Development And Study Of Measurement Methods For Jets And Bogging In A Fluidized Bed

In the Fluid Coking process, if the local concentration of liquid is very high, particles may stick together which can eventually result in process upset because of poor fluidization or even defluidization, a condition commonly known in industry as bogging . Using a capacitance sensor, the void distribution in a bed of coke particles can be visualized. The voidage fluctuations caused by gas bubbles have been shown to change dramatically as the bed becomes bogged. Therefore, capacitance sensors should be able to predict the bogging condition in fluid cokers. The first part of the thesis focused on designing noiseless capacitance sensors that can be used to measure the liquid concentration and void distribution in a fluidized bed. The effect of bogging on the distribution of a liquid sprayed into fluidized bed was then investigated by determining the impact of bogging on the breakage rate of the liquid-solid agglomerates. Pressure measurements are easier to perform in industrial units than capacitance measurements. The knowledge acquired with capacitance measurements was then applied to the design of early bogging detection methods from pressure measurements. Detection of bogging with acoustic measurements is discussed in the next section. The speed of sound was measured at different levels of particles cohesiveness and fluidization velocities. The last part of the thesis applies the capacitance sensors to the measurement of jet cavity fluctuations. Two types of jets were investigated: the supersonic gas jets and the jets formed when liquid is atomized with a gas into a fluidized bed

Non-invasive and non-intrusive diagnostic techniques for gas-solid fluidized beds – A review

Gas-solid fluidized-bed systems offer great advantages in terms of chemical reaction efficiency and temperature control where other chemical reactor designs fall short. For this reason, they have been widely employed in a range of industrial application where these properties are essential. Nonetheless, the knowledge of such systems and the corresponding design choices, in most cases, rely on a heuristic expertise gained over the years rather than on a deep physical understanding of the phenomena taking place in fluidized beds. This is a huge limiting factor when it comes to the design, the scale-up and the optimization of such complex units. Fortunately, a wide array of diagnostic techniques has enabled researchers to strive in this direction, and, among these, non-invasive and non-intrusive diagnostic techniques stand out thanks to their innate feature of not affecting the flow field, while also avoiding direct contact with the medium under study. This work offers an overview of the non-invasive and non-intrusive diagnostic techniques most commonly applied to fluidized-bed systems, highlighting their capabilities in terms of the quantities they can measure, as well as advantages and limitations of each of them. The latest developments and the likely future trends are also presented. Neither of these methodologies represents a best option on all fronts. The goal of this work is rather to highlight what each technique has to offer and what application are they better suited for

Control of detergent properties in a spray dryer process

EngDThis research details the building, implementation and validation of models designed for the control of specific powder detergent properties in a spray dryer process. Findings are reported in two sections; the control of moisture content, particle size distribution (PSD) and bulk density properties; the development of a process model for the online estimation and simulation of the process. The project was completed at Procter & Gamble’s Newcastle Innovation Centre, using a mixed flow spray dryer for the case study. Moisture content can be controlled using a soft sensor to enable estimation of this parameter at a higher sampling frequency than manual measurements of the powder. The proposed empirical model proved to be the most successful approach compared to heat and mass balances. Each model required adjustment of a parameter following the first manual measurement of moisture in a batch run. Control of PSD can be achieved through analysis of droplet size distribution. The dominant influence on the final PSD is the atomization of the slurry, which can be manipulated through changes to the ratio of air and slurry flow to the nozzle. However, numerous sources of variability necessitate continuous amendments to the atomizing air flow rate to maintain the PSD at the required target value. The use of an automatic cascade loop control strategy facilitated manipulation of the air flow to the nozzle, improving control of PSD considerably, halving the response time and reducing variability of mean particle size. Control of bulk density is dependent on an understanding of the key factors that determine the final density of the powder. The density model proposed incorporates statistics for the impact of packing, air entrapment and drying. The model details the limits of the rate of air injection into the slurry, its influence on density control and provides explanations for density changes during the process. viii Separate studies demonstrate the influence of each property on process conditions in each compartment of the mixed flow spray dryer. A model linking these properties to the process conditions has been formulated to provide optimal control strategies for the process. The spray drier involves 3 compartments; a spray chamber, an inner fluid bed and an outer fluid bed. Computational fluid dynamics are used to estimate flow properties and residence times of the chamber and a CSTR model is used to model the fluid beds. The constant drying rate curve (CDRC) and reactor engineering approach (REA) drying models have been implemented and fitted using historical data. A sigmoidal model approach to the CDRC has been included to enable a smoother transition between the constant and falling rate periods. Simulation of the process and online estimations of the powder’s properties were assessed. In each batch, the CDRC model provided the most accurate representation of the process. The CDRC model is recommended for control of the spray drying process and in simulation studies

Inverse solid-liquid fluidization of aerogel granules and its application in removing oil from water

