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Hydrothermal treatment of sludge within the pulp and paper industry can have a wide range of possible reactor solid loads for different sludge types. The objectives of this work were to determine the effect of reactor temperature and solid load on the properties of sludge hydrochar and to simulate hydrothermal treatment of sludge within a pulp and paper mill. Laboratory experiments were first performed within reactor temperature and solid load ranges of 180–260 °C and 10–50%, respectively, and the effects of sludge treatment were determined by comparing parallel mill-scale simulations. Based on the results, both reactor temperature and solid load had a statistically significant effect on the solid, ash, carbon and energy yields of sludge hydrochar. Increasing solid load minimized carbon dissolution to the liquid phase and increased the solid and energy yield of the attained hydrochar. According to mill-scale simulations in a 9 m 3 batch reactor, treating primary sludge alone produced an energy surplus of 22–36 GJ through char incineration, decreasing to 12–22 GJ and 3.4–9.1 GJ for mixed and secondary sludge, respectively. Mixing primary and secondary sludge reduced the overall energy surplus by 2–8% compared with treating the sludge streams separately in two reactors. [ABSTRACT FROM AUTHOR]

Abstract: The pulp and paper industry both uses and produces large amounts of energy and rising fuel prices bring along significant challenges to the sector. Several strategies can be applied in order to remain competitive e.g. an increase in energy efficiency, a switch in fuel and/or a novel energy conversion technology. In this study, we investigate if improved energy conversion strategies can reduce energy costs, primary energy use and CO2 emissions of paper mills within different European countries (The Netherlands, Poland and Sweden). Our results show that differences in history and availability of resources has led to different conversion strategies in the three countries. We found that a natural gas combined cycle, which is largely implemented in The Netherlands due to long term domestic availability of natural gas, has the lowest primary energy demand. Due to a long history of low electricity prices, CHP has not been common in Sweden. Many Swedish mills use biomass as an energy source and due to low CO2 emissions of the national grid the CO2 emission profile of the Swedish paper industry is very low. Our results imply that future conversion routes for the Swedish paper and board industry are again wood based; in case of increasing electricity prices these would be biomass gasification based CHP solutions. With a reduction of 800kg CO2/ton paper on average, a switch from coal to biomass would reduce CO2 emissions in the Polish pulp and paper industry with approximately 0.6Mton/year. A carbon price of 20–25€/ton would, according to our results, be enough to provoke this switch. Due to the high share of natural gas, the CO2 emission reduction potential of the Dutch paper industry (1.5Mton/year) is even larger than in Poland. Due to high biomass prices and relative low CO2 emission profile of natural gas, a carbon prices of more than 60€/ton CO2 would be needed to provoke a switch in The Netherlands. Provided with few alternatives, the most effective strategy in The Netherlands would be an increase in energy efficiency. [Copyright &y& Elsevier]

Abstract: The pulp and paper industry is one of the most energy-intensive industries worldwide. In 2007, it accounted for 5% of total global industrial energy consumption and 2% of direct industrial carbon dioxide (CO2) emissions. An energy audit is a primary step toward improving energy efficiency at the facility level. This paper describes a plant-wide energy audit aimed at identifying energy conservation and CO2 mitigation opportunities at a paper mill in Guangdong province, China. We describe the energy audit methods, relevant Chinese standards, methods of calculating energy and carbon indicators, baseline energy consumption and CO2 emissions of the audited paper mill, and nine energy-efficiency improvement opportunities identified by the audit. For each of the nine options, we evaluate the energy conservation and associated CO2 mitigation potential. The total technical energy conservation potential for these nine opportunities is 967.8terajoules (TJ), and the total CO2 mitigation potential is equal to 93,453tonnes CO2 annually, representing 14.4% and 14.7%, respectively, of the mill’s total energy consumption and CO2 emissions during the audit period. [Copyright &y& Elsevier]

Abstract: The systematic, transparent and accurate on-line energy information of the production process is quite the basis of mill energy management and conservation. An Energy Management System (EMS) was built according to the characteristics of the energy usage in a typical newsprint paper mill. The EMS first realized the process data acquisition and integration, second fulfilled the on-line energy information calculation from the integrated data. A water and steam properties query component based on IAPWS-IF97 was developed and plugged into the EMS to facilitate the energy calculation of water and steam. The practical performance in the paper mill showed that the integrated energy information of the whole mill was gained and the on-line energy supervisory was achieved. In the end a systematic, transparent and accurate energy usage profile is obtained and it would provide the valuable fundamental energy data for the further energy analysis and optimization in the EMS. [Copyright &y& Elsevier]

