Net CO2 Emission Reduction Research Articles

Integrated CO2 capture and conversion into methanol units: Assessing techno-economic and environmental aspects compared to CO2 into SNG alternative

Using carbon dioxide (CO2) as a raw-material to produce value-added chemicals has a strategic role to play in the decarbonization of energy resources and the transition to a climate-neutral economy. E-methanol, Synthetic Natural Gas (SNG) and e-kerosene are one of the most promising pathways to convert CO2. In this context, the aim of this work is to propose an optimized and integrated CO2 to methanol process and then to compare it to the CO2 to SNG process from economic and environmental points of views. An optimized reactor configuration in the CO2 to methanol conversion unit has been successfully implemented in Aspen Plus® and leads to a thermal energy self-sufficiency of this unit. A heat integration with an advanced capture unit has been performed where 5 % of the heat requirement could be provided from the conversion unit while 95 % come from external steam source. Techno-economic assessment of the optimized process showed that methanol is more profitable when it is used as a raw material to synthetize other chemicals. As an energy carrier, SNG is more interesting. Compared to the reference scenario, a net CO2 emission reduction of 70 % in the CO2 to SNG route and of 60 % in the CO2 to methanol route were obtained. Concerning the fossil depletion impact, in both cases, a reduction of more than 60 % was noticed (ca. 75 % in CO2 to SNG route and 61 % in CO2 to methanol case).

Energy efficiency of ecological buildings in Tunisia: Natural fiber composites and passive strategies impact

Improving the thermal insulation and energy efficiency of building envelopes is a major objective worldwide and has significantly developed in the recent years. This study aims to evaluate the impact of ecological additive and passive strategies on building energy efficiency. An experimental study was carried out to examine the effect of the incorporation of treated Alfa and Posidonia-Oceanica fibers on the thermal properties of cement and gypsum composite samples. The experimental results were then introduced in a numerical study using TRNSYS software to perform a comparison of the energy efficiency and thermal performance of three individual buildings; two ones constructed with our ecological materials and the third one with typical materials is considered as a reference case under the Tunisian climate. The obtained results indicate that the buildings built with Alfa fibers (BAF) and Posidonia-Oceanica fibers (BPOF) are economically effective since they allow a decrease of about 48.20% and 43.48% in heating, 45.71% and 42.77% in cooling, leading to a reduction in CO2 emission of 47.90% and 43.40%, respectively, in comparison with the reference case. The investigation also focuses on the improvement of the ecological building envelope by a storage wall integrated on the south front and shaded by solar movable overhangs during the summer season. The indoor climate results reveal that incorporating passive strategies into the building improves indoor air temperature and preserves a comfortable indoor relative humidity. Heating requirements decrease by 82.82% for BAF and by 79.76% for BPOF. The cooling requirements of the reference building are also reduced by 63.46% for BAF and 60.45% for BPOF by the use of natural night ventilation (4 ACH) and the appropriate shading for Trombe walls and windows. Consequently, the implementation of passive strategies on the ecological buildings led to a net reduction in CO2 emissions by up to 80.55% for BAF, compared to the reference case.

Addressing Health Equity in the Context of Carbon Capture, Utilization, and Sequestration Technologies.

To describe the role of health equity in the context of carbon capture, utilization, and sequestration (CCUS) technologies. CCUS technologies have the potential to both improve and worsen health equity. They could help reduce greenhouse gas emissions, a major contributor to climate change, but they could also have negative health impacts like air and noise pollution. More research is needed to fully understand the health equity implications of CCUS technologies. CCUS technologies have both health equity risks and benefits. Implementing misguided CCUS projects in vulnerable communities could exacerbate environmental injustice and health disparities and have the potential to increase carbon emissions. However, well-conceived projects could benefit communities through economic development. Governments, industry, and society should prioritize and expedite the reduction of CO2 emissions before considering carbon reductions via CCUS. Furthermore, CCUS projects must be thoroughly evaluated and should only proceed if they have demonstrated a net reduction in CO2 emissions and provide more benefits than risks to local communities. This underscores the importance of prioritizing health equity in the planning of CCUS projects.

