FIELD OF THE INVENTION
The present invention relates to a high temperature ash adhesion testing
system for measuring ash adhesion force on the boiler tubes at different
elevated temperatures in pulverized coal fired boilers .
BACKGROUND OF THE INVENTION
The fossil fuels like Coal, oil and gas are used in the boiler furnace to provide
the heat energy.The coal is the predominant fuel used in the utility boilers.
The pulverized coal fired boilers are one of the means in which the chemical
energy of the coal is used to convert to heat energy in the boiler, in which the
water is converted to steam which in-turn rotates the turbine to produce
electrical energy in the generators.
The Coal mined in India contains high ash content around 40-45% of ash
present in it. Combustion of this coal quality produces huge amount of ash.
During operation this ash which is present in the form of minute particles acts
as an abrasive. This abrasive nature of the ash laden flue gas continuously
collide on the surface of the water wall panel and some of these ash particles
get adhered to the surface of the water wall and then when more and more
particles starts adhering to the ash particles already present on the surface of
the tube they sinter due to the high temperature environment present in the
furnace. This sintered ash forms a layer on the tube surface and prevent
effective heat transfer and act as a thermal barrier.
The carbon in coal which forms ash due to the combustion of the fuel inside
the furnace along with other combustion gases flows in the furnace, circulates
and passes over the tubes of the furnace and settles on the surface of the

tubes under impact and affinity of the ash particles on the surface of the
water wall panel. This settling of the ash particles on the surface of the tube
wall reduces the heat transfer. The measurement of adhesion strength of ash
and tube material depends on exact simulation of actual boiler condition, the
temperature of boiler water wall tubes being lesser than the temperature of
moving ash particles.
Many coating have been used in prior art to reduce erosion of the parent tube
materials. Coatings are used to increase the heat transfer capability and
reduce erosion. The inherent erosive resistive property of the coatings,
reduces erosion and prevents ash deposition onto the tube surface material.
These coatings are applied on the surface of the boiler.
Adhesion of ash to the surface of the water wall panel is a common
phenomena in the boiler leads to shutdown of the power plant. These ashes
reduce the heat transfer of the boiler. To resolve the problem, various
coatings are applied on the surface of the boiler panels. Various test devices
are also available for testing of the coating, which however does not allow
testing of the adhesion force of ash.
However, it is necessary to propose a high temperature testing system to test
the adhesion force of the ash to surface of boiler tube material to decide on
the coating.
US Patent 4586371 teaches an anapparatus for applying a consistently
perpendicular tension force to a dolly for testing the adhesive bond strength
between a coating and a substrate. The tester comprises a ram passing
through an axially centered opening in a dolly bonded to the coating. Piston
and cylinder means are associated with the ram and the dolly so that pressure

within the piston chamber formed thereby causes the development of a
tension force within the dolly which is perpendicular to the coating being
tested because of its coaxially centered orientation with respect to the ram.
US Patent 4567758 an apparatus for testing bond strength of materials
comprising a housing having a cavity, an extrudable fluid seal received in the
cavity, and a passage for placing the fluid seal in communication with a source
of pressurized fluid. A material is attached to a fastener associated with the
housing, coaxial with the housing's longitudinal axis. The fastener, the
material being tested, and the extrusion boundary of the fluid seal are
independent of the pressurized fluid applied to the fluid seal.
US Patent 4606225 discloses a method of testing of a coating, comprises
applying a consistently perpendicular minimum tension force to a dolly for
testing to see if the adhesive bond strength between a coating and a
substrate meets a minimum specification for such bond. The tester comprises
a ram passing through an axially centered opening in a dolly bonded to the
coating. A piston and cylinder are associated with the ram and the dolly so
that pressure within the piston chamber formed thereby causes the
development of a tension force within the dolly which is perpendicular to the
coating being tested because of the coaxially centered orientation of the dolly
with respect to the ram. The pressure is increased only to a point wherein the
tension force is equal to a minimum specification for bonding adhesion. If the
coating has not separated from the substrate, the bond therebetween meets
the specification. The testing apparatus may then be removed by causing the
bonding agent attaching the dolly to the coating to fail as by heating.

