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Climate change mitigation induces strong growth in renewable electricity production, partly driven by shifts in environmental policies and regulation. Intermittent renewable electricity requires supporting systems in the form of sustainable hydrocarbon chemicals such as transportation fuels. Bulk chemical production fits well into a pulp mill environment, given their large volumes, stable operation, and ample supply of biomass-based carbon feedstock in the form of flue gases. Until now, the utilization of the flue gases from conventional operation of a pulp mill has received little attention. Harnessing these flue gases into usable products could offer additional value to mill operators, while also diversifying their product portfolio. However, electricity-based fuels and products require extra energy in the conversion step and may not be commercially competitive with current fossil products under the current regulation. There might also be uncertainties about future commodity prices. Thus, the objective of this study is to estimate the economic competitiveness and the added value of selected side products that could be produced alongside conventional pulp and paper products. A typical modern pulp mill is modeled in different product configurations and operational environments, which allows testing of various development paths. This illustrates how the overall energy and mass balance of a pulp mill would react to changes in different final products and other parameters. The focus of the study is in synthetic methanol, which is produced from flue gases and excess resources from the mill, with minimal interference to the pulping process. The results aid in assessing the necessity and magnitude of a premium payment for subsidizing green alternatives to replace current fossil fuels and chemicals. Additionally, the results function as an indicator of the development state of the pulp and paper industry in the turmoil of climate change regulation. The results indicate that pow-er-to-X systems offer one more viable pathway alternative for broadening the product portfolio of the pulp and paper sector, as well as opening new flexibility measures and services to grid stabilization. Market conditions were found to have a significant impact on the perceived profitability.

In this work, the aim was to study the distribution and accumulation of the non-process elements (NPEs) in the recovery cycle of Finnish pulp mills and look at whether the geographical location (North vs. South) correlates with the current Finnish NPE levels. In addition, a comparison to older similar Finnish measurements was made with an attempt to analyze the reasons behind differences in the most typical non-process elements, aluminum (Al), silicon (Si), calcium (Ca), phosphorus (P), magnesium (Mg), manganese (Mn), chlorine (Cl), and potassium (K), taking into account the main elements in the white liquor, sodium (Na) and sulfur (S). The extensive laboratory results gained in this study are from seven sampling points at six pulp mills and present analytical data of metal concentrations. The data obtained presents an update to previous NPE studies. The levels found did not statistically differ between North and South Finland. The NPE levels, apart from phosphorus, found in Finnish pulp mills today have not changed considerably compared to the levels in earlier investigations in the 1990s. In the newest data, the phosphorus concentration was consistently higher in the as-fired black liquor, electrostatic precipitator (ESP) ash, lime mud, and green liquor than in the previous results. In addition, the levels of Al, Si, Ca, P, and Mg in recovery boiler ESP ash were consistently higher compared to the older results. As the mills start to close their systems more, a stronger accumulation of NPEs can be expected, increasing the likelihood of more operational problems in the process. Further understanding of where the NPEs accumulate and how they can be most effectively removed will be valuable knowledge in the future.

Sustainability and efficient use of resources are becoming increasingly important aspects in the operation of all industries. Recently, some biomass-fired boilers have been equipped with increasingly complex condensing back-end heat recovery solutions, sometimes also using heat pumps to upgrade the low-grade heat. In kraft recovery boilers, however, scrubbers are still mainly for gas cleaning, with only simple heat recovery solutions. In this paper, we use process simulation software to study the potential to improve the power generation and energy efficiency by applying condensing back-end heat recovery on a recovery boiler. Different configurations are considered, including heat pumps. Potential streams to serve as heat sinks are considered and evaluated. Lowering the recovery boiler flue gas temperature to approximately 65°C significantly decreases the flue gas losses. The heat can be recovered as hot water, which is used to partially replace low-pressure (LP) steam, making more steam available for the condensing steam turbine portion for increased power generation. The results indicate that in a simple condensing plant, some 1%–4% additional electricity could be generated. In a Nordic mill that provides district heating, even more additional electricity generation, up to 6%, could be achieved. Provided the availability of sufficient low-temperature heat sinks to use the recovered heat, as well as sufficient condensing turbine swallowing capacity to utilize the LP steam, the use of scrubbing and possibly upgrading the heat using heat pumps appears potentially useful.

