Double Cyclone System
CHAPTER 1 INTRODUCTIONS 1.1 Objectives To have a better understanding on the working principle of double cyclone as one of the air pollution control devices. To study the effect of cyclone body diameter upon the collection efficiency. 1.1 Literature review Literally, cyclone or sometimes known as cyclone collectors, cyclone separators, centrifugal separators, and inertial separators are the pollution control devices that imply a centrifugal force to separate the dust particles from the gas streams. The operation of this device initially starts when the gas stream enters at angle and it is started to spin rapidly. Associated with that, the circular motion that subsequently creates the centrifugal force tends to throw the dust particles towards the wall of the cyclone. Lastly, after striking the wall, these dust particles will fall by gravity into a hopper located underneath. In the meantime, the opposing of these outward particle motions is the inward drag force, which tends to cause the clean flowing outward for discharging process. Figure 1.1: Mechanism of cyclone
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Double Cyclone System Besides, cyclones also can be classified into two, which namely as single-cyclone or multicyclone. And when comparing these two technologies, multi-cyclone which consist of several small cyclones working in parallel mode bring the greatest collection efficiency. This is due to the fact that multi-cyclone are much longer and smaller in diameter. As the length increases, it may enhance residence time for the particles to be trapped inside the device. Even more, longer in size may increase the surface area between the particles and the wall or surface of the cyclone. Meanwhile, at the smaller diameter, it may increase the centrifugal force. Therefore, the combination of these two factors may results in higher efficiency of the particles collection. Figure 1.2: Example of multi-cyclones
Apart from that, the cyclones also can be categorized into three classes which namely as high throughput, conventional or high efficiency. The determination of these kinds of cyclones usually depends on the industrial requirement or the manufacturers’ interest as well. The comparison between these devices is as following figure.
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Double Cyclone System Figure 1.3: Efficiency versus particle diameter for different types of cyclones
Along with the above figure, standard cyclone dimensions have been developed in order to ease the manufacturing of the equipment itself. The standard dimension is as illustrated in the next following diagram. Figure 1.4: Standard cyclone dimensions
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Double Cyclone System Alike with any other air pollution control devices, cyclones also equipped with its advantages and disadvantages. The advantages and disadvantages for this device are presented in the following table: Table 1.1: Advantages and disadvantages of cyclone as air pollution device CYCLONES Advantages
Low capital cost
No moving parts: lack of maintenance requirements and low operating cost Temperature and pressure limitations
Disadvantages
Low collection efficiency – especially for very small particles (< 10μm)
High operating cost – due to power required to overcome pressure drop
only dependent on the materials of Unable construction
to
handle
sticky
or
tacky
materials
Small space requirements Dry collection and disposal Therefore, in industry, there are two analyses that are required to be performed by the engineers. The analyses are basically comes in two forms, which namely as i. Performance analysis While conducting an experiment or works related to air pollution control devices, the main goal of applying these devices are to check the collection efficiency, η. Therefore, prior of calculating the efficiency, the dimension for each of the parameters should be known and established. ii. Design analysis Design analysis on the manufacturing of cyclone basically needs to consider few major things such as the (1) target performance, η, (2) type of cyclone required (conventional, high throughput or high efficiency) as well as (3) the characteristics of the dimensions for both of the particles and type of cyclones selected earlier.
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Double Cyclone System Table 1.2: Influence of varying several characteristics towards the efficiency Cyclone & Process Design Change
Pressure drop
Efficiency
Increase cyclone size (Dc)
Decreases
Decreases
Lengthen cylinder (Lc)
Decreases slightly
Decreases
Increase exit tube diameter (Dc)
Decreases
Increases
Increase inlet area-maintaining velocity Decreases
Decreases
Increase dust concentration
Decreases for large increases Decreases
Increase particle size and/ or density
No change
Increases
CHAPTER 2 METHODOLOGY 5
Double Cyclone System 2.1
Experiment 1: To study the effect of cyclone body diameter upon collection efficiency 1. The experiment for the big cyclone operation is prepared. 2. The weight of the empty feed container and the dust hopper are being weighted separately. 3. 50g of the sample should be weighed prior of being slowly poured into the feed container. 4. The air pump is connected to the feed container with the provided tubing and needle valves should be ensured to be initially closed. 5. The feed container then is attached to the holder and its position is adjusted so that the outlet of the feed container is just inside the inlet piping of cyclone. 6. The outlet dust filter is cleaned thoroughly. 7. Before conducting the experiment, all of the items and connections are being assembled and properly tightened. 8. The Main Switch is turned on and at the meantime, the START button is pushed for running the air blower. 9. The inverter controller is adjusted so that air velocity of 10 m/s may be achieved. 10. The computer is switched on and the EXPERIMENT button is clicked and subsequently, Experiment 1a is chosen. 11. Then, air pump is switched on and the needle is slowly opened until boiling phenomena is observed. 12. In the meantime, the stopwatch shall be started. 13. The RECORD button is clicked so that the airflow rates and pressure drops may be recorded along the experiments. 14. The experiment is conducted for 60 minutes. 15. Once the experiment has been completed, the air blower is switched off. 16. The feed container and the dust hopper are detached from the apparatus and are being
weighted separately later on. 17. The collection efficiency of the cyclone is determined then.
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Double Cyclone System
Vp ρp d p centrifugal force η = = drag force R μg
2
18. After that, the experiment will be repeated by using the small cyclone. Figure 2.1: Schematic diagram of double cyclone system
CHAPTER 3
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Double Cyclone System RESULTS AND DISCUSSION Pressure drop and collection efficiency are the two major criteria used to evaluate cyclone performance. Both properties are functions of cyclone dimensions: inlet height (W), inlet width (H), gas outlet diameter (De ), outlet duct length (S), cyclinder height (Lb), cyclone height (Lc), and dust outlet diameter (Do).
