Life Cycle Carbon Emissions Research Articles

Air source assisted ground source composite heat pump system: life cycle carbon emissions and simulation analysis

ABSTRACT Air source assisted ground source composite heat pump (DSHP) system is a combination of ground source heat pump (GSHP) and air source heat pump (ASHP) that makes use of both underground and outdoor temperatures to ensure long-term stability and reliability. The development of a carbon emission model for DSHP system involved a life-cycle assessment (LCA). This model was used to analyze the energy savings of DSHP in two different areas of China Nanjing and Hohhot. In both cases, an office building with an area of 3040 m2 was used as the subject of the study. The evaluation of energy savings using TRNSYS dynamic simulations revealed that the operation stage accounts for about 75%-85% of the carbon emission in the entire life cycle assessment of DSHP systems, Among them, refrigerant leakage produces a carbon footprint of more than 20%. The installation stage accounts for about 10% of the emissions, while the adjustment of the power energy structure during operation is crucial in achieving energy savings and emission reductions. A comparison study shows that DSHP can lower emissions by up to 23% when compared to traditional air conditioning systems like gas boiler and chiller system (BLR-CH). The use of DSHP is therefore a highly effective alternative for organizations committed to reducing their carbon footprint.

Life Cycle Assessment of Cold Spray Additive Manufacturing and Conventional Machining of Aluminum Alloy Flange

Cold spray additive manufacturing (CSAM) is generally used to repair worn components and build complex on-demand parts by depositing metal powder layer-wise using compressed air. Previous studies on CSAM were focused on printing parameters, materials properties, and printed part mechanical performance. However, the energy consumption and environmental impacts of CSAM processes have not yet been investigated, which are essential factors for sustainable manufacturing. This study aims to investigate the carbon footprint of the CSAM process and compare it with conventional machining processes and other additive manufacturing. The life cycle assessment methodology was followed to calculate the carbon footprint of a pipe flange, considering rod or tube as a feedstock. Results revealed that the machined flange from the tube had the lowest CO2-eq emissions of 31 kg CO2-eq due to low rough machining energy consumption and scrap production, compared to the machined flange from a rod and a printed flange from powder. Moreover, the life cycle carbon emissions increased by 8% and 19% in case of the printed and machined flanges, with uncertainties of 4% and 9%, respectively, when changing feedstock CO2 emissions. From a regional perspective, the CSAM process was responsible for the lowest CO2-eq emissions in Tasmania and South Australia.

Air Quality Implications of Using Ammonia as a Renewable Fuel: How Low Can NOx Emissions Go?

In addition to their lifecycle carbon emissions, another important issue with decarbonized energy pathways is their air quality, water, or land use implications. This paper considers the air quality issue for ammonia combustion. When directly combusting ammonia, reactions of its N atom with atmospheric oxygen lead to NOx emissions that are O(103) ppm, 2 orders of magnitude higher than EPA limits or the amount emitted by current natural-gas-fired technologies. In order to provide guidance to policymakers and technologists on what is fundamentally possible, this Perspective analyzes the fundamental minimum NOx emissions that can be produced from ammonia combustion. The analysis shows that it is possible to achieve quite low NOx emission levels of O(10) ppm, but these designs differ markedly from those used in today's lean, premixed combustion systems.

Techno-Economic Feasibility Study for Organic and Plastic Waste Pyrolysis Pilot Plant in Malaysia

