Hydrodynamics of Vortex Reactors for Chemical Industry€¦ · Riser/Circulating . Fluidized Bed ....

Laboratory for Chemical Technology, Ghent University

http://www.lct.UGent.be

Hydrodynamics of Vortex Reactors for Chemical Industry

Geraldine HeynderickxProf. dr. ir.

PIN-Nl Autumn Session, Woerden, The Netherlands, October 19th 2016

ConventionalFluidized Bed 1

Riser/Circulating Fluidized Bed 2

Rotating Fluidized Bed 3

Limitations:• Entrainment of particles at high

gas flow rates• Limited slip velocities (~ 1-2 m/s)

Advantages: • Dense particle bed • High gas feed flow rates• Higher slip velocity higher heat and mass transfer

Introduction

2


1. van Hoef et al., Ann. Rev. Fluid Mech. 40 (2008) 47-702. http://www.fluidcodes.co.uk/fbed.html3. adapted from Watano et al., Powder Tech.131 (2003) 250-255

Centrifugal instead of gravitational field → Process Intensification

Introduction

2

ConventionalFluidized Bed 1

Riser/Circulating Fluidized Bed 2

Rotating Fluidized Bed (RFB) 3

Limitations:• Entrainment of particles at high

gas flow rates• Limited slip velocities (~ 1-2 m/s)

Limitation:• Mechanical moving parts

cause abrasion


1. van Hoef et al., Ann. Rev. Fluid Mech. 40 (2008) 47-702. http://www.fluidcodes.co.uk/fbed.html3. adapted from Watano et al., Powder Tech.131 (2003) 250-255

Introduction

3

Gas-Solid Vortex Reactor (GSVR)


Gas injection through inclined slots

Fluidized Bed in

FC

FD

Vortex Reactor

Introduction

3


Fluidized Bed in

FC

FD

Vortex Reactor

• Advantages:– Higher slip velocity– Higher throughput operation– Enhanced heat and mass transfer

– No moving parts

• Possible applications:– Pyrolysis of biomass– Drying– Fluidization of cohesive particles– Particle spray coating

Gas-Solid Vortex Reactor (GSVR)

• Claims investigated:– Dense bed flow operation– High slip velocities

GFB

RFB

Outline

4


• Introduction

• Numerical methodology

• Results and discussion- Effect of gas flow rate

- Effect of particle density

- Effect of particle diameter

• Conclusions

Numerical methodology

5

GSVR geometrical parameters

DR 0.54 mDE 0.15 mLR 0.1 m

Injection slots 36Io 0.002 mα 10°


α

Numerical methodology

5

GSVR geometrical parameters

40°

DR 0.54 mDE 0.15 mLR 0.1 m

Injection slots 36Io 0.002 mα 10°

Mesh geometry: 3-D, 40° section of GSVU cold flow unit

Eulerian Eulerian simulation, KTGF used for solid phase

RNG k-ε turbulence model used (per phase)

Transient cold flow simulations, semi-batch operation

Gas used: Air (Incompressible, 1.225 kg/m3)

GSVR simulation parameters


α

0

2

4

6

8

0,1 0,15 0,2 0,25

Uθ(

s)(m

/s)

r (m)

experiment

simulation

Validation with Experimental data

6


Particle-fluid Interaction

Particle-wall interaction

Particle-particle

Interaction

Particle-fluid drag models

Particle-wall specularity coefficient

Particle-particle

restitution coefficient

Three main numerical parameters affecting GSVR flow

High Density Polyethylene(HDPE), 1 mm, 2 kg

Gas flow rate: 0.5 Nm3/s

-10123456

0 0,1 0,2

P gau

ge(k

Pa)

r (m)

experiment

Simulation

Outline

7


• Introduction





• Conclusions

0.15 150.3 300.4 42

0.5 550.65 700.8 85

Gas flow rate (Nm3/s) Gas Injection velocity at slots (m/s)

Key flow features investigated:• Bed pressure drop• Solids azimuthal velocity• Bed solids volume fraction• Slip velocities between the phases

Material: HDPE (950 kg/m3)Particle diameter: 1 mmBed mass: 2 Kg

0,3

0,35

0,4

0,45

0,5

0,55

0,6

0,1 0,3 0,5 0,7 0,9

ε s (a

ve)

