Complete process of design various section in separator

1. Quantifing separation performance in
gas/liquid separator
- Nikunj Dodiya (15BPE028)

2. Introduction
• There is a wide range of sizing methods for two-phase
separators, varying from the simple “back-of-the-
envelope” to the far more complicated
• several weaknesses associated with most of these
methods
1. Quantification of feed flow steadiness
2. Entrainment/droplet size distribution quantification
3. Velocity profile/distribution quantification
4. Separator component performance quantification

3. Separator parts

4. Separator
• The main objective is to remove droplets of a dispersed
phase from a second continuous phase.
• A secondary requirement is often for the separator to
have some capability to deal with intermittent
flow (slugging)
• Questions important in the sizing and performance
prediction
1. What is the flow pattern at the separator’s inlet?
2. How much of the dispersed phase (liquid droplets) is
present in entrained form?
3. What are the sizes of the droplets?

5. Flow pattern and entrainment

6. Flowpipe geometry
• What if the flow has changed direction, for example, at
elbows and fittings, or experienced other flow pattern
disruptions immediately upstream of the separator.
• Typical guidelines are:
1. Provide 10 diameters of straight pipe upstream of the
inlet nozzle without valves, expansions/contractions,
or elbows.
2. If a valve in the feed line near the separator is
required, it should only be a full port gate or ball
valve.

7. Entrainment
Fig. 5 effect of feedpipe velocity on liquid
entrainment

8. Entrainment cont-
• The degree of liquid entrainment is a function of the
following variables (among others)
1. Entrainment increases with increasing velocity
2. Entrainment increases with decreasing liquid
surface tension.
Pan and Hanratty (2002)

9. Entrainment cont-

10. Droplet Sizes and Distribution
Kataoka et al. (1983)
Kataoka (1983) and
Simmons and Hanratty
(2001)

11. Droplet Sizes and Distribution

12. Inlet Device
• Main function of an inlet device
1. Maximization of gas/liquid separation efficiency based on
inlet feed conditions
2. Minimization of droplet shearing
3. Provision of good downstream velocity distributions in the
separated phases
Inlet momentum

13. Inlet Device Separation Efficiency

14. Effect of the selected inlet device on downstream
velocity profiles without flow straightening devices

15. Gas Gravity Separation Section
• Primary function is to reduce the entrained liquid load
not removed by the inlet device.
• A secondary function is the improvement/straightening
of the gas velocity profile.
• Two approaches to sizing this part of the separator to
remove liquid droplets from the gas are the K method
(Souders-Brown equation ) and the droplet settling
theory.
• the droplet settling calculations aim at removing a
target liquid-droplet size (e.g., 150 μm) and all
droplets larger than the target size

16. Droplet Settling Calculations

17. Droplet setting calculation

18. Droplet setting calculation

19. Separator
Verticle separator :Using the droplet size
distribution and effective actual velocity
correlations,the terminal velocity equation can be
used to calculate the droplet removal efficiency of
the gas gravity separation section
Horizontal separator :
separation efficiency of droplets smaller than dp,100

20. Mist Extractor
Mist extractor
performance depend
1. Droplet removal
efficiency
2. Gas capacity
3. Liquid handling

21. Mesh Pads
• A methodology that can be used to quantify droplet
capture efficiency of a mesh-type mist extractor is as
follows:
1. Calculate the Stokes’ number (sometimes called the
inertial impaction parameter) from the following
equation
2. Calculate the single-wire removal efficiency
3. mesh-pad removal efficiency

22. • Vane-Type Mist Extractors
Droplet Removal Efficiency
• Demisting Cyclones
Droplet Removal Efficiency

23. Use of Different Mist Extractor
Types in Series
1. A mesh pad followed by a vane pack
2. A mesh pad followed by a demisting cyclone
bundle
• At high gas-flow rates, the mesh pad will be operating
above its capacity limit.
• The mesh pad provides good low-flow droplet
removal performance, while the secondary vane-pack
or demisting cyclone bundle provides high-flow
capacity with improved droplet removal performance
as a result of the larger droplets exiting the mesh pad

24. Liquid Gravity Separation Section
• The functions of the liquid gravity separation
section depend on the type of separator and its
application, including the following:
1. Degassing of the liquid.
2. Smoothing out of intermittent inlet flow surges
to provide steadier liquid flow to downstream
equipment/processing.
3. To maintain a liquid seal at the bottom of the
separator, a minimum requirement for
instrumentation layout and process control

25. Quantification of gas entrainment into
liquid by a plunging jet
1. Estimate the effective liquid-jet nozzle diameter.
2. Establish the length of the jet, which is typically the distance from the
inlet device outlet to the separator liquid level.
3. Calculate the effective jet velocity at the point where the jet enters the
liquid pool.
4. Calculate the jet Froude number.
5. Calculate the amount of gas entrained into the liquid pool by the jet.
6. Calculate the depth of penetration of bubbles by the plunging jet (the
release point of the bubbles).
7. Estimate the bubble size distribution.
8. Perform the bubble size separation calculations based on the separator
geometry, including whether vertical or horizontal, the flow rates,and fluid
properties. The calculations are analogous to those used for liquid droplet
settling in the gas gravity separation section

26. Handling Intermittent Flow
• If the slug/surge volumes cannot be quantified in advance with a
multiphase flow simulator, for example, the following approaches
provide allowance for intermittent feed flow behavior:
1. Inflate the steady-state flow rates, and size the vessel using
standard procedures. Table 6 provides typical flow-rate multipliers
based on the upstream feed supply configuration
2. Estimate the slug/surge volumes. This requires an understanding
of the various mechanisms that cause slugging and quantification of
the slug/surge volumes involved. In the absence of better
information, the slug size can be assumed to be from 3 to 5 seconds
of liquid-full flow at feedpipe velocity. In-plant separators
downstream of the inlet separation equipment would not be
expected to see large slugs. A slug size based on 1 sec of liquid-full
pipe at feed-flow velocity seems reasonable for these separators.

27. Handling intermittent flow

28. Conclusion
• The equations and methods that can be used to improve the
quantification of gas/liquid separation performance
compared with traditional techniques.
• The key aspects of the recommended methodology include
quantification of the following:
1. The amount of gas (liquid) entrained in the form of
droplets (bubbles)
2. The size distribution of the entrained droplets (bubbles)
3. The continuous phase (gas or liquid) velocities
4. Droplet (bubble) separation performance based on 1–3
above and the geometry of the separator
• Presented approach to gas/liquid separator design and
rating that more accurately reflects the physics involved.

29. Thank you

30. Reference
• Gas/Liquid Separators: Quantifying Separation Performance—Part 1, 2
& 3 -Mark Bothamley • JM Campbell/PetroSkills | 22 July 2013
• Simmons, M.J.H. and Hanratty, T.J. 2001. Droplet Size Measurements in
Horizontal Annular Gas-Liquid Flow. Int. J. Multiphase Flow 27 (5)
• Kataoka, I., Ishii, M., and Mishima, K. 1983. Generation and Size
Distribution of Droplets in Gas-Liquid Annular Two-Phase Flow. ASME
Journal
• Ishii, M. and Grolmes, M.A. 1975. Inception Criteria for Droplet
Entrainment in Two-Phase Concurrent Film Flow. AIChE J. 21 (2)
• Viles, J.C. 1993. Predicting Liquid Re-Entrainmen in Horizontal
Separators. J Pet Tech 45 (5)