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Environmental impact assessment of energy generation processes is essential to evaluate their contributions toward the global carbon footprint. Even though hydrogen is a non-carbonaceous energy source, the pathways undertaken for its production can have harmful environmental implications. Thus, this study focuses on investigating the exergoenvironmental performances of the copper-chlorine, iron-chlorine, and magnesium-chlorine thermochemical hydrogen generation processes. This study also performs a comparative exergoenvironmental analysis of the three processes. The performances of the various processes are examined based on of the environmental impact rates of exergy destruction, component-related environmental impact rates, cumulative environmental impact rates, and exergoenvironmental factors. The global warming potentials of the thermochemical cycles are also evaluated and compared for various electricity sources to obtain hydrogen. The modeling and simulation of each process are performed using Aspen-plus by considering various heat recovery approaches for thermal management. The results suggest that the environmental impact rates of exergy destruction are relatively much higher compared to the environmental impact rates associated with the components for all processes. Furthermore, the hydrolysis step yields the highest component-associated environment impact rate for all thermochemical cycles considered (Fe–Cl: 3497 mPts/h, Cu–Cl: 1997 mPt/h, and Mg–Cl: 910 mPts/h). Moreover, the magnesium-chlorine cycle results in the highest environmental impact rate of exergy destruction (650,328 mPts/h) while the iron-chlorine cycle has the highest component-related environmental impact rate (5219 mPts/h) among the three cycles. In addition, the global warming potential of the magnesium-chlorine cycle is relatively higher compared to the copper-chlorine cycle for several electricity sources. [Display omitted] • An exergoenvironmental analyses of three thermochemical cycles is performed. • Each cycle is incorporated with thermal management schemes for higher efficiencies. • Industrial waste flue gases are considered as a heat source for hydrolysis reaction. • A hydrogen production capacity of 668 kg/h is considered for each cycle. • A comparison of global warming potential for various electricity sources is made. [ABSTRACT FROM AUTHOR]

Exploitation of fossil fuel sources in the power generation and transportation sector has been a major source of carbon dioxide emissions that contributes to global warming. Replacement of hydrocarbon-based fuel sources with cleaner fuels is imperative for environmental preservation at the global level. In this regard, hydrogen can be used as an effective non-carbonaceous fuel option as well as an energy carrier. Canada is currently one of the economically advanced countries in the world and aims at achieving a net-zero economy by 2050. However, fossil fuels are still largely utilized for both transportation and power generation purposes. Slightly less than a quarter of the total grid power in Canada is supplied through fossil fuel combustion including natural gas, coal, and petroleum. As a matter of fact, Canada, as one of the top ten global producers of hydrogen, exhibits a great potential of achieving the goal of sustainable development. Thus, this paper discusses the current status, challenges, and opportunities offered by the hydrogen sector and its development in the near- and long-term future in Canada. The potential methods of hydrogen production in Canada are described by categorizing them according to the energy and feedstock sources required for their realization. In addition, the status of hydrogen storage and distribution in Canada is also discussed. Various sectors consuming hydrogen as the end-users in Canada are categorized based on hydrogen use as a fuel, a heating source, and an industrial feedstock and are comprehensively discussed. Several challenges and the necessary line-of-actions to establish a hydrogen economy in Canada in the long-term future are also discussed, and a road map for accomplishing the net-zero economy by 2050 is further explained based on achieving certain near-term, mid-term, and long-term goals. Moreover, the job creation opportunities in Canada are discussed by considering numerous critical sectors. [Display omitted] • Overview of Canada's global position with regards to hydrogen production. • Overview of Canada's natural resources and infrastructural potential. • Comprehensive discussion on hydrogen production pathways and end-use in Canada. • Identification of several key challenges to achieve net-zero economy by 2050. [ABSTRACT FROM AUTHOR]

