Gas maldistribution in fluidized beds

Gas maldistribution is one of the most common problems in large-scale fluidized beds. High superficial gas velocities should be used to create a high pressure drop across the distributor plate to achieve an even gas distribution within the bed. However, higher pressure drop leads to higher power consumption in blowers, which means higher operational costs. In addition, the superficial gas velocity in large-scale reactors is seldom constant. As long as gas velocity perturbations lead to pressure drop variations, it is important to maintain the distributor pressure drop as low as possible. Maldistribution depends on the superficial gas velocity, the type of solids used as bed material and the distributor plate design. Low values of superficial gas velocity are more prone to generate gas maldistribution and therefore, several authors recommend operating beyond a critical value of gas velocity, at which all distributor plate orifices or tuyeres are considered active. The type of solids used as bed material determines the tendency of the bed to agglomerate. Since agglomeration could lead to maldistribution and defluidization, it is important to select the bed material properly. The distributor design affects mainly to the pressure drop, which is also dependent of other variables such the superficial gas velocity, the number of orifices and its diameter, the distributor plate thickness, the temperature. . . Pressure measurements and visual inspection of the bed surface are robust techniques commonly used in fluidized bed reactors for monitoring purposes. Therefore, these techniques were employed in this thesis to study maldistribution. Visual inspection technique was employed in a 3D cylindrical bubbling fluidized bed to detect maldistribution in the bed surface. To create a controlled induced maldistribution, the half of the distributor plate cross-section was covered. It was found that a high superficial gas velocity could overcome maldistribution at the bed surface, even though the maldistribution problem could still prevail at the bottom of the bed. According to that, pressure fluctuations measurements were investigated as a detection method for maldistribution. Several monitoring methods based on the pressure signal analysis were studied to evaluate the boundary of maldistribution grade that can be detected. The effect of the pressure probe location was also investigated and it was concluded that pressure probes should be located at 50-75% of the bed height for maldistribution detection purposes. A single pressure probe could be suficient to detect maldistribution in a lab-scale fluidized bed; however, several pressure probes should be placed in a large-scale fluidized bed reactor to cover all the bed cross-section. Visual inspection technique was also employed to develop a model for estimating the size of the stagnant zones created by covered parts of the distributor plate. A correlation was obtained using Digital Image Analysis and Particle Image Velocimetry of pictures taken in a pseudo-2D fluidized bed. The proposed correlation, coupled with correlations from the literature, was extrapolated to a 3D facility. The model was found to predict the size of the stagnant zones in a 3D fluidized bed with a maximum relative error of 20% and it could be used to estimate the size of the distributor cross-section affected by maldistribution. The distributor plate performance under operational conditions was also investigated. The effect of temperature on the distributor pressure drop was studied for two different distributor plates (i.e. multiorifice and tuyere type) in a Biomass Bubbling Fluidized Bed Gasifier. The results were employed to develop a methodology to design gas distributor plates at elevated temperature. The model predicts accurately the minimum distributor open area needed to satisfy a distributor to bed pressure drop ratio for a given temperature and operation conditions.Uno de los problemas más comunes de los lechos fluidizados industriales es la mala distribución del gas en el lecho. Se deben emplear elevadas velocidades de gas para generar grandes pérdidas de carga en el distribuidor que garanticen la distribución uniforme del gas en el interior del lecho. Sin embargo, una elevada pérdida de carga en el distribuidor supone también un aumento en la potencia consumida por los elementos de impulsión del gas, que se traducen en un aumento de los costes de operación. Además, en los reactores industriales de lecho fluidizado la velocidad del gas es raramente constante. Dado que las perturbaciones en el flujo de gas generan a su vez perturbaciones en la pérdida de carga del distribuidor, es importante conseguir que esta pérdida de carga sea lo más baja posible. La mala distribución del gas depende de la velocidad superficial del gas, del tipo de sólido empleado como material inerte y de varios aspectos del diseño del distribuidor. Si se emplean velocidades de gas demasiado bajas, el gas es más propenso a la mala distribución, y por ello varios autores recomiendan operar por encima de un valor crítico de velocidad por encima del cual todos los orificios o campanas del distribuidor se consideran activos. El tipo de sólido empleado como material inerte determina la tendencia del lecho a la aglomeración. Es importante seleccionar un material adecuado puesto que la aglomeración del lecho puede conducir a la mala distribución del gas e incluso a la defluidización. El diseño del distribuidor afecta principalmente al valor de la pérdida de carga, que a su vez depende de otros factores como son la velocidad del gas, el número de orificios y su tamaño, el espesor de la placa distribuidora, la temperatura... Tanto las medidas de presión como el análisis visual de la superficie del lecho son técnicas de medida robustas que se utilizan comúnmente en la monitorización de reactores de lecho fluidizado. Por lo tanto, estas técnicas se han empleado en esta tesis para el estudio de la mala distribución del gas en el lecho. El análisis visual se utilizó en un lecho fluidizado cilíndrico (3D) para la detección de la mala distribución del gas en la superficie del lecho. Para conseguir un estado de mala distribución inducida se tapó la mitad de los orificios de la placa distribuidora. Se observó que, aunque una velocidad de gas elevada puede hacer que la mala distribución no se detecte en la superficie, el problema persiste en la zona baja del lecho. De acuerdo con este hecho, se investigó el uso de las medidas de fluctuaciones de presión en el interior del lecho como herramienta para la detección de la mala distribución del gas. Se emplearon varios métodos de monitorización basados en el análisis de las fluctuaciones de presión para establecer el umbral de grado de mala distribución que puede ser detectado. También se investigó el efecto de la localización de las sondas de presión y se concluyó que deben ser colocadas a una altura entre el 50 y el 75% de la altura total del lecho si el objetivo es detectar la mala distribución del gas. Una única sonda puede ser suficiente para la detección en un lecho de escala de laboratorio, sin embargo, se deberían emplear varias sondas en lechos industriales para poder cubrir la medida en toda la sección del lecho. El análisis visual se utilizó también para el desarrollo de un modelo capaz de estimar el tamaño de las zonas muertas generadas por el bloqueo de una parte de los orificios del distribuidor. Se obtuvo una correlación a partir del análisis digital de imagen y la velocimetría de partículas de imágenes tomadas en un lecho fluidizado bidimensional (2D). La correlación propuesta, junto a otras correlaciones de la literatura, se utilizó para extrapolar datos a un lecho 3D. Se observó que el modelo es capaz de predecir el tamaño de las zonas muertas en un lecho 3D con un error máximo del 20%, y puede además emplearse para estimar el tamaño de la sección afectada del distribuidor. Se estudió el efecto de la temperatura de operación en la pérdida de carga del distribuidor para dos tipos distintos de distribuidores (placa perforada y campanas) en una planta piloto de gasificación de biomasa en lecho fluidizado. Los resultados obtenidos se utilizaron en el desarrollo de una metodología para el diseño de distribuidores a alta temperatura. El modelo propuesto predice la mínima área de orificios necesaria para cumplir una relación dada de pérdida de carga entre el distribuidor y el lecho, y para una temperatura y condiciones de operación fijadas.The author deeply appreciates the funding support by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660),Programa Oficial de Doctorado en Ingeniería Mecánica y de Organización IndustrialPresidente: Bo Leckner.- Secretario: Celia Sobrino Fernández.- Vocal: José Antonio Almendros Ibáñe

