Guide for Vessel Sizing . Certified DATE DESCRIPTION ID. NO. /var/www/apps/conv

Guide for Vessel Sizing . Certified DATE DESCRIPTION ID. NO. /var/www/apps/conversion/tmp/scratch_3/325105058.doc of 19 DOC.NO. Table of Contents 1. Scope....................................................................................................................................3 2. Introduction..........................................................................................................................3 3. Selection Criteria for Vapor-Liquid Separators.....................................................................4 3.1 Orientation of the Vessel.............................................................................................................4 3.2 Feed Inlet....................................................................................................................................5 3.2.1 Inlet Nozzle..........................................................................................................................................5 3.2.2 Inlet device............................................................................................................................................5 3.3 Internals......................................................................................................................................6 3.4 Vessel Head.................................................................................................................................6 4. Design Criteria for Vapor / Liquid Separators......................................................................7 4.1 Definition of Levels....................................................................................................................7 4.2 Vertical Vessels...........................................................................................................................7 4.2.1 Diameter of a Vertical Vessel................................................................................................................7 4.2.2 Height of a Vertical Vessel....................................................................................................................8 4.3 Horizontal Vessels.......................................................................................................................9 4.3.1 Size of a Horizontal Vessel...................................................................................................................9 4.3.2 Feed Inlet Device for Horizontal Vessels...........................................................................................12 Either a 90º elbow, or a half-open pipe can be used as inlet device for a horizontal vessel. A 90º elbow is preferred as they are easier to fabricate. The following requirements are applicable for 90º elbow inlets:..12  The diameter of the elbow must be the same as the nozzle diameter.......................................................12 4.3.3 Boot.....................................................................................................................................................12 4.4 Additional Criteria....................................................................................................................14 4.4.1 Degassing............................................................................................................................................14 4.4.2 Foaming..............................................................................................................................................15 4.5 Sizing of Nozzles......................................................................................................................15 4.5.1 Feed Inlet Nozzle................................................................................................................................15 4.5.2 Vapor Outlet Nozzle...........................................................................................................................15 4.5.3 Liquid Outlet Nozzle..........................................................................................................................16 4.5.4 Manway..............................................................................................................................................16 4.5.5 Vents and Drains................................................................................................................................16 4.5.6 Nozzle Identification..........................................................................................................................16 4.6 Mist Eliminators.......................................................................................................................17 4.6.1 Sizing of Demister Pads.....................................................................................................................17 4.6.2 Demister in Vertical Vapor / Liquid Separators.................................................................................17 5. Design of Liquid / Liquid Separators..................................................................................18 5.1 Liquid-Filled Separators...........................................................................................................19 5.2 Liquid-Liquid Separators with Vapor Compartment..................................................................20 ID. NO. /var/www/apps/conversion/tmp/scratch_3/325105058.doc 1 of 40 DOC 6. Computer Programs............................................................................................................22 6.1 Depsep......................................................................................................................................22 6.2 Separator..................................................................................................................................22 6.3 Excel Functions........................................................................................................................22 6.3.1 Horizontal Vessel Liquid Volume.......................................................................................................22 6.3.2 Horizontal Vessel Liquid Level..........................................................................................................22 6.3.3 Vertical Vessel Liquid Volume............................................................................................................22 6.3.4 Vertical Vessel Liquid Level...............................................................................................................23 6.3.5 Segmental Area from Elevation.........................................................................................................23 7. Appendices..........................................................................................................................23 1. Scope This document shall be used for the process design of vessels, however, for specific projects, these design rules may be superseded or modified by client requirements. Applicable design rules for a specific project shall be specified in the Design Basis and / or the General Information and Instructions (GII) for the project. 