Life Cycle CO2 Emissions Research Articles

Benchmarking Performance Indices of Electrochemical CO2 Reduction to Ethylene Based on Prospective Life Cycle Assessment for Negative Emissions.

To mitigate global warming to the most ambitious targets, it is necessary to remove CO2 from the atmosphere and reduce fossil fuels use. The electrochemical conversion of CO2 to ethylene (C2H4) as a basic chemical is a promising technology that meets both requirements; however, its life cycle CO2 emissions remain inconclusive because of varying assumptions in the performance indices. This study aimed to set benchmarks for the four most sensitive indices to achieve -0.5 t-CO2/t-C2H4 by calculating net greenhouse gas (GHG) emissions through a prospective life cycle assessment of a model system including CO2 capture, CO2 enrichment, electrochemical conversion, CO2 recycling, and cryogenic separation. As a result, the electrochemical conversion process was the hotspot of life cycle emissions, and representative benchmarks were determined as follows: cell voltage, 3.5 V; C2H4 Faraday efficiency, 70%; conversion rate, 20%; and electrochemical CO2 recycling energy, 2.2 GJ/t-CO2. The gaps between the benchmarks and current top data of cell voltage and Faraday efficiency were <10%, and suppressing the performance degradation for up to one year was found to be a critical requirement. These results can direct research towards the development of a year-round stable system, rather than further improving the performance indices.

Too Far? Autonomous vehicles, travel demand, and carbon dioxide emissions in Sweden

This article envisions that by the middle of this century fully self-driving Autonomous Vehicles (AVs) are available for private use. By considering how AVs can affect the utility of being in the vehicle, and accounting for the utility of being able to transport oneself to and from various locations, we derive the consumer surplus of having an AV and evaluate that against the cost of adopting the technology. This break-even calculation is used to evaluate AV purchase and consequent impacts on increase in travel demand and lifecycle CO2 emissions for different income groups for different assumptions concerning the Value of Travel Time, transport demand elasticity, AV technology costs, interest rates, and the possibility to work in the car or not. The modelled results show that all income groups purchase AV given low technology cost, and the highest income groups purchase AV under most conditions. Changes in demand elasticity and the value of travel time have the largest effect on vehicle miles traveled, which could be as much as 50 additional kilometers daily per driver. Even in a scenario consistent with the Paris Agreement, this implies an annual carbon footprint of 0.42 – 0.86 metric tons of CO2 per driver from personal car travel in Sweden.

Study on Life-Cycle Carbon Footprints and an Uncertainty Analysis of Mega Sporting Events: An Analysis in China

This study proposes a model for the quantitative evaluation of the life-cycle carbon footprints of large sporting events and the uncertainties related to them. The model was used to analyze the case of a mega sporting event in Beijing, China. First, the quantitative model for the evaluation of the carbon footprints of mega sporting events includes a preparation stage, a holding stage, and an end stage. These stages consider the energy and resources used for construction, operation, transportation, catering, and accommodation. Second, this study proposes a prediction model using model-based and simulation-based methods to address the difficulty of obtaining traffic activity. Third, a semi-quantitative method that combines a data quality indicator and stochastic simulation is adopted for the uncertainty analysis of mega sporting events. Finally, a case study is used to indicate that the preparation stage of a mega sporting event accounts for the highest CO2 emissions at 92.1%, followed by 7.5% in the holding stage and 0.4% in the end stage. The total life-cycle CO2 emissions of a sustainable scenario of a mega sporting event in Beijing amount to 205,080.3 t CO2e, and the per capita CO2 emissions during the event’s holding stage amount to 0.26 t CO2e/person. The uncertainty in the input parameters is 0.0617, indicating that the uncertainty of the model is low, and the reliability of the results is high.

