Progress in biofuel production from gasification

Biofuels from biomass gasification are reviewed here, and demonstrated to be an attractive option. Recent progress in gasification techniques and key generation pathways for biofuels production, process design and integration and socio-environmental impacts of biofuel generation are discussed, with the goal of investigating gasification-to-biofuels’ credentials as a sustainable and eco-friendly technology. The synthesis of important biofuels such as bio-methanol, bio-ethanol and higher alcohols, bio-dimethyl ether, Fischer Tropsch fuels, bio-methane, bio-hydrogen and algae-based fuels is reviewed, together with recent technologies, catalysts and reactors. Significant thermodynamic studies for each biofuel are also examined. Syngas cleaning is demonstrated to be a critical issue for biofuel production, and innovative pathways such as those employed by Choren Industrietechnik, Germany, and BioMCN, the Netherlands, are shown to allow efficient methanol generation. The conversion of syngas to FT transportation fuels such as gasoline and diesel over Co or Fe catalysts is reviewed and demonstrated to be a promising option for the future of biofuels. Bio-methane has emerged as a lucrative alternative for conventional transportation fuel with all the advantages of natural gas including a dense distribution, trade and supply network. Routes to produce H2 are discussed, though critical issues such as storage, expensive production routes with low efficiencies remain. Algae-based fuels are in the research and development stage, but are shown to have immense potential to become commercially important because of their capability to fix large amounts of CO2, to rapidly grow in many environments and versatile end uses. However, suitable process configurations resulting in optimal plant designs are crucial, so detailed process integration is a powerful tool to optimize current and develop new processes. LCA and ethical issues are also discussed in brief. It is clear that the use of food crops, as opposed to food wastes represents an area fraught with challenges, which must be resolved on a case by case basis

An overview of advances in biomass gasification

Biomass gasification is a widely used thermochemical process for obtaining products with more value and potential applications than the raw material itself. Cutting-edge, innovative and economical gasification techniques with high efficiencies are a prerequisite for the development of this technology. This paper delivers an assessment on the fundamentals such as feedstock types, the impact of different operating parameters, tar formation and cracking, and modelling approaches for biomass gasification. Furthermore, the authors comparatively discuss various conventional mechanisms for gasification as well as recent advances in biomass gasification. Unique gasifiers along with multi-generation strategies are discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. A strategy to improve the feasibility and sustainability of biomass gasification is via technological advancement and the minimization of socio-environmental effects. This paper sheds light on diverse areas of biomass gasification as a potentially sustainable and environmentally friendly technology

COVID-19 pandemic and global carbon dioxide emissions: A first assessment

Anthropogenic carbon dioxide emissions are the main cause of global climate change. The COVID-19 pandemic has been one of the worst of its kind in the last century with regard to global deaths and, in the absence of any effective treatment, it led to governments worldwide mandating lock-down measures, as well as citizens voluntarily reducing non-essential trips and activities. In this study, the influence of decreased activity on CO2 emissions and on the economy was assessed. The US, EU-28, China and India, representing almost 60% of anthropogenic carbon emissions, were considered as reference entities and the trends were extrapolated to estimate the global impact. This study aimed to deduce initial estimates of anthropogenic CO2 emissions based on the available economic and industrial outputs and activity data, as they could not be directly measured. Sector-wise variations in emissions were modeled by assuming proportionality of the outputs/activities and the resulting emissions. A decline in road traffic was seen up to March 2020 and then a steady growth was observed, with the exception of China where road traffic started to recover by the end of January. The vast majority of passenger flights were grounded and, therefore, global air traffic plummeted by 43.7% from January to May 2020. A considerable drop in coal power production and the annual industrial growth rate was also observed. The overall economic decline led to a drop of 4.9% in annual global gross domestic product (GDP) for Q2 2020. The total global CO2 emissions reduction for January through April 2020 compared to the year before was estimated to be 1749 Mt. CO2 (14.3%) with a maximum contribution from the transportation sector (58.3% among total emissions by sector). Like other previous crises, if the economy rebounds as expected the reductions will be temporary. Long-term impacts can be minimized considering the business as well as lifestyle changes for travel, utilizing virtual structures created during this crisis, and switching to sustainable transportation

