Bed Pressure Drop Research Articles

Heat transfer and hydrodynamics of particles mixture in swirling fluidized bed

This work is an experimental study of heat transfer and bed hydrodynamic parameters affecting a bed particles-mixture in a swirling fluidized bed reactor. Two different materials (Geldart type- D), polyethylene (PE) beads with a diameter of 6 mm and sand with a mean diameter of 1.5 mm were used as bed materials fluidized by air. Different mass fractions of PE beads (0.25, 0.5 and 0.75) were used. The bed-wall heat transfer coefficient was calculated for different inlet air velocities and different axial heights. Both minimum fluidizing and minimum swirling velocities increased with increasing PE mass fraction. Increasing amount of PE beads increased the pressure drop of the bed. While increasing the percentage of PE beads resulted in decreasing the local heat transfer coefficient. The heat transfer coefficient reduced with increasing bed height for all PE beads mass fraction. The effect of using a central body with a cone shape on the operation of the reactor was also studied. Using a central body with cone shape causes enhancing the heat transfer and bed flow processes as a result of increasing the coefficient of heat transfer and decreasing bed pressure drop.

Computational investigation of hydrodynamics and solid circulation in fluidized bed column

Gas–solid fluidized beds are commonly used in applications where high heat and mass transfer is required, which are influenced by the quality of mixing in the bed. This largely depends on the design of gas distributor and operating conditions. Hence, in the current work, the influence of distributor design on hydrodynamics in a 3D bubbling fluidized bed column is investigated using CFD. Here, Euler-Euler model is used to predict the flow field. The predicted bed pressure drop is analyzed for various superficial gas velocities, and it has been validated with the experimental data. The solid circulation rate is calculated to quantify the flow field, and it is improved by incorporating various gas distributors such as flat, convex and concave perforated plates. The magnitude of solid circulation rate is found to be the highest for convex plate, showing that it is more advantageous than the conventional flat plate configuration. Further, the effect of operating temperature and the influence of baffle on gas–solid flow are analyzed. The rate of solid circulation is found to decrease with increase in temperature and in the presence of baffle.

Effect of interparticle force on gas dynamics in a bubbling gas–solid fluidized bed: A CFD-DEM study

The influence of cohesive interparticle force (IPF) on gas dynamics in a bubbling gas–solid fluidized bed was numerically investigated while the bed hydrodynamics was described with the help of computational fluid dynamics and discrete element method (CFD-DEM). The model was validated by experimental results in terms of total bed pressure drop profile, probability density distribution of instantaneous local bed voidage signals, and Eulerian solid velocity field. The results showed that the model can satisfactorily predict the hydrodynamics of a bubbling gas–solid fluidized bed that is impacted by the presence of cohesive IPF. The validated CFD-DEM model was adopted to delineate the effects of IPF on the distribution of fluidizing gas between the bubble and emulsion phases and bubble characteristics, such as bubble stability and rise path, which could hardly be explored experimentally. Simulation results revealed that the presence of IPF in the bubbling bed alters the distribution of the fluidizing gas between the bubble and emulsion phases in favor of an increase in the propensity of gas to pass through the bed in the emulsion phase. The results also indicated that the bubble stability increases and the straight rise path of bubbles changes to a tortuous path when enhancing IPF.

Adsorption of volatile organic compounds on modified spherical activated carbon in a new cyclonic fluidized bed

Volatile organic compounds (VOCs) are severe environmental pollutants that pose a serious threat to human health. In this study, a new type of cyclonic fluidized bed was designed to carry out absorption of VOCs by activated carbon, in which the collision and adsorption between activated carbon particles and VOC moleculars were enhanced by three-dimensional rotating turbulent shear. We studied the VOC adsorption efficiency of three kinds of modified spherical activated carbon (SAC-1, SAC-2, and SAC-3) and five kinds of cyclonic fluidized bed (S11-44, S11-33, S11-22, S13-22, and S16-22). The pressure drop of the cyclonic fluidized bed under different inlet flow rates, activated carbon dosages, and inlet VOC concentrations were also investigated. The results indicate that smaller inlet flow rate, larger activated carbon dosage, larger diameter and smaller inserted depth of the cyclone fluidized bed overflow pipe will lead to lower pressure drop and higher VOCs adsorption efficiency. The pitch-based SAC-1 and the S16-22 cyclonic fluidized bed had the highest adsorption efficiency (100%) and the lowest pressure drop (120 Pa). This study not only benefits VOC absorption but also serves as a useful guide for the development of cyclone separation technology in industrial processes.

