FIELD OF THE INVENTION
The present invention is directed to process and a system for flue gas conditioning in an
electrostatic precipitator involving ammonia and water fog (mist) targeted to enhance the
conductivity of the ash particles in the flue and thereby favour its increased ionization,
migration and charge dissipation and in the process further improve the efficiency of such
electrostatic precipitators. Importantly, the invention on one hand is directed to improve
the efficiency of the electrostatic precipitator so much so that it would favour achieving
emission in the order of even below 50 mg/Nm3, in a conventional ESP, designed for
emission of around 150 mg/Nm3 and on the other hand achieve such high standards of
emission control involving simple , cost-effective easily available resources such as
ammonia and simple devices to achieve the desired intimate mixing of the ammonia in
the water mist to enhance its conductivity. The process and system of the invention are
thus less complicated than any other gas conditioning measure presently available to the
art and importantly is found to be very safe and low cost solution to not only meet the
present day difficult and stringent statutory emission standards/norms but importantly
also have the necessary flexibility to further absorb future trends of tightening of
statutory limits of dust emission and related environmental issues.
BACKGROUND ART
It is known in the art of handling flue gas from boilers in various utilities and finally
exhaust through chimney or any other industrial process creating such environmental
hazard, an electrostatic precipitator plays the role of emission control device by arresting
the fly ashes /flying particulates in flue, before discharging to open atmosphere. It is
developed traditionally to collect and remove suspended particulate matters from the
exhaust gas stream of any industrial process in the industries that use ESP for emission
control of exhaust include Power, Cement, Chemicals, Metals/foundries, Paper and the
like. An ESP conventionally functions on the principle of electrostatically charging the
particulate matter, either fly ash or dust particles in the flue/gas or air stream. The
charged particles are then made to pass through a series of fields created between a pair

of electrodes in the flue/gas path favoring depositing the charged particles on the
oppositely polarized collection plates or similar other collection devices. When enough
dust has been accumulated on the collector plate, it is shaken and dislodged by any
suitable vibrating means to dislodge the dust and fall in the hopper below under the
action of gravity and finally removed by conveyor means for disposal out side the plant.
The conventional emission control of flue carrying fly ash or dust particles comprise the
basic steps of:
a. Ionization for charging of flying particles.
b. Migration for transporting of charged particles to the collecting surface.
c. Charge dissipation of the charged particles onto the collecting surface.
d. Rapping on the collecting electrodes for discharging the deposited particles
causing it to dropping into hopper below ; and
e. Particle removal by conveying the particles from hopper to disposal point.
The typical construction of an ESP of conventional configuration comprises sets of
negatively charged discharging electrodes and positively charged collecting
electrodes/plates, selectively spaced apart. A cluster of such sets is a field and a number
of such fields placed in series along the stream of Flue Gas inside ESP, adapted to
settling and removing fly ash and dust particles carried by the flue in power plat
application for favoured control of emission. The ionization of the ash particles in the
flue gas depends on the potential difference between the discharging and the collecting
electrodes and also on the resistivity of the ash particles. For Indian coal available and
used frequently having typically low sulphur content produces the fly ash on burning
which possesses resistivity as high as 1-5 x 1013 ohm-cm.
This has also been a common experience in the relevant prior art of dust/ash separation
by ESP that when the coal used is generating ash with high resistivity, and whenever the
ash content of coal is higher than design value, it becomes increasingly difficult for the
conventional configuration of ESP to trap enough fly ash/dust particle or other suspended

particles in fluid air/gas medium, to make the emission sufficiently clean as per statutory
acceptance standards before emission to the atmosphere. It is therefore a common
phenomenon in the application of ESP for the purpose of control of emission that even a
well designed ESP can fail to perform to the desired efficiency if the input ash particles
vary largely in quantity and also qualitatively.
The situation is further aggravated when all the fields in an ESP are not operating with
same degree of efficiency functionally or some of the fields are out of service completely.
This shift of the operation of an ESP from the ideal conditions, which is more often the
case than not, force many industries to emit gas along with dust particles/fly ash particles
in excess of the desired and also the statutory limits.
Thus it would not be out of place to mention about the importance of operational
efficiency of an ESP when installed in any industrial plant for emission control. The
performance of such an expensive equipment needs to be evaluated and justified in
respect of the high initial cost for the ESP sufficiently large to take care of all the above
mentioned aberrations and yet comply with the increasingly stringent statutory emission
limits/norms for disposal.
One way of improving the collection efficiency of the ESP known to persons skilled in
the art, that is directed to higher collection of dust particles/ashes on the collecting
electrode/collector plate, achieved through increasing the electrical conductivity of the
medium carrying such particles, obtainable by two ways:
a. The ash particles adapted to carry more charge by way of Ionization in strong
field migrate at faster speed towards the collector electrodes/plates in the fields,
resulting in more accumulation of ash and reduced re-entrainment in the cross
current of the flue gas.