Mitigation of global warming, energy security and industrial competitiveness urge the energy-intensive pulp and paper industry (PPI) to transform energy use practices. This study investigates how the PPI has responded to the need for the energy transition in the 2000s. Finland and Sweden as forerunners of energy-efficient operation and decarbonization of the PPI are used as target countries. Understanding of changes in energy consumption is complemented using decomposition analysis (Logarithmic Mean Divisia Index Method) and the energy efficiency index approach. Analysis of companies’ investments in energy technologies is used for explaining changes in energy production. Evidence of significant development towards the more sustainable operation of the PPI was found. Energy consumption per produced unit has decreased, i.e., energy efficiency has improved. Fossil fuels have been partially replaced with bio-based alternatives. Thus, the CO2 intensity has decreased substantially. The generation of renewable electricity has increased in both countries. Examples of Finland and Sweden indicate that the PPI has great potential to contribute to CO2 emission reduction worldwide in the future as energy efficiency can be further improved, and the share of fossil fuels can be decreased increasing the use of biofuels and self-generated green electricity at least in kraft pulp mills.

Bioenergy with CO2 capture and storage (BECCS) is a promising negative emission technology (NET). When using sustainably produced biomass as fuel, BECCS allows the production of power and heat with negative CO2 emissions. The main technical challenges hindering the deployment of BECCS technologies include energy penalties associated with the capture process. This work evaluates the performance of an advanced CO2 capture technology, chemical looping with oxygen uncoupling (CLOU), replacing a conventional fluidized bed boiler in the power boiler role in a large, modern integrated pulp and paper mill. Results from a MATLAB/Simulink reactor model were incorporated in a plant and integration model developed in a commercial process simulation software to quantify the performance of the CLOU-integrated cogeneration plant. The results show that in this specific application, the typically already low efficiency penalty of CLOU-based carbon capture and storage (CCS) systems could be eliminated entirely, and actually even a very small efficiency gain could be obtained. The highly efficient operation is possible due to the high moisture and hydrogen contents of the biomass and the separation of combustion products and excess air streams in the CLOU process; this provides an opportunity to recover a significant amount of heat by flue gas condensation at a higher temperature level than what is possible in a conventional boiler. Together with abundant low-temperature heat sinks available at the pulp and paper application allows freeing a considerable amount of low-pressure steam for expansion in the condensing turbine. The resulting increase in gross generator output proved enough to not only match, but very slightly exceed the approximately 18 MW parasitic load introduced by the CLOU system in comparison to the conventional boiler.

Bioenergy plays an important role in the climate neutrality targets of the EU. However, the status of bioenergy implementation varies greatly across the EU. The aim of this paper is to assess the role of bioenergy in different EU countries using EU experts’ opinions of bioenergy implementation in their own country. The paper identifies leading and lagging countries in biomass development by focusing on the current share of bioenergy in the total energy supply. The study shows differences in bioenergy development between Southern and Western EU countries with Northern and Eastern EU countries. The anti-bioenergy movement and continuing political support for the fossil fuel industry are important barriers inhibiting biomass development in many EU countries, especially in Southern Europe and Western Europe. Our analysis finds that the EU needs more factual bioenergy information and improved promotion of bioenergy throughout society, especially in southern and western parts of the EU. Bioenergy development in the EU can be looked at optimistically, especially in Northern and Eastern Europe. The experience of societal acceptance of bioenergy in countries such as Finland and Sweden is applicable to countries that have thus far seen less progress in bioenergy implementation such as Poland and the Netherlands. Publishers version

