Kraft Pulp Mill Research Articles

Characterization of a dusting lime kiln – A mill study

© 2017 TAPPI Press. All rights reserved. The white liquor preparation is one of the main purposes of the recovery cycle in a kraft pulp mill and the lime kiln, being the single unit operation handling bulk solid materials, poses particular challenges in the recovery cycle. In this study, the influence of a dusting lime kiln on the preparation of white liquor was studied. The investigation showed that the dusting lime kiln produced a burned lime with a substantial fraction of fines at the expense of the fraction of granules, whereas a clear lime kiln had virtually no fines and more granules instead. Burned lime from both dusting and clear periods were collected and separated into fines and granules. The different fractions were slaked and causticized in a synthetic green liquor. The study found that the fines always delivered a lower effective alkali in the resulting white liquor, and that the particle sizes of the lime mud were always larger than those originating from the granules, implying that the fines were sintered harder. The industrial consequence is that a dusting lime kiln increases the load on the kiln because the yield of effective alkali is lower; it also introduces a greater dead load into the liquor cycle.

Techno-economic analysis of ECF bleaching and TCF bleaching for a bleached eucalyptus kraft pulp mill

An early stage techno-economic analysis was performed to compare a traditional elemental chlorine free (ECF) sequence (O O D0 [EOP] D1 P) with the proposed totally chlorine free (TCF) sequence (O O A [ZEO]1 [ZEO]2 P)] for a bleached eucalyptus kraft pulp mill. Similar operating costs (ECF = US$465/a.d. metric ton; TCF = US$468/a.d. metric ton) and similar internal rate of return (ECF = 16.5%; TCF = 16.4%) were obtained. Although the TCF case has lower revenue with surplus steam, savings with chemicals (e.g., sodium chlorate and methanol) pays for the higher consumption of electricity. Probabilistic analyses were also performed to evaluate the financial risks associated with the variability of chemical costs and electricity price. Probabilistic analyses have shown that the price volatility of sodium hydroxide and sodium chlorate have a significant impact on the probability distribution of internal rate of return (IRR). Despite its promising potential, the new TCF sequence has only been tested in laboratory scale and further scaleup has to be performed to validate the technology. However, the techno-economic economic analysis shows that the proposed TCF technology has promising potential for future industrial application.

A Unified Total Site Heat Integration targeting method for isothermal and non-isothermal utilities

This paper presents a new unified Total Site Heat Integration (TSHI) targeting methodology that calculates improved TSHI targets for sites that requires isothermal (e.g. steam) and non-isothermal (e.g. hot water) utilities. The new method sums process level utility targets to form the basis of Total Site utility targets; whereas the conventional method uses Total Site Profiles based excess process heat deficits/surpluses to set Total Site targets. Using an improved targeting algorithm, the new method requires a utility to be supplied to and returned from each process at specified temperatures, which is critical when targeting non-isothermal utilities. Such a constraint is not inherent in the conventional method. The subtle changes in procedure from the conventional method means TSHI targets are generally lower but more realistic to achieve. Three industrial case studies representing a wide variety of processing industries, are targeted using the conventional and new TSHI methods, from which key learnings are found. In summary, the over-estimation of TSHI targets for the three case studies from using the conventional method compared to new method are 69% for a New Zealand Dairy Factory, 8% for the Södra Cell Värö Kraft Pulp Mill, and 12% for Petrochemical Complex.

A novel MILP approach for simultaneous optimization of water and energy: Application to a Canadian softwood Kraft pulping mill

An optimization methodology based on Mixed Integer Linear Programming (MILP) has been developed for simultaneous optimization of water and energy (SOWE) in industrial processes. The superstructure integrates non-water process thermal streams and optimizes the consumption of water, while maximizing internal heat recovery to reduce thermal utility consumption. To address the complexity of water and energy stream distribution in pulp and paper processes, three features have been incorporated in the proposed SOWE method: (a) Non-Isothermal Mixing (NIM) has been considered through different locations to reduce the number of thermal streams and decrease the investment cost by avoiding unnecessary investment on heat exchangers; (b) the concept of restricted matches combined with water tanks has been added to the superstructure; and (c) the Integer-Cut Constraint technique has been combined with the MILP model to systematically generate a set of optimal solutions to support the decision-making for cost-effective configurations. The performance of the proposed improved MILP approach has been evaluated using several examples from the literature and applied to a Canadian softwood Kraft pulping mill as an industrial case study. The results indicate that this approach provides enhanced key performance indicators as compared to conceptual and non-linear complex mathematical optimization approaches.

