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The production of heterogeneous solid waste, such as municipal solid waste (MSW), construction and demolition waste (CDW), and industrial solid waste (ISW), has increased dramatically in recent decades, and its management is one of today’s biggest concerns. Using waste as a resource to produce value-added materials such as char is one of the most promising strategies for successful and sustainable waste management. Virtually any type of waste, through various thermochemical technologies, including torrefaction, pyrolysis, hydrothermal carbonization, and gasification, can produce char with potential material and energy applications. Pyrolysis is the most widespread technology, and there are more studies on producing and applying waste-derived char using this technology. The properties of waste-derived char seem to be influenced by the conversion technology and conditions, as well as by the composition of the source waste. A literature search indicated that the properties of waste-derived char are highly variable with the composition of the raw material, with carbon content in the range 8–77%, a higher heating value of 2.5–28.4 MJ/kg and a specific surface area of 0.7–12 m2/g. Depending on the properties of char derived from waste, there are greater or minor difficulties in applying it, with ash content, heavy metals, and polycyclic aromatic hydrocarbon (PAH) concentrations being some of its limiting properties. Therefore, this review attempts to compile relevant knowledge on the production of waste-derived char, focusing on heterogeneous solid waste, applied technologies, and practical application routes in the real world to create a supply chain, marketing, and use of waste-derived char. Some challenges and prospects for waste-derived char are also highlighted in this study.

Process design critically depends on the characterization of fuels and their kinetics under process conditions. This study steps beyond the fundamental methods of thermogravimetry to modulated (MTGA) and Hi-Res™ (high resolution) techniques to (1) add characterization detail and (2) increase the utility of thermal analysis data. Modulated TGA methods overlay sinusoidal functions on the heating rates to determine activation energy as a function of temperature with time. Under devolatilization conditions, Hi-Res™ TGA maintains a constant mass loss with time and temperature. These two methods, run independently or overlaid, offer additional analysis in which multiple samples at different heating rates are run to different final temperatures. Advanced methods allow researchers to use fewer samples by conducting fewer runs, targeting practical experimental designs, and quantifying errors easier. The parameters of the studies included here vary the heating rate at 10, 30, and 50 °C/min; vary gas-phase oxygen for pyrolysis or combustion conditions; and particle size ranges of 100–125 µm, 400–425 µm, and 600–630 µm. The two biomass fuels used in the studies are pinewood from Northern Sweden and wheat straw. The influence of torrefaction is also included at temperatures of 220, 250, and 280 °C. Apparent activation energy results align with the previous MTGA data in that combustion conditions yield higher values than pyrolysis conditions—200–250 kJ/mol and 175–225 kJ/mol for pine and wheat combustion, respectively, depending on pre-treatment. Results show the dependence of these parameters upon one another from a traditional thermal analysis approach, e.g., the Ozawa-Flynn-Wall method, as well as MTGA and Hi-Res™ thermogravimetric investigations to show future directions for thermal analysis techniques.

The treatment of wastewater worldwide generates substantial quantities of sewage sludge (SS), prompting concerns about its environmental impact. Various approaches have been explored for SS reuse, with energy production emerging as a viable solution. This study focuses on harnessing energy from domestic wastewater treatment (WWT) sewage sludge through plasma gasification. Effective syngas production hinges on precise equipment design which, in turn, depends on the detailed feedstock used for characterization. Key components of plasma gasification include the plasma torch, reactor, heat exchanger, scrubber, and cyclone, enabling the generation of inert slag for landfill disposal and to ensure clean syngas. Designing these components entails considerations of sludge composition, calorific power, thermal conductivity, ash diameter, and fusibility properties, among other parameters. Accordingly, this work entails the development of an experimental setup for the plasma gasification of sewage sludge, taking into account a comprehensive sludge characterization. The experimental findings reveal that domestic WWT sewage sludge with 40% humidity exhibits a low thermal conductivity of approximately 0.392 W/mK and a calorific value of LHV = 20.78 MJ/kg. Also, the relatively low ash content (17%) renders this raw material advantageous for plasma gasification processes. The integration of a detailed sludge characterization into the equipment design lays the foundation for efficient syngas production. This study aims to contribute to advancing sustainable waste-to-energy technologies, namely plasma gasification, by leveraging sewage sludge as a valuable resource for syngas production.

Ghana is currently facing a waste crisis that presents considerable risks to its environment, economy, and public health. This investigation evaluates four prospective waste-to-energy options—namely, incineration, anaerobic digestion, gasification, and landfill gas—with the objective of mapping out a sustainable strategy for efficient waste management. Among these solutions, anaerobic digestion stands out as a superior option, offering renewable energy production, valuable bio-product creation, and a comparatively lower greenhouse gas emission effect. A cost analysis further reveals that utilizing biogas from anaerobic digestion is not only environmentally friendly but also economically more viable than relying on light crude oil. Producing 200 MW of energy using biogas costs 36% less, potentially resulting in monthly savings of USD 5.46 million for Ghana. However, several obstacles impede the development of WtE. Inaccurate waste data and a lack of clear policies on waste-to-energy hinder the harnessing of Ghana’s WtE potential. To address this, the study recommends (1) implementing a well-defined national strategy complete with regulations and incentives to attract investments and (2) conducting specialized research to optimize WtE technologies for Ghana’s unique waste composition and context. By surmounting these challenges, Ghana stands poised to secure a sustainable future, simultaneously meeting the targets of Sustainable Development Goals 7 and 11. This entails ensuring access to affordable, reliable, sustainable, and modern energy for all (SDG 7) and fostering inclusive, safe, resilient, and sustainable cities and human settlements (SDG 11).

In a circular economy, significant emphasis is given to the energetic valorization of agricultural byproducts. Cotton stalks are suitable as a feedstock for the production of bioenergy due to their high energy content. This study’s main focal areas are the economic viability and environmental implications of a system that can gasify or pyrolyze 25,500 tons of cotton stalk annually. To learn more about how gasification and pyrolysis affect the environment, a life cycle assessment (LCA) was conducted. This analysis evaluates the whole value chain and covers all stages of the cotton supply chain from cradle to gate, including production, harvest, transportation, and utilization. According to the findings, both systems exhibit economic viability, generating sizable profits and having quick payback times. However, despite its larger initial expenditure of EUR 2.74 million, the pyrolysis unit ends up being the better option because it has a payback period of 1.58 years, a return on investment (ROI) of 58% and a net present value (NPV) of EUR 21.5 million. Gasification is still an economically attractive alternative with a lower initial investment (EUR 1.81 million), despite having a lower ROI (36%) and NPV (EUR 10.52 million), as well as a longer payback period (2.41 years). However, the environmental implications of the gasification option are generally higher than those of pyrolysis. The impacts of gasification on fossil depletion (FDP) were estimated to be 5.7 million kg oil eq., compared to 5.3 million kg oil eq. for pyrolysis. Similarly, gasification resulted in 41.55 million kg U235 eq. and pyrolysis in 41.5 million kg U235 eq. related to impacts on ionizing radiation (IRP_HE). Other impact categories that emerge as the most important are freshwater eutrophication (FEP) and marine eutrophication (MEP).

A conceptual design of coffee stem biomass gasification was developed using the Aspen Plus process simulator, which was analyzed based on energy criteria such as the lower heating value of the produced synthesis gas and cold gas efficiency. The results yielded a lower heating value of 5.07 kJ/MJ, with a cold gas efficiency of 77.45% and a yield of 2.75 kg gas/kg biomass, all operating under optimal conditions with studied parameters including an air-to-biomass ratio between 1.8 and 2.5, gasifying agent temperature of 260 °C, and biomass moisture content below 10%. A sensitivity analysis was conducted on the formation of the most important compounds for synthesis gas quality (H2, CO, CO2, H2O, CH4). This involved understanding the reactions occurring throughout the gasification reactor and evaluating process parameters such as feed moisture content, gasification section temperature, and the ratio between feed and gasifying agent flows to optimize the process with the aim of improving product quality and reducing residue formation. The simulation scheme was validated against experimental data, yielding results consistent with reality. This contributed valuable information towards process optimization for projects targeting the Colombian coffee sector, paving the way for future gasifier designs tailored to the quantity of raw material to be processed.

