6 replies to this topic

[JoeWong]

Dear all,
I have a hot oil system with following design info :

Hot oil in close loop circuit with hot oil being heated by WHRU. Supplying hot oil to several users and return to WHRU via and recirculation pump.

Hot oil type = Therminol 66
Hot oil inventory = ~ 160 m3
WHRU inlet temperature = 210 degC
WHRU outlet temperature = 310 degC

1) Is the temperature rise of 100 degC reasonable ?

2) Initial start-up, we need to heat up the hot oil from ambient temp of 15 degC to 310 degC. We can not heat-up the hot oil so fast as high heat flux will degrade hot oil and risk of localise thermal shock induced stress cracking. Any rule of thumb that how fast ( XX degC / min) i can heat up the hot oil ? What's the basis ?

3) Any supporting document and paper relate to thermal shock ?



regards,

JoeWong

[abhi_agrawa]

joe,
I believe that the hot oil manufacturer would give you the max. allowable heating rate.

-abhishek

[djack77494]

JoeWong
I'm not sure about "thermal shock". What will be shocked? The heat transfer fluid or are you worried about the piping? I really don't think you need to worry about either, but I'd follow Abhi's advise and contact the supplier.

What you may need to worry about is high heat flux. This could result in excessive film temperatures at the walls where the heating is taking place. Again, ask the supplier for advise as needed.
Doug

[Dtan76]

Hi Joe

I had implemented similar hotr oil circulation system before in Africa/Sudan before (You can refer past topics posted in this forum (Ark/SG KIM/DTan76).

We're using BORNO Energia Italy package. The heat duty about 25MW, hot oil inlet/outlet temp: 150 C/250C and cold side (crude oil): 50C/80C. Not a problem here.

I just very busy at the moment due to heavy eng workload now. You can drop me your question and I need time to response.

Regards

[JoeWong]

Doug / Dtan76 / abhishek,
Thanks for your response.

I'm not sure about "thermal shock". What will be shocked? The heat transfer fluid or are you worried about the piping? I really don't think you need to worry about either, but I'd follow Abhi's advise and contact the supplier.

Thermal shock is potentially occur in WHRU heating coil and hot oil piping if we introduce heat too fast into the hot oil.

WHRU / Hot Oil
During initial start-up, the WHRU, hot oil as well as the piping is at ambient temperature (~15 degC). We will start-up the hot circulation and slowly introduce heat into hot through WHRU. As the hot oil temperature is low and the flue gas temperature is high (~550 deg), the heat flux will be higher than normal heat flux where the hot oil temperature is at 210 degC. Is my understanding correct ?
For this problem, we may check with the WHRU vendor in order to limit the flue gas flow so that high heat flux can be avoided.

Hot Oil Piping
As the hot oil is heated up in WHRU, the hot oil piping will start to pick up heat from hot oil. If the heat transfer is efficient and hot oil flow is too high, the piping temperature will increase very fast. Piping close to WHRU will experience quick temperature rise as compare to those piping far from WHRU. "heated" piping and "cold" piping will have different expansion. Then there is potential thermal shock. This is quite similar to the following example (i think) : If you pour hot water into a thick wall glass and a thin wall glass, the thick wall glass will break but not for thin wall glass.

I am interested in the hot oil temprature rising rate (XX degC / min) so that it will not results piping thermal shock.

What you may need to worry about is high heat flux. This could result in excessive film temperatures at the walls where the heating is taking place. Again, ask the supplier for advise as needed.

You are right. High heat flux will results high film temperature and rapid degradation. As per my discussion with vendor, the hot oil will degrade when it is in operation. High heat flux / high film tempearture will results faster degradation and shorthen life span of hot oil. On the other hand, high heat flux will reduce hot circulation rate as well as WHRU heating area and finally reduce capital cost. So i believe there should be some "optimum" point. Is my understanding correct ? Can somebody advise me the "optimum heat flux" ?




regards,

JoeWong

[gvdlans]

Did you contact Therminol Technical Service (see http://www.therminol...products/66.asp ) as suggested by a few of the other responders?

Your application doesn't seem extraordinary to me and it looks like you are seeing problems that simply aren't there.

[JoeWong]

Did you contact Therminol Technical Service (see http://www.therminol...products/66.asp ) as suggested by a few of the other responders?

Your application doesn't seem extraordinary to me and it looks like you are seeing problems that simply aren't there.

gvdlans,
Thanks for your link and comment.

Before i raise this post, i have discussed with local representative. They have given some good advices. One of the concern they raised was the temperature rise (dT = 100 degC) "looks" high base on their experiences. However, no concrete reason mentioned.
The representative did not advised any "optimum heat flux".

If any of you knows some experts good in this area, your advice is welcome.
Meanwhile i may rasie same query to the Technical center (via its website)


The initial heating rate and piping thermal shock issue, i doubt the representative can answer. Anyway will try my luck.

I understood hot oil system is not extra-ordinary to you (or many of others), it may be so simple for many who have gone through it. However, they are still many out there don't know the answer (like myself. Even now i haven't got any clue or answer for my questions)...Hope you understand.

JoeWong