810 research outputs found
A Conversation with Char Booth
No full textWelcome to a special audio edition of In the Library with the Lead Pipe. Ellie Collier talks to Char Booth, E-Learning Librarian at the University of California at Berkeley and author of Informing Innovation: Tracking Student Interest in Emerging Library Technologies at Ohio University, a book length research report recently published by ACRL and available [...
Biomass gasification: The understanding of sulfur, tar, and char reaction in fluidized bed gasifiers
No full textAs one of the currently available thermo-chemical conversion technologies, biomass gasification has received considerable interest since it increases options for combining with various power generation systems. The product gas or syngas produced from biomass gasification is environmental friendly alternatives to conventional petrochemical fuels for the production of electricity, hydrogen, synthetic transportation biofuels and other chemicals. The product gas normally contains the major components such as CO, H2, CO2, CH4 and H2O, in addition to some organic (e.g., light hydrocarbon species, tar) and inorganic (e.g., H2S, HCl, NH3) impurities depending on operational conditions and gasification processes. Among these impurities, tar can hamper filtration operation and cause equipment fouling due to condensation at lower temperatures, while H2S can cause corrosion as well as poisoning of catalysts. Therefore, to avoid these undesired problems, these compounds need to be removed or reduced to certain level prior to the end use of the product gas. Furthermore, the most important heterogeneous reactions occurring in biomass gasification are the water-gas and the Boudouard reactions. Concerning these reactions for several biomass fuels reliable char reaction kinetics are missing, though they are very important for the effective modeling and operation of gasification processes, and the conversion of char has a large influence on the overall gasification efficiency and the yield of the product gas. To improve the product gas quality and the overall gasification efficiency of the process, it is necessary to effectively measure and reduce the formation of sulfur and tar during biomass gasification, as well as to understand char reaction kinetics. This dissertation focuses on these three issues by performing biomass gasification experiments on both an atmospheric 100kWth steam-O2 blown circulating fluidized bed (CFB) gasifier at the Delft University of Technology (TUD) and a steam blown 30-40kWth pressurized bubbling fluidized bed (PBFB) gasifier at the Technical University Munich (TUM), and studying char reaction characteristics by using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared spectrometer (FTIR). The dissertation is divided into 10 chapters and organized as follows: Chapter 1 briefly addresses the background (i.e., world energy outlook and biomass conversion options) and motivation for this research, the methodology as well as the outline applied in this dissertation. Chapter 2 presents a broad literature overview which mainly consists of four parts: sulfur formation and capture methods, tar formation and measurement techniques, char reactions and kinetics models, and models of (C)FB biomass gasification. Desulfurization can be carried out both in situ by using calcium based sorbents such as limestone and dolomite, and downstream by using regenerable single, mixed, and supported metal oxides. A special attention is paid to experimental conditions of sulfidation and the regeneration of used sorbent materials. Tar formation, primary tar reduction by optimizing of operational conditions and tar measuring techniques in particular on-line during biomass gasification is further introduced. Subsequently, a brief literature study regarding char combustion and gasification with an emphasis on char conversion kinetic models is presented. Finally, currently developed models of CFB biomass gasification are discussed. Chapter 3 presents experimental setups and measuring techniques used in this research. Three different pelletized fuels: a commercial wood pellet product “Agrol”, willow, and a by-product obtained from ethanol production dried distiller’s grains with solubles (DDGS) have been tested on the CFB gasifier and the PBFB gasifier. The product gas produced from gasification has been analyzed using different analytical instruments. Three different tar measuring techniques have been used to quantify tar concentrations: a quasi-continuous TA120-3 on-line tar analyzer (OTA) using a flame ionization detector (FID) originally developed by IVD, an on-line laser instrument based on induced fluorescence spectroscopy (LIFS) developed by TUM and an off-line solid phase adsorption (SPA) technique developed by KTH. A TGA-FTIR