Fresh Bed Research Articles

Continuous flow column adsorption and desorption for the study of interaction of fluoroquinolone antibiotic ofloxacin hydrochloride with ZnO and CuO nanometal oxides in aqueous solution: (Continuous column adsorption desorption)

Broad-spectrum antibiotic, major veterinary medicines, due to large consumption and inappropriate disposal contribute a major part in generation of pharmaceutical pollutants in aquatic environment. The study investigates the interaction of nanometal oxides for adsorption and desorption of Fluoroquinolone antibiotic, ofloxacin hydrochloride from aqueous solution using vertical and sequential bed adsorption columns: designing parameters of adsorption column determined using bed depth service time model. To optimize the continuous flow column adsorption, varying initial drug concentration and flow rates have been studied using ZnO and CuO nanoparticles at pH 4, already determined for optimized batch studies. To access the characteristic behaviour of breakthrough curves, Thomas model and Yoon-Nelson models have been studied, which were in good agreement with experimental data. Sequential bed column shows slightly better results than vertical bed column as the sequential bed is simple and economical, the solution flows in continuous manner under gravity without any mechanical devices and come into contact with fresh adsorbent bed having same amount as that in vertical bed. Therefore sequential bed column can consider in small scale industries for pharmaceutical wastewater treatment. Column desorption experiments have also been carried out by using HCl/NaOH as desorbing agent for the regeneration of drug loaded adsorbent column.

Layer formation on quartz bed particles during fast pyrolysis of grass

Commercial fast pyrolysis technologies use bed materials, normally natural sand mainly consisting of quartz, acting as circulating heat carrier materials. Nowadays, the commercial conversion of biomass into fast pyrolysis bio-oil (FPBO) is still using ash-lean woody residues as a feedstock since the application of more abundant and possibly cheaper ash-rich agricultural biomass is currently at a significantly lower technology readiness level (TRL). To promote FPBO production from ash-rich biomass, the ash-related issues during the operation process need to be further studied. In the present investigation, the characteristics and formation process of layers formed on quartz bed particles, collected from a bench-scale fast pyrolysis unit based on the rotating cone technology, were studied. Two grass residues, representative of typical Si-K-rich agricultural biomass fuels, were used as feedstocks. Quartz bed particles at different sampling times from startup with fresh bed particles were collected. Scanning Electron Microscopy/Energy-Dispersive Spectroscopy (SEM/EDS) was employed to characterize the layer properties. Bed particle layers exhibited an uneven and discontinuous distribution on the quartz surface. This distribution over bed particles, as well as layer thickness, increased with the operational time. The dominating elements contained in layers were Si, K, Ca, and Cl (excluding O), which resembled that of individual bed ash particles found in the bed samples. In addition, the interpretation of the results was supported by thermodynamic equilibrium calculations. The findings suggest that the process of layer formation was governed by the direct adhesion of non-melted bed ash particles during the fast pyrolysis of grass.

Role of surface morphology in bed particle layer formation on quartz bed particles in fluidized bed combustion of woody biomass

The influence of quartz bed particle surface morphology on the bed particle layer and crack layer formation process in fluidized bed combustion of woody biomass was investigated in this work. Bed material samples were collected at different sampling times from the startup with a fresh bed in industrial scale bubbling fluidized bed (BFB) and circulating fluidized bed (CFB) boilers, both utilizing woody biomass. X-ray microtomography (XMT) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) were employed to characterize bed particle layers and crack layers in the samples. Results showed that there is a noticeable difference between the bed layer characteristics over the so-called “concave” and “convex”-shaped morphologies on the bed particle surface with respect to layer formation. The concave areas are mainly covered with a thin inner layer, whilst the convex display a comparably thick inner layer and an outer layer. In addition, 3D images of the particles revealed that the crack layers mainly originate from concave areas where the particle is less protected by an outer bed particle layer in conjunction with cracks in the inner layer.

Lost for Words – Bilateral Vocal Cord Paresis following Renal Dialysis of a Thyroidectomy Patient

A patient underwent a total thyroidectomy for a small papillary thyroid cancer. Her vocal cord function was assessed as being normal post-operatively. A week later she underwent her first veno-venous renal dialysis for deteriorating renal function during the post-operative period. Within 48 hours she had developed bilateral vocal cord paresis, presumed to be on the basis of bilateral recurrent laryngeal nerve oedema precipitated by massive fluid shifts in the fresh surgical bed. Her voice recovered over the subsequent days as her fluid balance normalized.

