Heat transfer in oxy-fuel fluidized bed boilers

In spite of the stabilization of coal demand in developed countries, the role of coal in the next decades energy mix is still essential. Particularly relevant will be in the great developing economies, such as India or China, where this fuel is abundant and avoid external energy dependences. In parallel, the international community needs to drive its efforts towards politics that commit fossil fuels energetic companies to drop their CO2 emissions drastically for 2015. In this regard, great advances have been made towards gaining plant efficiency and therefore, reducing the tones of CO2 per produced kWh. Still, emissions need a more drastic reduction if we want to avoid an increment of atmosphere temperature higher than 2ºC. Here, the CO2 capture and storage (CCS) technologies will have the potential of reducing up to 25% of CO2 from stationary sources as soon as they will be commercially available. Among the CO2 capture technologies, grouped in pre-combustion, post-combustion and oxy-fuel combustion, this last one is receiving outstanding support by the national and European authorities. The possibility of implementing oxy-fuel combustion into circulating fluidized bed technology, contributes to approaching the concept of clean-coal technology. Fluidized bed combustors have the outstanding feature of offering the possibility of burning a wide variety of fuels They have the possibility to capture SO2 emissions, adding in-bed limestone. Their working temperature is lower than in pulverized fuel boilers, which avoids thermal NOx formation. Additionally to these characteristics, already exploited under air-firing, applying oxy-fuel combustion technology and being able to capture the CO2 emissions from the coal combustion, or even from blends of coal and other fuels, makes oxy-fuel combustion in fluidized bed a great opportunity to turn the coal sustainable in the future power plant designs. About the implications derived of applying oxy-fuel technology to a commercial scale CFB boiler, scarce literature exits, especially when considering high O2 concentrations at inlet. A one dimensional model has been developed. The overall modeling strategy, in which the model has been based on, is explained in the first part of Chapter 2. It is based on the already known and validated air-firing semi-empirical expressions. The model has been divided into three sub-models interacting with each other: fluid-dynamics, combustion and energy balance of plant. For attributing reliability to the developed model, the scarce public experimental measurements of real air-firing boilers have been compared with the model results. Additionally, three studies regarding the modeling of large oxy-fuel CFB boilers have also been used for comparing the model predictions. In spite of having insufficient information about the published models details, the model developed in this work fairly fits the predictions in the literature. This has allowed making the sensibility analysis, trying to draw the main consequences of oxy-fuel deployment in CFB boilers. For retrofitting purposes, i.e. with no changes on an air-firing boiler configuration, the adequate O2 proportion of oxygen at entrance should be around 30%. Higher O2 concentrations lead to smaller cross sectional areas of the boiler. For a given fuel power required in a boiler, feeding 45% O2 in the comburent, would reduce the cross sectional area down to 54% of the original one. This involves a reduction of heat transfer surface along the boiler walls of 23% approximately. The immediate consequence is the need of resorting to external heat transfer surfaces, i.e., external heat exchangers (EHE). This device would need to remove almost 50% of the total heat of combustion in the case of feeding comburent with 60% O2 content. The importance of the EHE resides not only in compensating the reduction of heat transfer surface in the riser, but in managing higher amount of elutriated solids. The simulations have shown that higher solids densities in the boiler will enhance heat transfer coefficients to the riser walls. For certain boiler geometry, if increasing boiler load, higher recycled solids rate will be required. Feeding 60% of O2 at inlet, fuel input can be increased from 600 to 800 MW if elutriated solids increase from 25 to 40 kg/m2s. This refers us again to the higher solids crossing the EHE. An increase of 10% of heat removal will be required in this device for said changing load. Applying EHEs to conventional boilers was not essential during air-firing operation. But for oxy-fuel combustion it was here demonstrated to be crucial for accomplishing the boiler energy balance. However, several operational and design uncertainties will need to be solved, before deploying first demonstration oxy-CFB boiler. The design of the future EHE will imply two relevant distinguishing features of oxy-firing operation: the influence of gas composition on the determination of the heat transfer coefficients and the greater amount of elutriated solids, cooled down in the EHE. The CIRCE bubbling fluidized bed pilot