Abstract: Alarmingly low pulp prices in early 2009 left pulp and paper mills across North America desperate for any way to improve thin profit margins. One solution that continues to gain popularity among the industry is improved energy management systems for cogeneration systems, which use steam for two purposes – to provide heat for the pulping process and to generate electricity for sale to regional providers. This paper presents an energy optimization algorithm for use in a pulp and paper mill cogeneration system. The algorithm is applicable to a number of popular mill configurations, power sale contracts, and fuel purchasing scenarios. The method is also extended to address weather-dependent cooling limitations encountered by a mill cogeneration facility, in which case an iterative solution is proposed in order to maintain convexity of the optimization problem. Results are presented in the form of three case studies. [ABSTRACT FROM AUTHOR]

Abstract: Waste papers (newspaper, office paper, magazines and cardboard in this study) with 50–73% (w/w oven dry weight) carbohydrate contents have considerable potential as raw materials for bioethanol production. A particle size reduction step of wet blending prior to enzymatic hydrolysis of newspaper was found to increase the glucan conversion efficiency by up to 10%. High-solids loading hydrolysis at 15% (w/w) of four types of paper using two enzyme alternatives, Celluclast 1.5L supplemented with Novozyme 188 and Cellic Ctec 1 (Novozymes A/S, Demark), at various enzyme concentrations were successfully performed in a lab-scale overhead-stirred reactor. This work has identified the relative saccharification performance for the four types of paper and shows office paper and cardboard to be more suitable for producing bioethanol than newspaper or magazine paper. The experimental data were also very well described by a modified, simple three parameter glucan and xylan hydrolysis model. These findings provide the possibility for incorporating this validated kinetic model into process designs required for commercial scale bioethanol production from waste paper resources. [Copyright &y& Elsevier]

Increasing the conductivity of gas diffusion layers (GDLs) is an important way to improve the output performance of polymer electrolyte membrane fuel cells (PEMFCs). However, the complex porous fiber structures of GDLs significantly enhances the difficulty of quantitatively altering their conductivity which is determined by the carbon fibers and the conduction characteristics between fibers. In addition, the microstructures of various types of GDLs are different. Thus, it is a considerable challenge to explore the conductive mechanisms of these porous materials and optimize their structures to reduce their bulk resistances. In this work, a mathematical graph theory model that applies to the through-plane (T-P) bulk resistance prediction of two types of commonly used GDLs, carbon paper and carbon felt, is established to explain their different micro conduction mechanisms in depth. In addition to the number of fiber contact points, their distribution, as well as the resistance of the carbon fibers, are all important factors affecting the T-P conductivity. Optimizing fiber density and fiber diameter can significantly improve the T-P conductivity of carbon paper. In comparison, making the structure of carbon felt more compact so that the distribution of its contact points in the T-P direction can be more uniform will be more effective for the reduction of its T-P bulk resistance. Meanwhile, the T-P bulk resistance of carbon paper can also be effectively improved by optimizing the content and distribution of the binders. A method to decline the bulk resistance of carbon paper by aggregating the binders in the in-plane (I P) direction is proposed. The simulation results show that it can reduce the T-P bulk resistance of carbon paper by about 19.9% at a compressive stress of 1.5 MPa. This study provides further guidance for optimizing the structural designs of GDLs to optimize their conduction performance. • T-P bulk resistance prediction model suitable for different GDLs is constructed. • Micro conductivity mechanisms of carbon paper and carbon felt are compared. • Increasing fiber density and diameter improves carbon paper's T-P conductivity. • Making carbon felt's structure more compact can optimize its T-P conductivity. • To promote carbon paper's T-P conductivity by optimizing the binders inside. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Stepwise pyrolysis at 350 and 500 °C can separate products into two fractions. • First step liquid product was acidic and had high amounts of oxygenated compounds. • Products from the second step had high hydrocarbon contents and low acidity. • Interaction between cellulose and plastics during stepwise pyrolysis was observed. • Test on real wastes and discussion of scaling-up possibilities were presented. Abstract Mixed plastics and papers are two of the main fractions in municipal solid waste which is a critical environmental issue today. Recovering energy and chemicals from this waste stream by pyrolysis is one of the favorable options to achieve a circular economy. While pyrolysis products from plastics are mainly hydrocarbons, pyrolysis products from paper/biomass are highly oxygenated. The different nature of the two pyrolysis products results in different treatments and applications as well as economic values. Therefore, separation of these two products by multi-step pyrolysis based on their different decomposition temperatures could be beneficial for downstream processes to recover materials, chemicals and/or energy. In this work, stepwise pyrolysis of mixed plastics and paper waste was performed in a batch type fixed bed reactor using two different pyrolysis temperatures. Neat plastic materials (polystyrene, polyethylene) and cellulose mixtures were used as starting materials. Then, the same conditions were applied to a mixed plastics and paper residue stream derived from paper recycling process. The condensable products were analyzed by GC/MS. It was found that pyrolysis temperatures during the first and second step of 350 and 500 °C resulted in a better separation of the oxygenated and hydrocarbon condensates than when a lower pyrolysis temperature (300 °C) was used in the first step. The products from the first step were derived from cellulose with some heavy fraction of styrene oligomers, while the products from the second step were mainly hydrocarbons derived from polystyrene and polyethylene. This thus shows that stepwise pyrolysis can separate the products from these materials, although with some degree of overlapping products. Indications of interaction between PS and cellulose during stepwise pyrolysis were observed including an increase in char yield, a decrease in liquid yield from the first temperature step and changes in liquid composition, compared to stepwise pyrolysis of the two materials separately. A longer vapor residence time in the second step was found to help reducing the amount of wax derived from polyethylene. Results from stepwise pyrolysis of a real waste showed that oxygenated and acidic products were concentrated in the liquid from the first step, while the product from the second step contained a high portion of hydrocarbons and had a low acid number. [ABSTRACT FROM AUTHOR]