b. The charged ash particles dissipate the charge at faster speed to the collecting
electrode, due to higher conductivity of charged particles and the process is
continued even when the layer of ash on the collecting plate is relatively thicker.
Prior knowledge in the field also discloses experimental results/evidences with injection
of liquid ammonia subsequent to its vaporization using steam as the carrier medium with
varying magnitude of improvements in conductivity and collection efficiency of ash
particles. A publication by the Heavy Water Board of BARC
(http://www.heavywaterboard.org/docs/refart1.htm dated 11/3/00), disclosed such a
system using vaporized liquid ammonia embedded in steam for improving electrical
conductivity of charged particles and thus favoring improved collection in ESP,
comprising an ammonia storage tank, ammonia vaporizer, knock out drum, steam system,
instrumentation and controls. Ammonia is evaporated through a steam coil vaporizer and
the ammonia vapour is maintained at a constant pressure through a pressure regulator
valve and a pressure control system provided on the LP steam supply. A knock out drum,
is provided to de-entrain any ammonia liquid droplets entering the system. Down stream
of the ammonia knock-out drum, an auto regulating, pressure reducing valve with a pilot
valve facility is provided in order to maintain a constant down stream pressure of 2.8
kg/cm2 (g). The entire ammonia storage system is also provided with safety relieving
devices, pressure and temperature gauges, and a vent header at an elevation of 22 meters
in order to safely disperse ammonia in an unlikely emergency situation.
Thus the above said system of the prior art is complex and elaborate and in particular the
arrangement of vaporization of liquid ammonia and injecting of the same into the flue
gas, being mixed and conveyed with steam from a separate source, directed to improving
electrical conductivity of the ash particles and collection efficiency of the collector plates.
There has been therefore a continuing need in the field of emission control by the use of
ESP in power generating units or similar other industry where the emission contain flying
particles ashes of varying magnitude, to adopt simple and cost effective means and
processes for improving the ionization, migration and charge dissipation of fly ash or dust

particles of selective range of particulate size directed to favor higher and faster
collection and charge dissipation of ash particles on collector even under situations of
operation of plant with coal having high ash content or the ash particle having high
resistivity. There has been the need for a process that would be capable to not only faster
migration and collection of ash particles/dust but would also ensure charge dissipation for
neutralization on collector plates, favoring removal through conveyor to disposal point
and thereby maintaining statutory emission norms well within the limits at reasonable
cost of equipments and operations on a reliable and sustainable basis.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide a process and a system for
flue gas conditioning in an electrostatic precipitator involving readily and easily available
ammonia along with water fog (mist) which could enhance the conductivity of the ash
particles in the flue and thereby favour its increased ionization, migration and charge
dissipation and in the process further improve the efficiency of such electrostatic
precipitators.
Another object of the present invention is directed to a method and system for
conditioning flue gas involving ammonia along with water fog (mist) which would
facilitate improving the efficiency of the known electrostatic precipitator so much so that
it would favour achieving emission in the order of even below 50 mg/Nm3, as compared
to the standard permitted emission of around 150 mg/Nm3 prescribed for conventional
ESP operation and importantly achieve such high standards of emission control involving
simple, cost-effective and readily available resources.
A further object of the present invention is directed to a process and system for
conditioning flue gas involving use of ammonia which would be less complicated than
any other gas conditioning measure presently available to the art and importantly would
be very safe and low cost solution to not only meet the present day difficult and stringent

statutory emission standards/norms but importantly also have the necessary flexibility to
further absorb future trends of tightening of statutory limits of dust emission and related
environmental issues.
A further object of the present invention is directed to a method and system for
conditioning flue gas which would be adapted to contribute to the cleanliness of the
environment by emitting much lower SPM than is allowed by the statute today even
when the ash is generated in higher proportion or the ash having high resistivity for low
sulphur coal variety and the deposited layer is relatively thicker on the collector plate.
Another object of the present invention directed to a method and system of emission
control to improve collection efficiency by improving the electrical conductivity of ash
particles in flue gas medium in the ESP which would be adapted to further favour
automatic control to optimize the consumption of ammonia involved in the flue gas
conditioning.
A still further object of the present invention directed to a method and system of emission
control to improve collection efficiency by improving the electrical conductivity of ash
particles in flue gas medium in the ESP, wherein the method and the system would
enable the much required monitoring and control of the dosing of Ammonia in optimum
quantity during the process of flue gas conditioning thereby imparting the much required
flexibility in controlling the emission levels depending upon the varied operating
conditions including coal quality.
A still further object of the present invention directed to a system of safe emission control
to improve collection efficiency by improving the electrical conductivity of ash particles
in flue gas medium in the ESP, wherein the system is provided with adequate
precautionary measure to prevent ammonia gas leakage to ensure that the work
environment is free of any health hazard.

SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a process for
flue gas conditioning in an electrostatic precipitator comprising:
enhacing the conductivity of ash particles by dosing ammonia gas in the presence of
water fog such that the ammonia gets intimately and easily mix with the particles of
ash and thereby increase ionization ,migration and charge dissipation by enhanced
conductivity of the gas particles and improve efficiency of the electrostatic
precipitator.
In the above process for flue gas conditioning in an electrostatic precipitator compressed
air is used to atomize water into the required fog in said precipitator and the air trapped
from the FD fan discharge is used for conveying ammonia. Importantly, the air mixed
ammonia is distributed uniformly in the flue path of ESP.
In accordance with an aspect of the invention in the above process for flue gas
conditioning in an electrostatic precipitator the same advantageously provides for
monitoring and controlling the dosing of ammonia in optimum quantity.
Preferably in the above process for flue gas conditioning in an electrostatic precipitator
the same involves the use of specially designed spray nozzles adapted for perfect
atomization of water. Also, the process advantageously favours the use of service water
available within the plant for increasing conductivity of ash particles.

In accordance with yet another aspect of the present invention there is provided a process
for flue gas conditioning in an electrostatic precipitator comprising selectively stopping
spraying of ammonia during any disturbance leading to tripping of boiler and stoppage of
feeding of coal in the boiler.
In accordance with a preferred aspect the process for flue gas conditioning provides for
said step of controlled injection of ammonia wherein when the opacity of the flue gas
crosses a pre-selected limit preferably about 20mg/Nm3, a first solenoid valve is operated
and preset quantity of ammonia is allowed to flow whereby the action of ammonia on
flue gas is initiated in about 20-30 minutes to reduce opacity, in the instance after about
30 minutes the opacity is not maintained within 30 mg /Nm3, then a second solenoid is
adapted to be operated for flow of additional preset quantity ammonia and in the instance
the opacity is still found to cross 40 mg /Nm3 after about 30 minutes a third solenoid
valve is adapted to operate to feed in a further preset quality of ammonia and finally, in
the most unlikely event, if the opacity is still beyond 50 mg /Nm3 a bye-pass valve is
adapted to open manually to allow requisite flow for reducing the opacity to desired
level.
Also in the above process for flue gas conditioning when the opacity is decreasing the
withdrawal of ammonia is done in stages at pre selected opacity levels.

