High Global Warming Potential Research Articles

A computational drop-in assessment of hydrofluoroethers in Organic Rankine Cycles

Organic Rankine Cycles (ORCs) are experiencing a growing interest due to their ability to generate electricity from residual low waste heat sources. HFC-245fa is a representative working fluid for ORC applications, but it has recently been phased-out in new equipment because of its high global warming potential (GWP). In this work, the soft-SAFT molecular-based equation of state is used to evaluate the capacity of nine promising low-GWP hydrofluoroethers (HFEs) as alternative working fluids in ORC applications using different key performance indicators focused on energy efficiency and service fluids consumption. The thermodynamic model has been employed to characterize these fluids by describing saturated densities, vapor pressure, surface tension, temperature-enthalpy, and temperature-entropy diagrams, including further validation with binary mixtures. Then, based on technical criteria focused on the thermal efficiency and working and service fluids consumption, the soft-SAFT model has been used to conduct a feasibility study of HFEs as direct substitutes for HFC-245fa in such applications. Although pure fluids can not reach the same efficiency as the benchmark, HFE-356mmz, HFE-7000, and HFE-7100 appear as promising replacements, capable of approaching system requirements operating at low pressure with low cooling water and heating fluid flow rates, while exhibiting lower GWP values.

Impact of anaerobic digestion on reactive nitrogen gas emissions from dairy slurry storage

Biogas digesters are commonly used to treat animal manure/slurry, and abundant digested slurry is generated during the digestion process. Gas emissions from digested and raw slurry may vary with the change in slurry parameters after digestion, but the mechanism is not well understood. Gas emissions from raw dairy slurry (RS) and digested dairy slurry (BS) during 98 days of storage were investigated in this study to evaluate the effects of anaerobic digestion on reactive nitrogen emissions from slurry storage. Results showed that much higher N2O and NO emission and lower NH3 emission was achieved in BS than in RS. The mean gaseous emission of RS and BS accounted for 27.8% ± 6.9% and 17.1% ± 2.3% of the initial TN for NH3, 0.1% ± 0.1% and 3.5% ± 1.6% of the initial TN for N2O, and 0.0% ± 0.0% and 0.2% ± 0.0% of the initial TN for NO, respectively. Among all detected N2O-forming and reducing microbial genes, the abundance of amoA genes was the most closely related to N2O flux (r = 0.54, p < 0.01). More aerobic conditions occurred in BS, and dissolved oxygen (DO) increased to 0.4–1.6 mg L−1 after 35 days because the low organic matter of BS resulted in good infiltration of surface air into the slurry. The increased DO stimulated the growth of Nitrosomonas and the increase in amoA gene copies and contributed to the high N2O and NO emissions in BS through the nitrification process. Vulcanibacillus, Thauera, Castellaniella, and Thermomonas were the major denitrifying bacteria that occurred in BS and caused an incomplete denitrification process, which could be another reason for the increase in N2O and NO emissions from BS. Our study indicated that anaerobic digestion reduced the organic matter content of the slurry and caused an active microbial environment that facilitated the transformation of slurry N to N2O in BS storage, thus lowering the NH3 emission compared with RS storage. Therefore, aside from NH3, N2O should also be preferentially mitigated during BS storage because N2O is a greenhouse gas with high global warming potential.

Measurements of isobaric specific heat capacity (cp) for pure trans-1,3,3,3-tetrafluoropropene and (trans-1,3,3,3-Tetrafluoropropene + 1,1,1,2-tetrafluoroethane) binary mixtures at temperatures from (231.84 to 338.68) K and pressures up to 8.2 MPa

