FIELD OF INVENTION
The present invention relates in general to a method for cleaning barrier filters using double acting
back pulse globe control valve in pressurized fluidized bed gasification pilot plant. More
particularly, the present invention relates to an apparatus and a method for removing particulate
matter from a candle filter element.
BACKGROUND OF INVENTION
Dust particles, often referred to as particulate matter (PM); are considered as major pollutants
released during the coal gasification process. The synthesis gas (syngas) stemming out from coal
gasification plants contain particles (unburnt carbon, fly ashes, soot, etc.), which, if not removed,
can induce severe damage in downstream process for example, during conversion from coal to
methanol, hydrogen generation, power generation, etc. The problem becomes more serious if
syngas is used for chemical synthesis as in the Fischer-Tropsch catalyst reaction or in the water-
gas shift. The particles contained in syngas can reduce or inhibit the effect of catalyst. To address
this issue, a candle filter system has been installed to remove the dust particles in syngas at high
temperature (500°C–700°C) and pressure (3-10 kg/sq.cm) in downstream of pressurized fluidized
bed gasification pilot plant.
In order to remove the dust particles in syngas, a set of candles made with ceramic material are
installed. The syngas which is produced from fluidized bed gasification process is having dust
particles which contains unburnt carbon and fly ash. The system was cleaned by using series of
cyclones and then fed into the candle filter system. The filtered gas cleaned using a series of
cyclones enters into ceramic candle filters through small holes provided over candles. During the
passage of the syngas through the holes of candles, the candles get choked with dust and thus affect
the filter cleaning efficiency which in turn reduce the life of the candles.
In order to remove the dust layer trapped in the filter bundle, a pulse cleaning system has been
introduced. A pulse cleaning is very important for long term operation of candle filter system. The
main function of the back pulse valve is to provide pneumatic pressure wave to dislodge the ash
particles from the candle filter. The accumulated dust particulates over the candle elements is not

removed properly (in case of less frequency), as a result of which high pressure is developed. This
in turn affect the candle filter elements, candle filter system and also the testing performance.
Moreover, frequent pulsing is not recommendable because, the unnecessary strong pulse makes
the pores of the candle elements enlarged and it makes the larger ash particles penetrate through
the candles. This reduces the filtering efficiency which in turn affects the down the line systems.
Hence optimized pulse duration is important to increase the life of candle elements.
In view of achieving the optimized pulsing frequency and pulse duration, a back pulsing system
for the syngas cleaning has been developed in the present disclosure. The proposed arrangement
can serve the above mentioned purpose efficiently thereby increasing the lifetime of the candle
filter elements.
PRIOR ARTS OF THE INVENTION
There are some systems/methods known in the art so as to clean particulate matter from a candle
filter element in pressurized fluidized bed gasification pilot plant. These are discussed herein
below:
CZ295164B6 titled “Barrier filter cleaning process” relates to a method of cleaning a barrier filter.
The method comprising a plurality of filter elements of woven fabric or felt arranged to separate
particles from the polluted gas. The filter elements are cleaned separately or in groups by
compressed air pulses, their frequency, maximum pressure and duration can be varied by adjusting
to minimize overall dust emissions and maximize the life of the filter elements. The method is
particularly intended to optimize the cleaning of textile barrier filters having filter elements in the
form of hoses made of woven fabric or felt.
US7585343B2 titled “Filter cleaning system and method” generally relates to a system and method
for cleaning a filter. In particular, the invention relates to a system and method for reverse pulse -
jet cleaning of filters in an inlet housing of a gas turbine. The filter defines an upstream side at
which particulates are separated from a fluid stream passing through the filter and a downstream
side substantially free of the particulates. The cleaning system includes a blowpipe for supplying
a pressurized fluid. A one piece nozzle is made from a tubular member having a substantially
constant cross-section extending along the length of the member. The nozzle is permanently

