CO2eq Emissions Research Articles

Carbon feasibility of terminating plastic waste leakage by landfill mining: A case study based on practical projects in China

Over 900 million tons (Mt) of plastic waste (PW) are disposed in Chinese landfills, posing a permanent risk of migration through environmental media. Landfill mining has emerged as a promising solution to this problem but requires incineration and a substantial energy supply for the excavation, sorting and recycling processes, which themselves exert environmental impacts, particularly on climate change. Based on the life cycle assessment of pilot-scale demonstration projects, this study investigates the carbon feasibility of landfill mining followed by several PW treatments to quantify whether terminating PW leakage from landfills will produce unaffordable greenhouse gas emissions in the drive towards carbon neutrality. The changing trend of the carbon feasibility was deduced considering the decarbonization scenarios of electricity sector and petrochemical industries. When all the sorted PW is treated by incineration with power generation, the climate-change impact of mining is 134.10 kg CO2-eq per ton of aged refuse, projected to increase by 100.47 % in 2050. To completely eliminate the PW in Chinese landfills, the incineration pathway would generate a minimum of 2457.66 Mt CO2-eq emissions, equivalent to 17.69 % of the 2020 emissions in China by carbon flow analysis. In all scenarios, the most carbon-feasible solution was mechanical recycling of high-quality PW combined with chemical recycling of low-quality PW, although the industrial application of chemical recycling technologies remains uncertain. This study provides stakeholders with systematic guidance for balancing the trade-off between PW management and climate action.

Environmental Assessment of Demolition Tools Used in Townhouse Demolition: System Dynamics Modeling

To accommodate population growth and migration to cities, many infrastructures have been demolished to build new residential units. Demolition processes cause various environmental problems globally and locally. The selection of methods used in demolition is crucial to reduce the long-term environmental impact. This study considers various combination tools used in townhouse demolition in Thailand, examines their environmental impacts, and suggests the combination of the tools to be used in the long term. The system dynamics (SD) modeling approach is utilized in this study to capture the changes in townhouse units, sizes, demolition tools, demolition time, and the work rates of tools and their effects on the environment. This approach has the capability to model complex relationships and examine long-term trends. Secondary data are employed to identify variables necessary for SD model development, such as the different sizes of townhouses in Thailand, the various types of demolition tools used in the construction industry, and environmental impacts from building demolition. The simulation results revealed that Combination 4, i.e., the use of demolition robots and hydraulic splitters, is the most effective combination to reduce the final impact percentage in the long term. Compared with the other three combinations, it generates the lowest CO2eq emissions, energy consumption, noise, dust, and heat. If demolition robots are not yet available, Combination 1 (i.e., the use of excavators, jackhammers, and flame-cutters) offers the lowest environmental impact in the long term. This study provides guidelines for decision-makers in the construction industry to make sustainable choices of demolition tools and techniques used for townhouse demolition to reduce long-term environmental impacts.

CO2, CH4, and N2O emissions from dredged material exposed to drying and zeolite addition under field and laboratory conditions

Dredging, the removal of sediment from water courses, is generally conducted to maintain their navigability and to improve water quality. Recent studies indicate that dredging can significantly reduce aquatic greenhouse gas (GHG) emissions. These studies, however, do not consider the potential emission from the dredged material (sludge) in the depot. In addition, it is unknown if and how GHG emissions from sludge depots can be reduced. Here we present spatiotemporal variations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes, as well as environmental variables from a sludge depot located in the Netherlands. Measurements were conducted monthly from the time the depot was filled until the sludge was dry and the depot was abolished. We also experimentally assessed the GHG mitigation potential of 1) keeping the sludge permanently inundated, and 2) the addition of different amounts of zeolite to increase sludge nitrogen binding capacity to reduce N2O emissions. In the depot and in the laboratory, a decrease in moisture content coincided with increased CO2 and N2O emissions while CH4 emissions decreased. We observed that permanent inundation reduced emissions (∼4 times less CO2-eq than in drying sludge). Adding zeolite lowered N2O fluxes from permanently inundated sludge but did not reduce total GHG emissions. During the depot's operational period, average CO2, CH4, and N2O fluxes were 5078, 27, and 5 mg m−2 d−1, respectively. GHG emissions from drying sludge occurred mainly in the form of CO2 (73% of the total CO2-eq emissions), with average GHG emission rates comparable to those reported for ditches and ponds. We estimate that approximately 14 tons of CO2-eq were emitted from the 0.011 km2 depot, which contained ∼20,000 m3 of sludge, during its entire operational period, and we argue that more studies are needed, considering different sludge origins, to expand our understanding of sludge depots.