The Sequential Liquid-Lignin Recovery and Purification process: Analysis of integration aspects for a kraft pulp mill

The Sequential Liquid-Lignin Recovery and Purification process : Analysis of integration aspects for a kraft pulp mill

Tall oil production from black liquor: Challenges and opportunities

Abstract Tall oil is an important by-product of Kraft pulping processes. One possibility to improve the economic feasibility of Kraft pulp mills is to consider tall oil production from their wasted tall oil soaps. This review paper describes the current technology practiced to produce tall oil from the black liquor of Kraft pulping processes. Moreover, alternative processes to separate tall oil soap from black liquor, produce tall oil from the separated soap, purify tall oil, and to produce value-added products from tall oil are reviewed. The main perspectives and challenges associated with each process are comprehensively described. Currently, soap is separated from black liquor via decantation. To improve the efficiency of this separation, the application of neutral soluble colloids in dilute black liquor reported to be promising. Tall oil soap is converted to crude tall oil in the acidulation process via treating with sulfuric acid. However, the use of sulfuric acid forms calcium sulfate as a by-product of the process. The replacement of sulfuric acid with a sodium sesquisulfate solution is beneficial for decreasing the direct use of sulfuric acid in the tall oil production process. Crude tall oil can be used without purification as fuel. Its purification and subsequent reaction with methanol can lead to biodiesel production. However, this process may be complicated to implement in industry. The production of valuable lignin-based products from the tall oil production process may have benefits for the mills as these processes can be fully integrated into the Kraft pulping and tall oil production processes.

Equipment performance analysis of a Canadian Kraft mill. Part II: Diagnostics and identification of improvement projects

The Kraft process is an intensive user of capital, energy, water, and chemicals, and is particularly vulnerable in the present precarious economic situation. Therefore, Canadian Kraft pulp mills offer good potential for improvement, especially if the equipment and unit operations are diagnosed in details by means of specific key performance indicators (KPI). The characterization and performance analysis of equipment is a prerequisite to optimization. A thorough evaluation of the equipment performance must be done to assess the actual vs. the expected performance before proceeding to any kind of energy improvement project. A systematic methodology for equipment performance evaluation through key performance indicators (KPIs) is presented in Part I. New key performance indicators (KPIs) based on dimensional analysis as well as other conventional key performance indicators are used to efficiently analyze and diagnose the causes of inefficiencies of the equipment, and propose adequate remedial actions. The methodology has been applied to an Eastern Canadian Kraft mill and several improvement projects leading to 30% of energy savings are proposed, entailing a low investment cost and a payback of 1.1 a.

Physicochemical characterization of residue from the enzymatic hydrolysis of sugarcane bagasse in a cellulosic ethanol process at pilot scale

One of the major obstacles to use lignin as feedstock for value-added products at industrial scale is that its physicochemical characteristics can widely vary. Thus, it is necessary to know such characteristics before applying in the synthesis of products. In this study, we produce a lignocellulosic biomass in pilot scale composed of lignin (47%w/w) and cellulose fibers (40%w/w). This biomass was obtained from the enzymatic hydrolysis of sugarcane bagasse that was pretreated by a hydrothermal process (190°C/10min). After obtaining this residue, which is listed here as “Enzymatic Hydrolysis Residue Lignin” (EHRL), its physicochemical and thermal characterization was performed. A highly concentrated lignin from the LignoBoost process in Kraft pulp mill, lignin LignoBoost (LBL), was also evaluated in order to compare it with the EHRL. The C9-formulae of the lignin extracted from the EHRL is C9.0H11.2O4.3S0.08N0.17(OCH3)0.9(OHphenolic)0.7(OHaliphatic)0.6 and the C9-formulae of the LBL is C9.0H7.9O1.4S0.16N0.01(OCH3)1.1(OHphenolic)0.7(OHaliphatic)0.5. By the 2D Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC) technique, syringyl/guaiacyl ratios for the EHRL and the LBL are 1.8 and 4.8, respectively. Thus, the EHRL appears to be promising for phenolic composite, for instance, since it has lower methoxyl content. The EHRL showed larger range of fiber particle sizes (<4.05mm–0.4μm) than the LBL (0.4–1090μm).