GM (Nm3/s)

02468

101214

0,1 0,3 0,5 0,7 0,9

Uθ(

s)(m

/s)

GM (Nm3/s)

0

0,5

1

1,5

2

2,5

3

0 0,1 0,2

P gau

ge(k

Pa)

r (m)

Bed Height

Exhaust region

Solids volume fraction

8


0

1

2

3

4

5

6

7

0,1 0,3 0,5 0,7 0,9

ΔPbe

d(k

Pa)

GM (Nm3/s)

Bed region

Freeboard region ΔPbed

Dense bed over wide flow rate

HDPE, 1 mm, 2 kg

HDPE, 1 mm, 2 kg

HDPE, 1 mm, 2 kg

0.4 Nm3/s, HDPE, 1 mm, 2 kg

9

𝑼𝑼𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 = 𝑼𝑼𝜽𝜽𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝟐𝟐 + 𝑼𝑼𝒓𝒓

𝟐𝟐𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔

Slip velocityPIN-Nl Autumn Session, Woerden, The Netherlands, October 19th 2016

0

5

10

15

20

25

30

35

0,24 0,245 0,25 0,255 0,26 0,265 0,27Uθ

(m/s

)r (m)

gas

solids

-8-7-6-5-4-3-2-101

0,24 0,245 0,25 0,255 0,26 0,265 0,27

Ur

(m/s

)

gas

solids

9



Bed region

Bed region



Bed region

-8-7-6-5-4-3-2-101

0,24 0,245 0,25 0,255 0,26 0,265 0,27

Ur

(m/s

)

gas

solids

9



Bed region

Bed region


0123456789

10

0 0,5 1

Usl

ip(m

/s)

GM (Nm3/s)

High values of slip velocity


0

5

10

15

20

25

30

35

0,24 0,245 0,25 0,255 0,26 0,265 0,27Uθ

(m/s

)r (m)

gas

solids

HDPE, 1 mm, 2 kg

9




0123456789

10

0 0,5 1

Usl

ip(m

/s)

GM (Nm3/s)

High values of slip velocity

HDPE, 1 mm, 2 kg

0

500

1000

1500

2000

h (W

/m2 K

)Range for

GSVR: ~600 – 1900

W/(m2 K)

Now, Gunn correlation4 can be used to calculate Nu and the heat transfer coefficient (h)

𝑁𝑁𝑢𝑢 = 𝑓𝑓(𝜀𝜀𝑠𝑠 𝑎𝑎𝑎𝑎𝑎𝑎 ,𝑃𝑃𝑃𝑃,𝑅𝑅𝑅𝑅)

𝑅𝑅𝑅𝑅 = 𝑓𝑓(𝑈𝑈𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠)

Typical range for static

fluidized beds and risers: ~100 – 200 W/(m2 K)

1. Gunn, Int. J. Heat Transfer Sci. 21 (1978) 467

10

0123456789

10

0 0,5 1

Usl

ip (m

/s)

GM (Nm3/s)

SummaryPIN-Nl Autumn Session, Woerden, The Netherlands, October 19th 2016

0,3

0,35

0,4

0,45

0,5

0,55

0,6

0,1 0,3 0,5 0,7 0,9

ε s (a

ve)

GM (Nm3/s)

- High gas-solid slip velocities can be achieved - Dense particle bed over wide range of flow rate suggests stable operation- Dense beds leads to higher solids capacity per reactor volume

~ leads to Process Intensification

HDPE, 1 mm, 2 kgHDPE, 1 mm, 2 kg

Outline

11


• Introduction





• Conclusions

1900 Sand950 HDPE450 Biomass

Density (kg/m3) Representative material

Key flow features investigated:• Bed pressure drop• Solids azimuthal velocity• Bed solids volume fraction• Slip velocities between the phases

Gas flow rate: 0.4 Nm3/sParticle diameter: 1 mmBed mass: 2 kg

extra layers increase volume of the solids in the bed

Radial component of gas inflow

GSVR section

Effect on drag force

12

Total cross section available in solids (AT) = (APVP

) × VT

AP

VP− specific cross sectional area of particle

However, as particle density decreases and mass of solids is kept constant,

As, particle diameter for different materials constant,


Drag force ∝ Total cross section of solids

Where,

VT - total volume of solids in the system

(APVP

) = constant

VT AT

Drag force on bed increases due to higher solids cross sectional area

Higher drag force

Higher bed pressure

drop

extra layers increase volume of the solids in the bed

GSVR section

GSVR pressure profile

13


0

0,5

1

1,5

2

2,5

3

3,5

4

0,1 0,15 0,2 0,25

P gau

ge(k

Pa)

r (m)