Life cycle assessment of greenhouse gas emission from the dairy production system - review.

Climate change is altering ecological systems and poses a serious threat to human life. Climate change also seriously influences on livestock production by interfering with growth, reproduction, and production. Livestock, on the other hand, is blamed for being a significant contributor to climate change, emitting 8.1 gigatonnes of CO2-eq per year and accounting for two-thirds of global ammonia emissions. Methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) are three major greenhouse gases (GHG) that are primarily produced by enteric fermentation, feed production, diet management, and total product output. Ruminants account for three-quarters of total CO2-equivalent (CO2-eq) emissions from the livestock sector. The global dairy sector alone emits 4.0% of global anthropogenic GHG emissions. Hence, dairy farming needs to engage in environmental impact assessment. Public concern for a sustainable and environmentally friendly farming system is growing, resulting in the significant importance of food-based life cycle assessment (LCA). Over the last decade, LCA has been used in agriculture to assess total GHG emissions associated with products such as milk and manure. It includes the production of farm inputs, farm emissions, milk processing, transportation, consumer use, and waste. LCA studies on milk production would assist us in identifying the specific production processes/areas that contribute to excessive greenhouse gas emissions when producing milk and recommending appropriate mitigation strategies to be implemented for a clean, green, and resilient environment.

Effect of quality of separately collected glass, paper plus cardboard and lightweight packaging waste on environmental, energetic and economic sustainability of the material recovery facility operations

Low-quality materials contained in separately collected (SC) packaging waste generate environmental and economic burdens associated to both sorting operations of Material Recovery Facilities (MRFs) and landfilling of non-recyclable materials. In this study, based on quantification of both impurities and recyclable fractions, the quality of SC municipal packaging waste streams was determined by compositional analysis of the waste entering a MRF throughout a year. Foreign materials (% w/w) found in the monitored SC glass, paper plus cardboard and lightweight packaging waste, were on average 5.0, 14.7 and 23.0, respectively, while landfilled materials (% w/w) after MRF sorting operations were on average 4.3, 10.3 and 22.0, respectively. A Life Cycle Assessment study was conducted to determine the environmental impact of SC packaging waste streams quality of three different scenarios: current situation (CS), better (BS) and ideal (IS) scenario with reduced presence and absence, respectively, of improper materials in the three examined SC packaging waste streams. Emission of 32.1 kg CO2eq/twaste was calculated for the current situation with a reduction by 66.1% and 98.0% in CO2eq emission for BS and IS scenario, respectively. Similar emission reductions were calculated for ozone depletion, ionizing radiations, particle matter formation, fossil fuel depletion and primary energy demand impact categories. The environmental life cycle costing study demonstrated that total savings of € 35.2 and € 66.6 for each ton of SC packaging waste stream entering the MRF could be obtained for BS and IS scenario, respectively.

Tapping the Unused Energy Potential of Solar Water Pumps in India.

India seeks to deploy millions of solar water pumps to farmers who often lack access to electricity or face an unreliable power supply. Improving the use of this technology can bolster sustainable agriculture and expand clean energy services. We investigate farm-level impacts and opportunities with primary survey data (n = 292 farmers) and a large real-time pump operational data set (n = 1106 pumps). By modeling the potential solar generation of off-grid solar water pumps, we estimate 300-400 kWh/month of unutilized solar energy per pumping system, representing up to 95% of potential generation. While farmers report increased revenues and ease of pump operation, unsolved challenges concerning the lack of panel cleaning and tracking remain. Pump operational data show pump usage in the summer and monsoon seasons and an expansion of irrigation to grow crops in the winter. Relative to emissions associated with the use of diesel pumps, solar pumps that are highly utilized reduced life cycle CO2-eq emissions by 93% on average, while the pumping systems with the lowest use result in a net increase of 26% relative to the diesel alternatives. Based on observed usage rates, approximately 70% of pumps had positive environmental benefits. The high share of unutilized solar energy provides a significant opportunity to use the energy for nonpumping purposes.

