Fluidization conditions for

Large differences between thermocouple points 1 and 5 indicate that the bed is not in a fluidized state. This was confirmed by further experimental tests carried out on a three dimensional cold model. It was observed that the chips tend to lock with one another and cannot be fluidized under the design flow conditions in the reactor. It was also observed that some channeling also occurs in the bed. Further work is presently under way to determine the fluidizing conditions for other types of waste wood fuels. 

Fan LT, Chang CC, Yu YS, Takahash T, Tanaka Z. Incipient fluidization condition for a centrifugal fluidization bed. AIChE J 31 999-1009, 1985. 

Table 2. Operating Conditions for an Atmospheric Pressure Fluidized-Bed Combustor ...

When heavier refractories are required because of operating conditions, insulating brick is installed next to the shell and firebrick is installed to protect the insulating brick. Industrial experience in many fields of application has demonstrated that such a hning will success-billy withstand the abrasive conditions for many years without replacement. Most serious refractory wear occurs with coarse particles at high gas velocities and is usually most pronounced near the operating level of the fluidized bed. 

FIG. 23-43 Reactors for solids, (a) Temperature profiles in a rotary cement lain, (h) A multiple hearth reactor, (c) Vertical lain for lime burning, 55 ton/d. (d) Five-stage fluidized bed lime burner, 4 by 14 m, 100 ton/d. (e) A fluidized bed for roasting iron sulfides. (/) Conditions in a vertical moving bed (blast furnace) for reduction of iron oxides, (g) A mechanical salt cake furnace. To convert ton/d to kg/h, multiply by 907. 

Equation 6-108 is also a good approximation for a fluidized bed reactor up to the minimum fluidizing condition. However, beyond this range, fluid dynamic factors are more complex than for the packed bed reactor. Among the parameters that influence the AP in a fluidized bed reactor are the different types of two-phase flow, smooth fluidization, slugging or channeling, the particle size distribution, and the... 

Like enzymes, whole cells are sometime immobilized by attachment to a surface or by entrapment within a carrier material. One motivation for this is similar to the motivation for using biomass recycle in a continuous process. The cells are grown under optimal conditions for cell growth but are used at conditions optimized for transformation of substrate. A great variety of reactor types have been proposed including packed beds, fluidized and spouted beds, and air-lift reactors. A semicommercial process for beer used an air-lift reactor to achieve reaction times of 1 day compared with 5-7 days for the normal batch process. Unfortunately, the beer suffered from a mismatched flavour profile that was attributed to mass transfer limitations. 

The copper was efficiently recovered more than 95-98% from the wastewater of electronic industries within 2-3 hrs as a powder by employing the three-phase inverse fluidized-bed reactors. The addition of a small amount of gas(Uc= 0.001) or fluidized particles(W=1.0wt.%) into the inverse fluidized bed reactors resulted in the increase of the copper recovery and decrease in the size of copper powda-recovered. The value of copper recovery exhibited a maximum value with increasing gas or liquid velocity, amount of fluidized particles or distance between the two electrodes, but it increased gradually with increasing current density up to 3.5A/dm between the two electrodes. The optimum conditions for the maximum recovery of copper powder were UG=0.001m/s, Ul= O.OOlm/s, W=1.0wt.%, I=3.5A/dm and LAc=0.015m within this experimental conditions. 

Gas velocity is an important operating condition in the fluidized bed process and it can highly affect the attrition of dry sorbents. Therefore, the weight remaining in the bed with fluidization time for gas velocity of 20.59 cm/s, 25.74 cm/s, and 30.89 cm/s was measured to estimate the attrition of dry sorbent with gas velocity. As shown in Fig. 4, attrition mainly occurred in the early stage of fluidization. The attrition rate with time decreased and the regression equations fit natural log functions. In addition, Fig. 4 shows that the attrition of dry sorbents is highly affected by gas velocity in the fluidized bed process. 

The results of an example calculation for a recirculating fluidized bed coal devolatilizer of 0.51 m in diameter handling coal of average size 1200 pm at 870°C and 1550 kPa are presented in Fig. 11. The calculation is based on operating the fluidized bed above the draft tube at 4 times the minimum fluidization velocity. It is also based on the selection of a distributor plate to maintain the downcomer at the minimum fluidization condition. If the two-phase theory applies, this means that the slip velocity between the gas and the particles in the downcomer must equal to the interstitial minimum fluidizing velocity as shown below. 

The obvious measures of lowering superficial gas velocity in the bed and the selection of wall and/or particulate materials certainly exist. But, in a given process, there is often no practical way to implement such solutions. Fluidization conditions are dictated by the application for which the bed is intended furthermore, the choice of particulate materials can seldom be made on the basis of electrostatic considerations. 

Subsequently, simulations are performed for the air Paratherm solid fluidized bed system with solid particles of 0.08 cm in diameter and 0.896 g/cm3 in density. The solid particle density is very close to the liquid density (0.868 g/ cm3). The boundary condition for the gas phase is inflow and outflow for the bottom and the top walls, respectively. Particles are initially distributed in the liquid medium in which no flows for the liquid and particles are allowed through the bottom and top walls. Free slip boundary conditions are imposed on the four side walls. Specific simulation conditions for the particles are given as follows Case (b) 2,000 particles randomly placed in a 4 x 4 x 8 cm3 column Case (c) 8,000 particles randomly placed in a 4 x 4 x 8 cm3 column and Case (d) 8,000 particles randomly placed in the lower half of the 4x4x8 cm3 column. The solids volume fractions are 0.42, 1.68, and 3.35%, respectively for Cases (b), (c), and (d). 

Wilhelm and Kwauk (1948), in one of the earliest papers on fluidization, suggested that the Froude number, written for the minimum fluidizing condition, could be used to indicate the prevalent fluidization behaviour. Thus... 

Writing Ergun s equation for minimum fluidizing conditions, and assuming the particles to be spherical ( =1), gives... 

Kang, H.A. and Shin, M.G., Optimization of fluidized bed granulating conditions for powdered milk by response surface methodology, /. Korean Soc. Food Sci. Nut., 33 (2004) 225-228. 

Sawada, H. and Merson, R.L., Estimation of process conditions for bulk sterilization of particulate foods in water-fluidized beds, in Le Maguer, M. and Jelen, P. (eds.). Food engineering and process applications, volume 1 transport phenomena. International Congress on Engineering and Food, Edmonton 1985, Elsevier, London, 1986, 569-581. 

A spray granulation process was developed for a common pharmaceutical compound. The granulation process involved spraying of a 5% w/w binder solution onto the fluidized powder. Table 5 shows the data from the 15 kg run and resultant successful 150-kg run condition for a spray agglomeration process (138). 

It is noteworthy that the group classification depends not only on the particle but also on the gas properties. Moreover, the above classification is related to the fluidization in the presence of air at ambient conditions. For a different fluid and operating conditions, a powder may appear in a different group. Thus, Figure 3.52 can be helpful in classifying a powder only for ambient conditions and with air as the fluid. 

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