attached to the blowpipe at a first end portion. The nozzle is in fluid communication with the
blowpipe to direct a cleaning pulse of the pressurized fluid from a second opposite end portion
into the downstream side of the filter to dislodge particulates into the upstream side. An aspirator
is formed in the nozzle at an upstream location spaced from the second end portion of the nozzle.
The aspirator enables an additional volume of fluid to be delivered from the second end portion of
the nozzle than is delivered from the blowpipe to the first end portion of the nozzle. A diffuser is
fixed to at least one of the blowpipe and the nozzle. The diffuser directs a portion of the cleaning
pulse to a proxima l portion of the filter located adjacent to the tube sheet.
US4655799A titled “Pulse cleaning system for dust filters” relates in general to the filtration of
dust laden gases and more particularly to a bag type dust filter having an improved system for
cleaning of the filter bags. A cleaning system for dislodging dust from the filter bags of a dust filter
having dirty and clean air plenums separated by a tube sheet. The tube sheet is divided into
segments each having filter bag openings arranged in the same pattern. An air accumulator tank
which continuously receives compressed air is rotated in the clean air plenum with a connected
distribution arm which applies air pulses to the filter bags through discharge nozzles arranged in
the same pattern as the filter bag openings. A position sensor allows cleaning air in the tank to be
applied to the distribution arm only when the arm is aligned above a segment with all nozzles
centred on the filter bags. A quick acting diaphragm valve is combined with the air tank to control
air flow into the distribution arm at a location adjacent to the arm to minimize the response time.
KR101104837B1 titled “Regeneration apparatus and its method for filtration system with ceramic
candle filters” relates to a dust collecting apparatus and a dust collecting method of a dust
collecting system equipped with a ceramic candle filter. More particularly, the invention discloses
a dust collecting system for removal of particulate matters such as dust contained in a large amount
in syngas produced by IGCC coal gasification. The proposed dust collecting device and dust
collecting method of the dust collecting system includes back-spray gas that has been supplied to
each filter bundle in order to remove dusts attached to the plurality of filter bundles consisting of
a plurality of ceramic candle filters inside the dust collection chamber of the filter bundle it is
about.

The prior arts mentioned above do not provide any concept related to the usage of syngas as a
flushing media in a fluidized bed gasification pilot plant and the corresponding purification of the
syngas by means of a back pulsing system as discussed in the present disclosure.
OBJECTS OF THE INVENTION
It is an object of the present subject matter to overcome the aforementioned and other drawbacks
existing in the prior art systems and methods.
It is one object of the invention to provide a solution to dislodge the fine dust particles over candles
in a pressurized fluidized bed gasification pilot plant.
It is another object of the invention to use a pure synthesis gas as a flushing agent for dislodging
the dust particles over candles.
It is yet another object of the invention to propose a back pulsing device in pressurized fluidized
bed gasification pilot plant in order to dislodge dust particles over candles.
It is still another object of the invention to control the duration and the time interval of the operation
of the globe valve by means of a controller/timer.
These and other objects and advantages of the present subject matter will be apparent to a person
skilled in the art after consideration of the following detailed description taking into consideration
with accompanied drawings in which preferred embodiments of the present subject matter are
illustrated.
SUMMARY OF THE INVENTION
This summary is provided to introduce concepts related to an apparatus and the corresponding
method for remo ving particulate matter from candle filter elements. The concepts are further
described below in the detailed description. This summary is not intended to identify key features
or essential features of the claimed subject matter, nor is it intended to be used to limit the scope
of the claimed subject matter.
According to this invention, there is provided an apparatus for removing particulate matter from a
candle filter element. The apparatus includes a fluidized bed gasification pilot plant configured for
generation of synthesis gas (syngas); a plurality of candle filters configured for removal of dust