Performance enhancement by optimizing the reformer for an internal reforming methanol fuel cell

AbstractInternal reforming methanol fuel cell (IRMFC) has potential applications in portable or stationary power supply system, but currently performance of the IRMFC is limited by the low hydrogen production of its reformer. In order to produce more hydrogen with less volume, in this paper a single channel serpentine packed bed reformer was designed, and its bed size was optimized by experiment and numerical simulation to enhance heat transfer and increase catalyst utilization. It was found that with the bed diameter from 5.8 mm down to 3.8 mm, the reformer temperature distribution was more uniform but the bed pressure drop increased a lot. Considering performance and pressure drop, the reformer of 5 mm was optimal, per milliliters of which could supply 9.8 mL/min hydrogen at 453 K, almost twice as much as that by A. Mendes et al with one‐third of their catalyst loading. The reformer was quite stable, and less than 10% decline in methanol conversion was observed during the 100 hours period at 473 K. When incorporated into an IRMFC single cell, power density of the single cell reached 0.45‐0.55 W/cm2 at 453‐473 K under CH3OH solution and air feed, the highest in existing reports. The main drawback has to do with low stability of the IRMFC single cell at high current density.

Comparing ANSYS Fluent® and OpenFOAM® simulations of Geldart A, B and D bubbling fluidized bed hydrodynamics

PurposeThe purpose of this study is to assess the performance of ANSYS Fluent® and OpenFOAM®, at their current state of development, to study the relevant bubbling fluidized bed (BFB) characteristics with Geldart A, B and D particles.Design/methodology/approachFor typical Geldart B and D particles, both a three-dimensional cylindrical and a pseudo-two-dimensional arrangement were used to measure the bed pressure drop and solids volume fraction, the latter by digital image analysis techniques. For a typical Geldart A particle, specifically to examine bubbling and slugging phenomena, a 2 m high three-dimensional cylindrical arrangement of small internal diameter was used. The hydrodynamics of the experimentally investigated BFB cases were also simulated for identical geometries and operating conditions using OpenFOAM® v6.0 and ANSYS Fluent® v19.2 at identical mesh and numerical setups.FindingsThe comparison between experimental and simulated results showed that both ANSYS Fluent® and OpenFOAM® provide a fair qualitative prediction of the bubble sizes and solids fraction for freely-bubbling Geldart B and D particles. For Geldart A particles, operated in a slugging mode, the qualitative predictions are again quite fair, but numerical values of relevant slug characteristics (length, velocity and frequency) slightly favor the use of OpenFOAM®, despite some deviations of predicted slug velocities.Originality/valueA useful comparison of computational fluid dynamics (CFD) software performance for different fluidized regimes is presented. The results are discussed and recommendations are formulated for the selection of the CFD software and models involved.

High efficiency of toluene adsorption over a novel ZIF-67 membrane coating on paper-like stainless steel fibers

A novel microporous ZIF-67 membrane coating on paper-like stainless steel fibers (ZIF-67 membrane/PSSF) was successfully synthesized by a wet layup papermaking-sintering method followed by the seed-induced growth method. The effects of key factors such as crystallization temperature, synthesis time and Hmim/Co2+ (2-methylimidazole/cobalt chloride) molar ratio on the morphology structure of the samples were studied by the modern characterization techniques including SEM, EDX, TEM, XRD, BET, FTIR and TGA, respectively. The experimental result indicated that the as-synthesized ZIF-67 membrane/PSSF was extremely compact with the average membrane thickness of 4.8 μm. And the sample exhibited high BET surface area (440.9 m2/g), uniform pore size (1.881 nm) and large pore volume (0.2096 cm3/g). The adsorption breakthrough experiment of toluene was performed on different bed reactors filled with ZIF-67 membrane/PSSF and granular ZSM-5 zeolites, respectively. The experiment data was well fitted by Yoon–Nelson model, where the values of rate constant in the fixed bed with ZIF-67 membrane/PSSF increased by 32.2% compared with that of commercial ZSM-5 zeolites at the flow rate of 100 mL/min. And the bed pressure drop and length of unused bed (LUB) were dramatically reduced by 39.6% and 16.8% in 3 cm ZIF-67 membrane/PSSF fixed bed. In conclusion, mass transfer efficiency was significantly enhanced based the structured ZIF-67 membrane/PSSF fixed bed, and this new material is a promising adsorptive material for VOCs removal.

