Fluidized Bed A14

Experiment No. 5 FLUIDIZED BED Introduction

Many processes within within the chemical industry rely on fluidized bed reactors. For example, fluidized beds are used in catalytic cracking cracking and ammoxidation processes. During catalytic catalytic cracking fluidized beds serve as disengaging units for separating catalyst particles from product vapors. They are also used as regenerators, regenerators, in which high molecular weight carbonaceous carbonaceous products, called coke, coke, are burned off the catalyst catalyst to restore its activity [1]. More recently fluidized beds are beginning to see use as incinerators for hazardous waste destruction [2]. When using a fluidized bed for incineration only a small portion (usually less than 1%) of the bed is combustibles; and the inert material, sand or product ash, acts as a large thermal flywheel, smoothing process variations. This “smoothing of process process variations” is common to all fluidized beds. The vigorous “boiling motion,” or fluidization of the particles produces relatively high heat transfer rates within the bed and serves to smooth out thermal variations. variations. For example, it is common during during incineration for the fluid bed to operate at a steady state with less than 15 F (8.3 C) temperature 

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variation throughout the bed [2]. Fluidization of the bed occurs when the pressure drop of the gas passing up through the packing becomes greater than the force of gravity gravity acting on the bed of particles. particles. The pressure drop that must be overcome for fluidization affects the operating operating costs of the unit. Thus, it is important to predict the pressure drops over various packings as a function of the superficial gas velocity. Generally a scaled scaled down model of the apparatus is used for collecting preliminary preliminary data. These data, along with various relations, are used to predict operating conditions for the full sized apparatus. A pilot plant scale fluidized bed is located on the first floor of the the Unit Operations Laboratory. Laboratory. You will use this equipment to obtain pressure drop and fluidization velocity data for comparison with the empirical correlations given in McCabe, Smith and Harriott [3].

Equipment and Overall Procedure

The fluidized bed is located on the main floor of the Unit Operations Lab. Air passes from the blower through Schedule 40 steel pipe to the tower. An orifice meter is also located between the blower and the tower, and orifice coefficients are appended. In the cabinet are several packing materials for fluidization studies, graduated cylinders, an optical microscope, and plumber’s putty, stretch wrap, and/or duct tape for sealing the tower. It is very important to seal the tower carefully to avoid the safety hazard of spraying packing materials outside of the bed. Some documentation on the properties of available materials is attached. It is important to avoid mixing materials and to return them to the correctly labelled containers. The equipment can be run in both forward (fluidized bed) and reverse (packed bed) directions, but you will only study the forward direction. You should be able to correlate the pressure drop to superficial velocity for at least three different packing materials. Packing materials can be chosen to examine the effects of density, shape, and/or particle size. At least one packing should be used at three or four different bed heights. For each run you should be able to determine the minimum fluidization velocity and compare pressure drop as a function of velocity before fluidization to literature correlations for packed beds.

You should also be able to determine an expected value

for the minimum fluidization velocity and compare that to your measured value.

Pre-lab Requirements – (to be completed by the group)

1. Study the assigned reading and the PowerPoint notes for the fluidized bed lab (Fixed and Fluidized Bed Notes and Report Writing.ppt) 2. Familiarize yourselves with the equipment in the laboratory and draw a sketch of the equipment with the important pipes, valves, and meters labeled. (Do not run the equipment until your assigned lab period) 3. Prepare a data and results collection sheet showing the number of runs you plan to make, the data you plan to measure for each run, and the results you plan to calculate for each run. Put this same information on paper and in the form of an Excel file. 4. Complete the pre-lab questionnaire below and bring it with you to your lab session.

Fluidized Bed Pre-lab Questionnaire

1. List your objectives for the fluidized bed lab. 2. What safety precautions will you take to protect yourselves and the equipment? 3. Write a brief summary of the theory describing the relationship between pressure and velocity in a packed bed before and after fluidization. 4. Which materials do you plan to fluidize? 5. Which bed heights do you plan to study? 6. Referring to your sketch, indicate which valve(s) will be used to adjust the air velocity. 7. Explain briefly how the orifice meter will be used to measure the air velocity. 8. Calculate the superficial air velocity in the bed corresponding to a measured pressure drop of 3 inches of water across the orifice meter. 9. Sketch a graph of your expected results indicating the minimum fluidization velocity. 10. Explain how the bed porosity, particle diameter, particle density, and sphericity will be determined. 11. Assuming a void fraction of 0.4, calculate the expected pressure drop when air flows at a superficial velocity of 0.5 ft/s across a 4 inch high bed of 1 mm diameter polystyrene spheres according to the Ergun equation. 12. Explain briefly how the minimum fluidization velocity can be predicted. Before leaving the laboratory

You should generate log-log plots of pressure drop as a function of superficial velocity for the forward direction. Compare measured results to those calculated using the Ergun equation. For final reports

Report uncertainties in all measured quantities. For labs done during the 5th and 6th weeks, be sure to perform a complete error analysis on measured and computed quantities.

