| 1. |
- Darbandi, Tayebeh
(författare)
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Fine Particle Collection in Small-Scale Biofuel Boilers Using Packed-Bed Wet Scrubbers
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Small-scale biofuel boilers are one source of particulate matter (PM) emissions, advertently discharging PM into the air and affecting both human health and the environment. According to the World Health Organization, PM was the fifth leading factor of premature death in 2015. To address this issue, the European Commission’s Clean Air Policy Package was established in 2013, aiming to reduce emissions from energy sources by half by 2030. In Europe, small-scale biofuel boilers and domestic heating systems significantly contribute to the total PM emissions. Therefore, it is imperative to find an economical method for cleaning the flue gas expelled from small-scale boilers.The primary aim of this thesis is to investigate the mechanics of PM cleaning and identify the major parameters that influence cleaning efficiency in the case of flue gas in small-scale biomass boilers. To achieve this goal, an experimental setup has been constructed at Luleå University, comprising a 20kW boiler, three heat exchangers, a generator, and a packed-bed wet scrubber. The flue gas generated during combustion heats the water in the boiler, and heats the absorption solution in the generator, then the total flue gas flow through the absorber (packed bed wet scrubber). A packed-bed wet scrubber is used to bring the flue gas into contact with the absorption solution, thereby removing PM from the gas. The solution is then passed through a filter for purification. A portion of the solution is directed to the generator, where absorbed water in the scrubber is evaporated, and the concentrated solution is returned to the absorber. During an extensive 8-month study, the stability of the solution in collecting PM was tested and showed no signs of deterioration. The system’s average efficiency in collecting PM with a size range of D50 (0.8–10 µm) was found to be 60%. Additionally, the heat recovery of the system was improved by 18%.To elucidate the forces acting on PM within the wet scrubber, CFD simulations of various operational conditions were conducted using Ansys Fluent 19.2. These simulations revealed that the concentration gradient had the most significant impact on PM collection, which is explained by the diffusiophoresis phenomenon. However, the temperature gradient (thermophoresis) did not significantly affect PM collection. The influence of diffusiophoresis and thermophoresis on different PM sizes was also examined for varying flue gas velocities, temperatures, and water vapour mass fractions. The results showed that higher flue gas velocities and larger particle sizes decreased the particle collection efficiency. The simulation results were validated through comparisons with established empirical models.Next, the impact of the operational conditions on PM collection efficiency was investigated. Based on the simulations, experiments were conducted to analyse the effects of the water vapour concentration gradient, temperature gradient, and different heights of the packed-bed material in the absorber. The measurements indicated that higher water vapour concentrations increased the PM collection efficiency. To enhance the system’s efficiency, it is recommended to minimise the solution temperature and maximise the concentration of the absorption solution. Furthermore, a fully packed bed in the absorber provided higher particle collection performance than the half- and quarter-filled packed bed.Additional measurements were conducted to evaluate the influence of several other parameters on system efficiency: gas velocity, bed material, humidity, solution flow rate, and using water as a cleaning liquid.Higher flue gas velocities were observed to diminish the contact time between the flue gas and the absorption solution, increasing the effect of the drag force on PM, resulting in reduced collection efficiency. Moreover, an increased flue gas humidity had a positive impact on collection efficiency, primarily owing to its favourable effect on the diffusiophoresis force. A half-filled packed bed of steel pall rings showed higher performance compared with a half-filled packed bed of ceramic Berl saddles. The analysis also revealed no significant difference in efficiency between the wet scrubber column with a half-filled packed bed of steel pall rings and one with a half-filled packed bed of ceramic Berl saddles. A quarter-filled absorber of steel pall rings showed similar results to an empty absorber, indicating an inadequate pressure drop. Additionally, water was less effective than salt solutions, providing force in the opposite direction of the wet surface within the absorber and decreasing the particle collection efficiency.In the subsequent phase, the system’s ability to remove PM from various pelletised fuels was assessed. Each fuel type, including stem wood pellets, mine waste pellets, municipal solid waste pellets, and poplar pellets, exhibited different levels of PM emissions. In the case of stem wood pellet combustion, fine particles with diameters of less than 1 μm were predominant, and the trend was consistent for the other tested fuels. Notably, the system demonstrated 50% efficacy in reducing PM emissions from poplar pellets, which exhibited the highest levels of released PM, and the efficiency may be increased further by increasing the absorber height. The findings from this research may help in developing more efficient systems for cleaning the flue gas in small-scale boilers.
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| 2. |
- Honghao, Ren, et al.
(författare)
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A state-of-the-art review on connection systems, rolling shear performance, and sustainability assessment of cross-laminated timber
- 2024
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 317
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Tidskriftsartikel (refereegranskat)abstract
- Cross-laminated timber (CLT) is one of the most sustainable, robust, and green building materials nowadays and is normally used for walls, floors, or roofs. The number of studies on CLT has increased significantly since 2010, which shows the acceptance and needs of CLT. Connection systems, rolling shear performance, and sustainability are the popular and main research topics within CLT, including wooden connections, metallic connections, adhesive and rod connections, aspect ratio, bonding performance, life cycle assessment, carbon emission, and environmental impact. Based on these three branches, the current study conducts a literature review on CLT. This review article aims to provide a valuable view and better understanding of CLT, which are linked to (1) promoting the usage of CLT and (2) summarizing the weaknesses of the CLT’s research. This article presents a full background of the CLT research and gives potential research directions for CLT as a structural material. It revealed that the design and analytical methodologies for novel timber and steel connections are the main trends. As for the CLT’s rolling shear performance, standardized testing protocol, environmental impact, and bonding quality need further development. Furthermore, the data collection, selection, and influence of different policies are important for the CLT’s sustainability assessment.
