Heater Tube Temperatures

Can you please first honestly detail the purpose of this exercise? What you you actually want to gain from it? The burners and heaters were designed and working. What you want to do now?

The burners on the heater were changed out for larger burners without calculating the potential for overheating the tubes.

There's administrative controls in place to prevent us from going above the original design Btu output of the original burners, but we are looking at increasing the production of the unit by lifting these controls.

So yes they were designed and working but before we change something we have to prove it will work.

I know I can do heat transfer calculations to get what I need but I would prefer to use a code (API, ASME, etc.) to support my calculations and assumptions. Do you know of a code for this?

Ok now you are talking sense. It is obvious that you have both an on/off as well as high-limit temperature controller to safeguard. You have not explained burner capacity KW/m3/hr, Process, Batch/continuous, Product treated, drier/furnace etc. The only way you can increase production is my minimizing losses. Look the other way for good increase in production/gas saving with :

Oxygen-enrichment.

Combustion Air preheating.

Oxygen Trim online.

Proper Insulation.

Draft Control.

Modulating Burner Controls.

I'm not going to put in my process conditions here because I don't want someone to solve this for me. My focus on this is only two things: what are the tubes good for and what temperature will they see? If you know where I can get the calculations or standards for this let me know.

sorry i cannot help you in this

The temperatures the tubes see can be calculated from standard heat transfer methods, no codes required. Depending on the service conditions, the allowable temperatures can be found in ANSI B31.3 for pressure piping and ANSI B31.1 for boiler tubes.

It sounds to me as though you are describing essentially a heat exchanger, and there are plenty of references that ill detail how to calculate tube temperatures. The most difficult thing is to determine the overall heat transfer coefficient becasue you need to be able to detail what the film coefficients are. You have to specify the tube material, the surrounding gas with temperature and pressure conditions, and the fluid and conditions inside the pipe. You will have to search to see if film coefficient data is available.

You are correct, you have combined heat transfer mechanisms and most likely you are ducitng gasses around the tubes, so you have forced convection as well as radiation and some small amount of conduction from the heated pipe wall to the contained fluid.

The problem needs to be fleshed out a bit.

It is certainly possible to calculate an estimate of what the inside and outside tube temperatures are using basic heat transfer analysis, but you will need to now more about the surface film coefficients. So what is the tube material, roughness and what is the surrounding medium? How about the actual process temperatures (since film coefficients often vary with temperature)?

flushed out a bit , you mean? Again, what exactly do you want to gain from it? Will it reduce the size of the heat exchanger by 90% bringing down the cost? Will it speed up heating time to increase production? Please detail me the benefit of this nonsense exercise ?

I have the process conditions that I need (at least I think so), but I prefer not to post that on here because I don't like asking people to solve my problems for me.

I'm looking for a reference to a code or the equations. From the best I can tell, you will have radiation + convection (maybe forced but I don't know yet) outside the pipes and forced convection inside the pipes. I will also put in a factor for fouling and coking.

Thanks for your input though. If you know what I should use please let me know.

ok now that you are talking sense, i take back my words and put my input. you have to detail your process, heating system, size, production capacity, etc etc. i have put in my input.