Time (min) 0 10 20 30 40 50
Experiment 1a (Big cyclone) Q V 3
(m /hr) 132.55 132.39 130.22 132.24 132.19 132.23
DPT1
(m/s) 35863.10 35792.75 35773.81 35779.22 35765.70 35776.52
(in H2O) 0.51 0.51 0.52 0.52 0.52 0.53
Table 3.1: Final data collection for big cyclone
Time (min) 0 10 20 30 40 50
Experiment 1b (small cyclone) Q V (m3/hr) 91.83 92.59 92.53 92.17 92.15 92.12
(m/s) 24845.78 25051.41 25035.17 24937.77 24932.36 24924.24
DPT1 (in H2O) 0 0 0 0 0 0
Table 3.2: Final data collection for small cyclone Table 3.1 and Table 3.2 show the result for flowrate, velocity and pressure difference for big and small cyclone. As shown in the tables, the bigger cyclone has higher velocity compared to the smaller cyclone. This phenomenon proves that object with greater speed will have greater force and as the distance from the center goes further, the greater the force. Centrifugal force = mVc2r As propose by above relation, an object traveling in a circle experiences an outward force (toward the wall) called centrifugal force. This force, known as the centrifugal force, depends on 8
Double Cyclone System the mass of the object, the speed of rotation, and the distance from the center. More massive object will have greater force. Object with greater speed will have greater force and as the distance from the center goes further, the greater the force.
Figure 3: Velocity difference for Experiment 1(a) and 1(b) The centrifugal force is created when dust filled air enters the top of the cylindrical collector at an angle and is spun rapidly downward in a vortex (similar to a whirlpool action). As the air flow moves in a circular fashion downward, heavier dust particles are thrown against the walls of the collector, collect, and slide down into the hopper. As exhibited in Figure 3, big cyclone has higher velocity than small cyclone. Therefore, it will have greater centrifugal force. More dust will be thrown and collected into the hopper. Parameter Data Experiment 1(a) (big cyclone) 1(b)(small cyclone) Initial weight of sample in feed container, A 909.40 591.74 Final weight of sample in feed container, B 956.26 627.93 Initial weight of dust hopper, C 804.05 523.63 Final weight of dust hopper, D 813.51 530.19 Weight of sample collected in dust hopper, E 9.46 6.56 Collection efficiency, (%) 20.2 20.0 Table 3.3: Collection efficiency From both experiment, we can see that the collection efficiency for Experiment 1(a) with large cyclone is much higher than Experiment 1(b) (See Table 3.3). The collection efficiency is given by, η=centrifugal forcedrag force=Vpρpdp2Rμg
This results obviously violate the theory which increase the cyclone size will decrease the efficiency. From the literature, longer cyclone in relation to its diameter will provide more vortex revolutions and thus more chances for particle collection. However, taking into consideration on the length of the cyclones makes the results became logic. This is due to the fact that the bigger cyclone has longer body than the smaller one. It has been reported in the literature that a longer 9
Double Cyclone System cyclone in relation to its diameter will provide more vortex revolutions and thus more chances for particle collection. To further support the result, Table 3.4 below indicate the Overall cyclone collection efficiency(Stern, 1955)
Table 3.4: Overall cyclone collection efficiency (Stern, 1955) High efficiency
Particles (μm)
Conventional Cyclone
<5
<50
50 – 80
5 – 20
50 – 80
80 – 95
15 – 20
80 – 95
95 - 99
> 40
95 - 99
95 - 99
Cyclone
The collection efficiency obtained from this experiment does not reach the overall collection efficiency which had been published by Stern (1955). Referring Table 3.4, flour is considered 520μm in particle size. The conventional cyclone efficiency is around 50 to 80% and for high efficiency cyclone is 80-95%. The results obtained in this experiment are far from the efficiency published by Stern (1955). There are few factors that caused this error for example unsteady state flow rate and low maintenance of the equipment itself. The flour used in this experiment also needs to be known the exact size so that we can estimate the efficiency of the cyclone correctly.
CHAPTER 4 CONCLUSIONS AND RECOMMENDATIONS 3.1 Conclusions (ipah)
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Double Cyclone System 3.2 Recommendations In order to obtain the better results for the future work undertakings, some recommendation steps have been proposed for the implementation. These steps may be explained in detailed in the following: i. The handling of the dust sample should be properly managed so that, any spill over of the dust into the floor may bring an error while calculating for its actual efficiency. ii. The particle size for the dust sample, which is flour in this case, should be uniform while conducting the experiment. This is due to the reasons that, varying the size of the particle may results an inaccuracy which is in terms of collection efficiency.
CHAPTER 5 REFERENCES 1. EPA Air Pollution Technology Fact Sheet. Retrieved on Oct 5, 2010 from
http://www.p2pays.org/ref/10/09866.pdf.
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Double Cyclone System 2. Gaseous Emission - Control Technologies (Air-Quality Technology). Retrieved on Oct 5,
2010 from http://engineering.dartmouth.edu/~cushman/courses/engs37/Cyclones.pdf. 3. The Encyclopedia of Filters - Dust Collection. Retrieved on Oct 5, 2010 from
http://www.qfilter.com/Resource.aspx/DocumentDetail/15. 4. Dust
Collector.
Retrieved
on
Oct
5,
2010
from
http://en.wikipedia.org/wiki/Dust_collector. 5. Cyclones.
Retrieved
on
Oct
5,
2010
from
http://www.ezzesoft.com/files/CYCLONESver2.pdf. 6. Karl B. Schnelle and Charles A. Brown (2002). Chapter 21: Cyclone design, Air
Pollution Control Technology Handbook, CRC Press. 7. Lab manual double cyclone system.
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