Dynamic reduced order modeling of entrained flow gasifiers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references.Gasification-based energy systems coupled with carbon dioxide capture and storage technologies have the potential to reduce greenhouse gas emissions from continued use of abundant and secure fossil fuels. Dynamic reduced order models (ROMs) that predict the operation of entrained flow gasifiers (EFGs) within IGCC (integrated gasification combined cycle) or polygeneration plants are essential for understanding the fundamental processes of importance. Such knowledge can be used to improve gasifier reliability, availability and maintainability, leading to greater commercialization of gasification technology. A dynamic ROM, implemented in Aspen Custom Modeler, has been developed for a range of EFGs. The ROM incorporates multiple feedstocks, mixing and recirculation, particle properties, drying and devolatilization, chemical kinetics, fluid dynamics, heat transfer, pollutant formation, slag behavior and syngas cooling. The ROM employs a reactor network model (RNM) that approximates complex fluid mixing and recirculation using a series of idealized chemical reactors. The ROM was successfully validated for steady-state simulation of four experimental gasifiers. The throughputs of these gasifiers range from 0.1 to 1000 metric tonnes per day (3 kWth - 240 MWth). Sensitivity analysis was performed to identify the parameters most important to ROM accuracy. The most important parameters are found to be those that determine RNM geometry, particle physical and kinetic properties, and slagging. The ROM was used to simulate the steady-state and dynamic performance of a full-scale EFG system. In steady-state mode, the ROM was used to establish base case and fluxant requirements. The base case performance agreed with design specifications. Steady-state simulation was also used to determine important states for dynamic simulation. Six cases were examined in dynamic mode, including gasifier cold start. Dynamic results showed agreement with industrial experience for gasifier start-up times.by Rory F. D. Monaghan.Ph.D

Hydrogen storage of energy for small power supply systems

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 91-92).Power supply systems for cell phone base stations using hydrogen energy storage, fuel cells or hydrogen-burning generators, and a backup generator could offer an improvement over current power supply systems. Two categories of hydrogen-based power systems were analyzed: Wind-hydrogen systems and peak-shaving hydrogen systems. Modeling of base station requirements and alternative power supply system performance was carried out using MATLAB. Final results for potential alternative systems were compared to those for the current power systems. In the case of the wind- hydrogen systems, results were also compared to those of a wind-battery system. Overall feasibility was judged primarily on the net present cost of the power supply systems. Other considerations included conformity to present regulations. Sensitivity analysis of the wind-hydrogen model was carried out to identify the controlling variables. Numerous parameters were varied over realistic ranges. Important parameters were found to include wind resource, electrolyzer size, distance from electricity grid, price of diesel fuel, and electrolyzer and fuel cell cost. The model verified cell phone industry figures regarding the geographical conditions favorable to diesel genset use. Final results for wind-hydrogen systems suggest that for today's electrolyzer and fuel cell costs, wind-battery-diesel systems are the most suitable power system more than 8km from the existing electricity grid, with an annual average wind speed of 7m/s or more, and where diesel costs more than $2.20/gallon.(cont.) Thinking to the future, with 20$2/gallon. Within 8km the grid, in all cases, grid connection is most suitable. Outside this range, with diesel prices below $2/gallon, a genset only system is most suitable in most cases. Analysis of the peak-shaving hydrogen system suggests that it is not suitable for deployment under any realistic circumstances. Replenishment of hydrogen stores has a substantial power requirement.by Rory F.D. Monaghan.S.M

Cost estimation of a biorefining network for forest residues in Ireland

The forestry sector in the Republic of Ireland (ROI) is mainly focused on harvesting timber from the stems of spruce trees. The remaining 30-35% of unharvested wood volume, typically known as forest residues or brash, is left on the forest floor. Only a small geographically specific portion of forest residues are bundled and sold at low cost as fuel for industrial combined heat and power (CHP). The volume of unused forest residues in ROI is estimated to be 700 thousand m3 a-1, and its distribution is shown in Figure 1[1]. This significant quantity can be mobilized as biomass feedstock to biorefineries for high value bio-products. The composition, quantity and type of feedstock available in Ireland indicate that pyrolysis and hydrothermal liquefaction (HTL) are the most effective biorefining pathways. Bio-oils produced from pyrolysis have high energy value and HTL uses forest residues with high moisture content as feedstock saving the cost of drying. Both of these technologies have the capability to be energy neutral and therefore have potential at the small, distributed scale found in Ireland [2]. The highly dispersed nature of forest residues coupled with low energy density presents challenges in sustaining substantial availability of feedstock to the biorefinery. Selection of an optimum location for building a biorefinery can help design an efficient supply chain to reduce transportation cost and environmental impact. Multi-criteria decision analysis (MCDA) coupled with geographic information system (GIS) analysis is a popular and effective method to analyse location suitability. Localised criteria can either be factors, which influence location suitability, or constraints, which limit development in that vicinity. These criteria are weighted using the analytical hierarchy process (AHP) and combined in GIS to give a final site suitability map. Selection of the most cost-effective location out of all suitable sites requires a cost estimation model that will compare the operational cost for both technologies and transportation cost of the resources and final product. Please click Additional Files below to see the full abstract