The potential of wastewater-source heat pump in decarbonising buildings sector of China

ABSTRACT As China's economy and society continue to advance, there has been a notable enhancement in the quality of life for its people. However, the escalating energy consumption in buildings, particularly for heating and cooling purposes, has emerged as a pressing concern, accounting for nearly 60% of the overall energy consumption. In response to this challenge, heat pumps have emerged as a promising solution by efficiently meeting the demand for heating and cooling. Among these options, wastewater-source heat pumps (WWSHP) have garnered attention as an innovative choice, harnessing the waste heat in available wastewater resources in China to provide efficient heating and cooling services. The objective of this study was to comprehensively investigate the decarbonisation potential associated with sewage source heat pumps in China. By employing both techno-economic analysis and life cycle assessment methods, we conducted a thorough comparison between conventional heating and cooling systems and various heat pump systems. The results of our analysis demonstrate that WWSHPs not only exhibit the lowest greenhouse gas (GHG) emissions but also yield the lowest production costs. Our findings reveal that the potential capacity of WWSHPs amounted to a total of 2.4 EJ in 2020, with the capability to mitigate 99 Mt CO2-eq emissions and achieve cost savings of 24 billion RMB. Importantly, WWSHPs’ maximum potential cannot be fully realised by replacing heating alone. However, by replacing both heating and cooling options, WWSHPs unlock substantial decarbonisation potential and cost savings.

Nitrous oxide and methane emissions from a Ferralsol as affected by loblolly pine cultivation time in subtropical Brazil

We hypothesized that the age of loblolly pine stands influences soil methane (CH4) and nitrous oxide (N2O) emissions. This is a relevant topic to be studied in subtropical Brazil, where the pine plantation area is increasing considerably. We evaluated N2O and CH4 emissions for two years in a Ferralsol under loblolly pine (Pinus taeda L.) stands of 1, 9 and 18 year-olds and a native forest (NF). We calculated the net CO2eq emission by considering the N2O and CH4 emissions from soil and the carbon (C) accumulation as litter in the forest floor. The soil N2O emission reduced gradually over the loblolly pine cultivation years, whereas CH4 uptake rates showed no clear pattern. Soil N2O emission showed a positive relationship with soil temperature in NF, and with soil ammonium and nitrate intensities in the pine stands. Soil CH4 uptake was inversely related to water-filled pore space in the pine stands, but this relationship was not observed in NF. The soil CH4 uptake rate was 4.6 times higher (p < 0.10) in NF than the average uptake in loblolly pine stands. On the other hand, soil N2O emissions in 9 and 18-year-old stands were similar (p > 0.10) to those in NF (1.3 kg N ha−1 yr−1). Our results suggest that cultivation with loblolly pine for 18 years can reduce soil N2O emission, and the uptake of CH4 in this system offsets 17 % of N2O emissions. Furthermore, the C accumulation as litter in the forest floor of the mature pine stands (9- and 18-year-old) generated a net emission of −1.6 Mg CO2eq ha−1 yr−1, showing to be an expressive offsetting mechanism. Therefore, we conclude that aged loblolly forests can reach N2O emissions levels comparable to those of NF, and the C sequestration in these forests floor can significantly contribute to offset N2O emissions and act as sink for net atmospheric CO2eq.

Making green growth a reality: Reconciling sobriety with stakeholders' satisfaction.

