The document discusses the limitations of conventional stack dampers in fired heaters, particularly in controlling draft and ensuring efficient combustion. It introduces the 'smart stack damper' technology that features two independently operating blades, allowing for improved draft control under varying conditions. The smart stack damper aims to enhance the efficiency of fired heaters in petroleum refineries, with a quick return on investment for its implementation.

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Smart Stack Dampers for Fired Heaters
An Innovative Technology to Control Heater Draft

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 Major sections- Radiant , Convection & Stack
 Burn fuel gas with combustion air to generate heat
 Heat is transferred to the process in radiant and
convection section
 Flue gases are vented to the atmosphere safely
through stack
Fired Heaters
Fired Heaters are Major Consumers of Energy in the Petroleum Refineries
Radiant
Convection
Stack
Damper

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 Strive for perfect combustion
 Fuel side control: flowmeters, densitometers etc.
 Combustion air flow is dependent on:
 Burner air registers opening
 Stack damper opening
 Both are manually operated
 Air side control is basically missing??
Efficient Combustion
Inadequate Amount of Air Leads to Inefficiency
Combustion

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Excess O2 and Draft
 Excess air is measured by excess oxygen
 Oxygen Measurement: Major developments in the last 50 years
 Draft i.e. the negative pressure inside the heater
 Draft is maintained about 3-4 times the recommended value
 High draft causes considerable loss of energy
 Dampers are used to control the draft generated by the stack
Damper is the Final Control Element in the Fired Heater

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Dampers
 Why talk about dampers?
 Very little attention has been paid to
draft control
 Manually operated dampers
 Poor design and quality of stack damper
 Very few dampers operate properly in
the Industry
 Mostly dampers are left fully open
Damper is Very Insignificant but Important Component of the Fired Heater

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Fired Heater Draft Profile
 Flue gas pressure drop:
 Convection Section (Pb)
 Stack entry loss
 Damper loss
 Stack friction loss
 Stack exit loss
 Damper loss
 1.5 velocity heads (used in design calc)
 0.5 velocity head (fully open)
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
Pc
Fired Heaters has Negative Pressure Inside : Safe Equipment

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 Flue gas temperature is typically constant through out
the operation (may change by 50-100 °F at the most)
 Flue gas draft is dependent on ambient temperature
 Ambient temperature fluctuates 20-30 °F every day
 Flue gas pressure drop is proportional to (Firing Rate)2
 Excess draft available has to be used in the damper
CONVECTION
SECTION
STACK
________
BURNERS
0.05"- 0.1"
W.G. DRAFT
DRAFT AT RADIANT
SECTION OUTLET,
R0
RADIANTSECTION
Stack Design
Higher the Stack Temperature More is the Draft Available

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Available Pressure Drop Across Damper
0.00
0.20
0.40
0.60
0.80
1.00
1.20
30 46 62 78 94 110
PressureDrop,inchesWC
Heater Load, %
Draft Losses & Stack Effect Vs Heater Load
Stack Effect at 105F
Stack Effect at 60F
Stack Effect at 30F
Flue Gas Pressure Drop
Damper must consume more pressure drop
Heater Draft Availability Increases at Low Ambient Air Temp. & Reduced Load
Damper Must Consume More Pressure Drop

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 Designers provide ample margin( 10-20%) in
specifying fired heater heat duty
 API 560 standard specifies 120% overdesign on
the stack
 Stacks are designed for maximum summer
ambient temperatures 95-105°F
 Stack dia. and height are often decided by
structural stability & min. height considerations
Stacks and Dampers are Oversized
Consideration of Safety Margin is Always Good

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Conventional Stack 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
 10-15% area provided as clearance
around the blades
Parallel Blade
Dampers
Opposed Blade
Dampers
Conventional Dampers are not Good Enough to Provide Full Range Control

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 Needs to be adjusted continuously
 Dampers have non linear characteristics
 First 50% of damper opening controls 85%
of fluid flow
 System sensitivity changes throughout the
operating range
 Higher sensitivity - difficult damper
operation - poor draft control
HIGH
SENSIVITY
LOW
SENSIVITY
OVERSIZED
DAMPER
CURVE
LINEAR
(IDEAL)
CURVE
% DAMPER OPENING
%FULLFLOW
100
0
0
100
TYPICAL
Stack Dampers Controls
Draft Control Needs to be Continuous in Real Time

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 Damper should have a min 30% of the system pressure drop to be
controlling
 How to achieve 30% pressure drop in the damper?
 Reduce damper size- permanent pressure drop
 High pressure drop will increase the stack height substantially
 Our Solution:
A flexible plan by creating two sets of damper blades that are operating
independently. When needed we can close the damper blades to achieve the
required pressure drop and control linearly
Stack Damper Sizing
Draft Operation Should be Flexible & Reliable

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Smart Stack Damper
 Two damper blades configuration, multiple
blade dampers also possible
 Equal blade areas
 Two actuators to operate each blade individually
 Better controlling characteristics
 One set of blades provides macro control and
the other set provides micro control
Multiple Actuators
Smart Stack Damper has Linear Control Characteristics

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Stack Damper Sizing Case Study
Parameter Units Value
Heater Firing Rate MMBtu/hr 88.0
Flue Gas Quantity lb/hr 85,467
Flue Gas Pressure Drop in Convection IN WC 0.214
Stack Diameter ft 8.0
Stack Flue Gas Velocity ft/sec 15.0
Damper Loss (1.5 VH) In WC 0.036
Stack Loss In WC 0.092
Total System Losses In WC 0.342
1.5 Velocity Head Corresponds to 40% Opening Area

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 Stack damper pressure loss: 30% of the
total loss = 0.3 x 0.34 = 0.102 inch WC
 Damper loss = 0.5 VH (Fully Open)
 Velocity head = 45 ft/sec
 Net free area needed = 33.5% of the
stack for control
 How to get the controllability = 2/3
damper closed and 1/3 operating
Stack Damper Sizing
Smart Stack Damper Provide Full Range Control

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 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
API 560 Damper Design Guidelines
Minimum of One Blade for every 13 ft2 Cross Sectional Area

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Flue Gas Flow
A
•Actuator remains closed
•Actuator Remains open
-Position of Actuator / Dampers at heater start-up
B
Smart Stack Damper Blades
One Blade is Closed, Other is Operating during Start-up

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•Actuator remains 100% closed
•Actuator is partially closed to reduce the draft
-When the arch draft is higher than -0.1” WC
Flue Gas Flow
A
B
Position of Damper Blades when Draft is High
One Blade is 100% Closed, Other is Operating when Draft is High

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Flue Gas Flow
•Actuator is opened to increase the draft
•Actuator remains 100% open
-When the arch draft is lower than -0.1” WC
Position of Damper Blades when Draft is Low
A
B
One Blade is 100% Open, Other is operating when Draft is Low

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Summary
 Conventional dampers are not able to control draft of 0.1” WC at arch
 Smart Stack Damper provides flexibility of altering damper configuration
for various heater loads and ambient temperatures
 Smart Stack Damper enables one actuator could be used for major load
adjustments and other actuator for minor temperature adjustments
 With flexibility to operate the blades individually, efficient and accurate
control over draft can be obtained
 Existing dampers can be converted to smart stack dampers
Pay Out for Smart Stack Dampers is Typically in Weeks

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Thank You!