plant presents the adequate bubbling working regime to obtain results of heat transfer coefficient for a wide range of oxy-fuel conditions and extracting further conclusions on possible effects of gas composition on heat transfer coefficients. The range of O2 concentration at inlet reached values as high as 60%. Such a high concentration was scarcely achieved in pilot plants due, in most cases, to the limiting bed cooling capacity. Measurements of heat transfer coefficients were taken when cooling was needed to control the combustion temperature. Water could circulate through one or more of the four cooling jackets, depending on the cooling requirements. Heat transfer coefficients were indirectly measured by energy balance with the water mass flow and temperatures. There are no previous results on heat transfer measurements under oxy-fuel combustion, up to date. The pilot plant is characterized by two important performance parameters: the fluidizing velocity and the bed temperature. These two parameters are common for all the fluidized bed plants working on combustion. Particularly for characterizing oxy-fuel combustion, the composition of the oxidant gas is the other key parameter in the plant operation. These three factors have been analyzed and their influence on heat transfer was examined. The three of them are, however, interrelated. O2 concentration and bed temperature varied the gas density and thus, the fluidizing velocity. At the same time, the fluidizing velocity will affect the heat transfer coefficients and consequently, bed temperature would be influenced. For accounting for this kind of dependences, non-dimensional numbers have been used for comparison. It was detected no dominant effect of non-dimensional numbers on the heat transfer. This is mainly offset by the different fluidization velocities in AF and OF operation. In the former, uf was kept over 1 m/s, whereas OF required lower velocities, around 0.9 m/s. It was then determined the adequate semi-empirical correlations for the effective thermal conductivity and the residence time of particles at the heat transfer surface. Hence, a semi-empirical mechanistic approach is recommended for a good agreement with the experimental heat transfer coefficients obtained during oxy-fuel operation. It was demonstrated the relevance of the gaseous film resistance in the oxy-fuel tests, and a new empirical coefficient was deduced for both modes. As examined in Chapter 3, section 3.5, the recommended expressions to predict heat transfer coefficients during oxy-fuel combustion modified the thermal film resistance, fitting the empirical parameter M with experimental data. Where: M=6.51 for oxy-firing and M=11.33 for air-firing The larger amount of solids arriving at the EHE will influence the values and distribution of the average and local heat transfer coefficients, respectively. A review of the difficulties associated with the estimation of heat transfer to the tubes of a heat exchanger has been examined. By the use of a scaled-down EHE, it was possible to experimentally confirm the influence of heat transfer coefficients when horizontal movement of solids took place. The increase of solids rate stressed the inequalities of the local heat transfer coefficient, whereas the longer residence time taken by particles to travel through the EHE allows higher average heat transfer coefficient. The contribution of this parameter to the average heat transfer coefficient was correlated by means of a new expression, as developed in Chapter 4, section 4.4. This expression allows modifying the heat transfer coefficient previously deduced for stationary conditions, and therefore, accounting for the enhancement of heat transfer when recirculation of solids takes place. A real design of an EHE was then simulated and integrated in the existing CFB model previously developed. This is the first time that such a model is developed to predict the heat transfer area required in oxy-fuel operation. The EHE sub-model must fulfill the energy balance requirements previously set for the CFB model. The temperature, at which solids must be recycled back into the boiler, in order to keep the desired boiler temperature, is accomplished with this sub-model. The expressions for the heat transfer coefficient and the enhancement due to recycled mass flow of solids were included in the EHE sub-model. Hence, it was possible to determine the increase on the heat transfer surface, for different O2 concentration in the oxidant stream, and two ranges of boiler temperature required. It was then recognized that, in spite of doubling the heat transfer surface requirements, when O2 concentration increased 10%, the heat transfer surface increases less than expected if solids flow influence were not included in the heat transfer evaluation. This thesis demonstrates that heat transfer surface design, arrangement and allocation, will differ in future oxy-fuel CFB boilers. Particularly, the heat transfer in the EHE will need address the influence of fluidizing gas composition and recycled solids, for an adequate and efficient heat exchanger configuration