In accordance with a preferred aspect of the invention the process for flue gas
conditioning comprises initially following sequential steps of operation comprising:
starting air blower or the valve operatively connected with FD fan discharge duct
for supplying conveying air for ammonia dosing;
opening the cylinder valve;
regulating the pressure regulator at cylinder outlet such that the down stream
pressure becomes about 2.5 kg/cm2; and
charging compressed air in line by isolating valve manually to achieve air pr.
More than 4.5 kg/cm2
In accordance with yet another aspect of the present invention there is provided a system
for carrying out the process for flue gas conditioning in an electrostatic precipitator
comprising:
means for anhydrous ammonia dosing;
means for water fogging; and
control station adapted for selectively controlling said ammonia dosing and water
fogging for required conditioning of the flue gas by way of enhanced
conductivity of gas particles and thereby increasing ionization, migration and
charge dissipation for better entrapment of the dust in the precipitator.
In the above system for carrying out the process for flue gas conditioning the said means
for ammonia dosing comprises

ammonia dosing control system operatively connected to said electrostatic
precipitator inlet duct top preferably comprising
each pass of ESP inlet duct being provided with respective distribution pipeline,
each said respective distribution pipeline in the respective pass of the ESP having
provision of discharge of air and ammonia mixture such that each said hole
supplying said air and ammonia mixture face the gas flow rate with said
conveying air for the ammonia being sourced from FD fan discharge.
In the above system for carrying out the process for flue gas conditioning there is
provided water spray nozzles each having two input lines, one for water and the other for
compressed air, with both said air and water lines operatively connected to respective
common bus.
Advantageously, the above system for carrying out the process for flue gas conditioning
of the invention comprises ammonia and water fogging control station.
In accordance with a preferred aspect of the invention in the system for carrying out the
process for flue gas conditioning the said ammonia and water fogging control station
comprises:
ammonia storage outlet line connected to a pressure regulator.
plurality of ammonia supply pipelines are connected to outlet of pressure
regulator.

each said ammonia supply line comprising of one solenoid operated valve and
one flow regulator in series.
a by-pass line with one valve and one flow regulator in series are also connected
in parallel with above sets of solenoid valves & flow regulators,
a flow meter operatively connected with the common outlet line of all said
solenoid valves, said flow regulators & bye-pass line.
a bye-pass line with an isolating valve operatively connected in parallel to flow
meter.
isolating valve means as per system requirement for maintenance purpose,
a solenoid-operated valve being also mounted after the PRV, which is inter-
locked with master fuel relay of the Boiler,
an air actuated solenoid valve connected to water pipeline; and
a Pressure Switch operatively connected to compressed air line.
According to another aspect: in the above system each flow regulator of main
operating system is adapted to be pre-adjusted at requisite flow with respect to flue
volume at full load, the bye-pass flow regulator adapted to open manually for
requisite flow of ammonia with respect to desired opacity and a flow meter adapted to
show the total flow of ammonia to the system for monitoring with all by-pass lines
adapted to remain in isolated condition under normal conditions.
Importantly, the system of the invention favours controlled supply of the ammonia
based on the opacity of the flue gas such that when the opacity of the flue gas
crosses a pre-selected limit preferably about 20mg/Nm3, a first solenoid valve is

operated and a preset quantity of ammonia is allowed to flow whereby the action of
ammonia on flue gas is initiated in about 20-30 minutes to reduce opacity, in the
instance after about 30 minutes the opacity does not maintain within 30 mg /Nm3,
then a second solenoid is adapted to be operated for flow of additional preset quantity
ammonia and in the instance the opacity is still found to cross 40 mg /Nm3 after about
30 minutes, a third solenoid valve is adapted to operate and finally in the unlikely
event of the opacity remianing still beyond 50 mg /Nm3 a bye-pass valve is adapted to
open manually to allow requisite flow of ammonia for reducing the opacity to a
desired level.
The system for carrying out the process for flue gas conditioning also comprises said
bye-pass valve means and solenoid valve means adapted such that when the opacity is
decreasing the withdrawal of ammonia can be done in stages at pre selected opacity
levels.
Also, the solenoid valve at the downstream of PRV is adapted to open when master
fuel relay of an associated boiler is reset and the same is adapted to automatically
close with the tripping of the said master fule relay.
The air actuated solenoid is adapted to be energized through pressure switches when
air pressure is more than 4.5 kg/cm2.

In accordance with yet further aspect of the invention the system for carrying out the
process for flue gas conditioning comprises safety gadgets including an enclosure for
the ammonia injection control station, a sprinkler system preferably adapted for
remote operation incorporated around said ammonia injection system, a shed over the
ammonia cylinder and a water spraying system inside ammonia cylinder storage area.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1(a): is the schematic illustration of the working principle of conventional ESP.
Figure 1(b): is the illustration of the construction of conventional ESP showing the flue
path through the electrodes, spaced apart in side the duct, other components and the
collection for conveying for disposal.
Figure 2: is the schematic illustration of system of ammonia dosing and water fog
spraying arrangement according to the present invention for desired enhanced dust
collection and removal in ESP.
Figure 3: is the illustration of a sectional view (A-A) of the inlet duct, showing the
disposition of desired number of pipes with holes, connected to the ammonia header and
extending inside the inlet duct, for desired controlled ammonia dosing in the flue path.
Figure 4: is the illustration of the sectional view (B-B) of the inlet duct showing
schematically the disposition of the water nozzles inside the inlet duct for flue path and
supply line for compressed air for desired atomization of service water through said
nozzles.