Due to the increasingly serious greenhouse effect, R134a with high global warming potential (GWP) will be phased out gradually. Pure trans-1,3,3,3-Tetrafluoropropene (R1234ze(E)) and (R1234ze(E) + 1,1,1,2-tetrafluoroethane (R134a)) mixtures have become one of the most potential alternative refrigerants owing to lower GWP. The isobaric specific heat capacity (cp) is one of the most important thermophysical properties for the design of heat exchangers and the verification of the accuracy of the equation of state (EoS). In this paper, the cp of pure R1234ze(E) and (R1234ze(E) + R134a) mixtures at temperatures from (231.84 to 338.68) K was measured by a self-design flow calorimeter, and the pressures up to 8.2 MPa. A total of 160 liquid cp data are reported, including 57 data points for pure substance and 103 data points for mixtures. Uncertainties for temperature, pressure and cp were estimated to be less than 11 mK, 0.02 MPa and 1.0 %. In addition, the experimental data were compared with the pieces of literature data and the predictions of three models (Helmholtz energy EoS, Peng-Robinson (PR) EoS and corresponding states equation (CSE)). Among the three models, the Helmholtz energy EoS gives the best description, while the prediction performance of the PR EoS is the worst, especially in the low-temperature region and the near-critical region. Then, a brief investigation was performed to understand the reasons behind these discrepancies and found that the specific volume data have a significant impact on the cp prediction for PR EoS. When using the high-precision specific volume data in the cp calculation, the prediction performance of PR EoS will be significantly improved.

Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies

Abstract. The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past 2 decades, primarily as a result of the phaseout of ozone-depleting substances under the Montreal Protocol and the use of HFCs as their replacements. In 2015, large increases were projected in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 ∘C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries. Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2 eq. inferred HFC emissions continue to increase through 2019 (to about 0.8 GtCO2eq.yr-1) but are about 20 % lower than previously projected for 2017–2019, mainly because of the lower global emissions of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and the lower reported consumption of HFC-143a in China. Because this time period preceded the beginning of the Kigali provisions, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications in anticipation of national or global mandates. There are two new HFC scenarios developed based (1) on current trends in HFC use and Kigali-independent (K-I) control policies currently existing in several countries and (2) current HFC trends and compliance with the Kigali Amendment (KA-2022). These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2eq.yr-1 to 1.9–3.6 GtCO2eq.yr-1. The added provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 GtCO2eq.yr-1 in 2050. Without any controls, projections suggest a HFC contribution of 0.28–0.44 ∘C to global surface warming by 2100, compared to a temperature contribution of 0.14–0.31 ∘C that is projected considering the national K-I policies current in place. Warming from HFCs is additionally limited by the Kigali Amendment controls to a contribution of about 0.04 ∘C by 2100.

Design of Ionic Liquids for Fluorinated Gas Absorption: COSMO-RS Selection and Solubility Experiments.

In recent years, the fight against climate change and the mitigation of the impact of fluorinated gases (F-gases) on the atmosphere is a global concern. Development of technologies that help to efficiently separate and recycle hydrofluorocarbons (HFCs) at the end of the refrigeration and air conditioning equipment life is a priority. The technological development is important to stimulate the F-gas capture, specifically difluoromethane (R-32) and 1,1,1,2-tetrafluoroethane (R-134a), due to their high global warming potential. In this work, the COSMO-RS method is used to analyze the solute–solvent interactions and to determine Henry’s constants of R-32 and R-134a in more than 600 ionic liquids. The three most performant ionic liquids were selected on the basis of COSMO-RS calculations, and F-gas absorption equilibrium isotherms were measured using gravimetric and volumetric methods. Experimental results are in good agreement with COSMO-RS predictions, with the ionic liquid tributyl(ethyl)phosphonium diethyl phosphate, [P2444][C2C2PO4], being the salt presenting the highest absorption capacities in molar and mass units compared to salts previously tested. The other two ionic liquids selected, trihexyltetradecylphosphonium glycinate, [P66614][C2NO2], and trihexyl(tetradecyl)phosphonium 2-cyano-pyrrole, [P66614][CNPyr], may be competitive as far as their absorption capacities are concerned. Future works will be guided on evaluating the performance of these ionic liquids at an industrial scale by means of process simulations, in order to elucidate the role in process efficiency of other relevant absorbent properties such as viscosity, molar weight, or specific heat.

