Case studies in steam system auditing

CASE STUDIES OF STEAM SYSTEM AUDIT IN SOME PLANTS
By K.K.Parthiban, Venus Energy Audit System
Introduction
This article outlines the outcome of auditing of steam system conducted in process Industries. The
details of modifications / improvements carried out may be of use to other boiler users. During the
audit the operating staff had exchanged all their experiences and this had resulted in benefit of their
plant.
Case 1: Steam system auditing in a process industry
Interaction & listing of the problems
A detailed interaction with various level personnel in the plant resulted in a long list of the
problems that could be addressed in order to improve the plant efficiency. The list was quite
exhaustive and it included the finer details of the problems as experienced. The studies included
both the boiler and the entire steam & condensate system of the plant. For photos refer annexure.
The problem, causes & Remedial actions
Problem Cause Remedial action
Gauge glass There was excess chemical dosage.
thinning down. The boiler water pH used to go up
11.8. The normal pH recommended
was 9.5 to 10.5. See photo 3 & 4.
Replacement at an
interval of 10 days.
See photo 1.
Excess condensate
drainage at the first
trap itself along the
steam line.
Frequent choking
of the flue tubes in
the boiler.
Air
choking
preheater
On inspection of the boiler steam
drum internal, it was found that there
was scope for turbulence of boiler
water at the level gauge tapping. See
photo 2
Excess chemical dosage has led to
foaming inside the drum. See photo 6.
Steam risers did not have proper
baffles to prevent direct passage of
water to drier box. See photo 5 & 7.
Wood containing sodium / potassium
deposit in the tube sheet at the first
pass entrance. Such boilers need precollection
chamber & reduction flue
gas temperature to less than 650 deg C
before shell. See photo 7 & 8.
Boilers when fired with high moisture
fuels experience flue gas condensation
in APH tubes. Simultaneously it leads
to ash sticking to the moist surface and
leads to choking. See photo 11.
The plant personnel were educated
on the purpose of chemical dosing.
The antiscalant dosage was reduced
as the plant has very little make up
water.
Proposed for baffle box in front of
water level gauge. Steam separator
baffles added to reduce turbulence
inside the steam drum. See figure 1.
The chemical dosage was restricted
to maintain the boiler water pH to
10.5
Extensive modification carried out
in the drum as per figure 2.
Suggestion was given for an air
operated hose for cleaning the tube
sheet on line. This was
implemented and the benefits
obtained. See figure 3 & photo 9
&10.
Steam coil preheater is the right
solution. When the air is preheated
to 65 deg C, the condensation of
water can be avoided.
But for this plant pressure jet water

Corrosion of ducts
Excess
consumption
Improvement
process
performance.
fuel
in
Outside air ingress is seen in to APH
causing condensation of flue gas
moisture. See photo 12.
Boilers with biomass firing need
insulation right up to chimney inlet to
prevent moisture condensation in the
ducts. See photo 13 & 14.
Auto air vents were seen installed in
the steam piping. These were not
maintained. The steam was mistaken
as air by the operating staff. See photo
15.
So many valves were not insulated at
all. See photo 16 & 17
Steam loss was very high at the traps.
See 18.
Wrong trap arrangement was seen at
several places. Traps are not located
for easy inspection. See photo 19.
cleaning was advised.
Tubes fail periodically. It is
necessary to understand the
periodicity of replacement & plan
spare.
The inspection door needed
strengthening. Every time any
inspection door is opened only fresh
seal rope must be provided.
It was advised to insulate all the
ducts up to Chimney inlet and arrest
all ingress.
Advised to close the auto air vent.
Air vents are provided only in heat
exchangers. These are again
required if there is a possibility of
air trapping.
Valves are to be insulated with
removable pad insulation. This
brings down the radiation loss to
surrounding.
Traps at unnecessary places were
closed down.
Wherever the traps are required and
the traps had started passing steam,
the bypass lines were cracked
optimally to bring down the loss.
Right trap arrangement was given.
Wrong orientation of traps was
corrected.
Regular inspection of traps is a
must. For auditing IR camera &
ultrasonic probe come in handy. See
photo 19 & 20.
Case 2: Audit of a coal fired unit in a paper mill
The customer had requested for an audit of their plant to bring down the coal consumption. The
boiler was originally a husk fired. Later due to fuel price escalations, customer switched over to
coal firing most of the year.
The problem, causes & Remedial actions
Problem Cause Remedial action
High coal Vibratory feeder used in place of For coal feeders only rotary / drag
consumption rotary feeder. See photo 22.
The oxygen level was so much
hunting, ( see figure 24, 25 & 26) hat
chain feeder to be used.
Customer was advised about the art
of fuel feed regulation. The CO

