Search Results (56)

The combustion of fossil fuels is a major source of greenhouse gas emissions, drives climate change, and has intensified the search for cleaner energy alternatives such as biomass. Biomass derived from renewable organic materials, is considered a sustainable and carbon-neutral energy source. While biomass represents a renewable and clean energy source, its combustion, especially in pellet form, can produce various pollutants such as CO₂, SO₂, NO₂, CO, and PM. This study focuses on analyzing the combustion of six different pellet brands and the emissions they produce. A dedicated experimental procedure was designed and implemented to evaluate the combustion performance. The temperature shows a gradual increase in ambient temperature around 2.5 °C across all tests, with a similar behavior, the temperature of flue gas shows a similar behavior between tests with temperatures peaking around 300 °C and 340 °C. In the tests conducted, all pellets complied with the legal emission limits defined by legislation. The efficiency calculated using the direct method was lower by around 55%, primarily due to the use of an older boiler (manufactured in 2004) and short duration of the test. The indirect method shows better efficiency, around 70%, influenced by lower moisture content of the pellets. The results indicate that B pellets had a superior performance compared to the others evaluated. Full article

The combustion of gaseous fuels in condensing boilers contributes to the greenhouse gas and toxic compound emissions in exhaust gases. Hydrogen, as a clean energy carrier, could play a key role in decarbonizing the residential heating sector. However, its significantly different combustion behavior compared to hydrocarbon fuels requires thorough investigation prior to implementation in heating systems. This study presents experimental and theoretical analyses of the co-combustion of natural gas with hydrogen in low-power-output condensing boilers (second and third generation), with hydrogen content of up to 50% by volume. The results show that mixtures of hydrogen and natural gas contribute to increasing heat transfer in boilers through convection and flue gas radiation. They also highlight the benefits of using the heat from the condensation of vapors in the flue gases. Other studies have observed an increase in efficiency of up to 1.6 percentage points compared to natural gas at 50% hydrogen content. Up to a 6% increase in the amount of energy recovered by water vapor condensation was also recorded, while exhaust gas losses did not change significantly. Notably, the addition of hydrogen resulted in a substantial decrease in the emission of nitrogen oxides (NOx) and carbon monoxide (CO). At 50% hydrogen content, NO_x emissions decreased several-fold to 2.7 mg/m³, while CO emissions were reduced by a factor of six, reaching 9.9 mg/m³. All measured NO_x values remained well below the current regulatory limit for condensing gas boilers, which is 33.5 mg/m³. These results highlight the potential of hydrogen blending as a transitional solution on the path toward cleaner residential heating systems. Full article

In the high-temperature cooking process of Chinese-style catering, the oil fume accumulates on the inner wall of the flue during the cooling process, forming grease stains, which can easily trigger flue fires and cause a kitchen fire. Statistics indicate flue fires are a primary cause of kitchen fires in China. The changes in the composition of grease stains are due to different freezing points, which will adhere to different parts of the flue and be repeatedly heated and cooled if not cleaned in time. This leads to changes in combustion performance, subsequently affecting the progression of flue fire propagation. This paper takes grease deposits with different deposition times and locations in the flue of commercial kitchens as the research object. The research selected a medium-sized commercial kitchen flue (kitchen chimney) in Langfang City, with deposition times of the parts of the inlet and outlet for 2 months and grease in the inlet for a deposition time of 7 days, 60 days, and more than 1 year. This paper analyzed the grease deposits at different deposition positions at the flue inlet and outlet using a thermogravimetric analyzer and a gas-mass spectrometer. It is found that the primary components of the grease at the outlet have low molecular weight, thermal decomposition starting temperature ignition temperature, and activation energy in the first stage and will catch fire first; the grease at the inlet has a high comprehensive combustion performance, and the combustion is violent with little effect from the oxygen supply. Then, the pyrolysis analysis of grease stains located at the entrance of the flue is performed at different deposition times under air and nitrogen atmosphere. The results showed that the pyrolysis process of grease stains with a more than 1 year deposition time consists of two stages. One stage is the first weightlessness stage, which has the lowest activation energy, the longest combustion process, and the greatest fire risk; the other is the pyrolysis combustion process of grease stains with a deposition time of 7 days. Its activation energy is the highest, and the fire risk is the smallest. The research results can be a reference for the setting of the fire dampers and the cleaning time for the flue. Full article

