The repeatable and cost-efficient generation of nanobubbles is still a challenge. In most cases, the hydrodynamic generation of nanobubbles is used at larger scales. Therefore, every cost reduction possible in nanobubble generation is needed. In this work, we decided to check how the generation of nanobubbles changes when the surrounding liquid properties change. The generation of nanobubbles was carried out in a novel setup, designed by us. We investigated the minimum liquid velocity needed for nanobubble generation and propose correlations describing this based on the physicochemical properties of the liquid and gas phases. As carbon dioxide nanobubbles are commonly used for the treatment of ischemia and chronic wounds, the investigation of their stability enhancement is crucial for the wider public. We investigated the minimum rotation rate of the impeller needed for CO2 nanobubble generation and the influence of a biomedical surfactant (Pluronic P-123) addition and concentration ch... [more]

Carbon dioxide (CO2) is widely used in the prevention and control of spontaneous coal combustion. In this manuscript, three low-rank coals with different metamorphic degrees were selected as the research objects. The temperature-programmed experiments, in situ infrared cooling experiments, simulation of the competitive adsorption of CO2 and oxygen (O2) in coal pores, and simulation study of the CO2 inhibition of the coal oxygen composite reaction were used to obtain the role and effect of CO2 in preventing oxygen adsorption in coal at the low-temperature oxidation stage. It was concluded that CO2 can displace the O2 near the pore wall to physically prevent the adsorption of O2. Through the changing law of heating rate and a kinetics analysis, it was found that CO2 can increase its activation energy by 5.3−108.3% during the slow heating stage of coal and reduce its heat rate. At around 120 °C, coal loses the protective effect of CO2. From the changes in functional groups, it can be seen... [more]

Injecting CO2 into tight oil reservoirs is a potential approach for enhanced oil recovery (EOR) and CO2 sequestration. However, the effects of different pore-scales on EOR are poorly understood, and this has a significant impact on recovery. In this paper, a pore size correction model based on X-ray computerized tomography (CT) and nuclear magnetic resonance (NMR) was developed in order to establish the relationship between the pore radius and the transverse relaxation time. Different pore-scales are divided according to the cumulative distribution characteristics of the transverse relaxation time (T2). CO2 flooding and huff-n-puff experiments were conducted to investigate the dynamic displacement behaviors in different pore-scales. The results indicate that there are three pore-scales: micropores (T2 < 0.3 ms), intermediate pores (0.3 ms < T2 < 100 ms), and macropores (100 ms < T2). However, there are also pseudo-sweep pores (PPs), equilibrium pores (EPs), and sweep pores... [more]

International shipping is crucial for global freight transport, but is mainly based on fossil fuels, leading to significant greenhouse gas (GHG) emissions. Global GHG emissions must peak by 2025 and drop by at least 43% by 2030 to limit global warming within 1.5◦C. This calls for urgent action in all sectors as well as shipping. Scaling up alternative fuels may take too long, considering technical modifications onboard the vessels, as well as fuel production and infrastructure for distribution. Many alternative fuels are also inherently dependent on access to clean electricity, which is already in a shortage. Carbon capture from ships is another route to emission reduction that can be implemented faster and without increasing the demand for renewable electricity.
Tankers, dry bulk carriers, and container vessels contribute a majority of global shipping emissions and are therefore prime candidates for carbon capture and storage. Solvent-based post-combustion capture is mature and suita... [more]

Airfoil fin printed circuit heat exchangers (PCHEs) have broad application prospects in the naval, aerospace, electric power, and petrochemical industries. The channel structure is a critical factor affecting their thermal-hydraulic characteristics. In this study, a novel PCHE channel structure with staggered NACA 0025 airfoil-shaped fins was proposed; accordingly, the thermal-hydraulic characteristics of the novel channel structure using carbon dioxide as the working fluid at different fin heights under different operating conditions (trans-, near-, and far-critical) were investigated. The results indicated that the thermal-hydraulic performance of the PCHE under the trans-critical operating condition was better than that under the near-critical and far-critical operating conditions. Compared with conventional airfoil fin channels, the novel airfoil fin channel attained comparable comprehensive performance while reducing the fin volume by 50%, thus achieving a more lightweight PCHE de... [more]

