Stack dampers are one of the insignificant yet important component of fired heaters in the refining industry. Over 90% of the heaters in the USA are natural draft and are dependent upon the draft for efficient combustion of fuel gas with air. Stack dampers currently installed are highly oversized and are not able to control draft effectively. Furnace Improvements patent pending design overcomes these limitations and improves the damper control significantly by installing multiple actuators and changing the control characteristics of the dampers.

1. Smart Damper * Design provides
better control of fired heaters
Ashutosh Garg
Furnace Improvements Services Inc
*Patent Pending

2. Why Dampers??
Why talk about dampers?
Very insignificant component in the
fired heater
Not much attention paid to the design
and operation of the stack damper

3. Dampers can Saves Energy
Draft and Excess O2 are the two parameters
that are being monitored and controlled
Poor design and quality of final control
element- Stack dampers
Stack dampers are mostly manually operated
with a cable and manual winch
Very few dampers operate properly in the
Industry (most are left fully open)
For a manually operated damper, the stack
damper operation becomes very cumbersome

4. Fired Heater Operation
Fired Heater Operators are only adjusting
two items controlling the fired heaters
 Stack Damper
 Burner Registers
90% of fired heaters in US are natural draft
heaters
Draft control becomes very important for
efficient operation
Air leakage can misguide the operating
personnel

5. Manual Stack Damper Operation

6. Measured
Variable
Units of
Measurement
Before Draft
Change
After Draft
Change
Air flow % stoichiometric 115 99.6
Draft at the
bridgewall
in. H2O (mm
H20)
0.1 (2.5) 0 (0)
Draft at the floor
(burner)
in. H2O (mm
H20)
0.4 (10) 0.3 (7.5)
Air flow after the change = 115% *SQRT (0.3 / 0.4) = 99.6 % stoichiometric
30 ft (10 m) tall firebox, draft on target before small draft change, air flow moves to stoichiometric
Draft vs. Excess Oxygen

7. Stack Damper-
Closing will have
following effects:
 Reduced Oxygen in the flue gas
 Decreased draft at the radiant arch
 Firebox temperature will increase
 Stack temperature will go down
 Increased heater efficiency

8. Energy Consumption
A Typical refinery processing- 100,000 BPD
Energy Consumption of 0.40 MMBTU/BBL
$4 per MMBTU
Energy bill of $ 58.8 million per year.
Potential Saving
• 1% Efficiency improve • $587,000/Year

9. Case Study -1
 FIS performed a tuning job for a refinery
heater:
 Depentanizer reboiler heater
 Horizontal tube box
 Absorbed heat duty - 87 MMBtu/hr
 15 up fired burners
 Heater connected to a large common stack
 Two off take ducts provided with manual
dampers

10. -17.0
-15.0
-13.0
-11.0
-9.0
-7.0
-5.0
9:36 10:48 12:00 13:12 14:24 15:36 16:48
Draft,mmH2O
Time (7/22/2009)
Draft (B1402)

11. 0.0
1.0
2.0
3.0
4.0
5.0
6.0
9:36 10:48 12:00 13:12 14:24 15:36 16:48
ExcessOxygen,%
Time (7/22/2009)
Excess Oxygen (B1402)

12. 290
300
310
320
330
340
9:36 10:48 12:00 13:12 14:24 15:36 16:48
StackTemperature,°C
Time (7/22/2009)
Stack Temp. A
Stack Temp. B
Stack Temperature (B1402)

13. 78.0
79.0
80.0
81.0
82.0
83.0
84.0
9:36 10:48 12:00 13:12 14:24 15:36 16:48
ThermalEfficiency,%
Time (7/22/2009)
Thermal Efficiency (B1402)

14. Fired Heaters
Fired heaters are important part of Refining and
Petrochemical Industries.
Provide thermal energy to the fluids being heated by
combusting fuel
Combustion of hydrocarbon fuels requires air to
complete the reaction. Efficient combustion requires
minimum excess air.
Air is drawn from atmosphere and can be supplied by
natural means or by a fan.
Natural draft heaters get combustion air by means of
negative pressure created inside the radiant section.