Understanding the Absorption of Fluorinated Gases in Fluorinated Ionic Liquids for Recovering Purposes Using Soft-SAFT

It is proven that fluorinated gases (F-gases) have a vast impact on climate change due to their high global warming potential. Hence, it is imperative to search for new molecules to replace them in current applications, as well as technologies to capture, recover, and recycle F-gases to avoid their emissions to the atmosphere. One of the attractive technologies for this purpose is to absorb them in fluorinated ionic liquids (FILs), given their solubilization power. However, the complexity of FILs and the time-consuming experimental methodologies to fully characterize them hinder their prompt usage in this urgent field. In this work, the soft-Statistical Associating Fluid Theory (soft-SAFT) Equation of State is used as a tool to investigate the solubility of six different F-gases (R-32, R-125, R-134a, R-14, R-116, R-218) in five FILs ([C2C1Im][C4F9SO3], [C2C1Im][C4F9CO2], [C2C1py][C4F9SO3], [C2(C6F13)C1Im][N(CF3SO2)2], and [C2(C6F13)C1Im][N(C2F5SO2)2]). The robustness of the soft-SAFT approach allowed the establishment of new FIL models in a simple and fast way, and the calculation of F-gases solubility in them, in excellent agreement with existing experimental data. Once the models were assessed, a systematic study was performed regarding the structural features of FILs favoring their performance to absorb F-gases by using the soft-SAFT approach as a screening tool. It has been obtained that the solubility is favored by the presence of a perfluoroalkyl chain in the imidazolium cation, together with a bulkier anion. In all cases, [C2(C6F13)C1Im][N(C2F5SO2)2] shows a superior solubility of F-gases than the [C2(C6F13)C1Im][N(CF3SO2)2], also indicating that the addition of one carbon to the two anionic symmetric fluorinated chains contributes to the gas-philicity of the FILs. This work proves the relevance of using the soft-SAFT framework to obtain insights into the behavior of such complex systems and key trends, even when experimental data are scarce, as a step forward in assessing systems for separating and recovering F-gases.

LFG 엔진의 희박 과급 연소 조건에서 화염 속도 측정 및 계산

In order not to release Landfill gas (LFG) having a high global warming potential into the atmosphere and to burn in an internal combustion engine for power generation, a study was conducted to measure and calculate flame speed under turbocharged and lean burn conditions of spark ignition engine. By changing the ratio between methane and carbon dioxide, which are the main components of LFG, experiments were conducted to measure the flame speed using a constant volume combustion chamber. Also comparative analysis was performed with data obtained using CHEMKIN library with GRI 3.0 mechanisms. In addition, using the data obtained through numerical analysis the correlations were derived to calculate the flame speed as a function of equivalence ratio. This study concludes that the overall trend of LFG flame speed is in good agreement between the experimental and calculated results. Using the correlated equation derived from the results of this study, it is possible to estimate the flame speed of LFG under turbocharged and lean burn of spark ignition engine.

Process Simulation-Based Life Cycle Assessment of Dissolving Pulps.

Dissolving pulp (DP) is a specialty pulp product from a variety of lignocellulosic biomass (i.e., hardwoods (HW) and softwoods (SW)) with a broad range of applications. Conducting life cycle assessment (LCA) for DP end applications (e.g., textile products, specialty plastics) is challenging due to the lack of life cycle inventory (LCI) data and environmental information associated with different grades. This research addresses this challenge using process simulations to generate LCI for different DP grades (e.g., acetate and viscose) made from HW and SW, respectively. The LCA results show that biomass feedstock directly affects the environmental impacts of DP. For instance, HW acetate grade has higher global warming potential than SW acetate but lower environmental impacts in other categories related to ecosystems and human health. This HW versus SW comparison has similar results for viscose DP in all impact categories except eutrophication. Additionally, a hotspot analysis identifies that on-site emissions and chemicals are the main contributors to the environmental impacts across all grades in this study. The results and LCI data generated in this work provide critical information to support future LCA and sustainability assessment for end-products derived from DP.