Figure 5: is the schematic illustration of the control scheme for automated dry ammonia
gas injection mechanism in said flow control circuit/network to optimize ammonia
injection through Masibus controllers, according to the invention.
Figure 6(a): is the photograph of ammonia control unit.
Figure 6(b): is the inside view of the ammonia dosing local control panel.
Figure 6(c): is the automatic control and interlocking unit of the control system to ensure
desired optimum ammonia dosing.
Figure 7: is the illustration of the Piping layout and integration diagram for Ammonia
Dosing at ESP for the present invention.
Figure 8: is the graphical representation (bar chart) of the comparative figures for
Suspended Particles (SPM) before and after ammonia dosing mixed with water fog for a
number of experimental run of the system according to the present invention.
Figure 9: is the graphical presentation of the effect of reduction in SPM with selective
ammonia dosing in flue path for 20 hours.
Figure 10: is the illustration of actual quarterly measurement to check for compliance to
statutory norms of emission for different boiler-turbine units;
DETAILED DESCRIPTON OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The invention is found directed to separation of fly ash and dust particles even with high
resistivity of ash particles, typically as high as l-5x1013 ohm-cm for low sulphur Indian
Coal or with high ash content of coal, by increasing the collection efficiency of the
collecting electrodes. This cleaner emitted gas maintaining the statutory emission limits is

obtained by improving electrical conductivity of flue in the 'Fields' of the ESP. Such
improvement in electrical conductivity and increased deposition of ash particles of flue is
achieved by way of:
1. Ionizing the ash particles with more charge facilitating faster migration towards
collector plates resulting more collection and reduced re-entrainment in the cross
current of flue gas.
2. Improved conductivity of the flue gas medium carrying the fly ash particles favor
faster charge dissipation on collecting electrode, and continuing even when
relatively thicker ash layer is deposited on collector plate/electrode.
The inventive intent of the present invention is implemented in practice by a simple
system involving controlled injection of dry ammonia gas into the dust laden Flue gas
stream and atomized water fog (mist) by compressed air using specially configured spray
nozzles, to favour intimate association of the ammonia with the ash particles. The said
ammonia gas is being distributed uniformly through the entire flue path of ESP. It is
established that injection of dry ammonia gas in flue gas stream is a good way of
achieving the objective of increasing the electrical conductivity of the ash particle
suspended in flue gas. Again, it is also experimentally verified that water fogging helped
ammonia to get dissolved in the surface moisture, in a cost effective manner and
associate better with a particle of ash. The invention also makes advantageous use of the
solubility of ammonia in water, such that the mixture with embedded ash particles found
to increase ionization of particle, migration and charge dissipation because of enhanced
conductivity of ash particles, reducing the excess carried over fly ash/dust particles in
exhaust/emission, thereby also favouring improving conformity to pollution
control/statutory emission norms at lower costs through a simple method. The system of
the invention directed to achieve lesser ash content in emission from ESP, further impose
precision control through selective automation (Masibus controllers) to ascertain
optimized ammonia dosing through various gadgets comprising different flow control
valves and flow meter etc., at desired locations for a given input quantity and quality of
ash in flue. The system of the invention is further adapted to respond to air pressure

fluctuation or gas leakage and initiate preventive measures, making the system safe and
reliable and free of any occupational health hazard of operating personnel.
Reference is first invited to accompanying Figure 1(a), that illustrates the working
principle of conventional ESP systems and shows schematically how the electric field
assisted separation and collection of charged/ionized particles deposit on the collector
plate/electrode, in an electrical circuit providing the requisite ionization potential between
the electrodes selectively spaced apart, for the gas medium containing ash/dust particles
to be ionized, favoring migration and deposition on oppositely charged collector plate.
Reference is next invited to Figure 1(b) that illustrates the construction of an
conventional ESP wherein the various components are shown and the flow path of the
flue gas in relation to the electrodes/plates are indicated. An ESP possesses sets of
negatively charged discharging electrodes and the collecting electrodes, selectively
spaced apart. A number of such sets is called a "Field". A complete ESP will have a
number of such fields placed in series along the stream of Flue Gas. The ionization of ash
particles in the flue gas depends on the potential difference between the discharging and
the collecting electrodes and also on the resistivity of the ash particles. The fly ash
generated on combustion of the low sulphur coal available in India widely used in power
stations, having resistivity in the range of l-5x1013 ohm-cm. As the ash content of coal
used increases or the ash generated possess high resistivity, it becomes increasingly
difficult for the ESP to trap enough ash/dust from the flue to make the flue gas
sufficiently clean and their by a conventional ESP may fail to perform to the desired
efficiency and meet the emission statutory norms, especially when input ash particles
largely vary in quantity and quality. The efficiency of a conventional ESP may further
deteriorate if all the "Fields" is not functional to the same desired degree of efficiency
and some which are gone out of service altogether, thus violating acceptable emission
standards. As a consequence, some industries are forced to emit flue gases containing
dust particles in excess of the desired and also the statutory limits.