The notion of sobriety is considered a key variable in various energy transition scenarios. Often associated with a form of punitive ecology, it is, nevertheless, possible to make it a component that supports green growth, by linking it to the concept of "satisfaction". In this work, we have invented a way to achieve both "digital", "economic", and "ecological" sobriety, while ensuring the satisfaction of the end user. Directly correlated to the production of goods or services, the satisfaction function is built on the well-documented marginal utility function, which measures the need (or not) to consume further resources to satisfy the economic agents. Hence, it is justified and exists because it stands for the expectations of end users and makes sure the latter is met. This product itself is a function of the allocation of a set of resources, mapped using activity-based costing tools (ABC method). In this work, we focus on an AI proof-of-concept and demonstrate that it is possible to reach numerical sobriety by controlling the size of the training dataset while ensuring roughly the same model performance. In general, we show that it is possible to preserve the efficiency of AI processes while significantly minimizing the need for resources. In this sense, after establishing an analytical model, we suggest reducing the amount of data required to train the machine learning (ML) models, while guaranteeing zero change in terms of performance (say their accuracy). We show that it affects the energy consumed, and, thereby, the associated cost (i.e., economic and ecological) and the associated CO2eq emission. We thus confirm the existence of a "triangle of sobriety". It is defined as a virtual circle governed by a digital-economic-ecological sovereignty. We also propose that if AI production processes have a potential for sobriety, all identical activities have the same characteristics, thus opening the path to green growth.

A fuzzy cognitive map-based algorithm for predicting water consumption in Spanish healthcare centres

The management of water consumption in healthcare centres can have positive impacts on both the environmental performance and profitability of health systems. Computational tools assist in the decision-making process of managing the operation and maintenance of healthcare centres. This research aimed to integrate the empirical knowledge of experts in Healthcare Engineering and the historical data from 66 healthcare centres in a Fuzzy Cognitive Map. The outputs of the predictive model included water consumption, water cost, and CO2 emissions in healthcare facilities, along with eleven variables to discover the causes and consequences of water consumption in healthcare centres. A healthcare centre with about 12 350 users, located in a city that experiences an average of 1100 heating degree days, whose facilities be moderately energy-efficient contributing over 50% with renewable energies is expected to consume 8.4 dam3 of water with 32.1 k€ of cost, and contribute realising 30.8 ton CO2eq emissions. The use of Fuzzy Cognitive Maps for prediction can provide a high level of effectiveness in identifying the factors that contribute to water consumption and in designing key performance indicators to manage the environmental performance of healthcare buildings. This tool is extremely effective in enhancing the performance of the management division of health systems.

Two contrasting years of continuous N[formula omitted]O and CO[formula omitted] fluxes on a shallow-peated drained agricultural boreal peatland

Drained agricultural boreal peatlands comprise a large source of nitrous oxide (N2O) and carbon dioxide (CO2) but a small sink or source of methane (CH4). N2O fluxes have high spatial and temporal variability and are often measured with the chamber technique. Therefore, continuous measurements of N2O fluxes are needed to better understand how N2O emissions are triggered and to reduce the uncertainty of annual N2O budget estimations. Here we present a two-year-long time series of continuous measurements of CO2 and N2O fluxes of a shallow-peated drained agricultural boreal peatland cultivated for grass silage. The fluxes were measured with the area-averaging eddy covariance technique. Several N2O peak events were observed throughout all seasons. The peaks were associated with meteorological or management events, such as soil thawing or freezing, precipitation, fertilization and glyphosate application. The annual N2O budget was 4.74 ±0.47 and 6.08 ±0.49 kg N2O-N ha−1 y−1 in 2020 and 2021, respectively. The annual CO2 budget, comprising the sum of net ecosystem exchange and biomass export, was 3.70 ±0.22 and 5.54 ±0.33 t CO2-C ha−1 y−1 in 2020 and 2021, respectively. The N2O budget during the first, warmer winter was 106% higher than during the second, meteorologically more typical winter, due to the higher frequency of soil freezing–thawing cycles. The average annual N2O budget was 36%–50% lower than the IPCC Emission Factor (EF) while the CO2 budget was in accordance with the IPCC EF. CO2 emissions dominated the total CO2-eq emissions of our site but N2O also had a significant contribution of 12%. Our results also suggest that glyphosate application enhanced N2O emissions in the last quarter of 2021. However, the full rotation should be measured to confirm whether there is a need to re-evaluate the N2O IPCC EF for ‘grassland drained boreal’ land-use class.

What are the energy and greenhouse gas benefits of repurposing non-residential buildings into apartments?

