| 1. |
- Bäckström, Daniel, 1985, et al.
(författare)
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Particle composition and size distribution in coal flames - The influence on radiative heat transfer
- 2015
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 64, s. 70-80
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Tidskriftsartikel (refereegranskat)abstract
- Radiative heat transfer in a 77 kWth swirling lignite flame has been studied. The aim is to characterize different particle types present in a coal flame and to determine their influence on the radiative heat transfer. The study combines extractive particle measurements, radiative intensity measurements and detailed radiation modelling. The size distribution of the extracted particles was measured with a low pressure impactor and some of the size fractions were analysed with SEM–EDX. The measured total radiative intensity is compared with the modelled intensity based on the particle measurements in the same cross-section of the flame. The particle properties were calculated with Mie theory and the gas properties with a statistical narrow-band model. The results show that the contribution of coal/char particles dominates the radiative heat transfer in the investigated cross-section of the flame. The methodology applied in this work shows promising results for characterization of particle radiation in flames of practical size.
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| 2. |
- Dahlbom, Sixten, et al.
(författare)
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A theoretical evaluation of the impact of the type of reaction on heat production and material losses in biomass piles
- 2023
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Ingår i: Fire and Materials. - : John Wiley & Sons, Ltd. - 0308-0501 .- 1099-1018. ; 11:12, s. 2693-
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Tidskriftsartikel (refereegranskat)abstract
- Self-heating during storage of biomass in piles causes material losses, leads to emissions to air, and poses a risk of fire. There are different techniques to assess a biomass material's propensity for self-heating, some of these are briefly reviewed. One of these techniques is isothermal calorimetry, which measures thermal power from materials and produces time-resolved curves. A recently developed and published test standard, ISO 20049-1:2020, describes how the self-heating of pelletized biofuels can be determined by means of isothermal calorimetry and how thermal power and the total heat produced during the test should be measured by isothermal calorimetry. This paper supports interpretation of the result obtained by isothermal calorimetry; the mentioned standard provides examples of peak thermal power and total heat but does not provide any assistance on how the result from isothermal measurements should be interpreted or how the result from measurements on different samples could be compared. This paper addresses the impact of different types of reactions, peak thermal power, total heat released (heat of reaction), activation energy, heat conductivity, and pile size on the temperature development in a generic pile of biomass. This paper addresses important parameters when the result from isothermal calorimetry is evaluated. The most important parameter, with respect to temperature development in large piles, was found to be the total heat released. It was also proposed that safe storage times, that is, the time until a run-away of the temperature in the pile, could be ranked based on the time to the peak thermal power.
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| 3. |
- Gall, Dan, et al.
(författare)
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Online Measurements of Alkali and Heavy Tar Components in Biomass Gasification
- 2017
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 31:8, s. 8152-8161
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Tidskriftsartikel (refereegranskat)abstract
- Tar and alkali metal compounds are released during biomass gasification and have a major impact on the operation and performance of gasification processes. Herein we describe a novel method for characterization of alkali and heavy tar compounds in the hot product gas formed during gasification. Gas is continuously extracted, cooled and diluted, which results in condensation of tar and alkali into aerosol particles. The thermal stability of these particles is subsequently evaluated using a volatility tandem differential mobility analyzer (VTDMA) method. The technique is adopted from aerosol science where it is frequently used to characterize the thermal properties of aerosol particles. Laboratory studies show that pure and mixed alkali salts and organic compounds evaporate in well-defined temperature ranges, which can be used to determine the chemical composition of particles. The performance of the VTDMA is demonstrated at a 4 MWth dual fluidized bed gasifier using two different types of online sampling systems. Alkali metal compounds and a wide distribution of heavy tar components with boiling points above 400°C are observed in the product gas. Implications and potential further improvements of the technique are discussed.
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| 4. |
- Gall, Dan, et al.
(författare)
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Online Measurements of Alkali Metals during Start-up and Operation of an Industrial-Scale Biomass Gasification Plant
- 2018
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 32:1, s. 532-541
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Tidskriftsartikel (refereegranskat)abstract
- Alkali metal compounds may have positive influences on biomass gasification by affecting char reactivity and tar reforming but may also disturb the process by formation of deposits and agglomerates. We herein present results from online measurements of alkali compounds and particle concentrations in a dual fluidized bed gasifier with an input of 32 MWth. A surface ionization detector was used to measure alkali concentrations in the product gas, and aerosol particle measurement techniques were employed to study concentrations and properties of condensable components in the gas. Measurements were performed during start-up and steady-state operation of the gasifier. The alkali concentration increased to approximately 200 mg m-3 when fuel was fed to the gasifier and continued to rise during activation of the olivine bed by addition of potassium carbonate, while the alkali concentration was in the range from 20 to 60 mg m-3 during steady-state operation. Addition of fresh bed material and recirculated ash had noticeable effects on the observed alkali concentrations, and K2CO3 additions to improve tar chemistry resulted in increased levels of alkali in the product gas. Addition of elemental sulfur led to reduced concentrations of CH4 and heavy tars, while no clear influence on the alkali concentration was observed. The study shows that alkali concentrations are high in the product gas, which has implications for the fluidized bed process, tar chemistry, and operation of downstream components including coolers, filters, and catalytically active materials used for product gas reforming.
