Title of Invention	HOT GAS FILTER SYSTEM WITH SAFETY FILTER ASSEMBLY AND PRESSURE PULSE CLEANING
Abstract	Accordingly there is provided an improved hot gas filter system in which a safety filter made of sintered porous ceramic is mounted on the main ceramic filter by means of at least one high density ceramic gasket seal within a secure filter holder assembly. Such a safety filter is more porous and does not interfere with the normal filtration process by the main filter. In a situation of failure of the main filter due to breakage, the dusty gas passes through the safety filter and the dust quickly clogs the pores of the safety filter due to its deep bed filtration characteristics. The clogged safety filter does not allow the dust from the broken main filter to mix with the clean gas and thus protect the turbine and downstream components due to particle damage in the event of a main filter failure. This porous safety filter also modulates the pressure pulses during the cleaning cycle to output a higher and uniform cleaning intensity along the length of the main filter element because the porous safety filter is placed directly above the main filter and thus the dust on the main filter is dislodged with lower pressure pulse requirement.

Title of Invention

HOT GAS FILTER SYSTEM WITH SAFETY FILTER ASSEMBLY AND PRESSURE PULSE CLEANING

Abstract

Accordingly there is provided an improved hot gas filter system in which a safety filter made of sintered porous ceramic is mounted on the main ceramic filter by means of at least one high density ceramic gasket seal within a secure filter holder assembly. Such a safety filter is more porous and does not interfere with the normal filtration process by the main filter. In a situation of failure of the main filter due to breakage, the dusty gas passes through the safety filter and the dust quickly clogs the pores of the safety filter due to its deep bed filtration characteristics. The clogged safety filter does not allow the dust from the broken main filter to mix with the clean gas and thus protect the turbine and downstream components due to particle damage in the event of a main filter failure. This porous safety filter also modulates the pressure pulses during the cleaning cycle to output a higher and uniform cleaning intensity along the length of the main filter element because the porous safety filter is placed directly above the main filter and thus the dust on the main filter is dislodged with lower pressure pulse requirement.