Reducing poverty in the UK to mitigate energy poverty by the 10% and LIHC indicators: What tax changes are needed, and what are the consequences for CO2 emissions?

Energy poverty is driven by four factors: poverty; high energy prices; energy-inefficiency; and specific household characteristics. Increasingly refined definitions of energy poverty (and/or vulnerability) identify types or locations of households most likely to be suffering it. But there is also a place for a different approach, considering poverty reduction directly, as poverty is a necessary component within all energy poverty definitions. This paper investigates how high the UK's top marginal tax rates would need to be, to provide funds to lift low-income UK households above the poverty threshold as defined by the low-income-high-cost (LIHC) and 10% energy poverty indicators. It finds that the increased top tax rates would still be in line with those of other European OECD countries. Using recent and new research on income elasticities of CO2 emissions, it then estimates the net direct effects on CO2 emissions of this redistribution. For both scenarios the most likely effect is a small reduction in net CO2 emissions. Further, indirect downward pressures on CO2 emissions due to reduced income among the highest earners are likely to lead to yet more favourable outcomes for net CO2 emission reduction.

Computed-tomography-based discrete fracture-matrix modeling: An integrated framework for deriving fracture networks

Investigating the topology of natural fractures and associated flow properties allow for better understanding of fluid flow patterns and mechanical response in fractured reservoirs, key points in the energy supply through geothermal systems, or in the reduction of net CO2 emissions through carbon capture and storage (CCS) practices. However, limited information on the fracture networks is available from seismic data, which poses as a challenge in the accurate modeling of fractured reservoirs. This work proposes an integrated framework for obtaining fracture networks with real aperture distributions, based on X-ray computed tomography (CT) images of core plugs from naturally fractured rock formations. We adapt and employ segmentation, skeletonization and geometry generation algorithms that are available in open-source libraries and licensed software. In addition, we investigate the contributions of fractures and porous matrix to the equivalent permeability tensor through fluid flow simulations considering three different scenarios for the matrix permeability. This work is novel in the coordination of the steps involved in the generation of discrete fracture-matrix (DFM) models from CT-scans of core plugs.

Thermal and optical performance analysis of triangular solar air collectors and regional applicability in China

Improving the applicability of solar air collectors in different climatic regions is important for its popularization. In this study, a novel triangular solar air collector (TSAC) was proposed. The insulation material (TSAC_1), transparent cover plate (TSAC_2) or double transparent cover plate (TSAC_3) could be fitted on the side of TSAC to adapt to different climates. The optical model and heat transfer model of the TSACs were established and verified. Two optical efficiencies were defined and the optical properties of three TSACs were compared. The effect of environment temperature, global solar radiation, solar azimuth angle and insulation material absorption on the thermal performance of TSACs were analyzed. Based on meteorological parameters of eight cities in different climate and solar energy distribution regions, the applicability of TSACs was compared, and their life-cycle economics and CO2 emission reduction capacity were assessed. Results indicate that the TSAC_2 has the highest optical efficiency, and 15.2 % higher than that of TSAC_1. Three TSACs are suitable for different climatic regions, the average thermal efficiency of the optimal TSAC applied to the eight cities is 47.3 % during the heating period, which is 5.6 % higher than that of the single TSAC_1. TSACs have good economics in all climate regions, and the average net CO2 emission reduction of whole life cycle is 3230.3 kg.

Radically reducing UK energy poverty by the 10% and LIHC indicator through progressive fiscal policy: What would it cost, who would pay, and what are the consequences for CO2 emissions?

Energy poverty is driven by four factors: poverty; high energy prices; energy-inefficiency; and specific household characteristics. Increasingly refined definitions of energy poverty (and/or vulnerability) identify types or locations of households most likely to be suffering it. But there is also a place for considering poverty reduction directly, as poverty is a component within all energy poverty definitions. This paper investigates how high the UK's top marginal tax rates would need to be, to provide funds to lift low-income UK households above the poverty threshold as defined by the low-income-high-cost (LIHC) and 10% energy poverty indicators. It finds that the increased top tax rates would still be in line with those of other European OECD countries. Using recent research on income elasticities of CO2 emissions, it then estimates the net effects on CO2 emissions of this redistribution. For the 10% scenario the worst-case is a net 0.7% increase and, the best-case is a small reduction. For the LIHC scenario the worst-case increase is 2.21% and best-case increase is 0.7%. Indirect downward pressures on CO2 emissions due to reduced income among the highest earners are also likely to lead to further favourable outcomes for net CO2 emission reduction.

