FIELD OF THE INVENTION
The present invention generally relates to a methodology to find out high
temperature erosion resistance of different Indian fly ash at simulated boiler
conditions. More particularly the invention relates to a method for evaluation of
erosion property of fly ash produced in boilers.
BACKGROUND OF THE INVENTION
In coal-fired power stations, about 20% of the ash produced in the boilers is
deposited on the boiler walls, economisers, air-heaters and super-heater tubes. This
deposited ash is subsequently discharged as slag and clinker during the soot-
blowing process. The rest of the ash is entrained in the stream of flue gas leaving the
boiler. These ash particles collide with the boiler steel components and cause
extensive surface erosion. In advanced stages of erosion, the components get
perforated, and may fail once they lose their structural integrity. Such erosion,
together with the processes of blocking, fouling and corrosion, shortens the service-
life of boiler components. Once this happens, the power station unit has to be shut
down in order to replace the damaged components. The resulting penalty is not only
the cost of replacing the components but also the cost of stoppage of power
production. It is desirable, therefore, to be able to predict the rate of erosion of the
coal-fired boiler components in order to plan systematically for the maintenance or
replacement of these components and avoid forced outages.

Faced with deregulation, increasing retail competition and pressures to keep boilers
online, many coal-fired power generating stations have adopted strategies centred
on increasing unit availability, reliability and increasing the operational life of th
critical equipment. However, boiler tube failures continue to be the number one
cause of forced outages in fossil plants today. These.costly forced outages are
responsible.for an estimated six percent overall loss of unit availability. One of the
major causes for premature tube failure is excessive fireside boiler tube erosion
caused by the impact, cutting action and abrasive wear of fly ash entrained flue
gases undercutting the area they strike.
Power generation utilities and holding company goals are to extend times between
major planned boiler outages. Systems types and configurations, the age of the
plant, their specific plant operating demands and both preventative and general
maintenance philosophies can dictate the accomplishment of these goals. Extending
time between major outages two, four and even five years is resulting in increased
forced outages due to tube failures. An estimated seventeen causes of tube leaks
have been sited. However, one of the most problematic and hardest task is to predict
erosion-caused failures.

Erosion is defined as a process by which material is removed from the layers of a
surface impacted by a stream of abrasive particles. Fly-ash particles entrained in the
flue gas from boiler furnaces in coal-fired power plants can cause serious erosive
wear on steel surfaces along the flow path, thereby reducing the operational life of
the mild-steel heat transfer plates that are used in the rotary regenerative heat
exchangers.
In India, thermal power accounts for about 65-70% of the total installed power
generating capability and about 75-80% of the total electrical energy that is
generated annually. In the field of thermal power wherein fossil fuels are used, coal
based power generation dominates the scenario, accounting for about 85 to 90% of
the total thermal power generation. India has huge reserves of coal deposits
(estimated at around 180-200 billion tons); due to the abundant availability and the
low cost coal will continue to be the main fuel for electrical power generation for
many more years.
Most of the Indian coals as supplied to the Power stations are generally of the high
inert - low heating value type. (i.e. HHV < 3500 Kcal/Kg, Ash > 40%, Ash + Moisture
> 50%) and the thrust is and will be on the development of methods to be adopted
for using this coal in the most efficient manner and with least atmospheric pollution.
In Indian coal-fired power plants, erosion induced by fly ash has been a perennial
problem. This has long-term techno-economic implications on the life cycle
management of the power plant components. It has been observed that in coal-fired
power stations, about 20% of the ash produced in the boilers is deposited on the
boiler walls, economizers, air-heaters and super-heater tubes

Various investigators have addressed the problem of"solid particle erosion but the
work has remained confined to room temperature investigations. Many parameters
are now known to influence erosion behaviour. The magnitude and direction of an
ash particle's impact velocity relative to the target metal surface constitute essential
data needed for evaluating erosion of the surface due to particle impact. Magnitude
and direction of a particle's rebounding velocity depend upon the conditions at
impact and the specific particle-surface material combination.
US 7033673 B2, entitled "Erosion-resistant silicone coatings for protection of fluid-
handling parts", teaches use of compositions of silanol and trifunctional silanes
including their application and cure to form erosion-resistant silicone coatings on
fluid-handling parts. Methods of application, maintenance, and repair of these
coatings are also described. This is referring to erosion resistance of coatings
whereas the claimed patent refers to erosion resistance of fly ash.
US 7758917 ,B2,entitiled,"Method of producing an arc-erosion resistant coating and
corresponding shield for vacuum interrupter chambers", describes a method for
producing an arc-erosion resistant coating provides a substrate material with an arc-
erosion resistant layer by a cold-gas spraying method. The method can be used for
producing an arc-erosion resistant coating in inner regions of vacuum interrupter
chambers that are exposed to electric arcs. This is referring to arc-erosion resistant
coatings whereas the claimed patent pertained to erosion resistance of fly ash in
boiler components.

