Experiment research on grain drying process in the heat pump assisted fluidized beds

A heat pump assisted fluidized bed grain drying experimental system wasdeveloped. Based on this system, a serial of experiments was performed under four kinds of air cycleconditions. According to the experimental analysis, an appropriate drying medium-air cycle for theheat pump assisted fluidized bed drying equipment was decided, which is different from the commonlyused heat pump assisted drying system. The experimental results concerning the drying operationperformance of the new system show that the averaged coefficient of performance (COP) can reach morethan 2.5. The economical evaluation was performed and the power consumption for removing a kilogramwater from grains was about 0.485 kW-h/kg (H_2O), which shows its reasonable commercial efficiencyand great application potentiality in future market.

Fluidized-Bed Drying of Biological Materials:Two Case Studies

Drying is the last operation for processing most biomaterials. Due to the heat and moisture sensitivity of biomaterials, selections of drying methods and operating parameters are very important to keep the viability of these materials. In the present study, experiments were carried out in fluidized bed drying of photosynthetic microorganism liquid and mixed culture animal food. Results show that most activities can be kept in dried products. Appropriate operation parameters were determined.

Experimental Study of Drying Process of COLZA Seeds in Fluidized Bed Dryer by Statistical Methods

In this study the effect of initial parameters such as inlet gas temperature, initial particles temperature and gas velocity on temperature changes of solid particles and outlet gas temperature in a fluidized bed dryer was studied. For testing, an experimental setup was established. With combination of air and Colza seeds belonging to D groups of the Geldart classification (Geldart, 1986) fluidization regime was carried out. With five test series with maintaining the inlet gas temperature, solid particle temperature and outlet gas temperature during time were carefully measured. To analyze these data by using regression analysis to predict solid particle and outlet gas temperature, 2 correlations on initial pa-rameters were presented. The result has shown that temperature gradients in the beginning of fluidization, is very high and therefore the exponential functions in the regression model is used to predict the temperature changes.

Modularized dry coal beneficiation technique based on gas-solid fluidized bed

A 40-60 t/h modularized dry coal beneficiation process with a novel method to control the bed was designed around a gas-solid fluidized bed separator. Furthermore, the hydrodynamics of medium-solids consisting of wide-size-range magnetite powder （0.3-0.06 ram） and 〈1 mm fine coal were numerically studied. The simulation results show that the fluidization performance of the wide-size-range medium-solid bed is good. The separation performance of the modularized system was then investigated in detail using a mixture of 〈0.3 mm magnetite powder （mass fraction of 0.3-0.06 mm particles is 91.38 %） and 〈1 mm fine coal as solid media. The experimental results show that at separation densities of 1.33 g/cm^3 or 1.61 g/cm^3, 50-6 mm coal can be separated effectively with probable error, E, values of 0.05 g/cm^3 and 0.06 g/cm^3, respectively. This technique is beneficial for saving water resources and for the clean utilization of coal.

FINE COAL AND THREE PRODUCT DRY BENEFICIATION WITH VIBRATION AND DOUBLE-DENSITY FLUIDIZED BEDS

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Moving Behavior of an Object in Gas-Solid Fluidized Beds

The settling behavior of coarse particles in a gas-solid fluidized bed was experimentally studied by using magnetic tracer. It is well known that the calculation of terminal velocity is of interest in dense medium separation. However, this problem has not been completely solved up to now. In this work, the terminal velocity of an object mov-ing in a gas-solid fluidized bed was experimentally measured and theoretically calculated. The experimental results in-dicated that the plastic viscosity and yield stress of the bed increase as the size of fluidized particles increases, but it varies little when some coarser particles are mixed with the fluidized particles. The resistance to a rising object was an order magnitude greater than that to a settling object. The efficient buoyancy on a flaky object, which lies flatly on the gas distributor, was much less than that calculated by the Archimedes principle. The object does not always rise or set-tle with minimal projective area owing to radial motion of the fluidized particles. But in the lower part of the bed, the bar-shaped objects were likely with minimal projective area rising or settling.