Integrating a Biorefinery into an Operating Kraft Mill

Kraft pulp and paper mills have several advantages for serving the emerging biorefinery industry as a source of raw materials. This review examines technologies for producing liquid biofuels, chemicals, and advanced materials from woody feedstocks to generate new sources of revenue. Market pull comes in part from government policies that drive substitution of petroleum-based products with biobased equivalents. Kraft mills have ample networks to supply feedstocks, whether these are forest residues or byproduct side streams. Pulp mills are well suited to expand sufficiently to accommodate production of value added platform chemicals that are in demand because of brand owner sustainability commitments.

Effects of added materials on black liquor combustion

Black liquor is often mixed with various types of materials before being burned in a recovery boiler to meet specific needs of kraft pulp mills. A systematic study was conducted using a thermogravimetric combustor to examine how added materials might affect the combustion behavior of black liquors obtained from several pulp mills. The results show that adding soap, caustic, white liquor, and sawdust significantly reduces the liquor swelling tendency, thereby requiring a longer time for the liquor to burn completely. Adding makeup saltcake, precipitator ash, sodium sulfate, and biosludge, on the other hand, has little or no effect on the liquor combustion behavior.

Lignin separation from kraft black liquor by combined ultrafiltration and precipitation: a study of solubility of lignin with different molecular properties

Lignin from wood is by far the largest source of bio-based aromatic raw material. Today a vast amount of lignin is processes and incinerated in kraft pulp mills around the world. One possible option to utilize the energy surplus in a modern kraft pulp mill is to extract lignin from black liquor. Precipitation of lignin is one important step in an extraction process. This study investigates how the molecular size and functional groups of lignin influenced the precipitation yield. Cross-flow filtration was applied to fractionate lignin with different molecular weights from a black liquor, precipitation studies was made on the different fractions. The precipitated lignin was characterized by GPC, HPAEC-PAD and NMR analysis. The results show that it was possible to obtain a more homogenous lignin by fractionation using cross-flow filtration. It was found that the molecular properties of kraft lignin, i.e. molecular weight and functional groups, influenced the yield of lignin precipitation: at the same precipitation condition, lignin fraction with higher molecular weight has higher precipitation yield. Lignin fraction with lower molecular weight contains less amount of carbohydrates and methoxyl groups but higher amount of phenolic groups.

Managing total reduced sulfur emissions at a Canadian kraft pulp mill

This study addresses the challenges a dissolving-grade pulp mill in Canada faced in 2014 in meeting its total reduced sulfur (TRS) gas emission limit. These emissions from the recovery boiler exit are controlled by passing the boiler exit gas through a TRS scrubber system. The mill employs a cyclonic direct contact evaporator to concentrate black liquor to firing solids content. The off-gases from the direct contact evaporator flow to the effluent gas control system that consists of a venturi scrubber, a packed bed scrubber, and a heat recovery unit. Emissions of TRS greater than the regulated limit of 15 ppm were observed for a 4-month period in 2014. The level of emissions measured during this period was significantly higher than about 12 ppm, the expected average value based on historic experience. The problem persisted from mid-June 2014 until the annual mill shutdown in October 2014. The main TRS components detected and the performance of the Teller scrubber in capturing them are examined. Other potential causes for these emissions are identified, including mechanical problems such as broken packing in the TRS packed bed scrubber, broken baffle plates in the scrubber, and cyclone evaporator leaks causing air ingress. Repairs were carried out during the mill shutdown, which eliminated the TRS emissions problem.