1900 Kg/m3

950 Kg/m3

450 kg/m3

Bed pressure drop increases for lighter solids

0.4 Nm3/s, 1 mm, 2 kg

Radial component of gas inflow

Solids velocity

14


0

1

2

3

4

5

6

7

8

9

10

0,1 0,15 0,2 0,25

Uθ(

s)(m

/s)

r (m)

1900 kg/m3

950 kg/m3

450 kg/m3

Bed velocity increases

0.4 Nm3/s, 1 mm, 2 kg

Bed thickness increases

In the radial direction:

Wall normal force = centrifugal force – drag force

Solids velocity

14


0

1

2

3

4

5

6

7

8

9

10

0,1 0,15 0,2 0,25

Uθ(

s)(m

/s)

r (m)

1900 kg/m3

950 kg/m3

450 kg/m3


0.4 Nm3/s, 1 mm, 2 kg


In the radial direction:

Wall normal force = centrifugal force – drag force

In the azimuthal direction:

Frictional wall resistance = μ(wall normal force)

Higher drag force

Reduced wall friction

Solids velocity

14


0

1

2

3

4

5

6

7

8

9

10

0,1 0,15 0,2 0,25

Uθ(

s)(m

/s)

r (m)

1900 kg/m3

950 kg/m3

450 kg/m3


0.4 Nm3/s, 1 mm, 2 kg


Higher drag force

Reduced wall friction

Solids velocity

14


0

1

2

3

4

5

6

7

8

9

10

0,1 0,15 0,2 0,25

Uθ(

s)(m

/s)

r (m)

1900 kg/m3

950 kg/m3

450 kg/m3


0.4 Nm3/s, 1 mm, 2 kg0

0,5

1

1,5

2

2,5

F c/F

d(o

ver

the

bed)

1900 kg/m3950 kg/m3450 kg/m3

Smaller Fc/Fd causes less wall normal force from the solids


Slip velocity

15


Higher centrifugal force from

rotation

Solids bed becomes

more compact

Dense bed regime over a wide range of material density0

0,10,20,30,40,50,60,70,8

ε s( a

ve)

1900 kg/m3950 kg/m3450 kg/m3

Increased solids

velocity

Decreases relative velocity between phases 0

1

2

3

4

5

6

Usl

ip(m

/s)

1900 kg/m3950 kg/m3450 kg/m3

Same order of magnitude of slip velocities observed

0

0,5

1

1,5

2

2,5

3

3,5

4

0,1 0,15 0,2 0,25

Stat

ic G

auge

Pre

ssur

e (k

Pa)

Radius (m)

1900 Kg/m3

950 Kg/m3

450 kg/m3

Summary

16


00,10,20,30,40,50,60,70,8

Bed

s sol

ids f

ract

ion

1900 kg/m3950 kg/m3450 kg/m3

0.4 Nm3/s, 1 mm, 2 kg

- Pressure drop over the solids bed increases with decreasing solids density

- Decreasing density of material leads to increase in both drag force and centrifugal force over the bed at the given flow rate

- Dense bed is obtained without particle entrainment for different density materials for a given flow rate

Outline

17


• Introduction





• Conclusions

1 mm0.5 mm

Particle diameter:

Key flow features investigated:• Bed pressure drop• Fluidization regime• Bed solids volume fraction• Slip velocities between phases

Gas flow rate: 0.4 Nm3/sMaterial: HDPE (950 kg/m3)Bed mass: 2 kg

Effect on drag force

18

Total cross section available in solids (AT) = (APVP

) × VT

AP

VP− specific cross sectional area

However, since particle density decreases and mass of solids is kept constant,

Now, particle density and mass in each system constant,


Drag force ∝ Total cross section of solids

Where,

VT - total volume of solids in the system

(VT) = constant

AT

Drag force on bed increases due to higher solids cross sectional area(AP

VP) < (AP

VP)

