Partech Solved Problems 15 Problems [PDF]

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

1. A packed bed of solids of density 2000 kg/m3 occupies a depth of 0.6m in a cylindrical vessel of inside diameter 0.1m. The mass of solids in the bed is 5kg and the surface-volume mean diameter of the particles is 300 μm. Water (density 1000 kg/m3 and viscosity 0.001 Pas) flows upwards through the bed. a. What is the voidage of the packed bed? b. Use a force balance over the bed to determine the bed pressure drop when fluidized. c. Hence, assuming laminar flow and that the voidage at incipient fluidization is the same as the packed bed voidage, determine the minimum fluidization velocity. Verify the assumption of laminar flow.

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

2. A packed bed of solid particles of density 2500 kg/m3, occupies a depth of 1 m in a vessel of cross-sectional area 0.04 m2. The mass of solids in the bed is 50 kg and the surface-volume mean diameter of the particles is 1 mm. A liquid of density 800 kg/m3 and viscosity 0.002 Pa.s flows upwards through the bed. a. Calculate the voidage (volume fraction occupied by voids) of the bed. b. Calculate the pressure drop across the bed when the volume flow rate of liquid is 1.44 m3/h.

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

3. From the previous number, given that the volume flow rate is increased to 2.0 m3/h, calculare the pressure drop. Also, calculate the pressure drop across the bed when it becomes fluidized.

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

4. A packed bed consisting of uniform spherical particles of diameter 3 mm and density 4200 kg/m3, is fluidized by means of a liquid of viscosity 1mN.s/m2 and density 1100 kg/m3. Using Ergun’s equation for the pressure drop through a bed height and voidage as a function of superficial velocity, calculate the minimum fluidizing velocity in terms of settling velocity of the particles in the bed.

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

5. A bed of perfectly spherical solid particles with a diameter of 85μm and density of 3500 kg/m3 is fluidized using a gas of density 1.2 kg/m3 and a viscosity of 1.9 x 10-5 N.s/m2. Determine the minimum fluidizing velocity if a representative sample of particles extracted from the bed occupying a volume of 0.001 m3 has a mass of 2 kg.

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

6. Catalyst pellets 0.2” in diameter are to be fluidized with 100lb/hr of air at 1 atm and 170˚F in a vertical cylindrical vessel. The density of the catalyst particles is 60lb/ft^3 and Φs=0.6. If the given quantity of air is just sufficient to fluidize the solids, what is the vessel diameter? emf=0.45, viscosity=8.6x10^-6 lb/ft*s

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

7. We plan to pass air upward through a bed of solids resting on a screen. Will the solids fluidize?

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

8. A packed bed of spherical particles (dp=50micrometer, density of solid =400kg/m^3) is fluidized using air at 870˚C and pressure=2.76x10^4 N/m2. The packed–bed density is 1440 kg/m3 and superficial air velocity is 0.3m/s. Compare ‘pressure drop’ from Ergun’s equation and fluidizes bed condition-equation. viscosity=1.28 kg/m*s

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

9. Air ( Density= 1.22 Kg/m3, Viscosity = 1.9 X 10 –-5 pa.s) is flowing in a fixed bed of a diameter 0.5 m and height 2.5 m. The bed is packed with spherical particles of diameter 10 mm. The void fraction is 0.38. The air mass flow rate is 0.5 kg/s. Calculate the pressure drop across the bed of particles.

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

10. Air is moving upward in a bed packed with spherical coal particles of diameter 0.1 mm and density 103 kg/m3. The air properties are = 2.4 kg/m3 and region for fluidization. The void fraction of the bed is 0.38

= 1.9 X 10–5 pa.s. Find the

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

11. A catalyst tower 50 ft and 20 ft in diameter is packed with 1 1/4-in.- diameter spheres. Gas enters the top of the bed at a temperature of 450°F and leaves at the same temperature. The pressure at the bottom of the catalyst bed is 40 psia. The bed porosity is 0.36. If the gas has average properties similar to ethane and the time of contact (based on flow in the void space) between the gas and the catalyst is 10 seconds, what is the inlet pressure?

12. Determine the design diameter of the vessel required to fluidize catalyst of 7 mm diameter with 3,500 kg/s of air at 1 atm and 70°C. The properties of the catalyst are determined as follows. (Density = 950 kg/m3 ,Sphericity = 0.92)

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

13. Solid particles having a size of 0.15 mm, and a shape factor of 0.86, and a density of 1225 kg/m3 are to be fluidized using air at STP. The voidage at minimum fluidizing conditions is 0.45. a. If the cross section of the empty bed is 0.30 m 2 and the bed contains 330 kg of solid, calculate the minimum height of the fluidized bed. b. Calculate the pressure drop at minimum fluidizing conditions c. Calculate the minimum velocity for fluidization.

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

14. Water at 25°C is flowing by gravity through a filter bed of small particles having an equivalent diameter of 0.0060 m. The void fraction of the bed is measured as 0.42. The packed bed has a depth of 1.50 m. The liquid level of water above the bed is held constant at 0.40 m. What is the water velocity based on the empty cross section of the bed?

Fluidization

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Pamantasan ng Lungsod ng Maynila College of Engineering and Technology Chemical Engineering Department

15. A catalyst tower 50 ft and 20 ft in diameter is packed with 1 1/4-in. - diameter spheres. Gas enters the top of the bed at a temperature of 450°F and leaves at the same temperature. The bed porosity is 0.36. If the gas has average properties similar to ethane and the pressure drop is 15 psia, how long will the gas and the catalyst contact with each other based on flow in the void space?

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