Terms Of CO2 Emissions Research Articles

Optimization of Heat Pump Systems in Buildings by Minimizing Costs and CO2 Emissions

District heating systems are gaining global recognition as an essential tool for reducing greenhouse gas emissions and transitioning to a low-carbon-energy future. In this context, heat pumps are becoming an important technology, providing an effective solution for improving energy efficiency and reducing the reliance on fossil fuels in heating systems. Therefore, this study is focused on the optimal selection of heat pump systems for different types of buildings considering technical, economic, environmental, and social factors. This paper proposes a novel methodology based on mixed-integer nonlinear programming and multi-objective optimization that minimizes total costs and reduces CO2 emissions for heat production and supply systems over a desired period. The methodology is applied to various building types, including renovated and unrenovated apartment buildings, schools, kindergartens, and a supermarket. The study analyzes various types of heat pumps and electric heaters for space heating and domestic hot water production. Optimization results showed that the optimal heating system includes air-to-water heat pumps and electric heaters. Furthermore, for schools and a supermarket, these systems are combined with hybrid heat pumps. The goal of making the heating system neutral in terms of CO2 emissions was achieved for eight out of eleven buildings analyzed. The most profitable investments were in the heating systems of renovated five-story and unrenovated nine-story apartment buildings due to their low energy costs (0.0831 EUR/kWh), short payback periods, and high returns on investment.

Photovoltaic potential of public buildings in a world Heritage city: The case of San Cristóbal de La Laguna (Canary Islands, Spain)

Solar photovoltaic energy is increasingly positioned as an excellent renewable energy source to be implemented in energy communities. However, studies on photovoltaic potential are still required in order to enhance the clean energy transition in energy dependent systems, such as oceanic islands. This work is a study of photovoltaic potential of public building roofs in the World Heritage city of San Cristóbal de La Laguna in Tenerife (Canary Islands). The buildings selected for the study are sports centres, educational centres and civic centres, considering optimum and maximum production scenarios. The results showed the electricity generation capacity of each building, with 8811 and 861 MWh capacity for the maximum and optimum scenarios, respectively. In the optimal scenario, 56% of energy would be generated, of which 31% would be consumed on site, and the remaining 25% would be sent to the grid. The main difference is that in the case of optimal photovoltaic systems, economic profitability criteria take precedence, while in the case of maximum photovoltaic systems, the environmental benefits in terms of CO2 emissions into the atmosphere increase considerably. In the latter case, CO2 emissions are reduced by 771%, compared to 75% in the case of optimal photovoltaic systems.

Determination of properties and environmental impact due to the inclusion of cigarette fibers in mortar: a new solution to mitigate the CB pollution.

Cigarette butts generated are one of the major sources of total solid waste production and lead to environmental issues. This article has the objective of evaluating the effects of cellulose acetate microfibers (CAFs) sourced from discarded cigarette filters (CFs) as fiber reinforcement on the physico-mechanical properties and thermal conductivity of cementitious materials. To do so, mortar samples were prepared using different incorporated quantities of fibers (0.5, 1, 1.5, 2, 2.5, and 5% compared to the quantity of sand added to the mixture) and subjected to different tests to characterize the influence of CAFs on the microstructure of elaborated materials, considering the changes in workability time, compressive strength, flexural strength, density, water absorption, and microstructural analysis. Furthermore, the life cycle assessment (LCA) of mortar mixes in terms of CO2 emissions is made. The results revealed that the increasing percentages of CAFs reduced the dry density and compressive strength, by approximately 1.62-51% and 37-69.64%, respectively, and a notable enhancement of insulation characteristics by about 5-47.5% was achieved. Microstructure analysis confirmed the experimental investigation and revealed that adding more than 1% of fibers resulted in a significantly low unit weight with greater entrapped air content. The studies prove the possibility of recycling cigarette butts for insulating cementitious matrix. In addition, applying mortar containing acetate cellulose fibers is recognized as a more environmentally friendly mixture in terms of reducing CO2 emissions and could participate significantly in the achievement of SDGs.