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| 3. |
- Honghao, Ren, et al.
(författare)
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Proposing new adhesive-free timber edge connections for cross-laminated timber panels: A step toward sustainable construction
- 2024
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Ingår i: Case Studies in Construction Materials. - : Elsevier. - 2214-5095. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- The use of timber as a building material is becoming increasingly popular thanks to its superior environmental performance compared with concrete and steel. However, timber structures rely on solid connections to improve their weak expansibility. Steel connections can be prone to corrosion over time, leading to the decreased structural integrity. Additionally, steel connections require more material and energy to manufacture and install compared with timber connections. This article focuses on the flexural performance of cross-laminated timber (CLT) panels with adhesive-free edge connections under four-point bending tests. First, numerical models of experimentally tested CLT panels were constructed using the finite element (FE) software ABAQUS. Then, these FE models were validated with the comparisons of their results with those of the experimental tests. Afterward, four new adhesive-free edge connections using timber for the CLT panels were developed in this study, helping sustainable construction. Utilizing the designed edge connections of the current study, forty-one parametric studies were numerically conducted on the connected CLT panels to investigate their ultimate loads, strains, displacements, moment capacities, failure modes, and effective stiffness. The factors affecting the edge connections’ load-bearing capacity were also examined and discussed. The study provides helpful insights into the development of CLT as a sustainable construction material with improved adhesive-free edge connections.
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| 4. |
- Johansson, Lisen, et al.
(författare)
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A comprehensive review on properties of tailings-based low-carbon concrete: Mechanical, environmental, and toxicological performances
- 2024
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Ingår i: Developments in the Built Environment. - : Elsevier. - 2666-1659. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- With concrete’s key role in construction and infrastructure, the reduction of its carbon footprint is critical for addressing global carbon emissions. One strategy to reduce environmental impact from concrete production is to replace cement clinker or fine aggregates in concrete with industrial wastes. Mine tailings, being a high-volume under-utilized resource, possess properties making it suitable for use as a partial substitute for cement or fine aggregates. This review article provides an overview of the recent findings within the topic of tailings-based concrete (TBC). Many of the identified publications aimed to describe the mechanical performance of TBC, and to optimize the concrete mix with respect to the strength and durability. The recommended cement replacement ranged from 5 to 25% and the recommended fine aggregate replacement ranged from 20 to 60%. In general, the compressive strength was decreased with increasing use of tailings as a replacement of cement. For the use of tailings as replacement for fine aggregates, the correlation was more complex, normally the mechanical performance enhanced at low replacement levels, until it reached an optimum after which it decreased. CO2 savings for replacing fine aggregate with tailings were up to 12% and for the cement replacement up to 30%. When assessing the environmental performance, most of the publications did not account for the loss of its mechanical performance, which could lead to the risk of underestimating the environmental impact. This review not only provides a basis for understanding the mechanical, toxicological, and environmental performances of TBCs, but also links the perspectives together, unveiling the connections between them. Moreover, this review presents an organized overview of the topic of TBC and points out topics for future research.
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| 5. |
- Ren, Honghao, et al.
(författare)
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Flexural Behavior of Cross-Laminated Timber Panels with Environmentally Friendly Timber Edge Connections
- 2024
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Ingår i: Buildings. - : MDPI. - 2075-5309. ; 14:5
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Tidskriftsartikel (refereegranskat)abstract
- As a sustainable construction material, timber is more promoted than steel, concrete, and aluminum nowadays. The building industry benefits from using timber based on several perspectives, including decarbonization, improved energy efficiency, and easier recycling and disposal processes. The cross-laminated timber (CLT) panel is one of the widely utilized engineered wood products in construction for floors, which is an ideal alternative option for replacing reinforced concrete. One single CLT panel has an outstanding flexural behavior. However, CLT cannot be extended independently without external connections, which are normally made of steel. This article proposes two innovative adhesive-free edge connections made of timber, the double surface (DS) and half-lapped (HL) connections. These connections were designed to connect two CLT panels along their weak direction. Parametric studies consisting of twenty models were conducted on the proposed edge connections to investigate the effects of different factors and the flexural behavior of CLT panels with these edge connections under a four-point bending test. Numerical simulations of all the models were done in the current study by using ABAQUS 2022. Furthermore, the employed material properties and other relevant inputs (VUSDFLD subroutines, time steps, meshes, etc.) of the numerical models were validated through existing experiments. The results demonstrated that the maximum and minimum load capacities among the studied models were 6.23 kN and 0.35 kN, respectively. The load–displacement responses, strain, stress, and defection distributions were collected and analyzed, as well as their failure modes. It was revealed that the CLT panels’ load capacity was distinctly improved due to the increment of the connectors’ number (55.05%) and horizontal length (80.81%), which also reinforced the stability. Based on the findings, it was indicated that adhesive-free timber connections could be used for CLT panels in buildings and replace traditional construction materials, having profound potential for improving buildings’ sustainability and energy efficiency.
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