up-grading performance of heat exchangers and reducing ... · pdf filethermo-syphon reboilers...

© Copyright Cal Gavin 03/2007 www.calgavin.com

Up-grading performance of heat exchangers and

reducing fouling by retrofitting hiTRAN ® tube-side enhancement systems

www.calgavin.com

Heaters ● Coolers ● Condensers ● Vapourisers ● Reboilers ● Thermo-Syphon Reboilers ● Reactors ● Economisers ● Chillers ● Intercoolers ● Aftercoolers ● Oxidisers….


Cal Gavin LimitedEstablished in 1980Research, development and manufacture of enhancement technology for heat exchangersSectors include -

Oil exploration, production and refiningGas production, transmission and treatmentPetrochemical and downstream processingPlastics, polymers and resinsPower generation, refrigeration and speciality chemicals

Process Intensification engineers


Scope of Activities Include:

• De-bottlenecking – engineering solutions to overcome plant and process limitations

• Designing new enhanced exchangers• Simulating performance and upgrading existing exchangers (HTFS, HTRI, hiTRAN SP software)


The Problem….

To improve matters we increase Reynolds number (velocity)…… but Pressure drop increases to the power 2 as velocity is increased, whereas heat transfer increases linearly.

In plain tubes, frictional drag at the wall and shear forces within the fluid cause maldistribution (parabolic velocity profile)A thermally inefficient laminar boundary layer results. Heat transfer relies on conduction (across the fluid) and convection (physical mixing)Even in turbulent flow a significant boundary layer exists (single and 2 phase flow regimes)


Red dye:

A) Laminar flow

B) Pseudo turbulent flow

Blue dye:

Video presentation of flow (500 < Re < 8000)

• hiTRAN Matrix Elements remove the boundary layer and mix it with the bulk flow.

• Fluid from the centre is displaced in the direction of the wall

• Residence time of the fluid at the wall is considerably reduced.

• In plain tubes, even at Reynolds Numbers as high as 10,000, there is very little fluid mixing of the bulk flow with fluid at the wall.


Flow with hiTRAN, 20mm tube diameter (Please be patient to load the video)


mit Insert Plain tube

1.0

0.5

0.0

U/Umax

Flow velocity vectors of plain tube and immediately after the hiTRAN Element, measured with Laser PIV(Particle Image Velociometry – laminar flow)


after hiTRAN Element Plain tube

1.0

0.5

0.0

U/Umax

Flow velocity vectors of plain tube and immediately after the hiTRAN Element, measured with Laser PIV(Particle Image Velociometry – laminar flow)


Graphical representation of plain tube and hiTRAN matrix element performance range

1

10

100

1000

10 100 1000 10000 100000

Re [-]

heat

tran

sfer

fact

or [-

]

© Copyright Cal Gavin 03/2007 www.calgavin.com Page 1© Copyright Cal Gavin 03/2007 www.calgavin.com

Graphical representation of plain tube and hiTRAN matrix element performance, case study

1

10

100

10 100 1000 10000 100000

Re [-]

heat

tran

sfer

fact

or [-

]

0

0.2

0.4

0.6

0.8

1

pres

sure

dro

p [b

ar]

14*

3.8

20

1

2

2*

2 pass hiTRAN 8 pass plain

1 pass hiTRAN

hiTRAN tube pressure drop

plain tube pressure drop

1.2m/s0.3m/s

6.2m/s 42passes ~100 bar

200 400 1600 8200


For New Exchangers…. hiTRAN Systems benefit any duty where the main heat transfer resistance is on the tubeside• Plot space and weight is restricted• Where single pass is only option• Close temperature approaches• Stability in transition region• Longer operation under most fouling conditions


Upgrading existing exchangers• Higher heat loads• Higher / lower output temperatures• Lower energy requirements• Optimum use of existing hardware• Maintain performance with turn-down• Improved fluid distribution• Mitigation of reaction, crystallisation and deposition fouling


Case study 1: Air Cooled Lube Oil Cooler

Enhanced

Plain Bore Finned Tube

• Requires only 1/3 of the plot area• Achieves the same heat duty at the same pressure drop• Uses less than ½ of the fan power• Allows flexibility to design within noise level limits• Lowest cost option


