Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
1. Introduction
The plant consists of 1 x 16 TPH, 45 KSc., 420 oC, under bed fired
AFBC boiler commissioned in the Year 2009. The boiler design is
of bottom supported, Bi Drum with membrane water walls,
Economizer, convection & radiant super heaters. De-aerated de
min water is supplied at economizer inlet at 108 oC. The boiler is
designed to fire Indonesian Coal OR Lignite.
The boiler is presently operating with Indonesian coal alone.
The

boiler

has

been

experiencing

troubles

in

continuous

operation in the recent past. The major problems reported are

Low steam temperature, frequent failures of bed coils, high boiler
exit temperature affecting bag filter bags.
Though these types of industrial boilers are designed for
trouble free operation, but is operated based on process steam
demand and fluctuations. So the boiler pressure part components
are subjected to high thermal stresses, fatigue, erosion and
corrosion,

the failure mode is hard to predict.

A proper

inspection during shut downs with periodic replacement of

components before it reaches its end of life can ensure the
availability of the boiler plant to a large extent.
2. Observations on Operation of the Boiler
The boilers auto control loops of Deaerator pressure & level
control, Combustion control, Drum level, and Furnace pressure
controls are working in Auto mode and maintaining the process
parameters within acceptable limits.
a. The boiler is presently operating with
I.
A short fall in RSH outlet steam temperature with DSH
spray valve is fully closed.
II.
High Economizer inlet flue gas temperature.
III.
High Bag house inlet flue gas temperature.
IV.
High feed water temperature at economizer outlet.
This happening within few days of boiler operation, after cleaning
of pressure parts.
b. The bed material addition to furnace was informed as about 75
Kgs./ Day, as a mixture of used & fresh materials. The magnetic
particles in screened bed material as was found at 9.2%, which is
used as recycled bed material for charging to furnace.
Report By: A. Prakash, Boiler Consultant.
03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
c. The Un burnt carbon (UBC) in fly ash at Boiler Bank, APH & MDC
are on higher side. This could be due to higher fines in coal OR
lack of secondary air for complete combustion of carbon.
d. Boilers water and steam samples at the sample cooler outlet are
found to be steaming hot. For measurement of pH & conductivity
of samples, the samples need to be cooled to atmospheric
temperature (25 Deg. C) for authentic results being reported and
corrective actions can be taken immediately.
e. Some of the Economizer coil bends on left hand side were found
to have tube thickness of 2.67 2.8 mm. The original thickness of
tube is 3.60 mm. This is indicating ash erosion of bends.
Additional baffles were provided to prevent preferential flue gas
flow through this area.
f. The baffle plates provided between the Left side water wall in
RSH & CSH area are found to have more gap than required. This
needs to be corrected by providing additional plate so that the
gap is less than the tube tube gap in the next shutdown.
g. One of the bed coils on right rear side found to be eroded to such
level that there is loss of parent metal from the tube. All other
bed tubes were found to have high rate of erosion at areas above
the coal feed points.
h. Erosion on Both bottom as well as top loops were investigated
and found that the opening of coal nozzle inside furnace was high
in most of the nozzles. This was later corrected to 30 mm in 7
Nos. coal nozzles.
i. Its observed that moist fines in coal had clogged the vibrating
screen mesh feed point. Presently its being cleaned once in 2 3
Days.
3. Suggestions to Improve Boiler Efficiency.
The boiler efficiency for coal-fired units is calculated as per
ASME PTC 4.0 by indirect method. The major losses are namely
a.
b.
c.
d.
e.

Dry flue gas loss

Loss due to moisture in fuel
Loss due to Hydrogen in fuel
Loss due to un-burnt carbon
Radiation & Un accounted losses.

Report By: A. Prakash, Boiler Consultant.

