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Hot Oil Heater Not Hitting Spec

oil heater heat transfer troubleshooting heat exchanger oil heater process

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#1 georgiatech90

georgiatech90

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Posted 02 November 2017 - 12:13 PM

Hello,

 

I am currently trying to troubleshoot a hot oil heater that is operating abnormally. The heated oil line (seen below in red) is Therminol-66. The oil heater is a 3 pass helical exchanger using natural gas as the source of heat. 

 

process drawing.png

 

Currently the process (cold side) fluid, an evaporatable oil, is running at ~50% flow capacity. The two process exchangers normally have duties of 1.6MMbtu/h and 0.5MMbtu/h during full operating conditions. Simulated for current conditions (if the heating oil was at 650F as it should be) the duties are now 1MMbtu/h and 0.15MMbtu/h respectively. The hot Therminol-66 oil is running at it's full capacity. The burner is running at full capacity as well. 

 

Additionally, the flu gas out of the stack temperature is much higher than we expect, at 830F currently versus the spec of 630F. This would appear that the heater was either undersized or damaged. The heater was opened and inspected for damage and none was found. The heater is rated for 2.4MMbtu/h which is more than our expected duty of 2.1MMbtu/h. Doing hand calculations I found the oil duty for the spec to actually be closer to 2.7MMbtu/h.

 

To summarize,

Spec:

Oil in: 619F

Flu out: 630F

Oil out: 650F

NG in: N/A

 

Current:

Oil in: 510F

Flu out: 830F

Oil out: 551F

NG in N/A

 

I'm thinking the that it is possible the approach temperature on the spec is too close, at only 11F apart it is quite narrow. But in current operation the flu outlet is 830F versus an oil in of 510F. 

 

Any comments or suggestions would be greatly appreciated.

 



#2 Bobby Strain

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Posted 02 November 2017 - 12:53 PM

Maybe you should post a better representation of your heater. The sketch doesn't convey much information. Maybe a datasheet, too.

 

Bobby



#3 latexman

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Posted 02 November 2017 - 02:48 PM

Call the Therminol vendor (or hot oil heater vendor) and ask for help.  Therminol has a staff of experienced engineers for this exact reason.  They have helped me out several times.

 

Could it be fouling?  Either in the heater, process, or both.  Did it work okay before?  Or, is this a start-up?



#4 georgiatech90

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Posted 03 November 2017 - 08:56 AM

Call the Therminol vendor (or hot oil heater vendor) and ask for help.  Therminol has a staff of experienced engineers for this exact reason.  They have helped me out several times.

 

Could it be fouling?  Either in the heater, process, or both.  Did it work okay before?  Or, is this a start-up?

 

This is a startup, should have clarified that. We've been working with the vendor closely but they are at a loss as well. Their spec sheet said it could hit the target temperatures. At first we thought the baffles had come loose and combusted gas was bypassing the 3-pass and going straight out the flu stack, but after inspecting there was no issue. 

 

I am going to reccomend bypassing the process fluid around the 2 exchangers to see if we can get the temperature of the heating oil up to a reasonable level.






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