Organic and plastic waste (OPW) is diverted from landfills in order to lower carbon emissions. Nevertheless, modern pyrolysis techniques are frequently utilized in laboratories (using feedstocks that weigh less than 1 kg), which employ costly pure nitrogen gas (N2). This study developed a fast pyrolysis system to produce pyrolysis oil or liquid (PyOL) from OPW using flue gas as the pyrolysis agent. The added benefits included the efficient value-added chemical extractions and the non-thermal plasma reactor upgraded PyOL. OPW was also pyrolyzed at a pilot scale using flue gas fast pyrolysis in this study. In addition to lowering operational expenses associated with pure N2, flue gas reduced the lifecycle carbon emissions to create PyOL. The results indicated that considerable material agglomeration occurred during the OPW pyrolysis with an organic-to-plastic-waste (O/P) ratio of 30/70. Furthermore, the liquid yields were 5.2% and 5.5% when O/P was 100/0 (305 °C) and 99.5/0.5 (354 °C), respectively. The liquid yields also increased when polymers (polypropylene) were added, enhancing the aromatics. Two cases were employed to study their techno-economic feasibility: PyOL-based production and chemical-extraction plants. The mitigated CO2 from the redirected OPW and flue gas produced the highest revenue in terms of carbon credits. Moreover, the carbon price (from RM 100 to 150 per ton of CO2) was the most important factor impacting the economic viability in both cases. Plant capacities higher than 10,000 kg/h were economically viable for the PyOL-based plants, whereas capacities greater than 1000 kg/h were financially feasible for chemical-extraction plants. Overall, the study found that the pyrolysis of OPW in flue gas is a viable waste-to-energy technology. The low liquid yield is offset by the carbon credits that can be earned, making the process economically feasible.

Life-cycle carbon emissions from pilot zero-waste technologies in China

While low-carbon development and low-waste development are being pursued in numerous countries, it is crucial to integrate the benefits of carbon emissions reduction and economic costs to comprehensively evaluate the effectiveness of Zero-waste City technologies (ZWTs). This study provides a system accounting framework for estimating the life-cycle carbon emissions of the ZWTs. It is based on the hybrid method as a combination of the process analysis and the input-output analysis. The indicators of net carbon emissions, carbon emissions reduction, and net economic cost after accounting for carbon emission reductions are proposed to evaluate the integrated efficiency of the ZWTs. Based on the detailed input and output inventory of the ZWTs and the carbon emission intensity database of China, case studies are carried out to calculate the life-cycle carbon emissions of the pilot ZWTs in China. These technologies are divided into three categories as the technology to treat sludge, to treat domestic waste, and to treat mixed waste of sludge and kitchen waste. The results show that most of the pilot ZWTs have co-benefits of mitigating climate change while reducing solid waste. Among them, the dry anaerobic fermentation technology and the cement kiln co-processing technology are shown superior to similar technologies in terms of carbon emission reductions. After integrating the carbon emission reduction benefit to the economic cost, the sludge resource treatment technology and the grate domestic waste incineration technology are revealed cost less than the comparable technology. Finally, due to China's active promotion of renewable energy power generation to replace traditional coal-fired power generation, it is expected that the emission reduction capacity of sludge ZWTs will increase by 12.54% to 26.51% by 2035.

Carbon Emissions Assessment for Building Decoration Based on Life Cycle Assessment: A Case Study of Office Buildings

The continuous growth of interior decoration activities has caused a massive consumption of energy and materials, which has contributed to a large amount of carbon emissions in the construction sector. The carbon emissions of building decoration were overlooked in previous studies. Hence, the life cycle assessment (LCA) approach was employed to build a life cycle carbon emissions model for building decoration. An office building was selected to verify the availability. The results show that the carbon emissions intensity of the decoration project was 254.5 kg CO2 eq/m2. The operation stage was the most crucial carbon emissions contributor in the life cycle of building decoration, accounting for 49.8%; followed by the materials embodied impact stage, which contributed 36.3%; while the remaining three stages, namely, the decoration, transportation, and end-of-life stage, had less carbon emissions, accounting for 6.8%, 5.3%, and 1.8%. Improving the performance of inorganic materials, optimizing transportation routes and energy structure, and dismantling plan optimization can reduce carbon emissions. The findings of this study provide a theoretical basis and fundamental data for carbon emissions reduction and sustainable development strategies for building decoration.

