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:

- An insulated and lagged shell

- Collection plate or tubes

- Discharge electrodes

- Collection plate rappers/electrode vibrators

- Hoppers

- 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:

- High-Voltage, Single-Stage : ionization and collection steps are combined. They are

commonly referred to as Cottrell precipitators.

- 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:

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

3.0 MATERIALS & APPARATUS

- Electrostatic precipitator main unit

- Handheld anemometer

- Particle/dust analyzer unit

- Test sample

4.0 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

Fan Frequency (Hz) Fan Speed (m/s)

Particles Amount (kg)

Before Electric Field

is Ionized

After Electric Field is

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

Fan Frequency (Hz) Fan Speed (m/s)

Particles Amount (kg)

Before Electric Field

is Ionized

After Electric Field is

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

Fan

Frequenc

y (Hz)

Fan

Speed

(m/s)

Particles Amount(After –

Before)

Field

Ionized

(kg)

gas flow,V

(m3/s)

Efficiency

Ƞ=1−e−W e( A /V )

Before

Electric

Field is

Ionized

(kg)

After

Electric

Field is

Ionized

(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.

Fan

Frequenc

y (Hz)

Fan

Speed

(m/s)

Particles Amount(After –

Before)

Field

Ionized

(kg)

gas flow,V

(m3/s)

Efficiency

Ƞ=1−e−W e( A /V )

Before

Electric

Field is

Ionized

(kg)

After

Electric

Field is

Ionized

(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

2.17 3.12 3.67 4.4 4.810

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.43

0.3236

0.2828

0.24210.224

The graph of ESP efficiency against fan velocityFly ash

Fan Speed (m/s)

Efficie

ncy

, Ƞ

2.2 3.01 3.85 4.39 5.270

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45 0.4256

0.3332

0.27160.2426

0.2066

The graph of ESP efficiency against fan velocityCement

Fan Speed (m/s)

Efficie

ncy

, Ƞ

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 (Matts-

Ohnfeldtequation). 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:

- Low operating cost (except at very high efficiencies)

- Very high efficiency, even for smaller particles

- Ability to handle very large gas flow rates with low pressure losses

- Ability to remove dry as well as wet particles (= mist ok)

- Temperature flexibility in design

Disadvantages:

- High capital cost (= expensive to purchase and install)

- Taking a lot of space

- Not flexible once installed

- 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.