Análisis de Ciclo de Vida de la captura de CO2 en una central térmica y evaluación de alternativas basadas en energías renovables

En este proyecto se realiza el Análisis del Ciclo Vida (ACV), de una planta de captura y almacenamiento de CO2 (CAC) implementada en una central térmica convencional, con el objeto de evaluar los impactos ambientales asociados a su implantación en una central de generación eléctrica con combustible fósil, que en este trabajo es el lignito. Se realizan también el ACV de la central térmica convencional y el ACV de una turbina de viento. Para realizar los ACV, se utiliza el software SimaPro 8.02, que es una herramienta especializada para este tipo de análisis, cuyos procedimientos están estandarizados por la norma ISO 14044, 2006. Se ha aplicado la metodología IMPACT 2002+ en todos los ACV realizados en este trabajo, en la que los resultados representan los indicadores de daño a la salud humana, a la calidad del ecosistema, a los recursos naturales (agotamiento) y la contribución al cambio climático. El método IMPACT 2002+, que es una combinación y mejora de los métodos Eco-indicador 99 y CML 2001, utiliza indicadores de punto medio e indicadores de punto final ó indicadores de daño, proporcionando una perspectiva más completa de los daños y cargas ambientales. Finalmente, se comparan los resultados obtenidos de los ACV de la central térmica con captura de CO2 con los resultados obtenidos de la turbina de viento. Se discuten los resultados y se establecen las conclusiones oportunas. Los resultados que se obtienen indican que la planta de captura de CO2 permite reducir los impactos ambientales de forma muy importante con respecto a una central térmica convencional. Así, el impacto a las salud humana, a la calidad del ecosistema y al cambio climático al incluir la captura de CO2 en una central térmica de carbón, se reducen un 98-99% de sus valores originales sin captura de CO2. Asimismo, cuando se compara el impacto ambiental provocado por una central térmica con captura de CO2 con respecto al provocado por la generación eólica, se obtiene como resultado que el mayor impacto ambiental lo provoca la central térmica con captura. El mayor daño se produce a los recursos que utiliza la central térmica con captura frente a la generación eólica

Evaluación de sistemas de captura de CO2 en una planta de extracción de bitumen in situ

