FIELD OF THE INVENTION
The present invention relates to Hopper heating system for the electrostatic
precipitators in power plant applications.
BACKGROUND OF THE INVENTION
The electrostatic precipitators (ESP) is basically a pollution control equipment
widely used for collecting dust particles from the flue gas exhausted from plants
such as thermal power plants, cement plants, steel plants and glass plants.
The electrostatic precipitators are configured with number of field, which have
collecting and emitting electrodes. A high electric field is generated between the
electrodes to charge the dust particles and collect the charged particles on the
collecting electrodes.
The hot flue gases from the boiler enter the Precipitator at temperatures ranging
from 250 to 400°F. The hot flue gases are carrying particles of dust known as fly
ash, which are the remains of burning fossil fuels. The electrical charge created
in the ESP causes the fly ash to adhere to the collecting plates. The cleaned
gases exit the Precipitator and enter the plant stack for eventual release into the
atmosphere. The Thermal profiles from the top to the bottom of several
Precipitator casings showed a reducing temperature gradient. This is caused by:
• Natural Convection - hot gases are naturally carried upwards within the
Precipitator casing.
• Induced Convection - resulting from the hot gases being redirected by
baffles away from the collection hoppers and upwards into the Precipitator
casing.

The net effect of the natural and induced convection creates a stagnant gas
condition within the fly ash collection hoppers.
The application of thermal insulation to the exterior of the fly ash collection
hoppers cannot prevent the stagnant gases from cooling. As the gas temperature
falls the "dew point" is reached and condensation begins to form on the fly ash
collection hopper walls. Continued cooling of the flue gases may also result in the
temperature falling to the "moisture dew point" which results in increased levels
of condensation. Typical flue gas dew point temperatures range from 250 to
350°F with coal fired boilers and 300 to 400°F with oil fired boilers. Moisture dew
points vary between 100 to 180°F. Once condensation has taken place, two
problems exist:
• The condensate is usually a mild sulfuric acid resulting in corrosion and
pitting of the collection hoppers.
• The fly ash falling into the collection hoppers is a very hygroscopic
material and as it mixes with the condensate, it quickly changes from a
free-flowing, dry dust into a thick, immobile mud.
The second problem listed is by far the most serious, expensive and far-reaching
for plant operators.
When the fly ash agglomerates, it quickly builds up in the lower areas of the
collection hopper and quickly blocks the hopper outlet (throat). This blockage
must be immediately removed because continued build up of fly ash can cause:
• Structural damage to the Precipitator due to increased and unanticipated
weight factors (hoppers have been torn from casings).
• Arcing in the high voltage electrode system, resulting in reduced operating
efficiencies, fires within the Precipitator and significant and expensive
repairs.

It is, therefore, imperative that collection hoppers always remain clear,
essentially acting as a funnel to carry the collected fly ash directly into the fly ash
conveying system.
The obvious solution to this overall problem is to eliminate the condensation. If
this is achieved, the fly ash remains in a dry, free-flowing state and can be easily
evacuated from the hoppers and moved through the ash conveying system. The
elimination of condensation cannot be achieved by merely insulating the
collection hoppers. The answer is very basic- HEAT THE HOPPERS.
Before any type of heater can be selected, the heat energy required to prevent
condensation is calculated and is to be applied to prevent the condensation.
The ESP hoppers are provided with either tubular type electrical heaters Fig.3 or
Panel type electrical heaters Fig.4 to keep the ash particles in fluidized form. As
the electrical energy required for the ESP hopper heating system is enormous it
has become essential to propose an alternate Hopper heating system by making
use of the excess heat energy available in the power plants there by making the
alternate heating system cheaper without affecting the functional requirement of
the ESP hopper heating system.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a hopper heating
system for electrostatic precipitator utilizing heat energy in the form of hot
secondary air or hot primary air available in the power plants which eliminates
the disadvantages of existing state of art.
Another object of the present invention is to propose a hopper heating system
for electrostatic precipitator utilizing heat energy in the form of hot secondary air
or hot primary air available in the power plants which is cost effective.

