Pneumatically Controlled Multi-Stage Fluidized Beds

Comparison of hydrodynamics and operational characteristics of a multistage fluidized bed with high-density and low-density powders

Dynamic characterizations of gas–solid flow in a novel multistage fluidized bed via nonlinear analyses

The overall objectives of this project are to develop experimental techniques for measuring the forces of fluidized particles, and to predict the solid-gas performance in fluidized beds by using data analysis system, and by elucidating the intrinsic mechanism of erosion and attrition phenomena in fluidized beds. The reduction of erosion and attrition rates is one of the critical engineering problems for the design and operation of fluidized bed combustors. Specifically, the objectives are to: (1) develop the experimental techniques to measure the forces of solid particles prevailing in fluidized beds: (2) measure and characterize the forces of solid particles in various types of fluidized beds with various configurations (conventional and spouted fluidized beds) and with different scales (10, 20, and 30cm) under various fluidization conditions (particle size, bed aspect ratio and gas velocity); (3) find and verify the mechanism of erosion rates of in-bed tubes and attrition rates of fluidized particles by forces of solid particles in fluidized beds. We developed three different kinds of measurement methods, i.e., fracture sensitive sensor, piezoelectric sensor and gas pressure fluctuation method. By using these methods the exact forces of solid particles, including the transient corporate in fluidized beds, were systematically measured. Simultaneously, the erosion rates of in-bed tubes and attrition rates of fluidized particles were measured. 69 figs., 9 tabs.

The storage of thermal energy has been hindered by the low heat-transfer rate of the solid phase of the phase-changing materiel. With water being the heat-transfer fluid as well as the liquid phase in the liquid–solid two-phase system, a novel type of fluidized bed is designed in this study. Numerous hollow spheres are fabricated with phase-changing materiel encapsulated. Adding the solid–liquid phase-change material capsules to the flowing fluid, the capsules are dispersed suspended in the carrier. The large spheres, 25 mm in present experiment, possess the merits of guaranteeing energy-storage density and tolerating internal interface chaotic motion. Both the fluidization status and phase-changing process are recorded by photography combined with image-processing technology. It is found that the large spheres, with density less than water, can be fluidized by the downward flowing fluid. As the flow rate increases, the expansion ratio of the solid phase increases and the regimes of incipient fluidization and bubbling fluidization can be observed. In comparison to the fixed bed, the oscillation of pressure drop across a fluidized bed is more severe, but the averaged value is less than the fixed bed. The melting and solidifying can be accelerated by 22.6% and 50%, respectively, thus proving the superiority of the fluidized bed in improving the heat-transfer rate while charging/discharging the thermal energy. Three types of basic movement of the spheres are shown to contribute to the enhanced phase-changing rate, which are shifting, colliding and rotating.

Currently there are significant amounts of natural gas that cannot be produced and treated to meet pipeline specifications, because that would not be economically viable. This work investigates a bench scale multistage fluidized bed (MSFB) with shallow beds for sour gas removal from natural gas using a commercially available supported amine sorbent. A MSFB is regarded as a promising adsorber type for deep sour gas removal to parts per million concentrations. A series of experiments was conducted using carbon dioxide as sour gas and nitrogen to mimic natural gas. Removal below 3 mol ppm was successfully demonstrated. This indicates that gas bypassing is minor (that is, good gas–solid contacting) and that apparent adsorption kinetics are fast for the amine sorbent applied. Tray efficiencies for a chemisorption/adsorption system were reported for one of the first times. Current experiments performed at atmospheric pressure strongly indicate that deep removal is possible at higher pressures in a multistage fluidized bed.

Mechanical and dynamical characteristics of semifluidized beds of single‐size particles in solid‐liquid system were investigated. A semifluidized bed is a type of fluidized bed in which the bed expansion is partially restricted. The emphasis was placed on the study of packed bed formation and pressure drop increase when the semifluidized beds were formed by the compression of fluidized beds. The data showed good agreement with the theoretical and semiempirical equations based on a simple model of fluidized beds.The results of this investigation would also contribute to the understanding of fluidized beds.