Experimental hydrodynamic and bed characteristics of co-current gas-liquid-solid three phase semifluidization with liquid as the continuous phase

In this study, hydrodynamic parameters such as minimum liquid phase fluidization velocity semifluidization velocity pressure drop and height of top packed bed formation of a co-current gas-liquid -solid multiphase semifluidized bed were studied using the liquid as the continuous phase and air as the dispersed phase. Air, water, and acrylic beads of various sizes were used to represent the gas, liquid, and solid phases, respectively. The experiments were conducted in a vertical perspex column. The liquid and gas was co-currently fed into the column with varying flow rate. The column has three sections comprising of gas-liquid release section, main section, and gas-liquid distributor section, respectively. The significant outcomes of this study are reduced minimum fluidization velocity ranging from 0.004 to 0.01 m/s and minimum semifluidization velocity of 0.032–0.006 m/s compared to reported high values. Maximum bed pressure drop was found to be 5.6 kPa. Empirical mathematical correlations that represent the hydrodynamic and bed characteristics were developed from the experimental data which are also a new aspect of this study. Model results fitted well to the experimental values and the values obtained are quite useful for the various industrial application.

CFD-DEM modelling of mixing of granular materials in multiple jets fluidized beds

Jetting fluidized beds are widely used in industries for mixing of granular materials. The mixing efficiency is affected significantly by the number of jets and their locations. In this work, discrete particle model is used to simulate fluidized beds with different jet numbers, and the results are validated by physical experiments. Cases with different jet numbers (varying from one to five) but the same gas flow rates are compared in terms of the maximum bed pressure drop, bed height, mixing index, particle velocities and contact number. The results show that different jet numbers result in different flow patterns, which severely affect the mixing efficiency. The mixing efficiency in the one-jet case (spouted-bed) is 1.5–3 times higher than other cases due to a higher jet velocity and umbrella-type flow pattern. For the multiple jets, bubbles and vortex can form and promote particle mixing but not as efficient as the case of one jet. However, particle contacts in multiple jet cases is more uniform than the one-jet case. This implies that from the perspective of particle heat transfer, multiple jets can behave better than one jet.

Coarse-grained CFD-DEM simulation of biomass gasification in a fluidized bed reactor

Gas-solid fluidized beds play an important role in many industrial operations. However, there still is a lack of knowledge concerning the processes inside the bed, which impedes proper designing and upscaling of fluidized bed reactors. In this work, biomass steam gasification in a fluidized bed reactor is investigated with a coarse-grained CFD-DEM approach.The numerical model in the Eulerian-Lagrangian framework treats the gas phase as a continuum and describes the particle interactions with the discrete element method (DEM). The non-spherical shape of the particles is accounted for in the momentum exchange calculation with the gas phase. The considered systems consist of steam as the fluidization gas, entering the bottom region of the three dimensional reactor geometry through inclined nozzles in an inner duct at the center axis. The wood pellets are fed into the reactor from the top of the freeboard together with a nitrogen purge gas stream. Over time, different operation modes occur, since there is no solids removal from the gasifier and unconverted material is continuously added to the bed.Three different operation modes are investigated. For the start-up procedure, the reactor is filled with 2.565 kg of sand particles. The inert material is allowed to settle for three seconds and is fluidized for another three seconds until quasi steady-state is achieved. Afterwards, the wood pellets are added for 35 s at a rate of one pellet every two seconds and undergo the processes of heating, drying, pyrolysis and char conversion. From the simulation results and literature correlations, the average time intervals for pyrolysis and char conversion, as well as the respective particle properties (temperature, diameter, density) are estimated. With the knowledge of the average composition of reactive material in the reactor, variable operating points can be simulated.The other two cases investigated are after approximately 20 and 50 h of operating time. Additionally to the start-up procedure, 0.6 and 1.5 kg of inert residue are added to the sand particles. Again, the inert material is allowed to settle for three seconds and is fluidized for another three seconds. Subsequently, the average reactive material obtained from the start-up simulations is patched into the fluidized bed and wood pellets are fed to the freeboard.The following phenomena are implemented in the numerical model: gas-solid momentum exchange, solids collisional behavior, heat and mass transfer, particle shrinkage and change in material properties, pyrolysis, as well as homogeneous and heterogeneous chemical reactions.Simulation results are analyzed both qualitatively and quantitatively. The particle flow fields and the mixing between sand, residue, and wood are investigated for different fillings of the reactor. Bed pressure drop, product gas composition, and temperature are compared to experimental data in order to validate the numerical model.The results show, that the bed pressure drop, the gas composition, and the conversion time obtained with the numerical simulation agree well with experimental observations and literature correlations. This indicates that the proposed model can make a significant contribution towards understanding and improving the internal processes in fluidized bed reactors for biomass gasification and combustion.