Carbon capture and storage (CCS) technology can reduce CO2 emissions by 85 to 95% for power plants and kilns with high CO2 emissions. Among CCS technologies, carbon dioxide capture using steel slag is a method of carbonating minerals by combining oxidized metals in the slag, such as CaO, MgO, and SiO2, with CO2. This study assessed the amount of CO2 captured and the sequestration efficiency in operating a mineral carbonation plant with a CO2 capture capacity of 5 tons/day by treating the exhaust gas from a municipal waste incinerator and identified the characteristics of the mineral carbonation products. As a result, the average concentration of CO2 in the inflow and outflow gas during the reaction time was 10.0% and 1.1%, respectively, and the average CO2 sequestration efficiency was 89.7%. This resulted in a conversion rate of CaO of > 90%. This study manifested that mineral carbonation products are more stable than steel slag as a construction material and are effective at sequester... [more]

It is quite essential to obtain an excellent CO2 adsorption capacity, CO2 adsorption selectivity and water vapor stability at the same time for practical CO2 capture after combustion. Through the combination of ultramicropore and the high density of CO2-philic sites without OMSs, an ultra-microporous Cu-based metal−organic framework has been designed and synthesized, featuring a high CO2 capacity (99 cm3 g−1 and 56.6 cm3 g−1 at 273 K and 298 K, respectively), high selectivity over N2 (118 at a scale of CO2/N2 15/85, 298 K) and excellent water vapor stability, simultaneously. Theoretical calculations indicate that neighboring ketonic O atoms with suitable distance play vital roles in boosting CO2 selective capture.

This review investigates the effects of the Brazilian agriculture production and forestry sector on carbon dioxide (CO2) emissions. Residual biomasses produced mainly in the agro-industrial and forestry sector as well as fast-growing plants were studied. Possibilities to minimize source-related emissions by sequestering part of carbon in soil and by producing biomass as a substitute for fossil fuel were extensively investigated. The lack of consistency among literature reports on residual biomass makes it difficult to compare CO2 emission reductions between studies and sectors. Data on chemical composition, heating value, proximate and ultimate analysis of the biomasses were collected. Then, the carbon sequestration potential of the biomasses as well as their usability in renewable energy practices were studied. Over 779.6 million tons of agricultural residues were generated in Brazil between 2021 and 2022. This implies a 12.1 million PJ energy potential, while 4.95 million tons of for... [more]

Natural gas-fired combined cycle plants are nowadays one of the most efficient and environmentally friendly energy complexes. High energy efficiency and low specific emissions are achieved primarily due to the high average integral temperature of heat supply in the Brayton−Rankine cycle. In this case, the main sources of energy losses are heat losses in the condenser of the steam turbine plant and heat losses with the exhaust gases of the waste heat boiler. This work is related to the analysis of the thermodynamic and economic effects in the transition from binary to trinary cycles, in which, in addition to the gas and steam−water cycles, there is an additional cycle with a low-boiling coolant. A method for the feasibility study of a waste heat recovery unit for trinary plants is proposed. The schematic and design solutions described will ensure the increased energy and economic performance of combined cycle power plants. Based on the results of the thermodynamic optimization of the st... [more]

CO2 adsorption is one of the promising CCS technologies, and activated coke is a solid adsorbent with excellent adsorption properties. In this study, activated coke was prepared by using bituminous coal and coconut shells activated with KOH or CaCl2 in a physically activated atmosphere and modified with ammonia. The effect of the active agent impregnation ratio on the physicochemical properties of activated coke was investigated by N2 adsorption isotherms, scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR). The CO2 adsorption performance of activated coke was tested, and the effect of nitrogen-containing functional groups on CO2 adsorption was investigated by experiments and simulations. The results showed that the specific surface area of activated coke reached 629.81 m2/g at a KOH impregnation ratio of 0.5 and 610.66 m2/g at a CaCl2 impregnation ratio of 1. The maximum CO2 adsorption capacity of activated coke reached 71.70 mg/g and 90.99 mg/g for c... [more]

