Qualification of separation performance in gas\liquid separation
- 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
- 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)
- 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
- 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.
- 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)