Hydrogen is one of the highly promising clean solutions to address the concerns of energy security in the future given the rapid rate of depletion of naturally occurring hydrocarbon sources. However, it is of immense importance that hydrogen is obtained through sources that ensure sustainability. Thermochemical water-splitting processes are among such routes of hydrogen production that are both sustainable and environmentally benign. Thus, this study focuses on assessing the copper-chlorine thermochemical cycles that are among the more promising cycles of the chlorine family in terms of efficiency and cost-effectiveness. Moreover, this study considers a comparative exergoenvironmental evaluation of the four variants of the copper-chlorine cycle that vary in the number and the nature of steps. A comparison in this regard is carried out between the various steps of each cycle in terms of the component-associated environmental impact rates and environmental impact rates of energy transfer as well as the overall environmental impacts of all cycles. In addition, a comparison of the global warming potential of hydrogen synthesized through utilizing various electricity sources is also performed. Based on our evaluations, hydrolysis and electrolysis are the common steps in the five-step cycle, the four-step cycle, and the three-step cycle configuration 1 yielding the highest component-associated environmental impact rates and environmental impact rates of energy transfer, respectively. Conversely, in the three-step cycle configuration 2, the electrolysis and thermal decomposition steps yield the highest corresponding values, respectively. In addition, the three-step cycle configuration 2 (4,869 mPts/h) and the five-step cycle (3,194 mPts/h) have the highest and the lowest component-associated environmental impact rates, respectively while the five-step (530,694 mPts/h) and the four-step (248,050 mPts/h) cycles result in the highest and the lowest environmental impact rates of energy transfer, respectively. • Exergoenvironmental analyses of three variants of Cu–Cl thermochemical cycle. • Comparison of environmental impact rate of energy transfer. • Comparison of component-associated environmental impact rate. • Comparison of global warming potential for various electricity sources. [ABSTRACT FROM AUTHOR]

This paper develops a four-step copper-chlorine cycle for hydrogen production with conceptual modification through flash vaporization and evaluates its economic and environmental performances through exergy approach. The flash vaporization method is employed as a new approach for realizing the anolyte separation under vacuum conditions for reducing the thermal requirement of the anolyte separation step and consequently of the overall cycle. A flash vaporization is usually employed commercially for seawater desalination purposes. However, its utilization in a thermochemical hydrogen production process has not been considered previously which is really one of primary novelties of this investigation. The obtained results for the exergoeconomic and exergoenvironmental analyses of the conceptually modified cycle are also compared with those of the existing integrated cycle at the Ontario Tech University. The exergoeconomic analysis of the cycle has also been carried out for the cycle operating with and without waste heat recovery. In this regard, waste heat recovery from a steel furnace has been considered for supplying the required thermal energy for the hydrolysis step. The cost assessment of the cycle is carried out in the Aspen-plus. Compared with the existing cycle, the cycle with the proposed modification results in a lower unit cost of hydrogen. Moreover, a significant reduction in the unit cost of hydrogen is observed when waste heat recovery is considered for the modified cycle. The average unit hydrogen cost for the modified version of the cycle is evaluated to be 4.7 $/kg which reduces to 2 $/kg with incorporation of waste heat recovery. Furthermore, the overall environmental impact of the existing cycle can be potentially minimized by considering the proposed modification through flash vaporization. • Exergoeconomic and exergoenvironmental assessement of copper-chlorine cycle. • Comparative evaluation of cycle operating with and without waste heat recovery. • Comparative evaluation of the modified and existing integrated cycles. • Evaluation of exergy and unit exergy cost at each state point of the cycle. [ABSTRACT FROM AUTHOR]

Transportation is an economic sector that contributes significantly to global warming due to its high consumption of fossil fuels, and sustainably produced hydrogen is a major contender for an alternative clean energy source. Public transit is vital for environmental sustainability via reducing individual vehicle usage and traffic congestion, and the prospect of powering buses using hydrogen fuel has been extensively studied lately. This paper seeks to comprehensively review the current status of research on hydrogen-powered buses considering triple bottom line sustainability perspectives. A brief technical overview of prospective environmentally benign hydrogen production processes has been presented. Technological, economic, and environmental findings and research trends seen in recent analyses on hydrogen-powered buses have been summarized, along with the status quo of global hydrogen refuelling stations. Identified focal points for future studies include performance enhancements, refuelling infrastructure propagation, and policy formulation. The conclusions derived from this review will benefit the accelerated deployment of hydrogen-fuelled public transit fleets. • Environmentally benign hydrogen production is reviewed techno-economically. • The prospects of using hydrogen for public bus transport are discussed thoroughly. • Blue and green hydrogen production are likely to coexist in the hydrogen economy. • Costs and energy consumption of hydrogen-powered buses need improvement. • Refuelling facility deployment and public awareness of safety should be enhanced. [ABSTRACT FROM AUTHOR]