Investigation and analysis of a fluidized bed dryer by process tomography sensor

In the pharmaceutical industry,fluidized beds are typically used for pellets drying,coating and granulation.The gas-solids flow characteristic in the process plays an important role to control the heat and mass transfer as well as the end-point product quality.Therefore,it is necessary to investigate the flow characteristics based on advanced measurement technologies.In this research,electrical capacitance tomography(ECT)sensor with eight electrodes was used to investigate the pharmaceutical fluidized bed drying process with different operation conditions.Key process parameters including solids concentration,particle moisture and capacitance signals in the process are given and analysed based on the ECT sensor.In addition,the fluidized bed process with Wurster tube is also investigated based on this ECT sensor.The effect of Wurster tube on the hydrodynamic behaviour and the dominant frequency spectrum distribution in the chamber were analysed based on fast Fourier transform.Test results reveal that process moisture change can be addressed from the raw capacitance of adjacent electrode pair combined with calibration model.Experimental result also indicates that ECT technology can provide useful information for process monitor in a fluidized bed dryer.

Characteristics of fluidization and dry-beneficiation of a wide-size-range medium-solids fluidized bed

Wide-size-range medium-solids are used in a modularized coal beneficiation demonstration system with a gas-solid fluidized bed. The characteristics of fluidization and dry-beneficiation of the medium solids were studied. The numerical simulation results show that 0.15–0.06 mm fine magnetite powder can decrease the disturbances caused by the bubbles. This is beneficial to the uniformity of the gas-solid interactions and thus to the uniformity and stability of the bed density and height. The experimental results show that, with an increase in the fine coal content in medium solids, both the fluidization quality and the beneficiation performance of the bed decreased gradually. When the fine coal content was no more than 13%, a relatively high superficial gas velocity increased the beneficiation efficiency. When the content was more than 13%, part of the fine coal was separated, leading to product layers. The separation efficiency was therefore gradually decreased. The models for predicting the bed density standard deviation and the probable error, E, value were both proposed. The E value can reach to 0.04–0.07 g/cm^3 under the optimized experimental parameters. This work provides a foundation for the adjustment of the bed density and the separation performance of the modularized 40–60 ton per hour dry coalbeneficiation industrial system.

MECHANISM AND APPLICATION OF COAL DRY BENEFICIATION WITH AIR-DENSE MEDIUM FLUIDIZED BED

The mechanism of beneficiation with air dense fluidized bed has been theoretically studied in the paper. Focusing attention on the misplacing resources in separation process, the misplacing effects are divided into two parts called respectively as misplacing effect of viscosity and misplacing effect of motion. The proposed separation theory can reasonably explain the results of separation in different fluidization states. Experimental results in pilot and commercial plants showed that the air dense medium fluidized bed is a high efficiency dry cleaning technique. The dynamic stability of fluidized bed density is directly affected by the variation of fine coal content in fluidized bed and can be controlled in expected range through measurement of fluidized bed density and adjusting of split flow rate. With air dense medium fluidized bed, various coals of size 50—6 mm can be efficiently beneficiated. The separation density can be adjusted between 1.2—2.2 g/cm 3, and the probable error E p value is about 0.06.

RHEOLOGY OF GAS-FLUIDIZED BED

Coal dry beneficiation with fluidized beds belongs to dry dense m ediu m concentration . Therheology is im portant for studying the behavior of an object settling in gas fluidized beds . Inthis paper , The viscosity of fluidized beds w as measured using falling spheres . The rheologi cal characteristics of fluidized beds can be described with Bingha m fluid m odel . The efficientviscosity of fluidized beds can be calculated and plastic viscosity and yield stress of fluidizedbed can be obtained by linearly regressing experi mental data . The calculated results are veryagreeable with the experim ental data .