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| 5. |
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| 6. |
- Pushp, Mohit, et al.
(författare)
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Ageing tests closer to real service conditions using hyper-sensitive microcalorimetry, a case study on EPDM rubber
- 2023
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Ingår i: Polymer testing. - : Elsevier Ltd. - 0142-9418 .- 1873-2348. ; 120
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Tidskriftsartikel (refereegranskat)abstract
- Accelerated thermal ageing (ATA) coupled to mechanical testing is widely used to predict the lifetime of polymeric products. ATA implies that the mechanisms of ageing are the same at accelerated and service conditions, which may often not be the case. Hence, ageing closer to service conditions is of high importance, but require very sensitive tools. Therefore, a high sensitivity microcalorimetry (MC) method was applied here to assess if it can be a possible tool for lifetime/ageing prediction closer to service conditions. We chose to focus on a complex, yet commonly used, ethylene-propylene-diene terpolymer (EPDM) rubber. Arrhenius extrapolation of the heat flow data indicated two regimes at low and high temperature, with the former having the lower activation energy. The heat flow values measured by the MC revealed contributions from processes such as the melting of the antioxidant, its consumption at low temperature and the breakdown of residual peroxide. MC tests on the EPDM indicated a very low degree of oxidation appearing above 100 °C, too low to be observed with infra-red spectroscopy (FTIR), but noticeable with MC. The high sensitivity of the MC techniques enabled detection of early signs of polymer degradation/ageing and other thermally activated processes that take place at or close to service temperatures (such as those in nuclear power plants). The MC tests were combined with other techniques, such as scanning electron microscopy/energy dispersive X-ray spectroscopy, gas chromatography techniques, differential scanning calorimetry and FTIR to further understand the degradation mechanisms. © 2023 The Authors
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| 7. |
- Pushp, Mohit, et al.
(författare)
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Heat production in municipal and industrial waste as revealed by isothermal microcalorimetry
- 2022
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Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer Science and Business Media B.V.. - 1388-6150 .- 1588-2926. ; 147:15, s. 8271-
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Tidskriftsartikel (refereegranskat)abstract
- Self-ignited fires at municipal solid waste (MSW) storage sites are relatively common. The minimization of the phenomenon of self-heating in the waste can reduce the risks for smouldering combustion. The purpose of this work was to develop a method that can be used to measure and characterize the heat production in MSW. The method is based on isothermal heat conduction microcalorimetry (IMC). The heat production in MSW was determined based on sampling from two sites in two different geographical locations in Sweden. Both the original waste and milled/homogenised waste were tested. The heat production was measured at different temperatures together with gas analysis using micro-gas chromatography. The activity in the waste, in terms of its heat flow, increased when the temperature increased up to 60 °C and decreased at higher temperatures, e.g., 70 and 80 °C. The consumption of oxygen and the production of carbon dioxide, together with the heat production, indicated that aerobic metabolism was responsible for the heat production. This is further strengthened by the marginal heat production observed for ultraviolet treated waste. The results showed that IMC is a valuable tool for characterising the self-heating in municipal and industrial waste. © 2021, The Author(s).
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| 8. |
- Pushp, Mohit, et al.
(författare)
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Influence of Bed Material, Additives, and Operational Conditions on Alkali Metal and Tar Concentrations in Fluidized Bed Gasification of Biomass
- 2018
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 32:6, s. 6797-6806
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Tidskriftsartikel (refereegranskat)abstract
- Gasification of biomass results in release of tar and alkali metal compounds that constitute a significant challenge to the optimization of the gasification process. Here we describe on-line measurements of alkali, condensable tar, and particle concentrations in product gas from a 2-4 MWth dual fluidized bed gasifier, with the aims to characterize typical concentrations and contribute to the understanding of alkali-tar interactions. The influence of bed material, additives, and operational parameters on the concentrations is investigated. Alkali concentrations are measured with a surface ionization detector, and particle and tar concentrations are determined using aerosol measurement techniques. The gasification of wood chips using quartz or olivine as bed material results in an alkali concentration of 30-250 mg m-3, and the observed alkali levels are consistent with a significant release of the fuel alkali content. Addition of ilmenite to a quartz bed and additions of K2SO4 and K2CO3 to an olivine bed influence both alkali and heavy tar concentrations. The additions result in changes in alkali concentration that relaxes to a new steady state in tens of minutes. The concentration of condensable tar is lower for the olivine bed than for the quartz bed, and tends to decrease when potassium or sulfur is added. The concentration of condensable tar compounds is anticorrelated with the alkali concentration when a quartz bed is used, while no clear trend is observed with an olivine bed. An increase in steam flow rate results in a substantial decrease in heavy tar concentration from a quartz sand bed, while the alkali concentration increases slightly with increasing flow rate. This is in contrast to the alkali concentrations observed when using an activated olivine bed, where concentrations are higher and tend to decrease with increasing steam flow rate. The study confirms that several primary methods are available to optimize the alkali and tar behavior in the gasifier, and suggests that on-line monitoring is needed to systematically change the operational conditions and to study the underlying processes.