Full Text	2 FIELD OF INVENTION This present invention relates generally to hot gas cleanup system used for cleaning the coal gas from ash particles and impurities at high pressure and high temperature for protecting the turbine and downstream components in advanced coal based combined cycle power generation. More particularly, the invention relates to an improved hot gas filter system for filtration of fine ash particles of coal fuel gas. BACKGROUND OF THE INVENTION Coal is an abundant cheaper source of fossil fuel energy for electric power generation. The present thermal power plants burn coal to generate electric power at efficiency around 30% and the polluting emissions affect the atmosphere. Hence there is a necessity to burn coal in a more efficient way with a higher environmental performance. In the newer coal based combined cycles, the coal is burnt partially to gasify at high pressure and high temperature to generate coal fuel gas, also called syn gas to drive the toping Brayton gas turbine cycle and then a bottoming Rankine steam cycle in the integrated gasification combined cycle (IGCC) to achieve higher efficiency and lower emissions. 3 In the above coal gasification process, the high pressure high temperature coal fuel gas of carbon monoxide and hydrogen fuel has ash particulates which can adversely damage the costly turbine. Hence the coarse particles in the fuel gas are removed in cyclones and fine particles are removed in a wet venturi scrubber or dry hot gas filter having ceramic filter elements. The use of hot gas filter with ceramic filter elements can filter fine particles in the range of 0.1 - 20 microns to a very low concentration around 1 mg/Nm3 to meet the stringent demands of turbine requirements without cooling the gas. The existing hot gas filter system has a plurality of ceramic filter elements supported on a metallic tube sheet in a filter pressure vessel with an inlet on the filter side for the entry of dusty coal fuel gas and an outlet for the exit of filtered clean fuel gas. When the particles accumulate on the filter surface during filtration, the pressure drop increases and the filter surface is cleaned by a reverse pulse jet in an opposite direction through the filter elements at a pressure two to three times the operating pressure using a conventional jet pulse venturi to dislodge the dusty cake formed on the outer surface of the filter. The filtration process occurs at low velocities in the range of 50 - 200 metre/hour and at these low Reynolds number the flow induced vibration failure of filter elements do not occur. But the filter elements undergo a momentum shock during reverse pulse cleaning depending on the magnitude of the pulse pressure and the duration including a thermal shock due to cold pulse jet gas coming in 4 contact with the hot ceramic filter elements. This phenomenon lead to occasional breakage of brittle ceramic filter elements and consequently the dust concentration in the clean gas can increase above the required level and damage the turbine. This contingency leads to costly unscheduled shut down of power plant. In the prior art of US Patent 6312490, a fibrous filter has been described to serve as a failsafe device in the event of main filter damage. But this design involving a fibrous filter may not have sufficient strength to withstand the momentum shock during the pulse cleaning cycle, and may not further withstand the force required for effective sealing of the fibrous filter element in the assembly. Fibrous filer is susceptible to breakage easily. Further this art does not provide a secure assembly of the fibrous filter with the main filter. OBJECT OF THE INVENTION It is therefore an object of this invention to propose an improved hot gas filter system which eliminates the disadvantages of the prior art. Another object of this invention is to propose an improved hot gas filter system which enables a secured assembly of a sintered porous ceramic filter with the main filter of the system. 5 A further object of this invention is to propose an improved hot gas filter system which reduces the pulse cleaning pressure and provides uniform cleaning intensity along the main filter. SUMMARY OF THE INVENTION Accordingly there is provided an improved hot gas filter system in which a safety filter made of sintered porous ceramic is mounted on the main ceramic filter by means of at least one high density ceramic gasket seal within a secure filter holder assembly. Such a safety filter is more porous and does not interfere with the normal filtration process by the main filter. In a situation of failure of the main filter due to breakage, the dusty gas passes through the safety filter and the dust quickly clogs the pores of the safety filter due to its deep bed filtration characteristics. The clogged safety filter does not allow the dust from the broken main filter to mix with the clean gas and thus protect the turbine and downstream components due to particle damage in the event of a main filter failure. This porous safety filter also modulates the pressure pulses during the cleaning cycle to output a higher and uniform cleaning intensity along the length of the main filter element because the porous safety filter is placed directly above the main filter and thus the dust on the main filter is dislodged with lower pressure pulse requirement. 6 BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING Figure 1 shows a hot gas filter system according to the invention. Figure 2 schematically shows assembly of the safety filter with the main filter according to the present invention. DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION Hot gas filter system used in advanced coal based combined cycles has to be designed to operate at a pressure around 30 kg/sq. cm and temperature around 300 to 500 degree Celsius for removing fine ash particles in the range of 0.1 to 20 microns present in coal gasified fuel gas stream. As shown in figure - 1, the hot gas filter system (15) comprises of a ceramic insulation lined carbon steel pressure vessel (10) with an alloy steel or stainless steel metallic tube sheet (04) for supporting a plurality hundreds of ceramic filter elements (02) in groups. The high-pressure ash laden coal fuel gas stream enters an port (11) of the vessel (10) and the ash particles are filtered by said plurality of main filter elements (02) in groups and the filtered clean fuel gas is 7 allowed to exit out of the filter system. When the pressure drop of the filter system increases and reaches a particular value, due to the increasing ash dust layer on the filter surface, a pulse flow of nitrogen or of the cleaned fuel gas itself is activated through a pulse gas inlet (13) into a pulse gas plenum (14) and then through the group of filter elements (02) to dislodge the dust on the filter surfaces of the group and restore the pressure drop. The different groups of filter elements (02) are cleaned alternatively so that when one group is under pulse gas cleaning, the other groups will supply filtered clean gas to ensure continuous flow of clean gas for the process. The main filter elements (02) are porous ceramic like sintered silicon carbide or sintered aluminosilicate tube with a fine particulate coating of particular pore size distribution for removing fine ash particles on the surface of the filter itself so that fine particles do not enter deeply into the pore structure of the main filter, as otherwise it will not dislodge out easily during pulse cleaning. Figure - 2 illustrates a secure method of mounting a safety filter (01) made of sintered porous ceramic which is assembled above the main filter (02). The safety filter (01) is a porous ceramic annular tube of short length and is placed above the main filter (02) which has a sintered fine particulate coating (03) for filtering fine particles and such a coating is not required for the safety filter. The main filter (02) is supported on a metallic tube sheet (04) and is housed in a filter holder assembly (05) with a cushion of at least-one high-density ceramic fiber packing seal. (06). The filter holder (05) is welded to the tube sheet (04). 