Tray Design How to use the Baretti® design software

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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

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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

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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