Opportunities and challenges in sustainable treatment and resource reuse of sewage sludge: A review

Sludge or waste activated sludge (WAS) generated from wastewater treatment plants may be considered a nuisance. It is a key source for secondary environmental contamination on account of the presence of diverse pollutants (polycyclic aromatic hydrocarbons, dioxins, furans, heavy metals, etc.). Innovative and cost-effective sludge treatment pathways are a prerequisite for the safe and environment-friendly disposal of WAS. This article delivers an assessment of the leading disposal (volume reduction) and energy recovery routes such as anaerobic digestion, incineration, pyrolysis, gasification and enhanced digestion using microbial fuel cell along with their comparative evaluation, to measure their suitability for different sludge compositions and resources availability. Furthermore, the authors shed light on the bio-refinery and resource recovery approaches to extract value added products and nutrients from WAS, and control options for metal elements and micro-pollutants in sewage sludge. Recovery of enzymes, bio-plastics, bio-pesticides, proteins and phosphorus are discussed as a means to visualize sludge as a potential opportunity instead of a nuisance

Waste utilization via thermal plasma

The rising quantities of waste streams which is assumed to enhance further, in the near future due to developments in the industries and societies is a global concern. Pragmatic utilization of diverse wastes such as sewage sludge, refuse derived fuel (RDF), etc. can be a small but crucial step to answer the challenges of waste management coupled with the fulfillment of global energy requirements. This thesis is constructed on thermal plasma assisted pyrolysis and gasification of diverse wastes to assess the potential of thermal plasma to recover energy and material from waste streams. The core part of the thesis is built on both the modeling and experimental works which follow the topical and novel approach questions regarding the deployment of thermal plasma to process waste streams. A rigorous equilibrium model was developed employing RDF and sewage sludge to evaluate the potential of thermal plasma in treating difficult waste streams and also to examine the viability of co-valorization of wastes. Pyrolysis experiments were performed using methane as a model compound in a plasma reactor equipped with a direct current (DC) plasma torch in order to gauge the potential of thermal plasma for the production of hydrogen and solid carbon. Moreover, gasification and pyrolysis experiments with RDF as a model compound were carried out with variable CO2 input (coming from the membrane separation) to deduce the possibility of methanol synthesis. The feasibility of integrated thermal plasma- CCUS (Carbon Capture Utilization and Storage) system with regard to in-situ CO2 capture employing solid sorbents was examined by developing an equilibrium model using RDF as a model compound for plasma assisted CO2-sorption enhanced gasification. Thermal plasma assisted waste utilization has come up as a high potential technology for sustainable and eco-friendly pathway for waste processing

Productivity enhancement of stepped solar still by loading with magnets and suspended micro charcoal powder

Solar desalination technology is an eco-friendly and sustainable pathway to generate pure water. In the current investigation, the stepped solar still were loaded with 10 magnet rings and charcoal powder of 75 microns to make the still efficient. Three different types of solar stills namely, conventional stepped solar still (CSSS), magnetic stepped solar still (MSSS), and magnet charcoal stepped solar still (MCSSS) were tested simultaneously at 1 cm, 2 cm, and 3 cm depths of water. The deployment of magnets in MSSS and magnets and charcoal in MCSSS were found to significantly enhance the radiative, convective, and evaporative rates of heat transfer. The highest total heat transfer rate was found in MCSSS which was more than the rates in MSSS and CSSS by 30.94% and 91.70%, respectively. The cumulative yield outputs in MCSSS were 104.54% and 23.28%, respectively, higher than CSSS and MSSS. The exergetic efficiency in MCSSS was higher by 31.84% and 145.82%, respectively, in comparison to the MSSS and CSSS. In addition, an economic evaluation was carried out and the annual distillation cost and overall cost of one liter of water per 0.25 m(2) were found to be 48.6 and 0.029 USD, respectively. The results emphatically indicate that the proposed solar still is a simple and economical technique to improve the distillate output in an eco-friendly manner