8 The safety filter (01) is placed above the main filter (02) with an annular ceramic fiber gasket (07) interposed therein. A ceramic fibre packing seal (06) and the annular ceramic fiber gasket (07) act as a leak proof seal for the gas and also act as thermal expansion cushion. The main filter element (02) is below the tube sheet (04) in the dusty gas stream and the safety filter (01) is above the tube sheet (04) in the clean gas stream. The safety filter (01) is a porous annular filter made of sintered silicon carbide or sintered aluminosilicate with a high apparent porosity of around 50 to 60 % to offer low pressure drop during normal filtration and have sufficient mechanical strength. This porous safety filter is also of short length, for example, around 100 mm compared to the main filter having length around 2000 mm. During normal filtration, the gas filtered by the main filter (02) passes through the safety filter (01) with a low-pressure drop. When the main filter (02) fails due to breakage, the dusty gas enters the porous safety filter (01) and quickly clogs the pores in the safety filter (01) with dust particles and soon the clogged safety filter (01) does not allow the passage of dusty gas from the broken filter element (02) into the clean gas stream. The safety filter (01) thus acts like a fuse, cutting off the flow of dusty gas due to the breakage of the main filter (02) below it. This protective method prevents costly unscheduled shut down of power plant and the broken filter elements can be replaced during planned shut down and maintenance period. A metallic cover (08) is disposed at the top of the safety filter (01) to locate and close the safety filter (01) and form a leak proof seal using the annular ceramic fibre gasket (07) placed between the safety filter (01) and the top metallic cover (08). 9 At least two bolting screws (09) are provided which securely hold the entire safety filter assembly (01, 07, 09) in place over the main filter (02) and fastened into the threads of the filter holder (05). Since the safety filter (01) is directly disposed above the main filter (02), during the cleaning cycle the pulse gas passes through the safety filter into the main filter without any loss of pulse energy and this gives additional advantage in offering higher uniform cleaning intensity along the filter tube and the filters can be cleaned with lower pressure pulse magnitude than the conventional pulse jet cleaning with venturi and nozzle design. In the conventional jet pulse cleaning method, a venturi nozzle is positioned with a gap in the surrounding conical plenum above the group of filter elements to serve as clean gas path and there is a loss of pulse energy through this gap requiring higher pulse jet pressure. For example if the operating pressure is around 30 kg/sq.cm., the pulse pressure is of the order of 1.1 to 1. 4 times the operating pressure in the case of pressure pulse cleaning through the porous safety filter but in the conventional jet pulse venturi and nozzle case, the pressure pulse required is of the order of 3 to 4 times the operating pressure. Thus the safety filter design additionally brings down the pressure rating of pulse gas pressure vessels, pulse blow down valves and pulse gas lines, all leading to lowering of capital cost of the hot gas filter system. 10 WE CLAIM 1. An improved hot gas filter system (15) for filtration of fine ash particles of coal fuel gas including online pressure pulse cleaning, comprising : - a pressure vessel (10) with a metallic tubesheet (04) supporting a plurality of main filter elements (02) disposed in groups, the vessel (10) having at least one each inlet port (11) and outlet port (12) for allowing entry of high pressure ash laden gas, filtering the ash particles by the main filter elements (02), and exit of the filtered clean fuel gas out of the system (15), the group of main filter elements (02) being housed in a filter holder assembly (05) with at least one packing seal (06); - a pulse gas plenum (14) having at least one pluse gas inlet (13) disposed above said plurality of main filter elements (10) for transmitting pulse flow of nitrogen or cleaned fuel gas to dislodge the dust from the filter surface including restoration of the pressure drop; and 11 - at least one safety filter (01) placed above the main filter (02) with a gasket (07) interposed in between such that the main filter element (02) is disposed below the tube sheet (04) in the dusty gas stream and the safety filter (01) positioned above the tube sheet (04) in the clean gas stream, the pulse gas passing through the safety filter (01) into the main filter (02) without any loss of pulse energy allowing cleaning of the filters (01, 02) with lower pulse magnitude. 2. The system as claimed in claim 1, wherein the main filter elements (02) comprise porous ceramic like sintered silicon carbide or sintered aluminosilicate tube having a sintered fine particular coating (3), and wherein the safety filter (01) comprises a porous ceramic annular tube of shorter length, for example, around lOOmn compared to the length of the main filter (02) of length around 2000mm. 3. The system as claimed in claim 1, wherein the packing seal (06) comprises a high density ceramic fibre, wherein the gasket (07) comprises an annular ceramic fibre, and wherein the packing seal (06) and the gasket (07), acting as a leak proof seal for the gas including a thermal expansion cushion. 12 4. An improved hot gas filter system for filtration of fine ash particles of coal fuel gas including online pressure pulse cleaning as substantially described and illustrated herein with reference to the accompanying drawings. Accordingly there is provided an improved hot gas filter system in which a safety filter made of sintered porous ceramic is mounted on the main ceramic filter by means of at least one high density ceramic gasket seal within a secure filter holder assembly. Such a safety filter is more porous and does not interfere with the normal filtration process by the main filter. In a situation of failure of the main filter due to breakage, the dusty gas passes through the safety filter and the dust quickly clogs the pores of the safety filter due to its deep bed filtration characteristics. The clogged safety filter does not allow the dust from the broken main filter to mix with the clean gas and thus protect the turbine and downstream components due to particle damage in the event of a main filter failure. This porous safety filter also modulates the pressure pulses during the cleaning cycle to output a higher and uniform cleaning intensity along the length of the main filter element because the porous safety filter is placed directly above the main filter and thus the dust on the main filter is dislodged with lower pressure pulse requirement.

