Liquid Degassing Using Fine Droplets and Micro Bubbles

Transcription

1 Liquid Degassing Using Fine Droplets and Micro Bubbles

2 What is degassing: Background Information Removal of unwanted dissolved gases from liquid Why is it important Purification of the liquid Health, Safety and the Environment What were we dealing with H2S in liquid sulfur How did we do? Micro-bubbles Lab: de-oxygen using nitrogen, before field tests

3 Current (generalized) Degassing Techniques Mechanical Agitation Ultrasonic Membrane Gas Stripping Flash Vaporization, Spray tower

4 Degassing H2SX k1 k2 H2S(sol) H2S(gas) principles k-1 k-2 gas First step: decomposition (with catalysts). H2Sx H2S+S(x-1) Sulfur tank Final step: sweeping H2S gas from head space. * Boyle P., CPA Review, 1593), pp.2. H2Sx H2S+S(x-1) Second step: release of H2S from liquid to gas. Mass transfer can be improved by increase of: Concentration difference (Interfacial) Contact area Mass transfer coefficient (Residence) Time 4

5 Enersul HySpec degasser Gas out Air in Sulfur inlet Sulfur outlet Totally H2S in fed, ppm Totally H2S in out, ppm Totally residence time, minute Efficiency 96.9% 96.6% Two test records 5

6 Field test of the existing devices at Talisman Plant, Edson, AB 100 H 2 S Concentration, ppmw 10 1 H 2 S x Total H 2 S Catalyst Tank number

7 Other Devices Steam Sulfur Inlet Gas out Sulfur in H2S out Catalyst Sulfur Out Knull Holding degassing Sulfur in Catalyst Sulfur to storage Sulfur out SNEA degassing Sweep gas Texasgulf degassing * USA Patent 6,509,662, (01) * Texasgulf Inc. Canadian Patent 959, * USA patent 6,010,

8 Laboratory Experimental Setup Vacuum Sweep N2 VFD Bottom N2 into bubble generator Shroud Water outlet Water inlet Camera 8

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10 Bubble Generation Liquid in Compressed gas in Liquid out Liquid in 1 2 Gas sucked in Liquid out Porous tube bubble generator Cavitation tube bubble generator Bubble size increased after generating

11 Small N2 flow rate

12 Large N2 flow Much raten2 in Porous tube.

13 Flow into the tank

14 Real micro-bubbles generated by cavitation tube (picture shows water flow rate 3.5GPM, and pressure 50PSI. Tube center small hole: 3mm.

15 Micro-bubbles suspended in tank without agitating.

16 Micro-bubbles displaced in tank with agitation

17 Agitator is running at 700 rpm.

18 Micro-bubbles were separated from water after 10 seconds agitating.

19 Effect of Agitation and Injection of Micro-bubbles W/ 50 SCFH bottom N2 Without microbubbles

20 618 rpm,-100 pa, 3/8 hole No vacuum, 1/16 hole 618rpm,-100pa, 1/16 hole No agitation

21 618 rpm 3/8 shroud holes 0 rpm, 50 SCFH N2 618 rpm 1/16 shroud holes

22 100% 75% Effects of impeller 50% 25% 0% Only BT-6, No bottom bubbles Only HE-3, No bottom bubbles 50SCFH, BT-6 50SCFH, HE rpm S-4 BT-6 HE-3 Combination

23 Effect of residence time 75 SCFH & 999rpm 50 & SCFH & 380rpm

24 Field Tests

25 Gas Out VFDs Vacuum gauges Static mixer Bubble generator Air Air inlet Flow meter Top Air in Catalyst Flow Meter Pressure Meter Inlet sample Bubble generator Cell#1 outlet sample Sulphur outlet Cell#2 outlet sample Strainer Sulphur inlet Full Scale Prototype

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28 Bubbles in liquid sulfur seen from the observation window

