EXPERIMENT 4 ELECTROSTATIC PRECIPITATOR
1.0
OBJECTIVES:
To demonstrate the electrostatic precipitator working principle. To evaluate the effect of input velocity against separation efficiency and effect of particle size on separation efficiency.
2.0
INTRODUCTION:
Electrostatic precipitator is a device designed to reduce particulate emissions in the exhaust gas stream of an industrial application. It can collect particles with diameter of 0.1pm to 10.0pm, with a high efficiency (99%). An electrostatic precipitator contains some main components listed as follows:
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An insulated and lagged shell
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Collection plate or tubes
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Discharge electrodes
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Collection plate rappers/electrode vibrators
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Hoppers
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Electrical system
Precipitators function by charging the dust particles in the gas stream electrostatically with discharge electrode. The discharge electrode is a small diameter metal wire, used to ionize the gas. A strong electric freld will then be created. The charged particles are attracted to and deposited on flat collection plates or tubular collection electrode with an opposite charge relative to that of the discharge electrode. The strength of the electric field between the discharge and collection electrodes is controlled by the electrical system consists of high voltage component. When enough dust has accumulated, the rapper imparts a vibration to the collectors to dislodge the collected dust, causing it to fall with the force of gravity to hoppers below. Hoppers are used to temporarily store the dust. The dust is then removed by a conveyor system for disposal or recycling.
There are various sizes, types and designs of electrostatic precipitators depending on the specified dust characteristics and the gas volume to be treated. For large power plants, it may actually have multiple precipitators. Types of Precipitators
There are two main types of precipitators:
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High-Voltage, Single-Stage : ionization and collection steps are combined. They are commonly referred to as Cottrell precipitators.
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Low-Voltage, Two-Single : the ionizing section is followed by collection plates.
The high-voltage, single-stage precipitator is widely used in minerals processing operations while the low-voltage, two-stage precipitator is generally used for filtration in air-conditioning systems.
The two major types of high-voltage precipitators currently used are:
Plate : this is the majority of electrostatic precipitators installed. The collection electrodes are flat, parallel surfaces that are 8 to 12 in. apart. A series ofdischarge electrodes spaced along the centerline of two adjacent plates. The particles will'be discharged when the contaminated gases pass through the passage between the plates, collected particles are removed and deposited in hoppers at the base of the precipitator.
Tubular : The collection electrodes for tubular precipitator are in cylindrical shape,with discharge electrodes located on the axis of the cylinder. The contaminated gases flow around the discharge electrode inside of the cylinders. The charged particles adhere on the grounded walls of the cylinder. Tubular precipitators are often used for mist or fog collection or for adhesive, sticky, radioactive or extremely toxic materials.
Precipitator Efficiency
Precipitator performance depend on its size and collecting effrciency. Important parameters include the collecting are and the gas volume to be treated. Other key factors in precipitator performance include the electrical power input and dust chemistry.
Collection efficiency of precipitator can be calculated with the following Deutsch-Anderson equation: Ƞ= 1- e-We(A/V) Where:
3.0
4.0
Ƞ
= collection efficiency
We
= effective migration velocity, cm/s
A
= are of collecting electrodes, m2
V
= gas flow, m3/s
e
= natural logarithm base: 2.718
MATERIALS & APPARATUS
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Electrostatic precipitator main unit
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Handheld anemometer
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Particle/dust analyzer unit
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Test sample
PROCEDURE
1. The main power supply was switch on. 2. The axial flow fan by pressing RUN button on the fan speed controller was turn on. 3. The fan frequency must be set to 15 Hz. The inlet air flow rate with anemometer must be measured and then, this reading must be read. 4. The experiment must be conducted by blowing the sample into ESP. 5. The particles amount on the air duct outlet must be measured. Then, the reading should be read. 6. The ESP electric field was turn on by pressing the green start up button. 7. Keep supplying smokeldust from inlet. 8. The value displayed on particles was record down to the table provided. 9. The step must be repeat for different fan speed. 10. The ESP efficiency must be calculated. 11. The graph of ESP efficiency against fan velocity must be plotted. 12. Then, the experiment can be repeated for different types of dust.
