14a-finfan

Optimizing Performance

of

Air-Cooled Heat Exchangers

www.hudsonproducts.com

•Introduction•Understanding Air Cooled Exchangers•Most Common Performance Failures•Determine Current Performance•Performance Enhancement Options•Costs of Enhancement•Other Considerations

Overview

Introduction1930 Redwood Cooling Tower

Bare Tube Bundle with Plug Style Header Boxes

Induced Draft Fin-Fan® Air-Cooled Heat Exchanger

Introduction

• Petroleum Refining

• Oil & Gas Production

• Power Generation

• Petrochemical

• Gas Processing

• Oil and Gas Transport

Understanding ACHEs

®

Induced Draft

• Fans positioned above the exchanger bundle

• High velocity

• Reduces hot air recirculation

• Plenums protect exchanger bundle from elements

• Better air distribution across the bundle

• Better process control and stability

• Increases capacity in a fan-off or fan failure condition


® Air-Cooled Heat Exchangers (cont.)

• Fans and mechanical components positioned below exchanger bundle

• Lower horsepower requirements

• Maintenance personnel protected from high exit-air temperatures

• Well suited for high temperature service

Forced Draft

®Air-Cooled Heat Exchangers

Gas Pipeline Compression

®Air-Cooled Heat Exchangers

LNG Facility


Offshore Platforms

®


Cold Climate Designs

®

•Fan Assembly• Static Efficiency

• Mechanical Design - Tip Clearances - Inlet Bells

•Tube Selection• Fin Efficiency, Gap Resistance

• Single Tube Testing - Performance Verification

• Tube Side Fouling

• Air Side Fouling• Air Borne Contaminants

• Under specified Fouling Factors

• Hot Air Re-circulation• Plant Layout, Unit Design

Most Common Performance Failures

Determine Current Performance

• STEP #1: Obtain original data sheets.

– Check the current process conditions against the original design conditions.


• STEP #2: Perform visual inspection:– The fans

• Operational Issues - rotation, blade settings• Tip clearances correct?• Inlet bells?


• STEP #2: Continued– Air leaks - seals, plenums?– The mechanicals

• Belt condition?• Motor operational?• Fan Shaft condition?

Bearings


• STEP #2: Continued– The fin tubes

• Fin cleanliness, condition? (Top & Bottom)• Loose Wrap-On fins?• If embedded - tubes corroded?• Fins “crushed”? (Usually on top)• Tube spacing correct?• Tubes distorted from heat?• Tube side pressure drop? Within specifications?

Water Sprayed Finned Tubes

Finned Tubes

Wrap-On

Embedded

Hy-Fin®Extruded Serrated

Hy-Fin® Extruded


• STEP #2: Continued– The louvers and steam coils

• Louver operation, full range?• Actuator operation?• Correct operation direction?• Steam coil operation - summer, winter?• Is the steam coil blocked?

Louvers - Winterized Unit


• STEP #3: Air-side testing:

– Shaft speed measurement & adjustment to assure constant RPM for all fans


• STEP #3: Continued– Measurement

• voltage, amperage, horsepower power factor

– Adjustment of fan blade pitch • correct motor loading

– Measurement of air velocity • flow through the fin tube bundle.


• STEP #3: Continued

– Measurement • pressure drop across the fin tube bundle.• temperature rise across the fin tube bundle.

Determine Current Performance• Step #4 Calculate air side heat transfer rate:

Qair = (r V A) x (cp) x (Tout - Tin)r = average air density; lbm/cuftV = average measured velocity; ft/hrA = bundle face area; sqftcp = average air specific heat; Btu/lbm-FTout = average air temperature leaving bundle; FT in = average air temperature entering bundle; F


• STEP #4: Continued– Compare calculated air side heat transfer

• to the design duty.

– Air-side testing • baseline the unit to set enhancement goals


• STEP #5:

– Upon completion of tune up• assess performance enhancement options.

Performance Enhancement Options

• Fan Assembly:– Increase blade pitch on all fans IF motor horse

power is available. – Check tip clearances are not tight enough

• (< 3/8 inch), install tip seals.

– Consider Inlet Bells

Axial Flow Fans®

Efficient Air Flow

Inlet Bells Tip Seals and Seal Discs


– Fan Efficiency• Consider higher efficiency fans over low efficiency

straight chord aluminum blades.

Fan Cord Comparison

®

Fan Cord Comparison (cont.)

®


– Tube Side Fouling• Bundle inspection and cleaning• Plug and Gasket Replacement (also for cover plate

designs)

•Threading Problems - lubricants, material compatibility

•Machining and alignment


– Air Side Fouling• Air Borne Contaminants • Fin tubes condition, cleanliness

– Cleaning or retubing the bundle with equivalent or higher grade fin tubes

– Install bug screens

• Serrated type fin tube upgrade to maximize plot space and cooling capacity

Finned Tubes

Wrap-On

Embedded

Hy-Fin®Extruded Serrated

Hy-Fin® Extruded

Tube Out & Hydrotest Shop


– Bundle Condition

• Consider bundle replacement - shutdown restrictions • If fin tube corrosion is severe, headers may need

replacing to meet ASME MAWP requirements

Maximizing Potential Heat Duty

• Hot Air Recirculation – Inlet Air Temperature is Increased– Location– Original design - intake area– Consider exhaust stacks– Computation Fluid Dynamics Study

Exhaust Stacks

CFD Computational Fluid Dynamics

Features

• Engineering services which predict site-specific air behavior minimizing potential hot air recirculation

Air Behavior


• Adding Units

– Additional Flow, Cooling– Hydraulic Balance Consideration

• Tip Seals $500/Fan 3% to 8%• Inlet Bells $500/Fan 3% to 8%• Cleaning $?? 5% to ?%• Stacks $200/Lft 10% to 30%• Fan/Mech $10K/Fan 8% to 20%• New Bundle $30K-$80K 10%-40%• Humidification $600/Lft 20%-40%• Add Unit $100K-$250K ??

Cost of Enhancements

Other Considerations

• Tube rolling problems– Tube wall thickness, work hardening

• Preferred Piping Configuration– Hydraulic considerations– API allowable tolerances vs. Piping Code– Stub in Headers

Other Considerations

• Split Header Requirements– Sudden process changes, high temperatures, tube pullout

Optimizing Performance

of


www.hudsonproducts.com

14a-finfan

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