With increasing efforts to lower CO2 emissions globally, the demand for carbon-based resources in industries remains on a high level, leading to new technologies being able to provide those essential carbon sources. To the best of our knowledge, we were able to show for the first time the adaption of a readily available gasifier for the gasification of wood chips using only O2 (18.4–23.1 Vol.-%) and CO2 as gasification agents, creating a nitrogen-free product gas. It was found that the setup used was able to convert up to 27.2% of the CO2 from the gasification agent to CO, creating a promising route for the production of renewable carbon sources for future carbon-based applications. Furthermore, no decrease in gasification performance was observed as the cold gas efficiency was at 83.5–95.5% with only minor formation of tar.

This review examines the potential of municipal solid waste (MSW) as a renewable energy source, focusing on recent advances in thermochemical conversion technologies and their environmental impacts. The exponential growth of urban populations has led to a surge in MSW, necessitating sustainable waste management solutions. Traditional disposal methods, such as landfilling and incineration, have significant environmental drawbacks. However, advancements in waste-to-energy (WtE) technologies, including incineration, pyrolysis, and gasification, offer promising alternatives for energy recovery and resource utilization. This review explores the composition of MSW, its classification as a renewable resource, and the thermochemical conversion technologies that transform waste into energy. The environmental impacts of these technologies, particularly emissions and air quality concerns, are critically analyzed. The review highlights the evolving regulatory landscape and the implementation of advanced emission reduction systems. The findings underscore the importance of integrating innovative waste management strategies to promote a circular economy and achieve sustainable development goals.

To increase the carbon conversion of char in gasification, this paper aimed to reveal the gasification behaviours of char residues. Char residues with different ash contents in this work were prepared from Shenmu char and Tejing char. Those char residues were gasified by different CO2 gas mixtures at different temperatures. The gasification process of char residue was different from the end stage of the gasification process of the corresponding raw char: the gasification rate of the char residue increased at first and then decreased, whereas the gasification rate of the corresponding raw char kept decreasing during the end stage of gasification. The highest gasification rate was achieved at a lower conversion in the gasification of char residue than in the gasification of the corresponding raw char. Catalytic minerals, high temperature, and high CO2 partial pressure benefited the gasification of gasified char residues. The char residues that contained more catalytic minerals were more reactive in gasification and were less sensitive to changes in temperature and CO2 partial pressure. The Modified Random Pore Model (MRPM) and Random Pore Model (RPM) were used to predict the gasification kinetics of the chars, and the MRPM describes the gasification processes of gasified char residues well.

With the increasingly serious problems of energy shortage and environmental degradation, countries around the world are actively developing safe, environmentally friendly, and renewable energy. Biomass energy has become an ideal substitute for fossil fuels due to its abundant reserves, good renewable performance, and zero carbon emissions. This paper discusses the importance and potential of biomass energy as a renewable energy source for China’s energy development, mainly including the three biomass conversion methods of physics, chemistry, and biology, seven utilization technologies, such as direct combustion, gasification, and pyrolysis, and five application approaches, such as biomass power generation, biomass gas fuel, biomass liquid fuel, and bio-based materials. This review systematically analyzes the challenges faced by China’s development of biomass energy and discusses the future development direction of biomass. The utilization of biomass resources should take a comprehensive and high-value path. China is actively looking for new energy utilization paths, and biomass energy has become a key measure to cope with carbon emission reduction, climate change, and ecological environment protection.

The increasing amount of sewage sludge produced demands new methods of its management to minimize socioeconomic and environmental problems related to its current treatment. An effective solution may be the thermochemical conversion of sewage sludge through gasification. First, the most known sewage sludge gasification processes are presented along with the challenges that they face. Then the detailed characteristics of sewage sludge are discussed from the point of view of its use in the gasification process, as well as research on the kinetics of gasification of sewage sludge char using various models. As scientific reports on sewage sludge gasification focus on the influence of process parameters on gas yield and composition (especially H2 and tar content), the main part of the work is devoted to the discussion on the influence of temperature, type, and amount of the gasifying agent and the presence of a catalyst on these parameters. Moreover, the co-gasification of sewage sludge as well as advanced gasification methods, i.e., supercritical water gasification and plasma gasification, are analyzed. Finally, the possibilities of utilization of sewage sludge gasification process by-products were discussed and the impact of the process on the environment was assessed. The review concludes with indications of directions for further research.

The present study compares the performance of bubbling-bed updraft and a fixed-bed downdraft gasification systems for producing hydrogen-rich (H2) syngas from olive pomace on a semi-industrial scale. The focus is on examining the effects of temperature and efficiency ratio (ER) on the composition, low heat value (LHV), carbon conversion efficiency (CCE), and cold gas efficiency (CGE) of the produced syngas. The results presented for the fixed bed show the concentration of H2 (15.6–16.52%), CGE (58.99–66.80%), CCE (69.07–71.86%), and LHV (4.82–5.70 MJ/Nm3). The CGE reaches a maximum of 66.80% at a temperature of 700 °C and an ER of 0.20, while the syngas yield (2.35 Nm3/kg) presents a maximum at a temperature 800 °C and an ER of 0.21, with a tendency to decrease with the increase in the temperature. For the bubbling fluidized bed, results were shown for the concentration of H2 (12.54–12.97%), CGE (70.48–89.51%), CCE (75.83–78.49%), and LHV (6.10–6.93 MJ/Nm3), where, at a temperature of 700 °C and an ER of 0.23, the CGE is 89.51% and the LHV is 6.93 MJ/Nm3, with a tendency to decrease with the increase in the temperature, while the maximum syngas yield (2.52 Nm3/kg) occurs at a temperature of 800 °C and an ER of 0.23. Comparing the two gasification processes, the fixed bed has a higher concentration of H2 at all the temperatures and ERs of the experiments; however, the bubbling fluidized bed has a higher CGE. These findings have implications for applications involving syngas, such as energy production and chemical synthesis, and can guide process optimization and enhance energy efficiency. The information obtained can also contribute to emission mitigation strategies and improvements in syngas-based synthesis reactors.

Energy is a crucial factor for urban development. Cities have a crucial role in climate change, as they use 2/3 of the world’s energy, producing 70% of greenhouse gas (GHG) emissions. In order to reduce the large ecological footprint of the utilization of conversional energy sources (coal, gas, and oil) and enhance a nation’s energy independence (security), it is crucial to find alternative fuels. Biomass residues are characterized as a sustainable and carbon-neutral energy source. Hence, this review describes a critical assessment of not only the quality characteristics of several waste and biomass residues for bioenergy production and biofuels but also the value-added products that could be produced from wastes to enhance industry (e.g., pharmaceutical, cosmetics, packaging industry, etc.). Furthermore, the challenges and potential solutions of waste utilization for bioenergy production and the transformation of value-added products for urban sustainability are also explored. Despite the high-quality characteristics and the availability of these wastes, several critical factors should be taken into account. Biomass residues could contribute to sustainable development goals (SDG), such as sustainable cities and communities, clean energy, responsible consumption and production, the economic growth of a country, and, as a result, urban development.