Integration of new processes and geothermal heat into a wood processing cluster

In this study, process integration methods have been used to investigate the heat integration of new processes with a model wood processing cluster. Due to anticipated future demand for bio-derived fuels and chemicals, it is important to identify which emerging conversion processes would benefit from integration with existing facilities. Identifying specific integration schemes help quantify economic and environmental benefits and can assist the commercialisation and adoption of these new processes. The synergies gained through integration are examples of industrial symbiosis, which is the sharing of resources between co-located facilities. A background/foreground analysis of the grand composite curves was used to determine any heat recovery potential between the cluster and the new entrant and the effect on the utility system. The model cluster consisted of a thermo-mechanical pulp and paper mill, kraft pulp and paper mill and saw mill. Some of the processes had little or no integration potential due to having similar pinch temperatures as the cluster. Processes based on biomass gasification had large potential due to the pinch temperatures being very different and the shape of grand composite curve being complimentary. The integration of geothermal energy for process heat was also investigated and if available has a distinct advantage of allowing surplus black liquor to be used as a feedstock to some of the new processes. Results show that high pinch temperature processes show the greatest integration potential and can provide significant fuel reduction potential.

A case study for integrated forest biorefinery: Recovery of manool from evaporator condensate of a kraft pulp mill

The integrated forest biorefinery concept teaches the opportunity in producing value-added products from the pulp and paper manufacturing processes, in addition to the traditional pulp and paper products. Manool is a plant extractive that is available in many wood species, in particular, softwood, and can find high value applications, such as in the perfumery industry. The evaporator condensate from the kraft black liquor recovery process contains manool and can be a potential source for this valuable product. In this paper, the recovery of manool from the evaporator condensate that was further concentrated in a reverse osmoses (RO) process (known as the RO concentrate) in a kraft mill in Eastern Canada, was investigated. The results showed the manool content in the RO concentrate is in the range of 300–1500 mg/L for samples collected. A novel process was developed in recovering manool from the RO concentrate, which consists of (1) adsorption of manool (together with other organics) into absorbent, such as talc, (2) desorption from the adsorbent and (3) further upgrading of manool. About 90% of the manool from the RO concentrate can be adsorbed onto the talc under the optimal conditions. The adsorbed manool on talc can be subsequently regenerated by extraction using ethanol or dichloromethane, resulting in the crude manool product. The purity of this crude manool product was about 25%, which was further purified to 86% based on the chromatographic separation technology.

The impact of mechanical log surface damage on chip size uniformity during debranching and debarking Eucalyptus pulpwood logs using a single-grip harvester

Mechanised harvesting operations are becoming more prevalent in South Africa with the realisation that motormanual and manual harvesting operations pose significant health and safety risks to workers. The damage inflicted by single-grip harvester feed rollers and delimbing knives on log surfaces during debranching and debarking eucalypts, may affect eventual chip quality. Chip quality influences pulp quality and recovery in the kraft pulping process. This study investigates the influence of two mechanised debranching and debarking treatments on Eucalyptus pulp logs (threeand five-feed roller passes along the stem surface) by feed rollers and delimbing knives on chip uniformity, size and purity. The two mechanised treatments to three log classes (base, middle and top logs) were compared with chips produced from manually debarked logs. Manually debarked logs produced significantly less undesirable-sized chips than both three and five-pass processed logs. The volume of undesirablesized chips produced during chipping also increased with decreasing log size. Manually debarked logs produced chips with significantly less bark than three-pass-processed logs (0.008% vs 0.062%), and five-pass-processed logs produced chips with significantly less bark than three-pass-processed logs (0.018% vs 0.062%). Middle logs also produced chips with significantly less bark than base logs (0.016% vs 0.056%), and top logs produced chips with significantly less bark than base logs (0.017% vs 0.056%). In all cases the bark content on logs was considerably less than the maximum of 1.0% generally specified by kraft pulp mills.