29 De-H2S Efficiency vs. Agitation Speed (* test at: 2 GPM sulfur flow, 5 minutes residence time on cell #1, catalyst 10ppm) 100% 80% 60% Agitation on 125 SCFH air 75 SCFH air 1/16 holes 40% 20% Only agitation, 3/8 holes 0% rpm of cell #1

30 De-H2S efficiency vs. injected air flow rate (* test at: 2 GPM sulfur flow, 5 minutes residence time on cell #1, catalyst 10ppm) 70% 60% 50% 40% (Only bottom bubbles, no agitation.) 30% 20% SCFH

31 De-H2S efficiency vs. Headspace Negative Pressure (* test at: 2 GPM sulfur flow, 5 minutes residence time on cell #1, catalyst 10ppm) 100% 756rpm + inject air 125 SCFH 80% 60% 40% Only agitation 756rpm 20% 0% Pa on Cell#1

32 Comparison of different impellers 100% (* test at: 2 GPM sulfur flow, 5 minutes residence time on cell #1, catalyst 10ppm) 80% 60% S-4 impeller on 125 SCFH inject air 40% 20% Cell #1 rpm BT-6 impeller on 125 SCFH inject air 32

33 Residence Time (Test at: closed liquid sulfur in cell #1, initial catalyst 10ppm) 100% 80% 60% 40% 10 minutes: 95% 15 minutes: 99% 20% 0% mimute 100 SCFH, 749 rpm on 1/16"

34 Test of 2 cells in series (* test at: 2 GPM sulfur flow, 5 minutes residence time per each cell #1 and #2, catalyst 10ppm to #1, no additional catalyst to #2) 100% 80% 60% 40% 20% 82.97% 80.13% 96.62% 5 ppm Both cell#1 and cell#2 on 125 SCFH inject air and 764 rpm agitation 0% cell#1 cell#2 series of both

35 Related Basic Research

36 Bubble in liquid Turbulent Flow Gas film Laminar Flow Turbulent Flow Mass transfer: dm dt K l A( C C ) b Convection Diffusion Liquid film Gas Bubble Liquid dc dt K l A ( ) b C Cb m: Amount of mass transfer t: Time C: Dissolved gas concentration in liquid Cb: Gas concentration in bubble center Kl: Mass transfer coefficient A: Surface area of bubble Ab: Mass transfer area per unit volume * Lewis W. K., Whitman W. G., Principles of Gas Absorption, Industrial and Engineering Chemistry, 12(1924), pp

37 Physical model of bubble degassing C2 Mass balance: Rate of oxygen in Rate of change of oxygen content = Rate of oxygen out Q C M Q Z C Z Z Z3 M K A ( C C ) S z l b b Liquid C0 Gas Bubble generator Z Z1 Z+ΔZ C1 Q: Flow rate M: Rate of concentration change S: Section area Z: Bubble moving distance C0: Initial gas concentration in liquid Z2 QC Z K A ( C C ) S Z QC l b b Z Z Assume Cb=0, divide above equation by S Z, and let Z go to zero: Q S ln C C C 0 dc dz C C 0 K K l A exp( Q l A C b K l Ab S Z Q l b S Z) Kl Ab S C C0 Exp( Z) Q C C0 dc C Kl Ab S Q l 0 Z dz 37

38 Mass transfer coefficient Some important dimensionless groups and their definitions: Sherwood number Sh convectivediffusivity moleculardiffusivity K l D d K l ShD d Schmidt number Sc momentumdiffusivity moleculardiffusivity D Correlations for bubble mass transfer coefficient in turbulent flow: Sh (Re) ( Sc ) 0.33 Reynolds number of bubble in liquid: D: Gas diffusivity in liquid phase d: Bubble diameter μ: Viscosity of liquid ρ: Density of liquid Vs: Bubble relative velocity in liquid dv R s e 38

39 The Diffusion Coefficient of H2S in Liquid Sulfur H2SX k1 k2 H2S(sol) k-1 k-2 H2S(gas) Kinetic Parameters Unavailable: Diffusion Coefficient, Reaction Rate Constants