Assessing the Social and Environmental Impact of Healthcare Technologies: Towards an Extended Social Return on Investment

Stroke is the third leading cause of death and disability overall worldwide. Upper limb impairment is a common consequence for stroke survivors, having negative impact on their quality of life. Robotic rehabilitation, through repetitive and monitored movements, can improve their status. Developed by a team of researchers at Politecnico di Milano, AGREE is an exoskeleton for upper limb rehabilitation at the stage gate between translational research and clinical validation. Since the cost of this device is particularly high, the present study aimed to provide a framework for assessing its value. The Social Return on Investment (SROI) method, able to grasp the economic, social and environmental impact of an activity, was applied, using expert opinions of a pool of clinical engineers and healthcare professionals from different Italian hospitals to obtain information. Environmental impacts were estimated through Life Cycle Assessment in terms of CO2 emissions and incorporated in the analysis. Considering a 5-year period, the SROI for a single exoskeleton was 3.75:1, and the SROI for the number of exoskeletons projected to be sold was 2.868:1, thus resulting largely in value for money. This study provides a model for combining economic, social and environmental outcomes that, besides contributing to theory, could be useful for decision-making.

A comprehensive study on the compressive strength, durability-related parameters and microstructure of geopolymer mortars based on mixed construction and demolition waste

As a viable option to upcycle construction and demolition waste (CDW) into value-added materials, geopolymer technology is emerging. Most studies investigate CDWs in a separated form or in combination with mainstream pozzolanic/cementitious materials focusing only on fundamental properties of geopolymer pastes, not considering to scale such materials to the level of their application in the forms of structural mortars/concretes or to characterize long-term performance/durability. This study investigated the development and characterization of ambient-cured mortars with mixed CDW-based geopolymer binders and untreated fine recycled concrete aggregates (FRCA). Mixture of CDW-based roof tile (RT), red clay brick (RCB), hollow brick (HB), concrete (C), and glass (G) was used as the precursor, while ground granulated blast furnace slag (S) was used in some mixtures to partly replace CDW precursors. Compressive strength, durability-related parameters including drying shrinkage, water absorption, and efflorescence, microstructure and materials sustainability were evaluated. Results showed that 28 d compressive strength results above 30 and 50 MPa are achievable with the entirely CDW-based and slag-substituted mortars, which were found improvable to have entirely CDW-based structural concretes. Drying shrinkage of the mortars is slightly higher than that of conventional cementitious/geopolymeric systems although it can be minimized significantly through mixture optimization. Water absorption values remain comparable with the literature. CDW-based geopolymer mortars outperform Portland cement mortars in terms of CO2 emission and energy requirement. Our findings show that via utilizing CDW-based constituents in mixed form as precursor and waste aggregates, it is possible to develop greener construction materials with acceptable strength and long-term performance.

Simulation-based performance evaluation of large-scale thermal energy storage coupled with heat pump in district heating systems

Large-scale water-based thermal energy stores (TES) coupled with heat pumps (HPs) are a key element in District Heating (DH) systems to achieve an increase of the share of renewables.The implementation of a 1D equation- based TES model, coupled with a 2D or 3D finite element-based model of the surrounding ground provides a robust and reliable tool that can be used in the study of large-scale TES systems. In this work, a simplified equation-based model for the HP using the TES as evaporator heat source is implemented to investigate its impact on the TES performance and on the surrounding ground temperatures. Two TES types (buried tank and shallow pit) are analysed under the same conditions (size, envelope characteristics, ambient temperature, ground properties and system boundary conditions). The parameters used to evaluate the coupled TES-HP performance consider both the environmental aspect (ground temperature and CO2 emissions) and the technical performance (energy and exergy efficiency).The integration of the HP proves to be effective in increasing the TES efficiency by 6 % (from 87 %) compared to the reference case without an HP in case of an insulated tank TES, and by 16 % (from 64 %) in case of an insulated shallow pit. The TES exergy efficiency analysis emphasizes the better performance of the tank over the shallow pit, with the tank geometry outperforming the shallow pit in all the investigated configurations (+ 25 % in the reference case without HP, + 20 % with 6 MW HP). However, when extending the exergy analysis to the system, the difference in exergy efficiency between the two geometries is strongly reduced (+ 5 % on average for the tank with respect to the shallow pit); the impact of thermal insulation is also less noticeable. In particular, in the system analysis the configuration of shallow pit with HP shows a performance comparable with the tank without HP. In terms of CO2 emissions, the integration of the HP coupled with a TES allows for a reduction of 33 % for the tank and 29 % for the shallow pit compared to the respective reference cases, due to the better utilization of the TES capacity. The resulting ground temperature near the TES is also influenced by the use of the HP, with an average ground temperature 5 K lower than in the reference case without HP at a ground depth between of 7 to 15 m. The contribution of thermal insulation appears however necessary for both geometries, as it contributes most to the reduction of ground temperature.