Impacts of fresh bed materials on alkali release and fuel conversion rate during wood pyrolysis and char gasification

Bed materials provide efficient heat transfer and catalytic function in the thermochemical conversion of biomass, but their interactions with the fuel remain incompletely understood. In this study, the effects of bed materials on alkali release and fuel conversion during wood pyrolysis and CO2 gasification are investigated by online alkali detection combined with thermogravimetric analysis. The investigated bed materials include silica, sea sand, alumina and the natural ores olivine, ilmenite and dolomite. Only dolomite has a significant effect on fuel mass loss and alkali release during wood pyrolysis, while all bed materials influence char reactivity and alkali release during gasification. Sea sand, alumina and dolomite enhance the char gasification during the whole or most of the gasification process, which is related to alkali migration from the bed materials. All bed materials affect char reactivity and alkali release when the conversion approaches completion, and small amounts of some bed materials reduce the alkali release by an order of magnitude. The findings can be understood based on the chemical composition of the different materials. Silicon-rich materials reduce the levels of catalytically active alkali by formation of stable alkali silicates, and a similar explanation applies for ilmenite that captures alkali efficiently. Magnesium and calcium in contrast promote alkali release through their influence on alkali silicate chemistry. Analysis of char surfaces using scanning electron microscopy with energy dispersive spectroscopy indicates that low amounts of several elements are transferred from the bed material to the char where they may be directly involved in the char conversion process. The transferred elements are specific for each bed material and relates to their chemical composition. Mechanisms for material exchange between bed material and char are discussed.

Effect of fresh bed materials on alkali release and thermogravimetric behavior during straw gasification

Alkali-associated problems are key issues for the efficient use of straw that is available as a major renewable energy resource worldwide. The effects of six bed materials commonly used in fluidized bed reactors on straw pyrolysis and char gasification were evaluated using online monitoring of alkali release and thermogravimetric analysis. Scanning electron microscopy with energy dispersive spectroscopy was used to determine the elemental composition of the char surface. In the straw pyrolysis stage, alkali release is reduced by the addition of dolomite and silica due to alkali adsorption on the bed materials, and enhanced by the addition of alumina because of its high sodium content. In the char gasification stage, silica, sea sand, olivine, and ilmenite reduce the char reactivity and alkali release, which is attributed to transfer of Si and Ti from the bed materials to the char and reaction with alkali to form stable and catalytically inactive compounds. Alumina also reduces the char conversion rate by transfer of Al to the char and formation of K-Al-Si and Ca-Al-Si compounds, while alkali release from the straw and alumina blend remains high due to the high Na content in alumina. Dolomite initially appears to increase the char gasification reactivity, but the results are affected by conversion of volatile matter that deposited on the dolomite in the straw pyrolysis stage. Dolomite also significantly increases the alkali release, which is attributed to Ca reactions with aluminosilicate compounds that allow potassium to remain in volatile form. Fresh bed materials are concluded to have significant effects on straw conversion depending on their chemical composition, and the results can contribute to the understanding required for efficient use of straw in commercial applications of biomass thermochemical conversion.

Early layer formation on K-feldspar during fluidized bed combustion with phosphorus-rich fuel

K-feldspar was utilized as bed material for fluidized bed combustion of bark, chicken manure, and their mixture. Bed samples were extracted after 4 and 8 h and the samples were analyzed with scanning electron microscopy to study the impact of P-rich chicken manure on the bed material. The results were compared to fixed bed exposures with different orthophosphates to investigate their influence in detail.The fresh bed material used for this study exhibited an uneven surface with many cavities which facilitated the deposition and retention of the fuel ash. Utilizing pure chicken manure as fuel led to the formation of Ca- and P-rich particles which accumulated in these cavities. At the same time, larger ash particles were formed which consisted of the elements found in chicken manure ash. The co-combustion of bark and chicken manure led to the interaction of the two ash fractions and the formation of a thicker ash layer, which consisted of elements from both fuel ashes, namely Ca, P, Si, K and S. The layer appeared to be partially molten which could be favorable for the deposition of ash particles and thereby the formation of a mixed Ca/K-phosphate. Fixed bed exposures of the K-feldspar particles with Na3PO4 or K3PO4 caused particle agglomeration which means presence of alkali-phosphates should be limited.The co-combustion of bark with chicken manure showed promising results both regarding a shift from Ca-phosphates to more bioavailable Ca/K-phosphates and an acceleration in ash layer formation. The formation of an ash layer after only 4 h of exposure with the mixture of bark and chicken manure could be advantageous for catalytic activation of the bed material.

