3 replies to this topic

[Phukan]

In our delayed coker main fractionator, whenever water comes along with the top reflux (because of choked stand pipe of the boot leg interface level and hence wrong indication ), we tend to loose level in coker kero draw tray located 8 trays below. This phenomenon is also accompanied with decrease in the draw temperature. In fact, the first indication of water ingress with reflux is gradual decrease in its draw temperature, (other parameters remaining constant) followed by increase in stripper draw opening. Finally it settles down to a temperature of around 135^o C with stripper opening of 100%. Whatever we may do - by increasing the top reflux or decreasing the heat load in HGCO PA section, we fail to get condensation in the coker kero zone. level can only be brought back once interface indication is properly rectified.

Column Details

No of trays : 37
Top temp: 100
Top Pressure: 1.6 kg/cm^2..
Ck draw Temp: 180^o
Top Reflux flow : 65m³/hr.
CK draw tray :29 (counting from the top)



Can anyone please explain this phenomenon.

Regards,

Phukan

[Technical Bard]

Water has a very high heat of vapourization. If a significant amount of water enters the top trays, it absorbs significant heat from the column, and condenses naphtha range material - which is now cold and falling down the column. This mechanism extracts heat from the top of the column and will cool the kerosene draw. You probably also see the kerosene draw get "lighter" as it will probably contain more light ends. This amount of water ingress with the reflux would probably also destroy the trays in the column due to a pressure wave.

However, you appear to be seeing the opposite effect. A small amount of water could be creating a "stripping" effect - by lowering the hydrocarbon partial pressure in the top of the column. Heavier materials could then evaporate and end up in the coker naphtha.

[Padmakar Katre]

In our delayed coker main fractionator, whenever water comes along with the top reflux (because of choked stand pipe of the boot leg interface level and hence wrong indication ), we tend to loose level in coker kero draw tray located 8 trays below. This phenomenon is also accompanied with decrease in the draw temperature. In fact, the first indication of water ingress with reflux is gradual decrease in its draw temperature, (other parameters remaining constant) followed by increase in stripper draw opening. Finally it settles down to a temperature of around 135^o C with stripper opening of 100%. Whatever we may do - by increasing the top reflux or decreasing the heat load in HGCO PA section, we fail to get condensation in the coker kero zone. level can only be brought back once interface indication is properly rectified.

Column Details

No of trays : 37
Top temp: 100
Top Pressure: 1.6 kg/cm^2..
Ck draw Temp: 180^o
Top Reflux flow : 65m³/hr.
CK draw tray :29 (counting from the top)



Can anyone please explain this phenomenon.

Regards,

Phukan

Hi,
As you mentioned in your post, the culprit as your overhead reflux drum interface level indication which puts water in the column along with HC liquid reflux. Have you ever operated column with field operators continuously monitoring the boot water level and draining manually.

[26Edrian]

we're currently working on the design of a delayed coking unit inside a refinery. I find it quite hard to start with the material balance because I cant find the composition of my feed (vacuum residue). all I have now is the amount of the feed. Can you help me out guys. Thanks.