1,721,024 research outputs found
Laboratory study of interactions between biomass ash and alkali-feldspar bed material
No full textBed material reactivity and lifetime are dependent on the materials’ interactions with biomass ash. Literature on reactions between feldspar and ash elements is scarce, as it is a relatively new bed material and therefore less established. To gain a better understanding on the mechanism behind the observed activity of feldspar, and thereby increase the viability of its industrial application, a mixture of Na- and K-rich feldspar was exposed in a lab-scale furnace under fixed bed conditions. Ash interactions were mimicked by adding major biomass ash elements, such as Ca and K. The interaction of the particles with ash components in terms of layer formation and agglomeration were studied using SEM-EDS and compared to thermodynamic modelling calculations with FactSage. Microscopic analysis of the synthetically formed surface layers revealed similarities to ash layers formed on alkali-feldspar during biomass gasification. Ca reacted with feldspar forming a Ca-rich layer of about 10 μm thickness after 24 hours exposure. It could be shown that Na-feldspar reacts with KOH to form K-feldspar by expelling Na from the particles structure which accumulated in the surface layer. From the laboratory exposures it was further found that fresh feldspar particles tend to agglomerate when exposed to KOH from the beginning. By pre-exposing the particles to a Ca-salt and thereby forming a Ca-rich layer on the particles’ surface prior to the exposure to KOH, the agglomeration tendency could be mitigated due to the higher melting point of the elemental composition present in the Ca-rich layer. Pre-exposure to CaCl2 was therefore found to be an effective method against agglomeration
Characterization of ash component desorption on novel bed material for fluidized bed boilers
No full textThe use of biomass as a renewable fuel for production of heat and electricity is regarded as a key to reduce fossil fuel dependency, and thereby to reduce net CO2 emissions. Fluidized bed (FB) technology is widely accepted as the most energy efficient process for thermal conversion of biomass. One of the often-mentioned drawbacks is the building up of agglomerates within the process because of bed material-ash interaction. To avoid unplanned operational stops due to agglomeration, bed material is continuously replenished and spent bed material is removed in the form of bottom ash. The spent bed material cannot readily be reused and is usually deposited or used as construction filler material. Sand is the primary choice for bed material but novel bed materials are being tested to improve biomass conversion. Even though agglomeration is reduced and the energy efficiency of the conversion process is improved, bottom and fly ash are still being generated and need to be managed. To conceive new management strategies there is need to improve the understanding of the composition and stability of the compounds formed from the interaction between biomass ash and the novel bed materials. In the present work four bed materials (Olivine, Ilmenite, Feldspar and Manganese ore), all minerals, have been used in a biomass fueled 10MW CFB boiler. The materials have been sampled upon similar gas composition and time exposures in order to assure similarity in bed material “activity”. Bed material characterization followed by stepwise leaching have been used to identify opportunities in terms of pretreatment prior to deposition or/and the possibilities for alternative reuse
Oxidation and alkali sulphate-induced corrosion of aluminide diffusion coatings with and without platinum
No full textNi-based superalloys are extensively used as components in stationary gas turbines. The most frequently encountered form of such corrosion is alkali sulphate hot corrosion. Aluminide coatings are widely used to improve the oxidation resistance of Ni-base superalloy turbine components during high-temperature oxidation and/or corrosion. The environmental conditions of turbines have been simulated by salt deposition and subsequent tube-furnace laboratory experiments. Corrosion and oxidation exposures were performed on platinum-rich and platinum-free coatings. Traces of transient alumina were detected on platinum-rich samples during corrosion but were difficult to quantify. The aluminium oxide scale is thicker in the case of corrosion, which causes more spallation. In the platinum-rich coating, the depletion of the aluminium reservoir to 32% was first observed after 500 h of oxidation at 1050 \ub0C. Corrosion and oxidation exposures were performed on platinum-rich and platinum-free coatings
Water and energy savings from greywater reuse: a modelling scheme using disaggregated consumption data
Get PDFMunicipal drinking water supplies are under great stress globally, and one way to mitigate the problems is the reutilization of wastewater in various settings. In this paper, a greywater reuse scheme and the impact of system design and configuration on water and energy savings are investigated. The objective of the paper was to investigate the impact of hydraulic design and performance of a greywater treatment and reuse system on water and energy savings. A simulation model was created based on real, disaggregated water consumption data that predicts the reuse potential. Three scenarios were investigated; (1) greywater collection from the bathroom and reuse for toilet flushing, (2) greywater collection from bathroom sinks and showers, and reuse as hot water for sinks and showers, and (3) a combination of (1) and (2) where greywater collection from bathroom sinks and showers is used for toilet flushing, sinks and shower. The results indicate hot water reductions between 55.6 and 58.2%, while cold water reductions ranged from 5.8 to 30.6%. Reductions in energy for producing hot water between 43.5 and 46.8% were observed. Recommendations per connected user for hydraulic design ranged from 0.033 to 0.1\ua0dm3\ua0min−1, 3\ua0dm3, and 0.7–10\ua0dm3\ua0for treatment capacity, collection and holding tank volume
Use of natural ores in thermal conversion of biomass
No full textTo decrease the CO2 levels in the atmosphere without compromising with the electricity production and energy security two different issues have to be addressed – replacement of the current use of fossil fuels with CO2-neutral fuels and increase in the efficiency of the existing processes for thermal conversion. Fluidized bed (FB) thermal conversion is usually considered as the most energy efficient choice when biomass and municipal solid waste are used as fuels. The bed material that is used commonly within FB boilers is sand. With the demand to increase the efficiency of the electricity generation process, alternative bed materials have been tested. These materials are usually naturally occurring minerals containing transient oxides, most often Fe or Mn. The present paper presents three naturally occurring minerals that may be utilized as bed materials – olivine, ilmenite and manganese ore, while comparing with industrial silica sand for reference. The feasibility of their utilization as bed materials in thermal conversion of biomass on their further use is discussed
Laboratory study of interactions between biomass ash and alkali-feldspar bed material
No full textBed material reactivity and lifetime are dependent on the materials’ interactions with biomass ash. Literature on reactions between feldspar and ash elements is scarce, as it is a relatively new bed material and therefore less established. To gain a better understanding on the mechanism behind the observed activity of feldspar, and thereby increase the viability of its industrial application, a mixture of Na- and K-rich feldspar was exposed in a lab-scale furnace under fixed bed conditions. Ash interactions were mimicked by adding major biomass ash elements, such as Ca and K. The interaction of the particles with ash components in terms of layer formation and agglomeration were studied using SEM-EDS and compared to thermodynamic modelling calculations with FactSage. Microscopic analysis of the synthetically formed surface layers revealed similarities to ash layers formed on alkali-feldspar during biomass gasification. Ca reacted with feldspar forming a Ca-rich layer of about 10 μm thickness after 24 hours exposure. It could be shown that Na-feldspar reacts with KOH to form K-feldspar by expelling Na from the particles structure which accumulated in the surface layer. From the laboratory exposures it was further found that fresh feldspar particles tend to agglomerate when exposed to KOH from the beginning. By pre-exposing the particles to a Ca-salt and thereby forming a Ca-rich layer on the particles’ surface prior to the exposure to KOH, the agglomeration tendency could be mitigated due to the higher melting point of the elemental composition present in the Ca-rich layer. Pre-exposure to CaCl2 was therefore found to be an effective method against agglomeration
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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