Las arenas bituminosas son una combinación de arcilla, arena, agua y bitumen (una sustancia parecida a la brea) que se encuentra en grandes cantidades en diversas partes del mundo, sobre todo en Canadá, aunque también en Venezuela, Estados Unidos o Rusia. De estas arenas se extrae el bitumen, un hidrocarburo altamente viscoso del que se puede obtener petróleo crudo sintético tras su procesamiento y refinado. Recientemente se ha incrementado su explotación ya que pueden resultar unas grandes competidoras frente al petróleo, pues sólo las reservas de Canadá constituyen la tercera reserva probada de petróleo del mundo. El 80% de las arenas bituminosas debe extraerse empleando los llamados métodos de extracción in situ. La técnica de extracción in situ más extendida es la Segregación Gravitacional Asistida por Vapor, o proceso SAGD. Partiendo de la base teórica que explica el funcionamiento del proceso SAGD, se ha elaborado un modelo con el que poder analizar la operación de las plantas que emplean esta técnica. El proceso SAGD requiere para la extracción de un barril de bitumen 3,4 kWh de electricidad y 3 barriles de vapor de agua. Durante la simulación, el ritmo de extracción de bitumen de 100.000 bbl/d fija los requerimientos energéticos relativos al bitumen de la planta. El modelo se compone de una instalación de cogeneración, un generador de vapor y los pozos de extracción. Sus equipos se alimentan de gas natural, lo que implica emitir CO2 a la atmósfera. Debido a que éste es un gas de efecto invernadero, se estudia la implantación de dos sistemas de captura para mitigar sus emisiones. En primer lugar se ha determinado la operación de la planta sin captura de CO2, que se toma como referencia para comparar los efectos de la implantación de los sistemas de captura. Los resultados obtenidos de la simulación del modelo de referencia con EES, indican que tiene un consumo eléctrico de 14.354 kW, y de vapor, medido por la potencia térmica, de 60.800 kWt. Para satisfacer las demandas energéticas se queman 2,28 m3N/s de gas natural, emitiendo 4,49 kg/s de CO2. La primera posibilidad ha sido incluir en el modelo un sistema de captura basado en la absorción química con aminas. Para ello, es necesario implantar una unidad de absorción química y una unidad de compresión de CO2. De la primera se deriva un aumento de la potencia térmica, demandando 20.963 kWt extra. La segunda precisa 1.887 kW eléctricos. Satisfacer estas nuevas necesidades implica aumentar el consumo de combustible en la planta un 30,26%, creciendo también el CO2 generado. El 90% del CO2 que se genera, se captura, logrando evitar la emisión de 3,91 kg/s de CO2 respecto a la planta de referencia. Esto corresponde a emitir un 87,08% menos CO2 que en el caso de referencia. Como segunda opción para reducir las emisiones de CO2, se estudia la posibilidad de operar la planta SAGD en oxicombustión. Se requiere una unidad para separar el oxígeno del aire, que consume 5.114 kW de electricidad. Además, se deben aportar 1.557 kW al tren de compresores de CO2. El consumo de gas natural aumenta un 7,5% respecto a la planta de referencia, pero se consiguen evitar 4,01 kg/s de CO2, es decir, las emisiones son un 89,3% menores que en la configuración inicial. Respecto al CO2 evitado, no se puede concluir que una tecnología sea más apropiada que otra, ya que las diferencias no son los suficientemente grandes. Pero, dado que en términos energéticos la oxicombustión tiene repercusiones más leves sobre la planta que la unidad de absorción química, se concluye que ésta sería la tecnología más apropiada para su implantación en una planta SAGD. No obstante la captura con aminas también resulta una opción eficiente y viable a priori

ASS234, as a new Multi-Target Directed propargylamine for Alzheimer’s disease therapy

MU and JMC thank MINECO (Spain) for support (Grant SAF2012-33304; SAF2015-65586-R). RRR, MU, GE and JMC thank EU (COST Action 1103) for support.The complex nature of Alzheimer’s disease (AD) has prompted the design of Multi-Target-Directed Ligands (MTDL) able to bind to diverse biochemical targets involved in the progress and development of the disease. In this context, we have designed a number of MTD propargylamines showing antioxidant, anti-betaamyloid, anti-inflammatory, as well as cholinesterase and monoamine oxidase inhibition capacities. Here, we describe these properties in the MTDL ASS234, our lead-compound ready to enter in pre-clinical studies for AD, as a new multipotent, permeable cholinesterase/monoamine oxidase inhibitor, able to inhibit Aβ- aggregation, possessing antioxidant and neuroprotective properties.Publisher PDFPeer reviewe

Loss of Mitochondrial Ndufs4 in Striatal Medium Spiny Neurons Mediates Progressive Motor Impairment in a Mouse Model of Leigh Syndrome