IMECE2009-12985 REDUCED ORDER MODELING OF ENTRAINED FLOW SOLID FUEL GASIFICATION

ABSTRACT Reduced order models that accurately predict the operation of entrained flow gasifiers as components within integrated gasification combined cycle (IGCC) or polygeneration plants are essential for greater commercialization of gasification-based energy systems. A reduced order model, implemented in Aspen Custom Modeler, for entrained flow gasifiers that incorporates mixing and recirculation, rigorously calculated char properties, drying and devolatilization, chemical kinetics, simplified fluid dynamics, heat transfer, slag behavior and syngas cooling is presented. The model structure and submodels are described. Results are presented for the steady-state simulation of a two-metric-tonne-per-day (2 tpd) laboratory-scale Mitsubishi Heavy Industries (MHI) gasifier, fed by two different types of coal. Improvements over the state-of-the-art for reduced order modeling include the ability to incorporate realistic flow conditions and hence predict the gasifier internal and external temperature profiles, the ability to easily interface the model with plant-wide flowsheet models, and the flexibility to apply the same model to a variety of entrained flow gasifier designs. Model validation shows satisfactory agreement with measured values and computational fluid dynamics (CFD) results for syngas temperature profiles, syngas composition, carbon conversion, char flow rate, syngas heating value and cold gas efficiency. Analysis of the results shows the accuracy of the reduced order model to be similar to that of more detailed models that incorporate CFD. Next steps include the activation of pollutant chemistry and slag submodels, application of the reduced order model to other gasifier designs, parameter studies and uncertainty analysis of unknown and/or assumed physical and modeling parameters, and activation of dynamic simulation capability

Combined analytical strategies for chemical and physical characterization of tar from torrefaction of olive stone

The advance in analytical methodology is critical for progress in 1) biorefinery and 2) torrefaction product commercialization. The chemical characterisation of torrefaction liquid and concentrated tar produced by Arigna Fuels’ pyrolysis plant allowed identification of polar, volatile, non-volatile compounds, species containing organically bound sulphur and nitrogen heteroatoms. The results suggest that only combined use of ion chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, and 1H-13C HS-QC can provide comprehensive information on sugar-like material and lignin-derived compounds. Due to the technical robustness and short analysis time, Fourier Transform Ion Cyclotron Resonance Mass Spectrometer was found to be a promising tool for tar analysis containing heavy molecular compounds. Importantly from a technological standpoint, the presence of aromatic and saturated compounds in both liquid and concentrated tar samples indicated the predominance of lignin-derived compounds over products originating from cellulose and hemicellulose polymers.publishedVersio

Combined analytical strategies for chemical and physical characterization of tar from torrefaction of olive stone

The advance in analytical methodology is critical for progress in 1) biorefinery and 2) torrefaction product commercialization. The chemical characterisation of torrefaction liquid and concentrated tar produced by Arigna Fuels’ pyrolysis plant allowed identification of polar, volatile, non-volatile compounds, species containing organically bound sulphur and nitrogen heteroatoms. The results suggest that only combined use of ion chromatography with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, and 1H-13C HS-QC can provide comprehensive information on sugar-like material and lignin-derived compounds. Due to the technical robustness and short analysis time, Fourier Transform Ion Cyclotron Resonance Mass Spectrometer was found to be a promising tool for tar analysis containing heavy molecular compounds. Importantly from a technological standpoint, the presence of aromatic and saturated compounds in both liquid and concentrated tar samples indicated the predominance of lignin-derived compounds over products originating from cellulose and hemicellulose polymers.publishedVersio

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Display of Cell Surface Sites for Fibronectin Assembly Is Modulated by Cell Adherence to 1F3 and C-Terminal Modules of Fibronectin