Abstract: Evolutionary behavior of syngas chemical composition and yield have been examined for paper and cardboard at three different temperatures of 800, 900 and 1000°C using CO2 as the gasifying agent at constant flow rate. Specifically the evolution of syngas chemical composition with time has been investigated. Pyrolysis of the sample was dominant at the beginning of the gasification process as observed from the high initial devolatilization of the sample followed by char gasification of material to form syngas for a long period of time. Results provided the role of gasification temperature on kinetics of the CO2 gasification process. Increase in gasification temperature provided increased conversion of the sample material to syngas. Thus the sample conversion to syngas was low at the low temperature of 800°C while at elevated temperatures of 900 and 1000°C substantial enhancement of the kinetics process occurred. The evolution of extensive reaction rate of carbon-monoxide was calculated. Results show that increase in temperature increased the extensive reaction rate of carbon-monoxide. The global behavior of syngas chemical composition examined at three different temperatures revealed a peak in concentration of H2 to exhibit after few minutes into the gasification that changed with gasification temperature. At 800°C gasification temperature peak in H2 was displayed at 3min into gasification while it decreased to only 2min, approximately, at gasification temperatures of 900 and 1000°C. The effect of reactor temperature on CO mole fraction has also been examined. Increase in the gasification temperature enhances the mole fraction of CO yields. This is attributed to the increase in forward reaction rate of the Boudouard reaction (). The results show important role of CO2 gas for the gasification of wastes and low grade fuels to clean syngas. [Copyright &y& Elsevier]

Abstract: The transport of electrons through the gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells has a significant impact on the optimal design and operation of PEM fuel cells and is directly affected by the anisotropic nature of the carbon paper material. In this study, a three-dimensional reconstruction of the GDL is used to numerically estimate the directional dependent effective electrical conductivity of the layer for various porosity values. The distribution of the fibers in the through-plane direction results in high electrical resistivity; hence, decreasing the overall effective electrical conductivity in this direction. This finding is in agreement with measured experimental data. Further, using the numerical results of this study, two mathematical expressions were proposed for the calculation of the effective electrical conductivity of the carbon paper GDL. Finally, the tortuosity factor was evaluated as 1.7 and 3.4 in the in- and through-plane directions, respectively. [Copyright &y& Elsevier]