particles and contaminants from the syngas; a syngas receiver configured for collection of the pure
syngas ; a syngas compressor configured for pressurizing the clean synthesis gas for blowing off
the filter cake over a plurality of candle elements; a heater configured for removal of moisture
from the pressurized syngas stored in syngas receiver-II and a globe valve configured for pulsing
in order to remove dust accumulated over the plurality of candle elements. The size of the globe
valve ranges between 20 Nominal Bore (NB) to 30 Nominal Bore (NB) and the globe valve is
operated by a pneumatic double acting cylinder and a solenoid timer/controller is configured to set
a back pulsing frequency and a pulse duration wherein, the timing of opening and closing of the
globe valve depends on said back pulsing frequency and said pulse duration. Moreover, the globe
valve remains open for a time duration ranging from 30 milliseconds to 90 milliseconds, wherein
the globe valve starts to work at a range of time interval of every 30 seconds to 2 minutes depending
on the requirement. A 230 V AC supply is used to operate said solenoid controller/timer.
A method for removing particulate matter from a candle filter element using the apparatus, the
method comprising of feeding the raw syngas generated from the fluidized bed gasification pilot
plant into the candle filter system in order to remove the multitude of fly ash particles, particulate
matters and impurities present in the syngas; feeding the purified syngas to the syngas receiver for
storage by means of the syngas outlet; storing the purified syngas in the syngas receiver;
pressurizing the purified syngas using the syngas compressor for blowing off the filter cake over
the candle elements; storing the resultant syngas into the syngas receiver-II; removing the moisture
from the syngas using the heater; feeding the moisture free and dust free syngas into the globe
valve for dust removal over a plurality of candles; opening the globe valve on receiving the pulse
signal from the solenoid controller/timer; admitting the fresh syngas is the plurality of candle filter
elements by means of the globe valve, wherein a pressure wave is produced in the plurality of
candles and this pressure pulse dislodges the ash particles from the candle elements in the candle
filter system. Finally, the ash particles are collected in the bottom of the ash vessel by gravity for
analysis of the carbon content.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
It is to be noted, however, that the appended drawings illustrate only typical embodiments of the
present subject matter and are therefore not to be considered for limiting of its scope, for the
invention may admit to other equally effective embodiments. The detailed description is described

with reference to the accompanying figures. In the figures, a reference number identifies the figure
in which the reference number first appears. The same numbers are used throughout the figures to
reference like features and components. Some embodiments of system or methods or structure in
accordance with embodiments of the present subject matter are now described, by way of example,
and with reference to the accompanying figures, in which
Figure 1 illustrates the process flow diagram of ceramic element candle filter with pulse valve
arrangement in a fluidized bed gasification pilot plant in accordance with the present disclosure
(100).
DETAILED DESCRIPTION OF INVENTION WITH REFERENCE TO THE
DRAWINGS OF THE PREFERRED EMBODIMENTS
The following is a detailed description of embodiments of the disclosure depicted in the
accompanying drawings. The embodiments are in such detail as to clearly communicate the
disclosure. However, the amount of detail offered is not intended to limit the anticipated variations
of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the present disclosure as defined by the appended
claims.
While the embodiments of the disclosure are subject to various modifications and alternative
forms, specific embodiment thereof have been shown by way of example in the figures and will
be described below. It should be understood, however, that it is not intended to limit the disclosure
to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications,
equivalents, and alternative falling within the scope of the disclosure.
The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are
intended to cover a non-exclusive inclusion, such that a device, system, assembly that comprises
a list of components does not include only those components but may include other components
not expressly listed or inherent to such system, or assembly, or device. In other words, one or more
elements in a system or device proceeded by “comprises… a” does not, without more constraints,
preclude the existence of other elements or additional elements in the system or device.
Figure 1 illustrates the process flow diagram of ceramic element candle filter with back puls e
valve arrangement in a fluidized bed gasification pilot plant. In an embodiment, the arrangement

