TABLE OF CONTENT
NO
CONTENT
PAGE NUMBER
1
Abstract
2
2
Introduction
2
3
Procedure
4
4
Result and Discussion
5
5
Conclusion and recommendation
8
6
References
9
7
Appendix
9
1.0 ABSTRACT
In the study of mass transfer, an apparatus consisting of a vertical glass column was used. The lower portion of the column was filled with a fluidizing material. The fluidizing material that was used was dry silica sand. This experiment was conducted to study the operation of fluidized bed dryer as well as to plot the curve under fluidized bed condition. Temperatures were taken for a total 50 minutes across all 4 different temperature sensors, so as to be able to plot the drying curve under the fluidized bed condition.
2.0 INTRODUCTION
The upward flow of fluid through a bed of particles is a situation encountered both in nature, as with the natural movement of ground water, crude petroleum or natural gas, through porous media, and in industrial operations such as backwashing filters, ion-exchange processes, extraction of soluble components from raw materials and for certain types of chemical reactor (OKORONKWO, NWUFO and ANYANWU, 2013). It is well known that if the particles are loosely packed and the pressure drop due to the flow through the bed is equivalent to the weight of the bed, the phenomenon of fluidization occurs. The fluidized state occurs naturall y is called quick sand and industrially, use is made of the high rate of solids mixing that accompanies fluidization for various operations such as drying, coating, heat transfer and chemical reaction. This equipment is designed to allow the study of the characteristics of flow through fluidized bed of solid particles (OKORONKWO, NWUFO and ANYANWU, 2013). Although the majority of fluidized bed situations encountered by practicing engineers are three dimensional, in order that students can readily observe the important phenomenon of bubbling that occurs in gas-solid systems when the gas velocity is in the excess of t hat required for fluidization. The transparent walls allow studies to be made of bubble behaviour in the gas-solid system. Fluidization is chiefly an expanded condition in which the solid particles are supported by drag forces caused by the gas phase passing through the interstices among the particles at some critical velocity. It is an unstable condition in that the superficial gas velocity upward is less than the terminal settling velocity of the solid particles (OKORONKWO, NWUFO and ANYANWU, 2013). The gas velocity is not sufficient enough to entrain and convey continuously all the solids. When a group of particles is described as being fluidized, it is said that they are suspended through the drag caused by the upward flow of a fluid (OKORONKWO, NWUFO and ANYANWU, 2013). As the upward flow of fluid in a packed bed of solids is increased, the pressure drop increases proportionally. At certain velocity, the 2
force of drag on the particles is sufficient to counteract the force of gravity. Beyond this velocity, resistance to the flow is at a maximum and the bed pressure drop becomes constant with an increasing flow. This velocity is denoted as the minimum fluidization velocity and is a fundamental parameter used to characterize fluidization behaviour. The use of a fluidized bed dryer for drying farm products is widely known and accepted, and literally thousands of fluidized bed dryers are operating throughout the food and chemical processing industries. In contrast with this industrial development, the fundamental research on fluidized bed dryer has not made similar progress and the design of an industrial fluid bed dryer is still very much an art based on empirical knowledge (OKORONKWO, NWUFO and ANYANWU, 2013).
Figure 1: Fluidized bed dryer.
Advantages:
Efficient heat and mass transfer gives high drying rate so that drying times are shorter than static bed convection dryer. A batch of tabl et granules can be dried in 20 – 30 min, whereas in compartment bed dryer would require several hours (Islam, 2012). 3
The fluidized state of the bed gives drying from individual particles and not from the entire bed (Islam, 2012).
The temperature is uniform and can be controlled precisel y.
The containers are mobile, making the handling simple and reducing labour cost.
It produces a free flowing product.
Drying time is short, i.e. high output from a small floor space.
Capacity ranges from 5 – 200 kg.
Disadvantages:
Due to turbulence of the fluidized state, product loss may occur.
Liquid, too wet, sticky and adhesive materials can’t be dried.
The vigorous movement of the particles in the hot drying air may lead to the generation of electrostatic change (Islam, 2012).
The cleaning of screen and bag filter is troublesome to avoid contamination.
The harmonizer is precise equipment, so the machine is costly.
3.0 PROCEDURE
3.1 Starting procedure: 1.
An amount of dry silica sand was added in a container with a known amount of water. It was then weighed and the weight was recorded.
2.
Then the switched on the panel were ensured were at OFF position before connecting the power supply.
3.
Once the power supply was connected, the blower was started and the air flow rate was adjusted by using the valve V1.
4.
After that, the desired temperature of air was set in the DTC by operating the increment and decrement and the button of DTC was set as well.
