electrostatic precipitation %26 electrostatic precipitator

ELECTROSTATIC PRECIPITATION AND

ELECTROSTATIC PRECIPITATOR

Submitted To:

Group Name:

Group Members:

Department of Chemical



Submitted To:

Mr. A. N. Tabish

Fantastic Four

Group Members:

Iqra Sarfraz 08-BPK-66

Amna Iqbal 08-BPK-75

Sidra Hafeez 08-BPk -76

Jawaeria Altaf 08-BPK-77

Department of Chemical Engineering UET,

City Campus (KSK), Lahore



Engineering UET,

City Campus (KSK), Lahore

ELECTROSTATIC PRECIPITATION [1]:

“ Electrostatic precipitation is defined as the use of an electrostatic field for

precipitating or removing charged solid or liquid particles from a gas stream in which the

particles are carried in suspension.”

Principles of Electrostatic Precipitation [1]:

Basic Principle states that particles in a precipitation system are charged,

transported, neutralized, and removed.

Process of Precipitation [3]:

Process may occur within a single zone or be distributed into two zones:

• Charging Zone (intended to charge the particles).

• Collecting Zone (designed to settle the particles).

Efficiency of the Process [2]:

Electrostatic precipitation as practiced can remove some 98-99% of airborne dusts

and smokes, and about the same percentages of mould spores, but against the smaller

bacterial cells they are rather less effective, in the range of 95-97%.

Description of Mechanism [4]:

When particles in a gas are exposed to gaseous ions they become electrically

charged, this charge makes them mobile under the influence of an electric field. They

then drift toward an oppositely charged or grounded collector plate where they have their

charge neutralized. This is illustrated by the figure. Depending on the size of the particle

and the amount of charge it collects from the ions, the particle drift velocity may be from

0.1 to over 1.0 ft/sec. Once the charge is neutralized at the collector plate, the solid

particles can be either shaken or washed off under the influence of gravity. Electrostatic

precipitation uses these principles to remove particles of liquids and solids from gas

streams. Thus, the electrostatic precipitator must have:

• A method for ionizing the carrier gas.

• Directed flow of the feed gas through the ionizing region.

• An electric field to cause particle drift to the collecting electrode.

The charge to the carrier gas is supplied

generated by a non-uniform electric field. A corona is the local electrical breakdown of a

gas into electrically charged gaseous ions due to the high voltage. It is made possible by

the non-uniformity of the field, w

points, but weakens with distance from these regions. If the same voltage were applied as

a uniform field between flat electrodes, no breakdown would occur, it would not be

localized. In this case

between the plates rather than a corona

The common techniques for generating a non

wire or a rod equipped with many very sharp points as the discharge electrode. The thin

wire gives a relatively weak corona from the few small sharp imperfections in the wire

On the other hand, the sharp points intentionally placed on the rod literally spray a corona

into the gas phase. A number of different electrodes sharps have been tested to increase

corona discharge from sharp edges and points. However, if the percent of

escaping precipitation is plotted against corona power input per unit of gas flow, all the


, the electrostatic precipitator must have:

A method for ionizing the carrier gas.

Directed flow of the feed gas through the ionizing region.

An electric field to cause particle drift to the collecting electrode.

The charge to the carrier gas is supplied by a high voltage direct current

uniform electric field. A corona is the local electrical breakdown of a


uniformity of the field, which is very strong in the vicinity of thin wires or sharp



localized. In this case continuous breakdown would occur and would cause sparks

between the plates rather than a corona

The common techniques for generating a non-uniform field are to use either a thin


wire gives a relatively weak corona from the few small sharp imperfections in the wire



corona discharge from sharp edges and points. However, if the percent of



Directed flow of the feed gas through the ionizing region.

An electric field to cause particle drift to the collecting electrode.

by a high voltage direct current corona

uniform electric field. A corona is the local electrical breakdown of a


hich is very strong in the vicinity of thin wires or sharp



continuous breakdown would occur and would cause sparks

uniform field are to use either a thin


wire gives a relatively weak corona from the few small sharp imperfections in the wire.



corona discharge from sharp edges and points. However, if the percent of particles


data fall on a single correlating line. Thus, corona power input determines collection

efficiency for electrostatic precipitators.

ELECTROSTATIC

“An electrostatic precipitator is a large, industrial emission

designed to trap and remove dust particles from the exhaust gas stream of an industrial

process. “

Electrostatic precipitators are used for the collection

These are defined as follows:

• Dust----solid particles from 0.1 to 100 µm in diameter.

• Mist----liquid droplets suspended in a gas.

• Fume----solid or liquid particles formed by condensation from a vapor.

Construction of a

The basic ESP comprises

outlet transitions, dust collection,

supports the internal equipment such as collection surfaces, discharge electrodes and

rapping devices.


efficiency for electrostatic precipitators.