Geosynthetic MSE walls research and practice: past, present, and future (2023 IGS Bathurst Lecture)

The technology of geosynthetic mechanically stabilized earth (MSE) walls can help solve classical geotechnical earth retaining wall problems. It can also contribute to achieving the new required performance for infrastructures, such as reliance and sustainability. To further develop this technology, it is essential to analyze the history of its progress. This study summarizes the state-of-the-art research on the mechanical and soil interaction properties of geosynthetics, physical modeling and in situ measurements, analytical and numerical modeling, and reliability analyses by reviewing approximately 728 papers published in well-known international journals in this field and some notable conference paper contributions during the period of approximately 50 years from 1972 to 2023. The latest analytical methods, such as risk-based life cycle cost and CO2 emission assessments and damage/failure predictions, are introduced to evaluate the resilience and sustainability performance of geosynthetic MSE walls. Finally, the prospects of a seismic isolation technique with new types of geosynthetics and life cycle management using a long-term sensor for geosynthetic MSE walls are discussed.

Evaluation of Life Cycle CO2 Emissions for the LDR-50 Nuclear District Heating Reactor

The LDR-50 low-temperature nuclear reactor is designed for the Finnish and European district heating markets, as an environmentally sustainable heating option for the 2030s. While the carbon footprint of conventional electricity-producing reactors is known to be small, there have been no comprehensive studies on the emission reduction potential when the technology is applied to the heating sector. This paper aims to fill this knowledge gap by means of life cycle assessment (LCA) analysis. The carbon footprint of the LDR-50 heating plant is evaluated, and compared to conventional heating fuels, direct electric heating, and heat pumps. The results of the analysis show that the life cycle CO2 emissions are low, although there are still significant uncertainties related to the construction phase, due to missing data. In addition to carbon footprint, the analysis is also extended to other adverse environmental impacts. It is concluded that significant reductions in CO2 emissions can be achieved by replacing fossil heating fuels with nuclear energy. The technology is considered a viable option alongside biofuels and heat pumps. The overall environmental impacts are low, and the production does not compete for low-carbon electricity or scarce natural resources.

Environmental consequences in lifecycle changes of container shipping vessels

To estimate the average lifespan of container vessels, this study specified their most suitable lifespan distribution function using a comprehensive dataset comprising 2188 container vessels manufactured and retired between 1941 and 2018. The lifecycle CO2 emissions of vessels were estimated under different scenarios with varied average lifespans and average carbon intensity improvements per annum through stock-flow model analysis. The results indicated that a normal distribution best represented the lifespan distribution of container vessels, with an estimated average lifespan of approximately 24 years. Furthermore, scenario analyses revealed that shortening the lifespans of container vessels can effectively reduce lifecycle CO2 emissions. This study demonstrates the synergistic contribution of accelerating the replacement cycle of container vessels and implementing stronger energy efficiency regulations for emissions reduction, highlighting the importance of policies regulating vessel lifespans.

Towards climate neutrality in the Spanish N-fertilizer sector: A study based on radiative forcing

Agricultural systems in the 21st Century face the double challenge of achieving climate neutrality while maintaining food security. Synthetic fertilizers rich in nitrogen (N-fertilizers) boost agricultural production at the expense of increasing climate impact. Public policies, such as the Farm-to-Fork (F2F) Strategy, aim to reduce the extensive use of N-fertilizers with the ultimate goal of achieving a climate neutral European Union (EU). However, the strong link between N-fertilizers and GHG emissions (i.e., CO2, CH4 and, especially, N2O) highlights the need to better understand the climate impact of this sector. The present study conducts a climate impact analysis of Spanish N-fertilizer sector for two periods: (i) from 1960 to 2020 using real data and (ii) from 2021 to 2100 considering five forecasted scenarios. The scenarios range from business-as-usual practices to a full accomplishment of the goals pursued by the EU's F2F strategy. The system's climate stability and neutrality are analysed for the different scenarios based on radiative forcing (RF) metrics. Additionally, the study evaluates the short-term impact of the EU decarbonization goals on the climate impact of the Spanish N-fertilizer sector. The results of the study illustrate that the long-lasting climate impact of N2O and CO2 emissions compromise the capacity of N-fertilizer sector to achieve climate stability and approach climate neutrality. However, the decarbonisation of transport and N-fertilizer production activities is an important driver to substantially reduce the life cycle CH4 and CO2 emissions in the Spanish N-fertilizer sector. The results also highlight that more severe reductions on N-cycles than those suggested by the EU's F2F are required, especially to reduce the long-lasting N2O emissions in the N-fertilizer sector. Overall, the study concludes that using RF-based metrics increases robustness and transparency of climate assessments, which is necessary for a higher integration of climate science within public policymaking.