03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
The following controllable factors shall influence the boilers
thermal efficiency.
i) Fuel
The fuel shall be procured considering its suitability for
combustion in AFBC boiler and cost economics. The key
parameters to look for are
FC/VM Ratio: This ratio shall be maintained between 0.8
1.2. Lower FC shall reduce the Un burnt carbon loss and is
more reactive, so burns faster. The fixed carbon in coal
requires more retention time and higher temperature in the
furnace for complete combustion.
Hydrogen Content: The hydrogen in coal is formed during
the fixation process of coal. Though combustion of H 2 will
release heat, but the formation of water vapor results in loss
of heat energy. Generally coal shall have 2 5% of Hydrogen.
Moisture: Moisture in coal vaporizes absorbing useful heat
from combustion. Normally coal shall be containing 10 25%
of water. Lower water content increase the boiler efficiency.
Oxygen: Higher Oxygen in coal increase the reactivity index
and burns faster, in turn reduce un burnt carbon loss. The
normal range shall be 6 12%.
Ash: Higher ash content leads to sensible heat loss in fly ash
& bed ash (Un accounted losses).
Fines: Higher fines leads to higher un burnt carbon loss due
to low retention time. So the coal fines before crushing shall
be limited to less than 20% and 30% in coalbunker of boiler.
Oxides of Combustion: Certain oxides shall lead to severe
fouling and slagging on pressure part, which in turn reduces
heat absorption. This is accounted in Dry flue gas loss. This is
discussed in detailed elsewhere in this document.
ii) Operator controllable variables
Excess air & Oxygen in Flue Gas: The excess air shall be
controlled to 20 25%, as higher excess air leads to higher
Dry flue gas loss. The Oxygen in flue gas is maintained
Report By: A. Prakash, Boiler Consultant.
03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
between 3.8 4.2% for complete combustion of coal n the
operating range of 80 to 100% MCR of boiler. The Oxygen
analyzer shall be calibrated once in 15 days to provide reliable
readings.
Surface moisture in Coal: The coal shall be stored in
covered shed to protect from rain. Additional water sprayed
on coal to control dust shall be done judiciously.
Maintaining optimum bed height: The bed shall be
drained frequently and fresh bed material shall be added to
maintain bed chemistry. If not done, the bed material particle
becomes heavier and actual operating bed height drops. A
good fluidizing bed improves combustion efficiency and
reduces Un burnt carbon loss.
Optimizing Primary Air Pressure: The PA header pressure
shall be optimized to minimum possible. Higher header
pressure leads to carry over of fines resulting in higher un
burnt carbon loss.
Leakage of steam and Flue gas:

Any leakage of steam

and flue gas shall be attended online or in the next available

shutdown. The furnace pressure shall be maintained between
-2 to -5 mm WC to reduce losses.
iii)Immediate Action Plan
Maintain the magnetic particle percentage in bed as below
10%. The drained material shall be checked for magnetic
particles once in 3 days
Its recommended to drain bed at least once a shift from all
drain points till the red hot bed material starts to flow out.
Replenish the bed with fresh material. Recycling of bed
material shall be stopped. The addition & draining of bed
material shall be recorded in the operators logbook.
Keep vibrating screen opening at 8 mm Sq. mesh during
normal seasons & 10 mm Sq. mesh during rainy seasons.
The fines in coal to boiler to be controlled below 30 %.
The vibrating screen mesh shall require to be cleaned every
time before starting the feeding. Presently its being cleaned
once in 2 3 Days.
Report By: A. Prakash, Boiler Consultant.
03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
Leak testing for casings & ducting shall be carried out by
any one of the following methods
o Flame/Smoke testing
o By O2 measurement survey across every sections of
boiler ducting.
o The temperature drop across duct section is a good
indicator of air ingress.
o By pressurizing the furnace to above atmospheric
pressure.
iv)Long Term Action Plans
Injection Of Over fire Air: Introduction of secondary air at
1.5 meter above the bed coil shall increase retention time as
well as turbulence of fuel particles, resulting in higher
combustion efficiency and reduction in un burnt carbon loss.
4. Drop in Super heater Temperature.
Super heater coils were inspected for ash accumulation. It
was noted that most of the ash was loosely attached to the coil.
Below this layer, there is hard layer of slag could be seen. The
boiler bank, economizer & APH ash deposits are loose and could
be removed by Mechanical cleaning/Water washing.
The collected ash samples shall be sent for analysis of ash
oxides namely Al2O3, SiO2, Na2O, K2O, Fe2O3, MgO, CaO, P2O5, TiO2.
Also super heater hard deposits shall be also checked for IDT, HT,
ST and FT.
Fuel Related Issues
The fouling and slagging properties of various coal is sill a
major area of research by experts since long and various indices
have been developed for finding out the mechanisms of
deposition, few of the indices are listed below.
The coal analysis report dated 28.09.2015 for Ash Fusion
Temperature

