calcining energy and reportedly enhances product properties. However, a full-scale trial showed that pulper rejects increased when green liquor substitution levels approached 10%. Imaging experiments and laboratory pulping runs demonstrate that the slower diffusion of hydroxide in the presence of green liquor carbonate is likely responsible for the elevated rejects. Green liquor substitution becomes increasingly more viable with decreasing chip thickness. Hence, such an approach should be especially suited to sawdust pulping where diffusion is not rate determining. [ABSTRACT FROM AUTHOR]

Brownstock washing is a complex, dynamic process in which dirty wash water or weak black liquor (dissolved organic and inorganic material obtained from the pulp cooking process) is separated from pulp fibers. The use of material balance techniques is of great importance to identify potential problems and determine how well the system is operating. The kraft pulping industry was the first known to combine pulp washing with the recovery of materials used and produced in the wood cooking process. The motivation behind materials recovery is economic, and more recently, environmentally driven. The chemicals used in the kraft process are expensive as compared to those used in the sulfite process. For the kraft process to be economically viable, it is imperative that a very high percentage of the cooking chemicals be recovered. To reach such high efficiency, a variety of washing systems and monitoring parameters have been developed. Antifoam additives and processing aids have also played an important role in increasing washing effectiveness. Antifoam materials help attain washing effectiveness by preventing entrapped air from forming in the system, which allows for an easier, unimpeded flow of filtrate through the screens and washers. [ABSTRACT FROM AUTHOR]

Lignin has shown a great potential to produce fuels, value-added chemicals, and functional materials due to its high-energy density and intrinsic aromatic-based structure. Yet, the lignin precipitation of different biomasses needs investigation because most of the work has been performed on softwood and much less is known about hardwoods. In fact, the lignin from these two wooden biomasses vary in composition and pulping performance, which can reflect on lignin precipitation. Therefore, the present study investigated the precipitation and composition of 40 distinct kraft lignins obtained from pine, acacia, sweetgum, and eucalyptus black liquors. Two lignin fractions were precipitated at different pHs, according to known industrial lignin separation practices (pH = 9.5 and 2.5) from black liquors taken at different levels of pulping. Overall, lignin recovery increased with increasing lignin concentration in the black liquor, i.e., higher amounts of lignin were obtained at higher levels of delignification. In addition, pine lignins showed superior yields than the hardwoods and were around five times purer. Among the hardwoods, lignin recovery increased with the S–G ratio of the native lignin, and eucalyptus showed the best performance by achieving the highest yields and purities. Finally, the present work compared the lignin recovery yield and the purity of softwood and different hardwood lignins in a systematic way, which will increase awareness of this underutilized green material and could potentially increase the interest in establishing new lignin plants across the globe. [ABSTRACT FROM AUTHOR]

This work evaluates the findings of various research efforts and describes the development, use, and benefits of applying techno-economic models of different types to various production and bleach plant scenarios. During the late 1980s and early 1990s, researchers determined that bleach plants were releasing potentially significant quantities of chlorinated organics into receiving waters. This led to extensive research to develop bleaching chemicals to eliminate chlorine and hypochlorite from the bleaching sequence. Over time, 100% chlorine dioxide substitution for chlorine became the industry standard (today's elemental chlorine free [ECF] bleaching), and research efforts shifted toward chemical optimization of the ECF bleaching sequence. Several delignification stage and brightening stage models were developed and refined for use in bleach plant simulations to optimize chemical performance. Advances in computing power and the availability of packaged spreadsheet and simulation programs likewise led to the development of detailed material and energy balance models of the bleach plants. These simulations are used to minimize bleaching and pulp production costs, and to assist engineers in the development of justifications for capital expenditures. These models have been used to predict operating conditions that could lead to or reduce scale formation. They have also been extensively used to predict environmental performance of both new and modified bleach plants. [ABSTRACT FROM AUTHOR]

When hydrogen peroxide is mixed with caustic soda, an auto-accelerating reaction can lead to generation of significant amounts of heat and oxygen. On the basis of experiments using typical pulp mill process concentration and temperatures, a relatively simple kinetic model has been developed. Evaluation of these model results reveals that hydrogen peroxide-caustic soda systems are extremely sensitive to hydrogen peroxide:caustic soda ratio, transition metal contamination, and temperature. Small changes in initial conditions can result in a closed system becoming explosive. Analysis of model results was used to develop guidelines for safer application of hydrogen peroxide in a mill setting. [ABSTRACT FROM AUTHOR]

Most studies aimed at determining rates of hardwood delignification and carbohydrate degradation have focused on understanding the behavior of a single wood species. Such studies tend to determine either the delignification rate or the rate of carbohydrate degradation without examining the potential interactions resulting from related variables. The current study provides a comprehensive evaluation of lignin and carbohydrate degradation during kraft pulping of multiple hardwood species. The kraft delignification rates of Eucalyptus urograndis, E. nitens, E. globulus, sweet gum, maple, red oak, red alder, cottonwood, and acacia were obtained. The kinetics of glucan, xylan, and total carbohydrate dissolution during the bulk phase of the kraft pulping process for those species also were investigated. The wide ranges of delignification and carbohydrate degradation rates were correlated to wood chemical characteristics. It appears that the syringyl:guaiacyl lignin ratio and lignin-carbohydrate complexes are the main factors responsible for the differences in kraft pulping performance among the hardwoods studied. [ABSTRACT FROM AUTHOR]