system has been used to study the pyrolysis of three fuels and the reaction behavior of their residual chars: CFB-char obtained after three fuels gasification in the CFB gasifier and TG-derived PYR-Char obtained after three fuels pyrolysis in the TGA. The physical and chemical properties of CFB-chars were studied by using powder X-Ray diffraction (XRD), X-Ray fluorescence (XRF), N2 adsorption/desorption at -196 ºC and scanning electron microscopy (SEM) coupled with energy dispersive scattering (EDS). Although experimental study of sulfur distribution and capture during biomass gasification is very important, the process could be time-consuming as well as challenging due to limitations and availabilities of sulfur measuring techniques. Thus, thermodynamic equilibrium simulations concerning sulfur species have been performed in two parts using FactsageTM software package version 5.4.1 and the results are presented in chapter 4. Part 1: the distribution of sulfur species during the gasification of six different biomass fuels at various temperatures ranging from 700-1200 °C, where effects of different operational parameters, including fuel properties and types, temperature, pressure, equivalence ratio (ER) and mineral content on the distribution behavior of sulfur species are systematically investigated and compared with the available experimental data. Part 2: sulfur capture behavior of various sorbent materials like limestone, lime, CuO, ZnO, FeO and MnO by using a simulated gas composition obtained from three different gasifiers, where sulfidation and regeneration capacities of different sorbents are examined. In general, the predicted results show that H2S is the predominant sulfur species and its maximum concentration is closely related to the fuel-S content. For all the fuels, around 95% fuel-S is converted into H2S during the reaction. Minerals in the fuels, especially the metal Fe, play an important role in the retention of sulfur in the solid phase. Sulfidation and regeneration simulation results indicate that copper, manganese and zinc oxides are the most favorable metals, which are capable of reaching even ppb level at a temperature of about 650 °C, while at temperatures higher than 900 °C calcium based oxides exhibit a better potential than other metal oxides, only their desulfurization capabilities are strongly limited by the temperature range and gas composition especially the H2O and CO2 contents. Chapter 5 and chapter 6 mainly discuss the experimental results obtained from biomass gasification on both gasifiers. Chapter 5 analyses effects of operational conditions (e.g., steam to biomass ratio (SBR), ER, gasification temperature, pressure) and bed materials on the distribution of the main product gas, sulfur and tar formation from Agrol, willow and DDGS gasification. The results indicated that under atmospheric pressure higher temperatures and SBR were more favorable for H2 production but less advantageous for the formation of CO and CH4, whereas a higher SBR also led to a lower carbon conversion efficiency (CCE%), cold gas efficiency (CGE%) and heating values of the product gas. Higher pressures can significantly promote the formation of CH4. Due to a relatively high K and Cl content in DDGS fuel, continually adding 3 to 10% kaolin (based on feeding rate) into the reactor was needed to avoid agglomeration. Furthermore, different amounts of tar were produced from three fuels, but in all cases it mainly contains phenol, cresol, naphthalene, indene and pyrene. Higher temperatures and higher SBR were favorable for tar decomposition. Chapter 6 compares the results obtained from three tar measuring techniques in three different ways: on-line analysis behavior of the LIFS and OTA methods, individual tar components quantification of the SPA and LIFS methods and the total tar content analysis using the SPA, LIFS and OTA methods. Possibilities for improving the OTA analyzer have been recommended based on experimental results. The analyzed results showed that the measured concentrations of 10 individual tar species obtained from the CFB and PBFB atmospheric pressure tests using the SPA and LIFS methods agreed reasonably well with a difference of less than 10% between the measured tar concentrations. Both the LIFS and OTA methods can be used as an indicator to monitor the change of the gasifier performance in real time; however, it appeared that the LIFS method was more accurate, and a regular calibration -preferably daily- of the OTA method is required in order to achieve reliable tar measurement results. Chapter 7 and chapter 8 discuss the experimental results concerning the pyrolysis of three fuels, and gasification and combustion of their derived chars. Chapter 7, firstly presents the characterization results of CFB-Chars obtained from different