2 replies to this topic

[Vivienne]

We have been experiencing ammonium chloride plugging in our Naphtha hydrotreater Effluent Debutanizer that needs to water wash the tower in 9month interval. The unit has HPHS and a HPCS. Both HPHS and HPCS liquids are sent to the debutanizer tower. Both separators are operating at 2800Kpag. Is there a way to eliminate the fouling in our tower? This problem started when we replaced CDU overhead pH control from liquid ammonia to organic neutralizer. The reason for switching to organic eutralizer is due to difficulty in controlling the pH in our CDU overhead system. Moreover, the tower underwent a revamp (tray replacement from sieve trays to ECMD trays in order to improve fractionation) last December 2009. After the revamp, T-2401 service life shortened to 5 months. It appears that there is an accelerated deterioration of T-2401 performance due to fouling as a result of decreased in tray hole diameter from 0.5 inch to 0.19 inch. We believe that increasing the size of the tray hole diameter is a step forward in prolonging the fouling tendency but it is not to say that fouling will be eliminated. We are planning to have tray modification of the tower and also install a NHT feed coalescer to reduce/eliminate the liquid salts formed by the organic neutralizer. Does a coalescer and tray modification will end the problem? Do you have any suggestions?

[Himanshu Sharma]

It was a holiday today here and could see its your first post today ,else it would have been Communicate Clearly points in this paragraph .Its still the same advise,be more lucid.

Ok lemme try to help !

This is a common problem in Hydroprocessing units due to neutralization left overs in Overheads(CDU/Naphtha Columns/kero cuts pr widely speaking 160-350 deg c cuts).

My first question is that why Organic Amines ,they are expensive aren't they !.Properly designed wash water system with liquid ammonia are more reliable to me.Then there is fundamental mass transfer problem with Organic amines ,neutralizing amine is both soluble in the water and the hydrocarbon streams. The diffusivity between water and hydrocarbon depends on the molecular weight and type of neutralizing amine.on the other hand Ammonium Chloride is totally soluble in water with near zero solubility in HCs.

Even a feed coalescer will remove water and dissolved salts not the salt content in HCs.

Have you checked for salts depositions in compressors???

Moving towards the solution...

• Check your Desalter's Performance.
• Switch Back to Ammonia.(if you are dealing under cold climate there may be a possibility of freezing and thus an irregular flow rate,tell me if this is the case,we would try to resolve)
• To minimize carry over of NH4Cl and water, install coalesers packed with polypropylene wool upstream of the hydrotreater.

Hope this Helps...Happy Helping

[Hansson]

Hi Vivienne,

I have been working with a very similar unit and have on occasion run into fouling of the top tray of the debutanizer. The fouling has succesfully been removed by on-line water wash of the top tray. The water has been pumped into the hydrocarbon reflux to the tower. If this works for you, you do not have to make expensive equipmet changes upstream or on the unit.

Precipitation of NH4Cl and ammonium bisulfide is very temperature dependent and typically only the top tray or the top trays are affected unless you have really high concentrations of HCl and NH3 or NH3 and H2S. Do you know which trays are fouled?

Reducing the hole size on trays that are known to work in fouling service is a big NO NO. However, if it is only the top tray or trays that are actually fouling as I would expect, then not all trays have to be changed out.

Knowing the concentrations of NH3, HCl and H2S and knowing where the fouling is located is the keys to the problem. Is the cloride coming into the unit with the naphtha or with the hydrogen treat gas. Typically, the treat gas is the culprit. Then a small HCl trap on the hydrogen supply line could help.

Continuous water wash of the cooler between the hot and cold separator can also help to alleviate your problem.

Lowering the debutanizer pressure is not allways possible, but it too might help to minimise fouling due to precipitation of salt.

Good luck
Hansson