US 5486096, entitled"Erosion resistant surface protection", discloses a coating for
protection of air foil surfaces from erosion caused by the impingement of particles in
the incoming air stream of a gas turbine engine or on helicopter blades. The coating
consists of an epoxy film toughened with hard particles to improve the erosion
resistance and softer particles which impede the progression of cracks through the
coating. A method for applying the coating on gas turbine engine or on helicopter
blades is also described.
US 7998393 B2, entitled "Methods for making components having improved erosion
resistance" describes methods for making components having improved erosion
resistance including providing.a component having a surface, applying at least one
layer of an erosion system to at least a portion of the surface of the component, each
layer of the erosion system containing a support, and a toughened resin applied to
the support, and co-moulding of the component having the applied erosion system to
produce a coated component having 50% to 400% increase in erosion resistance
per layer of the erosion system.
US 20060281861 A,"1 Erosion resistant anti-icing coatings" teaches liquid and/or
solid anti-icing fillers and/or oils are combined with erosion resistant silicone and/or
fluorocarbon elastomeric materials to create erosion resistant anti-icing coatings.
These coatings may be utilized to prevent ice build-up on various gas turbine engine
components, aircraft components, watercrafts (i.e., boats and ships), power lines,
telecommunication lines, etc. This is referring to erosion resistant anti-icing coatings.

US Patent no. US7431566 B2, entitled "Erosion resistant coatings and methods
thereof gives erosion resistant coating processes and material improvements for
line-of-sight applications. The erosion resistant coating composition includes
nanostructured grains of tungsten carbide (WC) and/or submicron sized grains of
WC embedded into a cobalt chromium (CoCr) binder matrix. A high velocity air fuel
thermal spray process (HVAF) is used to create thick coatings in excess of about
500 microns with high percentages of primary carbide for longer life better erosion
resistant coatings. These materials and processes are especially suited for
hydroelectric turbine components. This is referring to erosion resistance of coatings
whereas the claimed patent refers to erosion resistance of fly ash in boiler
components.
US Patent no. 20090050314 A1 entitled "Surface improvement for erosion
resistance," discloses a technique of laser induced surface improvement which is
used for tool surfaces in down hole tools that experience erosion from slurry or high
velocity flows,.
US 20090028650 A1, entitled "Composition and method for increasing resistance to
erosion," lists out the compositions, admixtures and methods for resisting erosion
such as by wind and/or water are provided. The compositions comprise an emulsion,
dispersion or suspension of a hydrophilic polymer. In preferred embodiments, the
polymer comprises branched anionic polyacrylamide. The methods comprise
providing or forming an aqueous mixture of the compositions and applying them to
an area of land or material sought to be provided with erosion resistance.

US Patent No. US 4751046A, entitled "Austenitic stainless steel with high cavitation
erosion resistance", discloses an austenitic stainless steel alloy showing a high
cavitation erosion resistance making it particularly useful for the manufacture and/or
repair of hydraulic machine components.
US 4588440 A. entitled "Co containing austenitic stainless steel with high cavitation
erosion resistance" teaches a soft, austenitic stainless steel alloy showing a high
cavitation erosion resistance making it particularly useful for the manufacture and/or
repair of hydraulic machine components. This is referring to cavitation erosion
resistance of Co containing alloys.
EP 0042180 A1,entitled "A high cavitation erosion resistance stainless steel and
hydraulic machines being made of the same," indicates a stainless steel suitable for
use as water turbine elements for water power plants This is referring to cavitation
erosion resistance of stainless steel whereas the claimed patent refers to erosion
resistance of fly ash.
US 3622402 A,"Erosion-corrosion resistant coating," describes a process for
improving the erosion resistance and corrosion resistance of steel articles which
comprises boronizing said articles and thereafter coating said boronized articles with
chromium under conditions such that the chromium combines with the boron to •
produce an article bearing a coating containing a boride rich in chromium on the
surface of said article. This is referring to erosion resistance of coatings.

SUMMARY OF THE INVENTION
A methodology for finding high temperature erosion resistance for Indian coal fly ash
through high temperature air jet erosion tester is invented. The specimen of base
material is loaded high temperature environment with gravimetric and size
specifications in the specimen holder. At a time one fly ash with specific micron
range is loaded in the hopper. At the specific flow of the erodent is fixed and
temperature of the air as well the specimen experienced is measured with the
thermocouple. The weight of the high temperature experienced by the loaded
specimen is measured using the high resolution gravimetric analyzer. (Mass
balance with accuracy of 0.0001 g). Now the specimen is under known temperature
and time with specific velocity of the erodent. In this condition the specimen.is
eroded in the known temperature and the known angle of impingement. After the
tests, the Erosion tester is put off and brought to room temperature and thereafter
the samples were removed from the tester and brought to room temperature washed '
with acetone to remove the loose fly ash particles. After the test, gravimetric changes
are measured and are computed to measure its high temperature erosion resistance.
Both of the specimens before and after the tests are measured using an electronic
balance with an accuracy of 0.0001 g.
Materials Tested
Carbon steel IS 2062 as well coated specimens, Stainless steel and cladded
specimens were selected. for high temperature erosion testing. The list was
generated through a combination of those applied in the industry and those found
from erosion and/or erosion data of carbon steels, stainless steel alloys, nickel-
based alloys, tungsten carbide laser claddings and thermal spray coatings.