VP =ᴨdp

3

6

AP = ᴨdp2

(APVP

)

GSVR pressure profile

19

0,5

1

1,5

2

2,5

3

3,5

4

0,2 0,22 0,24 0,26

P gau

ge(k

Pa)

r (m)

1mm

0.5 mm

Bed pressure drop increases for smaller solids


(APVP

) < (APVP

)

VP =ᴨdp

3

6

AP = ᴨdp2

Higher drag force

Higher bed pressure

drop

0.4 Nm3/s, 950 kg/m3, 2 Kg

Fluidization regime

20


Iso-surface of solids fraction: 0.4 (yellow) and0.1 (blue) in the GSVR

0.4 Nm3/s, HDPE, 0.5 mm, 2 Kg

1 mm

0.5 mm

Exhaust Circumferential wall

0.4 Nm3/s, HDPE, 2 Kg

Contours of εs in transient state

0123456789

10

0,24 0,25 0,26

Usl

ip(m

/s)

r (m)

1mm

0.5 mm

Solids volume fraction

21


1 mm

0.5 mm

Exhaust Circumferential wall

0.4 Nm3/s, 950 kg/m3, 2 Kg

Slip velocity significantly falls due to bubbling

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,23 0,25 0,27

ε s

r (m)

1mm

0.5 mm


0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,23 0,25 0,27

ε s

r (m)

1mm0.5mm

Effect of gas flow rate

22

Bubbling diminishes

Gas flow rate: 0.4 Nm3/s Gas flow rate: 0.8 Nm3/s

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,23 0,25 0,27

ε s

r (m)

1mm0.5 mm


0.4 Nm3/s, 950 kg/m3, 2 Kg0.8 Nm3/s, 950 kg/m3, 2 Kg

0.5 mm 0.5 mm


Summary

23

0.5 mm Gas flow rate: 0.8 Nm3/s


0.5 mm Gas flow rate: 0.4 Nm3/s

- Decreasing particle diameter increases pressure drop over the solids bed

- Fluidization regime changes from uniform dense to bubbling flow regime

- Increasing gas flow rate diminishes bubble formation in bed

Iso-surfaces of solids fraction: 0.4 and 0.1 in the GSVR


Outline

24


• Introduction





• Conclusions

Conclusions

25


The GSVR achieves high gas-particle slip velocities without particleentrainment at high gas flow rates

The solids bed formed is comparatively dense and uniform over thewide range of gas flow rates and particle density studied

Bubbling bed behavior may develop in the GSVR depending on thegas throughput and particle diameter

Increasing gas flow rates in bubbling regime in GSVR does not entrainparticles as opposed to the conventional fluidized beds; ratherdiminishes bubbling making the bed more uniform

Acknowledgement

26


The research leading to these results has received funding from:

Thank you for your attention!List of SymbolsDR: reactor diameter [m]DE: exhaust diameter [m]LR: length of GSVR [m]IO: slot thickness [m]α: slot angleHDPE: High-Density Poly-ethyleneGM: gas flow rate [Nm3/s]r: radial coordinate [m]Pgauge: static gauge pressure [kPa]ΔPbed: bed pressure drop [kPa]εs: local solids volume fractionεs (ave): spatially-averaged solids volume fractionUθ(s): azimuthal solids velocity [m/s]Uθ(g): azimuthal gas velocity [m/s]Uslip: slip velocity [m/s]Nu: Nusselt numberRe: Reynolds numberFC: centrifugal force [N/m3]FD: drag force [N/m3]AP: cross sectional area of single particle [m2]VP: volume of single particle [m3]VT: total cross sectional area [m2]Mail me at: [email protected]

• the European Research Council

FP7/2007-2013/ ERC grant agreement

n° 290793

• VSC (Flemish Supercomputer Center),

funded by Ghent University, the

Hercules Foundation and the Flemish

Government – department EWI

Thank you for your attention!

Image courtesy: www.Dilbert.com

Hydrodynamics of Vortex Reactors for Chemical Industry€¦ · Riser/Circulating . Fluidized Bed ....

Documents

Transcript of Hydrodynamics of Vortex Reactors for Chemical Industry€¦ · Riser/Circulating . Fluidized Bed ....