Case study 2: Heavy Cycle Gas Oil Cooler

Enhanced

Plain Tube

•Requires less than ¼ of the effective heat transfer area•Achieves the same heat duty at the same pressure drop•Fluid residue time at the wall is reduced•Risk of thermal degradation fouling is lowered


Reducing fouling with hiTran Systems

Most exchanger fouling is strongly affected by tube-wall temperature and the rate of shear (mixing) at the tube wall

• Increased shear keeps particles in flow

• Higher tube-side co-efficient : lowers wall temperature when heating fluids (reduces cracking of hydrocarbons) increases wall temperature when cooling (reduces crystallisation fouling e.g. wax

formation)


Photographic Evaluation of hydro-dynamics

Talcum as suspension particles, 40 to 60 microns, 2500kg/m3

Constant Re no. of 750

• High shear rate at the wall causes homogenious distribution of particles

• Vortexes behind the wire loops causes high liquid mixing

Plain tube

hiTRAN tube


Crude Oil fouling research [University of Bath]

F

oulin

g re

sist

ance

[m2 K

/ W

* 10

4 ]

Time [hr]

Tube with matrix Element velocity 0.5m/sTwall = 218 °C

Time [hr]

Tube without matrix Elementvelocity 0.5m/sTwall = 216 °C

Arabian light crude oil

Advantageous effects:• Lower tube-wall temperature for same duty• Reduction in fluid volume which is heated above bulk temperature• Reduction in wall fluid residence time• Suppression of nucleation at the surface• Increased shear rate at the wall (higher removal rate)


Liquid film htc’s are relatively high compared to vapour phase

Mechanisms of Condensation

Vapour

•Film heat transfer coefficients depend on:

–whether film is laminar, laminar/wavy or turbulent–thickness of the film

•Vapour phase heat/mass transfer coefficients depend on:

–vapour velocity/turbulence/mixing–vapour transport properties–concentration of condensable components

Vapour phase htc’s relatively low


Enhancement of CondensersWire Matrix Elements enhance in-tube condensation by:• Film mixing • Film thinning• Film draining•Enhancing vapour phase

cooling•Increasing inter-phase mass transfer rates.

Typical applications:• Vent condensers• Vacuum condensers with inert components• Condensation of wide-boiling range mixtures• Reflux condensers


Mechanisms of Boiling and the impact of Matrix Elements

(Reboilers) • Increased convective boiling rate• Shorter sub-cooled length

• Viscous liquids• Low temperature driving forces

Typical applications for:

• More even tube-side temperature distribution

Sub-cooled

Pla

in

tube

Enh

ance

d tu

be


Where total vaporisation is required at high heat fluxes, enhancement is often applied to:

• Control film boiling• Mitigate mist carry-over• Enhance fluid distribution• Enhance wall wetting

LNG/LPG/Ethylene… vaporisersTypical applications:

Mechanism of Boiling and the impactof Matrix Elements – (vaporisers)

• Improve heat transfer in the superheated region


Case Study 1. Tar Heaters - Cabot Carbon UK Carbon Black manufacture

Installation 1982 – Lummus / Cal Gavin Design

Feedstock mixture of cracked bottoms with coal tar residues – ”high fouling fluid”

12 Exchangers fitted – 2 pass design

Heated with thermal fluid (was steam) to 280C+

Plain tube fouled to shut-down in 2-3 months

hiTRAN System fitted - constant performance maintained

Elements replaced 3 times in 24 years

Higher temperature process in 2006


Case study 2 Crude pre-heater - Wintershall Refinery (BP) - GermanyInstalation 1996 – 9 year operation

Vacuum residue tube side, Crude (preheat) shell-side

Process had a long history of fouling

Many un-planned shutdowns

Helical Baffle/hiTRAN installed – one shell only needed

(without enhancement 2 larger shells would be required)

Re-tubed in 2005, hiTRAN Elements removed and re-installed


Case Study 3 Dalia FPSO – Total Oil, Angola oil-water separation process

• design capacity of 240,000 barrels per day of crude, two million barrels of storage capacity