Critical review of nuclear power plant carbon emissions

Nuclear power plays a crucial role in achieving the target of carbon neutrality to build a sustainable society. However, it is not “carbon-free” when considering its entire life cycle. Therefore, accurate accounting and monitoring of its generated carbon emissions are required to avoid miscalculations of nuclear energy as a clean energy source. In this study, the life-cycle carbon emissions of nuclear power plants (NPPs) with different reactor types are reviewed. In addition to the characteristic differences among different reactors, disparities in the review results originate from the varying emissions at the respective stages of the nuclear fuel cycle, technology choices at each stage and accounting methods and boundaries. The carbon emissions resulting from NPP construction and operation are underestimated due to the limited data and methods, which creates uncertainty in the evaluation of NPP carbon emissions. An integrated framework for carbon emissions accounting considering the construction and operation of NPPs (CACO-NPP) is proposed. This integrated framework aims to improve the accounting accuracy for carbon emissions originating from NPPs. An emerging Generation III NPP with the latest technology, HPR1000 (an advanced pressurized water reactor), was adopted as a case study. The results show that the total emissions resulting from vegetation loss, equipment manufacturing and labor input during construction and operation are 1232.91 Gg CO2 with a carbon intensity of 1.31 g CO2/kWh, indicating the notable mitigation capability of Generation III NPPs. By combining the maturity of HPR1000 technology with successive design improvements, the carbon emissions of such reactor types could be further reduced. This development is very important for realizing China’s carbon neutrality target.

Prediction of carbon emissions peak and carbon neutrality based on life cycle CO2 emissions in megacity building sector: Dynamic scenario simulations of Beijing

In order to design an optimal carbon peak and carbon neutralization pathway for the high-density building sector, a dynamic prediction model is established using system-dynamics coupled building life cycle carbon emission model (SD-BLCA) with consideration of future evolutionary trajectory and time constraints. The model is applied in Beijing using the SD-BLCA combined with scenario analysis and Monte Carlo methods to explore optimal trajectory for its building sector under 30-year timeframe. The results indicate that by increasing the proportion of renewable energy generation by 7% and retrofitting 60 million m2 of existing buildings, these two mature measures can offset the growth of carbon emissions and achieve the peak target by 2025. However, achieving carbon neutrality necessitates a shift from isolated technologies to a comprehensive net-zero emissions strategy. The study proposes a time roadmap that integrates a zero-carbon energy supply system and the carbon reduction measures of the whole life cycle. This strategy primarily relies on renewable sources to provide heat, power, and hydrogen, resulting in estimated reductions of 29.8 Mt, 28.1 Mt, and 0.7 Mt, respectively. Zero energy buildings, green buildings, and renovated buildings can reduce carbon emissions through their own energy-saving measures by 8.4, 18.2, and 11.8 kg/m2, respectively.

Is constructed wetlands carbon source or carbon sink? Case analysis based on life cycle carbon emission accounting

Constructed wetlands (CWs) are widely used to polish the effluent of wastewater treatment plants and micro-polluted river or lake water. However, the impact of large-scale applications of CWs on carbon emissions is unclear. In this study, the carbon footprints of two full-scale hybrid CWs were determined based on life cycle assessment (LCA). Results showed that the carbon emission of CW ranged from 0.10 to 0.14 kg CO2-eq/m3, and was significantly correlated with the influent chemical oxygen demand loads and electricity consumption. However, CW would approach carbon neutrality during the service period when taking plant carbon sequestration into consideration. Compared with other advanced wastewater treatment technologies, CWs showed significant low-carbon emission and cost-effective benefits. This study clarified the role of CWs in the carbon cycle and would provide guidance for the construction and management of CWs.

A Life-Cycle Carbon Emissions Evaluation Model for Traditional Residential Houses: Applying to Traditional Dong Dwellings in Qandongnan, Guizhou Province, China

In recent years, due to the low energy utilization of the whole life-cycle of buildings, the diminished indoor and outdoor comfort of buildings, and the impact on the surrounding environment caused by the carbon emissions of the building life-cycle, the establishment of a whole life- cycle carbon emission evaluation model for buildings to improve their energy utilization at all stages of their life-cycle has received unprecedented attention. In China, the construction industry has become a major carbon emitter, and traditional houses, as a green development building type, are an effective way to achieve carbon neutrality in buildings; however, the existing green building evaluation system lacks quantitative indicators of carbon emissions in the building life-cycle. The exclusive evaluation indexes for regional and characteristic buildings, such as traditional houses, are neglected. This study explored the formula for calculating the life-cycle carbon emissions model of traditional residential houses under a carbon emission intervention and used real measurements of the physical environment. Based on the results of indoor and outdoor heat and humidity environmental tests of residential houses due to locality, four important factors affecting local green buildings in terms of energy utilization, site ecology and landscape, land saving, and material saving were extracted; on this basis, the whole life-cycle carbon emission evaluation model of traditional residential houses was constructed by combining the existing green building evaluation standards with the carbon emission indexes of the life-cycle of traditional residential houses.