analytical techniques; then it analyses the pyrolysis behavior of the three fuels under different heating rates (HR); finally it compares the gasification behavior of CFB-Char and char obtained after pyrolysis (PYR-Char) under different operational conditions (e.g., gasification temperature, CO2 concentration). The kinetic parameters have been determined using the volumetric reaction model (VRM) and the shrinking core model (SCM). The analyzed results from TGA-FTIR tests showed that Agrol and willow had a similar pyrolysis behavior, and the volatiles released from Agrol, willow and DDGS pyrolysis were mainly CO, CO2 and H2O, followed by a small amount of CH4. Char gasification rate increased with increasing temperature, CO2 concentration and HR. At low gasification temperature with low CO2 concentration, CFB-Chars were much more reactive than PYR-Chars. Agrol char samples despite showing large specific surface areas had a low reactivity, due to their low ash content and related high crystalline order. On the other hand, the large ash content in DDGS char, in particularly K component, might catalyze its char gasification, balancing the reduced surface area. Chapter 8 analyses the experimental results regarding the combustion of willow and DDGS CFB-chars, and pure charcoal under both isothermal and non-isothermal conditions, as well as the modeling results obtained from a 3D TG furnace model which has been built by using COMSOL MultiphysicsTM software in order to better understand both temperature and gas velocity profiles within the TG furnace under the condition with and without considering char combustion. The results showed that the char combustion rate increased with increasing either O2 concentrations or combustion temperatures. Within the temperature range of 750 to 900 °C, it was impossible to determine kinetic parameters for combustion experiments of DDGS and willow chars, but well possible for charcoal under conditions with 15 vol.% O2 (Ea was around 120 kJ/mol calculated by using the SCM model). Furthermore, a fairly good agreement was observed between the predicted results from COMSOL MultiphysicsTM model and experimental ones. Chapter 9 presents the modeling of the 100kWth steam-O2 blown CFB gasifier with an emphasis on the product gas distribution and equilibrium analysis of water-gas shift (WGS) reaction and methane steam reforming (MSR) reaction. Three different types of models: an equilibrium model (EM) and a kinetic model (KM) setup in Aspen PlusTM software, and a fluidization model (FM) written in C Language and compiled using software Bloodshed Dev-C++ have been developed. The modeling results achieved from different models are compared and validated with the experimental data. Compared to the product gas composition obtained from experiments, H2 concentration predicted from the EM model was much higher, while CO, CO2, H2O concentrations were slightly lower and almost no CH4 was predicted from the pure EM model; however, as expected, the concentrations of all gas species predicted from the KM model agreed fairly well with those obtained from experiments. Both the EM and KM models indicated that the WGS reaction and the MSR reaction largely influenced the concentration of H2, CO, CO2, H2O and CH4. Finally, chapter 10 concludes the main experimental and modeling results and provides some recommendations for further research as well.Process and EnergyMechanical, Maritime and Materials Engineerin
Improving the quality of waste-derived char by removing ash
No full textThis study characterized and removed ash from waste-derived char to improve the quality of char as fuel. Municipal solid waste (MSW) and automobile shredder residue (ASR) were carbonized at 450 ℃ and at 500 ℃ respectively in a rotary kiln with a nitrogen atmosphere for 1 h. MSW and ASR char were subjected to sieving and pulverization-sieving to screen incombustibles and the ash-rich fraction, after which float–sink separation, froth floatation, and oil agglomeration were applied to remove ash from the char. The established target quality was less than 30% ash content and more than 20000 kJ/kg heating value. However, the rate of combustibles recovery had to be lowered to produce a good quality of char along with a high heating value. MSW char attained the targeted quality level using froth floatation or oil agglomeration whereas neither separation method was able to make ASR-derived char satisfy the target. Based on the assumption that particle properties of char are determined by the weight ratio of combustibles and ash, the densities of combustibles and ash in char were estimated using the results of float–sink separation, X-ray diffraction (XRD) analysis, and elemental content. To verify the above assumption, an energy dispersive X-ray/scanning electron microscope (EDX/SEM) analyzer was used to observe char particles
