Bed Expansion in Upflow Moving Catalytic Packed/Expanded Bed Hydrotreating Reactor using

Gamma-Ray Densitometry

1VINEET ALEXANDER, 2HAMZA AL-BAZZAZ, AND MUTHANNA AL-DAHHAN*

1,*Chemical Engineering and Biochemical Engineering Department

Missouri University of Science and Technology, Rolla, MO 65409-1230. USA 2Kuwait Institute of Scientific Research, P.O Box 24885, 13109 Kuwait

Multiphase Reactors Engineering and Applications Laboratory (mReal)

Uplfow Packed and Expanded Bed Hydrotreater

> Upflow Hydrotreater treats heavy crude oil (Scheuerman, Johnson et al. 1993)

> Guard Reactor to Residual Desuflurization (RDS) reactors

> This technology has a conical bottom to catalyst bed and is a combination of fixed bed and moving bed (Krantz, Earls et al. 2002)

> Spent catalyst replacement through conical bottom > Upflow of gas and liquid over catalyst bed > It can handles feed with varying degree of

contaminants > It can improve the life cycle of fixed bed RDS

reactor

1

Upflow Hydrotreater

RDS Reactor

Problems In Industrial Reactor

> Coke deposition on one side of the reactor.

> Increased pressure drop either in the inlet distributor tray or in the outlet or both, and hence the total pressure drop over the reactor.

> Disturbance in the catalyst bed.

> Occasional difficulty in controlling the reactor temperature.

> Variations in product quality.

> Shortening catalyst cycle of fixed bed reactor.

> No clear pattern for these problems.

> Emergency shutdown.

2

Motivation > Efficient working of upflow hydrotreater with conical bottom has

huge impact on hydroprocessing industry > For proper working of this reactor; minimum random motion of and

back mixing of catalyst is required and the catalyst bed expansion shall not be more than 10 percent by volume

> Bed expansion are never evaluated and quantified in OCR reactor

3

Objectives > Implement a noninvasive radioactive technique called Gamma-

Ray Densitometry (GRD) along the axial length of the reactor for varying flow rate

> Demarcate packed and expanded bed region based on photon counts and flow regime trend

4

Gamma-Ray Densitometry (GRD)

5

Components of GRD

Sealed Source (Cs-137 is sealed In source holder which Has small opening for Radiation)

Detectors NaI scintillation detector mounted with lead collimator having a slit opening of 50mm (length) and 2mm(width)

Principle Behind GRD

The source and detector shall always be al igned.

The counts generated at energy peak-660Kev for Cs-137 (marked as green in the fig) is taken for analysis purpose.

• A focused beam of radiation is transmitted from the source, through the object under study, to the detector. • As the density of the material under investigation changes , the

amount of radiation receiving the detector changes.

Photon Count of GRD

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Attenuation of γ – Ray

The reduction in the radiation intensity from I0 to I can be expressed by The Beer –

Lambert’s law according to the following equation (Chen et al., 1998):

𝐼 = 𝐼0 𝑒−𝜇𝜌𝐿

Atmosphere I0 (Schlieper, 2000)

• I is the detected radiations (photons)

• 𝜌 is the density of the subject under study

• 𝜇 is the mass absorption coefficient of the subject under study

• L is the total length for gamma ray beam path through the absorbing medium

Experimental Setup

7

Schematic diagram of lab scale uplow packed/expanded bed reactor lab scale reactor

Experimental Condition

Liquid flow rate: 0.0175 cm/sec (Matching LHSV with industrial reactor) Gas flow Rate: 0.89 cm/sec to 5.9 cm/sec

Bed Expansion- Based on Photon Count

8

Comparison with Packed Bed Count

40000

45000

50000

55000

60000

65000

70000

75000

80000

85000

90000

0 0.5 1 1.5 2

Icl

Z/D

Packed Bed Case- Catalyst Bed Filled with Liquid

No Flow of Gas andLiquid

0

5

10

15

20

25

30

35

40

0 0.5 1 1.5 2

% c

ha

nge

Z/D

Change in photon count with respect to packed bed case for varying flow rate

0.89 cm/sec

1.28 cm/sec

2.56 cm/sec

3.8 cm/sec

5.13 cm/sec

5.90 cm/sec

• Icl is the photon count obtained for the case when catalyst bed is filled with liquid and no flow of gas and liquid • This case represents the condition of packed bed as there is no movement of solids • The photon counts are slightly increasing with height and is due to the increase in void space with height

• % change =[(I- Icl )/ Icl], whereas I is the photon count at flow rate, this represents the change in photon count with respect to packed bed • The % change is increasing steadily till Z/D=1.2, and then it fluctuates • Steady increase in the percentage change shows packed bed region and fluctuation represents expanded bed. • After Z/D=1.2 the bed expands