The Effect of Very Cohesive Ultra-Fine Particles in Mixtures on Compression, Consolidation, and Fluidization

This paper focuses on the effect of ultra-fine ( d < 10 µm) powders in mixtures with fine ( d < 100 µm) bulk material on compression processes and also evaluates the re-fluidization behavior of the compressed bed (history effect). Achieving this goal, different mixtures of fine and ultra-fine Ground-Carbonate-Calcium were compressed at three pressure levels. The results show that by increasing the applied pressure, the compressibility decreases due to change in compaction regime. Subsequently, for the higher pressure, the slope of packing density versus applied stress curves is noticeably different. However, this slope does not depend on the size distribution of mixtures, but on the type of material. Comparing fluidization and re-fluidization curves (bed pressure drop vs. gas velocity) shows an increase in the maximum bed pressure drop ( Δ P p e a k ) for re-fluidization. By increasing the portion of ultra-fine particles in the binary mixture, Δ P p e a k increases in a non-linear manner. Furthermore, the incipient fluidization point moves to a higher gas velocity. After compression, the peak of the bed pressure drop in the re-fluidization test happens at a lower gas velocity than in the initial fluidization test. Thus, the slope of the loading curve is much larger for re-fluidization. The opposite is observed for the unloading curves.

Uncertainty quantification of fluidized beds using a data-driven framework

We carried out a nondeterministic analysis of flow in a fluidized bed. The flow in the fluidized bed is simulated with National Energy Technology Laboratory's open source multiphase fluid dynamics suite MFiX. It does not possess tools for uncertainty quantification. Therefore, we developed a C++ wrapper to integrate an uncertainty quantification toolkit developed at Sandia National Laboratory with MFiX. The wrapper exchanges uncertain input parameters and key output parameters among Dakota and MFiX. However, a data-driven framework is also developed to obtain reliable statistics as it is not feasible to get them with MFiX integrated into Dakota, Dakota-MFiX. The data generated from Dakota-MFiX simulations, with the Latin Hypercube method of sampling size 500, is used to train a machine learning algorithm. The trained and tested deep neural network algorithm is integrated with Dakota via the wrapper to obtain low order statistics of the bed height and pressure drop across the bed. In addition, it can be used to obtain statistics with various distributions of the uncertain input variables and various uncertainty quantification methods. In addition, sensitivity analysis is carried out for 9 input parameters and two output parameters.

Transport hydrodynamics of particles in a gas–solid cyclone reactor using a dense discrete phase model and a particle size segmentation method

A downward gas–solid cyclone reactor (GSCR) was designed for the fluid catalytic cracking. It is expected that the over–cracking of light products can be suppressed by the gradient distribution and short residence time of particles. Besides, the mass and heat transfer of reactants are enhanced due to the existence of the swirling flow field in the new reactor. The dense discrete phase model (DDPM) coupled with particle size segmentation method (PSSM) was adopted to interpret particle transport hydrodynamics in the GSCR. The bed density and pressure drop of simulations were compared with those obtained experimentally. Simulated results show that the flow of gas and solids reaches their own macroscopically steady state after 2 s. In addition, the cluster–ring with a dilute “tail” and a dense “head” is observed in the numerical and experimental result. Furthermore, the mixing chamber is further divided into a diffusion chamber and an agglomeration chamber according to the distribution of axial bed density and the structure of the GSCR. The equal–area annulus method was proposed to investigate the radial particle distribution. In addition, the proportion of particles with diameter >0.10 mm is rarely in the diffusion chamber, whereas the number of particle sizes ranging from 0.08–0.11 mm accounts for a large proportion (66.39% at least) in other chambers.