The Zr Modified γ-Al2O3 Catalysts for Stable Hydrolytic Decomposition of CF4 at Low Temperature

CF4, one of the Perfluorocompounds (PFCs), also known as a greenhouse gas with high global warming potential. In this study, Zr/γ-Al2O3 catalysts were developed for CF4 decomposition. The addition of Zr onto γ-Al2O3 achieves a high CF4 conversion efficiency of 85% at 650 °C and maintain its activity for more than 60 h, which is obviously higher than that of bare γ-Al2O3 (50%). The mechanism involved in CF4 decomposition over the Zr/γ-Al2O3 are clarified that the surface Lewis acidity sites are the main active center for CF4 directly adsorbing and decomposing. The results of NH3-TPD and FT-IR analyses suggest that the amount of Lewis acidity sites on catalyst surface increases significantly after the introduction of Zr, thereby enhancing the activity of catalyst for CF4 decomposition. The results of XPS analyses confirms the electrons transfer from Zr to Al, which contribute to the increase in Lewis acidity sites. The results of this work will help the development of more effective catalysts for CF4 decomposition.

Investigating the arable land that is the main contributor to global warming between paddy and upland vegetable crops under excessive nitrogen fertilization

Methane (CH4) and nitrous oxide (N2O) have been considered as two of the major greenhouse gases (GHGs) from agricultural land. CH4 is normally emitted from water-logged paddy fields, while N2O is emitted from aerobic upland soils. Both of these arable lands are thought to be major GHG emission sites; however, the type of land that is responsible for the highest contribution to GHG emissions in the same region has not been studied. A two-year field study was conducted to calculate the contributions to global warming of rice paddy fields and red pepper cultivation in upland soil under different nitrogen (N) fertilization levels. Urea was applied as a source of nitrogen at four different levels (0, 50, 100, and 200% of the recommended doses for cultivation), and rice and red pepper were cultivated in paddy and upland fields, respectively, from May to October. CH4 and N2O were measured from both arable lands to quantify GHG fluxes.The CH4 emissions increased in a quadratic response with increasing nitrogen application level in rice paddy fields and upland soil, but rice paddies had significantly higher CH4 emissions than red pepper upland soils. In contrast, N2O emissions showed a linear correlation with increasing N fertilization level in both arable lands; however, upland soil showed significantly higher N2O emissions than rice paddy fields. The rice paddy field had much higher global warming potential (GWP) than upland soil under low levels of N fertilization (below 265 kg N ha−1) according to a carbon dioxide (CO2) equivalent comparison. However, upland soil showed a clearly higher GWP than rice paddy fields under excessive N fertilization. Therefore, we concluded that upland vegetable crops contributed the most to the GHG emissions caused by high N2O fluxes under excessive N fertilizer application.

Influence of seasonal and environmental variables on the emission of methane from the mangrove sediments of Goa.

Mangrove sediments are known sources for methane emission that has a very high global warming potential. The spatio-temporal emission of methane in the mangrove sediments was quantified in the present study using the static closed chamber technique. Besides, the effects of environmental parameters on methane emission were estimated at Betim (mouth), Chorão (midstream), and Volvoi (upstream) stations along the tropical Mandovi estuary. On an average, the methane emission at the upstream estuarine station at Volvoi was maximum (1268.68 ± 176nMcm-2h-1) compared to the other two stations. Annually, the methane emission was significantly influenced by physicochemical parameters like salinity at Betim and Volvoi and, the redox potential at the midstream station at Chorão. The variation of methane emission between the 3 stations (P < 0.001) is attributed to the variation in methanotrophy (P < 0.05) and methanogenesis (P < 0.05) influenced by differences in the concentration of nutrients (P < 0.05) and organic carbon (P < 0.05). Seasonally, the highest methane emission at Chorão was during the post-monsoon, at Betim was during the monsoon season (1305.34 ± 108.58nMcm-2h-1), and at the upstream station at Volvoi, the emission of methane was highest during the pre-monsoon season (1514.68 ± 130.94nMcm-2h-1). The influence of environmental parameters was more prominent on methane emission at the 3 stations during the monsoon season. Spearman's correlation analysis indicated that seasonal changes in methane emissionare not only attributed to the influence of seasonal rainfall that leads to the fresh water input, but also to the variation in biogeochemical parameters.