Optimized configuration to reduce H2 carbon footprint in a refinery

As hydrogen is increasingly being recognized as a critical energy vector in the energy transition, capturing CO2 from existing H2 production facilities plays a significant role towards decarbonisation. Air Liquide has industrialized an innovative technology Cryocap™ H2, combining membranes and cryogenic solutions to capture CO2 most efficiently, at the lowest cost, and at a very high purity. This paper illustrates the impact of cost-effective partial capture technology choices (e.g. amine wash versus Cryocap™ H2) to CO2 emission reduction rates and overall carbon footprint. Direct and indirect emissions (i.e. Scopes 1, 2, and 3) were defined for each technology choice, alongside scenarios for low, medium, and high carbon footprint environments. The paper also explores an optimization path on the CO2 emissions reduction rate using a network configuration within a refinery. The study demonstrates that with Scope 1 emissions, the partial capture net CO2 emission reduction rate is 62% with a Cryocap™ standalone, 80% with a Cryocap™ Network, but only 56% with an amine wash due to its additional requirement of steam. Analysis of all emissions Scopes illustrates that Cryocap™ 's net CO2 emissions reduction rate ranges from 52% to 66% across low, medium, to high carbon footprint scenarios, and 39% to 44% for amine wash. The advantageous case for Cryocap™ across all three Scopes remains regardless of the additional steam production method (i.e. natural gas vs electric boiler).

Impact of different trace elements on metabolic routes during heterotrophic growth of C. ljungdahlii investigated through online measurement of the carbon dioxide transfer rate.

Synthesis gas fermentation using acetogenic clostridia is a rapidly increasing research area. It offers the possibility to produce platform chemicals from sustainable C1 carbon sources. The Wood-Ljungdahl pathway (WLP), which allows acetogens to grow autotrophically, is also active during heterotrophic growth. It acts as an electron sink and allows for the utilization of a wide variety of soluble substrates and increases ATP yields during heterotrophic growth. While glycolysis leads to CO2 evolution, WLP activity results in CO2 fixation. Thus, a reduction of net CO2 emissions during growth with sugars is an indicator of WLP activity. To study the effect of trace elements and ventilation rates on the interaction between glycolysis and the WLP, the model acetogen Clostridium ljungdahlii was cultivated in YTF medium, a complex medium generally employed for heterotrophic growth, with fructose as growth substrate. The recently reported anaRAMOS device was used for online measurement of metabolic activity, in form of CO2 evolution. The addition of multiple trace elements (iron, cobalt, manganese, zinc, nickel, copper, selenium, and tungsten) was tested, to study the interaction between glycolysis and the Wood ljungdahl pathway. While the addition of iron(II) increased growth rates and ethanol production, added nickel(II) increased WLP activity and acetate formation, reducing net CO2 production by 28%. Also, higher CO2 availability through reduced volumetric gas flow resulted in 25% reduction of CO2 evolution. These online metabolic data demonstrate that the anaRAMOS is a valuable tool in the investigation of metabolic responses i.e. to determine nutrient requirements that results in reduced CO2 production. Thereby the media composition can be optimized depending on the specific goal.

CO2 mineralization of carbide slag for the production of light calcium carbonates

The production of polyvinyl chloride by calcium carbide method is a typical chemical process with high coal consumption, leading to massive flue gas and carbide slag emissions. Currently, the carbide slag with high CaO content is usually stacked in residue field, easily draining away with the rain and corroding the soil. In this work, we coupled the treatment of flue gas and carbide slag to propose a facile CO2 mineralization route to prepare light calcium carbonate. And the route feasibility was comprehensively evaluated via experiments and simulation. Through experimental investigation, the Ca2+ leaching and mineralization reaction parameters were determined. Based on the experiment, a process was built and optimized through Aspen Plus, and the energy was integrated to obtain the overall process energy and material consumption. Finally, the net CO2 emission reduction rate of the entire process through the life-cycle assessment method was analyzed. Moreover, the relationship between the parameters and the CO2 emission life-cycle assessment was established. The final optimization results showed that the mineralization process required 1154.69 kW·h·(t CO2)−1 of energy (including heat energy of 979.32 kW·h·(t CO2)−1 and electrical energy of 175.37 kW·h·(t CO2)−1), and the net CO2 emission reduction rate was 35.8%. The light CaCO3 product can be sold as a high value-added product. According to preliminary economic analysis, the profit of mineralizing can reach more than 2,100 CNY·(t CO2)−1.