Algae communities as primary producers are essential elements of aquatic ecosystems and contribute significantly to oxygen production, carbon dioxide fixation, and nutrient transport processes in water bodies. The use of algae-based carbon capture and storage technologies does not produce harmful by-products that require disposal, and the resulting algal biomass can be valuable across various industrial sectors. In this study, model experiments were conducted to develop sequential absorption–microalgae hybrid CO₂-capture methods. To facilitate CO₂ capture from flue gases, wood biomass ash (WBA), an agricultural by-product, was utilized for its alkaline properties, while the flue gas scrubbing medium was regenerated by algae that restored alkalinity during their growth. In our experiments, one of our goals was to determine the optimal conditions for achieving maximum algal biomass growth in the shortest possible time. The suitability of WBA for flue gas cleaning was tested via simulation of CO₂ introduction. Moreover, a method was developed to determine the dissolved inorganic carbon content with the use of an OxiTop device monitoring the changes in pressure. The applied device was a closed, static, and pressure-based respirometer originally designed to determine the biological activity of microorganisms in both solid and liquid samples. In addition, the effects of CO₂-enriched WBA extract on algae cultivation were also analyzed, confirming that it imposed no growth inhibition and identifying the concentration (10% WBA) that optimally promoted algal growth. The optimal initial algal concentration and nutrient conditions for maximum growth were also determined. Full article

The primary research aim of this manuscript was to present a simplified absorber model and analyse the simulation results of the absorber model created to which, by design, only water was added and the outlet flue gas temperature was optimal. The obtained simulation results of the simplified absorber model were appropriately compared with the operational results of absorbers operating in professional WtE installations. This study focused on the simulation duration. The primary tool used in the paper is OpenFOAM (v2112). Two solvers were used for the calculations: ReactingParcelFoam and LTSReactingParcelFoam. They ran numerical tests on simplified absorber models. We evaluated the results according to the simulation time. We also examined the difference between the measured and calculated flue gas outlet temperatures. The results will guide further research on the absorber. They will speed up and improve the modelling of chemical processes. The only challenge was to define the chemical reactions and add a calcium molecule to the water droplet model. This work shows that we can simplify the absorber’s geometric model. It kept a low relative error and cuts the compute time. Using a local time step instead of a global one in numerical calculations significantly reduced their run time. It did this without increasing the relative error. The research can help develop complex three-phase flow models in the absorber in the future. Full article

Limestone-gypsum wet flue gas desulfurization (WFGD) played a key role in SOx removal and clean emissions. However, it would also affect the condensable particulate matter (CPM) removal and compositions. The effects of the WFGD system on the removal of CPM and the contents of soluble ions in CPM were investigated in a spray desulfurization tower at varied conditions. The results indicate that the emission concentration of CPM decreased from 7.5 mg/Nm³ to 3.7 mg/Nm³ following the introduction of cold water spray and hot alkali droplet spray systems. This resulted in a CPM reduction rate of approximately 51%, reducing the percentage of CPM in total particulate matter and solving the problem of substandard particulate matter emission concentrations in some coal-fired power plants. The concentrations of NO₃⁻, SO₄²⁻, and Cl⁻ among the soluble ions decreased by 41–66.6%. As the liquid-to-gas ratio of the cold water spray and hot alkali droplet spray increased, CPM came into contact with more spray, which accelerated dissolution and chemical reactions. Consequently, the CPM emission concentration decreased by 17.4–19%. The liquid-to-gas ratio has a great effect on the ion concentrations of NO₃⁻, SO₄²⁻, Cl⁻ and NH₄⁺, with a decrease of 28–66%. The temperatures of the cold water spray and the hot alkali droplet spray primarily affect the ionic concentrations of SO₄²⁻ and Ca²⁺, leading to a decrease of 32.3–51%. When the SO₂ concentration increased from 0 mg/Nm³ to 1500 mg/Nm³, large amounts of SO₂ reacted with the desulfurization slurry to form new CPM and its precursors, the CPM emission concentration increased by 57–68.4%. This study addresses the issue of high Concentration of CPM emissions from coal-fired power plants in a straightforward and efficient manner, which is significant for enhancing the air quality and reducing hazy weather conditions. Also, it provides a theoretical basis and technical foundation for the efficient removal of CPM from actual coal-fired flue gas. Full article