This study examines the potential strategies for reducing embodied energy and greenhouse gas emissions through adaptive reuse of non-residential buildings for residential purposes, as compared to new construction of apartment buildings. Such an approach can address housing crises in urban areas with an abundance of underutilized non-residential buildings, promoting sustainable housing growth. A comprehensive assessment of repurposing in California reveals approximately 510 million m² of floor space across 230,000 non-residential buildings in the current building stock. The potential reduction in embodied energy and CO2eq emissions ranges from 0.14 to 1.4 billion GJ and 5.0–70 million metric tons for the state, respectively, contingent upon the percentage of repurposed floor space (10–100%) and adaptive reuse scenario (retaining structural components and façade or solely the structure). A repurposed building avoids about 56% of embodied energy, 34-48% of CO2 eq emissions, and 72% of materials by mass compared to building a new apartment building. However, various technical, financial, and regulatory challenges may hinder emissions reductions, necessitating proactive policy measures. Cities can potentially expedite the process by streamlining approvals for mixed-use adaptive reuse projects involving both commercial and residential spaces.

Tracking Carbon Flows from Coal Mines to Electricity Users in China Using an Ensemble Model.

Accurately tracking carbon flows is crucial for preventing carbon leakage and allocating responsibility for reducing CO2eq emissions. In this study, we developed an ensemble model to effectively track carbon flows within China's power system. Our approach integrates coal quality tests, individual power plant datasets, a dynamic material-energy flow analysis model, and an extended version of an interconnected power grid model that incorporates transmission and distribution (T&D) losses. Our results not only provide accurate quantification of unit-based CO2eq emissions based on coal quality data but also enable the assessment of emissions attributed to T&D losses and emission shifts resulting from interprovincial coal and electricity trade. Remarkably, for CO2eq emissions from coal-fired units, the disparity between the guideline and our study can be as high as [-95%, 287%]. We identify Guangdong, Hebei, Jiangsu, and Zhejiang provinces as the major importers of both coal and electricity, responsible for transferring nearly half of their user-based emissions to coal and power bases. Significantly, T&D losses, often overlooked, contribute to 15-20% of provincial emissions at the user side. Our findings emphasize the necessity of up-to-date life cycle emissions and spatial carbon shifts in effectively allocating emission reduction responsibilities from the national level to provinces.

Energy and environmental evaluation of alternative fuel vehicles in Maghreb countries

This study conducts a well-to-wheel assessment of alternative fuel vehicles in the Maghreb region, aiming to reduce greenhouse gas emissions from the transport sector. The research employs international standards, ISO 14040–14043, to assess diesel, hybrid-electric, battery-electric, and fuel-cell vehicles and highlights the potential benefits of transitioning to electric and fuel-cell vehicles in the Maghreb, offering energy efficiency and reduced environmental impact.The sensitivity analysis suggests that fuel-cell vehicles are the best alternative for Morocco and Algeria, while battery-electric vehicles are preferable in Tunisia. By 2030, fuel-cell vehicles in Morocco and Algeria would consume 128 ​MJ and 125 ​MJ and emit 7.9 CO2eq and 7.1 CO2eq emissions per 100 ​km, respectively, while in Tunisia, battery-electric vehicles are expected to consume 114 ​MJ and emit 6.55 CO2eq emissions per 100 ​km driven. Ultimately, the right adoption of alternative fuel vehicles in the Maghreb region implies half energy need cut off and 60% less GHG emissions from light-duty vehicles leading to improved environmental conditions, health outcomes, and economic growth.

Closing the loop of membranes by recycling end-of-life membranes: Comparative life cycle assessment and economic analysis

Membrane technology has been widely adopted in various industries. However, the inappropriate disposal of end-of-life (EoL) membrane is an urgent issue impeding the sustainability of membrane technology. Herein, we proposed a closed-loop pattern for membrane use by employing upcycling EoL low-pressure membranes and downcycling EoL high-pressure membranes. Life cycle assessment and economic analysis showed that applying the closed-loop recycling strategy could reduce the environmental impacts by 22–27%, in which 24% CO2-eq emissions would be saved with about 27.1% economic advantages, thanks to the reduction of new membrane production and EoL membrane disposal. Sensitivity analysis indicated that more benefits would be achieved through membrane recycling if the project lifetime or the recycled membrane lifetime were extended. Monte Carlo analysis suggested that the closed-loop scenario had less potential to create more environmental impacts than the non-recycling scenario. These results implied that the closed-loop recycling pattern provided a promising paradigm for sustainable membrane application.