A further object of the present invention is to propose a hopper heating system
for electrostatic precipitator utilizing heat energy in the form of hot secondary air
or hot primary air available in the power plants which improves efficiency of the
electrostatic precipitator.
A still further object of the present invention is to propose a hopper heating
system for electrostatic precipitator utilizing heat energy in the form of hot
secondary air or hot primary air available in the power plants which conserves
electricity in the system.
A yet further object of the present invention is to propose a hopper heating
system for electrostatic precipitator initializing heat energy in the form of hot
secondary air or hot primary air available in the power plants which is eco-
friendly.
SUMMARY OF THE INVENTION
As shown in Fig.5, hot secondary air or hot primary air with/without additional
heat input through oil burners and blowers is allowed to enter from one inclined
face of the hopper at a temperature 320°C to 350°C. The hot air passes through
various compartment inside the hopper and keep the hopper warm above 160°C
and prevents condensation of dust particles. The hot gas after releasing heat
inside the hopper passes through an outlet just opposite of inlet face at a
temperature range 160° to 180°C. The dust particle remains dust without any
agglomeration which helps in taking out the dust from the hopper.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows a perspective view of an electrostatic precipitator and the hopper

assembly
Fig.2 - shows an elevational front view of a typical hopper for the ESP
Fig.3 - shows an elevational front view of a typical hopper for the ESP in which
Tubular heater is erected
Fig.4 - shows an elevational front view of a typical hopper for the ESP in which
Panel type electrical heater is erected
Fig.5 - shows an elevational front view and plan view of a typical hoper for the
ESP showing the new hopper heating system according to the present
invention
Fig.6 - shows the schematic arrangement the new hopper heating system
according to the present invention
Fig.6 - shows the schematic arrangement the new hopper heating system
according to the present invention
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As shown in Fig.6, tapping of secondary air at a temperature of 300°C or primary
air at a temperature of 290°C that is supplied from the boiler furnace through a
steel pipe is being engaged to heat up a air pre-heater (1) wherein heat energy
is supplied from flue gas (2) and heat up the air at a temperature 320°-330°C
before taking entry in the precipitator (3). The hot primary air or hot secondary
air is further heated up as and when required through a burner (4) and blower
unit (5) and heated up air at a temperature of 350°-360°C and fed into the
hopper through an inlet point (6). The hot gas after releasing heat into the
hopper (7) comes out through an outlet point (8) in the temperature range 160°-
170°C. The outlet gas pipe is connecting to the chimney (10) along with clean
gas from electrostatic precipitator through a fan (9). The hoppers are being
heated up to 320-350°C which prevents condensation of dust particles and
allows the dust particles for free flow from the hopper.

WE CLAIM
1. A hopper heating system for electrostatic precipitator utilizing heat energy
in the form of hot secondary air or hot primary air available in power
plants comprising:
- tapping of hot secondary air (300-310°C) or hot primary air (290-300°C)
from the boiler through steel pipe;
- the hot secondary air or hot primary air is heated up in a air preheater (1)
by exchange of heat from inlet flue gas (320-330°C) and outlet flue gas
after releasing heat discharged at 160-170°C;
- the hot secondary air or hot primary air is further heated up to 350-360°C
as and when required by means of a oil burner (4) and blower (5);
- the hot secondary air or hot primary air is fed into the hopper (7) through
an inlet (6) wherein the hot gas released heat inside the hopper (7);
- the hot gas releasing heat comes out through an outlet (8) at a
temperature 150-160°C which is again connected to chimney along with
clean gas from electrostatic precipitator through a fan (9);

2. The hot gas tapped off from the power plant as claimed in claim 1
wherein the quantity of tapping off in the range of 5% to 40% of total hot
secondary air that is supplied to the boiler furnace.
3. The hot gas tapped off from the power plant as claimed in claim 1
wherein the quantity of 5% to 40% of total hot primary air that is
supplied to the boiler.
Dated this 16th day of January 2009.

1. A hopper heating system for electrostatic precipitator utilizing heat energy
in the form of hot secondary air or hot primary air available in power
plants comprising:
- tapping of hot secondary air (300-310°C) or hot primary air (290-300°C)
from the boiler through steel pipe;
- the hot secondary air or hot primary air is heated up in a air preheater (1)
by exchange of heat from inlet flue gas (320-330°C) and outlet flue gas
after releasing heat discharged at 160-170°C;
- the hot secondary air or hot primary air is further heated up to 350-360°C
as and when required by means of a oil burner (4) and blower (5);
- the hot secondary air or hot primary air is fed into the hopper (7) through
an inlet (6) wherein the hot gas released heat inside the hopper (7);
- the hot gas releasing heat comes out through an outlet (8) at a
temperature 150-160°C which is again connected to chimney along with
clean gas from electrostatic precipitator through a fan (9)