Carbon emissions reduction potentiality for railroad transportation based on life cycle assessment

This study addresses the comparative carbon emissions of different transportation modes within a unified evaluation framework, focusing on their carbon footprints from inception to disposal. Specifically, the entire life cycle carbon emissions of High-Speed Rail (HSR), battery electric vehicles, conventional internal combustion engine vehicles, battery electric buses, and conventional internal combustion engine buses are analyzed. The life cycle is segmented into vehicle manufacturing, fuel or electricity production, operational, and dismantling-recycling stages. This analysis is applied to the Beijing-Tianjin intercity transportation system to explore emission reduction strategies. Results indicate that HSR demonstrates significant carbon emission reduction, with an intensity of only 24 %–32 % compared to private vehicles and 47 %–89 % compared to buses. Notably, HSR travel for Beijing-Tianjin intercity emits only 24 % of private vehicle emissions, demonstrating the emission reduction benefits of transportation structure optimization. Additionally, predictive modeling reveals the potential for carbon emission reduction through energy structure optimization, providing a guideline for the development of effective transportation management systems.

4E analysis of a novel proton exchange membrane fuel cell/engine based cogeneration system with methanol fuel for ship application

Cleaner fuels and more efficient systems are important for achieving green, low-carbon ships. In this paper, a novel proton exchange membrane fuel cell/engine based cogeneration system with methanol fuel (MPEC system) for ship application is proposed. By the online catalytic reforming process of methanol, the obtained hydrogen through reforming can provide sufficient high heating value fuel to the MPEC system. The energy efficiency, exergy efficiency, economy and environment (4 E) analysis method is adopted for the comprehensive performance analysis of the MPEC system. The results show that the proposed MPEC system can achieve cogeneration efficiency and power generation efficiency as high as 81.84% and 50.46%, respectively, which performs that the generation efficiency is improved by 19.55% compared to the single engine, and the biggest exergy loss process occurs at the engine. The total life cycle carbon emission and levelized cost of energy of the MPEC system are 344.938 g/kWh and 0.1411 $/kWh, separately. Moreover, the effects of various parameters on the MPEC system performance are analyzed, mainly including steam carbon ratio, current density, etc. Overall, a low-carbon power system with high efficiency and good load performance is achieved by combining high-efficiency fuel cell with a powerful engine.

Electric vehicle lifecycle carbon emission reduction: A review

AbstractUnder the global carbon neutrality initiative, carbon emissions from the transportation sector are becoming increasingly prominent due to the growth in vehicle ownership. And electric mobility may be a potentially effective measure to reduce road traffic carbon emissions and achieve a green transformation of transportation. This paper systematically collates the relevant carbon accounting standards for the automotive industry and elaborates the current status of road transport greenhouse gas emissions by combining the data from the International Energy Agency. And by comparing the lifecycle carbon footprint of various energy types of vehicles, the necessity and feasibility of electric mobility to reduce carbon emissions are discussed. However, the comparison of vehicle lifecycle carbon footprints shows that electric vehicles (EVs) are not as environmentally friendly as expected, although they can significantly reduce road traffic carbon emissions. The high carbon emissions from the manufacturing process of the core components of EVs, especially the power battery, reduce the low‐carbon potential of electric mobility. Therefore, the carbon emission reduction strategies and outcomes of automakers in the automotive industry chain have been further reviewed. Finally, focusing on vehicle power batteries, this article reviews the technologies such as refined management and echelon utilization that can make EVs more environmentally friendly and promote carbon neutrality in the transportation sector.