In this study the specific exergy costing (SPECO) approach is employed on a four-step integrated thermochemical copper-chlorine (Cu Cl) cycle for hydrogen production for a second-law based assessment purposes. The Cu–Cl cycle is considered as one of the most environmentally benign and sustainable options of producing hydrogen and is thus investigated in this study due to its potential of ensuring zero greenhouse gas (GHG) emissions. Several conceptual Cu–Cl cycles have been exergoeconomically examined previously, however this study aims at investigating the four-step integrated Cu–Cl cycle developed at the Clean Energy Research Laboratory (CERL) at the Ontario Tech University thereby contributing to the thermo/exergoeconomic assessments of the thermochemical hydrogen production. In this study, the cycle is first thermodynamically modeled and simulated in a process simulation software (Aspen Plus) through exergy and energy approaches. The basic principles of the SPECO methodology are applied to the system and exergetic cost balances are performed for each cycle component. The exergetic costing of each cycle stream is then performed based on the cost balance equations. The purchased equipment cost and the hourly levelized capital cost rates for each cycle component is also obtained. The exergoeconomic factor, relative cost difference and exergy destruction cost rate for various cycle components are also evaluated. Moreover, the effect of several parameters on the total and hourly levelized capital cost rates is analyzed by performing a comprehensive sensitivity analysis. Based on the analysis, the exergy cost, the unit or specific exergy cost, and the unit costs of hydrogen are evaluated to be 6407.55 $/h, 0.042 $/MJ, and 4.94 $/kg respectively. • Exergoeconomic analysis of an integrated copper-chlorine thermochemical cycle. • Application of the specific exergy costing (SPECO) approach. • Unit cost of hydrogen estimated to be 4.94 $/kg. • Hydrogen production capacity of 1296 kg/h. [ABSTRACT FROM AUTHOR]

In this study, an exergoeconomic analysis is performed on an integrated four-step thermochemical copper-chlorine cycle developed at the Ontario Tech. University through exergy, cost, energy, and mass (EXCEM) method. A thermodynamic model is first constructed in Aspen-plus (a process simulation software) to simulate and investigate the integrated cycle through exergy and energy analyses. The capital costs, thermodynamic loss rates, and the ratio of the thermodynamic loss rate to the capital cost of various system's components are also determined. Moreover, the average unit cost of hydrogen is evaluated and the influence of several system's parameters on the unit cost of hydrogen is analyzed. The results show that the cost of hydrogen is strongly dependent on the production capacity of the plant. Based on the analysis, our system generates hydrogen at an average unit cost of 5.54 $/kg with a plant capacity of 1619.3 kg/h considering both internal (operating and maintenance costs, etc.) and external (costs of various inputs, etc.) parameters. • Exergoeconomic analysis of a new thermochemical copper-chlorine cycle. • Application of the exergy, cost, energy, and mass (EXCEM) method. • The average unit cost of hydrogen estimated to be 5.54 $/kg. • Hydrogen production capacity of 1619.3 kg/h. [ABSTRACT FROM AUTHOR]

The role of energy transition amidst the energy crisis and how policymakers can drive down emissions while focusing on energy security are critical. Given the geo-political situation, energy crisis volatility, energy shortage and climate change all affect the green transition and the short-term priorities for energy companies and policymakers. Energy security is not an isolated issue but has widespread implications as various sectors depend on energy supply to function properly. Governments around the world are faced with this trilemma, how to balance energy security with energy sustainability while also considering energy affordability. Sustainability has been in focus for about a decade. However, energy security is suddenly becoming one of the most important priorities that policymakers need to consider. Unfortunately, the renewable energy infrastructure is not yet ready to replace the growing volume of energy demand from hydrocarbon, which the world has been dependent on. This means, for now, a surge in energy generation through hydrocarbon to meet the existing energy demand deficit. However, it is important not to lose focus on the challenge of energy sustainability and climate change adaption and mitigation. Where trends like carbon capture and storage; solar, wind, hydro, green hydrogen, etc.; renewable energy infrastructure and integrations, with supply chain and engineering services consideration [in aspect for the growing market in this space] need better attention with regards to investment and full-scale implementation. This paper aims to analyze this 1st energy crisis of green transition with a priori on energy poverty with consideration of major influences and associated impacts. Furthermore, it proposes a specific framework for inclusive investigations, which considers the entire energy ecosystem with consideration of major influences, to enable the policymakers to better drive the green transition. This involves formulating energy policies that are not entirely conservative towards renewable energy sources but instead promote investments in both green and relatively more environmentally benign energy sources compared to high emission hydrocarbons. In this regard, this paper renders exhaustive prospects and recommendations. • The nexus between energy transition, energy poverty and their impacts are investigated. • Influence of climate change, COVID-19, geo-politics, and energy infrastructure on energy transition. • Exhaustive prospects and recommendations are rendered. • Requirement for inclusive investigations and recognition of energy poverty. [ABSTRACT FROM AUTHOR]