Packed Bed Region Expanded Bed Region

Bed Expansion- Based on Flow Regime

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Flow Regime in Packed Bed using Kolmogorov Entropy (KE)

0.72

0.74

0.76

0.78

0.8

0.82

0.84

0.86

0 1 2 3 4 5 6 7

Ko

lmo

goro

v En

tro

py

(Bit

s/Se

con

d)

Suepeficial Gas Velcoity (cm/sec)

KE plot at Z/D=0.30 and r/R=0

Z/D=0.30

Order decreases And move towards

Pulse flow

Enters Pulse

More Structure Of pulse

At Z/D = 0.3 and r/R = 0 (Bottom of the Bed)

𝐾𝐸 = −𝑓𝑠𝑙𝑛 1 −1

𝑏𝑚

• The flow regime is obtained from the KE plot at the bottom of the bed which is essentially packed for varying flow rate

• The flow regime for packed bed are bubbly , pulse, and spray flow. This is observed for increasing gas flow rate for fixed liquid velocity

• At our flow case we didn’t observe spray flow • The local maximum in the KE curve has been

employed as a criteria to identify the flow regime transition Nedeltchev, 2010).

• These maximum in the KE curve corresponding to the point of instability and the point of transition from one flow regime to another (Nedeltchev, 2010)

• The flow regime transition is seen at superficial gas velocity of 3.8 cm/sec

Bubble Flow

Pulse Flow More Ordered

Bed Expansion- Based on Flow Regime

10

0.7

0.75

0.8

0.85

0.9

0.95

0 2 4 6 8

KE

Superficial Gas Velocity (cm/sec)

Flow Regime trend of Packed Bed

z/d=0.48

Z/D=0.66

Z/D=0.30

Z/D=0.84

Z/D=1.02Bubble Flow Pulse Flow 0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

0 1 2 3 4 5 6 7

KE

Superficial Gas Velocity (cm/sec)

Flow regime Trend of Expanded Bed

Z/D=1.2

Z/D=1.38

Z/D=1.55

No clear Pattern

• KE values are plotted for varying flow rate of gas at fixed liquid velocity (0.0175 cm/sec) • From Z/D=0.30 to Z/D=1.02 the flow regime trend shows similar pattern of packed • The transitional velocity from bubbly to pulse flow for all the axial location in packed bed shows same at 3.8 cm/sec (gas)

• KE values are plotted for varying flow rate of gas at fixed liquid velocity (0.0175 cm/sec) • From Z/D=1.2 to Z/D=1.55 the flow regime trend irregular trend and is mainly due to random motion of solids at this point • This region depicts expanded bed part of the bed. • Above Z/D=1.02 the bed is in expanded bed state

Remarks > Gamma-Ray Densitometry is capable to demarcate the packed and

expanded bed region in upflow packed/expanded bed reactor > Bed demarcation is done based on the photon counts received at flow

rate conditions, and then comparison with the packed bed case when the catalyst bed is filled with liquid and no flow rate.

> Bed demarcation is also done based on chaotic analysis (KE) of time series of GRD for flow regime identification. The packed area shows similar flow regime trend and with same transitional velocity. The expanded bed region shows irregular flow regime trend

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Computed Tomography (CT)

S10

For Phase Distribution Measurements

Radioactive Particle Tracking (RPT)

R1

R2

δ

Sc

Parylene N

Sc46 particle coated with

parylene-N, tracking solids

Sc46 particle in polypropylene ball,

tracking liquid

Picture of RPT

RPT

Calibration

Tracer particle

holding assembly

In Situ

Manual

35 cm

35 cm

0.625

35 cm

3.61

Detector

An On-line Technique Using NGD as Gamma Ray Densitometry (GRD)

Source

For Pinpointing Flow Pattern (Regime), Radial/Diameter Profile of Phases’ Holdups Mal-distribution identification & Reduced Tomography

Other Selected Sophisticated Techniques at Glance

Heat Transfer Coefficients

Heat transfer probe

DC

Power

PC

DA

Q

Amplifier

Mass Transfer Probes

Gas-Solid optical probes

Pressure Transducers

FID

PC

Am

Pebble bed unit

Gas/Liquid Dynamics – Tracer Techniques

Optical Probes in Packed bed

Light

going

to the

probe

tip (475

nm)

Sol-

Gel

Overcoat

Rigs

Radioisotope Laboratory for Advancing Industrial Multiphase Processes

Dual Source Computed Tomography (DSCT) Technique

Non-Radioisotope Laboratory for Advancing Industrial Multiphase Processes

Microalgae Laboratory

(Biological Lab)

Acknowledgment