An Exploratory Study on the Impact of the Construction Industry on Climate Change

In the last decade, the construction industry in Egypt has been booming, and many mega projects are under construction. The lack of awareness of the construction industry’s impact on climate change could be very harmful in terms of CO2 emission, water and soil pollution, etc. This paper aims to explore the critical factors in the Egyptian construction industry that contributes to climate change. Moreover, given the shared features between the construction industry in Egypt and those in other countries, this research could also shed light on the general impacts of the construction industry on the various aspects of climate change. So, to achieve this aim, an intensive literature review was carried out to identify various factors contributing to climate change within the construction industry. This is followed by conducting 11 interviews with construction experts to explore any further factors throughout the lifecycle of a construction project. The identified factors from the literature review and the interviews were used to design a questionnaire survey to collect construction professionals’ opinions on the impact of these factors on climate change in Egypt. 48 valid responses were received. The collected data were statistically analyzed to rank and determine the criticality level of these factors. The results revealed that the most significant factors influencing climate change are the impact of industrial construction on climate change, the use of primary renewable energy as raw materials during the construction and use phases, and the effect of heavy civil and highway construction on climate change. The results also show that managing these factors requires considerable awareness and proactive actions during the project life cycle and pre-construction stage. The findings could inform decision-makers and construction professionals to raise awareness and make informed decisions to handle these key factors and minimize their potential contribution to climate change. Therefore, it can be recommended that construction clients may involve a climate change management plan as a requirement of tender documents.

Evaluation of Istanbul Strait (Bosphorus) passage simulations in terms of CO2 emissions

It is crucial to reduce CO2 emissions due to marine transportation, which has a direct effect on air pollution in channels such as the Istanbul Strait (Bosphorus), which has a high human population density in the vicinity. In this study, it is tried to evaluate whether it is possible to reduce CO2 emissions during the passage of the Bosphorus. For this purpose, a mathematical model including three different control systems, called MPC, PD, and PD-Fuzzy controllers, is created to evaluate the controller effect on CO2 emissions during the passage. Each control system is selected separately from the mathematical model and the Bosphorus passages are simulated. As a result of these simulations, the velocity of the ship, the route to be followed by the ship, and the change of the ship's rudder angle throughout the passage are obtained using each control system. In these simulations, it is assumed that there are no external forces, such as wind and current. The obtained results from the simulations are accepted as a reference and an evaluation is made in terms of CO2 emissions by including the number of commercial ships passing through the Bosphorus between 2006 and 2019. The calculated annual CO2 emissions that may occur in the Bosphorus passage with the various control systems are compared. The CO2 emissions increases approximately 1.86% depending on the selection of the control system for the determined ship for the Bosphorus passage simulations. As a result, it is emphasized that a more effective control system for reducing CO2 emissions in narrow channel passages such as the Bosphorus can exist.

Portfolios of sustainable practices for packaging in the circular economy: an analysis of Italian firms

PurposeThis study analyzes sustainable practices adopted by Italian firms to enhance the circularity of packaging and related results in terms of environmental improvements.Design/methodology/approachThe authors developed an empirical analysis using publicly available data from the National Consortium of Packaging (CONAI) in Italy, which consists of 603 circular packaging projects. The authors ran both descriptive and prescriptive analyses to determine individual sustainable practices and portfolios adopted to enhance packaging circularity and to verify related reductions in terms of CO2 emissions as well as energy usage and water consumption.FindingsThe findings reveal that firms are more accustomed to focusing on single sustainable practices than on portfolios of practices to achieve packaging circularity. Raw material saving and logistics optimization are the most frequent sustainable practices adopted by firms to improve circularity of packaging. The reuse of packaging allows firms to simultaneously reduce CO2 emissions, energy usage and water consumption. Preferences in terms of portfolio of sustainable practices are strictly linked to the types of materials used for packaging and environmental targets.Originality/valueThe authors investigate environmental practices that firms adopt to support packaging circularity, and the authors detect portfolios of sustainable practices that positively impact environmental performance indicators. This research extends a significant glimpse into the portfolio of sustainable practices for packaging in the circular economy implemented by firms, filling academic gaps and indicating business opportunities and avenues for economic development.

