Heat Recovery Solutions

From

Fintube Technologies, Inc

Date: October, 2008

© United States Steel Corporation

Fundamentals of Heat Recovery

• Recover heat that would otherwise be wasted up the stack..

• This energy has already been “ paid for ”

$$

• BENEFITS of HEAT RECOVERY Higher efficiency

Lower Pollution (Thermal and emissions) $$ saved

Opportunities for Heat Recovery

Packaged Boilers

Utility boilers

Furnaces

Ovens

Kilns

Fired Heaters

Diesel Generators

Process industries Chemical & petrochemical Food & beverage Paper Pharmaceuticals

Industrial applications Steel production Equipment manufacturers Textile industries

Other Hospitals Schools Laundries Offshore Platforms

Heat Flow

ECONOMIZER OR AIR HEATER

Example: Pulp and Paper

• Average total steam energy use, is 1,947 trillion Btu (end use).

• The sources of the steam in pulp and paper manufacturing include recovery boilers (at chemical pulping facilities), power boilers, and waste heat recovery boilers.

Example: Pulp and Paper

There is approximately 370,000 million Btu per hour (MMBtu/hr) of boiler capacity in the pulp and paper industry.

Approximately half of this boiler capacity is fired by waste fuels.

EXAMPLE : Heat Recovery in a 700 HP Boiler

300 ºF

460 ºF

271 ºF

210 ºF

24,150 lb/hr

30,202 SCFH

Fuel : Natural Gas Economizer Heat Recovery : 1,076,721 BTU/hrOperation Hours per Year : 7,000Boiler Efficiency : 80%Cost of Economizer : $13,500Cost of Installation : $10,000.00Cost of Natural gas : $ 8.00 /MMbtuFUEL SAVINGS :FUEL SAVINGS : ( 8.00( 8.00 $/MMbtu x 1.076 MMbtu/hr x 7000 hrs ) / 0.8 = $/MMbtu x 1.076 MMbtu/hr x 7000 hrs ) / 0.8 = $75,370$75,370 per yearper year

Installed Payback :Installed Payback :

($13,500) + ($10,000) / ($13,500) + ($10,000) / ($75,370) = 0.31 3.7 mon

Partial Experience List – Pulp & Paper

Economics of heat recovery are dictated by capital and operating costs Economics of heat recovery are dictated by capital and operating costs of the heat recovery equipment…of the heat recovery equipment…

Babcock & Wilcox - Economizer International Paper - Economizer Georgia Pacific - Economizer Boise Cascade - Economizer Smurfit Stone - Economizer Temple Inland - Steam Coil Air heaters Tolko Industries - High temperature air pre-heater

Irving Paper - Economizer Wausau Paper - Economizer Pepperell Paper - Economizer Tembec LVL - Air pre-heater West Fraser - Economizer

Higher Fuel price… Faster the ROI

Natural Gas Price Trend

Implications on Economizer Design

• Waste fuels

• Bare tube - Larger Units• Modular units• Fouling considerations

• High Operating Pressure

• High design pressure : heavier tube wall – SA-178 C / seamless

• High gas temperature : Casing and structure metallurgies

• Larger Boilers

• Larger economizers• Structural design to support large weights

Rectangular

Cylindrical

Basic Economizer Designs

• Built to Section I of the ASME code

• Vertical or horizontal gas flow

• From 100 hp to 100,000 pph designs

• Solid or serrated finned tubes

• Built-in soot-blowers

• Minimal transitions

• Vertical or horizontal gas flow

• Size ranges to 1,000,000+ pph

• Operating pressures from 50 psig to supercritical

• Horizontal or vertical tube designs

• Can support large loads• ASME Section I or VIII,

Division I

• Dirty Fuel Usageo # 6 oilo Coal

• Inline Soot-blowing• Normally Solid Fin with low fin

density

• Best Heat Transfer Characteristics• Clean Fuels

o Natural Gaso #2 Oil

• Mass soot-blowing if needed, lance parallel

• AeroSeg finned tubes

Tube Layout in Economizers

Square tube pitch Triangular tube pitch

Enhanced heat transfer surfaces significantly decrease the cost of heat recovery by making the unit very compact

Enhanced Heat Transfer Surfaces

Serrated (1970) Solid (1959)Studded

Externally finned tubesExternally finned tubes

Internally ribbed tubesInternally ribbed tubes

X-ID AeroSeg (2004 )

Finning Configurations

Fuel typeSquare tube

pitch with Solid Finning (fpi)

Triangular (Staggered) tube Serrated Finning

(fpi)

Sootblowers Recommended

Natural Gas Only N/ANatural Gas with #2 oil backup (<2 wks/yr)Natural Gas with #2 or #4 backup

N/A

N/A

6

5

4 - 5

No

No

NoNatural Gas with #5 or #6 Oil backup

#5 or #6 Oil

#2 or #4 Oil

Heavy Residual (Bunker C or Coal Tar)

N/A

4 - 5

3

N/A

Yes

Yes

Wood

3

2.5

2

N/A

N/A

N/A

Yes

Yes

Yes

• AeroSeg finned tubes are the new generation of finned tubes

• AeroSeg® finned tubes can significantly decrease the number of finned tubes in an HRSG, thus decreasing cost.