Optimal expansion for a clean power sector transition in Mexico based on predicted electricity demand using deep learning scheme

This study presents a mathematical programming approach for the strategic planning of electrical energy production. The proposed approach seeks the optimal selection of conventional and clean technologies and their production capacity in a given period. In addition, it aims to assess the amount of emissions generated and water consumption, without neglecting economic aspects. The planning considered in this study extends from 2020 to 2040, where the approach considers the implementation of deep learning models to forecast the future electricity demand of each year through historical data; thus obtaining a more precise energy configuration. Fossil fuels and biofuels are used as primary energy in the operation of different technologies. Therefore, both economic and environmental objectives are considered. The economic objective function determines the minimum total discounted cost, which encompasses energy production, operation, maintenance, primary energy, and investment costs. While the environmental objective focuses on reducing water consumption and emissions. Through Pareto curves, using the ɛ-constraint method, the proposed model determines the trade-offs between the total discounted cost and the CO2eq emissions generated. The Mexican electrical system is presented as a specific case study with real production data and available resources. The results show that it is possible to reduce the total discounted cost by up to 11.02%, while in environmental aspects, up to 28.27% in emissions and up to 20.23% in water consumption, achieving that the power produced by renewable energies increases progressively until reaching 70% of the energy demand in 2040, where the system is committed to implementing clean technologies and replaces a percentage of fossil fuels with biofuels in conventional technologies. The results highlight that by increasing the investment cost with clean technologies, the system is balanced with a lower total future cost in the planning presented, thus reducing the environmental burden, and determining trade-offs between cost and environmental aspects.

Minimizing Single-Family Homes’ Carbon Dioxide Emissions and Life Cycle Costs: An Improved Billiard-Based Optimization Algorithm Approach

In recent years, research has focused on designing buildings with higher energy efficiency and lower emissions by considering multiple objectives. This can impact financial savings, smaller environmental footprints, and energy consumption optimization. The purpose of the current study is to develop a new technique to solve this challenging multiple-objective optimization problem. While there are different methods to solve optimization problems, based on the NLP theory, there is not any metaheuristic algorithm that can solve all the problems accurately. Sometimes, the outcome of a basic algorithm is a local optimum. Therefore, to reach the global optimum, we propose the Improved Billiard-based Optimization Algorithm (IBOA). Moreover, in some cases, the basic model suffers from premature convergence, which prevents reaching an accurate result. Hence, this study aims to solve this problem and attain better convergence results using the proposed method to minimize CO2-eq emissions and life cycle costs. The design variables include some parameters of the envelope of a single-family residential dwelling to indicate the efficiency of the presented method. Based on the Pareto optimum solutions achieved, it is proved that the method is effective.

Environmental assessment of asphalt mixtures modified with polymer coated rubber from scrap tires