Method and evaluations of the effective gain of artificial intelligence models for reducing CO2 emissions

Nowadays, there is an increasing use of digital technologies and Artificial Intelligence (AI) such as Machine Learning (ML) models that leverage data to optimize the performances of systems in almost all activity sectors, including ML models for optimizing solutions related to CO2 capture from the atmosphere or CO2 emissions reduction from human activities. However, on the other hand, the use of AI models is leading to an increasing energy consumption that also raises environmental issues (in terms of CO2 emissions) which are less studied in the literature. This then raises the new question of a more realistic estimate of the carbon footprint (CO2 emissions in particular) of AI models in general, and particularly AI models aimed at reducing CO2 emissions. Thus, in this paper, for an AI model in this latter context, we propose a method to quantify both his negative impacts (quantity of CO2 emissions emitted by the training and use of the model) and his positive impacts (quantity of CO2 emissions saved when the model is used). The method is evaluated with three state-of-the-art AI models: (i) an artificial neural network model for managing the energy demand of Brazilian households, (ii) an adaptive neuro-fuzzy inference system for photovoltaic power forecast in Tunisia, (iii) and a Bayesian regression model for the electric vehicle routing problem in Sweden and Luxembourg. Results show that, if only the positive impacts are considered, the reduction of CO2 emitted due to the usage of the models is significant, but depends on each context (34%, 73%, and 9%, respectively). However, when both positive and negative impacts are considered, the negative impacts are sometimes higher than the positive impacts (the first and the third model) for a nominal use (1 user). Nevertheless, the balance becomes highly positive again, when these two projects are scaled up (realistic projections with many users). The second model cannot be scaled up, but the balance remains positive, even if the gains are much smaller. More generally, the CO2 emissions gain metrics provided by our method can be used as new metrics for comparing the efficiency of AI models (for reducing CO2 emissions) beyond predictive capacity-based traditional ML evaluation metrics. Based on the lessons learned from our study, we also provide seven global recommendations that can contribute to the reduction of the carbon footprint of ML models in general.

Emissions from Managed Agricultural Soils in Context of Consumption of Inorganic Nitrogen Fertilisers in Selected EU Countries

In addition to industry, transport, and waste management, the agricultural sector is also a major emitter of CO2 emissions. This article focuses on CO2 equivalent emissions from soil in the context of mineral nitrogen fertiliser management. The methodology itself consists of several successive phases, the first of which is to determine basic statistical characteristics for all EU countries, primarily in terms of mineral nitrogen fertiliser consumption, but also in terms of the area of crops grown. EU countries with similar cropping patterns were selected for comparison so that the results could be compared. The results show that there are quite significant differences in CO2 equivalent emissions between countries under similar conditions. At the same time, the values of the marginal increment of CO2 emissions as a function of mineral nitrogen fertiliser consumption were calculated. On the basis of the results of the selected countries, an upper limit in terms of CO2 emissions per hectare of arable land was also determined, and recommendations were made from a national perspective. The emissions themselves can be seen as a negative production externality that is not accounted for in the market mechanism and can thus also distort the price of agricultural production. The methodology used in this paper can be used to set an upper limit on CO2 emissions from soil due to the use of mineral nitrogen fertilisers and can then be used as an indicator for regulating and defining future agricultural policy instruments within the EU, where the objective is to reduce the level of CO2 emissions.

Satellite observations of seasonality and long-term trends in cirrus cloud properties over Europe: investigation of possible aviation impacts