2. Introduction In general the function of a vessel in a process unit is to either provide hold-up time or to make a separation between the various phases of a mixed process stream. In this design guide rules are given for the dimensioning of vessels, which are used for the separation of mixed process streams. They can be divided into two categories: Vapor / liquid separators, which are used to separate the vapor and liquid part of a mixed stream. Liquid / liquid separators, which are used to separate the two liquid phases of a mixed stream. ID. NO. /var/www/apps/conversion/tmp/scratch_3/325105058.doc 1 of 40 DOC For both types of separators the design rules will be given in this design guide. 3. Selection Criteria for Vapor-Liquid Separators The configuration of a vapor/liquid separator depends on a number of factors. Before making a vessel design one has to decide on the configuration of the vessel with respect to among others: Orientation Type of feed inlet Type of internals Type of heads Factors that help to make the chioce between the various alternatives are discussed in this chapter. 3.1 Orientation of the Vessel The selection of the orientation of a gas-liquid separator depends on several factors. Both vertical and horizontal vessels have their advantages. Depending on the application one has to decide on the best choice between the alternatives. Advantages of a vertical vessel are: a smaller plot area is required (critical on offshore platforms) it is easier to remove solids liquid removal efficiency does not vary with liquid level because the area in the vessel available for the vapor flow remains constant generally the vessel volume is smaller Advantages of a horizontal vessel are: it is easier to accommodate large liquid slugs; less head room is required; the downward liquid velocity is lower, resulting in improved de-gassing and foam breakdown; additional to vapor / liquid separation also a liquid / liquid separation can be achieved (e.g. by installing a boot). The preffered orientation for a number of typical vapor / liquid separation applications are: Application Preferred orientation Reactor Effluent Separator (V/L) Vertical Reactor Effluent Separator (V/L/L) Horizontal ID. NO. /var/www/apps/conversion/tmp/scratch_3/325105058.doc 1 of 40 DOC Reflux Accumulator Horizontal Compressor KO Drum Vertical Fuel Gas KO Drum Vertical Flare KO Drum Horizontal Condensate Flash Drum Vertical Steam Disengaging Drum Horizontal 3.2 Feed Inlet 3.2.1 Inlet Nozzle The feed nozzle size and the type of feed inlet device (if any) have an impact on the vapor / liquid separation that can be achieved. The feed nozzle is normally sized to limit the momentum of the feed. The limitation depends on whether or not a feed inlet device is installed. 3.2.2 Inlet Device Various inlet devices are available to improve the vapor / liquid separation. Among others the following inlet devices may be installed: A deflector baffle A slotted tee distributor A half-open pipe A 90˚ elbow A tangential inlet with annular ring A schoepentoeter For verticla drums, preferably a deflector baffle or a half open pipe shal be selected. In case of a slug flow regime in the inlet piping, or if a high liquid separation efficiency is required, a tangential inlet nozzle with annular ring can be used. However, in case a high liquid removal efficiency is required, the application of a wire mesh demister is preferred. For horizontal drums normally a 90˚ elbow or a slotted diverter is installed. In some cases a submerged inlet pipe is installed, but this shall not be done in the case of a two-phase feed. Normally the selected inlet device for a horizontal drum shall be: a 90˚ elbow or a slotted diverter in case of an all liquid or vapor-liquid feed a submerged pipe when the feed is a subcooled liquid and the mixing of liquid and blanket gas is to be minimized ID. NO. /var/www/apps/conversion/tmp/scratch_3/325105058.doc 1 of 40 DOC two 90˚ elbow inlets in case of high vapor loads 3.3 Internals After passing through the feed inlet, the vapor stream will still contain liquid in the form of droplets. The maximum soze of these entrained droplets depends on the vapor upflow velocity. A separation device can reduce this entrainment significantly. Wire mesh demister are the most commonly used as separation device. They are used for two reasons: To minimize entrainment Of the drum services having such a requirement, suction drum for reciprocating compressors are the most notable examples To reduce the size of a vessel The allowable vapor velocity in a drum can be increased significantly by using a wire mesh demister. So, when sizing is governed by vapor-liquid separation criteria, this will result in a smaller diameter of the vessel Major disadvantages of wire mesh demister are: They are not suitable for fouling services Their liquid removal decreases significantly at reduced throughput Although the size of the vessel often can be reduced by applying a wire mesh demister, there are also many services where there is normally no demister installed. Reflux accumulators, for example, seldom have mist eliminators. There are several other types of mist eliminators such as vanes, cyclones, and fiber beds. They are used when conditions are not favorable for wire mesh screens. Selection criteria for these types of internals are the required efficiency, capacity, turndown, ratio, maximum allowable pressure drop and fouling resistance. These types however will not be further addressed in this design guide. 3.4 Vessel Head Most vessels have 2:1 elliptical heads, welded to the shell of the vessels. However, in some cases other types of heads are used. The major alternatives are: Flat heads In case of small vertical vessels (diameter less than approximately 30”) often a flaged top head is used, which also serves to provide access to the vessel. Depending on the pressure rating, this type of head can either be flat or elliptical, and shall be selected in consultation with the mechanical engineer Hemispherical heads ID. NO. /var/www/apps/conversion/tmp/scratch_3/325105058.doc 1 of 40 DOC A hemispherical head should be considered for an extremely large, high-pressure vessel A dished head be considered in the case of a large diameter, low-pressure vessel 4. Design Criteria for Vapor / Liquid Separators 4.1 Definition of Levels In the sizing of vessels the the proper definition of hold-up time and liquid levels is important. For the design of vessels the following shall be used: Liquid hold-up time Working volume between High Liquid Level (HLL) and Low Liquid Level (LLL) HLL Upper end of the control span LLL Lower end of the control span HLA High Level Alarm, normally at 90% of the control span LLL Low Level Alarm, normally at 10% of the control span 4.2 Vertical Vessels 4.2.1 Diameter of a Vertical Vessel The design of a vapor-liquid separator is based on the terminal settling velocity of a liquid droplet of specified size, settling under the influence of gravity. This velocity is given by: v v l v v l P K C gD v           1 1 3 ) ( 4 (4.1) where v1 terminal settling velocity (m/s), ρl liquid density (kg/m3), ρv vapor density (kg/m3), Dp droplet diameter (m), g gravitational constant (9.81 m/s2), C dimensionless uploads/Litterature/ guide-for-vessel.pdf

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