BACKGROUND: Fibronectin-null cells assemble soluble fibronectin shortly after adherence to a substrate coated with intact fibronectin but not when adherent to the cell-binding domain of fibronectin (modules (7)F3-(10)F3). Interactions of adherent cells with regions of adsorbed fibronectin other than modules (7)F3-(10)F3, therefore, are required for early display of the cell surface sites that initiate and direct fibronectin assembly. METHODOLOGY/PRINCIPAL FINDINGS: To identify these regions, coatings of proteolytically derived or recombinant pieces of fibronectin containing modules in addition to (7)F3-(10)F3 were tested for effects on fibronectin assembly by adherent fibronectin-null fibroblasts. Pieces as large as one comprising modules (2)F3-(14)F3, which include the heparin-binding and cell adhesion domains, were not effective in supporting fibronectin assembly. Addition of module (1)F3 or the C-terminal modules to modules (2)F3-(14)F3 resulted in some activity, and addition of both (1)F3 and the C-terminal modules resulted in a construct, (1)F3-C, that best mimicked the activity of a coating of intact fibronectin. Constructs (1)F3-C V0, (1)F3-C V64, and (1)F3-C Delta(V(15)F3(10)F1) were all able to support fibronectin assembly, suggesting that (1)F3 through (11)F1 and/or (12)F1 were important for activity. Coatings in which the active parts of (1)F3-C were present in different proteins were much less active than intact (1)F3-C. CONCLUSIONS: These results suggest that (1)F3 acts together with C-terminal modules to induce display of fibronectin assembly sites on adherent cells

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Changes in symptomatology, reinfection, and transmissibility associated with the SARS-CoV-2 variant B.1.1.7: an ecological study

Background The SARS-CoV-2 variant B.1.1.7 was first identified in December, 2020, in England. We aimed to investigate whether increases in the proportion of infections with this variant are associated with differences in symptoms or disease course, reinfection rates, or transmissibility. Methods We did an ecological study to examine the association between the regional proportion of infections with the SARS-CoV-2 B.1.1.7 variant and reported symptoms, disease course, rates of reinfection, and transmissibility. Data on types and duration of symptoms were obtained from longitudinal reports from users of the COVID Symptom Study app who reported a positive test for COVID-19 between Sept 28 and Dec 27, 2020 (during which the prevalence of B.1.1.7 increased most notably in parts of the UK). From this dataset, we also estimated the frequency of possible reinfection, defined as the presence of two reported positive tests separated by more than 90 days with a period of reporting no symptoms for more than 7 days before the second positive test. The proportion of SARS-CoV-2 infections with the B.1.1.7 variant across the UK was estimated with use of genomic data from the COVID-19 Genomics UK Consortium and data from Public Health England on spike-gene target failure (a non-specific indicator of the B.1.1.7 variant) in community cases in England. We used linear regression to examine the association between reported symptoms and proportion of B.1.1.7. We assessed the Spearman correlation between the proportion of B.1.1.7 cases and number of reinfections over time, and between the number of positive tests and reinfections. We estimated incidence for B.1.1.7 and previous variants, and compared the effective reproduction number, Rt, for the two incidence estimates. Findings From Sept 28 to Dec 27, 2020, positive COVID-19 tests were reported by 36 920 COVID Symptom Study app users whose region was known and who reported as healthy on app sign-up. We found no changes in reported symptoms or disease duration associated with B.1.1.7. For the same period, possible reinfections were identified in 249 (0·7% [95% CI 0·6–0·8]) of 36 509 app users who reported a positive swab test before Oct 1, 2020, but there was no evidence that the frequency of reinfections was higher for the B.1.1.7 variant than for pre-existing variants. Reinfection occurrences were more positively correlated with the overall regional rise in cases (Spearman correlation 0·56–0·69 for South East, London, and East of England) than with the regional increase in the proportion of infections with the B.1.1.7 variant (Spearman correlation 0·38–0·56 in the same regions), suggesting B.1.1.7 does not substantially alter the risk of reinfection. We found a multiplicative increase in the Rt of B.1.1.7 by a factor of 1·35 (95% CI 1·02–1·69) relative to pre-existing variants. However, Rt fell below 1 during regional and national lockdowns, even in regions with high proportions of infections with the B.1.1.7 variant. Interpretation The lack of change in symptoms identified in this study indicates that existing testing and surveillance infrastructure do not need to change specifically for the B.1.1.7 variant. In addition, given that there was no apparent increase in the reinfection rate, vaccines are likely to remain effective against the B.1.1.7 variant. Funding Zoe Global, Department of Health (UK), Wellcome Trust, Engineering and Physical Sciences Research Council (UK), National Institute for Health Research (UK), Medical Research Council (UK), Alzheimer's Society