Abstract. Linear contrails and contrail cirrus induced by global aviation have long been known to contribute to climate change by warming the atmosphere. Besides increasing global cirrus cloudiness, aviation may also alter the properties of natural cirrus clouds by soot emissions which lead to more heterogeneous freezing. During the first COVID-19 lockdown in Europe, changes in the properties and occurrence of cirrus clouds were determined with the lidar measurements of CALIPSO, which are presumed to be caused by the corresponding reduction in civil aviation. In the 10 years before the COVID-19 outbreak, however, aviation grew strongly in terms of CO2 emissions and flight densities in Europe. In this study, 10-year lidar measurements with CALIPSO are analysed to determine the seasonality and long-term trends in cirrus clouds as well as their correlations with the ambient temperatures and air traffic. The results show that there is a distinct seasonal cycle in the occurrence rates (ORs) and particle linear depolarization ratio (PLDR) of cirrus clouds. In addition, cirrus clouds appear within a broader altitude range in winter than in summer and they are characterized by larger OR and PLDR values in winter than in summer. The monthly medians of PLDR as well as their deseasonalized time series in the 10-year period before COVID-19 both show positive trends, which are statistically significant according to the Mann–Kendall (MK) significance test. However, the ORs of cirrus clouds show a negative trend, which might be connected with the background meteorological conditions. Since the cirrus PLDR strongly depends on the ambient temperatures, the contributions induced by temperature are further removed from the cirrus PLDR with a simple linear regression model. The derived residuals show significant positive trends according to the MK test. To compare the cirrus PLDR and air traffic (with the CO2 emissions from aviation as a proxy), the deseasonalization of both datasets were previously conducted since the seasonal cycles in both are not consistent. The deseasonalized time series determined for the cirrus PLDR and CO2 emissions from aviation both show increasing trends and their correlation coefficient is r=0.54 at the confidence level above 99.5 %. Finally, comparisons between the cirrus PLDR and aviation in every season were made and revealed a strong correlation in other seasons than in summer.

Qualitative/Quantitative Comparison of Changes in Alanya Rural Architecture in terms of CO2 Emissions and Energy Conservation within the Scope of Sustainability

Due to the rapid growth and development caused mainly by tourism of Alanya, rural areas are affected, losing their original texture and authentic structures and being exposed to unqualified interventions. The aim of this study is to determine the original features and reveal the value of Alanya rural architecture within the framework of the sustainability principles, and to determine how these values have changed with the unqualified interventions, by detailing qualitatively and quantitatively on the basis of each intervention. Within the scope of the study, the rural architectural heritage in Alanya has been documented in terms of settlement texture, space organization, architectural elements, material, construction and energy efficiency. For the analysis, a rural house that preserves its original values was used. A comparison was made between the values of this house and the values obtained as a result of the changes in the other buildings in the area. In cases where these interventions are applied in various variations, the changes in the heating and cooling load of the house are compared with the CO2 emission. It has been determined that the rural houses of Alanya provide energy conservation in a way that is perfected by tradition, both in terms of settlement features and space and materials on the basis of structure. It has been determined that the heating/cooling energy requirement can decrease but the CO2 emission increases in the individual changes made by evaluating different types of deterioration. When the most common application variations detected in the field are evaluated, it has been determined that both the heating/cooling energy requirement and the CO2 emission have increased. Rural settlements and residences define an architecture that has reached the highest level in terms of convenience, functionality and economy. Since any intervention to these structures means the loss of their energy conservation properties as well as their originality, a very careful decision should be made. The study reveals the first data in which the rural architecture of Alanya is evaluated within the scope of sustainability and energy and CO2 emissions are compared depending on deterioration/changes.

Flight Procedure Analysis for a Combined Environmental Impact Reduction: An Optimal Trade-Off Strategy

Many attempts have been made to reduce aviation’s environmental impact, as aviation traffic has grown exponentially in recent decades. While some approaches focus on technology and fuel alternatives, others strive to develop improved operational measures within air traffic management as a short-term action to mitigate aviation-induced climate change, as well as air pollution. In this work, different flight procedures are analyzed in terms of emissions and noise impact to define optimal trade-offs. The investigation is based on flight data recorders, emissions, and noise prediction models. An aircraft trajectory simulation code with flight procedure optimization is also implemented to define an environmentally optimal trajectory. The results show that while noise and the emissions proportional to the burned fuel may be reduced for some trajectories, other non-CO2 emissions could drastically increase if too low idle-thrust levels are reached. Therefore, a minimum threshold for idle thrust is suggested as a key factor to define a truly optimal trajectory in terms of CO2 emissions, non-CO2 emissions, and noise.

Evaluation of a biomethane, food and biofertiliser polygeneration system in a circular economy system