Performance assessment of a rotary active magnetic regenerator prototype using gadolinium

• The cooling performance of a multi-bed AMR device with gadolinium is presented. • A cooling power of 818 W with a COP of 4.2 was achieved over a 10 K span. • The device can establish a 16.6 K span starting from room temperature in 25 min. • Active valve control can increase cooling power and COP by more than 70%. • A maximum second-law efficiency of 39.2% was obtained at a span of 7.3 K. We present the experimental results for a rotary magnetocaloric prototype that uses the concept of active magnetic regeneration, presenting an alternative to conventional vapor compression cooling systems. Thirteen packed-bed regenerators subjected to a rotating two-pole permanent magnet with a maximum magnetic field of 1.44 T are implemented. It is the first performance assessment of the prototype with gadolinium spheres as the magnetocaloric refrigerant and water mixed with commercial ethylene glycol as the heat transfer fluid. The importance of various operating parameters, such as fluid flow rate, cycle frequency, cold and hot reservoir temperatures, and blow fraction on the system performance is reported. The cycle frequency and utilization factor ranged from 0.5 to 1.7 Hz and 0.25 to 0.50, respectively. Operating near room temperature and employing 3.83 kg of gadolinium, the device produced cooling powers exceeding 800 W at a coefficient of performance of 4 or higher over a temperature span of above 10 K at 1.4 Hz. It was also shown that variations in the flow resistance between the beds could significantly limit the system performance, and a method to correct those is presented. The performance metrics presented here compare well with those of currently existing magnetocaloric devices. Such a prototype could achieve efficiencies as high as conventional vapor compression systems without the use of refrigerants that have high global warming potential.

Comparative life-cycle assessment of microalgal biodiesel production via various emerging wet scenarios: Energy conversion characteristics and environmental impacts

Various scenarios for biodiesel production from wet microalgae were recently reported to eliminate the energy consumption of microalgae drying. However, the comparative investigations on the environmental impacts and energy consumption of those scenarios were limited. In present study, four emerging scenarios (LE-PEF, IST-EAC, IST-MAT and LE-MHT) using different strategies and different solvents were analyzed and compared in term of net energy ratio (NER), greenhouse gas (GHG) emissions, ecotoxicity, and human toxicity. The results show that although the energy consumption of microalgae drying is eliminated, new energy consumption and environmental impacts were arising as solvent usage increased. The LCA results revealed that the solvent used during biodiesel production was the dominant contributor to the environmental impacts and energy consumption. The best NER (0.73), GHG emissions (−41.12 g CO2-eq MJ−1), human toxicity (2.15E-14 case MJ−1), and ecotoxicity (2.4E-4 PAF m3 d MJ−1) was observed in LE-MHT, mainly ascribed to the minimal usage of organic solvent. LE-PEF resulted in the worst environmental impact, owing to its over usage of chloroform, which is characterized by high global warming potential and high toxicity. Due to the extensive usage of solvent during in-situ transesterification, high NERs were reported for both IST-MAT and IST-EAC. The comparison between IST-MAT and IST-EAC demonstrated that the human toxicity was significantly decreased when hexane was replaced by ethyl acetate. The energy conversion characteristics and environmental performance could be further improved by minimizing solvent usage, using eco-friendly solvents, and increasing lipid recovery.