5.0
RESULTS
Test Sample 1 : Fly Ash Particles Amount (kg) Fan Frequency (Hz)
Fan Speed (m/s)
Before Electric Field After Electric Field is is Ionized
Ionized
15
2.17
29.070
29.091
20
3.12
29.078
29.116
25
3.67
29.068
29.081
30
4.40
29.060
29.088
35
4.81
29.064
29.131
Test Sample 1 : Cement Particles Amount (kg) Fan Frequency (Hz)
Fan Speed (m/s)
Before Electric Field After Electric Field is is Ionized
Ionized
15
2.20
29.075
29.105
20
3.01
29.049
29.071
25
3.85
29.047
29.070
30
4.39
29.049
29.090
35
5.27
29.043
29.092
CALCULATION Ƞ
= 1- e-We(A/V)
A
= 2.5m2
V
= [A × Fan Speed]
We
= 1.22
e
= 2.718
Test Sample 1: Fly Ash Particles Amount Fan
Fan
Frequency Speed (Hz)
(m/s)
Before
After
Electric
Electric
Field
is Field
Ionized
Ionized
(kg)
(kg)
(After – Before) is
Field Ionized
gas flow,V Efficiency ⁄
(m3/s)
(kg)
15
2.17
29.070
29.091
0.021
5.425
0.4300
20
3.12
29.078
29.116
0.038
7.800
0.3236
25
3.67
29.068
29.081
0.031
9.175
0.2828
30
4.40
29.060
29.088
0.028
11.000
0.2421
35
4.81
29.064
29.131
0.067
12.025
0.2240
Test Sample 2: Cement. Particles Amount Fan
Fan
Frequency Speed (Hz)
(m/s)
Before
After
Electric
Electric
Field
is Field
Ionized
Ionized
(kg)
(kg)
(After – Before) is
Field Ionized
gas flow,V Efficiency ⁄
(m3/s)
(kg)
15
2.20
29.075
29.105
0.030
5.500
0.4256
20
3.01
29.049
29.071
0.022
7.525
0.3332
25
3.85
29.047
29.070
0.023
9.625
0.2716
30
4.39
29.049
29.090
0.041
10.975
0.2426
35
5.27
29.043
29.092
0.049
13.175
0.2066
The graph of ESP efficiency against fan velocity Fly ash 0.5 0.45
0.43
0.4 0.3236
Efficiency ,Ƞ
0.35
0.2828
0.3
0.2421
0.25
0.224
0.2 0.15 0.1 0.05 0 2.17
3.12
3.67
4.4
4.81
Fan Speed (m/s)
The graph of ESP efficiency against fan velocity Cement 0.45
0.4256
0.4 0.3332
0.35
0.2716
Efficiency ,Ƞ
0.3
0.2426
0.25
0.2066
0.2 0.15 0.1 0.05 0 2.2
3.01
3.85 Fan Speed (m/s)
4.39
5.27
DISCUSSION
In this experiment, the efficiency of precipitator is calculate by Deutsch-Anderson equation: Ƞ= 1- e-We(A/V). and recorded to draw the graph. The patten of the graph show that the efficincy is decreasing as the fan speed is increased. The highest efficiency of the precipitator of the experiment with cement is 0.4256 when the fan speed was 2.20 m/s at the frequency 15 Hz. The lowest effecincy value is 0.2066 when the fan speed is 5.27 m/s at frequency 35 Hz. For the fly ash, the highest efficiency of the precipitator of the experiment at 15 Hz is 0.43 at fan speed was 2.17 m/s. At frequency 35 Hz, the value of effeciency is 0.224 at fan speed is 4.81 m/s.
CONCLUSION
Probably the best way to gain insight into the process of electrostatic precipitation is to study the relationship known as the Deutsch-Anderson equation. This equation is used to determine the collection efficiency of the precipitator under ideal conditions. The simplest form of the equation is given below.Ƞ= 1- e-We(A/V) This equation has been used extensively for many years to calculate theoretical collection efficiencies. Unfortunately, while the equation is scientifically valid, a number of operating parameters can cause the results to be in error by a factor of 2 or more. The Deutsch-Anderson equation neglects three significant process variables. First, it completely ignores the fact that dust reentrainment may occur during the rapping process. Second, it assumes that the particle size and, consequently, the migration velocity are uniform for all particles in the gas stream. As stated previously, this is not true; larger particles generally have higher migration velocity rates than smaller particles do.Third, it assumes that the gas flow rate is uniform everywhere across the precipitator and that particle sneakage (particles escape capture) through the hopper section does not occur. Particle sneakage can occur when the flue gas flows down through the hopper section instead of through the ESP chambers, thus preventing particles from being subjected to the electric field. Therefore, this equation should be used only for making preliminary estimates of precipitator collection efficiency.More accurate estimates of collection efficiency can be obtained by modifying theDeutsch-Anderson equation. This is accomplished either by substituting the effective precipitation rate, we, in place of the migration velocity, w, or by decreasing the calculation of collection efficiency by a factor of k, which is constant (MattsOhnfeldtequation). These calculations are used in establishing preliminary design parameters of ESPs.
QUESTIONS
1. Discuss the finding from the graph.
From the graph, found that the value of effeciancy decrease effect when the fan speed increase the velocity. It’s happened both of cement and fly ash.
2. What is eletrostatic precipitator (ESP)? State down the working of the ESP.
The Eletrostatic Precipitator is a device used to purify polluted air. It is mostly used in thermal power plants, cement plants, incinerator, restaurant kitchen and etc. it used to remove odor and control the atmospheric pollution.
3. State 2 method/ steps to increase the efficiency of ESP.
The efficiency of an ESP can be improved bu optimizing flow distribution inside the ESP using perforable plates and screens. Other tnhan that, the overall energy dfficiency of an ESP system is function of its components which include the variable frequency drive, step up transformer, motor cable, submersible motor and pump. By improving the performence of these individual components can incease the efficency of ESP
4. State the advantages and disadvantages of ESP unit.
Advantages:
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Low operating cost (except at very high efficiencies)
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Very high efficiency, even for smaller particles
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Ability to handle very large gas flow rates with low pressure losses
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Ability to remove dry as well as wet particles (= mist ok)
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Temperature flexibility in design
Disadvantages:
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High capital cost (= expensive to purchase and install)
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Taking a lot of space
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Not flexible once installed
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Failure to operate on particles with high electrical resistivity
5. State the application and where an ESP unit is normally installed.
Eletrostatic precipitator are found many on large power plants, cement plants, incenirators and various boiler applicatio. In the mood product industry, the dry eletrostatic precipitator proced by multi clones is now normally considered the best variable control technology for wood fined boiler emmisions. Wet eletrostatic precipitator have found interest from OSB and plywood veneer manufacturrs for controlling dryer exaust.