Thermochemical water-splitting processes are among the most promising options for producing sustainable and green hydrogen due to being extremely environmentally benign. Being extensively investigated in the literature, the thermochemical copper-chlorine cycle has demonstrated much promise in this regard as one of the most efficient options for thermochemically obtaining hydrogen. Thus, this study focuses on investigating the exergoeconomic performances of the different variants of the copper-chlorine cycle including the three-, four-, and five-step versions. All cycles are modeled and simulated in Aspen-plus software by considering a recovery of thermal energy from industrial waste flue gases in addition to internal heat recovery. Moreover, a hydrogen production capacity of 668 kg/h is considered for all cycles. The Specific Exergy Costing methodology is employed to study the exergoeconomic performance of each cycle. All cycles are initially examined in terms of the cost rates of energy transfer and hourly levelized cost rates for each step. The cycle variants are further examined through a comparative assessment of several performance parameters including hydrogen cost rates, overall cost rates of energy transfer, and overall hourly levelized cost rates. According to the performed analyses, the three-step variant of the cycle that constitutes a high-temperature electrolysis process produces hydrogen at the lowest cost rate (0.83 $/kg) while the four-step cycle produces hydrogen at the highest cost rate (1.82 $/kg). Furthermore, the hydrolysis step is found to have the highest hourly levelized cost rates for all variants of the cycle. Several factors that impact the hydrogen cost rate are also examined comprehensively. In addition, the extent to which the hydrogen cost rate is sensitive to those factors is discussed. [Display omitted] • Exergoeconomic analyses of three variants of thermochemical copper-chlorine cycle. • Thermal management schemes incorporated for each cycle. • Comparative assessment of the exergoeconomic performances of all cycles. • Hydrogen production capacity of 668 kg/h for each cycle. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive review on the status of renewable energy developments and hydrogen economy in the Middle East and North Africa region. This region is heavily reliant on fossil fuels for its domestic energy supply and is also considered a global energy exporter. In this regard, an overview of the current state of energy sector in the region is provided. Moreover, the region possesses great potential for renewable energy exploitation due to its climatic advantages. Therefore, the current status of renewable energy utilization within the region's various countries is reviewed by presenting several operational renewable energy-based plants and future projects for deployment of renewable power in the region. Green hydrogen is an important sustainable clean fuel, and its utilization is essential for both environmental preservation and energy security. Thus, the status of hydrogen production and utilization in the region is discussed considering the various operational systems and future hydrogen generation projects. The concept of source, system and service is also incorporated which considers the utilization of clean energy sources for sustainable hydrogen production through environmentally benign pathways. The potential deployment opportunities for the renewable hydrogen production are also discussed based on available renewable sources in the region. Moreover, this paper discusses the challenges of increasing renewable energy utilization in the region. Furthermore, this paper provides a road map for achieving renewable hydrogen economy including a reduction in domestic utilization of oil and gas sources, subsidization of renewable production sector, and financial support to hydrogen production and transportation infrastructure. • Providing an overview of the status of energy sector in the region. • Providing an overview of the status of renewable energy utilization in the region. • Discussing the challenges and opportunities of renewable and hydrogen energy development in the region. • Providing a road map for renewable hydrogen development in the region. [ABSTRACT FROM AUTHOR]