Today, most of the world’s electric energy is generated by burning hydrocarbon fuels, which causes significant emissions of harmful substances into the atmosphere by thermal power plants. In world practice, flue gas cleaning systems for removing nitrogen oxides, sulfur, and ash are successfully used at power facilities but reducing carbon dioxide emissions at thermal power plants is still difficult for technical and economic reasons. Thus, the introduction of carbon dioxide capture systems at modern power plants is accompanied by a decrease in net efficiency by 8–12%, which determines the high relevance of developing methods for increasing the energy efficiency of modern environmentally friendly power units. This paper presents the results of the development and study of the process flow charts of binary and trinary combined-cycle gas turbines with minimal emissions of harmful substances into the atmosphere. This research revealed that the net efficiency rate of a binary CCGT with integrated post-combustion technology capture is 39.10%; for a binary CCGT with integrated pre-combustion technology capture it is 40.26%; a trinary CCGT with integrated post-combustion technology capture is 40.35%; and for a trinary combined-cycle gas turbine with integrated pre-combustion technology capture it is 41.62%. The highest efficiency of a trinary CCGT with integrated pre-combustion technology capture is due to a reduction in the energy costs for carbon dioxide capture by 5.67 MW—compared to combined-cycle plants with integrated post-combustion technology capture—as well as an increase in the efficiency of the steam–water circuit of the combined-cycle plant by 3.09% relative to binary cycles. Full article

Recent advances in sensor technology for air pollution monitoring open new possibilities in the field of environmental epidemiology. The low spatial resolution of fixed outdoor measurement stations and modelling uncertainties currently limit the understanding of personal exposure. In this context, air quality sensor systems (AQSSs) offer significant potential to enhance personal exposure assessment. A pilot study was conducted to investigate the feasibility of the NO₂ sensor model B43F and the particulate matter (PM) sensor model OPC-R1, both from Alphasense (UK), for use in epidemiological studies. Seven patients with chronic obstructive pulmonary disease (COPD) or asthma had built-for-purpose sensor systems placed inside and outside of their homes at fixed locations for one month. Participants documented their indoor activities, presence in the house, window status, and symptom severity and performed a peak expiratory flow test. The potential inhaled doses of PM_2.5 and NO₂ were calculated using different data sources such as outdoor data from air quality monitoring stations, indoor data from AQSSs, and generic inhalation rates (IR) or activity-specific IR. Moreover, the relation between indoor and outdoor air quality obtained with AQSSs, an indoor source apportionment study, and an evaluation of the suitability of the AQSS data for studying the relationship between air quality and health were investigated. The results highlight the value of the sensor data and the importance of monitoring indoor air quality and activity patterns to avoid exposure misclassification. The use of AQSSs at fixed locations shows promise for larger-scale and/or long-term epidemiological studies. Full article

The development of wind power has brought about increasing challenges in decommissioning, among which DWTBs (decommissioned wind turbine blades) are the most difficult component to deal with. To enable the cost-effective, energy-efficient, and environmentally friendly large-scale utilization of DWTBs, an experimental study on thermogravimetric and pyrolysis characteristics of DWTBs was carried out. A new process involving recycling glass fiber with pyrolysis gas re-combustion and flue gas recirculation as the pyrolysis medium was innovatively proposed, and the simulation calculation was carried out. Thermogravimetric experiments indicated that glass fiber reinforced composite (GFRC) was the main heat-generating part in the heat utilization process of blades, and the blade material could basically complete pyrolysis at 600 °C. As the heating rate increased, the formation temperature, peak concentration, and proportion of combustible gas in the pyrolysis gas also increased. The highest peak concentration of CO gas was observed, with CO₂ and C₃H₆ reaching their peaks at 700 °C. The solid product obtained from pyrolysis at 600 °C could be oxidized at 550 °C for 40 min to obtain clean glass fiber. And the pyrolysis temperature increased with the increase in the proportion of recirculation flue gas. When the proportion of recirculation flue gas was 66%, the pyrolysis temperature could reach 600 °C, meeting the necessary pyrolysis temperature for wind turbine blade materials. The above research provided fundamental data support for further exploration on high-value-added recycling of DWTBs. Full article

