IPE-TM-320-06 — Jet Deck Design

1. Purpose

This procedure provides design criteria for determining the column diameter, active area, inlet and outlet area, tray spacing and downcomer size for jet deck tray designs. Jet deck trayed columns are used for liquid-liquid, counter-current extraction. The dense phase is the continuous phase maintained above each tray. The light phase is the discontinuous phase, jetted through the dense phase on each tray, causing contact between the two phases.

2. General

These trays are normally used in the following services.

Merox Extractors
Sulfolane Columns
LPG-Amine Absorbers
Phenol Recovery Unit – Columns
Phenol Unit – Cumene Feed Acid Column
Phenol Unit - Cumene – AMS Caustic Wash Column
Phenol Unit - Cumene – Solvent Caustic Was Column

Do not confuse these trays with ones that are used on the water wash column for the LPG feed to a Catalytic Condensation Unit. See Procedure for more information about those trays.

The Cumene – AMS Caustic Wash Column does not follow all of the standards in this procedure. Consult with the ATC for the design standard.

3. Guideline

In general, Merox units use pipe-type downcomers that cross from one side to the other. Using two downcomer pipes rather than one large pipe may be advantageous for large dense-phase flows. Sulfolane-raffinate-wash columns also usually have pipe-type downcomers. Amine absorbers may utilize chordal downcomers if the dense-phase flow is a large percentage of the light phase flow. Use a crossover type unless:

vessel diameter is less than or equal to 3'-6" (small columns need a vertical pipe type for maintenance access to the tray)
crossover pipes block off more than 30% of the projected area above the active area (use vertical pipe type)
column diameter would need to be increased to accommodate the oversized pan that is needed to fit in a two downcomer pipe design (use chordal type).
the downcomer diameter is greater than or equal to 12” (the slope in the downcomer is too small)

Crossover downcomer pipe designs are considered superior to chordal or vertical pipe designs as the diagonal pipe helps separate entrained light liquid that entered with the heavy liquid.

For specific details and guidance, consult the Process Specialist for the processes involved.

Standard Drawings 3-310 and 3-311 show the tray layouts for vertical and crossover pipe tray layouts.

A spreadsheet for tray sizing may be located by consulting the Treating Process Specialist.

4. Design Criteria

Diameter	Diameter
	First guess at diameter	AT = cross sect. area of column
	1. Merox Extractor and Sulfo. Raff.
	2. Amine Treating
Minimum Active Area, AA	Minimum Active Area, AA	Minimum Active Area, AA
	Merox Extractor, Sulfo. Raff. and Amine Treating

Minimum Downcomer Area	Minimum Downcomer Area	Minimum Downcomer Area
	1. Merox and Sulfo. Raff.	AD, ft2 = Veloc. = 0.2 ft/sec. max (5400 GPH/ft2)
	2. Amine Treating	AD, ft2 = Veloc. = 0.1 ft/sec. max (2700 GPH/ft2)

Minimum Inlet Pan Area Use the larger of: Ap, ft2 = 1.2 AD (h* + 1.0) h* = downcomer backup in ft at design hole velocity Vo, see below. If a pipe downcomer is used, the minimum pan chord height is downcomer pipe diameter plus 3 inches. Typical clearance is 3 inches on each side of the downcomer pipe. The minimum clearance between the pipe O.D. and the vessel wall is 2 inches and the minimum clearance between the pipe O.D. and the pan inside wall is 1 inch. This applies to both pans.

Overflow pan area - Usually the same as inlet pan but meets following:

