FIELD OF THE INVENTION
The present invention relates to a method for reducing agglomeration, sintering, shrinkage
and choking formation resulting from combustion of solid fuels in fuel firing systems.
BACKGROUND OF THE INVENTION
Sintering/particle to particle agglomeration and choking formation in boiler components
resulting from combustion of a solid carbonaceous fuel material is known in the art. During
combustion in boiler systems like FBC (Fluidized Bed Combustion ) and CFBC (Circulating
Fluidized Bed Combustion) the ash particles generated from the solid fuel will be in close
contact with each other in the furnace components at the operating range of temperatures
800 to 950°C. Solid carbonaceous fuel material comprise a combustible portion and non-
combustible portion. The non-combustion portion comprises different forms of moisture,
gases and minerals. The minerals originally present in the fuel are converted into ash during
combustion. The ash portion represented by oxides of Si, Al, Fe, Ti, Ca, Mg, Na, K, S and
other trace elements. The ash generated during combustion and if the ash chemistry is
related to a specified range of oxide composition, results in shrinkage/sintering and
subsequently forms choking type phenomenon in the fuel/ash path. Such type of choking
leads to forced shut down of the combustor. Depending on the chemistry or chemical
constituents of the ash, the ash particles undergo agglomeration and sintering leading to
choke formation in the fuel path. Once choke formation in the fuel/ash path of the furnace
components has started, the boiler has to be shutdown to clear the choking.
Canadian Patent publication CA 1202485 (Kekish et al) discloses a method of raising fusion
point of slag by addition of 0.5 to 10.0% by weight of the slag of a phosphate compound in
fuels forming slag. The addition of phosphate compound raises the fusion point of the slag
from 1480 to 1540°C.

Lasse Hoist Sorensen, So et al (US 6,615,751 Bl) discloses a method for reducing
agglomeration, sintering and deposit formation in gasification and combustion of biomass
with high content of potassium and/or sodium by the addition of a reactive phosphorous
compound.
Still the problem of sintering/agglomeration and choking of ash in furnace components
generated from combustion of solid fuels other than biomass in the combustion
temperature range of 750 to 1000°C exists. There is a need for an effective additive to
reduce the sintering of ash.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a method for reducing the
sintering of ash in operation of FBC /CFBC systems which eliminates the disadvantages of
the prior art.
Another object of the present invention is to propose a chemical modifier for shifting the
start of sintering of the ash generated in operation of FBC/CFBC Systems, to higher
temperature which allows the boiler operation without ash agglomeration and choking.
SUMMARY OF THE INVENTION
According to the invention, a process is developed to change the sintering pattern of some
type of solid fuel ashes which otherwise cause rapid sintering in the boiler operating
temperature range of 850 deg C- 900 deg C. The sintering pattern of at least four types of
fuel ashes generated out of combustion of respective fuels and four types of ashes
including additive mixtures generated in operation of fluidized bed firing systems, are
acquired and studied. The review of the results enables generating an inventive concept
including development of the invention, by which the problems related to sintering,
agglomeration and choking can be minimised.

According to the present invention, chemical modifier is added along with fuel to alter the
ash chemistry so that the rate and quantum of the shrinkage/sintering phenomenon is
reduced and choking formation is avoided.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 Shows shrinkage profiles of fuel A (with and without chemical modifier)
Figure 2 Shows shrinkage profiles of fuel B (with and without chemical modifier)
Figure 3 Shows shrinkage profiles of fuel C (with and without chemical modifier)
Figure 4 Shows shrinkage profiles of fuel D (with and without chemical modifier)
Table 1 Chemical composition of the ash generated from the boiler.
Table 2 Chemical composition of the chemical modifier according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
The present invention discloses a method for reducing ash particle
agglomeration/shrinkage/sintering and choking formation resulting from combustion of
solid carbonaceous fuels like lignite, sub-bituminous, bituminous and anthracite comprising
a combustible portion and non combustible portion. The chemical composition of the ash
generated from combustion of the fuel as analysed as per ASTM D 6349:09, are depicted in
Table-1.
The ash generated from the fuel by standard ASTM D-3174-89 at 800°C is used to prepare
ash pellet. When the ash pellet is subjected to further heat treatment, the ash particle tends
to start agglomeration around 850-860°C and sinters quickly as the temperature increases.
The sintering pattern of the ash specimen is illustrated by the area shrinkage profile and
maximum shrinkage is reached around 950 to 1000°C. Depending on the ash chemistry, the