PSICQUIC and PSISCORE: accessing and scoring molecular interactions

To the Editor.-- Author Manuscript.-- et al.This study was supported by the European Commission under the Serving Life-science Information for the Next Generation contract 226073; Proteomics Standards Initiative and International Molecular Exchange contract FP7-HEALTH-2007-223411; Apoptosis Systems Biology Applied to Cancer and AIDS contract FP7-HEALTH-2007-200767; Experimental Network for Functional Integration contract LSHG-CT-2005-518254; German National Genome Research Network; German Research Foundation contract KFO 129/1-2; US National Institutes of Health grant R01GM071909; the Italian Association for Cancer Research; a Wellcome Trust Strategic Award to the European Molecular Biology Laboratory–European Bioinformatics Institute for Chemogenomics Databases; Grand Challenges in Global Health Research, the Canadian Institutes of Health Research, Foundation for the National Institutes of Health and Genome British Columbia; and a German Research Foundation–funded Cluster of Excellence for Multimodal Computing and Interaction.Peer Reviewe

The access to broadband services as a strategy to retain population in the depopulated countryside in Spain

The aim of this paper is to analyze at what extent the connectivity of small localities is a determinant of their demography. Specifically, we pay attention to three factors: the evolution of the population; the distance, measured both in kilometres and travel time, to the province capital, the usual city where the largest set of services is available; and finally, the coverage of different kinds of broadband services (from ADSL or 3.5 G to the fastest ones FTTH) in rural areas. An econometric model was estimated where the dependent variable captures the increase of inhabitants along 2017–2020 of the 5955 Spanish municipalities with a population between 101 and 10,000 inhabitants (73.3 % of all municipalities). The results point out to the following facts: digital connectivity of small localities is a determinant of their demography, whatever the technology used, but physical distance remains being a significant factor on the population growth (both if it is measured of physical distance or travelling time) to explain the population growth of each locality

