Q & A > Question Details
we are facing problem of high skin temeprature in one of the pass of CDU charge heater (106,000BBl) refinery. After thermography, it shows even more. we have done following actions:
1. PUT manual the FC for that pass and manually maximized the flow through this pass only.
2. shut off the burner adjacent to this burner.
3. can not do the decoking for the crude heater. Furnace's Pigging is planned next year (2016).
But now, we are going to inject the LP steam online into one of the pass. LP steam is used only in case of:
- Furnace tripped due to pass flow low low.
- Furnace tube fire case.
What possible outcomes we can expect with this activity? will it benefit? is there any other technique to remove spalling?

Outcome:
Thanks for valuable comments.
In recent shutdown (planned turnedaround of the plant), we have managed to perform pigging of crude heater and after that, results are much better. no more skin temp issues. We have done pigging for pass more time, tube conditions are normal now.
 
Answers
15/04/2016 A: Krishna Chaitanya Voodi, Honeywell, krishnachaitanyavoodi@yahoo.in
You can check the flame position, length from the burner. Adjust the burner if necessary. Also, have a multiple pyrometer readings for the tubes with high temperature and also for the tubes adjacent to it and conclude based on the results. If you can see dark patches on the tubes. it might be of coke deposit on the tube. Conduct steam decoking if possible online.
17/05/2015 A: S Sivasankaran SABANAYAGAM, CPCL, cpclsiva@yahoo.com
In my opinion, injecting LP steam may not help you much. However step 1 and 2 would be really beneficial if the skin temp is really high.
You must ascertain whether the high skin reading is a actual. Most of the time, the element gets disconnected from the tube and it starts sensing flame temperature. Whether thermal imaging technique adopted is capable of completely filtering out the flame interference. Some times, thermal imaging also misleads and it picks up flame temperature also.
Are you observing any discoloration on the tube where high skin temperature is noted.
You may try to take temperature survey using pyrometer after cutting down the burner nearer to the suspected tube and compare with skin temperature. Also compare the pyrometer reading with other pass tubes.
What is the status of other skin temperature and Dp across inlet & outlet of the same pass. If all are showing high compared to other passes, then you can suspect coking inside the tubes which would have contributed to high skin temperature. In such case, you should plan for steam air decoking or pigging based on skin temp and visual inspection findings.
Other possibility is localised overheating of tubes due to continuous flame impingement which can be identified by visual inspection.
Most of the time, continuous monitoring of furnace and ensuring proper flame pattern would help to postpone the shutdown even if skin temp is nearing at its max design temp.
12/05/2015 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
In answer to your question about injecting lp steam...most heavy oil heaters use LP steam as Velocity Steam during lower rates to create turbulance and prevent laminar flow
12/05/2015 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
First are you sure it is an actual high skin temperature? I have seen a lot of times when the tube is coated in a scale that shows up on a thermography as false high temperature. See if you can find a spot that doesn't have scale and try to shoot that or get a contact thermocouple if the tube is accessable..... Is there any flame impingement?... this may not be obvious without a FLIR camera as a large portion of the flame is invisible to the naked eye... or an easier and less expensive method is to place a teaspoon of baking soda into the air register or observation port... The sodium in the baking soda will ionize and show the true flame..it's quite amazing. You can also try slumping the heater temperature for a short period of time and bringing it back up.... not enough to cause thermal shock but it may spall the scale off the tube skin.....