Biomethane is a viable alternative to natural gas and diesel for decarbonising hard-to-abate sectors such as agriculture, industry and heavy transport. Unlike conventional biogas upgrading, photosynthetic biogas upgrading cogenerates biomethane, biofertiliser and microalgal bioproducts with the potential to improve resource utilisation and process performance in a circular economy. In this paper, a photosynthetic biogas upgrading-based polygeneration process is proposed and analysed to co-produce biofuel (biomethane), bio-fertiliser (digestate) and food (Spirulina powder, protein supplement) using agricultural feedstock. Based on a multi-criteria performance assessment, the economic and environmental benefits of the process are demonstrated. Thermodynamic performance of the process revealed that reducing the energy for greenhouse heating to cultivate microalgae would enable a higher energy output than input. Using economic allocation, a carbon footprint of biomethane less than 10 gCO2-eq/MJ (lower than 32.9 gCO2-eq/MJ for sustainable biomethane use in transport in the EU Renewable Energy Directive (Recast) (RED-II)); Spirulina protein of 0.8 kgCO2-eq/100 g protein (compared to 50 kgCO2-eq/100 g protein for beef); and digestate of 0.4 kgCO2-eq/kgN (comparing positively to 1.5–3 kgCO2-eq/kgN for synthetic nitrogenous fertiliser) was achieved. Unlike the current RED-II mandated methodology, the analysis established that the energy, CO2 emissions, land and water footprints of each co-product are best represented using an economic allocation principle. Based on the extended nutrition profile, Spirulina as a complete food outperforms most meat and plant-based protein alternatives in terms of CO2 emissions, land, and water footprints.

A Review on Lignin-Based Carbon Fibres for Carbon Footprint Reduction

Carbon fibers (CFs) are made mostly from a non-environmentally friendly polyacrylonitrile (PAN) and little from rayon. PAN-based CFs, require huge amount of energy for its production aside its contributions to the global CO2 emission. Therefore, there is recourse to a more environmentally friendly sources of CFs biomass. Recently lignin has been recognized as a potential renewable raw material for carbon fibers to replace PAN-based. The magnitude and quality of CO2 emission of lignin-based CFs are dependent on the processing route. On this premise; this review examines the various lignin-based CFs processing route adopted by researcher in the recent past to establish the most viable route with minimum carbon footprint emission. Outcome of the review shows that the major advantages of aromatic polymer (AP) generated precursor over PAN is the presence of higher quantity of guaiacyl units and oxygen content which makes the stabilization phase efficient and faster requiring less energy. Though there are several methods and options for the various stages of conversion of lignocellulosic biomass into CFs as highlighted in the study, establishing an optimum processing route will be a trade-off amongst various issues of concern; carcinogenic risk, carbon footprint emission, CFs Yield and mechanical strength of the CFs. Inferences from the study shows that the L-CF significantly produced reduced climatic impact in terms of CO2 emission.

Transient simulation and techno-economic assessment of a near-zero energy building using a hydrogen storage system and different backup fuels

Proposing a cost-effective off-grid Hybrid Renewable Energy System (HRES) with hydrogen energy storage with a minimum CO2 emission is the main objective of the current study. The electricity demand of an office building is considered to be supplied by Photovoltaic Panels and wind turbines. The office building, modeled in Energy Plus and Open studio, has annual electricity consumption of 500 MWh electricity. 48.9% of the required electricity can be generated via renewable resources. Considering a system without energy storage, the remaining amount of electricity is generated from diesel generators. Hence, for reducing CO2 emission and fuel costs, a hydrogen energy storage system (ESS) is integrated into the system. Hydrogen ESS is responsible for supplying 38.6% of the demand electricity, which means that it can increase the energy supplying ability of the system from 48.9% to 87.5%. In addition to analyzing the application of the hydrogen storage system, the effect of four different kinds of fuel is considered as well. effects of Natural gas, Diesel, Propane, and LPG on the system's application are investigated in this study. Results indicate that natural gas emits less amount of CO2 compared to other fuels and also has a fuel cost of 3054 $/year, while hydrogen ESS is available. For the renewable system without ESS, the fuel cost rises to 10,266 $/year. However, liquid gas, Propane, and LPG have better performance in terms of CO2 emission and fuel cost, respectively.

Purification of magnesium chloride from mixed brines via hydrogen chloride absorption with ambient temperature and pressure regeneration of super azeotropic hydrochloric acid