Abstract: This paper presents the application of a comprehensive approach to the design of small scale sustainable distributed generation systems with special focus on energy recovery from paper production process sludge. The methodology integrates a detailed fluid-dynamic analysis tool with preliminary experimental analysis on a laboratory scale to guide the design of a prototype bubbling fluidized bed gasifier in the 85kW power range fitting with small and medium size paper production industries. Preliminary tests show stable operation even for this rather small power scale, and deviation from chemical equilibrium concentration in agreement with literature available data. Energy content in the sludge may be recovered along with a significant reduction of residual volume and mass. The concept may then be used to increase the overall sustainability of paper production. [Copyright &y& Elsevier]

Abstract: This paper studies allocation of fuel costs and CO2-emissions to heat and power in a CHP plant producing heat to an integrated pulp and paper mill and electricity to the liberalized electricity markets (or to the mill by the market price). The CHP plant and the mill are considered to be two separate economical units and both the mill and the CHP plant perspectives are discussed. Fuel costs and CO2-emissions are allocated using the energy, exergy and market based methods. The CHP plant purchases black liquor and bark from the mill. It also purchases oil from the markets to cover the whole fuel demand of the plant. The results indicate that the marked based method can be recommended as a “neutral” cost allocation method, because with that, the energy producer is not collecting extra margins from selling steam. This means that heat pricing is cost based. The results also indicate that depending on the emission factor and efficiency of alternative energy production form, the marked based method or the exergy method allocate the lowest CO2-emissions to heat. Therefore, the use of market based method for allocating costs and CO2 emissions can be recommended in order to use one single approach in both. [Copyright &y& Elsevier]

Abstract: Densified biomass pellets using waste wood sawdust (S) as main materials and wrapping paper fiber (P) as “solid bridge”, named as P/S-BPs, was prepared by a hydraulic press powder pelletizer under room temperature and pressure lower than10MPa. The effects of the addition of P to S and the compressed pressure on the density, resiliency (R), abrasion resistance (AR), impact resistance index (IRI)) and the combustion behavior of the P/S-BPs were investigated. The results showed that the addition of P to S greatly reduced the negative effects of resiliencies on the densities and mechanical properties of P/S-BPs during storage. For example, P/S-BPs compressed at 6MPa in a P/S mass ratio of 1–3 showed the smooth surface and low resiliency of 10% with a high relaxed density of 1.08kgm−3. This is due to the strengthened interlocking bonds through fabricating “solid bridge” and increasing attracting force by adding P to resist the disruptive force created by elastic recovery even under low pressure. Combustion results showed that the addition of P decreased the soot index (SI) due to the lower devolatilization rate and burnout rate, and increased the HHV per unit volume because of its high relaxed density. Thus, compression of waste P and S in a P/S mass ratio of 1–3 at room temperature under 6MPa is a cost-effective process to produce densified sustainable bio-fuel from waste S and P as well as dispose them. [Copyright &y& Elsevier]

Abstract: A detailed mathematical process integration model of a pulp and paper mill in the Northern Sweden has been developed. The main objective of this work has been set to describe the practical development of the model with particular emphasis on the development of the digester and evaporation plant sub-models. Actual plant measurements have been used to validate the model. By implementing the sub-models into the complete plant model, the influence of different operation parameters on the overall plant performance has been investigated. Furthermore, introductory studies with the main objective to minimize the plant energy cost have been carried out. [Copyright &y& Elsevier]

Abstract: The thermal behavior of semi-anthracite coal, paper sludge and their blends during pyrolysis and combustion processes was investigated in this study. The experiments were conducted in a differential thermogravimetric analyzer at different heating rates (10K/min, 20K/min and 30K/min) and at temperatures ranging from 310K to 1300K. The results revealed that de-volatilization of paper sludge occurred earlier with a higher rate, and that the process was further accelerated under oxygen-enriched conditions. The blends had integrative thermal profiles that reflected both paper sludge and coal. In addition, the blends showed different ignition and combustion behavior depending on the percentage of sludge. Two types of non-isothermal kinetic analysis methods were applied to evaluate the combustion processes. The kinetic parameters of the blends confirmed the improved ignition characteristics. In addition, both the TG profiles and activation energy indicated that the combustion of their blends with low percentages of sludge, such as 10 wt.%, were similar to that of coal. These experimental results help explain and predict the behavior of coal and paper sludge blends in practical applications. [ABSTRACT FROM AUTHOR]