Gas distributor and bed material effects in a cold flow model of a novel multi-stage biomass gasifier

A new three-stage biomass gasifier is proposed to generate product gas with low tar content. The first stage is dedicated for biomass pyrolysis. While the main roles of the second and third stages, which are superposed and separated by a gas distributor plate, are product pyrolysis gases combustion and gasification, respectively; noting that gasification is realized in a fluidized bed. In order to study and improve the process fundamentals, a cold flow model is developed to understand system dynamics and parameters. A computational fluid dynamics (CFD) study has been conducted using the Eulerian-multiphase model approach applied within the combustion and gasification zones. A complete CFD simulation of flow through the gas distributor is realized. Three values of the distributor perforated area: 1%, 3% and 5% and three bed materials were investigated to study the effect of the solid density and particle size on the fluidized bed. The aim of this work is to study the effect different parameters such as the distributor design, gas flow rate, fluidization velocity, solid density and solid particle size. In this work, gas and solid velocities above the distributor, pressure drop across the distributor, distributor to bed pressure drop ratio, solid volume fraction, bed pressure drop and the bed expansion ratio have been examined. Results show that the perforated area of a distributor has a great influence on the uniformity of the fluidization. The hydrodynamics of solid-gas fluidized beds are shown strongly affected by the gas flow rate and the properties of the bed material.

Simulation study of the effect of the restitution coefficient on interphase heat transfer processes and flow characteristics in a fluidized bed

This article discusses a simulation study performed to investigate the effect of particle collision on inter-particle and gas–solid heat transfer processes, and other related bed flow characteristics. The effect of particle elasticity is presented using different values of the particle–particle coefficient of restitution. The simulation study was carried out using a two-dimensional model of a fluidized bed reactor incorporated to ANSYS Fluent 16.2 software. Two different materials, steel beads and sand particles, were used as the bed material fluidized by air. The simulation results are compared to those from previous studies on fluidized bed reactors containing a single bed material. The coefficient of restitution affected the bed hydrodynamics. Specifically, an increasing coefficient of restitution resulted in an increasing bed pressure drop and decreasing void fraction, granular temperature, particle velocity, and collision frequency. Conversely, increasing the particle coefficient of restitution resulted in decreasing the particle–particle heat exchange coefficient and the gas–particle heat transfer coefficient. The gas–particle heat transfer coefficient for sand particles was higher than that for steel beads. The effect of the coefficient of restitution on the flow characteristics from a binary mixture bed was quite similar to those of single material beds found in previous studies. This study demonstrated that the restitution coefficient clearly affected both the particle–particle and gas–particle heat transfer processes.

An experimental investigation of wall-bed heat transfer and flow characteristics in a swirling fluidized bed reactor

The present work investigates the heat transfer between the immersed heater and bed and hydrodynamics of the bed in swirling fluidized bed. The heat transfer process and bed hydrodynamics characteristics for swirling fluidized bed reactor (SFBR) were compared to those of conventional fluidized bed reactor (CFBR). Then the influence of particle diameter on the bed flow characteristics and heat transfer process in SFBR were studied. The heat transfer coefficient was calculated at different superficial air velocities, radial positions, and bed heights. Compared to a CFBR, the bed pressure drop and distributor pressure drop for SFBR were lower, that characterizes swirling bed reactor. The heat transfer coefficient of SFBR was higher than the corresponding of CFBR at lower portion of the bed and it was lower at the upper portion of the bed for all radial positions and for all air superficial velocities. Increasing particle diameter in SFBR resulted in decreasing both the heat transfer coefficient and bed pressure drop.

Bed pressure drop of a bubbling fluidized-bed with overflow solid discharge

The pressure drop of a bubbling fluidized-bed that employed an in-bed inlet and an overflow outlet for continuous flow of solid particles was investigated with variation in the particle size and density, the solid flow rate and the gas velocity. The bed pressure drop decreased with increasing the gas velocity, but increased with the solid flow rate. The characteristics in lifting the solid particles vertically to the level of the overflow outlet by bubbles appeared different from the ones of particle entrainment and bed expansion. Regardless of size and density of particles, bed height in minimum fluidizing condition (pressure head by solid bed weight, Hmf,f) decreased with increasing the volume flow rate of bubble but increased with the mass flow rate of solid particles. The nominal vertical height from Hmf,f to the level of the overflow outlet that the particles should overcome in the course of discharging out of the fluidized-bed with the aid of bubbles increased as either the volume flow rate of bubble increased or the mass flow rate of solid particles decreased. The power consumed while bubbles lifted particles to be discharged appeared to be same at the fixed volume flow rate of bubble. A correlation was proposed successful even for predicting the bed pressure drop of the recycle chamber of the loop seal and the external solid circulation rate in the circulating fluidized-bed system.