Impact of nano-TiO2 addition on the reduction of net CO2 emissions of cement pastes after CO2 curing

This investigation aims to study the effect of nano-TiO2 addition on CO2 uptake of cement paste during CO2 curing. Cement paste mixtures with different percentages of nano-TiO2 (0%, 0.5%, 1%, 2%), and two different types of curing (normal curing (NC) at 23 °C and 50% RH, and CO2 curing (CC) that includes a 12-h curing in a chamber with 20% of CO2) were studied. Compressive strength, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and an estimation of the net CO2 emissions were performed for each studied mixture and curing condition. All samples were tested at 48 h. Results showed that the optimum percentage of nano-TiO2 in terms of compressive strength is lower for CO2 curing samples than for NC samples. XRD and TGA results exhibited that the use of nano-TiO2 promotes the CO2 capture during the CO2 curing. Since nano-TiO2 reduces the size of CH, it increases the CH surface area. This may enhance the CH reactivity with the CO2, producing an increase in the CO2 uptake. Results also showed that not considering the effect of nano-TiO2 on compressive strength and promotion of CO2 capture would highly overestimate the net CO2 emissions of cementitious materials with nano-TiO2. It highlights the importance of selecting an adequate functional unit for the analysis.

CO2 mineral sequestration by using blast furnace slag: From batch to continuous experiments

CO2 mineral sequestration is a promising strategy to combat global warming. Indirect CO2 mineral sequestration was proposed in our previous study by using blast furnace slag as feedstock. As the continuity of this research, the continuous experiment process was carried out in a self-designed rotary kiln, and the results were compared with those of the batch experiment. The results showed that several problematic situations, such as the formation of kiln rings, insufficient mass, and heat transfer, occurred in the continuous experiment. A “returning charge” operation by adding an inert component into the feedstock was suggested for the prevention of ring formation and achieved good results. The reaction conditions for the continuous experiment were harsher than those of the batch experiment due to the scale-up effects. Preliminary analysis of CO2 net-emission reduction was conducted based on the continuous experimental results. It was shown that the net reduction of CO2 emissions amounted to 36 kg for 1000 kg of blast furnace slag processed. The results demonstrated in this study can act as guidance for pilot- or industrial-scale applications of indirect CO2 mineral sequestration technologies, especially for process parameter optimization and equipment design.

The sponge effect and carbon emission mitigation potentials of the global cement cycle

Cement plays a dual role in the global carbon cycle like a sponge: its massive production contributes significantly to present-day global anthropogenic CO2 emissions, yet its hydrated products gradually reabsorb substantial amounts of atmospheric CO2 (carbonation) in the future. The role of this sponge effect along the cement cycle (including production, use, and demolition) in carbon emissions mitigation, however, remains hitherto unexplored. Here, we quantify the effects of demand- and supply-side mitigation measures considering this material-energy-emissions-uptake nexus, finding that climate goals would be imperiled if the growth of cement stocks continues. Future reabsorption of CO2 will be significant (~30% of cumulative CO2 emissions from 2015 to 2100), but climate goal compliant net CO2 emissions reduction along the global cement cycle will require both radical technology advancements (e.g., carbon capture and storage) and widespread deployment of material efficiency measures, which go beyond those envisaged in current technology roadmaps.

