In this study, municipal solid waste (MSW) composition in distinct world locations is compared and a case study is assessed. Three waste-to-energy (WtE) techniques are employed within the framework ...of an industrial partnership. Life cycle assessment (LCA) and a brief social contextualization including the production of renewable energy from the waste generated worldwide were held to attain a holistic view and attract the interest of multiple stakeholders.
Incineration depicted a sustainable profile with improved results for global warming potential and terrestrial ecotoxicity potential. Regular gasification revealed the best results for eutrophication, acidification, marine aquatic ecotoxicity and human toxicity potential. Two-stage plasma gasification showed negative values for all impact categories i.e. achieving environmental credits. The estimate of the electricity produced from the waste generated per capita showed a fair coverage of the electrical demand in distinct world areas.
To the best of the authors' knowledge, there are no reports connecting the electricity use, the waste production and the renewable energy achieved from WtE for different world regions. Therefore, this study supports the replacement of fossil fuels with renewable alternatives, reducing greenhouse gas emissions while maintaining the comfort and commodities suitable for a comfortable quality of life.
•Solid waste was characterized for distinct geographic zones.•Incineration, gasification and plasma were assessed for waste conversion.•Life cycle analysis was performed for a specific waste sample.•A life cycle cost assessment approach is also presented.•The electricity generated from waste might be used as alternative to fossil fuels.
Biomass is currently seen as a promising renewable energy source, which can be sustainably utilized in the production of fuels and electric energy adding no carbon dioxide to the environment. ...Co-gasification has unveiled its potential amongst thermal techniques, as a result of the valuable products obtained, strengthening a solid position in the conversion of residues. Thus, the prevention of a complete depletion of non-renewable sources is supported and the effects of their utilization alleviated.
Extensive literature review was conducted and, few reports on co-gasification of biomass and wastes were found. In this context, this review addresses their thermal conversion, highlighting issues related to the equipment, operating conditions and physicochemical phenomena involved in such a complex process. Among other conclusions, the most important finding of this work was the synergy often encountered between the two feedstocks, proving co-gasification can overcome several of the individual gasification issues enhancing products quality and yields over biomass or wastes alone, and attesting its environmental-friendly character, with lower greenhouse gas emissions. It was also possible to depict some trends on the effect of biomass and waste blending ratios, as well as elucidating some of the mechanisms involved in their interaction. These are majorly explained by the response of molecules during pyrolysis and by hydrogen transfer from waste polymers to biomass derivatives. Experimental conditions were also assessed, fluidized beds being reported as the most suitable reactors for biomass and wastes, under several different possible combinations of operational parameters. A critical discussion is presented, aiming to contribute to a more profound understanding of this matter, its key points and noteworthy potential.
This study is dedicated to present a reliable numerical methodology using Aspen Plus process simulator capable of performing a sensibility analysis of the downdraft gasification of Portuguese forest ...residues. Effects of critical parameters, including gasification temperature and steam-to-biomass ratio (SBR) on composition of the produced gas are discussed. The sensibility analysis is conducted using Aspen Plus simulator incorporating Fortran subroutines. The model is validated by experimental data and found to be in good agreement. The results of the sensibility analysis performed using air as gasification agent indicate that higher temperatures are favourable for a produced gas with higher hydrogen content and heating value. The simulation results also demonstrate that the use of steam as gasification agent allows increasing the hydrogen content and heating value of the produced gas in comparison to the use of air as gasifying agent. The knowledge of this data is decisive to the development of projects concerning the use of Portuguese forest residues as energy source.
•A reliable biomass gasification Aspen Plus model is developed.•A sensibility analysis to temperature and SBR is made.•Higher temperature favours the hydrogen content and heating value of produced gas.•Steam is better for the hydrogen content and heating value of produced gas.
•Steam gasification as an alternative for MSW treatment was studied.•A previously developed numerical model for MSW gasification was used.•Results were validated with data gathered from the ...literature.•Results were compared with previously studied biomass substrates.•Environment and economic assessment based on the results was conducted.
Waste management is becoming one of the main concerns of our time. Not only does it takes up one of the largest portions of municipal budgets but it also entails extensive land use and pollution to the environment using current treatment methods. Steam gasification of Portuguese municipal solid wastes was studied using a previously developed computational fluid dynamics (CFD) model, and experimental and numerical results were found to be in agreement. To assess the potential of Portuguese wastes, these results were compared to those obtained from previously investigated Portuguese biomass substrates and steam-to-biomass ratio was used to characterize and understand the effects of steam in the gasification process. The properties of syngas produced from municipal solid waste and from biomass substrates were compared and results demonstrated that wastes present the lowest carbon conversion, gas yield and cold gas efficiency with the highest tar content. Nevertheless, the pre-existing collection and transportation infrastructure that is currently available for municipal waste does not exist for the compared biomass resources which makes it an interesting process. In addition a detailed economic study was carried out to estimate the environmental and economic benefits of installing the described system. The hydrogen production cost was also estimated and compared with alternative methods.