Transition towards carbon neutrality will require application of negative carbon emission technologies (NETs). This creates a new opportunity for the industry in the near future. The pulp and paper industry already utilizes vast amounts of biomass and produces large amounts of biogenic carbon dioxide. The industry is well poised for the use of bioenergy with carbon capture and storage (BECCS), which is considered as one of the key NETs. If the captured carbon dioxide can be used to manufacture green fuels to replace fossil ones, then this will generate a huge additional market where pulp and paper mills are on the front line. The objective of this study is to evaluate future trends and policies affecting the pulp and paper industry and to describe how a carbon neutral or carbon negative pulp and paper production process can be viable. Such policies include, as examples, price of carbon dioxide allowances or support for green fuel production and BECCS implementation. It is known that profitability differs depending on mill type, performance, energy efficiency, or carbon dioxide intensity. The results give fresh understanding on the potential for investing in negative emission technologies. Carbon capture or green fuel production can be economical with an emission trade system, depending on electricity price, green fuel price, negative emission credit, and a mill’s emission profile. However, feasibility does not seem to evidently correlate with the performance, technical age, or the measured efficiency of the mill.

Polysulfide pulping is a method to increase the pulp yield in a kraft pulp mill. Higher production is in the core of pulp mill process development, but modifications in cooking raise questions on their effects on the other parts of the process. This study focuses on the impacts of polysulfide pulping on the energy use and production of kraft pulp mills. The impacts are estimated by calculating and analyzing the steam and electricity balances of reference softwood and hardwood mills. Energy generation using residual biomass is an essential part of the operation of a kraft pulp mill, and often a notable source of income. The results show that implementation of polysulfide cooking affects both energy consumption and production. Higher hemicelluloses content of pulp cooked using polysulfide liquor means that less organic material ends up in the black liquor. Subsequently, the recovery boiler energy production suffers. The reduced steam production together with increased steam consumption decreased electricity production, corresponding to a decline in sellable electricity of 22.4 % in the hardwood mill and 28.4 % in the softwood mill. The study shows that increasing the pulp production by investing in polysulfide cooking in stand-alone kraft pulp mills can be economically feasible.

This study evaluates the potential of the oxidative fast pyrolysis (OFP) of eucalyptus wood residues (EWR) for producing bio-oil to replace fossil fuels in the lime kilns of the pulp industry. OFP is an alternative to inert-atmosphere fast pyrolysis where separate heat addition stage is not required. OFP was studied by characterizing the fuel using proximate and elemental chemical analyses, thermogravimetric analysis and heating value. Then, OFP experiments in a pilot-scale autothermal fluidized reactor were done with EWR. Pyrolysis products were gases, bio-char and bio-oil (heavy and light). The gases were burnt, and the energy used for heating the fluidization air. Heavy bio-oil energy yield of 30% and 21.4 MJ kg−1 lower heating value indicate good potential for fuel applications. The results were used to model and evaluate industrial-scale cases. Integration with the pulp mill recovery boiler and steam cycle allows easy recovery of the considerable waste heat from the process itself, as well as the combustion of solid and gaseous residues. Economic analysis indicates profitability for OFP of fine EWRs from the mill. A higher net present value, but longer payback period, was obtained for a larger OFP plant using purchased feedstock. Stand-alone production was found unprofitable. Publishers version

A modern pulp mill generates a variety of different by-products and waste streams, some of these can be recycled, refined, sold, or used on-site for energy production. However, some, such as chemical and biological sludges produced in wastewater treatment cannot be reused or disposed of easily, mainly due to their high moisture content and poor drying characteristics. Tightening legislation regarding waste disposal as well as the growing need to increase the process efficiencies of pulp mills act as driving forces to find environmentally friendly and energy-efficient techniques for pulp mill sludge treatment. This study summarizes the current methods for pulp mill sludge handling and evaluates the potential of hydrothermal carbonization (HTC), a conversion process through which wet organic substrates can be transformed into a carbonaceous material (hydrochar). Depending on the process parameters, the material’s structure is modified, enabling hydrochar use in energy, soil conditioning and adsorption applications. The sludges were hydrothermally carbonized at 180, 200, 220 and 240 °C for 3 h. The hydrochar and liquid products’ main properties were analyzed. Their potential applications were also evaluated. The effective treatment of sludges from the pulp industry with HTC could transform energy-demanding waste into a value-added source of materials.