Natech risk and the impact of high-GWP content release on LCA of industrial components

Industrial facilities can be severely affected by natural hazards (NHs) often resulting in significant social, environmental, and economic consequences. One of the most serious consequences of Natech’s events is the accidental release of hazardous chemicals. While special attention has been paid to leakage prevention of toxic, flammable, or pollutant components to date, the possible effects in terms of green house gas (GHG) emissions have not been thoroughly investigated. NH can trigger, indeed, the release of high global warming potential (GWP) compounds such as fluorinated gases, nitrous oxides and others chemicals from collapsed components and/or structures. Nonetheless, conventional approaches to integrate NHs with LCA of buildings focus mostly on the embodied carbon metric, evaluated as in the Bill of Material procedure. As demonstrated by empirical evidence, these methods do not take into account the possible high-GWP compounds release in the case of extensive damage or collapse, which may lead to a general underestimation of the related carbon footprint. It is worth noticing that current international standards do not explicitly recommend the inclusion of these aspects in LCA procedures for structures. To cope with these issues, we introduce in this paper both the new concept of content release GHG emission potential (CGEP) and, a procedure, capable of integrating these effects with LCA. Finally, we provide some examples of industrial components characterized by a significant CGEP.

Recent Advances in Two-Phase Immersion Cooling with Surface Modifications for Thermal Management

This paper reviews the major researchers of liquid, immersion, and two-phase cooling. Currently, liquids are used instead of air to cool the growing data centers. Immersion cooling shows a higher heat transfer coefficient than conventional cooling (&lt;37 W/cm2). Because the use of liquids with high global warming potentials is prohibited, the number of liquids that can be used is limited. This paper discusses the existing, relevant literature from researchers who have studied the issue at least thrice. The authors were divided into those who focused on the surface and those who formed a structure on the surface. In summary, the authors suggested the following research directions: The experimental conditions of porous foam are not diverse, and there is a concern about the separation of foam and coating into the tub. The experimental conditions of the immersion tub should also be varied according to the heat and pressure over time. Structure-level research shows higher performance than surface-level research, but an economic feasibility study is required.

Advances, challenges, and perspectives of biogas cleaning, upgrading, and utilisation

Biogas as a renewable energy resource can be broadly recognised as a carbon–neutral fuel which reduces anthropogenic greenhouse gas emissions, mitigates global warming, and diversifies energy supply. However, the biogas share in the global renewable energy supply chain and technology deployment and maturity are not commensurate with the potential. The first half of this study critically reviews state of the art developments in biogas cleaning and upgrading technologies by considering their present status, current challenges, and barriers associated with their future development. The second part of this paper aims to address critical gaps in converting biogas to biomethane, proposing required pre-treatment steps for different technologies. The third part focuses on current policies concerning the strict regulations implemented for flaring consent applications. In this section, biogas upgrading technologies were compared by estimating the global warming potential (GWP) resulting from waste gases (WG). It was observed that due to high methane losses, WGs from membrane technologies have the highest GWP, but with flaring have the lowest GWP. In the last part of this review, the recent applications of biogas in cogeneration (CHP), tri-generation (CCHP), quad-generation systems, heat, and vehicles are discussed. The use of biogas by different technologies, and their resulting efficiencies were analysed in CHP applications, including microturbines, micro humid air turbine (mHAT), solid oxide fuel cells (SOFC) and hybrid systems of SOFC-microturbines.

Difluoromethane (HFC-32) and Pentafluoroethane (HFC-125) Sorption on Linde Type A (LTA) Zeolites for the Separation of Azeotropic Hydrofluorocarbon Refrigerant Mixtures.