40 Experimental: Pressure Decay Method Fume Hood Pressure transducer Valve #4 DAS Vacuum gauge Valve #5 Valve #2 Valve #3 Vacuum pump H 2 S Cylinder Sandbath Cylindrical Reactor Liquid Sulfur Valve #1 Compresse d air

41 1-D Diffusion: t c x c D t c S x H S H g S H k k k S eh c S eh c S eh c x Reversible Reactions: S x H S H S H g S H c k c k x c D t c ), (, 2 2 t a x x c D t c b S H g S H Liquid sulfur Pressurized H 2 S (g) x=a+b x=a x=0 Headspace Theory

42 a q x q q D ab p q D p b a k p k k t p c a k k b bc c n n n n g n n g n n n cos cos exp PV nrt 0), (, 2 2 t a x x c D t c b S H g S H ) ( 2 a x x c bm RT D t P S H s g ] 1 [exp ) tan( 0 ) ( t n p n n q g D ab n p n q g D n p b a k n p k k a n q n q c bm s RT g D i P t P Solving Partial Differential Equations

43 II. The Diffusion Coefficient of H2S in Liquid Sulfur Experimental vs. Numerical Simulations T= 403 K

44 II. The Diffusion Coefficient of H2S in Liquid Sulfur Experimental vs. Numerical Simulations T= 423 K

45 II. The Diffusion Coefficient of H2S in Liquid Sulfur Results Temperature, K Diffusivity, D g, 10-8 m 2 /s Reaction rate k 1, 10-5 s -1 Reaction rate k -1, 10-5 s -1 Equilibriu m pressure, 10 5 Pa c P 1000exp exp Verification Against the Solubility T 8.32 Temperature, K Eqn. 24 Total equilibrium H 2 S concentration, ppmw This study * R.A. Marriott, Ed Fitzpatrick, K.L. Lesage, Fluid Phase Equilib. 269 (2008)

46 III. Liquid Degassing Using Mono-dispersed and Polydispersed Droplets

47 Poly-dispersed Droplet System Gas Out Pressure Gauge Water Flow meter Inclined Plates Sponge Pad Nozzle Poly-dispersed Droplets Nitrogen Cylinder Water Pump Filter H2O Inlet Inlet sample Outlet Sample H2O

48 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets

49 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Theory Fick s law: Surrounding environment with inert gas pressure P Droplet z Hypothetical gas film j k c d c g c = c d > c g c = c g x φ θ r y Target gas Droplet boundary r =R V dc dt d A d j Interface: A cg PK H d k ( cd cg )

50 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Degassing Efficiency T G L L H H T G L L i H T G L L i H i f Q Q P K P K Q Q d kt c s P K Q Q c s P K c c exp Falling Droplets Hindered Particle Settling 1 n g bs V t V Sherwood Number D g kd Sh

51 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Mono-dispersed Droplet System Filter Generator head Orifice Pressure gauge Frequency generator Flow meter Water supply Gas straightener Water pump DO Measurement: Modified Micro-Winkler Titration Method Sampling chamber Nitrogen cylinder

52 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Results: Mono-dispersed Droplet System Degassing efficiency Mono-dispersed droplets Nitrogen gas flow rate 100ml/min Degassing efficiency Experimental data, 265 m Trendline Droplet diameter, m Nitrogen flow rate, l/min

53 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Results: Poly-dispersed Droplet System Degassing efficiency Q W =63.1ml/s Q W =126.2ml/s Q W =189.3ml/s Q W =220.8ml/s Nitrogen flow rate, l/s Degassing efficiency Inert gas to water flow ratio

54 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Droplet diameter, (μm) Results: Mono-dispersed Droplet System Gas flow rate, (ml/min) Liquid flow rate, (ml/hr) Residence time 10 2, (s) k 10 2, (cm/s) Sh Re Pe Sh=0.0016Pe , R 2 =0.951, 2000<Pe<45000