Combined Removal of Surface Moisture and Dust from Feed Coal for Coal Dry Cleaning with an Air-solid Fluidized Bed

A demonstration plant and a commercial plant employing coal dry cleaning technology with an air-solid fluidized bed were built in China. The operation practice of these two plants shows that the surface moisture and the fines or dust of feed coal must be well controlled as low as possible. For this purpose, a new process of combined removal of surface moisture and dust from feed coal using a vibrated fluidized bed dryer was investigated in a batch test apparatus and a pilot test system. A mathematical model on drying kinetics of coal surface moisture was developed and three empirical formulas of the model coefficient involving the main operating variables were determined based on the test results from the batch test apparatus. The mathematical model shows that the surface moisture retained in coal during drying decreases exponentially with drying time. According to this model, a new divisional heat supply mode, in which the inlet gas of higher temperature was introduced into the fore part of the dryer and the inlet gas of lower temperature into the rear part of the dryer, was employed in the pilot test system. The pilot tests show that 1） the new divisional heat supply mode is effective for lowering down the average temperature and reducing the total heat loss of the outlet gas off the dryer, 2） the moist coal of about 60 g/kg surface moisture contentcan be dried to about 10 g/kg, and simultaneously the fines （〈1mm in diameter） adhering to the surface of coarse coal particles are completely washed off by the gas flow.

Motion analysis of waste rock in gas-solids fluidized bed in coal dry beneficiation

Through the analysis of forces acting on the waste rock in the gas solid fluidized bed, the waste rock velocity equations and displacement equations in the gas solids fluidized bed were achieved and the influential factors of the waste rock motion in the fluidized bed were studied in this paper. The conclusions show that the primary factors influencing the waste rock motion are the waste rock grain size and the scraper velocity according to the computer simulation. This has provided the theoretical foundation both for improving the separating effect and ascertaining the length of the separating cell.

DRY CLEANING OF COAL WITH AIR DENSE MEDIUM FLUIDIZED BED

This paper deals with the experimental study of dry cleaning of coal with air dense medium fluidized bed. This technique opens up an efficient way of coal separation for vast areas in the country where water resources are in short supply or coals tend to slime seriously in wet process. Tests show that it can separate any kind of coal (6--50mm) efficiently. The probable error E, can reach 0.05--0.08. The separating density can be adjusted in the range of 1.0--2.0 g/cm^3. This technique brings about enormous economic benifits.

Fluidized Bed Superheated Steam Dryer for Bagasse: Effects of Particle Size Distribution

Fluidized bed superheated steam drying is one of the technologies successfully applied to drying pulp in the sugar beet industry. It has the technological advantages of energy efficiency and safety (inert environment) required for use in drying bagasse. A comparison of the particle size distribution of bagasse and beet pulp was evaluated in terms of fluidization. The size distribution of bagasse particles is from 2 to 10 times broader than the equivalent distribution of beet pulp particles. The mean particle size of the bagasse is 1/3 of the mean size of the beet pulp. Fluidization tests proved that bagasse fluidization is possible. It was found that beet pulp and bagasse particles clearly differ on shape and size distribution which in turn will affect the design of the ancillary equipment and the fluidization systems if sugarcane bagasse is to be dried using superheated steam technology.

The Ejffect of Vertical Internal Baffles on Fluidization Hydrodynamics and Grain Drying Characteristics

The effect of vertical internal baffles on the particle mixing and graindrying characteristics in a batch fluidized bed column is investigated. Experimental work wascarried out in a 3m high rectangular fluidized bed dryer of cross sectional area of 0.15 m x 0.61 mat different operating conditions using paddy, a group D particle, as the fluidizing material. Theresults of the study showed that the fluidized bed dryer system with vertical internal baffles gavebetter particle mixing effect in the bed of particles than that without vertical internal baffles.This is due to the fact that the vertical internal baffle act as gas bubble breakers by breaking upthe large gas bubbles into smaller ones. The smaller bubbles cause a more vigorous mixing in the bedof particles before finally erupting at the bed surface. This improves the contacting efficiencyand enhanced the heat and mass transfer of the fluidized bed system. Thus a higher drying rate wasobtained in the falling rate period because the higher contacting efficiency increases theevaporation rate at the particle surface. However, the drying rate in the diffusion region showslittle improvement because the moisture diffusivity does not depend on the contacting efficiency.The fluidized bed dryer with vertical internal baffles could therefore be used in the initial rapiddrying stage in a two stage drying strategy for paddy. The insertion of vertical internal bafflesinto a fluidized bed system improves the processing of Group D particles in a fluidized bed systemespecially if the system is large in scale.