Pyrolysis is a recognized alternative for the sustainable management of contaminated organic waste, as it yields energy-rich gas, oil, and a carbon-rich biochar product. Low-volatility compounds, however, such as heavy metals (HMs; As, Cd, Cu, Cr, Ni, Pb, and Zn) typically accumulate in biochars, limiting their application potential, especially for soil improvement. The distribution of HMs in pyrolysis products is influenced by treatment temperature and the properties of both the HMs and the feedstock. There is a significant knowledge gap in our understanding of the mass balances of HMs in full-scale industrial pyrolysis systems. Therefore, the fate of HMs during full-scale relevant pyrolysis (500–800 °C) of seven contaminated feedstocks and a clean wood feedstock were investigated for the first time. Most of the HMs accumulated in the biochar (fixation rates (FR) >70%), but As, Cd, Pb, and Zn partly partitioned into the flue gas at temperatures ≥ 600 °C, as demonstrated by FRs of <30% for some of the feedstocks. Emission factors (EFs, mg per tonne biochar produced) for particle-bound HMs (<0.45 µm) were 0.04–7.7 for As, 0.002–0.41 for Cd, 0.01–208 for Pb, and 0.09–342 for Zn. Only minor fractions of the HMs were found in the condensate (0–11.5%). To investigate the mobility of HMs accumulated in the biochars, a novel leaching test for sustained pH drop (at pH 4, 5.5 and 7) was developed. It was revealed that increasing pyrolysis temperature led to stronger incorporation of HMs in the sludge-based biochar matrix: after pyrolysis at 800 °C, at pH 4, <1% of total Cr, Cu, Ni, and Pb and < 10% of total As and Zn contents in the biochars were leached. Most interestingly, the high HM mobility observed in wood-based biochars compared to sewage-sludge-based biochars indicates the need to develop specific environmental-management thresholds for soil application of sewage-sludge biochars. Accordingly, more research is needed to better understand what governs the mobility of HMs in sewage-sludge biochars to provide a sound basis for future policy-making. Full article

The problem of As pollution emission from sludge during combustion has received widespread attention. The impact of flue gas components on the interaction with CaO and As during sludge combustion was analyzed using a series of experimental characterization methods. The strength of the activity of As₂O₃ on the CaO(001) surface as well as on the CO₂/SO₂/H₂O+CaO(001) surface with different O adsorption sites was revealed by combining with Density Functional Theory (DFT). According to the results, CO₂ in the flue gas reacted with CaO in a reversible carbonation reaction, which optimized the pore structure of the solid phase products and promoted the capture of As by CaO. SO₂ in the flue gas reacted with CaO in a sulfation reaction reaction to block the pores, which was not conducive to the capture of As by CaO. The presence of moisture led to poor pore structure collapse of the solid phase products as well as the formation of gehlenite, which reduced the enrichment of As by CaO. DFT calculations showed that the adsorption of As₂O₃ molecules on the CO₂+CaO(001) surface was affected by the position of the O active site, and the adsorption energy at the O_C1 top site was higher than that on the clean surface, which was favorable for the stable adsorption of As₂O₃ molecules. The existence of SO₂ decreased As₂O₃ molecules’ adsorption energy on the CaO(001) surface, which was unfavorable for the adsorption of As₂O₃ molecules. There were two main effects of H₂O molecules on the adsorption of As₂O₃ on the CaO(001) surface. One was the H₂O molecules weakened the interaction between the As atoms and O_surf atoms, which was unfavorable to the adsorption of As₂O₃ molecules; the other was the existence of stronger adsorption of O atoms in H₂O molecules on As atoms in As₂O₃ molecules, which made As₂O₃ molecules adsorbed at the top of O_H0 adsorbed with adsorption energies much larger than that of clean surface, and the adsorption was more stable. Full article