This paper presents the results of a simulation study on the selection of an energy-optimal refrigeration system based on natural refrigerants as a function of outdoor climate parameters as a decision variable in a supermarket application. Simulations were conducted for twelve locations. Three new original refrigeration systems were presented: Cascade R744/R717 which is an advanced booster extended with an ammonia condensing system (CASC_1); Cascade R744/R717 with CO2 pump-fed MT and pressure-fed LT evaporators (CASC_2); and the R717 booster with CO2 pump-fed MT and LT evaporators (CB_NH3). As a reference system, a CO2 booster system with multi-ejectors and flooded evaporators (CB_EJ) was adopted. The CB_EJ system has been confirmed to be energy optimal for cold and temperate climates (Cfb, Dfa and cooler). In warm temperate climates (Csa, BSk, Cfa and similar), the energy consumption of CB_NH3 was the lowest. CASC_2 and CB_NH3 are energy optimal for hot climates (BWh, Af, Aw). The CB_... [more]

The role of interzonal airflows is especially pronounced in naturally ventilated buildings. In such buildings, reversed airflows in the ventilation stacks might occur as well. This affects the air exchange rate and contaminant distribution in buildings. A significant increase in carbon dioxide concentration is a characteristic phenomenon for poorly ventilated rooms. This paper demonstrates the application of metabolic carbon dioxide concentration measurements for interzonal airflow estimation in naturally ventilated buildings. The presented method is based on the continuous measurements of CO2 concentration at one point in each zone. These measurements are used to estimate airflow pattern in a multizone building by applying an inverse analysis. The developed methodology employs an iterative Levenberg-Marquardt procedure to maximise the nonlinear likelihood function. The validity of the method was verified against measurements carried out in a single naturally ventilated room. Further,... [more]

When gas hydrates dissociate into gas and liquid water, many gas bubbles form in the water. The large bubbles disappear after several minutes due to their buoyancy, while a large number of small bubbles (particularly sub-micron-order bubbles known as ultra-fine bubbles (UFBs)) remain in the water for a long time. In our previous studies, we demonstrated that the existence of UFBs is a major factor promoting gas hydrate formation. We then extended our research on this issue to carbon dioxide (CO2) as it forms structure-I hydrates, similar to methane and ethane hydrates explored in previous studies; however, CO2 saturated solutions present severe conditions for the survival of UFBs. The distribution measurements of CO2 UFBs revealed that their average size was larger and number density was smaller than those of other hydrocarbon UFBs. Despite these conditions, the CO2 hydrate formation tests confirmed that CO2 UFBs played important roles in the expression of the promoting effect. The ana... [more]

CO2 diffusion coefficient plays a crucial part in saline aquifers for the CO2 storage and the safety of long-term sequestration. Therefore, it is particularly important to measure the diffusion coefficient accurately. As far as we know, there are currently no CO2 brine diffusion data in real cores under reservoir temperature and pressure conditions. In this paper, a study on the CO2 diffusion coefficient diffused in a brine-saturated Berea core along the radial direction was conducted at temperatures of 313.15 K to 373.15 K and pressures of 8 MPa to 30 MPa. On account of the experimental results, the effect of permeability, NaCl concentration, temperature and pressure on the CO2 diffusivity is analyzed. The results in this study indicate that the diffusion coefficient increases with increasing permeability, pressure and temperature and decreases with increasing NaCl concentration. However, the relationship between pressure and the diffusion coefficient is not linear. As the pressure gr... [more]