This work describes and discusses sources of noncondensible gases (NCG) in modern kraft pulp mills and modern NCG collection from process units where odor emissions can occur if these gases are released to the surroundings. A mill-wide overview of NCG sources and collection in modern pulp mills is provided. Using modern practices, malodorous gases can be collected to the extent that a pulp mill is essentially odor free. The key to limiting complaint-causing odors is prevention of these emissions during process disturbances, equipment malfunctions, operator errors, and other unforeseen occurrences.

In this work, the production viability, physical, chemical and mechanical properties of briquettes produced from mixtures of coffee shrub residues and pinewood, were evaluated. The densification was carried out under constant operating conditions (temperature of 120 °C, pressure of 8.27 MPa) in a piston-press type laboratory-scale briquetting machine. Coffee shrub residues were mixed with pinewood in ratios of 25%, 50% and 75%. In addition, reference briquettes of pure pinewood and of each type of coffee shrub residue were produced. To characterize the raw material, ash content, volatile matter, fixed carbon together with the calorific value of produced samples, were measured. To characterize the suitability of the briquettes produced: apparent density, energy density, tensile strength, and equilibrium moisture content were determined. The highest values of energy density (19133–19899 MJ m−3), tensile strength (415–569 kgf), apparent density (1107–1163 kg m−3) and favorable values of equilibrium moisture content (9–11 wt %) were obtained from a mixing ratio of 75% of pinewood. The novel contribution of this research was to develop briquettes with appropriate physical and mechanical parameters from new raw materials that could serve as sustainable fuel sources for local firing systems.

This work aims to assess the adequacy of the often made two dimensional mesh simplification in ash deposition models. Little information is available regarding its validity due to the heavy computational costs that a proper three-dimensional grid model would entail. We have implemented a case study (a deposition probe in a kraft recovery furnace) with 2D and 3D mesh models in order to compare their results regarding the ash deposition and the fluid flow. An additional simulation has been carried out to compare the results between URANS and DES turbulence models. For the particular case studied in this article, the two-dimensional simplification is justified as the results did not vary notably whereas entailing remarkably smaller computational costs. Nonetheless, the usage of DES turbulence model yielded moderately different results, qualitatively closer to deposit observations, justifying perhaps the three-dimensional approach when accuracy is needed for the deposition of fine particles on the lee edges of the tubes. Publisher's version

Chemical quantitative characterization of biomass is relevant for waste to energy recovery technologies. In the present work, selected agroindustry solid residues from coffee crops – parchment and coffee shrub, i.e., stem, branches and leaves – were characterized. Properties such proximate, ultimate and biochemical composition, energy content, and thermogravimetric analysis, were evaluated. Results showed high values of higher heating value and volatile matter content. The silica contents are small for all samples. Additionally, the high content of extractives and lignin, reveal that these residual biomasses are more suitable for charcoal than cellulose pulp production. The extensive residue characterization provided valuable data that helped in outcome of the evaluation of different conversion technologies as being an environmentally friendly alternative, contributing to sustainable, reliable, carbon-neutral form of modern energy and upgrade the large quantity of waste generated by the coffee industry into energetically valued residues, by improving their management.

A refining model is developed to analyses the refining process’s energy efficiency based on the refining variables. A simulation model is obtained for longer-term refining energy analysis by further developing the MATLAB Thermo-Mechanical Pulping Simulink toolbox. This model is utilized to predict two essential variables for refining energy efficiency calculation: refining motor-load and generated steam. The conventional variable for presenting refining energy efficiency is refining specific energy consumption (RSEC), which is the ratio of the refining motor load to throughput and does not consider the share of recovered energy from the refining produced steam. In this study, a new variable, corrected refining specific energy consumption (CRSEC), is introduced and practiced for better representation of the refining energy efficiency. In the calculation process of the CRSEC, recovered energy from the refining generated steam is considered useful energy. The developed model results in 160% and 78.75% improvement in simulation model determination coefficient and error, respectively. Utilizing the developed model and hourly district heating demand for CRSEC calculation, results prove a 22% annual average difference between CRSEC and RSEC. Findings confirm that the wintertime refining energy efficiency is 27% higher due to higher recovered energy in the heat recovery unit compared to summertime.

