tray design - baretti · 2016. 2. 18. · 2015 web tray design software rev 1 page 7 19/02/16....
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Tray Design How to use the Baretti® design software
Your Worldwide Partner
2015 Web Tray Design Software Rev 1 Page 2 19/02/16
Tray Design Basics
q Column Diameter Sizing
q If the tower diameter is unknown
q Diam (m)=( (V * (Dv/(Dl-Dv))^0.5 * 15 )/3.14)^0.5*2
q Where V= vapor load in m3 / sec q Dv = Vapor density in kg/m3
q Dl = Liquid density in kg/m3
2015 Web Tray Design Software Rev 1 Page 3 19/02/16
Use of BARETTI® Software
q Open Baretti Trays Hydraulic Calculation Software q Input general project data q Fluids input
q Enter all lines of Liquid and Vapor loads q Enter also
q The System Factor ( Foaming tendency) q The multipliers ( make a calculation at increased or decreased
loads from the design rate) q Each data has controlling limits. If the input exceed these
limits an alert is given, but if correct the data can be confirmed can
q Store each line of fluids input
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Use of BARETTI® Software q Geometry Input
q Open the windows of the geometry and enter all data for each group of identical trays
q For units selection, following are main points: q Valves : Type and number
Floating : The leg length (11.1 is std.) is the total length .The net rise is this number reduced by the tray thickness
Fix : The valve rise is net above the tray (Std. 11.1 Baretti SVG and 8 BV-0)
q Sieve trays : Hole size and number q DC Slope:
q 100% means straight DC and automatically all Dcs are sized based on the given Side DC area
q X% Mean that the Dcs are sloped and the % is the ratio between the bottom and the top areas
q 0% Means that the DC inputs will not be modified ( Specified geometry)
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Use of BARETTI® Software
q Geometry Input (continue)
q DC Clearance q Select a clearance that allows correct outlet velocities ( see later points)
q Swept back weirs q In case of swept back weirs input the needed total length of the side weir
q Picket fence q Input the % of the weir length to be blocked
q For 4 pass trays, you can select q AA= (1) if Active areas are equal q AA = (0) if Flow paths are equal
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BARETTI® Valves
q Floating Valves :
q Baretti BDH : standard valve q Baretti BV-1 : round valve
q Fix Valves:
q Baretti SVG : standard valve q Baretti BV-0 : high performance micro valve
2015 Web Tray Design Software Rev 1 Page 7 19/02/16
Downcomer Design
q Number of passes q Depending on the size of the column and the specific liquid load
one or more passes can be used q As rule of thumb the specific liquid load on the weir should not
exceed 1.5 m3/min/m. This value can be reduced by q Making a longer outlet weir q Increase the number of passes ( 1,2 and 4)
q The liquid inlet velocity into the top downcomer (Vin) area should be limited as follows:
q Dl/Dv >500 Vin< 0.17 q Dl/Dv >100 and Dv/Dl <500 Vin< 0.12 q Dl/Dv >10 and Dv/Dl <100 Vin< 0.1 q Dl/Dv <10 and Vin< 0.08
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Tray Spacing selection
q Tray spacing q The standard tray spacing are:
q 250-300 mm for column to be installed under roof
q 350-450 for superfractionators in order to reduce column height
q 610mm for traditional applications
q 760 – 900 mm for very large columns and very high liquid trays
q Effects of tray spacing selection
q The column capacity is function of the tray spacing. In fact the higher is the tray spacing the higher can be the vapor/liquid mix layer on the tray or the spray
q To obtain a short column a low tray spacing can be used. As a result the column becomes larger
q For foaming systems is suggested to use standard or higher tray spacing, since the stable layer of foam can touch the next tray and reduce the tray efficiency
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Downcomer Clearance
q DC clearance q The DC clearance has to be
calculated based on the liquid exiting velocity
q The limit velocity through the DC clearance is 0.45 - 0.50 m/sec. This to reduce the discharge pressure drop
q For mechanical reasons the DC clearance should be limited to 20 mm for towers up to 3 m diameter and 25 mm for bigger columns
q In case of low liquid rates the above limits can be still applied , but an inlet weir should be used to keep the seal
q Recessed sump q If the liquid load is very high
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Outlet Weir
q Outlet weir height q The standard weir height is 50
mm q For absorbers and all systems
where the contact time is basic use 65mm
q For low pressure systems use 30-40 mm weir. A low weir can effect the tray efficiency
q For low liquid trays: q Use Notched or picket fence
design q If liquid crest is lower than 5 mm
use a splash baffle positioned before the outlet weir (250mm High)
q Adjustable weirs q Unless differently specified use
adjustable outlet weir if the liquid crest at design is lower than
q 20 mm for columns < 3000 mm q 30 mm for columns > 3000 mm
q Swept Back weirs q SBW can be used in following
cases: q When a lower crest can help
reducing the tray pressure drop q To reduce the side dead areas
and improve the efficiency of the tray
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General Design Points
q Valve density q Baretti BDH max 130 / m2
q Baretti SVG max 130 / m2
q Baretti BV-0 max 300 / m2
q Sieve Max 14% open area
q Tray thickness (C.A. Included) q Baretti BDH 2 - 5 mm q Baretti SVG 2 - 5 mm q Baretti BV-0 2 - 3mm q Sieve 2 - 5 mm
q Bubble promotors q Consult Baretti if needed
q Dual weight valves q Use this feature to maximize the tray
turndown
q Flow path length q Minimum 400mm
q Baffles q Anti jump baffles, normally not
needed q Splash Baffle , as in previous page q Parallel Baffles: to used only when
tower is oversized.(Run parallel to flow , 300 mm high)
q Split Flow baffles. To be used to increase the DC capacity. Consult Baretti
q Seal pan q To be used always to seal DC of
lower tray. Depth =TS+150mm
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