Influence of standing wave characteristics on hydrodynamic behaviours in sound-assisted fluidization of Geldart group A powder

This study aimed to investigate the hydrodynamic behaviours of sound-assisted fluidization of Geldart group A powders under the effects of standing wave characteristics resulting from varying sound wave properties. The sound wave properties used in this were a sound frequency ranging from 0 to 500 Hz at a fixed sound pressure level of 80 dB, and the hydrodynamic behaviours observed included the total bed pressure drop, fixed bed pressure drop, incipient fluidization velocity, and complete fluidization velocity (minimum fluidization velocity). It was found that for full fluidization, the total bed pressure drop was always equal to the weight of the bed per cross-sectional area. However, the fixed bed pressure drop increased with sound frequency, in comparison with conventional fluidization. In addition, with increasing sound wave frequency, the minimum fluidization velocity decreased and reached a local minimum at a critical sound frequency of 50 Hz. After this point, a further increase in the sound frequency caused the minimum fluidization velocity to increase again and eventually level off. This pattern of variation was found to be consistent with the standing wave characteristics in the fluidization medium, where the average magnitude of the sound pressure level varied periodically and exponentially around the critical frequency for each harmonic number. It was also noted that the local minimum of the minimum fluidization velocity can have multiple values according to the periodic variation pattern of the standing wave in the fluidized bed. Finally, by considering the gas oscillation velocity caused by a particular pattern of the standing wave inside the fluidized bed, fixed bed pressure drop correlations were proposed based on the revised Ergun equation and Ergun equation, including their empirical closure equations.

Catalytic oxidation of tricholoethylene over Cr/ZSM‐5/PSSF zeolite membrane catalysts prepared by chemical vapor deposition

AbstractBACKGROUNDChemical vapor deposition (CVD) is a promising catalyst preparation method owing to high dispersion and small particles of metallic oxides. Besides, the ZSM‐5 zeolite membrane is used to treat volatile organic compounds (VOCs) due to relatively high contact efficiency, lower bed pressure drop and mass transfer resistance than granular ZSM‐5, giving good stability of the metal catalysts. However, Cr modified ZSM‐5 zeolite membrane prepared by CVD for trichloroethylene (TCE) catalytic oxidation was still not well‐studied. In the present study, a series of Cr(x)/ZSM‐5/PSSF (x = 1, 3, 5 and 7) catalysts with different Cr loadings was prepared by CVD and further characterized by nitrogen gas (N2) adsorption and desorption, X‐ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature‐programmed desorption (NH3‐TPD) and X‐ray photoelectron spectroscopy (XPS), as well as catalytic performance for TCE oxidation.RESULTSThe results showed that the Cr2O3 species were uniformly dispersed on the surface of ZSM‐5/PSSF, and that the Cr(1)/ZP catalyst exhibited the best catalytic activity for TCE oxidation owing to more Cr6+ species and adsorbed oxygen. It also demonstrated that the Cr(1)/ZP catalyst shows superior catalytic performance for TCE oxidation, giving a T90 that is about 62 °C (c.15%) lower than 1% Cr/ZSM‐5 particle catalyst. Furthermore, it exhibited an excellent stability after online testing at 440 °C for 30 h, and then dropped from 91% to 62% after 95 h, finally remaining at 62% after 120 h.CONCLUSIONThe study demonstrated that Cr/ZSM‐5 zoelite membrane catalysts prepared by CVD show better catalytic behavior and stability for catalytic oxidation of TCE than Cr/ZSM‐5 zoelite catalysts. © 2019 Society of Chemical Industry

Effect of Flow-pattern Reconstruction on Combustion Efficiency and Pollutant Emission in CFB Boiler

The effect of flow-pattern reconstruction on combustion efficiency and pollutant emission in CFB boilers was investigated with a 1-D CFB combustion model. The results from the 1-D model agree well with the field test data. It was found that, the mass fraction of fine coal particles should be increased at lower bed pressure drop to achieve flow-pattern optimization. As the bed pressure drop decreases, the carbon content decreases first and then increases, both in fly and bottom ash. The change of bed pressure drop is the main factor in the influence of flow-pattern optimization on SO2 emission. The higher the bed pressure drop is, the lower the SO2 emission concentration is. Bed pressure drop and coal size distribution are the chief factors of NOx emission concentration in flow-pattern optimization. With the decrease in bed pressure drop and increase in mass fraction of fine particles, NOx emission concentration decreases first and then increases. SO2 emission concentration can be decreased below 100 mg/m3 by increasing Ca/S, while the original emission concentration of NOx increases. Therefore, other assistant adjustments are also needed to achieve flow pattern optimization, such as the secondary air proportion and CaO particle size distribution.