LECTROSTATIC PRECIPITATORS [7]:

An electrostatic precipitator is a large, industrial emission


Electrostatic precipitators are used for the collection of dusts, mists, and fumes.

These are defined as follows:

solid particles from 0.1 to 100 µm in diameter.

liquid droplets suspended in a gas.

solid or liquid particles formed by condensation from a vapor.

Precipitator [8]:

The basic ESP comprises a casing with inlet transition, gas distribution devices

outlet transitions, dust collection, hoppers and support steel. The casing



An electrostatic precipitator is a large, industrial emission-control unit. It is


of dusts, mists, and fumes.

solid or liquid particles formed by condensation from a vapor.

gas distribution devices,

The casing encloses and


The most common material of construction for the casing and internal equipment is

mild steel, stainless steel and PVC materials are also

Working of a Precipitator

Working of an ESP comprises of s

• Ionization - Charging of particles

• Migration - Transporting the charged particles to the collecting surfaces

• Collection - Precipitation of the charged particles onto the collecting surfaces

• Charge Dissipation

surfaces

• Particle Dislodging

hopper

• Particle Removal

Designs of Electrostatic Precipitators:

• Wire-in-Plates Designs

The plate type units

the gas (air).


mild steel, stainless steel and PVC materials are also used in special applications

Precipitator [7]:

Working of an ESP comprises of six activities as follows:

Charging of particles

Transporting the charged particles to the collecting surfaces

Precipitation of the charged particles onto the collecting surfaces

Charge Dissipation - Neutralizing the charged particles on the collecting

Particle Dislodging - Removing the particles from the collecting surface to the

Removal - Conveying the particles from the hopper to a disposal point

Designs of Electrostatic Precipitators:

Plates Designs

The plate type units are the most common designs for dry dust removal from


used in special applications.

Transporting the charged particles to the collecting surfaces

Precipitation of the charged particles onto the collecting surfaces

Neutralizing the charged particles on the collecting

Removing the particles from the collecting surface to the

Conveying the particles from the hopper to a disposal point

dry dust removal from

• Wire-in-Pipe Designs

Pipe designs are mainly used for the removal of liquid or sludge particles and

volatilized fumes.

Division of Precipitators

Electrostatic precipitators are divided into two broad classes, depending on whether

the ionizing and collecting functions are combined or separated, in the

the central wire ionizing electrode is also one of the electrodes establishing th

causes the particle drift. In

electrodes are of widely different diameters so that corona discharge and ionization occur

only in the vicinity of the small diameter portion of the centr

two-stage unit is used industrially with a negative corona and washing of the collector

plates is done to recover the particles.

Types of Electrostatic

There are two types of electrostat

1. Dry Electrostatic

The dry ESP is the most common

dry state, such as cement and ash.

Pipe Designs


volatilized fumes.

Division of Precipitators [4]:


the ionizing and collecting functions are combined or separated, in the

the central wire ionizing electrode is also one of the electrodes establishing th

causes the particle drift. In two-stage unit the ionizing electrodes and the drift field


only in the vicinity of the small diameter portion of the central electrode. This type of

stage unit is used industrially with a negative corona and washing of the collector

plates is done to recover the particles.

f Electrostatic Precipitators:

There are two types of electrostatic precipitators, dry, and wet.

Dry Electrostatic precipitator [9]:

The dry ESP is the most common. It collects and removes the particulate matter in

dry state, such as cement and ash.



the ionizing and collecting functions are combined or separated, in the single-stage unit

the central wire ionizing electrode is also one of the electrodes establishing the field that

the ionizing electrodes and the drift field


al electrode. This type of

stage unit is used industrially with a negative corona and washing of the collector

wet.

oves the particulate matter in a

Operation [9]:

A dry electrostatic precipitator is used for removing dust particulates from a

flowing gas stream and comprises of an upright cylindrical vessel, each of precipitator

stages have particulate charging electrodes and associated collector electrodes, arranged

in a controlled flow path. A dust hopper located beneath each stage; and dust chutes

extending from the hoppers to discharge outlets at the bottom of the vessel. The particles

will be drawn towards plates hanging on the side of the device, where they will collect.

Periodically, the plates will be struck by a hammer, or something like it, or vibrated,

causing the particles, now discharged, to fall off. They are then collected, and disposed of

accordingly.

Applications [10]:

Some of the usual applications of dry ESP are:

1. Removal of dirt from flue gases in steam plants.

2. Cleaning of air to remove fungi and bacteria in establishments producing

antibiotics and other drugs, and in operating rooms.

3. Cleaning of air in ventilation and air conditioning systems.

2. Wet Electrostatic Precipitator:

Wet precipitators are used to strip gasses of "wet" particles, such as resin, oil, paint,

tar, acid, or anything that can't be handled well dry.