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| 9. |
- Pushp, Mohit, et al.
(författare)
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Infrared Spectroscopy for Online Measurement of Tars, Water, and Permanent Gases in Biomass Gasification
- 2021
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 75:6, s. 690-697
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Tidskriftsartikel (refereegranskat)abstract
- Online measurements of the raw gas composition, including tars and water, during biomass gasification provide valuable information in fundamental investigations and for process control. Mainly consisting of hydrocarbons, tars can, in principle, be measured using Fourier transform infrared (FT-IR) spectroscopy. However, an instrument subjected to raw gas runs the risk of condensation of tars on optical components and subsequent malfunction. Therefore, an external cell, heated to at least 400 ℃, has been designed to ensure that tars remain in the gas phase during FT-IR measurements. The cell was used for on-line FT-IR measurements of permanent gases (CO, CO2, CH4), water, and tars during the operation of a lab-scale downdraft gasifier using wood pellets, bark pellets, and char chips. Based on calibration, the measurement error of permanent gases was estimated to be 0.2%. Concentrations evaluated from spectral signatures of hydrocarbons in tar are in good agreement with results from solid-phase adsorption measurements and correlated well with operational changes in the gasifier. © The Author(s) 2021.
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| 10. |
- Pushp, Mohit
(författare)
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Microcalorimetry and Infrared Spectroscopy : Thermal processes related to solid waste, ageing rubber, phase change materials, and biomass gasification
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microcalorimetry (MC) is a unique technique for an online measurement of heat production. It can be applied to solids, liquids, or gases. MC can be used to measure the heat involved in either exothermic or endothermic processes. The heat signal obtained from MC is a lumped parameter so chemical, biological, and physical changes involving heat are measured simultaneously. In this study MC has been used to study the thermal processes in municipal solid waste, phase change materials and polymeric materials. A self-heating phenomenon, which may lead to significant heat production in piles of stored municipal solid waste, was studied with MC. This enabled us to understand the propensity of self-heating in municipal solid waste in storage conditions closer to real-life. The results showed that the self-heating in the solid waste was due to the aerobic metabolism of microorganisms. With the development of a third generation MC and better temperature control mechanisms, MC can be operated in non-isothermal mode as a differential scanning calorimeter (DSC). However, MC is capable of measuring heat flow using significantly larger sample masses than DSC. The larger sample mass is more representative of complex/heterogeneous materials, like cementitious blocks. Hence, MC was applied here to determine if it could be a useful tool in characterizing the thermal properties (latent heat and specific heat) of cementitious grout containing phase change materials (PCMs). It was observed that the phase changes (melting and crystallization) due to the PCM could be accurately characterized with MC. Performance of PCM can be investigated using thermal cycling tests that mimic real-life temperature scans. The high sensitivity of MC (μW/10000 mg) means that chemical changes can be measured at least 100 K lower than DSC (μW/~30 mg). The increased sensitivity opens up the possibility of measuring the ageing/degradation of polymers at closer to real-life temperatures and conditions. This is advantageous, since the normally used accelerated testing at significantly higher temperatures leads to degradation conditions that do not resemble service conditions. It is shown here, with the MC technique on a highly filled ethylene propylene diene monomer (EPDM) material, that the ageing processes, as well as the activation energy of the ageing processes, at close to real-life temperature are different from those at high temperature. With the high sensitivity of the MC, local thermal processes on a small scale could be readily observed, such as the melting of the antioxidant and further reactions in the peroxide cross-linking system. Hence, the results indicate that MC is a promising technique for measuring chemical changes and reaction parameters closer to the real-life temperatures in complex systems like highly filled EPDM rubber. To relate heat flow data to chemical mechanisms, post analysis of polymeric materials should be carried out with alternate techniques, for example, infrared spectroscopy (FTIR), gas chromatography and scanning electron microscopy coupled to energy dispersive X-ray. In principle, the signature of hydrocarbons can be detected using FTIR. However, subjecting the instrument to the raw gas from biomass gasification runs the risk of condensation of tars on optical components and subsequent malfunction. As a solution, an external cell that can be heated to at least 400 °C was designed to ensure that tars remain in the gas phase. The on-line measurements for permanent gases, water and tars were made using a lab-scale downdraft gasifier. Concentrations of permanent gases are in good agreement with Micro-GC and spectral signatures of tars are comparable with measurements using the solid phase adsorption (SPA) technique.
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