Up-grading performance of heat exchangers and reducing fouling by retrofitting hitran tubeside enhancement systems

Transcription

1 Up-grading performance of heat exchangers and reducing fouling by retrofitting hitran tubeside enhancement systems m Heaters Coolers Condensers Vapourisers Reboilers Thermo-Syphon Reboilers Reactors Economisers Chillers Intercoolers Aftercoolers Oxidisers. Page 1

2 Cal Gavin Limited Process Intensification engineers Established in 1980 Research, development and manufacture of enhancement technology for heat exchangers Sectors include Oil exploration, production and refining Gas production, transmission and treatment Petrochemical and downstream processing Plastics, polymers and resins Power generation, refrigeration and Copyright Cal Gavin 03/2007 speciality chemicals Page 2

3 Scope of Activities Include: Designing new enhanced exchangers Simulating performance and upgrading existing exchangers (HTFS, HTRI, hitran SP De-bottlenecking engineering software) solutions to overcome plant and process limitations Page 3

4 The Problem. 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) 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. Page 4

5 Video presentation of flow (500 < Re < 8000) Blue dye: Red dye: B) Pseudo turbulent flow A) Laminar hitran flow 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 Copyright Cal Gavin is 03/ ,000, there very little fluid mixing of the bulk flow with Page 5

6 Flow with hitran, 20mm tube diameter (Please be patient to load the video) Page 6

7 Flow velocity vectors of plain tube and immediately after the hitran Element, measured with Laser PIV (Particle Image Velociometry laminar flow) mit Insert Plain tube U/Umax Page 7

8 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 U/Umax Page 8

9 Graphical representation of plain tube and hitran matrix element performance range heat transfer factor [-] Re [-] Page 9

10 Graphical representation of plain tube and hitran matrix element performance, case study heat transfer factor [-] pass plain * * m/s 42passes ~100 bar 1 pass hitran 0.3m/s 1.2m/s Re [-] Copyright Cal Cal Gavin Copyright Gavin 03/ / pressure drop [bar] 2 pass hitran plain tube pressure drop hitran tube pressure drop Page101 Page

11 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 Stability in transition region approaches Longer operation under most fouling conditions Page 11

12 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 Page 12

13 Case study 1: Air Cooled Lube Oil Cooler 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 Plain Bore Finned Tube Enhanced Page 13

14 Case study 2: Heavy Cycle Gas Oil Cooler 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 Plain Tube Enhanced Page 14

15 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) Page 15

16 Photographic Evaluation of hydro-dynamics Talcum as suspension particles, 40 to 60 microns, 2500kg/m 3 Constant Re no. of 750 Plain tube hitran tube High shear rate at the wall causes homogenious distribution of particles Vortexes behind the wire loops causes high liquid mixing Page 16

17 Fouling resistance [m2 K / W * 104] Crude Oil fouling research [University of Bath] Arabian light crude oil Tube without matrix Element velocity 0.5m/s Twall = 216 C Time [hr] Tube with matrix Element velocity 0.5m/s Twall = 218 C Time [hr] 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) Page 17

18 Page 18

19 Mechanisms of Condensation Film heat transfer coefficients depend on: whether film is laminar, laminar/wavy or turbulent Liquid filmofhtc s are relatively thickness the film Vapour high compared to vapour phase 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 Page 19

20 Enhancement of Condensers Wire Matrix Elements enhance intube 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 Page 20

21 Enhanced tube Plain tube Mechanisms of Boiling and the impact of Matrix Elements (Reboilers) Subcooled Increased convective boiling rate Shorter sub-cooled length More even tube-side temperature distribution Typical applications for: Viscous liquids Low temperature driving forces Page 21

22 Mechanism of Boiling and the impact of Matrix Elements (vaporisers) Where total vaporisation is required at high heat fluxes, enhancement is often Control film boiling applied to: Mitigate mist carry-over Enhance fluid distribution Enhance wall wetting Improve heat transfer in the superheated region Typical applications: LNG/LPG/Ethylene vaporisers Page 22

23 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 Page 23

24 Case study 2 Crude pre-heater - Wintershall Refinery (BP) - Germany Instalation 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 Page 24

25 Case Study 3 Dalia FPSO Total Oil, Angola oil-water separation process 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] / Duty [MW] 7.94 Tube OD diameter [mm] 25.4 FPSO Dalia with installed Crude / Oil Interchangers on the Top deck design capacity of 240,000 barrels per day of crude, two million barrels of storage capacity shell side kg/hr wet crude oil is heated from 50.5 C to 60.7 C tube side kg/hr dry crude oil is cooled from 87.5 C to 70.1 C Copyright Cal Gavin 03/2007 Page 25

26 Case study 3 Conventional Size comparison - Conventional / HELITRAN plain / single.seg mental. HELITRAN OHTC [W/m2K] Tube side: HTC [W/m2K] dp [bar] Flow velocity [m/sec] Reynolds [-] Residence time [sec] Shell siede HTC [W/m2K] dp [bar] Flow velocity [m/sec] Reynolds Wall temperatures [ C] Geometry Shell in series [-] Shell in parallel [-] Total no. of Shells [-] Tube Flow path [m] Tube length [m] Total tube count [-] Tube passes [-] Total HT area [m2] Plot space [m2] Weight wet [kg] Exchanger costs [%] hitran / helical baffle gain x x ~ ½ ½ ¼ 3 ~4 1/8 ~¼ ~¼ ¼ 1/3 ~1/3 Page 26

27 Case study 4 Client: Contractor: Exchanger: Fluid : Process Air-cooled Exchanger Upgrade Reliance Industries, Surat, India Bechtel Limited Product Fractionator Bottoms Cooler Vacuum Gas Oil Plant Problem Planned major upgrade - increased throughput - change in feedstock Existing exchanger 65% undersurfaced for new duty No space available for new exchangers Limited pressure loss available Page 27

28 HiTRAN 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 Benefits Reuse of existing bays, fans, structures - no modifications No additional structures required Proven heat transfer performance Significant cost reduction Page 28

29 Texas Tower Feed / Effluent Exchanger May tubes - 12 metres vertical - 2 joined hitran Elements / tube Benefits : increased product throughput higher return temperature to furnace - increased energy efficiency Increased plant profit! Page 29

30 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) Page 30

31 Crude Desalter Exchanger Fabricator: EIGSA Designer: Cal Gavin Ltd End User: Pemex Country: Mexico Plant: Dos Bocas terminal Plain tube - 20 shells hitran 8 Shells Tubeside: desalted crude Shellside: wet crude Page 31

32 Column Top Condenser Fabricator: Doosan Mecatec Designer: DOW Chemicals + Cal Gavin Ltd End User: Sinopec Country: China Two new plants: Zhenhei and Tianjinn Note : Combined heat and mass transfer - one stage effective Small unit 7000 tubes - 5 metres dia Large unit 9000 tubes 7 Page 32

33 Case Study 10 Retrofit heat recovery of feed/effluent exchanger User: Location: Service: Exchanger: LUKOIL refinery Volgograd, Russian Hydrocarbon TEMA AES with Helical baffles 2 parallel trains of 3 horizontal stacked shells in series Benefits Increased performance of exchangers Reduced maldistribution on tubeside 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 Page 33 Increased plant profit!

34 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 Page 34