• Cost models show that with tube-layouts ideal for AeroSeg, HRSG module costs can be reduced by up to 8%.

• Pursuit of higher efficiencies have driven rapid increases in gas turbine exhaust temperature and mass flow rates.

• AeroSeg finned tubes are ideally suited to handle higher heat duties since they can transfer more heat without a proportional increase in pressure drop.

AeroSeg® finned tubes in HRSGs

What is X-ID® ?

• X-ID is an internally enhanced tube.

• Tube augmentation (passive or active) techniques are used to increase the heat transfer rate.

• The augmentation in an X-ID tube is achieved by helical ribs on the inside of the tube.

• Ribs modify the behavior of the fluid flow leading to heat transfer augmentation.

What is X-ID® ?

Boundary Layer

HeatHeatTransferTransferRateRate

FlowFlow

• Increases overall boiler efficiency by transferring more heat than a bare tube.

– Tube-side heat transfer rate 85% greater than bare tube.– Increased boiler efficiency – Number of tubes in boiler can be reduced.– X-ID boiler requires less space (smaller design size).– Cost savings on larger boilers up to 20%.

– “Foul less” than plain tubes – Self-Cleaning.– Same tube expanders as for plain tubes– Can be rolled, beaded, seal-welded.

X-ID® Tubes in Firetube Boilers

• Need “high quality” heat.– High enough temperature of gas stream.

• Amount of heat recovery is limited by corrosion considerations. This dictates feed-water temperature and gas exit temperatures .

– Oxygen corrosion : ( minimum feed-water temp = 180 F to de-aerate)

• Use stainless steel tubes if water temperature is lower than 180 F.

– Acid dew-point ( ~ 210 F - ~ 250 F) for sulphur bearing fuels• Use feed-water pre-heat systems to raise tube-wall temperature.• As a practical matter, most samples of gases from combustion

processes where coal or oil is the fuel, contain about 10%-12% water….Gases from combustion processes where natural gas is the fuel contain about 22% water because the fuel has more hydrogen to form water.

PROPER SIZING OF HEAT RECOVERY EQUIPMENT IS VERY IMPORTANT TO AVOID PROBLEMS IN THE ECONOMIZER AS WELL AS THE STACK.

Considerations in Heat Recovery Equipment

• Acid dew-point depends on sulfur content of fuel • Stack temperature after economizer is dictated by acid-dew point.

• Wall temperature is controlled by feed-water temperature

Fuel Typical Stack temperature

(◦F)

Recommended minimum feed-water temp (◦F)

Natural gas 260 – 280 F 180 F

# 2 Oil ( < 0.5% S) 300 – 325 F 210 F

#6 Oil ( ~ 2% S ) 350 F 240 F

Acid dew-point Corrosion

Corrosion Considerations

Pitting Corrosion• Feedwater quality and temperature• Oxygen removed adequately?• Chemical / Mechanical /Thermal de-aeration…If not, use stainless

steel tubes

• Undeaerated

Feedwater

• <9 Months

Performance of Products has been extensively tested

Fintube R & D encompasses four key areas :

• Performance of Externally finned tubing• Performance of Internally enhanced X-

ID tubes• Computational Fluid Dynamics (CFD)• Fundamental Research

Fresh air inlet

Inlet duct

Gas burner

Finned tube bundleExhaust duct

65’ Overall length of test facility

ESCOA Engineering Manual

• Available size ranges and fin parameter combinations

• New rating calculations

• General information on all divisions

• Fintube Test Facility Data

• Updated Library

• Fintube History

Download online at

www.fintubetech.com

SUMMARY

• Recovering heat from flue gas can result in significant energy savings

• Enhanced heat transfer surfaces like finned tubes make economizers, air pre-heaters, waste heat boilers very economical…Typical payback is less than one (1) year

• Is Time for Heat Recovery!!

Muchas Gracias!!

aletasybirlos.com

© United States Steel Corporation