Process simulation of an efficient temperature swing adsorption concept for biogas upgrading

Experimental and theoretical studies were carried out to investigate the performance of a batch, fluidized/expanded ion-exchange system. Exchange of phenylalanine on cation exchange resin was studied in the linear velocity range 5.5-39.8 cm/min. The breakthrough curves were obtained at various design and operating conditions with changes of column size, distributor, bed type, bed height, flow rate, and number of stages. The breakthrough data were analyzed by two theoretical models. A CSTR-type model which we called a lumped model fitted the data well when bed aspect ratio (bed height/bed diameter) was less than 1.5 and column diameter was less than 4 cm. We considered the fluidized bed as a bed that can be well simulated by the lumped model (uniform mixing), and the expanded bed as a bed where the lumped model fails because of reduced backmixing. Another model, which is adapted from a packed bed model (VERSE) with axial dispersion, film diffusion, and intraparticle diffusion, fitted the data for both fluidized beds and expanded beds successfully. Experimental and theoretical results showed the bed type changed from a fluidized bed to an expanded bed as the bed aspect ratio increases. The breakthrough curves for the expanded bed and a packed bed were almost identical except at very short times. When sieve plates were used as liquid distributors, the plate with more holes of a smaller size was most efficient. Mass transfer at different flow rates and the effects of bed type and multiple stages are discussed

In the present study reduction of nitrogen oxides using reburning technology, during combustion of sewage sludge (fuel I) and the mixture of sewage sludge, wasted bleaching earth and CaO (fuel II), was carried out. The experimental works were conducted in a laboratory-scale fluidized bed reactor (power up to 10 kW) with application of two types of beds: chemically inert bed (sand) and chemically active bed (CaO). The second combustion (reburning) zone in the reactor was formed by dosing into an area above the bed, additional gaseous fuel (propane). Obtained reduction in emissions of nitrogen oxides in both types of beds was at a level 70% - 79%. Additionally bed of CaO has the desulfurizing effect and also reduces the CO concentration in the exhaust fumes. A significant drawback of active bed is the adverse effect on increase of the primary NO which enters the second combustion zone. The result of this fact is higher NOx emission during combustion of the same fuel in bed of CaO in comparison to the combustion of this fuel in the sand bed, when the same maximum degree of reduction of NOx will be obtained for both types of beds.

Fundamental particle fluidization behavior and handling of nano-particles in a rotating fluidized bed

The local void around a sphere in a packed bed or in the emulsion phase of a fluidized bed has been calculated theoretically; and measured as a function of the radial distance from the centre of the sphere. Effects of this distribution on the burning rate and Sherwood number have been investigated for two types of bed e.g. where inerts are of the same size as the carbon particle and where the inerts are smaller than the carbon particle. Even though the present analysis studies the effect on the diffusive component of the mass transfer alone, the results suggest that the distribution of voidage will yield Sherwood numbers higher than that calculated from the constant voidage assumption. The voidage distribution explains the increase in burning rate of carbon with increasing size of the inerts.

