Hydrocarbon Engineering

August

2019

HYDROCARBON

ENGINEERING

interaction of vapour and liquid for mass transfer. This can

be achieved by creating a system that reduces the

generation of localised high vapour velocities, as well as

reducing the froth height, which increases the vapour

handling capacity of the tray.

A successful valve design

An example of a proven design is Sulzer’s UFM floating

valve, which has been successfully installed in over

470 columns for various applications (Figure 1). This features

a distinctive dome-like or umbrella shape that reduces the

vapour velocity above the valve by approximately 40%,

compared to conventional designs. As a result, good mixing

on the tray deck and minimal entrainment are ensured. In

addition to addressing entrainment, UFM valves can offer

capacity increases of 15 – 20% over conventional float

valves, while maintaining high efficiencies throughout a

wide range of operating conditions (Figure 2).

Maximising column capacity

In addition to carefully considering the optimal design of

valves, tray technology manufacturers should also

investigate how other components can play a role, including

downcomers, which can be optimised for larger column

throughput. In particular, in high capacity columns, the

bubbling area for vapour-liquid contact should be

maximised for optimal mass transfer. While doing so, it is

important to ensure sufficient top area and volume for the

downcomers for froth disengagement.

An effective approach is combining high capacity decks

with carefully designed downcomers, which enhance both

the vapour and liquid handling capacity. In addition, it is

possible to convert the unperforated deck close to the

column support rings into a useful bubbling area. To further

boost the capacity, the periphery of these trays can be

equipped with directional and movable valves (Figure 3).

These tilt at an angle when opened, sending the right

amount of vapour flow to the intended direction, boosting

the capability of trays to handle higher vapour loads and

increasing the overall column capacity.

Based on these principles, Sulzer developed UFMPlus

high performance trays, equipped with UFM valves and

push valves (UFM PV) on the decks, and enhanced

downcomers (Figure 4). This solution can be applied on

services such as superfractionators, light hydrocarbon

fractionators and splitters in chemical and petrochemical

applications, where float valves are typically used.

Dealing with column fouling

Special considerations should be taken when the feed

contains fine particles or the process stream may

polymerise to form sediments on the trays over time. This

can occur in fouling services, such as stripping sections of

crude and vacuum distillation units, coker fractionators,

polyvinyl chloride slurry strippers and beer distillation

columns. In these situations, offering fouling resistance to

extend the equipment service life is extremely important.

In these cases, movable valves are unsuitable, as they

tend to get stuck with particles during operation, leading to

increased pressure drop, vapour maldistribution and

premature flooding. Traditionally, large fixed valves are

usually used for these fouling services, however, they may

suffer from some losses in capacity and efficiency as

compared to smaller valves.

To provide an ideal solution for such operations, it is

necessary to develop valves that can meet high hydraulic

Figure 2.

CFD study of vapour flow from conventional valves (left) and CFD study of vapour flow from UFM valves

(right).

Figure 1.

UFM high-capacity floating valve.