Wide band energy analysis of fluidized bed pressure fluctuation signals using a frequency division method

A statistical method based on approximation of the cumulative energy distribution by Student's t-distribution is proposed for the unbiased frequency domain division. The proposed method fixes the number of samples needed to estimate the power spectrum and its corresponding cumulative energy distribution using the Kolmogorov&-Smirnov test. The reliability of the method to divide the frequency domain was shown for different fluidization velocities by changing the bed aspect ratio and using different pressure probes. Water-induced defluidization tests were conducted to illustrate the use of wide band energy as a monitoring tool. The Student's t-distribution results are compared with an analysis performed using the traditional visual inspection method. The energy of the power spectrum contained within the frequency regions obtained by the visual method is not able to detect changes in the bed aspect ratio or the start of the rotating distributor. No meaningful differences could be observed in the frequency regions using different quality pressure sensors because the approach using Student's t-distribution focuses on the sharp energy increase produced by the primary frequencies of the power spectrum. The sensitivity exhibited by the proposed frequency division approach for the range of fluidization conditions tested improves the use of the energy contained in these regions as a diagnostic tool in fluidized bed processes.The author would like to express appreciation for the financial support from Projects DPI2009-10518 (MICINN) and CARDENER-CM (S2009ENE-1660).Publicad

Fluvial base level control on the differential rejuvenation of the Olvera- Zaframagón gypsum karst system (NE Cádiz province)

El presente trabajo analiza la evolución del relieve en un sector localizado entre la depresión del Guadalquivir y la cuenca de Ronda, en la Cordillera Bética noroccidental, representado por extensos afloramientos de arcillas y yesos triásicos, sobre los que destacan relieves rocosos aislados formados por bloques de calizas jurásicas, como el peñón de Zaframagón, al oeste del municipio de Olvera. Estos bloques dibujan una antigua superficie de erosión con pendiente hacia el NO, muy probablemente asociada a la progresiva continentalización de la cuenca del Guadalquivir durante el Plioceno. Los afloramientos triásicos están afectados por una intensa karstificación en forma de dolinas y simas y otras depresiones de fondo plano, de tipo polje, en las zonas interfluviales. La incisión diferencial de los ríos Guadamanil y Guadalporcún, en la parte alta de la cuenca del río Guadalete, parece haber condicionado el desarrollo vertical de las formas kársticas. El río Guadalporcún corta transversalmente al peñón de Zaframagón a través de un corto pero profundo cañón, que ha actuado como obstáculo a la incisión del río, lo que ha provocado una menor tasa de encajamiento con respecto al río Guadamanil. Este encajamiento diferencial ha afectado al desarrollo de las formas kársticas de absorción que drenan a uno y otro río, generando simas más profundas en la vertiente que drena al Guadamanil. Por otro lado, en las laderas del valle de este río se ha reconocido una secuencia de surgencias escalonadas, cuyas alturas con respecto al cauce coinciden con las alturas generales asignadas a los niveles de terrazas cuaternarias definidos para la cuenca fluvial del Guadalete. Todos estos aspectos apuntan a que el desarrollo vertical del karst de Olvera-Zaframagón durante el Pleistoceno ha estado muy condicionado por el comportamiento del nivel de base, tanto a escala regional como local.The present work deals with the relief evolution in an area of the northwestern sector of the Betic Ranges. It is characterized by extensive outcrops of Triassic clays and gypsums over which several isolated reliefs of Jurassic carbonate rocks stand out, like the Zaframagón Rock, West of Olvera village. The flattened summits of all these carbonate blocks delimit an old erosion surface sloping NW, very probably related to the progressive continentalization of the nearby, formerly marine, Guadalquivir Tertiary Depression during the Pliocene. The Triassic gypsums are presently affected by intense karstification in form of dolines and shafts, as well as other flat-bottomed depressions similar to poljes in the interfluve areas. Differential incision in the Guadamanil and Guadalporcún Rivers, located in the head of the Guadalete fluvial basin, seems to have conditioned the vertical development of karst forms in the region. The Guadalporcún River crosses the Zaframagón Rock through a short but deep gorge. The Rock has acted as an obstacle to the river incision and this has hampered its vertical erosion if compared to the one of the Guadamanil River. This differential incision has affected the development of absortion karst forms which drain to both rivers: dolines and shafts are deeper when draining to the Guadamanil River valley. The slopes of the valley are plenty of active and inactive springs, drawing a sequence of stepped outflow points, whose relative heights coincide with the general heights assigned to the Quaternary fluvial terrace levels regionally defined for the Guadalete River basin. All these aspects suggest a strong relationship between the Pleistocene vertical development of the Olvera-Zaframagón karst system and the behavior of the base level, both at regional and local levels

