Estudio de la reactividad en fase gas y sobre lecho de carbonizado del alquitrán generado durante la devolatilización de biomasa y resíduos

Texto completo descargado de TeseoAutothermal air-blown gasification in a fluidized bed gasifier (FBG) is a promisingalternative for the valorization of biomass and waste for medium scale plants.However this gasification procedure presents two limitations: the incomplete fuelconversion and the high dew point of the gas caused by the high concentration ofheavy tars in it. Measures have been developed to overcome these limitations, but theincrease in the costs prevents their use for power production in medium-scaleprocesses. Aiming at overcoming the inherent limitations of conventional FBG, a newthree-stage gasification technology (FLETGAS process) is under development by theBioenergy Group at the University of Seville. The three stages comprises: 1- FBgasification at low temperature (700-800°C), 2- oxidation/reforming of the gas at hightemperature (1200°C maximum) and 3- catalytic filtration in a char moving bed. Thepresent thesis deals with the formation and conversion of tars and light hydrocarbonswithin the different stages of the new gasifier with the objective of determining theoperating conditions for the reduction of the concentration of heavy tars in the gasand thus, to produce a gas with a dew point low enough to be burnt in a gas engine.The first part of the thesis (Chapters 3 and 4) deals with the influence of operatingconditions over the composition of volatiles produced during dried sewage sludge(DSS) devolatilization of in an FB. The effects of the temperature, steam concentrationand thermal division of the reactor (dense bed and freeboard) on composition of tarsand hydrocarbons during both primary generation (dense bed) and subsequentconversion of these along the gasifier (freeboard) have been investigated. The resultsallow understanding of the main conversion mechanisms taking place in the gasifier,demonstrating that the achievement of two thermal zones in the reactor has asignificant influence on tar and light hydrocarbons composition of the gas producedduring devolatilization, whereas the steam in the fluidization agent hardly affect tarcomposition up to 900°C. The results have been used for the establishment ofoperation conditions in the first stage of the FLETGAS gasifier.The second part of the thesis (Chapter 5) investigates the conversion of modelaromatic tars (naphthalene and toluene) over various chars in a laboratory fixed bedreactor. The experimental results have demonstrated that the char bed effectivelyreduces the tar concentration. Almost complete conversion has been measured attemperatures above 850°C, residence time of 0.3 s and steam concentration above 15vol%. Empirical kinetic expressions for tar conversion over the different chars havebeen obtained accounting for char deactivation. The use of this kinetics for simulatingthe FLETGAS process has demonstrated that the third stage of the new gasifier is ableto convert the heavy tars to the extent necessary for the production of gas with thedesired dew point. This work establishes the experimental conditions (temperature,gas residence time and steam concentration) necessary to maintain high enough therate of tar conversion over the char bed, i.e. minimizing the deactivation.La gasificación autotérmica de biomasa y residuos en lecho fluido para generación eléctrica distribuida presenta notables ventajas respecto a otras opciones. No obstante esta tecnología presenta ciertas limitaciones que frenan su implantación comercial: la limitada conversión del combustible, debida a la incompleta conversión del carbonizado, y la elevada temperatura de condensación del gas, causada por la alta concentración de alquitranes pesados en éste. Las medidas que se han desarrollado para hacer frente a ambos problemas se basan en métodos complejos o caros, haciendo inviable la implantación de esta tecnología en sistemas de pequeña o mediana escala. El Grupo de Bioenergía de la Universidad de Sevilla está desarrollando una nueva tecnología (FLETGAS) que persigue el objetivo de obtener un gas combustible a partir de biomasas y residuos apto para ser quemado en motores de gas. El sistema se basa en tres etapas: gasificación en lecho fluido a baja temperatura (700-800°C), reformado con vapor a alta temperatura (1200°C) y filtración en un lecho móvil de carbonizado. La presente tesis estudia la formación y conversión de alquitranes e hidrocarburos ligeros en las diferentes etapas del nuevo gasificador con objeto de determinar las condiciones de funcionamiento que permitan reducir la concentración de alquitranes pesados en el gas producto y, por tanto, producir un gas con un punto de rocío suficientemente bajo para ser quemado en un motor.En la primera parte de la tesis (Capítulos 3 y 4) se estudia la influencia de las condiciones de operación sobre los productos de la devolatilización de lodos secos de depuradora (DSS) en un lecho fluido de laboratorio. Se ha determinado el efecto de la temperatura y la el vapor sobre la composición de alquitrán, estableciéndose los principales mecanismos de conversión durante la generación primaria de volátiles (en el lecho denso) y secundaria (freeboard). Se ha estudiado también el efecto de la operación con dos temperaturas diferentes en el reactor (lecho denso y freeboard), demostrando que este modo de operación influye decisivamente en la composición de los volátiles. Por el contrario, a temperaturas inferiores a 900°C, el vapor afecta muy poco a la cantidad y naturaleza de los alquitranes generados. Se han obtenido correlaciones entre hidrocarburos ligeros y alquitranes que sirven para estimar de forma rápida el punto de rocío del gas.En la segunda parte de la tesis (capítulo 5) se ha investigado la conversión de alquitranes aromáticos (naftaleno y tolueno) sobre varios lechos de carbonizado en un reactor de lecho fijo de laboratorio. Los resultados experimentales han demostrado que el lecho de carbonizado reduce eficazmente la concentración de alquitrán. A temperaturas superiores a 850°C, tiempos de residencia de 0,3 s y concentraciones de vapor de más del 15 vol% se alcanzan conversiones casi completas de los alquitranes analizados. Se han obtenido expresiones cinéticas para la conversión de alquitrán sobre los diferentes carbonizados teniendo en cuenta su desactivación. Se ha utilizado la cinética obtenida para simular el proceso FLETGAS corroborando trabajos anteriores (Nilsson et al., 2012) donde se demostraba que la tercera etapa del nuevo gasificador sería capaz de convertir el alquitrán pesado hasta los niveles necesarios para generar un gas de salida con el punto de rocío deseado