Global adoption of single-shot targeted intraoperative radiotherapy (TARGIT-IORT) for breast cancer-better for patients, better for healthcare systems.

Micro abstractTargeted intraoperative radiotherapy (TARGIT-IORT) is delivered immediately after lumpectomy for breast cancer. We estimated its impact. At least 44,752 patients with breast cancer were treated with TARGIT-IORT in 260 centres in 35 countries, saving >20 million miles of travel and preventing ~2,000 non–breast cancer deaths. The TARGIT-IORT website (https://targit.org.uk/travel) provides maps and tools to find the nearest centre offering TARGIT-IORT and travel savings.BackgroundTargeted intraoperative radiotherapy (TARGIT-IORT) delivers radiotherapy targeted to the fresh tumour bed exposed immediately after lumpectomy for breast cancer. TARGIT-A trial found TARGIT-IORT to be as effective as whole-breast radiotherapy, with significantly fewer deaths from non–breast cancer causes. This paper documents its worldwide impact and provides interactive tools for clinicians and patients.MethodCentres using TARGIT-IORT provided the date of the first case and the total number of patients. We plotted these data on a customised Google Map. An interactive web-based tool provided directions to the closest centre. Using the data from the TARGIT-A trial, we estimated the total savings in travel miles, carbon footprint, and the number of non–breast cancer deaths that might be prevented.ResultsData from 242 (93%) of the 260 centres treating patients from 35 countries were available. From the first patient treated in 1998 to early 2020, at least 44,752 women with breast cancer have been treated with TARGIT-IORT. The TARGIT-IORT website (https://targit.org.uk/travel) displays the Google Map of centres with number of cases and an interactive tool for patients to find the nearest centre offering TARGIT-IORT and their travel savings. Scaling up to the already treated patients, >20 million miles of travel would have been saved and about 2,000 deaths prevented.ConclusionOne can ascertain the number of patients treated with a novel treatment. These data show how widely TARGIT-IORT has now been adopted and gives an indication of its beneficial worldwide impact on a large number of women with breast cancer.

Geochemical and isotopic study of phreatic aquifer in an arid area, case study of El Golea region (Algerian Sahara)

Shallow groundwater is a major reservoir of water in arid areas. This water is characterized by strong mineralization which represents a major quality problem for human consumption and even for its use in agriculture. For this reason, geochemical, statistical and isotopic studies were conducted to obtain an overview of the processes that control water mineralization in the oasis of El Golea (Algerian Sahara). Spatial distributions of EC in this area show that the highest concentrations are situated close to the El Golea Lake formed by evaporitic rock. Geochemical and statistical analysis and data from 28 water points in the phreatic aquifer of the El Golea oasis show a strong correlation between electrical conductivity and the majority of chemical elements, indicating the influence of the interaction between fresh water and bed rock on this mineralization. The results obtained indicate that Carbonate minerals (calcite) are oversaturated in all groundwater samples. The ionic ratios demonstrate the role of weathering, dissolving, ion exchange, and evaporation procedures in mineralization acquisition. The scatter plot of that relates δ 2 H = f (δ 18 O) reveals that all of the samples were founds to be below both the GMWL of Craig (1961) and the Sfax local meteoric boundaries (South Tunisia) indicating that groundwater samples have an old origin. This isotopic composition depletion can be explained by the presence of mixes of phreatic groundwater and Continental Intercalaire (CI) (W2).

Hydrogeological mapping from Landsat 8, SRTM images, vertical electrical soundings and hydraulic parameters of aquifers: Case study of the South Western part of Baleng Watershed

The main aim of this study is to carry out a hydrogeological assessment to reveal suitable sites for the implantation of hydraulic structures like water boreholes. Petrographic studies put into place granitic rocks with numerous biotite in the Northern part of the map and basaltic rocks with phenocryst of olivine in the South. Lineaments extracted from satellite images revealed two major trends of N50–60°E and N70–80°E. A total of sixty-four Vertical Electrical Sounding (VES) data were acquired using Schlumberger configuration array, 2-D sections and hydraulic parameters of aquifers were deduced. The geoelectric sections characterize the subsurface into four geoelectric layers namely: topsoil with (resistivity values lower than 300 Ω m), weathered basement with (resistivity values ranging between 300 and 600 Ω m), fractured basement (resistivity ranging between 600 and 800 Ω m) and a more or less fresh bed rock with resistivity value up to 4000 Ω m. The hydraulic assessment of aquifers revealed a high conductivity value of 34 m/day, porosity of 41% and a high transmissivity of 429 m2/day indicating a highly interconnected fractured basement of the study area. Groundwater potential map revealed Toungang, Lafé and Ndionkou villages as suitable sites for water boreholes implantation with an average aquifers roof depth ranging between 1to 31 m.