It is apparently clear from the schematic illustration of a standard ESP configuration as
shown in accompanying Figure 1(b) that the flue gas flows past the "Field", comprising
a number of sets of paired discharging and collecting electrodes and wherein the dust/ash
particles are deposited on the collector plate based on the electro potent force of the
electrostatically charged field facilitating the speed of migration and rate of releasing
charge to the collector. The deposited particles form a layer thick enough to retard
migration and deposition of particles further and a vibratory mechanism attached to the
collector electrode operatively dislodge the collected ash/dust particles in to a hopper to
be carried to the disposal point by conveyor means or temporary storage in silos. Thus the
performance of the conventional ESP configuration suffers from the limitation due to low
collection efficiency or poor separation of dust/ash from exhaust flue, particularly when
the resistivity of ash is high or the coal generating adverse variation in the quality and
quantity is used under compulsive situation, forcing the ESP system failing to maintain
the statutory or desired emission norms and creating environmental pollution.
The present invention is thus directed to a simple and cost effective ESP system
developed to overcome the limitation and disadvantages of the existing system and would
also operate efficiently when the coal having high ash content or high resistivity of fly
ash, by improving the electrical conductivity of flue particles or dust containing medium
by selective optimum dosing of anhydrous ammonia gas mixed with atomized water
fog/mist, resulting more ionization of particles to improve separation efficiency, such that
the clean flue gas well within the statutory emission norms is discharged at the disposal
point on economic and sustainable basis.
Reference is now invited to the accompanying Figure 2, that illustrates the schematic
arrangement of the ESP system having improved efficiency, according to the present
invention, provided with means for controlled optimized ammonia dosing in dust laden
flue gas stream conveyed trough a control network and automated control unit. An
embodiment of the present invention that worked experimentally in one of the power
generating plant of the applicants, is illustrated in said Figure 2 for describing the
manner of implementation of the present invention comprising ammonia dosing and

water fog (mist) spraying for carrying the ammonia particles favoring improved electrical
conductivity and improved separation and deposition efficiency of the collector
electrodes of the ESP. The present system is an integrated safe, compact and cost
effective one favoring stronger field ionization, faster migration and efficient deposition
on collector plate and thereby improved emission control well within the statutory limits,
even under the adverse ash generation condition for inferior quality of coal supply under
compulsive situation and the deposition efficiency is still maintained even with heavy
layer deposited on the collector plate.
The accompanying Figure 2, clearly highlights the disposition of the ammonia dosing
provision in the two separate passes, A & B, of the inlet ducts through selective numbers
of pipes one end of which are connected to the ammonia header and the other ends
extending inside the duct for uniform dosing, through a plurality of perforations on the
walls of said pipe. The sections of the inlet duct at AA and BB further illustrated in the
accompanying Figures 3 & 4, respectively. Figure 3 shows the location of the ammonia
dosing through a header and the injecting pipes Ø 15mm, preferably eight in numbers each
of which is having 19 numbers of 6mm diameter holes staggeringly located for uniform
injection of optimum quantity of dry ammonia gas.
Accompanying Figure 4 illustrates the disposition of the selectively configured nozzles
for atomization of service water by means of compressed air, to form and spray the fog or
mist for transporting ammonia gas to be closely associated with the particulates such as to
favor improving electrical conductivity of the ash/dust particles in the medium. There is
provision for at least four nozzles in each pass of the inlet duct of flue gas, from which
the spray of atomized water/fog is controlled by a set of different control valves. The
design of the spray nozzles favor perfect atomization of water to form fog/mist using
compressed air such that when the anhydrous ammonia gas comes in contact with the
water particles, they get intimately associated with the ash/dust particles and thereby
improving the ionization with more charge and thus increasing the speed of migration
and deposition and separation by faster collection on the collector electrode.

The system of the present invention was standardized incorporating automation, which
enabled the plant to respond to the various conditions of ESP and the varying quantity
and quality of the input ash. The automation in using exact optimized quantity of
ammonia for the right duration, to maintain the dust emission within the desired limit.
This desired limit is even far below the present statutory requirements. The different
subsystems of the ESP with high collection efficiency according to the invention are
described below:
AMMONIA DOSING SYSTEM
The dry commercially available ammonia gas, which is easily and economically available
in standard containers, are used for the dosing purpose. Such dosing system is
schematically illustrated in accompanying Figure 3 and also in the PI diagram of Figure
7 illustrating the ammonia dosing system. Usually 80mm NB MS pipes have been erected
from Ammonia injection control system to ESP inlet duct top where this line is bifurcated
and each time is connected with two individual 50mm NB bus/injection header from
where 8 numbers of pipes of 15mm NB are inserted in each pass of ESP inlet duct. There
are 19 numbers of holes of 6mm size have been drilled in each such 15mm NB pipe for
discharging air and ammonia mixture inside the flue inlet duct. The 15mm NB pipes are
selectively disposed in the flue path of the ESP inlet duct such that the holes drilled on
them for discharging anhydrous ammonia gas, are facing the flow of gas/flue. The
conveying air is supplied from FD fan discharge and connected with 80mm NB pipe.
WATER FOGGING
The accompanying Figure 4 illustrates the arrangement of spray nozzles and the water
and compressed air line distribution in the inlet duct flue passes of the water fogging
system of the invention. Each water spray nozzle have two input pipe lines, one is for
supply of service water having 25mm NB and the other is for compressed air in the
pressure range of 5 to 6 kg/cm2, preferably at 6 kg/cm2, through the 15mm NB line. Both