CO2 system integrated with ejector and mechanical subcooling: A comprehensive assessment

To achieve the goal of clean annual space heating and cooling for residential buildings, the concept of annual space heating and cooling transcritical CO2 system combined with ejector and mechanical subcooling is proposed. The problem of large throttling loss and performance degradation when CO2 system is applied for residential space heating and cooling can be solved. A theoretical model of the new proposed system is developed, and then optimized by the method of genetic algorithm. Moreover, taking an ordinary residential building located in 70 cities belonging to different climate zones as the application scenario, the seasonal, annual, environmental, and economic performance of eight heating and cooling solutions are compared and discussed. The results indicate that the COP and exergy efficiency of the new proposed system is significantly improved in contrast to conventional mechanical subcooling system, which increases by 11.48% and 21.64% in heating mode, and 8.99% and 8.69% in cooling mode, respectively. The annual performance coefficient of the new proposed system is 7.21%∼8.21% higher than conventional mechanical subcooling system. Additionally, the life cycle carbon emissions of the new proposed system can be significantly reduced by 12.23%∼89.58% compared with the combined solution of coal-fired boiler and R32. With the advancement of CO2 technology, it is possible to improve the economic performance of CO2 systems and the price of the new proposed system is lower than all solutions when the price of compressor is reduced by 60%. This study can provide a theoretical reference for the development and optimization of CO2 combined heating and cooling system, and provide a feasible solution for residential annual space heating and cooling.

A multi-objective modeling and optimization approach to municipal solid waste collection for classified treatment in China towards sustainable development

With the popularity of waste classification and increasing requirements for coordinated waste management towards sustainability, it is essential to study how to generate efficient waste collection solutions for classified treatment towards social-economic and environmental goals. We proposed a new methodological framework to identify not only the optimal routes for different collection modes in classification but also the most desirable mode under different decision preferences, by a novel multi-objective optimization model applicable to different collection modes with addressing economic, environmental and social dimensions of sustainability. We incorporated the lifecycle carbon emissions of fuel and the economic and environmental impacts of vehicle idling due to queening to make the model more realistic and comprehensive. To solve the model, we proposed a modified metaheuristic algorithm based on particle swarm optimization and genetic algorithm. Through the case study in a pilot waste classification city of China, we demonstrated the effectiveness of the designed algorithm and the applicability of the proposed methodological framework. The results indicate that there are strong synergies between environmental and economic objectives, but trade-offs between social and environmental/economic objectives. “Classification then combined-collection” should be given priority under economic and environmental preferences, while “Classification then separated-collection” should be adopted under social preference.

Up on the roof: a review of design, construction, and technology trends in vertical extensions

New spaces to accommodate growing urban populations should be created in a way that also reduces building lifecycle carbon emissions. In this context, the vertical extension (VE) has emerged as a novel building typology that can increase space in cities through the construction of additional floor area atop existing base buildings. This paper presents a review of 172 VE projects worldwide to provide an understanding of their design and construction trends, and to classify the technologies applied. Results show that VE construction has accelerated significantly over the past decade. Although most VEs consist of only small vertical additions, often one to two storeys, higher VEs can be built with innovative structural strategies and lightweight materials. Industrial buildings are often found to provide significant opportunities for VE due to their higher structural capacity. By comparing the characteristics and design of VEs, typologies based on architectural, structural, and construction technologies are presented.

Carbon footprints in pork production and consumption in China from 2005 to 2020

Livestock farming accounts for 14.5% of global total anthropogenic greenhouse gas (GHG) emissions. China has been a major contributor to global GHG emissions from livestock and is the biggest pork producer and consumer worldwide. However, those factors driving GHG emissions from pork production and consumption in China have not been thoroughly assessed. Here, we used the Global Livestock Environmental Assessment Model (GLEAM) and the Logarithmic Mean Divisia Index (LMDI) method to identify and assess the major drivers contributing to the life-cycle carbon emissions embodied in China's pork production and consumption from 2005 to 2020. Our results show that CO2 emissions accounted for 99% of the total GHG emissions in the pig industry, primarily released from the processing and transporting of pig feed. These two sectors contributed more than 90% to the total CO2 emission. CH4 was mainly emitted from enteric fermentation and manure management of pigs, which accounted for a tiny portion of total carbon emissions in the pork industry. Among the primary factors driving pork-induced carbon emissions in China, the reduction of pork emission intensity (PPE) significantly slowed down growing carbon emissions, attributed to the improvements in pork production technology and the promotion of green farming. Our finding reveals that the growing population primarily contributed to elevated carbon emissions before 2015 due to increasing demands for pork meat. Since 2015, the rapid growth of the aged population in China has decreased pork consumption capacity and carbon emissions from pork consumption. The result indicates, for the first time, that the population aging in China, the largest pork consumer in the world, would play a vital role in reducing pork consumption-induced carbon emissions. Such an effect would become more significant in the future, along with the growing aged population in China, favoring the country's GHG emission mitigation increasingly.