Full Text

2
FIELD OF INVENTION
This present invention relates generally to hot gas cleanup system used for
cleaning the coal gas from ash particles and impurities at high pressure and high
temperature for protecting the turbine and downstream components in advanced
coal based combined cycle power generation. More particularly, the invention
relates to an improved hot gas filter system for filtration of fine ash particles of
coal fuel gas.
BACKGROUND OF THE INVENTION
Coal is an abundant cheaper source of fossil fuel energy for electric power
generation. The present thermal power plants burn coal to generate electric
power at efficiency around 30% and the polluting emissions affect the
atmosphere. Hence there is a necessity to burn coal in a more efficient way with
a higher environmental performance.
In the newer coal based combined cycles, the coal is burnt partially to gasify at
high pressure and high temperature to generate coal fuel gas, also called syn
gas to drive the toping Brayton gas turbine cycle and then a bottoming Rankine
steam cycle in the integrated gasification combined cycle (IGCC) to achieve
higher efficiency and lower emissions.

3
In the above coal gasification process, the high pressure high temperature coal
fuel gas of carbon monoxide and hydrogen fuel has ash particulates which can
adversely damage the costly turbine. Hence the coarse particles in the fuel gas
are removed in cyclones and fine particles are removed in a wet venturi scrubber
or dry hot gas filter having ceramic filter elements. The use of hot gas filter with
ceramic filter elements can filter fine particles in the range of 0.1 - 20 microns to
a very low concentration around 1 mg/Nm3 to meet the stringent demands of
turbine requirements without cooling the gas.
The existing hot gas filter system has a plurality of ceramic filter elements
supported on a metallic tube sheet in a filter pressure vessel with an inlet on the
filter side for the entry of dusty coal fuel gas and an outlet for the exit of filtered
clean fuel gas. When the particles accumulate on the filter surface during
filtration, the pressure drop increases and the filter surface is cleaned by a
reverse pulse jet in an opposite direction through the filter elements at a
pressure two to three times the operating pressure using a conventional jet pulse
venturi to dislodge the dusty cake formed on the outer surface of the filter. The
filtration process occurs at low velocities in the range of 50 - 200 metre/hour
and at these low Reynolds number the flow induced vibration failure of filter
elements do not occur. But the filter elements undergo a momentum shock
during reverse pulse cleaning depending on the magnitude of the pulse pressure
and the duration including a thermal shock due to cold pulse jet gas coming in

4
contact with the hot ceramic filter elements. This phenomenon lead to occasional
breakage of brittle ceramic filter elements and consequently the dust
concentration in the clean gas can increase above the required level and damage
the turbine. This contingency leads to costly unscheduled shut down of power
plant.
In the prior art of US Patent 6312490, a fibrous filter has been described to serve
as a failsafe device in the event of main filter damage. But this design involving
a fibrous filter may not have sufficient strength to withstand the momentum
shock during the pulse cleaning cycle, and may not further withstand the force
required for effective sealing of the fibrous filter element in the assembly.
Fibrous filer is susceptible to breakage easily. Further this art does not provide a
secure assembly of the fibrous filter with the main filter.
OBJECT OF THE INVENTION
It is therefore an object of this invention to propose an improved hot gas filter
system which eliminates the disadvantages of the prior art.
Another object of this invention is to propose an improved hot gas filter system
which enables a secured assembly of a sintered porous ceramic filter with the
main filter of the system.