the water and the air pipelines are connected to their respective common bus of 50mm
NB. A solenoid valve S4 is fitted in 50mm NB water line and pressure switch PS1 is
mounted on the 50mm NB common air bus for safe operation i.e. water flow will be cut-
off in case of low air pressure (below 4.5 kg/ cm2).
SCHEME FOR THE AUTOMATIC INJECTION CONTROL SYSTEM/MECHANISM
Reference is now invited to the accompanying Figure 5, there are two Masibus
controllers which can take one 4-20mA input each and generate 2 contact outputs with
three set points such as C1, C2, and C3, which go on to energize the timer and thus the
respective solenoid valves S1, S2, and S3 in respective pipe lines in the auto
injection/distribution system. One toggle switch is installed in order to select "in service"
or maintenance mode and it will inhibit solenoid valves S1, S2 or S3 from opening
directly in order to inhibit the dosing process. There is another solenoid valve S4, which
get energized after 'atomizing air pressure OK' signal from pressure switch PSl is
received. A manual bypass branch is provided through the valve V3 and the flow
regulator FR4 to ensure dosing in case of maintenance of main auto control branch
equipments. The parameters maintained during the dosing process are -(a) pressure at
upstream of the PRV (pressure regulating valve mounted on ammonia gas cylinder) is
10kg/cm2 and at down stream of PRV is 2.5 kg/cm2;(b) flow regulator at each branch will
be preset at requisite quantity;(c) the pressure corresponding to "Atomizing air pressure
OK" signal is set at 4.5kg/cm2 rising in PS1.
The above logical process parameters are incorporated in fly ash PLC. The SPM signal
brought from DCS to Masibus controllers, which is housed in a local JB. The total dosing
hardware except the PRV are housed in an enclosed chamber with air purging facility.
The in-service/maintenance switch is mounted in the local JB.
AMMONIA INJECTION AND WATER FOGGING CONTROL STATION

The control station comprises one pressure regulator mounted at ammonia cylinder outlet
line and regulator outlet is connected with 6mm NB stainless steel pipe. Three numbers
solenoid valves (S1, S2 & S3) and 3 numbers flow regulators (FR1, FR2, & FR3) are
connected in parallel with the pressure regulator outlet pipe as shown in the
accompanying Figure 5. One bypass line with one valve (V3) and one flow regulator
(FR4) in series are also connected in parallel with the other three-solenoid valve operated
lines. Finally one flow meter (FM) is connected with the common outlet line to monitor
optimum flow of ammonia to the carrying airbus. One bypass line with one valve (V7) is
connected in parallel to the final flow meter (FM). There are also provisions for
necessary isolating valves (e.g. V2, V4, V5, V6 etc) suitably mounted in the control
network at selective locations based on system requirements for maintenance purpose.
One solenoid-operated valve (V1) is also mounted after the PRV, which is interlocked
with master fuel relay of the boiler. Referring back to accompanying Figure 2, it may be
noted that an air actuated solenoid valve (S4) is connected with 50mm NB water line to
favor air assisted spray of atomized water fog through the nozzles and one pressure
switch (PS1) is connected in 50mm NB compressed air line which enable operation of
solenoid valve S4 by sensing and sending 'atomization pressure OK' signals. The system
thus ensure the controlled injection of dry ammonia gas along with water fogging in
desired weight proportion such that the intimate association of dust/ash particles with wet
ammonia favour achieving improved electrical conductivity of the ash particles and
thereby improved ionization, migration and collection on the collector electrodes/plates
in the fields of the ESP.
IMPLEMENTING THE DRY AMMONIA GAS AND WATER FOG SPRAY
CONTROL AND THE LOGIC CONTROL FOR DESIRED CONTROLLED RATE OF
DOSING
As already described the system maintains the pressure of ammonia gas downstream of
the PRV at 2.5kg/cm2. Each flow regulator of main operating system is preadjusted at
requisite flow with respect to volumetric flow of flue at full load. The Bye-pass flow

regulator is opened manually for requisite flow of ammonia with respect to desired
opacity.
Final flow meter indicates the total flow of ammonia to the system. All bye-pass lines are
normally kept in isolated condition from the main flow path. When the opacity of the flue
gas crosses 20mg/Nm3, the first solenoid valve (S1) operates to allow preset quantity of
ammonia gas to the system. The action of ammonia on flue gas is initiated within about
20-30 minutes time and the opacity starts falling. If after 30 minutes, the opacity does not
maintain within 30 mg /Nm3, then the second solenoid valve (S2) will automatically
operate for an additional flow of ammonia gas. If the opacity still crosses 40 mg /Nm3
after 30 minutes time, the third solenoid valve (S3) comes into operation. Finally, if the
quantity of ammonia dosing is found to be not enough to arrest the increasing rate of
opacity beyond 50 mg /Nm3, the bye-pass valve (V3) is opened manually to allow
requisite quantity of ammonia to reduce the opacity value.
When the opacity is decreasing, the ammonia flow is gradually withdrawn at successive
opacity of 35, 25 & 18 mg /Nm3, by gradual closing of valve V3, if opened, and
automatic switching off of S3, S2 & S1 solenoid valves respectively in succession. The
Solenoid valve at the downstream of PRV opens when master fuel relay (MFR) of the
associated boiler is reset and same will automatically close with the tripping of MFR. The
solenoid valve S4 gets energized by C4 through pressure switch PS1 when air pressure is
more than 4.5kg/cm2. The automated operation of the local control unit as illustrated in
the accompanying Figure 6(a) and 6(b), involving the pressure switch and flow
controller receiving signal such as to operatively control dosing by the operation of
selective solenoid valves energized by timer corresponding to set points to favor
obtaining desired opacity of flue ensuring favored higher electrical conductivity leading
to faster ionization, migration and deposition of ash/dust particles and substantially clean
emission.
OPERATING PROCEDURE

The process of operation of the system of controlled ammonia injection along with water
fog for enhanced collection and separation of ash/dust particles from the flue in ESP are
implemented in the following sequences:
1. The air blower is to be started or valve of 80mm NB pipe connected with FD Fan
discharge duct is to be opened for supplying conveying air for ammonia injection.
2. The ammonia gas cylinder valve is opened.
3. The pressure regulating valve (PRV) at cylinder outlet is to be opened so that the
down stream pressure is adjusted to 2.5kg/cm2.
4. Compressed air line is charged by opening isolating valve manually to achieve air
pressure more than 4.5 kg/cm2.
5. The automatic charging of the ammonia gas and fog is implemented as already
described based on the threshold limit of the opacity of flue achieved.
OPERATIONAL SAFETY MEASURES:
Following steps are taken to combat the health hazard relating to handling or leakage of
the dry ammonia gas when come in contact with operators body or exposer to eye etc:
1. The ammonia pipeline is checked for leak-proofness or any damage, being
hydraulically pressure tested at 50 kg/cm2.
2. Low-pressure line of ammonia is also tested for leaks.
3. The enclosure provided to house the operating devices of the system for ammonia
injection control station also provide for additional safety.