A holistic life cycle assessment of steel bridge deck pavement

Transportation serves as a cornerstone of economic development and is a significant contributor to carbon emissions. This study established a life cycle assessment model that incorporates refined carbon emission calculation parameters, streamlining the computation process while maintaining precision. A case study was conducted to quantify the life-cycle CO2 emissions of steel bridge deck pavements, a pivotal component within the transport network. The study suggests using the average annual CO2 emissions as a metric to gauge the carbon emission potential of steel bridge deck pavements with different service lives. This study addresses a void in the existing work by standardizing the grading of typical pavement diseases and quantifying the carbon emissions of the corresponding maintenance measures. It reveals that the pivotal determinant of life-cycle CO2 emissions for steel bridge deck pavements is the service performance of the paving material. Comparative analysis indicates that epoxy asphalt concrete could be deemed a low-carbon material, achieving a 77.6% reduction in life-cycle carbon emissions compared to gussasphalt concrete. Emissions during the maintenance phase constitute 66.7%–71.4% of the total life-cycle emissions, predominantly due to end-of-life and traffic delay units. The methodology and calculated data presented herein can inform subsequent carbon reduction strategies in transportation and promote the development of resilient infrastructure, thus making a substantial contribution towards carbon neutrality and climate change mitigation.

On the cost of zero carbon electricity: A techno-economic analysis of combined cycle gas turbines with post-combustion CO2 capture

To achieve a sustainable electricity grid, affordable and dispatchable power capacity that supports grid stability and does not increase atmospheric CO2 levels will be required. Combined cycle gas turbines (CCGTs) with post-combustion CO2 capture (PCC) can meet these requirements by capturing and permanently storing all combustion CO2 emissions and, coupled with negative emissions technologies, any remaining life-cycle emissions. For the first time, we present a comprehensive analysis of the technical and financial challenges of producing zero-carbon electricity from CCGTs on a life-cycle basis. We conclude that when the design is optimised, fossil CO2 capture fractions can be increased from 96% to 100% with minimal process modification, commercially available technology and an additional 0.5% decrease in thermal efficiency. This represents a significant 60–70% reduction in the additional efficiency penalty required to reach zero CO2 emission operation. The Cost of CO2 Avoided of 100% fossil CO2 capture is just 128 £/tCO2, a 3 £/tCO2 increase over the 95% gross CO2 capture fraction required to permit PCC projects in the UK. Indeed, within the bounds of the UK power CCS business model, we show that 100% fossil CO2 capture maximises both variable and capacity payments to the producer, resulting in a 2% decrease in the cost of power produced. For zero-carbon electricity on a life-cycle basis, the recapture and permanent geological storage of all remaining life-cycle CO2e emissions from plant construction & decommissioning, CO2 T&S network operation and the natural gas supply chain (operational CO2e emissions and methane leakage) increases the median Cost of CO2 Avoided to 178 £/tCO2 (130–371 £/tCO2), leading to the novel conclusion that a market mechanism equating to a CO2 price of over 178£/tCO2 is likely sufficient to incentivise the development of truly CO2-neutral CCGTs.

Modelling and analysis of heat pump integrated Photovoltaics-Wind systems for an agricultural greenhouse in Turkey