rate of ash shrinkage and total shrinkage percentage compared to original ash pellet
specimen varies for different fuel ashes. The shrinkage pattern for fuel ashes A,B,C &D are
shown in Fig.1-4.
In the same way the ash is generated from the mixture of fuel 93% by weight and chemical
modifier 5P/o by weight at 800°C according to the procedure described in standard ASTM D-
3174-89, reduces the phenomenon of agglomeration, sintering, and choking of the fuel
firing system. The composition of the chemical modifier is depicted at Table-2.
When the new ash pellets (prepared from the fuel with additive mixture) are also subjected
to similar heat treatment, marginal shift in the shrinkage profile to higher temperature and
reduction in the quantum of total shrinkage percentage are observed. The shift to higher
temperature and reduction in total shrinkage percentage indicate that particle to particle
agglomeration which reduces sintering of fuel ash only when the chemical modifier is added
to the fuel before becoming ash. The reduction in sintering phenomenon of the ash with
and without addition of chemical modifier is shown for all the fuel ashes A, B, C&D in Fig.l-
4.
According to the present invention, addition of a chemical modifier in sufficient amounts to
the fuels with high sintering characteristics reduces the agglomeration and sintering during
combustion. Such additives typically dilute and shift the sintering pattern to a higher
temperature.
The additive may be either added along with the fuel in required proportion before
preparing the fuel, in a device so that the fuel / additive mixture enters the combustor
through the fuel feed system or can be added separately into the combustor from a
separate bunker where the prepared additive is stored and fed in the required rate
corresponding to the fuel feed rate to attain the desired fuel / additive proportion.

While this invention has been described with respect to particular embodiments thereof, it
is apparent that numerous other forms and modifications of this invention will be obvious to
those skilled in the art. The appended claims and this invention generally should be
construed to cover ail such obvious forms and modifications which are within the true spirit
and scope of the present invention.

WE CLAIM :
1. A method for reducing agglomeration, sintering, shrinkage, and choking formation in
a fuel firing system of a boiler, comprising the steps of:
- addition of a chemical modifier at an effective amount at about a
temperature of 800°C to the ash generated through operation of the
boiler, wherein the chemical composition of the additive by weight % of
SiO2, Al2O3,Fe2O3,TiO2, CaO, Mgo, Na2O,K2O,gnition loss respectively is
85-98, 0-4, 0-4, 0-2, 0-2, 0-2, 0-2, 0-2, and 0-2, wherein the chemical
composition of the ash generated by wekjht% of SO2, AI2O3, Fe2O3, TIO2,
Cao, Mgo, Na2O, K2A SO3 is 40-55,35-42,0-5,1-2,3-10,1-6,0-3,0-2, and
1-6 respectively, and wherein the effective amount of the additive is
between 0-20% by weight.
2. The method as claimed in claim-1, wherein the effective amount of chemical
modifier along with the fuel before combustion.
3. The method as claimed in claim-1 wherein the boiler is one of circulating fluidized
bed combustion (CFBC) and fluidized bed combustion (FBC).
4. The method as claimed in claim-1, wherein the choking is formed at any location in
the fuel/ash path of the firing system.
5. The method as claimed in any of the preceding claims, wherein the solid fuels is one
of lignite, sub-bituminous coal, bituminous coal and anthracite.

6. The method as claimed in claim 1, wherein the chemical modifier is one of sand or
red sand or clay or any materials having said chemical composition.
7. The method as claimed in claim 1, wherein the chemical modifier is added at the
conveyor along with fuel or separately into the combustor.
8. The method as claimed in any of the proceeding claims, wherein the reduction of
sintering /shrinkage is achieved by shifting the shrinkage profile to at least 30 to 50
deg C higher than the profiles for fuel ashes without additive and wherein the
quantum of shrinkage reduction is achieved upto 10 to 30% at the operating
temperature range of (850 to 900 deg C) of the CFBC/FBC.

The invention relates to a method for reducing agglomeration, sintering, shrinkage, and
choking formation in a fuel firing system of a boiler, comprising the steps of :addition of a
chemical modifier at an effective amount at the conveyor along with fuel or separately into
the combustor, wherein the chemical composition of the additive by weight % of Sio2,
AI2O3, Fe2O3, TiO2, CaO, Mgo, Na2O, K2O, ignition loss respectively is 85-98, 0-4, 0-4,0-2,0-
2,0-2,0-2,0-2, and 0-2, wherein the chemical composition of the ash generated by weight
%of SiO2, AI2O3, Fe2O3,TiO2, Cao, Mgo, Na2O, K2O, SO3 is 40-55,35-42,0-5,1-2,3-10,1-6,0-
3,0-2, and 1-6 respectively, and wherein the effective amount of the additive is between 0-
20% by weight