15. Fired Heater Draft Profile
Flue Gas Pressure Drop:
 Convection Section
 Stack Entry
 Damper
 Stack friction
 Stack exit loss
All these losses are directly
proportional to the square of the flow
of the gases
Pc
(SE)a STACK
EFFECT
IN STACK
(SE)c
NEGATIVE PRESSURE
0.05"- 0.1" W.G. AT
TOP OF RADIANT
SECTION
Pb
(SE)r
Pa
NEGATIVE
PRESSURE
POSITIVE
PRESSURE
0
STACK
EXIT LOSS

16. Stack Design
Draft available
 Due to radiant section height
 Due to convection section
 Due to stack height
Flue gas temperature is typically constant through
out the whole range of operation (may change by
50-100 F at the most)
Flue gas draft availability remains constant
irrespective of heater plant load
CONVECTION
SECTION
STACK
________
BURNERS
0.05"- 0.1"
W.G. DRAFT
DRAFT AT RADIANT
SECTION OUTLET,
R0
RADIANTSECTION

17. Draft
Draft is usually measured at the arch or
below convection section.
The pressure here is the highest (-0.1 in
WC).
The draft is measured in inches of water.
The draft is measured using a water
manometer or draft gauge.
Stack
Convection
Section
Radiant
Section
DG
DG
DG
DG
PT
PI

18. Draft Control
Furnace draft is controlled
by stack damper
Stack damper acts as a
control valve controlling the
upstream arch draft
Excess draft or insufficient
draft are not good for
operation
Draft / Stack O2 Control system
Heater
Process Fluid
Burners
Fuel gas
Control Valve
Draft
To Air preheater
PIC

19. Tramp Air Leakage
Fired heater is not a pressure tight enclosure.
Air can leak from all the openings
 Peep Doors, Header Boxes, Tube
Penetrations etc.
Air leakage is proportional to the
differential pressure. Higher draft means
higher air leakage.
This air does not mix with fuel and shows up
in O2 analyzers. It absorbs the heat that should
be transferred to the heater tubes
All air entering heater should be entering
through the burners that are on

20. Stacks are Oversized
Fired heaters are built for long life of 20-
40 years
Feedstocks and operating conditions
change
Process Licensors and Designers provide
ample margin( 10-20%) in specifying fired
heater heat duty
API 560 Standard specifies 120%
overdesign on the stack designs
Stacks are also designed for maximum
ambient temperatures 95-105°F.

21. Stacks are Oversized
Stacks design use 1.5 velocity heads
pressure drop across damper, we need only
less than 0.5 in fully open position
Stack diameters and height are often
decided by structural stability and
minimum height considerations
Stacks produces very high draft in fired
heaters during normal operation.
Oversized stacks provide flexibility to
operators to fire the heater harder when
needed, which may be only 10% of the
time

22. Fired Heater Operation
Operators need to adjust stack damper
continuously for draft control in fired
heaters
Draft keeps on changing due to change
in ambient temperature.
Night time cooler air temperature
produces higher drafts, almost 0.1 to
0.15 inch extra draft is available
High draft can even affect the flame
patterns and burner operation
Tramp air leakage can misguide the
operating personnel

23. Stack Damper Design
Stack dampers have 2 inch
gap between damper blades
and refractory.
This leads to almost 10 to
15% area being always
available for flue gas flow.
It reduces the
controllability of the stack
damper.
4'-0"I/SREF.
1"
5'-0"I/SREF.
AREA IN FULLY CLOSED POSITION
OPEN AREA
FLOW BLOCKAGE AREA
~3.68 SQ.FT.
~15.95 SQ.FT.
2"
4'-4"I/SREF.
AREA IN FULLY CLOSED POSITION
OPEN AREA
FLOW BLOCKAGE AREA
~2.07 SQ.FT.
~12.68 SQ.FT.
1"
AREA IN FULLY CLOSED POSITION
OPEN AREA
FLOW BLOCKAGE AREA
~1.97 SQ.FT.
~10.59 SQ.FT.
FLUE GAS
DIRECTION
C STACKL
C SHAFT #1L
C SHAFT #2L
FLUE GAS
DIRECTION
C STACKL
C SHAFT #1L
C SHAFT #2L
FLUE GAS
DIRECTION
C STACKL
C SHAFT #1L
C SHAFT #2L

24. Conventional Dampers
Parallel or Opposed Blade
Operation
All the blades are operated
with a single actuator
All the damper blades move
at the same angle
Non-Linear damper flow
characteristics
Parallel Blade
Dampers
Opposed Blade
Dampers

25. Stack Dampers
Opposed blades vs. Parallel Blades

26. Smart Stack Damper Characteristics
Smart Damper is customized to the particular heater
Heater draft profile is checked from 40 % to 120% load and pressure
drop across stack damper is calculated
Heater draft profile is also calculated at minimum, average and maximum
ambient temperatures
Two sets of damper blades are adjusted in such a way that one set of
dampers is taking care of load variations( macro) and the other one is
adjusting ambient temperature variations ( micro).
In very large dampers, we may need third set of pneumatic operator to
improve the control.