Polymer coated rubber (PCR) is an engineered crumb rubber developed to address the drawbacks of regular crumb rubber in asphalt mixtures, such as the absorption of asphalt binder and premature cracking. Assessing the use of PCR using life cycle assessment (LCA) is important to evaluate whether its use lowers the environmental impact of asphalt mixtures. In LCA, the choice of allocation procedure significantly impacts the results. The cut-off method is often used in LCA studies of products containing recycled materials. The objectives of this work were to evaluate: i) if asphalt mixtures modified with PCR had lower environmental impact than mixtures modified with synthetic polymers, ii) if using more PCR decreased the environmental impact of the asphalt mixtures, iii) if the results changed by using different allocations methods, and finally, iv) if the environmental impact of asphalt mixtures changed when considering the long-term mechanical performance of the blends. In this work, the global warming potential (GWP), fossil depletion, and cumulative energy demand of one ton of asphalt mixture were calculated using the cut-off method, economic allocation, and system expansion. For the system expansion, the recovery energy in cement kilns from scrap tires was compared to burning petroleum coke or natural gas. The LCA of asphalt mixtures modified with two amounts of PCR (0.5% and 1% by weight of total mixture) compared to the synthetic polymer styrene-butadiene-styrene (SBS) was performed by including results of the experimental investigation (asphalt mixture design and mechanical testing conducted in the asphalt laboratory at Michigan State University). Results were different based on the allocation method considered. Overall, the GWP of PCR 0.5% and PCR 1% mixtures was lower than the SBS mixture, except in one case. The GWP of PCR 1% was 2% higher than the SBS mix when petroleum coke was used in the system expansion. Adding more PCR did not necessarily increase the environmental benefits. PCR 1% had a higher GWP than PCR 0.5% (2.6%, 2.7%, and 6.3% by using cut-off, economic allocation, and system expansion, respectively), except for the system expansion using natural gas as a replacement, which was 3.7% lower than the PCR 0.5%. However, the system expansion with natural gas had the lowest GWP compared to the other methods. On the contrary, the system expansion considering petroleum coke had the highest CO2eq emissions among all the methods used. The GWP of PCR 0.5% and PCR 1% was similar by using cut-off and economic allocation. As the cement industry transition to low-carbon energy, the carbon footprint associated with using scrap tires in pavements will decrease when using system expansion, while it will remain the same with the cut-off method. Considering the mechanical performance of the mixtures, the GWP for the pavement with 0.5% PCR was 8.04% lower over its service life than the synthetic polymer blend.

Carbon-neutral light olefins production for energy decarbonization: Process development and techno-econo-environmental analysis

Low-carbon olefins, as important platform molecules, are generally produced by limited fossil energy, resulting in massive carbon emissions and intensive energy consumption inevitably. Therefore, it is necessary to develop clean and sustainable alternatives. With this in mind, three low-carbon olefin production processes using waste CO2 and green H2 were proposed, including the methanol-mediated (Option A) and Fischer-Tropsch synthesis (FTS)-based CO2-to-olefin (CTO) processes. Herein, the FTS-based CTO processes are classified into the direct (Option B) and indirect routes (Option C) without/with the reverse water–gas-shift unit. Meanwhile, rigorous process models were established, and detailed mass and energy balances of three processes were obtained with the aid of the process simulator. Moreover, in order to evaluate the feasibility and compare the differences in process performances of three proposed processes quantitatively, comprehensive techno-econo-environmental assessments of three processes were conducted at the system level. The results indicate that, firstly, from a technical perspective, the FTS-based processes are more competitive than the methanol-mediated process due to their higher energy efficiency (67.93%) and carbon utilization efficiency (84.22%). Secondly, from an economic perspective, the methanol-mediated process has a better economic prospect in the minimum olefin selling price (2527.08 $/tonne C2–C4 olefins). Lastly, from an environmental perspective, the methanol-mediated process is more environmentally friendly owing to its lower CO2-eq emissions (61.13 kg CO2-eq/tonne C2–C4). Moreover, for two FTS-based processes, the direct route is favorable in energy efficiency and minimum olefin selling price, whereas the indirect route is preferable in the carbon utilization efficiency and environmental impacts. Overall, the study provides novel approaches for the production of low-carbon olefins, and is of significant importance for reducing carbon footprint and achieving carbon neutrality.

Environmental and techno-economic viability of using hydrogen in the vehicle sector for a rapid energy transition in Argentina

Argentina has a wide availability of renewable resources, which provides important advantages for the hydrogen vector incorporation. The province of Córdoba is an excellent model case for the study of the rapid incorporation of hydrogen as fuel, to replace 20% V/V of natural gas consumed in vehicular use. This does not involve major changes in infrastructure or modifications to the vehicles. This paper computes and analyzes the levelized cost of hydrogen with the emissions associated for each part of the complete hydrogen supply chain. Two different production sources were used: renewable energies sources and the Argentine electrical grid; and two production pathways: in situ and centralized production. Comparing the same volume of proposed hydrogen compressed natural gas and current CNG, a cost decrease in the majority of the scenarios and a CO2eq emission reduction ranging from 19.5 to 8.2% are achieved, even if the hydrogen is produced using the carbon-intensive grid electricity.