Fluidization is a very well known unit operation used in the chemical industry for various purposes. Inverse solid-liquid fluidization, where the solid particles to be fluidized are less dense than the fluid, is one of the several different kinds of fluidization being studied for its potential in industrial applications. The present work focuses on finding the hydrodynamic characteristics (minimum fluidization velocity, bed expansion and pressure drop) of an inverse fluidized bed of aerogel granules and using this system to remove oil from an oil-water mixture. The solid particles employed for this study are low density (100 kg/m3) surface treated hydrophobic aerogel (Nanogel®) granules of size in the range of 0.5 to 2.3 mm. These particles are highly porous characterized by a nanosized pore structure and a very high surface area. Since their density is lower than water, they are fluidized downward in a solid-liquid inverse fluidized bed column. In this work, a constant flow of an oil-water mixture is passed through an inverse fluidized bed of aerogel granules. The oil concentration was determined by measuring the Chemical Oxygen Demand (COD) using a colorimeter. Once the aerogel granules are saturated, they were entrained from the fluidized bed, and separated from the clean stream of water with a fibrous filter

Modeling, identification and control of a cold flow circulating fluidized bed

Circulating fluidized bed (CFB) is used extensively in petrochemical industries especially for fluid catalytic cracking, coal combustion or gasification and various other chemical processes. In this work, data are used to identify cold flow circulating fluidized bed\u27s (CFCFB) multiple sub models and to combine them into a single nonlinear model such that solids circulation rate can be estimated from the move air flow and riser aeration fed to the device, and the total pressure drop developed across the riser at extremely different experimental conditions.;The present work begins with a complete black box model of a state-space description arising from the system identification and converts it into a model without any fictitious variable such that the interaction among the variables under consideration can be analyzed. Furthermore, this concept separates a state into stochastic and deterministic components which gives the nature of noise acting on the measurement device and rationalizes if there exists a certain relationship between independent and dependent variable. In this thesis, the state is a solids circulation rate. Independent parameters that comprise of aerations flow rates including move air flow, riser aeration and loop seal fluidization air are used to obtain deterministic component of a measured solids circulation rate. On the other hand, easily measurable dependent variables like the pressure drops across various sections of the machine are used to predict its stochastic counterpart.;A real time pressure drop model based on the Recursive Prediction Error Method (RPEM) is built to predict the split of move air flow between the standpipe and L-valve. The split estimate is of paramount importance while simulating the phenomenological model of the standpipe or in other applications, if required. Additional aeration fed across the various sections of standpipe act as the fluidization bias and their routes determination within the component may help to maintain their required level to assist in solids movement during operation while minimizing excessive flows. The path determination is also predicted using RPEM on a discrete time pressure drop model such that the user can operate them at the desired intensity according to their operating requirements.;Generally, a PID controller is not portable , i.e., a controller designed for one plant is usually not applicable to another plant. To resolve this long-standing issue of portable controllable design, the controller scaling method can be used to control similar plants that are different only in gain and frequency scales, thus avoiding tedious control redesign. The adaptive PID control algorithm is then tested on the benchmark NETL CFCFB plant by controlling solids circulation rate according to the reference solids flow rate obtained from the Knowlton\u27s correlation utilizing average voidage in a moving bed condition and the move air flow.;The optimal control of solids circulation rate affecting the heat and mass transfer characteristics which in turn impacts the efficiency of various chemical processes is necessary in CFB units. An example might be the catalytic systems that recirculate catalyst in a reaction/recirculation cycle. In the case of such units in which the addition of catalyst is small and need not be steady, the main solids flow-control problem is to maintain balanced inventories of catalyst in and controlled flow from and to the reactor and regenerator. This flow of solids from an oxidizing atmosphere to a reducing one, or vice versa, usually necessitates stripping gases from the interstices of the solids as well as gases absorbed by the particles. Steam is usually used for this purpose. The point of removal of the solids from the fluidized bed is usually under a lower pressure than the point of feed introduction into the carrier gas. The pressure is higher at the bottom of the solids draw-off pipe due to the relative flow of gas counter to the solids flow. The gas may either be flowing downward more slowly than the solids or upward. The standpipe may be fluidized, or the solids may be in moving packed bed flow with no expansion. Gas is introduced at the bottom (best for group B) or at about 3-m intervals along the standpipe (best for group A). The increasing pressure causes gas inside and between the particles to be compressed. Unless aeration gas is added, the solids could defluidize and become a moving fixed bed with a lower pressure head than that of fluidized solids. Thus, this observation leads to the fact that the gas velocity in the standpipe might be the main parameter to control the solids circulation rate. (Abstract shortened by UMI.)

The effects of a counter-current interstitial flow on a discharging hourglass

This work experimentally investigates the effects of an interstitial fluid on the discharge of granular material within an hourglass. The experiments include observations of the flow patterns, measurements of the discharge rates, and pressure variations for a range of different fluid viscosities, particle densities and diameters, and hourglass geometries. The results are classified into three regimes: (i) granular flows with negligible interstitial fluid effects; (ii) flows affected by the presence of the interstitial fluid; and (iii) a no-flow region in which particles arch across the orifice and do not discharge. Within the fluid-affected region, the flows were visually classified as lubricated and air-coupled flows, oscillatory flows, channeling flows in which the flow preferentially rises along the sidewalls, and fluidized flows in which the upward flow suspends the particles. The discharge rates depends on the Archimedes number, the ratio of the effective hopper diameter to the particle diameter, and hourglass geometry. The hopper-discharge experiments, as well as experiments found in the literature, demonstrate that the presence of the interstitial fluid is important when the nondimensional ratio (N) of the single-particle terminal velocity to the hopper discharge velocity is less than 10. Flow ceased in all experiments in which the particle diameter was greater than 25% of the effective hopper diameter regardless of the interstitial fluid