This study focused on modelling and analysing photovoltaics and wind systems to meet the heating demand of a commercial greenhouse. The aim is to evaluate technical, economic, and environmental performances of the related systems and to determine the optimum configuration. A novel approach was introduced by integrating hybrid energy systems with large-scale wind turbines and developing a dynamic heat transfer model. A large commercial greenhouse with an area of 26,640 m2 located in Izmir, Turkey was selected for considering Mediterranean climate, and a detailed heat transfer model of the greenhouse were developed considering heat transfers by convection, radiation, ventilation, and infiltration. A combination of air source heat pumps, photovoltaic panels and wind turbines were used for meeting the heating demand of the related greenhouse. Five different on-grid energy systems scenarios, namely (i) Photovoltaics-Heat Pump, (ii) Photovoltaics-Wind Turbine- Heat Pump, (iii) Wind Turbine- Photovoltaics- Heat Pump (iv) Wind Turbine- Heat Pump, and (v) only Heat Pump were considered. The system modelling with a detailed heat transfer analysis of the greenhouse was made by MATLAB. The energy analysis of the systems was performed on an hourly basis for one calendar year. The annual heating demand and the corresponding electricity consumption of the greenhouse were calculated as 497.37 and 114.07 kWh/m2, respectively. Net Present Value, Levelized Cost of Energy and CO2 savings were used to evaluate economic and environmental performances of the systems. Among five on-grid energy system scenarios, the first scenario, consisting of 5271 photovoltaic panels and 20 heat pumps, emerged as the most economically attractive choice with Net Present Value and Levelized Cost of Energy of $547,440.40 and 0.080146 $/kWh, respectively. Critical parameters affecting the economy of this scenario were found to be electricity prices, tomato yield, and photovoltaic panel prices. For environmental evaluation the fourth scenario, integrating wind turbines and heat pumps, achieves the highest CO2 savings of 2,064.73 tons due to increased renewable electricity production and lower life-cycle CO2 emissions of wind turbines compared to photovoltaic systems. This analysis enhanced the understanding of energy dynamics in greenhouse environments, contributing to the advancement of sustainable practices in agriculture.

An application of the graph approach to life-cycle optimisation of vehicle electrification

Although durable goods with low energy consumption are being promoted to achieve a decarbonised society, from the perspective of life-cycle assessment, the choice of new durable goods may increase CO2 emissions. To address this problem, research has been conducted on product replacement based on life-cycle optimisation (LCO), a method for identifying a replacement life span that minimises life-cycle CO2 emissions. However, several additional assumptions complicate the analysis of replacement patterns of products and conditional formulas because cumulative emissions do not increase linearly when considering energy mix and technology improvement, and it is difficult to extend the model to optimisation methods in previous LCO studies. This study developed a new LCO approach by applying the shortest path problem to graph theory. Our methodology can contribute to the following: (i) it is computationally inexpensive; (ii) it is intuitively easy to add complex conditions, such as various policy scenarios and parameter changes; and (iii) once the graph of replacement patterns is defined, the optimal solution can be derived using existing solution methods, such as the Dijkstra algorithm. As a case study, we focused on vehicle replacement, which is a major source of CO2 emissions and is being electrified. In particular, we identified vehicle switching paths that minimise life-cycle CO2 emissions by considering changes in Japan’s energy mix and alternative fuel vehicle (AFV) characteristics. We determined that the optimal vehicle replacement path method to reduce CO2 emissions is to switch first to plug-in hybrid electric vehicles (PHEVs) and then to battery electric vehicles (BEVs). Thus, we suggest that the transition to electric vehicles requires a step-by-step process. This methodology is not only conducive to AFV deployment for decarbonisation but can also be applied to other products, such as air conditioners and lighting. Thus, various transition policies could be formulated using our methodology.

Life Cycle CO2 Emissions Analysis of a High-Tech Greenhouse Horticulture Utilizing Wood Chips for Heating in Japan

High-tech greenhouse horticulture offers efficient crop cultivation that is unaffected by outdoor climate. However, compared to conventional cultivation systems, energy requirements, such as greenhouse heating and control, are larger, and concerns about the associated increase in CO2 emissions exist. Although several previous studies have analyzed CO2 emissions from high-tech greenhouse horticulture, few have covered the entire life cycle. This study aimed to analyze CO2 emissions from high-tech greenhouse horticulture for tomatoes in Japan across the entire life cycle. A hybrid method combining process and input–output analyses was used to estimate life cycle CO2 (LC-CO2) emissions. The emission reduction potential of replacing liquefied petroleum gas (LPG) for greenhouse heating with wood chips was also examined. The results show that LC-CO2 emissions were estimated to be 3.67 kg-CO2 per 1 kg of tomato, 55.6% of which came from the production and combustion of LPG for greenhouse heating. The substitution of LPG with wood chips has the potential to reduce LC-CO2 emissions by up to 49.1%. However, the improved LC-CO2 emissions are still higher than those of conventional cultivation systems; thus, implementing additional measures to reduce LC-CO2 emissions is crucial.