27. Smart Stack Damper
Two damper blades configuration, multiple
blade dampers also possible
Two actuators operate each blade or set of
blades individually, in multiple blades more
flexibility is available
Better controlling characteristics
One blade provides macro control and the other
provides micro control

28. Salient Features
Better controlling characteristics
Sized like a control valve
Operator friendly
Avoid tramp air leakage
Can be controlled from the
control room

29. API 560 Damper Design Guidelines
Dampers -13 ft2 / blade
Stack diameters vs. Number of blades in
a damper
 < 4 ft.- single blade
 < 6 ft.- two blades
 < 7 ft.- three blades
 < 8 ft.- four blades

30. Stack Damper with 2 Blades
Conventional Design Smart Stack Damper

31. Stack Damper with 2 Blades
Parallel Blade Dampers
Opposed Blade Dampers
Conventional Design
Proposed Design with Two Control Drivers
Control Driver
FIS Patent Pending

32. Case study
A petrochemical plant had a steam superheater
producing 250,000 lbs./hr
Firing rate almost 300 MMBtu/hr
Heater runs at 100% load at the start up
condition, once every 2-3 years
Heater is running at 150,000 lbs./hr of steam
rate during normal operation
How to control the draft in the heater during
normal operation?

33. Draft Profile: Stack Rating Condition
0
29
58
87
116
145
-0.550 -0.410 -0.270 -0.130 0.010 0.150
ELEVATION,(FT)
PRESSURE, (INCHES WC)
DRAFT PROFILE: RATING AT 100% LOAD, 85ºFAMBIENT TEMPERATURE
(-) PRESSURE (+) PRESSURE
BURNER= -0.384" WC
STACK EXIT= 0.0" WC
FLUE GAS PRESSURE DROP (INCHES WC)
CONVECTION+STACK ENTRY: 0.228
ACROSS DAMPER : 0.126
STACK EXIT : 0.082
ARCH = -0.200" WC
CONVECTION= -0.262" WC
DAMPER = -0.388" WC
STACK EFFECT (INCHES WC)
RADIANT SECTION : 0.184
CONVECTION SECTION : 0.166
STACK HEIGHT : 0.470

34. Available Pressure Drop Across Damper
0.05
0.20
0.35
0.50
0.65
0.80
30% 46% 62% 78% 94% 110%
Pressure,inchesWC
Heater Load, %
Flue Gas Pressure Drop and Stack Effect Vs Heater Load
Flue Gas Pressure Drop
Stack Effect
ΔPacrossdamper=0.126"WC
ΔPacrossdamper=0.236"WC
ΔPacrossdamper=0.286"WC
ΔPacrossdamper=0.312"WC

35. Pressure Drop Comparison: 85ºF Vs 30ºF
0.05
0.15
0.25
0.35
0.45
0.55
30% 46% 62% 78% 94% 110%
Pressure,inchesWC
Heater Load, %
Available Pressure Drop Across Damper Vs Heater Load
Available Pressure Drop at 30F
Available Pressure Drop at 85F

36. Existing Stack Damper
Parallel Blade Damper
This damper has very little controllability

37. Proposed Stack Dampers
Two Operators – Opposed Blade Dampers
FIS Patent Pending
In this damper, we can block 50% area and control the draft from 50 to 100% load

38. Proposed Stack Dampers
Four Operators
And so on…..
FIS Patent Pending
This design with 4
actuators provides the
best control with 4
actuators.
Recommended for
very large diameter
stacks in the range of
10-12 onwards

39. Summary
Conventional dampers are not able to control draft accurately of 0.1 inch
WC at arch.
Smart Stack Damper provides flexibility of altering damper characteristics
for various heater loads and ambient temperatures
Smart Stack Damper enables one actuator could be used for majorload
adjustments and other actuator for minor temperature adjustments
With flexibility to operate the blades individually, efficient and accurate
control over draft can be obtained.
Pay out for smart damper is typically in weeks.
Existing dampers can be converted to Smart Stack Dampers.

40. Thank you
Questions & Comments
Welcomed