The cleavage of lignin bonds in a wood matrix is an important step in the processes employed in both the biorefinery and pulp and paper industries. β-O-4 ether linkages are susceptible to both acidic and alkaline hydrolysis. The cleavage of α-ether linkages rapidly occurs under mildly acidic reaction conditions, resulting in lower molecular weight lignin fragments. Acidic reactions are typically employed in the biorefinery industries, while alkaline reactions are more typically employed in the pulp and paper industries, especially in the kraft pulping process. By better understanding lignin reactions and reaction conditions, it may be possible to improve silvicultural and breeding programs to enhance the formation of easily removable lignin, as opposed to more chemically resistant lignin structures. In hardwood species, the S/G ratio has been successfully correlated to the amount of β-O-4 ether linkages present in the lignin and the ease of pulping reactions. [ABSTRACT FROM AUTHOR]

Researchers have been attempting to improve the yield of bleachable-grade kraft pulp for several decades. Wood is typically one of the major costs associated with kraft pulping. Therefore, it is typically assumed that improving pulp yield or conversely, reducing the amount of wood required to make a specific mass of pulp, is a cost-effective, lucrative endeavor. Although this may be true, it is important to understand the impact of increasing pulp yield on the interconnected processes within an integrated pulp and paper mill and to fully evaluate the cost implications on these processes. The current work employed several sets of laboratory pulping conditions and a WinGEMS model of a pulp mill, fully integrated with chemical recovery, power, and recausticization, and pulp drying islands to determine where the largest cost impact associated with improved pulp yield may be experienced. [ABSTRACT FROM AUTHOR]

Most studies aimed at determining rates of hardwood delignification and carbohydrate degradation have focused on understanding the behavior of a single wood species. Such studies tend to determine either the delignification rate or the rate of carbohydrate degradation without examining the potential interactions resulting from related variables. The current study provides a comprehensive evaluation on both lignin and carbohydrate degradation during kraft pulping of multiple hardwood species. The kraft delignification rates of E. urograndis, E. nitens, E. globulus, sweet gum, maple, red oak, red alder, cottonwood, and acacia were obtained. Furthermore, the kinetics of glucan, xylan, and total carbohydrate dissolution during the bulk phase of the kraft pulping process for the above species were also investigated. The wide ranges of delignification and carbohydrate degradation rates were correlated to wood chemical characteristics. It appears that the S/G ratio and lignin- carbohydrate-complexes (LCCs) are the main characteristics responsible for the differences in kraft pulping performance among the hardwoods studied. [ABSTRACT FROM AUTHOR]

Variability in wood properties has a major impact on pulp quality and the cost associated with pulp production. Frequently, accounting data for green tons of wood across the mill scales and the tons of pulp produced suggest that the pulp mill has affected the pulp yield because the tons of purchased wood divided by the tons of pulp produced changes. The current work examines the impact of the time -- from when a tree is harvested in the forest to the time it is brought across the scales at the mill -- on accounting yield and operating cost. Percentage weight loss (assumed to be changes in moisture content) were determined for Pinus taeda, Eucalyptus dunni, and Eucalyptus grandis over a 12-week period in the winter and summer seasons. Wood samples were obtained immediately after being harvested. The percentage weight loss within the first 5 days of storage varied from 2% to 13%, depending upon species and season, and reached 36% after 11 weeks of storage. For a 1000 tons/day mill with a 55% pulping yield on o.d. fiber, the difference between using fresh-cut wood verses cut trees that have been stored for 11 weeks is 1130 green tons. Assuming the mill pays $45/green ton, the change in green log usage between fresh-cut and 11-week-old logs can cost the mill US$50,850 per day. [ABSTRACT FROM AUTHOR]

The Evádale, TX, USA, mill recently engaged in a major lime kiln and recausticizing upgrade. The centerpiece of the project was to upgrade the existing lime kiln feed system to a new LimeFlash feed system, a trademarked technology from Andritz. The feed system in Evádale is the first installation in North America of this technology, and the second installation in the world. The feed system increased the capacity of the lime mud dryer (LMD) fed kiln from 350 tons/day of lime product to 480 tons/day of kiln product, with less than 3% carbonate. The system mixes hot flue gasses with the lime mud before the gas enters the feed end housing, which allows the kiln to operate at a higher feed end temperature without plugging and lime splitting. In startup and low capacity situations, lime mud is fed directly into the kiln rotating part, which eliminates potential plugging problems. Startup and operational experience, along with selected environmental performance, is reviewed. [ABSTRACT FROM AUTHOR]