Principle:

It operates on the principle of uni-polar particle charging in the corona discharge

and particle precipitation under the field of their own space charge.

Operation [11]:

In WESP, the dust is removed by

plates by water sprays

Some systems use very little water and produce

clarifier and solid concentrator.

the primary target for the WESP is the submicron particular focus on heavy metals and

soot.

Applications:

1. Incinerators for industrial

2. Incinerators for municipal waste.

3. Boilers, melting furnaces,

Precipitator Selection

In the selection process the engineer specifies the particular applications, the gas

flow, temperature, pressure, dust concentration,

altitude, and as much other pertinent data as are available to him. In some cases it is

recognized that data on dust chemistry, fore example, may not exist.

The efficiency of

the dust is removed by continuous or periodic irrigation of the collection

or a water film.

Some systems use very little water and produce sludge like residue others use a

clarifier and solid concentrator. Sometimes with pH adjustment and with flocculation aids

he primary target for the WESP is the submicron particular focus on heavy metals and

Incinerators for industrial waste.

Incinerators for municipal waste.

elting furnaces, desulfurizing systems.

Precipitator Selection [12]:


flow, temperature, pressure, dust concentration, efficiency required, residual permissible,



The efficiency of electrostatic precipitators can be increased by:

or periodic irrigation of the collection

like residue others use a

ment and with flocculation aids

he primary target for the WESP is the submicron particular focus on heavy metals and


efficiency required, residual permissible,



reased by:

• Larger collection surface areas and lower air flow rates give more time and

area for dust particle to collect.

• Increased speed of dust particles towards collection electrodes.

Advantages of Electrostatic Precipitation [5]:

1. High removal efficiency of fine particles/droplets.

2. Collection of either dry powder materials or wet fumes/mists.

3. Substances of a wide range of gas temperature up to approx 700 degree C.

4. Low operating costs, except at very high removal efficiencies.

Disadvantages of Electrostatic Precipitation [5]:

1. High capital costs.

2. Unable to collect gaseous pollutants.

3. Large space requirement.

4. Inflexibility of operating conditions.

Applications of Electrostatic Precipitation [6]:

The earliest applications were to the smelting and sulfuric acid industries and at

cement mills. Other important applications include removal of tar from coke-oven gases;

removal of acid fumes in petroleum refineries and chemical plants; recovery of such

industrially valuable materials as the oxides of tin and copper.

Expected Future Developments [13]:

The following trends and emphasis in electrostatic precipitator development are

forecast over the next few years.

1. Use of additives for gas conditioning to reduce the high resistivity problem.

2. Use of computer models for precipitator design and performance analysis.

3. Use of wet precipitators in controlling fine particles.

References:

1. Lawrence K Wang, and Norman C. Pereira, “Hand Book of Environmental

Engineering: Air and Noise Pollution Control”, Vol. 1, Ed. 1979, the Humana

Press Inc., pp. 103 and 104.

2. Lawrence K. Wang, Norman C. Pereira, Yung-Tse Hung, “Handbook of

Environmental Engineering: Air Pollution Control Engineering”, Vol. 1, Ed.

2004, the Humana Press Inc., pp. 154.

3. Mazen Abdel-Salam, “High Voltage Engineering: Theory and Practice”, Ed. 2,

Macrel Dekker Inc., pp. 645-646

4. Robert B. Long, “Separation Processes in Waste Minimization”, Ed. 1995,

Marcel Dekker Inc., pp. 278-280.

5. Lawrence K. Wang, Norman C. Pereira, Yung-Tse Hung, “Handbook of

Environmental Engineering: Air Pollution Control Engineering”, Vol. 1, Ed.

2004, the Humana Press Inc., pp.154.

6. http://www.britannica.com/EBchecked/topic/184043/electrostatic-precipitation

7. http://www.neundorfer.com/knowledge_base/electrostatic_precipitators.aspx

8. William L Heumaan, “Industrial Air Pollution Control Systems”, Ed. 1997,

Macrel Dekker Inc., pp. 472-474.

9. http://everything2.com/title/Electrostatic+Precipitator

10. http://www.ppcesp.com/ppcart.html

11. Walter R. Niessen, “Combustion and Incineration Processes”, Ed. 2002, pp.

575-576.

12. John. J. McKetta, “Unit Operations Handbook: Mechanical Separation and

Materials Handling”, Vol. 2, Library of Congress Cataloging-in-Publication

Data, pp. 339.

13. Lawrence K Wang, and Norman C. Pereira, “Hand Book of Environmental

Engineering: Air and Noise Pollution Control”, Vol.1, Ed.1979, the Humana

Press Inc., pp.141.

electrostatic precipitation %26 electrostatic precipitator

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