Exploring hydrogen metallurgy to CO2 emissions reduction in China’s iron and steel production: An analysis based on the life cycle CO2 emissions – LEAP model

Previous research has primarily assessed the environmental impact of hydrogen metallurgy from technical or project perspectives, lacking a life cycle perspective. The impact of continued cleanliness of the hydrogen production mix and power generation structure on carbon dioxide (CO2) emissions from the hydrogen metallurgy production process has not been investigated on a medium to long-term scale, which does not provide an adequate and comprehensive view of the contribution of hydrogen metallurgy to China’s emissions reduction, resulting in short-sighted technology choices. To address this lack, we construct a bottom-up energy system model that combines life cycle CO2 emissions with long-range energy alternatives planning (LEAP), including iron and steel (IS) production, power generation, and hydrogen production. Setting development paths of two typical hydrogen metallurgy technologies, including business-as-usual (BAU) and hydrogen metallurgy (HM) scenarios, we carefully evaluate the CO2 emissions impact of hydrogen metallurgy from a whole industry perspective and in each IS production stage. The results suggest that the hydrogen metallurgy transition will help the iron and steel industry (ISI) to achieve peak and deep carbon reduction. Under the HM scenario, CO2 emissions from the ISI would decrease to 816.28 million tons (Mt) in 2050, representing an additional 281.13 Mt reduction over the BAU scenario. Hydrogen metallurgy can accelerate CO2 reduction in raw material acquisition and material processing phases but may increase CO2 emissions in manufacturing and recycling phases. In 2050, hydrogen metallurgy will contribute an additional 12.49 Mt and 300.95 Mt of CO2 reduction to the raw material acquisition and material processing phases, respectively. However, CO2 emissions in the manufacturing and recycling phases would be 32.15 Mt and 0.22 Mt more than in the BAU scenario due to the increased electricity consumption and scrap demand of electric arc furnace (EAF) steelmaking, respectively. Over time, the optimization of hydrogen production and power supply mix will gradually reduce CO2 emissions in each IS production process. In 2050, the CO2 intensity of the hydrogen-rich shaft furnace direct reduced iron (H2-DRI)-EAF process will drop to 753.41 kgCO2/t, which is lower than all other processes except the 100 % scrap-based EAF process. Advancing the development of the H2-DRI-EAF process can effectively achieve CO2 emissions reduction while alleviating dependence on scrap resources. The results are expected to inform government policy on the development of hydrogen metallurgy in China and other countries.

Strategic roadmap for optimising vehicle emission reductions and electrification

Prompted by policy support, battery electric vehicles (BEVs) have become increasingly popular in many countries and economies. To ensure that vehicle electrification contributes to reduction in emissions, governments should develop appropriate transition plans that consider the lifecycle CO2 emissions of these vehicles. In this study, we aimed to establish an emission reduction-focused transition trajectory for vehicle electrification using lifecycle optimisation. Through a Japan-centric case study spanning from 2005 to 2055, we identified an optimal fuel-type progression for car owners, underlining the potential for BEVs to be introduced in the 2030s, a decade ahead of the baseline, if higher emission reduction can be attained. Policymakers are advised to facilitate a gradual shift toward hybrid electric vehicles and plug-in hybrid electric vehicles that initially outperform BEVs in emissions, until a robust level of lifecycle CO2 reduction is achieved within the automotive sector. This study contributes to the discourse by offering a strategic roadmap for maximising emission reduction through targeted vehicle electrification, making it pertinent and informative for both policymakers and stakeholders. The insights underscore the critical role of deliberate policy interventions in orchestrating a sustainable and effective transition toward a lower-emission transportation paradigm.