(AFT)

is

indicating

an

Initial

Deformation

Temperature (IDT) of 1076 Deg. C, Softening Temperature (ST) of

1099 Deg. C, Hemispherical Temperature (HT) of 1108 Deg. C and
Fluid temperature (FT) of 1166 Deg. C in reducing atmosphere.
The IDT & FT is LOW, which is the cause of fouling in super
heaters. The IDT must be at least 150 Deg. C higher than the
Report By: A. Prakash, Boiler Consultant.
03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
operating

temperatures.

So

its

recommended

that

while

procuring coal specify

a. The IDT > 1300 Deg. C in reducing atmosphere.
b. The Fe2 O3 content < 6%
The following indices calculations shall be useful to judge the
suitability of coal.

Ash is classified as Bituminous when

Report By: A. Prakash, Boiler Consultant.

03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.

With

the

above

formulae

and

available

data

on

fusion

temperature the following are concluded.

Parameter
Ash Fusion

Value
Temperature 1099o C

Propensity
High - Severe

(ST)
Slagging Index
1082 o C
Severe
Further analysis could be done with elemental oxide analysis
report is available.
Use of On Line Soot Removal System
a. Steam Soot Blowers
It is one of the well-proven ways to remove soot from heat
transfer surfaces. It uses super heated steam at high
velocities to dislodge the soot. It can be installed in all
sections of the boiler and shall be effectively used for cleaning
water wall, super heaters and economizers.
In Asian Paints, based on the deposition patterns, 3 nos.
Long Retractable Soot blower shall be required for RSH, CSH
and Boiler bank zones. The installation involves high capital
cost, the piping covered under IBR This requires new openings
in water all and extended platforms for maintenance.
b. Sonic Soot Blowers
Relatively cost effective compared to steam soot blower.
As per the available information, sonic soot blowers are
generally installed on Economizers, Air heaters, bag filters
and SCR units where the temperatures are much lower.
Its advised that Asian Paints shall contact the sonic soot
blower suppler and enquire whether they can supply and
install for Super heater sections in AFBC boiler.
c. Explosive cleaning
Due to lack of experienced agencies available in India, this
is not popular method in our sub continent.
5. Frequent failures of Bed coils
The In-bed tubes in fluidized bed boiler are susceptible for
erosion by fluidizing media and the higher turbulences at under

Report By: A. Prakash, Boiler Consultant.

03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
bed feed points. As the boiler operating pressure increases, the
metal working temperature also increases and are prone for
erosion. So the bed tubes are provided with studs, which shall
take the blunt of fluidization and protect the parent metal from
eroding.
Also as stated above, maintaining a good fluidization by
proper bed height, bed particle chemistry and optimized PA
Header pressure, the erosion rate can be further controlled, so
i.

that the life of bed tubes shall be extended to 1 to 2 years.

