10 replies to this topic

[Arsal]

We have 20 no's of crude preheat shell and tube exchanger from Crude pump to preflash column,having a crude in tube side.We are facing a Heat Exchanger fouling problem due to which Heat exchanger train pressure become higher upto 280 psig on maximum throughput.(54000 BPSD).So feed limitation occured.

 

Normally Our planned Turnaround(Shutdown) will come after 03 Years and our fouling problem is to be started after 2 Years.

 

Please explain why Crude heat exchanger fouling occurs,which impurities can majorly take part in fouling?

How to overcome these Heat transfer losses(due to fouling) without Mechanical cleaning?

[Zauberberg]

The only proven way to confirm the cause of fouling is to analyze the deposits during unit turnaround. This will give a clearer picture of what are the likely culprits. There are so many possible causes of fouling that it makes it virtually impossible to provide a straightforward answer without having more information.

 

While the unit is running, you can perform exchanger calculations with given stream properties and see if you are getting reasonable velocities on the tube side, at design flowrates. If the SOR velocities are too low, the problem may be as simple as that.

[gegio1960]

Hi rao.

I share Zaub points and like to add some other ones...

1) what is your starting pressure drop (with clean exchangers)?

2) do you measure, time by time, the DP for each HE? on this base, could you identify critical HE?

3) is your plant working close to the original design?

4) which crude(s) do you process?

5) have you ever tried to simulate/analyze/optimize the preheating train performance?

of course, a PFD of your PHT would help a lot.

good luck!

[P.K.Rao]

Besides what Zauberberg and Gegio advocated check all the crudes that are processed  for sediment and calcium content. If they are high, they could be a reason

[Arsal]

Thanks to all, now i would like to add some more relevant data as well.

Crude : Arab Light

BS &W = .05 

Starting Exchanger train pressure  (Clean ex-changer) = 220 psig ,Starting Pressure drop =0.3-0.6 barg and for the time being it will become up to : 0.5-1.5 Barg.

Yes Plant is working close to the original design.

 

i think this data will helpful to answer this question.

 

Mr P.K rao

we are not checking calcium in crude ,and only checked salt content in crude i.e less than 3 PTB normally.

Can you please explain how high Calcium contents cause fouling (due to polymerization or any thing else).and what is the significance to check calcium?and how to control if high?

Edited by rao arsalan, 18 February 2015 - 06:42 AM.

[P.K.Rao]

If it is Arab Light, there is no need because calcium content in it is low. In some other crudes, like Maya, Doba, Eosene etc calcium content is high. Calcium would be present as calcium napthenate if it is high. This calcium naphthenate forms deposits which could be a reason for this phenomenon.

[gegio1960]

1) I agree that ARL is not known as a "fouling" crude.

2) My main suspects are now on the pressure drop figures: 0.3-0.6 bar, but also 0.5-1.5 bar, are well below the usual pressure drops of a PHT in a CDU (20 shells in this case). It seems the velocity is too low amd that is in favour of fouling generation.

3) Also, pumps/valves systems seem not adequate

4) Other info are missed (eg single DPs, PFD, etc) to further proceed with the analysis.

5) Please clarify the reference point for the 220 psig (about 14.5 barg): at pump discharge? at the inlet of the 1st HE? where else?

6) Moreover, normally the PHT is made of 2 parts, before and after the desalter, with a booster pump in between....

[Arsal]

Please tell abbreviation of PHT?

220 PSIG at the inlet of the 1st HE.

Our process flow scheme is as follow:

FEED PUMP------PREHEAT EXCHANGER(11 NOS)-------------DESALTER---------------PREHEAT EXCHANGER(09 NOS)---------------PREFLASH COLUMN-----------------PREFLASH BOTTOM PUMP---------------PREHEAT EXCHANGER(05 NOS)-------------FIRE HEATER---------COLUMN

​Normally fouling occurs after desalter  (affected portion is in bold letter)

[gegio1960]

Sorry, PHT is PreHeating Train.

Let's continue our troubleshooting... once said that the given pressure drop data are not realistic (where is the DP of the mixing valve?)

I've to repeat some points:

1) The PFD (process flow diagramo) shall be available.

2) Have you measured the DP of each single HE?

3) What do you know about the crude vaporization in the PHT (position and amount)?

4) What about the dehydration performances of the desalter?

5) Process parameters of the single HEs after the desalter shall be reviewed.

6) An increased pressure profile (ie more pressure in the last HEs) should improve the situation. 

[Arsal]

This mentioned DP( 0.5-1.5 bar/Each exchanger) which have been found at each exchanger ,this was also checked by master pressure gauge as well.

Mixing valve DP is 10-15 PSIG

Dehydration performance has also been measured and in controlled because BS&W at desalter outlet is .05 wt%.

No information about crude vaporization in PHT?tell me how it find out?

[gegio1960]

ok, now we have another piece of the mosaic.

you can evaluate vaporization by means of a simulation... or a heat balance around the last HE of the PHT.

do you know the in/out temperatures (and pressures) of the two sides (shell and tubes) of the last HE of the PHT?

also required are:

1) the flowrates of the two fluids (crude and ???)

2) the main properties of the ??? fluid (at least the specific gravity, also useful the viscosity)