The objective of this paper is to analyse role of forest industry in meeting energy and climate targets that aim to mitigating global change. Finland as an important forest industry country with the ambitious target of becoming carbon neutral by 2035 is selected to a target county. This study aims to present a plausible assessment of the future of the Finnish forest industry until 2035 based on literature and a scenario building approach. The focus is on energy use and fossil carbon dioxide (CO2) emissions. The results suggest that electricity consumption will decrease, whereas electricity production will increase, which indicates that forest industry can provide more renewable electricity to the grid. Heat consumption may even increase as a result from building new biorefineries, but those mills can most probably meet their heat demand by combusting biofuels. Changes in forest industry’s direct fossil CO2 emissions can reduce Finnish fossil CO2 emissions 2─4% in comparison to 2018. Biofuels production is likely to rise, but the extent remains to be seen. It is concluded that the Finnish forest industry can contribute significantly to meeting national climate policy targets, and forest industry in general can play a role in mitigating global change. Additionally, it was found that development of the Finnish forest industry will probably be limited by the requirement for sustainable wood harvesting, which may also be a problem for other forest industry countries.

European Union set an ambitious 20% target of its energy consumption from renewable resources 20% by 2020. The aim of this paper is to assess the contribution of solid biomass to renewables use in the EU. During 2010–2018 the share of solid biomass increased from 6.1% to 8.0% of total GFEC, an increase of almost 300 PJ. The paper identifies leading and lagging countries in biomass development by focusing on their current solid biomass share in GFEC. The study shows that leading countries have reached or are close to reach their target, while lagging countries are far from their targets. ETS and non-ETS targets play both a role in the growing use of solid biomass. Despite some challenges, the forest biomass sector allows the sustainable increase of bioenergy in the EU, when the harvest level remains below 90% of net annual increment (except for natural disasters) and there is a stable division between fuelwood and harvested wood for solid products. Forests available for wood supply (FAWS) should be treated differently from non-FAWS areas (protected forests, biodiversity areas), because of different carbon dynamics. The EU Member States may wish to introduce a fixed ratio between FAWS and non FAWS areas, in order to optimally meet the corresponding wishes in EU’s forest and biodiversity strategies.

Bioenergy with CO2 capture and storage (BECCS) is a promising negative emission technology (NET). When using sustainably produced biomass as fuel, BECCS allows the production of power and heat with negative CO2 emissions. The main technical challenges hindering the deployment of BECCS technologies include energy penalties associated with the capture process. This work evaluates the performance of an advanced CO2 capture technology, chemical looping with oxygen uncoupling (CLOU), in conjunction with biomass-fired combined heat and power (CHP) generation. Results from a MATLAB/Simulink reactor model were incorporated in a plant and integration model developed in a commercial process simulation software to quantify the key performance indicators of the CLOU-integrated CHP plant. Both energy and exergy analysis were conducted. The results show a remarkably low efficiency penalty of 0.7% compared to a conventional reference plant, and a high carbon capture efficiency of 97%. The low efficiency penalty is due to the high moisture and hydrogen contents of the biomass, and the separation of combustion products and excess air streams in the CLOU process, these together provide an opportunity to recover a significant amount of heat by flue gas condensation at a higher temperature level than what is possible in a conventional boiler. The condensing heat recovery yields an 18 MW generator power increase (3 MW loss in net power output) for the CLOU plant, in the reference plant with conventional boiler, the same scheme could achieve an increase of 9 MW (generator) and a decrease of 8 MW (net).