5.
Once the air was allowed to flow pass through the bypass line valve, the heater was started.
6.
Then, when the desired temperature was attained, the column lid was opened to fill the conical portion of the dryer with the wet silica sand. Right after that, the lid was closed.
7.
The hot air was allowed to flow at a prefixed flow rate and temperature to pass through the dryer.
4
8.
Then at regular 10 minutes intervals of time, measurable amount of the wet material was taken out to measure the weight.
9.
The measured material was dried completel y and weighed again.
3.2 Closing procedure: 1.
Once the experiment was over, the blower was switched off consequently the main power supply.
Figure 2: Block diagram of fluidized bed dryer.
4.0 RESULTS AND DISCUSSION
The table 1 displays the recorded values when the experiment was conducted. The recorded observations were the weight of the sample taken after dr ying, WD, for every regular 10 minutes time interval, t and manometer readings, h 1 and h2. There were 4 different temperature sensors readings as well that was noted, the inlet wet bulb temperature of air, T W1, the inlet dry bulb temperature of air, Td1, the outlet of the wet bulb temperature of air, T W2 and the outlet of dry bulb temperature of air, Td2. 5
Table 1: Recorded values during the experiment observation. t(min) 10 20 30 40 50
WD (g) 40.90 14.87 68.61 37.82 0.78
h1(cm) 0 0 0 0 0
h2 (cm) 24.6 24.6 25.5 25.4 25.5
TW1 (⁰C) 62.3 64.0 62.9 64.2 63.5
Td1 (⁰C) 62.5 65.7 64.9 65.7 63.1
TW2 (⁰C) 52.1 54.4 56.5 57.8 57.9
Td2 (⁰C) 54.2 56.0 58.1 59.1 57.8
WD = Weight of the sample taken after drying, h1 and h2 = manometer readings, TW1 = inlet wet bulb temperature of air, TW2 = outlet of the wet bulb temperature of air, Td1 = inlet dry bulb temperature of air, and, Td2 = outlet of dry bulb temperature of air. The temperature recorded during the observation shows a fluctuating result as per table 1. The moisture reduction was fast at the first 10 minutes but slower at the 20 th minute. The moisture reduction was the fastest at the 30th minute of the experiment. The least amount of moisture reduction took place at the end of the experiment.
Experimental Calculation The table 2 displays calculated values attained from the observation readings. The time interval is converted into seconds and the final moisture content of the sample, x was able to be calculated accordingly. Table 2: The final moisture content of sample at regular 10 minutes interval. t(sec) 600 1200 1800 2400 3000
X (kg water/kg dry solid) 1.9734 1.7351 2.4862 1.9374 1.6491
6
X = Final moisture content of sample.
3 ) 2.5 d i l o s y 2 r d g k 1.5 / r e t a w 1 g k ( X
y = 0.0004x + 0.9953
0.5 0 0
500
1000
1500
2000
2500
3000
3500
t (sec)
Figure 3: The effect of final moisture content of sample against time.
Since air was allowed to flow through a bed of solid powdered material in upward direction with the velocity greater than the settling rate of the particles, the solid particles will be blown up and become suspended in the air stream. At the stage solid bed looks like the boiling liquid, therefore this stage is called as fluidised. Use of hot air to fluidizing the bed increased the drying rate of the material at the first 10 minutes and at the 30 th minute. As per the experiment conducted, the variation in the value of X had an effect on the drying time during the constant rate period because the larger the value of X of the solid studied, the longer the drying constant rate period.
Theoretical Calculation The table 3 displays calculated values of the rate of drying, Nth at regular 10 minutes of time intervals. The values attained as per sample calculation in the appendix section. Table 3: Rate of drying at every 10 minutes interval. t(sec) 600 1200 1800 2400 3000
Nth (kg water evaporated/sec) 0.001215 0.001271 0.000878 0.000935 0.000938 7
Nth = Rate of drying.
0.0014 c e 0.0012 s / d e t 0.001 a r o p 0.0008 a v e r e 0.0006 t a w g 0.0004 k ( h t 0.0002 N
0 0
500
1000
1500
2000
2500
3000
3500
Time (s)
Figure 4: Effect of rate of drying against time.
Since the X values varied, it shows that the rate of drying will be longer. But the rate of drying was at its highest at the 20 th minute though the X value was small. The sample of wet material used was more than the final content of the sample. As the particles move along the hot air, there is always a chance of losing the fine particles. To prevent this, a filter bag is used and a cover filter is setup behind the outlet so that only moist air goes out. Hence, the final sample weight after drying was 162.98g.
