Adding additional nozzle to furnace

[ctmecheng]

I am trying to design an additional nozzle on an existing furnace and I have a question that my see elementary to some but I would rather ask than continue falsely. I have been reviewing Part UG of the BPVC, specifically UG-37 through UG-45, and most of these sections discuss nozzles on round vessels. Are these equations discussed in these sections applicable to flat surfaces? If so, some equations ask for the radius of the vessel, R, but is it safe to assume that R would also be the distance from the center of the rectangular furnace to the center of the nozzle hole in the furnace wall?

Thank your for your help.

 

[racookpe1978]

The boiler and pressure vessel codes are usually "almost" irrelevant for the burner-side of the boilers: Their rules relate to the steam and pressurized feedwater coming well after the fired gasses have past by the tubes. Not the the burner configuration, which is very strictly controlled by the flame size, position, orientation and length: That hot gas flow is more critical to performance than the number of burners set in a flat wall.

 

[ctmecheng]

racookpe1978,

What would be the first course of action into designing this nozzle? My manager wanted me to use our Compress Software for BPV but per Section II Part D Subpart 1 the maximum temperature allowed for A-36 is 650 deg F. We want to be able to determine if there needs to be a reinforcing pad for the nozzle. I have already looked at UG-37 and followed the calculations to determine if it needed one. From that section of the code it indicated that it does not need a reinforcement pad but this does not take into account the design temperature. We received today that the design temperature is 1368 deg F and internal pressure is 15 psi. The furnace is also lined with a internal castable insulation. I have also attached a drawing which will depict our current problem. Your help is much appreciated.

Thank you.

 

[marty007]

I don't like this design, because it is now allowing the carbon steel in the vessel wall to locally reach much higher temperatures than before.

One of the main purposes of refractory is to keep the pressure shell cool, allowing the use of carbon steel over other much more expensive temperature resistant materials. What you are now doing is providing a direct conduction path for the outer shell to reach much higher temperatures.

The design temperature that you were provided (1368°F) is very likely the design temperature on the inside surface of the refractory, the actual design temperature of the shell is likely much cooler (500-600°F range) due to the refractory.

 

[ctmecheng]

marty007,

That was my thoughts exactly, my manager, a civil engineer, suggested this design. I expressed my concerns about that issue. How would we then add the nozzle to the furnace and eliminate or minimize the thermal conduction traveling thought he nozzle to the furnace wall?

Is there a program that I could look into that will provide a more accurate analysis that includes the design temperature of the furnace, the thermal considerations of the refractory, and the external loads on the nozzle.

Right now we are using Compress Build 7400 and I do not think this is the correct program to be using. Just for knowledge, I am a young engineer only of out school for almost 3 years and I am trying to teach myself some of these things. We currently do not have a mechanical engineer above me to help teach and advise.

thank you for all of your help.

 

[racookpe1978]

Try this: Analyze the configuration with that software then, but with ALL the carbon steel at 1368 degrees and Max Allowed Pressure of all gasses. Look at plastic yield over time, not the immediate stress conditions at time=0.0

 

[ctmecheng]

racookpe1978,

The Compress software will not let me use a internal temperature of 1368 degrees due to Section VIII. The max temperature allowed is 650 degrees.

Would it be good practice to do a simple heat loss calculation through an insulated wall to determine what the inner and outer wall surface temperature of the furnace, and use those temperatures as my inside and outside temperature? The internal pressure is low, I believe it is 15 PSI.

Also, am I correct in thinking that during steady state operation the internal temperature of the nozzle will reach the same internal temperature of the furnace? If that is the case can I do a another heat loss calculation through the nozzle (radially) and then through the furnace wall to determine the effected area that will reach elevated temperature?

 

[racookpe1978]

See? The program is not permitting you to even begin an analysis (of a future failure) which you know is partially valid: True, the nozzle will vary from 1368 (or more!) degrees right at the connection weld (the highest stress point in any case) down to some lower temp outside the refractory, liner, insulation and insulation covering plate. But the metal and weld will be plastically yielding down inside anyway even if you "overwrite" common sense and type in a false 650 degree value.

 

[marty007]

Let's back up a bit here...

What is the purpose of the nozzle? Instrumentation or process?

If this is for a thermowell for example, you should be able to pack insulation around the thermowell, protecting the nozzle/shell weld from the high temperatures. In which case, the shell/nozzle weld would be at a much cooler temperature and you could design for the same shell design temperature.

If this is for process however, you're in a tougher situation, and you'd likely have to look at expanding the nozzle diameter and refractory lining the ID of the nozzle neck.

Let us know what you decide, helps us all.

 

[ctmecheng]

Marty007,

The nozzle is for an instrument. It is a laser diode. There will be a second nozzle directly across the furnace from this nozzle and it will be used to measure the composition of the gas inside the furnace, if I am not mistaken. I did not realize that the inside of the nozzle could be insulated as well. This may help considerably.

Thank you for your insight

 

[marty007]

You're welcome, good luck.