Conventional air quality monitoring has been traditionally carried out in a few fixed places with expensive measuring equipment. This results in sparse spatial air quality data, which do not represent the real air quality of an entire area, e.g., when hot spots are missing. To obtain air quality data with higher spatial and temporal resolution, this research focused on developing a low-cost network of cloud-based air quality measurement platforms. These platforms should be able to measure air quality parameters including particulate matter (PM10, PM2.5, PM1) as well as gases like NO, NO₂, O₃, and CO, air temperature, and relative humidity. These parameters were measured every second and transmitted to a cloud server every minute on average. The platform developed during this research used one main computer to read the sensor data, process it, and store it in the cloud. Three prototypes were tested in the field: two of them at a busy traffic site in Stuttgart, Marienplatz and one at a remote site, Ötisheim, where measurements were performed near busy railroad tracks. The developed platform had around 1500 € in materials costs for one Air Quality Sensor Node and proved to be robust during the measurement phase. The notion of employing a Proportional–Integral–Derivative (PID) controller for the efficient working of a dryer that is used to reduce the negative effect of meteorological parameters such as air temperature and relative humidity on the measurement results was also pursued. This is seen as one way to improve the quality of data captured by low-cost sensors. Full article

Despite their key role in integrated waste management, direct (incineration) and indirect (gasification/pyrolysis) waste combustion processes are still opposed by some of the general public due to the past emission levels of air pollutants. In fact, although the release of air pollutants (especially dioxin) to the atmosphere from waste combustion processes has gradually decreased over the years, thanks to the introduction of stricter regulations and more advanced removal technologies, there is still an unsolved problem regarding the public acceptance of waste-to-energy facilities. The aim of this paper is to provide an overview of the state-of-the-art air pollution control (APC) technologies used in waste combustion facilities. Air pollution control technologies are designed to reduce or eliminate the emissions of harmful pollutants into the atmosphere. These technologies are important for safeguarding public health, protecting ecosystems, complying with regulations, and promoting a more sustainable and resilient future for both local and global communities. This paper will highlight the complexity behind emission control and the efforts made by this sector over the years. This paper will also propose suggested configurations based on the interactions/complementarity between different APC technologies and recent findings to improve their performance. Full article

The air pollution situation in the German city of Stuttgart is very important, as high pollutant concentrations are measured here compared to other German cities. This is mainly due to Stuttgart’s geographical location as it is in a basin covered by hills on three sides. This leads to reduced wind speeds that inhibit pollutant dispersion. One of the main contributors to the pollutant concentrations in Stuttgart is local traffic. To improve the air quality in Stuttgart, a diesel traffic ban was introduced on 1 January 2019, and is ongoing. In this study, the urban climate model PALM-4U was applied to obtain the pollutant distribution along the federal highways B14 and B27 of Stuttgart to evaluate the impact of the diesel traffic ban on air quality. The simulations were carried out in two areas of the city, namely the city center and Kaltental Valley, with domain sizes of 3.2 km × 2 km and 3.2 km × 1.6 km, respectively, and with a grid size of 10 m for each domain. The influence of traffic emissions on the air quality of Stuttgart was studied for a typical summer day. The results showed that air pollutant concentrations were highest near federal highways B14 and B27 (e.g., NO₂ concentration peaks of around 200 µg/m³). Also, a significant reduction of around four times in air pollutant concentrations was observed in the study area after the diesel traffic ban was introduced. Full article

Global warming stands as one of the most significant challenges facing our planet, primarily due to the substantial emissions of greenhouse gases into the atmosphere. Among the major contributors to these emissions is the cement industry, which ranks as one of the largest sources of CO₂ pollutants. To address this issue, a potential solution involves partially substituting cement with alternative materials, particularly waste generated by other industries. The aim of this study was to investigate the opportunity of using an industrial waste which originates from the cleaning of flue gas in the production of expanded clay as a supplementary cementitious material. The influence of expanded clay kiln dust on the properties of Portland cement was estimated by XRD, thermal, calorimetry and compressive strength analysis. The expanded clay kiln dust was used as received and it was additionally thermally activated at 600 °C. It was determined that the original dust can be distinguished by average pozzolanic activity; meanwhile, the pozzolanic activity of additionally activated waste increased by one third. Portland cement was replaced with both types of waste in various proportions. It was found that the additive of the investigated waste accelerates the primary hydration of Portland cement, generates the pozzolanic reaction, and incites the formation of calcium silicate hydrates and hydrates containing aluminum compounds. The addition of up to 25 wt.% of activated expanded clay kiln dust leads to a higher compressive strength of samples of Portland cement. Full article