Thermochemical water-splitting cycles have the potential of producing large-scale and cost-effective sustainable hydrogen in an environmentally benign manner. Limited exergoenvironmental assessments have been reported in the literature which generally considers thermochemical hydrogen production and specifically the copper-chlorine (Cu–Cl) cycle in thid regard. Thus, the present investigation aims at assessing the four-step integrated Cu–Cl thermochemical cycle set-up located at the Ontario Tech University thereby contributing to the environmental impact assessment of thermochemical hydrogen production. In this study, the exergy analysis of the cycle is first performed by thermodynamically modeling and simulating the cycle in Aspen-plus. The fundamental principles of the exergoenvironmental analysis, analogous to the specific exergy costing (SPECO) methodology of the exergoeconomic evaluation, are applied to the cycle and the balanced environmental impact equations for all cycle components are developed. Based on the balanced environmental impact equations, the environmental impact rate, and the specific environmental impact at each state point is evaluated. The environmental impact levels for all the major cycle components are also obtained. The exergoenvironmental factor, the relative difference of the specific environmental impacts, and the environmental impact rate of exergy destruction for various cycle components are in this regard evaluated. Furthermore, the influence of various parameters on the cumulative and component-related rate of environmental impact as well as the exergoenvironmental factor is analyzed by conducting a detailed sensitivity analysis. According to the obtained results, the rate of environmental impact corresponding to exergy destruction dominates the component-related rate of environmental impact and thus the potential reduction in the cumulative environmental impact for various components could be achieved by improving their exergy efficiencies. The hydrolysis step accounts for 60% of the component-related environmental impact while the thermolysis step accounts for the highest environmental impact of exergy destruction ranging between 41 and 42%. The percentage difference between fossil fuel-based and renewable electricity in terms of the global warming potential ranges between 80% and 98% with the highest difference for wind and nuclear-based electricity. • Exergoenvironmental analysis of an integrated copper-chlorine thermochemical cycle. • Hydrolysis step has the highest component-related environmental impact. • Thermolysis step has the highest environmental impact of exergy destruction. • Hydrogen production capacity of 1296 kg/h. [ABSTRACT FROM AUTHOR]

• Thermodynamic modeling of an integrated copper-chlorine cycle. • Performance assessment of this cycle through energy and exergy efficiencies. A comprehensive multi-objective optimization study for the cycle. • Obtaining trade-off points based on pareto frontier solutions for optimal performance. This paper considers a multi-objective optimization study performed on an integrated copper-chlorine cycle for hydrogen production developed and built at the Ontario Tech. University using genetic algorithm. The system is thermodynamically modeled in the Aspen-plus software considering all components in the cycle. A varied range of steam-to-copper ratios is selected for this study and four different cases are considered based on various steam input temperatures. The objective of this study is to maximize the rate of hydrogen production and overall system exergy efficiency, hence minimizing overall cost of cycle operation. The results of the multi-objective optimization study are presented in the form of the Pareto frontier solutions for identification of the optimal points. A comparison of the optimization results with Aspen-plus simulations is also presented for validation purposes. For all the cases considered, the optimal trade-off point results in steam-to-copper ratios ranging from 15.7 to 16.9. The steam input temperature is found to have a significant influence on the exergy efficiency and overall operating cost. The highest exergy efficiency is reported as 17.8% at a steam input temperature of 300 °C, while the minimum exergy efficiency is obtained to be 6.5% at a steam input temperature of 25 °C. [ABSTRACT FROM AUTHOR]

