This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Applications of Fluidisation”.
1. Which of the following is true about fluidized beds?
a) Intense mixing leads to non-uniform temperature
b) Fluidized solids can be easily transferred from one reactor to another
c) Heat transfer in a fluidized bed is moderate
d) Heat exchangers are present over the circumference of the fluidized bed
View Answer
Explanation: Fluidized beds are known for their excellent heat transfer capabilities. The heat exchangers are immersed in the beds rather than being present above the beds. Intense mixing in a fluidized bed implies uniform temperature.
2. Which of the following is false about fluidized bed catalytic cracking?
a) It cracks longer molecules into shorter compounds
b) Catalytic reactions in the catalytic riser take 2-4 seconds to complete
c) Stacked configuration covers more space than side-to-side configuration
d) Carbon produced during cracking gets deposited on the catalyst
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Explanation: In both stacked and side-to-side configurations, the reactor and the catalyst regenerator are placed in different vessels. In stacked configuration, the reactor is placed above the regenerator to save space whereas, in side-to-side configuration the vessels are placed next to each other.
3. Which of the following is not true about Fischer process?
a) Low temperature Fischer-Tropsch process uses fluidized beds
b) High temperature Fischer-Tropsch process uses fluidized catalysts
c) Cobalt is not suitable for high temperature Fischer Tropsch process
d) The commercial Fischer Tropsch process uses iron based catalyst
View Answer
Explanation: Low temperature Fischer-Tropsch process uses fixed bed reactors. The high temperature Fischer-Tropsch process uses fluidized catalysts at around 300°C and fluidized beds. Iron based catalysts are now used based on the desired product specifications. Cobalt is not advised during high temperature Fischer Tropsch process due to methane formation.
4. Which of the following parameters does not need to be controlled in a fluidized bed dryer?
a) Apparatus parameters
b) Product parameters
c) Process parameters
d) Raw material parameters
View Answer
Explanation: Parameters are controlled in a fluidized bed dryer to improve the efficiency and operation of the bed and optimize the production. Apparatus, product and process parameters are controlled by the equipment, product and process respectively.
5. Which of the following is not an apparatus parameter in fluidized bed dryer?
a) Size of distributor plate
b) Position of distributor plate
c) Shape of the equipment
d) Height of nozzle
View Answer
Explanation: The position of the air distribution plate affects the pattern of airflow. An annular instrument gives a more appropriate and better product. The height of the nozzle is very crucial when used as a coating device.
6. Which of the following is a disadvantage of fluidized dryers?
a) High maintenance cost
b) High pressure drop
c) Low thermal efficiency
d) Low rates of moisture removal
View Answer
Explanation: Fluidized dryers have high rate of moisture removal due to their excellent mass transfer and heat transfer capacities. Fluidized dryers have high thermal efficiency. There is a high pressure drop when the entire bed is subjected to gas.
7. Which of the following is a modified fluidized bed dryer?
a) Plug flow fluidized bed dryer
b) Semi-continuous fluidized bed dryer
c) Hybrid fluidized bed dryer
d) Batch fluidized bed dryers
View Answer
Explanation: Modified fluidized bed dryers are built to overcome the problems that are faced by conventional fluidized bed dryers. These modified fluidized bed dryers are used in several industrial processes. Recent fluidized bed dryers also implement heat pumps.
8. Which of the following is not an application of fluidization?
a) Fluidized bed tunnels are used for large food products
b) Fluidized bed coater is used for making barrier films on tablets
c) Fluidized beds are used in catalytic processes
d) Fluidized bed dryers are used for drying powders
View Answer
Explanation: Fluidized beds can be used to accelerate fringing in Individual Quick Freezing units (IQF). These units are used to freeze and store small food products, usually slices. These are stored individually so that the final product is a big block of ice.
9. Which of the following is not a disadvantage of Fluidized bed granulator?
a) A fluidized bed granulator cannot be efficiently used in a batch process
b) A fluidized bed granulator has a long resident time
c) A fluidized bed granulator cannot be automated
d) A fluidized bed granulator produces low density granules
View Answer
Explanation: A fluidized bed can be automated once the parameters are optimized and is one of the advantages of fluidized bed granulators. The low density granules are lighter due to lower gravity, and can get carried away easily. The residence time, which is the granulation period, also increases in a fluid bed granulator. A fluidized bed granulator cannot achieve the same degree of densification in batch mode as it does in continuous mode.
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