COKER HEATER TEMP. LIMIT

[Pannalal Chakraborty]

Hi all,

We have a Coker charge Heater designed for 50 kg/cm2 & 612 C. The inlet op. pr. generally remains at 30 kg/cm2. My question is

a) As the Heater operates at much lower pr., whether we can raise the operating temp. limit from 612 C ?. Whether any code/std supports that ?

b) Regarding the turbulising steam injection at radiation inlet – is there any laid down / thumb rules/upper & lower limts about the amount/ratio (w.r.t the feed rate) steam to be injected.

Looking forward to an early reply.

Regards

PLC

[Alfredo Velasco]

There are many independent variables to say your fired heater can reach more than 612 C.

I´d recommend you to make a heat balance in your heater and stablish the maximum pressure drop, delta p on transfer lines, etc.

Remember that for this kind of heaters, the design procedure must stablish at least two cases: SOR and EOR. What is your inlet pressure at SOR conditions? What would be the p-inlet at EOR cond?

[Pannalal Chakraborty]

Thanks.

The inlet pr. (SOR) is approx 26 kg/cm2 at convection inlet. At EOR, it becomes approx 30-32 kg/cm2. The inlet pump is designed for 50 kg/cm2 pressure, assuming worst case condition of 3 mm coke deposits in radiatoion tubes – which is never reached. The limiting temp. (as per the original calc which I have seen) has been established by assuming worst combination of pressure & temp. on 7 th tube from outlet (total 34 tubes in a pass) and assuming 22 kg/cm2 pr. in that tube (which is very very high – should have been approx 8-9 kg/cm2, considering outlet pr. -4-4.5 kg/cm2). After that assumption, back -calculation was done to reach the figure of design limit -612 C.
Now, as that design pr. will never be reached, higher op. temp. shoud have been allowed. However, the concerned aquthority is asking for some code/std. or Recomm. Practice reference for changing the op. temp. limits.

‘Hope you can help.

Regards

Chakra

[Alfredo Velasco]

I would recommend you to follow the rules of API 530 and verify the elastic and rupture stresses along the radiant coil. Of course, you are making an important assumption about the fluid pressure on 7th tube.

The best way to check the performance and limits is making a thermomechanical simulation of the entire heater. This way will let you to avoid other kind of problems, not only the high tube skin temperature.

You can access our e-mail for more details in a.velasco@combustia.com

Best regards and look

[Author]

Posts