Inability of mitochondria to generate energy leads to severe and often fatal myoencephalopathies. Among these, Leigh syndrome (LS) is one of the most common childhood mitochondrial diseases; it is characterized by hypotonia, failure to thrive, respiratory insufficiency and progressive mental and motor dysfunction, leading to early death. Basal ganglia nuclei, including the striatum, are affected in LS patients. However, neither the identity of the affected cell types in the striatum nor their contribution to the disease has been established. Here, we used a mouse model of LS lacking Ndufs4, a mitochondrial complex I subunit, to confirm that loss of complex I, but not complex II, alters respiration in the striatum. To assess the role of striatal dysfunction in the pathology, we selectively inactivated Ndufs4 in the striatal medium spiny neurons (MSNs), which account for over 95% of striatal neurons. Our results show that lack of Ndufs4 in MSNs causes a non-fatal progressive motor impairment without affecting the cognitive function of mice. Furthermore, no inflammatory responses or neuronal loss were observed up to 6 months of age. Hence, complex I deficiency in MSNs contributes to the motor deficits observed in LS, but not to the neural degeneration, suggesting that other neuronal populations drive the plethora of clinical signs in LS

RAS at the Golgi antagonizes malignant transformation through PTPRκ-mediated inhibition of ERK activation

© The Author(s) 2018.RAS GTPases are frequently mutated in human cancer. H- and NRAS isoforms are distributed over both plasma-membrane and endomembranes, including the Golgi complex, but how this organizational context contributes to cellular transformation is unknown. Here we show that RAS at the Golgi is selectively activated by apoptogenic stimuli and antagonizes cell survival by suppressing ERK activity through the induction of PTPRκ, which targets CRAF for dephosphorylation. Consistently, in contrast to what occurs at the plasma-membrane, RAS at the Golgi cannot induce melanoma in zebrafish. Inactivation of PTPRκ, which occurs frequently in human melanoma, often coincident with TP53 inactivation, accelerates RAS-ERK pathway-driven melanomagenesis in zebrafish. Likewise, tp53 disruption in zebrafish facilitates oncogenesis driven by RAS from the Golgi complex. Thus, RAS oncogenic potential is strictly dependent on its sublocalization, with Golgi complex-located RAS antagonizing tumor development.We are grateful to Drs: Ignacio Rubio, Yardena Samuels, Mariano Barbacid and Javier León for providing reagents; and Alicia Noriega, Sandra Zunzunegui y Victor Campa for technical support. Crespo laboratory is supported by grant SAF-2015 63638R (MINECO/ FEDER, UE); by Red Temática de Investigación Cooperativa sobre el Cáncer (RTICC). RD/12/0036/0033 and by Asociación Española Contra el Cáncer (AECC), grant GCB141423113. Work in the Hurlstone laboratory was unded by a grant from the European Research Council (ERC-2011-StG-282059 PROMINENT). B.C. is supported by a Retos Jóvenes Investigadores grant SAF2015-73364-JIN (AEI/FEDER, UE) and a grant from Fundación Francisco Cobos. X.R.B. is supported by grants from the CastillaLeón Government (BIO/SA01/15, CSI049U16), MINECO (SAF2015-64556-R, RD12/ 0036/0002), Worldwide Cancer Research (14-1248), Ramón Areces Foundation, andAECC (GC16173472GARC). Spanish funding to P.C., B.C., and X.R.B. is partially supported by the European Regional Development Fund

Loss of mitochondrial Ndufs4 in striatal medium spiny neurons mediates progressive motor impairment in a mouse model of leigh syndrome

Altres ajuts: Juan del la Cierva (IJCI-2015-24576)Inability of mitochondria to generate energy leads to severe and often fatal myoencephalopathies. Among these, Leigh syndrome (LS) is one of the most common childhood mitochondrial diseases; it is characterized by hypotonia, failure to thrive, respiratory insufficiency and progressive mental and motor dysfunction, leading to early death. Basal ganglia nuclei, including the striatum, are affected in LS patients. However, neither the identity of the affected cell types in the striatum nor their contribution to the disease has been established. Here, we used a mouse model of LS lacking Ndufs4, a mitochondrial complex I subunit, to confirm that loss of complex I, but not complex II, alters respiration in the striatum. To assess the role of striatal dysfunction in the pathology, we selectively inactivated Ndufs4 in the striatal medium spiny neurons (MSNs), which account for over 95% of striatal neurons. Our results show that lack of Ndufs4 in MSNs causes a non-fatal progressive motor impairment without affecting the cognitive function of mice. Furthermore, no inflammatory responses or neuronal loss were observed up to 6 months of age. Hence, complex I deficiency in MSNs contributes to the motor deficits observed in LS, but not to the neural degeneration, suggesting that other neuronal populations drive the plethora of clinical signs in LS