Worldwide use of hydrofluorocarbons (HFCs) is currently being regulated and phased out because of high global warming potentials (GWPs). Separation techniques for recycling refrigerants are needed so that HFCs can be dealt with responsibly. Many HFCs currently in use are azeotropic or near-azeotropic refrigerant blends and must be separated so that the components can be recycled and repurposed effectively. One such refrigerant is R-410A, which is a near-azeotropic 50/50 wt % mixture of pentafluoroethane (HFC-125) and difluoromethane (HFC-32). This study examined the use of the LTA zeolites for separating HFC-32 from HFC-125. Pure gas isotherms were measured using a XEMIS gravimetric microbalance with zeolites 3A, 4A, and 5A. Reversible sorption was observed for HFC-32 with zeolites 4A and 5A, whereas irreversible sorption was observed for HFC-125 with zeolite 5A. Negligible sorption was observed for HFC-125 with zeolites 3A and 4A, and although sorption of HFC-32 with zeolite 3A was observed, the process was slow, making the sorbent not commercially viable. The enthalpy of adsorption was predicted using the vapor adsorption equilibrium (VAE) analogue of the Clausius-Clapeyron equation and measured using a calorimeter for HFC-125 and HFC-32 with zeolite 5A and for HFC-32 with zeolite 4A. Molecular-level interactions between the LTA zeolites and HFCs were discussed and used to interpret pure gas isotherms and enthalpy of adsorption results. Overall, zeolites 4A and 5A were found to be good candidates for kinetically and thermodynamically separating R-410A, respectively.

A comprehensive study of drop-in alternative mixtures for R134a in a mobile air-conditioning system

• A comprehensive method to evaluate refrigerant alternatives is developed. • No mixture has higher COP, higher Q, lower GWP, and lower flammability than R134a. • Mixing R134a or R227ea with R152a creates a promising alternative to R134a. • The results of mixtures are compared to R134a and guide the design of alternatives. • The method can be extended for searching alternatives for other fluids. R134a will be phased out soon due to its high GWP. Replacing R134a with a low Global Warming Potential (GWP) and non– or slightly flammable fluids in the systems in stock should maintain the same level of system performance. This study focuses on the drop-in alternatives for R134a regarding a Mobile Air-Conditioning system. A simulation model coupled with a microchannel heat exchanger model is developed and validated for calculating the system Coefficient of Performance (COP) and capacity of the Mobile Air-Conditioning system. A comprehensive method is developed to evaluate the alternative candidates combining the performance simulation and the flammability estimated of mixtures. The evaluation includes the system performance, environmental impact, and flammability of alternative mixtures. 15 pairs of binary mixtures from six pure fluids (R134a, R1234yf, R1234ze(E), R32, R227ea, and R152a) with 99 compositions are evaluated as R134a drop-in replacements, and the results are discussed. There is no perfect mixture found that is nonflammable, has low GWP, and has higher system efficiency and capacity than R134a in this study. Using R152a as a drop-in replacement of R134a can increase the system efficiency and capacity, but R152a is flammable. By adding R134a or R227ea to R152a can reduce the flammability of the mixture. R152a/R134a, R152a/R1234yf, and R32/R152a have higher COP and capacity than R134a, but they are not safe or environmental friendly enough. The mixtures for replacing R134a as drop-in alternatives with low Global Warming Potential (less than 150 or 700), nonflammable or slightly flammable are listed and discussed. The method developed in this study can be extended to evaluate alternatives for replacing other working fluids in any thermal application that will be restricted.

Life cycle assessment comparison between zircon and alumina sand applied to ceramic tiles