Progress on suspended nanostructured engineering materials powered solar distillation : a review

Sustainable solar energy powered desalination is a high priority research area, nowadays. Fresh potable water is one of humanity?s fundamental needs for living and flourishing. Efficient techniques for producing pure water from saline water and industrial wastewater with less conventional energy use or using renewable energy are urgently needed. Solar stills are one of such alternatives to produce pure water using solar energy. Novelty of this write up is discussion of basic concepts such as working principle of nanofluid, heat transfer in nanofluid and different preparation methods. These areas are discussed to bring the readers closer to the present scenario of suspended nanostructured engineering materials for solar distillation. Cost analysis with and without suspended nanoparticles are also summarized. Authors have also thrown light on effects of NPs (nanoparticles) on environment and health of living beings as a means to promote this technology. An important result is that nanofluids thermal conductivity is proportional to nanoparticles concentration to a certain limit. So, each nanoparticle has its optimum concentration where thermal conductivity is maximum in order to give maximum yield of pure water

Biomass conversion by gasification process

Biomass gasification is a prominent thermochemical technique to transform biomass into usable energy and products with diverse end applications. This chapter provides an overview of the essentials such as classification of feedstocks, influence of various parameters, techno-economics and, finally, the limitations and benefits of different gasification technologies. Progress in the gasification pathway along with the reduction in adverse socio-environmental effects are indispensable to enhance the sustainability and long-term viability of biomass gasification. This chapter clarifies several aspects of biomass gasification as a promising technology

Progress in waste utilization via thermal plasma

As the world races toward its urban future, the quantity of wastes, one of the vital by-products of an enhancement in the standards of living, is exponentially rising. The treatment of wastes employing plasma is an upcoming area of research and is globally used for the simultaneous processing of diverse wastes coupled with the recovery of energy and materials. Ground-breaking and cost-effective thermal plasma technologies with high efficiencies are a prerequisite for the growth of this technology. This paper delivers an evaluation of the fundamentals such as the generation and characteristics of the thermal plasma along with the various types of wastes treatable by thermal plasma and the related issues. Furthermore, the authors discuss different types of advanced technologies as well as the material and energy recovery techniques and their present status worldwide, at lab-scale and industrial scale. The application of different thermal plasma technologies is discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. Mathematical modeling studies are also assessed with an objective to derive ideal conditions and permissible limits for the reactors and to test a variety of waste materials. A strategy to improve the feasibility and sustainability of waste utilization is via technological advancement and the minimization of environmental effects and process economics. This paper sheds light on diverse areas of waste utilization via thermal plasma as a potentially sustainable and environmentally friendly technology.</p

Historic review and recent progress in internal design modification in solar stills

Solar still, which uses solar renewable energy sources, especially solar energy, to produce pure water, is a promising technology as it is abundantly available and eco-friendly. Researchers have innovated in internal and external designs to enhance distillate productivity in solar desalination systems. The present review paper discusses the major internal modifications done in history and recent past to enhance the distillate output. Six sub-sections have been developed concerning historic internal modifications that discuss types of basin liners, water depth, stones, dyes, phase change materials, and weirs. It has been found that among all the historic internal modifications, phase change materials were the most effective with distillate yield enhancement of up to 80%. The limitation in distillate yield made the researchers to perform further modifications to enhance the productivity, and hence, recent internal designs have also been discussed. Recent internal modifications have six sub-sections: fins, wicks, nanofluids, nanostructures, dynamic modifications, and natural materials. Among the recent, dynamic modifications were the most efficient with productivity enhancement of up to 300%, with a maximum cumulative yield of 8.78 kg/m(2)/day for the rotating wick solar still compared to CSS which gave only 2.21 kg/m(2)/day. Such a kind of review work has not been performed till date, which covers all the internal design modifications in one paper exhaustively. Furthermore, gaps have been identified, and future perspectives have been presented in the conclusion section. It has been observed that nanostructures, nanoparticles, and dynamic modifications are the most promising internal modifications in recent times that can boost distillate productivity to a greater degree