• shell side 1073500kg/hr wet crude oil is heated from 50.5 °C to 60.7 °C

• tube side 802170kg/hr dry crude oil is cooled from 87.5 °C to 70.1°C

TEMA Type BES

Temp. shell in / out [°C] 50.5 / 60.7

Temp. tube in / out [°C] 87.5 / 70.1

Massflow shell / tube [kg/s] 298.2 / 222.8

Duty [MW] 7.94

Tube OD diameter [mm] 25.4

FPSO Dalia with installed Crude / Oil Interchangers on the Top deck


Case study 3 Size comparison - Conventional / HELITRANplain /

single.Segmental.

hiTRAN® / helical baffle

gain

OHTC [W/m2K] 59.9 242.7 4x

Tube side:HTC [W/m2K] 95 770 8xdp [bar] 140 150Flow velocity [m/sec] 0.92 0.45 ½Reynolds [-] 1680 800 ½Residence time [sec] 102 27 ¼Shell siede HTC [W/m2K] 455 789 ~2dp [bar] 1.50 1.25Flow velocity [m/sec] 0.41 1.3 3Reynolds 250 635Wall temperatures [°C] 59.2 65.6GeometryShell in series [-] 3 1Shell in parallel [-] 3 2Total no. of Shells [-] 9 2 ~4Tube Flow path [m] 94.5 12.2 1/8Tube length [m] 5.25 6.096Total tube count [-] 16002 3640 ~¼Tube passes [-] 6 2Total HT area [m2] 6420 1704 ~¼Plot space [m2] 104.5 26.2 ¼Weight wet [kg] 401148 130716 1/3Exchanger costs [%] 100 35 ~1/3

Conventional HELITRAN


Case study 4 Process Air-cooled Exchanger Upgrade Client: Reliance Industries, Surat, India Contractor: Bechtel Limited Exchanger: Product Fractionator Bottoms Cooler Fluid : Vacuum Gas Oil

Plant Problem -Plant Problem - Planned major upgrade - increased

throughput - change in feedstock Existing exchanger 65% under-

surfaced for new duty No space available for new

exchangers Limited pressure loss available


HiTRANHiTRAN®® Enhancement Solution Enhancement Solution Keep frames and fans

Fit new 2 pass bundles with optimised hiTRAN ® System

instead of 6 pass plain tube design

Up-grade meets new duty plus 10% spare capacity

New duty achieved within allowable pressure drop

The BenefitsThe Benefits Reuse of existing bays, fans, structures - no modifications

No additional structures required

Proven heat transfer performance

Significant cost reduction


“Texas Tower” Feed / Effluent Exchanger May 2007

1700 tubes - 12 metres vertical - 2 joined hiTRAN Elements / tube Benefits :-• increased product throughput • higher return temperature to furnace - increased energy efficiency • Increased plant profit!


Texas Tower – RUHR OEL (BP AMERICA INC)

Benefits:

Retrofit upgrade delivers 15% increased throughput

0.8MW heat recovery

Reduction of 1700t/yr carbon emission recovery from fired heater

Direct reduction of energy input of 25 TJoule/year ( ~50000Euro/yr)


Crude Desalter Exchanger

Fabricator: EIGSADesigner: Cal Gavin

LtdEnd User: PemexCountry: MexicoPlant: Dos Bocas

terminal

Plain tube - 20 shellshiTRAN - 8 ShellsTubeside: desalted

crudeShellside: wet crude


Column Top Condenser

Fabricator: Doosan MecatecDesigner: DOW Chemicals +

Cal Gavin LtdEnd User: SinopecCountry: ChinaTwo new plants: Zhenhei and

TianjinnNote :Combined heat and mass

transfer- one stage effective

Small unit 7000 tubes - 5 metres dia

Large unit 9000 tubes – 7 metres dia


Case Study 10

Retrofit heat recovery of feed/effluent exchanger

User: LUKOIL refineryLocation: Volgograd, RussianService: HydrocarbonExchanger: TEMA AES with Helical baffles 2 parallel trains of 3 horizontal stacked shells in seriesBenefits• Increased performance of

exchangers• Reduced maldistribution on tube-

side• Reduced energy consumption of

fired heater 2.2 MW (4.6 MW at new capacity)

• Fuel saving of $233,000 per year• Enables higher plant throughput• Increased plant profit!


Thank you for your attention

Please tell us what improvements you would like to make to the operation of your plant.

Martin Gough – Cal Gavin Limited

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