The goal of the study is to assess and compare the use of opacifier (whitener) materials zircon sand and alumina applied in ceramic tiles production. This study provides a comparison using a cradle-to-gate life cycle assessment (LCA) approach, giving an overview of the differences from an environmental perspective between these materials in body mixtures to obtain tiles with a high degree of whiteness. This ISO compliant study is backed by an independent critical review panel and presents the first European-representative LCA comparison between zircon and alumina, using primary data from industry. A super white (with CIELab coordinate L*>85) ceramic tile can be produced using zircon or alumina as opacifier, with different mixtures. For zircon data, a previous ISO reviewed LCA and its associated paper has been used. This data comes from Zircon Industry Association members. For alumina, the eco-profile of alumina and bauxite developed by the European Aluminium has been used and is available in the “Environmental Profile Report for the European Aluminium Industry”. This study considers the use phase of the compared materials as whiteners. Milling phase data was collected from specific producers and tile mixture preparation data was taken from wider industrial bodies. Sensitivity and scenario analysis were used to understand the main differences between mixtures and influences between materials. Comparing the use of zircon sand with alumina in different ceramic mixtures, the primary result is that tiles using zircon had lower environmental burdens for almost all the analysed impact potentials. The alumina mixtures investigated show about 20% higher Global Warming Potential (GWP), Eutrophication Potential (EP), Acidification Potential (AP), Photochemical Ozone Creation Potential (POCP), Abiotic Depletion Element and Fossil Potential (ADPe/f) and Primary Energy Demand (PED). The Ozone Depletion Potential (ODP) is the only potential impact that is similar for zircon mixtures and alumina mixtures. The milling process is not negligible for all the impact categories considered in this study. The results of the study show that main differences between zircon and alumina mixtures are closely tied to the environmental performance of regional grid electricity generation. This study quantifies and compares the environmental impacts associated with the production of super-white ceramic tile mixture with two different whiteners: zircon and alumina. With this study, ceramic tile producers are given a tool to guide their choices in opacifier material selection, using a rational, scientific and peer-reviewed methodology, ensuring objective comparison between two materials.

Short-Term and Long-Term Effects of Natural and Artificial Carbonaceous Substrates on Greenhouse Gas Fluxes

The emissions of two greenhouse gases (GHG), carbon dioxide (CO2) and nitrous oxide (N2O), from six substrates with different carbonaceous content were compared in short and long-term incubation experiments. Three natural soils and three artificial chars were mixed with carbon (C) poor soil (Cambisol) to simulate real conditions after application of char to farmland. The natural soils were a Cambisol, an Anthrosol and a Histosol with C contents of 1.3%, 4.4% and 13.2%, respectively. The three chars produced through thermal conversion of wood chips by hydrothermal carbonisation (HTC), fluidized bed gasification and pyrolysis had C contents of 56.9%, 75.4% and 79.9%, respectively. Emission rates of CO2 and N2O from the rewetted substrates were measured by gas chromatography over a short time of 72 h and over a long period of nearly two years. The short-term CO2 emissions from the natural soils showed a clear relationship to their C content. The emission rate for the Histosol/Cambisol mixture was three times higher than that for the pure Cambisol, 77.1 vs. 23.5 mg CO2-C kg−1 organic matter (OM) per hour. The C emission rates for the char/Cambisol mixtures were much lower, ranging between 3.0 and 9.1 mg CO2-C kg OM−1 h−1 , and did not correspond to their total C contents. Comparison between the two incubation lengths showed that the long-term CO2 emission rates were generally one order of magnitude lower than the short-term rates. The final emission rates for natural substrates over a period of two years were still twice those for artificial char substrates, between 2.2–3.5 mg CO2-C kg OM−1 h−1 and 1.3–1.8 mg CO2-C kg OM−1 h−1 , respectively. Although the contents of total nitrogen (Ntot) and extractable nitrogen (Nmin) were considerable in the chars under study, enhanced N2O release was not observed in the incubation experiments. Instead, N2O emission rates in the three mixtures of chars and Cambisol were lower by one to two orders of magnitude compared to the pure Cambisol in short-term incubations. Even long-term N2O emissions were 5 to 9 times lower. The highest degree of N2O reduction was found for the HTC char. Because of the high global warming potential of N2O, this positive effect of chars may play an important role in mitigating emissions of CO2 equivalents. Both CO2 and N2O must be taken into account when balancing GHG emitted after chars (biochar, gasifier char, HTC char) are applied to soil.