Temperature influence on the fast pyrolysis of manure samples: Char, bio-oil and gases production
No full textFast pyrolysis characterization of three dry manure samples was studied using a pyrolyzer. A heating rate of 600°C/s and a holding time of 10 s were selected to reproduce industrial conditions. The effect of the peak pyrolysis temperature (600, 800 and 1000°C) on the pyrolysis product yield and composition was evaluated. Char and bio-oil were gravimetrically quantified. Scanning electron microscopy (SEM) was used to analyse the char structure. H2, CH4, CO and CO2 were measured by means of gas chromatography (GC). A decrease in the char yield and an increase of the gas yield were observed when temperature increased. From 800°C on, it was observed that the char yield of samples Dig R and SW were constant, which indicated that the primary devolatilization reactions stopped. This fact was also corroborated by GC analysis. The bio-oil yield slightly increased with temperature, showing a maximum of 20.7 and 27.8 wt.% for samples Pre and SW, respectively, whereas sample Dig R showed a maximum yield of 16.5 wt.% at 800°C. CO2 and CO were the main released gases whereas H2 and CH4 production increased with temperature. Finally, an increase of char porosity was observed with temperature.Energy TechnologyLarge Scale Energy Storag
Open Access to Undergraduate and Graduate Theses and Dissertations: Faculty from Pomona and Harvard Voice Their Views, What are Yours?
No full textFirst, Harvard University faculty talk about open access, publishing and the dissertation (8 minute video).
Gary King is a professor of quantitative social science at Harvard University
Stuart Shieber is a professor of computer science and head of the library’s office for scholarly communications at Harvard University
Next, Char Miller, Pomona College, talks about open access, digital publishing, and the undergraduate thesis. To view the video of Char\u27s talk, see the arrow at the end of this record.
Char Miller is Director of the Environmental Analysis Program at Pomona College and the W. M. Keck Professor of Environmental Analysis. He received his Ph.D. from the Johns Hopkins University and B.A. from Pitzer College. He is author of a number of award-winning books and articles. Prof. Miller is a regular contributor of essays, commentary, and reviews to professional journals, newspapers, and online media; his blog, Golden Green, explores environmental issues in California and the West for KCET.org.
Prof. Miller joined the Environmental Analysis Program in 2007, after a 26-year stint at Trinity University in San Antonio, Texas. This Claremont Colleges intercollegiate major is deeply interdisciplinary in its focus – which means that seniors are writing theses in the sciences, social sciences, and humanities. Char has worked closely with the Claremont Colleges Library to open undergraduate work to the public, which has provided a “clarifying urgency” in their research and writing.
Professor Miller\u27s talk was first given as the opening keynote speech at the USETDA Conference in July 2013
Comparison of structural models for high-ash char gasification
No full textStructural models for the gasification of high-ash char are developed from different approaches to the depiction of the char pore structure. The description of the pore structure of a high-ash char particle is based on the structural characteristics of high-ash containing coal reject char. A finite overlapping grain model (FOG), modified random pore model (MRP) and a model based on the percolation theory on Bethe lattice (PBL) are formulated. These models take into account the effect of ash content by considering it as an inactive inclusion. Comparisons of these models are present based on the parametric simulation results. It has been shown that both the MRP and PBL models can predict similar behavior of high-ash char gasification. The effect of ash content on the surface area and reaction rate evolution is shown to be significant. The percolation model has an advantage in that it can describe the closed pore evolution and predict particle fragmentation
Livelihood vulnerability of char land communities to climate change and natural hazards in Bangladesh: an application of livelihood vulnerability index