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

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

Cabbage and fermented vegetables : From death rate heterogeneity in countries to candidates for mitigation strategies of severe COVID-19

Large differences in COVID-19 death rates exist between countries and between regions of the same country. Some very low death rate countries such as Eastern Asia, Central Europe, or the Balkans have a common feature of eating large quantities of fermented foods. Although biases exist when examining ecological studies, fermented vegetables or cabbage have been associated with low death rates in European countries. SARS-CoV-2 binds to its receptor, the angiotensin-converting enzyme 2 (ACE2). As a result of SARS-CoV-2 binding, ACE2 downregulation enhances the angiotensin II receptor type 1 (AT(1)R) axis associated with oxidative stress. This leads to insulin resistance as well as lung and endothelial damage, two severe outcomes of COVID-19. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is the most potent antioxidant in humans and can block in particular the AT(1)R axis. Cabbage contains precursors of sulforaphane, the most active natural activator of Nrf2. Fermented vegetables contain many lactobacilli, which are also potent Nrf2 activators. Three examples are: kimchi in Korea, westernized foods, and the slum paradox. It is proposed that fermented cabbage is a proof-of-concept of dietary manipulations that may enhance Nrf2-associated antioxidant effects, helpful in mitigating COVID-19 severity.Peer reviewe

Nrf2-interacting nutrients and COVID-19 : time for research to develop adaptation strategies

There are large between- and within-country variations in COVID-19 death rates. Some very low death rate settings such as Eastern Asia, Central Europe, the Balkans and Africa have a common feature of eating large quantities of fermented foods whose intake is associated with the activation of the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) anti-oxidant transcription factor. There are many Nrf2-interacting nutrients (berberine, curcumin, epigallocatechin gallate, genistein, quercetin, resveratrol, sulforaphane) that all act similarly to reduce insulin resistance, endothelial damage, lung injury and cytokine storm. They also act on the same mechanisms (mTOR: Mammalian target of rapamycin, PPAR gamma:Peroxisome proliferator-activated receptor, NF kappa B: Nuclear factor kappa B, ERK: Extracellular signal-regulated kinases and eIF2 alpha:Elongation initiation factor 2 alpha). They may as a result be important in mitigating the severity of COVID-19, acting through the endoplasmic reticulum stress or ACE-Angiotensin-II-AT(1)R axis (AT(1)R) pathway. Many Nrf2-interacting nutrients are also interacting with TRPA1 and/or TRPV1. Interestingly, geographical areas with very low COVID-19 mortality are those with the lowest prevalence of obesity (Sub-Saharan Africa and Asia). It is tempting to propose that Nrf2-interacting foods and nutrients can re-balance insulin resistance and have a significant effect on COVID-19 severity. It is therefore possible that the intake of these foods may restore an optimal natural balance for the Nrf2 pathway and may be of interest in the mitigation of COVID-19 severity