The article deals with the problem of the effects of using a wooden church on thermal and humidity conditions forming inside. Religious services in the studied site were provided several times a year. The building was not used in the remaining time. The analysis of the effects of the frequency of religious services and the number of people at the services on the formation of temperature and humidity conditions in the wooden church is provided in this paper. The effect of the presence of people in the church on CO2 concentration fluctuations was also studied. Analysis of the results showed that external conditions have the greatest effect on internal microclimate substitutions. The presence of people affects temporary fluctuations in internal parameters. Both the number of people attending the service and the time of year are important. An indoor air temperature amplitude of 9.4 °C was recorded during the winter period. The CO2 level in the church during the service exceeded the limit v... [more]

The hotel sector is characterized by high thermal demands and a large carbon footprint, which greatly contributes to the global warming effect. Consequently, there is a need to investigate solutions that can reduce energy usage within this sector by means of environmentally friendly and sustainable technologies. Integrated CO2 heat pump systems for heating, cooling, and hot water production in hotels have demonstrated promising results. This paper theoretically compares the energy consumption, environmental impact, and cost of three different design concepts for integrated CO2 units equipped with thermal storage. The main characteristics of the evaluated designs are single-stage compression, parallel compression, and ejector-supported parallel compression. Furthermore, two separate hot water charging strategies were implemented and investigated over a large span of ambient temperatures and loads. The evaluations were carried out by considering eight different European locations, rangin... [more]

The formation of hydroquinone (HQ) clathrate and the guest behaviors of binary (CH4 + CO2) gas mixtures were investigated by focusing on an application to separate CO2 from landfill gases. Spectroscopic measurements show that at two experimental pressures of 20 and 40 bar, CO2 molecules are preferentially captured in HQ clathrates regardless of the gas composition. In addition, preferential occupation by CO2 is observed more significantly when the formation pressure and the CH4 concentration are lower. Because the preferential occupation of CO2 is found with binary (CH4 + CO2) gas mixtures regardless of the composition of the feed gas, a clathrate-based process can be applied to CO2 separation or concentration from landfill gases or (CH4 + CO2) mixed gases.

The objective of the present study is the parametric investigation of a ground source heat pump for space heating purposes with boreholes. The working fluid in the heat pump is CO2, and the geothermal field includes boreholes with vertical heat exchangers (U-tube). This study is conducted with a developed model in Engineering Equation Solver which is validated with data from the literature. Ten different parameters are investigated and more specifically five parameters about the heat pump cycle and five parameters for the geothermal unit. The heat pump’s examined parameters are the high pressure, the heat exchanger effectiveness, the temperature level in the heater outlet, the flow rate of the geothermal fluid in the evaporator and the heat exchanger thermal transmittance in the evaporator. The other examined parameters about the geothermal unit are the ground mean temperature, the grout thermal conductivity, the inner diameter of the U-tube, the number of the boreholes and the length... [more]

The work at hand assesses several driving factors of carbon emissions in terms of urbanization and energy-related parameters on a panel of emerging European economies, between 1990 and 2015. The use of machine learning algorithms and panel data analysis offered the possibility to determine the importance of the input variables by applying three algorithms (Random forest, XGBoost, and AdaBoost) and then by modeling the urbanization and the impact of energy intensity on the carbon emissions. The empirical results confirm the relationship between urbanization and energy intensity on CO2 emissions. The findings emphasize that separate components of energy consumption affect carbon emissions and, therefore, a transition toward renewable sources for energy needs is desirable. The models from the current study confirm previous studies’ observations made for other countries and regions. Urbanization, as a process, has an influence on the carbon emissions more than the actual urban regions do,... [more]

There is a groundswell of interest in applying phototrophic microorganisms, specifically microalgae and cyanobacteria, for biotechnology and ecosystem service applications. However, there are inherent challenges associated with conventional routes to their deployment (using ponds, raceways and photobioreactors) which are synonymous with suspension cultivation techniques. Cultivation as biofilms partly ameliorates these issues; however, based on the principles of process intensification, by taking a step beyond biofilms and exploiting nature inspired artificial cell immobilisation, new opportunities become available, particularly for applications requiring extensive deployment periods (e.g., carbon capture and wastewater bioremediation). We explore the rationale for, and approaches to immobilised cultivation, in particular the application of latex-based polymer immobilisation as living biocomposites. We discuss how biocomposites can be optimised at the design stage based on mass transfe... [more]