Two-fluid modelling for cylindrical fluidized beds using kinetic theory for rough spheres

Recently,we have extended the kinetic theory of granular flow (KTGF) to include friction between the spherical particles and tested it in rectangular geometries.In this study,the extended KTGF implemented in cylindrical coordinates is used to model the more-commonly employed cylindrical bubbling fluidized beds.Special attention is paid to the anti-symmetric part of the velocity gradient in the solids stress tensor.For verification of the implementation,a comparison of the present model in the limit of zero friction with the original (frictionless) KTGF model was made.Subsequently,simulations of bubbling fluidized beds of inelastic particles were performed using our extended KTGF and an effective KTGF model for inelastic particles of Jenkins and Zhang.The simulation results show good agreement for the time-averaged solids volume fraction distribution and solids circulation patterns.Finally,our model is validated by predicting the individual bubble behavior in dense bubbling fluidized beds containing different granular materials in a comparison with experimental data from Verma et al.(2014).The extended KTGF leads to an improved agreement with experimental bubble data.Compared to previous work (Yang et al.,2016b,2017c),and by introducing cylindrical coordinates,the current work demonstrates that the extended KTGF improves predictions for the temporal bubble behavior of cylindrical fluidized beds.

An Experimental Investigation on the Drying of Sliced Food Products in Centrifugal Fluidized Bed

An experimental investigation on the fluidization and drying characteristics of sliced food products in a centrifugal fluidized bed dryer was carried out. The rotating speed ranges from 300 rpm to 500 rpm.Sliced potato and radish were used as the testing materials. The results show that the sliced materials can be fluidised well in the centrifugal fluidized bed. The fiuidized curve has a maximum value and the critical fiuidised velocities Vary with the type of the test material, its shape and dimension as well as operating parameters. The sliced food materials can be dried very well and fast in the ceotrifugal fiuidised bed with a large productivity. The factors that influence the drying process were examined and discussed. The final shape and inner structure of the dried products were observed.The water recovery characteristics of the dried products were also investigated.

Experimental study on drying kinetics of anchovy using centrifugal fluidized bed technique

The present study investigated the drying kinetics of anchovy experimentally using centrifugal fluidized bed technique.The main purpose was to experimentally investigate the effect of the inlet air temperature on the drying kinetics of anchovy in a centrifugal fluidized bed dryer,to fit the experimental data to the widely used mathematical models of drying.Further,the effective moisture diffusivity and activation energy in anchovy drying were investigated in the current work.The drying experiment was conducted at drying air temperatures ranging over 70-120°C.The air velocity and rotating speed of the air-distributor were fixed at 1.5 m/s and 150 r/min,respectively.Pressure drop across bed was approximately 390 Pa,while the layer height was fixed at approximately 2 cm.The anchovies were dried starting from 412%db down to 16%db;drying time ranged from 64 min to 172 min.It was found that the drying temperature was a significant factor in decreasing the moisture content,moisture diffusivity and drying time.The moisture diffusivity and activation energy were investigated at 0.11×10-9-0.25×10-9 m2/s and 20.32 kJ/mol,respectively.When compared to existing models,the Midilli model proved to be in good agreement with change in moisture ratio.