Enriching Low-Concentration Coalbed Methane Using a Hydrophobic Adsorbent under Humid Conditions

Under practical conditions, the mixture of gases that enters a pressure swing adsorption (PSA) unit must be completely dehydrated; water vapor could have negative impacts on the uptake capacity and long-term stability of many sorbents. The use of hydrophobic adsorbents may eliminate the dehydration step. In this work, the superhydrophobic sorbent silicalite-1 was chosen and the hydrophobic mechanism was studied using density functional theory (DFT) calculations. For the separation experiments, the wet gas mixture (CH4/N2/H2O(v)) with varying relative humidities (30, 50, and 100% RH) was fed to a fresh bed. There was almost no change of CH4 breakthrough time compared with the dry condition. Only a slight reduction (less than 0.5 min) was observed in a water vapor-presaturated (continuous 36 h) bed. These breakthrough results show that the presence of water has limited influence on CH4/N2 separation using silicalite-1. Finally, PSA experiments were conducted under both dry and humid conditions (100% RH); after 60 cycles, the fluctuation of purity and recovery was less than 2%, confirming that the presence of water vapor had negligible influence on CH4 enrichment performance using a hydrophobic sorbent.

Investigation of steam regeneration strategies for industrial-scale temperature-swing adsorption of benzene on activated carbon

Large-scale separation of substances present at low concentrations is readily performed by adsorption in packed beds that requires recurring energy-intensive regeneration of the adsorbent. The present work uses numerical simulations previously developed for industrial-scale packed-bed benzene sorption on activated carbon with temperature-swing regeneration by steam to investigate the influence of steam properties and regeneration strategy on total energy performance and breakthrough behaviour.It is shown that using saturated steam lowers both the steam mass and energy consumption during regeneration of a fixed amount of benzene, whereas using superheated steam returns the bed to a more fresh-like state after each regeneration stage. The most promising variation tried implies a 19% reduction in the energy consumption. Furthermore, the importance of accounting for the real industrial cycling conditions in the optimization of packed-bed adsorbers is highlighted. It is shown that the participation of different sections of the bed during adsorption varies with the regeneration strategy, but is never as localized as predicted from a model for a fresh bed without cycling. Finally, the present results also show that the effluent purity attained during regeneration increases when high-temperature saturated steam is used, e.g. a 60-degree increase in steam temperature raises the purity by 11%.

Successful Rescue of the Victim Exposed to a Super High Dose of Iridium-192 during the Nanjing Radiological Accident in 2014.

Here we report on the interventions taken to treat a patient exposed to high-dose radiation and provide a protocol for treating such patients in the future. The patient, Mr. Wang, was a 58-year-old male janitor who was accidentally exposed to a 192Ir source with an activity of 966.4 GBq or 26.1 Ci. The dose estimated to the lower right limb was 4,100 Gy, whereas the whole-body effective dose was 1.51 Gy. The diagnosis was made according to the results of the patient dose estimation and clinical manifestations. Systemic treatment included stimulating bone marrow hematopoietic cells, enhancing immunity, anti-infection and vitamin supplements. The treatment of radiation-induced skin lesions consisted of several debridements, two skin-flap transplantations and application of mesenchymal stem cells (MSCs). Skin-flap transplantations and MSCs play important roles in the recovery of skin wound. A combination of antibiotics and antimycotic was useful in reducing inflammation. The application of vacuum sealing drainage was effective in removing necrotic tissue and bacteria, ameliorating ischemia and hypoxia of wound tissue, providing a fresh wound bed for wound healing and improving skin or flap graft survival rates. The victim survived the accident without amputation, and function of his highly exposed right leg was partially recovered. These results demonstrate the importance of collaboration among members of a multidisciplinary team in the treatment of this patient.

Online Measurements of Alkali Metals during Start-up and Operation of an Industrial-Scale Biomass Gasification Plant

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...