This paper presents a thermodynamic study on a newly built lab-scale thermochemical copper-chlorine (Cu-Cl) cycle installed at the Clean Energy Research Laboratory (CERL) at the Ontario Tech University. This study analyzes every component of the system through energy and exergy analysis by considering the heat inputs, outputs and exergy destruction within the various units of the Cu–Cl cycle. The system is modeled and simulated using the Aspen-plus software. The mass, energy and exergy balance equations for each system component are written for analysis and assessment purposes. Based on the analysis, the maximum heat input is required for the hydrolysis reactor while the HCl-condenser-1 is found to reject the maximum heat. The results suggest that the thermolysis reactor experienced the highest exergy destruction. The effect of the flow rates of certain species within the cycle on the performance of various system units, such as heat transfer rates and production flow rates are also investigated. The overall energy and exergy efficiencies of the system are evaluated to be 6.8% and 10.4%, respectively. • Thermodynamic analysis of a new copper-chlorine thermochemical cycle. • Mass, energy, entropy and exergy balance-based investigation. • Overall system energy and exergy efficiencies of 20.9% and 31.46% respectively. • Hydrogen production rate of 1.62 kg/h. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive review on the various techniques and routes of solar hydrogen production. The solar energy options considered are thermal energy, electrical energy, photonic energy, and hybrid options. The hybrid option includes thermal and electrical, electrical and photonic, biochemical and thermal, and biochemical and photonic energies. Some relevant literature review with their key findings, conclusions, and suggestions is presented. Various methods of solar energy-based hydrogen production are explained and briefly discussed. The technologies available for realizing these methods are also presented. Some recent advances in solar hydrogen generation is also presented in which some novel techniques are discussed. Some plant configurations are also discussed and compared to consider the factors which influence the cost of hydrogen. This review article also aims to comparatively assess and evaluate the several routes of producing hydrogen using solar energy. The comparative evaluation is performed using two sets of criteria. Criteria set 1 consists of environmental impact and cost of hydrogen production. Criteria set 2 comprises energy and exergy efficiencies, sustainability indices and hydrogen production rates. High-temperature energy methods show much better efficiencies and hydrogen yield while at the same time are more environmentally harmful. Photonic and biochemical energy routes are more environmentally friendly and sustainable, but have low efficiencies. • Identifying potential solar hydrogen production methods for application in various sectors. • Categorizing the potential methods for various applications and possibilities under various conditions. • Discussing the challenges and opportunities as well as future directions of the considered methods. • Comparatively evaluating the considered methods. [ABSTRACT FROM AUTHOR]

• Thermodynamic analysis of a new copper-chlorine thermochemical cycle. • Heat recovery within the cycle for improving efficiencies. • System energy and exergy efficiencies of 6.8% and 10.4% respectively without heat recovery. • Highest obtained energy and exergy efficiencies of 10.7% and 16.3% respectively with heat recovery. This paper develops a thermal management method for the integrated lab-scale copper-chlorine cycle built in the Clean Energy Research Laboratory at the Ontario Tech. University for hydrogen production and studies thermodynamically through energy and exergy approaches. The performance of the system is assessed based on the overall system energy and exergy efficiencies. The approach is further implemented to study the possible options for the highest amount of heat recovery within the cycle. Six different steam and heat recovery configurations are considered in this study based on the various streams recovered within the cycle, with each configuration having a different steam-to-copper molar ratio. The criteria for assessing the performance of each configuration are the exergy destruction of the heater-1 of the system, net thermal exergy, net heat input, and hydrolysis unit heat input, the temperature achieved after heat recovery and the overall system energy and exergy efficiencies. The temperature achieved after heat recovery and the steam-to-copper molar ratio are found to be the key aspects impacting the performance of each configuration. The overall energy and exergy efficiencies of the system without considering heat recovery are evaluated to be 6.8% and 10.4%, respectively while the highest energy and exergy efficiencies obtained after considering heat recovery are found to be 10.7% and 16.3% respectively which shows the influence of heat recovery on the performance of the system. [ABSTRACT FROM AUTHOR]

When air flows through pipe systems that include a corrugated segment, a whistling tone is generated and increases in intensity with increasing flow velocity. This whistling sound is related to the particular geometry of corrugated pipes, which is in the form of alternating cavities. This whistling is an environmental noise problem as well as a possible structural danger because of the resulting induced vibration. This paper studies the whistling behavior of various pipe systems with a combination of smooth and corrugated pipes through a series of experiments. The considered pipe systems consist of two smooth pipes attached at the upstream and downstream ends of a corrugated segment. Experiments with smooth and corrugated pipes, which had inner diameters of 15.25 and 16.5 mm, respectively, and various lengths, were performed for flow velocities of up to approximately 30 m/s. The minimum and maximum Strouhal numbers ( S t ) obtained during our experiments were 0.25 and 0.38, respectively. For all pipe configurations investigated in this study, the lowest Mach number at which whistling was observed was 0.017, and the maximum was 0.093. The lowest frequency at which whistling was detected in our experiments was 650 Hz, and the highest was 3080 Hz. The results presented in the form of different variables and dimensionless parameters, including the frequency, Mach number, Strouhal number, and Helmholtz number. The average mode gap and number of excited acoustic modes were also taken into account for all considered configurations. The pipe systems with longer corrugated segments had broader whistling ranges than did configurations with shorter segments, indicating that the number of cavities inside the corrugated pipe has a direct effect on whistling. Increasing the smooth pipe length (either upstream or downstream) resulted in a decrease in the average mode gap between successive modes. The number of excited acoustic modes was primarily related to the corrugated segment length, but the smooth pipe length also had a pronounced effect on the excited modes for a constant corrugation length. The highest number of excited modes (13) was seen in the case of corrugated length 450 mm and smooth pipe length (either upstream or downstream) 400 mm while the lowest number of excited modes (1) was observed for corrugated length 250 mm and smooth pipe length (downstream) 300 mm and 400 mm. [ABSTRACT FROM AUTHOR]