A method to improve fluidization quality in gas-solid fluidized bed for fine coal beneficiation

Dry coal separation has become essential in China because it does not consume water and it reduces environmental pollution. In this study, a method for improving fluidization quality in a fluidized bed separator using a micropore sponge is proposed. The separator is used for fine coal beneficiation. The pressure drop across the distributor and bed fluidization characteristics were analyzed to evaluate fluidization quality. The beneficiation efficiency for fine coal was further investigated by using a laboratory-scale fluidized bed with and without a micropore sponge. With the sponge, the highest pressure drop fluctuation factor decreased from 0.23 to 0.16, indicating an improvement in density stability. The modified separation method reduced the ash content of a sample of fine coal from 23.83% to 10.70%. The probable error efficiency value E for -6 + 3 mm coal was 0.12g/cm^3, close to the efficiency error values reported for other dry-beneficiation techniques. The separation results show that using a sponge in the fluidized bed can readily improve the efficiency of fine coal beneficiation.

DEVELOPMENT OF COAL DRY BENEFICIATION WITH AIR-DENSE MEDIUM FLUIDIZED BED IN CHINA

In China more than two-thirds of available coal reserves are in arid areas, where, to beneficiate the run-of-mine coal, there is not enough water resource required by conventional processing. Developing efficient dry beneficiation technology is of great significance for efficient coal utilization in China, notably the clean coal technology (CCT). The dry coal beneficiation technology with air-dense medium fluidized bed utilizes air-solid suspension as beneficiating medium whose density is consistent for beneficiation, similar in principle to the wet dense medium beneficiation using liquid-solid suspension as separating medium. The heavy portion in feedstock whose density is higher than the density of the fluidized bed will sink, whereas the lighter portion will float, thus stratifying the feed materials according to their density. In order to obtain efficient dry separation in air-dense medium fluidized bed, stable fluidization with well dispersed micro-bubbles must be achieved to ensure low viscosity and high fluidity. The pure buoyancy of beneficiation materials plays a main role in fluidized bed, and the displaced distribution effect should be restrained. The displaced distribution effects include viscosity displaced distribution effect and movement displaced distribution effect. The former is caused by viscosity of the fluidized bed. It decreases with increasing air flow velocity. Movement displaced distribution effect will be large when air flow rate is too low or too high. If medium particle size distribution and air flow are well controlled, both displaced distribution effects could be controlled effectively. A beneficiation displaced distribution model may be used to optimize beneficiation of feedstock with a wide particle size distribution and multiple components in the fluidized bed. The rheological characteristics of fluidized beds were studied using the falling sphere method. Experimental results indicated that the fluidized bed behaves as a Bingham fluid. The plastic viscosity and yield stress can be obtained by measurement of the terminal settling velocity of spheres and linear regression of the experimental data. Both plastic viscosity and yield stress increase with increasing size of the fluidized particles. The drag coefficient can be calculated with favorable agreement with experimental data. The first dry coal beneficiation plant with air-dense medium fluidized bed was established by CUMT with an output of 320000 t·a-1 and a probable error Ep value up to 0.05 was achieved. The plant was accepted by the Chinese government in June, 1994. Since then, new applications have been found including a 700000 t·a-1 dry coal beneficiation plant put up for commercial testing. To realize coal dry beneficiation of full size range of 300-0 mm, further research on dry coal beneficiation of different size fractions has been under way at the Mineral Processing Research Center of CUMT, leading to the following results: Dry beneficiation technology with a vibrated air-dense medium fluidized bed for fine coal of size fraction 6-0.5 mm Ash content was reduced from 16.57% to 8.35%, with yield up to 80.20% and Ep value up to 0.065. Coal dry beneficiation technology with a deep air-dense medium fluidized bed for >50 mm coal An Ep value up to 0.02 was achieved. This technology is of great value for waste removal from 300-50 mm large feedstock, especially for big surface mines in China. Coal triboelectric cleaning technology for <1 mm pulverized Coal Coal is comminuted down to 320 mesh (0.043 mm) to fully liberate the embedded minerals, yielding an ultra-low ash coal (less than 2%). Currently a pilot system with triboelectric cleaning has successfully passed technical appraisal. Three-product beneficiation technology with dual-density fluidized bed This technology yields three products: clean coal, middling and tailing, with the following typical results: Ep value of 0.06-0.09 for the upper layer with a density of 1.5-1.54 g·cm-3 and Ep value of 0.09-0.11 for the lower layer with density of 1.84-1.9 g·cm-3.