Effect of bed planting systems and mulching on yield and economics of soybean and wheat in Soybean-Wheat cropping system under water stress condition in dry areas of Punjab

An experiment was conducted at Ludhiana, during Kharif and Rabi season on loamy sand soil consisting of twelve treatment combination arranged in split plot design and replicated three times with three bed planting, viz., Fresh bed (FB), Permanent bed (PB) and Alternate bed (FB/PB) in main plot two crop residue management viz., residue incorporation/ mulching (R) and no incorporation / no mulching (R0) and two seed rate/ nitrogen level viz., 75 kg ha-1 (S100) and 93.75 kg ha-1 (S125) / 90 kg N ha-1 (N90) and 120 kg N ha-1 (N120) in sub plot. In soybean treatment, R recorded significantly higher grain (22.60 q ha-1) and straw (44.50 q ha-1) yield as compared to R0. FB/ PB recorded highest grain (22.60 q ha-1) and straw (43.90 q ha-1) yield followed by PB (21.40 q ha-1) and FB (21.20 q ha-1). S125 recorded higher grain (22.30 q ha-1) and straw (44.80 q ha-1) yield then S100. Highest gross return (Rs ha-1), Net return (Rs ha-1), and B:C ratio was also obtained under FB/PB, R and S125 treatment as compared to other treatment . In wheat treatment FB recorded highest grain (41.40 q ha-1) and straw (53.60 q ha-1) then FB/PB and PB. R treatment recorded higher grain (41.10 q ha-1) and straw (53.30 q ha-1) yield then R0. N120 treatment recorded higher grain (41.20 q ha-1) and straw (53.30 q ha-1) yield. Highest net return (Rs 29442.20 ha-1) and B:C ratio (2.05) was obtained under PB then FB and FB/PB. R0 treatment recorded higher net return (Rs 30873.86 ha-1) and B: C ratio (2.15) then R treatment. N120 treatment recorded higher net return (Rs 29402.56 ha-1) and B:C ratio (2.0) under water stress condition in dry areas.

Rape. Again And Again / Just Lust. In New Scotland / Black Grail. Among The Rocks / Christ! Anyone? / Your White Whore. Giggling

“Hello, professor!” you salute mechuckling,crucifying me with one short gestureon the fresh bed sheets,“plunging and plunging”,imagining that you sink into me againstmy willlike the slave tradersof...

Effect of Tillage Options and Straw Management on Crops Productivity and Soil Fertility in Rice-Wheat-Cropping Pattern

A field experiment was conducted during winter season to study the productivity under threeN fertilizer levels (80,100 and 120% N of recommended dose), two levels of straw retention (0 and 30%)and three tillage options (permanent raised bed, fresh bed and conventional tillage practice) in a Rice-Wheat cropping system. Tillage options have been found to affect thousand grain weight (TGW) and grainyield where 49.6, 52.9 and 54.7 g for TGW and 3.77, 3.98 and 4.41 t/ha for grain yield for conventional,permanent bed and fresh bed, respectively were found for wheat. The spikes/m2 was 343, 322 and 337while, the spikelets/spike were recorded as 17.2, 17.6 and 17.8 for conventional, permanent and fresh bed,respectively. Different tillage options were found to cause the formation of grains/spike, 43.2, 49.7 and50.8, respectively. Therefore, other yield components were assumed to be enhanced in response to freshbed tillage option. Fresh bed with 30% straw retention produced highest productivity and similar resultswere also obtained from permanent beds with 30% straw retention. Fresh bed with 120% recommendedN produced the highest productivity for wheat which was similar to permanent bed with 120% N. Theincrease in yield was associated with progressive increase in all growth components and will give a newinsight to identify the strategy for the development of wheat and other crops cultivation.

Productivity, profitability, and energetics: A multi-criteria assessment of farmers’ tillage and crop establishment options for maize in intensively cultivated environments of South Asia