The gasification of olive cake is a promising method for converting this material into valuable energy. This work offers interesting results about the effect of equivalence ratio and temperature on the composition and quality of the produced gas obtained during olive cake gasification in a fluidized bed plant with air as a gasification agent. Additionally, the efficiency of the gasification process was evaluated. The results show that, for a specific temperature, an equivalence ratio of 0.3 showed a higher cold gas efficiency. For example, at 850 °C and an equivalence ratio of 0.1, the cold gas efficiency was 22.7%; however, at the same temperature but at an equivalence ratio of 0.3, the cold gas efficiency was increased to 61.2%. In addition, for a constant equivalence ratio, by increasing the operating temperature, there was no significant increase in the lower heating value of the exit gas, and the gas flow was practically constant with temperature, but it varied substantially with the equivalence ratio, reaching values in the range of 3.44–14.89 NL/min (825.6–3573.6 NL/kg feed). Finally, the production of CO, H2, and CH4 is estimated to be higher for tests conducted with an equivalence ratio of 0.3.

This paper presents an innovative mathematical model of solid fuel gasification, which is not described in the available literature. The calculation of the components of the heterogeneous phase (including both solid and gaseous phases) as well as the calculation of the homogeneous phase (only gaseous components) is based on the balance of the total amounts of carbon, oxygen, hydrogen, and nitrogen entering the reactor space. Additionally, this paper introduces a new method for calculating the composition of the gaseous phase, based on reducing the heterogeneous mixture (composed of solid and gaseous phases) to a homogeneous gaseous phase. This approach to calculating the gaseous phase composition in the solid fuel gasification process has not been found by the authors in the cited literature. This paper also presents a model for calculating the heterogeneous and gaseous phases using the number of moles that participate in the assumed chemical reactions of the solid fuel gasification process. This approach to calculating the composition of the heterogeneous and gaseous phases of the solid fuel gasification process is also not represented in the cited literature. For comparison with the literature data, municipal solid waste (MSW) and cashew nut shell (Cashew Shell Char (CNSC)) were used as fuels in the calculation of gasification composition. The results of the calculation of the gaseous phase composition using the model presented in the paper show good agreement with the data from the literature. The calculation of the composition of the heterogeneous mixture during the steam gasification of MSW (α = 0.4) shows the presence of a solid phase (carbon) up to approximately 735 °C. At that temperature, the synthetic gas contains only gaseous components: CO = 33.10%, H2 = 52.70%, CH4 = 2.54%, CO2 = 4.97, H2O = 5.93% and N2 = 0.76%. Increasing the temperature above 735 °C eliminates the solid phase from the equilibrium mixture. The literature data on solid fuel gasification generally do not consider the proportion of the solid phase (carbon) in the equilibrium mixture. To satisfy the material balance at the input and output of the gasification reactor, it is necessary to determine the proportion of the solid phase (carbon) in the equilibrium mixture. Since the proportion of the solid phase (carbon) in the heterogeneous equilibrium mixture can only be determined through measurement, the development and application of a mathematical model in engineering practice is of great importance, so this developed model can be considered a useful tool for simulating the influence of process parameters on gas characteristics.

This study aims to provide an overview of the growing need for renewable energy conversion and aligns with the broader context of environmentally friendly energy, specifically through producing syngas from biomass. Unlike natural gas, which is mainly composed of methane, syngas contains a mixture of combustible CO, H2, and CnHm. Therefore, optimizing its production requires a thorough examination of various operational parameters such as the gasifying agent, the equivalence ratio, the biofuel type, and the state, particularly in densified forms like pellets or briquettes. As new biomass sources are continually discovered and tested, operational parameters are also constantly evaluated, and new techniques are continuously developed. Indeed, these techniques include different gasifier types and the use or non-use of catalysts during biofuel conversion. The present study focuses on these critical aspects to examine their effect on the efficiency of syngas production. It is worth mentioning that syngas is the primary gaseous product from gasification. Moreover, it is essential to note that the pyrolysis process (prior to gasification) can produce, in addition to tar and char, a mixture of gases. The common feature among these gases is their versatility in energy generation, heat production, and chemical synthesis. The analysis encompasses the resulting gas features, including the yield and composition, mainly through the hydrogen-to-carbon monoxide ratio and the carbon monoxide-to-carbon dioxide ratio, as well as the lower heating value and considerations of the tar yield.

In recent decades, growing energy demand, coupled with concerns about climate change, has led to the exploration of sustainable energy sources. Among these, biomass gasification stands out as a promising method for generating heat and power. This research delves into the potential impact of biomass gasification within the global energy landscape, focusing particularly on its application in cogeneration plants. Utilizing Aspen Plus software V10, this study undertook the modeling and optimization of a biomass cogeneration plant. Through simulation, it was found that a biomass flow rate of 5 kg/s yielded 6.172 MW of power output. Additionally, the study revealed several key factors that influence power generation: increasing biomass and airflow rates, increasing gasification temperature, and reducing water flow rate. By doubling the biomass flow rate to 10 kg/s and increasing the temperature to 800 °C, power generation increases by 41.75%. Moreover, the study demonstrates that Portuguese municipal waste is an efficient source of energy production, with higher cold gas and overall efficiencies compared to forest and vine-pruning residues.

Computational modeling is a powerful tool for studying and investigating the behavior of fluidized bed gasifiers and the modeling of the initial devolatilization step is necessary to provide a reliable description of the whole process involving the feedstock decomposition and the subsequent gasification reaction. In this work, a bench-scale fluidized bed reactor was used to examine the devolatilization of different carbonaceous materials within the temperature range from 650 to 850 °C. The experimental test campaign was used to derive the linear correlation factor to describe the devolatilization in terms of product distribution as a function of temperature and highlight the different behavior between lignocellulosic and plastic feedstocks. Furthermore, the experimental data were used to develop concise kinetic expressions able to fit the experimental devolatilization times ranging from 75 in the case of poplar at a lower temperature and 22 s for the Organic Fraction of Municipal Solid Waste (OFMSW) at a higher temperature. The obtained model produces a simple kinetic expression where the size of the particle is enclosed in the kinetic parameters. The kinetic model sided by the application of linear correlations describes the overall thermal decomposition in a fluidized bed, simplifying its modeling in commercial simulation software, even when particles are considered as point-like bodies.

Solution plasma is a gas-phase discharge in the vapor bubbles in a solution and has the potential to efficiently produce H2 by decomposing aqueous alcohols. However, the mechanism of alcohol decomposition in solution plasma remains unclear. In this study, lower monohydric alcohols (methanol and ethanol, as well as 1- and 2-propanol) were treated in solution plasma, and in this paper, the gasification mechanism is discussed. The gases produced from these alcohols were mainly H2 and CO, with small ratios of C1–C3 hydrocarbons. Thus, the O/C ratio in the product gas was close to 1 for all alcohols, and most of the C atoms in the alcohols were bonded to O atoms. This excess of O atoms could have only come from water, suggesting a strong contribution of OH radicals from water for gasification. However, the C1–C3 hydrocarbons were produced solely by the decomposition of the alcohol. For both decomposition routes, possible reaction pathways are proposed that are consistent with the experimental facts such as the composition of the product gas and the intermediates detected.