includes a fluidized bed gasification pilot plant (1) responsible for generation of syngas (2), a
candle filter system (3) responsible for removal of dust particles and other contaminants from the
syngas. The arrangement further includes a syngas receiver (5) wherein the purified syngas (4) is
collected followed by compression and subsequent reception by means of a syngas compressor (6)
and syngas receiver-II (7), respectively. The purified syngas is then fed into a heater (8) for
removal of moisture from the syngas. The moisture free syngas is then fed into the globe valve (9)
with pneumatic double acting cylinder (12) integrated with solenoid.
In an aspect, the back pulsing frequency and the pulse duration is set through the timer/controller
(11). The controller provides pulse signal to the solenoid valve. Consequently, the solenoid valve
admits the air into the pneumatic cylinder. The cylinder diaphragm moves and it opens the valve
momentarily. At the end of pulse signal the solenoid valve closes and the air supply to the double
acting actuator cylinder reverses. This makes the cylinder diaphragm to move other way and the
globe valves goes to close pulse.
In another aspect, the globe valve is used for regulating the flow of syngas and also for pulsing in
order to remove dust accumulated over candle elements with help of a solenoid controller/timer.
In another aspect, the size of the globe valve (9) ranges between 20 Nominal Bore (NB) -30
Nominal Bore (NB). In a preferred embodiment, the size of the globe valve is maintained to 25
NB.
In another aspect, the solenoid is normally open type, two ways and 230V AC supply (10) has
been used. The operation of globe valve is entirely dependent upon the solenoid operation which
in turn depends upon the solenoid controller/timer (11).
In yet another aspect, the globe valve (9) remains open for a time duration range of 30 milliseconds
to 90 milliseconds as required. Moreover, the globe valve starts to open at a range of time interval
of every 30 seconds to 2 minutes depending on the dust concentration. If the dust concentration is
more on candles, the globe valve remains open for more time and the dust concentration is less
on candles, the globe valve remains open for less time.

In yet another aspect, the entire operation is very fast and the valve opens for a fraction of second
and closes. Moreover, the solenoid valve operates with pneumatic media and is generated using
the air compressor (13). The generated air from the air compressor (13) is sent to air receiver (14)
for storage and is used for solenoid valve operation.
In a preferred embodiment, syngas is a fuel gas mixture and primarily including hydrogen (H2),
carbon monoxide (CO) and a lesser amount of carbon dioxide (CO2) and methane (CH4).
The composition of syngas is given as example without restricting scope of the invention to the
same. Thus, other compositions of syngas readily apparent to a person skilled in the art are
understood to be within purview of the invention.
Working of the invention
The invention disclosed in the present subject matter aims towards utilization of the pure syngas
as a flushing agent in order to ensure a long term operation of the candle filter system. This
prevents the life of the catalyst used along with syngas for generation of the methanol in coal gas
applications. The raw syngas generated from the fluidized bed gasification pilot plant (1) is fed
into the candle filter system (3) in order to remove the fly ash particles, particulate matters and
other impurities present in the syngas. The raw syngas is cleaned by a series of cyclones in the
candle filter system and the resultant pure syngas, being free from the impurities, is fed to the
syngas receiver (5) for storage by means of the syngas outlet (4). After storing the cleaned syngas
in syngas receiver (5), a slip stream of syngas sent to other applications such as power generation,
liquid fuels, chemicals, etc. Additionally, a slip stream of syngas is sent to syngas compressor (6)
for pressurization. The cleaned syngas is pressurized in the range of 3 bar to 5 bar more than the
syngas generated pressure and sent to syngas receiver-II (7). The syngas compressor (6) is used
for pressurizing the clean synthesis gas for blowing off the filter cake over the candle elements.
The pressurized syngas which was stored from syngas receiver-II (7) is then sent to heater (8) for
removal of moisture from syngas. Consequently, a moisture free and dust free syngas is supplied
to globe valve (9) for dust removal over candles. Then the solenoid controller/ timer (11) provides
pulse signal to the solenoid valve as a result of which the globe valve (9) opens and the fresh

syngas is admitted into the filter assembly which produces a pressure wave in the candles and this
pressure pulse dislodges the ash particles from the candle elements in the candle filter system (3).
As a result, the ash particles fall in the bottom of the ash vessel by gravity and collected at regular
intervals for analysis of the carbon content. In this way, a double back flushing mechanis m is
achieved in the present disclosure. The pulsing frequency and the period can be optimized by
measuring pressure drop across the candle filter assembly.
Test Results
The observations obtained by testing the proposed apparatus as disclosed in the present subject
matter is listed as follows:
a) The apparatus is able to clean the dust concentration over the candle filters at an interval
of 30 seconds to 120 seconds with the differential pressure across the candles being 350
mmWC.
b) The dust concentration in syngas (at the inlet of the candle filter) is varied from
575.45 mg/Nm3 to 1007.9 mg/Nm3 and the outlet dust concentration is varied from 31.768
mg/Nm3 to 36.004 mg/Nm3.
c) The maximum pressure difference across the candle filter assembly is 379 mmWC.
d) The maximum temperature of the pure syngas admitted into the globe control valve as a
flushing agent is 180.6 0C.
Advantages of the invention
The arrangement described in the present disclosure is having the following advantages:
a) Generation of pure syngas as the flushing agent
b) Removal from the impurities present in the raw syngas by the globe valve using the
mechanism of double back flushing.
Additionally, This invention increases the gas clean-up system efficiency by using double acting
pneumatic operated globe control valve instead of gate valve in fluidized bed gasification pilot
plant. Also the quality of the syngas improves in fluidized bed gasifier by utilizing fresh synthesis
gas for purging the dust particle over candle elements. By utilization of the clean syngas in place