Rapidly increasing catastrophic environmental incidents and changes in global climate have compelled researchers to take proactive measures for climate change mitigation. Consequently, reducing greenhouse gas emissions has become one of the most significant global targets. The transportation sector has a massive carbon footprint accounting for 22% of the total carbon dioxide emissions. In this regard, road transport contributes the largest fraction of the total emissions within the transportation sector. Conversely, the railway which is the cleanest form of transportation contributes slightly more than 1% of the total emissions. Moreover, since most of the rail systems are operated by government or private companies, it is relatively convenient to implement policies and replace conventional technology with environmentally friendly ones. This could be achieved by taking certain measures from technical and operational viewpoints for conserving energy to lower the carbon intensity of all transport modalities. Hence, this review paper focuses on investigating the railway sector to encourage a modal shift to the least carbon-intensive option. This study provides a critical review of the past and present rail technologies in terms of the environmental, economic, social, and technical perspectives. Moreover, a comparative assessment of the various locomotive types has been performed. The results reveal that battery-hydrogen hybrid locomotives are the best choice to be considered as a future locomotive technology. Hydrogen locomotives have the potential to be a promising alternative to diesel railway locomotives. However, certain technical barriers need to be overcome to enhance the overall system's performance and reliability to further improve the viability of its deployment in the railway sector. [Display omitted] • A critical review of the various rail technologies is provided through different viewpoints. • The assessment constitutes environmental, economic, social, and technical perspectives. • A decision-support tool for comparison of four rail technologies is also developed. • Battery-hydrogen hybrid locomotive results in the highest score of 1.47. • Standalone hydrogen locomotive results in the second highest score of 1.38. [ABSTRACT FROM AUTHOR]

[Display omitted] • Renewable natural gas (RNG) can be produced from landfill gas, wastewater sludge, and animal waste. • Triple bottom line performance of waste-derived gaseous fuel was assessed using LCA and LCC. • Animal manure-derived RNG production provides the best environmental performance. • LFG-derived RNG yield the highest suitability from neutral and environmental perspectives. • RNG production suitability varies with regional conditions and decision contexts. Renewable natural gas (RNG) is one of the most prominent fuels that help reduce upstream emissions from conventional natural gas networks without significant infrastructure changes. While the current resources for RNG are insufficient, there is a substantial interest in establishing the viability of integrating RNG into the gaseous-fuel industry portfolio. However, holistic studies that support the assessment and selection of the fuel production paths are limited. Therefore, the current study attempts to close that gap by introducing a systematic approach to assess the project viability of RNG investments. Twelve waste-to-RNG configurations were evaluated based on three types of waste feedstock and four biogas upgrade technologies in three selected population centres. Life cycle environmental and life cycle cost assessment tools were employed to determine the ecological footprint and economic performance of RNG production routes. Multi-criteria decision-making was applied using the TOPSIS method under varying stakeholder perspectives to derive suitability indices for RNG investments. Finally, recommendations were provided based on the results obtained for successfully implementing waste-to-RNG supply chain paths. According to study findings, not all RNG production methods guarantee positive returns. The least environmental impacts were assured by the anaerobic digestion of animal manure. However, the lowest returns were obtained via the same route. From a pro-economic and neutral decision perspective, landfill gas-based RNG production achieved higher suitability scores. The proposed framework is flexible and can be customized to suit varying decision priorities. The findings are geared towards supporting utility providers, community developers, and potential investors to foresee the success of planned RNG projects to ensure sustainable gaseous fuel networks. [ABSTRACT FROM AUTHOR]