Reported in the article is further progress in the development of the novel pulsed detonation gun (PDG) technology for the conversion of organic wastes into syngas in a two-component gasifying agent (GA) containing ultra-superheated steam and carbon dioxide obtained by pulsed detonations of a natural gas–oxygen mixture at a frequency of 1 Hz. Experimental studies were carried out on a waste converter with a 40 dm3 flow reactor and two PDGs with a total volume of 2.4 or 3.2 dm3, which is approximately a factor of 6 and 4.5 less than in previous studies, respectively. The objective of the research was to find the design and operation parameters of the waste converter that provide a minimum amount of CO2 in the gasification products. Waste machine oil was used as a feedstock. It is shown that, compared with the earlier experiments with a higher average temperature of the reactor wall and with a PDG of a much larger volume, the contents of H2, CO, CH4, and CO2 in the syngas remained virtually unchanged, whereas the efficiency of the gasification process increased significantly: the use of 1 g of natural gas made it possible to gasify up to 4 g of the feedstock. It is also shown that the determining role in the gasification process of liquid feedstock is played by the feedstock residence time in the PDG rather than in the reactor. The minimum ratio between the flow rates of the GA and liquid feedstock, the minimum ratio between the flow rates of combustible gas and liquid feedstock, as well as the actual GA consumption in the gasification process are determined experimentally.

Sewage sludge to energy conversion is a sustainable waste management technique and a means of militating against the environmental concerns associated with its disposal. Amongst the various conversion technologies, anaerobic digestion and gasification have been identified as the two most promising. Therefore, this study is focused on a detailed evaluation of the anaerobic digestion and gasification of sewage sludge for energy production. Moreover, the key challenges hindering both technologies are discussed, as well as the practical measures for addressing them. The applicable pretreatment measures for efficient transformation into valuable energy vectors were further evaluated. Specifically, the study evaluated various properties of sewage sludge in relation to gasification and anaerobic digestion. The findings showed that a high ash content in sewage sludge results in sintering and agglomeration, while a high moisture content promotes tar formation, which has been identified as one of the key limitations of sewage sludge gasification. More importantly, the application of pretreatment has been shown to have some beneficial features in promoting organic matter decomposition/degradation, thereby enhancing biogas as well as syngas production. However, this has additional energy requirements and operational costs, particularly for thermal and mechanical methods.

The formulation of the CFD-DEM model, CD-MELT, is established in this study to include three-phase non-isothermal processes with simultaneous combustion and melting for gasification simulations. To demonstrate the model capability, CD-MELT is used to assess the need for slag recycling for the non-isothermal melting of municipal solid wastes (MSW) in a prototype waste-to-energy research facility. The simulation encompasses the full fixed-bed slagging gasification process, including chemical reactions and melting of MSW and slag. In order to assess the need for slag recycling, comparisons are made for the two cases of with and without, in terms of the slag mass, liquid slag volume fraction, exit gas composition, and temperature distribution in the gasifier. The prediction results enable the tracking of liquid molten slag as it permeates through the solids-packed bed for the first time in the literature as far as we are aware, which is crucial to address design considerations such as distribution of bed temperature and optimal location for slag-tap holes at the bottom, as well as potential slag clogging within the porous media. The model also predicts an uneven and intermittent slag permeation through the packed bed without the recycling, and provides a plausible explanation for the operators’ experience of why slag recycling is important for process stability. Finally, the predicted slag outlet temperature using the proposed CFD approach also agrees well with the measurement data published in an earlier case study for the same facility.

The Adrar region (Algeria) has a total of 397,800 date palm trees (Phoenix dactylifera L.). Due to annual palm cleaning, large quantities of lignocellulosic biomass are produced. Depending on the variety, an average of 65 kg of biowaste is obtained per palm tree. Since the value of this biowaste is underrated, most of the palms are burned outdoors, causing air and visual pollution. This work explores the gasification potential of lignocellulosic waste from date palms (Phoenix dactylifera L. Takarbouche variety) into useful energy. The technology investigated is air updraft fixed-bed gasification, thanks to an originally designed and built reactor, with the capability to process 1 kg of feedstock. Four types of palm waste—namely, palms, petioles, bunch, and bunch peduncles—are first characterized (bulk density, proximate analysis, fixed carbon, elemental composition, and calorific value) and then used as feedstock for two gasification tests each. The syngas produced for the four date palm wastes is combustible, with an outlet temperature between 200 and 400 °C. The operating temperature inside the gasifier varies according to the feature of the biomass cuts (from 174 °C for the peduncles to 557 °C for palms). The experimental setup is also equipped with a cyclone, allowing for the recovery of some of the tar produced during the tests. Finally, the results show that the residence time has a positive effect on the conversion rate of date palm waste, which can significantly increase it to values of around 95%.

This article establishes a thermodynamic model of a dual-fluidized bed biomass gasification process based on the Aspen Plus software platform and studies the operational control characteristics of the dual-fluidized bed. Firstly, the reliability of the model is verified by comparing it with the existing experimental data, and then the influence of different process parameters on the operation and gasification characteristics of the dual-fluidized bed system is investigated. The main parameters studied in the operational process include the fuel feed rate, steam/biomass ratio (S/B), air equivalent ratio (ER), and circulating bed material amount, etc. Their influence on the gasification product composition, reactor temperature, gas heat value (QV), gas production rate (GV), carbon conversion rate (ηc), and gasification efficiency (η) is investigated. The study finds that fuel feed rate and circulating bed material amount are positively correlated with QV, ηc, and η; ER is positively correlated with GV and ηc but negatively correlated with QV and η; S/B is positively correlated with GV, ηc, and η but negatively correlated with QV. The addition of CaO is beneficial for increasing QV. In actual operation, a lower reaction temperature in the gasification bed can be achieved by reducing the circulating bed material amount, and a larger temperature difference between the combustion furnace and the gasification furnace helps to further improve the quality of the gas. At the same time, GV, ηc, and η need to be considered to find the most optimized operating conditions for maximizing the benefits. The model simulation results agree well with the experimental data, providing a reference for the operation and design of dual-fluidized beds and chemical looping technology based on dual-fluidized beds.

With the increase in the world population and economic activity, the production of sewage sludge has grown, and its management has become an environmental problem. The most traditional method of managing sewage sludge is to dispose of it in landfills and on farmland. One way to valorize sewage sludge is to use thermochemical conversion processes to produce added-value products such as biochar, biofuels, and renewable gases. However, due to the high moisture content, thermochemical conversion using processes such as pyrolysis and traditional gasification involves multiple pre-treatment processes such as material drying. Hydrothermal thermochemical processes usually require high pressures, which pose many challenges to their application on a large scale. In this work, the advantages and disadvantages of the different existing thermochemical processes for the recovery of sewage sludge were analyzed, as well as the resulting industrial and environmental challenges. A SWOT analysis was carried out to assess the different thermochemical processes in terms of technical feasibility, economic viability, and broader market considerations.

For achieving CO2 thermal reduction, a technology combining solid carbon activation and high-temperature CO2 reduction was proposed, named as activated-reduction technology. In this study, this technology is realized by using a circulating fluidized bed and downdraft reactor. Reduced agent parameters (O2/C and CO2 concentration) greatly affect the reduction effect of CO2. In addition, the effect of the activation process on different carbon-based materials can help to broaden the range of carbon-based materials used for CO2 reduction, which is also an important issue. The following three points have been studied through experiments: (1) the influence of the characteristics of the reduced agent (CO2 concentration and O2/C) on CO2 reduction; (2) the performance of different chars in CO2 reduction; and (3) the activation effect of solid carbon. The activation process can develop the pore structure of coal gasification char and transform it into activated char with higher reactivity. The CO concentration in the tail gas is a crucial factor limiting the effectiveness of CO2 reduction, with an experimentally determined upper limit of around 55% at 1200 °C. If CO concentration is far from the upper limit, temperature becomes the significant influencing factor. When the reduced agent O2/C is 0.18, the highest net CO2 reduction of 0.021 Nm3/kg is achieved at 60% CO2 concentration. When the reduced agent CO2 concentration is 50%, the highest net CO2 reduction of 0.065 Nm3/kg is achieved at 0.22 O2/C. Compared with CPGC, YHGC has higher reactivity and is more suitable for CO2 reduction. The activation process helps to reduce the differences between raw materials.

