Fouling factor for crude oils?

[KernOily]

Do you guys have any 'reasonable' design values for S&T HEX fouling factors for various crude oils? I'll take anything you got at this point. Thanks!
Pete

 

[TD2K]

Anything? Oh boy, this is going to be fun.

Seriously, TEMA suggests the following for crude oil. Obviously, a lot depends on the crude oil in question.

I'll give you the numbers for greater than 4 ft/sec, let me know if you want them for less than that:

up to 250F, dry or raw crude, 0.002

250 to 350F, dry crude, 0.002, raw crude, 0.004

350 to 450F, dry crude, 0.003, raw crude, 0.005

450F and higher, dry crude, 0.004, raw crude, 0.006

Note, for raw crude, TEMA actually calls this 'salt' with the comment 'assumes desalting at approx. 250F'.

I'm not really sure what this means, I've assumed this refers to crude before desalting even though this is usually done before you get the crude over 300F or so so I'm a little puzzled by data for 450F (maybe for systems that don't desalt?).

Directionally, my assumption makes sense. If I haven't removed the salt, the crude's fouling tendency is going to be higher than if it's been desalted.

 

[KernOily]

TD2K I knew I could count on you to come through for me. ;-)

What do they mean by 'raw' crude? I assume that is pipeline crude with the BS&W still in it?

Do they provide any kind of allowance or variance for API gravity? I am certain that one would use a different f for 40° sweet vs., say, 14° sour. This particular crude is 16° sour.

What is the TEMA reference that you got those from?

Hey I owe you a sodie pop!!!! ;-) Thanks!
Pete

 

[TD2K]

Pete, that's what I assume raw crude it. Straight out of the tank at the refinery with BS&W, salt, etc in it (less than 10 lbs salt/1000 bbl and 0.5% water would be my guess). The 'dry' crude would be after desalting and dehydration in the desalters.

Reference was out of TEMA, 8th edition, section 10. They didn't give any correction/adjustment factors for density (would I miss that given some of the crap you produce down there in CA ;-)) While I would expect there to be some differences, maybe not. The lower end of the TEMA recommendation is 0.002 for everything from gasoline up to light gas oil.

 

[KernOily]

Bruce thanks for the clarification. I'm playing process engineer again. I used 0.002 based on your first post.

'Crap' is exactly right. Plenty of sand, H2S, foam, water, red rags, beanie weenie cans, what-have-you. I remember when I first came to work out here I was over at Mobil - San Ardo (12.5° API sour) one time during January. I happened to be in the maint. planner's office and a call came over the radio that a well had blown its stuffing box and had made a goodly sized oil mess on the ground. By the time they stopped the well, the oil on the ground had cooled. And hardened. They sent two guys over there with shovels and a pickup truck to clean it up... First time I'd ever seen an oil mess cleaned up using shovels and tossed into the back of a pickup!!! Thanks!
Pete

 

[TD2K]

I audited a heat exchanger course when I was over in Saudi put on by the Center for Professional Advancement (auditing the courses were the only way I would get to go and most of them were well worth the appraisal I had to write up on the course). The two guys who taught it discussed fouling factors and had pretty strong opinions against the usual reaction being to automatically throw in a bigger factor 'for safety'.

Their reasoning went that a fouling factor (or oversurface) increases the required area. That decreases the velocity on both sides of the exchanger and directionally increases the chance for fouling. They instead suggested looking at the effect on the exchanger performance if it did foul assuming it was not designed with the additional area from day 1 (eg, you don't cool down the hot side quite as much and don't heat up the cold side, driving down Q and increasing LMTD) and then review what the impact was on the process before deciding on your fouling factors or oversurface.

I'll take a look at the notes and see if they had any other recommendations other than the TEMA numbers, suspect if they had anything, those were what they had.

 

[TD2K]

Sorry Pete. The course notes just give some of the TEMA values.

 

[KernOily]

Thanks Bruce!
Pete Thanks!
Pete