Hybrid Electric Propulsion

Abstract Electrified propulsion holds the promise of reducing aviation’s CO2 emissions footprint through three means: access to green grid electric energy, improvements in aircraft performance through new airframe and propulsion system architectures and enabling further optimization of the gas turbine cycle. Charging an aircraft battery pack with green electric energy and using this energy to drive electric propulsors results in a zero emissions vehicle. This is practical for light aircraft and short missions. Boosting a Jet-A burning gas turbine with green electric energy (again stored in a ground charged battery), in either a parallel or series turbo-electric architecture can yield a net reduction in CO2 emissions, as long as the fuel burn required to carry the weight of a discharged battery pack does not overcome the reduction in fuel burn afforded by the ground charged battery. Several studies have indicated that a net savings is possible with cell level energy densities approach ∼ 500 whr/kg, a reasonable target for the 2030 time frame. Electrified propulsion can also enable unique aircraft configurations, employing a veryhigh efficiency prime mover (gas turbine) designed for running only a generator at peak efficiency, and/or distributing the propulsors throughout the aircraft, for improvement in L/D and propulsive efficiency.

Interaction of Regulatory Aspects for Carbon Capture and Utilization Applications

AbstractCarbon capture and utilization (CCU) technologies can lead to a net reduction of CO2 emissions but also to a transfer from emissions between different regulatory areas. This paper presents a tool to evaluate the impact of CCU technology within the European regulatory framework with respect to the accounting of carbon transferred between the CO2 source and its subsequent application. Additional emissions caused by energy requirements of the capture or any conversion steps are not considered. The tool is applied to a variety of possible combinations and their respective impact evaluated.

Modeling and performance analysis of subcritical and supercritical coal-fired power plants with biomass co-firing and CO2 capture

Coal-fired power plants are the largest source of carbon dioxide (CO2) emissions into the atmosphere, and these emissions can be effectively reduced by improving the efficiency of the plants, co-firing sustainably grown biomass and applying carbon capture and storage technologies. In this study, the energy and environmental performances of both subcritical (SubC) and supercritical (SC) pulverized coal-fired power plants with biomass co-firing and integrated with an advanced amine-based postcombustion CO2 capture system were evaluated and compared. The impact of biomass (hybrid poplar) addition was investigated at different co-firing ratios varying up to 30% on a heat input basis. All plant configurations were modeled and simulated with Aspen Plus process simulation software. The results show that the use of a SC steam cycle has a positive impact on the energy and environmental performance of the investigated plants, improving the efficiency by 2.4% points and reducing the total fuel consumption and CO2 emissions by 6% in comparison to those of the SubC cases. Biomass co-firing has a negative impact on the energy performance of plants while significantly reducing fossil-based carbon emissions. The reduction of net CO2 emissions is almost proportional to the biomass percentage in the feed. At 30% biomass co-firing, the net plant efficiency is reduced by approx. 1% point, while the net CO2 emissions are 28% lower than those in coal-fired only plants. The introduction of CO2 capture has a major impact both on the emissions generated and on the energy efficiency. Depending on the plant type and co-firing ratio used, the net plant efficiencies are 8.7–9.3% points lower than those of non-capture cases. The net CO2 emissions achieve negative values when carbon is captured from the biomass co-firing plants.

Experimental Determination of Co2 Mineralization Depth of Slag Minerals at Co2 Concentrations Available in Iron and Steelmaking Flue Gases

We report the diffusion coefficient relevant to CO2 mineralization using minerals commonly encountered in ironmaking and steelmaking slag. Diffusion coefficients were gained from CO2 mineralization achieved under passive conditions consistent with processes that are likely to maintain net CO2 emission reduction. In other words, no chemical, thermal, or mechanical enhancement was applied. Tests were performed at 30 ˚C with molar CO2 concentrations of 5%, and 20%. We applied the diffusion coefficients using the shrinking core model with a modification to account for the full particle size distribution of a sample and the fractal surface roughness. Results indicate that CO2 mineralization efficacy is highly variable among minerals common to slag; thus, the slow kinetics and low conversion common to slag-based CO2 mineralization is likely due in part to blockage of reactive species by unreactive species. Further, the modified shrinking core model matches early phase CO2 mineralization rates where the traditional models fail. Analysis of slag-based CO2 mineralization methods should thus account for the specific mineralogy, particle size distribution, and micromorphology of tested slag.