Effect of Stud Metallurgy
Compared to carbon steel studs, alloy steel (SA 213) or Stainless
steel (SS 304H) studs have higher oxidation temperature. The
oxidation temperature is of much significance as the stud tip
temperature is higher than the tube metal working temperature
and carbon steel shall start oxidizing. The higher the oxidization
temperature it gives better erosion resistance, hence most
suitable for studs.
In Asian paints, the present studs on in bed tubes in boiler has
its MOC Carbon steel.

ii.

Effect of Stud Density

The higher the number of studs per cross section of tubes shall
provide better protection for the parent metal of tubes. The
studs is attached from 4 O clock to 8 O Clock positions on the
tube. Of late, boiler manufacturers have experimented on
various patterns of studding and arrived at the optimum
studding pattern.
The present stud pattern in Asian Paints is 3 2 3, which shall
be increased to 5 4 5 to give higher coverage and prevent
channeling of fluidizing material between studs.

iii.

Non-Eroding Refractory Application

In the past decade the use of high alumina (Al 2O3 > 90%)
refractory application in AFBC boiler has become popular to
protect in bed tubes from erosion. This is available in the brand
name PHOCAST 90XR. Apart from being erosion resistant, this

Report By: A. Prakash, Boiler Consultant.

03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
refractory can conduct heat compared to conventional refractory
materials.
Application of this refractory is mainly limited to high erosion
prone areas like coal feed points, bends in bed coils etc. Now a
days many users are applying this refractory on new bed coils
prior to erection/replacement.
6. Note On Boiler Capacity
The boiler can be operated safely at 110% MCR loads, provided
i.

such operations are limited to 30 minutes in every 8 hours.

Present Full Load Operation
The boiler is presently operated at close to 100% MCR, as
Indicated on un compensated Feed water flow meter (Main
Steam Flow meter is not working). The ID & FD fans are running
at full speed in VFD mode and the pressure drop across bag filter
is 110 mm WC (Designed to operate at < 80 mm WC.). The

ii.

boiler has a peak load of 110% MCR.

Full load Capacity Enhancement with Non Pressure Parts
Modification.
In MDC & Bag Filter, its recommended that
In the MDC, dummy openings shall be put in service by
providing additional separator cones so as to reduce the dust
loading in Bag filter. In Bag filter the dummy openings shall be
taken in line with bags & purging arrangement.
After completion of this the bag filter purging shall be put in
Differential pressure mode, so that the excessive purging
cycles shall be eliminated while operating in Timer mode,
which shall reduce the chances of filter bags potential damage.
Since without modifying the pressure parts the boiler capacity
enhancement cannot be done beyond 110% MCR, the present
ID, FD are suitable for the present operation.

iii.

Full

Load

Capacity

Enhancement

by

Pressure

Parts

Modification
The boiler has been checked for circulation up to 110% MCR.
Enhancing the capacity above this shall require circulation
calculation check, as the pressure drop in entire circuit will
Report By: A. Prakash, Boiler Consultant.
03.10.2015

Date:

Report On M/s Asian Paints Limited, Penta Division,

Cuddalore.
increase. The most likely changes shall be on supply and risers,
super heater coils etc.
7. Other Recommendations
I.
The dust extraction system in the coal plant shall be put in
service. This shall control the dust contamination in the coal
handling plant. Its important to make sure that the DE system is
II.

properly earthed to prevent fire in the bag house of DE system.

It is recommended to provide an airside by pass for air heater to
protect it from dew point corrosion while start ups and low load

III.

operations.
Since the operation of the boiler is governed by the emission
norms, its recommended to have a stand by Bag filter of

IV.

similar capacity.
The boiler feed water pump is currently operating with efficiency
less than 60%. The possibility of energy efficient pump shall be
enquired with pump suppliers. The new pump shall be selected
to

V.

have

maximum

efficiency

in

present

maximum

load

conditions.
The boiler feed water pumps shall be fitted with Automatic Re
Circulation valves. Its an improvement from the present
arrangement of pressure switch based pneumatic control valves.

Report By: A. Prakash, Boiler Consultant.

03.10.2015

Date: