Distillation columns and pipework in a refinery unit

Inside a delayed coking unit, once foam at the top of the coke drum passes the safe level, the pressure drop across the desulphuriser climbs with it, the throughput of the unit is pushed down, and the risk of column coking and drum flooding rises at the same time.

Chemi Tech supplies defoamers for delayed coking, atmospheric and vacuum distillation and desulphurisation units in refineries, drawn from the defoamer KM-600 series; the proportioning is set by the properties of the feedstock oil, the column temperature and the trend in the foam layer height. The KM-600 series is designed around high-temperature resistance and resistance to oil fouling, and its structure stays stable where the tower overhead runs hotter; KM-660 in the same series resists both acid and alkali and withstands high temperature, and is the better fit where the acid value of the feedstock is on the high side and the tower overhead temperature is high as well. Chemi Tech completes the temperature-resistance and compatibility comparison against the properties of the feedstock oil and the column temperature, and selects the model that fits on that basis.

Advantages of Chemi Tech Defoamers

Chemi Tech defoamer KM-600 series withstands high temperature and resists oil fouling, and its defoaming action does not decay readily in the harsh conditions of the coke drum and the desulphuriser; at the same time it places no scaling burden on the columns or the heat exchange system, and the medium inside the column stays clean; further, its knock-down speed matches the swing in the foam layer height, and the tower overhead level comes back down smoothly; it fits delayed coking, atmospheric and vacuum distillation and desulphurisation units alike, so a refinery does not have to stock separately for each unit.

Industry Pain Points and Solutions

Foam in refinery units is mostly not caused by the defoamer failing but by swings in the feedstock properties and the column temperature pushing the foam up time and again; the consequence is an unstable tower overhead level and a rising pressure drop.

The first problem to show up is foam at the top of the coke drum running away. After the feedstock is switched, the foam layer inside the column rises with it, the level reading becomes unstable, and the risk of drum flooding rises. Chemi Tech's approach is to add the high-temperature-resistant KM-600 at the tower overhead reflux section, so that the agent is fully dispersed before the foam accumulates.

The second is the condition of a high feedstock acid value. Feedstock with a high acid value places greater demands on the tolerance of the agent, and ordinary defoamers fail quickly in that environment. Chemi Tech's KM-660 resists both acid and alkali and withstands high temperature, and performs steadily where the acid value is high and the tower overhead temperature is high as well.

There is also the rise in the desulphuriser pressure drop. Once foam is carried over to the desulphuriser it blocks the trays and the heat exchange section, the pressure drop climbs with it, and the throughput is forced down. Chemi Tech compares durability against the column temperature and the foam layer trend, and calibrates the addition level and the top-up points as one, so that the abnormal rise in the pressure drop is held down.

Typical Conditions and Verification

Customer: a refinery delayed coking unit in Shandong, for defoaming in the coke drum and the desulphurisation section.

At this plant the coke drum built a thick layer of foam after the feedstock was switched, the tower overhead level was unstable, the desulphuriser pressure drop ran high over the long term, and the throughput was constrained. The solution Chemi Tech defoamer gave for this was: against the properties of the feedstock oil and the column temperature, the KM-600 series was selected, the dosing point was set at the tower overhead reflux section, and the addition level was banded by foam layer height. After the solution was in place, the tower overhead level held steady, the desulphuriser pressure drop returned to its normal range, and the throughput recovered with it.

Frequently Asked Questions

Will a defoamer added to a refinery unit affect the heat transfer of the columns or the cleanliness of the medium?

It is not entirely without effect, since a few categories break down or coke at high temperature and add to the burden on the columns in turn. For refinery systems, Chemi Tech has put the KM-600 series through temperature-resistance and coking comparisons, and at normal addition levels the columns and the heat exchange system perform steadily. The addition level depends on the properties of the feedstock oil and the column temperature, and Chemi Tech gives its recommendation after the temperature-resistance comparison.