Assessment of the potential carbon footprint of engineered processes for the mineral carbonation of PGM tailings

The engineered sequestration of carbon dioxide (CO2) emissions through mineral carbonation typically requires energy intensive conditions and chemical reagents to accelerate the naturally slow reaction processes. In order to be an effective carbon dioxide mitigation strategy, engineered mineral carbonation processes have to result in a net reduction of CO2 emissions. This is particularly the case for feedstock such as platinum group metal (PGM) tailings, which are comprised largely of the relatively inert pyroxene mineral. This study evaluated the viability of using these tailings for carbon sequestration through mineral carbonation on the basis of an assessment of the potential carbon footprint of selected engineered processes. The processes selected include the ammonium salts process, the direct aqueous process, the Åbo Akademi University (ÅAU) multi-stage gas-solid route, a mineral acid pH swing process and Lackner’s multi-stage HCl extraction process. Aspen Plus v8 software was used for mass and energy balance modelling, whilst the Life Cycle Assessment (LCA) software programme SimaPro v7.7.3 was used for carbon emissions accounting. The selected processes all resulted in higher emissions of carbon dioxide than those sequestered. This was particularly the case for Lackner’s multi stage HCl process (18 295 kg-CO2e) and the indirect aqueous ammonium salts (8 798 kg-CO2e) processes. The process having the lowest carbon footprint was the ÅAU process (1 354 kg-CO2e), followed by the direct aqueous process (2 364 kg-CO2e) and the mineral acid pH swing (3 126 kg-CO2e). The unit processes making the most significant contribution to the carbon footprint of the mineral carbonation process systems are heat requirements and chemical reagent make-up. Sensitivity analysis shows that the direct aqueous and ÅAU process emissions can be reduced beyond the CO2 emissions threshold when conversion is increased.

Mitigation of carbon footprints through a blend of biofuels and oxygenates, combined with post-combustion capture system in a single cylinder CI engine

Abstract Mitigation of carbon footprints in compression ignition (CI) engines can be achieved using biofuels (carbon neutral and carbon dioxide (CO2) sequestration effects), with oxygenates and effective post-combustion capture systems. The present study focuses on the net reduction of CO2 emissions through the combination of karanja oil methyl ester (KOME), orange oil (ORG), oxygenates blended fuel and zeolite-based post-combustion capture system (ZPCS) in a single cylinder CI engine. KOME emitted higher CO2 emissions as compared to the diesel. Blending equal volume of ORG with KOME reduced CO2 emissions further by 27% compared to KOME but still higher compared to diesel by 11%, at 100% load condition. Four oxygenates, namely methanol (M), ethanol (E), n-butanol (B) and n-pentanol (P) were blended 20% by volume with the KOME-ORG. KOME-ORG + M20 emitted minimum CO2 compared to other oxygenate blends due to stoichiometric carbon balance, about 38% less compared to KOME nearly reaching diesel emission characteristics at 100% load. Additionally ZCPS was placed in the exhaust line and tested with all oxygenate blends with KOME-ORG, methanol blend led to 65% reduction in CO2 emissions compared to KOME and 53% reduction compared to diesel, at 100% load.

Process simulation and energy integration in the mineral carbonation of blast furnace slag

Abstract Large quantities of blast furnace (BF) slag and CO2 are discharged annually from iron and steel industries, along with a large amount of waste heat. The mineral carbonation of BF slag can not only reduce emissions of solid waste but also realize the in-situ fixation of CO2 with low energy consumption if integrated with the waste heat utilization. In this study, based on our previous works, Aspen Plus was employed to simulate and optimize the carbonation process and integrate the process energy. The effects of gehlenite extraction, MgSO4 carbonation, and aluminum ammonium sulfate crystallization were studied systematically. The simulation results demonstrate that 2.57 kg of BF slag can sequester 1 kg of CO2, requiring 5.34 MJ of energy (3.3 MJ heat and 2.04 MJ electricity), and this energy includes the capture of CO2 from industrial flue gases. Approximately 60 kg net CO2 emission reduction could be achieved for the disposal of one ton of BF slag. In addition, the by-product, aluminum ammonium sulfate, is a high value-added product. Preliminary economic analysis indicates that the profit for the whole process is 1127 CNY per ton of BF slag processed.