References

1.

Gates, B. C., Katzer, J. R., and Schuit, C. C. A., Chemistry of Catalytic Processes, McGraw-Hill, New York, NY (1979).

2.

Mullen, J. F., “Consider Fluid-Bed Incineration for Hazardous Waste Destruction,” Chem. Eng. Progress, 50-58, June 1992.

3.

McCabe, Smith and Harriott, Unit Operations of Chemical Engineering, Seventh Edition, McGraw-Hill, New York, NY (2005).

Aluminum oxide (40 mesh)

Glass beads, extra couse

Crushed glass, medium

Crushed glass, course

Kramer Industries, Inc. 140 Ethel Road West Unit U Piscataway, NJ 08854

phone: 888-515-9443 fax: 732-650-0556 www.KramerIndustriesOnline.com

“ Right From The Start”

KramBlast Crushed Glass Grit Source Content

100% post-consumer, recycled bottle glass

Shape

Angular

Color

Mixed

Hardness

5.0 – 6.0 (MOHS scale)

Bulk Density

~100 lbs/ft^3

Free Silica Content

Undetectable

Heavy Metals

Undetectable

Standard Grades

Extra Coarse

8 - 12 mesh (1.70 – 2.36 mm)

Coarse

12 - 30 mesh (0.56 – 1.70 mm)

Medium

30 - 70 mesh (0.21 – 0.56 mm)

Fine

-80 mesh (<0.16 mm)

Crushed Glass Grit 051512



“Right From The Start”

Glass Beads Shape

Spherical

Color

Clear

Density

2.5 g/cc

Specific Gravity

2.45 – 2.50

Free Silica Content Chemistry

0% Soda-lime glass

Grade

Mesh Size

Particle Size

Extra Coarse

20/30 Mesh

560 – 850 micron

Extra Coarse

30/40 mesh

425 – 560 micron

Coarse

40/50 mesh

325 – 425 micron

Coarse

50/70 mesh

212 – 325 micron

Medium

70/100 mesh

180 – 250 micron

Medium-Fine

100/170 mesh

90 – 150 micron

Fine

170/325 mesh

45 – 90 micron

CF0009D Glass Bead 0514



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Plastic Abrasive Blast Media Plastic Types

Hardness (MOHS / Barcol)

Urea (Medium) Melamine (Hard) Acrylic (Soft) Urea: 3.5 / 54-62 Melamine: 4.0 / 64-74 Acrylic: 3.2-3.5 / 46-54

Shape

Angular

Color

Mixed

Density

Bulk Density

Urea: 1.5 g/cc Melamine: 1.5 g/cc Acrylic: 1.15 – 1.20 g/cc ~50 lbs/ft^3

Available Grades

8-12 Mesh

1.70 – 2.36 mm

10-20 Mesh

0.85 – 2.00 mm

12-16 Mesh

1.20 – 1.70 mm

16-20 Mesh

0.85 – 1.20 mm

20-30 Mesh

0.56 – 0.85 mm

30-40 Mesh

0.42 – 0.56 mm

40-60 Mesh

0.25 – 0.42 mm

60-80 Mesh

0.16 – 0.25 mm

Plastic Abrasive 061110



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White Aluminum Oxide Grit #40 Mesh Typical Physical Properties Color Grain Shape Crystallinity Hardness Specific Gravity Bulk Density

White Angular Coarse Crystal 9 Mohs 3.8 106 lbs / ft 3

Proximate Chemical Analysis Al2O3 TiO2 SiO2 Fe2O3

99.72 % 0.00 % 0.00 % 0.00 %

CaO MgO Na2O K2O

0.02 % 0.00 % 0.26 % 0.00 %

Particle Size Distribution Size Grading Specification1 Lower Limit Upper Limit 0.0 % 0.0 % 0.0 % 30.0 % 65.0 % 100% 0.0 % 100% 0.0 % 3.0 %

Screen Size 25 35 +45 50 -50 3

40 (CONTROL )

40.0 %

100 %

Notes: ANSI Testing Methods: Size Grading B74-12-2001; Bulk Density B74-4-1997

1

Specification for percentage retained on each screen size for given grade of prod uct. Results of a recent batch. 3 Control screen for quick confirmation of product grade. 2

% Retention 0.0 % 3.1 % 91.1 % 4.6 % 1.2 % 48.2 %

Fluidized Bed A14

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