5.0 CONCLUSION AND RECOMMENDATION
The study of fluidized bed dryer was a success as the plot of curve under the fluidized bed condition was attained. As per the experimental calculation, the final moisture content of the sample from the final reading of the experiment was 1.6491 kg water/kg dry solid. Whereas, as per the theoretical calculation, the final rate of drying that was 0.0009388 kg water evaporated/second. Comparing the experimental and theoretical values, it shows that at the same regular 10 minutes interval amount of water theoretically evaporated is a very small amount. The study of drying in a fluidized bed dryer showed that this equipment can be used to dry cohesive particulate materials, resulting in uniform distribution of the gas inside the bed thus providing a uniform drying of the solid. Analysing the effect of the temperature and moisture content in relation to the time of drying in the constant and falling period, it can be
8
deduced that it takes a total of 50minutes with an optimum temperature of 60 ⁰C to reduce the moisture content. There are few necessary recommendations that should be practiced in the laboratory when this experiment is being conducted. Do not switch on the heater before starting the blower of the set-up. It is important that the flow air should not be higher than the fluidizati on velocity.
6.0 REFERENCES
Choudhary, A. (2016). Principle and Working of Fluidized Bed Dryer (FBD). [online] Pharmaguideline.com. Available at: http://www.pharmaguideline.com/2014/08/principleand-working-of-fluidized-bed-dryer-fbd.html Islam, M. (2012). Fluidized Bed Dryer. [Blog] Learning A to Z. Available at: http://atozstudyzone.blogspot.my/2012/11/fluidized.html OKORONKWO, C., NWUFO, and ANYANWU, E. (2013). Experimental Evaluation of A Fluidized Bed Dryer Performance. The International Journal of Engineering and Science, [online]
2(6),
pp.45-53.
Available
at:
http://www.theijes.com/papers/v2-
i6/Part.2/F0262045053.pdf
7.0 APPENDIX
Manometer difference,
−ℎ = 0−24.6 =0.246 ℎ = ℎ100 100 Area of the orifice,
= 4 = 4 0.026 = 0.000531
9
Area of the pipe,
= 4 = 4 0.052 = 0.00212 Head loss,
= ℎ ( −1)= 0.246 (1000 1.21 −1)=203.0597 Volumetric flow rate of air,
2 ××0.6× 2 ×9.81× √ = = √0.00212 −0.000531 =0.0208 −
Acceleration due to gravity,
= =0.020771903×1.21=0.0251 Table 4: Calculated values of as per observation. Manometer difference, h 0.246 0.246 0.255 0.244 0.246
Head loss, H
203.0598 203.0598 210.4888 201.4089 203.0598
Volumetric flow rate of air, Qa 0.020772 0.020772 0.021148 0.020687 0.020772
Acceleration due to gravity, G 0.025134 0.025134 0.02559 0.025032 0.025134
Experimental Calculation: Moisture content of material at t = 0,
268.91−200 =0.34455 = − = 200 10
Moisture content of material at any time,
= 268.91−40.90 =5.5748 = − 40.90 Final weight of sample after drying, W*= 162.98 g
Initial moisture content of material,
∗ − 162.98−40.90 ∗ = = 40.90 =2.9848 Final moisture content of sample,
− = 0.34455−5.5748 =1.9734 = − ∗ 0.34455−2.9848 Table 5: Experimental calculations. Moisture content of material at any time, C 5.555012 17.02959 2.907594 6.088842 342.7179
Initial moisture content of material, C* 2.984841 9.960323 1.375455 3.30936 207.9487
Final moisture content of sample, x 1.973442 1.735174 2.486206 1.937491 1.649164
Theoretical Calculation: To calculate the humidity of air at the temperatures respectively by psychometric chart, Humidity of air inlet,
= =0.1740(1829)=0.1080 11
Humidity of air outlet,
= =0.0962(1829)=0.0597 Humidity difference,
= − = 0.1080 −0.0597 = 0.0483 Rate of drying,
= − =0.025134×0.0483=0.001215 Table 6: Theoretical calculations. Humidity of air at inlet, y1 0.1740 0.1914 0.1792 0.1938 0.1938
Humidity of air at outlet, y2 0.0962 0.1099 0.1239 0.1337 0.1337
Humidity of air at inlet, Y1 0.1080 0.1188 0.1112 0.1203 0.1203
Humidity of air at outlet, Y2 0.0597 0.0682 0.0769 0.0829 0.0829
Humidity difference, Y 0.0483 0.0506 0.0343 0.0373 0.0373
Rate of drying, Nth 0.001215116 0.001271902 0.000878819 0.000935009 0.000938833
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