The thermodynamic modeling of waste oil (WO) gasification by a high-temperature gasification agent (GA) composed of an ultra-superheated H2O/CO2 mixture is carried out. The GA is assumed to be obtained by the gaseous detonation of fuel–oxidizer–diluent mixture in a pulsed detonation gun (PDG). N-hexadecane is used as a WO surrogate. Methane or the produced syngas (generally a mixture of H2, CO, CH4, CO2, etc.) is used as fuel for the PDG. Oxygen, air, or oxygen-enriched air are used as oxidizers for the PDG. Low-temperature steam is used as a diluent gas. The gasification process is assumed to proceed in a flow-through gasifier at atmospheric pressure. It is shown that the use of the detonation products of the stoichiometric methane–oxygen and methane–air mixtures theoretically leads to the complete conversion of WO into a syngas consisting exclusively of H2 and CO, or into energy gas with high contents of CH4 and C2-C3 hydrocarbons and an LHV of 36.7 (fuel–oxygen mixture) and 13.6 MJ/kg (fuel–air mixture). The use of the detonation products of the stoichiometric mixture of the produced syngas with oxygen or with oxygen-enriched air also allows theoretically achieving the complete conversion of WO into syngas consisting exclusively of H2 and CO. About 33% of the produced syngas mixed with oxygen can be theoretically used for PDG self-feeding, thus making the gasification technology very attractive and cost-effective. To self-feed the PDG with the mixture of the produced syngas with air, it is necessary to increase the backpressure in the gasifier and/or enrich the air with oxygen. The addition of low-temperature steam to the fuel–oxygen mixture in the PDG allows controlling the H2/CO ratio in the produced syngas from 1.3 to 3.4.

In this work, a simplified comprehensive three-dimensional numerical model is developed to study the effect of hydrogen production on co-gasification of biomass and low-density polyethylene (LDPE). CFD software AVL Fire 2020 inbuilt algorithms were employed to develop the gas phase while the solid phase was developed by user-defined FORTRAN subroutines. Solid hydrodynamics, fuel conversion, homogenous and non-homogenous chemical reactions, and heat transfer, including radiation, subroutines were defined and incorporated into AVL FIRE explicitly. Species concentrations of the syngas were analyzed for co-gasification of Beechwood and LDPE for three distinct types of bed materials (silica sand, Na-Y zeolite, and ZSM-5 zeolite). Then, the model is validated with experiment results available in the literature for a lab-scale fluidized bed reactor. The highest hydrogen production was observed in Na-Y zeolite followed by ZSM-5 zeolite and silica in both numerical and experimental analysis for the co-gasification of Beechwood and LDPE, providing a reasonable agreement between the numerical and the experimental results. Therefore, the current model predicts the enhancement of the quality of hydrogen-rich syngas through the application of co-pyrolysis within a fluidized bed reactor, incorporating a catalytic bed material.

This study investigates gasification using wood chips (WC) and corn cobs (CC) for hydrogen-rich syngas production. A simulation model developed in Aspen Plus was used to evaluate the performance of biomass gasification. The model incorporates a system of Fortran subroutines that automate the definition of input parameters based on the analysis of biomass composition. Furthermore, the model’s equilibrium constants were adjusted based on experimentally measured gas concentrations, increasing the precision of the variations. The numerical results predicted hydrogen yields of 65–120 g/kg biomass, with 60–70% energy efficiency for steam gasification (versus 40–50% for air gasification). The hydrogen concentration ranged from 34% to 40%, with CO (27–11%), CO2 (9–20%), and CH4 (CO2 emissions by up to 20%. Higher biomass moisture content promoted hydrogen production by up to 15% but reduced energy efficiency by up to 10% if excessive. Steam gasification with wood chips and corn cobs shows promising potential for hydrogen-rich syngas production, offering benefits such as reduced emissions (up to 30% less CO) and sustainability by utilizing agricultural residues.

The main energy used today is fossil energy which is decreasing and cannot be replaced. Meanwhile, the Indonesian people themselves are facing a problem as well as a great opportunity, namely, plastic waste and the potential of use rice husks, respectively. This study aimed to determine the most effective flame and most effective temperature for combustion in rice husk gasification, and to determine the temperature in the distillation reactor, and then to determine the mass of oil produced from the pyrolysis process and determine the quality of PP (polypropylene) plastic pyrolysis oil. The method used was direct experiment. The test was carried out using two furnaces and was carried out in parallel six times. The results showed that the gasification of rice husk briquettes could be a source of combustion in the pyrolysis process. The time used in the pyrolysis process was 260 min while the average flame duration in the furnace over six test was 43.33 min. The average flame temperature over the six periods of combustion was 733.89 °C. Additionally, the average temperature at the bottom of the reactor was 593.564 °C, and the average temperature in the reactor chamber was 143.319 °C. This process was categorized as low-temperature pyrolysis. The mass produced from 3000 g of shredded PP (polypropylene) plastic waste produces 1.29 L of fuel oil. It is of note that the quality of plastic pyrolysis oil is not greatly different from kerosene, with a thermal efficiency of 38.60%.

Biomass is a renewable energy source gaining attention for its potential to replace fossil fuels. Biomass gasification can produce hydrogen-rich gas, offering an environmentally friendly fuel for power generation, transportation, and industry. Hydrogen is a promising energy carrier due to its high energy density, low greenhouse gas emissions, and versatility. This study aims to develop a hydrogen generation plant using a dual fluidized bed gasifier, which employs steam as a gasifying agent, to convert olive pomace waste from the Lebanese olive oil industry into hydrogen. The process is simulated using Aspen Plus and Fortran coding, and it includes a drying unit, gasification unit, gas cleaning unit, steam methane reformer unit, water–gas shift reactor unit, and a pressure swing adsorption unit. The generated gas composition is verified against previous research. Sensitivity analyses are conducted to investigate the impacts of the steam-to-biomass ratio (STBR) and gasification temperature on gas composition, demonstrating a valid STBR range of 0.5 to 1 and a reasonable gasification temperature range of 700 °C to 800 °C. Further sensitivity analyses assess the impact of reformer temperature and the steam-to-carbon ratio (S/C) on the gas composition leaving the steam methane reformer.

The continuous tightening of legislation regulating the agricultural usage of sewage sludge in the province of Catalonia (Spain) leads us to propose its gasification to produce hydrogen-rich syngas. A thermodynamic equilibrium model was developed using Aspen Plus® to simulate the air and steam gasification of sewage sludge from a wastewater treatment plant in Catalonia. The syngas generated is analyzed in terms of composition and lower heating value (LHV), as a function of equivalence ratio (ER), gasification temperature (Tgas), steam-to-biomass ratio (SBR), and moisture content (MC). Results show that air-blown gasification finds the highest LHV of 7.48 MJ/m3 at 1200 °C, ER of 0.2, and MC of 5%. Using steam as the gasifying agent, an LHV of 10.30 MJ/m3 is obtained at SBR of 0.2, MC of 5%, and 1200 °C. A maximum of 69.7% hydrogen molar fraction is obtained at 600 °C, MC of 25%, and SBR of 1.2. This study suggests using steam as a gasifying agent instead of air since it provides a higher LHV of the syngas as well as a hydrogen-richer syngas for the implementation of gasification as an alternative method to sewage sludge treatment in the region of Catalonia. Since the economic aspect should also be considered, in this regard, our sensitivity analysis provided important data demonstrating that it is possible to reduce the gasification temperature without significantly decreasing the LHV.