Erosion Testing
When evaluating the relative erosion resistance of materials, a number of factors
must be considered. Temperature, velocity of the impacting particle, their size and
. shape and the impacting angle are obvious factors that can be controlled in
standardized testing. However, comprehensively evaluating their performance is
limited. Standardized testing procedures, such as ASTM G76, reduce a number of
variables with the intent of providing a common baseline for comparison.
Erodent
High temperature erosion tests were carried out using the bed ash from different
thermal power stations as the erodent material. The particle morphology was a
mixture of both round and' angular with a mean particle size of 556 microns. The
erodent material particles were comprised of high concentrations of silicon and
calcium with minor concentrations of aluminum, magnesium, sulfur, iron,
phosphorus, titanium and chlorine.
Test Conditions
Specimen :CS IS 2062, Coated/Cladded, SS 309, SS410 and P91 base/weld
Specimen size : 25 X 25 X 5 mm
Particle Velocity :30m/s
Temperatures : Ambient - 800 deg.C
Impact Angles : 30 degrees, 60 degrees, 90 degrees
Test Duration : 0.5hour - 3 hours
Loading : 10gm/min
Fly ash temperature : 100 deg.C

Tests focused on elevated temperature solid-particle erosion under generally
oxidizing conditions.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method for evaluation of
erosion property of fly ash produced in boilers.
Another object of the invention is to propose a method for evaluation of erosion
property of fly ash produced in boilers in which specific fly ash collected from Indian
Thermal power stations with different angle of impingement are tested.
A still another object of the invention is to propose a method for evaluation of
erosion property of fly ash produced in boilers in which erosion resistance of base
material and Weld material with a particular fly ash erodent is evaluated
Yet another object of the invention is to propose a method for evaluation of erosion
property of fly ash produced in boilers which evaluates high temperature erosion
resistance with different temperature and specific fly ash.
A further object of the invention is to propose a method for evaluation of erosion
property of fly ash produced in boilers in which evaluation of high temperature
erosion resistance of different fly ash collected from Indian Thermal power stations
with different coated/cladded specimen is done.

A still further object of the invention is to propose a method for evaluation of erosion
property of fly ash produced in boilers in which high temperature erosion resistance
of specific fly ash collected from Indian Thermal power stations with different time
duration of erosion testing are evaluated.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows flow chart of the methodology for evaluation of high temperature
erosion resistance of different fly ash collected from Indian power plants
Figure 2 - Shows the methodology for evaluation of high temperature erosion
resistance of fly ash with the different angle of impingement (sample holder)
DETAILED DESCRIPTION OF THE INVENTION
The methodology for evaluation of high temperature erosion resistance of fly ash
with the base/weld metal /coated/cladded specimen in simulated boiler condition
with Indian coal ash/ fly ash is given in figure-1.The methodology has multiple steps
for the evaluation of erosion resistance of fly ash collected from Indian power plants:
In figure -2, fly ash feed control (1) where a pre heated fly ash, sieved to required
size is taken. From there the fly ash is poured to a hopper (2) A fly ash flow controller
(3) transfer the fly ash to a mixing chamber (7). An air flow regulator (4) and an Air

flow controller (5), connected to a Control panel (6) having a pre-set test time
duration.Air is pumped to the mixing chamber (7) where the specific fly ash collected
is mixed with preheated air. A Pre weighed specimen (8) sized to suit a specific
impingement angle holder (9) is placed and then loaded in an erosion chamber (10)
where the fly ash is impinged at the angle where the specimen kept under said set
flow of fly ash and at said set temperature. Now the specimen is under erosion with
the specific fly ash, temperature, flow rate and specific angle of impingement. After
the set time, the fly ash eroded the specimen and the testing equipment is put off.
The specimen is removed after the chamber (7) comes down to room temperature
and taken for gravimetric estimation. The fly ash in the erosion chamber (10) is
collected through an outlet and'to a fly ash collector (11).

WE CLAIM:
A method for evaluation of erosion property of fly ash produced in boilers,
comprising the steps of :
- preferably a sample for erosion testing, the sample being formed by welding
and coating of a base material consisting of cast steel and stainless steel
nickel alloy, wherein an initial gravimetric measurement and dimensional
measurement of the sample is made to correspond the measurement and
weight of an impingement angle holder;
- providing a first device for flowing fly ash on the sample, the fly ash collected
from a power plant using Indian coal, the collected fly ash pre-heated, sieved
and poured into a hopper of said first device, the first device further having a
mixing chamber for mixing air with the pre-heated ash, an air flow regulator
and an air flow controller connected to a control panel pre-set with a test
time duration ;
- providing a second device for conducting erosion testing of the sample, the
second device having an erosion chamber for impinging fly ash on the sample
through said first device, and an outlet connecting a fly ash collector;

- placing the sample with the sample holder inside the second device and
allowing the sample to undergo fly ash impingement for said set time at
temperature and flow rate set by the air flow regulator and the air flow
controller; and
allowing the erosion chamber to return at room temperature after completion
of fly ash impingement and conducting gravimetric estimation of the sample
erosion.