4. Sprinkler system has been incorporated around ammonia injection station that can
be operated remotely to entrap traces of ammonia gas in surrounding to be
dissolved and settled down.
5. A Shed is provided over ammonia cylinder to avoid exposure to direct sunlight.
6. Water spraying system provided inside NH3 Cylinder storage area to entrap traces
of leakage.
7. Sufficient care is taken during Nh3 cylinders handling and transportation to use
point/storage etc.
8. Following periodic checks in the long term operation further ensured safe
operation:
a. Monthly checking of NH3 concentration in surrounding;
b. Atmosphere around ammonia injection control station is checked;
c. Monthly checking of flue gas for NH3 content;
d. Monthly checking of ash for NH3 content;
e. Physical checking of ESP internals ducts ID fan impeller, casing etc for
any deposition or damage by erosion etc.
OBSERVED RESULTS OF THE SYSTEM IN OPERATION
The accompanying Figure 8 shows the graphical representation (bar chart) of the
comparative figures for Suspended Particles (SPM) before and after ammonia dosing
mixed with water fog for a number of experimental run of the system according to the
present invention. The experimental observation while implementing an embodiment of
the present invention establishes results in terms of achieving emission in the order of
below 50 mg /Nm3, as compared to the normal emission of 150 to 300 mg/Nm3 obtained
in conventional ESP operation. The effect of reduction in SPM with selective ammonia

dosing in flue path for 20 hours is shown graphically in accompanying Figure 9,
according to the controlled ammonia dosing system in ESP operation as of the present
invention. Accompanying Figure 10 illustrates the actual quarterly measurement to
check for compliance to statutory norms of emission for different boiler-turbine units in
power plants. The above results thus establish the satisfactory separation and deposition
of ash/dust particles from the flue prior to disposal in environment, well within the
statutory emission norms.
It is thus possible by way of this invention to achieve an automated system for emission
control in ESP in a cost effective, safe and simple manner. The present invention is
directed to a system involving controlled injection of dry ammonia gas in selectively
preset logic controlled incremental dosing along with preferred mixing with water fog
atomized through nozzle by compressed air such as to reduce the ash content by
increasing the electrical conductivity of particles and their ionization, migration and
increased deposition on the collector plate of ESP field and thereby the measure of
opacity of the flue and the final emission contains ash particles at the point of disposal
consistently well within desired as well as the statutory pollution control limits, thus
protecting environment at less cost even while enabling use of high ash content coal or
the high resistivity of ash particles.

WE CLAIM:
1. A process for flue gas conditioning in an electrostatic precipitator comprising:
enhacing the conductivity of ash particles by injecting ammonia gas in the
presence of water fog such that the ammonia gets intimately and easily mixed
with the particles of ash and thereby increase ionization ,migration and charge
dissipation by enhanced conductivity of the gas particles and improve efficiency
of the electrostatic precipitator.
2. A process for flue gas conditioning in an electrostatic precipitator as claimed in
claim 1 wherein compressed air is used to atomize water into the required fog in
said precipitator and the air trapped from the FD fan discharge is used for
conveying ammonia.
3. A process for flue gas conditioning in an electrostatic precipitator as claimed in
anyone of claims 1 or 2 wherein the air mixed ammonia is distributed uniformly
in the flue path of ESP.
4. A process for flue gas conditioning in an electrostatic precipitator as claimed in
anyone of claims 1 to 3 comprising monitoring and controlling the dosing of
ammonia in optimum quality.

5. A process for flue gas conditioning in an electrostatic precipitator as claimed in
anyone of claims 1 to 4 comprising using spray nozzles adapted for perfect
atomization of water.
6. A process for flue gas conditioning in an electrostatic precipitator as claimed in
anyone of claims 1 to 5 comprising using service water available within the plant
for increasing conductivity of ash particles.
7. A process for flue gas conditioning in an electrostatic precipitator as claimed in
anyone of claims 1 to 6 comprising selectively stopping spraying of ammonia
during any disturbance leading to tripping of boiler and stoppage of feeding of
coal in the boiler.
8. A process for flue gas conditioning as claimed in anyone of claims 1 to 7 wherein
when the opacity of the flue gas crosses a pre-selected limit preferably about
20mg/Nm3, a first solenoid valve is operated and preset quantity of ammonia is
allowed to flow whereby the action of ammonia on flue gas is initiated in about
20-30 minutes to reduce opacity, in the instance after about 30 minutes the
opacity is not maintained within 30 mg /Nm3, then a second solenoid is adapted to
be operated for flow of additional preset quantity ammonia and in the instance the
opacity is still found to cross 40 mg /Nm3 after about 30 minutes a third solenoid
valve is adapted to operate to feed in a further preset quality of ammonia and
finally, in the unlikely event, if the opacity is still beyond 50 mg /Nm3 a bye-pass