The effect of temperature on the distributor design in bubbling fluidized beds

In this paper the effect of the temperature on the distributor pressure drop ratio is studied. There is a lack of information in the literature concerning the effect of the temperature on the performance of the distributor plate, and its possible role on non-uniform gas distribution. The effect of temperature on the distributor pressure drop has been experimentally established for the first time for two different air distributor plates, multiorifice and tuyere. The distributor pressure drop curves were obtained at different temperatures by means of pressure measurements. The well-known orifice equation was used to predict the distributor pressure drop at different temperatures and a good agreement with the experimental data was found. A methodology to obtain the distributor open area as a function of the bed temperature for different bed aspect ratios was developed. It was found that when operating at higher temperatures the distributor pressure drop decreases for the same gas velocity due to the decrease in the gas density. The resulting decrease of the distributor to bed pressure drop ratio shows that gas distributor plates have to be designed at the operating temperature instead at the ambient temperature to avoid non-uniform gas distributions and to save cost in manufacturing and operation.The financial support from projects DPI2009-10518 (MICINN) and CARDENER-CM (S2009ENE-1660) is very much acknowledged

Stagnant regions estimation in fluidized beds from bed surface observations

A novel approach to estimate the size of stagnant regions in large-scale fluidized beds by means of experimental data obtained from images recorded on the bed surface was presented. For this purpose, the internal structure of an induced maldistributed pseudo-2D fluidized bed was first studied. Half of the total distributor area was covered to generate an induced stagnant region. The size and shape of this area was studied for several relative gas velocities and bed aspect ratios. The defluidized area was found to be almost independent of the bed aspect ratio, however, it was found to decrease for higher relative gas velocities. A solids recirculation zone was also found above the defluidized zone. The size of this zone increases with relative gas velocity, suggesting that it is strongly related to bubble motion. A correlation was developed to relate the visible bubble flow to the size of the defluidized zone. The results obtained in the 2D bed were extrapolated to a 3D cylindrical fluidized bed with a half-covered distributor plate to estimate the volume of the defluidized zone. The visible bubble flow in the 3D facility was estimated. Using the proposed correlation for the defluidized volume in the 2D bed was used to estimate the defluidized volume in the 3D bed. Finally, the calculated values of the defluidized volume were compared with the experimental values in the 3D facility, obtaining a maximum relative error of 20% in the estimations

Eigenvectors of a kurtosis matrix as interesting directions to reveal cluster structure

In this paper we study the properties of a kurtosis matrix and propose its eigenvectors as interesting directions to reveal the possible cluster structure of a data set. Under a mixture of elliptical distributions with proportional scatter matrix, it is shown that a subset of the eigenvectors of the fourth-order moment matrix corresponds to Fisher's linear discriminant subspace. The eigenvectors of the estimated kurtosis matrix are consistent estimators of this subspace and its calculation is easy to implement and computationally efficient, which is particularly favourable when the ratio n/p is large.Publicad

Experimental quantification of the particle-wall frictional forces in pseudo-2D gas fluidised beds

In this work a novel measurement technique for pseudo-2D fluidised beds is developed. The objective is to give an estimation of the overall frictional force between the solids and the front and rear walls of the bed. For doing this, the measured pressure signal in the bed is processed in combination with the solids distribution (i.e. centre of mass position, velocity and acceleration) obtained from digital image analysis of the optically accessible front view of the bed. This is performed by acquiring the pressure signal in the bed simultaneously to the digital images. Both the pressure and the digital images are connected through a simple force balance in the bed, and a particle-wall interaction coefficient is obtained assuming that the overall frictional force is proportional to the centre of mass velocity. The particle-wall interaction coefficient found using this technique is of the order of 40-120 kg/m(2) s in the bed tested, and the standard deviation of the frictional forces reaches more than 70% of the weight of the bed. Therefore, the results indicate that the contribution of the particle-to-wall friction on the fluctuation of the pressure drop in a pseudo-2D bed is not negligible.This work has been partially funded by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660).Publicad