of nitrogen, the nitrogen composition decreases in syngas. The conversion efficiency of the
downstream systems also increases by decreasing the nitrogen composition in syngas.
It should be noted that the description and figures merely illustrate the principles of the present
subject matter. It should be appreciated by those skilled in the art that conception and specific
embodiment disclosed may be readily utilized as a basis for modifying or designing other
structures for carrying out the same purposes of the present subject matter. It should also be
appreciated by those skilled in the art that by devising various arrangements that, although not
explicitly described or shown herein, embody the principles of the present subject matter and are
included within its spirit and scope. Furthermore, all examples recited herein are principally
intended expressly to be for pedagogical purposes to aid the reader in understanding the principles
of the present subject matter and the concepts contributed by the inventor(s) to furthering the art
and are to be construed as being without limitation to such specifically recited examples and
conditions. The novel features which are believed to be characteristic of the present subject matter,
both as to its organization and method of operation, together with further objects and advantages
will be better understood from the following description when considered in connection with the
accompanying figures.
Although embodiments for the present subject matter have been described in language specific to
package features, it is to be understood that the present subject matter is not necessarily limited to
the specific features described. Rather, the specific features and methods are disclosed as
embodiments for the present subject matter. Numerous modifications and adaptations of the
system/device of the present invention will be apparent to those skilled in the art, and thus it is
intended by the appended claims to cover all such modifications and adaptations which fall within
the scope of the present subject matter.
It will be understood by those within the art that, in general, terms used herein, and especially in
the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms
(e.g., the term “including” should be interpreted as “including but not limited to,” the term
“having” should be interpreted as “having at least,” the term “includes” should be interpreted as
“includes but is not limited to,” etc.). It will be further understood by those within the art that if a
specific number of an introduced claim recitation is intended, such an intent will be explicitly

recited in the claim, and in the absence of such recitation no such intent is present. For example,
as an aid to understanding, the following appended claims may contain usage of the introductory
phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such
phrases should not be construed to imply that the introduction of a claim recitation by the indefinite
articles “a” or “an” limits any particular claim containing such introduced claim recitation to
inventions containing only one such recitation, even when the same claim includes the introductory
phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or
“an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true
for the use of definite articles used to introduce claim recitations. In addition, even if a specific
number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize
that such recitation should typically be interpreted to mean at least the recited number (e.g., the
bare recitation of “two recitations,” without other modifiers, typically means at least two
recitations, or two or more recitations). Furthermore, in those instances where a convention
analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended
in the sense one having skill in the art would understand the convention (e.g., “a system having at
least one of A, B, and C” would include but not be limited to systems that have A alone, B alone,
C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.).
In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in
general such a construction is intended in the sense one having skill in the art would understand
the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited
to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C
together, and/or A, B, and C together, etc.). It will be further understood by those within the art
that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether
in the description, claims, or drawings, should be understood to contemplate the possibilities of
including one of the terms, either of the terms, or both terms. For example, the phrase “A or B”
will be understood to include the possibilities of “A” or “B” or “A and B.”
It will be further appreciated that functions or structures of a plurality of components or steps ma y
be combined into a single component or step, or the functions or structures of one-step or
component may be split among plural steps or components. The present invention contemplates
all of these combinations. Unless stated otherwise, dimensions and geometries of the various
structures depicted herein are not intended to be restrictive of the invention, and other dimensions

or geometries are possible. In addition, while a feature of the present invention may have been
described in the context of only one of the illustrated embodiments, such feature may be combined
with one or more other features of other embodiments, for any given application. It will also be
appreciated from the above that the fabrication of the unique structures herein and the operation
thereof also constitute methods in accordance with the present invention. The present invention
also encompasses intermediate and end products resulting from the practice of the methods herein.
The use of “comprising” or “including” also contemplates embodiments that “consist essentially
of” or “consist of” the recited feature.