Spatiotemporal carbon footprint and associated costs of wind power toward China's carbon neutrality

The global shift to net-zero emissions necessitates large-scale wind power deployment and associated wind-turbine production. There's an urgent need to spatiotemporal analyze wind power's carbon footprints and costs along its industrial chain for policy-making towards net-zero manufacturing. Here, we integrate the China-focused Global Change Assessment Model (GCAM-China) and Life-Cycle Assessment (LCA) to explore the evolution of carbon footprint of wind power and resulted cost competitiveness from 2017 to 2060 in China, the foremost global manufacturer of wind turbines with a relatively high industrial carbon intensity. Findings show the national life-cycle CO2 emissions amounted to 26.20 g/kWh in 2017, forecasted to decrease to 8.61 g/kWh by 2060, benefiting primarily from the carbon-neutral electric power system. The study underscores inter-provincial collaboration for cleaner manufacturing; 44.1 % of nationwide wind power carbon footprints stem from coal-dependent North China. Carbon pricing may differentially impact wind power manufacturing's cost competitiveness due to regional disparity of carbon-intensities.

Powering aircraft with 100 % sustainable aviation fuel reduces ice crystals in contrails

Abstract. Powering aircraft by sustainable aviation fuels (SAFs) is a pathway to reduce the climate impact of aviation by lowering aviation lifecycle CO2 emissions and by reducing ice crystal numbers and radiative forcing from contrails. While the effect of SAF blends on contrails has been measured previously, here we present novel measurements on particle emission and contrails from 100 % SAF combustion. During the ECLIF3 (Emission and CLimate Impact of alternative Fuels) campaign, a collaboration between the Deutsches Zentrum für Luft- und Raumfahrt (DLR), Airbus, Rolls-Royce, and Neste, the DLR Falcon 20 research aircraft performed in situ measurements following an Airbus A350-941 source aircraft powered by Rolls-Royce Trent XWB-84 engines in 1 to 2 min old contrails at cruise altitudes. Apparent ice emission indices of 100 % HEFA-SPK (hydro-processed esters and fatty acids–synthetic paraffinic kerosene) were measured and compared to Jet A-1 fuel contrails at similar engine and ambient ice-supersaturated conditions within a single flight. A 56 % reduction in ice particle numbers per mass of burned fuel was measured for 100 % HEFA-SPK compared to Jet A-1 under engine cruise conditions. The measured 35 % reduction in soot particle numbers suggests reduced ice activation by the low-sulfur HEFA fuel. Contrail properties are consistently modeled with a contrail plume model. Global climate model simulations for the 2018 fleet conservatively estimate a 26 % decrease in contrail radiative forcing and stronger decreases for larger particle reductions. Our results indicate that higher hydrogen content fuels as well as clean engines with low particle emissions may lead to reduced climate forcing from contrails.

Climate change adaptation and mitigation potential of EVs in Tokyo metropolitan area

Penetration of low heat-emitting electric vehicles (EVs) in urban areas is expected to have a positive effect on climate change adaptation by improving the thermal environment, and indirect mitigation by reducing building CO2 emissions. To assess these effects, a case study was conducted in Tokyo using an urban canopy model. We quantified the impact and characterize its spatio-temporal structure, through a comparative evaluation with other forms of e-mobility (hybrid electric vehicles and fuel cell vehicles) and established UHI measures (ground greening and cool roofs). EVs showed the largest effect among all e-mobilities, both in absolute temperature reduction (ΔT) and cooling efficiency (ΔT per reduced heat), owing to the positive feedback on atmospheric stability. The ΔT caused by EV is more pronounced in the morning and evening hours, and in urban centers. On the other hand, the ΔT due to UHI measures peaks at midday and is more pronounced in suburban areas. In other words, they complement each other spatially and temporally. The peak ΔT caused by the EVs exceeded that of the UHI measures by approximately 40% of the total area. The contribution of indirect CO2 mitigation is negligible in the life-cycle CO2 emissions of EVs.