Upgrading biomass waste streams can improve economics in wood industries by adding value to the process. This work considers use of a hydrothermal carbonization (HTC) process for the residual feedstock after lignin and hemicelluloses extraction. Batch experiments were performed at 200&ndash, 240 &deg, C temperatures and three hours residence time with an 8:1 biomass to water ratio for two feedstocks: Raw spruce and spruce after lignin extraction. The proximate analysis and heating value showed similar results for both feedstocks, indicating that the thermochemical conversion is not impacted by the removal of lignin and hemicelluloses, the pretreatment processing slightly increases the heating value of the treated feedstock, but the HTC conversion process produces a consistent upgrading trend for both the treated and untreated feedstocks. The energy yield was 9.7 percentage points higher for the treated wood on average across the range temperatures due to the higher mass yield in the treated experiments. The energy densification ratio and the mass yield were strongly correlated with reaction temperature, while the energy yield was not. Lignocellulosic composition of the solid HTC product is mainly affected by HTC treatment, the effect of lignin extraction is negligible.

The goal of the study was to develop an optimization methodology combining a cost model, a 2-D heat transfer model, and load variation, executable in a feasible time in a personal computer. The objective function to maximize is the annual net cash flow. For this purpose, the cogeneration plant performance is determined at different load points as a function of the condenser performance using IPSEpro process simulation software. This data is then used to implement the calculation process to obtain the objective function value. Due to the computationally heavy heat transfer model, and each objective function evaluation requiring multiple runs, one per load point, improving optimizer performance was given particular attention. A novel hybridization of cuckoo search and a greedy differential evolution strategy was created for this; the new algorithm is shown to perform better than either of its parent algorithms or other benchmarks, finding optimal solution reliably, and within approximately half the number of function evaluations as required by the parent algorithms.

Russia accounts for approximately 20% of the world's forest cover. More than 59% of the total territory of the Russian Federation is classified as forest land. However, the forest sector contributes only 1.3% to Russian gross domestic product and the Russian forest industry accounts for less than 4% of the world's forest products trade. This paper analyzes the most significant challenges facing Russian forest management including example of wood chips export to the EU and will suggest specific policy proposals that could be made in order to improve the forest management and forest transportation in Russia. Russian forestry has a lot of challenges such as lack of proper forest infrastructure, inadequate forest fire protection, unqualified personnel and unclear legislation. Most of these challenges are linked to one another and solving one problem can lead to the solution of others. The improvement of Russian forest governance is difficult and hard for policy, but without significant changes in current Russian forest management practices, forest degradation in Russia will continue to increase. The degradation of Russian forests could lead to a loss of global resources in general.

The study analyzes a potential to improve the local waste and wastewater management in a Finnish community. The Lappeenranta wastewater treatment plant (WWTP) is used as a case study. Two different technological setups are considered for improving the wastewater treatment plant. These are used to construct four alternative wastewater reclamation scenarios. The mass and energy balances for the considered scenarios are developed and used as input for the profitability evaluation. The utilization of the sewage sludge from the WWTP and municipal solid waste fraction that cannot be recycled for the generation of heat and electricity at the CHP plant is investigated with the aim to improve the economic performance of the wastewater treatment facility. The studied scenarios are initially compared based on their investment and operational costs. The cost of water treatment increases significantly in the case of the investigated tertiary treatment systems: higher amounts of chemicals and electricity are needed to improve the water quality. At the same time, the study indicates that the profitability of a WWTP integrated with a CHP plant can be reasonably high in a wide range of likely price scenarios for alternative wastewater purification systems. The results of the analysis showed a significant potential for the investigated wastewater reclamation systems to improve the efficiency of solid waste and wastewater management in the community.

Wood-fired small- and medium-scale combined heat and power (CHP) plants are a proven technology for producing domestic, carbon-neutral heat and power. Hydrothermal carbonization (HTC) is a promising conversion technology for producing an improved, more versatile wood fuel. By integrating the HTC and CHP processes, the HTC process can be notably simplified. This study compares six different integration schemes to non-integrated plants. The overall energy conversion efficiencies were similar in all six schemes, but there were differences in power output and in plant complexity, and thus likely differences in investment cost and operability. The most promising cases were evaluated at varying HTC temperatures. This comparison showed that temperatures over 220 °C became problematic for the simpler heat recovery schemes, which resulted in poor efficiencies.