5
A further object of this invention is to propose an improved hot gas filter system
which reduces the pulse cleaning pressure and provides uniform cleaning
intensity along the main filter.
SUMMARY OF THE INVENTION
Accordingly there is provided an improved hot gas filter system in which a safety
filter made of sintered porous ceramic is mounted on the main ceramic filter by
means of at least one high density ceramic gasket seal within a secure filter
holder assembly. Such a safety filter is more porous and does not interfere with
the normal filtration process by the main filter. In a situation of failure of the
main filter due to breakage, the dusty gas passes through the safety filter and
the dust quickly clogs the pores of the safety filter due to its deep bed filtration
characteristics. The clogged safety filter does not allow the dust from the broken
main filter to mix with the clean gas and thus protect the turbine and
downstream components due to particle damage in the event of a main filter
failure. This porous safety filter also modulates the pressure pulses during the
cleaning cycle to output a higher and uniform cleaning intensity along the length
of the main filter element because the porous safety filter is placed directly
above the main filter and thus the dust on the main filter is dislodged with lower
pressure pulse requirement.

6
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a hot gas filter system according to the invention.
Figure 2 schematically shows assembly of the safety filter with the main filter
according to the present invention.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
PRESENT INVENTION
Hot gas filter system used in advanced coal based combined cycles has to be
designed to operate at a pressure around 30 kg/sq. cm and temperature around
300 to 500 degree Celsius for removing fine ash particles in the range of 0.1 to
20 microns present in coal gasified fuel gas stream.
As shown in figure - 1, the hot gas filter system (15) comprises of a ceramic
insulation lined carbon steel pressure vessel (10) with an alloy steel or stainless
steel metallic tube sheet (04) for supporting a plurality hundreds of ceramic filter
elements (02) in groups. The high-pressure ash laden coal fuel gas stream
enters an port (11) of the vessel (10) and the ash particles are filtered by said
plurality of main filter elements (02) in groups and the filtered clean fuel gas is

7
allowed to exit out of the filter system. When the pressure drop of the filter
system increases and reaches a particular value, due to the increasing ash dust
layer on the filter surface, a pulse flow of nitrogen or of the cleaned fuel gas
itself is activated through a pulse gas inlet (13) into a pulse gas plenum (14) and
then through the group of filter elements (02) to dislodge the dust on the filter
surfaces of the group and restore the pressure drop. The different groups of
filter elements (02) are cleaned alternatively so that when one group is under
pulse gas cleaning, the other groups will supply filtered clean gas to ensure
continuous flow of clean gas for the process.
The main filter elements (02) are porous ceramic like sintered silicon carbide or
sintered aluminosilicate tube with a fine particulate coating of particular pore size
distribution for removing fine ash particles on the surface of the filter itself so
that fine particles do not enter deeply into the pore structure of the main filter,
as otherwise it will not dislodge out easily during pulse cleaning.
Figure - 2 illustrates a secure method of mounting a safety filter (01) made of
sintered porous ceramic which is assembled above the main filter (02). The
safety filter (01) is a porous ceramic annular tube of short length and is placed
above the main filter (02) which has a sintered fine particulate coating (03) for
filtering fine particles and such a coating is not required for the safety filter. The
main filter (02) is supported on a metallic tube sheet (04) and is housed in a
filter holder assembly (05) with a cushion of at least-one high-density ceramic
fiber packing seal. (06). The filter holder (05) is welded to the tube sheet (04).