Operating optimization of biomass direct-fired power plant integrated with carbon capture system considering the life cycle economic and CO2 reduction performance

Biomass direct-fired power plant integrated with carbon capture system can achieve negative CO2 emission during the power generation, which provides an important technology pathway for the transformation of energy system towards carbon neutrality. Understanding the economic competitiveness and CO2 reduction potential of the plant, and identifying the optimal operating mode are the key to fully exert the advantages of the technology. For this reason, this paper develops life cycle economic and CO2 emission assessment models for the biomass direct-fired circulating fluidized bed boiler power plant (BCFBP) integrated with solvent-based post-combustion carbon capture (PCC) system. The levelized cost and CO2 emission of energy indexes are then applied to evaluate the performance of the BCFBP-PCC system. Based on the life cycle assessment, a novel economy and CO2 reduction dual-objective operating optimization approach is proposed for the BCFBP-PCC to find the optimal hourly power generation and CO2 capture level of the plant under given market conditions. The static investment payback period is employed as a constraint in the optimization to narrow down the range of the solution set and provide clearer guidance for system operation. This paper provides the first work pioneered the economic and negative carbon operation optimization of the BCFBP-PCC system.

Analysis and optimization of a sustainable hybrid solar-biomass polygeneration system for production of power, heating, drying, oxygen and ammonia

In this study, we introduce an innovative polygeneration system that combines solar and biomass energies to generate power, heating, hot air for the drying process, oxygen, and ammonia. The proposed polygeneration system comprises a solar tower subsystem (STS) integrated with two energy storage tanks (cold and hot), a gas turbine cycle (GTC), an organic Rankine cycle (ORC), a proton exchange membrane (PEM) electrolyzer, a thermoelectric generator (TEG), a cryogenic air separation unit (CASU), and an ammonia synthesis reactor (ASR). The GTC and the ORC equipped with the TEG are utilized for power production. The steam for the gasification process, hot air for the drying process and heating are produced by three regenerators. The PEM electrolyzer is used for the decomposition of water into hydrogen and oxygen, while the air separator (cryogenic method) is employed for the separation of air into nitrogen and oxygen. The separated oxygen is stored in an oxygen tank, while nitrogen and hydrogen are utilized for the ammonia generation. The system is evaluated from energy, exergy, economic and, environmental standpoints. Based on the findings, the proposed system is capable of generating approximately 163 MW of net power, 150 MW of heating, 100 MW of drying, 21.7 kmol/hr of oxygen and 23.24 kg/hr of ammonia. The total energy and exergy efficiencies, as well as the life cycle cost (LCC) and CO2 emissions are determined to be 70.68 %, 48.71 %, 1.175 × 109 $ and 381.3 kg/MWh, respectively. Additionally, a multi-objective Grey Wolf optimization algorithm is utilized to optimize the exergy efficiency, LCC, and CO2 emissions. The optimized results yield an exergy efficiency of 51.02 %, an LCC of 1.16 × 109 $, and a CO2 emissions of 359.73 kg/MWh. The proposed system demonstrates encouraging thermodynamic and economic performances, providing an appealing solution for efficient utilization of abundant solar and biomass resources.

Life cycle CO2 emission assessment of an organic Rankine cycle based geothermal power plant

Abstract Geothermal resources are well-recognized as a clean and low-carbon emission energy resource for power generation and heat supply. However, CO2 emissions occur during the construction, operation, and decommission stages of geothermal power plants. In this work, the life cycle CO2 emission characteristics of a geothermal power plant based on the organic Rankine cycle are systematically evaluated. The effect of the organic working medium and the recuperative cycle on CO2 emissions of the whole system are analyzed. Sensitivity analysis is conducted by varying the parameters of output power and the sources of the substituted electricity. Results reveal that a considerable amount of CO2 would be released due to the construction of geothermal wells and plants; however, the production of electricity could offset a much larger amount of CO2 emission. The net CO2 emission of the considered geothermal system during its lifespan reaches approximately −300 thousand tCO2e. In addition, the total amount of CO2 emission reduction relies heavily on the output power and the substituted electricity sources.