The possibilities of pistachio shell biochar production on laboratory-scale gasification and pyrolysis devices have been described by several previous studies. Nevertheless, the broader results of the pistachio shell co-gasification process on pilot-scale units have not yet been properly investigated or reported, especially regarding the detailed description of the biochar acquired during the routine operation. The biochar was analysed using several analytical techniques, such as ultimate and proximate analysis (62%wt of C), acid–base properties analysis (pH 9.52), Fourier-transform infrared spectroscopy (the presence of –OH bonds and identification of cellulose, hemicellulose and lignin), Raman spectroscopy (no determination of Id/Ig ratio due to high fluorescence), and nitrogen physisorption (specific surface 50.895 m2·g−1). X-ray fluorescence analysis exhibited the composition of the main compounds in the biochar ash (32.5%wt of Cl and 40.02%wt of Na2O). From the energy generation point of view, the lower heating value of the producer gas achieved 6.53 MJ·m−3 during the co-gasification. The relatively high lower heating value of the producer gas was mainly due to the significant volume fractions of CO (6.5%vol.), CH4 (14.2%vol.), and H2 (4.8 %vol.), while hot gas efficiency accomplished 89.6%.

Seaweed can be a desirable source of renewable energy or fuel after it has been processed by combustion, thermochemical conversion by gasification, pyrolysis, or hydrothermal liquefaction (HTL) or biochemical conversion routes like anaerobic digestion (AD). This work explores how well the measured properties of seaweed pellets match the specifications for the various fuel and energy conversion options listed. Blends of hay, wood chips, sawdust, and seaweed were pelletized. Eight pellet blends with dominant seaweed content and minimum acceptable mechanical strength and stability were produced and their physical and chemical properties were reported. The seaweed pellets had an energy content of around 14 MJ/kg, and each pellet could withstand almost 200 N of compression force. Their water content was around 5% or less and their ash content was around 20–34%. According to the results, a higher wood content increased the energy content of the pellets. Among those properties measured in this project, none of them contradicted the typical specifications of combustion, HTL, and AD. However, the low water content and low strength of some pellet types were unable to meet the specifications for certain types of gasification and pyrolysis.

The study concerns promising coal-fired power plants that can gain an advantage over traditional options in the context of decarbonization. The calculations show that combined-cycle plants with integrated coal gasification and carbon dioxide recirculation may have better technical and economic characteristics compared to existing gasification processes (one- and two-stage). The recirculation of carbon dioxide improves the efficiency of the gasification process (the combustible gases yield and the fuel carbon conversion degree) and reduces the energy costs of the flue gas cleaning and carbon capture unit, thereby improving the economic performance of the plant. The estimates show that the decrease in the efficiency of electricity production associated with the removal of carbon dioxide is approximately 8% for the recirculation of combustion products and 15–16% for traditional processes, and the increase in the cost of electricity is 20–25% versus 35–40%, respectively.

Global energy security relies on fossil-based resources that are affiliated with the source of global warming, apart from punches of political and economic instabilities. Biomass is a promising alternative carbonaceous feedstock used for the production of clean energy that could have the potential to substitute for fossil fuels. This study aims to present a conceptual design that considers the criteria to identify the upper theoretical limits of biomass conversion, thus providing the potential approach to the conversion of three biomass (by-products: dry molasses, dry bagasse, and dry filter cake) through gasification, in order to contribute the biomass carbon-capturing by the model assessment of stoichiometric mass conversion and energy efficiency indicators into simple thermodynamic energy vectors, such as alcohols, alkanes, and syngas (a mixture of carbon monoxide and hydrogen). Modeling plays up the importance of stoichiometric efficiency of biomass conversion with the supply of oxygen and hydrogen. This realizes that the multi-product diversification of feedstock into syngas, hydrocarbons, and alcohol through integrated process schemes could have the potential to fill the energy gap and help to manage environmental load. In regard to biomass conversion results, the mass conversion and energy conversion efficiencies of dry bagasse have better conversion potential than molasses and F. cake (% mass conversion = 129 in syngas, 54.4 in alkane, and 43.4 in alcohol; % energy conversion = 94.3 in syngas and 93.3 in alkane and alcohol).

The conversion of locally available, low-value materials to useful products and media, thereby replacing high-quality and high-cost resources, belongs to one of the pillars of the circular economy of industrial conditions. A study on the potential implementation of a mixed oxygen- and steam-blown heavy vacuum residue gasifier in a refinery, processing 5 to 6 million t of crude oil per year, is performed, evaluating its mass and energy balance, and identifying and assessing the synergies of gasifier placement in a refinery, rather than its erection as a stand-alone plant. Industrial heat and power plants, as well as hydrogen production plants, represent the production units that are directly affected by gasifier implementation, while several other technical and economic issues result in: the operation of the steam network, in heavy residues’ handling, and in the refinery’s natural gas balance. Natural gas is currently the most important resource for hydrogen production in the refinery, and its partial replacement by hydrogen from a gasifier has different energetic and environmental impacts, based on the considered natural gas composition (current situation: natural gas with 10% vol. renewable hydrogen and natural gas with 20% vol. renewable hydrogen content). The power production and the overall refinery’s power balance, the carbon dioxide emissions both within the refinery and external ones, and natural gas balance change are all evaluated. The preliminary results show that while gasifier commissioning is associated with an over EUR 1 billion investment, it can represent one of the few available solutions of how to reasonably dispose of heavy residues, utilizing it from both energy content and material potential point of views.

Solid biomass is usually simulated by decomposing it into a solid phase (carbon, ash, and sulfur) and a gas phase (water and diatomic molecules of H2, N2, O2, and Cl2) from the proximate and ultimate analysis before entering a reactor operating under chemical equilibrium when using Aspen Plus. However, this method prevents the use of energy integration for the feed stream from the system inlet to the reactor. This paper proposes an approach to solving this issue, considering biomass with both known and unknown chemical compositions; the latter involves the decomposition of biomass into complex molecular compounds. Different process arrangements were assessed to achieve a realistic simulation, and a sensitivity analysis was carried out to examine the effect of the concentration and heating upstream of the reactor, focused on supercritical water gasification (SCWG) of orange peel. This process is very energy-intensive, so the approach is useful for a better calculation of the energy requirement and exergy losses in a plant; these are usually and mainly related to the train of heat exchangers. In addition to this application to SCWG, this approach can be used for any other thermochemical process, such as gasification, pyrolysis, or combustion, and for any real biomass. Upon a base case study using a wet biomass of 10,000 kg/h with 90 wt.% water where the SCWG reaction takes place at 240 bar and 800 °C, if the temperature at the SCWG reactor inlet increases from 350 °C to 400 °C, the heat exchange increases by 57% from 4 MW and by 34% if the water content decreases to 70 wt.%, although more heat relative to the solid is saved.

Syngas from biomass gasification represents an interesting alternative to traditional fuels in spark-ignition (SI) internal combustion engines (ICEs). The presence of inert species in the syngas (H2O, CO2, N2) reduces the amount of primary energy that can be exploited through combustion, but it can also have an insulating effect on the cylinder walls, increasing the average combustion temperature and reducing heat losses. A predictive numerical approach is here proposed to derive hints related to the possible optimization of the syngas-engine coupling and to balance at the best the opposite effects taking place during the energy conversion process. A three-dimensional (3D) computational fluid dynamics (CFD) model is developed, based on a detailed kinetic mechanism of combustion, to reproduce the combustion cycle of a cogenerative engine fueled by syngas deriving from the gasification of different feedstocks. Numerical results are validated with respect to experimental measurements made under real operation. Main findings reveal how heat transfer mainly occurs through the chamber and piston walls up to 50° after top dead center (ATDC), with the presence of inert gases (mostly N2) which decrease the syngas lower calorific value but have a beneficial insulating effect along the liner walls. However, the overall conversion efficiency of the biomass-to-ICE chain is mostly favored by high-quality syngas from biomasses with low-ashes content.

