when good isn’t enough: advancing firetube boiler...
TRANSCRIPT
When Good Isn’t Enough: Advancing Firetube Boiler Design
Presented by Steve Connor August, 2014
What We are Covering Today
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Summary Focus areas for design change
The final results The design solutions
Brief on boiler evolution
Market drivers demanding
change
Advancing Firetube
Boiler Design
Boiler Evolution
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• Egyptian boilers 5 – 6 BC • Hero’s Engine; 1st Century
BC
Hero’s Engine
Burner
Boiler
Steam drum
Egyptian Boilers
SOME OF THE FIRST
DISCOVERED BOILERS
Boiler Evolution
• Bronze cast Hot Water boiler
• 80 AD
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HOT WATER BOILER FOUND
IN EUROPE
Boiler Evolution
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Steam Locomotives
NOTE:
These firetube boilers could weigh up to
200,000lbs and reach speeds of 100mph
Boiler Evolution
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Steam Locomotive Cut-A-Way
Furnace
Convection
Steam dome
Tube sheet
NOTE:
These boilers were an integral part in leading the way in the industrial revolution starting in
the 1860’s.
Boiler Evolution
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Titanic Titanic Boiler Room
NOTE:
The Titanic was powered by 29 boilers that contained 159
furnaces which were fired with 825 tons of coal per day.
Boiler Evolution
• Shaft Horsepower based on 100 DF feedwater to reach 70 psi saturated
• 2,546 BTU/HR • Boiler horsepower: 33,475
BTU/HR • 2,546/33475 = 8% FTSE
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NOTE:
At this time, boiler efficiency was not nearly as important as
the motive power.
Boiler Evolution
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1946 1957 and Beyond
A STANDARD FOR FIRETUBE
CONSTRUCTION WAS CREATED
Market Drivers
• Energy Conservation • Footprint (square footage
and weight) • Emissions
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What is driving the market today?
Focus Areas
• Reduce number of passes and tube count
• Improved radiant and convective heat transfer
• Enhance heat transfer coefficient & Reynolds number
• Lower furnace heat release rates
• Enhanced combustion & control
• CFD modeling • Structural analysis
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Where should we focus our attention?
Improving Radiant & Convective Heat Transfer
• Lower heat release • Less weight • Smaller footprint • Longer life
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Radiant
Convective
125,000 BTU/Ft3
BENEFITS FROM THE AREAS OF FOCUS
Reducing Weight and Footprint
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• 30% less weight • 15% less floor space
Larger furnace Improve convection heat transfer
2 pass
NOTE:
These are attractive features to architects designing new boiler
rooms when faced with budget restraints.
Radiant Heat Transfer
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• Large Delta T • High velocity • Turbulence • Excellent heat exchange • 60% of the heat energy absorbed
Furnace
NOTE:
The furnace transfers the greatest amount of heat than anywhere else in the boiler.
Convective Heat Transfer
Typical Boiler Tube
Extended Tube Surface
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Boundary layer
Fins Dimples Spiraled
INCREASED INERTIA FORCES
= INCREASED HEAT
TRANSFER
Increasing Efficiency While Reducing Footprint
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1st pass
2nd pass
Gas exit
Focus Areas
• Reduce number of passes and tube count
• Improved radiant and convective heat transfer
• Enhance heat transfer coefficient & Reynolds number
• Lower furnace heat release rates
• Enhanced combustion & control
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How do we address market needs with regards to Efficiency and Emissions?
Low Emission & High Efficiency Burner
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High Efficiency Low NOx Burner
Matching Burner to Furnace
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20% firing rate 40% firing rate
• Time • Temperature • Turbulence
FACTORS TO CONSIDER
Combustion Control
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Gun Burner- Single Point Positioning
FGR
Air Fuel
Drive motor Jackshaft
Combustion Control
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Parallel Positioning System
Controlling Excess Air
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15% excess air
Stoichiometric
Controlling Excess Air
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RULE OF THUMB
For every 2% increase in O2, you lose 1% in efficiency
Controlling Excess Air
Excessive Time at Mid to Low Fire
Optimum range
Energy loss
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Controlling the Excess Air
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VFD Modulating Burner
Controlling Excess Air
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Engineering, Designing & Testing for Constant 3%O2
Emission Reduction
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Flue Gas Recirculation
Integral burner Gun burner
FGR
Emission Reduction
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Fuel Air
Designing Boilers in the 21st Century
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Is boiler R&D like it was in the past?
Computation Fluid Dynamics & Finite Element Analysis
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CFD Modeling
FEA Proving
Structural Verification
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Structural Analysis & Evaluation
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Plain Furnace Corrugated Furnace
Corrugated furnace reduces plate thickness, but adds corrugating cost.
Metal Stresses
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Tensile Strength
Metal Deformation
Tube Sheets
Tubes & Ligaments
Furnace
The Prototypes are Constructed
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NOTE:
The prototypes take a fraction of the time to create now than in the past thanks to advances
in computer technology
The End Result
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• 150, 200 & 250# Steam • 30# & 125# HW • 100 – 2200 HP • Natural gas & #2 oil or
combination • <60&30 PPM NOx 100-1200 HP
10:1 turndown with 3% O2 • <9 PPM NOx 100–1200 HP
(integral), 1300–2200 HP (Gun) • <5 PPM 500 – 680 HP (integral) • Parallel positioning standard • Nominal Efficiency 82.5% 100 –
2200 HP
CBEX Elite
CBEX Elite Features
Main Feature Set
• 150, 200 & 250# Steam • 30# & 125# HW • 100 – 1200 HP • Natural gas & #2 oil or
combination • <9 PPM NOx available • Parallel positioning
available 100-800 HP standard 900 – 1200 HP
• Turndown: 4:1 – 10:1 • O2: 3.5 (Mid-HF) – 8% (LF) • Efficiency: 81%
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CBEX Premium
CBEX Premium Features
The Design Outcome
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C-B Elite “Life Cycle Leader”
C-B Premium “The Value Choice”
. 15% Less Floor Space
. 20 – 30% Less Weight
Burner and Furnace Matching
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Maximizing Radiant Heat Absorbtion
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60%
Extended Tube Surfaces
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2nd pass
Spiraled Tubes
Flue gas outlet
Maximize Combustion Control
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Single Point Parallel Positioning
Market Drivers
• Energy Conservation • Footprint • Emissions • Maintained price/value
relationship • Increased boiler life
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Summary • Firetube boilers have been evolving for years based on
customer needs. • The heating surface and gas passes can be reduced if
provisions are made for increasing radiant and convective heat transfer coefficients & Reynolds numbers.
• Extended surfaces in the tubes breakup the laminar flow, increasing heat transfer
• Reducing thermal NOx is a time/temperature relationship • Imperative the burner and the furnace be matched to
optimize results. • A 2% increase in O2 = 1% loss in efficiency • Most burners lose efficiency at mid to low fire • When selecting a boiler, check the efficiencies at all firing
rates. • Single point positioning is fine if burner doesn’t modulate
much.
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