valve is adapted to open manually to allow requisite flow for reducing the opacity
to desired level.
9. A process for flue gas conditioning as claimed in anyone of claims 1 to 8 wherein
when the opacity is decreasing the withdrawal of ammonia is done in stages at pre
selected opacity levels.
10. A process for flue gas conditioning as claimed in anyone of claims 8 or 9
comprising initially following sequential steps of operation comprising:
starting air blower or the valve operatively connected with FD fan discharge duct
for supplying conveying air for ammonia injection;
opening the cylinder valve;
opening the pressure regulator at cylinder outlet such that the down stream
pressure becomes about 2.5 kg/cm2; and
charging compressed air in line by isolating valve manually to achieve air pr.
more than 4.5 kg/cm2
11. A system for carrying out the process for flue gas conditioning in an electrostatic
precipitator as claimed in anyone of claims 1 to 10 comprising:
means for anhydrous ammonia dosing ;
means for water fogging; and
control station adapted for selectively controlling said ammonia dosing and water
fogging for required conditioning of the flue gas by way of enhanced conductivity

of gas particles and thereby increasing ionization, migration and charge
dissipation for better entrapment of the dust in the precipitator.
12. A system for carrying out the process for flue gas conditioning as claimed in
claim 11 wherein said means for ammonia dosing comprises
ammonia injection control system operatively connected to said electrostatic
precipitator inlet duct top preferably comprising
each pass of ESP inlet duct being provided with respective distribution pipeline,
each said respective distribution pipeline in the respective pass of the ESP having
provision of discharge of air and ammonia mixture such that each said hole
supplying said air and ammonia mixture face the gas flow rate with said
conveying air for the ammonia being sourced from FD fan discharge.
13. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 or 12 comprising water spray nozzles each having two input
lines ,one for water and the other for compressed air, with both said air and water
lines operatively connected to respective common bus .
14. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 to 13 comprising ammonia and water fogging control station.
15. A system for carrying out the process for flue gas conditioning as claimed in
claim 14 wherein said ammonia and water fogging control station comprises:

ammonia storage outlet line connected to a pressure regulator,
plurality of ammonia supply pipelines are connected to outlet of pressure
regulator.
each said ammonia supply line comprising of one solenoid operated valve and one
flow regulator in series.
a by-pass line with one valve and one flow regulator in series are also connected
in parallel with above sets of solenoid valves & flow regulators,
a flow meter operatively connected with the common outlet line of all said
solenoid valves, said flow regulators & bye-pass line.
a bye-pass line with an isolating valve operatively connected in parallel to flow
meter.
isolating valve means as per system requirement for maintenance purpose,
a solenoid-operated valve being also mounted after the PRV, which is inter-
locked with master fuel relay of the Boiler,
an air actuated solenoid valve connected to water pipeline; and
a Pr.Sw. operatively connected to compressed air line.
16. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 to 15 wherein each flow regulator of main operating system
is adapted to be pre-adjusted at requisite flow with respect to flue volume at full
load, the bye-pass flow regulator adapted to open manually for requisite flow of
ammonia with respect to desired opacity and a flow meter adapted to show the

total flow of ammonia to the system for monitoring with all by-pass lines adapted
to remain in isolated condition under normal conditions.
17. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 to 16 adapted such that when the opacity of the flue gas
crosses a pre-selected limit preferably about 20mg/Nm3, a first solenoid valve is
operated and a preset quantity of ammonia is allowed to flow whereby the action
of ammonia on flue gas is initiated in about 20-30 minutes to reduce opacity, in
the instance after about 30 minutes the opacity does not maintain within 30 mg
/Nm3, then a second solenoid is adapted to be operated for flow of additional
preset quantity ammonia and in the instance the opacity is still found to cross 40
mg /Nm3 after about 30 minutes a third solenoid valve is adapted to operate and
finally in the unlikely event of the opacity remaining still beyond 50 mg /Nm3 a
bye-pass valve is adapted to open manually to allow requisite flow of ammonia
for reducing the opacity to a desired level.
18. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 to 17 comprising said bye-pass valve means and solenoid
valve means adapted such that when the opacity is decreasing the withdrawal of
ammonia can be done in stages at pre selected opacity levels.
19. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 to 18 wherein the solenoid valve at the downstream of PRV
is adapted to open when master fuel relay of an associated boiler is reset and the

same is adapted to automatically close with the tripping of the said master Me
relay.
20. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 to 19 wherein the air actuated solenoid is adapted to be
energized through pressure switches when air pressure is more than 4.S kg/cm2.
21. A system for carrying out the process for flue gas conditioning as claimed in
anyone of claims 11 to 20 comprising safety gadgets including an enclosure for
the ammonia injection control station, a sprinkler system preferably adapted fro
remote operation incorporated around said ammonia injection system, a shed over
the ammonia cylinder and a water spraying system inside ammonia cylinder
storage area.
22. A process for flue gas conditioning involving electrostatic precipitator and a
system for carrying out such a process substantially as herein described and
illustrated with reference to the accompanying figures.

A process for flue gas conditioning in an electrostatic precipitator(ESP) and a system
thereof involving ammonia and water fog (mist) targeted to enhance the conductivity of
the ash particles in the flue, favouring increased ionization, migration and charge
dissipation to improve the efficiency of ESP. Importantly, the invention is directed not
only to improve the efficiency of ESP system but would favour achieving emission in the
order of even below 50 mg/Nm3, as compared to the general designed emission of around
150 mg/Nm3 for conventional ESP operation which also is often unachievable because
of usual operational aberrations. The system achieve high standards of online emission
control involving cost-effective easily available resources like anhydrous ammonia and
simple devices for desired intimate mixing of the ammonia in the water mist to improve
conductivity. The system is less complicated than any other gas conditioning measure
presently available and very safe and low cost solution to meet the present day difficult
and stringent statutory emission standards/norms and also capable to further absorb future
trends of tightening of statutory emission limits.