A Tar Conversion Model for Fluidized Bed Biomass Gasifiers

A comprehensive tar conversion model for biomass gasification has not been developed up to date due to the great deal of processes involved, whose stoichiometry and kinetics are not well known. Therefore, simplified schemes of reactions are assumed in existing models, reducing their capability to predict the tar composition in the gas. In this work a model to predict tar composition from wood gasification was developed. The model takes into account both tar generation from the fuel and secondary transformations of the gas in the gasifier, mainly focused on conditions applicable to fluidized beds. The model comprises a limited number of tar compounds and reactions representing the main tar species and conversion mechanisms, which stoichiometry and kinetics are based on literature data. Comparison with measurements from literature data is presented to discuss the applicability of the model

Dynamic assessment of Waste-to-Energy Schemes in Current European Landfill-Dominant Regions

Even when European regulation has been encouraging landfill reduction in the last decades, 13 out of 28 EU countries still landfill more than 50% of their municipal solid waste (MSW), mainly located in Southern and Eastern Europe. In this paper, waste-to-energy (WtE) schemes based on gasification are proposed in order to minimize the landfill disposal in European landfill-dominant regions. These schemes are assessed by means of a dynamic GHG emissions methodology since comparing with a dynamic reference system (i.e. methane emissions are delayed several years after the landfilling of the wastes and the emissions continue unevenly for at least 20 years more). The evolution of current waste management system and mix of electricity production is also modeled. The results reveal that the incorporation of gasification-based WtE plants in dominated-landfill European countries has a positive climate impact compared to current waste management in the short term. The long-term climate impact is, however, not secure since it depends on the evolution of the reference system in the analyzed region. Among the assessed configurations, the fluidised bed gasifier with internal combustion engine (FBG/ICE) configuration achieves the best climate benefit since has the highest energy efficiency.Ministerio de Economía y Competitividad CTM2016-78089-

Techno-Economical Analysis for a 3 MWth Gasification Plant Revamping: Use of Enriched Air and Steam as Gasifying Agent

An assessment of the revamping of a 3 MWth atmospheric­pressure bubbling fluidized bed biomass gasifier was made in order to study the techno­economical viability of changing the gasifying agent from air to a mixture of enriched air based on membrane technology (up to 40% in volume oxygen) and low­pressure saturated steam. The expected changes in the gasification yields were obtained from extrapolating the yields of the non­condensable main gases (H2, CO, CO2 and CH4) measured in a 100 kWth pilot plant facility. The main variables for the economical sensitivity analysis included the initial investment for the new equipment, the operating hours per year and the plant capacity (biomass flowrate). Net present values of up to 180 k€ and internal rate of return of up to 20% could be achieved. The results show that this gasification concept seems to be an interesting and viable option for standalone direct air­blown fluidized bed gasifiers

Experimental Investigation of Olive Tree Pruning Gasification in a Bench-Scale Fluidized Bed

Olive tree pruning was gasified in a laboratory fluidized bed reactor using air as gasifying agent. Different operating temperatures (800, 850 and 900 ºC) and equivalence ratios (ER) (0.12-0.35) were tested and additional tests were performed varying the particle size of the fuel, the biomass feed rate and the oxygen content in the air (13-40%). The composition of the product gas was determined measuring light gas components (CO2, CO, CH4, H2, C2H4, C2H2, C3, N2), tar, inorganic contaminants (NH3, HCN, H2S, HCl), and water. Solid samples collected from the cyclone and the fluidized bed were also examined. It was found that for low temperature (800 ºC) the gasification efficiency was low (0.58) due to the low char conversion. On the contrary at 900 ºC, the gasification efficiency was above 70% even for the highest ER tested (0.35). The quality of the gas was significantly improved by using O2-enriched air up to 40%

Influence of the Stoichiometric Ratio on Tar Composition during Fluidized Bed Gasification

Fluidized bed gasification is a promising technology for the energetic valorization of biomass and wastes. However the presence of heavy tars limits the use of the gas to applications where the gas is not cooled. Several parameters such as the temperature profile inside the gasifier and the gas residence time influence the concentration and composition of the tar mixture and thus the gas dew point. In autothermal air-blown fluidized bed gasifiers the stoichiometric ratio (fed air/stoichiometric air) determines the reactor temperature but the influence over the tar composition depends on the competition of the different fractions (light gas, char and tar) for the oxygen available. This paper analyzes the tar composition in the gas produced during the conversion of biomass pellets in a fluidized bed reactor when the stoichiometric ratio is raised from 0 (pyrolysis) to 0.21 (standard autothermal gasification with air). The tests were conducted at 800°C and 900°C and constant gas residence time and volatiles/carrier gas ratio. The results are discussed and compare with previous literature works, explaining some aspects of existing tar conversion models for biomass gasification.Junta de Andalucía P12-TEP-1633Ministerio de Economía y Competitividad CTM2016-78089-