A study of the impact of intelligent well technology on reservoir development

Abstract unavailable please refer to PDF

Measurement of Interphase Forces based on Dual-modality ERT/DP Sensor in Horizontal Two-phase Flow Gas-water

In order to better understand the mechanisms of two-phase flow and the prevailing flow regimes in horizontal pipelines, the evaluation of interphase forces is paramount. This study develops a method to quantitatively estimate the interphase force in two-phase gas-water flow in horizontal pipeline. The electrical resistance tomography technology is used to measure the void fraction, while the differential pressure perpendicular to the horizontal pipe is measured in different flow patterns via a Differential Pressure sensor. The inner pipe diameter is 50 mm, the water flow range from 3.26 m3/h to 7.36 m3/h, the gas flowrate range from 1 to 60 l/min, which covered a range of flow patterns, the absolute pressure range from0.07 MPa to 0.12 MPa. The relationship between the differential pressure drop and interphase force is established, and the effects of these forces on the flow are analyzed. Experimental results indicate that the dual-modality measurement system was successfully provided a quantitative evaluation of inter-phase forces in two-phase horizontal gas-water flow

Experimental investigation of the pebble bed structure by using gamma ray tomography

Pebble Bed Reactors offer a future for new nuclear energy plants. They are small, inherently safe, and can be competitive with fossil fuels. The fuel forms a randomly stacked pebble with non-uniform fuel densities. The thermal-mechanical behavior of pebble bed reactor core is depends strongly on the spatial variation of packing fraction in the bed and in particular on the number of contacts between pebbles, and between the pebbles and the blanket walls. To investigate these effects, experimental data to characterize bed structure are needed along with other numerical simulation and computational tools for validation. In this study, a powerful technique of high-energy gamma-ray computed tomography (CT scanner system) is employed for the first time for the quantification of the structure of pebble bed in term of the cross-sectional time-averaged void and distributions, it radial profiles and the statistical analysis. The alternative minimization (AM) iteration algorithm is used for image reconstruction. The spatial resolution of the CT scan is about 2 mm with 100 x 100 pixel used to reconstruct the cross-sectional image. Results of tomography with this advanced technique on three different pebble sizes at different axial levels are presented. The bed consisted of a glass spheres (Marbles) with a diameter d1= 1.27 cm, d2= 2.54 cm and d3= 5 cm in a Plexiglas cylinder with diameter D = 30.48 cm (D/d1 = 24, D/d2 = 12 and D/d3 = 6), and had an average void fraction ε̄1= 0.389, ε̄2= 0.40 and ε̄3 =0.43, respectively. The radial void fraction profile showed large oscillations with the bigger pebble diameters and the void fraction is higher on the wall with a minimum void fraction of 0.33 at 0.68 pebble diameter away from the wall. It was found that the void distribution in random packed bed depends strongly on the pebble diameter with respect to the bed diameter (D/dp) and the packing mode. The oscillation is quiet large with the smaller aspect ratio (D/dp) and decreases as the aspect ratio increases (D/dp). It has been shown that increasing the bed height has no influence on the radial void fraction at the three levels of the bed. It can be seen that there is an agreement between the experimental results and the exponential expression model at the smaller sphere diameter (D/dp=24). Comparison between the experimental and calculated methods were presented and discussed --Abstract, page iii

Hydrodynamic of a co-current gas liquid upflow in a moving packed bed reactor with porous catalysts

In this study, the hydrodynamic, i.e. flow regime identification, line average liquid holdup, and the internal liquid holdup of a co-current moving packed bed reactor were studied. For the sake of hydrodynamics study, moving bed reactor is investigated as two-phase upflow packed bed reactor. Scaled down configuration was used to simulate of the moving bed reactors utilized in the industrial process. First, line average liquid holdup is measured with different geometrical configurations covering empty, dry, wet, and packed column under flowrates operation conditions. A new methodology has been developed to determine the line average liquid holdup for a porous catalyst. Second, flow regime is identified by variation of superficial gas velocity at constant liquid superficial velocity. The experiments were carried out in an 11 - inch inner diameter Plexiglas column using the air-water system, at superficial gas velocities in the range of 0.6 to 7.7 cm/s and at a constant liquid superficial velocity of 0.017 cm/s. Gamma ray densitometry (GRD) technique was used to obtain the line average liquid holdup and to identify the flow regime at different axial and radial positions along the column. The obtained results showed that the flow regimes are bubble flow and pulse flow regimes with a transition flow in-between under the operation conditions used. The result showed that the liquid holdup decreased as the superficial gas velocity increased. It was also found that the liquid holdup radial distribution was not uniform. These kinds of information are essential to improve the performance of the reactor --Abstract, page iv