A closed loop case study of decentralized food waste management: System performance and life cycle carbon emission assessment

Food waste (FW) has become a worldwide issue, while anaerobic digestion (AD) has appeared as a widely adopted technology to recover energy and resources from FW. Compared to many existing case studies of centralized AD system, the comprehensive study of decentralized micro-AD system from both system energy efficiency and carbon emission perspective is still scanty, particularly system operated under ambient temperature conditions. In this study, an actual decentralized micro-AD system with treating capacity of 300 kg FW/d for a local hawker center in Singapore was reported and evaluated. The results showed that 1894.5 kg of FW was treated and 173 m3 biogas with methane content of 53 % was produced during the experimental period of 75 days. The methane yield results showed a high FW degradation efficiency (87.87 %). However, net energy consumption and net carbon emission were observed during the experimental period. Nevertheless, energy self-efficiency and carbon neutrality, even net energy output and carbon reduction, can be achieved by increasing daily FW loading and biogas engine efficiency. Specifically, the FW loading for system energy self-efficiency was identified as 159 kg/d for engine efficiency of 35 % at a high kitchen waste/table waste ratio (63 %/37 %, with covid-19 dine-in restrictions); while they were 112 and 58 kg/d for engine efficiency of 25 % and 35 %, respective, at a low kitchen waste/table waste ratio (31 %/69 %, without covid-19 dine-in restrictions). The carbon emission ranged from 156.08 kg CO2-eq/t FW to −77.35 kg CO2-eq/t FW depending on the FW loading quantity and engine efficiency. Moreover, the sensitivity analysis also showed that the used electricity source for substitution influenced the carbon emission performance significantly. The obtained results imply that the decentralized micro-AD system could be a feasible FW management solution for energy generation and carbon reduction when the FW loading and engine electrical efficiency are carefully addressed.

Towards sustainable passenger transport: Carbon emission reduction scenarios for a medium-sized city

The sustainability of transportation systems is frequently linked to human preferences, hence it is pertinent to align quotidian commuting choices with sustainable development goals. The main goal of the present research was to simulate eight scenarios designed to reduce the carbon dioxide emissions of passenger transport in a Colombian medium-sized city, taking into account the Global Warming Potential (GWP) of public and private vehicles, obtained by means of Life-Cycle Assessment (LCA). In this work we compared the environmental efficiency of the scenarios in order to make a contribution to the scientific discussion on sustainable mobility policies. Measures such as reducing the number of the most polluting vehicles, optimising the modal shares of public and private transportation systems, integrating electric vehicles, increasing the use of bicycles, and reducing mobility, have been tested. The results show that the current annual emissions from passenger transport in the selected city (263.98 kt CO2-eq) could be decreased by up to 64.28% by implementing a 50% reduction in individual Trips per Day (TpD) and distances travelled by private and public vehicles. In addition, increasing the public bus fleet by 50% could yield a 56.92% reduction in the carbon dioxide released, while using an average occupancy of 30 passengers in buses could decrease the total emissions by 25.73%. Augmenting the occupancy ratio of private vehicles was shown to yield a 22.71% reduction in carbon dioxide released. Also, increasing the electric vehicle fleets by 50% can produce carbon emission reductions of 17.96% for the current energy mix and 20.08% for a 100% renewable energy mix; while boosting the use of bicycles and increasing the diesel car fleet yielded reductions of 9.24% and 5.06%, respectively. This article concludes that managing mobility and restricting commuting could be the most sustainable measure for life-cycle carbon emission reduction.

Bayesian optimization + XGBoost based life cycle carbon emission prediction for residential buildings—An example from Chengdu, China

Bayesian optimization + XGBoost based life cycle carbon emission prediction for residential buildings—An example from Chengdu, China