The valorization of untreated municipal waste (MSW) biochar for energetic uses, through its co-gasification with olive stone (OST) biochar under a steam or carbon dioxide atmosphere, was investigated. The experiments were conducted in a fixed bed unit and a thermal analysis–mass spectrometer system. The thermal behavior, reactivity, conversion, product gas composition, syngas yield and energy potential were determined, while the influence of the fuel’s internal structure, chemical functional groups and operating conditions were examined. The concentrations of H2 and CO2 in the product gas mixture under a steam atmosphere were increased with steam/biochar ratio, while that of CO was reduced. At a steam/biochar = 3 H2 yield, the higher heating value and conversion for the OST were 52.8%, 10.8 MJ/m3 and 87.5%; for the MSW, they were 44.4%, 9.9 MJ/m3 and 51.5%, whereas for their blend, they were 50%, 10.6 MJ/m3 and 76.6%, respectively. Under a carbon dioxide atmosphere, the reactivity and conversion of the OST biochar (84%) were significantly higher as compared with the MSW biochar (50%). The higher heating value of the product gas was 12.4–12.9 MJ/m3. Co-gasification of the MSW with OST (in proportions 30:70) resulted in the enhanced reactivity, conversion, syngas yield and heating value of product gas compared with gasification of solely MSW material.

Among the technologies for the recovery of energy from waste, in particular residual municipal solid waste (rMSW), combustion is the most widely used thermo-chemical treatment process associated with thermal and electric power production by a steam cycle, named, shortly, Waste to Energy (WtE). Today, more than 500 WtE plants in the EU, about 400 in China and 76 in the USA are in operation, based on efficient technologies and advanced air pollution control systems. Energy recovery can be accomplished also by means of gasification; however, the presence of impurities together with the atmospheric pressure, at which syngas is normally produced, impose the feeding of syngas to a conventional steam cycle, leading to generally lower performances than WtE. The energy recovered by WtE offsets traditional energy sources such as fossil fuels and related emissions, providing savings in term of climate change. However, the savings obtainable by replacing electricity and/or heat will diminish as the energy systems will hopefully become increasingly renewable. Over this medium–long-term horizon, one possibility is to capture the CO2 from WtE flue gases and to store/use it. From the life cycle assessment perspective, it has been calculated that the introduction of CO2 capture and storage in WtE, despite energy penalties, is able to reduce the impact on climate change. The alternative approach, proposed to contain the emissions of greenhouse gases in the thermal treatment of waste, is using the carbon contained in it to produce commonly used chemical compounds (waste to chemicals). The benefits, in terms of reductions of greenhouse gases, are expected from the possibility of obtaining chemicals that can replace their analogue normally produced from fossil sources. To date, only one WtC demonstration plant is operating by being fed by rMSW-derived waste, and some similar initiatives are planned, but still adequate assurances in terms of robust knowledge of the involved complex processes, above all, if applied to highly inhomogeneous feed streams such as those obtained from rMSW, are not available. Once the several initiatives come to completion, it will enable waste management professionals to assess performance and to begin to consider such a facility in their planning.

The gasification performance of lignite/barley straw mixtures for syngas production was investigated. The experiments were carried out under a steam or carbon dioxide atmosphere, in fixed-bed and thermogravimetric–mass spectrometry systems. The thermal behavior, reactivity, conversion, product gas composition, liquid and gaseous by-products and interactions between fuels were determined and correlated with the structural characteristics and inherent minerals in ashes, which were analyzed via mineralogical, chemical and fusibility tests. Devolatilization of the materials up to 600 °C resulted in the carbon enrichment of chars and a 30–90-fold increase in the specific surface area. Gaseous and liquid by-products with higher heating values of 5–7 MJ/m3 and 20–28 MJ/kg could offer valuable energy. Upon steam gasification up to 1000 °C, product gas was enriched in hydrogen and carbon monoxide. The syngas yield and heating value of the gas mixture were higher for barley straw fuel (0.77 m3/kg, 11.4 MJ/m3), which, when blended with the lignite, produced upgraded products. Upon carbon dioxide gasification up to 1000 °C, barley straw char exhibited a 3-times higher rate than the lignite, as well as higher conversion (94.5% vs. 62.9%) and a higher syngas yield (0.84 m3/kg vs. 0.55 m3/kg). Lignite/barley straw blends showed synergistic effects and presented higher gasification reactivity and conversion in comparison to lignite. The overall performance of lignite was improved with the steam reagent, while that of barley straw was improved with the carbon dioxide reagent.

Waste from scrap tyres, due to its high volume (17 million Mg per year) and durability resulting from the physical and chemical properties, requires innovative approaches for efficient and environmentally friendly management. In many countries, the landfilling of waste tyres is banned (e.g., EU, USA, UK); however, waste tyres can be a source of valuable materials such as carbon black, pyrolysis oil, hydrogen-rich syngas, tyre char, as well as energy. The purpose of this article is to provide a synthesis of the state of knowledge regarding the thermal conversion of waste tyres by pyrolysis and gasification, taking into account the use of different measurement techniques and reactor types. These technologies are forward-looking and have a high degree of flexibility in terms of product sourcing, depending on the process conditions. The properties of waste from used tyres were analysed, i.e., the composition of the content of individual components and the main chemical substances. The results encompassed ultimate and proximate analyses of rubber from tyres, as well as the physical and chemical parameters of the tyre char obtained through pyrolysis. This article compiles available literature data regarding the impact of process and raw material parameters, such as temperature and time conditions, pressure, particle size, and catalyst addition on the pyrolysis and gasification processes. It also explores the influence of these factors on the yield and properties of the products, including pyrolysis oil, gas, synthesis gas, and tyre char.

A techno-economic assessment and environmental and social sustainability assessments of novel Fischer–Tropsch (FT) biodiesel production from the wet and dry gasification of biomass-based residue streams (bark and black liquor from pulp production) for transport applications are presented. A typical French kraft pulp mill serves as the reference case and large-scale biofuel-production-process integration is explored. Relatively low greenhouse gas emission levels can be obtained for the FT biodiesel (total span: 16–83 g CO2eq/MJ in the assessed EU countries). Actual process configuration and low-carbon electricity are critical for overall performance. The site-specific social assessment indicates an overall positive social effect for local community, value chain actors, and society. Important social aspects include (i) job creation potential, (ii) economic development through job creation and new business opportunities, and (iii) health and safety for workers. For social risks, the country of implementation is important. Heat and electricity use are the key contributors to social impacts. The estimated production cost for biobased crude oil is about 13 €/GJ, and it is 14 €/GJ (0.47 €/L or 50 €/MWh) for the FT biodiesel. However, there are uncertainties, i.e., due to the low technology readiness level of the gasification technologies, especially wet gasification. However, the studied concept may provide substantial GHG reduction compared to fossil diesel at a relatively low cost.

Agricultural residues are a source of energy derived through various conversion processes. They are gaining attention as a solution to limited energy access in developing countries in which a majority of the population depends on agriculture for a living at a time when global population growth is outpacing the depreciation of conventional energy sources. This study characterized residues generated along the main agri-food value chains in Uganda for gasification by reviewing relevant literature and through field measurements and laboratory experiments. Maize, beans, cassava, banana, coffee, and sugarcane are the most important value chains, occupying 5.73 million hectares, and accounting for 40% of the country’s total area under cultivation. In terms of biomass residues, banana, maize, and sugarcane are the most feasible options, producing 4.18, 2.2, and 0.6 metric tons of biomass waste per ton, respectively. The bulk densities vary from 65.5 to 160 kg/m3, moisture content from 6.67 to 22.5%, and heating values from 12.6 to 16.74 MJ/kg for all residues. In terms of principal elements, oxygen has the highest proportion of 38.76–57.25% followed by carbon, 33.46–47.9%, and hydrogen 6%. The lignocellulosic composition is 23.46–41.38% hemicellulose, 9.9–55% cellulose, and 5.77–35% lignin. The three value chains have the potential to generate 172.2 PJ annually, which is enough to offset 50% of the cooking energy demands for Uganda. The main disadvantage of this is the low bulk density, which raises production costs and reduces conversion efficiency. Bulk density can be improved by densification through the compaction of residues. Given their composition and current utilization, maize stover, banana leaves, banana pseudo stems, and sugarcane tops are promising gasification feedstocks.

