Column Feed Locations

1. Purpose

This procedure provides guidelines for proper column feed location.

2. Two Pass Trays

2.1 Reboiler Return Below Trays

To prevent a two nozzle reboiler return, a two pass bottom tray shall always have side downcomers (reference Figure 1).

2.2 Feed With Trays Above and Below

A feed with two pass trays above and below shall always be fed onto a tray with a center downcomer. Trapping out the downcomers from the tray above the feed is unnecessary and there is no need to rotate the trays that are above or below the feed (reference Figure 1).

2.3 Simple Columns With Trays Above and Below a Feed

Based on the above points, simple columns with two pass trays in the top and the bottom shall have an even number of trays in the bottom. See Section 4 for further explanation.

3. Four Pass Trays

3.1 Reboiler Return Below Trays

A bottom four pass tray shall have side downcomers and two reboiler return nozzles. These nozzles are parallel to, and centered between, the downcomers. This results in vapor distribution that is superior to that of a single nozzle (reference Figure 2).

3.2 Feed Onto a Tray

A four pass feed tray shall have side downcomers. With this arrangement, the feed distributor does not need a three way split. However, it is necessary to rotate the four pass trays located below the feed 90 degrees in relation to the trays above the feed (reference Figure 2).

3.3 Columns With Trays in the Bottom

A four pass bottom section of a column shall have an odd number of trays.

4. Changing the Number of Trays in a Section

Changing the number of trays in a section to meet the requirements of Sections 2.3 or 3.3 does not mandate a change in the total number of trays in the column. Usually, moving the feed tray up or down by one tray is satisfactory.

Figure 1

Inlets at 2-Pass Trays

USE THIS

Trays below feed are same orientation as trays above feed

NOT THIS

Trays below feed are rotated 90 from trays above feed

USE THIS

NOT THIS

Figure 2

Inlet for 4-Pass Trays

USE THIS

Trays below feed are rotated 90 from trays above feed

NOT THIS

Trays below feed are rotated 90 from trays above feed

USE THIS

NOT THIS