Synthesis, biological evaluation, and molecular modeling of nitrile-containing compounds : exploring multiple activities as anti-Alzheimer agents

Funding: EC COST Actions D34 and CM1103 for Short-term Scientific Mission funding (EM, DS, MM); the School of Biology at the University of St. Andrews (EJS, RRR); the Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, Universidade de Lisboa (AN, ACJ, TR, MCC); FCT, the Portuguese Foundation for Science and Technology (Project PTDC/SAU-NEU/64151/2006 (MCC), and project grant (DS) Vega 2/0127/18 and the contract No. APVV-15-0455 of Slovak Research and Development Agency (MM).Based on the monoamine oxidase (MAO) inhibition properties of aminoheterocycles with a carbonitrile group we have carried out a systematic exploration to discover new classes of carbonitriles endowed with dual MAO and AChE inhibitory activities, and Aβ anti‐aggregating properties. Eighty‐three nitrile‐containing compounds, 13 of which are new, were synthesized and evaluated. in vitro screening revealed that 31 , a new compound, presented the best lead for trifunctional inhibition against MAO A (0.34 μM), MAO B (0.26 μM), and AChE (52 μM), while 32 exhibited a lead for selective MAO A (0.12 μM) inhibition coupled to AChE (48 μM) inhibition. Computational analysis revealed that the malononitrile group can find an advantageous position with the aromatic cleft and FAD of MAO A or MAO B. However, the total binding energy can be handicapped by an internal penalty caused by twisting of the ligand molecule and subsequent disruption of the conjugation ( 32 in MAO B compared to the conjugated 31 ). Conjugation is also important for AChE as well as the hydrophilic character of malononitrile that allows this group to be in close contact with the aqueous environment as seen for 83 . Although the effect of 31 and 32 against Aβ1–42, was very weak, the effect of 63 and 65 , and of the new compound 75 , indicated that these compounds were able to disaggregate Aβ1–42 fibrils. The most effective was 63 , a (phenylhydrazinylidene)propanedinitrile derivative that also inhibited MAO A (1.65 μM), making it a potential lead for Alzheimer's disease application.PostprintPeer reviewe

Defined neuronal populations drive fatal phenotype in a mouse model of leigh syndrome

Altres ajuts: Seattle Children's Research Institute: Seed Funds;NINDS: R01 NIH/NS 102796; University of Washington Neurological Surgery Department: Ellenbogen Neurological Surgery Research Funds; University of Washington: The Ryan J. Murphy SUDEP Research Funds; Mitochondrial Research Guild: Seed FundsMitochondrial deficits in energy production cause untreatable and fatal pathologies known as mitochondrial disease (MD). Central nervous system affectation is critical in Leigh Syndrome (LS), a common MD presentation, leading to motor and respiratory deficits, seizures and premature death. However, only specific neuronal populations are affected. Furthermore, their molecular identity and their contribution to the disease remains unknown. Here, using a mouse model of LS lacking the mitochondrial complex I subunit Ndufs4, we dissect the critical role of genetically-defined neuronal populations in LS progression. Ndufs4 inactivation in Vglut2expressing glutamatergic neurons leads to decreased neuronal firing, brainstem inflammation, motor and respiratory deficits, and early death. In contrast, Ndufs4 deletion in GABAergic neurons causes basal ganglia inflammation without motor or respiratory involvement, but accompanied by hypothermia and severe epileptic seizures preceding death. These results provide novel insight in the cell type-specific contribution to the pathology, dissecting the underlying cellular mechanisms of MD