55 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Gas to liquid flow rate ratio Mean diameter, (μm) k 10 2, (cm/s) Sh Re Pe E E E E E E E E E E E E E E E E E Sh= Pe , R 2 =0.996, 7500<Pe<20000 Sh= Pe , R 2 =0.984, Pe<7500

56 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Sherwood number Eqn Poly-dispersed droplets 3. Mono-dispersed droplets 4. Eqn Eqn / 2 2 / Pe Sh= Pe , 7500<Pe<20000 Sh= Pe , Pe<7500 Sh=0.0016Pe , 20000<Pe<45000 Sh= Re 1/2 Sc 1/ ReSc 1/3 Peclet number * L. Steiner, Chemical Engineering Science 41 (1986) * A. Saboni, Journal of the University of Chemical Technology and Metallurgy 43 (2008) Sh 1 Sh 3k v 0.67Re Pe Re 15 1/3 kv Re 1/3 1/3 1 Pe Re Pe1

57 III. Liquid Degassing Using Mono-dispersed and Poly-dispersed Droplets Degassing efficiency Argon Nitrogen Stagnant gas pressure, kpa Degassing efficiency Water flow 63.1 ml/s, spiral-type nozzle Water flow 63.1 ml/s, fog-type nozzle Water flow ml/s, fog-type nozzle Nitrogen flow rate, ml/s

58 Liquid Degassing Using Mono-dispersed and Polydispersed Droplets Pilot Unit

59 IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation

60 IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation Turbulent Flow Laminar Flow Turbulent Flow Gas film Convection Liquid film O2 Bubble Diffusion Liquid

61 V bs IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation Bubble Size and Gas Holdup L 2 b gd 1 g Re V bs V t (1 g ) n1 n1 L b f fb f bf ( L b )g L g g f fb (1 g ) f bf 0 Re t (2.33Ga Ga ) 13.3 V f V b 2 f bf 3C D L 4d b (1 g ) 1.7 V bs U G g U L 1 g

62 IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation Batch Reactor j k c l c b c b (P 0 4 / r) s c i c l l 1 g g g K H V dc dt l A b j A k( c c ) b b l K H s P r c 1 exp 6k i gt d b 1 1 l g K H P 0 4 g g r

63 IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation Continuous Reactor Q L + Q G Y Bubble X Z Z+ Z Z dc w dz D g 6A g (c l c b ) Q L d b Q L + Q G M D g 6AZ g d b c l c b Z K H s P r c 1 exp D i g 6A g Z Q L d b 1 1 l g K H P 0 4 g g r

64 IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation Nitrogen injection rate, (SCFH) Agitation rate, (rpm) d b, (m)10 3 ε g, (%) U G, (m/s)10 3 U bs, (m/s)

65 IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation N Q g

66 IV. Liquid Degassing Using A Combination of Micro Bubbles and Mechanical Agitation Nitrogen injection rate, (SCFH) d b, (m) 10 3 ε g, (%) U G, (m/s) 10 3 U L, (m/s) 10 4 U bs, (m/s)

67 Volumetric Liquid-Phase Mass Transfer Coefficient in Gas-Inducing Agitated Tank Reactors

68 0.25 Existing correlation +20% % measured k L a (s -1 ) Forrester (six-bladed concave, s/dt=0.5) Poncin (double disc, s/dt=0.9) 0.05 Poncin (double disc, s/dt=1.23) Kasundra (double disc, s/dt=0.66) Kasundra (modified double disc, s/dt=0.66) Kasundra (PBTD 45, s/dt=0.66) predicted k L a (s -1 ) Kasundra (PBTD 60, s/dt=0.66)

69 kla, s Impeller speed, Hz

70 Acknowledgement Yiming Ji Harry Lei Hesheng Yu Enersul Inc. and its employees NSERC University of Calgary University of Alberta