•Evaluation of Portuguese municipal solid waste gasification was conducted.•Previously studied biomass substrate was used as benchmark.•Numerical model built upon a reliable set of experimental runs ...was used.•Thermodynamic analysis on steam as gasifying agent was showed.•A CFD model was combined with RSM to optimize exergy efficiency.
The presented study focuses on a thermodynamic analysis conducted on steam gasification of Portuguese municipal solid wastes (MSW). Current literature addressing this issue is extremely scarce due to the complexity in handling MSW’s heterogeneity. To fill this significant gap, a mathematical model built upon a reliable set of experimental runs from a semi-industrial gasifier was used to evaluate the effects of reactor temperature and steam-to-biomass ratio (SBR) on produced gas and tar content. Results from a previously studied biomass substrate were used as benchmark. Numerical results were validated with both experimental results and existing literature. Increase in gasification temperature led to a clear increase in both exergy values and exergy efficiency. On the other hand, increase in SBR led to a sharp increase in the exergy values when steam was first introduced, leading to relatively constant values when SBR was further increased. Regarding exergy efficiency, SBR led to a clear maximum value, which in the case of forest residues was found at SBR=1, while for MSW at 1.5. In order to promote a more hydrogen-rich gas, data obtained from the numerical model was used to design an exergy efficiency optimization model based on the response surface method. Maximum hydrogen efficiency was found at 900°C with a SBR of 1.5 for MSW and 1 for forest residues. Surprisingly, forest residues and MSW presented virtually the same maximum hydrogen efficiency.
Considering waste as a possible new resource for useful purposes is one of the strategies included in the circular economy principles. In fact, industrial processes are seen as great contributors to ...the formation of waste streams. With the aim to attain more sustainable and resilient systems, in this study, a process flow chart was elaborated in an Aspen Plus computer simulator, to obtain the production of pure glycerol from crude glycerol (a by-product of biodiesel production). This process occurs through fractional vacuum distillation, the methanol recovery route in the deacidification process and the removal of methanol from the reaction medium. The separation stages of the crude glycerol implemented enabled a degree of purification of 99.77%, meeting the specifications of the pharmaceutical use. The developed model allowed for the optimization of the purification process, raising by 40% the mass flow rate of pure glycerol. A conclusion could be drawn that the use of crude glycerol is an excellent option for the development of new products with greater added-value, contributing to the zero waste principles and to the circular economy.
The gasification of MSW (municipal solid wastes) using CO2 as a gasifying agent has been object of growing interest in recent years. Although quite limited, studies have shown that CO2 can behave as ...a catalyst and accelerate the thermal cracking of volatiles as well as minimize tar formation, and even give a positive contribute to environment. Despite these promising features, it is still necessary to develop mathematical models able to assist the advance of this technology.
A previously published numerical model validated for numerous substrates (including MSW) and operating conditions in a pilot scale plant was used as a baseline to study MSW gasification with air-CO2 mixtures. Real MSW data from Oporto metropolitan area were used as model inputs and numerical results were validated against experimental ones.
Results demonstrate that increasing CO2 content boosts carbon conversion, CO2 conversion, and cold gas efficiency while mitigating tar production. Also, due to the ability to tailor H2/CO ratio, air-CO2 mixtures can be used for catalyst-based Fischer–Tropsch synthesis and particularly for the production of specific chemicals such as urea, methanol and acetic acid.
•A previously developed CFD model was used to predict MSW gasification.•Influence of CO2 addition in MSW gasification was studied.•Applications for MSW gasification were analyzed.•Influence of operational parameters in tar content was studied.•Influence of CO2 content on syngas quality indices was studied.
Plasma gasification is a thermal treatment successfully applied to waste streams, especially for solid residues. It sets an upgrade to more common waste-to-energy (WtE) techniques as incineration or ...gasification, granting lower levels of pollutant emissions, less landfilled materials and higher conversion efficiencies and producer gas quality. A life cycle assessment (LCA) of plasma gasification for one ton of a defined stream of solid waste is presented and compared to the hypothetical outcomes of incineration, highlighting the need to implement such sustainable techniques rather than more polluting ones. CML 2001 methodology was applied, enabling the evaluation of eleven impact categories, all of them depicting avoided burdens for the environment. Enhanced efficiency and cleanliness were seen due to the plasma step and to the replacement of part of the electrical grid mix by the produced electricity. Plasma gasification presented an overall better performance than incineration, portraying savings in energy and material resources as well as lower emissions to freshwater. Additionally, lower amounts of air contaminants were seen as well as almost triple of the produced electricity.
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 (<4%). The gasification temperature increased hydrogen production by up to 40% but also increased 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 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.
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