Energy retrofitting for buildings has gained great attention in recent years due to the significant benefits of reducing environmental impacts and costs. Generally, retrofit planning involves considering criteria such as energy savings, emissions savings, and cost savings. However, the rapid transition of climate and extreme climate forces integrate climate adaptation into retrofit practices. This study examines strategies and modifications necessary to transform the current climate mitigation-based retrofit processes into frameworks that simultaneously improve climate mitigation and adaptation. A comprehensive literature review is conducted on building energy retrofit studies based on climate adaptation. It was found that future climate events are anticipated to be more related to overheating than under-cooling in many regions. Passive retrofit strategies can reduce overheating risks substantially, while the dependency on active cooling is unavoidable in warm climatic regions in future climates. Retrofit strategies designed based on traditional approaches may not be effective and may even worsen the risks of overheating in the future climate due to drastic climate change. Climate resiliency criteria must be adapted to the building retrofit field. Climate modelling and energy simulation have a substantial role in designing retrofits, and yet significant research and development is required to penetrate the current retrofit practices. The synthesis of the findings guides the systematic and careful designing and implementation of building energy retrofits. These findings offer valuable insights to policymakers, urban planners, and researchers seeking to improve buildings' energy performance and resiliency and act as a guideline to implement climate change adaptation strategies. • Reviewed climate adaptation-based retrofit designing and planning studies. • Revealed a significant gap in existing retrofit frameworks that consider both climate mitigation and adaptation. • Highlighted careful design and implementation of retrofits is necessary to overcome future climate risks. • Presented a comprehensive guideline to integrate climate adaptation aspects into current retrofit practices. • Suggested future research directions, including the development of climate resilience benchmarks. [ABSTRACT FROM AUTHOR]

Production of hydrogen fuel from municipal solid waste can serve as a potential solution to two looming environmental crises: global warming caused by undesirable emissions of greenhouse gases and the ever-increasing generation and accumulation of waste in the environment. However, the actual implementation and continuous operation of waste-to-hydrogen conversion facilities require consideration of numerous factors. This study explored the variability of several factors related to waste-to-hydrogen, such as location selection, geographic availability of municipal solid waste, pricing of by-products and waste acceptance, constantly fluctuating energy costs, and carbon credit market values from potential carbon trading systems. Four waste conversion processes previously studied for their triple-bottom-line sustainability have been used as baseline scenarios. The variability of multiple factors and their impacts were assessed via parametric analyses. The effects of these fluctuating factors on the economic and environmental performances of waste-to-hydrogen conversion and the establishment of processing facilities were captured. The results of this study will be beneficial for the industry, private investors, policymakers, and governments while making critical decisions such as location selection, deriving price formulas, and selecting plant capacity. • Implementation of four waste-to-hydrogen processes is studied. • Variabilities impacting levelized cost of hydrogen and global warming are assessed. • Economies of scale attained in all processes except waste pyrolysis. • Waste gate fee, carbon credits, and by-product sales reduce levelized costs. • Areas with high population density are suited for waste-to-hydrogen implementation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sustainability of four waste-to-hydrogen conversion methods is evaluated. • Pyro-gasification and bioreactor landfills are assessed in hydrogen production. • Lifecycle thinking and VIKOR method-based multicriteria decision-making are used. • Reactor heating method, electricity mix, and waste transportation fuel are varied. • Gasification provides highest yields; pyrolysis causes lowest lifecycle impacts. Waste-derived hydrogen (H 2) has been identified as a clean energy source which could simultaneously abate greenhouse gas (GHG) emissions and avert municipal solid waste (MSW) from being deposited in perpetual landfills. In this study, four waste-to-hydrogen processes – gasification, pyrolysis, integrated pyrolysis-gasification, and landfill bioreactor technology – are studied with MSW as feedstock. Following technological evaluations, life cycle assessment and life cycle costing are performed for different scenarios and configurations to evaluate their environmental footprint, levelized cost of H 2 , and energy return on investment. Finally, multicriteria decision-making was applied using the VIKOR method under four weighting schemes to evaluate the four processes under varying decision-making contexts. Gasification results in the highest H 2 outputs and energy returns, whereas pyrolysis produces the lowest levelized cost due to its biochar by-product formation. Nevertheless, all four technologies proved to be performing optimally under different weightings of environmental, economic, and social elements, suggesting the versatility of the waste-to-hydrogen concept and its suitability to be applied in various decision-making contexts. The results and novelties of this study would contribute toward planning and investment decision-making in sustainable H 2 production and clean energy. [ABSTRACT FROM AUTHOR]