OBJECTS OF THE INVENTION
It is therefore an object invention is to propose a high temperature ash
adhesion testing system for measuring ash adhesion force on the boiler tubes
at different elevated temperatures in pulverized coal fired boilers.
Another object of the invention is to propose a high temperature ash adhesion
testing system for measuring ash adhesion force on the boiler tubes at
different elevated temperatures in pulverized coal fired boilers, which
measured under slagging/fouling environment simulated inside the boiler.
A further object of the invention is to propose a high temperature ash
adhesion testing system for measuring ash adhesion force on the boiler tubes
at different elevated temperatures in pulverized coal fired boilers, which
enables to evaluate ash deposition behaviour of different coatings including
the parent material of boiler tubes.
SUMMARY OF THE INVENTION
The present invention provides a high temperature ash adhesion testing
system for measuring ash adhesion force on the boiler tubes at different
elevated temperatures in pulverized coal fired boilers. The inventive system
allows measurement of adhesive strength between tube surface materials,
which can be the tube substrate or of a coating at a specific temperature and
ash particles at a slightly higher temperature as exposed in furnace. It is
known that some coatings reduce the erosion of the panel surfaces and
enhance the heat transfer, which coated surfaces and the parent material
towards the adhesion of the ash particles can be easily identified through the
inventive system.

The inventive system is capable to test the effectiveness of a coating by
allowing bonding of fly ash at different temperatures on to a coated/uncoated
substrate. The bonding is allowed to happen for a specific period of time by
simulating actual boiler working conditions. The temperature for the substrate
and that of fly ash pellet are maintained at different levels. The ash particles
are allowed to stick for a pre-determined time the temperature is reduced and
the tube material is allowed to cool and backward tensile forced is given to
substrate which is now bonded with ash pellet. A load cell in the testing
system is used for determining the adhesive force between the ash and
coated surface.
The high temperature ash adhesion testing system of the invention, is used to
predict the slagging ash adhesion force for various coals before molten state at
different temperatures. Further, the system can predict the fouling ash adhesion
force for various coals at different temperatures.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1, shows a schematic diagram of a high temperature ash adhesion
testing system according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
ASH ADHESION TEST
Figure 1 shows the overall arrangement of a testing system with one each
temperature controller unit and ONE cooling unit. The adhesion tester contains
a fixed (5) and a movable stage (1) respectively. The force between the two

stages (5,1) is measured by a load cell (2) connected to a force sensing unit
(3). The force is applied by a double acting hydraulic cylinder (4).
The Heating elements are placed between the fixed and movable stages (5,1)
which are controlled to a desired temperature by a separate PID ( Proportional
Integral Derivative) controller (6). Coated specimen (7) to be tested is placed
on the lower stage, which is covered by a punch and die set (8). An ash pellet
(9) is placed inside the die and force is applied for a particular period of time.
To simulate the boiler environment the temperature of the ash is maintained
at 900°C and the coated specimen (7) is maintained at 600°C. A cooling
device is attached to the specimen to maintain said temperature. The cooling
device consists of a pump (10) and a water reservoir (11).
After maintaining for particular time period, a tensile load is applied by the
double acting cylinder (4). The force need to separate the ash form the coated
substrate (7) is sensed by the load cell (2) and measured. This measured
value is the adhesion force of the ash applicable on the tube material which is
used in the boilers.

WE CLAIM :
1. A high temperature ash adhesion testing system for measuring ash
adhesion force on the boiler tubes at different elevated temperatures in
pulverized coal fired boilers, comprising:
- a shaped body demarcated by a fixed stage (5) located at bottom
portion of the body, and a moving stage (1) at upper portion;
- a force sensing unit (3) connected to a load cell, the force sensing unit
(3) measuring the force between said two stages (5,1);
- a coated specimen (7) to be tested placed on the moving stage (5)
being covered by a punch and die set (8) which accommodates an ash
pellet (9);
- heating elements controllable by a PID Controller (6) placed between
said two stages (5,1);
- a cooling device (10,11) attached to said specimen (7) for particular
period;
- a double acting hydraulic cylinder (4) for application of tensile load to
separate the ash from the coated substrate (7), the load cell (2)
sensing and measuring the adhension force.
2. The system as claimed in claim 1, wherein the temperature of the ash
and the coated specimen is respectively maintained at 900°C and
600°C.

3. The system as claimed in claim 1, wherein the cooling device comprises
a pump (10) and a water reservoir (11).

ABSTRACT

The invention relates to a high temperature ash adhesion testing system
for measuring ash adhesion force on the boiler tubes at different elevated
temperatures in pulverized coal fired boilers, comprising: a shaped body
demarcated by a fixed stage (5) located at bottom portion of the body, and
a moving stage (1) at upper portion; a force sensing unit (3) connected to
a load cell, the force sensing unit (3) measuring the force between said
two stages (5,1); a coated specimen (7) to be tested placed on the moving
stage (5) being covered by a punch and die set (8) which accommodates
an ash pellet (9); heating elements controllable by a PID Controller (6)
placed between said two stages (5,1); a cooling device (10,11) attached to
said specimen (7) for particular period; a double acting hydraulic cylinder
(4) for application of tensile load to separate the ash from the coated
substrate (7), the load cell (2) sensing and measuring the adhension force.