One of the major anthropogenic sources of greenhouse gases is the operation of building stock. Improving its energy efficiency has the potential to significantly contribute to achieving climate change mitigation targets. The purpose of this study was to roughly estimate such potential for the operation of the national building stock of Czechia to steer the national debate on the development of related national plans. The estimation is based on a simplified energy model of the Czech building stock that consists of sub-models of residential and nonresidential building stocks, for which their future energy consumptions, shares of energy carriers and sources, and emission factors were modeled in four scenarios. Uncertainties from the approximation of the emission factors were investigated in a sensitivity analysis. The results showed that the operation of the Czech building stock in 2016 totaled 36.9 Mt CO2, which represented 34.6% of the total national carbon dioxide emissions. The four b... [more]

A countermeasure to global warming is removing high CO2 amounts from the atmosphere and locating the emitted CO2 into long-term stable carbon storage sites. The sequestration technologies must be reliable, long-lasting, and environmentally friendly. An alternative and innovative approach that may meet the sequestration requirements is CO2 storage as clathrate hydrates in marine environments. Extensive research has been devoted to CO2-CH4 replacement in natural gas hydrates. Another option is the direct formation of CO2 hydrates into deep ocean water or into marine underfloor sediments. This article deals with the positioning of direct hydrate-based CO2 storage among the other traditional geological options and the discussion of new, by-far, state-of-the-art knowledge required for the development of a hydrate-based CO2 storage pathway that is reliable, stable, durable, efficient, and environmentally benign.

One method to reduce CO2 emissions from vehicle exhaust is the use of liquified petroleum gas (LPG) fuel. The global use of this fuel is high in European countries such as Poland, Romania, and Italy. There are a small number of computational models for the purpose of estimating the emissions of LPG vehicles. This work is one of the first to present a methodology for developing microscale CO2 emission models for LPG vehicles. The developed model is based on data from road tests using the portable emission measurement system (PEMS) and on-board diagnostic (OBDII) interface. This model was created from a previous exploratory data analysis while using gradient-boosting machine learning methods. Vehicle velocity and engine RPM were chosen as the explanatory variables for CO2 prediction. The validation of the model indicates its good precision, while its use is possible for the analysis of continuous CO2 emissions and the creation of emission maps for environmental analyses in urban areas. T... [more]

Currently, 90% of Kazakhstan’s oil is situated in 15 oil and gas fields where simple cycle gas turbines are utilized for electricity generation. The need for developing techniques to enhance the efficiency and eco-friendliness of fuel consumption in Kazakhstan’s oil fields is imperative. In this article, methods for improving the energy efficiency of a simple gas turbine power plant functioning in an oil field are discussed, with consideration given to the impact of ambient temperature and specific environmental constraints, such as water scarcity and high temperatures. Two schemes to increase efficiency are evaluated: the first involves the utilization of a waste heat boiler for steam production intended for technological purposes, while the second involves electricity generation through a combination of a waste heat boiler and a steam turbine. Models based on Aspen HYSYS were formulated, with actual gas turbine power plant operation taken into account. Analysis indicated that a waste... [more]

Global fossil fuel consumption has induced emissions of anthropogenic carbon dioxide (CO2), which has emanated global warming. Significant levels of CO2 are released continually into the atmosphere from the extraction of fossil fuels to their processing and combustion for heat and power generation including the fugitive emissions from industries and unmanaged waste management practices such as open burning of solid wastes. With an increase in the global population and the subsequent rise in energy demands and waste generation, the rate of CO2 release is at a much faster rate than its recycling through photosynthesis or fixation, which increases its net accumulation in the atmosphere. A large amount of CO2 is emitted into the atmosphere from various sources such as the combustion of fossil fuels in power plants, vehicles and manufacturing industries. Thus, carbon capture plays a key role in the race to achieve net zero emissions, paving a path for a decarbonized economy. To reduce the c... [more]