WE CLAIM:
1. An apparatus (100) employed for removal of particulate matter from a candle filter
element, the apparatus comprising:
- a fluidized bed gasification pilot plant (1) is configured for generation of
synthesis gas (syngas) (2);
- a plurality of candle filters (3) is connected to said fluidized bed gasification
pilot plant (1), wherein the plurality of candle filters (3) are configured for
removal of a multitude of dust particles and contaminants from the syngas (2);
- a syngas receiver (5) is attached to the plurality of candle filters (3) wherein
said syngas receiver (5) is adapted for collection of the purified syngas by a
syngas outlet (4);
- a syngas compressor (6) is coupled to said syngas receiver (5), wherein the
syngas compressor (6) is provided for pressurizing a purified syngas for
blowing off a filter cake over a plurality of candle elements, wherein a syngas
receiver-II (7) being attached to the syngas compressor (6), is used for storing
the pressurized syngas;
- a heater (8) is coupled to the syngas receiver-II (7), wherein the heater (8)
removes moisture from the syngas; and
- a globe valve (9) is connected to the heater (8) wherein the glove valve (9) is
provided for pulsing in order to remove dust accumulated over the plurality of
candle elements.

2. The apparatus (100) employed for removal of particulate matter from the candle filter
element as claimed in claim 1, wherein the globe valve (9) is operated by a pneumatic
double acting cylinder (12).
3. The apparatus (100) employed for removal of particulate matter from the candle filter
element as claimed in claims 1-2, wherein a solenoid timer/controller (11) is configured
to set a back pulsing frequency and a pulse duration wherein, the timing of opening and
closing of the globe valve (9) depends on said back pulsing frequency and said pulse
duration.

4. The apparatus (100) employed for removal of particulate matter from the candle filter
element as claimed in claims 1-3, wherein the size of the globe valve (9) ranges between
20 Nominal Bore (NB) to 30 Nominal Bore (NB).
5. The apparatus (100) employed for removal of particulate matter from the candle filter
element as claimed in claims 1-4, wherein the globe valve (9) remains open for a time
duration ranging from 30 milliseconds to 90 milliseconds, wherein the globe valve (9)
starts to work at a range of time interval of every 30 seconds to 2 minutes.
6. The apparatus (100) employed for removal of particulate matter from the candle filter
element as claimed in claims 1-5, wherein a 230 V AC (10) supply is used to operate
said solenoid controller/timer (11).
7. A method for removal of particulate matter from the candle filter element using the
apparatus (100) as claimed in claims 1-6, the method comprising:

- feeding the raw syngas generated from the fluidized bed gasification pilot plant
(1) into the candle filter system (3) in order to remove the multitude of fly ash
particles, particulate matters and impurities present in the syngas;
- fe eding the purified syngas through a syngas outlet (4) to the syngas receiver
(5) for storage;
- storing the purified syngas in the syngas receiver (5);
- pressurizing the purified syngas using the syngas compressor (6) for blowing
off the filter cake over the plurality of candle elements;
- storing the resultant syngas into the syngas receiver-II (7);
- removing the moisture in the syngas using the heater (8);
- feeding the moisture free and dust free syngas into the globe valve (9);
- opening the globe valve (9) on receiving the pulse signal from the solenoid
controller/timer (11);
- admitting the fresh syngas in the plurality of candle filter elements (3) by the
globe valve (9), wherein a pressure wave is produced in a plurality of candles

and this pressure pulse dislodges ash particles from the candle elements in the
candle filter system (3); and
- collecting said ash particles in the bottom of the ash vessel by gravity for
analysis of the carbon content.