Service Minimum Residence Time, minutes

Merox Extractor – LPG 0.5

Merox Extractor – Naphtha 2.0

Sulfo. Raff. 0.5

Amine Treating 1.5

Holes	Holes	Holes
	Use a diameter of 3/8" (10 mm) for initial rating. Use smaller hole size if necessary to obtain a hole pitch of 3 to 5" (75-125 mm). The minimum hole size is 1/4" (6 mm).	Use a diameter of 3/8" (10 mm) for initial rating. Use smaller hole size if necessary to obtain a hole pitch of 3 to 5" (75-125 mm). The minimum hole size is 1/4" (6 mm).	Use a diameter of 3/8" (10 mm) for initial rating. Use smaller hole size if necessary to obtain a hole pitch of 3 to 5" (75-125 mm). The minimum hole size is 1/4" (6 mm).
	For Merox Extractor and Amine Treating, obtain the hole velocity from the Treating Operating Technical Services group. Typical hole velocities are as follows: Service Hole Velocity, ft/s Merox Extractor – LPG 7.0 Merox Extractor – Naphtha 6.0 Sulfolane Raff. 6.0 Amine Treating 4.5 Higher velocities are sometimes used to provide additional turndown capacities.	For Merox Extractor and Amine Treating, obtain the hole velocity from the Treating Operating Technical Services group. Typical hole velocities are as follows: Service Hole Velocity, ft/s Merox Extractor – LPG 7.0 Merox Extractor – Naphtha 6.0 Sulfolane Raff. 6.0 Amine Treating 4.5 Higher velocities are sometimes used to provide additional turndown capacities.	For Merox Extractor and Amine Treating, obtain the hole velocity from the Treating Operating Technical Services group. Typical hole velocities are as follows: Service Hole Velocity, ft/s Merox Extractor – LPG 7.0 Merox Extractor – Naphtha 6.0 Sulfolane Raff. 6.0 Amine Treating 4.5 Higher velocities are sometimes used to provide additional turndown capacities.
Inlet and Outlet Weir/Height	Inlet and Outlet Weir/Height	Inlet and Outlet Weir/Height	Inlet and Outlet Weir/Height
		Use 1.0 ft (300 mm) for each.
Downcomer Clearance	Downcomer Clearance	Downcomer Clearance	Downcomer Clearance
		Use the larger of : 2 inch (50 mm) Curtain exit area equal to downcomer cross-sectional area Round the downcomer clearance to the next higher 1/2 inch (10 mm)	Use the larger of : 2 inch (50 mm) Curtain exit area equal to downcomer cross-sectional area Round the downcomer clearance to the next higher 1/2 inch (10 mm)

Overflow Pan Depth

Use 2 ft (600 mm). This includes the 1 ft (300 mm) weir plus 1 ft (300 mm) below the tray floor.

Top Inlet Distributor

No distributor is used here. But the liquid does enter behind an inlet weir.

Bottom Inlet Distributor

Use a single pipe that has perforations that are in two rows, each 45º off the bottom. For the maximum flow case, the typical hole velociticies are 10 ft/s for Merox Extractor – LPG, 6 ft/s for Merox Extractor – Naphtha, and 6.5 ft/s for Amine Treating.

Use hole diameter of 3/8” (10 mm)

Use of a Blind Tray

Frequently a blind tray is used below the bottom inlet distributor to avoid excessive fluid circulation in the bottom.

Level Interface Location

Level interface is at the bottom of these columns

Tray Spacing	Tray Spacing
	H = H (1 - fL) + L fL


	g = 32.2 ft/s2 C = 0.66 Vo = design hole velocity (ft/s)
	H = density of dense phase (clear) (lb/ft3)
	L = density of light phase (clear) (lb/ft3)
	H = correct density of dense phase (lb/ft3)
	fL = volume fraction of light component in dense phase due to slow settling in downcomer Service fL
	Merox Extractor (LPG/Caustic) 0.15 Merox Extractor (Naphtha/Caustic) 0.15 Amine Absorber (LPG/Amine) 0.15 Sulfolane Raff. 0
	h = downcomer back-up in ft at velocity V
	Use a rounded-up number for tray spacing. Use a minimum tray spacing of 5 feet (1500 mm) LPG services Use a minimum tray spacing of 6 feet (1800 mm) for naphtha services

Calculation Tool

” and “s” may be of value. Consult with the Tool sponsor.

Typical Heavy to Light Liquid Volumetric Ratio

Merox Extractor – LPG	2-5%
Merox Extractor – Naphtha	10-20%
Sulfolane Raff.	5%
Amine Treating	20%