BackgroundThe article is devoted to the development of new utilization methods of exhaust gases by cleaning them from fine particles, dust and harmful gas components. The basic design solutions, which allow to increase the degree of exhaust gases cleaning, were presented. The effectiveness of design solutions was supported by the results of experimental studies. Analysis of the research results allowed developing of new designs of equipment for dehydration in fluidized bed. The article also presents the calculation algorithm of eco-friendly dryers with fluidized bed.MethodsPhysical modeling was based on methods of similarity theory. In studies in dryers experimental models the installation scale was changed (compared with industrial conditions). Geometric similarity was maintained by equity of constants and invariants of geometric similarity. Always similarity of respective particles movement and their trajectories in industrial design and in experimental models was also maintained. The creation of graphical dependences was carried out by differential methods of mathematical analysis and integral calculus. The reliability of obtained experiment results was caused by the application of time-tested in practice methods.Results and discussionControl of product fractional composition allowed to make a selection of required fractions (including the fine granules) in a certain place of device. This allowed to increase the degree of purification of exhaust gas even before it output from the dryer working space. The process of separating the granules into fractions and the selection of fine fraction can be performed due to structural changes in dryer units and selection of optimal hydrodynamic conditions of fluidizing agent motion. Installation of special units in the dryers allowed to extract other contaminants from the exhaust gases.ConclusionsProposed constructive solutions for fluidized bed dryers allowed to:- provided of granules classification to the desired number of fractions with a simultaneous release and discharged of fine fraction from the working volume of dryer without the exhaust gases;- increased the degree of monodispersity of commodity granules on 25–35%;- reduced the amount of dust in the exhaust gases on 35–65%;- reduced the ammonia content in the exhaust gas on 90–95%.

In the industrial processes that employ the fluidized bed technology (gasification of coal or biomasses, polymerization, etc.), solids of various kinds are simultaneously subjected to fluidization. Due to the fact that solids that differ in density and/or size differently react to the frictional force exerted by the gas stream, mixtures of two solids tend to form, when fluidized, segregated layers rich in either of their components. A peculiar case, in this frame, is that of homogeneous mixtures whose denser component is also the smaller one and achieves the fluidized state at the bottom of the column, while the other solid, bigger and lighter, forms a packed layer on top of it.With reference to this special type of binary systems, several series of experiments are presented that provide their initial and final fluidization velocities at varying composition. Following what done in a recent study on beds of two solids differing in density or size, it is shown that the theoretical equations for calculating uif and uff keep their validity even when applied to mixtures that exhibit an unusual fluidization pattern. Calculated values of the initial and final fluidization velocities are characterized by a low error level, fully comparable with that encountered with other types of binary beds.

In this paper the operation and performance of a high temperature solid oxide fuel cell (SOFC) stack on biomass syn-gas from a demonstration biomass gasification combined heat and power (CHP) plant is investigated. The objective of this work is to develop a computer simulation model of a biomass-SOFC CHP system, flexible enough for use in industry, capable of predicting system performance under various operating conditions and using diverse fuels. The biomass gasifier is of the dual fluidised bed (DFB) type with steam as the gasifying agent and is operated at atmospheric pressure. The tubular SOFC configuration, developed by Siemens Power Generation Inc (SPGI), is selected. It is considered to be the most advanced design and is approaching commercialisation. The SOFC stack model, developed using the chemical process flowsheet simulator Aspen Plus, is of equilibrium type and is based on Gibbs free energy minimisation. The SOFC model performs heat and mass balances and considers the ohmic, activation and concentration losses for the voltage calculation. Data available in the literature on the SPGI SOFC operating on natural gas is used to validate the model. The system model predicts thermodynamic condition and composition of all internal flow streams, the heat generated by the SOFC stack, voltage (V), current (I) and efficiency. Operating parameters are varied over a wide range, parameters such as fuel utilisation factor (Uf), current density (j) and steam to carbon ratio (STCR) have significant influence. The results indicate that there must be a trade-off between voltage, efficiency and power with respect to j and the SOFC stack should be operated at low STCR and high Uf, within certain limits. SOFC stack operation on biomass syn-gas is compared to operation on natural gas and as expected there is a drop in performance, which is attributed to increased input fuel and air flow due to the lower quality of the fuel gas. The optimum realistic operating conditions with regard to SOFC stack performance are identified. High electrical efficiencies are predicted making these systems very attractive for CHP applications.

E Butenko* Author Affiliations Azov Sea State Technical University, Ukraine Received: April 30, 2019 | Published: May 03, 2019 Corresponding author: E Butenko, Azov Sea State Technical University, Ukraine DOI: 10.26717/BJSTR.2019.17.003044