Awareness of the consequences of waste mismanagement has resulted in urban planners looking for effective disposal techniques with the added benefit of energy generation. The decision regarding an energy conversion technique to adopt on a community level is based on different technology assessment factors with maximum weightage on environmental effects. Gasification techniques in general and thermal gasification strategies in particular are appropriate methods when environmental impacts are to be minimized. Thermal gasification techniques have evolved with different configurations, syngas generation rates, and other advantages and disadvantages; hence, the selection of the right technique is essential, and establishing guidelines for decision-makers is necessary. The six different gasifiers considered in the present study were updraft gasifiers, downdraft gasifiers, cross-draft gasifiers, bubbling fluidized bed gasifiers, circulating fluidized bed gasifiers, and dual-bed fluidized bed gasifiers. The assessments performed in the present study are based on the attributes of the different techniques using the multi-criteria decision method. Multi-criteria decision analysis is an appropriate method proven to be an ideal procedure in these situations. Attribute values for gasifier performance, environmental effects, economic performance indices, and fuel requirements were determined from collected waste assessment data and published information. Analysis was performed for both recycling and non-recycling scenarios of waste utilization by applying different weight scenarios for the attributes. Results of the study indicate that downdraft gasifiers showed the best performance in terms of environmental effects under the recycling scenario, with 0.1% and 0.0125% by volume of carbon dioxide and methane emissions, and under the non-recycling scenario, with 0.125% and 0.02% by volume of carbon dioxide and methane emissions. Downdraft gasifiers had high overall rankings in performance when evaluated against different entropy weights for both scenarios. The results of the study can be applied to urban communities in different climatic regions as well as for different scales of operation.

This study presents the experimental results obtained from hybrid filtration combustion using biomass pellets. The experiments were carried out using a porous media gasifier filled with pellets and inert material. The gasifying agent used was an air–steam mixture, with 40% being steam. The dependence of the temperature in the gasifier’s reaction zone from the volume percentage of inert porous material in the gasifier, the specific heat capacity of this material, as well as the air–steam blowing rate, was investigated. The multifactor experiment method was used. A maximum temperature of 1245 °C was achieved using 28 vol% of porous material with a heat capacity of 1000 J/(kg·°C) and at a blowing rate of 42 m3/h. The maximum hydrogen content in the syngas was 28 vol%. This was achieved at an air–steam blowing rate of 42 m3/h and 40 vol% porous material, with a heat capacity of 1000 J/(kg·°C). The calorific value of the syngas was 12.6 MJ/m3. The highest CO content in the gas was 28 vol% and was obtained at 20 vol% porous material with a heat capacity of 1000 J/(kg·°C) and a blowing rate of 42 m3/h. The obtained information is applicable in the design, management, and control of gas production by way of a hybrid filtration combustion process in a downdraft gasifier.

In recent decades, economic development and population growth has been accompanied by the generation of billions of tonnes of solid residues or municipal “wastes”, a substantial portion of which is composed of plastics and biomass materials. Combustion-based waste-to-energy is a viable and mature method of extracting calorific value from these end-of-life post-recyclable materials that are otherwise landfilled. However, alternative thermochemical methods, such as gasification, are becoming attractive due to the ability to synthesize chemical precursors for supply chain recirculation. Due to the infancy of gasification technology deployment, especially in the context of anthropogenic CO2 emission reduction, additional systems engineering studies are necessary. Herein, we conduct an attributional life cycle analysis to elucidate the syngas production and environmental impacts of advanced thermochemical gasification methods for the treatment of biomass and plastic wastes obtained from municipal solid wastes, using a comprehensive thermodynamic process model constructed in AspenTech. Feedstock composition, process parameters, and gasification methods are varied to study the effects on syngas quality, yield, power generation potential, and overall greenhouse gas emissions. Steam-based gasification presents up to 38% reductions in CO2 emissions when compared to conventional thermochemical methods. Using gasifier-active materials, such as metal hydroxides, can also further reduce CO2 emissions, and realizes a capture load of 1.75 tonnes of CO2 per tonne of plastic/stover feedstock. This design alteration has implications for reductions in CAPEX due to the mode of CO2 capture utilized (e.g., solid sorbent vs. liquid SELEXOL). The use of renewable energy to provide a method to generate steam for this process could make the environmental impact of such MSW gasification processes lower by between 60–75% tonnes of CO2 per tonne of H2. Overall, these results can be used to inform the guidance of advanced waste gasification methods as a low-carbon transition towards a circular economy.

In this study, a technical analysis of synthesis gas (syngas) and biodiesel blend utilized in an internal combustion engine is presented. The experimental setup is composed of an engine workbench coupled with a downdraft gasifier which was fed with forest biomass and municipal solid waste at a blending ratio of 85:15, respectively. This research paper aims to contribute to the understanding of using fuel blends composed of synthesis gas and biodiesel, both obtained from residues produced in a municipality, since the waste-to-energy approach has been trending globally due to increasing waste generation allied with rising energy demand. The experiments’ controlling parameters regarding the engine are rotation and torque, exhaust gas temperature, and fuel consumption. The gasification parameters such as the oxidation and reduction temperatures, pressures at the filter, hood, and reactor, and the volume of tars and chars produced during the thermochemical process are also presented. Ultimate and proximate analyses of raw materials and fuels were performed, as well as the chromatography of produced syngas. The syngas produced from forest biomass and MSW co-gasification at a blending ratio in mass of 85:15 presented an LHV of around 6 MJ/m3 and 15% of H2 in volume. From the experiment using syngas and biodiesel blend in the engine, it is concluded that the specific consumption at lower loads was reduced by 20% when compared to the consumption of the same engine operating with regular diesel. The development of co-gasification of forest and municipal waste may then be an interesting technology for electrical energy decentralized generation.

The use of biomass can be a strategic way to realize a carbon-neutral energy plan, ensuring a fuel feedstock. Residual biomass arising from pruning is demonstrated to be an important energy resource in terms of quantity and quality. In the Salento peninsula, Apulia Region, in the south of Italy, a dramatic outbreak of Xylella fastidiosa has decimated olive trees since 2013, gaining a considerable amount of wood biomass. This paper, starting from the need to find a way to optimize the use of this available stock, reviews the main technologies on the utilization of olive wood for energy purposes. In particular, processes and products are here described, and an energy analysis compares lower heating value (LHV), higher heating value (HHV), mass yield, process operating conditions, and energy generated and spent by the process in order to find the most effective technology in order to optimize the energy use of olive biomass. The conclusions show the advantages and disadvantages of each technology. Pyrolysis performs well, showing the best results for both char HHV and syngas yield under different operating conditions. Gasification seems to be the most appropriate among conversion technologies to optimize olive tree pruning for energy purposes, as it can be used to produce both electrical and thermal energy. In terms of economic valorization, char is the most promising material representing a value-added product, the quality and versatility of which ranges from fuel to soil improvers and additives for the construction of supercapacitors. Conversely, its disadvantages are mainly represented by high ash content, which can slightly decrease the boiler efficiency. Finally, the amount of alkali metals can produce several problems, such as fouling, slagging, corrosion, etc., posing a challenge for combustion control and pollutant minimization.