8
The safety filter (01) is placed above the main filter (02) with an annular ceramic
fiber gasket (07) interposed therein. A ceramic fibre packing seal (06) and the
annular ceramic fiber gasket (07) act as a leak proof seal for the gas and also act
as thermal expansion cushion. The main filter element (02) is below the tube
sheet (04) in the dusty gas stream and the safety filter (01) is above the tube
sheet (04) in the clean gas stream. The safety filter (01) is a porous annular
filter made of sintered silicon carbide or sintered aluminosilicate with a high
apparent porosity of around 50 to 60 % to offer low pressure drop during
normal filtration and have sufficient mechanical strength. This porous safety filter
is also of short length, for example, around 100 mm compared to the main filter
having length around 2000 mm. During normal filtration, the gas filtered by the
main filter (02) passes through the safety filter (01) with a low-pressure drop.
When the main filter (02) fails due to breakage, the dusty gas enters the porous
safety filter (01) and quickly clogs the pores in the safety filter (01) with dust
particles and soon the clogged safety filter (01) does not allow the passage of
dusty gas from the broken filter element (02) into the clean gas stream. The
safety filter (01) thus acts like a fuse, cutting off the flow of dusty gas due to the
breakage of the main filter (02) below it. This protective method prevents costly
unscheduled shut down of power plant and the broken filter elements can be
replaced during planned shut down and maintenance period.
A metallic cover (08) is disposed at the top of the safety filter (01) to locate and
close the safety filter (01) and form a leak proof seal using the annular ceramic
fibre gasket (07) placed between the safety filter (01) and the top metallic cover
(08).

9
At least two bolting screws (09) are provided which securely hold the entire
safety filter assembly (01, 07, 09) in place over the main filter (02) and fastened
into the threads of the filter holder (05).
Since the safety filter (01) is directly disposed above the main filter (02), during
the cleaning cycle the pulse gas passes through the safety filter into the main
filter without any loss of pulse energy and this gives additional advantage in
offering higher uniform cleaning intensity along the filter tube and the filters can
be cleaned with lower pressure pulse magnitude than the conventional pulse jet
cleaning with venturi and nozzle design. In the conventional jet pulse cleaning
method, a venturi nozzle is positioned with a gap in the surrounding conical
plenum above the group of filter elements to serve as clean gas path and there
is a loss of pulse energy through this gap requiring higher pulse jet pressure.
For example if the operating pressure is around 30 kg/sq.cm., the pulse pressure
is of the order of 1.1 to 1. 4 times the operating pressure in the case of pressure
pulse cleaning through the porous safety filter but in the conventional jet pulse
venturi and nozzle case, the pressure pulse required is of the order of 3 to 4
times the operating pressure. Thus the safety filter design additionally brings
down the pressure rating of pulse gas pressure vessels, pulse blow down valves
and pulse gas lines, all leading to lowering of capital cost of the hot gas filter
system.

10
WE CLAIM
1. An improved hot gas filter system (15) for filtration of fine ash particles of
coal fuel gas including online pressure pulse cleaning, comprising :
- a pressure vessel (10) with a metallic tubesheet (04) supporting a
plurality of main filter elements (02) disposed in groups, the vessel
(10) having at least one each inlet port (11) and outlet port (12)
for allowing entry of high pressure ash laden gas, filtering the ash
particles by the main filter elements (02), and exit of the filtered
clean fuel gas out of the system (15), the group of main filter
elements (02) being housed in a filter holder assembly (05) with at
least one packing seal (06);
- a pulse gas plenum (14) having at least one pluse gas inlet (13)
disposed above said plurality of main filter elements (10) for
transmitting pulse flow of nitrogen or cleaned fuel gas to dislodge
the dust from the filter surface including restoration of the pressure
drop; and

11
- at least one safety filter (01) placed above the main filter (02) with
a gasket (07) interposed in between such that the main filter
element (02) is disposed below the tube sheet (04) in the dusty
gas stream and the safety filter (01) positioned above the tube
sheet (04) in the clean gas stream, the pulse gas passing through
the safety filter (01) into the main filter (02) without any loss of
pulse energy allowing cleaning of the filters (01, 02) with lower
pulse magnitude.
2. The system as claimed in claim 1, wherein the main filter elements (02)
comprise porous ceramic like sintered silicon carbide or sintered
aluminosilicate tube having a sintered fine particular coating (3), and
wherein the safety filter (01) comprises a porous ceramic annular tube of
shorter length, for example, around lOOmn compared to the length of the
main filter (02) of length around 2000mm.
3. The system as claimed in claim 1, wherein the packing seal (06)
comprises a high density ceramic fibre, wherein the gasket (07) comprises
an annular ceramic fibre, and wherein the packing seal (06) and the
gasket (07), acting as a leak proof seal for the gas including a thermal
expansion cushion.