During the last several years, the increasing cost and decreasing availability of mixed southern hardwoods have resulted in financial and production difficulties for southern U.S. mills that use a significant percentage of hardwood kraft pulp. Traditionally, in the United States, hardwoods are not plantation grown because of the growth time required to produce a quality tree suitable for pulping. One potential method of mitigating the cost and supply issues associated with the use of native hardwoods is to grow eucalyptus in plantations for the sole purpose of producing hardwood pulp. However, most of the eucalyptus species used in pulping elsewhere in the world are not capable of surviving in the southern U.S. climate. This study examines the potential of seven different cold-tolerant eucalyptus species to be used as replacements for, or supplements to, mixed southern hardwoods. The laboratory pulping and bleaching aspects of these seven species are discussed, along with pertinent mill operational data. Selected mill trial data also are reviewed. [ABSTRACT FROM AUTHOR]

The MeadWestvaco mill in Evádale, TX, USA, in conjunction with VOW Resources LLC, has constructed and commissioned a green biogas skid-mounted pilot plant to evaluate the potential of various organic waste streams to produce high-quality biogas. It is the fourth plant in the world incorporating this technical approach to biogas production. At initial startup, the plant used cow manure as organic feedstock. To commission the plant for verifying the VOW bioaugmentation process, the transition was made to using brown grease. After the brown grease commissioning trials are completed, the plant will be transitioned to a number of paper mill-generated organic wastes to acquire the design parameters and engineering data that will aid in construction of a full-scale bio-gas facility. [ABSTRACT FROM AUTHOR]

Several mills in North America have been successful in using xylanase enzymes expressed from Trichoderma reesei (a fungus) as part of their bleaching sequence for many years. These mills process hardwood and softwood species, with and without oxygen delignification. These mills also use three-, four-, and five-stage bleaching sequences. North American mills tend to report increased pulp brightness ceilings and decreased bleaching costs as benefits associated with the application of enzymes in the bleaching process. Laboratory testing suggests that eucalyptus pulp is highly susceptible to fungal- and bacterial-derived enzyme bleaching and should result in significant cost savings in South American mills. At least four different mills in South America have attempted to perform enzyme bleaching trials using bacterial-derived enzymes. Each of these mill trials resulted in significantly increased operating costs and/or unsustainable operating conditions. More recently, one of these South American mills performed a short trial using a commercially available, fungal-derived enzyme. This trial was technically successful. This report attempts to determine why the South American mill experiences with bacterial-derived enzymes have been poor, while North American mills and the one South American mill trial have had good results with fungal- derived enzymes. Operating conditions and trial goals for the North and South American mills also were examined. [ABSTRACT FROM AUTHOR]

Mixed US southern hardwood chips were impregnated and cooked under various conditions in the laboratory. Kappa numbers between 15 and 55 were obtained. The reject content, kappa number, and yield were studied as a function of time, temperature, and alkali charge in the cooking. The results indicate that by using modern cooking technology, i.e. CompactCooking™, an optimal point with respect to the studied pulp parameters can be found. Selected pulps were bleached to high brightness with several different bleaching sequences. These pulps were beaten in a PFI mill and their physical properties were compared at a constant bulk. High kappa, well impregnated fully bleached pulps exhibited improved yield with equivalent or better physical properties as compared to conventional kraft pulps. The high kappa, well impregnated pulps were also found to have improved bleachability as compared to conventionally cooked, bleachable grade kappa number pulps. [ABSTRACT FROM AUTHOR]

The article illustrates the principles that lie behind detonations caused by reactive hazards. It shows how the primer supports the aim of the U.S. Chemical Safety and Hazards Investigation Board to have chemical engineering teachers lecture to their students about reactive hazards and what causes them. It addresses how accidental explosions of certain chemicals such as hydrogen peroxide occurs and how factors such as pressure spikes, interaction with other unstable chemicals and materials, and industrial processes such as bleaching, cause them.

The article focuses on the study which examines the effectiveness of nonprocess-element reduction method which controls thermal cycling of the recovery boiler during liquor processing. According to the study, electrostatic precipitator ash can help to reduce concentration levels of potassium (K) and chloride (Cl) in an ash leaching system to improve chloride dioxide generator operation. During the process, there were about 55% of Cl content, 50% of K content and 80% of soda ash were recovered.

The article presents the study which evaluated the potential for using a chip Impresafiner to rapidly and selectively transport enzymes to a desired reaction. The researchers investigated several different enzyme blends and for each application the specific refining energy that is required is being determined. It found that the effect of different enzyme blends upon the total specific refining energy requirements associated with mechanical pulping. It further states that the application of the enzyme blend during the first pretreatment stage further reduced the total demand by an additional 19.5%.

The article presents a comparison of various pre-bleaching techniques for hardwood kraft brownstock pulp to determine their effect on bleaching cost. It examines five pre-bleaching methods including xylanase enzyme pretreatment, mild acid pretreatment, and xylanase enzyme with acidic peroxide pretreatment. It states that enzyme pretreatment has successfully reduced the overall costs of bleaching to 89%. It mentions that most of the savings can be attributed directly to the enzyme treatment, since acidification alone resulted in a net cost savings of U.S.$ 0.14/ton.