Desalination is an important source of potable water for a large portion of the world that is expected to expand in response to population increase and climate change. Despite its benefits, desalination produces a hypersaline waste, termed ‘brine’, which has negative impacts on the marine ecosystem and is costly to dispose of safely. An integral step in making desalination more environmentally friendly is the elimination of liquid wastes, so-called ‘Zero Liquid Discharge’. To make Zero Liquid Discharge financially viable, it is critical to separate and purify the constituent salts into products. We report on the design and operation of a system for continuous production of high purity Mg-chloride from desalination brine. This system is part of a Zero Liquid Discharge process that makes desalination net negative in terms of CO2 emissions by converting magnesium chloride into magnesium carbonate. Precipitation of sodium and potassium chloride from brine was achieved by absorption of a super azeotropic HCl gas. The super azeotropic HCl gas was regenerated by mixing the acidified brine in a low-temperature, saturated magnesium chloride solution. The system recovered 89% of the Mg2+ content of desalination brine as 99.6 mol% purity magnesium chloride. This level of recovery and purity without the use of consumable chemicals is not found elsewhere in industry or the literature. Internal regeneration of HCl reached 66% at a HCl concentration of 54 wt%. Empirical results suggest a longer operation would yield 92% regeneration of 65 wt% HCl. Using lessons learned from this test program, a range of long-term continuous operation conditions were found that could regenerate >95% of HCl at a concentration of >90 wt%. Such performance may make this novel HCl regeneration process interesting to industries that require hydrochloric acid recycling, such as hydrometallurgy. With the recovery and purity of magnesium chloride achieved in the current system, desalination brine can be converted into product streams, including those applicable for atmospheric CO2 removal.

Contribution of CO2 Emissions from Basic Oxygen Steelmaking Process

The steelmaking process is an energy-intensive multi-stage process, and the step involving the conversion of molten iron to steel, commonly performed in a basic oxygen furnace (BOF), makes an important contribution to greenhouse gas generation. The effective utilization of energy is one of the major challenges in the process, as minor variations of operational parameters can have significant negative effects on the converter in terms of CO2 emissions. A recent study published by the same authors analyzed the BOF process by developing a general mass and energy balance model. The present study utilizes these models to quantify the contribution of global warming potential (GWP) from the BOF and analyses its sensitivity with the parameters such as hot metal composition, the temperature of hot metal, tapping temperature, scrap quantity, and levels of post-combustion. The term GWP in this study refers to the quantified CO2 values obtained by summing up the carbon dioxide associated with the production of CaO associated with the mass of flux and carbon dioxide generated from the off-gas (considering C in hot metal is completely oxidized to CO2). The results from the analysis indicates that for a tapping temperature increase from 1650 °C to 1683 °C, the percentage change in the global warming potential (GWP) was found to be approximately 1%. The study identified that increasing the scrap percentage in the feed would be the most effective approach to effectively utilizing chemical energy from the process and reduce CO2 emissions. However, increasing scrap above 30% of the total feed is likely to raise issues around: (a) the presence of residual elements in scrap affecting the quality of liquid steel, (b) the effective utilization of post-combustion heat within the furnace, and (c) the recovery of off-gas heat for scrap preheating (assuming no steam recovery from the off-gas system). If these issues could be addressed at the industrial level, a significant reduction in CO2 emissions from the BOF process could be achieved.

Mechanical Characteristics of GGBFS/FA-Based Geopolymer Concrete and Its Environmental Impact

Geopolymer concrete is considered to be one of the best alternatives to portland cement concrete, partially or totally, not only because it decreases the CO2 emissions released during ordinary portland cement (OPC) production, but also due to its acceptable mechanical and durability properties. This study presents the experimental results of using fly ash (FA) and ground granulated blast-furnace slag (GGBFS) on fresh and hardened geopolymer concrete properties, considering the effects of several parameters such as binder type and content, alkaline binder ratio, molarity, Si/OH ratio, cement ratio in the binder, water addition, and curing temperature. These parameters were studied over a wider range than in previous research using local by-product waste to determine the validity of the additives for massive production of geopolymer concrete. The studied properties were the slump, 7- and 28-day cube compressive strength, tensile strength, and modulus of elasticity. For all studied mixes, the increase of the binder content, sodium hydroxide concentration, and cement ratio of the binder enhanced the concrete properties, whereas the increase of the alkaline binder ratio, Si/OH ratio in the solution, and additional water decreased the concrete properties. An increase of curing temperature from 30°C to 90°C improved the fly ash–based geopolymer concrete mechanical properties by an average of 35%; in contrast, the same increase in temperature decreased the concrete mechanical properties of GGBFS-based geopolymer concrete by an average of 22%. Equations for tensile strength and modulus of elasticity in terms of compressive strength were proposed and were compared with equations from standards and equations previously proposed in the literature. Finally, the environmental impact in terms of CO2 emissions was found to be on average 90% less than that of conventional concrete of the same grade.