Supplementary information: Life Cycle Assessment of lignin extraction in a softwood kraft pulp mill

Supplementary information: Life Cycle Assessment of lignin extraction in a softwood kraft pulp mill

Lignin as a Binder Material for Eco-Friendly Li-Ion Batteries.

The industrial lignin used here is a byproduct from Kraft pulp mills, extracted from black liquor. Since lignin is inexpensive, abundant and renewable, its utilization has attracted more and more attention. In this work, lignin was used for the first time as binder material for LiFePO4 positive and graphite negative electrodes in Li-ion batteries. A procedure for pretreatment of lignin, where low-molecular fractions were removed by leaching, was necessary to obtain good battery performance. The lignin was analyzed for molecular mass distribution and thermal behavior prior to and after the pretreatment. Electrodes containing active material, conductive particles and lignin were cast on metal foils, acting as current collectors and characterized using scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge cycles. Good reversible capacities were obtained, 148 mAh·g−1 for the positive electrode and 305 mAh·g−1 for the negative electrode. Fairly good rate capabilities were found for both the positive electrode with 117 mAh·g−1 and the negative electrode with 160 mAh·g−1 at 1C. Low ohmic resistance also indicated good binder functionality. The results show that lignin is a promising candidate as binder material for electrodes in eco-friendly Li-ion batteries.

Life Cycle Assessment of lignin extraction in a softwood kraft pulp mill

Life Cycle Assessment of lignin extraction in a softwood kraft pulp mill

Historical decline and altered congener patterns of polychlorinated dibenzo-p-dioxins and dibenzofurans in fish and sediment in response to process changes at a pulp mill discharging into Jackfish Bay, Lake Superior.

Improved regulations for pulp and paper mill effluents and an industry shift away from elemental chlorine bleaching in the 1990s greatly reduced the release of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) into the environment. However, the high potential of these contaminants to persist in sediment and bioaccumulate in biota means that they have remained a concern. To document current contamination from bleached kraft pulp mill effluent, PCDD/Fs were measured in white sucker (Catostomus commersoni) collected from Jackfish Bay, Lake Superior. These values were contrasted to historically reported fish data as well as PCDD/F patterns from dated sediment cores. Patterns of PCDD/Fs in sediment cores from Jackfish Bay and reference sites demonstrated a relationship between contamination and mill process changes. During the peak PCDD/F contamination period (1991), when the mill was still using elemental chlorine, the contamination patterns in fish and sediment were distinct and dominated by 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,3,7,8-tetrachlorodibenzofuran. Following the reduction in the use of elemental chlorine during the early 1990s, a rapid decline was observed in PCDD/F contamination of fish tissue, and levels are now approaching background conditions with congener patterns more reflective of atmospheric sources. Although surface sediments from Jackfish Bay continue to have elevated PCDD/Fs, with some locations exceeding sediment quality guidelines, they do not appear to be highly bioavailable to benthic fish.

Integration of Biomass Conversion Technologies and Geothermal Heat Into a Model Wood Processing Cluster

Due to the anticipated future demand for bio-derived fuels and chemicals it is important to identify which processes would benefit from integration with existing industrial clusters, especially those producing wood based products such as pulp and paper. Specific integration schemes need to be identified and benefits, both economic and environmental, quantified to assist the successful commercialisation and adoption of these new technologies. These synergies are examples of industrial symbiosis; the sharing of resources, including utilities and services between different co-located production facilities. Total site analysis is an important tool to accomplish this task. A model of a typical wood processing cluster including a thermomechanical pulp and paper mill, kraft pulp and paper mill, and saw mill have been used to evaluate the integration potential of possible new entrants into the cluster. A background/foreground analysis was used to assess any heat recovery potential between the cluster and the new entrant. Some of the processes considered had little or no integration potential due to having approximately the same pinch temperature as the cluster. Large potential was found to occur where the pinch temperatures were dissimilar and the shape of the grand composite curves complimentary. The integration of geothermal heat as a means of generating surplus black liquor as a feed to a biorefinery process was also examined.