the fuel did not burn in the furnace
resulting in high carbon in bed ash
itself. See photo 23.
The surface temperature audit by IR
camera proved that lot of scope exists
in reducing the heat loss to ambient.
See photo 27, 28 & 29.
Process side heat loss was also high.
In the paper industry, the drying
cylinders meant for drying the paper
was without the end radiation shields.
ppm exceeded 5000 ppm.
Insulation was advised to this
customer.
The surface temperatures between
the case with radiation shield & the
case without the shield were shown
to client. One can see the IR camera
outputs at the annexure. See photo
30 & 31.
Case 3: Audit of a biomass fired boiler in a paper mill
The customer had requested for an operational audit of their boiler to bring down the fuel
consumption and to address the dust complaint from nearby factories. The boiler was originally a
wood fired boiler. Later due to non availability of wood the boiler was converted to FBC firing
with external refractory furnace walls. The biomass fuels used include rice husk, tamarind shell,
ground nut shell, coffee husk.
The problem, causes & Remedial actions
Clinker
in bed.
formation
ID fan capacity
inadequate
Chimney failure
Dust
from
factory.
complaint
adjourning
The fuels used have ash fusion
temperatures as low as 750 deg C.
There was clinker formation above the
bed on the wall due to high free board
temperature excursions & due to
presence of uncooled walls.
It was seen that the air / flue gas
ducting is designed in a haphazard
manner. See photo 34.
It was seen that the ID fan is provided
with a damper right at the fan inlet.
Such obstructions bring down the fan
performance. See photo 33.
This is a common phenomenon in
many plants. The cause is the high
moisture content in fuel & low
exhaust temperature.
Though the ash content is less, due to
improper combustion, improper ash
collection system combined with
condensation of water vapor has
caused carbon particulate.
Furnace is not provided with over-fire
air arrangement. High volatile fuels
The combustion temperatures were
adjusted for a lower bed
temperature.
The biomass of fouling nature
needs waterwall furnace enclosure.
Only flue gas recycling is to be
done now to reduce the furnace
temperature.
Ducting reengineering was advised
to bring down the draft loss.
Customer was advised to remove
the flap from the damper and to
provide multi flap damper in the
MDC outlet duct.
The exhaust temperature at chimney
top should be over 110 deg C. This
can be improved by insulating the
gas ducting up to chimney inlet.
Customer was advised for rotary
ash feeder at all ash collection
points. In addition unconventional
dust traps as seen in photo 32 & 33
were added.
Customer was advised to
incorporate secondary air system.

Frequent boiler
feed pump failure
Conclusion
need a good turbulence above the bed,
particularly in over bed feed system.
This is required to burn off the
unburnt gases.
The feed pump suction piping is with
mistakes that take away the NPSH.
See photo 35, 36 & 37.
Seeing the CO values in the flue gas
at shell outlet the over-fire air has to
be adjusted.
Customer was advised to remove
the thermocouple & flow meter
immediately. If problem persists,
globe valve shall be replaced with
gate valve.
Generally in all the plants there remains a good scope for fuel savings & for improving the steam
generating & distributing system. There are numerous cases where plant engineers & operators
have incorporated many improvements. The users could bring out their achievements in this boiler
meet in the further years.

Photo 1: Gauge glass seen eroded. This failure
took place every week.
Photo 2: Gauge glass located close to risers.
This causes turbulence in water level gauge.
Figure 1:
Photo 3: Excess chemicals have led to whitish
deposit seen in the shell above the tubes.
Photo 4: Rear tube sheet seen with whitish
deposit. If hardness salts are present, tubes
would be seen with deposits.

Photo 5: A baffle box provided at one end of the
drum did not have level equalizer. The steam
water mixture would have to climb over the box.
Photo 6: Steam separator seen with foaming
mark indicating the drum was under turbulent
water level.
Figure 2:
Photo 7: Risers do not have a cap. Thus the
water can go directly to the steam pipe nearby.
Photo 8: Inlet of the I pass tubes at shell. A view
after cleaning. Old deposits could be seen.

Figure 3:
Photo 9: Compressor lined up for ash deposit
removal.
Photo 10: Cleaning ports in the inspection door.
Compressed air line is taken out of port.
Photo 11: Fresh air ingress to APH causes gas
condensation leading to corrosion & choking.
Photo 12: Improper APH inspection door
seating leads to cold ingress.

Photo 13: Shell intermittent hopper (not
insulated?)with improper flange seating
allowing air ingress.
Photo 14: MDC cones seen coated with
condensed ash deposits. Insulation is advised.
Photo 15: Unnecessary air vent in main steam
line. At high points, only a vent is required for
air release during hydrotest.
Photo 16:Uninsulated valves result in heat loss.
Photo 17: Uninsulated valves result in heat loss.
Photo 18: Steam seen gushing out of trap. There
were traps downstream & hence this was closed.

Photo 19: In accessible traps – not suited for
regular check.
Photo 20: Auditing equipment – Infrared camera
– for identifying defective trap, bearings &
electrical panels.
Photo 21: Energy audit equipment – ultrasonic
probe for various application
Photo 22: Vibratory feeder being used for coal
feeding in an FBC boiler. Boiler designed for
husk.
Photo 23: Unburnt coal seen in the bed ash
itself. It is not practically adjust required coal
feed rate with vibratory feeder. The LOI ranged
to 2% in this case.
Photo 24: The Oxygen analyzer is provided to
ensure Oxygen is available for combustion. If
load is varying then the minimum Oxygen has
to be 3.5%.
.

Photo 25
Photo 26
Photo 27: Uninsulated areas in a bi-drum boiler
Photo 28: Almost at all sealbox the temperatures
run over the stipulated ambient + 20 deg C. Max
temperature is 197 deg C.
Photo 29: Close to the bottom drum, in the
finned area, temperature is seen to be maximum
of 202 deg C.
Photo 30: In a paper industry, the drying
cylinders are not covered by many. This one is
without a cover. We may see the peak
temperature is 154 deg C.

Photo 31: This cylinder is with a cover. These
drying cylinders rotate at a speed. Naturally the
convection heat loss will be predominant as
compared to radiation mode heat loss.
Photo 32: Ideas to reduce dust emission in small
boilers
Photo 33: A way to reduce dust emission.
Further at all ash collection points rotary feeders
added.
Photo 34. Haphazard ducting adds up to higher
draft loss. Customer had gone ahead with
replacement of fans.
Photo 35, 36 & 37 show the mistakes made in feed pump suction piping that the frequently the
pumps fails to pump due to cavitation. Thermocouple in the line, flow meter & globe valve in pump
suction line creates loss of NPSH.