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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Contact Us

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David Brick Sales Engineer dbrick@cleaverbrooks.com 414-577-2736 cleaverbrooks.com