Many countries have limited low-cost biomass resources to satisfy their own demand for bioenergy; consequently, international trade in biomass in various liquid and solid forms is ­increasing. The aim of this study is to present a quantitative overview of the development of international biomass trade for energy purposes. This paper focuses on the main biomass producing and consuming countries, as well as exporters and importers of liquid and solid biofuels, such as wood pellets, biodiesel, and bio-ethanol, and biomass products, for example industrial roundwood. The study ­discusses changes in trends that have occurred over the past decade, and investigates emerging energy ­biomass trade streams. Due to increased demand for wood pellets from the heating and ­industrial sectors, global wood pellet markets and international trade have increased significantly in the past decade. The United States and Brazil remain leaders in bio-ethanol production with about 45 Mt and 24 Mt respectively. In recent years, Asian markets such as China (industrial roundwood), South Korea (wood pellets), Malaysia, and Indonesia (palm oil) have developed considerably. In the EU-28, more than 60% of total palm oil consumption is used for energy purposes. The EU is the global leader in biomass for energy utilization and also the main importer of most biomass products, particularly wood pellets.

Spent coffee grounds (SCGs) and tea leaf residues are investigated as a potential source of bioenergy and biochemicals and compared to several woody biomasses. The effect of initial processing (coffee roasting and tea oxidizing) on feedstock composition and thermal behavior is assessed experimentally and analytically. In addition to proximate and ultimate analyses, the materials are examined by combustion tests coupled with Fourier-transform infrared spectroscopy and thermogravimetric analysis coupled with mass spectrometry in oxidizing and inert atmospheres. The biggest differences in composition of the samples are found in the high elemental N and S contents of SCGs (2.9 wt% of N and 0.1 wt% of S on average) and especially tea leaf residues (4.5 wt% of N and 0.2 wt% of S on average). The elevated N and S values lead to NO and SO2 release during combustion. Overall, the obtained levels of reactivity and heating values (with a maximum higher heating value of 24 MJ kg−1 for the Arabica-Robusta coffee blend) confirm the significant energy potential of both the coffee and tea samples. Mass spectrometry analysis of the studied materials reveals higher heterogeneity of macromolecular composition of coffee and tea samples compared to woody biomasses. Pyridine, pyrazine, phenols and acetic acid are the most abundant among detected species and have demonstrated beneficial characteristics for a broad spectrum of human activities. The composition characteristics and reactivity test results presented in this work promote more effective valorization and usage of these currently little used biomass residues.

Many countries have limited, low-cost biomass resources to satisfy their own demand for bioenergy. International trade of biomass in various solid and liquid forms is consequently increasing. The aim of this study is to present a quantitative overview of the development of international biomass trade for energy purposes, including a discussion of methodological issues. The paper focuses on the production, export, and import of solid and liquid biofuels, including industrial roundwood, wood chips, fuel wood, wood pellets, biodiesel, and bioethanol. The study highlights changes in trends that have occurred over the past decade. Trade on global bioenergy markets is increasing: total trade of biomass for energy purposes is estimated as having increased twofold from around 780 PJ in 2004 to 1250 PJ in 2015. Despite the importance of the bioenergy market and the growth of biomass trade for energy, accurate evaluation of energy-related biomass trade faces several methodological challenges, such as uncertainties in international statistics, inconsistent data regarding export and import ­volumes, as well as limited information about the final use of traded products.

Torrefied biomass has considerable potential as a biomass fuel to replace coal in energy and process heat production. The aim of this paper is to evaluate the potential of torrefied biomass in different industries, both power and non-power generation industries, and considers the impact of such use on the international biomass market. The power generation sector has been so far the leader in testing torrefied biomass use with other industrial demand lagging behind. There are promising technical possibilities for greater torrefied biomass use in a number of other areas such as the steel, non-metallic minerals, as well as the pulp and paper industries. Although a large increase in torrefied biomass consumption by industry is not immediately foreseeable, industrial use by actors outside the energy generation sector could increase demand for torrefied biomass in general and, as a result, stimulate development of global torrefied biomass markets. Results show that the torrefied biomass demand significantly depends on the bioenergy markets. It seems that despite of the challenges, the growth of torrefied biomass demand will have a large progress in coming years. Post-print / final draft

Iron oxide pellets are currently one of the main feedstocks in iron-making processes, and increasing over the years. They are mostly produced in moving-grate induration furnaces. Several mathematical models describing the pellet induration process have been published over the last 50 years. Despite being a topic of research for a long period, a relative small amount of journal papers is available in the main academic databases. In addition, the model assumptions have not changed considerably over time, regardless the development of faster computational tools. The purpose of this paper is to provide a review regarding the available mathematical models for travelling-grate iron ore induration furnaces, pointing at some opportunities and aspects to improve the accuracy of these models.