No full textBangladesh is one of the most vulnerable countries in the world to climate change. In general, Char land (Riverine Island) communities are frequently affected by floods, riverbank erosion, and other climatic hazards, including drought, cyclones, tornadoes, salinity intrusion, water logging, cold waves, etc., which cause many to lose their sources of livelihoods and properties and make them more vulnerable. Using survey data of 262 rural households, this study investigates the extent of livelihood vulnerability to climate change and natural hazards in the Char land communities by applying the climate change vulnerability index (CVI) (i.e., UN-IPCC vulnerability framework) and the livelihood vulnerability index (LVI) to develop context-specific interventions for building climate and livelihood resilience. The two approaches to vulnerability assessment were modified to incorporate local contexts and indigenous knowledge into 41 sub-components. The result shows that LVI and CVI values are different between Char land communities. The LVI index shows that households in Char Jotindro-Narayan (0.148) are more vulnerable than those in Char Kulaghat (0.139). The CVI values for Char Jotindro-Narayan (0.633) are slightly lower than for Char Kulaghat (0.639). The major vulnerability factors were access to food and water, social networks, natural disasters, and climatic variability. The study also indicates that flood, riverbank erosion, unemployment, and access to communication, market, and basic service opportunities are the major biophysical and socioeconomic factors determining livelihood vulnerability. Context-specific sustainable policies and development initiatives are required to improve the adaptive capacity of Char land communities across Bangladesh, thereby building their climate and livelihood resilience. © 2022, The Author(s), under exclusive licence to Springer Nature B.V
Thermal behaviour of rainbow trout and Arctic char in cages moored in stratified water
No full textUsing implanted acoustical tags, the body temperature and external water temperature of rainbow trout and Arctic char were monitored in commercial fish pens moored in an environment which was extremely stratified with respect to temperature and salinity. Both species regulated body temperature between 13 and 14-degrees-C, and none of the fish made excursions into deeper, cooler salt water. Char avoided warmer surface water. Several trout exhibited diurnal cycles in preferred temperature that fluctuated 3-4-degrees-C.PT: JSource type: Electronic(1
Simulation of Coal Combustion by AUSM Turbulence-Chemistry Char Combustion Model and a Full Two-Fluid Model
No full textAn algebraic unified second-order moment (AUSM) turbulence-chemistry model of char combustion is introduced in this paper, to calculate the effect of particle temperature fluctuation on char combustion. The AUSM model is used to simulate gas-particle flows, in coal combustion in a pulverized coal combustor, together with a full two-fluid model for reacting gas-particle flows and coal combustion, including the sub-models as the k-epsilon-k(p) two-phase turbulence niodel, the EBU-Arrhenius volatile and CO combustion model, and the six-flux radiation model. A new method for calculating particle mass flow rate is also used in this model to correct particle outflow rate and mass flow rate for inside sections, which can obey the principle of mass conservation for the particle phase and can also speed up the iterating convergence of the computation procedure effectively. The simulation results indicate that, the AUSM char combustion model is more preferable to the old char combustion model, since the later totally eliminate the influence of particle temperature fluctuation on char combustion rate
Inhibition effect of H2 on char gasification during chemical looping gasification of biomass
No full textChemical looping gasification (CLG) of biomass produces high contents of syngas, which would have inhibition effect on the gasification of its biomass char. Experiments using a rice husk char as fuel and a low-cost red mud as oxygen carrier for CLG investigation were performed, and effects of temperature, concentrations of steam and H2 on gasification rate were evaluated. Meanwhile, the mathematical models coupling with reaction and diffusion were established focusing on the H2 inhibition on syngas distributions inside and surrounding a single char particle. The results indicated that H2 in the reaction atmosphere has an inhibition effect on its char conversion, and at a high temperature the inhibition effect tends to be stronger. The shrinking core model (spherical symmetry) was found to be suitable to describe the char conversion under the present conditions with the reaction kinetic parameters of E = 128.8 kJ mol−1 and A = 451.2 s−1. In the internal diffusion of a single char particle, the concentrations of CO and H2 both decrease with the increase of dimensionless radius due to the consumption of carbon. In the external diffusion of the char particle, the concentrations of CO and H2 decrease with the increase of the dimensionless radius. The accumulation of H2 inside the char particle prevents CO production, thus inhibiting char gasification
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