Responding to increasing demand from poultry and fish feed industries, maize area is rapidly expanding in South Asia. Current tillage and crop establishment (TCE) practices are however associated with high levels of input use, including direct and indirect forms of energy. In Bangladesh, policy makers emphasize the need to reduce the USD 1.4 billionyear−1 agricultural energy subsidy. Bangladeshi farmers cultivate maize during the winter rabi season, when yield potential is high. But when poorly managed, farmers’ investments in TCE practices may erode farm-level profitability, while inefficiently utilizing energy. Resource-conserving TCE options may however provide an alternative for maintaining or raising yields, while increasing farmers’ income and reducing energy use. We present a multi-criteria assessment of the productivity, profitability and energetics of alternative TCE options, including zero (ZT), reduced (RT), and strip tillage (ST), in addition to fresh (FBs) and permanent bed planting (PBs), contrasted with conventional tillage (CT) in Bangladesh’s main maize producing agro-ecological zones (AEZs). Trials were conducted in 184 farmers’ fields in Bangladesh’s northwestern districts with coarse-textured soils (Rangpur and Rajshahi in AEZs 3 and 11, respectively) and in one eastern district with fine-textured soils (Comilla in AEZ 19). Trials spanned the 2009–2010 to 2012–2013 rabi seasons. Significant TCE effects on grain yield were observed in AEZs 3 and 11, but not in AEZ 19. Compared to CT, grain yields under FBs, PBs and ST were significantly higher in AEZ 3, and also under FBs and PBs in AEZ 11. Production cost was 7.8% lower, while net profit and benefit-to-cost ratios for the alternative TCE options were 13.7 and 20% greater than CT, although data were inconsistent in AEZ 19. Across AEZs, total energy inputs were significantly higher for CT (30.3.5×103 to 33.8×103MJha−1) compared to alternative options (28.3×103 to 32.7×103MJha−1). Permanent beds required the lowest diesel energy compared to CT. Similarly, energy use efficiency (EUE) was significantly higher for PBs and ST compared to CT in AEZ 3 (7.17–8.08MJMJ−1) and for PBs and FBs in AEZ 11 (8.55–10.26MJMJ−1). Among all options, PBs, FBs and ST provided greater benefits in terms of increased yield and profits, increased EUE, and reduced economic risks in AEZs 3 and 11, but less so in AEZ 19. Poor performance in the latter region was due mainly to poorly-drained low- to medium-low land types that delayed maize planting and impeded optimal establishment. Further efforts are needed to untangle the determinants of spatially variable performance to refine recommendation domains for TCE options for maize in South Asia.

An Agglomeration Index for CaO Addition (as CaCO3) to Prevent Defluidization: Application to a Full-Scale Poultry Litter Fired FBC

Agglomeration of ash in fluidized bed combustors may result in defluidization and subsequent downtime of the installation. Previous research has shown that Ca-based additives can prevent agglomeration, but the added amount was determined arbitrarily and testing occurred only on lab scale or pilot scale. This paper presents a statistical approach, based on a newly developed agglomeration index, to calculate the amount of CaO that should be added (in the form of a Ca-based mineral, e.g., CaCO3) to the fluidized bed in order to prevent agglomeration. The agglomeration index is based on an understanding of the reactions occurring in the ash, for instance, the formation of potassium silicates with low melting points, and the formation of calcium phosphates and calcium silicates with high melting points. Full-scale testing of partial replacement of silica sand by calcite (CaCO3) as fresh bed material showed that the increased CaO concentration in the ash, with respect to normal operation, appears to reduce both wall and in-bed agglomeration problems. As a measure for agglomeration risk, differential bed pressure variations were statistically analyzed. In the test periods during which CaCO3 was added, the bed pressure variations were smaller and less frequent, and the severity of agglomeration was thus reduced. The proposed strategy can be applied for fuels that are commonly perceived as difficult or unsuited for fluidized bed combustion, and also for other additives than CaCO3, e.g., Al-based minerals.

Time Dependence of Bed Particle Layer Formation in Fluidized Quartz Bed Combustion of Wood-Derived Fuels

Formation of sticky layers on bed particles has been considered as a prerequisite for bed agglomeration in fluidized bed combustion of wood-derived fuels. The present investigation was undertaken to determine the quartz bed particle layer formation process in fluidized bed combustion of wood-derived fuels. Bed material samples from three different appliances, bench-scale bubbling fluidized bed, full-scale bubbling fluidized bed, and full-scale circulating fluidized bed, at different sampling times from startup with a fresh bed were collected. Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD) were used to explore layer morphology and chemical composition and to gain information on crystalline phases of the layers and coatings. Significant differences in layer morphology and composition were found for quartz bed particles with different ages. For bed samples with operational duration of less than 1 day, only one thin Ca-, Si-, O-, and K-rich homogeneous quartz bed particle layer that has a relatively high K/Ca molar ratio was found. For quartz bed particles with an age from around 1 day to 2 weeks, an outer more particle-rich coating layer was also found. During the initial days of this period, the layer growth rate was high but decreased over time, and decreasing K/Ca and increasing Ca/Si molar ratios in the inner bed particle layer were observed. For bed particles with age between 2 and 3 weeks, a much lower layer growth rate was observed. At the same time, the Ca/Si molar ratio reached high values and the K concentration remained on a very low level. In addition to these layer formation processes mentioned, also an inner–inner/crack layer was also formed in the circulating fluidized bed quartz bed particles simultaneously with the inner bed particle layer.