Mathematical models of circulating fluidized bed (CFB) combustion systems vary from simple lumped models to full-scale 3D models with multi-phase flow fields. Models help to predict the behavior of the boiler under new operating conditions and to understand the underlying phenomena. Is it more important to make experiments or models? The answer is both. The real values can be assessed with the help of experiments and refined models. Is a complex model always better than a simple one? A simple model can be more easily modified and better adapted to the actual use. A 1,5-dimensional model of a CFB furnace is the simplest possible model that takes into account the most important heat transfer and flow features. Of these solids circulation is the most important factor that determines the amount of heat transfer at the furnace walls. Consequently, regulating the solids circulation is the fundamental means of load control in CFB furnaces. One dimensional model takes into account only the vertical flow direction, but 1,5-dimensional model considers solids circulation inside the furnace as well. The internal circulation is up to 2 times greater than the circulation around the solids separator and return in CFB combustors. 1,5-dimensional model is also called the core-annulus model. The furnace is considered as a cylinder with an annular space around it. The hot solids flow upwards along the cylinder and downwards along the annular space. In this study, a core-annulus model is implemented using a commercial IPSEpro software. The developed model consists of several modules. The mathematical principles of each module is described. The software is also presented briefly. The new model is applied to study the behavior of a large biomass boiler. The model inputs include mass flows of fuel and air, fuel type and parameters regarding the solids amount, size and distribution. In addition to inputs for the design operation, other scenarios are considered such as partial load and burning of different fuels. Strengths and weaknesses of the model are also assessed and pathways of future research are reviewed.

Biomass conversion via thermal processes to generate energy will be an important part of the future energy landscape. The objective of this study was to determine the kinetic parameters of five types of eucalyptus wood derived from different clones, sugarcane bagasse, elephant grass, bamboo and fibers of coconut fruit. The framework to describe the kinetic pyrolysis consists of a fuel model including four constituents, namely hemicelluloses, cellulose, lignin and extractives. Each pseudo-component was converted via two competing reactions into volatile and char. A statistical fit was achieved with mass loss rate data, obtained from the pyrolysis modeling and the thermogravimetric analysis, providing satisfactory statistical variance. In the end of the kinetic parameters optimization, the activation energies for reaction of hemicelluloses, cellulose and lignin were obtained as 179.98, 130.0 and 40 kJ mol−1, respectively, whereas the decomposition of the pseudo-components resulted in relatively similar values of pre-exponential factor for all biomasses evaluated. The experimental results and kinetic parameters provide useful data to improve design of thermochemical conversion units.

This work is concerned with the research field of ash deposition phenomena. An unsteady CFD model of the convective section of a 100-kW PC pilot-scale combustor is implemented aiming to simulate and study the ash deposition trends. Emphasis is placed at analyzing how particles of different sizes may contribute differently to the deposit buildup. A discrete particle tracking and a rebound–stick submodel are used. Four simulation cases are implemented to investigate the effect of the inlet flow velocity and the fouling conditions (clean vs. fouled tubes). The sticking efficiencies decreased with the particle diameter d p after being constant and higher than 95% for d p 1 μ m. It also seemed to decrease with the flue gas inlet velocity. The normalized particle arrival rates to the tubes were rather constant up to particle sizes of d p = 8 μ m. The studied cases of faster flow inlet velocity showed higher values for both the deposition and arrival trends as a consequence of a higher overall particle Stokes’ number and the total ash mass input to the model. The cases with fouled tubes presented higher deposition rates (approximately, 7.91% more for the fast velocity case) than what is observed for clean tubes.