12
4. An improved hot gas filter system for filtration of fine ash particles of coal
fuel gas including online pressure pulse cleaning as substantially described
and illustrated herein with reference to the accompanying drawings.

Accordingly there is provided an improved hot gas filter system in which a safety
filter made of sintered porous ceramic is mounted on the main ceramic filter by
means of at least one high density ceramic gasket seal within a secure filter
holder assembly. Such a safety filter is more porous and does not interfere with
the normal filtration process by the main filter. In a situation of failure of the
main filter due to breakage, the dusty gas passes through the safety filter and
the dust quickly clogs the pores of the safety filter due to its deep bed filtration
characteristics. The clogged safety filter does not allow the dust from the broken
main filter to mix with the clean gas and thus protect the turbine and
downstream components due to particle damage in the event of a main filter
failure. This porous safety filter also modulates the pressure pulses during the
cleaning cycle to output a higher and uniform cleaning intensity along the length
of the main filter element because the porous safety filter is placed directly
above the main filter and thus the dust on the main filter is dislodged with lower
pressure pulse requirement.

Documents:

00651-kol-2007-claims.pdf

00651-kol-2007-correspondence others 1.1.pdf

00651-kol-2007-correspondence others.pdf

00651-kol-2007-description complete.pdf

00651-kol-2007-drawings.pdf

00651-kol-2007-form 1.pdf

00651-kol-2007-form 18.pdf

00651-kol-2007-form 2.pdf

00651-kol-2007-form 3.pdf

00651-kol-2007-gpa.pdf

651-KOL-2007-(09-04-2012)-CORRESPONDENCE.pdf

651-KOL-2007-(09-04-2012)-PA-CERTIFIED COPIES.pdf

651-KOL-2007-(13-08-2012)-CORRESPONDENCE.pdf

651-KOL-2007-(17-05-2012)-ABSTRACT.pdf

651-KOL-2007-(17-05-2012)-AMANDED CLAIMS.pdf

651-KOL-2007-(17-05-2012)-AMANDED PAGES OF SPECIFICATION.pdf

651-KOL-2007-(17-05-2012)-EXAMINATION REPORT REPLY RECEIVED.pdf

651-KOL-2007-(17-05-2012)-OTHERS.pdf

651-KOL-2007-CORRESPONDENCE 1.1.pdf

651-KOL-2007-CORRESPONDENCE.pdf

651-KOL-2007-EXAMINATION REPORT.pdf

651-KOL-2007-FORM 18.pdf

651-KOL-2007-FORM 3.pdf

651-KOL-2007-GPA.pdf

651-KOL-2007-GRANTED-ABSTRACT.pdf

651-KOL-2007-GRANTED-CLAIMS.pdf

651-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

651-KOL-2007-GRANTED-DRAWINGS.pdf

651-KOL-2007-GRANTED-FORM 1.pdf

651-KOL-2007-GRANTED-FORM 2.pdf

651-KOL-2007-GRANTED-LETTER PATENT.pdf

651-KOL-2007-GRANTED-SPECIFICATION.pdf

651-KOL-2007-OTHERS.pdf

651-KOL-2007-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

253763

Indian Patent Application Number

651/KOL/2007

PG Journal Number

34/2012

Publication Date

24-Aug-2012

Grant Date

22-Aug-2012

Date of Filing

27-Apr-2007

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049

Inventors:

#	Inventor's Name	Inventor's Address
1	NARAYANAN RAM MOHAN	BHARAT HEAVY ELECTRICALS LTD., HIGH PRESSURE BOILER PLANT TIRUCHIRAPALLI - 620 014
2	RAJAMANNAR KANNAN	BHARAT HEAVY ELECTRICALS LTD., HIGH PRESSURE BOILER PLANT TIRUCHIRAPALLI - 620 014
3	TIRUCHI RAJAGOPAL VAIDNATH	BHARAT HEAVY ELECTRICALS LTD., HIGH PRESSURE BOILER PLANT TIRUCHIRAPALLI - 620 014
4	KANDASAMY SHANMUGAM	BHARAT HEAVY ELECTRICALS LTD., HIGH PRESSURE BOILER PLANT TIRUCHIRAPALLI - 620 014

PCT International Classification Number

B01D46/24; B01D46/24

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA